KR20010086305A - Synthesis of tetramethylammonium hydroxide - Google Patents

Abstract

PURPOSE: A synthesis of tetramethylammonium hydroxide is provided in which the operation is carried out continuously under stationary conditions obtained in order to prepare tetramethylammonium hydroxide by electrolysis of a tetramethylammonium salt in a cell with a cation-exchange membrane. CONSTITUTION: The process for the preparation of tetramethylammonium hydroxide by electrolysis of a tetramethylammonium salt in a cell with a cation-exchange membrane is characterized in that the operation is carried out continuously under stationary conditions (concentrations of the solutions in the cell for a fixed current density) obtained, on the one hand, by the introduction, into the anode electrolysis loop, of a tetramethylammonium salt solution which is more concentrated than that present in the cell and by an input of water into the cathode loop and, on the other hand, by the withdrawal of a portion of each of the solutions circulating in the anode and cathode loops, wherein the tetramethylammonium salt is the chloride, the hydrogencarbonate or the hydrogen sulphate, the operation is carried out with a cathode for the evolution of hydrogen or the reduction of oxygen, the cathode is made of stainless steel or of nickel, the cathode is based on platinized or silvered carbon, and the anode is based on platinum or on a ruthenium, iridium or platinum oxide.

Description

Synthesis of tetramethylammonium hydroxide {SYNTHESIS OF TETRAMETHYLAMMONIUM HYDROXIDE}

The present invention relates to tetramethylammonium hydroxide, and more particularly, to the synthesis of the compound by a continuous electrolysis process under stationary conditions.

Tetramethylammonium hydroxide (TMAH), one of the most widely used products in the electronics industry (developing, etching, planarization and photoresist removal), has practically two stages: first synthesis of tetramethylammonium salts, and then electrolysis By conversion of the salts to hydroxides.

According to patents JP 57-155390, US Pat. No. 4,634,509 and US Pat. No. 4,776,929, the electrolysis step is carried out in an electrochemical cell comprising two compartments separated by a cation-exchange membrane and two electrodes, to the anion of the tetramethylammonium salt at the positive electrode. To oxidation, reduction of water at the cathode, and transfer of tetramethylammonium cation (TMA ⁺ ) through the membrane. The methods disclosed in the above patents all proceed in the same way: after filling the anode circuit with a concentrated solution of TMA ⁺ salt and deionized or demineralized water containing 0.1 to 1% TMAH in the cathode circuit to ensure minimum conductivity, Initiate electrolysis. This mode of operation allows the TMAH to crystallize in the form of the pentahydrate at 50% by weight, and after a certain time, it depends on the volume and current of the closed loop so that there are no more TMA ⁺ ions in the anode circuit. Therefore, it is necessarily discontinuous.

This way of working has several disadvantages:

1) The catholyte solution is not very conductive initially, and as a result, a high resistance drop occurs. During electrolysis, its conductivity increases, but at the same time the conductivity of the anode compartment decreases. Therefore, overall, the resistance drop of the system is always very high, which is very disadvantageous for the cell voltage. That is, the battery voltage varies between 7 and 11 V for a current density of 1 kA / m 2 and between 15 and 23 V for a current density of 2 kA / m 2. This high resistance drop can lead to a significant rise in temperature through the Joule effect.

2) The concentrations of TMAH and TMA ⁺ salts (eg hydrochloride) vary continuously. Therefore, the membrane never operates under stationary conditions, which is detrimental to the life of the membrane, resulting in a decrease in the yield and quality of the TMAH synthesized.

In order to overcome this drawback, the present invention is directed to a battery having a cation-exchange membrane under stationary conditions, i.e., under conditions in which the parameters of the electrolytic cell, in particular, the concentrations of various solutions, remain stable for at least a fixed time for a fixed current density. Provided are methods for the synthesis of TMAH by continuous electrolysis of TMA ⁺ salts.

