WO2017013297A1 - Dehydration of sorbitol to isosorbide in the absence of a solvent by means of heterogeneous catalysis using sulphonic resins as catalysts - Google Patents

Dehydration of sorbitol to isosorbide in the absence of a solvent by means of heterogeneous catalysis using sulphonic resins as catalysts Download PDF

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WO2017013297A1
WO2017013297A1 PCT/ES2016/070550 ES2016070550W WO2017013297A1 WO 2017013297 A1 WO2017013297 A1 WO 2017013297A1 ES 2016070550 W ES2016070550 W ES 2016070550W WO 2017013297 A1 WO2017013297 A1 WO 2017013297A1
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sorbitol
range
catalyst
isosorbide
reaction
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Spanish (es)
French (fr)
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Pedro Jesús Maireles Torres
María José GINÉS MOLINA
José SANTAMARÍA GONZÁLEZ
Ramón Moreno Tost
Josefa María MÉRIDA ROBLES
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Universidad De Málaga
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J31/00—Catalysts comprising hydrides, coordination complexes or organic compounds
    • B01J31/02—Catalysts comprising hydrides, coordination complexes or organic compounds containing organic compounds or metal hydrides
    • B01J31/06—Catalysts comprising hydrides, coordination complexes or organic compounds containing organic compounds or metal hydrides containing polymers
    • B01J31/08—Ion-exchange resins
    • B01J31/10—Ion-exchange resins sulfonated
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C29/00—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring
    • C07C29/48—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring by oxidation reactions with formation of hydroxy groups
    • C07C29/50—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring by oxidation reactions with formation of hydroxy groups with molecular oxygen only
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07D—HETEROCYCLIC COMPOUNDS
    • C07D493/00—Heterocyclic compounds containing oxygen atoms as the only ring hetero atoms in the condensed system
    • C07D493/02—Heterocyclic compounds containing oxygen atoms as the only ring hetero atoms in the condensed system in which the condensed system contains two hetero rings
    • C07D493/04—Ortho-condensed systems
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07H—SUGARS; DERIVATIVES THEREOF; NUCLEOSIDES; NUCLEOTIDES; NUCLEIC ACIDS
    • C07H1/00—Processes for the preparation of sugar derivatives

Definitions

  • the present invention relates to catalytic processes aimed at the transformation of biomass, in particular lignocellulose, into high value-added chemicals and biofuels. More particularly it refers to the dehydration of sorbitol to isosorbide by heterogeneous catalysis, using as a catalyst a sulfonic resin.
  • biomass processing is carried out. sustainable and integrated way, for conversion into a broad spectrum of chemicals and energy.
  • Two categories of biomass-derived resources are distinguished: those of first generation from high-starch edible plant crops such as sugar cane, beets, sweet sorghum, and vegetable oils, animal fats, etc., and the second generation that use lignocellulosic biomass, Jatropha oil, microalgae, etc.
  • a very important aspect is the use of lignocellulose present in forest, agricultural, agri-food, urban and industrial waste, since it is the main component of biomass.
  • Lignocellulosic biomass is a molecular complex consisting primarily of cellulose, hemicellulose, and lignin. The latter prevents access to sugars Being around the cellulose and hemicellulose present in the biomass, it is necessary to take a slow retratam of it in order for the carbohydrates to be affordable.
  • Iignocellulosic biomass can be treated by two procedures: thermal and hydrolysis,
  • thermochemical route implies a treatment at high temperatures and pressures.
  • the strategies to highlight in this way are gasification, pyrolysis and liquefaction. It is the process commonly used for catalytic conversion or fuel production, as is the case of the Fischer-Tropsch or hydro-oxygenation process.
  • o In the case of performing a hydrolysis or fractionation of the Iignocellulosic biomass, it is possible to isolate lignin and sugars to be treated through biological (enzymatic catalysis) or chemical processes (acid catalysis).
  • hydrolysis can be favored by increasing the system temperature above 225 ° C, combining it with the use of acidic metal catalysts.
  • One of the most attractive routes of cellulose transformation is its conversion to glucose.
  • Glucose is an important precursor to a broad spectrum of chemicals with high added value.
  • sorbitol stands out, one of the polyalcohols obtained by reduction, being a very important product from an industrial point of view.
  • Sorbitol is one of the most important platform products, which is obtained by reducing the glucose present in the lignocellulose composition, in particular in hernicellulose and cellulose.
  • Sorbitol is the hydrogenated form of glucose. It can be easily obtained from cellulose with very low production costs, being an ideal compound for the synthesis of derivatives of great interest in the industry, cellulose hydrolysis and subsequent catalytic hydrogenation of the resulting glucose can also lead to products of degradation of the resulting sorbitol.
  • Isosorbide is a versatile platform chemical, due to its high stability and the two functional hydroxyl groups that allow various chemical modifications, since which can be converted into other functional groups, being able to generate different monomers used for the production of polymeric materials.
  • Isosorbide has excellent physical-chemical properties applicable to different fields of industry, being an extraordinary pharmaceutical intermediate (diuretic, and mainly to treat hydrocephalus and glaucoma), it is used as an additive to improve the resistance and stiffness of polymers such as polyethylene terephthalate (PET), and as a monomer for the production of biodegradable polymers.
  • polymers such as polyethylene terephthalate (PET)
  • PET polyethylene terephthalate
  • the compounds derived from isosorbide are isosorbide dinitrate and mononitrate, the latter being a compound widely used as a vasodilator for angina pectoris and congestive heart failure.
  • Isosorbide derivatives also find applications such as fuels or fuel additives, due to the high energy content that aiphatic substituents can provide (dimethyl isosorbide (DMI)).
  • DMI dimethyl isosorbide
  • Dehydration of sorbitol to isosorbide takes place through two consecutive stages. It begins with a first cyclization with loss of a water molecule where the chemical intermediates can be formed: 2,5-sorbitan and 1,5-sorbitan, which do not evolve to isosorbide, so they can be considered reaction byproducts, and the 1,4-sorbitan and 3,6-sorbitan, which progress to isosorbide. Subsequently, the second dehydration occurs, with a new cyclization that generates the isosorbide molecule.
  • this reaction is carried out using homogeneous acid catalysis, in the presence of liquid mineral acids, which leads to problems with corrosion of the reactors, neutralization stages and catalyst separation that cannot be reused.
  • solid catalysts represent a more sustainable alternative from an economic and environmental point of view, in addition to allowing in some cases a modulation of selectivity.
  • one of the objectives of Green Chemistry is the substitution of liquid mineral acids used in homogeneous catalytic processes by solid acid catalysts.
  • reaction systems aqueous solutions in gas and liquid phase, use of molten sorbitol have been studied in the presence of a broad spectrum of solid acid catalysts.
  • solid acid catalysts such as zeolites (Andrews et al. WO2001092266 A2, 2001; Liu et al., EP2146998 Al, 2010), tetravalent metal phosphates (Gu et al. ., Catal. Lett. 133 (2009) 214-220), heteropolyacids supported on silica (Sun et al., Korean J. Chem. Eng. 28 (2011) 99-105), sulfated copper oxide (Xia et al. , Catal. Commun. 12 (2011) 544-547), silicotungstic acid (Oltmanns et al., Appl. Catal.
  • sulfonic resins also used as ion exchangers.
  • These ionic exchange resins may have acidic or basic gnipos, in the event that cationic or ammonium exchange is pursued, respectively.
  • cation exchange resins become important, since they have strong acidic sulfonic gnipos (-S03H). They can also be used in a wide pH range.
  • the present invention relates to the development of a heterogeneous catalytic process for the dehydration of sorbitol, obtained from glucose from lignocellulosic biomass, to isosorbide, in a sustainable and efficient way, by proposing the replacement of liquid acid catalysts by solid acid catalysts that subside. the environmental, corrosion and separation problems involved in homogeneous catalysis.
  • styrene-divinylbenzene resins with acidic sulfonic groups whose polymeric structure consists of macroporous polystyrene cross-linked with divinylbenzene, with an acidity of 5.2 eq / kg, with a percentage of residual moisture of the 3%, with a particle size in the range 425-1200 micrometers, a specific area in the range 20-50 m 2 / g, a pore volume in the range 0.2-0.6 ml / g, an average diameter of the pore in the range 23-70 nm, and a thermal stability that extends to a maximum temperature of 180 ° C, as a solid acid catalyst in a heterogeneous catalytic process for the dehydration of sorbitol to isosorbide.
  • the invention relates to the use of styrene-divinylbenzene resins with acidic sulfonic groups whose polymeric structure consists of macroporous polystyrene cross-linked with divinylbenzene, with an acidity of 5.2 eq / kg, with a moisture percentage 3% residual, with a particle size in the range 425-1200 micrometers, a specific area in the range 35-50 m 2 / g, a pore volume in the range 0.2-0.5 ml / g, a average pore diameter in the range 23.1-42.5 nm, and a thermal stability that extends to a maximum temperature of 180 ° C, as a solid acid catalyst in a heterogeneous catalytic process for the dehydration of sorbitol to isosorbide.
  • the invention relates to the use of styrene-divinylbenzene resins with acidic sulfonic groups whose polymeric structure consists of macroporous polystyrene crosslinked with divinylbenzene, with an acidity of 5.2 eq / kg, with a moisture percentage 3% residual, with a particle size in the range 600-850 micrometers, a specific area in the range 20-40 m 2 / g, a pore volume in the range 0.2-0.6 ml / g, a average pore diameter in the range 40-70 nm, and a thermal stability that extends to a maximum temperature of 180 ° C, as a solid acid catalyst in a heterogeneous catalytic process for the dehydration of sorbitol to isosorbide.
  • a second object of the invention relates to a heterogeneous catalytic process for the dehydration of sorbitol to isosorbide which comprises the use of a styrene divinylbenzene resin with acid sulfonic groups as a solid acid catalyst according to the first object of the invention.
  • the process comprises (i) the addition to a reactor of the catalyst and sorbitol in a ratio sorbitol mass: catalyst in the range 10: 1-20: 1, preferably 20: 1; (ii) the reaction of the sorbitol mixture: catalyst under stirring, in the absence of solvent, and at a temperature in the range 140-180 ° C, preferably in the range 140-160 ° C, more preferably at 140 ° C, during a reaction time in the range 90 minutes - 12 hours, preferably in the range 10-12 hours, more preferably for 10 hours; (iii) dilution of the volume of melt resulting from the reaction with distilled water; and (iv) the separation of the catalyst from the sugars by microfiltration of the volume of molten diluted in water.
  • the reaction is carried out at atmospheric pressure without an inert atmosphere.
  • the reaction is carried out at atmospheric pressure but in an inert atmosphere by introducing a stream of an inert gas, for example N 2 .
  • the reaction is carried out under vacuum conditions.
  • the catalytic process comprises, after the step of separating the catalyst from the sugars formed by the dehydration of sorbitol, a step of recovering the catalyst for subsequent reuse, said step comprising washing the catalyst and its drying.
  • the present invention refers to the "S of sulphonic resins, different (among others) from Amberlyst-type resins (which have differences in porosity level, particularly having a smaller average pore diameter than resins whose use is referred to in the present invention), as solid acid catalysts for the dehydration of sorbitol to isosorbide, yields in isosorbide being reached close to 70%, with a total conversion of sorbitol, when molten sorbitol is used at 140 ° C, in the absence of solvent, then 10-hour reaction, when a sorbitolxatalizer mass ratio of 20: 1 is used.
  • the reaction is carried out by melting the sorbitol (mp 95 ° C) at 140 ° C, and conversions close to 100% are achieved after 3 hours of reaction, with yields to isosorbide of 43% which increases to 74.8% at 12 hours.
  • This evolution is justified by the formation of sorbitan, monobit dehydration products of sorbitol, of which 1,4- and 3,6-sorbitan are the only ones that evolve towards isosorbide.
  • catalysts can be reused, being stable in the reaction medium without loss. significant of its catalytic activity.
  • the remaining sorbitol and reaction products are dissolved in water to separate them from the catalyst.
  • the present invention allows the process to be carried out either at atmospheric pressure or under vacuum conditions.
  • the proposed catalysts require lower reaction temperatures to achieve yield values comparable to the data described in the state of the art on dehydration of sorbitol to isosorbide.
  • Figure 4 FTIR spectra of the Purolite CT269DR and CT269DR * (after reaction).
  • Figure 5 Comparison of conversion, selectivity, performance of catalytic resins for 10 hours at 140 ° C.
  • Figure 6 Catalytic activity of Purolite CT269DR as a function of reaction temperature.
  • Figure 7 Kinetic study of sorbitol dehydration at 140 ° C, up to 12 h of reaction time.
  • Figure 8 Kinetic study of sorbitol dehydration at 140 ° C, up to 44 h of reaction time
  • Figure 10 Study of the influence of the size of Purolite CT269DR at 140 ° C, during 90 min with 2 g sorbitol.
