CA1058634A - Process for producing pure racemic acid and mesotartaric acid - Google Patents
Process for producing pure racemic acid and mesotartaric acidInfo
- Publication number
- CA1058634A CA1058634A CA246,655A CA246655A CA1058634A CA 1058634 A CA1058634 A CA 1058634A CA 246655 A CA246655 A CA 246655A CA 1058634 A CA1058634 A CA 1058634A
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- Canada
- Prior art keywords
- acid
- free
- process according
- hydrolysis
- alkali
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/90—Regeneration or reactivation
- B01J23/92—Regeneration or reactivation of catalysts comprising metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07D—HETEROCYCLIC COMPOUNDS
- C07D301/00—Preparation of oxiranes
- C07D301/02—Synthesis of the oxirane ring
- C07D301/03—Synthesis of the oxirane ring by oxidation of unsaturated compounds, or of mixtures of unsaturated and saturated compounds
- C07D301/12—Synthesis of the oxirane ring by oxidation of unsaturated compounds, or of mixtures of unsaturated and saturated compounds with hydrogen peroxide or inorganic peroxides or peracids
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/50—Improvements relating to the production of bulk chemicals
- Y02P20/584—Recycling of catalysts
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
- Low-Molecular Organic Synthesis Reactions Using Catalysts (AREA)
- Catalysts (AREA)
- Epoxy Compounds (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
The present invention provides a process for producing pure racemic acid and mesotartaric acid by reacting alkali maleates with aqueous hydrogen peroxide in the presence of alkali tungstate, in which the molar ratio of hydrogen peroxide to maleic acid is greater than 1, the alkali salts of the cis-epoxy succinic acid so obtained together with the alkali tungstate are converted into the free epoxy succinic acid and the free tungstate acid by passing them over a strongly acid cation exchanger and the free cis-epoxy succinic acid is hydrolysed to racemic acid and mesot-artaric acid in the absence of free tungstic acid which is removed with an anion exchanger prior to hydrolysis in the case of a catalyst-free hydrolysis or in the presence of free tungstic acid which is removed by an anion exchanger after the hydrolysis in the case of a catalyst-containing hydrolysis, the racemic acid is crystallized from the tungstic-acid-free hydrolysis mixture.
The mesotartaric acid remaining in the mother liquor is recovered therefrom either by crystallization or by evaporating to dryness and the anion exchanger changed with tungstic acid is regenerated with dilute alkali liquor.
The present invention provides a process for producing pure racemic acid and mesotartaric acid by reacting alkali maleates with aqueous hydrogen peroxide in the presence of alkali tungstate, in which the molar ratio of hydrogen peroxide to maleic acid is greater than 1, the alkali salts of the cis-epoxy succinic acid so obtained together with the alkali tungstate are converted into the free epoxy succinic acid and the free tungstate acid by passing them over a strongly acid cation exchanger and the free cis-epoxy succinic acid is hydrolysed to racemic acid and mesot-artaric acid in the absence of free tungstic acid which is removed with an anion exchanger prior to hydrolysis in the case of a catalyst-free hydrolysis or in the presence of free tungstic acid which is removed by an anion exchanger after the hydrolysis in the case of a catalyst-containing hydrolysis, the racemic acid is crystallized from the tungstic-acid-free hydrolysis mixture.
The mesotartaric acid remaining in the mother liquor is recovered therefrom either by crystallization or by evaporating to dryness and the anion exchanger changed with tungstic acid is regenerated with dilute alkali liquor.
Description
The present invention relates to a process for producing racemic acid and mesotartaric acid by epoxidation of an alkali salt of maleic acid with hydrogen peroxide in the presence of alkali tungstates in an aqueous medium at elevated temperatures, conversion into the free acid and subsequent hydrol-ysis.
Several synthetic methods are known for producing racemic acid from maleic acid by catalytic hydroxylation with hydrogen peroxide. Thus, for example, free maleic acid is reacted in aqueous solution with hydrogen peroxide in the presence of alkali tungstates or molybdates, whereupon the intermediately formed epoxy succinic acid is hydrolyzed by boiling and the racemic acid thus formed is recrystallized from hydrolysis solution (see Church and Blumberg, "Ind. Eng. Chem. 43 (8), 1780 ff"). The mother liquor of the racemic-acid crystallization is recycled to the reaction. The recycling and reuse of the mother liquor after the crystallization is of decisive importance for the economy of the synthetic production of racemic acid since the mother liquor contains the tungstate or molybdate catalyst used as well as a high proportion of maleic acid which cannot be passed to waste. It is known that this process is carried out so that approximately 60~ of the maleic acid used is reacted (loc.
cit.) However, the recycling of the mother liquor has great disadvantages since during its circulation it may become contamin-ated with impurities, which have an adverse effect onthe quality of the racemic acid obtained.
It has now been found that on recycling the mother liquor the rate of epoxidation substantially decreased because of saturation with tartaric acid (see laid-open German Specification No. 2,016,668). Further, in the epoxidation the tartaric acid recycled with the mother liquor is irreversibly oxidized by hydro-gen peroxide to valueless decomposition products such as formic acid, carbonic acid and water (see laid-open German Specification No. 2 016 668). In fact, according to the process of the laid-open German Specification No. 2 016 668 attempts were made to avoid the disadvantages described hereinbefore by, prior to the recycling of the mother liquor, precipitating the tartaric acid contained therein as a potassium or calcium salt. However, it was found that the recovered calcium salt was not completely free from tungsten and further that the tartaric acid may be recovered from its salts only with some difficulty. Further, the tungstate catalyst must be precipitated after several opera-ting cycles as calcium salt and recovered therefrom or otherwise its activity diminishes. Yet again the racemic acid obtained by said process is not sufficiently pure for food purposes. When racemic acid is to be used instead of tartaric acid in the food industry, very high purity requirements must be satisfied with respect to the content of maleic acid and fumaric acid as well as with respect to the content of traces of heavy metals, i.e., in the present case with respect to the content of tungstate and molybdate.
Since some of the processes described are carried out with an excess of maleic acid (see Church and Blumberg loc. cit.
and laid-open German Specification No. 2,016,668), the racemic acid must be crystallized from a solution rich in maleic acid and is rendered impure by adhering maleic acid. Thus the higher the yield in which the racemic acid is crystallized the greater the impurity of the solution. Under the conditions of the reaction, some of the maleic acid must undergo a change to fumaric acid.
Because of the sparingly solubility of the fumaric acid, said acid crystallizes out together with the racemic acid, which is thus rendered impure, and can be separated only with difficulty.
In the known processes the racemic acid obtained must be crystallized from the solutions, which still contain the entire catalyst. A complete separation of the catalyst is not possible since particularly in the case of tungsten, the tungstic acid tends to adhere to the crystallized racemic acid and renders it impure until it assumes a blue coloration.
According to the laid-open German Specification No.
1,643,891 it is known that some of the disadvantages can be avoided by producing calcium tartrate by the catalyzed reaction of acid calcium maleate with hydrogen peroxide. However, it is difficult to liberate racemic acid from calcium tartrate, for example, by reaction with sulphuric acid as in the case of natural tartaric acid. The solubility products of the gypsum thus obtained and of calcium tartrate do not differ sufficiently so that losses are caused by the tartrate content of the gypsum or when an excess of sulphuric acid is used, then the tartaric acid must be recovered from a solution containing sulphuric acid, whereby additional difficulties are caused.
The production of mesotartaric acid from maleic acid and hydrogen peroxide in the presence of tungstate, i.e., via cis-epoxy succinic acid, has not been known. Mesotartaric acid has been obtained, for example, only in the hydrolysis of trans-epoxy succinic acid (see Kuhn and Ebel, Berichte 58 B, 919 (1925).
The present invention provides a process in which racemic acid is produced in high yields and with a high degree of purity, primarily the purity required for food, as well as mesotar-taric acid while simultaneously recovering the catalyst.
It has now been found that racemic acid can be obtained in a continuous or discontinuous process in high yields and with a very high degree of purity in addition to mesotartaric acid by the reaction of the alkali maleates with aqueous hydrogen peroxide in the presence of alkali tungstate when the ratio of hydrogen peroxide to maleic acid is greater than 1 and when thealkali salts of the cis-epoxy succinic acid so formed together with the alkali ~058634 tungstate are converted into free cis-epoxy succinic acid and free tungstic acid by passing them over a strongly acid cation exchanger, when required after destroying the hydrogen peroxide, whereupon hydrolysis of the free cis-epoxy succinic acid to racemic acid and mesotartaric acid may be carried out either in the presence of in the absence of tungstic acid. In the case of the catalyst-free hydrolysis the tungstic acid is removed by anion exchangers prior to the hydrolysis and in the case of the catalyst-containing hydrolysis the tungstic acid is removed with anion exchangers after the hydrolysis. The racemic acid is then crystallized from the tungstic-acid-free hydrolysis mixture in a conventional manner, when required by evaporation of water, and by reducing the temperature, whereupon the mesotartaric acid remains in the mother liquor and is removed therefrom by crystal-lization or by evaporation to dryness, and is recovered when required in mixture with tartaric acid, non-reacted cis-epoxy succinic acid and maleic acid while the anion exchanger charged with the tungstic acid is regenerated in a conventional manner with a dilute alkali liquor and, if required, the solution of the alkali tungstates is returned directly to the epoxidation stage, if desired after treatment with active carbon.
According to the process of the present invention the dl-tartaric acid is for the first time technically crystallized from a solution which is practically free from tungstic acid and is free from maleic acid except for an exceedingly small residue and therefore can be recovered from this solution with a degree of purity suitable for food.
It was also found for the first time that mesotartaric acid is formed in the hydrolysis of cis-epoxy succinic acid and it was found th~t its proportion is influenced by the manner in which the hydrolysis is carried out, i.e., by the presence or absence of the tungstate catalyst.
By combining the individual steps in accordance with the invention, i.e., starting from the salts of the maleic acid, which are reacted with excess hydrogen peroxide in the presence of the tungstates by recovering both the free cis-epoxy succinic acid and the free tungstic acid with the aid of cation exhangers as well as by the hy~rolysis techniques described hereinbefore and the removal of the tungstic acid by anion exchangers and by processing the solution by fractional crystallization dl-tartaric acid is produced having a high degree of purity and the mesotar-taric acid so obtained is recovered. Further the tungstate catalyst can be recovered in a very simple manner and virtually quantitatively and recycled, in aqueous solution, directly to the epoxidation stage without cumbersome processing. Again, the process according to the invention can be carried out technically in a simple manner as only aqueous solutions are used up to the crystallization of the tartaric acid and the handling of solids, which as is well known is difficult, is completely avoided.
