CA2138153C - Electrochemical preparation of dicarboxylic acids - Google Patents
Electrochemical preparation of dicarboxylic acids Download PDFInfo
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- CA2138153C CA2138153C CA002138153A CA2138153A CA2138153C CA 2138153 C CA2138153 C CA 2138153C CA 002138153 A CA002138153 A CA 002138153A CA 2138153 A CA2138153 A CA 2138153A CA 2138153 C CA2138153 C CA 2138153C
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
- C07C51/02—Preparation of carboxylic acids or their salts, halides or anhydrides from salts of carboxylic acids
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
- B01D61/42—Electrodialysis; Electro-osmosis ; Electro-ultrafiltration; Membrane capacitive deionization
- B01D61/44—Ion-selective electrodialysis
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
- B01D61/42—Electrodialysis; Electro-osmosis ; Electro-ultrafiltration; Membrane capacitive deionization
- B01D61/44—Ion-selective electrodialysis
- B01D61/445—Ion-selective electrodialysis with bipolar membranes; Water splitting
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- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
- Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
- Separation Using Semi-Permeable Membranes (AREA)
Abstract
The invention concerns the electrochemical preparation of dicarboxylic acids by subjecting an aqueous solution containing essentially the alkali-metal salt of a dicarboxylic acid of the general formula (I): HOOC-(CH2)n-COOH, in which n may be an integer from 1 to 8, or mixtures of such dicarboxylic acids, to an electrochemical treatment.
Description
The present invention relates to a process for the electrochemical preparation of dicarboxylic acids.
Salts of the dicarboxylic acids I are obtained in a number of industrial processes, for example in the alkaline hydrolysis of polyamides. To isolate the free acids the salts are acidified, for example with hydrochloric acid according to FR-A-926,873 (published on October 14, 1947) or with sulfuric acid according to tfS-A-2,840,606 (published on April 15, 1955).
The disadvantage of this is the formation of salts such as sodium chloride or sodium sulfate and their disposal.
The preparation of an organic acid by electrodialysis is known, for example from DE-A-2,547,101 (published on May 6, 1976) which describes the electrodialysis of salt solutions of glycine, diglycinE~, triglycine, citric acid, tartaric acid, acetic acid, acrylic acid, malefic acid and ascorbic acid in a four-compartment electrolysis cell.
SU-A-401,131 (published on October 5, 1976) describes the electrochemical preparation of oxalic acid from sodium oxalate.
It is an object of the present invention to provide a process for preparing dicarboxylic acids in high purity and yield without the known disadvantages.
We have found that this object is achieved by a process for the electrochemical preparation of dicarboxylic acids, which comprises subjecting an aqueous solution containing essentially an alkali metal salt of a dicarboxylic acid of the general formula I:
HOOC-(CH2)n-COOH I
where n is an integer from 1 to 8, or mixtures thereof, to an electrochemical treatment.
The alkali metal salt used is in general the lithium, sodium or potassium salt. It is of course also possible to use mixed salts, ie. salts with two different alkali metal rations, or acid salts, ie. salts with a free acid group, or mixtures thereof.
Examples are dilithium, disodium and dipotassium malonate, succinat:e, glutarate, adipate, pimelate, octane-dioate, nonanedioate and decanedioate, sodium potassium adipate, preferably dilithium adipate, disodium adipate, dipotassium adipate, sodium potassium adipate, dilithium l0 octanedioate, disodium octanedioate and dipotassium octanedioate, particularly preferably disodium adipate.
From obsE~rvatians to date the manner of the electro-chemical treatment has in principle no bearing on the success of the process of the invention.
Fig. 1 i:~ a diagrammatical representation of a three compartment electrolysis cell comprising three liquid cycles 20 KL1 to KL3.
Fig. 2 i.s a diagrammatical representation of a four compartment electrolysis cell comprising four liquid cycles KL1 to KL4.
Fig. 3 is a diagrammatical representaiton of a membrane stack cell comprising three liquid cycles KL1 to KL3.
The elecarochemical treatment may for example take 30 one of the following forms (a) to (f):
(a) In this version the splitting of the dicarboxylate salt into tree corresponding dicarboxylic acid and the corresponding base can be carried out in a two-part electrodialysis cell using bipolar membranes. In general, the electrodialysis cell has between the anode and the cathode from 1 to 200, preferably from 20 to 70, A
2a electrodialys.is units separated from one another by bipolar membranes. The bipolar membranes are separated from one another by ration exchange membranes, so that an electrodialysi.s unit has the following structure: bipolar membrane (anode side) -anolyte compartment - ration exchange membrane - catolyte compartment - bipolar membrane (cat.hode side). The individual electrodialysis cells are preferably electrically connected in series.
In this version it is advantageous to feed the aqueous dicarboxylate salt solution into the anolyte compartment. In the electric field of an applied direct voltage the a7_kali metal rations generally migrate through the ration e~;change membrane into the catolyte compart ment . The hydroxyl anions required for compensating the ~~,~~ra~orl nharrtoc arc , X1_38153 - 3 - O.Z. 0050/43332 formed by the dissociation of the water in the bipolar :membranes on the cathode side. In this way the corresponding alkali metal hydroxide solution collects in the catolyte compartment. In the anolyte compartment the dicarboxylate anion can combine with the hydrogen ions from the bipolar membrane on the anode side to form the free dicarboxylic acid.
It is advantageous to feed the dicarboxylate salt solution into the anolyte compartments in parallel.
The product streams from the anolyte compartments, containing the free acid and unconverted dicarboxyl-ate salt, and the product streams from the catolyte compartments are advantageously combined with one another. The free dicarboxylic acid is in general obtained by crystallization from the combined product streams from the anolyte compartment without coprecipitation of the corresponding dicarboxylate salt, which is preferably subjected again to the electrod.ialysis process.
The ealectrodialysis process can be carried out not only continuously but also batchwise. A prefer-red form of the continuous process involving a plurality of electrodialysis cells comprises splitting the total conversion between from 2 to 20, preferably from 4 to 6, electrodialysis cells and achieving only partial conversion in each electro-dialysis; cell.
It is particularly advantageous here to guide the flows in countercurrent. The outflow from an anolyte compartment forms the inflow into the next anolyte compartment, etc., so that the outflow from the last anolyte compartment is rich in dicarboxylic acid and lean in dicarboxylate salt. The outflow from the last catolyte compartment, containing a low concentration of alkali metal hydroxide, forms the inflow into the last but one catolyte compartment, etc., so that the first unit has a high - 4 - O.Z. 0050/43332 concentration of dicarboxylate salt in the anolyte compartment and a high concentration of alkali metal hydroxide in the catolyte compartment. The result is that the alkali metal hydroxide concentration differences in the anolyte and catolyte compartments are small within a unit. This ultimately leads in general to an energy saving due to a higher current yield and on average to lower cell voltages.
The current densities are in general within the range from 0.1 to 1, preferably from 0.3 to 0.5, kA/m'. Tree cell voltage is in general from 3 to 8, V
per electrodialysis unit.
The pH is in general within the range from 2 to 10 in the anolyte compartments and within the range greater than 13 in the catolyte compartments.
The compartment width is in general from 0.2 to 5, preferably from 0.5 to 1, mm.
The e:lectrodialysis temperature is in general within the range from 40 to 110°C, preferably from 65 to 90°C.
The inflow and outflow velocities are in general within the range from 0.05 to 0.2 m/sec.
The concentration of dicarboxylate salt used is in general from 5 to 40% by weight, preferably from 10 to 20% by weight.
If desired, the conductivity in the anolyte system c:an be increased by adding salts or acids such as sodium sulfate or sulfuric acid. Substances of this type are in general added within the range from 0.1. to 10% by weight, preferably from 1 to 6%
by weight, based on the total weight of the solution present in the anolyte compartment.
To the catolyte compartment it is advantageous to add the substances which are obtained in the course of the operation, preferably the corresponding alkali metal hydroxide such as sodium hydroxide or potassium hydroxide, preferably sodium hydroxide.
_~138~53 - 5 - O.Z. 0050/43332 The inflow into the catolyte compartment gener-ally comprises fully demineralized water, but at the beginning it is preferable to employ the from 1 to 25, preferably from 5 to 10, % strength by weight alkali metal hydroxide solution formed in the course of the electrodialysis.
To increase the conductivity, the anolyte com partment may have added to it for example an oxo acid such as sulfuric acid, phosphoric acid and nitric acid.
(b) A three-part electrodialysis cell with bipolar membranes has the advantage over the procedure described under (a) that the feed materials need not be very pure. Furthermore, in general, significantly lower salt contents are obtained not only in the dicarboxylic acid solution obtained but also in the corresponding alkali metal hydroxide solution.
The three-compartment system contains not only a cation exchange membrane but also an anion exchange membrane, so that the structure of an electrodialy sis cell is as follows: bipolar membrane (anode side) - anolyte compartment - anion exchange membrane - center compartment - cation exchange membrane - catolyte compartment - bipolar membrane (cathode side).
The dicarboxylate salt solution is advantageously introduced into the center compartment. Under the influence of a direct current electric field the dicarbox:ylate anions generally migrate through the anion eacchange membrane into the anolyte compart-ment, where they can combine with the hydrogen ions present there to form the free acid. Apart from selectivity losses of the anion exchange membrane the free acid can be withdrawn from the anolyte compartment devoid of salt. As in (a) the catolyte compartment yields the alkali metal hydroxide solution. The outflow from the center compartment, - 6 - O.Z. 0050143332 still containing residual quantities of dicarboxylate salt, can be disposed of or advantageously added again to the feed for the electrod:Lalysis process. Again as in (a) the flows can be guided countercurrently in order to increase the current yield.
To increase the conductivity the anolyte compart ment can have added to it for example an oxoacid such as sulfuric acid, phosphoric acid or nitric acid.
The catolyte compartment can advantageously have added to it the substances which are obtained in the course o:E the operation, preferably the correspond-ing alkali metal hydroxide such as sodium hydroxide or potass;ium hydroxide, preferably sodium hydroxide.
As for the rest, the process of (b) can be carried .out under the same conditions as described under (a).
