CN1312400A

CN1312400A - Synthesizing of tetramethylammonium

Info

Publication number: CN1312400A
Application number: CN01104629A
Authority: CN
Inventors: F·安多尔法托
Original assignee: Atofina SA
Current assignee: Arkema France SA
Priority date: 2000-01-13
Filing date: 2001-01-13
Publication date: 2001-09-12
Also published as: FR2803856A1; FR2803856B1; JP2001271193A; KR20010086305A; GB0100628D0; US20010025798A1; GB2358195A; DE10101494A1

Abstract

In order to prepare tetramethylammonium hydroxide by electrolysis of a tetramethylammonium salt in a cell with a cation-exchange membrane, the operation is carried out continuously under stationary conditions 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.

Description

Synthesis of tetramethylammonium hydroxide

The present invention relates to tetramethylammonium hydroxide, and more particularly, it is an object of the present invention to synthesize such a compound under fixed conditions by a continuous electrolytic method.

Tetramethylammonium hydroxide (TMAH) is the most used product in the electronics industry (display, etch, polish and photoresist clean) and is obtained in two steps, in practice, by first synthesizing the tetramethylammonium salt and then converting this salt to the hydroxide by electrolytic means.

According to the patents JP57-155390, US4634509 and US4776929, this electrolysis step is carried out in an electrochemical cell having two chambers separated by a cation-exchange membrane and two electrodes, the oxidation reaction of tetramethylammonium salt anions at the anode being carried out and the reduction reaction of tetramethylammonium cations (TMA) at the cathode water being carried out⁺) Transferred through the membrane. The processes described in these patents above are performed in exactly the same way: TMA⁺The anode circuit is filled with a concentrated salt solution and the cathode circuit is filled with deionized or demineralized water containing 0.1-1% TMAH to ensure minimal conductivity, and then subjected to electrolysis.This mode of operation is forced to be discontinuous because at 50 wt% TMAH pentahydrate crystallizes and over time there is no more TMA in the anode loop⁺This time depends on the loop volume and current.

This type of operation has a number of drawbacks:

1) initially, the catholyte is less conductive, and the resistive voltage drop is large. During electrolysis, the conductivity of the catholyte increases, but at the same time it is the conductivity of the electrolyte in the anode compartment that decreases. Overall, the resistive voltage drop of the system is therefore always very high, which strongly constrains the voltage of the cell, with a current density of 1kA/m²The voltage fluctuation range is 7-11 volts (V), and the current intensity is 2kA/m²The voltage fluctuation range is 15-23V. Such high resistance voltage drops can cause the temperature to rise significantly due to joule effect.

2) TMAH and TMA⁺The concentration of the salt (e.g. chloride) is constantly changing. Therefore, such membranes never operate under fixed conditions, which is detrimental to membrane lifetime and ultimately leads to reduced yield and quality of synthesized TMAH.

In order to overcome the defects, the invention provides a TMAH synthesis method, which is to continuously electrolyze TMA in an electrolytic cell of a cation exchange membrane under a fixed condition⁺Continuous electrolysis of TMA with salt, i.e. for a fixed current density, under conditions in which the cell parameters, in particular the concentrations of the different solutions, are always stable over time⁺And (3) salt.

The method for preparing TMAH of the invention is to electrolyze tetramethylammonium salt in a cation exchange membrane electrolytic cell, and is characterized in that the method is continuously operated under the fixed condition achieved by adopting the following method: on the one hand, by feeding a tetramethylammonium salt solution of higher concentration than the cell in the electrolytic anode circuit and water in the cathode circuit, and on the other hand, taking off a portion of each solution circulating in the anode and cathode circuits.

Both measures (addition and withdrawal) ensure optimum transport of the cell membranesThus, better performance can be achieved and maintained over time. It follows from this that, at voltage values much lower than those indicated in the above-mentioned patents, the cell voltage does not vary with time (for example, at a current density of 3 kA/m)²The voltage is 7-11V). In this case, the cell membrane is always operated under optimal conditions, which leads to high and stable values of current efficiency, stable pH in the anode compartment and also limits side reactions. All of these enable the lifetime of the membrane to be optimized and a stable quality of synthetic TMAH to be obtained, minimizing energy consumption, e.g. at a current density of 3kA/m²About 3000kWh/T (TMAH) continuously, whereas in the prior art, the current density was 2kA/m²In this case, 4700kWh/T (TMAH) is preferred.