  • styrene-divinylbenzene resins with acid sulfonic groups are styrene-divinylbenzene resins with acid sulfonic groups.
  • Three commercial Purolite resins have been used: CT275DR, CT269DR and PD206. These types of resins have large diameter pores, which facilitate access to acid sites and avoid diffusional limitations that could appear with microporous materials. Be It deals with resins with a high concentration of acid centers. Its rnacroporous skeleton is formed by polyvinylbenzenesulfonic groups.
  • This technique allows the determination of the percentage composition of C, N, H and S of the resins studied. It is based on the complete oxidation of the sample by combustion with pure oxygen, in a controlled atmosphere, at a temperature of up to 1100 ° C.
  • the different resulting combustion products, C () 2, i and 2 O. 802 and N2 are subsequently quantified by IR and thermal conductivity sensor.
  • the percentages of carbon range between 35 and 45% with respect to the weight of the sample, while the mass C / S ratios indicate that the degree of sulfonation of these resins is different (Table 3).
  • Table 3 the lowest values are found for reams that have higher specific surfaces, that is, the CT269DR and CT275DR purolites, so it is expected that this suitable combination of high acidity and high surface area results in optimal catalytic behavior.
  • ATD-TG Differential and thermogravimetric thermal analysis
  • FTIR Fourier transform infrared spectroscopy
  • This technique consists in the study of the interaction of infrared radiation with matter. This spectroscopy allows to identify chemical species through the determination of the frequency at which the different functional groups have characteristic absorption bands in the IR spectrum. The concentration of the species is determined from the intensities and areas of the sample bands.
  • Figure 4 shows, as an example, the FTIR spectrum of the CT269DR resin, before and after the reaction. Both spectra are identical, indicating that the resin resists thermally, maintaining its structural integrity after the catalytic process.
  • the vibration modes associated with the sulphonic groups, with symmetric and asymmetric tensions of the S 0 to 620 and 1220 e and the voltage vibration CS at 1050 enr ⁇ , are masked by the intense bands of the organic skeleton of the Purolite resin , formed by divinylbenzene groups.
  • This reaction system consists of a discontinuous hatch reactor immersed in a silicone bath.
  • the reaction is carried out by introducing 2 g of sorbitol and 100 mg of catalyst into the reactor, which in turn is immersed in a liquid bath located on a heating plate, with magnetic stirring at 600 rpm, at 140 ° C for 10 hours, as standard reaction conditions.
  • the reaction time measurement starts once the bath thermometer reaches that temperature, and the reaction is interrupted by cooling the reactor in a cold water bath
  • the melt volume is diluted to 100 ml with distilled water. A fraction is taken from this solution, which is microfiltered and analyzed.
  • ICP-OES inductively coupled plasma emission spectrometry
  • this resin has been screened to obtain particle sizes in the ranges: [0.40-0.50], [0.50-, 71], [0.71-1.00] and [1.00- 1.18] mm.
  • the catalytic data demonstrate an improvement in performance with the use of the catalyst with the smallest particle size, between 0.4-0.5 mm, for which the highest sorbitol conversion is obtained.
  • the study was carried out at 140 ° C with the same sorbitol / catalyst mass ratio, but at 90 minutes of reaction in all cases ( Figure 10).
  • the catalytic activity data obtained in each cycle is shown in the bar chart of Figure 11. A slight decrease in conversion is observed after the first cycle. However, it is possible to maintain an average yield of 27-29% in isosorbide in the first 3 cycles.
  • measures CHNS chemical composition of the catalysts used were made after 2 and 4 or or reaction cycles. The data obtained are shown in Table 6 where no loss of sulfonic groups is observed. The C and H content increases slightly over the 4 cycles, corresponding to the possible carbonaceous residues. This increase in the amount of carbon leads to a continuous increase in the mass C / S ratio, after each cycle or catalytic.
  • Melt reaction system by an inert atmosphere stream
  • a stream of N2 is introduced into a flask with three mouths and an outlet, with the intention of removing the water vapor generated during the dehydration reaction.
  • the temperature is controlled by an external thermometer immersed in the silicone bath at 140 ° C, but in turn a thermometer is introduced through one of the mouths to know the thermal gradient when an inert gas is used.
  • Both the temperature and the reaction time are kept constant, 140 ° C for 10 hours; however, it is necessary to increase the initial sorbitol mass in the system to 4 g to provide a sufficient mass in the reactor, although the sorbitol / catalyst mass ratio of 20: 1 is maintained.
  • the nitrogen injection removes the water formed, but also causes a decrease in the reaction temperature, by removing heat from the medium, observing a difference of up to 30 ° C between the heating bath and the reaction atmosphere, with a negative effect on the evolution of the catalytic dehydration process.
  • CT269DR resin exhibits greater mechanical stability, which ensures its structural integrity in the reaction conditions.
  • reaction temperature was evaluated in the range between 100 and 160 ° C, 140 ° C being the optimum value, sufficiently far from the degradation temperature of the CT269DR resin (180 ° C).
  • the kinetic study showed that a complete conversion of sorbitol is achieved after 3 hours of reaction, but with an isosorbide yield of 43.2%, requiring 10 hours to obtain maximum yield (68.9%).
  • the catalyst is stable under the reaction conditions, as can be inferred from the sulfur analysis of the catalyst used and in the reaction medium.
  • the optimum catalyst loading and particle size have been 100 mg of catalyst panicles with sizes between 0.4 and 0.5 mm.
  • the chemical analysis of the catalysts used confirmed the stability of the catalyst.

Abstract

The invention relates to the dehydration of sorbitol to isosorbide in the absence of a solvent by means of heterogeneous catalysis using sulphonic resins as catalysts. The present invention, which solves problems associated with homogeneous catalysis as well as requirements of other sulphonic resins and other catalysts, relates to the use of different styrene-divinylbenzene resins, the polymer structure of which consists of macroporous polystyrene cross-linked with divinylbenzene, as solid acid catalysts in a heterogeneous catalytic process for dehydrating sorbitol to isosorbide. The invention also relates to heterogeneous catalytic processes for dehydrating sorbitol to isosorbide in the absence of a solvent, either at atmospheric pressure or in vacuum conditions, which comprise: adding the resins used as catalysts in a sorbitol:catalyst mass ratio between 10:1 and 10:2; reacting at 140-180° C for 1.5-12 hours; subsequently diluting the melt volume; and separating the catalyst and sugars by microfiltration.

Description

Deshidratación de sorbitol a isosorbida en ausencia de disolvente mediante catálisis heterogénea usando resinas sulfónicas como catalizadores  Dehydration of sorbitol to isosorbide in the absence of solvent by heterogeneous catalysis using sulfonic resins as catalysts
SECTOR TÉCNICO TECHNICAL SECTOR
La presente invención se refiere a procesos catalíticos dirigidos a la transformación de la biomasa, en particular la lignocelulosa, en productos químicos de alto valor añadido y biocombustibles. Más particularmente se refiere a la deshidratación de sorbitol a isosorbida mediante catálisis heterogénea, utilizando como catalizador una resina sulfónica. The present invention relates to catalytic processes aimed at the transformation of biomass, in particular lignocellulose, into high value-added chemicals and biofuels. More particularly it refers to the dehydration of sorbitol to isosorbide by heterogeneous catalysis, using as a catalyst a sulfonic resin.
ESTADO DE LA TÉCNICA STATE OF THE TECHNIQUE
En los últimos años, el aprovechamiento de la biomasa como materia prima renovable y sostenible para la producción de biocombustibles, energía y productos químicos ha ido recibiendo un interés creciente. En este sentido, una alternativa a la refinería tradicional donde se procesan materias primas de origen fósil (petróleo, gas natural) es la biorrefinería, donde mediante diferentes procesos mecánico-físicos, bioquímicos, químicos y termoquímicos se realiza el procesamiento de la biomasa, de forma sostenible e integrada, para su conversión en un amplio espectro de productos químicos y energía. In recent years, the use of biomass as a renewable and sustainable raw material for the production of biofuels, energy and chemicals has been receiving increasing interest. In this sense, an alternative to the traditional refinery where raw materials of fossil origin (oil, natural gas) are processed is the biorefinery, where by means of different mechanical-physical, biochemical, chemical and thermochemical processes, biomass processing is carried out. sustainable and integrated way, for conversion into a broad spectrum of chemicals and energy.
Se diferencian dos categorías de recursos derivados de la biomasa: los de primera generación procedentes de cultivos de plantas comestibles de alto contenido en almidón como son la caña de azúcar, remolacha, sorgo dulce, y de aceites vegetales, grasas animales, etc., y los segunda generación que emplean biomasa lignocelulósica, aceite de Jatropha, microalgas, etc. Two categories of biomass-derived resources are distinguished: those of first generation from high-starch edible plant crops such as sugar cane, beets, sweet sorghum, and vegetable oils, animal fats, etc., and the second generation that use lignocellulosic biomass, Jatropha oil, microalgae, etc.
Un aspecto muy importante es el aprovechamiento de la lignocelulosa presente en residuos forestales, agrícolas, agroalimentarios, urbanos e industriales, ya que es el principal componente de la biomasa. A very important aspect is the use of lignocellulose present in forest, agricultural, agri-food, urban and industrial waste, since it is the main component of biomass.
La biomasa lignocelulósica se trata de un complejo molecular constituido fundamentalmente por celulosa, hemicelulosa, y lignina. Este último impide el acceso a los azúcares. Al estar rodeando a la celulosa y hemicelulosa presentes en la biomasa, es necesario un p retratam lento de ésta para que los carbohidratos sean asequibles. Lignocellulosic biomass is a molecular complex consisting primarily of cellulose, hemicellulose, and lignin. The latter prevents access to sugars Being around the cellulose and hemicellulose present in the biomass, it is necessary to take a slow retratam of it in order for the carbohydrates to be affordable.
La transformación de la materia de origen biomásico a monómeros sencillos es viable y factible aunque las dificultades que presentan los distintos componentes de la lignoceluiosa para hacerlos accesibles son objeto de investigación, y todavía se requiere el desarrollo de tecnologías adecuadas para obtener altos rendimientos en glucosa desde biomasa iignocelulósica. Estudios recientes han demostrado la viabilidad de realizar un pretratamiento de la celulosa, aumentando el área superficial de la biomasa, rompiendo el sello de lignina y eliminando la hemicelulosa presente, para poder así modificar la estructura y facilitar los procesos posteriores [N. Mosier, C. Wyman, B. Dale, R. Eiander, Y. Lee, M. Hoitzapple, M. Ladisch, Bioresour Technol 96 (2005) 673-686], Como es previsible, esta etapa preliminar de tratamiento encarece el sistema de producción de azúcares de la biomasa, lo que supone un nuevo reto para la comunidad científica. The transformation of matter of biomasic origin into simple monomers is feasible and feasible although the difficulties presented by the different components of lignocellulose to make them accessible are subject to investigation, and the development of appropriate technologies is still required to obtain high glucose yields from iignocellulosic biomass. Recent studies have demonstrated the feasibility of pretreating cellulose, increasing the surface area of the biomass, breaking the lignin seal and eliminating the hemicellulose present, in order to modify the structure and facilitate subsequent processes [N. Mosier, C. Wyman, B. Dale, R. Eiander, Y. Lee, M. Hoitzapple, M. Ladisch, Bioresour Technol 96 (2005) 673-686], As expected, this preliminary stage of treatment makes the system more expensive production of sugars from biomass, which represents a new challenge for the scientific community.
La biomasa Iignocelulósica se puede tratar mediante dos procedimientos: térmico e hidrólisis, Iignocellulosic biomass can be treated by two procedures: thermal and hydrolysis,
o La ruta termoquímica implica un tratamiento a altas temperaturas y presiones. Las estrategias a destacar en esta vía son gasificación, pirólisis y licuefacción. Es el proceso comúnmente usado para la conversión catalítica o producción de combustibles, como es el caso del proceso Fischer-Tropsch o de hidrodesoxigenación. o En el caso de realizar una hidrólisis o fraccionamiento de la biomasa Iignocelulósica se consigue aislar la lignina y los azúcares para ser tratados a través de procesos biológicos (catálisis enzimática) o químicos (catálisis ácida).  o The thermochemical route implies a treatment at high temperatures and pressures. The strategies to highlight in this way are gasification, pyrolysis and liquefaction. It is the process commonly used for catalytic conversion or fuel production, as is the case of the Fischer-Tropsch or hydro-oxygenation process. o In the case of performing a hydrolysis or fractionation of the Iignocellulosic biomass, it is possible to isolate lignin and sugars to be treated through biological (enzymatic catalysis) or chemical processes (acid catalysis).
