KR100765018B1 - Process for improving the purity of quaternary ammonium hydroxides by electrolysis - Google Patents

Abstract

The present invention relates to a method of using a cation selective membrane to improve the purity of a composition comprising quaternary ammonium hydroxides by electrolysis,

The process is characterized in that it is particularly suitable for improving the purity of aqueous solutions comprising tetramethylammonium hydroxides used in the preparation of 4-aminodiphenylamine for many reaction cycles.

Description

PROCESS FOR IMPROVING THE PURITY OF QUATERNARY AMMONIUM HYDROXIDES BY ELECTROLYSIS}

[Technical Field]
The present invention relates to a method for improving the purity of a composition comprising quaternary ammonium hydroxide.

[Background]
Quaternary ammonium hydroxides such as tetramethylammonium hydroxide (TMAH) are used as developer for photoresist, especially in the manufacture of printed circuit boards and microelectronic chips, and as the base in the production of 4-aminodiphenylamine (4-ADPA). Is used. Alkylated derivatives of 4-ADPA, such as N- (1,3-dimethylbutyl) -N'-phenyl-p-phenylenediamine (6PPD), are used as antidegradants in rubber products such as tires and in rubber compositions. .

In the preparation of the 4-ADPA, the base, which is generally present in the form of an aqueous solution, is recycled several times (hereinafter referred to as the recycle base). However, after several reaction cycles, the active content of the aqueous base solution is reduced to the point where it can no longer be used in the manufacturing process, and to some extent the recycled aqueous base solution is purged and replaced with fresh base solution, or all discarded, This increases the manufacturing cost of 4-ADPA and 6PPD. The present invention provides a solution to this waste problem. In addition, as the number of reaction cycles increases, liquid-liquid separation of the aqueous base solution from the 4-ADPA-comprising organic phase proceeds very difficult.

When TMAH is used as the base, the purged / discarded aqueous recycle base solution is one of the starting materials for the preparation of 4-ADPA-aniline as well as tetramethylammonium acetate, formate, chloride, carbonate and oxalate. Such as various tetramethylammonium (TMA) salts. Various other salts and other organic impurities are also included in small amounts.

Quaternary ammonium hydroxides are generally prepared by electrolysis. For example, TMAH is prepared from tetramethylammonium chloride using two zone electrolysis cells comprising an anolyte zone containing an anode and a catholyte zone comprising a cathode. The zone is separated by a cation selective membrane. Such membranes are also referred to in the art as cation-exchange membranes. In this preparation method, the quaternary ammonium salt used to prepare the quaternary ammonium hydroxide is charged to the anolyte zone of the electrolysis cell.

It is also known in the art to improve the purity of mixtures comprising quaternary ammonium hydroxides by electrolysis.

For example, US Pat. No. 4,714,530 discloses a process for preparing high purity quaternary ammonium hydroxides by electrolysis using two zone electrolysis cells equipped with cation-exchange membranes, wherein an aqueous solution comprising quaternary ammonium hydroxides is prepared. Fill the anolyte zone.

US Pat. No. 5,389,211 describes quaternary ammonium hydroxides by electrolysis using an electrolysis cell comprising at least two intermediate zones in which the anolyte and catholyte zones are separated by at least two non-ion dividers and / or cation selective membranes. A method of improving the purity of an organic or inorganic hydroxide such as is disclosed. A mixture comprising hydroxide is charged in the anolyte zone. It is disclosed that the catholyte zone and the middle zone may also include organic or inorganic hydroxides prior to the start of electrolysis. The purpose of filling purified zones with intermediate zones is disclosed to avoid increasing impurities in the zones (col. 12, II. 47-51).

The methods of US Pat. No. 4,714,530 and US Pat. No. 5,389,211 relate to a method for improving the purity of waste aqueous solutions of quaternary ammonium hydroxides used as developer for photoresists in printed circuit boards and microelectronic chips, the solutions being generally high amounts of halogens. It includes. However, aqueous waste solutions comprising quaternary ammonium hydroxides obtained during the preparation of 4-ADPA generally do not have similarly high halogen content; Generally other anions and organic impurities described above, in particular aniline, are included.

The inventors have found that a large amount of solid material is formed at the anode by electrolysis which is carried out by charging the anolyte zone of the two zone electrolysis cell immediately after the start of the electrolysis of the recycle TMAH obtained in the preparation of 4-ADPA. , It was found that the electrode and anolyte zones were contaminated and the electrolysis stopped practically after a while (see Comparative Examples A and B).