(c) In principle it is also possible to use electro dialysis cells having four compartments. The layout generalhy resembles that of an electrodialysis cell with three compartments except that, to protect the bipolar :membranes from possible fouling, a further ion exchange membrane, preferably a cation exchange membrane, is included. In general, an electrodialy _ sis unit will have the following structure: bipolar membrane ( anode side ) - anolyte compartment - cation exchange membrane - anode-near center compartment anion exchange membrane - cathode-near center compartment - cation exchange membrane - catolyte compartment - bipolar membrane (cathode side).
The d:icarboxylate salt solution is advantageously introduced into the cathode-near center compartment with the dicarboxylic acid solution being withdrawn from the anode-near center compartment and the alkali metal hydroxide solution from the cathode compartment.
.. .~~38I53 - 7 - O.Z. 0050/43332 In other respects, the process of (c) can be carried out under the same conditions as described under (b).
( d ) The e7Lectrochemical cleavage of the dicarboxylate salt into the dicarboxylic acid and the correspond ing base can be carried out under a further embodi ment in a two-part membrane electrolysis cell known per se from chlor-alkali electrolysis. The membrane electrolysis cell comprises in general from 1 to 100, preferably from 20 to 70, electrolysis units grouped together in a block. In this block, the individual electrolysis units can be electrically connected in series by electrically connecting the cathode of one unit to the anode of the next unit or by using internally connected bipolar electrodes.
The products generally flow in and out via separate collector lines for each compartment type. The two part membrane electrolysis unit generally has the following structure going from the anode to the cathode:
anode - anolyte compartment - cation exchange mem-brane - catolyte compartment - cathode.
The aqueous dicarboxylate salt solution is advan tageously introduced into the anolyte compartment.
Under t:he electric field of the applied direct _ voltage the alkali metal cations generally migrate through the cation exchange membrane into the catolyte; compartment, where they are converted into alkali. The hydroxyl anions required for compensat-ing the separated charges are released in the cathode reaction. The cathode reaction can be for example the cathodic evolution of hydrogen or a cathodic reduction of oxygen. The anolyte compart-ment generally retains the organic acid radical which combines with the hydrogen ions or their hydrated forms released in the course of the anode reaction to form the corresponding free acid. An _~138I53 - 8 - O.Z. 0050/43332 example of an anode reaction is the anodic evolution of oxygen or the anodic oxidation of hydrogen. The anode compartment will thus have in general become leaner i.n the salt and richer in the free dicar boxylic acid.
The membrane electrolysis process can be carried out not only batchwise but also continuously. If it is carried out over the continuous process, one option is to divide the conversion between from 2 to 20, preferably from 4 to 6, cells and to guide the flows countercurrently (see (a)).
The d.icarboxylate salt solution used, which may contain a plurality of such salts, has in general a concentration of from 1% by weight up to the satura-tian limit of the salt(sj, preferably from 5 to 35, particularly preferably from 15 to 30, % by weight.
The current densities are in general within the range from 0.5 to 10, preferably from 1 to 4, kA/mz.
The cell voltage is in general from 3 to 10 V, preferably from 4 to 6 V, per membrane electrolysis unit.
The pH is in general within the range from 2 to 10 in th.e anolyte compartments and within the range greater than 13 in the catolyte compartments.
The compartment width is in general from 0.5 to 10, preferably from 1 to 5, mm.
The temperature selected for carrying out the membranes electrolysis process is in general within the range from 50 to 110°C, preferably from 65 to 90°C.
To ensure mass transport, the compartment con-tents are in general recirculated either by means of pumps or through natural convection, ie. through the mammoth pump effect due to gas evolution at the electrodes. The flow velocities in the compartments are in general within the range from 0.05 to 0.5, preferably from 0.1 to 0.2, m/sec.
Salts of the dicarboxylic acids I are obtained in a number of industrial processes, for example in the alkaline hydrolysis of polyamides. To isolate the free acids the salts are acidified, for example with hydrochloric acid according to FR-A-926,873 (published on October 14, 1947) or with sulfuric acid according to tfS-A-2,840,606 (published on April 15, 1955).
The disadvantage of this is the formation of salts such as sodium chloride or sodium sulfate and their disposal.
The preparation of an organic acid by electrodialysis is known, for example from DE-A-2,547,101 (published on May 6, 1976) which describes the electrodialysis of salt solutions of glycine, diglycinE~, triglycine, citric acid, tartaric acid, acetic acid, acrylic acid, malefic acid and ascorbic acid in a four-compartment electrolysis cell.
SU-A-401,131 (published on October 5, 1976) describes the electrochemical preparation of oxalic acid from sodium oxalate.
It is an object of the present invention to provide a process for preparing dicarboxylic acids in high purity and yield without the known disadvantages.
We have found that this object is achieved by a process for the electrochemical preparation of dicarboxylic acids, which comprises subjecting an aqueous solution containing essentially an alkali metal salt of a dicarboxylic acid of the general formula I:
HOOC-(CH2)n-COOH I
where n is an integer from 1 to 8, or mixtures thereof, to an electrochemical treatment.
The alkali metal salt used is in general the lithium, sodium or potassium salt. It is of course also possible to use mixed salts, ie. salts with two different alkali metal rations, or acid salts, ie. salts with a free acid group, or mixtures thereof.
Examples are dilithium, disodium and dipotassium malonate, succinat:e, glutarate, adipate, pimelate, octane-dioate, nonanedioate and decanedioate, sodium potassium adipate, preferably dilithium adipate, disodium adipate, dipotassium adipate, sodium potassium adipate, dilithium l0 octanedioate, disodium octanedioate and dipotassium octanedioate, particularly preferably disodium adipate.
From obsE~rvatians to date the manner of the electro-chemical treatment has in principle no bearing on the success of the process of the invention.
Fig. 1 i:~ a diagrammatical representation of a three compartment electrolysis cell comprising three liquid cycles 20 KL1 to KL3.
Fig. 2 i.s a diagrammatical representation of a four compartment electrolysis cell comprising four liquid cycles KL1 to KL4.
Fig. 3 is a diagrammatical representaiton of a membrane stack cell comprising three liquid cycles KL1 to KL3.
The elecarochemical treatment may for example take 30 one of the following forms (a) to (f):
(a) In this version the splitting of the dicarboxylate salt into tree corresponding dicarboxylic acid and the corresponding base can be carried out in a two-part electrodialysis cell using bipolar membranes. In general, the electrodialysis cell has between the anode and the cathode from 1 to 200, preferably from 20 to 70, A
2a electrodialys.is units separated from one another by bipolar membranes. The bipolar membranes are separated from one another by ration exchange membranes, so that an electrodialysi.s unit has the following structure: bipolar membrane (anode side) -anolyte compartment - ration exchange membrane - catolyte compartment - bipolar membrane (cat.hode side). The individual electrodialysis cells are preferably electrically connected in series.
In this version it is advantageous to feed the aqueous dicarboxylate salt solution into the anolyte compartment. In the electric field of an applied direct voltage the a7_kali metal rations generally migrate through the ration e~;change membrane into the catolyte compart ment . The hydroxyl anions required for compensating the ~~,~~ra~orl nharrtoc arc , X1_38153 - 3 - O.Z. 0050/43332 formed by the dissociation of the water in the bipolar :membranes on the cathode side. In this way the corresponding alkali metal hydroxide solution collects in the catolyte compartment. In the anolyte compartment the dicarboxylate anion can combine with the hydrogen ions from the bipolar membrane on the anode side to form the free dicarboxylic acid.
It is advantageous to feed the dicarboxylate salt solution into the anolyte compartments in parallel.
The product streams from the anolyte compartments, containing the free acid and unconverted dicarboxyl-ate salt, and the product streams from the catolyte compartments are advantageously combined with one another. The free dicarboxylic acid is in general obtained by crystallization from the combined product streams from the anolyte compartment without coprecipitation of the corresponding dicarboxylate salt, which is preferably subjected again to the electrod.ialysis process.
The ealectrodialysis process can be carried out not only continuously but also batchwise. A prefer-red form of the continuous process involving a plurality of electrodialysis cells comprises splitting the total conversion between from 2 to 20, preferably from 4 to 6, electrodialysis cells and achieving only partial conversion in each electro-dialysis; cell.
It is particularly advantageous here to guide the flows in countercurrent. The outflow from an anolyte compartment forms the inflow into the next anolyte compartment, etc., so that the outflow from the last anolyte compartment is rich in dicarboxylic acid and lean in dicarboxylate salt. The outflow from the last catolyte compartment, containing a low concentration of alkali metal hydroxide, forms the inflow into the last but one catolyte compartment, etc., so that the first unit has a high - 4 - O.Z. 0050/43332 concentration of dicarboxylate salt in the anolyte compartment and a high concentration of alkali metal hydroxide in the catolyte compartment. The result is that the alkali metal hydroxide concentration differences in the anolyte and catolyte compartments are small within a unit. This ultimately leads in general to an energy saving due to a higher current yield and on average to lower cell voltages.
The current densities are in general within the range from 0.1 to 1, preferably from 0.3 to 0.5, kA/m'. Tree cell voltage is in general from 3 to 8, V
per electrodialysis unit.
The pH is in general within the range from 2 to 10 in the anolyte compartments and within the range greater than 13 in the catolyte compartments.
The compartment width is in general from 0.2 to 5, preferably from 0.5 to 1, mm.
The e:lectrodialysis temperature is in general within the range from 40 to 110°C, preferably from 65 to 90°C.
The inflow and outflow velocities are in general within the range from 0.05 to 0.2 m/sec.
The concentration of dicarboxylate salt used is in general from 5 to 40% by weight, preferably from 10 to 20% by weight.
If desired, the conductivity in the anolyte system c:an be increased by adding salts or acids such as sodium sulfate or sulfuric acid. Substances of this type are in general added within the range from 0.1. to 10% by weight, preferably from 1 to 6%
by weight, based on the total weight of the solution present in the anolyte compartment.
To the catolyte compartment it is advantageous to add the substances which are obtained in the course of the operation, preferably the corresponding alkali metal hydroxide such as sodium hydroxide or potassium hydroxide, preferably sodium hydroxide.
