WO1996010536A1 - Method for making phosphated alkaline salts, resulting salts and silicas, and detergent or foodstuff containing such salts - Google Patents

Method for making phosphated alkaline salts, resulting salts and silicas, and detergent or foodstuff containing such salts Download PDF

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Publication number
WO1996010536A1
WO1996010536A1 PCT/BE1994/000065 BE9400065W WO9610536A1 WO 1996010536 A1 WO1996010536 A1 WO 1996010536A1 BE 9400065 W BE9400065 W BE 9400065W WO 9610536 A1 WO9610536 A1 WO 9610536A1
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silica
phosphoric acid
silicate
phosphate
sodium
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PCT/BE1994/000065
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French (fr)
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Jacques R. J. Moise
Philippe J. M. Cappelle
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Societe Chimique Prayon-Rupel
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Priority to PCT/BE1994/000065 priority Critical patent/WO1996010536A1/en
Priority to EP94927463A priority patent/EP0784594A1/en
Priority to MA24021A priority patent/MA23675A1/en
Priority to TNTNSN95100A priority patent/TNSN95100A1/en
Priority to IL11548195A priority patent/IL115481A0/en
Priority to TR95/01208A priority patent/TR199501208A2/en
Publication of WO1996010536A1 publication Critical patent/WO1996010536A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • A—HUMAN NECESSITIES
    • A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
    • A23L—FOODS, FOODSTUFFS, OR NON-ALCOHOLIC BEVERAGES, NOT COVERED BY SUBCLASSES A21D OR A23B-A23J; THEIR PREPARATION OR TREATMENT, e.g. COOKING, MODIFICATION OF NUTRITIVE QUALITIES, PHYSICAL TREATMENT; PRESERVATION OF FOODS OR FOODSTUFFS, IN GENERAL
    • A23L29/00—Foods or foodstuffs containing additives; Preparation or treatment thereof
    • A23L29/015—Inorganic compounds
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/26—Phosphates
    • C01B25/30—Alkali metal phosphates
    • C01B25/301—Preparation from liquid orthophosphoric acid or from an acid solution or suspension of orthophosphates
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/26—Phosphates
    • C01B25/38—Condensed phosphates
    • C01B25/40—Polyphosphates
    • C01B25/41—Polyphosphates of alkali metals
    • C01B25/412—Preparation from alkali metal orthophosphates
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/113—Silicon oxides; Hydrates thereof
    • C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
    • C01B33/14—Colloidal silica, e.g. dispersions, gels, sols
    • C01B33/152—Preparation of hydrogels
    • C01B33/154—Preparation of hydrogels by acidic treatment of aqueous silicate solutions
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/113—Silicon oxides; Hydrates thereof
    • C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
    • C01B33/18—Preparation of finely divided silica neither in sol nor in gel form; After-treatment thereof
    • C01B33/187—Preparation of finely divided silica neither in sol nor in gel form; After-treatment thereof by acidic treatment of silicates
    • C01B33/193—Preparation of finely divided silica neither in sol nor in gel form; After-treatment thereof by acidic treatment of silicates of aqueous solutions of silicates
    • C—CHEMISTRY; METALLURGY
    • C11—ANIMAL OR VEGETABLE OILS, FATS, FATTY SUBSTANCES OR WAXES; FATTY ACIDS THEREFROM; DETERGENTS; CANDLES
    • C11D—DETERGENT COMPOSITIONS; USE OF SINGLE SUBSTANCES AS DETERGENTS; SOAP OR SOAP-MAKING; RESIN SOAPS; RECOVERY OF GLYCEROL
    • C11D3/00—Other compounding ingredients of detergent compositions covered in group C11D1/00
    • C11D3/02—Inorganic compounds ; Elemental compounds
    • C11D3/04—Water-soluble compounds
    • C11D3/06—Phosphates, including polyphosphates
    • C—CHEMISTRY; METALLURGY
    • C11—ANIMAL OR VEGETABLE OILS, FATS, FATTY SUBSTANCES OR WAXES; FATTY ACIDS THEREFROM; DETERGENTS; CANDLES
    • C11D—DETERGENT COMPOSITIONS; USE OF SINGLE SUBSTANCES AS DETERGENTS; SOAP OR SOAP-MAKING; RESIN SOAPS; RECOVERY OF GLYCEROL
    • C11D3/00—Other compounding ingredients of detergent compositions covered in group C11D1/00
    • C11D3/02—Inorganic compounds ; Elemental compounds
    • C11D3/04—Water-soluble compounds
    • C11D3/06—Phosphates, including polyphosphates
    • C11D3/062—Special methods concerning phosphates
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/64—Nanometer sized, i.e. from 1-100 nanometer
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/11—Powder tap density
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    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
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    • C01P2006/12—Surface area
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    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/19—Oil-absorption capacity, e.g. DBP values
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
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    • C01P2006/60—Optical properties, e.g. expressed in CIELAB-values
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    • C01—INORGANIC CHEMISTRY
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    • C01P2006/60—Optical properties, e.g. expressed in CIELAB-values
    • C01P2006/62—L* (lightness axis)
    • C—CHEMISTRY; METALLURGY
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    • C01P2006/60—Optical properties, e.g. expressed in CIELAB-values
    • C01P2006/63—Optical properties, e.g. expressed in CIELAB-values a* (red-green axis)
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
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    • C01P2006/60—Optical properties, e.g. expressed in CIELAB-values
    • C01P2006/64—Optical properties, e.g. expressed in CIELAB-values b* (yellow-blue axis)
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    • C01P2006/90—Other properties not specified above

