CN1312400A - Synthesizing of tetramethylammonium - Google Patents

Abstract

For the preparation of tetramethylammonium hydroxide by electrolysis of tetramethylammonium salt in a cation-exchange membrane electrolytic cell, continuous operation is carried out under fixed conditions achieved by adopting, on the one hand, a higher concentration of Tetramethylammonium salt solution, and water was added to the cathode circuit, and on the other hand, a portion of each solution was withdrawn to circulate in the anode and cathode circuits.

Description

Synthesis of Tetramethylammonium Hydroxide

The present invention relates to tetramethylammonium hydroxide, more particularly, the object of the present invention is to adopt continuous electrolysis method to synthesize this compound under fixed conditions.

Tetramethylammonium hydroxide (TMAH) is the most used product in the electronics industry (display, etching, polishing and photoresist cleaning). This product is actually obtained in two steps, that is, first synthesize tetramethylammonium salt, This salt is then converted to hydroxide using electrolysis.

According to patents JP57-155390, US4634509 and US4776929, this electrolysis step is carried out in an electrochemical electrolysis cell with two chambers separated by a cation exchange membrane and two electrodes, at the anode the tetramethylammonium salt anion Oxidation reactions take place, reduction reactions take place at the cathode water, and tetramethylammonium cations (TMA ⁺ ) are transferred across the membrane. The methods described in these above-mentioned patents are carried out in exactly the same way: the anode circuit is filled with a concentrated solution of TMA ⁺ salt, the cathode circuit is filled with deionized or demineralized water containing 0.1-1% TMAH in order to guarantee a minimum conductivity, and then electrolysis. This mode of operation is forced to be intermittent, since pentahydrate crystallizes at 50% by weight of TMAH and there is no more TMA ⁺ in the anode circuit after a time, which depends on the circuit volume and current.

This type of operation has a number of drawbacks:

1) Initially, the catholyte is not very conductive, and the resistive voltage drop is large at this time. During electrolysis, the conductivity of the catholyte increases, but at the same time it is the conductivity of the anode compartment electrolyte that decreases. Overall, the resistive voltage drop of the system is therefore always very high, which strongly constrains the voltage of the electrolytic cell, which fluctuates in the range of 7-11 volts (V) at a current density of 1kA/ ^m2 at a current density of 2kA/m ² , the voltage fluctuation range is 15-23V. Such a high resistive voltage drop can lead to a large temperature rise due to the Joule effect.

2) Concentrations of TMAH and TMA ⁺ salts (eg chloride) are always changing. Therefore, this membrane is never operated under fixed conditions, which is detrimental to the lifetime of the membrane and ultimately leads to a decrease in the yield and quality of the synthesized TMAH.

In order to overcome these drawbacks, the present invention now proposes a method for the synthesis of TMAH by continuous electrolysis of the TMA ⁺ salt in an electrolytic cell with a cation exchange membrane under fixed conditions, i.e. for a fixed current density, at electrolytic cell parameters, particularly is the concentration of different solutions, always stable over time under the condition of continuous electrolysis of TMA ⁺ salt.

The method for preparing TMAH in the present invention is to electrolyze tetramethylammonium salt in a cation exchange membrane electrolytic cell, which is characterized in that it operates continuously under fixed conditions achieved by adopting the following method: on the one hand, by adding a ratio of the electrolytic A higher concentration of tetramethylammonium salt solution is pooled and water is added to the cathodic circuit, and on the other hand, a portion of each solution is withdrawn which is circulated in the anode and cathode circuits.

These two approaches (adding and withdrawing) ensure optimal operation of the electrolytic cell membranes and thus achieve relatively good properties and maintain these properties over time. It can also be concluded that the voltage of the electrolytic cell does not change with time (for example, when the current density is 3kA/m ² , the voltage is 7-11V) under the condition that the voltage value is much lower than the value indicated in the above-mentioned patent. At this time, the membrane of the electrolytic cell is always operated under the optimal condition, which makes the current efficiency value high and stable, the pH of the anode chamber is stable, and side reactions are also limited. All of these can optimize the life of the membrane and obtain a stable quality of synthetic TMAH to minimize energy consumption, for example, when the current density is 3kA/ ^m2 , continuous about 3000kWh/t(TMAH), while in the prior art, the current When the density is 2kA/ ^m2 , it is preferably 4700kWh/t (TMAH).

