EP0648865A1 - Process and apparatus for producing arsine electrolytically - Google Patents

Abstract

Process for generating arsine by an electrolytic route from an electrochemical cell (12) in which are arranged a cathode (7) fed with H<+> and AsO2<-> ions, where two concurrent reactions take place producing arsine and gaseous hydrogen respectively, and an anode (3) where a reaction which is the source of H<+> ions takes place, the ratio of the concentrations H<+>/As at the cathode being controlled and kept constant.

Description

The invention relates to a method and a device for generating arsine (AsH₃) by electrolytic means.

Gas hydrides are a key point in the semiconductor industry. We can thus cite the example of silane used as a precursor for the manufacture of silicon substrates or for the production of silica deposits, or even the example of arsine as a source of arsenic for doping semi- conductive or for the growth of epitaxial layers of GaAsP.

The use of arsine is not without posing safety problems linked to the highly toxic nature of this gas, justifying its handling under very careful conditions (use of hoods, etc.), both in terms of its production. than its storage or its transport in the form of bottles containing a generally reduced concentration of arsine in a carrier gas.

It therefore appeared interesting to develop a method of producing (or generating) arsine on site (or "on site"), making it possible to produce on site, at the inlet of the reactor using this hydride, arsine in good conditions of safety and purity.

Electrolytic reduction of solutions containing arsenic salts quickly appeared to be a good answer to this problem.

Thus, document US-A-1,375,819 proposes a process for the production of arsine by electrolysis of a solution of an arsenic oxide (such as As₂O₃) in an acid medium (sulfuric acid) in which is also sulphate of potassium (K₂SO₄) The electrolyser used is of the tank type, the cathode is made of carbon covered with mercury, the anode is made of simple carbon. The configuration adopted gives rise to the production of a gas which is in fact a mixture of oxygen, hydrogen and arsine. If no precise composition of the mixture is announced, it can easily be deduced from this configuration that it does not separate the gases emitted at the cathode and at the anode, that it does not prevent the AsO₂⁻ ions present in solution to oxidize at the anode, thereby reducing the yield of arsine.

In this context, document US-A-4,178,224 (VR Porter) proposes an electrolytic arsenic production system based on the following principle: the electrolytic cell is here also of the tank type, but consists of two concentric compartments playing the role of electrodes. These two electrodes are separated in their upper part by a solid cylindrical barrier (and concentric around the anode) whose objective is the separation of the gases produced at the anode and the cathode, before their evacuation from the top of the cell. . This "upper" barrier is supplemented by a "lower" barrier (always cylindrical and concentric around the anode), continuous or not with the preceding barrier, the objective of which is here also to separate the gases produced, at the bubbling stage. , but also to allow the passage of H⁺ ions from the anode to the cathode where they will feed the arsine formation reaction. This second barrier is envisaged in a material such as porous polypropylene, or PVC but in the latter case, provision is made for the presence of a small window at the bottom of the cell to allow the H⁺ ions to pass. These two barriers could be combined, according to this document, into a single solid barrier, but here again, an opening is then to be provided in the lower part to allow the H⁺ ions to pass. The cathode is supplied with an acid solution (H₂SO₄) of NaAsO₂, injected between the anode and the cathode from a container outside the cell, using a pump. Nevertheless, the results obtained show that the mixture produced at the cathode (Example 1) only reaches 20% of arsine in hydrogen in steady state, and not more than 38% at peak.

Mention may also be made of document EP-A-393 897, here again proposing production of arsine by electrolytic means. The electrolytic cell is of the bac type, containing a NaOH sodium hydroxide solution, the electrodes are both constituted by arsenic. If the yield of arsine announced is high (of the order of 97% in hydrogen), the flow rate achieved is however very low (of the order of 15 cm³ / h at atmospheric pressure).