The method of the present invention is also very well applicable to the synthesis of technical grade TMAH as well as to the synthesis of electronic quality grade TMAH. As starting material TMA⁺Salts, preferably tetramethylammonium chloride (TMA-Cl), tetramethylammonium bicarbonate (TMA-HCO) are used₃) Or tetramethylammonium hydrogen sulfate (TMA-HSO)₄). The anodic reactions corresponding to each of the above salts are listed in the following table:

kind of salt	The corresponding anode reaction:
kind of salt	The corresponding anode reaction:	TMA-Cl	Cl^-→½Cl₂+e^-
TMA-HCO₃	HCO₃ ^-→CO₂+¼O₂+½H₂O+e^-	TMA-Cl	Cl^-→½Cl₂+e^-
TMA-HCO₃	HCO₃ ^-→CO₂+¼O₂+½H₂O+e^-	TMA-HSO₄	H₂O→½O₂+2H⁺+2e^-

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

By reducing water to OH^-Ions and hydrogen, or by reduction of oxygen to OH with water^-The ions can all generate hydroxide ions at the cathode.

FIG. 1 shows a schematic diagram of the electrolysis principle in the case of operation with the cathodic reduction of water, giving off hydrogen, such a cathode being preferably made of stainless steel or nickel. The apparatus of fig. 1 comprises:

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

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

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

-feeding the more concentrated tetramethylammonium salt solution to the storage tank (5) of the anode circuit via a line (5'),

-softened or deionized water is added to the reservoir (6) of the cathode circuit through a pipe (6'),

-a portion of the tetramethylammonium salt solution coming out of the anode degassing tank (3) is discharged via a line (7') to a discharge tank (7)

A reservoir 8 of synthetic TMAH solution taken from the cathode circuit at the cathode degassing tank (4) outlet □ through a pipe (8').

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

-oxidation of chloride ions to chlorine at the anode according to the following reaction:

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

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

-separating the anolyte, the catholyte and the produced gas by means of a cation exchange membrane.

The cathode circuit and the resulting TMAH reservoir solution may be protected with hydrogen, nitrogen, argon or a mixture of these gases. In this case, the plant used in the operating situation in which the cathode reduces water and releases hydrogen is modified as shown in fig. 3, in which the protected area is indicated by a dotted line, the protective gas is added via line (10) and the hydrogen produced by the cathodic reaction is withdrawn via line (11) leaving the reservoir (8) for the TMAH synthesis solution.

FIG. 4 shows a schematic diagram of the electrolysis principle in the case of an operation in which the cathode (preferably a platinum-or silver-plated carbon-based cathode) reduces oxygen, wherein the cathode compartment (2) is supplied with oxygen via a line (12) and a line (10) is used for this purposeThe hydrogen gas is discharged. In the case of TMA-Cl electrolysis to TMAH, as shown in fig. 5, the cell now operates on the same principle as before, except that instead of reducing water to hydrogen and hydroxide ions at the cathode, the oxygen is reduced to hydroxide ions with water according to the following reaction: in this case, oxygen, nitrogen, argon or mixtures of these gases can be used for possible protection.

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

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 ensure good current efficiency and good purity of the synthesized TMAH, the film should be TMA⁺Ion permeable, but starting salt anion (Cl)^-、HCO^-Etc.) and OH^-Is impermeable. Furthermore, in order to separate the acidic medium, even the weakly basic medium, from the very strongly basic medium (TMAH)The membrane should be chemically stable in both media. In addition, to minimize the resistive voltage drop, the film should be as conductive as possible. To meet all these requirements, ion exchange membranes are generally composed of at least two layers of polymer, these layers often being co-compressed (collimines). These polymers may be composed of perfluorosulfonated chains and/or perfluorocarboxylic acid chains. Some such films are described, for example, in patents US4401711, EP165466, US4604323, EP253119 and EP 753534. Nafion from DuPont (DuPont de Nemours) is particularly found on the market^N324, N902 and N966, Flemion of Asahi Glass^Or Aciplex from Asahi Chemicals^。

In order to achieve the same expansion ratio for different polymers and thus avoid membrane damage (e.g. delamination), it is necessary to adjust the anolyte and catholyte concentrations. Such membrane damage can in fact lead to a reduction in the performance of the cell, since OH^-The ions may be oxidized at the anode to form oxygen, which, on the other hand, leads to a decrease in purity of the synthesized TMAH, since film peeling may cause TMA⁺The salt solution flowed into TMAH.