The method of the invention is also very well applicable to the synthesis of technical grade TMAH as well as to the synthesis of electronic quality TMAH. As starting material TMA ⁺ salt, preference is given to using tetramethylammonium chloride (TMA-Cl), tetramethylammonium hydrogencarbonate (TMA-HCO ₃ ) or tetramethylammonium hydrogensulfate (TMA-HSO ₄ ). The anodic reactions corresponding to each of the above salts are listed in the table below: type of salt The corresponding anodic reaction: TMA-Cl Cl ⁻ →½Cl ₂ +e ⁻ TMA-HCO ₃ HCO ₃ ^- → CO ₂ + ¼ O ₂ + ½ H ₂ O + e ^- TMA-HSO ₄ H ₂ O→½O ₂ +2H ⁺ +2e ^-

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

Hydroxide ions are generated at the cathode by reducing water to ^OH- ions and hydrogen, or by reducing oxygen to ^OH- ions with water.

Accompanying drawing 1 has shown the schematic diagram of the principle of electrolysis under the operation situation that the cathode reduces water and emits hydrogen, and this cathode is preferably made of stainless steel or nickel. Figure 1 equipment includes:

- an electrolytic cell consisting of an anode compartment (1) and a cathode compartment (2), which compartments are separated by a cation exchange membrane (m),

- an anode degassing tank (3) for removing the gases produced by the anode reaction through the pipe (9),

- a cathode degassing tank (4) for removing the hydrogen gas produced by the cathode reaction through the pipe (10),

- feeding the relatively concentrated tetramethylammonium salt solution to the storage tank (5) of the anode circuit through the pipe (5'),

- supply of demineralized or deionized water to the storage tank (6) of the cathode circuit through the pipe (6'),

- a part of the tetramethylammonium salt solution coming out from the anode degassing tank (3) is discharged to the discharge tank (7) through the pipeline (7')

- Storage tank 8 for the synthetic TMAH solution withdrawn from the cathode circuit through the pipe (8') at the outlet of the cathode degassing tank (4).

As illustrated by Figure 2 in the case of electrolysis of TMA-Cl to TMAH, the electrolytic cell operates according to the following principle:

- Chloride ions are oxidized to chlorine at the anode according to the following reaction:

- Water is reduced to hydrogen and hydroxide ions at the cathode according to the following reaction:

-TMA ⁺ ions are transferred through the cation exchange membrane, accompanied by a certain number of water molecules (the number of which varies with the properties of the membrane and the current density),

- Separation of anolyte, catholyte and generated gases by means of a cation exchange membrane.

The cathode loop and resulting TMAH stock solution can be protected with hydrogen, nitrogen, argon or mixtures of these gases. In this case, the equipment used in the case of operation in which the cathode reduces water and releases hydrogen is modified as shown in Figure 3, wherein the protected area is indicated by a dotted line, the protective gas is added through the pipeline (10), and the cathode reaction produces The hydrogen is extracted by the pipeline (11) leaving the synthetic TMAH solution storage tank (8).

Accompanying drawing 4 has represented the schematic diagram of electrolysis principle under the operation situation of oxygen reduction of cathode (preferably platinum-plated or silver-plated carbon base cathode), wherein is supplied cathode chamber (2) oxygen by pipeline (12), and pipeline (10) is used for discharging hydrogen. In the case of the electrolysis of TMA-Cl to TMAH, as shown in Figure 5, the electrolytic cell now operates on the same principle as before, except that instead of reducing water at the cathode, water reduces oxygen to hydroxide ions according to the following reaction into hydrogen and hydroxide ions: Oxygen, nitrogen, argon or mixtures of these gases can be used for possible protection in this case.

The two electrodes can be placed against the membrane (so-called "zero-gap" installation), or the cathode can be placed a few millimeters from the membrane (so-called "finish-gap" installation).

In an electrolytic cell, the important element is the membrane, since it is this element that ensures a good separation of the two solutions. To guarantee good current efficiency and good purity of the synthesized TMAH, the membrane should be permeable to TMA ⁺ ions but impermeable to feedstock salt anions (Cl ⁻ , HCO ⁻ etc.) and OH ⁻ . Furthermore, in order to separate acidic media, even weakly basic media, from very strongly basic media (TMAH), its membrane should be chemically stable in both media. In addition, the membrane should be as conductive as possible in order to minimize the resistive voltage drop. In order to meet all these requirements, ion exchange membranes generally consist of at least two polymer layers, which are often co-extruded together. These polymers may consist of perfluorosulfonated chains and/or perfluorocarboxylic acid chains. Some such membranes are described, for example, in patents US4401711, EP165466, US4604323, EP253119 and EP753534. On the market, one can find, inter alia, ^Nafion® N324, N902 and N966 from DuPont de Nemours, Flemion® from Asahi Glass ^{or Aciplex®} from Asahi Chemicals.

In order to achieve the same expansion ratio for the different polymers and thus avoid membrane damage (eg delamination of the layers), it is necessary to adjust the concentrations of the anolyte and catholyte. This membrane damage can in fact lead to a decrease in the performance of the electrolytic cell, because ^OH- ions may be oxidized at the anode to generate oxygen, and on the other hand, it leads to a decrease in the purity of the synthesized TMAH, because the membrane stripping may cause the TMA ⁺ salt solution to flow into the TMAH.