_~138~53 - 5 - O.Z. 0050/43332 The inflow into the catolyte compartment gener-ally comprises fully demineralized water, but at the beginning it is preferable to employ the from 1 to 25, preferably from 5 to 10, % strength by weight alkali metal hydroxide solution formed in the course of the electrodialysis.
To increase the conductivity, the anolyte com partment may have added to it for example an oxo acid such as sulfuric acid, phosphoric acid and nitric acid.
(b) A three-part electrodialysis cell with bipolar membranes has the advantage over the procedure described under (a) that the feed materials need not be very pure. Furthermore, in general, significantly lower salt contents are obtained not only in the dicarboxylic acid solution obtained but also in the corresponding alkali metal hydroxide solution.
The three-compartment system contains not only a cation exchange membrane but also an anion exchange membrane, so that the structure of an electrodialy sis cell is as follows: bipolar membrane (anode side) - anolyte compartment - anion exchange membrane - center compartment - cation exchange membrane - catolyte compartment - bipolar membrane (cathode side).
The dicarboxylate salt solution is advantageously introduced into the center compartment. Under the influence of a direct current electric field the dicarbox:ylate anions generally migrate through the anion eacchange membrane into the anolyte compart-ment, where they can combine with the hydrogen ions present there to form the free acid. Apart from selectivity losses of the anion exchange membrane the free acid can be withdrawn from the anolyte compartment devoid of salt. As in (a) the catolyte compartment yields the alkali metal hydroxide solution. The outflow from the center compartment, - 6 - O.Z. 0050143332 still containing residual quantities of dicarboxylate salt, can be disposed of or advantageously added again to the feed for the electrod:Lalysis process. Again as in (a) the flows can be guided countercurrently in order to increase the current yield.
To increase the conductivity the anolyte compart ment can have added to it for example an oxoacid such as sulfuric acid, phosphoric acid or nitric acid.
The catolyte compartment can advantageously have added to it the substances which are obtained in the course o:E the operation, preferably the correspond-ing alkali metal hydroxide such as sodium hydroxide or potass;ium hydroxide, preferably sodium hydroxide.
As for the rest, the process of (b) can be carried .out under the same conditions as described under (a).
(c) In principle it is also possible to use electro dialysis cells having four compartments. The layout generalhy resembles that of an electrodialysis cell with three compartments except that, to protect the bipolar :membranes from possible fouling, a further ion exchange membrane, preferably a cation exchange membrane, is included. In general, an electrodialy _ sis unit will have the following structure: bipolar membrane ( anode side ) - anolyte compartment - cation exchange membrane - anode-near center compartment anion exchange membrane - cathode-near center compartment - cation exchange membrane - catolyte compartment - bipolar membrane (cathode side).
The d:icarboxylate salt solution is advantageously introduced into the cathode-near center compartment with the dicarboxylic acid solution being withdrawn from the anode-near center compartment and the alkali metal hydroxide solution from the cathode compartment.
.. .~~38I53 - 7 - O.Z. 0050/43332 In other respects, the process of (c) can be carried out under the same conditions as described under (b).
( d ) The e7Lectrochemical cleavage of the dicarboxylate salt into the dicarboxylic acid and the correspond ing base can be carried out under a further embodi ment in a two-part membrane electrolysis cell known per se from chlor-alkali electrolysis. The membrane electrolysis cell comprises in general from 1 to 100, preferably from 20 to 70, electrolysis units grouped together in a block. In this block, the individual electrolysis units can be electrically connected in series by electrically connecting the cathode of one unit to the anode of the next unit or by using internally connected bipolar electrodes.
The products generally flow in and out via separate collector lines for each compartment type. The two part membrane electrolysis unit generally has the following structure going from the anode to the cathode:
anode - anolyte compartment - cation exchange mem-brane - catolyte compartment - cathode.
The aqueous dicarboxylate salt solution is advan tageously introduced into the anolyte compartment.
Under t:he electric field of the applied direct _ voltage the alkali metal cations generally migrate through the cation exchange membrane into the catolyte; compartment, where they are converted into alkali. The hydroxyl anions required for compensat-ing the separated charges are released in the cathode reaction. The cathode reaction can be for example the cathodic evolution of hydrogen or a cathodic reduction of oxygen. The anolyte compart-ment generally retains the organic acid radical which combines with the hydrogen ions or their hydrated forms released in the course of the anode reaction to form the corresponding free acid. An _~138I53 - 8 - O.Z. 0050/43332 example of an anode reaction is the anodic evolution of oxygen or the anodic oxidation of hydrogen. The anode compartment will thus have in general become leaner i.n the salt and richer in the free dicar boxylic acid.
The membrane electrolysis process can be carried out not only batchwise but also continuously. If it is carried out over the continuous process, one option is to divide the conversion between from 2 to 20, preferably from 4 to 6, cells and to guide the flows countercurrently (see (a)).
The d.icarboxylate salt solution used, which may contain a plurality of such salts, has in general a concentration of from 1% by weight up to the satura-tian limit of the salt(sj, preferably from 5 to 35, particularly preferably from 15 to 30, % by weight.
The current densities are in general within the range from 0.5 to 10, preferably from 1 to 4, kA/mz.
The cell voltage is in general from 3 to 10 V, preferably from 4 to 6 V, per membrane electrolysis unit.
The pH is in general within the range from 2 to 10 in th.e anolyte compartments and within the range greater than 13 in the catolyte compartments.
The compartment width is in general from 0.5 to 10, preferably from 1 to 5, mm.
The temperature selected for carrying out the membranes electrolysis process is in general within the range from 50 to 110°C, preferably from 65 to 90°C.
To ensure mass transport, the compartment con-tents are in general recirculated either by means of pumps or through natural convection, ie. through the mammoth pump effect due to gas evolution at the electrodes. The flow velocities in the compartments are in general within the range from 0.05 to 0.5, preferably from 0.1 to 0.2, m/sec.
- 9 - O.Z. 0050/43332 (e) A particularly preferred embodiment is the electrochemical cleavage of the dicarboxylate salts into the corresponding dicarboxylic acids and bases in a thrE~e-part membrane electrolysis cell.
The three-part membrane electrolysis unit has in general i:he following structure:
anode - anolyte compartment - cation exchange membrane - center compartment - cation exchange membrane - catolyte compartment - cathode.
The aqueous dicarboxylate salt solution is in general :introduced into the center compartment. To increase the electric conductivity in the center compartment, a mineral acid or a salt can be added to the cE:nter compartment electrolyte. Examples are sulfuric acid, nitric acid, sodium sulfate and sodium nitrate.
The center compartment generally retains the organic acid radical, which can react with the hydrogen ions liberated in the course of the anode reaction and which have migrated into the center compartment through the anode-side cation exchange membrane to fona the free acid. The acid is in general removed from the center compartment system together with unconverted salt . The anolyte used can be an aqueous mineral acid such as sulfuric acid, nitric acid or hydrochloric acid, preferably sulfuric acid. The anolyte's essential function is, together with the anode-side cation exchange mem brane, t~o protect the organic dicarboxylic acid from anodic oxidation.
As for the rest, the process of (e) can be carried out under the conditions described at (d).
(f) The e:lectrachemical splitting of the dicarboxy-late salts into the corresponding dicarboxylic acids and basea can also be carried out in a four-part membrane electrolysis cell.
The four-part membrane electrolysis unit 2.138153 - 10 - O.Z. 0050/43332 generall~,r has the following structure:
anode - anolyte compartment - cation exchange membrane - anode-near center compartment - anion exchange membrane - cathode-near center compartment - cation exchange membrane - catolyte compartment -cathode.
The aqueous dicarboxylate salt solution is advantageously introduced into the cathode-near center compartment.
To increase the electric conductivity in the center compartment, a mineral acid or a salt such as sulfuric acid, nitric acid, sodium sulfate or sodium nitrate can be added to the center compartment electrol:Yte .
The acid anion generally passes from the cathode-near center compartment into the anode-near center compartment, where it reacts with hydrogen ions, which are evolved in the course of the anode reac-tion and pass into the anode-near center compartment through 'the anode-side cation exchange membrane, to form the free acid. The acid is in general withdrawn from the center compartment system in high purity.
The remaining salt solution is in general withdrawn from the cathode-near center compartment and recir-culated into the adipate dissolution stage as a part-stream or disposed of.. The anolyte used is in general an aqueous mineral acid, preferably sulfuric acid. The anolyte's essential function, together with the anode-side cation exchange membrane, is to protect the organic acid from anodic oxidation.
As for the rest, the process of (f) can be carried out under the conditions mentioned at (d).
In the above-described alternatives the cation exchange membranes used are particularly preferably polymers based on perfluorinated olefins or copolymers of styrene and clivinylbenzene containing sulfonic acid and if desired carboxyl groups as charge carriers. Very . 21 3815 3 - 11 - O.Z. 0050/43332 particular preference is given to using membranes that contain sulfonic acid groups only, since in general they are more resiE;taut to fouling by multivalent cations than other membranes. Membranes of this type are known (for example Nafion~ membranes of type 324). They consist of a copolymer o:E tetrafluoroethylene with a perfluorinated monomer that contains sulfone groups. In general they have a high chemical and thermal stability. The ion exchange membrane can be reinforced with a Teflon~
support fabric. It is also possible to use copolymers based on styrene and divinylbenzene.
Suitable anion exchange membranes are for example the membranes described in detail in EP-A-449,071 (pu-bushed on October 2, 1991 ) so no details will be given here.
The ellectrode materials used can be in general perforated materials, for example in the form of nets, lamellae, oval profile webs or round profile webs.
Theoxygen overvoltage at the anodes is in general set at less than 400 mV within the current density ranges according to the invention in order that the formation of ozone or per-compounds may be prevented.