Detailed description of the invention
Surprisingly, the inventors have found that the above problems are not much reduced or even occur when electrolysis is carried out according to the present invention.

The method for improving the purity of a composition comprising quaternary ammonium hydroxide according to the present invention comprises the following steps:

(a) preparing an electrolysis cell comprising an anolyte zone comprising an anode, a catholyte zone comprising a cathode, and at least one intermediate zone separating the anolyte zone from the catholyte zone with a cation selective membrane;

(b) optionally filling water comprising a supporting electrolyte into the anolyte zone, optionally filling water with quaternary ammonium hydroxide into the catholyte zone, and containing the composition comprising the quaternary ammonium hydroxide to be purified in an intermediate zone. Charging to;

(c) passing an electrical current through the electrolysis cell to produce a purified aqueous quaternary ammonium hydroxide solution in the catholyte zone; And

(d) recovering the purified aqueous quaternary ammonium hydroxide solution from the catholyte zone.

In the case of the recycle base obtained in the preparation of 4-ADPA, the negative electrode of the aqueous solution comprising acetate, formate, chloride, carbonate and oxalate with anions of a smaller amount than present in the recycle base by the process of the invention Recovered from the liquid zone, the aqueous solution contains a large amount of quaternary ammonium hydroxide content if desired. Generally, the recovered aqueous base solution also comprises a portion / fraction of the neutral organic compound present in the recycle base, such as aniline.

Due to the fact that the anolyte zone and the catholyte zone comprise an aqueous solution, oxygen gas is formed at the anode and hydrogen gas is formed at the cathode. The presence of tetramethylammonium carbonate and / or tetramethylammonium bicarbonate in the middle zone can lead to the formation of carbon dioxide gas depending on the pH of the aqueous solution in the middle zone. The gas is controlled and treated by conventional methods.

The process of the present invention can be carried out using any known electrolysis cell equipped with a conventional electrode and a cation selective membrane, provided that the electrode and membrane are formed with a solution formed and filled in the anolyte zone, the middle zone and the catholyte zone. There must be compatibility.

The anode and the cathode can be made of various materials. The anode should be suitable for oxygen formation / release and the cathode should be suitable for hydrogen formation / release. Suitable anodes and cathodes are known to those skilled in the art. The cathode may also be an oxygen reduction / oxygen depolarizing cathode. Preferably, dimensionally stable anodes (DSA) and stainless steel cathodes are used for oxygen release.

The cation selective membrane may be one used for electrolysis of quaternary ammonium salts to quaternary ammonium hydroxides and for electrolytic purification of quaternary ammonium hydroxides. One skilled in the art can use a variety of suitable cation selective membranes. There is a difference between perfluorinated and non-perfluorinated films. Preferably, the cation selective membrane used according to the invention is a perfluorinated membrane made of polytetrafluoroethylene, for example marketed under the name Nafion from DuPont. Other suitable cation selective membranes include membranes made of polyethylene, polypropylene, polyvinylchloride, polystyrene-divinylbenzene and (sulfonated) polysulfones.

Apart from the fact that cation selective membranes pass cations and prevent the transport of anions, the membrane is also selective for the cation form. For example, proton selective membranes are known in the art.

In the process of the invention, at least two cation selective membranes are used. The membranes may be the same or different. In practice two identical cation selective membranes are used. Preferably, the process of the present invention selects quaternary ammonium ions present in the composition comprising a proton-selective membrane separating the anolyte zone and the intermediate zone and a quaternary ammonium hydroxide to be purified separating the intermediate zone and the catholyte zone. Using a conventional membrane.

The electrolysis cell used in the process of the invention comprises at least one intermediate zone. Thus, the cell comprises three or more zones, each separated by a cation selective membrane described above. Preferably, three zone electrolysis cells are used because the use of two or more cation selective membranes increases not only the electricity consumption but also the cost of the electrolysis cell, ie the operating cost. In general, including an additional cation selective membrane will increase the purity of the quaternary ammonium hydroxide aqueous solution recovered in the catholyte zone.

If a high purity quaternary ammonium hydroxide aqueous solution is desired, two or more intermediate zones are consequently used, and according to the method of the present invention, the composition comprising the quaternary ammonium hydroxide to be purified is filled next to the intermediate zone, which is the anolyte zone. In such cases, the other intermediate zone (s) and catholyte zone will generally comprise an aqueous solution of quaternary ammonium hydroxide of high purity, i.

