WO2019206694A1 - Process to increase the fraction of trans-isomers of a mixture of 2,4-diamino-1-methylcyclohexane and 2,6-diamino-1-methylcyclohexane - Google Patents

Process to increase the fraction of trans-isomers of a mixture of 2,4-diamino-1-methylcyclohexane and 2,6-diamino-1-methylcyclohexane Download PDF

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Publication number
WO2019206694A1
WO2019206694A1 PCT/EP2019/059587 EP2019059587W WO2019206694A1 WO 2019206694 A1 WO2019206694 A1 WO 2019206694A1 EP 2019059587 W EP2019059587 W EP 2019059587W WO 2019206694 A1 WO2019206694 A1 WO 2019206694A1
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mcda
trans
cis
weight
enriched
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PCT/EP2019/059587
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French (fr)
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Lukas SCHULZ
Sebastian WLOCH
Alexander Panchenko
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Basf Se
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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C209/00—Preparation of compounds containing amino groups bound to a carbon skeleton
    • C07C209/82—Purification; Separation; Stabilisation; Use of additives
    • C07C209/86—Separation
    • C07C209/88—Separation of optical isomers
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C209/00—Preparation of compounds containing amino groups bound to a carbon skeleton
    • C07C209/68—Preparation of compounds containing amino groups bound to a carbon skeleton from amines, by reactions not involving amino groups, e.g. reduction of unsaturated amines, aromatisation, or substitution of the carbon skeleton
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C2601/00—Systems containing only non-condensed rings
    • C07C2601/12—Systems containing only non-condensed rings with a six-membered ring
    • C07C2601/14—The ring being saturated