1 is a block diagram of electrolysis when working with a cathode for the reduction of water and the release of hydrogen.

2 shows the principle of operation of an electrolytic cell in the case of electrolysis of TMA-Cl to TMAH.

3 shows an apparatus used when working with a cathode for the reduction of water and the release of hydrogen.

4 is a block diagram of electrolysis when working with a cathode for the reduction of oxygen.

5 shows the principle of operation of the electrolytic cell in the case of electrolysis of TMA-Cl to TMAH.

6 shows an experimental setup used in the examples.

Explanation of symbols in the drawings

1: anode compartment 2: cathode compartment

3: anode gas removal tank 4: cathode gas removal tank

5, 6, 8: storage tank 7: discharge tank

5 ', 6', 7 ', 8', 9, 10, 11, 12: pipe

The process according to the invention for the production of TMAH by electrolysis of tetramethylammonium salt in a cell with a cation-exchange membrane is carried out by anodizing the tetramethylammonium salt solution with the above operation, on the one hand, more concentrated than present in the cell. Characterized in that it is carried out under stationary conditions obtained by injecting into a closed circuit and introducing water into the cathode closed circuit, or on the other hand by removing a portion of each solution circulating in the anode and cathode closed circuits. do.

These two means (injection and removal) ensure the optimum operation of the membrane of the electrolytic cell, thereby enabling to obtain better performance and to maintain it for more than a prescribed time. Also, as a result, at much lower values than those indicated in the patent, the battery voltage is maintained for more than the specified time (for example, 7 to 11 V for a current density of 3 kA / m 2). In addition, the membrane operates continuously under optimum conditions providing stable pH, high and stable current efficiency values and limited side reactions in the anode compartment. This all optimizes the life of the membrane, obtains a constant quality of the TMAH to be synthesized, and minimizes energy consumption (eg for up to 4,700 kWh / t (TMAH) at 2 kA / m 2 in the prior art, At about 3 000 kWh / t (TMAH) continuously at 3 kA / m 2).

The process according to the invention applies both to the synthesis of industrial TMAH and to the synthesis of electronic-grade TMAH. Preferably, as starting TMA ⁺ salt, tetramethylammonium chloride (TMA-Cl), tetramethylammonium hydrogencarbonate (TMA-HCO ₃ ) or tetramethylammonium hydrogensulfate (TMA-HSO ₄ ) is used. The anodic reaction corresponding to each of these salts is shown in Table 1 below:

Kind of salt Corresponding anode reaction TMA-Cl _{^{Cl - → 1/2 Cl 2}} + e - TMA-HCO _{3 ^{HCO 3 - → CO 2 + 1/4}} O 2 + 1/2 H 2 O + e - TMA-HSO _{4 H 2 O → 1/2 O} 2 + 2 H + + 2 e -

Preferred anodes are based on platinum or ruthenium, iridium or platinum oxides.

The preparation of hydroxide ions at the cathode can occur by the reduction of water to OH ^- ions and hydrogen, or the reduction of oxygen and water to OH ^- ions.

1 of the accompanying drawings shows a block diagram of electrolysis when working with a cathode for the reduction of water and the release of hydrogen. The cathode is preferably made of stainless steel or nickel. The apparatus according to FIG. 1 consists of:

An electrolytic cell consisting of a positive electrode compartment 1 and a negative electrode compartment 2 separated by a cation-exchange membrane m,

Via pipe 9 an anode gas removal tank 3 for removing the gas generated by the anode reaction,

A cathode gas removal tank 4 for removing hydrogen generated by the cathodic reaction, via a pipe 10,

A tank 5 for storing a more concentrated solution of tetramethylammonium salt injected into the anode closed circuit via a pipe 5 ',

A tank 6 for storing demineralized or deionized water which is injected into the cathode closed circuit via a pipe 6 ',

A tank 7 for withdrawing a part of the tetramethylammonium salt solution from the anode gas removal tank 3, via a pipe 7 ′,

A tank 8 for storing the synthetic TMAH solution exiting the cathode closed circuit at the outlet of the cathode degassing tank 4, via a pipe 8 ′.