Quaternary ammonium hydroxide-comprising compositions to be purified according to the process of the invention generally comprise from 1% to 45% by weight, preferably from 5% to 40% by weight, more preferably from 10% to 35% by weight of 4 It is an aqueous solution containing secondary ammonium hydroxide. The composition may comprise an organic solvent. Inorganic hydroxides such as sodium hydroxide, potassium hydroxide or cesium hydroxide may also be included.

Quaternary ammonium hydroxide-comprising compositions for use in the methods of the present invention may include certain quaternary ammonium hydroxides. Generally, the composition comprises tetrahydrocarbylammonium hydroxide or hydrocarbylene di (trihydrocarbyl) ammonium hydroxide. The composition may also include a mixture of quaternary ammonium hydroxides and inorganic hydroxides. Typical examples are tetramethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, choline hydroxide, phenyltrimethylammonium hydroxide, benzyltrimethylammonium hydroxide and bis-dibutylethyl hexamethylene diammonium hydroxide (hexamethylene 1,6-di ( Dibutylethyl) ammonium dioxide). Other suitable examples are described in the aforementioned documents, ie US 4,714,530 (col. 2, I. 60 to col. 3, I.2) and US 5,389,211 (col. 5, II. 43-60). Preferably, the composition comprises tetramethylammonium hydroxide (TMAH). More preferably, the composition to be purified according to the invention is an aqueous solution used for the preparation of 4-ADPA for a plurality of reaction cycles (ie recycle bases), most preferably an aqueous solution comprising TMAH. Recycle bases generally include aniline. Recycling bases may also include inorganic hydroxides.

At the start of the electrolysis, the anolyte zone optionally comprises water comprising a supporting electrolyte and the catholyte zone optionally comprises water comprising quaternary ammonium hydroxides. Preferably demineralized or soft water is used in the process of the invention. The term "supporting electrolyte" is known to those skilled in the art. Certain supporting electrolytes can be used. The supporting electrolyte is mainly present to increase the conductivity of the anolyte solution. In the catholyte zone, the increase in conductivity of the catholyte solution is effected by including quaternary ammonium hydroxide. The presence of electrolytes in the anolyte and catholyte zones allows current to flow through the electrolysis cell immediately after the start of electrolysis. It is known that the process of the invention in which the electrolyte-comprising aqueous solution is present in the anolyte and catholyte zones is not critical. The choice will be primarily determined by the desired purity and the desired active content of the quaternary ammonium hydroxide aqueous solution to be recovered in the catholyte zone. Preferably, the desired active content is 15% to 25% by weight, more preferably about 20% by weight.

Preferably, the anolyte solution includes a supporting electrolyte. More preferably, the anolyte zone comprises sulfuric acid or phosphoric acid, more preferably an aqueous strong acid solution such as sulfuric acid. The actual anolyte solution starts with 1 wt% to 10 wt%, preferably 3 wt% to 9 wt%, more preferably 3 wt% to 5 wt% aqueous sulfuric acid solution. Preferably, the volume of the aqueous solution present in the anolyte zone (i.e. water consumed during electrolysis and transported to the catholyte zone), the active content and the amount of impurities are recorded and the volume and active content adjusted if necessary. . If the amount of impurities is undesirably high, the entire anolyte solution can be removed and replaced with a fresh solution.

Preferably, the catholyte zone comprises an aqueous quaternary ammonium hydroxide solution such as quaternary ammonium hydroxide present in the composition to be purified. The actual catholyte solution starts with 1% to 35% by weight, preferably 5% to 25% by weight, more preferably 5% to 20% by weight of aqueous quaternary ammonium hydroxide solution. Preferably, the catholyte zone is filled with an aqueous solution of quaternary ammonium hydroxide of high purity, i.e. the desired purity. The active content can be varied as desired. More preferably, an aqueous TMAH solution is used as the starting catholyte solution.