Definitions

  • Object of the present invention is a process to increase the fraction of trans-isomers of a mix- ture of 2,4-diamino-1-methylcyclohexane and 2,6-diamino-1-methylcyclohexane, shortly re- ferred to as MCDA, by a continuous process, wherein a) an auxiliary compound having a boiling point at 50 mbar which is at least 5°C higher than the boiling point of MCDA at 50 mbar and MCDA are fed to a first distillation column, referred to as K1 , thus obtaining a mixture comprising a trans-enriched MCDA fraction, referred to as trans-enriched MCDA-1 , and optionally auxiliary compound and a mixture of a cis-enriched MCDA fraction, referred to as cis-enriched MCDA-1 , and auxiliary compound, b) the mixture of the cis-enriched MCDA-1 and the auxiliary compound obtained in step a) is transferred to a second distillation
  • both amino groups of the compound are bonded to a six-membered ring system both amino groups may be found on the same side of the ring-system (cis-isomer) or on opposite side of the ring system (trans-isomer).
  • isomerism has an impact on the physical and chemical properties and hence on the suitability of the compound for certain technical applica- tions.
  • trans isomers for further use in polymer synthesis.
  • WO 2017/093308 discloses a process for the isomerization of 2,4-diamino-1-methyl-cyclohex- ane, 2,6-diamino-1-methylcyclohexane or mixtures thereof at elevated temperatures in contact with an heterogenous catalyst.
  • Unpublished patent application INV 170153 describes a crystallization process to obtain a trans- enriched phase and a cis-enriched phase of a mixture of 2,4-diamino-1-methylcyclohexane and 2,6-diamino-1-methylcyclohexane.
  • the process should be easy to perform and should require a minimum of investment costs and should consume as low energy as possible and result in a trans-enriched mixture of 2, 4-diamino-1 -methyl-cyclohexane and 2,6-diamino-1-methylcyclohexane with a content of trans isomers as high as possible.
  • MCDA 2,4-diamino-1-methylcyclohexane and 2,6-diamino-1-methylcyclohexane are shortly referred to as MCDA.
  • Such mixtures are notably obtained by hydrogenation of a mixture of 2,4 - and 2,6- di-amino- toluene.
  • 2,4-diamino-1 -methylcyclohexane and 2,6-diamino-1 -methylcyclohexane comprise trans-iso- mers having the two amino groups in trans position to the cyclohexane ring as well as cis-iso- mers having the two amino groups in cis position to the cyclohexane ring.
  • the MCDA comprises 50 to 95 % by weight of 2,4-diamino-1 -methylcyclohexane and 5 to 50 % by weight of 2,6-diamino-1 -methylcyclohexane.
  • the MCDA may also comprise other compounds with two amino groups, such as, for example, 2,3-diaminomethylcyclohexane and 3,4-diaminomethylcyclohexane.
  • the proportion of other compounds with two amino groups is typically 0% to 5% by weight, notably 0% to 1 % by weight, most preferably 0% to 0.5%, respectively 0% to 0.1 % by weight, based on the total weight of the di-amino-compound.
  • the ranges of further compounds with two amino groups mentioned in the preceding sentence apply also to all preferred compositions of any MCDA, including any cis-en- riched and any trans-enriched MCDA.
  • the MCDA may comprise the following cis- and trans isomers:
  • 2,4 isomer cis of formula 1 is also referred to as cis- isomer 1 or isomer 1
  • 2,6 isomer cis of formula 2 is also referred to as cis-isomer 2 or isomer 2
  • 2,4 isomer trans of formula 3 is also referred to as trans-isomer 3 or isomer 3
  • 2,4 isomer trans of formula 4 is also referred to as trans-isomer 4 or isomer 4
  • 2,6 isomer trans of formula 5 is also referred to as trans-isomer 5 or isomer 5
  • 2,4 isomer cis of formula 6 is also referred to as cis-isomer 6 or isomer 6 and
  • 2,6 isomer cis of formula 7 is also referred to as cis-isomer 7 or isomer 7.
  • Compounds 2 and 7 are meso forms and do not have enantiomers.
  • Compounds 1 and 3 - 6 have two enantiomeric forms (mirror and mirror image). Any reference to compounds 1 and 3-6 includes both enantiomeric forms of compounds 1 and 3-6.
  • the MCDA consists of
  • the MCDA consists of
  • the MCDA comprises in total 5 to 60% by weight of trans isomers and 40 to 95 % by weight of cis isomers. More preferably, the MCDA comprises in total 20 to 50% by weight of trans isomers and 50 to 80 % by weight of cis isomers. Most preferably, the MCDA comprises in total 35 to 50% by weight of trans isomers and 50 to 65 % by weight of cis isomers.
  • the auxiliary compound has a boiling point at 50 mbar which is at least 5°C higher, preferably at least 10°C higher, more preferably at least 30°C higher than the boiling point of MCDA at 50 mbar.
  • MCDA has a boiling point of about 210°C at 1 bar (atmospheric pressure) and of about 1 15°C at 50 mbar, depending on the exact composition of the MCDA.
  • the auxiliary compound has a boiling point of 210 to 300° C at 1 bar, more preferably of 215 to 250°C at 1 bar, with the provision that its boiling point at 50 mbar is at least 5°C higher than the corresponding boiling point of MCDA.
  • butane-1 ,4-diol has a boiling point of 230°C at 1 bar and of 155°C at 50 mbar.
  • the auxiliary compound is an aliphatic compound which comprises at least one hy- droxy group and which may furthermore comprise ether groups.
  • the auxiliary compound is an alkane diol, specifically a C3- to C8-alkane diol, such as propane diol, butane diol or pentane diol.
  • the auxiliary compound is a butane diol, notably butane-1 ,4-diol.
  • MCDA and the auxiliary compound may be mixed and fed to the first distillation column, referred to as K1 , as mixture or they may be fed separately to K1.
  • K1 the first distillation column
  • MCDA and the auxiliary compound are fed separately to K1.
  • the amount of auxiliary compound is preferably 5 to 1000 parts by weight per 100 parts by weight of MCDA, more preferably 20 to 500 parts by weight per 100 parts by weight of MCDA and most preferably 200 to 400 parts by weight per 100 parts by weight of MCDA.
  • K1 may be a packed column having structured packings or random packings or a tray column having trays such as dualflow trays, sieve trays, bubble-cap trays or valve trays.
  • K1 is preferably operated with a reflux ratio (reflux/distillate removal) in the range from 0.1 to in- finity, preferably from 1 to 20.
  • the number of theoretical plates in K1 is preferably 10 to 150, more preferably of 30 to 1 10.
  • the temperature at the top of K1 is preferably 30 to 280°C and the pressure at the top of K1 is preferably 1 to 1000 mbar.
  • the temperature at the top of K1 is more preferably 80 to 180°C and the pressure at the top of K1 is more preferably 10 to 500 mbar.
  • the temperature at the top of K1 is most preferably 80 to 150°C and the pressure at the top of K1 is most preferably 10 to 150 mbar.
  • the distillation in K1 is conducted in the absence of oxygen.“Absence” is understood to mean that the proportion by volume of oxygen is less than 0.1 %, especially less than 0.01 % and very particularly less than 0.001 %, based on the total volume of the distillation column.
  • the auxiliary component is fed in in the upper part of K1 and the MCDA is fed in the lower part of K1.
  • the auxiliary is fed in at least 10 or even at least 20 theoretical plates above the feed of the MCDA.
  • trans-enriched MCDA-1 A mixture comprising a trans-enriched MCDA fraction, referred to as trans-enriched MCDA-1 , and optionally auxiliary compound is obtained and drawn off from K1 , preferably at the top.
  • the mixture consists of 40 to 100% by weight of trans-enriched MCDA-1 and 0 to 60% by weight of the auxiliary compound.
  • the mixture consists of 60 to 100% by weight of trans-enriched MCDA-1 and 0 to 40% by weight of the auxiliary compound.
  • the mixture consists of 65 to 100% by weight of trans-enriched MCDA-1 and 0 to 35% by weight of the auxiliary compound.
  • the trans-enriched MCDA-1 comprises preferably
  • a mixture of a cis-enriched MCDA fraction, referred to as cis-enriched MCDA-1 , and the auxil- iary compound are obtained in K1 and removed from K1 , preferably at the bottom.
  • the mixture comprises 50 to 90% by weight of the auxiliary compound and 10 to 50% by weight of the cis-enriched MCDA-1.
  • the cis-enriched MCDA-1 comprises preferably
  • the trans-enriched MCDA-1 obtained in step a) has a reduced content of cis-isomers 1 , 6 and 7.
  • the cis-enriched MCDA-1 comprises at least 70% by weight of cis isomers 1 , 6 and 7 of the MCDA fed to K1 in step a).
  • the cis-enriched MCDA-1 comprises at least 80% by weight of cis isomers 1 , 6 and 7 of the MCDA fed to K1 in step a).
  • the cis-enriched MCDA-1 comprises at least 90% by weight of the cis isomers 1 , 6 and 7 of the MCDA fed to K1 in step a).
  • the trans-enriched MCDA-1 comprises 70 to 95 % by weight of trans-isomers and 5 to 30 % by weight of cis-isomers.
  • the mixture of cis-enriched MCDA-1 and the auxiliary compound obtained in step a) are trans- ferred to second distillation column, referred to as K2, where the auxiliary compound is sepa- rated from the mixture, thus obtaining a cis-enriched MCDA-1 which is essentially free of auxil- iary compound and obtaining separately the essentially pure auxiliary compound.
  • K2 may be a packed column having structured packings or random packings or a tray column having trays such as dualflow trays, sieve trays, bubble-cap trays or valve trays. K2 is preferably operated with a reflux ratio (reflux/distillate removal) in the range from 0.1 to in- finity, preferably from 1 to 20.
  • the number of theoretical plates in K2 is preferably 10 to 150, more preferably of 30 to 1 10.
  • the temperature at the top of K2 is preferably 30 to 280°C and the pressure at the top of K2 is preferably 1 to 1000 mbar.
  • the temperature at the top of K2 is more preferably 80 to 180°C and the pressure at the top of K2 is more preferably 10 to 500 mbar.
  • the temperature at the top of K2 is most preferably 80 to 150°C and the pressure at the top of K2 is most preferably 10 to 150 mbar.
  • the distillation in K2 is conducted in the absence of oxygen.“Absence” is understood to mean that the proportion by volume of oxygen is less than 0.1 %, especially less than 0.01 % and very particularly less than 0.001 %, based on the total volume of the distillation column.
  • the cis-enriched MCDA-1 is preferably removed from the top and the auxiliary compound is removed from the bottom.
  • the cis-enriched MCDA-1 obtained in step b) is passed to a reactor, referred to as R1 , where the trans content of the cis-enriched MCDA-1 is increased by isomerization at a catalyst thus obtaining an isomerized MCDA, referred to as MCDA-ISO.
  • the isomerization of the cis-enriched MCDA-1 may be performed in the liquid or in the gaseous phase.
  • the isomerization is performed in the liquid phase which means that the isomerization is performed under a temperature and pressure where the cis-enriched MCDA-1 is liquid.
  • the isomerization is performed at an elevated pressure, for example a pressure of 20 to 300 bars.
  • the isomerization is performed at a temperature from 20 to 300°C, more preferably from 50 to 200°C and most preferably from 80 to 180°C.
  • the isomerization is performed in the presence of hydrogen.
  • Hydro- gen may be used as gas to establish the above pressure in the reactor.
  • the isomerization is performed at a catalyst.
  • the catalyst may be a heterogeneous or homogenous hydrogenation catalyst.
  • a heterogeneous catalyst is used in the isomerization step.
  • the heterogeneous catalyst may be a supported or an unsupported catalyst.
  • a suitable unsup- ported catalyst is, for example, Raney nickel or Raney cobalt.