Mediante hidrólisis ácida solo se pueden alcanzar rendimientos del 70%, pero haciendo uso de la hidrólisis enzimática se obtienen valores de hasta un 95% [T. Lloyd, C. Wyman, Bioresour Technol 96 (2005) 1967-1977], Este hecho se justifica atendiendo a que en la hidrólisis ácida se tiene un sistema heterogéneo formado un sólido biomásico y el reactivo ácido líquido, pudiendo aparecer limitaciones de transferencia de masa. Por otra parte, para solventar este inconveniente y obtener directamente polioles, tales como el sorbitol, desde la celulosa, se están investigando sistemas donde la celulosa se hidroliza por los protones provenientes de las moléculas del agua y los sitios ácidos de la superficie catalítica, siendo la etapa determinante del proceso, y posteriormente se realiza una hidrogenación sobre un catalizador metálico [G. Liang, C. Wu, L. He, J. Ming, H. Cheng, L. Zhuo, F. Zhao, Oreen Chem 13 (2011) 839-842]. Además, se puede favorecer la hidrólisis aumentando la temperatura del sistema por encima de 225°C, combinándolo con el uso de catalizadores metálicos ácidos. Una de las rutas más atractivas de transformación de la celulosa es su conversión a glucosa. La glucosa es un importante precursor de un amplio espectro de productos químicos de alto valor añadido. Through acid hydrolysis only yields of 70% can be achieved, but using enzymatic hydrolysis values of up to 95% are obtained [T. Lloyd, C. Wyman, Bioresour Technol 96 (2005) 1967-1977], This fact is justified in view of the fact that in acid hydrolysis there is a heterogeneous system formed a biomass solid and the liquid acid reagent, and mass transfer limitations may appear . On the other hand, to solve this problem and directly obtain polyols, such as sorbitol, from cellulose, systems where cellulose is hydrolyzed by protons from water molecules and acidic sites of the catalytic surface are being investigated. the determining stage of the process, and then hydrogenation is performed on a metal catalyst [G. Liang, C. Wu, L. He, J. Ming, H. Cheng, L. Zhuo, F. Zhao, Oreen Chem 13 (2011) 839-842]. In addition, hydrolysis can be favored by increasing the system temperature above 225 ° C, combining it with the use of acidic metal catalysts. One of the most attractive routes of cellulose transformation is its conversion to glucose. Glucose is an important precursor to a broad spectrum of chemicals with high added value.
De todos los posibles derivados de la glucosa, destaca el sorbitol, uno de los polialcoholes obtenido mediante reducción, siendo un producto muy importante desde el punto de vista industrial. Of all the possible glucose derivatives, sorbitol stands out, one of the polyalcohols obtained by reduction, being a very important product from an industrial point of view.
El sorbitol es uno de los productos plataforma más importantes, que se obtiene por reducción de la glucosa presente en la composición de la lignocelulosa, en particular en la hernicelulosa y celulosa. Sorbitol is one of the most important platform products, which is obtained by reducing the glucose present in the lignocellulose composition, in particular in hernicellulose and cellulose.
El sorbitol es la forma hidrogenada de la glucosa. Se puede obtener fácilmente desde la celulosa con costes de producción muy bajos, siendo un compuesto ideal para la síntesis de derivados de enorme interés en la industria, la hidrólisis de la celulosa y la posterior hidrogenación catalítica de la glucosa resultante puede conducir también a productos de degradación del sorbitol resultante. Sorbitol is the hydrogenated form of glucose. It can be easily obtained from cellulose with very low production costs, being an ideal compound for the synthesis of derivatives of great interest in the industry, cellulose hydrolysis and subsequent catalytic hydrogenation of the resulting glucose can also lead to products of degradation of the resulting sorbitol.
Se traía de un proceso continuo o en serie que requiere alta temperatura y presión para la hidrogenación, un posterior filtrado y un refinado por intercambio iónico, donde finalmente se concentra el sorbitol. It was a continuous or series process that requires high temperature and pressure for hydrogenation, subsequent filtration and refining by ion exchange, where sorbitol is finally concentrated.
Es un producto de interés, ya que puede transformarse en biocombustibles, a través de un reformado en fase acuosa (APR), o a productos de alto valor añadido como glicoles, tras una hidrodeoxigenación en fase acuosa. It is a product of interest, since it can be transformed into biofuels, through a reformed in aqueous phase (APR), or to products of high added value such as glycols, after hydrodeoxygenation in aqueous phase.
Entre los compuestos obtenidos derivados del sorbitol cabe destacar la isosorbida y el 1,4- sorbitan, compuestos extensamente empleados en la industria farmacéutica, como surfactantes, aditivos alimentarios y en la síntesis de tereftalato de poliet.il eno. Además, son de especial interés también el ácido ascórbico (vitamina C) y el dinitrato de isosorbida, por sus aplicaciones en medicina, La deshidratación de sorbitol a isosorbida se realiza mediante catálisis homogénea, en presencia de ácidos minerales fuertes como catalizadores, entre los que destacan los ácidos sulfúrico (H2S04), clorhídrico (HC1) y fosfórico (H3PO4). Estos sistemas presentan conversiones elevadas a bajas temperaturas, pero conllevan una serie de inconvenientes, tales como altos costes de separación y problemas de corrosión en los equipos. Consecuentemente, para solucionar estos problemas, a día de hoy, las investigaciones se dirigen al desarrollo de procesos de catálisis heterogénea, donde se emplean catalizadores sólidos ácidos como zeolitas, metales fosfatados, resinas de intercambio iónico, entre otros. Al reemplazar los catalizadores líquidos por sólidos ácidos se evitan los problemas de separación y corrosión, aunque cabe destacar que las selectividades al producto de interés deben mejorarse, además de solventarse los posibles problemas de desactivación y lixiviación del catalizador. Por otro lado, la separación de los distintos productos de mezcla supone un reto importante, debido a los compuestos diferentes que se pueden obtener con propiedades químicas similares. Por ello, se requiere la optimización del proceso de deshidratación para alcanzar el máximo rendimiento en isosorbida. Among the compounds obtained derived from sorbitol, isosorbide and 1,4-sorbitan, compounds widely used in the pharmaceutical industry, such as surfactants, food additives and in the synthesis of polye.il eno terephthalate. In addition, ascorbic acid (vitamin C) and isosorbide dinitrate are also of special interest, due to their applications in medicine. Dehydration of sorbitol to isosorbide is carried out by homogeneous catalysis, in the presence of strong mineral acids as catalysts, among which The sulfuric acids (H2S04), hydrochloric (HC1) and phosphoric (H3PO4) stand out. These systems have high conversions at low temperatures, but entail a series of inconveniences, such as high separation costs and corrosion problems in the equipment. Consequently, to solve these problems, today, research is aimed at the development of heterogeneous catalysis processes, where solid acid catalysts such as zeolites, phosphated metals, ion exchange resins, among others are used. When replacing liquid catalysts with acid solids, separation and corrosion problems are avoided, although it should be noted that the selectivities to the product of interest must be improved, in addition to solving the possible problems of catalyst deactivation and leaching. On the other hand, the separation of the different mixing products is an important challenge, due to the different compounds that can be obtained with similar chemical properties. Therefore, optimization of the dehydration process is required to achieve maximum isosorbide yield.
En los últimos años, ha crecido de forma importante el interés en la producción de sorbitol y su deshidratación a isosorbida en presencia de catalizadores heterogéneos, y el reto consiste en su obtención directa a partir de celulosa, en lugar de usar la glucosa como materia prima. In recent years, interest in the production of sorbitol and its dehydration to isosorbide has increased significantly in the presence of heterogeneous catalysts, and the challenge is to obtain it directly from cellulose, instead of using glucose as a raw material. .
La isosorbida es un producto químico plataforma versáti l, debido a su alta estabi lidad y a los dos grupos hidroxilo funcionales que permiten diversas modificaciones químicas, ya que se pueden convertir en oíros grupos funcionales, pudiendo generar diferentes monómeros usados para la producción de materiales poliméricos. Isosorbide is a versatile platform chemical, due to its high stability and the two functional hydroxyl groups that allow various chemical modifications, since which can be converted into other functional groups, being able to generate different monomers used for the production of polymeric materials.
La isosorbida presenta excelentes propiedades físico-químicas aplicables a distintos campos de la industria, tratándose de un extraordinario intermedio farmacéutico (diurético, y principalmente para tratar la hidrocefalia y el glaucoma), se usa como aditivo para mejorar la resistencia y la rigidez de polímeros como el tereftalato de polietileno (PET), y como monómero para la producción de polímeros biodegradables. Entre los compuestos derivados de la isosorbida se encuentran el dinitrato y mononitrato de isosorbida, siendo este último un compuesto extensamente utilizado como vasodilatador para la angina de pecho y la insuficiencia cardíaca congestiva. Isosorbide has excellent physical-chemical properties applicable to different fields of industry, being an extraordinary pharmaceutical intermediate (diuretic, and mainly to treat hydrocephalus and glaucoma), it is used as an additive to improve the resistance and stiffness of polymers such as polyethylene terephthalate (PET), and as a monomer for the production of biodegradable polymers. Among the compounds derived from isosorbide are isosorbide dinitrate and mononitrate, the latter being a compound widely used as a vasodilator for angina pectoris and congestive heart failure.
Los derivados de la isosorbida también encuentran aplicaciones como combustibles o aditivos de combustibles, debido al alto contenido energético que pueden aportar los sustituyentes aíifáticos (dimetil isosorbida (DMI)). Isosorbide derivatives also find applications such as fuels or fuel additives, due to the high energy content that aiphatic substituents can provide (dimethyl isosorbide (DMI)).
La deshidratación de sorbitol a isosorbida tiene lugar a través de dos etapas consecutivas. Comienza con una primera ciclación con pérdida de una molécula de agua donde se pueden formar los intermedios químicos: 2,5-sorbitan y 1,5-sorbitan, que no evolucionan a isosorbida, por lo que se pueden considerar subproductos de reacción, y el 1,4-sorbitan y 3,6-sorbitan, que progresan a isosorbida. Posteriormente, se produce la segunda deshidratación, con una nueva ciclación que genera la molécula de isosorbida. Actualmente, esta reacción se realiza empleando catálisis ácida homogénea, en presencia de ácidos minerales líquidos, lo que conlleva problemas de corrosión de los reactores, etapas de neutralización y separación del catalizador que no puede reutilizarse. En este contexto, el desarrollo de catalizadores sólidos representa una alternativa más sostenible desde el punto de vista económico y medioambiental, además de permitir en algunos casos una modulación de la selectividad. Por otra parte, uno de los objetivos de la Química Verde es la sustitución de los ácidos minerales líquidos usados en procesos catalíticos homogéneos por catalizadores sól idos ácidos. Así, se han estudiado varios sistemas de reacción (disoluciones acuosas en fase gas y líquida, uso de sorbitol fundido) en presencia de un amplio espectro de catalizadores sólidos ácidos. Dehydration of sorbitol to isosorbide takes place through two consecutive stages. It begins with a first cyclization with loss of a water molecule where the chemical intermediates can be formed: 2,5-sorbitan and 1,5-sorbitan, which do not evolve to isosorbide, so they can be considered reaction byproducts, and the 1,4-sorbitan and 3,6-sorbitan, which progress to isosorbide. Subsequently, the second dehydration occurs, with a new cyclization that generates the isosorbide molecule. Currently, this reaction is carried out using homogeneous acid catalysis, in the presence of liquid mineral acids, which leads to problems with corrosion of the reactors, neutralization stages and catalyst separation that cannot be reused. In this context, the development of solid catalysts represents a more sustainable alternative from an economic and environmental point of view, in addition to allowing in some cases a modulation of selectivity. On the other hand, one of the objectives of Green Chemistry is the substitution of liquid mineral acids used in homogeneous catalytic processes by solid acid catalysts. Thus, several reaction systems (aqueous solutions in gas and liquid phase, use of molten sorbitol) have been studied in the presence of a broad spectrum of solid acid catalysts.