The process of the invention can be carried out in a batchwise or semi-continuous or continuous manner. In practice the placement method is used. Preferably, the process of the present invention is electrolyzed until substantially all quaternary ammonium ions are removed before filling the middle zone with a batch of the composition comprising the quaternary ammonium hydroxide to be purified, and then filling the next batch with the middle zone. It is carried out in a way. In the case of the recycle base, it has been found to be beneficial to dilute the recycle base with water before filling the middle section of the electrolysis cell. The treated batches present in the intermediate zone are removed in whole or in part and replaced by later batches, respectively, or the later batches and the remaining portions are mixed. In the case of the recycle base, preferably a part of the treated batch, ie the so-called heel, is mixed with the new part of the recycle base. More preferably, approximately equal parts of the heel and fresh recycle base are filled in the middle zone.

In a preferred embodiment of the process of the invention, the middle zone is washed with a suitable solvent. It has been found that some solid material is formed in the intermediate zone after a number of batch treatments. As a result, the membrane separating the anolyte zone from the intermediate zone and the intermediate zone flow circulation equipment, ie the circulation loop, the loop filter and the circulation vessel, are contaminated. Suitable solvents are those which dissolve the solid material formed without affecting any part of the electrolysis device. This can be readily determined by one skilled in the art. Suitable solvents include aniline, N, N-dimethylformamide, N-methyl-2-pyrrolidone and dimethyl sulfoxide. In the case of the recycle base, it is preferred that aniline is used as the solvent. The washing step is often carried out using a large amount of solvent as necessary. In addition, the above can be easily determined by those skilled in the art. In the case of batch mode operation of the process of the invention, the washing is actually carried out at the end of each batch process. Preferably, after washing with a suitable solvent, the middle zone is washed with water before the new batch is filled in the middle zone. When using aniline as a solvent and in the case of recycle base, it is then preferable to remove the aniline by washing with water.

The solvent washing step is generally carried out at elevated temperature, preferably at 40 ° C. to 80 ° C., more preferably at 40 ° C. to 60 ° C., and most preferably at 40 ° C. to 50 ° C. Water washing is generally carried out at a temperature of 20 ° C to 50 ° C.

Electrolysis of compositions comprising quaternary ammonium hydroxides to be purified is generally carried out by applying a direct current between the anode and the cathode at a current density of at least 4,000 A / m 2. The actual range is from 500 A / m 2 to 1,500 A / m 2. Preferably, a current is applied to the electrolysis cell for a sufficient time to transport all quaternary ammonium ions from the intermediate zone to the catholyte zone. An important parameter that records the progress of the method of the present invention is the pH of the aqueous solution in the middle zone.

During the electrolysis of the composition containing the quaternary ammonium hydroxide to be purified, for example, when an aqueous sulfuric acid solution is used as the anolyte, the pH of the solution in the intermediate zone is the proton transport from the anolyte zone to the intermediate zone and the catholyte from the intermediate zone. Quaternary ammonium ions to the zone are reduced by transport. Anions such as chlorine ions cannot pass through the cation selective membrane separating the catholyte zone and the intermediate zone. However, weak acids such as acetic acid can pass through the cation selective membrane by dispersion. Preferably, the electrolysis stops at a point in the intermediate zone at which the pH becomes 1-7, more preferably 4-7, even more preferably 4-6, most preferably about 5.

In the case of the recycle base obtained in the preparation of 4-ADPA and when the invention is carried out in a batch manner, the pH in the intermediate zone is reduced from a value of at least 10 to the desired final pH value. When only a portion of the treated composition present in the intermediate zone is replaced by the next batch or the method is carried out in continuous operation, the pH can maintain a certain selected value, i.e. 5 to 7.

In general, the aqueous solution present in each zone of the electrolysis cell is circulated by pumping action using conventional methods such as a circulation loop, a circulation vessel and a separate pump for each zone. The circulation loop may have a filter.

During electrolysis, the solution temperature in the zone is generally maintained at 10 ° C. to 90 ° C., preferably at 40 ° C. to 80 ° C., more preferably at 40 ° C. to 60 ° C., and most preferably at 40 ° C. to 50 ° C.

The invention is illustrated by the following examples.

Example 1 and Example 2

Two one-batch experiments consisted of a three-zone micro, comprising an anolyte zone containing an anode, a catholyte zone comprising a cathode, and an intermediate zone separating the anolyte and catholyte zones by two cation selective membranes. It was carried out using a three-compartment Micro Flow Cell (manufactured by ElectroCell). EPDM gaskets and Teflon frames were used.