  • a supported catalyst comprises catalytically active metals that are applied to a support.
  • a suitable support is, for example, cal- cium carbonate, silicon oxide, zirconium dioxide or aluminum oxide.
  • Suitable catalysts comprise, for example, an active metal or a mixture of active metals selected from the groups IVb, Vb, Vlb, VI lb, VI I lb, lb or lib of the periodic system.
  • Preferred catalysts comprise an active metal or a mixture of active metals selected from nickel, palladium, platinum, cobalt, rhodium, iridium, copper, manganese, tin or ruthenium.
  • a most preferred catalyst is a catalyst comprising ruthenium on a zirconium dioxide support.
  • the catalyst may, for example, be installed as fixed bed in the reactor.
  • the fixed bed is positioned in a way, that the total stream of cis-enriched MCDA-1 passes through the fixed bed.
  • the product of the isomerization has an increased content of trans-isomers; the product is re- ferred to as MCDA-ISO
  • MCDA-ISO comprises preferably
  • MCDA-ISO obtained in step c) has an increased content of trans-isomers compared to the cis-enriched MCDA-1.
  • the total content of all trans isomers in MCDA-ISO is at least 5%, more prefera- bly at least 10 % higher than the total content of all trans isomers in cis-enriched-MCDA-1.
  • MCDA-ISO is passed to K1.
  • MCDA-ISO may be fed separately to K1 or may be combined with any of the other feeds to K1.
  • MCDA-ISO is separately fed to K1.
  • K1 MCDA-ISO is distilled together with MCDA and the auxiliary compound.
  • auxiliary compound is added to the mixture comprising the trans-enriched MCDA-1 which has been obtained in step a).
  • the mixture and any auxiliary compound added in this step e) are mixed in a suitable mixing device to prepare a homogeneous solution.
  • the mixture, respectively solution, is passed to a crystallization unit.
  • the auxiliary compound is the same compound as used in K1. In the whole process the same auxiliary compound is used.
  • auxiliary compound added in this step e) may be freshly added auxiliary compound or auxil- iary compound recycled from the process.
  • auxiliary compound obtained from the distillation in step b) or g) may be used.
  • the amount of any auxiliary compound added in step e) depends on the amount of auxiliary compound in the mixture obtained in step a).
  • the content of auxiliary compound in the mixture, respectively solution, passed to the crystallization unit is 10 to 200 parts by weight of the auxiliary compound per 100 parts by weight of trans-enriched MCDA-1.
  • the content of auxiliary compound in the mixture, respectively solution, passed to the crystallization unit is 15 to 100 parts by weight of the auxiliary compound per 100 parts by weight of trans-enriched MCDA-1.
  • the content of auxiliary compound in the mixture, respectively solution, passed to the crystallization unit is 20 to 80 parts by weight of the auxiliary compound per 100 parts by weight of trans-enriched MCDA-1.
  • the trans-enriched MCDA-1 as such has a melting point significantly below -60°C. Due to the content of the auxiliary compound in the mixture comprising trans-enriched MCDA-1 , the melt- ing point increases.
  • the mixture of trans-enriched MCDA-1 and auxiliary compound preferably has a melting point of -10 to +100°C and more preferably a melting point of +20 to +50°C.
  • the mixture of trans-enriched MCDA-1 and auxiliary compound is preferably kept at a temperature which is higher than the melting point or equal to the melting point to form a homo- geneous solution.
  • the mixture and the obtained homogeneous solution are kept at a temperature of 0 to 100°C, more preferably at a temperature of +20 to 60°C, with the provision that the selected temperature is equal or preferably higher than the melting point.
  • the solution having this temperature is passed from the mixing device to the crystallization unit.
  • the solution is cooled to a temperature of preferably -15 to +85°C and more preferably of 0 to +35°C, respectively +5 to +20°C.
  • the solu- tion is cooled to a temperature which is at least 5°C, more preferably at least 15°C below the melting point of the solution.
  • the crystallization unit may consist of one or more crystallizers.
  • the crystallizers are operated in line and the solution or suspension (if crystals are already obtained) is passed from one crystallizer to the next crystal- lizer, each crystallizer being kept at a lower temperature than the preceding crystallizer and the final crystallizer being kept at the desired final temperature.
  • a crystallized mixture of the auxiliary compound and a cis-enriched MCDA fraction referred to as cis-enriched MCDA-2
  • a mother liquid comprising a trans-en- riched MCDA fraction referred to as trans-enriched MCDA-2
  • auxiliary compound ob- tained.
  • the crystallized mixture of the auxiliary compound and cis-enriched MCDA-2 is withdrawn from the crystallization unit, for example by filtration.
  • the trans-enriched MCDA-2 preferably comprises
  • the trans-enriched MCDA-2 consists to 70% to 100% by weight of trans-isomers. More preferably, the trans-enriched MCDA-2 consists to 80 to 99% by weight of trans-isomers.
  • the trans-enriched MCDA-2 comprises 0 to 3 % by weight of the 2,6-isomer cis 2. to step f)
  • the mother liquid obtained in step e) and comprising auxiliary compound and trans-enriched MCDA-2 is passed to a third distillation column, referred to as K3, where the auxiliary corn- pound is separated from the mother liquid thus obtaining the isolated trans-enriched MCDA-2.
  • step f) correspond to the distillation in step b) and details regarding K2 and its operation in step b) apply to K3 and its operation in this step f).
  • the trans-enriched MCDA-2 is obtained at the top of K3 and the auxiliary compound is obtained at the bottom of K3.
  • This isolated trans-enriched MCDA-2 is the final product of the process. to step g)
  • the auxiliary compound obtained in step f) is recycled to the process. It may be recycled to any suitable process step. Preferably, it is recycled to the stream from the top of K1 to the mixing device of step e) to step h)
  • Example 1 crystallization of a mixture comprising MCDA and butane-1 ,4 diol
  • composition of MCDA is listed in the table.
  • content of cis-isomers and trans-isomers of formulas 1 to 7 is defined in weight %.
  • the content of the isomers 1 to 7 was determined by gas chromatography.
  • butane-1 ,4-diol shortly referred to as BDO, was used as solvent.
  • the melting point of the mixture of MCDA and BDO was determined as follows:
  • MCDA and BDO were mixed at an elevated temperature to obtain a clear solution.
  • the melting point of the mixture was determined by cooling the mixture until first crystals appeared, after- wards the suspension was heated up again, until all crystals dissolved.
  • the corresponding tem- perature is referred to as melting point of the solution.
  • the melting point has been determined with a turbidity probe. A solution without any turbidity corresponds to a solution without any crystals respectively solids.
  • a seed of crystals has been prepared using a so called“seeding loop”.
  • the solution is cooled down until first solid particles appear and afterwards the suspension is heated up again to the melting point to dissolve some of the solid particles.
  • a so- lution comprising a small number of solid particles (seed) is obtained, which is then used for the crystallization process.
  • the example was performed in a one-liter double jacketed crystallizer, equipped with three baf- fles and a two-stage pitch blade stirrer, which was operated at 600 rpm. Furthermore, the crys- tallizer was equipped with a temperature and pressure sensor, as well as a turbidity probe to detect the formation of solid particles. It was possible to take samples of mother liquor which was free of solids via a filter fritte from the crystallizer, additionally a filter nutsche was mounted below the crystallizer to separate the mother liquor from the crystals.
  • the crystallizer was charged with 400 g of the MCDA/BDO solution.
  • a cooling crystallization was performed, by applying a linear cooling ramp with -1 K/h. Specific temperatures (listed in the tables) were kept constant for some hours, so that the solid-liquid equilibrium could be fully established. At these temperatures samples (about 3 g) from the solid- free mother liquor were taken and analyzed by gas chromatography. The yield of trans-enriched mother liquid was determined in a second run. At a pre-determined temperature which usually corresponded to a temperature listed in the tables of the examples, the whole suspension was transferred from the crystallizer on the filter nutsche. The crystals were separated from the mother liquor. Both fractions crystals and mother liquor were analyzed by GC and the masses of both fractions were determined.
  • the melting point of the MCDA used was: -92°C.
  • MCDA and BDO were mixed in a ratio of 65 : 35 party by weight.
  • the melting point of the mix- ture of MDCA and BDO was +44.5°C.
  • the example was repeated. At 20.0°C the crystals (comprising MCDA and BDO) were isolated from the suspension as described above. The isomer composition of the MCDA of the crystals was determined, see last line of the table. The yield of crystals was 35.7% by weight and the yield of mother liquid was 64.3 % by weight (both comprising MCDA and BDO). The total yield of trans-isomers in the final mother liquid was 77% by weight of all trans isomers of the starting solution.
  • Example 2 is a simulation.
  • the auxiliary compound is butane-1 ,4-diol.
  • the feeds and the energy consumption of the process shown in Figure 1 have been calculated.
  • the process of Figure 1 corresponds to the process of this invention with process steps a) to h).
  • K1 , K2, K3, R1 and C1 in Figure 1 have the same meaning as defined in the specification.
  • the streams between the units of the process have been numbered from 1 to 9.
  • Table 2 mass flows (kg/h) and composition in % by weight
  • the comparison example is also a simulation.
  • the auxiliary compound is butane-1 ,4-diol.
  • the mass flows and the energy consumption of the comparison process shown in Figure 2 have been calculated.
  • the comparison process of Figure 2 does not comprise step h).
  • the compari- son process is a process wherein the crystallized mixture of step e) containing cis-enriched MCDA and the auxiliary component are fed to a fourth distillation column, referred to as K4, where the auxiliary compound is separated from the crystal phase thus obtaining the isolated cis-enriched MCDA-2.
  • the distillation in K4 corresponds to the distillation K2 and its operation in step b) apply to K4 and its operation.
  • the cis-enriched MCDA-2 is obtained at the top of K4 and the auxiliary compound is obtained at the bottom of K4.
  • the auxiliary compound obtained K4 is recycled to the process. It may be recycled to any suita- ble process step. Preferably, it is recycled to the stream from the top of K1 to the mixing device of step e)
  • K1 , K2, K3, R1 and C1 as well as streams“M” and“A” in Figure 2 have the same meaning as in example 2.
  • Table 3 mass flows (kg/h and composition in % by weight
  • Reaction pressure 50 bar absolute; reaction temperature 150 °C; Weight hourly space velocity (WHSV) 1 kg/(kg * h); heterogeneous catalyst under hydrogen-atmosphere.
  • WHSV Weight hourly space velocity
  • Crystallizer C1 (Crystallization), in example 2 and the comparison example:
  • the process of the comparison example produces in addition -35% of a MCDA product with -80% trans isomers (Stream No.1 1), which is not usable for all applications that require a high purity of trans type MCDA.