En la bibliografía (trabajos científicos y patentes) se ha publicado el uso de catalizadores ácidos sólidos tales como zeolitas (Andrews et al. WO2001092266 A2, 2001; Liu et al., EP2146998 Al, 2010), fosfatos de metales tetravalentes (Gu et al., Catal. Lett. 133 (2009) 214-220), heteropoliácidos soportados sobre sílice (Sun et al., Korean J. Chem. Eng. 28 (2011) 99-105), óxido de cobre sulfatado (Xia et al., Catal. Commun. 12 (2011) 544-547), ácido silicotúngstico (Oltmanns et al., Appl. Catal. A 456 (2013) 168-173), fosfatos de metales trivalentes (Igert et al., WO2014023789 Al, 2014), titania sulfatada (Ahmed et al., Chem. Eng. Se. 93 (2013) 91-959), óxido de estaño sulfatado (Dabbawala et al, Catal. Commun. 42 (2013) 1-5), zirconia sulfatada (Khan et al., Appl. Catal. A 452 (2013) 34-48), fosfato de niobilo (Xi et al., Appl. Catal. A 469 (2014) 108-115), óxido de tántalo fosfatado (Zhang et al., Catal. Commun. 43 (2014) 29-33) y ácidos de Brónsted y Lewis de muy diversa naturaleza (Dabbawala et al., Appl. Catal. A 492 (2015) 252-261). Los datos catalíticos recogidos en estos trabajos reflejan rendimientos máximos de isosorbida cercanos al 70%, pero empleando disoluciones acuosas de sorbitol a alta temperatura en fase gas, o mediante el uso de microondas. The use of solid acid catalysts such as zeolites (Andrews et al. WO2001092266 A2, 2001; Liu et al., EP2146998 Al, 2010), tetravalent metal phosphates (Gu et al. ., Catal. Lett. 133 (2009) 214-220), heteropolyacids supported on silica (Sun et al., Korean J. Chem. Eng. 28 (2011) 99-105), sulfated copper oxide (Xia et al. , Catal. Commun. 12 (2011) 544-547), silicotungstic acid (Oltmanns et al., Appl. Catal. A 456 (2013) 168-173), trivalent metal phosphates (Igert et al., WO2014023789 Al, 2014 ), sulfated titania (Ahmed et al., Chem. Eng. Se. 93 (2013) 91-959), sulfated tin oxide (Dabbawala et al, Catal. Commun. 42 (2013) 1-5), sulfated zirconia ( Khan et al., Appl. Catal. A 452 (2013) 34-48), niobyl phosphate (Xi et al., Appl. Catal. A 469 (2014) 108-115), phosphate tantalum oxide (Zhang et al. ., Catal. Commun. 43 (2014) 29-33) and Brónsted and Lewis acids of very diverse sa nature (Dabbawala et al., Appl. Catal. A 492 (2015) 252-261). The catalytic data collected in these works reflect maximum yields of isosorbide close to 70%, but using aqueous solutions of sorbitol at high temperature in the gas phase, or through the use of microwaves.
En la actualidad, se siguen buscando sistemas catalíticos activos y selectivos para la transformación del sorbitol en isosorbida, y entre los catalizadores ácidos estudiados se encuentran las resinas sulfónicas, empleadas también como cambiadores iónicos. Estas resinas de cambio iónico pueden presentar gnipos ácidos o básicos, en íunción de que se persiga intercambio catiónico o amónico, respectivamente. En relación a la reacción de deshidratación del sorbitol, las resinas de intercambio catiónico cobran importancia, ya que poseen gnipos sulfónicos (-S03H) ácidos fuertes. Además pueden usarse en un amplio rango de pH. Uno de los sistemas propuestos hasta ahora con este tipo de materiales consiste en emplear Amberlyst™ 35 (Hu et al., US 2007/0173653, 2007; Holladay et al., US 7649099 B2, 2010; Moore and Sanborn, US 6849748 B2, 2005; Polaert et al., Chem. Eng. J. 222 (2013) 228- 239). Por ejemplo, en í. Polaert, M. Félix, M. Fornasero, S. Marcotte, J. Buvat, L. Este!, Chem Eng J 222 (2013) 228-239 se refiere el uso de .Amberlyst™ 35 seca (8.16%w/ ), calentando con microondas a presión atmosférica, obteniéndose una selectividad a isosorbida de! 70%. Currently, active and selective catalytic systems are still being sought for the transformation of sorbitol into isosorbide, and among the acid catalysts studied are sulfonic resins, also used as ion exchangers. These ionic exchange resins may have acidic or basic gnipos, in the event that cationic or ammonium exchange is pursued, respectively. In relation to the dehydration reaction of sorbitol, cation exchange resins become important, since they have strong acidic sulfonic gnipos (-S03H). They can also be used in a wide pH range. One of the systems proposed so far with this type of materials is to use Amberlyst ™ 35 (Hu et al., US 2007/0173653, 2007; Holladay et al., US 7649099 B2, 2010; Moore and Sanborn, US 6849748 B2, 2005; Polaert et al., Chem. Eng. J. 222 (2013) 228-239). For example, in í. Polaert, M. Felix, M. Fornasero, S. Marcotte, J. Buvat, L. Este !, Chem Eng J 222 (2013) 228-239 refers to the use of dry Amberlyst ™ 35 (8.16% w /), heating with microwave at atmospheric pressure, obtaining an isosorbide selectivity of! 70%
En la patente US 6849748 B2 se recogen los resultados obtenidos con Amberlyst 35 y otras resinas sulfónicas (Amberlyst 15, Dowex 50WX4 y RCP 21H), donde se emplea también sorbitol fundido, pero en condiciones de vacío (1-10 torr), y la mezcla se destila a vacío. La patente US2007/0173653 Al (Hu et al., 2007) hace referencia al uso de Amberlyst-35, pero trabaja con disoluciones acuosas de sorbitol en fase gas. In US 6849748 B2 the results obtained with Amberlyst 35 and other sulfonic resins (Amberlyst 15, Dowex 50WX4 and RCP 21H) are collected, where molten sorbitol is also used, but under vacuum conditions (1-10 torr), and the mixture is distilled under vacuum. US2007 / 0173653 Al (Hu et al., 2007) refers to the use of Amberlyst-35, but works with aqueous solutions of sorbitol in the gas phase.
Más recientemente, Zhang y colaboradores han comparado una Amberlyst- 15 y polímero mesoporoso superhidrofóbico basado en P-S03-H como catalizadores ácidos [J. Zhang, L, Wang, F. Liu, X. Meng, J. Mao, F. Xiao, Catal Today 242 (2015) 249-254], A 140°C, durante 10 horas, la resina mostró una elevada conversión (94.3%) y selectividad a isosorbida de 71,8%, pero que aumentaba hasta 87.9% y la conversión de sorbitol prácticamente fue completa (99%) con el polímero mesoporoso. Además, posteriores estudios de reutilización corroboraron el excelente comportamiento del polímero P-S03-H durante 5 ciclos, manteniendo una selectividad del 77.7%, superior al valor del primer ciclo de la Amberíyst-15 y muy por encima de los 3 ciclos de reutil ización de la misma, donde pierde su actividad y sólo alcanza un 15,4% de selectividad a isosorbida. DESCRIPCIÓN DE LA INVENCIÓN More recently, Zhang et al. Have compared an Amberlyst-15 and superhydrophobic mesoporous polymer based on P-S03-H as acid catalysts [J. Zhang, L, Wang, F. Liu, X. Meng, J. Mao, F. Xiao, Catal Today 242 (2015) 249-254], At 140 ° C, for 10 hours, the resin showed a high conversion (94.3 %) and isosorbide selectivity of 71.8%, but increased to 87.9% and the conversion of sorbitol was practically complete (99%) with the mesoporous polymer. In addition, subsequent reuse studies corroborated the excellent performance of the P-S03-H polymer for 5 cycles, maintaining a selectivity of 77.7%, higher than the value of the first Amberíyst-15 cycle and well above the 3 reuse cycles of it, where it loses its activity and only reaches 15.4% isosorbide selectivity. DESCRIPTION OF THE INVENTION
La presente invención se refiere al desarrollo de un proceso catalítico heterogéneo para la deshidratación del sorbitol, obtenido de la glucosa proveniente de la biomasa lignocelulósica, a isosorbida, de forma sostenible y eficiente, planteando la sustitución de catalizadores ácidos líquidos por catalizadores ácidos sólidos que subsanen los problemas medioambientales, de corrosión y de separación que conlleva la catálisis homogénea. De este modo, constituye un primer objeto de la invención el uso de resinas de estireno- divinilbenceno con grupos sulfónicos ácidos cuya estructura polimérica consiste en poliestireno macroporoso entrecruzado con divinilbenceno, con una acidez de 5.2 eq/Kg, con un porcentaje de humedad residual del 3%, con un tamaño de partícula comprendido en el rango 425-1200 micrómetros, una área específica comprendida en el rango 20-50 m2/g, un volumen de poros comprendido en el rango 0.2-0.6 ml/g, un diámetro medio del poro comprendido en el rango 23-70 nm, y una estabilidad térmica que se extiende hasta una temperatura máxima de 180 °C, como catalizador ácido sólido en un proceso catalítico heterogéneo para la deshidratación de sorbitol a isosorbida. En una realización particular de dicho primer objeto, la invención se refiere al uso de resinas de estireno-divinilbenceno con grupos sulfónicos ácidos cuya estructura polimérica consiste en poliestireno macroporoso entrecruzado con divinilbenceno, con una acidez de 5.2 eq/Kg, con un porcentaje de humedad residual del 3%, con un tamaño de partícula comprendido en el rango 425-1200 micrómetros, una área específica comprendida en el rango 35-50 m2/g, un volumen de poros comprendido en el rango 0.2-0.5 ml/g, un diámetro medio del poro comprendido en el rango 23.1-42.5 nm, y una estabilidad térmica que se extiende hasta una temperatura máxima de 180 °C, como catalizador ácido sólido en un proceso catalítico heterogéneo para la deshidratación de sorbitol a isosorbida. En otra realización particular de dicho primer objeto, la invención se refiere al uso de resinas de estireno-divinilbenceno con grupos sulfónicos ácidos cuya estructura polimérica consiste en poliestireno macroporoso entrecruzado con divinilbenceno, con una acidez de 5.2 eq/Kg, con un porcentaje de humedad residual del 3%, con un tamaño de partícula comprendido en el rango 600-850 micrómetros, una área específica comprendida en el rango 20-40 m2/g, un volumen de poros comprendido en el rango 0.2-0.6 ml/g, un diámetro medio del poro comprendido en el rango 40-70 nm, y una estabilidad térmica que se extiende hasta una temperatura máxima de 180 °C, como catalizador ácido sólido en un proceso catalítico heterogéneo para la deshidratación de sorbitol a isosorbida. The present invention relates to the development of a heterogeneous catalytic process for the dehydration of sorbitol, obtained from glucose from lignocellulosic biomass, to isosorbide, in a sustainable and efficient way, by proposing the replacement of liquid acid catalysts by solid acid catalysts that subside. the environmental, corrosion and separation problems involved in homogeneous catalysis. Thus, it is a first object of the invention to use styrene-divinylbenzene resins with acidic sulfonic groups whose polymeric structure consists of macroporous polystyrene cross-linked with divinylbenzene, with an acidity of 5.2 eq / kg, with a percentage of residual moisture of the 3%, with a particle size in the range 425-1200 micrometers, a specific area in the range 20-50 m 2 / g, a pore volume in the range 0.2-0.6 ml / g, an average diameter of the pore in the range 23-70 nm, and a thermal stability that extends to a maximum temperature of 180 ° C, as a solid acid catalyst in a heterogeneous catalytic process for the dehydration of sorbitol to isosorbide. In a particular embodiment of said first object, the invention relates to the use of styrene-divinylbenzene resins with acidic sulfonic groups whose polymeric structure consists of macroporous polystyrene cross-linked with divinylbenzene, with an acidity of 5.2 eq / kg, with a moisture percentage 3% residual, with a particle size in the range 425-1200 micrometers, a specific area in the range 35-50 m 2 / g, a pore volume in the range 0.2-0.5 ml / g, a average pore diameter in the range 23.1-42.5 nm, and a thermal stability that extends to a maximum temperature of 180 ° C, as a solid acid catalyst in a heterogeneous catalytic process for the dehydration of sorbitol to isosorbide. In another particular embodiment of said first object, the invention relates to the use of styrene-divinylbenzene resins with acidic sulfonic groups whose polymeric structure consists of macroporous polystyrene crosslinked with divinylbenzene, with an acidity of 5.2 eq / kg, with a moisture percentage 3% residual, with a particle size in the range 600-850 micrometers, a specific area in the range 20-40 m 2 / g, a pore volume in the range 0.2-0.6 ml / g, a average pore diameter in the range 40-70 nm, and a thermal stability that extends to a maximum temperature of 180 ° C, as a solid acid catalyst in a heterogeneous catalytic process for the dehydration of sorbitol to isosorbide.
