RU2369666C1 - Method of obtaining arsine and device to this end - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to chemical engineering and can be used in microelectronics, fibre optics and solar energy. Arsine is obtained through electrolysis of aqueous solution of arsenic oxide at pH 2-6 in a cell, in which the cathode and anode space is divided by a membrane made from asbestos cloth. The electrodes are in form of bimetallic plates, consisting of iron-zinc, stainless steel-zinc, copper-zinc, chrome-zinc, and molybdenum-zinc pairs, where the zinc side of the bimetallic electrode serves as the cathode, and the non-zinc side of the next electrode serves as the anode in the given cell. The negative terminal of the current source is connected to the first cathode, and the positive terminal to the next anode. All cells are connected by a channel at the bottom, through which electrolyte flows into the anode and cathode zones. At the top, all cathode and anode zones are connected by two channels for outlet of anode and cathode gases, respectively. Adsorbers with activated carbon are also fitted. All adsorbers are fitted with devices which keep their temperature in the -30-50°C range.

EFFECT: proposed method and device allow for large-scale production of arsine.

8 cl, 1 dwg

Description

The invention relates to the field of chemical technology, in particular to the production of arsenic hydride, and can be used in the production of semiconductor structures in microelectronics and solar energy.

All methods for producing arsine are divided into three groups (A.F. Zhigach, D. S. Stasinevich "Chemistry of hydrides", publishing house "Chemistry", Leningrad branch, 1969, p. 63): decomposition of metal arsenides by acids, exchange the reaction between arsenic compounds and other hydrides, the restoration of arsenic compounds with hydrogen. Due to the high toxicity of arsine, for industrial production in quantities of several tons per year, one of the most important issues in the implementation of the technology is the problem of neutralizing production waste and the ability to stop the synthesis process in the shortest possible time. From this point of view, the most suitable method is electrolysis, in which synthesis is carried out by reducing arsenic compounds with atomic hydrogen released at the cathode during the electrolysis of an aqueous solution of arsenic compounds.

Known methods for the electrochemical production of arsine.

US Pat. No. 5,474,659 (c. No. 08/292346), IPC C25B 1/00, describes a method for producing arsine in an electrochemical cell in which the cathode is made of an electrically conductive substrate with elemental arsenic fixed to it. Because Arsine synthesis by this method is carried out due to the consumption of cathode material, then in the process of obtaining large quantities of arsine it is necessary to replace the cathode, which in industrial conditions is quite complicated and most importantly a dangerous operation.

US Pat. No. 5,158,656, IPC H04N 3/69, proposes a cathode of an alloy or solid solution or a mixture of arsenic with various metals, which does not eliminate the disadvantages of the above patent.

The closest method is US patent No. 5425857, IPC С25В 1/02, 9/00, which proposes the process of electrolytic production of arsine in an electrochemical cell, including the anode and cathode, which consists in the fact that:

(i) are fed to the cathode of ions H ⁺ and AsO ₂ ^- a predetermined ratio (0.7-1.5), so that the cathode flow two competing reactions: producing arsine and hydrogen gas.

(ii) a reaction is carried out supplying the cathode with H ⁺ ions.

The H ⁺ / As ratio is controlled by installing a cation exchange membrane between the anode and cathode, supplying an electrolyte flow to the cathode zone at a rate that reduces arsenic concentration by no more than 10%, introducing the required amount of acidic acid into the depleted electrolyte introduced into the cathode zone As ₂ O ₃ solution to maintain a constant concentration of As ₂ O ₃ . The cathode is made of a material that provides the generation of arsine - lead or copper, coated with a layer of bismuth, lead, thallium or cadmium.

Hydrogen from a mixture of arsine with hydrogen is removed on the membrane module by pumping out the gas that has penetrated through the membrane and purging it with nitrogen or sulfur hexafluoride. The mixture is pre-dried in the refrigerator on the Pelet effect, molecular sieves or a combination thereof and is cleaned of dust.