Advantageously, the method of the present invention can be carried out under the following conditions:

- a current density of 1-5 kA/m ² , preferably 3-4 kA/m ² ,

- a temperature between room temperature and 80°C, preferably 40-60°C,

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

- The tetramethylammonium salt concentration in the anode circuit is 15-40% by weight, preferably 20-35% by weight.

TMA + salt ^and water are added by adding a concentrated TMA ⁺ salt solution to the anode loop in order to compensate for the TMA ⁺ salt and water consumed by the electrochemical reaction at the anode and transported through the membrane. Likewise, the addition of water to the cathode loop, together with the water transferred from the anode compartment to the cathode compartment through the membrane, should be used to compensate for the water consumed by the electrochemical reaction at the cathode and also provide the water required to achieve the desired final TMAH concentration. The addition of these waters and the concentration of the TMA ⁺ salt depend inter alia on the properties of the membrane used, the chosen current density, the electrode surface area and the desired TMAH concentration.

Example

The following examples illustrate, but do not limit, the invention and were carried out using the experimental apparatus shown in FIG. 6 .

The electrolytic cell consists of two independent circuits, an anode circuit and a cathode circuit:

- The anode circuit consists of a PTFE-based chamber that enables the circulation of the anolyte in the electrochemical cell and houses the anode (consisting of titanium coated with _RuO2 - _TiO2 ). This chamber is connected to the anolyte/gas degassing column where the TMA ⁺ salt solution is also added and the lean anolyte is drawn off. During electrolysis, the gas generated at the anode is drawn from behind the electrodes, and the anolyte (difference in density of the two-phase mixture and solution) is circulated through the "rising gas". The temperature is regulated by heating coils surrounding the degassing column.

- The cathode circuit is symmetrical in the anode chamber, also based on the same operating principle. A cation exchange membrane is placed between the anode and cathode. The anode is in close contact with the membrane and the cathode is 4 mm from the membrane ("finishing gap" installation), the cathode consists of a nickel grid or a stainless steel plate with small holes drilled for gas extraction. Add demineralized water and draw off the synthesized TMAH in a degassing column.

The electrolytic cell working surface area is 50 cm ² . The material used for the electrochemical cells and the different pipes is PTFE, and the material used for auxiliary equipment (columns and tanks) is polypropylene.

The entire cathodic circuit was protected with a mixture of hydrogen (generated at the cathode) and argon (infused) in order to limit the dissolution of atmospheric _CO2 in the TMAH.

The electrolyte is cycled due to the density difference produced by the released gas (chlorine or _CO2 at the anode and hydrogen at the cathode, depending on the feed salt).

The water injected into the cathode loop to maintain the TMAH concentration was distilled water.

Chlorine gas produced during testing with TMA-Cl was destroyed with sodium hydroxide and sodium sulfite in a recovery column (not shown).

Seal the TMAH storage bottle and install an extraction/evacuation valve in the lower part. Two anti-return bottles, one filled with water and the other empty, are protected from contamination by the external atmosphere. Samples were taken in a glove box under controlled atmosphere (argon or nitrogen).

Operate the electrolytic cell according to the following scheme:

- fill the anode compartment with TMA ⁺ brine solution at the electrolysis operating concentration,

- filling the cathode chamber with an aqueous solution of TMAH at the electrolytic operating concentration,

- purge with argon to protect the cathode circuit (especially for products used in electronics if one wishes to limit the dissolution of _CO2 in the air into the TMAH),

- The heating coil heats up the device to the required temperature and gradually increases the current density.

Example 1

The electrochemical cell consisted of a _RuO2 - _TiO2 anode deposited on expanded titanium, a stainless steel cathode (orifice plate) and a ^Nafion® N324 membrane previously conditioned by impregnation with a 10% TMAH solution for 24 hours. This cation exchange membrane is a membrane with perfluorosulfonated chains sold by DuPont.

The anode loop was filled with 735 grams of 243 g/L TMA-HCO ₃ aqueous solution. The cathode loop was filled with 780 grams of a 237 g/L TMAH aqueous solution. The entire device is heated with heating coils, and the cathode circuit is protected with argon gas injection. When the fluid temperature reaches 50°C, it is energized, and the current increases from 1 ampere to 15 amperes within 3 minutes, that is, 3kA/m ² .

Adding water is 100 g/h, adding TMA-HCO ₃ is 125 g/h (588 g/L solution).

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

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

b) The TMA-HCO ₃ concentration was 247 g/l in the evacuated tank and 260 g/l in the anode degassing column. The current efficiency of the anode reaction was 97%.

c) The voltage of the electrolytic cell is still stable at 10V and 3kA/m ² , that is, the energy consumption is 3138kWh/t(TMAH).