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Abstract

A process to increase the fraction of trans-isomers of a mixture of 2,4- diamino-1-methylcyclohexane and 2,6-diamino-l-methylcyclohexane, shortly referred to as MCDA, by a continuous process, comprising various steps of distillation, isomerization and crystallization in the presence of an auxiliary compound having a boiling point at 50 mbar which is at least 5°C higher than the boiling point of MCDA at 50 mbar, such as an alkanediol.

Description

Process to increase the fraction of trans-isomers of a mixture of 2,4-diamino-1-methylcyclohex- ane and 2,6-diamino-1-methylcyclohexane
Description
Object of the present invention is a process to increase the fraction of trans-isomers of a mix- ture of 2,4-diamino-1-methylcyclohexane and 2,6-diamino-1-methylcyclohexane, shortly re- ferred to as MCDA, by a continuous process, wherein a) an auxiliary compound having a boiling point at 50 mbar which is at least 5°C higher than the boiling point of MCDA at 50 mbar and MCDA are fed to a first distillation column, referred to as K1 , thus obtaining a mixture comprising a trans-enriched MCDA fraction, referred to as trans-enriched MCDA-1 , and optionally auxiliary compound and a mixture of a cis-enriched MCDA fraction, referred to as cis-enriched MCDA-1 , and auxiliary compound, b) the mixture of the cis-enriched MCDA-1 and the auxiliary compound obtained in step a) is transferred to a second distillation column, referred to as K2, where the auxiliary compound is separated from the mixture by distillation and is recycled to K1 , c) the cis-enriched MCDA-1 obtained in b) is passed to a reactor, referred to as R1 , where the trans content of the cis-enriched MCDA-1 is increased by isomerization at a catalyst thus ob- taining an isomerized MCDA, referred to as MCDA-ISO, d) the MCDA-ISO obtained in step c) is passed to K1 e) optionally auxiliary compound is added to the mixture comprising the trans-enriched MCDA- 1 obtained in step a) and the obtained mixture is passed to a crystallization unit, where a crystallized mixture of the auxiliary compound and a cis-enriched MCDA fraction, referred to as cis-enriched MCDA-2, is separated thus leaving a mother liquid comprising a trans-en- riched MCDA fraction, referred to as trans-enriched MCDA-2, and auxiliary compound, f) the mother liquid obtained in step e) is passed to a third distillation column, referred to as K3, where the auxiliary compound is separated from the mother liquid thus obtaining the iso- lated trans-enriched MCDA-2, g) the auxiliary compound obtained in step f) is recycled to the process h) the cis-enriched MCDA-2 obtained in step e) together with some auxiliary compound is passed to K2 Compounds with two amino groups are used in various technical applications. They are used in chemical synthesis, for example for the synthesis of di-isocyanates. Compounds with two amino groups are also used as monomers in polymerization, for example for the preparation of poly- ureas or polyurethanes.
If the two amino groups of the compound are bonded to a six-membered ring system both amino groups may be found on the same side of the ring-system (cis-isomer) or on opposite side of the ring system (trans-isomer). Such isomerism has an impact on the physical and chemical properties and hence on the suitability of the compound for certain technical applica- tions. Most suitable are trans isomers for further use in polymer synthesis.
Compounds such as 2,4-diamino-1-methylcyclohexane, 2,6-diamino-1-methylcyclohexane or mixtures thereof usually are mixtures of trans-isomers and cis-isomers.
The separation of trans-isomers and cis-isomers of 2,4-diamino-1-methylcyclohexane, 2,6-dia- mino-1-methylcyclohexane or mixtures thereof by distillation is described in WO 2016/083210. As the boiling points of the trans-isomers and cis-isomers are rather close, the distillation results in two phases, one trans-enriched phase and one cis-enriched phase which still comprise signif- icant fractions of the other isomer. Furthermore, the distillation requires high energy.
WO 2017/093308 discloses a process for the isomerization of 2,4-diamino-1-methyl-cyclohex- ane, 2,6-diamino-1-methylcyclohexane or mixtures thereof at elevated temperatures in contact with an heterogenous catalyst.
Unpublished patent application INV 170153 describes a crystallization process to obtain a trans- enriched phase and a cis-enriched phase of a mixture of 2,4-diamino-1-methylcyclohexane and 2,6-diamino-1-methylcyclohexane.
It was an object of this invention to provide a process to produce mixtures of 2,4-diamino-1-me- thyl-cyclohexane and 2,6-diamino-1-methylcyclohexane with an increased content of trans iso- mers. The process should be easy to perform and should require a minimum of investment costs and should consume as low energy as possible and result in a trans-enriched mixture of 2, 4-diamino-1 -methyl-cyclohexane and 2,6-diamino-1-methylcyclohexane with a content of trans isomers as high as possible.
Accordingly, the process defined above has been found.
To MCDA
Mixtures of 2,4-diamino-1-methylcyclohexane and 2,6-diamino-1-methylcyclohexane are shortly referred to as MCDA. Such mixtures are notably obtained by hydrogenation of a mixture of 2,4 - and 2,6- di-amino- toluene.
2,4-diamino-1 -methylcyclohexane and 2,6-diamino-1 -methylcyclohexane comprise trans-iso- mers having the two amino groups in trans position to the cyclohexane ring as well as cis-iso- mers having the two amino groups in cis position to the cyclohexane ring.
Preferably, the MCDA comprises 50 to 95 % by weight of 2,4-diamino-1 -methylcyclohexane and 5 to 50 % by weight of 2,6-diamino-1 -methylcyclohexane.
The MCDA may also comprise other compounds with two amino groups, such as, for example, 2,3-diaminomethylcyclohexane and 3,4-diaminomethylcyclohexane. The proportion of other compounds with two amino groups is typically 0% to 5% by weight, notably 0% to 1 % by weight, most preferably 0% to 0.5%, respectively 0% to 0.1 % by weight, based on the total weight of the di-amino-compound. The ranges of further compounds with two amino groups mentioned in the preceding sentence apply also to all preferred compositions of any MCDA, including any cis-en- riched and any trans-enriched MCDA.
The MCDA may comprise the following cis- and trans isomers:
Figure imgf000005_0001
2,4-Isomer 2,6-Isomer 2,4-Isomer 2,4-Isomer cis CIS trans trans
Figure imgf000005_0002
5 6 7
2,6-Isomer 2,4-Isomer 2,6-Isomer
trans cis cis In this patent application,
2,4 isomer cis of formula 1 is also referred to as cis- isomer 1 or isomer 1
2,6 isomer cis of formula 2 is also referred to as cis-isomer 2 or isomer 2
2,4 isomer trans of formula 3 is also referred to as trans-isomer 3 or isomer 3
2,4 isomer trans of formula 4 is also referred to as trans-isomer 4 or isomer 4
2,6 isomer trans of formula 5 is also referred to as trans-isomer 5 or isomer 5
2,4 isomer cis of formula 6 is also referred to as cis-isomer 6 or isomer 6 and
2,6 isomer cis of formula 7 is also referred to as cis-isomer 7 or isomer 7.
Compounds 2 and 7 are meso forms and do not have enantiomers. Compounds 1 and 3 - 6 have two enantiomeric forms (mirror and mirror image). Any reference to compounds 1 and 3-6 includes both enantiomeric forms of compounds 1 and 3-6.
In a preferred embodiment, the MCDA consists of
0 to 80 % by weight of the 2,4-isomer cis (1 )
0.1 to 80 % by weight of the 2,6-isomer cis (2)
0.1 to 80 % by weight of the 2,4-isomer trans (3)
0.1 to 80 % by weight of the 2,4-isomer trans (4)
0.1 to 80 % by weight of the 2,6-isomer trans (5)
0 to 80 % by weight of the 2,4-isomer cis (6)
0 to 80 % by weight of the 2,6-isomer cis (7) and
0 to 5 % by weight of other compounds with two amino groups based on the total amount of MCDA.
More preferably, the MCDA consists of
20 to 50 % by weight of the 2,4-isomer cis (1 )
1 to 10 % by weight of the 2,6-isomer cis (2)
5 to 25 % by weight of the 2,4-isomer trans (3)
5 to 25 % by weight of the 2,4-isomer trans (4)
1 to 10 % by weight of the 2,6-isomer trans (5)
5 to 25 % by weight of the 2,4-isomer cis (6)
1 to 10 % by weight of the 2,6-isomer cis (7) and
0 to 5 % by weight of other compounds with two amino groups