Sodium, potassium and ammonium compounds, preferably the sodium compounds are suitable as alkali maleates and alkali tungstates. The amounts of alkali maleate are such that the reaction takes place in a homogeneous mediumduring the entire time of the reaction. When using sodium maleate the reaction solution should preferably contain lO to 20% by weight of maleic acid.
The molar ratio of hydrogen peroxide to maleic acid must be between l.01 and 5:1, preferably between l.l and 2:1. A
ratio between l.l and 1.3 : l is particularly favourable. The starting concentration of the aqueous hydrogen peroxide solution can be arbitrarily chosen. The excess of hydrogen peroxide should be such that even in case of losses of hydrogen peroxide due to decomposition there always is an excess of hydrogen peroxide relative to maleic acid during the entire reaction.
The reaction is carried out at pH values between 3 and 5.5, preferably at pH values from 4 to 5 and at temperatures from 70 to 90C, although higher temperatures up to the boiling point of the aqueous solution and lower temperatures down to the limit of solubility of the maleate applied or of the epoxy succinate formed during the reaction are feasible.
The catalyst, i.e., the alkali tungstate may be used in amounts of 0.5 to 5, preferably 1 to 2 mole %, relative to the maleic acid used.
The reaction of sodium salts of maleic acid with hydrogen peroxide in the presence of sodium tungstate to the sodium salts of cis-epoxy succinic acid also is known (see G.B. Payne, P.H. Williams, J. org. Chem. 24 (1959), 54), but their conversion corresponding to the further steps of the process according to the invention for producing tartaric acid is not known.
In the process according to the invention the alkali maleate can be used in a prepared form or it can also be formed _ situ in the reactor. Maleic acid or maleic anhydride can be used as the starting material.
After the epoxidation reaction the hydrogen peroxide and the other peroxide compounds, such as per tungstates are, if required removed. For removing the peroxide compounds known chemical reactions and the known decomposition of these compounds which is catalyzed by metals can be used. The operation is pref-erably so carried out such that the solution is not rendered impure and a catalyst containing platinum on a solid support is used, for example, 0.01 to 5% by weight of platinum on a chemically inert support material having very few pores and consisting of more than 90~ of SiO2, preferably 0.05 to 0.5% of Pt. With this catalyst the peroxide compounds can be decomposed in the solutions concerned at temperatures from 20 to 100C, preferably from 60 to 80C, under standard pressure.
A particularly preferred manner of carrying out the process up to the stage of the peroxide decomposition is explained hereafter with reference to the accompanying drawing in which, Figure l is a flow sheet of the process according to one embodiment of the present invention.
An aqueous solution of hydrogen peroxide and maleic acid is fed through pipe 17 and an aqueous solution of sodium tungstate and a solution of caustic soda are fed through pipe 18 into a continuously operated reactor, which works as an ideal vessel with stirrer with complete remixing of the solution, which is kept at a constant temperature by a heat exchanger. From the reactor l the solution flows into a reactor 2, which is basically equipped in the same way as reactor 1 and into which, if required, additional aqueous solution of caustic soda can be fed through the pipe 20 in order to adjust to a desired pH value. Oxygen, which may be formed by decomposition of hydrogen peroxide exhausts respectively through the pipes l9 and 21.
The reaction mixture leaving the reactor 2 is fed to a secondary reaction zone, asa flow pipe in the form of 3 through pipe 22. The reacted mixture is fed through pipe 23 from pipe 3 found from below into the column 4. Column 4 is filled with a decomposition catalyst and the oxygen formed by decomposition leaves the column 4 through the pipe 24 while the solution flows through the pipe 25 into an intermediate tank 5, in which it must be kept at a temperature above the temperature of crystallization of the dissolved solids.
As strongly acid cation exchangers for producing the free cis-epoxy succinic acid all the commercial types, primarily those based on polystyrene, or polystyrene divinly benzene, may be used, preferably those containing free sulphonic-acid groups.
For successfully carrying out the process it is immaterial whether known parallel-flow, counterflow or continuous ion-exchange processes are used. However, it is advantageous to carry out the 1~58634 regeneration of the cation exchange resin in a counterflow to the charging, whereby the process is not limited. In this manner the known advantages of the counterflow process, such as low residual content of alkali in the exchanged solution and low requirement of regenerating agent, and thus its greater economy are utilized.
Methods which avoid the exchanged solution being too highly diluted with the wash water obtained in the regeneration of the exchange resins are particularly favourable since the water of dilution must be additionally evaporated in the subsequent processing.
A particularly preferred method of producing the cis-epoxy succinic aid by ion exchange is also set forth in Figure 1.
The solution in the tank 5 is fed at a temperature above the crystallization temperature through the pipe 26 and from below into column 6, filled with ion exchange resin. From column 6 the solution is fed through pipe 26a into a similar column 7, which is operated as a fine purifier. An aqueous solution of the epoxy-succinic acid and tungstic acid runs off at the top of the column 7 through pipe 27. The column 6 is preferably operated until alkali escapes, whereupon the pipe 26 is switched over to column 7, a freshly regenerated column 8 serving as the fine purifier and column 6 then is in turn regenerated. When this manner of carrying out the process is continued a quasi-continuous flow can be obtained. It was found to be favourable that the exchange bed be so dimensioned that the operation is carried out below a velocity of flow at which the resin is suspended or fluidized which fluidization tends to detract from the ion exchange. This method also does not require additional technical devices for operating countercurrent filters (see K.
Dorfner, ion exchangers, Walter de Gruyter & Co., Berlin (1970).
The method described above can be carried out in a particularly simple manner, especially in association with the process according to the invention since, primarily, the reaction in the-reactors 1,
Several synthetic methods are known for producing racemic acid from maleic acid by catalytic hydroxylation with hydrogen peroxide. Thus, for example, free maleic acid is reacted in aqueous solution with hydrogen peroxide in the presence of alkali tungstates or molybdates, whereupon the intermediately formed epoxy succinic acid is hydrolyzed by boiling and the racemic acid thus formed is recrystallized from hydrolysis solution (see Church and Blumberg, "Ind. Eng. Chem. 43 (8), 1780 ff"). The mother liquor of the racemic-acid crystallization is recycled to the reaction. The recycling and reuse of the mother liquor after the crystallization is of decisive importance for the economy of the synthetic production of racemic acid since the mother liquor contains the tungstate or molybdate catalyst used as well as a high proportion of maleic acid which cannot be passed to waste. It is known that this process is carried out so that approximately 60~ of the maleic acid used is reacted (loc.
cit.) However, the recycling of the mother liquor has great disadvantages since during its circulation it may become contamin-ated with impurities, which have an adverse effect onthe quality of the racemic acid obtained.
It has now been found that on recycling the mother liquor the rate of epoxidation substantially decreased because of saturation with tartaric acid (see laid-open German Specification No. 2,016,668). Further, in the epoxidation the tartaric acid recycled with the mother liquor is irreversibly oxidized by hydro-gen peroxide to valueless decomposition products such as formic acid, carbonic acid and water (see laid-open German Specification No. 2 016 668). In fact, according to the process of the laid-open German Specification No. 2 016 668 attempts were made to avoid the disadvantages described hereinbefore by, prior to the recycling of the mother liquor, precipitating the tartaric acid contained therein as a potassium or calcium salt. However, it was found that the recovered calcium salt was not completely free from tungsten and further that the tartaric acid may be recovered from its salts only with some difficulty. Further, the tungstate catalyst must be precipitated after several opera-ting cycles as calcium salt and recovered therefrom or otherwise its activity diminishes. Yet again the racemic acid obtained by said process is not sufficiently pure for food purposes. When racemic acid is to be used instead of tartaric acid in the food industry, very high purity requirements must be satisfied with respect to the content of maleic acid and fumaric acid as well as with respect to the content of traces of heavy metals, i.e., in the present case with respect to the content of tungstate and molybdate.
Since some of the processes described are carried out with an excess of maleic acid (see Church and Blumberg loc. cit.
and laid-open German Specification No. 2,016,668), the racemic acid must be crystallized from a solution rich in maleic acid and is rendered impure by adhering maleic acid. Thus the higher the yield in which the racemic acid is crystallized the greater the impurity of the solution. Under the conditions of the reaction, some of the maleic acid must undergo a change to fumaric acid.
Because of the sparingly solubility of the fumaric acid, said acid crystallizes out together with the racemic acid, which is thus rendered impure, and can be separated only with difficulty.
In the known processes the racemic acid obtained must be crystallized from the solutions, which still contain the entire catalyst. A complete separation of the catalyst is not possible since particularly in the case of tungsten, the tungstic acid tends to adhere to the crystallized racemic acid and renders it impure until it assumes a blue coloration.
According to the laid-open German Specification No.
1,643,891 it is known that some of the disadvantages can be avoided by producing calcium tartrate by the catalyzed reaction of acid calcium maleate with hydrogen peroxide. However, it is difficult to liberate racemic acid from calcium tartrate, for example, by reaction with sulphuric acid as in the case of natural tartaric acid. The solubility products of the gypsum thus obtained and of calcium tartrate do not differ sufficiently so that losses are caused by the tartrate content of the gypsum or when an excess of sulphuric acid is used, then the tartaric acid must be recovered from a solution containing sulphuric acid, whereby additional difficulties are caused.
The production of mesotartaric acid from maleic acid and hydrogen peroxide in the presence of tungstate, i.e., via cis-epoxy succinic acid, has not been known. Mesotartaric acid has been obtained, for example, only in the hydrolysis of trans-epoxy succinic acid (see Kuhn and Ebel, Berichte 58 B, 919 (1925).
The present invention provides a process in which racemic acid is produced in high yields and with a high degree of purity, primarily the purity required for food, as well as mesotar-taric acid while simultaneously recovering the catalyst.