Suitable anode materials of low oxygen overvol tage are for example titanium supports with electrically conducting interlayers of borides and/or carbides and/or silicides of subgroups IV to VI such has tantalum borides, titanium borides or titanium suboxide, doped or undoped tin oxides, or tantalum and/or niobium with or without platinum metal doping, whose surface has in general been doped with electrically conducting, non-stoichiometri.c mixed oxides of subgroups IV to VI and metals or metal oxides of the platinum group or platinum metal compounds such as platinates. On top of these interlayers i.s in general the active electrode material, which preferably consists of mixed oxides of tantalum with iridium,, platinum or rhodium and platinates of the type Lio,3Pt,~0~. To enlarge the surface area it is customary to use superficially roughened or macroporous _ _138153 - 12 - O.Z. 0050/43332 titanium supports.
The cathodes are in general made of electrode materials having a low hydrogen overvoltage in order to avoid additional voltage losses in the membrane electrolysis or electrodialysis cell. Suitable cathodes are for examp:Le iron or nickel supports which have been surface coatE:d with finely divided cobalt, nickel, molybdenum, tungsten, manganese, Raney metal compounds of nickel or of cobalt, nickel- or cobalt-aluminum alloys, or nickel-iron alloys or cobalt-iron alloys containing from 65 to 90% by weight of iron.
To i.a~prove selectivity and membrane life the cathode side can be equipped with cation exchange mem-branes containing hydroxyl ion blockers. The selectivity can be further improved by keeping the level of calcium, magnesium and aluminum ions and also the silica content in each case lbelow 5 ppm.
The d:icarboxylic acid I obtained by the electro chemical treatment is in general present as an aqueous solution having a concentration within the range from 1 to 30, preferably from 4 to 30, % by weight. This solu-tion can contain the conductivity salt, if present, in a concentration within the range from 0.05 to 15, prefer-ably from O.OIi to 6, % by weight and the mineral acid, if present, in a concentration within the range from 0.05 to 15,_ preferably from 0 to 6, % by weight.
The alkali obtained according to the invention generally contains an alkali metal hydroxide in a con centration within the range from 5 to 35, preferably from 15 to 25, % by weight.
To obtain the dicarboxylic acid in pure form, it is in general crystallized out of the solution obtained according to the invention, then separated off, for example by filtration, and dried.
The d.icarboxylic acid is preferably obtained from the electrodi~alysis or membrane electrolysis solutions by cooling or evaporation crystallization. Then the _2138153 - 13 - O.Z. 0050/43332 dicarboxylic acids are in general separated from the resulting suspensions, for example by filtration, decant-ing or centrii:uging.
The cooling crystallization is customarily carried out ait from 0 to 50C, preferably at from 15 to 40C, advantageously at pressures within the range from 1 to 100 kPa, preferably from 4 to 20 kPa.
The clicarboxylic acids separated off can be preferably obtained in a pure form by washing, for example with water or Cl-C,-alkanols, and if desired by recrystallizai:ion. If a plurality of dicarboxylic acids are present at: the same time, the individual dicarboxylic acids can be isolated in pure form by utilizing the solubility differences in a conventional manner such as fractional crystallization.
The ac;ueous solutions obtained by crystallization and washing can be concentrated in a conventional manner and resubject:ed to a crystallization, for example by adding them to as-electrodialyzed or as-electrolyzed solutions that have still to be crystallized.
An essential advantage of the process of the invention over known processes is that it eliminates the f ormation and disposal of salts which are customarily obtained when the dicarboxylic acids are freed from their salts by acidification.
Hatchwise electrolysis in a three-compartment electrolysis cell as per variant e) The three-compartment electrolysis cell used was that diagrammatically depicted in Figure 1 with three liquid cycles (RL1 to RL3). All product-contacting parts with the exception of the electrodes consisted of poly-propylene, glass or quartz. The anode (E1) (in compart-ment (A)) was a titanium expanded-mesh anode having an area of 100 cm~ and a coating suitable for oxygen evolu-tion. The cathode (E2) (in compartment (C)) likewise had an area of 1.00 cm~. It consisted of a chromium-nickel - 14 - O.Z. 0050/43332 stainless steel (1.4571) which had been coated with a nickel network activated for hydrogen evolution. The two membranes (M1 and M2) of the type NafionA324 were posi-tioned directly on the electrodes (E1 and E2, respec-tively) and were separated from each other by a 1 mm wide center compartment (B) with a polypropylene spacer.
The anode (RL1) and cathode (RL2) cycles were kept in natural circulation owing to the gas evolutions at the electrodes. The cycle of the center compartment (B), (RL3), w.as recirculated using a cycle pump (P). The flow velocity in the center compartment (H) was 0.1 m/
sec.
The anolyte used comprised 1131 g of 5% strength by weight sulfuric acid introduced at location (1), the catolyte comprised 1161 g of 5% strength by weight sodium hydroxide solution introduced at location (2), and the center compas-tment electrolyte comprised 995 g of 27%
strength by weight sodium adipate solution to which 21 g of 96% strength by weight sulfuric acid were added so that 1015 g of a solution containing 22% by weight of sodium adipate, 2.9% by weight of adipic acid and 2.8% by weight of sodium sulfate were introduced at location (3).
A temperature of 80°C, atmospheric pressure, a current density of 3.0 kA/m', a cell voltage of 4.0 V (at the beginning) and 5.3 V (at the end of the run) produced in a current 'yield of 83% and after a reaction time of 2h 26min the following electrolytes:
anolyte (removed at location (4)): 729 g of 6.9% strength by weight sulfuric acid, catolyte (re:moved at location (5)): 1294 g of 10.9%
strength by weight sodium hydroxide solution, center compartment electrolyte (removed at location (6)):
904 g of a solution containing 20.4% strength by weight adipic acid, 1.2% by weight of sodium adipate and 3.2% by weight of sodium sulfate.
Batchwise crystallization 900 g of the center compartment electrolyte 213$I,~~
The three-part membrane electrolysis unit has in general i:he following structure:
anode - anolyte compartment - cation exchange membrane - center compartment - cation exchange membrane - catolyte compartment - cathode.
The aqueous dicarboxylate salt solution is in general :introduced into the center compartment. To increase the electric conductivity in the center compartment, a mineral acid or a salt can be added to the cE:nter compartment electrolyte. Examples are sulfuric acid, nitric acid, sodium sulfate and sodium nitrate.
The center compartment generally retains the organic acid radical, which can react with the hydrogen ions liberated in the course of the anode reaction and which have migrated into the center compartment through the anode-side cation exchange membrane to fona the free acid. The acid is in general removed from the center compartment system together with unconverted salt . The anolyte used can be an aqueous mineral acid such as sulfuric acid, nitric acid or hydrochloric acid, preferably sulfuric acid. The anolyte's essential function is, together with the anode-side cation exchange mem brane, t~o protect the organic dicarboxylic acid from anodic oxidation.
As for the rest, the process of (e) can be carried out under the conditions described at (d).
(f) The e:lectrachemical splitting of the dicarboxy-late salts into the corresponding dicarboxylic acids and basea can also be carried out in a four-part membrane electrolysis cell.
The four-part membrane electrolysis unit 2.138153 - 10 - O.Z. 0050/43332 generall~,r has the following structure:
anode - anolyte compartment - cation exchange membrane - anode-near center compartment - anion exchange membrane - cathode-near center compartment - cation exchange membrane - catolyte compartment -cathode.
The aqueous dicarboxylate salt solution is advantageously introduced into the cathode-near center compartment.
To increase the electric conductivity in the center compartment, a mineral acid or a salt such as sulfuric acid, nitric acid, sodium sulfate or sodium nitrate can be added to the center compartment electrol:Yte .
The acid anion generally passes from the cathode-near center compartment into the anode-near center compartment, where it reacts with hydrogen ions, which are evolved in the course of the anode reac-tion and pass into the anode-near center compartment through 'the anode-side cation exchange membrane, to form the free acid. The acid is in general withdrawn from the center compartment system in high purity.
The remaining salt solution is in general withdrawn from the cathode-near center compartment and recir-culated into the adipate dissolution stage as a part-stream or disposed of.. The anolyte used is in general an aqueous mineral acid, preferably sulfuric acid. The anolyte's essential function, together with the anode-side cation exchange membrane, is to protect the organic acid from anodic oxidation.
As for the rest, the process of (f) can be carried out under the conditions mentioned at (d).
In the above-described alternatives the cation exchange membranes used are particularly preferably polymers based on perfluorinated olefins or copolymers of styrene and clivinylbenzene containing sulfonic acid and if desired carboxyl groups as charge carriers. Very . 21 3815 3 - 11 - O.Z. 0050/43332 particular preference is given to using membranes that contain sulfonic acid groups only, since in general they are more resiE;taut to fouling by multivalent cations than other membranes. Membranes of this type are known (for example Nafion~ membranes of type 324). They consist of a copolymer o:E tetrafluoroethylene with a perfluorinated monomer that contains sulfone groups. In general they have a high chemical and thermal stability. The ion exchange membrane can be reinforced with a Teflon~
support fabric. It is also possible to use copolymers based on styrene and divinylbenzene.
Suitable anion exchange membranes are for example the membranes described in detail in EP-A-449,071 (pu-bushed on October 2, 1991 ) so no details will be given here.
The ellectrode materials used can be in general perforated materials, for example in the form of nets, lamellae, oval profile webs or round profile webs.
Theoxygen overvoltage at the anodes is in general set at less than 400 mV within the current density ranges according to the invention in order that the formation of ozone or per-compounds may be prevented.
Suitable anode materials of low oxygen overvol tage are for example titanium supports with electrically conducting interlayers of borides and/or carbides and/or silicides of subgroups IV to VI such has tantalum borides, titanium borides or titanium suboxide, doped or undoped tin oxides, or tantalum and/or niobium with or without platinum metal doping, whose surface has in general been doped with electrically conducting, non-stoichiometri.c mixed oxides of subgroups IV to VI and metals or metal oxides of the platinum group or platinum metal compounds such as platinates. On top of these interlayers i.s in general the active electrode material, which preferably consists of mixed oxides of tantalum with iridium,, platinum or rhodium and platinates of the type Lio,3Pt,~0~. To enlarge the surface area it is customary to use superficially roughened or macroporous _ _138153 - 12 - O.Z. 0050/43332 titanium supports.