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

current density of 1-5kA/m²Preferably 3-4kA/m²，

-a temperature of room temperature to 80 ℃, preferably 40-60 ℃,

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

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

By feeding concentrated TMA to the anode loop⁺Salt solution plus TMA⁺Salt and water to compensate for TMA consumed at the anode electrochemical reaction and transfer through the membrane⁺Salt and water. Similarly, water in the cathode loop, along with water transferred from the anode to the cathode compartment through the membrane, should be used to compensate for water consumed by the cathodic electrochemical reaction and also provided to achieve the desired final TMAHWater of the required concentration. Adding these Water and TMA⁺The concentration of the salt depends on, among other things, the nature of the membrane used, the selected current density, the electrode surface area and the desired concentration of TMAH.

Examples

The following examples illustrate the invention, but do not limit it, and these examples are carried out using the experimental set-up shown in FIG. 6.

The cell consists of two independent circuits, one anode circuit and one cathode circuit:

the anodic circuit consists of a PTFE-based chamber which allows the circulation of an anolyte in the electrochemical cell and is equipped with an anode (coated with RuO)₂-TiO₂Titanium composition of (a). The chamber was connected to an anolyte/gas degassing column to which TMA was also added⁺A salt rich solution and a lean anolyte is withdrawn. During electrolysis, the gas generated at the anode is withdrawn from behind the electrodes and the anolyte (density difference between the two-phase mixture and the solution) is circulated by the "up gas". The temperature was adjusted by heating coils around the degassing column.

The cathode circuit is symmetrical in the anode compartment and is also based on the same operating principle. The cation exchange membrane is arranged between the anode and the cathode. The anode was attached to the membrane and the cathode was 4 mm from the membrane ("finish gap" mounting), the cathode consisting of a nickel grid or stainless steel plate with small holes drilled for gas extraction. Demineralized water was added to the degassing column and the synthesized TMAH was withdrawn.

The working surface area of the electrolytic cell is 50 cm². The material used for the electrochemical cell and the different pipes was PTFE and the material used for the ancillary equipment (columns and tanks) was polypropylene.

The entire cathode circuit is protected with a mixture of hydrogen (produced at the cathode) and argon (injected) in order to limit the CO in the air₂Dissolved in TMAH.

The electrolyte is circulated due to the density difference generated by the released gas (chlorine or CO is released at the anode depending on the raw material salt₂Hydrogen gas is released at the cathode).

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

Chlorine gas generated during the test with TMA-Cl was destroyed in a production column (not shown) with sodium hydroxide and sodium sulfite.

The TMAH reservoir bottle was sealed and fitted with a draw/evacuate valve in the lower portion. Two anti-return bottles, one filled with water and the other empty, which are capable of avoiding contamination by the external atmosphere. Samples were taken under a controlled atmosphere (argon or nitrogen) in a glove box.

The cell was operated according to the following protocol:

operating the TMA of concentration with electrolysis⁺The saline solution fills the anode compartment,

filling the cathodic compartment with an aqueous solution of TMAH at the electrolysis operating concentration,

purging with argon to protect the cathode circuit (if it is desired to limit the CO in the air)₂Dissolved in TMAH, especially for electronic products),

heating coils to bring the device to the desired temperature and gradually increase the current density.

Example 1

Electrochemical cell made of RuO deposited on titanium₂-TiO₂Anode, stainless steel cathode (orifice plate) and Nafion^N324 film, which was previously conditioned by immersion in a 10% TMAH solution for 24 hours. This cation exchange membrane is a membrane with perfluorinated sulfonated chains sold by dupont.

The anode was charged with 735 g of 243 g/l TMA-HCO₃An aqueous solution. The cathode circuit was charged with 780 grams of 237 grams/liter aqueous TMAH solution. The whole device is heated by a heating coil, and argon is injected into a cathode loop for protection. The fluid is energized when the temperature reaches 50 ℃ and the current is increased from 1 ampere to 15 amperes in 3 minutes, i.e. 3kA/m²。

Adding water at a ratio of 100 g/h, adding TMA-HCO₃Was 125 g/h (588 g/l solution).

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

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

b) TMA-HCO in an evacuated canister₃The concentration was 247 g/l and 260 g/l in the anode degassing column. The current efficiency of the anodic reaction was 97%.

c) The voltage of the electrolytic cell is 10 volts and 3kA/m²It is still stable, i.e. energy consumption is 3138kWh/T (TMAH).

Examples 2 to 6

Other embodiments of the invention were carried out as in example 1, but using other materials (membranes, cathodes) and/or using other tetramethylammonium salts (TMA-X, X representing an anion) and/or varying TMA-X and TMAH concentrations.

Nafion^The N902 and N966 membranes are cation exchange membranes sold by dupont.