In a preferred embodiment, the MCDA comprises in total 5 to 60% by weight of trans isomers and 40 to 95 % by weight of cis isomers. More preferably, the MCDA comprises in total 20 to 50% by weight of trans isomers and 50 to 80 % by weight of cis isomers. Most preferably, the MCDA comprises in total 35 to 50% by weight of trans isomers and 50 to 65 % by weight of cis isomers.
Any reference to MCDA in this patent application denominates the MCDA used as starting prod- uct for the process.
To step a)
The auxiliary compound has a boiling point at 50 mbar which is at least 5°C higher, preferably at least 10°C higher, more preferably at least 30°C higher than the boiling point of MCDA at 50 mbar.
MCDA has a boiling point of about 210°C at 1 bar (atmospheric pressure) and of about 1 15°C at 50 mbar, depending on the exact composition of the MCDA.
Preferably, the auxiliary compound has a boiling point of 210 to 300° C at 1 bar, more preferably of 215 to 250°C at 1 bar, with the provision that its boiling point at 50 mbar is at least 5°C higher than the corresponding boiling point of MCDA.
For example, butane-1 ,4-diol has a boiling point of 230°C at 1 bar and of 155°C at 50 mbar.
Preferably, the auxiliary compound is an aliphatic compound which comprises at least one hy- droxy group and which may furthermore comprise ether groups.
More preferably, the auxiliary compound is an alkane diol, specifically a C3- to C8-alkane diol, such as propane diol, butane diol or pentane diol.
Most preferably, the auxiliary compound is a butane diol, notably butane-1 ,4-diol.
MCDA and the auxiliary compound may be mixed and fed to the first distillation column, referred to as K1 , as mixture or they may be fed separately to K1. Preferably, MCDA and the auxiliary compound are fed separately to K1.
The amount of auxiliary compound is preferably 5 to 1000 parts by weight per 100 parts by weight of MCDA, more preferably 20 to 500 parts by weight per 100 parts by weight of MCDA and most preferably 200 to 400 parts by weight per 100 parts by weight of MCDA.
K1 may be a packed column having structured packings or random packings or a tray column having trays such as dualflow trays, sieve trays, bubble-cap trays or valve trays.
K1 is preferably operated with a reflux ratio (reflux/distillate removal) in the range from 0.1 to in- finity, preferably from 1 to 20. The number of theoretical plates in K1 is preferably 10 to 150, more preferably of 30 to 1 10.
The temperature at the top of K1 is preferably 30 to 280°C and the pressure at the top of K1 is preferably 1 to 1000 mbar. The temperature at the top of K1 is more preferably 80 to 180°C and the pressure at the top of K1 is more preferably 10 to 500 mbar. The temperature at the top of K1 is most preferably 80 to 150°C and the pressure at the top of K1 is most preferably 10 to 150 mbar.
Preferably, the distillation in K1 is conducted in the absence of oxygen.“Absence” is understood to mean that the proportion by volume of oxygen is less than 0.1 %, especially less than 0.01 % and very particularly less than 0.001 %, based on the total volume of the distillation column.
In a preferred embodiment, the auxiliary component is fed in in the upper part of K1 and the MCDA is fed in the lower part of K1. Most preferably, the auxiliary is fed in at least 10 or even at least 20 theoretical plates above the feed of the MCDA.
A mixture comprising a trans-enriched MCDA fraction, referred to as trans-enriched MCDA-1 , and optionally auxiliary compound is obtained and drawn off from K1 , preferably at the top.
Preferably, the mixture consists of 40 to 100% by weight of trans-enriched MCDA-1 and 0 to 60% by weight of the auxiliary compound.
More preferably, the mixture consists of 60 to 100% by weight of trans-enriched MCDA-1 and 0 to 40% by weight of the auxiliary compound.
Most preferably, the mixture consists of 65 to 100% by weight of trans-enriched MCDA-1 and 0 to 35% by weight of the auxiliary compound.
The trans-enriched MCDA-1 comprises preferably
0 to 10 % by weight of the 2,4-isomer cis (1 )
5 to 30 % by weight of the 2,6-isomer cis (2)
10 to 45 % by weight of the 2,4-isomer trans (3)
10 to 35 % by weight of the 2,4-isomer trans (4)
5 to 25 % by weight of the 2,6-isomer trans (5)
0 to 5 % by weight of the 2,4-isomer cis (6)
0 to 5 % by weight of the 2,6-isomer cis (7)
0 to 5 % by weight of other compounds with two amino groups based on the total amount of trans-enriched MCDA-1. A mixture of a cis-enriched MCDA fraction, referred to as cis-enriched MCDA-1 , and the auxil- iary compound are obtained in K1 and removed from K1 , preferably at the bottom. Preferably, the mixture comprises 50 to 90% by weight of the auxiliary compound and 10 to 50% by weight of the cis-enriched MCDA-1.
The cis-enriched MCDA-1 comprises preferably
40 to 80 % by weight of the 2,4-isomer cis (1 )
0.1 to 15 % by weight of the 2,6-isomer cis (2)
0.1 to 15 % by weight of the 2,4-isomer trans (3)
0.1 to 15 % by weight of the 2,4-isomer trans (4)
0.1 to 5 % by weight of the 2,6-isomer trans (5)
10 to 30 % by weight of the 2,4-isomer cis (6)
0.1 to 5 % by weight of the 2,6-isomer cis (7) and
0 to 5 % by weight of other compounds with two amino groups based on the total amount of cis-enriched MCDA-1.
Preferably, the trans-enriched MCDA-1 obtained in step a) has a reduced content of cis-isomers 1 , 6 and 7.
Preferably, the cis-enriched MCDA-1 comprises at least 70% by weight of cis isomers 1 , 6 and 7 of the MCDA fed to K1 in step a).
More preferably, the cis-enriched MCDA-1 comprises at least 80% by weight of cis isomers 1 , 6 and 7 of the MCDA fed to K1 in step a).
Most preferably, the cis-enriched MCDA-1 comprises at least 90% by weight of the cis isomers 1 , 6 and 7 of the MCDA fed to K1 in step a).
In a preferred embodiment, the trans-enriched MCDA-1 comprises 70 to 95 % by weight of trans-isomers and 5 to 30 % by weight of cis-isomers.
To step b)
The mixture of cis-enriched MCDA-1 and the auxiliary compound obtained in step a) are trans- ferred to second distillation column, referred to as K2, where the auxiliary compound is sepa- rated from the mixture, thus obtaining a cis-enriched MCDA-1 which is essentially free of auxil- iary compound and obtaining separately the essentially pure auxiliary compound.
K2 may be a packed column having structured packings or random packings or a tray column having trays such as dualflow trays, sieve trays, bubble-cap trays or valve trays. K2 is preferably operated with a reflux ratio (reflux/distillate removal) in the range from 0.1 to in- finity, preferably from 1 to 20.
The number of theoretical plates in K2 is preferably 10 to 150, more preferably of 30 to 1 10.
The temperature at the top of K2 is preferably 30 to 280°C and the pressure at the top of K2 is preferably 1 to 1000 mbar. The temperature at the top of K2 is more preferably 80 to 180°C and the pressure at the top of K2 is more preferably 10 to 500 mbar. The temperature at the top of K2 is most preferably 80 to 150°C and the pressure at the top of K2 is most preferably 10 to 150 mbar.
Preferably, the distillation in K2 is conducted in the absence of oxygen.“Absence” is understood to mean that the proportion by volume of oxygen is less than 0.1 %, especially less than 0.01 % and very particularly less than 0.001 %, based on the total volume of the distillation column.
In K2, the cis-enriched MCDA-1 is preferably removed from the top and the auxiliary compound is removed from the bottom.
To step c)
The cis-enriched MCDA-1 obtained in step b) is passed to a reactor, referred to as R1 , where the trans content of the cis-enriched MCDA-1 is increased by isomerization at a catalyst thus obtaining an isomerized MCDA, referred to as MCDA-ISO.
The isomerization of the cis-enriched MCDA-1 may be performed in the liquid or in the gaseous phase. Preferably, the isomerization is performed in the liquid phase which means that the isomerization is performed under a temperature and pressure where the cis-enriched MCDA-1 is liquid.
Preferably, the isomerization is performed at an elevated pressure, for example a pressure of 20 to 300 bars.
Preferably, the isomerization is performed at a temperature from 20 to 300°C, more preferably from 50 to 200°C and most preferably from 80 to 180°C.
In a preferred embodiment, the isomerization is performed in the presence of hydrogen. Hydro- gen may be used as gas to establish the above pressure in the reactor.
The isomerization is performed at a catalyst.