The cathodes are in general made of electrode materials having a low hydrogen overvoltage in order to avoid additional voltage losses in the membrane electrolysis or electrodialysis cell. Suitable cathodes are for examp:Le iron or nickel supports which have been surface coatE:d with finely divided cobalt, nickel, molybdenum, tungsten, manganese, Raney metal compounds of nickel or of cobalt, nickel- or cobalt-aluminum alloys, or nickel-iron alloys or cobalt-iron alloys containing from 65 to 90% by weight of iron.
To i.a~prove selectivity and membrane life the cathode side can be equipped with cation exchange mem-branes containing hydroxyl ion blockers. The selectivity can be further improved by keeping the level of calcium, magnesium and aluminum ions and also the silica content in each case lbelow 5 ppm.
The d:icarboxylic acid I obtained by the electro chemical treatment is in general present as an aqueous solution having a concentration within the range from 1 to 30, preferably from 4 to 30, % by weight. This solu-tion can contain the conductivity salt, if present, in a concentration within the range from 0.05 to 15, prefer-ably from O.OIi to 6, % by weight and the mineral acid, if present, in a concentration within the range from 0.05 to 15,_ preferably from 0 to 6, % by weight.
The alkali obtained according to the invention generally contains an alkali metal hydroxide in a con centration within the range from 5 to 35, preferably from 15 to 25, % by weight.
To obtain the dicarboxylic acid in pure form, it is in general crystallized out of the solution obtained according to the invention, then separated off, for example by filtration, and dried.
The d.icarboxylic acid is preferably obtained from the electrodi~alysis or membrane electrolysis solutions by cooling or evaporation crystallization. Then the _2138153 - 13 - O.Z. 0050/43332 dicarboxylic acids are in general separated from the resulting suspensions, for example by filtration, decant-ing or centrii:uging.
The cooling crystallization is customarily carried out ait from 0 to 50C, preferably at from 15 to 40C, advantageously at pressures within the range from 1 to 100 kPa, preferably from 4 to 20 kPa.
The clicarboxylic acids separated off can be preferably obtained in a pure form by washing, for example with water or Cl-C,-alkanols, and if desired by recrystallizai:ion. If a plurality of dicarboxylic acids are present at: the same time, the individual dicarboxylic acids can be isolated in pure form by utilizing the solubility differences in a conventional manner such as fractional crystallization.
The ac;ueous solutions obtained by crystallization and washing can be concentrated in a conventional manner and resubject:ed to a crystallization, for example by adding them to as-electrodialyzed or as-electrolyzed solutions that have still to be crystallized.
An essential advantage of the process of the invention over known processes is that it eliminates the f ormation and disposal of salts which are customarily obtained when the dicarboxylic acids are freed from their salts by acidification.
Hatchwise electrolysis in a three-compartment electrolysis cell as per variant e) The three-compartment electrolysis cell used was that diagrammatically depicted in Figure 1 with three liquid cycles (RL1 to RL3). All product-contacting parts with the exception of the electrodes consisted of poly-propylene, glass or quartz. The anode (E1) (in compart-ment (A)) was a titanium expanded-mesh anode having an area of 100 cm~ and a coating suitable for oxygen evolu-tion. The cathode (E2) (in compartment (C)) likewise had an area of 1.00 cm~. It consisted of a chromium-nickel - 14 - O.Z. 0050/43332 stainless steel (1.4571) which had been coated with a nickel network activated for hydrogen evolution. The two membranes (M1 and M2) of the type NafionA324 were posi-tioned directly on the electrodes (E1 and E2, respec-tively) and were separated from each other by a 1 mm wide center compartment (B) with a polypropylene spacer.
The anode (RL1) and cathode (RL2) cycles were kept in natural circulation owing to the gas evolutions at the electrodes. The cycle of the center compartment (B), (RL3), w.as recirculated using a cycle pump (P). The flow velocity in the center compartment (H) was 0.1 m/
sec.
The anolyte used comprised 1131 g of 5% strength by weight sulfuric acid introduced at location (1), the catolyte comprised 1161 g of 5% strength by weight sodium hydroxide solution introduced at location (2), and the center compas-tment electrolyte comprised 995 g of 27%
strength by weight sodium adipate solution to which 21 g of 96% strength by weight sulfuric acid were added so that 1015 g of a solution containing 22% by weight of sodium adipate, 2.9% by weight of adipic acid and 2.8% by weight of sodium sulfate were introduced at location (3).
A temperature of 80°C, atmospheric pressure, a current density of 3.0 kA/m', a cell voltage of 4.0 V (at the beginning) and 5.3 V (at the end of the run) produced in a current 'yield of 83% and after a reaction time of 2h 26min the following electrolytes:
anolyte (removed at location (4)): 729 g of 6.9% strength by weight sulfuric acid, catolyte (re:moved at location (5)): 1294 g of 10.9%
strength by weight sodium hydroxide solution, center compartment electrolyte (removed at location (6)):
904 g of a solution containing 20.4% strength by weight adipic acid, 1.2% by weight of sodium adipate and 3.2% by weight of sodium sulfate.
Batchwise crystallization 900 g of the center compartment electrolyte 213$I,~~
- 15 - O.Z. 0050/43332 solution thus obtained were introduced at 80°C into a vacuum vessel with reflux condenser and then cooled down over 100 min i,o 10°C by continuously reducing the inter-nal pressure (absolute) from 1013 mbar to 12 mbar. The resulting adipic acid crystals were then separated off by means of a v<icuum nutsche at a filtration pressure of 450 mbar and washed with 700 g of water which had a temperature close to 0°C. The crystalline product thus washed was thE:n dissolved in 420 g of water, giving a 30%
strength by weight adipic acid solution. Then the crystallization process was repeated. Drying the crystal line product obtained in the second crystallization process at 80°C and 100 mbar (absolute) left 175 g of adipic acid having a purity of 99.8% and an ash content of less than ~B ppm.
Continuous crystallization Example 1 was repeated except that the adipic acid was purii:ied by continuous crystallization. For this two vacuum vessels (0.75 1 nominal capacity, with stirrer) were connected in series. The absolute pressure of the first atage (vessel 1) was 95 mbar (corresponding to a boiling 'temperature of the adipate solution used of 45°C), the absolute pressure of the second stage was 12 mbar (corresponding to a boiling temperature of the adipate solution used of 10°C). The liquid level was kept constant in the two vessels by using a membrane metering pump to pump 0.75 kg/h of adipate solution continuously into the first vacuum vessel and decompressioning under a blanket of liquid. A level control valve was used to likewise introduce 0.75 kg/h of the solution contained in the first vacuum vessel into the second vacuum vessel, the solution transported from the first into the second vacuum vessel likewise being decompressioned "dipped". A
charge (900 g) of the adipic acid crystallized out of the second vesse7L was separated off by means of a vacuum nutsche at a filtration pressure of 450 mbar and washed with 700 g of: water which had a temperature of close to 2~38~~
strength by weight adipic acid solution. Then the crystallization process was repeated. Drying the crystal line product obtained in the second crystallization process at 80°C and 100 mbar (absolute) left 175 g of adipic acid having a purity of 99.8% and an ash content of less than ~B ppm.
Continuous crystallization Example 1 was repeated except that the adipic acid was purii:ied by continuous crystallization. For this two vacuum vessels (0.75 1 nominal capacity, with stirrer) were connected in series. The absolute pressure of the first atage (vessel 1) was 95 mbar (corresponding to a boiling 'temperature of the adipate solution used of 45°C), the absolute pressure of the second stage was 12 mbar (corresponding to a boiling temperature of the adipate solution used of 10°C). The liquid level was kept constant in the two vessels by using a membrane metering pump to pump 0.75 kg/h of adipate solution continuously into the first vacuum vessel and decompressioning under a blanket of liquid. A level control valve was used to likewise introduce 0.75 kg/h of the solution contained in the first vacuum vessel into the second vacuum vessel, the solution transported from the first into the second vacuum vessel likewise being decompressioned "dipped". A
charge (900 g) of the adipic acid crystallized out of the second vesse7L was separated off by means of a vacuum nutsche at a filtration pressure of 450 mbar and washed with 700 g of: water which had a temperature of close to 2~38~~
- 16 - O.Z. 0050/43332 0°C. The crystalline product thus washed was then diss-olved in 420 ~g of water, giving a 30% strength by weight adipic acid solution. Then the crystallization process was repeated. Drying the crystalline product obtained-in the second crystallization process at 80°C and 100 mbar (absolute) gave 175 g of adipic acid having a purity of 99.8% and an ash content of less than 8 ppm.
Batchwise electrolysis in a three-compartment electro-lysis cell as per variant f) The four-compartment electrolysis cell used is diagrammatically depicted in Figure 2 with four liquid cycles (RL1 i:o RL4). All product-contacting parts with the exception, of the electrodes consisted of polypropy-lene, glass or quartz. Anode (E1) (in compartment (A)) was a titanium expanded-mesh anode having an area of 100 cm2 and a caating suitable for oxygen evolution.
Cathode (E2) (in compartment (D)) likewise had an area of 100 cm~. It consisted of chromium-nickel stainless steel (1.4571) which had been coated with a nickel network activated for hydrogen evolution. The two electrode-near cation exchange membranes (M1 and M3) of the type Nafion~
324 were positioned directly on the electrodes (E1 and E2 respectively) and were separated by two center compart-meats, (B) and (C), each 1 mta in width, with a centrally disposed anion exchange membrane.(M2) of the type Tokuy ama Soda~ AMH. The center compartments, (B) and (C), were provided with two polypropylene spacers which served to keep the flow channel free and to prevent direct contact between the membranes.
The anode (KL1) and cathode (RL4) cycles were kept in natural circulation owing to the gas evolutions at the electrodes. The cycles of the center compartments (B) and (C), (KL2) and (RL3), were recirculated using the cycle pumps (P1) and (P2). The flow velocities in the center compartments (B) and (C) were in each case 0.1 m/
sec.