• d'atteindre des concentrations élevées d'arsine dans le gaz de sortie;
• d'obtenir des débits suffisamment élevés, au moins égaux à 1 litre/heure, sans dégradation du rendement en arsine;
• d'obtenir une bonne stabilité des caractéristiques de concentration du mélange produit;
• d'éviter l'utilisation, comme matière première, de sels de sodium (tel NaAsO₂) de façon à éviter la précipitation de sels tels que Na₂SO₄, et donc le risque d'une présence éventuelle de sodium dans la phase gazeuse, toujours préjudiciable aux utilisations ultérieures dans l'industrie électronique.

The object of the present invention is to provide a process for the generation of arsine by electrolytic means, allowing:

• achieve high concentrations of arsine in the outlet gas;
• obtain sufficiently high flow rates, at least equal to 1 liter / hour, without degrading the arsine yield;
• to obtain good stability of the concentration characteristics of the mixture produced;
• avoid the use, as raw material, of sodium salts (such as NaAsO₂) so as to avoid the precipitation of salts such as Na₂SO₄, and therefore the risk of a possible presence of sodium in the gas phase, always detrimental to subsequent uses in the electronics industry.

To do this, the invention proposes a process for generating arsine by electrolytic route from an electrochemical cell where a cathode supplied with H⁺ and AsO₂⁻ ions are arranged, where two competing reactions producing respectively produce arsine and hydrogen gas, and an anode, where a reaction source of H⁺ ions takes place, in which the ratio of H⁺ / As concentrations to the cathode is controlled and kept constant.

The reaction source of H⁺ ions can for example consist of the electrolysis of water (in the case of a conventional plane anode supplied with acid solution) or also by the oxidation of hydrogen (supply of gaseous hydrogen d '' a gas diffusion electrode). This second type of electrode having a very large specific surface, generally has catalyst particles (platinum type) at the gas / liquid interface on which the hydrogen will oxidize to H⁺ ions, and on the gas side is treated so as to be made hydrophobic.

The Applicant has indeed highlighted the key role of the H⁺ / As ratio at the cathode, and its influence on the yield of arsine obtained (concentration of arsine in the mixture gas obtained at the cathode). Each cell geometry corresponds to an optimum of the H⁺ / As ratio to be respected and maintained.

• On sépare, par une membrane cationique, la cellule électrochimique en deux compartiments anodique et cathodique, permettant ainsi la maitrise des flux de matière à l'intérieur de la cellule;
• On assure une circulation du fluide alimentant le compartiment cathodique suffisamment élevée pour obtenir un taux de conversion en arsenic à la cathode inférieur à 10 %;
• On alimente le compartiment cathodique en ions H⁺ et AsO₂⁻ via un saturateur constitué par une réserve de composé solide As₂O₃ que vient balayer une solution acide.

According to one aspect of the invention, the H⁺ / As ratio is controlled by the following steps:

• The electrochemical cell is separated, by a cationic membrane, into two anodic and cathodic compartments, thus allowing the control of material flows inside the cell;
• The circulation of the fluid supplying the cathode compartment is sufficiently high to obtain a conversion rate of arsenic at the cathode of less than 10%;
• The cathode compartment is supplied with H⁺ and AsO₂⁻ ions via a saturator constituted by a reserve of solid compound As₂O₃ which is swept away by an acid solution.

The conversion rate is understood to mean, according to the invention, the ratio: (As ^e -As ^s ) / As ^e , where As ^e represents the concentration of arsenic in the fluid supplying the cathode compartment, and As ^s this same concentration in the outlet fluid which is recycled to the storage tank supplying the cathode compartment.