The operating conditions and the results obtained after 16 hours of operation are summarized in the following table, in which:

-E_cellvoltage (V) representing the electrolytic cell, and

- η represents the current efficiency, i.e. the ratio of the fraction of current available for carrying out the desired reaction to the total current used, η_aRepresenting the current efficiency of the anodic reaction (oxidation of chloride ions to Cl)₂Or bicarbonate ion oxidation to CO₂) And η_cRepresenting the current efficiency of the cathodic reaction (hydroxide ion synthesis).

The cell energy consumption expressed in kWh/ton TMAH can be given the formula W =295E_cell/η_cCalculated from the data in the table.

Examples	1	2	3	4	5	6
Examples	1	2	3	4	5	6	Film	N324	N966	N966	N324	N902	N324
Cathode electrode	Stainless steel	Nickel (II)	Stainless steel	Stainless steel	Nickel (II)	Nickel (II)	Film	N324	N966	N966	N324	N902	N324
Cathode electrode	Stainless steel	Nickel (II)	Stainless steel	Stainless steel	Nickel (II)	Nickel (II)	X^-Anion(s)	HCO₃ ^-	Cl^-	Cl^-	Cl^-	Cl^-	HCO₃ ^-
Start [ TMA-X ]	243 g/l	254 g/l	203 g/l	249 g/l	200 g/l	320 g/l	X^-Anion(s)	HCO₃ ^-	Cl^-	Cl^-	Cl^-	Cl^-	HCO₃ ^-
Start [ TMA-X ]	243 g/l	254 g/l	203 g/l	249 g/l	200 g/l	320 g/l	Adding [ TMA-X ]	588 g/l	505 g/l	580 g/l	533 g/l	250 g/l	602 g/l
Evacuation [ TMA-X ]	247 g/l	243 g/l	191 g/l	235 g/l	176 g/l	332 g/l	Adding [ TMA-X ]	588 g/l	505 g/l	580 g/l	533 g/l	250 g/l	602 g/l
Evacuation [ TMA-X ]	247 g/l	243 g/l	191 g/l	235 g/l	176 g/l	332 g/l	Beginning (TMAH)	237 g/l	106 g/l	107 g/l	247 g/l	100 g/l	244 g/l
Store (TMAH)	244 g/l	105 g/l	105 g/l	235 g/l	105 g/l	253 g/l	Beginning (TMAH)	237 g/l	106 g/l	107 g/l	247 g/l	100 g/l	244 g/l
Store (TMAH)	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_b	94％	93％	92.5％	95％	91.8％	92％	η_a	97％	97.5％	98％	94％	95.4％	nd^(a)
η_b	94％	93％	92.5％	95％	91.8％	92％	E_cell	10V	9V	8V	11V	7V	10V

(a) nd = not measured

Examples 7 to 10

The following table summarizes four examples which were run using the same equipment but were run without fixed TMA-X concentrations (example 10) or TMA-X and TMAH concentrations (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.

Examples	7	8	9	10
Examples	7	8	9	10	Film	N902	N902	N902	N902
Cathode electrode	Nickel (II)	Stainless steel	Stainless steel	Nickel (II)	Film	N902	N902	N902	N902
Cathode electrode	Nickel (II)	Stainless steel	Stainless steel	Nickel (II)	X^-Anion(s)	Cl^-	Cl^-	Cl^-	HCO₃ ^-
Start [ TMA-X ]	247 g/l	328 g/l	248 g/l	335 g/l	X^-Anion(s)	Cl^-	Cl^-	Cl^-	HCO₃ ^-
Start [ TMA-X ]	247 g/l	328 g/l	248 g/l	335 g/l	Adding [ TMA-X ]	247 g/l	328 g/l	248 g/l	335 g/l
Finally [ TMA-X ]^(b)	144 g/l	270 g/l	160 g/l	222 g/l	Adding [ TMA-X ]	247 g/l	328 g/l	248 g/l	335 g/l
Finally [ TMA-X ]^(b)	144 g/l	270 g/l	160 g/l	222 g/l	Beginning (TMAH)	50 g/l	250 g/l	248 g/l	107 g/l
Finally (TMAH)^(b)	203 g/l	320 g/l	159 g/l	106 g/l	Beginning (TMAH)	50 g/l	250 g/l	248 g/l	107 g/l
Finally (TMAH)^(b)	203 g/l	320 g/l	159 g/l	106 g/l	Test time
	8 hours	8 hours	8 hours	4 hours	Test time
	8 hours	8 hours	8 hours	4 hours	η_a	84％	59％	82％	86％
η_b	80％	59％	78％	89％	η_a	84％	59％	82％	86％
η_b	80％	59％	78％	89％	E_cell	7.5V	7V	7V	10V

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

Claims

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.