It has now been found that racemic acid can be obtained in a continuous or discontinuous process in high yields and with a very high degree of purity in addition to mesotartaric acid by the reaction of the alkali maleates with aqueous hydrogen peroxide in the presence of alkali tungstate when the ratio of hydrogen peroxide to maleic acid is greater than 1 and when thealkali salts of the cis-epoxy succinic acid so formed together with the alkali ~058634 tungstate are converted into free cis-epoxy succinic acid and free tungstic acid by passing them over a strongly acid cation exchanger, when required after destroying the hydrogen peroxide, whereupon hydrolysis of the free cis-epoxy succinic acid to racemic acid and mesotartaric acid may be carried out either in the presence of in the absence of tungstic acid. In the case of the catalyst-free hydrolysis the tungstic acid is removed by anion exchangers prior to the hydrolysis and in the case of the catalyst-containing hydrolysis the tungstic acid is removed with anion exchangers after the hydrolysis. The racemic acid is then crystallized from the tungstic-acid-free hydrolysis mixture in a conventional manner, when required by evaporation of water, and by reducing the temperature, whereupon the mesotartaric acid remains in the mother liquor and is removed therefrom by crystal-lization or by evaporation to dryness, and is recovered when required in mixture with tartaric acid, non-reacted cis-epoxy succinic acid and maleic acid while the anion exchanger charged with the tungstic acid is regenerated in a conventional manner with a dilute alkali liquor and, if required, the solution of the alkali tungstates is returned directly to the epoxidation stage, if desired after treatment with active carbon.
According to the process of the present invention the dl-tartaric acid is for the first time technically crystallized from a solution which is practically free from tungstic acid and is free from maleic acid except for an exceedingly small residue and therefore can be recovered from this solution with a degree of purity suitable for food.
It was also found for the first time that mesotartaric acid is formed in the hydrolysis of cis-epoxy succinic acid and it was found th~t its proportion is influenced by the manner in which the hydrolysis is carried out, i.e., by the presence or absence of the tungstate catalyst.
By combining the individual steps in accordance with the invention, i.e., starting from the salts of the maleic acid, which are reacted with excess hydrogen peroxide in the presence of the tungstates by recovering both the free cis-epoxy succinic acid and the free tungstic acid with the aid of cation exhangers as well as by the hy~rolysis techniques described hereinbefore and the removal of the tungstic acid by anion exchangers and by processing the solution by fractional crystallization dl-tartaric acid is produced having a high degree of purity and the mesotar-taric acid so obtained is recovered. Further the tungstate catalyst can be recovered in a very simple manner and virtually quantitatively and recycled, in aqueous solution, directly to the epoxidation stage without cumbersome processing. Again, the process according to the invention can be carried out technically in a simple manner as only aqueous solutions are used up to the crystallization of the tartaric acid and the handling of solids, which as is well known is difficult, is completely avoided.
Sodium, potassium and ammonium compounds, preferably the sodium compounds are suitable as alkali maleates and alkali tungstates. The amounts of alkali maleate are such that the reaction takes place in a homogeneous mediumduring the entire time of the reaction. When using sodium maleate the reaction solution should preferably contain lO to 20% by weight of maleic acid.
The molar ratio of hydrogen peroxide to maleic acid must be between l.01 and 5:1, preferably between l.l and 2:1. A
ratio between l.l and 1.3 : l is particularly favourable. The starting concentration of the aqueous hydrogen peroxide solution can be arbitrarily chosen. The excess of hydrogen peroxide should be such that even in case of losses of hydrogen peroxide due to decomposition there always is an excess of hydrogen peroxide relative to maleic acid during the entire reaction.
The reaction is carried out at pH values between 3 and 5.5, preferably at pH values from 4 to 5 and at temperatures from 70 to 90C, although higher temperatures up to the boiling point of the aqueous solution and lower temperatures down to the limit of solubility of the maleate applied or of the epoxy succinate formed during the reaction are feasible.
The catalyst, i.e., the alkali tungstate may be used in amounts of 0.5 to 5, preferably 1 to 2 mole %, relative to the maleic acid used.
The reaction of sodium salts of maleic acid with hydrogen peroxide in the presence of sodium tungstate to the sodium salts of cis-epoxy succinic acid also is known (see G.B. Payne, P.H. Williams, J. org. Chem. 24 (1959), 54), but their conversion corresponding to the further steps of the process according to the invention for producing tartaric acid is not known.
In the process according to the invention the alkali maleate can be used in a prepared form or it can also be formed _ situ in the reactor. Maleic acid or maleic anhydride can be used as the starting material.
After the epoxidation reaction the hydrogen peroxide and the other peroxide compounds, such as per tungstates are, if required removed. For removing the peroxide compounds known chemical reactions and the known decomposition of these compounds which is catalyzed by metals can be used. The operation is pref-erably so carried out such that the solution is not rendered impure and a catalyst containing platinum on a solid support is used, for example, 0.01 to 5% by weight of platinum on a chemically inert support material having very few pores and consisting of more than 90~ of SiO2, preferably 0.05 to 0.5% of Pt. With this catalyst the peroxide compounds can be decomposed in the solutions concerned at temperatures from 20 to 100C, preferably from 60 to 80C, under standard pressure.
A particularly preferred manner of carrying out the process up to the stage of the peroxide decomposition is explained hereafter with reference to the accompanying drawing in which, Figure l is a flow sheet of the process according to one embodiment of the present invention.
An aqueous solution of hydrogen peroxide and maleic acid is fed through pipe 17 and an aqueous solution of sodium tungstate and a solution of caustic soda are fed through pipe 18 into a continuously operated reactor, which works as an ideal vessel with stirrer with complete remixing of the solution, which is kept at a constant temperature by a heat exchanger. From the reactor l the solution flows into a reactor 2, which is basically equipped in the same way as reactor 1 and into which, if required, additional aqueous solution of caustic soda can be fed through the pipe 20 in order to adjust to a desired pH value. Oxygen, which may be formed by decomposition of hydrogen peroxide exhausts respectively through the pipes l9 and 21.
The reaction mixture leaving the reactor 2 is fed to a secondary reaction zone, asa flow pipe in the form of 3 through pipe 22. The reacted mixture is fed through pipe 23 from pipe 3 found from below into the column 4. Column 4 is filled with a decomposition catalyst and the oxygen formed by decomposition leaves the column 4 through the pipe 24 while the solution flows through the pipe 25 into an intermediate tank 5, in which it must be kept at a temperature above the temperature of crystallization of the dissolved solids.
As strongly acid cation exchangers for producing the free cis-epoxy succinic acid all the commercial types, primarily those based on polystyrene, or polystyrene divinly benzene, may be used, preferably those containing free sulphonic-acid groups.
For successfully carrying out the process it is immaterial whether known parallel-flow, counterflow or continuous ion-exchange processes are used. However, it is advantageous to carry out the 1~58634 regeneration of the cation exchange resin in a counterflow to the charging, whereby the process is not limited. In this manner the known advantages of the counterflow process, such as low residual content of alkali in the exchanged solution and low requirement of regenerating agent, and thus its greater economy are utilized.
Methods which avoid the exchanged solution being too highly diluted with the wash water obtained in the regeneration of the exchange resins are particularly favourable since the water of dilution must be additionally evaporated in the subsequent processing.
A particularly preferred method of producing the cis-epoxy succinic aid by ion exchange is also set forth in Figure 1.
The solution in the tank 5 is fed at a temperature above the crystallization temperature through the pipe 26 and from below into column 6, filled with ion exchange resin. From column 6 the solution is fed through pipe 26a into a similar column 7, which is operated as a fine purifier. An aqueous solution of the epoxy-succinic acid and tungstic acid runs off at the top of the column 7 through pipe 27. The column 6 is preferably operated until alkali escapes, whereupon the pipe 26 is switched over to column 7, a freshly regenerated column 8 serving as the fine purifier and column 6 then is in turn regenerated. When this manner of carrying out the process is continued a quasi-continuous flow can be obtained. It was found to be favourable that the exchange bed be so dimensioned that the operation is carried out below a velocity of flow at which the resin is suspended or fluidized which fluidization tends to detract from the ion exchange. This method also does not require additional technical devices for operating countercurrent filters (see K.
Dorfner, ion exchangers, Walter de Gruyter & Co., Berlin (1970).
The method described above can be carried out in a particularly simple manner, especially in association with the process according to the invention since, primarily, the reaction in the-reactors 1,
2, 3 and 4 defines the concentration and the mass flow (per hour) of the solution to be exchanged by the cation exchange columns 6, 7 and 8 so that higher mass flows per hour which cause the suspension of the resin and reduce the efficiency of the exchange are not required.
The washing of an exhausted exchange column and its re-generation will now be explained hereafter with reference to Figure 1, using column 8 as an example. This method has proved to be particularly advantageous with respect to saving wash water and preventing the product solution from being diluted too much while the losses of product are only low. Thus, the process can be so carried out that the solution in the column is displaced by a subsequent solution. It is merely necessary to take precau-tions that the regenerating acid is not mixed with the flow of product.
The contents of the column 8 is returned first to the tank 5 through the pipe 28, the tank 9 and the pipe 29 and then rewashed with preconcentrated wash water from tank 10, pipe 31 and column 8. The discharge from column 8 also returns to the tank 5 through the pipe 28, tank 9 and pipe 29, whereupon it is rewashed with distilled water through the pipe 32. This discharge is fed to the tank 10 through the pipe 28, tank 9 and pipe 30 and is reused in the next cycle. The subsequent regener-ation with rewashing can be carried out in a conventional manner, for example, with dilute hydrochloric acid, as defined by the resin producers, through the pipes 33/34 and 35. It is advantageous to drain the last wash water and to charge the empty column 8 in order to avoid unnecessary dilution of the product.
The aqueous solution of epoxy succinic acid and tungstic acid which is obtained after the cation exchanger and still contains small amounts of non-reacted maleic acid and small amounts of tartaric acid is then reacted to form tartaric acid at temperatures from 50 to 200C, preferably at temperature~ from 100 to 150C.
The procedure may be such that the solution, through the pipe 27, is boiled directly in the tank 11, for example, for 5 hours under reflux. However, the procedure may also be such that the solution from pipe 27 is passed through the pipe 37 to the anion exchangers 13 and 14 at temperatures of approximately 20 to 95C. These temperatures are limited by the stability of the anion exchangers.
The solution of the epoxy succinic acid, which is free from tungstic acid and is discharged through the pipe 40, is then hydrolyzed.