The balance of chemical reactions occurring at the anode and at the cathode is as follows:

At the saturator :

$$\text{As₂O₃ + H₂O → 2 HAsO₂}$$

At the anode :

$$\text{H₂O → 1/2 O₂ + 2 H⁺ + 2e (H₂ → 2 H⁺ + 2e for a gas diffusion electrode)}$$

At the cathode :

$$\text{As + 3 H⁺ + 3e → AsH₃}$$

   réaction concurrente à la cathode : H⁺ + 1e → 1/2 H₂ $$\text{HAsO₂ + 3 H⁺ + 3e → As + 2 H₂0}$$

$$\text{As + 3 H⁺ + 3e → AsH₃}$$

concurrent reaction at the cathode: H⁺ + 1e → 1/2 H₂

According to one of the embodiments of the invention, the reserve of As₂O₃ (saturator) is located in the circuit between the cathode compartment and the storage of acid solution which comes to sweep the saturator.

According to another implementation of the invention, the reserve of As₂O₃ (saturator) is located in the circuit inside the storage of acid solution, within this solution, thus ensuring close contact between this solution and the walls of the saturator.

• de laisser passer les ions H⁺ produits à l'anode vers la cathode, où ils iront alimenter la réaction de formation d'arsine;
• d'isoler les gaz produits à l'anode de ceux produits à la cathode;
• d'empécher que les ions AsO₂⁻, en solution du coté compartiment cathode, passent du côté anode et aillent s'oxyder sur l'anode, diminuant d'autant le rendement en arsine.

By cationic membrane is meant, according to the invention, an ion exchange membrane allowing:

• allowing the H⁺ ions produced at the anode to pass to the cathode, where they will feed the arsine formation reaction;
• isolating the gases produced at the anode from those produced at the cathode;
• to prevent the AsO₂⁻ ions, in solution on the cathode compartment side, from passing on the anode side and going to oxidize on the anode, thereby reducing the yield of arsine.

A material such as that sold under the name NAFION ^{R is} suitable for the preparation of such a membrane.

The use of the As₂O₃ saturator avoids the use of sodium salts, but also constitutes a kind of buffer capacity which ensures a regular and constant concentration of AsO₂⁻ ions in the medium supplying the cathode.

The acid medium used in the composition of the mixtures supplying the two compartments may include phosphoric, perchloric, or preferably sulfuric acid.

The electrodes used for the implementation of the invention are advantageously made up as follows: at the cathode, a material promoting the formation of arsine to the detriment of the competing reaction of hydrogen formation, advantageously a material such as copper on which a deposit of bismuth, lead, or thallium or cadmium was carried out, with an electrode area of the order of 70 cm². At the anode, a material such as titanium on which a deposit of ruthenium oxide or iridium was deposited, or an electrode for example of the felt type, will be used, depending on the case (conventional electrolysis or gas electrode). carbon.

• grâce à l'utilisation d'électrodes appropriées,
• par l'utilisation d'une membrane cationique disposée entre les deux électrodes permettant une bonne maitrise des flux de matière intervenant d'une électrode à l'autre,
• par un apport régulier et constant en ions AsO₂⁻ à l'aide d'un saturateur As₂O₃, et
• par l'établissement d'une vitesse de circulation de fluides elevée permettant une bonne maitrise du taux de conversion à la cathode,

   est étroitement lié à la géométrie de cellule utilisée (surface d'électrodes..). A chaque géométrie, correspond un rapport H⁺/As optimum. Cependant, ce rapport sera avantageusement maintenu, selon l'invention, dans la gamme [0.7, 1.5] préférentiellement dans la gamme [0.75, 1.25].The H⁺ / As ratio thus set up and kept constant:

• through the use of appropriate electrodes,
• by the use of a cationic membrane placed between the two electrodes allowing good control of the material flows occurring from one electrode to the other,
• by a regular and constant supply of AsO₂⁻ ions using an As₂O₃ saturator, and
• by establishing a high fluid circulation speed allowing good control of the cathode conversion rate,

is closely linked to the cell geometry used (electrode surface, etc.). Each geometry has an optimum H⁺ / As ratio. However, this ratio will advantageously be maintained, according to the invention, in the range [0.7, 1.5] preferably in the range [0.75, 1.25].