Definitions

  • the present invention relates to a process for the production of high purity phosphatic alkaline salt, in particular a tripolyphosphate, such as sodium tripolyphosphate meeting the purity requirements of the detergency industry from phosphoric acid obtained. wet.
  • a tripolyphosphate such as sodium tripolyphosphate meeting the purity requirements of the detergency industry from phosphoric acid obtained. wet.
  • the known processes for the manufacture of such a salt are characterized by the precipitation of the impurities provided by phosphoric acid during the partial neutralization of this acid by means of sodium hydroxide, the elimination , by filtration, phosphates of the various metals constituting the impurities and the recovery of a purified sodium phosphate solution.
  • Belgian Patent No. 869,169 from the company Pelt & Hooykaas describes a process treating the filter cakes recovered during the purification of the liquors used to produce sodium tripolyphosphate.
  • This process consists in drying and calcining the residue in the presence of a mineral flux which can either be a metallurgical slag, or the residue itself previously calcined and melted.
  • a mineral flux which can either be a metallurgical slag, or the residue itself previously calcined and melted.
  • This calcination which takes place at a temperature between 700 and 1300 ° C., makes it possible to eliminate the organic compounds, to reduce the volume and form an open landfill without the risk of pollutants such as heavy metals being leached from storage.
  • This residue can also be ground to be used as a road base.
  • the F / Mg ratio is adjusted to 1 by adding alkaline fluorides.
  • magnesium compounds precipitate and are easily recovered by filtration, which makes it possible to obtain solutions making it possible to produce a sodium tripolyphosphate whose magnesium content satisfies the requirements of detergency.
  • the acid to be purified is brought into contact with a nonaqueous solvent to give an organic phase rich in H 3 P0 4 .
  • This organic phase is brought into contact with an alkaline aqueous sodium phase (Na 2 C0 3 or Na 2 HC0 3 or NaOH) so that a part, for example from 15 to 35%, of the phosphoric acid is transformed into corresponding sodium salts.
  • the organic phase is reextracted with water.
  • the aqueous phase thus produced is adjusted to a pH of between 4 and 6 with NaOH in order to precipitate the polyvalent ions.
  • the precipitate is removed by filtration and the residual solution is adjusted to pH 8 with NaOH in order to produce sodium tripolyphosphate.
  • the iron By neutralizing at least the first proton of H 3 PO 4 of a phosphoric acid containing 50 to 500 ppm of Fe relative to P 2 0 5 by 1 to 50 kg of lime of which at least 75% is below 10 ⁇ m , the iron can be precipitated in such a way that the 10 to 50 ppm of Fe remaining in solution can no longer constitute a deactivator of the perborate bleach which is also added to the detergent with sodium tripolyphosphate.
  • Document BR-9304577 from the company SERANA describes an integrated process for purifying phosphoric acid by precipitation of impurities for the manufacture of detergent. By partial neutralization of the acid, the process makes it possible to remove, by precipitation, contaminants such as Fe, Al, F, SO 4 and Mg.
  • sodium phosphate solutions containing 45% P 2 0 5 , and less than 0.15% F, 22 ppm Mg, 40 ppm S0 4 , 40 ppm Fe, 10 ppm Al can be produced.
  • These solutions are of sufficient quality to produce sodium phosphates of technical quality, such as, for example, sodium tripoly ⁇ phosphate for use in detergency.
  • the present invention relates to a process for the manufacture of alkaline phosphates (Li, Na, K) of technical or food quality with a low content of metallic impurities, for example titanium and iron, from phosphoric acids which may contain up to at 100 ppm of these impurities.
  • the process according to the invention comprises the reaction of phosphoric acid with an aqueous solution of an alkali silicate, such as a sodium, potassium or lithium silicate, so as to form , on the one hand, a solution of the corresponding phosphate salt and, on the other hand, of micro-amorphous silica retaining the impurities contained in the phosphoric acid used, the phosphate salt and the silica obtained then being separated one of the other.
  • an alkali silicate such as a sodium, potassium or lithium silicate
  • alkaline silicate as a source of the alkali metal makes it possible to obtain significant chemical purification, despite the fact that the alkali silicate can contain up to 100 ppm of titanium, while the corresponding hydroxide is practically free of it.
  • the siliceous product obtained met, after drying, the most stringent requirements as to its use as precipitated silica or as silica gel.
  • the process for manufacturing the alkaline phosphate salt according to the invention therefore also makes it possible to solve a serious environmental problem created by the factories for manufacturing such micro-amorphous silicas.
  • the process according to the invention is especially useful for the manufacture of sodium phosphate and in particular sodium tripolyphosphate, it is also advantageous for the manufacture of phos- phates of other alkali metals.
  • this process allows the manufacture of dilute potassium phosphate solutions which are capable, after concentration and possibly adjustment of the pH using potassium hydroxide, of producing phosphates or technical and food grade potassium pyrophosphates while maintaining the quality of the co-produced silica.
  • the silicas which are obtained as co-products are of the micro-amorphous or non-crystalline type and are essentially characterized by very high specific surfaces between 10 and 800 m 2 / g as well as by extremely porous degrees. high, as evidenced by the low apparent densities.
  • These micro-amorphous solids whose general physico-chemical properties and the main formation mechanisms are described in the work of ILER (The Chemistry of Silica, John Wiley, 1979), are composed of primary colloidal particles of nanosize metrics which, by coagulation, gave rise to a gel or a precipitate.
  • the process according to the invention consists in reacting with phosphoric acid an alkaline silicate in the form of an aqueous solution whose molar ratio Si0 2 / M 2 0
  • reaction products obtained are formed, on the one hand, of an alkaline phosphate salt in solution and, on the other hand, of silica which can be in a precipitated form or in the form of a gel.
  • reaction products are then separated from each other and, if necessary, subjected to different treatments according to the applications envisaged.
  • the chemical composition of the phosphate solution obtained, as well as the physicochemical characteristics of the siliceous product depend on many operating variables: dilutions of the phosphoric acid and silicate solutions, order and speed of addition of said solutions, their temperature , the molar ratios Si0 2 / M 2 0 and P 2 0, / M 2 0, the stirring of the reactor, etc., M being Na, K or Li.
  • the reaction is advantageously carried out in a stirred batch reactor.
  • the working method described below is particularly favorable because it provides easily recoverable silica precipitates on an industrial scale. Their good filterability allows, in fact, an easy separation of the solid and the phosphate solution.
  • the final physicochemical properties of these silicas provide them with excellent performance in various fields of application.
  • the total quantity of sodium silicate necessary for the reaction is introduced beforehand into the reactor in the form of an aqueous solution at a weight concentration of Si0 2 which is advantageously between 6 and 12%.
  • a solution of phosphoric acid is added thereto progressively, the H 3 PO 4 titer is preferably between 30 and 50%.
  • the acid feed rate is one of the operating variables.
  • the reaction mixture is stirred throughout the addition.
  • the amount of phosphoric acid added depends in particular on the M / P ratio of the sodium phosphate sought.
  • the final H 3 P0 4 / M 2 0 molar ratio will however be greater than 0.80, so that the aqueous phase has a pH less than or equal to 9 when separating the silica. This also applies if the silicate used is a potassium or lithium silicate.
  • Different techniques may be suitable for separating precipitated silica from phosphated mother liquors, such as, for example, vacuum or filter press filtration methods.
  • a washing step for example by supplying fresh water, can be useful to guarantee an optimal phosphate yield.
  • the relatively dilute sodium phosphate filtrate is then reconcentrated, for example using a multiple-effect evaporator.
  • the filter cake, containing the precipitated silica can be dried by various common methods, the choice of the dryer being largely dictated by the physical presentation of the desired finished product.
  • the most suitable devices there are trays dryers, flash dryers and air towers.
  • This type of device is particularly advantageous because it directly supplies a finished product in the form of microbeads, the main properties of which are their excellent fluidity and their non-pulverulent nature, and this without requiring any further treatment, as is the case. other drying processes.
  • the proposed method for producing silica gels from alkali silicate and phosphoric acid also presents several variants. The main process steps are described below. We start by neutralizing the silicate in aqueous solution by reaction with phosphoric acid so as to form a colloidal solution. One of the operating variables is the generally acidic pH of the reaction mixture. This mixing operation is carried out in a stirred reactor. The hydrosol thus obtained is then kept at rest for the time necessary to transform it into a hydrogel.
  • One of the possible methods is the rapid gelation method, which consists in mixing silicate and phosphoric acid continuously using a sprayer placed above a conveyor belt, the reaction conditions being chosen so as to that the gelling process is almost instantaneous.
  • the gel is then shaped, washed with water to extract the phosphate salt therefrom, and finally dried. Washing with water is carried out for example in a counter-current reactor.
  • the final density of the gel also largely depends on the drying process used. Flash-type drying, for example, provides less dense gels, characterized by larger pore sizes, than the same, more slowly dried silicas.
  • STPP sodium tripolyphosphate
  • the general physicochemical characteristics of the silicas obtained are listed below. It is obviously possible to modulate these properties and to adapt them to the specificities of each field of application by optimizing the reaction conditions between the silicate and the phosphoric acid or by modifying the post-treatments which one inflicts on the silica after separation of the phosphate solution.
  • the residual moisture in the silica is made up of two different types of water.
  • the weight loss at 105 ° C indicates the "free water” content. This can be easily adjusted by adjusting the operating conditions of the dryer.
  • the weight loss at 1000 ° C of the silica which will be expressed relative to the dried product at 105 ° C, is between 3 and 8% and reflects, for its part, the "bound water” content of the silica.
  • the structure in the form of porous and open aggregates which characterizes the precipitated silicas according to the invention generally results in very low apparent densities.
  • This physical structure also gives them a remarkable absorption power, as shown for example by the dibutylphthalate absorption test (DBP).
  • DBP dibutylphthalate absorption test
  • This measurement is carried out in accordance with standard NF ISO 4656/1.
  • the DBP intakes thus measured are between 50 and 300 g of DBP per 100 g of silica according to the operating conditions adopted during the precipitation of the silica.
  • the particle size characteristics of the silicas obtained vary according to the drying and final shaping processes used.
  • precipitated silica dried by a "flash" process for example, it has been observed that the average size of the particles obtained is around 15 ⁇ m and that the rejection on a sieve 40 ⁇ m, measured according to the sieving method ISO 787/18 wet, does not exceed 0.2% after ultrasonic dispersion.
  • the Si0 2 content of the silica determined by gravimetry and expressed relative to the dry product at 105 ° C., essentially depends on the degree of washing achieved during the separation. Weight contents of Si0 2 of more than 93% are easily obtained.
  • the acidity of the silica depends on the H 3 P0 4 / M 2 0 ratio.
  • a correction of pH by addition of acid or alkali after the separation of the phosphate solution is however possible.
  • a separation around pH 7 is particularly favorable, since, on the one hand, this pH practically corresponds to that of sodium tripolyphosphate and, on the other hand, the pH of the silica thus obtained is compatible with the majority of applications. - tions, any acidity correction is therefore superfluous.
  • Example 1 The sodium silicate in the starting solution had a Si0 2 / Na 2 0 molar ratio of 3.32 and titrated 35.8% of dry matter. It was a solution of industrial origin of current quality whose iron, aluminum and titanium contents were respectively 50, 160 and 50 ppm.
  • the sodium silicate solution was first diluted by adding demineralized water to a weight concentration of SiO 2 of 8.0%. After having brought 2649 kg of this diluted solution to a well-stirred reactor and having raised its temperature to 73 ° C by an indirect heating system, the feeding of phosphoric acid could begin. This solution was supplied with an H 3 P0 4 concentration of 45%, the titer adjustment also being made. by adding demineralized water. The reaction mixture was stirred throughout the acidification. After an hour and a half of reaction, the temperature was brought to 85 ° C. After three hours, the volume of solution supplied reached 475 1. Next, the suspension obtained, the pH of which measured at the temperature indicated above was close to 7.0, was cooled to 60 ° C, then filtered and washed on filter press.
  • the filter cake containing the silica was reliquified by mechanical stirring before being dried in an atomization tower.
  • the pH of the product was adjusted by a small addition of phos ⁇ phoric acid before drying.
  • the final precipitated silica was in the form of microbeads and had the following characteristics: BET surface (m 2 / g) 172
  • CTAB area 160 DBP absorption (g / lOOg) 250
  • Example 2 The precipitation reaction was carried out under operating conditions identical to those of Example 1, except that the addition of phosphoric acid ended at pH 8.0. The mixed filtrates then reached an Na / P ratio of 2.05, which was then adjusted to that of disodium phosphate by adding phosphoric acid. The anhydrous disodium phosphate that we prepared from this corrected solution had the following characteristics: P 2 0 5 (%) 49.9
  • the filter cake was subjected to a fairly large pH correction by adding phosphoric acid, followed by a second washing with water to remove the excess salt formed during this adjustment.
  • the characteristics of the precipitated silica obtained at the outlet of the atomizing dryer were practically identical to those of Example 1.
  • Example 3 The precipitation reaction was carried out under operating conditions identical to those of Example 1, except that the addition of phosphoric acid was terminated at pH 5.8. The mixed filtrates then reached an Na / P ratio of 1.21, which was adjusted to that of monosodium phosphate by addition of phosphoric acid. Anhydrous sodium phosphate prepared from this phosphate solution had the following characteristics: P 2 0 5 (%) 59.1
  • Example 4 The filter cake obtained according to the procedure of Example 1 was dried using a flash dryer.
  • CTAB area (m 2 / g) 158 DBP absorption (g / 100g) 245
  • CTAB area (m / g) 106 DBP absorption (g / 100 g) 205
  • Example 6 The raw materials were practically of the same purity as those of Example 1. 1567 g of silicate diluted with 6.38% of Si0 2 were rapidly mixed with 933 g of acid titrating 10% of H 3 P0 4 . This operation was carried out in a vigorously agitated berlin, after which the reaction mixture was kept at rest. The Si0 2 concentration there was 4.0% and the pH there reached 5.2. After half an hour, the hydrogel formed was fragmented by mechanical stirring in the berlin, where it then underwent several successive washes with demineralized water, the water used for the last washing being very slightly basic so as to neutralize the suspension. The gel was finally dried in an oven at 105 ° C.
  • the sodium phosphate of the filtrate was at an Na / P ratio of 1.05, finally adjusted to that of the sodium phosphate by addition of phosphoric acid.
  • the anhydrous monosodium phosphate which was prepared from this phosphate solution had the following characteristics: P 2 0 5 (%) 59.0
  • Example 7 The method was the same as that of Example 6, except that the last step of washing the gel was carried out with an ammonia solution at pH 9 and that the gel thus washed underwent another time of maturation. one hour before drying.
  • the analysis of sodium phosphate was practically identical to that of the previous example.
  • the physical structure of the silica gel obtained was greatly modified: BET surface (m 2 / g) 360
  • Example 8 The method of Example 3 was applied to the case of potassium silicate.
  • the iron, aluminum and titanium contents of the potassium silicate used were relatively equivalent to those of the preceding sodium silicate and the molar ratio Si0 2 / K 2 0 chosen was identical to the Si0 2 / Na 2 0 ratio of Example 3. L analysis of the monopotassium phosphate obtained was this:
  • the silicas obtained as co-products of the purification process according to the invention have in particular the characteristics required to serve as a reinforcing filler in certain elasto ers.
  • the silicas in question give them, in effect, high-performance mechanical properties while considerably increasing their resistance to wear.
  • the fields of application of precipitated silicas are numerous.
  • the reinforcement of the rubbers mentioned above the fluidification and the anti-caking effect ("anti-caking") on many pulverulent materials, the absorption or placing on the support of liquid active ingredients. des, the improvement of the whiteness and opacity of emulsion papers and paints, the use of the thickening and pseudo-plastic power of these silicas in toothpastes, as well as in certain cleaning products.
  • the silicas resulting from the present invention can also be used to structure the excessively smooth surfaces of certain plastic films, papers, coatings or paints. Silica then plays an anti-blocking or anti-slip role, or possibly acts as a matting agent. The apti- Study in printing or impregnation can also be improved by these silicas.
  • silica gels are also numerous. They are often used as an absorbent, and in particular as a desiccant when the absorbed substance is water. A second equally important sector of application is that of coatings, where silica gels are used mainly as a matting agent. Furthermore, silica gels also have certain fields of application in common with precipitated silicas, such as for example the fluidification and the anti-caking effect of powders, and the function of anti-blocking in certain plastic films. Other uses, such as supported catalysts and the packing of chromatographic columns are however reserved for gels.
  • the potassium and sodium salts find their application both as adjuvants in detergents and in agriculture and the food industry.
  • an essential advantage of the process according to the invention is that it makes it possible to obtain two reaction products which, thanks to their purity, find many industrial applications, unlike which is the case with conventional processes which give, in addition, alkaline phosphated salt, a non-recoverable residue.