.~1~81~3 - 17 - O.Z. 0050/43332 The anolyte used comprised 1108 g of 5.1%
strength by weight sulfuric acid introduced at location (1), the catolyte comprised 1101 g of 4% strength by weight sodium hydroxide solution introduced at location ( 2 ) , the electrolyte of the anode-near center compartment (B) comprised 1097 g of 2.1% strength by weight sulfuric acid introduced at location (3), and the electrolyte of the cathode-near center compartment (C) comprised 1505 g of 27% strengi:h by weight sodium adipate solution intro duced at locaition (4).
During the reaction a total of 900 g of water was additionally introduced into the cathode-near center compartment ( C ) .
A temperature of 80°C, atmospheric pressure, a current densiity of 3 . 0 kA/ms, a cell voltage of 7 . 0 V ( at the beginning) and 8.7 V (at the end of the run) produced with a current yield of 75% and after a reaction time of 5 h, during which the pH in the cathode-near center compartment (C) was within the range from 10 to 12, the following electrolytes:
anolyte (removed at location (5)): 793 g of 7.1% strength by weight sulfuric acid, catolyte (removed at location (6)): 1584 g of 13.3%
strength by weight sodium hydroxide solution, product of the anode-near center compartment (B) (removed at location (7)): 2034 g of a solution containing 15.1%
strength by weight adipic acid, 1.1% by weight of sulfuric acid, product of the cathode-near center compartment (C) (removed at location (8)): 1061 g of a 1.4% strength by weight sodium. adipate solution.
eatchwise electrolysis in a membrane stack cell as per variant b) The membrane stack cell used is diagrammatically depicted in :Figure 3 with three liquid cycles (KL1 to RL3). All product-contacting parts with the exception of 2.1.38153 - 18 - O.Z. 0050/43332 the electrodEa consisted of polypropylene, glass or polytetrafluo:roethylene. Anode (E1) (in compartment (A)) was a titanium expanded-mesh anode having an area of 320 cm' and a coating suitable for oxygen evolution.
Cathode (E2) (in compartment (D)) likewise had an area of 320 cm~. It consisted of a chromium-nickel stainless steel (1.4571) which had been coated with a nickel network activated for hydrogen evolution.
The compartments (A) and (B1), (D1) and (H2), (D2) and (B3) and also (D3) and E were in each case separated from each other by a bipolar membrane (from DE
A 40 26 154). The compartments (B1) and (C1), (B2) and (C2) and also (H3) and (C3) were kept separated from each other by anion exchange membranes (Tokuyama~ Soda AMX).
The compartments ( C 1 ) and ( D1 ) , ( C2 ) and ( D2 ) and also (C3) and (D3) were kept separated from each other by cation exchange membranes (TokuyamaA Soda CMX). The membrane spacings were in each case 0.5 mm.
All liquid cycles with the exception of those of the anode (A) and cathode (E) compartments were recircu lated by means of cycle pumps, (P1) to (P3), the flow velocity being in each case 0.1 m/sec.
The electrolyte used in the acid medium comprised 10000 g of 1.5% strength by weight sulfuric acid intro duced at location (1), the electrolyte in the basic medium_compri.sed 5000 g of 1% strength by weight sodium hydroxide so7Lution introduced at location (2) and the center compartment electrolyte comprised 5000 g of 20%
strength by weight sodium adipate solution introduced at location (3).
A temperature of 55°C, atmospheric pressure, a current density of 0.31 kA/ms, a cell voltage of 13 V (on average) produced with a current yield of 70% and after a reaction time of 13 h the following electrolytes:
dialysis product (removed at location (4)): 11555 g of 6.4% strength by weight adipic acid which additionally contained 1.3% strength by weight of sulfuric acid, . ~~38.~53 - 19 - O.Z. 0050/43332 "basic" electrolyte (removed at location (5)): 6597 g of 6.9% strength by weight sodium hydroxide solution, "depleted" center compartment electrolyte (removed at location (6)): a 1.8% strength by weight solution of sodium adipate.
The apparatus used was an electrodialysis cell having four compartments, the anode compartment being separated from the anode-near center compartment ("acid compartment" _ "SK") by a bipolar exchange membrane (obtained by adhesively bonding a cation exchange mem-brane of the type Selemion~ CMV to an anion exchange membrane of tlhe type Selemion~ AMV as per EP-A 103 959), the acid compartment from the cathode-near center com-partment ("base compartment" _ "BK") by a cation exchange membrane of the type Selemion~ CMV, and the base compart ment from the cathode compartment by a bipolar exchange membrane as used for separating the anode compartment from the acid compartment. The electrodes used were platinum electrodes.
The effective area of a membrane was 3.14 cm~, and the membrane spacing 1 cm. Compartments SK and BK
were each connected to a cycle, while the anode and cathode compartments were connected to a common cycle consisting of reservoir vessel and pump. The temperature setting was by heat exchangers integrated into the cycles. The monitoring of the process was by pH and conductivity measurement in the acid and base cycle.
The materials introduced were into the acid cycle 83.4 g of a solution containing as the solid sodium adipate in a concentration of 0.68 eq/kg, into the base cycle 24.2 g of a dilute NaOH solution having a concen tration of 0.08 eq/kg, and into the electrode rinse cycle dilute NaOH having a concentration of 0.1 eq/kg. The solutions were recirculated and the electrodialysis was carried out at 35°C with a constant current of 0.3 A. The process was discontinued at a pH in the acid cycle of _~138I53 - 20 - O.Z. 0050/43332 about 2.4. Toward the end of the electrodialysis the adipic acid partially precipitated in the reservoir vessel. The e:~cit stream from the acid cycle comprised a total of 79.6 g of solution and solid containing 56.1 meq of adipic acid and 0.4 meq of the bis-Na salt (material yield: 99.6%, acid purity: 99.1% by weight, current yield: 76%). 'The sodium hydroxide solution produced had a concentration of 2.1 eq/kg.
Example 4 was repeated except that the materials introduced were in the case of the acid cycle 82.7 g of a sodium ad3.pate solution (0.49 eq/kg) and an NaOH
concentration of 0.09 eq/kg, in the case of the base cycle 23.9 g of a dilute NaOH solution having a concen-tration of 0.075 eq/kg and in the case of the electrode rinse cycle dilute NaOH having a concentration of 0.1 eq/
kg . The solutions were recirculated and the electrodialy-sis was carried out at 35°C with a constant current of 0.3 A. The process was discontinued at a pH in the acid cycle of about 2.4. The exit stream from the acid cycle comprised 78.5 g of a solution containing 39.9 meq of adipic acid and 0.3 meq of the bis-Na salt (material yield: 99.2%,, acid purity: 99.0% by weight, current yield: 72%). The sodium hydroxide solution produced had a concentration of 1.75 eq/kg.
Example 4 was repeated except that the materials introduced were in the case of the acid cycle 98.2 g of a solution containing 1.64 eq/kg sodium adipate, in the case of the base cycle 39.3 g of a dilute NaOH solution having a concentration of 0.08 eq/kg and in the case of the electrode rinse cycle dilute NaOH having a concent-ration of 0.1 eq/ kg. The solutions were recirculated and the electrod:ialysis was carried out at 60°C with a constant current of 0.3 A. The process was discontinued at a pH in the acid cycle of about 2. The exit stream from the acid cycle comprised 76.9 g of a solution _2138153 - 21 - O.Z. 0050/43332 containing 2.07 eq/kg of adipic acid and < 0.01 eq/kg of Na+ (material yield: 99.1%, acid purity: > 99.4% by weight, current yield: 49%). The solution was cooled to 0°C, and the precipitated solid was filtered off, washed with cold watE:r and dried. The crystallization yield was 82%, the acid content of the crystalline product > 99.96%
by weight (Nay content < 0.01% and bis-Na salt content < 0.04% by weight). The sodium hydroxide solution prod-uced had a concentration of 2.1 eq/kg.
EXAI~LE 7 The apparatus used was an electrodialysis cell having five <:ompartments, the anode compartment being separated from the anode-near center compartment ("acid compartment" ~~ "SR") by a bipolar exchange membrane (see Example 4 ) , t:he acid compartment from the diluate com-partment ("DR") by an anion exchange membrane (Selemion~
AMV), the diluate compartment from the cathode-near center compartment ("base compartment") by a cation exchange membrane (SelemionA CMV), the base compartment from the cai:hode compartment by a bipolar exchange membrane (seE; Example 4). The electrodes used in the anode and cathode compartments were in each case platinum electrodes.
The effective area of a membrane was 3.14 cm=, the membrane spacing was 1 cm. The compartments SR, DR
and_BR were each connected to a cycle, while the anodes and cathodes compartments were connected to a common cycle, consisting of reservoir vessel and pump. The temperature fsetting was by heat exchangers integrated into the cycles. The monitoring of the processes was by pH and conductivity measurement in the acid, diluate and base cycle.
The materials introduced were into the acid cycle 42.9 g of wager, in the diluate cycle 90.6 g of a solu tion containing as solid sodium adipate in a concentra tion of 1.60 eq/kg, into the base cycle 39.3 g of a dilute NaOH solution having a concentration of _ X1381 ~3 - 22 - O.Z. 0050/43332 0.08 eq/kg, and into the electrolyte rinse cycle dilute NaOH having a concentration of 0.1 eq/kg. The solutions were recirculated and the electrodialysis was carried out at 60°C with a constant current of 0.3 A. The process was discontinued a,t a conductivity value in the diluate cycle of 0.2 mS/cm (starting value = 117). The exit mixture from the acid cycle comprised 77.5 g of solution having an adipic acid concentration of 1.82 eq/kg and an Na+
concentration of 0.03 eq/kg (material yield: 99.6%, acid purity: 98.0% by weight, current yield: 50%). The solu-tion was coolE:d down to 0°C, and the precipitated solid was filtered off, washed with cold water and dried. The crystallization yield was 86%, the acid content of the crystalline product was > 99.96% by weight (Na content < 0.01% and b:is-Na salt content < 0.04% by weight). The sodium hydroxide solution produced had a concentration of 1.89 eq/kg. The degree of depletion in the diluate cycle was 99.6%.