The hydrolysis of aqueous cis-epoxy-succinic acid solution is known (see R, Kuhn and F. Ebel, Ber. 58 B, 919 (1925); G. Wode, Svensk Kem. Tids. 40, 221 (1928) and C.A. 23 (1929, 2344 as well as laid-open German Specification 2 400 767).
Surprisingly it was found that the proportion of mesotar-taric acid, which is unexpectedly formed in the hydrolysis of the cis-epoxy succinic acid, depends on whether the hydrolysis is carried out prior to or after the anion exchange. This is so much more surprising since according to R. Kuhn et al. (loc. cit.) and the laid-open German Specification No. 2,400,767 even in the hydrolysis of an aqueous solution of cis-epoxy succinic acid, which correspon-ds to the solution obtained after the anion exchanger in the process according to the invention, only dl-tartaric acid is formed.
However, according to the process of the invention it was found that the proportion of mesotartaric acid formed can be substantially reduced when the hydrolysis is carried out in the presence of 0.1 to 5, preferably 1 to 2 mole % of tungstic acid relative to the cis-epoxy succinic acid, i.e., prior to the anion exchange as will be seen from Examples 4 and 5 given hereinafter.
According to the process of the invention it is also possible to so adjust the conditions according to requirements that selectively more or less mesotartaric acid is formed. Thus, depending on requirements, more or less dl-tartaric acid can be obtained and in cases in which dl-tartaric acid can be used only insufficiently or not at all it can be made up or replaced by mesotartaric acid. For example, this is the case when the solubility of the dl-tartaric acid is not sufficient for specific purposes. Since the dl-tartaric acid differs from the natural tartaric acid by its substantially poorer solubility while the solubility of mesotartaric acid is close so that of natural tartaric acid, a solution having higher proportions of mesotartaric acid can be produced whenever the solubility of the dl-tartaric acid is not sufficient for the purpose concerned in a technical field of application, as for example, in the building material industry or in the galvanic industry.
The use of anion exchangers for removing tungstate-containing compounds even in the presence of polybasic, complex-forming acids, such as citric acid, is known per se (see D. Shishkov, E. Koleva, Doklady, Bolg. Akad. Nauk 17 (10) 909 (1964) and C.Z.
(1966) 27-538). It was found that there usually is a possibility of purifying racemic-acid solutions by passing them over anion exchangers. Any type of commercial anion exchanger can be used, preferably weakly basic anion exchangers based on polystyrene or polystyrene/divinyl benzene and having macroporous structures and amino functions as exchange-active groups.
In the process according to the invention it is immater-ial whether the anion exchange is carried out by means of a known parallel-flow, counterflow or continuous ion-exchange process.
This exchange process is also shown in Figure 1, i.e., in the columns 12, 13 and 14 which can be correspondingly controlled as described for the cation exchange in the columns 6, 7 and 8.
Accordingly three columns are used which are charged from below in a counterflow to the regeneration. Two of these columns are in series connection while the third column is in the regeneration.
The first exchange column is operated preferably up to the discharge of tungsten while the second exchange column, which is always freshly regenerated, serves for fine purification. At variance with the cation exchange, one of the usual countercurrent techni-ques, for example, the fluidized bed process, must be applied (see Dorfner loc. cit.). The regeneration and washing of an exhausted column are described with reference to Figure 1, using the column 12 as an example, that is to say a most favourable method. The contents of the column 12 is displaced first with distilled water through pipe 47 and returned by way of the pipe 39 for use in the anion exchangers 13 or 14. As little water as possible is used so that the product is not unnecessarily diluted.
Usually 1 to 5 bed volumes of water are sufficient. Then, as recommended by the resin producers, theregeneration is carried out with dilute solution of caustic soda through the pipe 48/49 and the regenerate is washed with water until it is free from alkali.
The regenerate running off through pipe 50 contains the tungstate catalyst in addition to small amounts of tartaric acid, epoxy-succinic acid and maleic acid and/or their sodium salts. In a diluted aqueous solution said tungstate catalyst can be returned to the reaction stage almost quantitatively and can be used, for example, for preparing the mixture in pipe 18.
It is required to install at least sufficient anion exchange resin in the columns 12, 13 and 14 such that the regener-ation and the washing of an anion exchange column by the capacity of the installed resin occurs only so infrequently so that the amount of water introduced with the wash water and with the dilute solution of caustic soda and returend through pipe 50 can be used for the production of the solution fed into the reactors l and 2 through pipes 17, 18, and 20.
Prior to its reuse the regnerate in pipe 50 is treated with active carbon since it was found that when carrying out the process continuously yellowish-brown impurities are occasionally adsorbed to the anion exchange resin. During the regeneration of the resin said impurities get into the regenerate in pipe 50 and render it impure. The purification can be so carried out that 0.05 to 1% by weight, preferably 0.1 to 0.4~ by weight of active carbon, relative to the solution, is stirred in, preferably at room temperature. After a period of 5 minutes to 5 hours the solution is filtered off the active carbon and the completely uncolored solution is reused. Temperatures higher or lower than room temper-ature can also be used. Methods other than the stirring-in method, for example, columnar methods, in which the colored solution is passed over an active-carbon tower, can also be used.
The solution present in pipe 40 after hydrolysis and anion exchange can then be processed. Such solution is essentially free from tungstic acid and contains the entire dl-tartaric acid as well as corresponding amountsof mesotartaric acid and possibly unreacted epoxy succinic acid in addition to small amounts of maleic acid, which was either not reacted or not separated at the anion exchanger, or traces of fumaric acid (see Church and Blumberg loc. cit.).
If required, after evaporating water, the solution is cooled, the racemic acid is filtered off, rewashed with water and subsequently dried. For example, after evaporating to dryness, the mesotartaric acid can be recovered in mixture with non-crystal-lized racemic acid and the residual contents of maleic acid cis-epoxy succinic acid. The evaporation is suitably carried out at temperatures between 40 and 50C, preferably between 60 and 110C
and the crystallization at temperatures from 1 to 25C.
In order to produce particularly pure racemic acid, the solution is suitably subjected to fractional crystallization. For this purpose, in a preferred manner of carrying out the process (see Fig. 1) the solution is passed from the pipe 40, for example, to a rotary evaporator 15, in which a partial amount of water is distilled off through pipe 41, under vacuum or pressure.
The amount of water depends on the concentration of the solution of racemic acid, mesotartaric acid, cis-epoxy succinic acid and maleic acid coming from the anion exchanger and on the expected degree of purity of the racemic acid. The solution with increased concentration is fed to a crystallization and filtration stage through pipe 43 so that racemic acid which had been once crystallized is obtained in pipe 45 and the aqueous mother liquor (referred to hereafter as Mula I) is obtained in pipe 46. The pipes 42 and 44 serve merely for ventilation and for maintaining the pressure.
The Mula I thus obtained can then be evaporated in a corresponding manner to a further racemic acid fraction, which can have a lower degree of purity corresponding to the solubility and concentration of the other components. The number of fractions can be chosen arbitrarily. However, it is favourable to crystallize not more than 2 to 4 fractions and to evaporate the last mother liquor to dryness.
When processing the last mother liquor it was found to be favourable that said mother liquor contains as little cis-epoxy succinic acid as possible since this acid does not readily crystallize and tends to stick, thus rendering the processing more difficult. However, since even at high reaction rates of 98 to 99% of cis-epoxy succinic acid in the mother liquors during the hydrolysis the concentration increases distinctly, it is, technical-ly speaking, particularly favourable to carry out the evaporation under conditions at which the hydrolysis of the epoxy succinic acid is continued (see Example 2 hereinafter)in order to avoid long reaction times for the actual hydrolysis in the tank 11. For example, a mother liquor can be subjected, with advantage, to an after-saponification (see Example 3 hereinafter) since at this point the total volumne of the solution is distincltly lower than that of the ~058634 solution in the only hydrolysis in tank 11 and since thus only small tanks are required.
As mentioned hereinbefore, the advance in the art of the process according to the invention lies first in the produc-tion or racemic acid, which is very pure with respect to maleic acid, fumaric acid and impurities caused by the catalyst.
According to Deutsches Arzneimittelbuch 7, for natural tartaric acid and maximum content of heavy metals (in terms of lead) of 20 p.p.m. is admissible. The tungsten content of the dl-tartaric obtained by means of the process according to the invention is lower than S p.p.m. According to the US Food Chemical Index of 1966, dl-malic acid, which is produced from maleic acid and is used in the food sector, may contain a maximum of 0.05%
by weight of maleic acid and 0.7% by weight of fumaric acid.
The dl-tartaric obtained according to the process of the invention contains less than 0.02% by weight of maleic acid and fumaric acid and thus has the degree of purity required for food. Moreover, as mentioned hereinbefore, the process according to the invention is technically easy to carry out since only aqueous solutions are used up to the crystallization of the tartaric acid. Further, the recovered catalyst can be immediately returned to the reaction stage.
The present invention will be further illustrated by way of the following Examples.
Example 1 The process is carried out in an apparatus corresponding to Figure 1. The data hereafter relate to a continuous procedure upon reaching the steady state.
2.27 moles/h of maleic acid and 2.76 moles/h of H2O2 in 820 g/h of an aqueous solution are fed to reactor 1 through pipe 17 and 3.6 moles/h of NaOH and 0.032 mole/h of Na2WO4 in 830 g/h of an aqueous solution are fed to reactor 1 through pipe 18.
Small amounts of an acid mixture recycled through pipe 50 are also fed to reactor 1. Moreover, 80 g/h of an aqueous solution with 0.395 mole/h of NaOH are additionally added in reactor 2 through 20. The reactors 1, 2 and 3 are operated at a temperature of approximately 80C. The operating volume of reactor 1 is 1650 ml and that of reactor 2 is 1280 ml. The secondary reaction zone 3 consists of a tube having a length of 5.40 m and a diameter of 38 mm. The tube is packed with 4 mm Raschig rings.
The column 4 is operated at approximately 80C and con-sists of a tube (38 mm diameter), which is filled with 1100 ml of a catalyst consisting of 0.1% of platinum on a chemically inert support having very few pores. More than 90% of said support consists of silicon dioxide. The granular size of said support is between 3 and 5 mm.