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  • Detergent Compositions (AREA)

Abstract

A method for making high-purity phosphated alkaline salts, particularly a tripolyphosphate, by reacting phosphoric acid with an aqueous solution of an alkaline silicate such as a sodium, potassium or lithium silicate, to give the corresponding phosphated salt along with micro-amorphous silica which retains most of the impurities contained in the phosphoric acid used, whereafter the resulting phosphated salt and silica are separated.

Description

PROCEDE DE FABRICATION DE SELS ALCALINS PHOSPHATES, SELS ET SILICES OBTENUS, AINSI QUE DETERGENT OU PRODUIT ALIMENTAIRE CONTENANT CES SELSPROCESS FOR THE MANUFACTURE OF ALKALINE PHOSPHATE SALTS, SALTS AND SILICA OBTAINED, AS WELL AS DETERGENT OR FOOD PRODUCT CONTAINING SUCH SALTS
La présente invention est relative à un 5 procédé de fabrication de sel alcalin phosphaté de haute pureté, notamment d'un tripolyphosphate, tel que du tripolyphosphate de sodium répondant aux exigences de pureté de l'industrie de la détergence à partir d'acide phosphorique obtenu par voie humide. 0 D'une façon générale, les procédés connus pour la fabrication d'un tel sel se caractérisent par la précipitation des impuretés apportées par l'acide phosphorique lors de la neutralisation partielle de cet acide au moyen d'hydroxyde de sodium, l'élimination, par 5 filtration, des phosphates des différents métaux consti¬ tuant les impuretés et la récupération d'une solution de phosphate sodique purifiée.The present invention relates to a process for the production of high purity phosphatic alkaline salt, in particular a tripolyphosphate, such as sodium tripolyphosphate meeting the purity requirements of the detergency industry from phosphoric acid obtained. wet. In general, the known processes for the manufacture of such a salt are characterized by the precipitation of the impurities provided by phosphoric acid during the partial neutralization of this acid by means of sodium hydroxide, the elimination , by filtration, phosphates of the various metals constituting the impurities and the recovery of a purified sodium phosphate solution.
De plus, certaines tentatives ont été effectuées pour traiter ou valoriser les gâteaux de 0 filtration constitués des phosphates de ces métaux.In addition, certain attempts have been made to treat or enhance the filter cakes made up of phosphates from these metals.
Ainsi, le brevet belge n° 869.169 de la société Pelt & Hooykaas décrit un procédé traitant les gâteaux de filtration récupérés lors de la purification des liqueurs servant à produire le tripolyphosphate de 5 sodium.Thus, Belgian Patent No. 869,169 from the company Pelt & Hooykaas describes a process treating the filter cakes recovered during the purification of the liquors used to produce sodium tripolyphosphate.
Ce procédé consiste à sécher et à calciner le résidu en présence d'un fondant minéral qui peut être soit une scorie métallurgique, soit le résidu lui-même préalablement calciné et fondu. 0 Cette calcination, qui s'effectue à une température comprise entre 700 et 1300°C, permet d'éli¬ miner les composés organiques, de réduire le volume et de former une décharge à ciel ouvert sans risque que des polluants tels que les métaux lourds soient lixiviés à partir du stockage.This process consists in drying and calcining the residue in the presence of a mineral flux which can either be a metallurgical slag, or the residue itself previously calcined and melted. This calcination, which takes place at a temperature between 700 and 1300 ° C., makes it possible to eliminate the organic compounds, to reduce the volume and form an open landfill without the risk of pollutants such as heavy metals being leached from storage.
Ce résidu peut également être broyé pour être utilisé en tant que soubassement routier.This residue can also be ground to be used as a road base.
Par ailleurs, dans le document n° SE- 7809656, la société Boliden décrit un procédé de purifi¬ cation en magnésium de l'acide phosphorique utilisant deux étapes de neutralisation avec un ajustement en fluorure de magnésium après le premier stade.Furthermore, in document No. SE- 7809656, the company Boliden describes a process for purifying magnesium of phosphoric acid using two stages of neutralization with adjustment of magnesium fluoride after the first stage.
Lors de la première neutralisation, le ratio F/Mg est ajusté à 1 en y ajoutant des fluorures alcalins. A une température comprise entre 50 et 100°C, des composés magnésiens précipitent et sont aisément récupérés par filtration, ce qui permet d'obtenir des solutions permettant de produire un tripolyphosphate de sodium dont le contenu en magnésium satisfait les exigences de la détergence.During the first neutralization, the F / Mg ratio is adjusted to 1 by adding alkaline fluorides. At a temperature between 50 and 100 ° C, magnesium compounds precipitate and are easily recovered by filtration, which makes it possible to obtain solutions making it possible to produce a sodium tripolyphosphate whose magnesium content satisfies the requirements of detergency.
Le document US-A-4.285.920 de la société STAUFFER CHEMICAL concerne un procédé de purification d'acide phosphorique obtenu par voie humide en vue de produire des produits pour la détergence.Document US-A-4,285,920 from the company STAUFFER CHEMICAL relates to a process for the purification of phosphoric acid obtained by the wet method with a view to producing products for detergency.
L'acide à purifier est mis en contact avec un solvant non aqueux pour donner une phase organique riche en H3P04. Cette phase organique est mise en contact avec une phase aqueuse alcaline sodée (Na2C03 ou Na2HC03 ou NaOH) de façon qu'une partie, par exemple de 15 à 35 %, de l'acide phosphorique soit transformée en des sels de sodium correspondants. La phase organique est réextraite avec de l'eau. La phase aqueuse ainsi produite est ajustée à un pH compris entre 4 et 6 avec NaOH en vue de précipiter les ions polyvalents. Le précipité est éliminé par filtration et la solution résiduelle est ajustée à pH 8 avec NaOH en vue de produire du tripolyphosphate de sodium. Dans le document BE-898556, les sociétés RHONE-POULENC CHIMIE et PCUK Belgium décrivent un procédé de purification d'acide phosphorique obtenu par voie humide par ajout de chaux en vue de précipiter et d'éliminer les impuretés de fer pour la production de tripolyphosphate de sodium.The acid to be purified is brought into contact with a nonaqueous solvent to give an organic phase rich in H 3 P0 4 . This organic phase is brought into contact with an alkaline aqueous sodium phase (Na 2 C0 3 or Na 2 HC0 3 or NaOH) so that a part, for example from 15 to 35%, of the phosphoric acid is transformed into corresponding sodium salts. The organic phase is reextracted with water. The aqueous phase thus produced is adjusted to a pH of between 4 and 6 with NaOH in order to precipitate the polyvalent ions. The precipitate is removed by filtration and the residual solution is adjusted to pH 8 with NaOH in order to produce sodium tripolyphosphate. In document BE-898556, the companies RHONE-POULENC CHIMIE and PCUK Belgium describe a process for the purification of phosphoric acid obtained by the wet method by adding lime in order to precipitate and eliminate iron impurities for the production of tripolyphosphate sodium.
En neutralisant au moins le premier proton de H3PO4 d'un acide phosphorique contenant de 50 à 500 ppm de Fe par rapport au P205 par 1 à 50 kg de chaux dont au moins 75 % est en dessous de 10 μm, on parvient à précipiter le fer de façon telle que les 10 à 50 ppm de Fe restant en solution ne peuvent plus constituer un désactivateur de l'agent de blanchiment au perborate qui est également ajouté dans le détergent avec le tripoly- phosphate de sodium.By neutralizing at least the first proton of H 3 PO 4 of a phosphoric acid containing 50 to 500 ppm of Fe relative to P 2 0 5 by 1 to 50 kg of lime of which at least 75% is below 10 μm , the iron can be precipitated in such a way that the 10 to 50 ppm of Fe remaining in solution can no longer constitute a deactivator of the perborate bleach which is also added to the detergent with sodium tripolyphosphate.
Le document BR-9304577 de la société SERANA décrit un procédé intégré pour purifier de l'acide phosphorique par précipitation d'impuretés pour la fabrication de détergent. Par neutralisation partielle de l'acide, le procédé permet d'éliminer par précipitation des contaminants tels que Fe, Al, F, S04 et Mg. Ainsi, des solutions de phosphates de sodium contenant 45 % P205, et moins de 0,15 % F, 22 ppm Mg, 40 ppm S04, 40 ppm Fe, 10 ppm Al, peuvent être produites. Ces solutions sont de qualité suffisante pour produire des phosphates sodiques de qualité technique, tels que, par exemple, le tripoly¬ phosphate de sodium à usage en détergence.Document BR-9304577 from the company SERANA describes an integrated process for purifying phosphoric acid by precipitation of impurities for the manufacture of detergent. By partial neutralization of the acid, the process makes it possible to remove, by precipitation, contaminants such as Fe, Al, F, SO 4 and Mg. Thus, sodium phosphate solutions containing 45% P 2 0 5 , and less than 0.15% F, 22 ppm Mg, 40 ppm S0 4 , 40 ppm Fe, 10 ppm Al, can be produced. These solutions are of sufficient quality to produce sodium phosphates of technical quality, such as, for example, sodium tripoly¬ phosphate for use in detergency.
Enfin, il est bien connu également que des procédés plus récents ont permis d'obtenir du tripoly¬ phosphate de sodium de plus haute pureté encore en utilisant des acides phosphoriques purs qu'ils soient obtenus par voie thermique ou qu'ils résultent d'une purification par extraction liquide-liquide d'acides phosphoriques obtenus par voie humide. Pour ces procédés de fabrication de tripolyphosphate de sodium, l'étape de purification chimique des solutions de phosphates sodiques n'existe donc plus, ce qui est une grande simplification. En effet, ceci permet d'éviter la pré-neutralisation à un pH intermédiaire, la filtration des composés insolubles contenant les impuretés ainsi que le problème de l'éli¬ mination du déchet solide résultant de cette filtration. Néanmoins, les procédés de purification de l'acide phosphorique par extraction liquide-liquide éprouvent parfois des difficultés pour éliminer suffi¬ samment certains cations, tels le titane, qui peuvent en fin de compte pénaliser la qualité du tripolyphosphate de sodium produit. Ceci est toujours le cas lorsqu'il s'agit de purifier des acides phosphoriques obtenus par voie humide à haute teneur en titane, tels que les acides phosphoriques produits à partir des phosphates de Kola.Finally, it is also well known that more recent methods have made it possible to obtain sodium tripoly¬ phosphate of even higher purity by using pure phosphoric acids whether they are obtained thermally or whether they result from a purification by liquid-liquid extraction of phosphoric acids obtained by wet process. For these sodium tripolyphosphate manufacturing processes, the step of chemical purification of sodium phosphate solutions therefore no longer exists, which is a great simplification. Indeed, this makes it possible to avoid pre-neutralization at an intermediate pH, the filtration of insoluble compounds containing the impurities as well as the problem of the elimination of solid waste resulting from this filtration. Nevertheless, the processes for purifying phosphoric acid by liquid-liquid extraction sometimes find it difficult to sufficiently remove certain cations, such as titanium, which can ultimately penalize the quality of the sodium tripolyphosphate produced. This is always the case when it comes to purifying phosphoric acids obtained by wet process with a high titanium content, such as phosphoric acids produced from Kola phosphates.