Un segundo objeto de la invención se refiere a un proceso catalítico heterogéneo para la deshidratación de sorbitol a isosorbida que comprende el uso de una resina de estireno divinilbenceno con grupos sulfónicos ácidos como catalizador ácido sólido conforme al primer objeto de la invención. En una realización preferente de dicho segundo objeto, el proceso comprende (i) la adición a un reactor del catalizador y del sorbitol en una relación másica sorbitol: catalizador comprendida en el rango 10: 1 - 20: 1, preferente 20: 1; (ii) la reacción de la mezcla sorbitol: catalizador en agitación, en ausencia de disolvente, y a una temperatura comprendida en el rango 140-180 °C, preferentemente en el rango 140-160 °C, más preferentemente a 140 °C, durante un tiempo de reacción comprendido en el rango 90 minutos - 12 horas, preferentemente en el rango 10-12 horas, más preferentemente durante 10 horas; (iii) la dilución del volumen de fundido resultante de la reacción con agua destilada; y (iv) la separación del catalizador de los azúcares mediante microfiltración del volumen de fundido diluido en agua. En una realización particular de la invención, la reacción se realiza a presión atmosférica sin atmósfera inerte. En otra realización particular de la invención, la reacción se realiza a presión atmosférica pero en atmósfera inerte introduciendo una corriente de un gas inerte, por ejemplo N2. En otra realización particular de la invención, la reacción se realiza en condiciones de vacío. Alternativamente, y en otra realización particular de la invención, el proceso catalítico comprende, tras la etapa de separación del catalizador de los azúcares formados mediante la deshidratación del sorbitol, una etapa de recuperación del catalizador para su posterior reutilización, dicha etapa comprendiendo el lavado del catalizador y su secado. A second object of the invention relates to a heterogeneous catalytic process for the dehydration of sorbitol to isosorbide which comprises the use of a styrene divinylbenzene resin with acid sulfonic groups as a solid acid catalyst according to the first object of the invention. In a preferred embodiment of said second object, the process comprises (i) the addition to a reactor of the catalyst and sorbitol in a ratio sorbitol mass: catalyst in the range 10: 1-20: 1, preferably 20: 1; (ii) the reaction of the sorbitol mixture: catalyst under stirring, in the absence of solvent, and at a temperature in the range 140-180 ° C, preferably in the range 140-160 ° C, more preferably at 140 ° C, during a reaction time in the range 90 minutes - 12 hours, preferably in the range 10-12 hours, more preferably for 10 hours; (iii) dilution of the volume of melt resulting from the reaction with distilled water; and (iv) the separation of the catalyst from the sugars by microfiltration of the volume of molten diluted in water. In a particular embodiment of the invention, the reaction is carried out at atmospheric pressure without an inert atmosphere. In another particular embodiment of the invention, the reaction is carried out at atmospheric pressure but in an inert atmosphere by introducing a stream of an inert gas, for example N 2 . In another particular embodiment of the invention, the reaction is carried out under vacuum conditions. Alternatively, and in another particular embodiment of the invention, the catalytic process comprises, after the step of separating the catalyst from the sugars formed by the dehydration of sorbitol, a step of recovering the catalyst for subsequent reuse, said step comprising washing the catalyst and its drying.
En este contexto, la presente invención refiere el «so de resinas sulfónicas, diferentes (entre otras) de las resinas tipo Amberlyst (las cuáles presentan diferencias a nivel de porosidad, particularmente presentando un menor diámetro medio de poro que las resinas cuyo uso se refiere en la presente invención), como catalizadores sólidos ácidos para la deshidratación del sorbitol a isosorbida, alcanzándose rendimientos en isosorbida cercanos al 70%, con una conversión total de sorbitol, cuando se usa sorbitol fundido a 140°C, en ausencia de disolvente, después de 10 horas de reacción, cuando se emplea una relación másica sorbitolxatalizador de 20: 1. La reacción se lleva a cabo fundiendo el sorbitol (p.f 95°C) a 140°C, y se alcanzan conversiones cercanas al 100% después de 3 horas de reacción, con rendimientos a isosorbida del 43% que se incrementa hasta el 74.8% a las 12 horas. Esta evolución se justifica por la formación de sorbitanes, productos de monodeshidratación del sorbitol, de los cuales el 1,4- y 3,6-sorbitan son los únicos que evolucionan hacia la isosorbida. In this context, the present invention refers to the "S of sulphonic resins, different (among others) from Amberlyst-type resins (which have differences in porosity level, particularly having a smaller average pore diameter than resins whose use is referred to in the present invention), as solid acid catalysts for the dehydration of sorbitol to isosorbide, yields in isosorbide being reached close to 70%, with a total conversion of sorbitol, when molten sorbitol is used at 140 ° C, in the absence of solvent, then 10-hour reaction, when a sorbitolxatalizer mass ratio of 20: 1 is used. The reaction is carried out by melting the sorbitol (mp 95 ° C) at 140 ° C, and conversions close to 100% are achieved after 3 hours of reaction, with yields to isosorbide of 43% which increases to 74.8% at 12 hours. This evolution is justified by the formation of sorbitan, monobit dehydration products of sorbitol, of which 1,4- and 3,6-sorbitan are the only ones that evolve towards isosorbide.
Estos catalizadores se pueden reutilizar, siendo estables en el medio de reacción sin pérdida significativa de su actividad catalítica. Por otra parte, el sorbitol remanente y los productos de reacción se disuelven en agua para separarlos del catalizador. La presente invención permite realizar el proceso bien a presión atmosférica bien en condiciones de vacío. Los catalizadores propuestos requieren menores temperaturas de reacción para alcanzar valores de rendimiento comparables a los datos descritos en el estado de la técnica sobre deshidratación de sorbitol a isosorbida. These catalysts can be reused, being stable in the reaction medium without loss. significant of its catalytic activity. On the other hand, the remaining sorbitol and reaction products are dissolved in water to separate them from the catalyst. The present invention allows the process to be carried out either at atmospheric pressure or under vacuum conditions. The proposed catalysts require lower reaction temperatures to achieve yield values comparable to the data described in the state of the art on dehydration of sorbitol to isosorbide.
A lo largo de la descripción y las reivindicaciones la palabra "comprende" y sus variantes no pretenden excluir otras características técnicas, componentes o pasos. Para los expertos en la materia, otros objetos, ventajas y características de la invención se desprenderán en parte de la descripción y en parte de la práctica de la invención. Los siguientes ejemplos y figuras se proporcionan a modo de ilustración, y no se pretende que sean limitativos de la presente invención. Throughout the description and claims the word "comprises" and its variants are not intended to exclude other technical characteristics, components or steps. For those skilled in the art, other objects, advantages and features of the invention will be derived partly from the description and partly from the practice of the invention. The following examples and figures are provided by way of illustration, and are not intended to be limiting of the present invention.
DESCRIPCIÓN DE LAS FIGURAS DESCRIPTION OF THE FIGURES
Figura 1 : Isotermas de adsorción-desorción de N2. Figure 1: Adsorption-desorption isotherms of N2.
Figura 2: Espectro FTIR de sorbitol. Figure 2: Sorbitol FTIR spectrum.
Figura 3 : Espectro FTIR de isosorbida. Figure 3: FTIR spectrum of isosorbide.
Figura 4: Espectros FTIR de la Purolita CT269DR y CT269DR* (después de reacción).  Figure 4: FTIR spectra of the Purolite CT269DR and CT269DR * (after reaction).
Figura 5: Comparación de conversión, selectividad, rendimiento de las resinas catalíticas durante 10 horas a 140°C. Figure 5: Comparison of conversion, selectivity, performance of catalytic resins for 10 hours at 140 ° C.
Figura 6: Actividad catalítica de la Purolita CT269DR en función de la temperatura de reacción.  Figure 6: Catalytic activity of Purolite CT269DR as a function of reaction temperature.
Figura 7: Estudio cinético de la deshidratación de sorbitol a 140°C, hasta 12 h de tiempo de reacción.  Figure 7: Kinetic study of sorbitol dehydration at 140 ° C, up to 12 h of reaction time.
Figura 8: Estudio cinético de la deshidratación de sorbitol a 140°C, hasta 44 h de tiempo de reacción  Figure 8: Kinetic study of sorbitol dehydration at 140 ° C, up to 44 h of reaction time
Figura 9: Influencia de la masa de resina CT269DR a 140°C, durante 90 min con 2 g de sorbitol. Figure 9: Influence of the mass of CT269DR resin at 140 ° C for 90 min with 2 g of sorbitol.
Figura 10: Estudio de la influencia del tamaño de la Purolita CT269DR a 140°C, durante 90 min con 2 g sorbitol. Figure 10: Study of the influence of the size of Purolite CT269DR at 140 ° C, during 90 min with 2 g sorbitol.
Figura 11 : Estudio de reutilización de la Purolita CT269DR a 140°C, durante 90 min con 2g sorbitol. MODOS DE REALIZACIÓN DE LA INVENCIÓN  Figure 11: Reuse study of Purolite CT269DR at 140 ° C, for 90 min with 2g sorbitol. EMBODIMENTS OF THE INVENTION
La constitución y características de la invención se comprenderán mejor con ayuda de la siguiente descripción de ejemplos de realización, debiendo entenderse que la invención no queda limitada a estas realizaciones, sino que la protección abarca todas aquellas realizaciones alternativas que puedan incluirse dentro del contenido y del alcance de las reivindicaciones. Asimismo, el presente documento refiere diversos documentos como estado de la técnica, entendiéndose incorporado por referencia el contenido de todos estos documentos, así como de el contenido completo de los documentos a su vez referidos en dichos documentos, con objeto de ofrecer una descripción lo más completa posible del estado de la técnica en el que la presente invención se encuadra. La terminología utilizada a continuación tiene por objeto la descripción de los ejemplos de modos de realización que siguen y no debe ser interpretada de forma limitante o restrictiva. The constitution and characteristics of the invention will be better understood with the aid of the following description of embodiments, it being understood that the invention is not limited to these embodiments, but that the protection encompasses all those alternative embodiments that may be included within the content and content. scope of the claims. Likewise, the present document refers to various documents as prior art, being understood by reference the content of all these documents, as well as the complete content of the documents referred to in said documents, in order to offer a description as possible complete state of the art in which the present invention fits. The terminology used below is intended to describe the examples of embodiments that follow and should not be construed as limiting or restrictive.
A continuación, para ilustrar la invención, se describen los resultados obtenidos usando diferentes resinas sulfómcas comerciales de tipo Purol ita, cuya estructura polimérica consiste bien en poliestireno macroporoso entrecruzado con divinilbenceno (CT275DR y CT269DR) bien en poliestireno en gel entrecruzado con divinilbenceno (PD206), como catalizadores para la deshidratación de sorbitol a isosorbida. Descripción de los Catalizadores Next, to illustrate the invention, the results obtained using different commercial sulphonic resins of the Purol ita type are described, the polymeric structure of which consists either of macroporous polystyrene cross-linked with divinylbenzene (CT275DR and CT269DR) or polystyrene gel intercrossed with divinylbenzene (PD206) , as catalysts for the dehydration of sorbitol to isosorbide. Description of the Catalysts
Dentro de la amplia gama de resinas de cambio iónico existentes se encuentran las resinas de estireno-divinilbenceno con grupos sulfónico ácidos. Se han usado tres resinas comerciales de tipo Purolita: CT275DR, CT269DR y PD206. Este tipo de resinas presentan poros de gran diámetro, que facil itan el acceso a los sitios ácidos y evitan las limitaciones difusionales que podrían aparecer con materiales microporosos. Se trata de resinas con una alta concentración de centros ácidos. Su esqueleto rnacroporoso está formado por grupos polivinübencenosulfónico. Within the wide range of existing ion exchange resins are styrene-divinylbenzene resins with acid sulfonic groups. Three commercial Purolite resins have been used: CT275DR, CT269DR and PD206. These types of resins have large diameter pores, which facilitate access to acid sites and avoid diffusional limitations that could appear with microporous materials. Be It deals with resins with a high concentration of acid centers. Its rnacroporous skeleton is formed by polyvinylbenzenesulfonic groups.
Figure imgf000013_0001
Figure imgf000013_0001
Tabla 1. Características fisicoquímicas de las resinas Purolita empleadas  Table 1. Physicochemical characteristics of Purolite resins used
Las principales características físico químicas de las resinas se muestran en Tabla 1. Propiedades texturales The main physical chemical characteristics of the resins are shown in Table 1. Textural properties
La determinación de las propiedades texturales de catalizadores sólidos es muy importante en catálisis heterogénea, ya que este proceso es un fenómeno superficial. Los parámetros texturales se han deducido a partir de las isotermas de adsorción-desorción de N2 a -196°C. Los datos de superficie específica BET, volumen de poro y diámetro medio de poros, determinados según los métodos de Brunauer-Emmett-Teller (BET) y Barrett-Joyner- H alenda (BJH), se presentan en la Tabla 2. The determination of the textural properties of solid catalysts is very important in heterogeneous catalysis, since this process is a superficial phenomenon. The textural parameters have been deduced from the adsorption-desorption isotherms of N2 at -196 ° C. The BET specific surface area, pore volume and average pore diameter data, determined according to the methods of Brunauer-Emmett-Teller (BET) and Barrett-Joyner-H alenda (BJH), are presented in Table 2.