The residual content of H2O2 in the mass flow in the pipe 23 is approximately 0.6%. Upon leaving the decomposition catalyst the hydrogen peroxide in the pipe 25 is almost quantitatively destroyed. Approximately 1720 g/h of an aqueous solution, which contains approximately 0.011 mole/h of maleic acid and 0.25 mole/h of tartaric acid in the form of their sodium salts in addition to cis-epoxy succinic acid flow through pipe 25 into the intermediate tank 5, which is kept at a temperature of 40C. The solution is fed to the cation exchangers 6 and 7 through pipe 26, which is heated to approximately 40C. The diameter of the exchange columns is 10 mm. The columns are filled with approximately 11 litres of a cation exchanger, based on polystyrene containing free sulphon-ic acid groups, and a small amount of inert resin. In the swollen state the exchange resin fills approximately 95% of the free space between two sieve plates.
At the beginning of the charging cycle column 4 is filled with product and column 7 is emptied after the regeneration.
An average of 3500 to 4000 g/h is conveyed at a constant flow ~058634 from the tank 5 corresponding to the feed through pipes 25 and 29. As soon as the sodium ions start to break through at the top of the column 6 the flow through pipe 26 is switched over to column 7, from where it is conveyed to the completely regenerated column 8. The washing and regenerating of an exhausted column is explained hereafter,using the column 8 as an example. First, the column 8 is emptied into tank 9 through pipe 28. From tank 9 the flow is returned to tank 5 through pipe 29. The preconcentrated wash water in tank 10 is then used for rewashing. The discharge is also returned to tank 5 by way of the tank 9. The column 8 is then rewashed with 4.5 kg of water completely free from salt. This water is returned through pipe 28 tank 9 and pipe 30 to tank 10.
The column is then regenerated with 13.5 kg of a 6.5% by weight hydrochloric acid through the pipe 33/34 and rewashed with 15 litres of water, which is completely free from salt. On the average, the washing and regenerating operation must be repeated every 4.5 to 5 hours.
From pipe 27 an average of approximately 2700 g/h of an aqueous solution of cis-epoxy succinic acid containing 11 mole ~ of tartaric acid, relative to the total acid, traces of maleic acid and the entire tungstic acid flows to the tank 11 in a concentration of 0.84 mole of dibasic acid per 1000 g. The washing operation at the cation exchanger merely resulted in a dilution of approximately 64% of the initial concentration of losses amounting to approximately 0.5% of the material applied. In tank 11 the solution is boiled for 5 hours under reflux at approximately 100C. In order to make the further operation continuous, a second tank is run in parallel in a two point control arrangement (not shown).
On completing the hydrolysis and cooling to room temperature, 2700 g/h of an aqueous solution are passed through pipe 37/38 from below over the anion exchange columns 13, 14. The anion exchange columns 13 and 14 are in cascade connection.
Along with the aqueous solution 2.03 moles/h of racemic acid, 0.13 mole/h of mesotartaric acid, 0.06 mole/h of cis-epoxy succinic acid and 0.01 mole/h of maleic acid as well as the entire tungsten catalyst are conveyed. Three columns having inside diameters of approximately 43 mm are used as anion exchangers and filled with approximately 1.3 litres of a macroporous, monofunctional weakly basic anion exchange resin based on polystyrene, occupying (in the non-charged state) approximately 60% of the space between two sieve plates. The ion exchange is carried out according to the fluidized bed process. After 24 hours when the tungsten breaks through a column is regenerated as previously described and is switched, as a fine purification column, behind the column which is operated to the change-over point as a fine purification column.
The washing and regenerating operation is described here-after, using the column 12 as an example. First, the column con-tents is displaced with 3.5 kg of water, which is completely free from salt, through pipe 47 and returned through pipe 39. Accord-ing to the data provided by the resin producer, 3.2 kg of a 4% by weight solution of caustic soda are used for regenerating through the pipe 48/49, whereupon 5.2 kg of water, which is completely free from salt, are used for washing until the solution is free from alkali. In order to prevent the product from being diluted, the water level is always kept only slightly above the resin.
In order to remove a yellow colouration, the aqueous regenerate is treated for approximately 30 minutes with 0.2% of pulverized active carbon and then filtered off the active carbon, whereupon it is returned through the pipe 50 for reuse.
On the average per unit of time 2.23 moles/h of dibasic acids and approximately 2500 g/h of water flow through pipe 40 and are fed to a rotary evaporation 15, in which approximately 1400 ml 105~634 of water per hour are evaporated in vacuo at a temperature of approximately 80C through pipe 41. The solution, whose concentra-tion is thus increased, is discontinuously cooled in a vessel with stirrer (not shown) to approximately 5C. The crystallized racemic acid is filtered off and twice rewashed with 10% by weightof cold distilled water, relative to the solids. Upon drying (converted into gram per hour) 209g/h, i.e., 61,5% (rela-tive to maleic acid) of a racemic acid containing a maximum of 2 to 3 p.p.m. of tungsten and less than 0.02% of maleic acid and fumaric acid are obtained.
Approximately 1200 g/h of the mother liquor of this first inlet state still contain 96% of racemic acid, 19.5 g of mesotartaric acid, 7.9 g of cis-epoxy succinic acid and 1.1 g of maleic acid. On evaporating approximately 800 ml/h of water at approximately 80C, followed by crystallization at approximately 5C and rewashing with cold water as in the first crystallization and drying, 74 g/h of dl-tartaric acid (21.6% relative to maleic acid) containing approximately 0.02 to 0.03% of maleic acid, less than 0.02% of fumaric acid and less than 5 p.p.m. of tungsten are obtained.
The mesotartaric acid fraction of 15.1%, relative to maleic acid, can be obtained by evaporation to dryness. It contains 38.5% by weight of mesotartaric acid in addition to 43.5% by weight of racemic acid, 15.6% by weight of epoxy succinic acid and 2.4% by weight of maleic acid. The mixture as such can be used industrially. However, it can also be purified by further fractional crystallization and the racemic acid can be separated more completely.
From the regenerate of the ion exchanger in pipe 50, 8.9 kg of a solution containing 247.7 g of sodium tungstate, i.e., 99.75% of the amount used, and samll amounts of the sodium salts of acid encountered in the reaction are obtained every 24 hours.
1~58634 This solution-made up with caustic soda solution, water and very small amounts of sodium tungstate-results in a mixture which i9 fed into the reaction stage directly through the pipe 18.
Example 2 A flow of 2500 g/h of H2O and an average of 2.23 moles/h of dibasic acids are drawn off through pipe 40, as explained in Example 1, but the flow is then fed to a rotary evaporator having an operating content of 1950 ml. In said rotary evaporator approximately 1400 ml of water are evaporated under pressure at a boiling temperature of 112C, followed by processing as described in Example 1. Thus, in the first crystallization 62.5%
of racemic acid (relative to maleic acid) of corresponding purity are obtained. After the secondevaporation and crystallization, which is carried out as in Example 1, 22% of racemic acid having the same purity as in Example 1 are obtained. Then, on evapora-tion to dryness a mixture of mesotartaric acid (6%), racemic acid (6%), maleic acid (0.5%) and epoxy succinic acid (0.3%), each percentage relative to maleic acid used is obtained.
In contrast to Example 1, in which a mesotartaric acid fraction containing 15.6~ of epoxy succinic acid is obtained, the mesotartaric acid fraction obtained in the present case contains only 2.1% of epoxy succinic acid, the difference being converted into racemic acid and mesotartaric acid. Moreover, a less tacky product is thus obtained, facilitating the processing.
Example 3 In order to improve the reaction with respect to epoxy succinic acid, a secondary hydrolysis of the mother liquor of the second crystallization can be carried out as is evident from this example.
1 litre of the mother liquor of the second crystalliza-tion obtained according to example 1 was boiled in a glass flask for 5 hours under reflux. The solution contained 1.01 moles of a mixture of dibasic acids per 1000 g. The mixture consisted of 15.5 mole ~ of maleic acid, 35 mole % of racemic acid, 37 mole %
of mesotartaric acid and 12.5 mole % of epoxy succinic acid. After 5 hours of secondary hydrolysis the solution contained 14.5 mole % of maleic acid, 42 mole % of racemic acid, 39 mole % of mesotar-taric acid, 1 mole % of fumaric acid and approximately 3.5 mole of epoxy succinic acid.
The rate of reaction in the secondary hydrolysis, rela-tive to epoxy succinic acid, is 72%, whereby additional racemic acid and mesotartaric acid are formed.
Example 4 A solution obtained according to Example 1 through pipe 27 was nDt hydrolysed but was first passed over an anion exchanger, as generally described in Example 1.
The solution contained 0.97 mole of a mixture of dibasic acid per 1000 g, i.e., 0.20 mole of tartaric acid per 1000 g and 0.75 mole of epoxy succinic acid per 1000 g. The tungsten content of the solution was lower than 2 p.p.m. (not detectable). After the hydrolysis at 95C the product distribution, relative to the initial content of epoxy succinic acid and tartaric acids, was as follows:
-mole % of mesotartaric epoxy succinic selectivity of dl-tartaric acid acid mesotartaric mlnutes acid acid, relative to tartaric acids formed 210 S9 9 32 13.2 285 65 11 24 14.5 403 70 14 16 16.7 1390 83 17 (< 0.5) 17 According to the procedure described in Example 1 a selectivity of 6% of mesotartaric acid relative to tartaric acids formed at a rate of reaction of epoxy succinic acid of 97%
105863~
was attained.
The analytical data in Example 4 were obtained with the aid of a method of nuclear resonance.
Example 5 300 g of a solution, which contained 1.31 moles of dibasic acids per 1000 g and had been produced analogously to the product obtained by way of the pipe 27 in Example 1, had a content of 0.013 moles of tungstic acid per 1000 g. The solution was boiled in a glass flask for 5 hours with reflux.
Relative to the acid applied, 4.3 mole % of epoxy succinic acid, 9.2 mole % of mesotartaric acid and 86.4 mole %
of dl-tartaric acid were obtained. The selectivity of mesotartaric acid, relative to tartaric acids formed, was 9.6%.