La présente invention est relative à un procédé de fabrication de phosphates alcalins (Li, Na, K) de qualité technique ou alimentaire à faible teneur en impuretés métalliques, par exemple en titane et en fer, à partir d'acides phosphoriques pouvant contenir jusqu'à 100 ppm de ces impuretés. A cet effet, le procédé suivant l'inven¬ tion, comprend la mise en réaction d'acide phosphorique avec une solution aqueuse d'un silicate alcalin, tel qu'un silicate de sodium, de potassium ou de lithium, de manière à former, d'une part, une solution du sel phosphaté correspondant et, d'autre part, de la silice micro-amorphe retenant les impuretés contenues dans l'acide phosphorique mis en oeuvre, le sel phosphaté et la silice obtenus étant ensuite séparés l'un de l'autre.The present invention relates to a process for the manufacture of alkaline phosphates (Li, Na, K) of technical or food quality with a low content of metallic impurities, for example titanium and iron, from phosphoric acids which may contain up to at 100 ppm of these impurities. To this end, the process according to the invention comprises the reaction of phosphoric acid with an aqueous solution of an alkali silicate, such as a sodium, potassium or lithium silicate, so as to form , on the one hand, a solution of the corresponding phosphate salt and, on the other hand, of micro-amorphous silica retaining the impurities contained in the phosphoric acid used, the phosphate salt and the silica obtained then being separated one of the other.
De façon surprenante, l'utilisation de silicate alcalin, comme source du métal alcalin, permet d'obtenir une purification chimique importante, malgré le fait que le silicate alcalin peut contenir jusqu'à 100 ppm de titane, alors que l'hydroxyde correspondant en est pratiquement exempt.Surprisingly, the use of alkaline silicate as a source of the alkali metal makes it possible to obtain significant chemical purification, despite the fact that the alkali silicate can contain up to 100 ppm of titanium, while the corresponding hydroxide is practically free of it.
Ce résultat remarquable peut avantageuse- ment être obtenu en précipitant sous des conditions contrôlées de pH, température et concentration, de la silice qui coprécipite une grande partie des impuretés cationiques, dont le titane et le fer, qui sont encore présents dans le mélange réactionnel. Après élimination de cette silice suivant un procédé de séparation courant, on obtient une solu¬ tion de phosphate alcalin diluée de haute pureté qui, après concentration, peut être utilisée pour des appli¬ cations qui requièrent les plus hautes exigences de qualité.This remarkable result can advantageously be obtained by precipitating, under controlled conditions of pH, temperature and concentration, silica which coprecipitates a large part of the cationic impurities, including titanium and iron, which are still present in the reaction mixture. After removal of this silica according to a current separation process, a dilute alkaline phosphate solution of high purity is obtained which, after concentration, can be used for applications which require the highest quality requirements.
De façon encore plus surprenante, il est apparu que le produit siliceux obtenu répondait, après séchage, aux exigences les plus sévères quant à son emploi en tant que silice précipitée ou comme gel de silice.Even more surprisingly, it appeared that the siliceous product obtained met, after drying, the most stringent requirements as to its use as precipitated silica or as silica gel.
Or, il se fait que la fabrication de telles silices micro-amorphes via les procédés classi¬ ques conduit à la production simultanée d'un sous- produit constitué de solutions très diluées de sulfate alcalin, et notamment de sulfate de sodium, qui sont des effluents rejetés tels quels dans les rivières par les unités de production en activité.However, it happens that the manufacture of such micro-amorphous silicas via the conventional methods leads to the simultaneous production of a by-product consisting of very dilute solutions of alkali sulfate, and in particular sodium sulfate, which are effluents discharged as such into rivers by active production units.
Le procédé de fabrication du sel de phosphate alcalin, suivant l'invention, permet donc de solutionner également un grave problème d'environnement créé par les usines de fabrication de telles silices micro-amorphes.The process for manufacturing the alkaline phosphate salt according to the invention therefore also makes it possible to solve a serious environmental problem created by the factories for manufacturing such micro-amorphous silicas.
Quoique le procédé, suivant l'invention, est surtout utile pour la fabrication de phosphate de sodium et notamment de tripolyphosphate de sodium, il est également intéressant pour la fabrication de phos- phates d'autres métaux alcalines. Ainsi, en partant d'une solution de silicate de potassium, ce procédé permet la fabrication de solutions diluées de phosphates potassiques qui sont capables, après concentration et éventuellement ajustement du pH à l'aide d'hydroxyde de potassium, de produire des phosphates ou pyrophosphates potassiques de qualité technique et alimentaire tout en maintenant la qualité de la silice coproduite.Although the process according to the invention is especially useful for the manufacture of sodium phosphate and in particular sodium tripolyphosphate, it is also advantageous for the manufacture of phos- phates of other alkali metals. Thus, starting from a potassium silicate solution, this process allows the manufacture of dilute potassium phosphate solutions which are capable, after concentration and possibly adjustment of the pH using potassium hydroxide, of producing phosphates or technical and food grade potassium pyrophosphates while maintaining the quality of the co-produced silica.
De même, ce qui a été établi pour les phosphates et polyphosphates sodiques et potassiques peut être étendu aux phosphates et polyphosphates de lithium, en partant évidemment d'une solution de sili¬ cate de lithium.Likewise, what has been established for sodium and potassium phosphates and polyphosphates can be extended to lithium phosphates and polyphosphates, obviously starting with a solution of lithium silicate.
L'intérêt industriel de ce nouveau procédé dépend bien sûr aussi des caractéristiques physiques de la silice obtenue. Or, des essais de fabrication ont démontré que certaines conditions de réaction entre le silicate et l'acide phosphorique permettent d'obtenir des gels ou précipités de silice aux propriétés physico- chimiques remarquables pouvant être pleinement valori¬ sées dans de nombreuses applications.The industrial interest of this new process naturally also depends on the physical characteristics of the silica obtained. However, manufacturing tests have demonstrated that certain reaction conditions between the silicate and the phosphoric acid make it possible to obtain gels or precipitates of silica with remarkable physicochemical properties which can be fully developed in many applications.
Les silices que l'on obtient comme copro¬ duits sont de type micro-amorphe ou non-cristallin et se caractérisent essentiellement par de très hautes εurfa- ces spécifiques comprises entre 10 et 800 m2 /g ainsi que par des degrés de porosité extrêmement élevés, ce dont témoignent les faibles densités apparentes. Ces solides micro-amorphes, dont les propriétés physico-chimiques générales et les mécanismes de formation principaux sont décrits dans l'ouvrage de ILER (The Chemistry of Silica, John Wiley, 1979) , se composent de particules colloïda¬ les primaires de tailles nano étriques qui, par coagula¬ tion, ont donné naissance à un gel ou à un précipité.The silicas which are obtained as co-products are of the micro-amorphous or non-crystalline type and are essentially characterized by very high specific surfaces between 10 and 800 m 2 / g as well as by extremely porous degrees. high, as evidenced by the low apparent densities. These micro-amorphous solids, whose general physico-chemical properties and the main formation mechanisms are described in the work of ILER (The Chemistry of Silica, John Wiley, 1979), are composed of primary colloidal particles of nanosize metrics which, by coagulation, gave rise to a gel or a precipitate.
D'autres détails et particularités de l'invention ressortiront de la description plus détail¬ lée donnée ci-après, contenant des exemples de réalisa- tion pratiques permettant d'illustrer davantage l'inven¬ tion. Ces exemples ne limitent bien entendu pas la portée de l'invention.Other details and particularities of the invention will emerge from the more detailed description given below, containing examples of embodiments. tion to illustrate the invention further. These examples do not of course limit the scope of the invention.
Comme déjà indiqué ci-dessus, le procédé suivant 1 ' invention consiste à mettre en réaction avec de l'acide phosphorique un silicate alcalin sous forme de solution aqueuse dont le rapport molaire Si02/M20As already indicated above, the process according to the invention consists in reacting with phosphoric acid an alkaline silicate in the form of an aqueous solution whose molar ratio Si0 2 / M 2 0
(M=Li,Na,K) et de préférence compris entre 1 et 4.(M = Li, Na, K) and preferably between 1 and 4.
Les produits de réaction obtenus sont formés, d'une part, d'un sel alcalin phosphaté en solu¬ tion et, d'autre part, de silice qui peut être sous une forme précipitée ou sous forme d'un gel.The reaction products obtained are formed, on the one hand, of an alkaline phosphate salt in solution and, on the other hand, of silica which can be in a precipitated form or in the form of a gel.
Ces produits de réaction sont ensuite séparés l'un de l'autre et, le cas échéant, soumis à différents traitements suivant les applications envisa¬ gées.These reaction products are then separated from each other and, if necessary, subjected to different treatments according to the applications envisaged.
La composition chimique de la solution de phosphate obtenue, ainsi que les caractéristiques physico-chimiques du produit siliceux dépendent des nombreuses variables opératoires : dilutions des solu¬ tions d'acide phosphorique et de silicate, ordre et vitesse d'addition desdites solutions, leur température, les rapports molaires Si02/M20 et P20,/M20, l'agitation du réacteur, etc, M étant Na, K ou Li. Si le coproduit recherché est une silice précipitée, la réaction est avantageusement réalisée dans un réacteur discontinu agité. La méthode de travail décrite ci-après est particulièrement favorable parce qu'elle fournit des précipités de silice facile- ment valorisables à l'échelle industrielle. Leur bonne filtrabilité permet, en effet, une séparation aisée du solide et de la solution phosphatée. En outre, les propriétés physico-chimiques finales de ces silices leur assurent d'excellentes performances dans différents domaines d'application. Selon une des méthodes possibles, si par exemple on part d'un silicate de sodium, la quantité totale de silicate de sodium nécessaire à la réaction est préalablement introduite dans le réacteur sous forme d'une solution aqueuse à une concentration pondérale en Si02 qui est avantageusement comprise entre 6 et 12 %. Après avoir éventuellement ajusté la température de ladite solution entre 15 et 100°C, on y ajoute progres¬ sivement une solution d'acide phosphorique dont le titre en H3P04 se situe de préférence entre 30 et 50 % . Le débit d'alimentation de l'acide fait partie des varia¬ bles opératoires. Le mélange réactionnel est agité tout au long de l'addition. La quantité d'acide phosphorique ajoutée, quant à elle, dépend notamment du rapport M/P du phosphate sodique recherché. Le rapport molaire H3P04/M20 final sera toutefois supérieur à 0,80, de façon à ce que la phase aqueuse ait un pH inférieur ou égal à 9 au moment de séparer la silice. Ceci s'applique également si le silicate utilisé est un silicate de potassium ou de lithium.The chemical composition of the phosphate solution obtained, as well as the physicochemical characteristics of the siliceous product depend on many operating variables: dilutions of the phosphoric acid and silicate solutions, order and speed of addition of said solutions, their temperature , the molar ratios Si0 2 / M 2 0 and P 2 0, / M 2 0, the stirring of the reactor, etc., M being Na, K or Li. If the desired co-product is a precipitated silica, the reaction is advantageously carried out in a stirred batch reactor. The working method described below is particularly favorable because it provides easily recoverable silica precipitates on an industrial scale. Their good filterability allows, in fact, an easy separation of the solid and the phosphate solution. In addition, the final physicochemical properties of these silicas provide them with excellent performance in various fields of application. According to one of the possible methods, if for example one starts from a sodium silicate, the total quantity of sodium silicate necessary for the reaction is introduced beforehand into the reactor in the form of an aqueous solution at a weight concentration of Si0 2 which is advantageously between 6 and 12%. After having optionally adjusted the temperature of said solution between 15 and 100 ° C., a solution of phosphoric acid is added thereto progressively, the H 3 PO 4 titer is preferably between 30 and 50%. The acid feed rate is one of the operating variables. The reaction mixture is stirred throughout the addition. The amount of phosphoric acid added, for its part, depends in particular on the M / P ratio of the sodium phosphate sought. The final H 3 P0 4 / M 2 0 molar ratio will however be greater than 0.80, so that the aqueous phase has a pH less than or equal to 9 when separating the silica. This also applies if the silicate used is a potassium or lithium silicate.