According to one aspect of the invention, a step is carried out, downstream of the generator, of separation of the hydrogen / arsine mixture produced at the cathode, by treating this mixture on a membrane module, making it possible to obtain at the outlet (or rejection) of modulates a higher arsine concentration than in the arsine / hydrogen mixture treated at the entrance to the module, but also to obtain a high stability of this concentration.

An assembly of one or more semi-permeable membranes mounted in series or in parallel, having good separation properties of arsine with respect to a carrier gas (selectivity), will advantageously be used to carry out this concentration step. this is the case for membranes of the polyimide or polyaramide (aromatic polyimide) type.

According to one of the embodiments of the invention, for the cases where the mixture arrives on the module at low pressure, this low pressure is compensated for by carrying out, on the permeate side of the membrane, a vacuum drawing or else a scanning with using a "tool" gas, so as to lower the partial pressure of the hydrogen (which we want to separate from arsine) on the permeate side.

"Low pressure" is understood to mean, according to the invention, a pressure lying in the range 10⁴ Pa to 5 x 10⁵ Pa absolute.

Preferably, to carry out a permeate-side sweep of the membrane, a gas, other than that which it is desired to separate, and moreover having a low permeation of the permeate towards the interior of the membrane, so as to prevent this gas "tool" does not pollute the interior of the membrane and therefore does not affect the result obtained at the output of the module. Advantageously, according to the invention, nitrogen, or even SF comme, will be used as the "tool" gas.

According to one aspect of the invention, before arriving on the membrane module, the mixture produced at the cathode undergoes at least one drying operation, on a device such as a refrigerant (for example with Peltier effect), or else a molecular sieve, or a combination of these two means, and where appropriate, at least one filtering operation on a particle filter.

Another object of the invention is to propose a device for implementing the method according to the invention.

The device comprises at least one electrochemical cell where at least one cathode is placed, supplied with H⁺ and AsO₂⁻ ions, where two competing reactions take place, producing respectively arsine and hydrogen gas, and at least one anode. , where a reaction source of H⁺ ions takes place; a cationic membrane separating the electrochemical cell into two compartments, anodic and cathodic; and to supply the cathode compartment with H⁺ and AsO₂⁻ ions, a saturator constituted by a reserve of As₂O₃, which is swept away by an acid solution.

According to one of the embodiments of the invention, the source reaction of H⁺ ions at the anode is the electrolysis of water, the anode compartment is then supplied with an acid solution. According to another implementation of the invention, the source reaction of H⁺ ions at the anode is the oxidation of hydrogen and we are then in the presence of a gas diffusion electrode supplied with hydrogen gas.

According to one aspect of the invention, the saturator is located between the electrochemical cell and the storage tank for the acid solution supplying the cathode compartment.

According to another aspect of the invention, the saturator is located inside the storage tank for the acid solution supplying the cathode compartment, within this acid solution.

Preferably, a material will be used for the cathode which favors the arsine formation reaction to the detriment of the hydrogen formation reaction, such as copper on which a deposit of bismuth, lead, or thallium or cadmium has been carried out. . AT the anode, a material such as titanium on which a deposit of ruthenium oxide or iridium was deposited, or an electrode of the carbon felt type, for example (conventional electrolysis or gas electrode) will be used, as the case may be .

According to one aspect of the invention, the device comprises, downstream of the electrochemical cell, a membrane module, on which the arsine / hydrogen mixture produced at the cathode undergoes a separation step, so as to obtain at the module output, a higher arsine concentration than in the initial mixture.

According to one of the embodiments of the invention, the membrane module is connected to means allowing the permeate side of the membrane to be evacuated, so as to bring the pressure on the permeate side to a value of the order of 1 to 100 Pa (primary vacuum).