Figure imgf000013_0002
Figure imgf000013_0002
Tabla 2. Propiedades texturales de las resinas sulfónicas  Table 2. Textural properties of sulfonic resins
Los valores obtenidos reflejan que las Purolitas secas, CT269DR y CT275DR, son las que poseen mayores áreas superficiales. Además, a pesar de que la Purolita CT269DR muestra aproximadamente eí doble de superficie BET que la CT275DR, su diámetro medio de poros es considerablemente inferior (Tabla 2). Por otra parte, la Purolita PD206 posee menores valores de los parámetros texturales evaluados. Estos valores de parámetros texturales coinciden con las especificaciones aportadas por la empresa que suministra las resinas (Purolite), aunque los valores de volumen de poros son ligeramente inferiores. En la Figura 1 se presentan las isotermas de adsorción-desorción de nitrógeno a -196°C. Para as resinas CT269DR y CT275DR, las isotermas se ajustan ai tipo IV en la clasificación de la IUPAC, correspondiente a la adsorción en multicapas sobre materiales mesoporosos. Por otro lado, la Purolita PD206 presenta una isoterma característica de sólidos no porosos, sin ciclo de histéresis ni cantidad apreciable de nitrógeno adsorbido. Análisis elemental (EA) The values obtained reflect that the dry Purolites, CT269DR and CT275DR, are those with the greatest surface areas. Also, even though the Purolite CT269DR shows Approximately twice the surface area BET than CT275DR, its average pore diameter is considerably smaller (Table 2). On the other hand, the Purolite PD206 has lower values of the textural parameters evaluated. These textural parameter values coincide with the specifications provided by the company that supplies the resins (Purolite), although the pore volume values are slightly lower. Figure 1 shows the adsorption-desorption isotherms of nitrogen at -196 ° C. For CT269DR and CT275DR resins, the isotherms conform to type IV in the IUPAC classification, corresponding to multilayer adsorption on mesoporous materials. On the other hand, Purolite PD206 has a characteristic isotherm of non-porous solids, without hysteresis cycle or appreciable amount of adsorbed nitrogen. Elementary Analysis (EA)
Esta técnica permite la determinación de la composición porcentual de C, N, H y S de las resinas estudiadas. Se basa en la completa oxidación de la muestra mediante una combustión con oxígeno puro, en atmósfera controlada, a una temperatura de hasta 1100°C. Los diferentes productos de combustión resultantes, C()2, i i 2 O. 802 y N2, son posteriormente cuantificados mediante IR y sensor de conductividad térmica. Los porcentajes de carbono oscilan entre 35 y 45 % respecto al peso de la muestra, mientras que las relaciones másicas C/S nos indican que ei grado de sulfonación de estas resinas es diferente (Tabla 3). Asi, los menores valores se encuentran para las resmas que poseen mayores superficies específicas, es decir, las purolitas CT269DR y CT275DR, por lo que es de esperar que esta combinación adecuada de elevada acidez y alta superficie se traduzca en un óptimo comportamiento catalítico. This technique allows the determination of the percentage composition of C, N, H and S of the resins studied. It is based on the complete oxidation of the sample by combustion with pure oxygen, in a controlled atmosphere, at a temperature of up to 1100 ° C. The different resulting combustion products, C () 2, i and 2 O. 802 and N2, are subsequently quantified by IR and thermal conductivity sensor. The percentages of carbon range between 35 and 45% with respect to the weight of the sample, while the mass C / S ratios indicate that the degree of sulfonation of these resins is different (Table 3). Thus, the lowest values are found for reams that have higher specific surfaces, that is, the CT269DR and CT275DR purolites, so it is expected that this suitable combination of high acidity and high surface area results in optimal catalytic behavior.
Figure imgf000014_0001
Tabla 3. Composición química másica de la Purolita CT269DR a diferentes tiempos de reacción
Figure imgf000014_0001
Table 3. Mass chemical composition of Purolite CT269DR at different reaction times
Análisis térmico diferencial y termogravimétrico (ATD-TG) Mediante el análisis térmico diferencial y termogravimétrico se obtiene información estructural sobre las variaciones de masa que experimenta un sólido en función de la temperatura, asociadas a transiciones de fase y procesos endotérmicos o exotérmicos que experimenta la muestra al someterla a un incremento de temperatura. En la curva ATD-TG de la Purolita CT269DR se observa una primera pérdida de peso de un 15%, asociada con un efecto endotérmico centrado en lOC C, atribuible a la pérdida de agua de hidratación. Differential and thermogravimetric thermal analysis (ATD-TG) By means of differential and thermogravimetric thermal analysis, structural information is obtained on the mass variations that a solid experiences as a function of temperature, associated with phase transitions and endothermic or exothermic processes experienced by the sample when subjected to an increase in temperature. In the ATD-TG curve of Purolite CT269DR, a first weight loss of 15% is observed, associated with an endothermic effect centered on lOC C, attributable to the loss of hydration water.
A mayor temperatura, en la curva ATD se aprecian dos efectos exotérmicos muy intensos, asociados a la descomposición de los grupos sulfónicos (pérdida de peso alrededor de 275°C) y a la combustión del esqueleto orgánico entre 300-55Q°C. A partir de estos datos térmicos se puede deducir que a temperaturas de trabajo superiores a 200°C se produce la degradación de este material ío que limita la temperatura de trabajo, Para la Purolita CT275DR se obtienen curvas similares, con porcentajes de pérdidas de peso y efectos térmicos análogos a los de la resina CT269DR. Sin embargo, la purolita PD206 requiere una temperatura cercana a 750°C para su combustión total At a higher temperature, two very intense exothermic effects are observed in the ATD curve, associated with the decomposition of sulfonic groups (weight loss around 275 ° C) and the burning of the organic skeleton between 300-55Q ° C. From these thermal data it can be deduced that at work temperatures higher than 200 ° C degradation of this material occurs that limits the working temperature. Similar curves are obtained for Purolite CT275DR, with percentages of weight losses and thermal effects analogous to those of the CT269DR resin. However, the PD206 purolite requires a temperature close to 750 ° C for total combustion
Espectroscopia infrarroja por transformada de Fourier (FTIR) Fourier transform infrared spectroscopy (FTIR)
Esta técnica consiste en el estudio de la interacción de la radiación infrarroja con la materia. Esta espectroscopia permite identificar especies químicas a través de la determinación de la frecuencia a la que los distintos grupos funcionales presentan bandas de absorción características en el espectro IR. La concentración de las especies se determina a partir de las intensidades y áreas de las bandas de la muestra. This technique consists in the study of the interaction of infrared radiation with matter. This spectroscopy allows to identify chemical species through the determination of the frequency at which the different functional groups have characteristic absorption bands in the IR spectrum. The concentration of the species is determined from the intensities and areas of the sample bands.
En los espectros infrarrojos de las muestras sólidas de sorbitol e isosorbida (Figuras 2 y 3} se observan, entre 3000 y 3500 cn ^ , bandas características de las vibraciones de tensión de los grupos O-H, destacando la extensa anchura en el caso del sorbitol debido al mayor contenido de grupos hidroxilo de la molécula, que favorecen la formación de enlaces de hidrógeno. Por otra parte, las vibraciones de tensión de los enlaces C-H aparecen entre 2800 y 3000 cm-1, y las vibraciones de tensión de los enlaces C-0 de estos alcoholes entre 1050 y 1150 cm-1. En la región del espectro FTIR entre 700 y 1400 cnH se detectan numerosas bandas asociadas a los diferentes modos de vibración de deformación de las moléculas de sorbitol e isosorbida. In the infrared spectra of the solid samples of sorbitol and isosorbide (Figures 2 and 3), they observe, between 3000 and 3500 cn ^, characteristic bands of the voltage vibrations of the OH groups, highlighting the wide width in the case of sorbitol due to the higher content of hydroxyl groups of the molecule, which favor the formation of hydrogen bonds. On the other hand, the tension vibrations of the CH bonds appear between 2800 and 3000 cm-1, and the tension vibrations of the C-0 bonds of these alcohols between 1050 and 1150 cm-1. In the region of the FTIR spectrum between 700 and 1400 cnH, numerous bands associated with the different deformation vibration modes of sorbitol and isosorbide molecules are detected.
En la Figura 4 se muestra, como ejemplo, el espectro FTIR de la resina CT269DR, antes y después de reacción. Ambos espectros son idénticos, lo que indica que la resina resiste térmicamente, manteniendo su integridad estructural después del proceso catalítico. Los modos de vibración asociados a l os grupos sulfónicos, con tensiones simétricas y asimétricas de los enlaces S=0 a 620 y 1220 e r y la vibración de tensión C-S a 1050 enr^, se encuentran enmascaradas por las intensas bandas del esqueleto orgánico de la resina Purolita, formada por grupos divinilbenceno. Figure 4 shows, as an example, the FTIR spectrum of the CT269DR resin, before and after the reaction. Both spectra are identical, indicating that the resin resists thermally, maintaining its structural integrity after the catalytic process. The vibration modes associated with the sulphonic groups, with symmetric and asymmetric tensions of the S = 0 to 620 and 1220 e and the voltage vibration CS at 1050 enr ^, are masked by the intense bands of the organic skeleton of the Purolite resin , formed by divinylbenzene groups.
Medidas de la actividad catalítica Measures of catalytic activity
Se han usado diferentes sistemas de reacción para el estudio de la deshidratad ón de sorbitol mediante catál isis heterogénea ácida: con o sin corriente de N2 y en condiciones de vacío para eliminar el agua formada en el proceso de deshidratación. Different reaction systems have been used for the study of sorbitol ion dehydration by means of heterogeneous acid catalyst: with or without N2 current and under vacuum conditions to eliminate the water formed in the dehydration process.
Sistema de reacción en fundido sin atmósfera inerte Este sistema de reacción consiste en un reactor hatch discontinuo sumergido en un baño de silicona. Melt reaction system without inert atmosphere This reaction system consists of a discontinuous hatch reactor immersed in a silicone bath.
La reacción se lleva a cabo introduciendo 2 g de sorbitol y 100 mg de catalizador en el interior del reactor, que a su vez se sumerge en un baño de si licona situado sobre una placa calefactora, con agitación magnética a 600 rpm, a 140°C durante 10 horas, como condiciones de reacción estándar. La medida del tiempo de reacción se inicia una vez que el termómetro del baño alcanza dicha temperatura, y se interrumpe la reacción enfriando el reactor en un baño de agua fría. The reaction is carried out by introducing 2 g of sorbitol and 100 mg of catalyst into the reactor, which in turn is immersed in a liquid bath located on a heating plate, with magnetic stirring at 600 rpm, at 140 ° C for 10 hours, as standard reaction conditions. The reaction time measurement starts once the bath thermometer reaches that temperature, and the reaction is interrupted by cooling the reactor in a cold water bath
Una vez transcurrido el tiempo de reacción, el volumen de fundido se diluye hasta 100 mi con agua destilada. De esta disolución se toma una fracción, que se microfiltra y pasa a analizarse. After the reaction time has elapsed, the melt volume is diluted to 100 ml with distilled water. A fraction is taken from this solution, which is microfiltered and analyzed.
En todos los casos se alcanzan conversiones de sorbitol cercanas ai 100%, pero con rendimientos en isosorbida entre el 70 y 75% (Figura 5). El estudio de la influencia de la temperatura de reacción se ha llevado a cabo con un tiempo de reacción de 90 minutos (Figura 6). Se observa un moderado aumento del rendimiento en isosorbida en el intervalo de 140-160°C, con un incremento de la conversión del 24%, hasta lograr una conversión superior al 90% a 160°C. Asumiendo 180°C como la temperatura de trabajo máxima que asegura la estabilidad térmica del catalizador, se ha elegido 140°C como temperatura de reacción para los posteriores ensayos catalíticos. In all cases, sorbitol conversions close to 100% are achieved, but with isosorbide yields between 70 and 75% (Figure 5). The study of the influence of the reaction temperature has been carried out with a reaction time of 90 minutes (Figure 6). A moderate increase in isosorbide yield is observed in the range of 140-160 ° C, with a 24% increase in conversion, to achieve a conversion greater than 90% at 160 ° C. Assuming 180 ° C as the maximum working temperature that ensures the thermal stability of the catalyst, 140 ° C has been chosen as the reaction temperature for subsequent catalytic tests.