Différentes techniques peuvent convenir pour séparer la silice précipitée des eaux-mères phos¬ phatées, comme par exemple les méthodes de filtration sous vide ou sur filtre-presse. Une étape de lavage, par exemple par alimentation d'eau fraîche, peut être utile pour garantir un rendement en phosphate optimal. Le filtrat composé de phosphate de sodium relativement dilué est alors reconcentré, par exemple à l'aide d'un évaporateur à multiples effets. Le gâteau de filtration, contenant la silice précipitée, peut être séché via différents procédés courants, le choix du sécheur étant en grande partie dicté par la présentation physique du produit fini souhaité. Parmi les appareils les mieux appropriés il y a lieu de noter les sécheurs à plateaux, les sécheurs flash et les tours d'ato isation. Le dernier type d'appareil est particulièrement avantageux parce qu'il fournit directement un produit fini sous forme de microperles dont les propriétés principales sont leur excellente fluidité et leur caractère non-pulvérulent, et cela sans nécessiter de traitement ultérieur comme c'est par contre le cas des autres procédés de séchage. La méthode proposée pour produire les gels de silice à partir de silicate alcalin et d'acide phosphorique présente également plusieurs variantes. Les étapes principales du procédé sont décrites ci- dessous. On commence par neutraliser le silicate en solution aqueuse par réaction avec l'acide phosphorique de manière à former une solution colloïdale. Le pH, généralement acide, du mélange réactionnel constitue une des variables opératoires. Cette opération de mélange s'effectue dans un réacteur agité. L'hydrosol ainsi obtenu est alors maintenu au repos le temps nécessaire pour le transformer en hydrogel. Un des procédés possibles est la méthode de gélification rapide, qui consiste à mélanger le silicate et l'acide phosphorique en continu au moyen d'un pulvérisateur placé au-dessus d'une bande de transport, les conditions de réaction étant choisies de manière à ce que le processus de gélification soit pratiquement instantané. Le gel est ensuite mis en forme, lavé à l'eau pour en extraire le sel phosphaté et, enfin, séché. Le lavage à l'eau se réalise par exemple dans un réacteur à contre-courant.Different techniques may be suitable for separating precipitated silica from phosphated mother liquors, such as, for example, vacuum or filter press filtration methods. A washing step, for example by supplying fresh water, can be useful to guarantee an optimal phosphate yield. The relatively dilute sodium phosphate filtrate is then reconcentrated, for example using a multiple-effect evaporator. The filter cake, containing the precipitated silica, can be dried by various common methods, the choice of the dryer being largely dictated by the physical presentation of the desired finished product. Among the most suitable devices there are trays dryers, flash dryers and air towers. The last This type of device is particularly advantageous because it directly supplies a finished product in the form of microbeads, the main properties of which are their excellent fluidity and their non-pulverulent nature, and this without requiring any further treatment, as is the case. other drying processes. The proposed method for producing silica gels from alkali silicate and phosphoric acid also presents several variants. The main process steps are described below. We start by neutralizing the silicate in aqueous solution by reaction with phosphoric acid so as to form a colloidal solution. One of the operating variables is the generally acidic pH of the reaction mixture. This mixing operation is carried out in a stirred reactor. The hydrosol thus obtained is then kept at rest for the time necessary to transform it into a hydrogel. One of the possible methods is the rapid gelation method, which consists in mixing silicate and phosphoric acid continuously using a sprayer placed above a conveyor belt, the reaction conditions being chosen so as to that the gelling process is almost instantaneous. The gel is then shaped, washed with water to extract the phosphate salt therefrom, and finally dried. Washing with water is carried out for example in a counter-current reactor.
Certains post-traitements de la silice, appliqués après formation du gel, tels que le lavage par de l'ammoniaque et le vieillissement en milieu basique, permettent de faire varier les caractéristiques poreuses de la silice. La densité finale du gel dépend aussi en grande partie du procédé de séchage utilisé. Un séchage de type flash, par exemple, fournit des gels moins denses, caractérisés par des tailles de pores plus élevées, que les mêmes silices séchées plus lentement. Les avantages de la présente invention apparaissent clairement au tableau suivant qui compare les niveaux de concentration typiques en fer, aluminium et titane qu'atteint par exemple le tripolyphosphate de sodium (STPP) préparé selon la méthode classique ou selon le nouveau procédé de purification suivant l'in¬ vention. Certain post-treatments of silica, applied after gel formation, such as washing with ammonia and aging in basic medium, make it possible to vary the porous characteristics of the silica. The final density of the gel also largely depends on the drying process used. Flash-type drying, for example, provides less dense gels, characterized by larger pore sizes, than the same, more slowly dried silicas. The advantages of the present invention appear clearly in the following table which compares the typical concentration levels of iron, aluminum and titanium which, for example, reaches sodium tripolyphosphate (STPP) prepared according to the conventional method or according to the new purification process according to the invention. 'invention.
Figure imgf000013_0001
La dernière ligne du tableau est donnée à titre de comparaison. On y fait l'hypothèse que les quantités élevées de fer, d'aluminium et de titane habituellement présentes dans les silicates de qualité industrielle se retrouveraient entièrement dans le tripolyphosphate de sodium final. On y suppose par ailleurs un pH de filtration égal à 7.
Figure imgf000013_0001
The last line of the table is given for comparison. It is hypothesized that the high amounts of iron, aluminum and titanium usually present in industrial grade silicates would be found entirely in the final sodium tripolyphosphate. It also assumes a filtration pH equal to 7.
Etant donné le niveau de pureté assez médiocre du silicate alcalin utilisé, la qualité surpre¬ nante du sel phosphaté séparé entre pH 9 et 5 souligne bien le caractère original du procédé suivant l'inven¬ tion. Ce dernier réduit jusqu'à cinquante fois la teneur en titane et près de quarante fois les teneurs en fer et en aluminium. Il apparaît donc que la silice coprécipite la plus grande partie de ces impuretés.Given the fairly mediocre level of purity of the alkaline silicate used, the surprising quality of the phosphate salt separated between pH 9 and 5 underlines the original character of the process according to the invention. The latter reduces the titanium content up to fifty times and the iron and aluminum contents almost forty times. It therefore appears that silica coprecipitates most of these impurities.
Les caractéristiques physico-chimiques générales des silices obtenues sont reprises ci-dessous. Il est évidemment possible de moduler ces propriétés et de les adapter aux spécificités de chaque domaine d'application en optimisant les conditions de réaction entre le silicate et l'acide phosphorique ou en modi¬ fiant les post-traitements que l'on inflige à la silice après séparation de la solution phosphatée. L'humidité résiduelle de la silice est composée de deux types d'eau différents. La perte de poids à 105°C indique la teneur en "eau libre". Celle- ci peut être facilement ajustée en réglant les condi¬ tions de fonctionnement du sécheur. La perte de poids à 1000°C de la silice, qui sera exprimée par rapport au produit séché à 105°C, se situe entre 3 et 8 % et reflète, quant à elle, la teneur en "eau liée" de la silice. Ces molécules d'eau sont contenues en partie dans les liaisons silanols (-Si-OH) qui couvrent la surface des particules de silice. Le reste de "l'eau liée" est rattaché par ponts hydrogène aux liaisons en question. Cette hydratation, dont dépendent les pro¬ priétés de surface du solide, détermine par conséquent aussi ses interactions avec le milieu d'utilisation.The general physicochemical characteristics of the silicas obtained are listed below. It is obviously possible to modulate these properties and to adapt them to the specificities of each field of application by optimizing the reaction conditions between the silicate and the phosphoric acid or by modifying the post-treatments which one inflicts on the silica after separation of the phosphate solution. The residual moisture in the silica is made up of two different types of water. The weight loss at 105 ° C indicates the "free water" content. This can be easily adjusted by adjusting the operating conditions of the dryer. The weight loss at 1000 ° C of the silica, which will be expressed relative to the dried product at 105 ° C, is between 3 and 8% and reflects, for its part, the "bound water" content of the silica. These water molecules are contained in part in the silanol bonds (-Si-OH) which cover the surface of the silica particles. The rest of the "bound water" is linked by hydrogen bridges to the bonds in question. This hydration, on which the surface properties of the solid depend, consequently also determines its interactions with the environment of use.
Une autre propriété des silices qui influence énormément leur comportement dans les applica¬ tions est leur surface spécifique. Celle-ci est mesurée selon deux méthodes complémentaires, mais dont les résultats sont à peu près identiques en absence de microporosité. Il s'agit, d'une part, de la méthode de BRUNAUER, EMMETT et TELLER (BET) et, d'autre part, de la mesure d'adsorption du bromure de cétyl-, triméthylammo- nium (CTAB) en solution aqueuse, telle que décrite dans la norme NF T 45-007. Le choix des conditions d'obten¬ tion de la silice permet de moduler ces surfaces BET et CTAB dans une fourchette extrêmement large s 'étendant de 10 à 800 m2/g.Another property of silicas which greatly influences their behavior in applications is their specific surface. This is measured using two complementary methods, but the results of which are almost identical in the absence of microporosity. It is, on the one hand, the BRUNAUER, EMMETT and TELLER (BET) method and, on the other hand, the measurement of adsorption of cetyl-, trimethylammonium bromide (CTAB) in aqueous solution , as described in standard NF T 45-007. The choice of conditions for obtaining silica makes it possible to modulate these BET and CTAB surfaces in an extremely wide range extending from 10 to 800 m 2 / g.