The catalyst may be a heterogeneous or homogenous hydrogenation catalyst. Preferably, a heterogeneous catalyst is used in the isomerization step. The heterogeneous catalyst may be a supported or an unsupported catalyst. A suitable unsup- ported catalyst is, for example, Raney nickel or Raney cobalt. A supported catalyst comprises catalytically active metals that are applied to a support. A suitable support is, for example, cal- cium carbonate, silicon oxide, zirconium dioxide or aluminum oxide.
Suitable catalysts comprise, for example, an active metal or a mixture of active metals selected from the groups IVb, Vb, Vlb, VI lb, VI I lb, lb or lib of the periodic system.
Preferred catalysts comprise an active metal or a mixture of active metals selected from nickel, palladium, platinum, cobalt, rhodium, iridium, copper, manganese, tin or ruthenium.
A most preferred catalyst is a catalyst comprising ruthenium on a zirconium dioxide support.
The catalyst may, for example, be installed as fixed bed in the reactor. In a preferred embodi- ment, the fixed bed is positioned in a way, that the total stream of cis-enriched MCDA-1 passes through the fixed bed.
The product of the isomerization has an increased content of trans-isomers; the product is re- ferred to as MCDA-ISO
MCDA-ISO comprises preferably
20 to 60 % by weight of the 2,4-isomer cis (1 )
0.1 to 10 % by weight of the 2,6-isomer cis (2)
5 to 25 % by weight of the 2,4-isomer trans (3)
5 to 25 % by weight of the 2,4-isomer trans (4)
0.1 to 10 % by weight of the 2,6-isomer trans (5)
0 to 20 % by weight of the 2,4-isomer cis (6)
0 to 10 % by weight of the 2,6-isomer cis (7) and
0 to 5 % by weight of other compounds with two amino groups based on the total amount of cis-enriched MCDA-ISO.
Preferably, MCDA-ISO obtained in step c) has an increased content of trans-isomers compared to the cis-enriched MCDA-1.
More preferably, the total content of all trans isomers in MCDA-ISO is at least 5%, more prefera- bly at least 10 % higher than the total content of all trans isomers in cis-enriched-MCDA-1.
To step d) MCDA-ISO is passed to K1. MCDA-ISO may be fed separately to K1 or may be combined with any of the other feeds to K1. In a preferred embodiment MCDA-ISO is separately fed to K1. In K1 MCDA-ISO is distilled together with MCDA and the auxiliary compound.
To step e)
Optionally, auxiliary compound is added to the mixture comprising the trans-enriched MCDA-1 which has been obtained in step a). Preferably, the mixture and any auxiliary compound added in this step e) are mixed in a suitable mixing device to prepare a homogeneous solution.
The mixture, respectively solution, is passed to a crystallization unit.
The auxiliary compound is the same compound as used in K1. In the whole process the same auxiliary compound is used.
Any auxiliary compound added in this step e) may be freshly added auxiliary compound or auxil- iary compound recycled from the process. Preferably, auxiliary compound obtained from the distillation in step b) or g) may be used.
The amount of any auxiliary compound added in step e) depends on the amount of auxiliary compound in the mixture obtained in step a).
Preferably, the content of auxiliary compound in the mixture, respectively solution, passed to the crystallization unit is 10 to 200 parts by weight of the auxiliary compound per 100 parts by weight of trans-enriched MCDA-1.
More preferably, the content of auxiliary compound in the mixture, respectively solution, passed to the crystallization unit is 15 to 100 parts by weight of the auxiliary compound per 100 parts by weight of trans-enriched MCDA-1.
Most preferably, the content of auxiliary compound in the mixture, respectively solution, passed to the crystallization unit is 20 to 80 parts by weight of the auxiliary compound per 100 parts by weight of trans-enriched MCDA-1.
The trans-enriched MCDA-1 as such has a melting point significantly below -60°C. Due to the content of the auxiliary compound in the mixture comprising trans-enriched MCDA-1 , the melt- ing point increases.
The mixture of trans-enriched MCDA-1 and auxiliary compound preferably has a melting point of -10 to +100°C and more preferably a melting point of +20 to +50°C. Hence, the mixture of trans-enriched MCDA-1 and auxiliary compound is preferably kept at a temperature which is higher than the melting point or equal to the melting point to form a homo- geneous solution. Preferably, the mixture and the obtained homogeneous solution are kept at a temperature of 0 to 100°C, more preferably at a temperature of +20 to 60°C, with the provision that the selected temperature is equal or preferably higher than the melting point. Preferably, the solution having this temperature is passed from the mixing device to the crystallization unit.
In the crystallization unit, the solution is cooled to a temperature of preferably -15 to +85°C and more preferably of 0 to +35°C, respectively +5 to +20°C. In a preferred embodiment, the solu- tion is cooled to a temperature which is at least 5°C, more preferably at least 15°C below the melting point of the solution.
The crystallization unit may consist of one or more crystallizers.
In case of one crystallizer (referred to as C1) the solution is cooled in this crystallizer to the de- sired final temperature.
In case of more than one crystallizers, the crystallizers are operated in line and the solution or suspension (if crystals are already obtained) is passed from one crystallizer to the next crystal- lizer, each crystallizer being kept at a lower temperature than the preceding crystallizer and the final crystallizer being kept at the desired final temperature.
From the crystallization step a crystallized mixture of the auxiliary compound and a cis-enriched MCDA fraction, referred to as cis-enriched MCDA-2, and a mother liquid comprising a trans-en- riched MCDA fraction, referred to as trans-enriched MCDA-2, and auxiliary compound are ob- tained.
The crystallized mixture of the auxiliary compound and cis-enriched MCDA-2 is withdrawn from the crystallization unit, for example by filtration.
The trans-enriched MCDA-2 preferably comprises
0 to 10 % by weight of the 2,4-isomer cis (1 )
0 to 5 % by weight of the 2,6-isomer cis (2)
10 to 55 % by weight of the 2,4-isomer trans (3)
10 to 45 % by weight of the 2,4-isomer trans (4)
5 to 25 % by weight of the 2,6-isomer trans (5)
0 to 5 % by weight of the 2,4-isomer cis (6)
0 to 5 % by weight of the 2,6-isomer cis (7)
0 to 5 % by weight of other compounds with two amino groups based on the total amount of trans-enriched MCDA-2. Preferably, the trans-enriched MCDA-2 consists to 70% to 100% by weight of trans-isomers. More preferably, the trans-enriched MCDA-2 consists to 80 to 99% by weight of trans-isomers. Preferably, the trans-enriched MCDA-2 comprises 0 to 3 % by weight of the 2,6-isomer cis 2. to step f)
The mother liquid obtained in step e) and comprising auxiliary compound and trans-enriched MCDA-2 is passed to a third distillation column, referred to as K3, where the auxiliary corn- pound is separated from the mother liquid thus obtaining the isolated trans-enriched MCDA-2.
The distillation in step f) correspond to the distillation in step b) and details regarding K2 and its operation in step b) apply to K3 and its operation in this step f).
Preferably, the trans-enriched MCDA-2 is obtained at the top of K3 and the auxiliary compound is obtained at the bottom of K3. This isolated trans-enriched MCDA-2 is the final product of the process. to step g)
The auxiliary compound obtained in step f) is recycled to the process. It may be recycled to any suitable process step. Preferably, it is recycled to the stream from the top of K1 to the mixing device of step e) to step h)
The crystallized mixture of the auxiliary compound and the cis-enriched MCDA-2, obtained in step e) is passed to K2.
By the process of this invention a mixture of 2, 4-diamino-1 -methyl-cyclohexane and 2,6-dia- mino-1-methylcyclohexane with a significantly increased content of trans isomers is obtained. The process is easy to perform and combines process steps of distillation, isomerization and crystallization in a very effective way and requires a minimum of energy and auxiliary corn- pound. Examples
Example 1 : crystallization of a mixture comprising MCDA and butane-1 ,4 diol
The specific composition of MCDA is listed in the table. In the table the content of cis-isomers and trans-isomers of formulas 1 to 7 (see above formulas in the specification) is defined in weight %. The content of the isomers 1 to 7 was determined by gas chromatography.