As shown in Fig. 2, in the case of electrolysis of TMA-Cl to TMAH, the electrolytic cell operates according to the following principle:

Oxidation of chloride ions to chlorine at the anode according to the reaction

_{^{2 Cl - → Cl 2 + 2}} e -

-Reduction of water to hydrogen and hydroxide ions at the cathode according to the following reaction:

^{_{2 H 2 O + 2 e -}} → H 2 + 2 OH -

The transfer of TMA ⁺ ions through the cation-exchange membrane, achieved by a number of molecules of water (variable depending on the nature and current density of the membrane),

Separation of the anolyte, catholyte and product gases by a cation-exchange membrane.

The cathode closed circuit and the reservoir of TMAH prepared can be inactivated with hydrogen, nitrogen, argon or a mixture of these gases. In this case, the apparatus used when working with the cathode for the reduction of water and the release of hydrogen is modified as shown in FIG. In FIG. 3, the deactivated region is indicated by the dotted line, the inert gas is injected through the pipe 10, and the hydrogen generated by the cathodic reaction comes out of the tank 8 for storing a solution of the synthesized TMAH. Discharge through (11).

A block diagram of electrolysis when working with a cathode (preferably a cathode based on platinum or silver coated carbon) for the reduction of oxygen is shown in FIG. 4 of the accompanying drawings. In FIG. 4, the cathode compartment 2 is supplied with oxygen through a pipe 12, and the pipe 10 serves as an oxygen discharge pipe. As shown in Fig. 5, in the case of electrolysis of TMA-Cl to TMAH, the electrolytic cell also reduces the reduction of water to hydrogen and hydroxide ions at the cathode and to the hydroxide ions of oxygen and water according to the following reaction. Except for replacing with, it works according to the same principle as above:

_{O 2 + 2 H 2 O +} 4 e - → 4 OH -

In this case, any inactivation can be carried out with oxygen, nitrogen, argon or a mixture of these gases.

The two electrodes may be pressed against the membrane (so-called "zero gap" arrangement) or the cathode may be several mm away from the membrane (so-called "finite gap" arrangement).

In electrolytic cells, an important component is the membrane. The reason is that this ensures good separation of the two solutions. In order to ensure high purity of the synthesized TMAH and good current efficiency, the film TMA ⁺ ions, while the permeability, from salt anions (Cl ^-, HCO ₃ ^-, etc.), and OH ^- are to be impermeable. In addition, in order to remove from a very basic medium (TMAH) to an acidic medium, in fact a weakly basic medium, the membrane must be chemically stable in both media. Moreover, in order to minimize the resistance drop it should be as conductive as possible. To meet all these criteria, ion-exchange membranes typically consist of two or more polymer layers, and these layers are typically mutually laminated with one another. The polymer may be composed of perfluorosulfonated and / or perfluorocarboxylated chains. Such membranes are disclosed, for example, in patents US 4,401,711, EP 165,466, US 4,604,323, EP 253,119 and EP 753,534. These are especially trademarked Nafion in DuPont de Nemours. Trade names Flemion from N324, N902 and N966, Asahi Glass 892 and 893, or the trade name Aciplex from Asahi Chemicals Sold as 4203.

In order to obtain the ideal degree of swelling of the various polymers and, accordingly, to avoid deterioration of the film (for example due to the cracking of the layers), it is necessary to adjust the concentrations of the positive and negative electrolytes. This leads to degradation of the cell because, on the one hand, the OH ⁻ ions can be oxidized at the anode to form oxygen, and on the other hand the splitting of the membrane allows the flow of the TMA ⁺ salt solution into the TMAH. This is because the purity of the synthetic TMAH is induced.