To implement this method, a device is proposed, including:

- an electrochemical cell with a cathode supplied with hydrogen ions and AsO ^- ₂ , and an anode, where H ⁺ ions are generated;

- a cation exchange membrane separating the anode and cathode;

- means for supplying the cathode zone ions H ⁺ and AsO ₂ ^- content and stabilization AsO ₂ ^- in the electrolyte by introducing an acidic solution As ₂ O ₃ of the saturator;

- a saturator is installed between the electrochemical cell and the tank with a supply of acidic solution going to the cathode, or in the tank itself with a reserve solution;

- a cathode made of lead or copper coated with bismuth, lead, thallium or cadmium;

- a membrane module for separating hydrogen from arsine;

- a device for pumping gas passing through the membrane;

- a device for removing this gas with nitrogen or sulfur hexafluoride;

- devices for drying and dust removal of a mixture of arsine with hydrogen;

- a flat anode provided with an acidic solution, or a gas hydrogen anode.

These method and device are designed to produce relatively small amounts of arsine (about 3 l / h, i.e. 0.2-0.3 kg / day) for supplying it as a small additive to devices where semiconductor structures are created.

For the production of arsine in the amount of several tons per year (i.e. 10-100 kg / day), using the method according to the US patent adopted as a prototype will require solving several problems:

- sequential inclusion of several (10-20) electrolyzers, because it is difficult to provide the necessary current strength at a voltage of 3-6V with parallel connection;

- maintaining the ratio of H ⁺ / As within the specified limits,

- arsenic stabilization systems,

- purification of arsine from impurities CO ₂ , CO, CH ₄ and others,

- purification of waste gases from arsine,

- regeneration of molecular sieves,

- the use of such harmful substances as lead, thallium, cadmium, bismuth.

The technical result of the proposed device is to eliminate the disadvantages of the known method and device when implementing large-capacity production of arsine.

The technical result is achieved by the fact that in the known method, including electrolysis of an aqueous solution of arsenic oxide in an electrochemical cell with separated anode and cathode zones, drying of arsine using refrigerators and molecular sieves and purification from dust, zinc is used as the cathode material, as an electrolyte - an aqueous solution saturated with arsenic oxide with a pH of 2-6, and purification from impurities is additionally carried out on activated carbon and a molecular sieve while cooling them to -30-50 ° C.

The electrolyte is saturated by passing the depleted electrolyte through a container with arsenic oxide powder,

In the known device for producing arsine, including an electrochemical cell, with solid flat electrodes, with separated anode and cathode zones, devices for feeding electrolyte into it with an adjustable concentration of arsenic and devices for drying arsine and cleaning it from dust, several cells are assembled into a single electrolyzer, where the electrodes are made in the form of bimetallic plates consisting of pairs of iron-zinc, stainless steel - zinc, copper-zinc, chromium - zinc, molybdenum-zinc, lead - zinc, and the zinc side of the bimetallic ele The cathode serves as the cathode, and not the zinc side of the next electrode serves as the anode in this cell. The negative pole of the current source is connected to the first cathode, and the positive pole is connected to the last anode, all the cells at the bottom are connected by channels to supply electrolyte to the cathode and anode zones, and at the top all the cathode and anode zones are connected by two channels to output the anode and cathode gases, respectively.

The anodic and cathodic zones of the cell are separated by a membrane of asbestos tissue.

Additionally, activated charcoal adsorbers are installed. All adsorbers are equipped with devices to maintain their temperature at the level of -30-50 ° С

Before the electrolyte enters the electrolyzer, a container is installed in which the arsenic oxide powder is in an amount sufficient to maintain the concentration of arsenic in the electrolyte at a saturation level during the production of arsine.

The use of zinc as a cathode material provides the necessary conditions for the reduction of arsenic to arsine and is easily applied to metals used for anodes.

A diagram of the proposed device is shown in the drawing, where

1 - container with arsenic oxide powder and electrolyte; 10 - replaceable refrigerator 11 - replaceable refrigerator; 2 - electrolyzer: 2.1-2.3 electrodes, 12 - tubes for draining water from refrigerators, 2.4, 2.5 - asbestos membrane 13 - adsorber with molecular 3 - water refrigerator, sieve 4 - capacity for separating anolyte, 14 - adsorber with activated carbon, 5 - water refrigerator, 6 - furnace for decomposition of arsine, 15 - condenser-evaporator, 7 - dust filter, 16 - cylinder 8 - capacity for separation of catholyte 17 - furnace for decomposition of arsine, 9 - water refrigerator, 18 - dust filter.

The device operates as follows.