In the example, butane-1 ,4-diol, shortly referred to as BDO, was used as solvent.
The melting point of the mixture of MCDA and BDO was determined as follows:
MCDA and BDO were mixed at an elevated temperature to obtain a clear solution. The melting point of the mixture was determined by cooling the mixture until first crystals appeared, after- wards the suspension was heated up again, until all crystals dissolved. The corresponding tem- perature is referred to as melting point of the solution. The melting point has been determined with a turbidity probe. A solution without any turbidity corresponds to a solution without any crystals respectively solids.
A cooling crystallization was performed.
In a first step a seed of crystals has been prepared using a so called“seeding loop”. For the seeding loop, the solution is cooled down until first solid particles appear and afterwards the suspension is heated up again to the melting point to dissolve some of the solid particles. A so- lution comprising a small number of solid particles (seed) is obtained, which is then used for the crystallization process.
The example was performed in a one-liter double jacketed crystallizer, equipped with three baf- fles and a two-stage pitch blade stirrer, which was operated at 600 rpm. Furthermore, the crys- tallizer was equipped with a temperature and pressure sensor, as well as a turbidity probe to detect the formation of solid particles. It was possible to take samples of mother liquor which was free of solids via a filter fritte from the crystallizer, additionally a filter nutsche was mounted below the crystallizer to separate the mother liquor from the crystals.
The crystallizer was charged with 400 g of the MCDA/BDO solution.
A cooling crystallization was performed, by applying a linear cooling ramp with -1 K/h. Specific temperatures (listed in the tables) were kept constant for some hours, so that the solid-liquid equilibrium could be fully established. At these temperatures samples (about 3 g) from the solid- free mother liquor were taken and analyzed by gas chromatography. The yield of trans-enriched mother liquid was determined in a second run. At a pre-determined temperature which usually corresponded to a temperature listed in the tables of the examples, the whole suspension was transferred from the crystallizer on the filter nutsche. The crystals were separated from the mother liquor. Both fractions crystals and mother liquor were analyzed by GC and the masses of both fractions were determined.
The melting point of the MCDA used was: -92°C.
MCDA and BDO were mixed in a ratio of 65 : 35 party by weight. The melting point of the mix- ture of MDCA and BDO was +44.5°C.
In Table 1 below the weight fraction of the isomers (1 ) to (7) of MCDA is listed with decreasing temperature. For each line in the table the sum of all isomers of MCDA add to 100%. The corn- position of the liquid phase was measured, only.
Table 1 : crystallization, weight % of MCDA isomers
Figure imgf000016_0001
The example was repeated. At 20.0°C the crystals (comprising MCDA and BDO) were isolated from the suspension as described above. The isomer composition of the MCDA of the crystals was determined, see last line of the table. The yield of crystals was 35.7% by weight and the yield of mother liquid was 64.3 % by weight (both comprising MCDA and BDO). The total yield of trans-isomers in the final mother liquid was 77% by weight of all trans isomers of the starting solution.
Example 2
Example 2 is a simulation. The auxiliary compound is butane-1 ,4-diol. The feeds and the energy consumption of the process shown in Figure 1 have been calculated. The process of Figure 1 corresponds to the process of this invention with process steps a) to h). K1 , K2, K3, R1 and C1 in Figure 1 have the same meaning as defined in the specification. In Figure 1 , the streams between the units of the process have been numbered from 1 to 9. In ad- dition, there is the stream of MCDA fed to K1 , denominated“M” in Figure 1 and correspondingly in Table 2. Furthermore, there is a stream of auxiliary compound denominated“A” from the ves- sel“Aux” in Figure 1 to K1 and/or to stream 2.
In the Table 2 below, the total mass flow of each stream in kg/h as well as the calculated con- tent of MCDA isomers (1) to (7) and of the auxiliary compound (Aux) of each stream are listed in weight %.
Table 2: mass flows (kg/h) and composition in % by weight
Figure imgf000017_0001
Comparison example
The comparison example is also a simulation. The auxiliary compound is butane-1 ,4-diol. The mass flows and the energy consumption of the comparison process shown in Figure 2 have been calculated. The comparison process of Figure 2 does not comprise step h). The compari- son process is a process wherein the crystallized mixture of step e) containing cis-enriched MCDA and the auxiliary component are fed to a fourth distillation column, referred to as K4, where the auxiliary compound is separated from the crystal phase thus obtaining the isolated cis-enriched MCDA-2.
The distillation in K4 corresponds to the distillation K2 and its operation in step b) apply to K4 and its operation.
Preferably, the cis-enriched MCDA-2 is obtained at the top of K4 and the auxiliary compound is obtained at the bottom of K4.
The auxiliary compound obtained K4 is recycled to the process. It may be recycled to any suita- ble process step. Preferably, it is recycled to the stream from the top of K1 to the mixing device of step e)
K1 , K2, K3, R1 and C1 as well as streams“M” and“A” in Figure 2 have the same meaning as in example 2.
In the Table 3 below, the total mass flow of each stream in kg/h as well as the calculated con- tent of MCDA isomers (1) to (7) and of the auxiliary compound (Aux) of each stream are listed in weight %.
Table 3: mass flows (kg/h and composition in % by weight
Figure imgf000019_0001
Details of the simulated processes of example 2 and the comparison example:
Column K1 (Extractive distillation), in example 2 and the comparison example:
Head pressure 50 mbar absolute; top temperature 1 12 °C; bottom temperature 149 °C; prefera- bly equipped with structured packing (or crossflow trays, dualflow trays or random packing); equivalent to ~80 theoretical stages.
Column K2 (solvent recovery), in example 2 and the comparison example:
Head pressure 50 mbar absolute; top temperature 1 12 °C; bottom temperature 151 °C; prefera- bly equipped with structured packing (or crossflow trays, dualflow trays or random packing); equivalent to ~80 theoretical stages.
Column K3 (Mother liquid purification), in example 2 and the comparison example: Head pressure 50 mbar absolute; top temperature 1 12 °C; bottom temperature 151 °C; prefera- bly equipped with structured packing (or crossflow trays, dualflow trays or random packing); equivalent to ~40 theoretical stages. Column K4 (Crystal purification), applies to comparison example, only.
Head pressure 50 mbar absolute; top temperature 1 12 °C; bottom temperature 151 °C; prefera- bly equipped with structured packing (or crossflow trays, dualflow trays or random packing); equivalent to ~80 theoretical stages. Reactor R1 (Isomerization), in example 2 and the comparison example:
Reaction pressure 50 bar absolute; reaction temperature 150 °C; Weight hourly space velocity (WHSV) 1 kg/(kg*h); heterogeneous catalyst under hydrogen-atmosphere.
Crystallizer C1 (Crystallization), in example 2 and the comparison example:
Pressure 1 bar; crystallization end temperature 10 °C; start solvent content 35 wt.-%; end solids content 35 %.
The calculated total energy consumption for both processes is similar. With the process of ex- ample 2 the additional distillation column (K4) and its periphery (heat exchangers, piping, pumps, auxiliary) are not required. Furthermore, the overall yield from crude MCDA (only about 40% by weight of trans isomers, stream“M” in Table 2) to high purity trans-enriched MCDA-2 (>95% trans type isomers, stream No. 9 in Table 2) is -65% in case of the comparison example (see Table 3: stream 9/ stream M =1.25/1.92=0.65) to about 100 % (see Table 2: stream 9/ stream M = 1.25/1.25 = 1 ).
The process of the comparison example produces in addition -35% of a MCDA product with -80% trans isomers (Stream No.1 1), which is not usable for all applications that require a high purity of trans type MCDA.