The process according to the invention is advantageously carried out under the following conditions:

A current density of 1 to 5 kA / m 2, preferably 3 to 4 kA / m 2,

A temperature of room temperature to 80 ° C., preferably 40 to 60 ° C.,

A concentration of TMAH in the cathode closed circuit of 5-40% by weight, preferably 10-25% by weight,

A concentration of tetramethylammonium salt in the anode closed circuit of 15-40% by weight, preferably 20-35% by weight.

The introduction of TMA ⁺ salt and water through a concentrated solution of TMA ⁺ salt injected into the anode closed circuit is determined to compensate for the consumption of TMA ⁺ salt and water associated with the electrochemical reaction and migration through the membrane at the anode. Similarly, the introduction of water into the cathode closed circuit, together with the water traveling from the anode compartment to the cathode compartment, is required to compensate for the water consumed by the electrochemical reaction at the cathode and also to obtain the desired final concentration of TMAH. Contribute to the provision of water. The introduction and concentration of these TMA ⁺ salts depends in particular on the nature of the membrane used, the current density chosen, the area of the electrode and the desired concentration of TMAH.

Example

The following examples, which are described without restricting the present invention, were made by the experimental apparatus shown in FIG.

The cell consists of two independent circuits, a positive circuit and a negative circuit:

The anode circuit allows the anode electrolyte to circulate in the electrochemical cell and consists of a PTFE-based compartment containing the anode (made of RuO ₂ -TiO ₂ coated titanium). This compartment is connected to the anolyte / gas removal column, where addition of concentrated TMA ⁺ salt solution and draining of the depleted anolyte is also performed. During electrolysis, the gas generated at the anode is discharged through the back of the electrode, and the circulation of the anode electrolyte is carried out by "gas lift" (relative density difference between the two-phase mixture and the solution). The temperature is adjusted using a heating tape around the degassing column.

The cathode circuit is symmetrical with the anode compartment and is based on the same working principle as above. The cation-exchange membrane is located between the anode and the cathode. The anode consists of a stainless steel sheet or nickel grid which is pressed against the membrane and the cathode and is perforated with a small hole for outgassing and is 4 mm away from the membrane ("finite gap" arrangement). Introduction of demineralized water and discharge of synthetic TMAH takes place in the gas removal column.

The working area of the battery is 50 cm 2. The material used for electrochemical cells and various pipes is PTFE, and polypropylene is used for accessories (columns and tanks).

All cathode closed circuits are inactivated by a mixture of hydrogen (occurring in the cathode) and argon (injection) in order to limit the decomposition of atmospheric CO ₂ in TMAH.

The circulation of the electrolyte is caused by the relative density difference due to gas evolution (depending on the starting salt, chlorine or CO _{2 at the} anode, and hydrogen at the cathode).

The water injected into the cathode circuit to maintain the concentration of TMAH is distilled water.

Chlorine produced from TMA-Cl is extinguished in a gas scrubbing column (not shown) using sodium hydroxide and sodium sulfite during the test.

The TMAH reservoir is sealed and its bottom part is equipped with a discharge / discharge valve. Two non-return vessels, ie vessels containing water and empty vessels, enable the prevention of contamination by the outside atmosphere. Samples are taken under controlled atmosphere (argon or nitrogen) in a glove box.

The battery works in the following manner:

-Charge the anode compartment with an aqueous solution of TMA ⁺ salt at the working concentration of electrolysis,

Charge the aqueous TMAH solution to the cathode compartment at the working concentration of electrolysis,

-Purge the cathode circuit with argon to inactivate it (if the limitation of decomposition of atmospheric CO ₂ in TMAH is required, especially for the electronics industry),

Switch on the heating tape to bring the device to the desired temperature and gradually increase the current density.