In the first experiment, namely Example 1, two Nafion 117 membranes (manufactured by DuPont) were used. At the beginning of the experiment, the anode was platinum, which was subsequently replaced by a dimensionally stable anode (DSA) for oxygen release (both from ElectroCell). The cathode is stainless steel (manufactured by ElectroCell). The anolyte solution was changed several times to contain an average of 2.17 wt% aqueous H ₂ SO ₄ and 4.59 wt% aqueous acetic acid (HAc), increasing the amount of tetramethylammonium (TMA) -acetate in the middle zone. The starting catholyte solution is 6.7% by weight aqueous tetramethylammonium hydroxide (TMAH). The recycle base contains 12.85% by weight of TMAH and is charged to the middle section of the electrolysis cell.

In a second experiment, namely Example 2, two Nafion 324 membranes (manufactured by DuPont) were used. The anode is a DSA for oxygen release. The cathode is stainless steel. The anolyte is 2.50 wt% aqueous H ₂ SO ₄ and the catholyte is 4.94 wt% aqueous TMAH. The recycle base contains 19.90 wt.% TMAH and is filled in the middle zone.

The results described in Table 1 to 3 is recirculated within TMA- acetate recovered from the catholyte solution by the electrolysis zone of TMAH, TMA- formate, TMA- chloride, TMA ₂ - of oxalate-carbonate and TMA ₂ The base is considerably purified in that the amount is significantly lower in the solution present in the middle zone, and no TMAH remains in the middle zone, while the TMAH content in the aqueous solution recovered in the catholyte zone is clearly increased. In addition, some aniline is present in the aqueous solution recovered in the catholyte zone.

Detection limits are as follows: TMA-acetate (0.0023 wt%), TMA-formate (0.0013 wt%), TMA-chloride (0.0015 wt%), TMA ₂ -carbonate (0.0350 wt%) , TMA ₂ -oxalate (0.0027 wt.%) And TMAH (0.0100 wt.%).

Electrolysis data Example One 2 Average current efficiency (%) 32 60 Average current density (A / ㎡) 700 450 Temperature (℃) 45 45 Final pH of the intermediate zone 5.2 1.1 DC voltage (V) 7 7.5

Initiated and Recovered Base Compositions Example 1 A _start A _final I _start I _final C _start C _final TMA-acetate weight% 0.86 4.44 nd 0.06 TMA-formate weight% 1.34 1.05 nd 0.04 TMA-chloride weight% 0.03 0.003 nd 0.002 TMA ₂ -carbonate weight% 11.55 0.61 nd 0.49 TMA ₂ -oxalate weight% 2.05 1.58 nd 0.02 TMAH weight% 12.85 nm 6.7 24.0 aniline weight% 1.33 0.35 nd 0.59 H ₂ SO ₄ weight% 2.17 nd HAc weight% 4.59 nd weight g 3536.8 3030.9 832.6 722.7 726.8 765.2 Collected Sample g 179.2 164.9

_Initiation A is the initiating solution in the anolyte zone, A _final is the final anolyte solution, I _initiation is the initiating solution in the middle zone, I _final is the final solution in the middle zone, C _initiation is the starting catholyte solution, and C _Final is the final catholyte solution, TMA stands for tetramethylammonium, nm is not measurable (below detection limit), and nd is not measured.

Initiated and Recovered Base Compositions Example 2 A _start A _final I _start I _final C _start C _final TMA-acetate weight% 1.23 1.45 nd 0.05 TMA-formate weight% 0.83 1.00 nd 0.08 TMA-chloride weight% 0.02 0.003 nd 0.002 TMA ₂ -carbonate weight% 9.65 0.64 nd 0.23 TMA ₂ -oxalate weight% 1.55 2.05 nd 0.02 TMAH weight% 19.90 nm 4.94 25.6 aniline weight% 2.68 nd nd nd H ₂ SO ₄ weight% 2.50 3.03 weight g 790.6 408.2 932.6 438.2 607.2 954.1 Added water g 50.7 323.0 Collected Sample g 213.0 318.9 186.2

_Initiation A is the initiating solution of the anolyte zone, A _final is the final anolyte solution, I _initiation is the initiating solution in the middle zone, I _final is the final solution in the middle zone, C _initiation is the starting catholyte solution, and C _Final is the final catholyte solution, TMA stands for tetramethylammonium, nm means not measurable (below detection limit), nd means not measured.