La structure en forme d'agrégats poreux et ouverts qui caractérise les silices précipitées suivant 1 'invention se traduit généralement par des densités apparentes très faibles. Cette structure physique leur confère par ailleurs un pouvoir d'absorption remarqua¬ ble, comme le montre par exemple le test d'absorption de dibutylphtalate (DBP) . Cette mesure est réalisée suivant la norme NF ISO 4656/1. Les prises de DBP ainsi mesurées se situent entre 50 et 300 g de DBP par 100 g de silice selon les conditions opératoires adoptées lors de la précipitation de la silice.The structure in the form of porous and open aggregates which characterizes the precipitated silicas according to the invention generally results in very low apparent densities. This physical structure also gives them a remarkable absorption power, as shown for example by the dibutylphthalate absorption test (DBP). This measurement is carried out in accordance with standard NF ISO 4656/1. The DBP intakes thus measured are between 50 and 300 g of DBP per 100 g of silica according to the operating conditions adopted during the precipitation of the silica.
Les caractéristiques granulométriques des silices obtenues varient selon les procédés de séchage et de mise en forme finale utilisés. Dans le cas de silice précipitée séchée par un procédé "flash", par exemple, il a été constaté que la taille moyenne des particules obtenues se situe aux environs de 15 μm et que le refus sur tamis 40 μm, mesuré selon la méthode de tamisage humide de la norme ISO 787/18, ne dépasse pas 0,2 % après dispersion aux ultrasons. La teneur en Si02 de la silice, déterminée par gravimétrie et exprimée par rapport au produit sec à 105°C, dépend essentiellement du degré de lavage atteint lors de la séparation. Des teneurs pondérales en Si02 de plus de 93 % sont aisément obtenues.The particle size characteristics of the silicas obtained vary according to the drying and final shaping processes used. In the case of precipitated silica dried by a "flash" process, for example, it has been observed that the average size of the particles obtained is around 15 μm and that the rejection on a sieve 40 μm, measured according to the sieving method ISO 787/18 wet, does not exceed 0.2% after ultrasonic dispersion. The Si0 2 content of the silica, determined by gravimetry and expressed relative to the dry product at 105 ° C., essentially depends on the degree of washing achieved during the separation. Weight contents of Si0 2 of more than 93% are easily obtained.
L'acidité de la silice, évaluée suivant la méthode ISO 787/9, dépend du rapport H3P04/M20. Une correction de pH par addition d'acide ou d'alcalin après la séparation de la solution phosphatée est toutefois possible. Une séparation aux environs de pH 7 est particulièrement favorable, puisque, d'une part, ce pH correspond pratiquement à celui du tripolyphosphate de sodium et que, d'autre part, le pH de la silice ainsi obtenue est compatible avec la majorité des applica- tions, toute correction d'acidité étant donc superflue.The acidity of the silica, evaluated according to the ISO 787/9 method, depends on the H 3 P0 4 / M 2 0 ratio. A correction of pH by addition of acid or alkali after the separation of the phosphate solution is however possible. A separation around pH 7 is particularly favorable, since, on the one hand, this pH practically corresponds to that of sodium tripolyphosphate and, on the other hand, the pH of the silica thus obtained is compatible with the majority of applications. - tions, any acidity correction is therefore superfluous.
L'invention est illustrée davantage par les exemples concrets donnés ci-après.The invention is further illustrated by the concrete examples given below.
Exemple 1 Le silicate de sodium en solution de départ présentait un rapport molaire Si02/Na20 de 3,32 et titrait 35,8% de matière sèche. Il s'agissait d'une solution d'origine industrielle de qualité courante dont les teneurs en fer, aluminium et titane étaient respec¬ tivement de 50, 160 et 50 ppm. La solution d'acide phosphorique à traiter titrait 78 % de H3P04 et les trois impuretés susmentionnées y atteignaient des niveaux de concentration de 80, 60 et 50 ppm.Example 1 The sodium silicate in the starting solution had a Si0 2 / Na 2 0 molar ratio of 3.32 and titrated 35.8% of dry matter. It was a solution of industrial origin of current quality whose iron, aluminum and titanium contents were respectively 50, 160 and 50 ppm. The phosphoric acid solution to be treated titrated 78% H 3 P0 4 and the three aforementioned impurities there reached concentration levels of 80, 60 and 50 ppm.
La solution de silicate de sodium a d'abord été diluée par addition d'eau déminéralisée jusqu'à une concentration pondérale en Si02 de 8,0 %. Après avoir amené 2649 kg de cette solution diluée dans un réacteur bien agité et avoir élevé sa température jusqu'à 73°C par un système de chauffage indirect, l'alimentation de l'acide phosphorique a pu commencer. Cette solution a été alimentée à une concentration en H3P04 de 45 %, l'ajustement du titre se faisant également par addition d'eau déminéralisée. Le mélange réaction- nel a été agité tout au long de l'acidification. Après une heure et demie de réaction, la température a été portée à 85°C. Après trois heures, le volume de solu- tion alimenté atteignait 475 1. Ensuite, la suspension obtenue, dont le pH mesuré à la température indiquée ci- dessus était proche de 7,0, a été refroidie à 60°C, puis filtrée et lavée sur filtre-presse.The sodium silicate solution was first diluted by adding demineralized water to a weight concentration of SiO 2 of 8.0%. After having brought 2649 kg of this diluted solution to a well-stirred reactor and having raised its temperature to 73 ° C by an indirect heating system, the feeding of phosphoric acid could begin. This solution was supplied with an H 3 P0 4 concentration of 45%, the titer adjustment also being made. by adding demineralized water. The reaction mixture was stirred throughout the acidification. After an hour and a half of reaction, the temperature was brought to 85 ° C. After three hours, the volume of solution supplied reached 475 1. Next, the suspension obtained, the pH of which measured at the temperature indicated above was close to 7.0, was cooled to 60 ° C, then filtered and washed on filter press.
Les filtrats mélangés des étapes de filtration et de lavage, dont le rapport Na/P était égal à 1,63, ont été reconcentrés par évaporation jusqu'à une concentration en P205 de 32 %. Après ajustement du ration Na/P moyennant une faible addition de soude caustique, la solution concentrée a été séchée par atomisation. Après calcination, l'analyse du tripoly¬ phosphate de sodium en poudre obtenu était la suivante : P205 (%) 57,7The mixed filtrates from the filtration and washing stages, the Na / P ratio of which was 1.63, were reconcentrated by evaporation to a P 2 O 5 concentration of 32%. After adjusting the Na / P ration with a small addition of caustic soda, the concentrated solution was spray-dried. After calcination, the analysis of the sodium tripoly¬ phosphate powder obtained was as follows: P 2 0 5 (%) 57.7
Tripolyphosphate (%) 97,6Tripolyphosphate (%) 97.6
Pyrophosphate (%) 2,4 Orthophosphate (%) <0,1Pyrophosphate (%) 2.4 Orthophosphate (%) <0.1
Perte à 105°C (%) 0,12Loss at 105 ° C (%) 0.12
Insolubles dans l'eau (%) 0,10Insoluble in water (%) 0.10
Blancheur CIE (1) (%) L=97,0 a=0,0 b=0,6Whiteness CIE (1) (%) L = 97.0 a = 0.0 b = 0.6
Fe (ppm) 3,2 Al (ppm) 1,3Fe (ppm) 3.2 Al (ppm) 1.3
Ti (ppm) 1,0Ti (ppm) 1.0
(1) Commission Internationale de l'Eclairage(1) International Lighting Commission
Le gâteau de filtration contenant la silice a été reliquéfié par agitation mécanique avant d'être séché dans une tour d'atomisation. Le pH du produit a été ajusté par un petit apport d'acide phos¬ phorique avant séchage. La silice précipitée finale se présentait sous forme de microperles et possédait les caractéristiques suivantes : Surface BET (m2/g) 172The filter cake containing the silica was reliquified by mechanical stirring before being dried in an atomization tower. The pH of the product was adjusted by a small addition of phos¬ phoric acid before drying. The final precipitated silica was in the form of microbeads and had the following characteristics: BET surface (m 2 / g) 172
Surface CTAB (mVg) 160 Absorption de DBP (g/lOOg) 250CTAB area (mVg) 160 DBP absorption (g / lOOg) 250
Densité apparente tassée (g/dm3) 296Packed bulk density (g / dm 3 ) 296
Perte à 105°C (%) 5,9Loss at 105 ° C (%) 5.9
Perte à 1000°C (sur produit sec à 105°C) (%) 5,2 Si02 (sur produit sec à 105°C) (%) 93,5 pH 6,8Loss at 1000 ° C (on dry product at 105 ° C) (%) 5.2 Si0 2 (on dry product at 105 ° C) (%) 93.5 pH 6.8
Exemple 2 La réaction de précipitation a été réali¬ sée dans des conditions opératoires identiques à celles de l'Exemple 1, sauf que l'addition d'acide phosphorique s'est terminée à pH 8,0. Les filtrats mélangés attei¬ gnaient alors un ratio Na/P de 2,05, qui a ensuite été ajusté à celui du phosphate disodique par addition d'acide phosphorique. Le phosphate disodique anhydre que nous avons préparé à partir de cette solution corrigée avait les caractéristiques suivantes : P205 (%) 49,9Example 2 The precipitation reaction was carried out under operating conditions identical to those of Example 1, except that the addition of phosphoric acid ended at pH 8.0. The mixed filtrates then reached an Na / P ratio of 2.05, which was then adjusted to that of disodium phosphate by adding phosphoric acid. The anhydrous disodium phosphate that we prepared from this corrected solution had the following characteristics: P 2 0 5 (%) 49.9
Fe (ppm) <0,1Fe (ppm) <0.1
Al (ppm) 1,6 Ti (ppm) <1Al (ppm) 1.6 Ti (ppm) <1
Le gâteau de filtration a été soumis à une correction de pH assez importante par addition d'acide phosphorique, suivie d'un second lavage à l'eau pour éliminer l'excédent de sel formé lors de cet ajustement. Les caractéristiques de la silice précipitée obtenue à la sortie du εécheur atomiseur étaient pratiquement identiques à celles de l'Exemple 1.The filter cake was subjected to a fairly large pH correction by adding phosphoric acid, followed by a second washing with water to remove the excess salt formed during this adjustment. The characteristics of the precipitated silica obtained at the outlet of the atomizing dryer were practically identical to those of Example 1.
Exemple 3 La réaction de précipitation a été réali- sée dans des conditions opératoires identiques à celles de l'Exemple 1, sauf que l'addition d'acide phosphorique s'est terminée à pH 5,8. Les filtrats mélangés attei¬ gnaient alors un ratio Na/P de 1,21, que 1 'on a ajusté à celui du phosphate monosodique par addition d'acide phosphorique. Le phosphate monosodique anhydre préparé à partir de cette solution phosphatée avait les caracté¬ ristiques suivantes : P205 (%) 59,1Example 3 The precipitation reaction was carried out under operating conditions identical to those of Example 1, except that the addition of phosphoric acid was terminated at pH 5.8. The mixed filtrates then reached an Na / P ratio of 1.21, which was adjusted to that of monosodium phosphate by addition of phosphoric acid. Anhydrous sodium phosphate prepared from this phosphate solution had the following characteristics: P 2 0 5 (%) 59.1
Fe (ppm) 24 Al (PPm) 1,7Fe (ppm) 24 Al (PPm) 1.7
Ti (ppm) 1,9Ti (ppm) 1.9
Aucun ajustement de pH n'a été nécessaire au niveau du gâteau de silice. Les caractéristiques de la silice précipitée obtenue à la sortie du sécheur atomiseur étaient pratiquement identiques à celles de l'Exemple 1.No pH adjustment was necessary at the level of the silica cake. The characteristics of the precipitated silica obtained at the outlet of the atomizer dryer were practically identical to those of Example 1.
Exemple 4 Le gâteau de filtration obtenu suivant le mode opératoire de l'Exemple 1 a été séché au moyen d'un sécheur flash. La silice précipitée finale, qui se présentait cette fois sous forme de poudre, avait les caractéristiques physico-chimiques suivantes : Surface BET (m2/g) 175Example 4 The filter cake obtained according to the procedure of Example 1 was dried using a flash dryer. The final precipitated silica, this time in the form of a powder, had the following physicochemical characteristics: BET surface (m 2 / g) 175
Surface CTAB (m2/g) 158 Absorption de DBP (g/100g) 245CTAB area (m 2 / g) 158 DBP absorption (g / 100g) 245
Densité apparente tassée (g/dm3) 190Packed bulk density (g / dm 3 ) 190