The same solution was passed over a weakly basic, macroporous anion exchanger based on polystyrene with exchange-active amino groups and after the exchange it contained less than 2 p.p.m. of tungsten. The acid concentration was 1.335 moles of dibasic acid per 1000 g of solution. 300 g of the solution were boiled for S hours under reflux. After processing, 64.1 mole %
of dl-tartaric acid, 17.2 mole % of mesotartaric acid and 18.3 mole % of epoxy succinic acid of the acids applied were obtained.
The selectivity of mesotartaric acid was 21.2%, relative to tartaric acids formed.
The analytical results of Example 5 were obtained by fractional crystallization on evaporating and identifying the fractions.
The washing of an exhausted exchange column and its re-generation will now be explained hereafter with reference to Figure 1, using column 8 as an example. This method has proved to be particularly advantageous with respect to saving wash water and preventing the product solution from being diluted too much while the losses of product are only low. Thus, the process can be so carried out that the solution in the column is displaced by a subsequent solution. It is merely necessary to take precau-tions that the regenerating acid is not mixed with the flow of product.
The contents of the column 8 is returned first to the tank 5 through the pipe 28, the tank 9 and the pipe 29 and then rewashed with preconcentrated wash water from tank 10, pipe 31 and column 8. The discharge from column 8 also returns to the tank 5 through the pipe 28, tank 9 and pipe 29, whereupon it is rewashed with distilled water through the pipe 32. This discharge is fed to the tank 10 through the pipe 28, tank 9 and pipe 30 and is reused in the next cycle. The subsequent regener-ation with rewashing can be carried out in a conventional manner, for example, with dilute hydrochloric acid, as defined by the resin producers, through the pipes 33/34 and 35. It is advantageous to drain the last wash water and to charge the empty column 8 in order to avoid unnecessary dilution of the product.
The aqueous solution of epoxy succinic acid and tungstic acid which is obtained after the cation exchanger and still contains small amounts of non-reacted maleic acid and small amounts of tartaric acid is then reacted to form tartaric acid at temperatures from 50 to 200C, preferably at temperature~ from 100 to 150C.
The procedure may be such that the solution, through the pipe 27, is boiled directly in the tank 11, for example, for 5 hours under reflux. However, the procedure may also be such that the solution from pipe 27 is passed through the pipe 37 to the anion exchangers 13 and 14 at temperatures of approximately 20 to 95C. These temperatures are limited by the stability of the anion exchangers.
The solution of the epoxy succinic acid, which is free from tungstic acid and is discharged through the pipe 40, is then hydrolyzed.
The hydrolysis of aqueous cis-epoxy-succinic acid solution is known (see R, Kuhn and F. Ebel, Ber. 58 B, 919 (1925); G. Wode, Svensk Kem. Tids. 40, 221 (1928) and C.A. 23 (1929, 2344 as well as laid-open German Specification 2 400 767).
Surprisingly it was found that the proportion of mesotar-taric acid, which is unexpectedly formed in the hydrolysis of the cis-epoxy succinic acid, depends on whether the hydrolysis is carried out prior to or after the anion exchange. This is so much more surprising since according to R. Kuhn et al. (loc. cit.) and the laid-open German Specification No. 2,400,767 even in the hydrolysis of an aqueous solution of cis-epoxy succinic acid, which correspon-ds to the solution obtained after the anion exchanger in the process according to the invention, only dl-tartaric acid is formed.
However, according to the process of the invention it was found that the proportion of mesotartaric acid formed can be substantially reduced when the hydrolysis is carried out in the presence of 0.1 to 5, preferably 1 to 2 mole % of tungstic acid relative to the cis-epoxy succinic acid, i.e., prior to the anion exchange as will be seen from Examples 4 and 5 given hereinafter.
According to the process of the invention it is also possible to so adjust the conditions according to requirements that selectively more or less mesotartaric acid is formed. Thus, depending on requirements, more or less dl-tartaric acid can be obtained and in cases in which dl-tartaric acid can be used only insufficiently or not at all it can be made up or replaced by mesotartaric acid. For example, this is the case when the solubility of the dl-tartaric acid is not sufficient for specific purposes. Since the dl-tartaric acid differs from the natural tartaric acid by its substantially poorer solubility while the solubility of mesotartaric acid is close so that of natural tartaric acid, a solution having higher proportions of mesotartaric acid can be produced whenever the solubility of the dl-tartaric acid is not sufficient for the purpose concerned in a technical field of application, as for example, in the building material industry or in the galvanic industry.
The use of anion exchangers for removing tungstate-containing compounds even in the presence of polybasic, complex-forming acids, such as citric acid, is known per se (see D. Shishkov, E. Koleva, Doklady, Bolg. Akad. Nauk 17 (10) 909 (1964) and C.Z.
(1966) 27-538). It was found that there usually is a possibility of purifying racemic-acid solutions by passing them over anion exchangers. Any type of commercial anion exchanger can be used, preferably weakly basic anion exchangers based on polystyrene or polystyrene/divinyl benzene and having macroporous structures and amino functions as exchange-active groups.
In the process according to the invention it is immater-ial whether the anion exchange is carried out by means of a known parallel-flow, counterflow or continuous ion-exchange process.
This exchange process is also shown in Figure 1, i.e., in the columns 12, 13 and 14 which can be correspondingly controlled as described for the cation exchange in the columns 6, 7 and 8.
Accordingly three columns are used which are charged from below in a counterflow to the regeneration. Two of these columns are in series connection while the third column is in the regeneration.
The first exchange column is operated preferably up to the discharge of tungsten while the second exchange column, which is always freshly regenerated, serves for fine purification. At variance with the cation exchange, one of the usual countercurrent techni-ques, for example, the fluidized bed process, must be applied (see Dorfner loc. cit.). The regeneration and washing of an exhausted column are described with reference to Figure 1, using the column 12 as an example, that is to say a most favourable method. The contents of the column 12 is displaced first with distilled water through pipe 47 and returned by way of the pipe 39 for use in the anion exchangers 13 or 14. As little water as possible is used so that the product is not unnecessarily diluted.
Usually 1 to 5 bed volumes of water are sufficient. Then, as recommended by the resin producers, theregeneration is carried out with dilute solution of caustic soda through the pipe 48/49 and the regenerate is washed with water until it is free from alkali.
The regenerate running off through pipe 50 contains the tungstate catalyst in addition to small amounts of tartaric acid, epoxy-succinic acid and maleic acid and/or their sodium salts. In a diluted aqueous solution said tungstate catalyst can be returned to the reaction stage almost quantitatively and can be used, for example, for preparing the mixture in pipe 18.
It is required to install at least sufficient anion exchange resin in the columns 12, 13 and 14 such that the regener-ation and the washing of an anion exchange column by the capacity of the installed resin occurs only so infrequently so that the amount of water introduced with the wash water and with the dilute solution of caustic soda and returend through pipe 50 can be used for the production of the solution fed into the reactors l and 2 through pipes 17, 18, and 20.
Prior to its reuse the regnerate in pipe 50 is treated with active carbon since it was found that when carrying out the process continuously yellowish-brown impurities are occasionally adsorbed to the anion exchange resin. During the regeneration of the resin said impurities get into the regenerate in pipe 50 and render it impure. The purification can be so carried out that 0.05 to 1% by weight, preferably 0.1 to 0.4~ by weight of active carbon, relative to the solution, is stirred in, preferably at room temperature. After a period of 5 minutes to 5 hours the solution is filtered off the active carbon and the completely uncolored solution is reused. Temperatures higher or lower than room temper-ature can also be used. Methods other than the stirring-in method, for example, columnar methods, in which the colored solution is passed over an active-carbon tower, can also be used.
The solution present in pipe 40 after hydrolysis and anion exchange can then be processed. Such solution is essentially free from tungstic acid and contains the entire dl-tartaric acid as well as corresponding amountsof mesotartaric acid and possibly unreacted epoxy succinic acid in addition to small amounts of maleic acid, which was either not reacted or not separated at the anion exchanger, or traces of fumaric acid (see Church and Blumberg loc. cit.).
If required, after evaporating water, the solution is cooled, the racemic acid is filtered off, rewashed with water and subsequently dried. For example, after evaporating to dryness, the mesotartaric acid can be recovered in mixture with non-crystal-lized racemic acid and the residual contents of maleic acid cis-epoxy succinic acid. The evaporation is suitably carried out at temperatures between 40 and 50C, preferably between 60 and 110C
and the crystallization at temperatures from 1 to 25C.
In order to produce particularly pure racemic acid, the solution is suitably subjected to fractional crystallization. For this purpose, in a preferred manner of carrying out the process (see Fig. 1) the solution is passed from the pipe 40, for example, to a rotary evaporator 15, in which a partial amount of water is distilled off through pipe 41, under vacuum or pressure.
The amount of water depends on the concentration of the solution of racemic acid, mesotartaric acid, cis-epoxy succinic acid and maleic acid coming from the anion exchanger and on the expected degree of purity of the racemic acid. The solution with increased concentration is fed to a crystallization and filtration stage through pipe 43 so that racemic acid which had been once crystallized is obtained in pipe 45 and the aqueous mother liquor (referred to hereafter as Mula I) is obtained in pipe 46. The pipes 42 and 44 serve merely for ventilation and for maintaining the pressure.
The Mula I thus obtained can then be evaporated in a corresponding manner to a further racemic acid fraction, which can have a lower degree of purity corresponding to the solubility and concentration of the other components. The number of fractions can be chosen arbitrarily. However, it is favourable to crystallize not more than 2 to 4 fractions and to evaporate the last mother liquor to dryness.
When processing the last mother liquor it was found to be favourable that said mother liquor contains as little cis-epoxy succinic acid as possible since this acid does not readily crystallize and tends to stick, thus rendering the processing more difficult. However, since even at high reaction rates of 98 to 99% of cis-epoxy succinic acid in the mother liquors during the hydrolysis the concentration increases distinctly, it is, technical-ly speaking, particularly favourable to carry out the evaporation under conditions at which the hydrolysis of the epoxy succinic acid is continued (see Example 2 hereinafter)in order to avoid long reaction times for the actual hydrolysis in the tank 11. For example, a mother liquor can be subjected, with advantage, to an after-saponification (see Example 3 hereinafter) since at this point the total volumne of the solution is distincltly lower than that of the ~058634 solution in the only hydrolysis in tank 11 and since thus only small tanks are required.
As mentioned hereinbefore, the advance in the art of the process according to the invention lies first in the produc-tion or racemic acid, which is very pure with respect to maleic acid, fumaric acid and impurities caused by the catalyst.