A solution having a temperature of 80°C and containing d:isodium adipate in a concentration of 1.98 eq/kg and adipic acid in a concentration of 2.14 eq/kg ways cooled down to 20°C. The crystalline product formed was filtered off, then washed with cold water and dried. The crystalline product contained 0.05%
by weight of lVa+ (corresponds to.a purity of adipic acid of 99.8% by weight), the aqueous phase 2.12 eq/kg of Na, adipate and 1,.10 eq/kg of adipic acid (H* depletion about 50%).
150 g of a solution containing Nay adipate in a concentration of 0.99 eq/kg and adipic acid in a concen-tration of 1.00 eq/kg was extracted three times at 40°C
with 150 g of methyl tert-butyl ether and the extracts were distilled. The following amounts of adipic acid were obtained:
1st fraction _ _~~~8158 - 23 - O.Z. 0050/43332 Amount = 3.10 g (corresponds to 28.3% of the adipic acid contained) Purity = 99.95% by weight 2nd fraction Amount = 2.26 g (corresponds to 20.6% of the adipic acid contained) Purity = 99.79% by weight 3rd fraction Amount = 1.86 g (corresponds to 17.0% of the adipic acid contained) Purity = 99.95% by weight Examples 8 and 9 show that adipic acid can be separated with high purity from a mixture of disodium adipate and ,adipic acid. The solution which had been depleted in ~adipic acid can be recirculated into the electrodialysis.
Batchwise electrolysis in a three-compartment electro-lysis cell as per variant f) The four-compartment electrolysis cell used is diagrammatically depicted in Figure 2 with four liquid cycles (RL1 i:o RL4). All product-contacting parts with the exception, of the electrodes consisted of polypropy-lene, glass or quartz. Anode (E1) (in compartment (A)) was a titanium expanded-mesh anode having an area of 100 cm2 and a caating suitable for oxygen evolution.
Cathode (E2) (in compartment (D)) likewise had an area of 100 cm~. It consisted of chromium-nickel stainless steel (1.4571) which had been coated with a nickel network activated for hydrogen evolution. The two electrode-near cation exchange membranes (M1 and M3) of the type Nafion~
324 were positioned directly on the electrodes (E1 and E2 respectively) and were separated by two center compart-meats, (B) and (C), each 1 mta in width, with a centrally disposed anion exchange membrane.(M2) of the type Tokuy ama Soda~ AMH. The center compartments, (B) and (C), were provided with two polypropylene spacers which served to keep the flow channel free and to prevent direct contact between the membranes.
The anode (KL1) and cathode (RL4) cycles were kept in natural circulation owing to the gas evolutions at the electrodes. The cycles of the center compartments (B) and (C), (KL2) and (RL3), were recirculated using the cycle pumps (P1) and (P2). The flow velocities in the center compartments (B) and (C) were in each case 0.1 m/
sec.
.~1~81~3 - 17 - O.Z. 0050/43332 The anolyte used comprised 1108 g of 5.1%
strength by weight sulfuric acid introduced at location (1), the catolyte comprised 1101 g of 4% strength by weight sodium hydroxide solution introduced at location ( 2 ) , the electrolyte of the anode-near center compartment (B) comprised 1097 g of 2.1% strength by weight sulfuric acid introduced at location (3), and the electrolyte of the cathode-near center compartment (C) comprised 1505 g of 27% strengi:h by weight sodium adipate solution intro duced at locaition (4).
During the reaction a total of 900 g of water was additionally introduced into the cathode-near center compartment ( C ) .
A temperature of 80°C, atmospheric pressure, a current densiity of 3 . 0 kA/ms, a cell voltage of 7 . 0 V ( at the beginning) and 8.7 V (at the end of the run) produced with a current yield of 75% and after a reaction time of 5 h, during which the pH in the cathode-near center compartment (C) was within the range from 10 to 12, the following electrolytes:
anolyte (removed at location (5)): 793 g of 7.1% strength by weight sulfuric acid, catolyte (removed at location (6)): 1584 g of 13.3%
strength by weight sodium hydroxide solution, product of the anode-near center compartment (B) (removed at location (7)): 2034 g of a solution containing 15.1%
strength by weight adipic acid, 1.1% by weight of sulfuric acid, product of the cathode-near center compartment (C) (removed at location (8)): 1061 g of a 1.4% strength by weight sodium. adipate solution.
eatchwise electrolysis in a membrane stack cell as per variant b) The membrane stack cell used is diagrammatically depicted in :Figure 3 with three liquid cycles (KL1 to RL3). All product-contacting parts with the exception of 2.1.38153 - 18 - O.Z. 0050/43332 the electrodEa consisted of polypropylene, glass or polytetrafluo:roethylene. Anode (E1) (in compartment (A)) was a titanium expanded-mesh anode having an area of 320 cm' and a coating suitable for oxygen evolution.
Cathode (E2) (in compartment (D)) likewise had an area of 320 cm~. It consisted of a chromium-nickel stainless steel (1.4571) which had been coated with a nickel network activated for hydrogen evolution.
The compartments (A) and (B1), (D1) and (H2), (D2) and (B3) and also (D3) and E were in each case separated from each other by a bipolar membrane (from DE
A 40 26 154). The compartments (B1) and (C1), (B2) and (C2) and also (H3) and (C3) were kept separated from each other by anion exchange membranes (Tokuyama~ Soda AMX).
The compartments ( C 1 ) and ( D1 ) , ( C2 ) and ( D2 ) and also (C3) and (D3) were kept separated from each other by cation exchange membranes (TokuyamaA Soda CMX). The membrane spacings were in each case 0.5 mm.
All liquid cycles with the exception of those of the anode (A) and cathode (E) compartments were recircu lated by means of cycle pumps, (P1) to (P3), the flow velocity being in each case 0.1 m/sec.
The electrolyte used in the acid medium comprised 10000 g of 1.5% strength by weight sulfuric acid intro duced at location (1), the electrolyte in the basic medium_compri.sed 5000 g of 1% strength by weight sodium hydroxide so7Lution introduced at location (2) and the center compartment electrolyte comprised 5000 g of 20%
strength by weight sodium adipate solution introduced at location (3).
A temperature of 55°C, atmospheric pressure, a current density of 0.31 kA/ms, a cell voltage of 13 V (on average) produced with a current yield of 70% and after a reaction time of 13 h the following electrolytes:
dialysis product (removed at location (4)): 11555 g of 6.4% strength by weight adipic acid which additionally contained 1.3% strength by weight of sulfuric acid, . ~~38.~53 - 19 - O.Z. 0050/43332 "basic" electrolyte (removed at location (5)): 6597 g of 6.9% strength by weight sodium hydroxide solution, "depleted" center compartment electrolyte (removed at location (6)): a 1.8% strength by weight solution of sodium adipate.
The apparatus used was an electrodialysis cell having four compartments, the anode compartment being separated from the anode-near center compartment ("acid compartment" _ "SK") by a bipolar exchange membrane (obtained by adhesively bonding a cation exchange mem-brane of the type Selemion~ CMV to an anion exchange membrane of tlhe type Selemion~ AMV as per EP-A 103 959), the acid compartment from the cathode-near center com-partment ("base compartment" _ "BK") by a cation exchange membrane of the type Selemion~ CMV, and the base compart ment from the cathode compartment by a bipolar exchange membrane as used for separating the anode compartment from the acid compartment. The electrodes used were platinum electrodes.
The effective area of a membrane was 3.14 cm~, and the membrane spacing 1 cm. Compartments SK and BK
were each connected to a cycle, while the anode and cathode compartments were connected to a common cycle consisting of reservoir vessel and pump. The temperature setting was by heat exchangers integrated into the cycles. The monitoring of the process was by pH and conductivity measurement in the acid and base cycle.
The materials introduced were into the acid cycle 83.4 g of a solution containing as the solid sodium adipate in a concentration of 0.68 eq/kg, into the base cycle 24.2 g of a dilute NaOH solution having a concen tration of 0.08 eq/kg, and into the electrode rinse cycle dilute NaOH having a concentration of 0.1 eq/kg. The solutions were recirculated and the electrodialysis was carried out at 35°C with a constant current of 0.3 A. The process was discontinued at a pH in the acid cycle of _~138I53 - 20 - O.Z. 0050/43332 about 2.4. Toward the end of the electrodialysis the adipic acid partially precipitated in the reservoir vessel. The e:~cit stream from the acid cycle comprised a total of 79.6 g of solution and solid containing 56.1 meq of adipic acid and 0.4 meq of the bis-Na salt (material yield: 99.6%, acid purity: 99.1% by weight, current yield: 76%). 'The sodium hydroxide solution produced had a concentration of 2.1 eq/kg.
Example 4 was repeated except that the materials introduced were in the case of the acid cycle 82.7 g of a sodium ad3.pate solution (0.49 eq/kg) and an NaOH
concentration of 0.09 eq/kg, in the case of the base cycle 23.9 g of a dilute NaOH solution having a concen-tration of 0.075 eq/kg and in the case of the electrode rinse cycle dilute NaOH having a concentration of 0.1 eq/
kg . The solutions were recirculated and the electrodialy-sis was carried out at 35°C with a constant current of 0.3 A. The process was discontinued at a pH in the acid cycle of about 2.4. The exit stream from the acid cycle comprised 78.5 g of a solution containing 39.9 meq of adipic acid and 0.3 meq of the bis-Na salt (material yield: 99.2%,, acid purity: 99.0% by weight, current yield: 72%). The sodium hydroxide solution produced had a concentration of 1.75 eq/kg.
Example 4 was repeated except that the materials introduced were in the case of the acid cycle 98.2 g of a solution containing 1.64 eq/kg sodium adipate, in the case of the base cycle 39.3 g of a dilute NaOH solution having a concentration of 0.08 eq/kg and in the case of the electrode rinse cycle dilute NaOH having a concent-ration of 0.1 eq/ kg. The solutions were recirculated and the electrod:ialysis was carried out at 60°C with a constant current of 0.3 A. The process was discontinued at a pH in the acid cycle of about 2. The exit stream from the acid cycle comprised 76.9 g of a solution _2138153 - 21 - O.Z. 0050/43332 containing 2.07 eq/kg of adipic acid and < 0.01 eq/kg of Na+ (material yield: 99.1%, acid purity: > 99.4% by weight, current yield: 49%). The solution was cooled to 0°C, and the precipitated solid was filtered off, washed with cold watE:r and dried. The crystallization yield was 82%, the acid content of the crystalline product > 99.96%
by weight (Nay content < 0.01% and bis-Na salt content < 0.04% by weight). The sodium hydroxide solution prod-uced had a concentration of 2.1 eq/kg.