Perte à 105°C (%) 5,5Loss at 105 ° C (%) 5.5
Perte à 1000°C sur produit sec à 105°C) (%) 5,1 Si02 (sur produit sec à 105°C) (%) 93,7 pH 6,9Loss at 1000 ° C on dry product at 105 ° C) (%) 5.1 Si0 2 (on dry product at 105 ° C) (%) 93.7 pH 6.9
Taille moyenne des particules (d50 volumique) (μm) 13 Refus sur tamis 40 μm (%) 0,16Average particle size (volume d50) (μm) 13 Refusal on sieve 40 μm (%) 0.16
Exemple 5 Mis à part la température initiale de la réaction qui était ici de 78°C au lieu de 73°C, la méthode de travail était identique à celle de l'Exemple 1. D'ailleurs, l'analyse du tripolyphosphate de sodium obtenu après traitement des filtrats était pratiquement la même. Par contre, la silice précipitée finale présentait des caractéristiques physico-chimiques très différentes, offrant d'autres possibilités au niveau des applications :EXAMPLE 5 Apart from the initial reaction temperature which was 78 ° C. here instead of 73 ° C., the working method was identical to that of Example 1. Besides, the analysis of sodium tripolyphosphate obtained after treatment of the filtrates was practically the same. On the other hand, the final precipitated silica exhibited very physicochemical characteristics. different, offering other possibilities in terms of applications:
Surface BET (m2/g) 118BET area (m 2 / g) 118
Surface CTAB (m /g) 106 Absorption de DBP (g/100 g) 205CTAB area (m / g) 106 DBP absorption (g / 100 g) 205
Densité apparente tassée (g/dm3) 275Packed bulk density (g / dm 3 ) 275
Perte à 105°C (%) 6,2Loss at 105 ° C (%) 6.2
Perte à 1000°C (sur produit sec à 105°C) (%) 5,1 Si02 (sur produit sec à 105°C) (%) 93,4 pH 6,7Loss at 1000 ° C (on dry product at 105 ° C) (%) 5.1 Si0 2 (on dry product at 105 ° C) (%) 93.4 pH 6.7
Exemple 6 Les matières premières étaient pratique¬ ment de la même pureté que celles de l'Exemple 1. 1567 g de silicate dilué à 6,38 % de Si02 étaient rapidement mélangés à 933 g d'acide titrant 10 % de H3P04. Cette opération était réalisée dans un berlin vigoureusement agité, ce après quoi le mélange réactionnel était maintenu au repos. La concentration en Si02 y était de 4, 0 % et le pH y atteignait une valeur de 5,2. Après une demie heure, l'hydrogel formé était fragmenté par agitation mécanique dans le berlin, où il subissait ensuite plusieurs lavages successifs à l'eau déminérali¬ sée, l'eau utilisée pour le dernier lavage étant très légèrement basique de façon à neutraliser la suspension. Le gel était finalement séché dans une étuve à 105°C.Example 6 The raw materials were practically of the same purity as those of Example 1. 1567 g of silicate diluted with 6.38% of Si0 2 were rapidly mixed with 933 g of acid titrating 10% of H 3 P0 4 . This operation was carried out in a vigorously agitated berlin, after which the reaction mixture was kept at rest. The Si0 2 concentration there was 4.0% and the pH there reached 5.2. After half an hour, the hydrogel formed was fragmented by mechanical stirring in the berlin, where it then underwent several successive washes with demineralized water, the water used for the last washing being very slightly basic so as to neutralize the suspension. The gel was finally dried in an oven at 105 ° C.
Le phosphate sodique du filtrat se situait à un ratio Na/P de 1,05, finalement ajusté à celui du phosphate monosodique par addition d'acide phosphorique. Le phosphate monosodique anhydre qui a été préparé à partir de cette solution phosphatée avait les caracté¬ ristiques suivantes : P205 (%) 59,0The sodium phosphate of the filtrate was at an Na / P ratio of 1.05, finally adjusted to that of the sodium phosphate by addition of phosphoric acid. The anhydrous monosodium phosphate which was prepared from this phosphate solution had the following characteristics: P 2 0 5 (%) 59.0
Fe (ppm) 23Fe (ppm) 23
Al (ppm) 1,7 Ti (ppm) 2,0 Les caractéristiques physico-chimiques du gel de silice obtenu étaient les suivantes :Al (ppm) 1.7 Ti (ppm) 2.0 The physicochemical characteristics of the silica gel obtained were as follows:
Surface BET (m2/g) 740 Volume poreux (ml/g) 0,42BET surface (m 2 / g) 740 Pore volume (ml / g) 0.42
Taille moyenne des pores (n ) 2Average pore size (n) 2
Absorption de DBP (g/lOOg) 85DBP absorption (g / lOOg) 85
Perte à 1000°C (sur produit sec à 105°C) (%) 8,1Loss at 1000 ° C (on dry product at 105 ° C) (%) 8.1
Exemple 7 La méthode était la même que celle de l'Exemple 6, sauf que la dernière étape de lavage du gel a été effectuée par une solution ammoniaque à pH 9 et que le gel ainsi lavé a subi encore un temps de matura¬ tion de une heure avant séchage. L'analyse du phosphate monosodique était pratiquement identique à celle de l'exemple précédent. Par contre, la structure physique du gel de silice obtenu était fortement modifiée : Surface BET (m2/g) 360Example 7 The method was the same as that of Example 6, except that the last step of washing the gel was carried out with an ammonia solution at pH 9 and that the gel thus washed underwent another time of maturation. one hour before drying. The analysis of sodium phosphate was practically identical to that of the previous example. On the other hand, the physical structure of the silica gel obtained was greatly modified: BET surface (m 2 / g) 360
Volume poreux (ml/g) 1,0 Taille moyenne des pores (nm) 12Pore volume (ml / g) 1.0 Average pore size (nm) 12
Absorption de DBP (g/lOOg) 205DBP absorption (g / lOOg) 205
Perte à 1000°C (sur produit sec à 105°C) (%) 5,5Loss at 1000 ° C (on dry product at 105 ° C) (%) 5.5
Exemple 8 La méthode de l'Exemple 3 a été appliquée au cas du silicate de potassium. Les teneurs en fer, aluminium et titane du silicate potassique utilisé étaient relativement équivalentes à celles du silicate de sodium précédent et le rapport molaire Si02/K20 choisi était identique au rapport Si02/Na20 de l'Exemple 3. L'analyse du phosphate monopotassique obtenu était celle-ci :Example 8 The method of Example 3 was applied to the case of potassium silicate. The iron, aluminum and titanium contents of the potassium silicate used were relatively equivalent to those of the preceding sodium silicate and the molar ratio Si0 2 / K 2 0 chosen was identical to the Si0 2 / Na 2 0 ratio of Example 3. L analysis of the monopotassium phosphate obtained was this:
P205 (%) 52,1P 2 0 5 (%) 52.1
Fe (ppm) 21Fe (ppm) 21
Al (ppm) 1,3 Ti (PPm) 1,7 Le remplacement du sodium par le potassium au sein du milieu réactionnel a influencé les caracté¬ ristiques de la silice précipitée, comme on peut le constater ci-dessous : Surface BET (m2/g) 205Al (ppm) 1.3 Ti (PPm) 1.7 The replacement of sodium with potassium in the reaction medium has influenced the characteristics of the precipitated silica, as can be seen below: BET surface (m 2 / g) 205
Surface CTAB (m2/g) 180CTAB area (m 2 / g) 180
Absorption de DBP (g/100 g) 270DBP absorption (g / 100 g) 270
Densité apparente tassée (g/dm3) 290Packed bulk density (g / dm 3 ) 290
Perte à 105°C (%) 5,2 Perte à 1000°C (sur produit sec à 105°C) (%) 4,9Loss at 105 ° C (%) 5.2 Loss at 1000 ° C (on dry product at 105 ° C) (%) 4.9
Si02 (sur produit sec à 105°C) (%) 93,4 pH 6,5Si0 2 (on dry product at 105 ° C) (%) 93.4 pH 6.5
Les silices obtenues comme coproduits du procédé de purification suivant l'invention présentent notamment les caractéristiques requises pour servir de charge renforçante dans certains élasto ères. Les silices en question leur confère, en effet, des proprié¬ tés mécaniques performantes tout en augmentant considé¬ rablement leur résistance à l'usure. Les domaines d'application des silices précipitées sont nombreux. Parmi les plus évidents citons le renforcement des caoutchoucs mentionné ci- dessus, la fluidification et l'effet anti-mottant ("anti-caking") sur de nombreux pulvérulents, l'absorp- tion ou la mise sur support de matières actives liqui¬ des, l'amélioration de la blancheur et de l'opacité des papiers et peintures émulsion, la mise à profit du pouvoir épaississant et pseudo-plastique de ces silices dans les pâtes dentifrices, ainsi que dans certains produits d'entretien. Les silices découlant de la présente invention peuvent également servir à structurer les surfaces excessivement lisses de certains films plastiques, papiers, coatings ou peintures. La silice y joue alors un rôle anti-bloquant ou anti-glisse, ou intervient éventuellement comme agent matant. L'apti- tude à l'impression ou à l'imprégnation peut être également améliorée par ces silices.The silicas obtained as co-products of the purification process according to the invention have in particular the characteristics required to serve as a reinforcing filler in certain elasto ers. The silicas in question give them, in effect, high-performance mechanical properties while considerably increasing their resistance to wear. The fields of application of precipitated silicas are numerous. Among the most obvious, let us mention the reinforcement of the rubbers mentioned above, the fluidification and the anti-caking effect ("anti-caking") on many pulverulent materials, the absorption or placing on the support of liquid active ingredients. des, the improvement of the whiteness and opacity of emulsion papers and paints, the use of the thickening and pseudo-plastic power of these silicas in toothpastes, as well as in certain cleaning products. The silicas resulting from the present invention can also be used to structure the excessively smooth surfaces of certain plastic films, papers, coatings or paints. Silica then plays an anti-blocking or anti-slip role, or possibly acts as a matting agent. The apti- Study in printing or impregnation can also be improved by these silicas.
Les domaines d'application des gels de silice sont également nombreux. Ils sont souvent utilisés en tant qu'absorbant, et en particulier comme dessicant lorsque la substance absorbée est l'eau. Un second secteur d'application tout aussi important est celui des coatings, où les gels de silice interviennent surtout comme agent matant. Par ailleurs, les gels de silice ont aussi certains domaines d'application en commun avec les silices précipitées, comme par exemple la fluidification et l'effet anti-mottant des poudres, et la fonction d'anti-bloquant dans certains films plastiques. D'autres usages, tels que les catalyseurs supportés et les garnissages de colonnes chromatographi- ques sont par contre réservés aux gels.The fields of application of silica gels are also numerous. They are often used as an absorbent, and in particular as a desiccant when the absorbed substance is water. A second equally important sector of application is that of coatings, where silica gels are used mainly as a matting agent. Furthermore, silica gels also have certain fields of application in common with precipitated silicas, such as for example the fluidification and the anti-caking effect of powders, and the function of anti-blocking in certain plastic films. Other uses, such as supported catalysts and the packing of chromatographic columns are however reserved for gels.
Pour ce qui concerne le sel alcalin phosphaté obtenu, grâce à sa grande pureté obtenue par la mise en oeuvre du procédé suivant l'invention, les sels de potassium et de sodium trouvent leur application aussi bien comme adjuvants dans les détergents que dans l'agriculture et l'industrie des produits alimentaires.With regard to the phosphated alkaline salt obtained, thanks to its high purity obtained by the implementation of the process according to the invention, the potassium and sodium salts find their application both as adjuvants in detergents and in agriculture and the food industry.
Il résulte, par conséquent, de ce qui précède qu'un avantage essentiel du procédé suivant l'invention est qu'il permet d'obtenir deux produits de réaction qui, grâce à leur pureté, trouvent de nombreu¬ ses applications industrielles, contrairement à ce qui est le cas des procédés classiques qui donnent, en plus, du sel alcalin phosphaté, un résidu non valorisable. It follows, therefore, from the above that an essential advantage of the process according to the invention is that it makes it possible to obtain two reaction products which, thanks to their purity, find many industrial applications, unlike which is the case with conventional processes which give, in addition, alkaline phosphated salt, a non-recoverable residue.