Example 1

Preconditioned conditions Nafion by immersion in a positive electrode formed of RuO ₂ -TiO ₂ deposited on expanded titanium, a negative electrode made of stainless steel (perforated plate), and 10% TMAH solution for 24 hours. N324 membrane was mounted on the electrochemical cell. The cation-exchange membrane is a membrane having a perfluorosulfonated chain commercially available from DuPont de Nemours.

735 g of 243 g / L TMA-HCO ₃ aqueous solution was charged to the positive electrode circuit. 780 g of 237 g / L TMAH aqueous solution was charged to the cathode circuit. The entire assembly was heated with a heating tape and the cathode circuit was inactivated by injecting argon. When the temperature of the fluid reached 50 ° C., the electricity supply switch was turned on to increase the current by 1 A (ie 3 kA / m 2) every 3 minutes until it reached 15 A.

The amount of water introduced was 100 g / h and the amount of TMA-HCO ₃ was 125 g / h (588 g / L solution).

After 16 hours of operation under these conditions, the following results were obtained:

a) The concentration of TMAH was 244 g / l in the storage tank and 235 g / l in the degassing column of the cathode circuit. The current efficiency for the cathode reaction was 94%.

b) The concentration of TMA-HCO ₃ was 247 g / l in the discharge tank and 260 g / l in the anode gas removal column. The current efficiency for the anodic reaction was 97%.

c) The voltage in the electrolytic cell remained stable at a value of 10 V at 3 kA / m 2 (ie energy consumption = 3,138 kWh / t (TMAH)).

Examples 2-6

Repeat the procedure of Example 1, using another material (membrane, cathode) and / or starting from another tetramethylammonium salt (TMA-X, X represents an anion) and / or of TMA-X and TMAH Another embodiment according to the present invention was prepared by changing the concentration.

Nafion N902 and N966 membranes are cation-exchange membranes commercially available from DuPont de Nemours.

Working conditions and the results obtained after working for 16 hours are summarized in Table 2 below.

In Table 2, the E _cell represents the voltage (V) of the cell, η represents the current efficiency, that is, the ratio of the part of the current actually used to carry out the desired reaction with respect to the total current used, and η _a represents the positive reaction (chlorine). Current efficiency for the oxidation of ions to Cl ₂ or oxidation of hydrogencarbonate ions to CO ₂ ), and η _c represents the current efficiency for cathode reactions (synthesis of hydroxide ions).

The energy consumption (W) of the electrolytic cell expressed in tonnes of kWh / TMAH can be calculated from the data in Table 2 below by the formula W = 295 × E _cell / η _c .

Example One 2 3 4 5 6 membrane N324 N966 N966 N324 N902 N324 cathode Stainless steel nickel Stainless steel Stainless steel nickel nickel X ^- anion HCO ₃ ^- Cl ^- Cl ^- Cl ^- Cl ^- HCO ₃ ^- [TMA-X], depart 243 g / ℓ 254 g / ℓ 203 g / ℓ 249 g / ℓ 200 g / ℓ 320 g / ℓ [TMA-X], Introduction 588 g / ℓ 505 g / ℓ 580 g / ℓ 533 g / ℓ 250 g / ℓ 602 g / ℓ [TMA-X], discharge 247 g / ℓ 243 g / ℓ 191 g / ℓ 235 g / ℓ 176 g / ℓ 332 g / ℓ [TMAH] from 237 g / ℓ 106 g / ℓ 107 g / ℓ 247 g / ℓ 100 g / ℓ 244 g / ℓ [TMAH], save 244 g / ℓ 105 g / ℓ 105 g / ℓ 235 g / ℓ 105 g / ℓ 253 g / ℓ η _a 97% 97.5% 98% 94% 95.4% nd ^(a) η _c 94% 93% 92.5% 95% 91.8% 92% E _battery 10 V 9 V 8 V 11 V 7 V 10 V (a) nd = not measured

Comparative Examples 7 to 10

4, prepared using the same apparatus as above, but under non-stop conditions for the concentrations of TMA-X (Example 10), or under non-stop conditions for the concentrations of TMA-X and TMAH (Examples 7-9). Four examples are summarized in Table 3 below. Evaluation of the obtained result shows that the efficiency is much lower than Examples 1 to 6 according to the present invention.