According to another implementation of the invention, the membrane module is connected to a gas source, making it possible to carry out a scanning of the permeate side of the membrane, using this gas, which advantageously will have according to the invention low permeation of the permeate towards the inside of the membrane, such as nitrogen or SF₆.

According to one aspect of the invention, the device comprises, upstream of the membrane module, at least one device for drying the mixture produced at the cathode, such as a refrigerant, for example with Peltier effect, or else a molecular sieve, or a combination of these two means, and where appropriate, at least one particle filter.

• La figure 1 est une représentation schématique d'une cellule électrolytique entrant dans l'élaboration d'un générateur convenant pour la mise en oeuvre du procédé selon l'invention;
• La figure 2 représente une courbe donnant, pour une cellule selon la figure 1, la variation de la concentration d'arsine dans le mélange produit en fonction du rapport H⁺/As à la cathode, réalisée en plomb, et pour une densité de courant i= 500 A/m².
• La figure 3 représente une courbe illustrant pour une cellule selon la figure 1, l'influence de la densité de courant (rapportée à la surface d'électrode) sur le débit d'arsine à la cathode.
• La figure 4 est une représentation schématique d'une installation globale comprenant un générateur convenant pour la mise en oeuvre du procédé selon l'invention.

Other characteristics and advantages of the present invention will emerge from the following description of embodiments given by way of illustration but in no way limited, made in relation to the appended drawings, in which:

• Figure 1 is a schematic representation of an electrolytic cell used in the development of a generator suitable for the implementation of the method according to the invention;
• FIG. 2 represents a curve giving, for a cell according to FIG. 1, the variation of the concentration of arsine in the mixture produced as a function of the H⁺ / As ratio at the cathode, made of lead, and for a current density i = 500 A / m².
• FIG. 3 represents a curve illustrating for a cell according to FIG. 1, the influence of the current density (relative to the electrode surface) on the flow of arsine at the cathode.
• Figure 4 is a schematic representation of an overall installation comprising a generator suitable for implementing the method according to the invention.

• D'un compartiment anodique 1, relié au pôle positif d'un générateur électrique, comportant une anode 3 où se produit une réaction d'oxydation de l'eau, conduisant à la formation d'oxygène gazeux et d'ions H⁺. Cette anode est constituée de titane sur lequel a été effectué un dépot d'oxyde de ruthénium. Le compartiment anodique est alimenté en une solution acide 1M d'acide sulfurique contenue dans un bac de stockage anodique 4, via une ligne d'alimentation 5 par l'intermédiaire d'une pompe 6.
• D'un compartiment cathodique 2, relié au pôle négatif d'un générateur électrique, comportant une cathode 7, où se produisent deux réactions concurrentes, la première de formation d'arsine gazeux, la seconde de formation d'hydrogène gazeux. Cette cathode est constituée de plomb, elle présente une surface d'électrode de l'ordre de 70 cm². Le compartiment cathodique est alimenté en composé HAsO₂, donc en ions AsO₂⁻, par une ligne 17, via un saturateur 8 constitué par une réserve de composé solide As₂O₃, que vient balayer, par l'intermédiaire d'une pompe 9, une solution acide 1M d'acide sulfurique 19, contenue dans un bac de stockage cathodique 10.
• D'une membrane cationique 11 en NAFIONR séparant les deux compartiments.

We recognize in Figure 1 an electrochemical cell 12, consisting of:

• An anode compartment 1, connected to the positive pole of an electric generator, comprising an anode 3 where an oxidation reaction of water takes place, leading to the formation of gaseous oxygen and H⁺ ions. This anode consists of titanium on which a deposit of ruthenium oxide has been carried out. The anode compartment is supplied with a 1M acid solution of sulfuric acid contained in an anode storage tank 4, via a supply line 5 via a pump 6.
• A cathode compartment 2, connected to the negative pole of an electric generator, comprising a cathode 7, where two competing reactions take place, the first of which forms arsenic gas, the second which forms hydrogen gas. This cathode is made of lead, it has an electrode area of the order of 70 cm². The cathode compartment is supplied with HAsO₂ compound, therefore in AsO₂⁻ ions, by a line 17, via a saturator 8 constituted by a reserve of solid compound As₂O₃, which is swept, via a pump 9, an acid solution 1M sulfuric acid 19, contained in a cathode storage tank 10.
• A cationic membrane 11 in NAFIONR separating the two compartments.