Comparative Examples A and B

Two 1-batch experiments were carried out using an anolyte zone containing an anode and a catholyte zone comprising a cathode, which zones were used using a two-zone micro flow cell (manufactured by ElectroCell) separated by a cation selective membrane. It became. EPDM gaskets and Teflon frames were used.

In the first experiment, namely Comparative Example A, a Nafion 450 membrane (manufactured by DuPont) was used. The anode is a platinum electrode and the cathode is stainless steel. The recycle base is charged to the anolyte zone and contains 13.61% by weight of TMAH. The starting catholyte solution is 13.85% by weight of aqueous TMAH.

In a second experiment, Comparative Example B, a Nafion 117 membrane was used. The anode is DSA for oxygen release and the cathode is stainless steel. The recycle base was charged to the anolyte zone and contained 12.68 wt% TMAH and the catholyte was 12.09 wt% aqueous TMAH. The results of the experiments are shown in Tables 4-6.

It was found that a large amount of solid material formed at the anode contaminated the electrode and anolyte zones and had to be removed periodically in order to carry out electrolysis continuously. Eventually, the electrolysis actually stopped (TMA ⁺ bound to carbonate was not carried from the anolyte zone to the catholyte zone). As a result, electrolysis cannot be carried out long enough for an economically advantageous recovery of the TMAH to be obtained. In addition, the removal of the solid is time consuming and cumbersome.

Electrolysis data Comparative Example A B Average current efficiency (%) 35 19 Average current density (A / ㎡) 1300 2400 Temperature (℃) 46 47 DC voltage (V) 7.7 8.2

Initiated and Recovered Base Compositions Comparative Example A A _start A _final C _start C _final TMA-acetate weight% 0.74 0.66 nm nm TMA-formate weight% 1.09 1.02 nm nm TMA-chloride weight% 0.02 0.02 nm nm TMA ₂ -carbonate weight% 12.08 18.18 0.16 0.32 TMA ₂ -oxalate weight% 1.89 1.43 nm nm TMAH weight% 13.61 0.33 13.85 21.98 aniline weight% 1.90 0.44 nd 0.24 weight g 900 830 750 420 Added water g 100 Collected Sample g 240 240

_Initiation A is the starting anolyte solution, A _final is the final anolyte solution, C _initiation is the starting catholyte solution, C _final is the final catholyte solution, nm is not measurable (below detection limit), and nd is not measured It means not.

Initiated and Recovered Base Compositions Comparative Example B A _start A _final C _start C _final TMA-acetate weight% 0.67 1.08 nm nm TMA-formate weight% 1.06 1.25 nm nm TMA-chloride weight% 0.02 0.02 nm nm TMA ₂ -carbonate weight% 13.25 24.98 nm nm TMA ₂ -oxalate weight% 1.86 1.65 nm nm TMAH weight% 12.68 nm 12.09 23.44 aniline weight% 1.79 0.56 nd 0.47 weight g 900 570 750 530 Added water g 100 Collected Sample g 120 120

_Initiation A is the starting anolyte solution, A _final is the final anolyte solution, C _initiation is the starting catholyte solution, C _final is the final catholyte solution, nm is not measurable (below detection limit), and nd is not measured It means not.

Example 3

A three-compartment Multi Purpose Cell (manufactured by ElectroCell) equipped with a DSA anode, a stainless steel cathode and two Nafion 324 cation selective membranes was prepared in a manner similar to that described in Examples 1 and 2. Thus (ie 12.5 V, 40-50 ° C., final pH 5), it was operated with 42 batches of recycle base for 1,095 h total (electrolysis) time. The composition to be electrolyzed every hour is a mixture of 1,600 g of fresh recycle base with a composition similar to the compositions described in Examples 1 and 2 and a so-called 1,600 g of a previously treated batch of recycle base (ie a total weight of 3,200 g) Each batch having 700 g of heel discarded. At the end of each batch process, the purified TMAH aqueous solution is recovered from the catholyte zone, the intermediate zone including the flow circulation loop and the circulation vessel is emptied and the circulation vessel is filled with 1,000 g of aniline. The aniline is circulated for 30 minutes through the intermediate zone at a temperature of 50 ° C. After that, the aniline wash was removed and repeated with warmed water, 1,000 g of water circulated for 5 minutes at a temperature of 20-50 ° C. during the washing procedure. After each wash procedure, the next 3,200 g batch of recycle base added to the heel was charged to the middle zone and subjected to electrolysis.