Arsenic oxide powder is poured into tank 1 and an electrolyte is poured, which is a saturated aqueous solution of arsenic oxide with a pH of 2-6 so that the electrolyzer, consisting of the required number of cells (for example, 10), is completely filled with electrolyte and the electrolyte level reaches Ѕ heights of containers 4, 8. In refrigerators 3, 5, 9, the temperature is set + 5 + 10 ° С, in one of the refrigerators 10 or 11 the temperature is set in the range -35-45 ° С, in the cryostats of the adsorbers the temperature is set in the range -30- 50 ° C, and in the condenser evaporator -100-140 ° C. In decomposition ovens 7.17, a temperature of + 400 + 450 ° C is set. The electrolyzer is connected to a DC source, providing a voltage on each of its cell 5-6 V and a current density on the electrodes in the range of 0.2-0.6 A / cm ² . During operation, a mixture of cathode gas bubbles with electrolyte from the cathode zones of all cells and anode gas bubbles with electrolyte from the anode zones respectively enter containers 8 and 4, from which the electrolyte enters container 1, which ensures continuous electrolyte circulation and arsenic concentration is maintained in it at a level close to saturation. Anode gas after passing through the furnace 6 and the filter 7 is discharged into the atmosphere. After passing through the refrigerators 9, 10 (9, 11), the cathode gas is freed from the bulk of the water vapor and diarsin. As it is filled with water (ice), refrigerator 10 (11) is turned off for heating and water discharge, and refrigerator 11 (10) is connected. On a molecular sieve adsorber cooled to -30-50 ° C, the gas is purified from H ₂ O to a dew point of -85-90 ° C, from CO ₂ and others to a level below 0.5 ppm, and on a cooled activated charcoal adsorber it is cleared of impurities of CH ₄ and others to a level of 0.5 ppm. In the condenser of the evaporator, hydrogen is separated, residues N ₂ and O ₂ . Hydrogen passes through the furnace at a temperature of about 450 ° C, through a dust filter and enters the adsorber regeneration unit (not shown in the drawing) or is used for other purposes. After heating the condenser-evaporator, arsine purified to the 5N level (i.e., containing 99.999% of the main substance) enters the consumer cylinder. The combination of the proposed measures provides an increase in productivity up to 10-100 kg per day and a deeper cleaning of impurities.

Claims (8)

1. A method of producing arsine, comprising the electrolysis of an aqueous solution of arsenic oxide in an electrochemical cell; drying arsine with refrigerators and molecular sieves and dust removal, characterized in that zinc is used as the cathode material, a saturated aqueous solution of arsenic oxide with a pH of 2-6 is used as the electrolyte, and purification from impurities is additionally carried out on activated carbon. 2. The method according to claim 1, characterized in that the purification of arsine from impurities is carried out on a molecular sieve and activated carbon at a temperature in the range of -30 ... -50 ° C. 3. The method according to claim 1, characterized in that the saturation of the electrolyte with arsenic oxide is carried out by passing the depleted electrolyte through a container with arsenic oxide powder. 4. A device for producing arsine, comprising an electrochemical cell with solid flat electrodes, with anode and cathode zones separated, a device for supplying arsenic oxide saturated with arsenic oxide and a device for drying and dusting arsine, characterized in that several cells are assembled in a single electrolyzer, where the electrodes are made in the form of bimetallic plates consisting of pairs of iron-zinc, stainless steel-zinc, copper-zinc, chromium-zinc, molybdenum-zinc, the zinc side of the bimetallic electrode serves as the cathode, and n the zinc side of the next electrode serves as the anode in the cell; minus the current source is connected to the first cathode, and plus to the last anode, all the cells below are connected by a channel through which electrolyte enters the anode and cathode zones, and above all the cathode and anode zones are connected by two channels to output the anode and cathode gases, respectively. 5. The device according to claim 4, characterized in that the anode and cathode zones of the cell are separated by a membrane of asbestos tissue. 6. The device according to claim 4, characterized in that the adsorbers with activated carbon are additionally installed. 7. The device according to PP.4 and 6, characterized in that the adsorbers are additionally equipped with devices to maintain their temperature at -30 ... -50 ° C. 8. The device according to claims 4 and 5, characterized in that before the entrance of the electrolyte into the electrolyzer, a container is installed in which arsenic oxide powder is located.

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