According to Deutsches Arzneimittelbuch 7, for natural tartaric acid and maximum content of heavy metals (in terms of lead) of 20 p.p.m. is admissible. The tungsten content of the dl-tartaric obtained by means of the process according to the invention is lower than S p.p.m. According to the US Food Chemical Index of 1966, dl-malic acid, which is produced from maleic acid and is used in the food sector, may contain a maximum of 0.05%
by weight of maleic acid and 0.7% by weight of fumaric acid.
The dl-tartaric obtained according to the process of the invention contains less than 0.02% by weight of maleic acid and fumaric acid and thus has the degree of purity required for food. Moreover, as mentioned hereinbefore, the process according to the invention is technically easy to carry out since only aqueous solutions are used up to the crystallization of the tartaric acid. Further, the recovered catalyst can be immediately returned to the reaction stage.
The present invention will be further illustrated by way of the following Examples.
Example 1 The process is carried out in an apparatus corresponding to Figure 1. The data hereafter relate to a continuous procedure upon reaching the steady state.
2.27 moles/h of maleic acid and 2.76 moles/h of H2O2 in 820 g/h of an aqueous solution are fed to reactor 1 through pipe 17 and 3.6 moles/h of NaOH and 0.032 mole/h of Na2WO4 in 830 g/h of an aqueous solution are fed to reactor 1 through pipe 18.
Small amounts of an acid mixture recycled through pipe 50 are also fed to reactor 1. Moreover, 80 g/h of an aqueous solution with 0.395 mole/h of NaOH are additionally added in reactor 2 through 20. The reactors 1, 2 and 3 are operated at a temperature of approximately 80C. The operating volume of reactor 1 is 1650 ml and that of reactor 2 is 1280 ml. The secondary reaction zone 3 consists of a tube having a length of 5.40 m and a diameter of 38 mm. The tube is packed with 4 mm Raschig rings.
The column 4 is operated at approximately 80C and con-sists of a tube (38 mm diameter), which is filled with 1100 ml of a catalyst consisting of 0.1% of platinum on a chemically inert support having very few pores. More than 90% of said support consists of silicon dioxide. The granular size of said support is between 3 and 5 mm.
The residual content of H2O2 in the mass flow in the pipe 23 is approximately 0.6%. Upon leaving the decomposition catalyst the hydrogen peroxide in the pipe 25 is almost quantitatively destroyed. Approximately 1720 g/h of an aqueous solution, which contains approximately 0.011 mole/h of maleic acid and 0.25 mole/h of tartaric acid in the form of their sodium salts in addition to cis-epoxy succinic acid flow through pipe 25 into the intermediate tank 5, which is kept at a temperature of 40C. The solution is fed to the cation exchangers 6 and 7 through pipe 26, which is heated to approximately 40C. The diameter of the exchange columns is 10 mm. The columns are filled with approximately 11 litres of a cation exchanger, based on polystyrene containing free sulphon-ic acid groups, and a small amount of inert resin. In the swollen state the exchange resin fills approximately 95% of the free space between two sieve plates.
At the beginning of the charging cycle column 4 is filled with product and column 7 is emptied after the regeneration.
An average of 3500 to 4000 g/h is conveyed at a constant flow ~058634 from the tank 5 corresponding to the feed through pipes 25 and 29. As soon as the sodium ions start to break through at the top of the column 6 the flow through pipe 26 is switched over to column 7, from where it is conveyed to the completely regenerated column 8. The washing and regenerating of an exhausted column is explained hereafter,using the column 8 as an example. First, the column 8 is emptied into tank 9 through pipe 28. From tank 9 the flow is returned to tank 5 through pipe 29. The preconcentrated wash water in tank 10 is then used for rewashing. The discharge is also returned to tank 5 by way of the tank 9. The column 8 is then rewashed with 4.5 kg of water completely free from salt. This water is returned through pipe 28 tank 9 and pipe 30 to tank 10.
The column is then regenerated with 13.5 kg of a 6.5% by weight hydrochloric acid through the pipe 33/34 and rewashed with 15 litres of water, which is completely free from salt. On the average, the washing and regenerating operation must be repeated every 4.5 to 5 hours.
From pipe 27 an average of approximately 2700 g/h of an aqueous solution of cis-epoxy succinic acid containing 11 mole ~ of tartaric acid, relative to the total acid, traces of maleic acid and the entire tungstic acid flows to the tank 11 in a concentration of 0.84 mole of dibasic acid per 1000 g. The washing operation at the cation exchanger merely resulted in a dilution of approximately 64% of the initial concentration of losses amounting to approximately 0.5% of the material applied. In tank 11 the solution is boiled for 5 hours under reflux at approximately 100C. In order to make the further operation continuous, a second tank is run in parallel in a two point control arrangement (not shown).
On completing the hydrolysis and cooling to room temperature, 2700 g/h of an aqueous solution are passed through pipe 37/38 from below over the anion exchange columns 13, 14. The anion exchange columns 13 and 14 are in cascade connection.
Along with the aqueous solution 2.03 moles/h of racemic acid, 0.13 mole/h of mesotartaric acid, 0.06 mole/h of cis-epoxy succinic acid and 0.01 mole/h of maleic acid as well as the entire tungsten catalyst are conveyed. Three columns having inside diameters of approximately 43 mm are used as anion exchangers and filled with approximately 1.3 litres of a macroporous, monofunctional weakly basic anion exchange resin based on polystyrene, occupying (in the non-charged state) approximately 60% of the space between two sieve plates. The ion exchange is carried out according to the fluidized bed process. After 24 hours when the tungsten breaks through a column is regenerated as previously described and is switched, as a fine purification column, behind the column which is operated to the change-over point as a fine purification column.
The washing and regenerating operation is described here-after, using the column 12 as an example. First, the column con-tents is displaced with 3.5 kg of water, which is completely free from salt, through pipe 47 and returned through pipe 39. Accord-ing to the data provided by the resin producer, 3.2 kg of a 4% by weight solution of caustic soda are used for regenerating through the pipe 48/49, whereupon 5.2 kg of water, which is completely free from salt, are used for washing until the solution is free from alkali. In order to prevent the product from being diluted, the water level is always kept only slightly above the resin.
In order to remove a yellow colouration, the aqueous regenerate is treated for approximately 30 minutes with 0.2% of pulverized active carbon and then filtered off the active carbon, whereupon it is returned through the pipe 50 for reuse.
On the average per unit of time 2.23 moles/h of dibasic acids and approximately 2500 g/h of water flow through pipe 40 and are fed to a rotary evaporation 15, in which approximately 1400 ml 105~634 of water per hour are evaporated in vacuo at a temperature of approximately 80C through pipe 41. The solution, whose concentra-tion is thus increased, is discontinuously cooled in a vessel with stirrer (not shown) to approximately 5C. The crystallized racemic acid is filtered off and twice rewashed with 10% by weightof cold distilled water, relative to the solids. Upon drying (converted into gram per hour) 209g/h, i.e., 61,5% (rela-tive to maleic acid) of a racemic acid containing a maximum of 2 to 3 p.p.m. of tungsten and less than 0.02% of maleic acid and fumaric acid are obtained.
Approximately 1200 g/h of the mother liquor of this first inlet state still contain 96% of racemic acid, 19.5 g of mesotartaric acid, 7.9 g of cis-epoxy succinic acid and 1.1 g of maleic acid. On evaporating approximately 800 ml/h of water at approximately 80C, followed by crystallization at approximately 5C and rewashing with cold water as in the first crystallization and drying, 74 g/h of dl-tartaric acid (21.6% relative to maleic acid) containing approximately 0.02 to 0.03% of maleic acid, less than 0.02% of fumaric acid and less than 5 p.p.m. of tungsten are obtained.
The mesotartaric acid fraction of 15.1%, relative to maleic acid, can be obtained by evaporation to dryness. It contains 38.5% by weight of mesotartaric acid in addition to 43.5% by weight of racemic acid, 15.6% by weight of epoxy succinic acid and 2.4% by weight of maleic acid. The mixture as such can be used industrially. However, it can also be purified by further fractional crystallization and the racemic acid can be separated more completely.
From the regenerate of the ion exchanger in pipe 50, 8.9 kg of a solution containing 247.7 g of sodium tungstate, i.e., 99.75% of the amount used, and samll amounts of the sodium salts of acid encountered in the reaction are obtained every 24 hours.
1~58634 This solution-made up with caustic soda solution, water and very small amounts of sodium tungstate-results in a mixture which i9 fed into the reaction stage directly through the pipe 18.
Example 2 A flow of 2500 g/h of H2O and an average of 2.23 moles/h of dibasic acids are drawn off through pipe 40, as explained in Example 1, but the flow is then fed to a rotary evaporator having an operating content of 1950 ml. In said rotary evaporator approximately 1400 ml of water are evaporated under pressure at a boiling temperature of 112C, followed by processing as described in Example 1. Thus, in the first crystallization 62.5%
of racemic acid (relative to maleic acid) of corresponding purity are obtained. After the secondevaporation and crystallization, which is carried out as in Example 1, 22% of racemic acid having the same purity as in Example 1 are obtained. Then, on evapora-tion to dryness a mixture of mesotartaric acid (6%), racemic acid (6%), maleic acid (0.5%) and epoxy succinic acid (0.3%), each percentage relative to maleic acid used is obtained.
In contrast to Example 1, in which a mesotartaric acid fraction containing 15.6~ of epoxy succinic acid is obtained, the mesotartaric acid fraction obtained in the present case contains only 2.1% of epoxy succinic acid, the difference being converted into racemic acid and mesotartaric acid. Moreover, a less tacky product is thus obtained, facilitating the processing.
Example 3 In order to improve the reaction with respect to epoxy succinic acid, a secondary hydrolysis of the mother liquor of the second crystallization can be carried out as is evident from this example.
1 litre of the mother liquor of the second crystalliza-tion obtained according to example 1 was boiled in a glass flask for 5 hours under reflux. The solution contained 1.01 moles of a mixture of dibasic acids per 1000 g. The mixture consisted of 15.5 mole ~ of maleic acid, 35 mole % of racemic acid, 37 mole %
of mesotartaric acid and 12.5 mole % of epoxy succinic acid. After 5 hours of secondary hydrolysis the solution contained 14.5 mole % of maleic acid, 42 mole % of racemic acid, 39 mole % of mesotar-taric acid, 1 mole % of fumaric acid and approximately 3.5 mole of epoxy succinic acid.