The capacity of the remaining electrolysis cell does not actually change, i.e. 24.31 mol TMA ⁺ / m ² / h for the first batch and 24.99 mol TMA ⁺ / m ² / h for the 42nd batch (TMA ⁺ is tetramethyl Ammonium ions). Inspection of the electrolysis cell after the procedure of the 42nd batch shows no dirt on the membrane separating the anolyte zone from the intermediate zone.

Comparative Example C

A three-zone multi-perforose cell equipped with a DSA anode, a stainless steel cathode and two Nafion 324 cation selective membranes was prepared according to a method analogous to that described in Examples 1 and 2 (ie, 12.5 V, 40-50 ° C., Final pH 5) Operated with 25 batches of recycle base for 450h total (electrolysis) time. The composition to be hydrolyzed every hour is a mixture of 1,600 g of fresh recycle base with a composition similar to the compositions described in Examples 1 and 2 and a so-called 1,600 g of a previously treated batch of recycle base (ie a total weight of 3,200 g) Each batch with) and discards 700 g of heel.

The capacity of the electrolysis cell was reduced from 27.75 mol TMA ⁺ / m ² / h for the first batch to 6 mol TMA ⁺ / m ² / h or less for the 25th batch. After the procedure of batch 25, the results of the electrolysis cell inspection showed that the membrane separating the anolyte zone from the intermediate zone was dirty, and that the solids were in an aqueous solution in the middle zone and the connected liquid circulation system, ie the circulation loop in the middle zone, the loop filter. And in the circulation vessel.

Claims (20)

As a method for improving the purity of an aqueous waste solution containing quaternary ammonium hydroxide, The method comprises the following steps (a) to (d): (a) an anolyte zone comprising an anode, a catholyte zone comprising a cathode and at least one intermediate zone, said intermediate zone being catholyte and catholyte zones by means of a cation selective membrane; Preparing an electrolysis cell separated from the; (b) filling the anolyte zone with water or water comprising a supporting electrolyte, filling the catholyte zone with water or quaternary ammonium hydroxide and containing the quaternary ammonium hydroxide to be purified. Filling a waste aqueous solution into an intermediate zone; (c) passing an electrical current through the electrolysis cell to produce a purified aqueous quaternary ammonium hydroxide solution in the catholyte zone; And (d) recovering the purified aqueous quaternary ammonium hydroxide solution from the catholyte zone. The method of claim 1, Charging the anolyte zone with a strong acid aqueous solution. The method of claim 2, Charging the anolyte zone with 1% to 10% by weight aqueous sulfuric acid solution. The method according to any one of claims 1 to 3, Charging the intermediate zone with an aqueous solution comprising tetramethylammonium hydroxide (TMAH). The method of claim 4, wherein The intermediate zone is charged with an aqueous solution comprising from 5 wt% to 40 wt% TMAH. The method of claim 4, wherein The intermediate zone is charged with an aqueous solution comprising TMAH used for the preparation of 4-aminodiphenylamine in a plurality of reaction cycles. The method of claim 6, Wherein said intermediate zone is charged with an aqueous solution comprising aniline and containing TMAH for the production of 4-aminodiphenylamine in a plurality of reaction cycles. The method of claim 1, Charging said catholyte zone with an aqueous quaternary ammonium hydroxide solution identical to the quaternary ammonium hydroxide present in the composition to be purified. The method of claim 1, The catholyte zone is charged with 5% to 25% by weight aqueous TMAH solution. The method of claim 1, Wherein said electrolysis cell is a three zone cell having one anolyte zone, one catholyte zone and one intermediate zone. The method according to claim 1 or 10, Electrolysis is stopped when the pH in said intermediate zone reaches 1-7. The method of claim 11, Electrolysis is stopped when the pH in said intermediate zone reaches 4-7. The method of claim 1, Using the same cation selective membrane to separate the intermediate zone from the anolyte zone and the catholyte zone. The method of claim 13, The cation selective membrane is a perfluorinated membrane. The method of claim 1, Wherein the method is carried out in a batchwise manner. The method of claim 1, Washing the middle zone with a suitable solvent. The method according to claim 15 or 16, Washing the middle zone with a suitable solvent at the end of each batch process. The method of claim 16, The solvent is aniline. The method of claim 16, And after washing the intermediate zone with a suitable solvent, washing the intermediate zone with water. The method of claim 18, Washing the middle zone with aniline followed by water.