Claims

Claims
1. A process to increase the fraction of trans-isomers of a mixture of 2,4-diamino-1-methylcyclo- hexane and 2,6-diamino-1-methylcyclohexane, shortly referred to as MCDA, by a continuous process, wherein a) an auxiliary compound having a boiling point at 50 mbar which is at least 5°C higher than the boiling point of MCDA at 50 mbar and MCDA are fed to a first distillation column, referred to as K1 , thus obtaining a mixture comprising a trans-enriched MCDA fraction, referred to as trans-enriched MCDA-1 , and optionally auxiliary compound and a mixture of a cis-enriched MCDA fraction, referred to as cis-enriched MCDA-1 , and auxiliary compound, b) the mixture of the cis-enriched MCDA-1 and the auxiliary compound obtained in step a) is transferred to a second distillation column, referred to as K2, where the auxiliary compound is separated from the mixture by distillation and is recycled to K1 , c) the cis-enriched MCDA-1 obtained in b) is passed to a reactor, referred to as R1 , where the trans content of the cis-enriched MCDA-1 is increased by isomerization at a catalyst thus ob- taining an isomerized MCDA, referred to as MCDA-ISO, d) the MCDA-ISO obtained in step c) is passed to K1 e) optionally auxiliary compound is added to the mixture comprising the trans-enriched MCDA- 1 obtained in step a) and the obtained mixture is passed to a crystallization unit, where a crystallized mixture of the auxiliary compound and a cis-enriched MCDA fraction, referred to as cis-enriched MCDA-2, is separated thus leaving a mother liquid comprising a trans-en- riched MCDA fraction, referred to as trans-enriched MCDA-2, and auxiliary compound, f) the mother liquid obtained in step e) is passed to a third distillation column, referred to as K3, where the auxiliary compound is separated from the mother liquid thus obtaining the iso- lated trans-enriched MCDA-2, g) the auxiliary compound obtained in step f) is recycled to the process h) the cis-enriched MCDA-2 obtained in step e) together with some auxiliary compound is passed to K2
2. Process according to claim 1 , wherein the MCDA comprises 50 to 95 % by weight of 2,4- diamino-1-methylcyclohexane and 5 to 50 % by weight of 2,6-diamino-1-methylcyclohex- ane. The process according to claim 1 or 2, wherein the MCDA may comprise the following trans-isomers and cis-isomers
Figure imgf000022_0001
1 2 3 4
2,4-Isomer 2,6-Isomer 2,4-Isomer 2,4-Isomer
CIS CIS trans trans
Figure imgf000022_0002
5 6 7
2,6-Isomer 2,4-Isomer 2,6-Isomer
trans CIS CIS
4. The process according to claim 3, wherein the MCDA consists of
0 to 80 % by weight of the 2,4-isomer cis (1 )
0.1 to 80 % by weight of the 2,6-isomer cis (2)
0.1 to 80 % by weight of the 2,4-isomer trans (3)
0.1 to 80 % by weight of the 2,4-isomer trans (4)
0.1 to 80 % by weight of the 2,6-isomer trans (5)
0 to 80 % by weight of the 2,4-isomer cis (6)
0 to 80 % by weight of the 2,6-isomer cis (7) and
0 to 5 % by weight of other compounds with two amino groups based on the total amount of MCDA.
5. The process according to any of claims 1 to 4, wherein the MCDA comprises in total 5 to 60% by weight of trans isomers and 40 to 95 % by weight of cis isomers.
6. Process according to any of claims 1 to 5, wherein the auxiliary compound is an alkane diole.
7. Process according to any of claims 1 or 6, wherein the auxiliary compound is butane-1 ,4- diol.
8. Process according to any of claims 1 to 7, wherein the cis-enriched MCDA-1 comprises at least 90% by weight of the cis isomers 1 , 6 and 7 of the MCDA fed to K1 in step a) 9. Process according to any of claims 1 to 8, wherein the trans-enriched MCDA-2 consists to
70% to 100% by weight of trans-isomers.
PCT/EP2019/059587 2018-04-26 2019-04-15 Process to increase the fraction of trans-isomers of a mixture of 2,4-diamino-1-methylcyclohexane and 2,6-diamino-1-methylcyclohexane WO2019206694A1 (en)

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WO2022009860A1 (en) * 2020-07-08 2022-01-13 三菱瓦斯化学株式会社 Aliphatic diamine isomerization method, diisocyanate production method, polyurethane production method, and polyurethane

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IN170153B (en) 1986-11-27 1992-02-15 Schloemann Siemag Ag
WO2016083210A1 (en) 2014-11-25 2016-06-02 Basf Se Method for producing cis- and trans-enriched mdach
WO2017093308A1 (en) 2015-12-04 2017-06-08 Basf Se Isomerization of mdach

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IN170153B (en) 1986-11-27 1992-02-15 Schloemann Siemag Ag
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WO2017093308A1 (en) 2015-12-04 2017-06-08 Basf Se Isomerization of mdach

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WO2022009860A1 (en) * 2020-07-08 2022-01-13 三菱瓦斯化学株式会社 Aliphatic diamine isomerization method, diisocyanate production method, polyurethane production method, and polyurethane
CN115768742A (en) * 2020-07-08 2023-03-07 三菱瓦斯化学株式会社 Method for isomerizing aliphatic diamine, method for producing diisocyanate, method for producing polyurethane, and polyurethane

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