Example 2-6

Other embodiments of the present invention are carried out as in Example 1, but using other materials (membrane, cathode) and/or using other tetramethylammonium salts (TMA-X, X represents anion) and/or changing TMA-X and TMAH concentration.

Nafion ^(R) N902 and N966 membranes are cation exchange membranes sold by DuPont.

The operating conditions and results obtained after 16 hours of operation are compiled in the table below, where:

-E _cell represents the voltage (V) of the electrolytic cell, and

- η represents the current efficiency, i.e. the ratio of the fraction of current effectively used to carry out the desired reaction to the total current used, η _a represents the current efficiency of the anodic reaction (oxidation of chloride ions to Cl _or bicarbonate ions to CO ₂ ) and _ηc represent the current efficiency of the cathodic reaction (hydroxide ion synthesis).

The energy consumption of the electrolytic cell expressed in kWh/ton TMAH can be calculated using the data in the table using the formula W=295E _cell /η _c . Example 1 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 ^- start [TMA-X] 243 g/l 254 g/l 203 g/l 249 g/l 200g/L 320 g/l Join [TMA-X] 588 g/L 505 g/l 580 g/l 533 g/l 250g/L 602 g/l Empty [TMA-X] 247 g/l 243 g/l 191 g/l 235 g/l 176 g/l 332 g/l start [TMAH] 237 g/l 106 g/l 107 g/l 247 g/l 100g/L 244 g/l storage [TMAH] 244 g/l 105 g/l 105 g/l 235 g/l 105 g/l 253 g/l n _a 97% 97.5% 98% 94% 95.4% nd ^(a) _ηb 94% 93% 92.5% 95% 91.8% 92% E _cell 10V 9V 8V 11V 7V 10V

(a)nd=not tested

Example 7-10

The table below compiles four examples that were run using the same equipment, but with varying concentrations of TMA-X (Example 10) or TMA-X and TMAH (Examples 7-9). The results obtained from the study show that the efficiency is much lower than that of Examples 1-6 of 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 ^- start [TMA-X] 247 g/l 328 g/l 248 g/l 335 g/l Join [TMA-X] 247 g/l 328 g/l 248 g/l 335 g/l Last [TMA-X] ^(b) 144 g/l 270 g/l 160 g/l 222 g/l start [TMAH] 50 g/l 250g/L 248 g/l 107 g/l Last [TMAH] ^(b) 203 g/l 320 g/l 159 g/l 106 g/l Test time 8 hours 8 hours 8 hours 4 hours n _a 84% 59% 82% 86% _ηb 80% 59% 78% 89% E _cell 7.5V 7V 7V 10V

(b) In these comparative examples, the operating conditions are not fixed. Here, the last [TMA-X] and the last [TMAH] should be understood as the concentration of the solution in the degassing column after the test.

Claims (13)

1. A process for the preparation of tetramethylammonium hydroxide by electrolysis of tetramethylammonium salts in cation exchange membrane cells, characterized by continuous operation under fixed conditions (concentration in the cell for a certain current density) achieved by: on the one hand, a higher concentration of tetramethylammonium salt solution than in the cell is fed to the electrolysis anode circuit and water is fed to the cathode circuit, and on the other hand, a portion of each solution circulating in the anode and cathode circuits is withdrawn.

2. The method of claim 1, wherein the tetramethylammonium salt is chloride, bicarbonate, or bisulfate.

3. The method according to claim 1 or 2, wherein a dehydrogenized cathode operation is used.

4. The method of claim 3, wherein the cathode is stainless steel or nickel.

5. The method of claim 1 or 2, wherein a cathode operation of reducing oxygen is used.

6. The method of claim 5, wherein the cathode is a platinized or silvered carbon substrate.

7. The method of any one of claims 1-6, wherein the anode is based on platinum or ruthenium, iridium, or platinum oxide.

8. The method of any one of claims 1-7, wherein the current density is 1-5kA/m²Preferably 3-4kA/m²。

9. The process according to any one of claims 1 to 8, wherein it is carried out at a temperature of from room temperature to 80 ℃, preferably from 40 to 60 ℃.

10. The method according to any of claims 1-9, wherein the TMAH concentration in the cathode circuit is 5-40% by weight, preferably 10-25% by weight.

11. The method according to any one of claims 1-10, wherein the concentration of tetramethylammonium salt in the anode loop is 15-40% by weight, preferably 20-35% by weight.

12. The process of any one of claims 1-11 wherein the cation exchange membrane is comprised of at least two layers of polymers having perfluorinated sulfonated chains and/or perfluorinated carboxylic acid chains.

13. A method according to any one of claims 1 to 12 wherein the cathode loop and the resultant stock solution of tetramethylammonium hydroxide are protected with hydrogen, nitrogen, argon or a mixture of these gases.

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