A continuación se ha realizado un estudio cinético, a 140°C, utilizando 2 g de sorbitol y 100 mg de Purolita CT269DR, hasta alcanzar 22 horas de reacción (Figuras 7 y 8). De la Figura 7 se deduce que a bajos tiempos de reacción, alrededor de 180 minutos, se logra conversión casi completa del sorbitol, pero con un rendimiento en isosorbida de tan solo un 43,2%. Para obtener el máximo rendimiento se deben alcanzar entre 10-12 horas, y a partir de este tiempo de reacción (Figura 8) se produce una caída del rendimiento a isosorbida, pudiéndose atribuir a posibles reacciones secundarias de la isosorbida o simplemente a procesos pirolíticos como consecuencia de los elevados tiempos y temperatura de reacción. A kinetic study was then carried out, at 140 ° C, using 2 g of sorbitol and 100 mg of Purolite CT269DR, until reaching 22 hours of reaction (Figures 7 and 8). From Figure 7 it follows that at low reaction times, about 180 minutes, almost complete conversion of sorbitol is achieved, but with an isosorbide yield of only 43.2%. To obtain maximum performance, 10-12 hours must be reached, and from this reaction time (Figure 8) there is a drop in the yield to isosorbide, which can be attributed to possible side reactions of the isosorbide or simply to pyrolytic processes as a consequence. of the high reaction times and temperature.
La evaluación de la estabilidad de la Purolita CT269DR se ha realizado mediante el análisis químico CHNS de los catalizadores usados, después de diferentes tiempos de reacción. En este sentido, es importante mantener la concentración de grupos sulfónicos en la resina para preservar su actividad catalítica. En general, se aprecia que no se produce pérdida de grupos sulfónicos en la resina CT269DR, ya que el contenido en azufre de los catalizadores usados se mantiene prácticamente constante en todas las muestras (Tabla 4). The stability evaluation of the Purolite CT269DR has been carried out by CHNS chemical analysis of the catalysts used, after different reaction times. In this sense, it is important to maintain the concentration of sulfonic groups in the resin to preserve their catalytic activity. In general, it is appreciated that there is no loss of sulfonic groups in the CT269DR resin, since the sulfur content of the catalysts used remains virtually constant in all samples (Table 4).
CT 2&9BR CT 2 & 9BR
Figure imgf000018_0001
Figure imgf000018_0001
Tabla 4. Composición química másica de la Purolita CT269DR a diferentes tiempos de reacción  Table 4. Mass chemical composition of Purolite CT269DR at different reaction times
Para completar este estudio sobre la estabilidad de los catalizadores, se han realizado los análisis por espectrometría de emisión de plasma acoplado inductivamente (ICP-OES) de los líquidos de reacción obtenidos durante el estudio cinético. El procedimiento ICP-OES se fundamenta en la detección de los fotones emitidos por los átomos/iones presentes en la muestra estudiada. Utiliza un sistema de plasma con acoplamiento inductivo como fuente de atomización y excitación para generar dichos iones, y mide la radiación UV-VIS de las líneas de emisión atómica características de cada elemento. To complete this study on the stability of the catalysts, the analyzes by inductively coupled plasma emission spectrometry (ICP-OES) of the reaction liquids obtained during the kinetic study have been performed. The ICP-OES procedure is based on the detection of the photons emitted by the atoms / ions present in the sample studied. It uses a plasma system with inductive coupling as a source of atomization and excitation to generate these ions, and measures the UV-VIS radiation of the atomic emission lines characteristic of each element.
Tiempo CoEseerstraciión S Time CoEseerstraciión S
[mía] [mg/Lj SO  [mine] [mg / Lj SO
30 ¾ 0,09  30 ¾ 0.09
180 4,79 0,08  180 4.79 0.08
300 4,84 0,02 300 4.84 0.02
•420 Sf£ 0,-08 • 420 S f £ 0, -08
600 6,40 0,06  600 6.40 0.06
720 7,00 ¾Í0  720 7.00 ¾Í0
Tabla 5. Datos de concentración de S en el líquido de reacción determinados por ICP-OES  Table 5. S concentration data in the reaction liquid determined by ICP-OES
Los datos relativos a las concentraciones de azufre indican una cantidad máxima en disolución de 7 ppm tras 12 horas de reacción, correspondiente a 5,38% de la cantidad máxima lixi viable (130 ppm). Por tanto, se puede considerar que la lixiviación de la fase activa del catalizador es prácticamente insignificante (Tabla 5). Data related to sulfur concentrations indicate a maximum amount in solution of 7 ppm after 12 hours of reaction, corresponding to 5.38% of the maximum viable lixi amount (130 ppm). Therefore, the leaching of the The active phase of the catalyst is practically insignificant (Table 5).
Para optimizar la carga de catalizador se realizó un estudio variando su masa entre 25 y 200 mg (Figura 9). La máxima convers ón de sorbitol se logra con 150 mg de catalizador, pero el rendimiento en isosorbida aumenta muy poco cuando se incrementa la cantidad de catalizador entre 100 y 200 mg. Por ello, se ha estimado que 100 mg es la carga óptima en l a reacción, puesto que es necesario duplicar la masa de catalizador hasta 200 mg para conseguir tan solo elevar un 7% el rendimiento. Debido a la diversidad de tamaños de partículas que pudiera presentar esta resina Purolita CT269DR, se ha considerado de interés real izar un estudio sobre su influencia en el comportamiento catalítico. Para ello se ha tamizado esta resina para obtener tamaños de partícula en los rangos: [0,40-0,50], [0,50-,71], [0,71-1,00] y [1,00-1,18] mm. Los datos catalíticos demuestran una mejora del rendimiento con el uso del catalizador con el menor tamaño de partícula, comprendido entre 0,4-0,5 mm, para el que se obtiene la mayor conversión de sorbitol. El estudio se realizó a 140°C con la misma relación másica sorbitol/catalizador, pero a 90 minutos de reacción en todos los casos (Figura 10). To optimize the catalyst load, a study was carried out varying its mass between 25 and 200 mg (Figure 9). The maximum conversion of sorbitol is achieved with 150 mg of catalyst, but the yield in isosorbide increases very little when the amount of catalyst is increased between 100 and 200 mg. Therefore, it has been estimated that 100 mg is the optimal load in the reaction, since it is necessary to double the mass of catalyst to 200 mg to only increase the yield by 7%. Due to the diversity of particle sizes that this Purolite CT269DR resin could present, it has been considered of real interest to conduct a study on its influence on catalytic behavior. For this, this resin has been screened to obtain particle sizes in the ranges: [0.40-0.50], [0.50-, 71], [0.71-1.00] and [1.00- 1.18] mm. The catalytic data demonstrate an improvement in performance with the use of the catalyst with the smallest particle size, between 0.4-0.5 mm, for which the highest sorbitol conversion is obtained. The study was carried out at 140 ° C with the same sorbitol / catalyst mass ratio, but at 90 minutes of reaction in all cases (Figure 10).
Finalmente, se ha evaluado la reutilización del catalizador para comprobar su viabilidad en un proceso industrial heterogéneo. Para ello, se prepararon 5 reactores, que se hicieron reaccionar a 140°C durante 90 minutos, con 2 g de sorbitol y 100 mg de catalizador CT269DR. Al finalizar el tiempo de reacción, el fundido de cada reactor se llevó a la dilución pertinente con agua destilada, y los diferentes sólidos recuperados se reunieron en un único lote, que se lavó con agua destilada y se secó en un horno a 100°C durante una hora. De este sólido se tomaron cantidades de muestra suficiente para realizar un segundo ciclo en cuatro reactores idénticos, y así se repitió la experiencia hasta repetir eí experimento durante 4 ciclos. Finally, the reuse of the catalyst has been evaluated to verify its viability in a heterogeneous industrial process. For this, 5 reactors were prepared, which were reacted at 140 ° C for 90 minutes, with 2 g of sorbitol and 100 mg of CT269DR catalyst. At the end of the reaction time, the melting of each reactor was brought to the relevant dilution with distilled water, and the different solids recovered were collected in a single batch, which was washed with distilled water and dried in an oven at 100 ° C for an hour. Sufficient amounts of sample were taken from this solid to perform a second cycle in four identical reactors, and so the experience was repeated until the experiment was repeated for 4 cycles.
En el diagrama de barras de la Figura 11 se representan los datos de actividad catalítica obtenidos en cada ciclo. Se observa una leve disminución de conversión tras el primer ciclo. Sin embargo, es posible mantener un rendimiento medio del 27-29% en isosorbida en los 3 primeros ciclos. Con el objetivo de comprobar si existe lixiviación de la fase activa del catalizador en el medio de reacción, se han realizado medidas de la composición química CHNS de los catalizadores usados, tras el 2o y 4o ciclos de reacción. Los datos obtenidos se muestran en la Tabla 6 donde no se observa pérdida de grupos sulfónicos. El contenido en C e H aumenta ligeramente a lo largo de los 4 ciclos, correspondiendo a l os posibles residuos carbonosos. Este aumento de la cantidad de carbono conduce a un aumento continuo de la relación másica C/S, después de cada cic o catalítico. The catalytic activity data obtained in each cycle is shown in the bar chart of Figure 11. A slight decrease in conversion is observed after the first cycle. However, it is possible to maintain an average yield of 27-29% in isosorbide in the first 3 cycles. In order to check for leaching of the active phase of the catalyst in the reaction medium, measures CHNS chemical composition of the catalysts used were made after 2 and 4 or or reaction cycles. The data obtained are shown in Table 6 where no loss of sulfonic groups is observed. The C and H content increases slightly over the 4 cycles, corresponding to the possible carbonaceous residues. This increase in the amount of carbon leads to a continuous increase in the mass C / S ratio, after each cycle or catalytic.
Figure imgf000020_0001
Figure imgf000020_0001
Tabla 6. Composición porcentual de la Purolita CT269DR tras 4 ciclos de reutilización  Table 6. Percent composition of Purolite CT269DR after 4 reuse cycles
Sistema de reacción en fundido mediante una corriente de atmósfera inerte En el segundo sistema de reacción se introduce una corriente de N2 en un matraz con tres bocas y una salida, con la intención de retirar el vapor de agua generado durante la reacción de deshidratación. La temperatura se controla mediante un termómetro externo sumergido en eí baño de silicona a 140°C, pero a su vez se introduce un termómetro a través de una de las bocas para conocer el gradiente térmico cuando se emplea un gas inerte de arrastre. Melt reaction system by an inert atmosphere stream In the second reaction system, a stream of N2 is introduced into a flask with three mouths and an outlet, with the intention of removing the water vapor generated during the dehydration reaction. The temperature is controlled by an external thermometer immersed in the silicone bath at 140 ° C, but in turn a thermometer is introduced through one of the mouths to know the thermal gradient when an inert gas is used.
Tanto la temperatura como el tiempo de reacción se mantienen constantes, 140°C durante 10 horas; sin embargo, es necesario aumentar la masa de sorbitol inicial en el sistema a 4 g para proporcionar una masa suficiente en el reactor, aunque se mantiene la relación másica sorbitol/catalizador de 20: 1 Both the temperature and the reaction time are kept constant, 140 ° C for 10 hours; however, it is necessary to increase the initial sorbitol mass in the system to 4 g to provide a sufficient mass in the reactor, although the sorbitol / catalyst mass ratio of 20: 1 is maintained.
Para conseguir elevar el rendimiento de reacción al máximo se ha usado un sistema en el cual se hace pasar flujo de nitrógeno a través de la atmósfera de reacción para retirar el agua formada durante el proceso de deshidratación, y así desplazar la reacción hacia la formación de isosorbida. En un ensayo previo se observó cómo el rendimiento de la reacción se duplicaba desde un 23,7 a n 41,5% a bajos tiempos de reacción (90 min) (Tabla 7). Sin embargo, se realizó el experimento durante el tiempo optimizado (lOh) con la Purolita tamizada y sin tamizar, y se encontró en ambos casos que el flujo de nitrógeno no mejoraba el rendimiento de la reacción. La inyección de nitrógeno retira el agua formada, pero también provoca una disminución de la temperatura de reacción, al retirar calor del medio, observándose una diferencia de hasta 30°C entre el baño calefactor y la atmósfera de reacción, con un efecto negativo en la evolución del proceso catalítico de deshidratación. In order to maximize the reaction efficiency a system has been used in which nitrogen flow is passed through the reaction atmosphere to remove the water formed during the dehydration process, and thus move the reaction towards the formation of isosorbide In a previous test it was observed how the reaction yield doubled from 23.7 to 41.5% at low reaction times (90 min) (Table 7). However, the experiment was carried out during the optimized time (10 Oh) with the sieved and unselected Purolite, and it was found in both cases that the flow of nitrogen did not improve the yield of the reaction. The nitrogen injection removes the water formed, but also causes a decrease in the reaction temperature, by removing heat from the medium, observing a difference of up to 30 ° C between the heating bath and the reaction atmosphere, with a negative effect on the evolution of the catalytic dehydration process.
Conve sión Conve sion
Selectividad Selectivity
Figure imgf000021_0001
Figure imgf000021_0001
Tabla 7. Influencia del tipo de atmósfera de reacción sobre el comportamiento catalítico.  Table 7. Influence of the type of reaction atmosphere on the catalytic behavior.