Example 7 8 9 10 membrane N902 N902 N902 N902 cathode nickel Stainless steel Stainless steel nickel X ^- anion Cl ^- Cl ^- Cl ^- HCO ₃ ^- [TMA-X], depart 247 g / ℓ 328 g / ℓ 248 g / ℓ 335 g / ℓ [TMA-X], Introduction 247 g / ℓ 328 g / ℓ 248 g / ℓ 335 g / ℓ [TMA-X], final ^(b) 144 g / ℓ 270 g / ℓ 160 g / ℓ 222 g / ℓ [TMAH] from 50 g / ℓ 250 g / ℓ 248 g / ℓ 107 g / ℓ [TMAH], final ^(b) 203 g / ℓ 320 g / ℓ 159 g / ℓ 106 g / ℓ Continuation of the test 8 h 8 h 8 h 4 h η _a 84% 59% 82% 86% η _c 80% 59% 78% 89% E _battery 7.5 V 7 V 7 V 10 V (b) The operating conditions in these comparative examples are not stationary, and the terms "[TMA-X], final" and "[TMAH], final" refer to the concentration of the solution present in the degassing column at the end of the test. I understand.

According to the present invention, continuous operation of the TMA ⁺ salt in a cell with a cation-exchange membrane under stationary conditions, i.e., under conditions where the parameters of the electrolytic cell, in particular the concentration of the various solutions, remain stable for at least a fixed time for a fixed current density A method of synthesizing TMAH by electrolysis is provided.

Claims (13)

In a method for preparing tetramethylammonium hydroxide by electrolysis of tetramethylammonium salt in a cell having a cation-exchange membrane, the above operation, on the one hand, provides a more concentrated solution of tetramethylammonium salt than is present in the cell. Quiescent conditions obtained by injecting into the anode electrolytic closed circuit and by introducing water into the cathode closed circuit, or on the other hand by removing a portion of each solution circulating in the anode and cathode closed circuit (for a fixed current density The concentration of the solution in the battery). The process according to claim 1, wherein the tetramethylammonium salt is chloride, hydrogencarbonate or hydrogensulfate. The process according to claim 1 or 2, wherein the operation is carried out with a cathode for evaporation of hydrogen. 4. A process according to claim 3 wherein the cathode is made of stainless steel or nickel. The process according to claim 1 or 2, wherein the operation is carried out with a cathode for the reduction of oxygen. 6. The method of claim 5 wherein the negative electrode is a platinum or silver coated carbon substrate. The production method according to any one of claims 1 to 6, wherein the anode is based on platinum or ruthenium, iridium or platinum oxide. The production method according to any one of claims 1 to 7, wherein the current density is 1 to 5 kA / m 2, preferably 3 to 4 kA / m 2. 9. The process according to claim 1, wherein the operation is carried out at a temperature from room temperature to 80 ° C., preferably from 40 to 60 ° C. 10. The production process according to any one of claims 1 to 9, wherein the concentration of TMAH in the cathode closed circuit is 5 to 40% by weight, preferably 10 to 25% by weight. The production process according to any one of claims 1 to 10, wherein the concentration of the tetramethylammonium salt in the anode closed circuit is 15 to 40% by weight, preferably 20 to 35% by weight. The process according to claim 1, wherein the cation-exchange membrane consists of at least two polymer layers having perfluorosulfonated and / or perfluorocarboxylated chains. 13. A process according to any one of the preceding claims, wherein the cathode closed circuit and the reservoir of tetramethylammonium hydroxide to be prepared are inactivated with hydrogen, nitrogen, argon or a mixture of these gases.