Claims

REVENDICATIONS
1. Procédé de fabrication de sels alca¬ lins phosphatés de haute pureté, notamment d'un tripoly¬ phosphate, caractérisé en ce qu'il comprend la mise en réaction d'acide phosphorique avec une solution aqueuse d'un silicate alcalin, tel qu'un silicate de sodium, de potassium ou de lithium, de manière à former le sel phosphaté correspondant et de la silice micro-amorphe retenant la majorité des impuretés contenues dans l'acide phosphorique mis en oeuvre, le sel phosphaté et la silice obtenus étant ensuite séparés l'un de l'autre.1. A process for the production of high purity phosphate alkaline salts, in particular a tripoly¬ phosphate, characterized in that it comprises reacting phosphoric acid with an aqueous solution of an alkali silicate, such as '' a sodium, potassium or lithium silicate, so as to form the corresponding phosphate salt and micro-amorphous silica retaining the majority of the impurities contained in the phosphoric acid used, the phosphate salt and the silica obtained being then separated from each other.
2. Procédé suivant la revendication 1, caractérisé en ce que l'on utilise de l'acide phosphori¬ que ayant été soumis à une purification préalable telle que les impuretés passant dans la silice lors de la réaction avec le silicate alcalin ne nuisent pas à la qualité de la silice pour l'utilisation envisagée de cette dernière.2. Method according to claim 1, characterized in that phosphori¬ acid is used which has been subjected to a preliminary purification such that the impurities passing through the silica during the reaction with the alkali silicate do not harm the quality of the silica for the intended use of the latter.
3. Procédé suivant l'une ou l'autre des revendications 1 et 2, caractérisé en ce que l'on règle les conditions de réaction entre l'acide phosphorique et le silicate alcalin d'une manière telle que la silice obtenue forme un précipité pouvant être séparé par filtration du sel phosphaté obtenu en solution. 3. Method according to either of Claims 1 and 2, characterized in that the reaction conditions between the phosphoric acid and the alkaline silicate are adjusted in such a way that the silica obtained forms a precipitate can be separated by filtration from the phosphate salt obtained in solution.
4. Procédé suivant l'une ou l'autre des revendications 1 ou 2, caractérisé en ce que l'on règle les conditions de réaction entre l'acide phosphorique et le silicate alcalin d'une manière telle que la silice obtenue forme un gel, ce dernier étant alors séparé de la solution contenant le sel phosphaté et soumis à un lavage à l'eau.4. Method according to either of Claims 1 or 2, characterized in that the reaction conditions between the phosphoric acid and the alkali metal silicate are regulated in such a way that the silica obtained forms a gel , the latter then being separated from the solution containing the phosphate salt and subjected to washing with water.
5. Procédé suivant l'une quelconque des revendications 1 à 4, caractérisé en ce que le silicate alcalin mis en réaction présente un rapport molaire Si02/M20, dans lequel M représente Na, K et/ou Li compris entre 1 et 4. 5. Method according to any one of claims 1 to 4, characterized in that the alkali silicate reacted has a molar ratio Si0 2 / M 2 0, in which M represents Na, K and / or Li of between 1 and 4.
6. Procédé suivant l'une quelconque des revendications 1 à 5, caractérisé en ce que l'on utilise une solution aqueuse d'un silicate alcalin dont la concentration pondérale en Si02 est comprise entre 1 et 12 %.6. Method according to any one of claims 1 to 5, characterized in that an aqueous solution of an alkali silicate is used whose weight concentration of Si0 2 is between 1 and 12%.
7. Procédé suivant l'une quelconque des revendications l à 3, 5 et 6, caractérisé en ce que la réaction précitée est réalisée sous agitation.7. Method according to any one of claims l to 3, 5 and 6, characterized in that the aforementioned reaction is carried out with stirring.
8. Procédé suivant l'une quelconque des revendications 1 à 7, caractérisé en ce que la réaction est réalisée en discontinu.8. Method according to any one of claims 1 to 7, characterized in that the reaction is carried out batchwise.
9. Procédé suivant l'une quelconque des revendications 1 à 3 et 5 à 8, caractérisé en ce que l'on ajoute l'acide phosphorique d'une manière sensible- ment progressive au silicate alcalin, tout en soumettant le mélange réactionnel à une agitation.9. Method according to any one of claims 1 to 3 and 5 to 8, characterized in that the phosphoric acid is added in a substantially progressive manner to the alkali silicate, while subjecting the reaction mixture to a agitation.
10. Procédé suivant la revendication 9, caractérisé en ce que l'on ajuste la température de la solution contenant le silicate alcalin entre 15 et 100°C avant l'addition progressive de l'acide phosphorique.10. Method according to claim 9, characterized in that one adjusts the temperature of the solution containing the alkali silicate between 15 and 100 ° C before the gradual addition of phosphoric acid.
11. Procédé suivant l'une quelconque des revendications 1 à 10, caractérisé en ce que l'on règle, dans le mélange réactionnel précité, le rapport M/P pour que le rapport molaire H3P04/M20 final soit supérieur à 0,80 et que le pH de la phase aqueuse soit inférieur ou égal à 9 au moment de séparer la silice.11. Method according to any one of claims 1 to 10, characterized in that one regulates, in the above-mentioned reaction mixture, the M / P ratio so that the final H 3 P0 4 / M 2 0 molar ratio is greater at 0.80 and that the pH of the aqueous phase is less than or equal to 9 when separating the silica.
12. Sel alcalin phosphaté obtenu par la mise en oeuvre du procédé suivant l'une quelconque des revendications 1 à 11. 12. Phosphated alkaline salt obtained by implementing the method according to any one of claims 1 to 11.
13. Silice obtenue par la mise en oeuvre du procédé suivant l'une quelconque des revendications 1 à 11.13. Silica obtained by implementing the method according to any one of claims 1 to 11.
14. Détergent comprenant un sel phosphaté de potassium et/ou de sodium obtenu par la mise en oeuvre du procédé suivant l'une quelconque des revendi¬ cations 1 à 11. 14. Detergent comprising a phosphate salt of potassium and / or sodium obtained by implementing the process according to any one of claims 1 to 11.
15. Produit alimentaire comprenant un sel alcalin, notamment un sel de sodium et/ou de potassium, obtenu par la mise en oeuvre du procédé suivant l'une quelconque des revendications 1 à 11. 15. Food product comprising an alkaline salt, in particular a sodium and / or potassium salt, obtained by carrying out the process according to any one of claims 1 to 11.
PCT/BE1994/000065 1994-10-03 1994-10-03 Method for making phosphated alkaline salts, resulting salts and silicas, and detergent or foodstuff containing such salts WO1996010536A1 (en)

Priority Applications (6)

Application Number Priority Date Filing Date Title
PCT/BE1994/000065 WO1996010536A1 (en) 1994-10-03 1994-10-03 Method for making phosphated alkaline salts, resulting salts and silicas, and detergent or foodstuff containing such salts
EP94927463A EP0784594A1 (en) 1994-10-03 1994-10-03 Method for making phosphated alkaline salts, resulting salts and silicas, and detergent or foodstuff containing such salts
MA24021A MA23675A1 (en) 1994-10-03 1995-09-28 PROCESS FOR THE MANUFACTURE OF HIGH PURITY ALKALINE PHOSPHATE SALTS, SALTS AND SILICAS OBTAINED, AS WELL AS DETERGENT OR FOOD PRODUCT CONTAINING THIS SALT
TNTNSN95100A TNSN95100A1 (en) 1994-10-03 1995-10-02 PROCESS FOR THE MANUFACTURE OF HIGH PURITY ALKALINE PHOSPHATE SALTS, SALTS AND SILICAS OBTAINED, AS WELL AS DETERGENT OR FOOD PRODUCT CONTAINING THIS SALT
IL11548195A IL115481A0 (en) 1994-10-03 1995-10-02 Process for the manufacture of alkali metal phosphate salts of high purity salts and silicas obtained and detergent or alimentary product containing this salt
TR95/01208A TR199501208A2 (en) 1994-10-03 1995-10-03 The method of manufacturing high purity phosphate alkali salts, salts and silicas obtained, as well as detergents or food products containing these salts.

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/BE1994/000065 WO1996010536A1 (en) 1994-10-03 1994-10-03 Method for making phosphated alkaline salts, resulting salts and silicas, and detergent or foodstuff containing such salts

Publications (1)

Publication Number Publication Date
WO1996010536A1 true WO1996010536A1 (en) 1996-04-11

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Country Status (6)

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EP (1) EP0784594A1 (en)
IL (1) IL115481A0 (en)
MA (1) MA23675A1 (en)
TN (1) TNSN95100A1 (en)
TR (1) TR199501208A2 (en)
WO (1) WO1996010536A1 (en)

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1078134A (en) * 1952-06-13 1954-11-16 Degussa Process for preparing highly divided powder silica
FR1134178A (en) * 1954-11-05 1957-04-08 Columbia Southern Chem Corp Improvements with siliceous pigments
FR2159580A5 (en) * 1971-11-04 1973-06-22 Sifrance
FR2272033A1 (en) * 1974-05-22 1975-12-19 Sifrance
JPS601115A (en) * 1983-06-16 1985-01-07 Central Glass Co Ltd Amorphous silica for transparent dentifrice and its production
JPS62113713A (en) * 1985-11-14 1987-05-25 Osaka Soda Co Ltd Production of silica gel

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1078134A (en) * 1952-06-13 1954-11-16 Degussa Process for preparing highly divided powder silica
FR1134178A (en) * 1954-11-05 1957-04-08 Columbia Southern Chem Corp Improvements with siliceous pigments
FR2159580A5 (en) * 1971-11-04 1973-06-22 Sifrance
FR2272033A1 (en) * 1974-05-22 1975-12-19 Sifrance
JPS601115A (en) * 1983-06-16 1985-01-07 Central Glass Co Ltd Amorphous silica for transparent dentifrice and its production
JPS62113713A (en) * 1985-11-14 1987-05-25 Osaka Soda Co Ltd Production of silica gel

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
DATABASE WPI Section Ch Week 0785, Derwent World Patents Index; Class D21, AN 85-041557 *
PATENT ABSTRACTS OF JAPAN vol. 011, no. 326 (C - 454) 23 October 1987 (1987-10-23) *

Also Published As

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TNSN95100A1 (en) 1996-02-06
IL115481A0 (en) 1996-01-19
TR199501208A2 (en) 1996-06-21
EP0784594A1 (en) 1997-07-23
MA23675A1 (en) 1996-04-01

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