Sistema de reacción en fundido a vacio Vacuum Fade Reaction System
Con la finalidad de aumentar el rendimiento de la reacción también se ha usado un sistema similar al anterior, pero sustituyendo la corriente de nitrógeno por un sistema de vacío. El resto de parámetros se mantuvieron invariables. In order to increase the yield of the reaction a system similar to the previous one has also been used, but replacing the nitrogen stream with a vacuum system. The rest of the parameters remained unchanged.
Finalmente, se ha planteado otro método para eliminar el agua de la reacción, como es acoplar una bomba de vacío aí sistema de reacción. En este caso se obtiene una leve mejora a bajos tiempos de reacción. A pesar de ello, no se lograron mejorar los rendimientos alcanzados con el uso de corriente de nitrógeno en la atmósfera de reacción (Tabla 8).
Figure imgf000022_0001
Finally, another method has been proposed to remove the water from the reaction, such as coupling a vacuum pump to the reaction system. In this case a slight improvement is obtained at low reaction times. Despite this, the yields achieved with the use of nitrogen current in the reaction atmosphere were not improved (Table 8).
Figure imgf000022_0001
RendimienUs | 25,05 31, .03 41,47 23,70  Yield | 25.05 31, .03 41.47 23.70
Tabla 8. Comparación del comportamiento catalítico empleando diferentes sistemas de reacción, partiendo de sorbitol fundido Table 8. Comparison of catalytic behavior using different reaction systems, based on molten sorbitol
Conclusiones Conclusions
Entre las resinas sulfónicas estudiadas, ios mejores rendimientos en isosorbida se lograron con las Puroiitas CT269DR y CT275DR, con valores cercanos al 70% cuando se empleó sorbitol fundido a 140°C, con relaciones másicas sorbitol : catalizador de 20: 1. Se trata de dos resinas mesoporosas con valores de diámetro medio de poro suficientemente elevados para asegurar el acceso de las moléculas de sorbitol hacia los sitios activos y la posterior salida de productos de reacción. En el caso de la resina PD206, su baja estabilidad térmica (120°C) limita su empleo en estas condiciones de reacción. Among the sulfonic resins studied, the best yields in isosorbide were achieved with the Puroiites CT269DR and CT275DR, with values close to 70% when sorbitol molten at 140 ° C was used, with sorbitol mass ratios: catalyst of 20: 1. two mesoporous resins with values of average pore diameter sufficiently high to ensure the access of the sorbitol molecules to the active sites and the subsequent exit of reaction products. In the case of PD206 resin, its low thermal stability (120 ° C) limits its use in these reaction conditions.
Por otra parte, ía resina CT269DR exhibe una mayor estabilidad mecánica, lo que asegura su integridad estructural en las condiciones de reacción. On the other hand, the CT269DR resin exhibits greater mechanical stability, which ensures its structural integrity in the reaction conditions.
La influencia de la temperatura de reacción se evalúo en el intervalo entre 100 y 160°C, encontrándose 140°C como valor óptimo, suficientemente alejado de la temperatura de degradación de la resina CT269DR (180°C). The influence of the reaction temperature was evaluated in the range between 100 and 160 ° C, 140 ° C being the optimum value, sufficiently far from the degradation temperature of the CT269DR resin (180 ° C).
El estudio cinético demostró que se logra una conversión completa del sorbitol después de 3 horas de reacción, pero con un rendimiento en isosorbida del 43,2%, requiriéndose 10 horas para obtener el máximo rendimiento (68,9%). El catalizador es estable en las condiciones de reacción, como se puede inferir del análisis de azufre del catalizador usado y en el medio de reacción. The kinetic study showed that a complete conversion of sorbitol is achieved after 3 hours of reaction, but with an isosorbide yield of 43.2%, requiring 10 hours to obtain maximum yield (68.9%). The catalyst is stable under the reaction conditions, as can be inferred from the sulfur analysis of the catalyst used and in the reaction medium.
La carga de catalizador y el tamaño de partícula óptimos han sido 100 mg de panículas de catalizador con tamaños entre 0,4 y 0,5 mm. Por otra parte, se ha podido reutilszar el catalizador durante 4 ciclos de reacción, después de una etapa intermedia de lavado y secado en homo a 100°C durante una hora entre cada ciclo, manteniéndose un rendimiento medio de isosorbída del 27-29%. El análisis químico de ios catalizadores usados confirmó la estabilidad del catalizador. The optimum catalyst loading and particle size have been 100 mg of catalyst panicles with sizes between 0.4 and 0.5 mm. On the other hand, it has been possible to reuse the catalyst for 4 reaction cycles, after an intermediate stage of washing and drying in homo at 100 ° C for one hour between each cycle, maintaining an average isosorbide yield of 27-29%. The chemical analysis of the catalysts used confirmed the stability of the catalyst.

Claims

REIVINDICACIONES
1. Uso de resinas de estireno-divinilbenceno con grupos sulfónicos ácidos cuya estructura polimérica consiste en poliestireno macroporoso entrecruzado con divinilbenceno, con una acidez de 5.2 eq/Kg, con un porcentaje de humedad residual del 3%, con un tamaño de partícula comprendido en el rango 425-1200 micrómetros, una área específica comprendida en el rango 20-50 m2/g, un volumen de poros comprendido en el rango 0.2-0.6 ml/g, un diámetro medio del poro comprendido en el rango 23-70 nm, y una estabilidad térmica que se extiende hasta una temperatura máxima de 180 °C, como catalizador ácido sólido en un proceso catalítico heterogéneo para la deshidratación de sorbitol a isosorbida. 1. Use of styrene-divinylbenzene resins with acid sulfonic groups whose polymeric structure consists of macroporous polystyrene cross-linked with divinylbenzene, with an acidity of 5.2 eq / Kg, with a percentage of residual humidity of 3%, with a particle size comprised of the range 425-1200 micrometers, a specific area in the range 20-50 m 2 / g, a pore volume in the range 0.2-0.6 ml / g, an average pore diameter in the range 23-70 nm , and a thermal stability that extends to a maximum temperature of 180 ° C, as a solid acid catalyst in a heterogeneous catalytic process for the dehydration of sorbitol to isosorbide.
2. Uso según la reivindicación anterior de resinas de estireno-divinilbenceno con grupos sulfónicos ácidos cuya estructura polimérica consiste en poliestireno macroporoso entrecruzado con divinilbenceno, con una acidez de 5.2 eq/Kg, con un porcentaje de humedad residual del 3%, con un tamaño de partícula comprendido en el rango 425-1200 micrómetros, una área específica comprendida en el rango 35-50 m2/g, un volumen de poros comprendido en el rango 0.2-0.5 ml/g, un diámetro medio del poro comprendido en el rango 23.1-42.5 nm, y una estabilidad térmica que se extiende hasta una temperatura máxima de 180 °C, como catalizador ácido sólido en un proceso catalítico heterogéneo para la deshidratación de sorbitol a isosorbida. 2. Use according to the preceding claim of styrene-divinylbenzene resins with acid sulfonic groups whose polymeric structure consists of macroporous polystyrene cross-linked with divinylbenzene, with an acidity of 5.2 eq / Kg, with a residual moisture percentage of 3%, with a size of particle in the range 425-1200 micrometers, a specific area in the range 35-50 m 2 / g, a pore volume in the range 0.2-0.5 ml / g, an average pore diameter in the range 23.1-42.5 nm, and a thermal stability that extends to a maximum temperature of 180 ° C, as a solid acid catalyst in a heterogeneous catalytic process for the dehydration of sorbitol to isosorbide.
3. Uso según la reivindicación 1 de resinas de estireno-divinilbenceno con grupos sulfónicos ácidos cuya estructura polimérica consiste en poliestireno macroporoso entrecruzado con divinilbenceno, con una acidez de 5.2 eq/Kg, con un porcentaje de humedad residual del 3%, con un tamaño de partícula comprendido en el rango 600-850 micrómetros, una área específica comprendida en el rango 20-40 m2/g, un volumen de poros comprendido en el rango 0.2-0.6 ml/g, un diámetro medio del poro comprendido en el rango 40-70 nm, y una estabilidad térmica que se extiende hasta una temperatura máxima de 180 °C, como catalizador ácido sólido en un proceso catalítico heterogéneo para la deshidratación de sorbitol a isosorbida. 3. Use according to claim 1 of styrene-divinylbenzene resins with acidic sulfonic groups whose polymeric structure consists of macroporous polystyrene cross-linked with divinylbenzene, with an acidity of 5.2 eq / Kg, with a residual moisture percentage of 3%, with a size of particle in the range 600-850 micrometers, a specific area in the range 20-40 m 2 / g, a pore volume in the range 0.2-0.6 ml / g, an average pore diameter in the range 40-70 nm, and a thermal stability that extends to a maximum temperature of 180 ° C, as a solid acid catalyst in a heterogeneous catalytic process for the dehydration of sorbitol to isosorbide.
4. Procedimiento catalítico heterogéneo para la deshidratación de sorbitol a isosorbida caracterizado porque comprende el uso de una resina de estireno divinilbenceno con grupos sulfónicos ácidos como catalizador ácido sólido conforme a cualquiera de las reivindicaciones 1 a 3. 4. Heterogeneous catalytic process for the dehydration of sorbitol to isosorbide characterized in that it comprises the use of a styrene divinylbenzene resin with acid sulfonic groups as a solid acid catalyst according to any one of claims 1 to 3.
5. Procedimiento según la reivindicación anterior caracterizado por que comprende: 5. Method according to the preceding claim characterized in that it comprises:
-la adición a un reactor del catalizador y del sorbitol en una relación másica sorbitol: catalizador comprendida en el rango 10: 1 - 20: 1;  -the addition to a reactor of the catalyst and sorbitol in a mass ratio sorbitol: catalyst in the range 10: 1-20: 1;
-la reacción de la mezcla sorbitol: catalizador en agitación, en ausencia de disolvente, y a una temperatura comprendida en el rango 140-180 °C durante un tiempo de reacción comprendido en el rango 90 minutos - 12 horas;  -the reaction of the sorbitol mixture: catalyst under stirring, in the absence of solvent, and at a temperature in the range 140-180 ° C for a reaction time in the range 90 minutes - 12 hours;
-la dilución del volumen de fundido resultante de la reacción con agua destilada; y  -the dilution of the volume of melt resulting from the reaction with distilled water; Y
-la separación del catalizador de los azúcares mediante microfiltración del volumen de fundido diluido en agua.  -the separation of the catalyst from the sugars by microfiltration of the volume of molten diluted in water.
6. Procedimiento según la reivindicación anterior caracterizado por que la mezcla de reacción se hace reaccionar a una temperatura comprendida en el rango 140-160 °C durante un tiempo de reacción comprendido en el rango 10-12 horas. Method according to the preceding claim characterized in that the reaction mixture is reacted at a temperature in the range 140-160 ° C for a reaction time in the range 10-12 hours.
7. Procedimiento según la reivindicación anterior caracterizado por que la mezcla de reacción se hace reaccionar a una temperatura de 140 °C durante un tiempo de reacción de 10 horas. 7. Method according to the preceding claim characterized in that the reaction mixture is reacted at a temperature of 140 ° C for a reaction time of 10 hours.
8. Procedimiento según cualquiera de las reivindicaciones 5 a 7 caracterizado por que la mezcla sorbitol: catalizador se hace reaccionar a presión atmosférica sin atmósfera inerte. Method according to any one of claims 5 to 7, characterized in that the sorbitol: catalyst mixture is reacted at atmospheric pressure without an inert atmosphere.
9. Procedimiento según cualquiera de las reivindicaciones 5 a 7 caracterizado por que la mezcla sorbitol: catalizador se hace reaccionar en atmósfera inerte mientras se le hace pasar una corriente de gas inerte (N2). 9. Process according to any of claims 5 to 7 characterized in that the sorbitol: catalyst mixture is reacted in an inert atmosphere while a stream of inert gas (N 2 ) is passed through it.
10. Procedimiento según cualquiera de las reivindicaciones 5 a 7 caracterizado por que la mezcla sorbitol: catalizador se hace reaccionar en condiciones de vacío. Method according to any one of claims 5 to 7, characterized in that the sorbitol: catalyst mixture is reacted under vacuum conditions.
11. Procedimiento según cualquiera de las reivindicaciones 5 a 10 caracterizado por que comprende, tras la etapa de separación del catalizador de los azúcares formados mediante la deshidratación del sorbitol, una etapa de recuperación del catalizador para su posterior reutilización, dicha etapa comprendiendo el lavado del catalizador y su secado. Method according to any one of claims 5 to 10, characterized in that it comprises, after the catalyst separation stage of the sugars formed by dehydration of sorbitol, a catalyst recovery stage for subsequent reuse, said step comprising washing the catalyst and its drying.
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