EXAI~LE 7 The apparatus used was an electrodialysis cell having five <:ompartments, the anode compartment being separated from the anode-near center compartment ("acid compartment" ~~ "SR") by a bipolar exchange membrane (see Example 4 ) , t:he acid compartment from the diluate com-partment ("DR") by an anion exchange membrane (Selemion~
AMV), the diluate compartment from the cathode-near center compartment ("base compartment") by a cation exchange membrane (SelemionA CMV), the base compartment from the cai:hode compartment by a bipolar exchange membrane (seE; Example 4). The electrodes used in the anode and cathode compartments were in each case platinum electrodes.
The effective area of a membrane was 3.14 cm=, the membrane spacing was 1 cm. The compartments SR, DR
and_BR were each connected to a cycle, while the anodes and cathodes compartments were connected to a common cycle, consisting of reservoir vessel and pump. The temperature fsetting was by heat exchangers integrated into the cycles. The monitoring of the processes was by pH and conductivity measurement in the acid, diluate and base cycle.
The materials introduced were into the acid cycle 42.9 g of wager, in the diluate cycle 90.6 g of a solu tion containing as solid sodium adipate in a concentra tion of 1.60 eq/kg, into the base cycle 39.3 g of a dilute NaOH solution having a concentration of _ X1381 ~3 - 22 - O.Z. 0050/43332 0.08 eq/kg, and into the electrolyte rinse cycle dilute NaOH having a concentration of 0.1 eq/kg. The solutions were recirculated and the electrodialysis was carried out at 60°C with a constant current of 0.3 A. The process was discontinued a,t a conductivity value in the diluate cycle of 0.2 mS/cm (starting value = 117). The exit mixture from the acid cycle comprised 77.5 g of solution having an adipic acid concentration of 1.82 eq/kg and an Na+
concentration of 0.03 eq/kg (material yield: 99.6%, acid purity: 98.0% by weight, current yield: 50%). The solu-tion was coolE:d down to 0°C, and the precipitated solid was filtered off, washed with cold water and dried. The crystallization yield was 86%, the acid content of the crystalline product was > 99.96% by weight (Na content < 0.01% and b:is-Na salt content < 0.04% by weight). The sodium hydroxide solution produced had a concentration of 1.89 eq/kg. The degree of depletion in the diluate cycle was 99.6%.
A solution having a temperature of 80°C and containing d:isodium adipate in a concentration of 1.98 eq/kg and adipic acid in a concentration of 2.14 eq/kg ways cooled down to 20°C. The crystalline product formed was filtered off, then washed with cold water and dried. The crystalline product contained 0.05%
by weight of lVa+ (corresponds to.a purity of adipic acid of 99.8% by weight), the aqueous phase 2.12 eq/kg of Na, adipate and 1,.10 eq/kg of adipic acid (H* depletion about 50%).
150 g of a solution containing Nay adipate in a concentration of 0.99 eq/kg and adipic acid in a concen-tration of 1.00 eq/kg was extracted three times at 40°C
with 150 g of methyl tert-butyl ether and the extracts were distilled. The following amounts of adipic acid were obtained:
1st fraction _ _~~~8158 - 23 - O.Z. 0050/43332 Amount = 3.10 g (corresponds to 28.3% of the adipic acid contained) Purity = 99.95% by weight 2nd fraction Amount = 2.26 g (corresponds to 20.6% of the adipic acid contained) Purity = 99.79% by weight 3rd fraction Amount = 1.86 g (corresponds to 17.0% of the adipic acid contained) Purity = 99.95% by weight Examples 8 and 9 show that adipic acid can be separated with high purity from a mixture of disodium adipate and ,adipic acid. The solution which had been depleted in ~adipic acid can be recirculated into the electrodialysis.
Claims (8)
1. A process for preparing adipic acid by subjecting an aqueous solution of an alkali metal salt of adipic acid to electrolysis in a three-part membrane electrolysis cell comprising an anode, a cathode, an anolyte compartment, a catolyte compartment, a center compartment and two cation exchange membranes, which comprises performing the electrolysis with addition of a mineral acid or of a salt to the center compartment to obtain a solution of adipic acid and a solution of an alkali metal hydroxide.
2. A process as claimed in claim 1, wherein the mineral acid or salt used is sulfuric acid, nitric acid, sodium sulfate or sodium nitrate.
3. A process as claimed in claims 1 or 2, wherein the electrolysis is carried out at a temperature within the range from 50 to 110°C.
4. A process as claimed in any one of claims 1 to 3, wherein the flows are guided countercurrently.
5. A process as claimed in any one of claims 1 to 4, wherein adipic acid is isolated from the solution containing adipic acid by crystallization.
6. A process as claimed in claim 5, wherein the crystallization i;s carried out at a temperature within the range from 0 to 50°C and at pressures within the range from 1 to 100 kPa.
7. A process as claimed in claim 5 or 6, wherein the crystallization is carried out at a temperature within the range from 15 to 40°C and at pressures within the range from 4 to 20 kpa.
8. The use of any one of the process of claims 5 to 7 for preparing adipic acid of high purity.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE4219758A DE4219758A1 (en) | 1992-06-17 | 1992-06-17 | Process for the electrochemical production of dicarboxylic acids |
| DEP4219758.9 | 1992-06-17 | ||
| PCT/EP1993/001450 WO1993025299A1 (en) | 1992-06-17 | 1993-06-09 | Electrochemical method for the preparation of dicarboxylic acids |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2138153A1 CA2138153A1 (en) | 1993-12-23 |
| CA2138153C true CA2138153C (en) | 2000-05-16 |
Family
ID=6461168
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002138153A Expired - Fee Related CA2138153C (en) | 1992-06-17 | 1993-06-09 | Electrochemical preparation of dicarboxylic acids |
Country Status (8)
| Country | Link |
|---|---|
| EP (1) | EP0646042B1 (en) |
| JP (1) | JPH07507598A (en) |
| AT (1) | ATE173177T1 (en) |
| CA (1) | CA2138153C (en) |
| DE (2) | DE4219758A1 (en) |
| DK (1) | DK0646042T3 (en) |
| ES (1) | ES2123650T3 (en) |
| WO (1) | WO1993025299A1 (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE4342668A1 (en) * | 1993-12-15 | 1995-06-22 | Basf Ag | Process for the recovery of carboxylic acids from their salts |
| US5928485A (en) * | 1996-04-08 | 1999-07-27 | E. I. Du Pont De Nemours And Company | Process for isolation of dicarboxylic acids and hydroxycarboxylic acids |
| FR2754192B1 (en) * | 1996-10-04 | 1998-12-04 | Rhone Poulenc Fibres & Polymer | PROCESS FOR THE EXTRACTION OF AMINE COMPOUNDS FROM A LIQUID MEDIUM |
| US6004445A (en) * | 1997-06-30 | 1999-12-21 | Electrosynthesis Company, Inc. | Electrochemical methods for recovery of ascorbic acid |
| AU5091699A (en) | 1998-07-07 | 2000-01-24 | E.I. Du Pont De Nemours And Company | A process for the isolation of aromatic hydroxycarboxylic acids |
| DE19849922A1 (en) | 1998-10-29 | 2000-05-04 | Degussa | Process for the treatment of aqueous solutions containing bases and organic acids |
| JP6717935B2 (en) * | 2015-06-11 | 2020-07-08 | ビーエル テクノロジーズ、インコーポレイテッド | Bipolar electrodialysis method and system |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3964985A (en) * | 1974-10-29 | 1976-06-22 | Ionics, Incorporated | Electrodialysis apparatus and process for ion modification |
| US4781809A (en) * | 1986-07-21 | 1988-11-01 | Ionics, Incorporated | Recovering free organic acids from solutions in which they occur with other organic matter |
| DE3926634A1 (en) * | 1988-08-11 | 1990-02-15 | Fraunhofer Ges Forschung | Multi-cell electrodialysis appts. - esp. for organic acid recovery from salt |
| DE3926642C2 (en) * | 1988-08-11 | 1998-02-26 | Fraunhofer Ges Forschung | Process for obtaining an acid from its salt |
| US5288378A (en) * | 1990-09-28 | 1994-02-22 | Alliedsignal Inc. | Guard membranes for use in electrodialysis cells |
-
1992
- 1992-06-17 DE DE4219758A patent/DE4219758A1/en not_active Withdrawn
-
1993
- 1993-06-09 WO PCT/EP1993/001450 patent/WO1993025299A1/en active IP Right Grant
- 1993-06-09 JP JP6501110A patent/JPH07507598A/en active Pending
- 1993-06-09 DK DK93912921T patent/DK0646042T3/en active
- 1993-06-09 AT AT93912921T patent/ATE173177T1/en not_active IP Right Cessation
- 1993-06-09 DE DE59309129T patent/DE59309129D1/en not_active Expired - Lifetime
- 1993-06-09 EP EP93912921A patent/EP0646042B1/en not_active Expired - Lifetime
- 1993-06-09 CA CA002138153A patent/CA2138153C/en not_active Expired - Fee Related
- 1993-06-09 ES ES93912921T patent/ES2123650T3/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
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| JPH07507598A (en) | 1995-08-24 |
| DK0646042T3 (en) | 1999-07-26 |
| EP0646042B1 (en) | 1998-11-11 |
| DE59309129D1 (en) | 1998-12-17 |
| WO1993025299A1 (en) | 1993-12-23 |
| DE4219758A1 (en) | 1993-12-23 |
| ATE173177T1 (en) | 1998-11-15 |
| CA2138153A1 (en) | 1993-12-23 |
| ES2123650T3 (en) | 1999-01-16 |
| EP0646042A1 (en) | 1995-04-05 |
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