The rate of reaction in the secondary hydrolysis, rela-tive to epoxy succinic acid, is 72%, whereby additional racemic acid and mesotartaric acid are formed.
Example 4 A solution obtained according to Example 1 through pipe 27 was nDt hydrolysed but was first passed over an anion exchanger, as generally described in Example 1.
The solution contained 0.97 mole of a mixture of dibasic acid per 1000 g, i.e., 0.20 mole of tartaric acid per 1000 g and 0.75 mole of epoxy succinic acid per 1000 g. The tungsten content of the solution was lower than 2 p.p.m. (not detectable). After the hydrolysis at 95C the product distribution, relative to the initial content of epoxy succinic acid and tartaric acids, was as follows:
-mole % of mesotartaric epoxy succinic selectivity of dl-tartaric acid acid mesotartaric mlnutes acid acid, relative to tartaric acids formed 210 S9 9 32 13.2 285 65 11 24 14.5 403 70 14 16 16.7 1390 83 17 (< 0.5) 17 According to the procedure described in Example 1 a selectivity of 6% of mesotartaric acid relative to tartaric acids formed at a rate of reaction of epoxy succinic acid of 97%
105863~
was attained.
The analytical data in Example 4 were obtained with the aid of a method of nuclear resonance.
Example 5 300 g of a solution, which contained 1.31 moles of dibasic acids per 1000 g and had been produced analogously to the product obtained by way of the pipe 27 in Example 1, had a content of 0.013 moles of tungstic acid per 1000 g. The solution was boiled in a glass flask for 5 hours with reflux.
Relative to the acid applied, 4.3 mole % of epoxy succinic acid, 9.2 mole % of mesotartaric acid and 86.4 mole %
of dl-tartaric acid were obtained. The selectivity of mesotartaric acid, relative to tartaric acids formed, was 9.6%.
The same solution was passed over a weakly basic, macroporous anion exchanger based on polystyrene with exchange-active amino groups and after the exchange it contained less than 2 p.p.m. of tungsten. The acid concentration was 1.335 moles of dibasic acid per 1000 g of solution. 300 g of the solution were boiled for S hours under reflux. After processing, 64.1 mole %
of dl-tartaric acid, 17.2 mole % of mesotartaric acid and 18.3 mole % of epoxy succinic acid of the acids applied were obtained.
The selectivity of mesotartaric acid was 21.2%, relative to tartaric acids formed.
The analytical results of Example 5 were obtained by fractional crystallization on evaporating and identifying the fractions.
Claims (17)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for producing pure racemic acid and mesotartaric acid by reacting alkali maleates with aqueous hydrogen peroxide in the presence of alkali tungstate, in which the molar ratio of hydrogen peroxide to maleic acid is greater than 1, the alkali salt of the cis-epoxy succinic acid so obtained together with the alkali tungstate are converted into the free epoxy succinic acid and the free tungstic acid by passing them over a strongly acid cation exchanger, and the free cis-epoxy succinic acid is hydrolysed to racemic acid and mesotartaric acid in the absence of free tungstic acid which is removed with an anion exchanger prior to hydrolysis in the case of a catalyst-free hydrolysis or in the presence of free tungstic acid removed by an anion exchanger after the hydrolysis in the case of a catalyst-containing hydrolysis, the racemic acid is crystallized from the tungstic-acid-free hydrolysis mixture, the mesotartaric acid remaining in the mother liquor is recovered therefrom either by crystallization or by evaporating to dryness and the anion exchanger charged with tungstic acid is regenerated with dilute alkali liquor.
2. A process according to claim 1, in which molar ratio of hydrogen peroxide to maleic acid is between 1.01 and 5:1.
3. A process according to claim 1, in which molar ratio of hydrogen peroxide and maleic acid is between 1.1 to 2:1 and 1.1 to 1.3:1.
4. A process according to claim 1, 2 or 3 in which the reaction is carried out in a rotary reactor.
5. A process according to claim 1, 2 or 3 in which the reaction is carried out in at least two rotary reactors in cascade.
6. A process according to claim 1, 2 or 3 in which the reaction is carried out in two reactors in cascade and in a succeeding flow tube.
7. A process as claimed in claim 1, in which excess hydrogen peroxide is destroyed before passage over the strongly acid cation exchanger.
8. A process according to claim 7, in which excess peroxide compounds are destroyed by passing the reaction mixture at 20 to 100°C over a catalyst having very few pores and containing more than 90% by weight of SiO2 and from 0.01 to 5% by weight of Pt.
9. A process according to claim 1, in which three cation exchangers based on polystyrene or polystyrene divinyl benzene containing free sulphonic acid groups are used as strongly acid cation exchangers, two of the exchangers being in cascade while the third anion exchanger is in regeneration.
10. A process according to claim 9, in which the cation exchangers are washed with wash water of increased concentration from an earlier cycle.
11. A process according to claim 1, 2 or 3 in which the racemic acid is recovered by fractional crystallization from the solution obtained after the anion exchanger.
12. A process according to claim 1, 2 or 3 in which weakly basic, macroporous resins based on polystyrene or polysty-rene divinyl benzene and exchange-active amino groups are used as anion exchangers.
13. A process according to claim 1, in which three anion exchangers are used, two of said anion exchangers being in cascade and the third in regeneration.
14. A process according to claim 13, in which a first cation exchanger is operated until sodium breaks through, and a first anion exchanger is operated until tungsten breaks through, a freshly regenerated exchanger replacing in each case as a second exchanger.
15. A process according to claim 1, 2 or 3, in which the mother liquor obtained after the crystallization of the racemic acid is subjected to an after-saponification.
16. A process as claimed in claim 1 in which the regenerated solution containing alkali tungstates is recycled directly to the epoxidation reaction.
17. A process according to claim 16, in which prior to recycling the tungstate solution is purified with active carbon.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE2508228A DE2508228C3 (en) | 1975-02-26 | 1975-02-26 | Process for the production of pure grape acid and mesotartaric acid |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1058634A true CA1058634A (en) | 1979-07-17 |
Family
ID=5939822
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA246,655A Expired CA1058634A (en) | 1975-02-26 | 1976-02-26 | Process for producing pure racemic acid and mesotartaric acid |
Country Status (6)
| Country | Link |
|---|---|
| AT (1) | AT334330B (en) |
| BE (1) | BE827604A (en) |
| CA (1) | CA1058634A (en) |
| DE (1) | DE2508228C3 (en) |
| SE (1) | SE426059B (en) |
| ZA (1) | ZA761030B (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101759554A (en) * | 2009-12-31 | 2010-06-30 | 杭州临安金龙化工有限公司 | Method for treating and utilizing potassium hydrogen tartrate mother liquor |
| TWI480259B (en) * | 2009-06-02 | 2015-04-11 | Akzo Nobel Chemicals Int Bv | Process for the preparation of a composition comprising meso-tartaric acid |
| CN115253364A (en) * | 2022-08-10 | 2022-11-01 | 安徽海蓝生物科技有限公司 | Centrifugation process and centrifugation equipment for tartaric acid solution |
| CN115286498A (en) * | 2022-08-23 | 2022-11-04 | 佳化化学科技发展（上海）有限公司 | Preparation method of meso-tartaric acid |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2754325A (en) * | 1952-05-27 | 1956-07-10 | Shell Dev | Oxidation with peroxides |
| DE1643891A1 (en) * | 1967-10-05 | 1971-05-19 | Degussa | Process for the production of calcium tartrate |
| DE2140055C3 (en) * | 1971-08-10 | 1980-10-02 | Joh. A. Benckiser Gmbh, 6700 Ludwigshafen | Process for the production of grape acid |
| JPS5136249B2 (en) * | 1973-01-13 | 1976-10-07 | ||
| DE2542536C3 (en) * | 1975-09-24 | 1982-05-19 | Degussa Ag, 6000 Frankfurt | Setting retarder for technical gypsum plaster |
-
1975
- 1975-02-26 DE DE2508228A patent/DE2508228C3/en not_active Expired
- 1975-02-28 AT AT155775A patent/AT334330B/en not_active IP Right Cessation
- 1975-04-04 BE BE6044978A patent/BE827604A/en not_active IP Right Cessation
-
1976
- 1976-02-20 ZA ZA1030A patent/ZA761030B/en unknown
- 1976-02-25 SE SE7602406A patent/SE426059B/en not_active IP Right Cessation
- 1976-02-26 CA CA246,655A patent/CA1058634A/en not_active Expired
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| TWI480259B (en) * | 2009-06-02 | 2015-04-11 | Akzo Nobel Chemicals Int Bv | Process for the preparation of a composition comprising meso-tartaric acid |
| CN101759554A (en) * | 2009-12-31 | 2010-06-30 | 杭州临安金龙化工有限公司 | Method for treating and utilizing potassium hydrogen tartrate mother liquor |
| CN101759554B (en) * | 2009-12-31 | 2013-08-14 | 杭州临安金龙化工有限公司 | Method for treating and utilizing potassium hydrogen tartrate mother liquor |
| CN115253364A (en) * | 2022-08-10 | 2022-11-01 | 安徽海蓝生物科技有限公司 | Centrifugation process and centrifugation equipment for tartaric acid solution |
| CN115253364B (en) * | 2022-08-10 | 2023-10-31 | 安徽海蓝生物科技有限公司 | Centrifugal process and centrifugal equipment for tartaric acid solution |
| CN115286498A (en) * | 2022-08-23 | 2022-11-04 | 佳化化学科技发展（上海）有限公司 | Preparation method of meso-tartaric acid |
Also Published As
| Publication number | Publication date |
|---|---|
| DE2508228A1 (en) | 1976-09-09 |
| DE2508228B2 (en) | 1979-12-13 |
| DE2508228C3 (en) | 1987-01-22 |
| AT334330B (en) | 1976-01-10 |
| BE827604A (en) | 1975-10-06 |
| ZA761030B (en) | 1977-01-26 |
| ATA155775A (en) | 1976-05-15 |
| SE426059B (en) | 1982-12-06 |
| SE7602406L (en) | 1976-08-27 |
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