Figure 2 illustrates the performance obtained using a generator such as that described above, using a current density (relative to the electrode surface) of 500A / m². The observed evolution confirms the existence of an optimum for the H⁺ / As ratio, close to 1 for this cell geometry, giving rise to the production at cathode 7 of an arsine / hydrogen mixture containing 95% of arsine, with a flow rate of 50 l / h / m² (m² of electrode). The performances decrease rapidly around the optimum value.

FIG. 3 illustrates, under these same cell and electrode conditions, the influence of the current density on the flow of arsine produced at cathode 7, this for a H⁺ / As ratio close to 1. It can be seen, in the range [200 A / m², 1500 A / m²] of current density an increasing flow of arsine, from around 25 l / h / m² to around 225 l / h / m².

An electrochemical cell 12 such as that described in FIG. 1 is recognized in FIG. 4.

On the anode side, the compartment of the cell 12 is supplied with acid solution stored in the tank 4, via line 5 which here also incorporates a flow sensor 13. The tank 4 includes means for discharging the oxygen produced at the anode to a vent 14, via a valve 15 if necessary, and a pressure sensor 16.

On the cathode side, the cell compartment 12 is supplied with AsO₂⁻ ions by the storage tank 10, via line 17 which includes a flow sensor 18. The reserve of As₂O₃ (saturator 8) is here included in the storage 10, within the acid liquid 19, continuously swept by it, to allow the continuous dissolution of the compound As₂O₃ in the solution, leading to its saturation in AsO₂⁻ ions.

The cathode container 10 includes means for evacuating gas to a vent 20, via a valve 21 if necessary. This evacuation is in particular used during the purging operations of the system.

We also note the presence, on the top of the tank 10, of an inlet 22 of inert gas (such as nitrogen), passing through a flow meter 23 and a non-return valve 24, to supply the tank 10 with nitrogen. inlet 25. This nitrogen inlet is particularly used to carry out storage purge cycles, at the start of the installation, but also to purge the downstream of the installation via a line 48 derived from line 25.

The tank 10 also includes a pressure sensor 26, and a temperature sensor 28.

The arsine / hydrogen mixture produced at the cathode of cell 12 is first treated on a refrigerant 27 (the temperature of which is controlled by a sensor 29), so as to purify the mixture in question of a large part of its humidity.

At the outlet of the refrigerant 27, via a valve 44, the mixture undergoes a second purification of water on a molecular sieve 30, before passing over a particle filter 31. The mixture then approaches a semi-permeable membrane module 32 of the type with hollow fibers, the active layer of which is a polyaramide (aromatic polyimide) offering a total module exchange surface of approximately 0.25 m².

The installation allows the permeate side of the membrane to be evacuated by a line 35, at a pressure of the order of 10 Pa absolute (primary vacuum).

The mixture enriched in arsine, at the outlet (rejection) of membrane, is then directed via a line 46 comprising a non-return valve 33 to a buffer capacity 34 from which the mixture is directed. via a line 47 comprising a pressure sensor 36, to the reactor 39 using arsine. Optionally, the mixture is filtered on a particulate filter 38. A vent 40 is provided if necessary at the end of the line 47.

All along the route there are valves of two types, depending on the fluids transported from the valves for the liquid circuit (such as valves 41, 42 etc.), and for the gas pipeline (such as valves 43, 44, 45 etc.).

The application of this installation made it possible to obtain, at the outlet of the cathode compartment, concentrations of arsine in hydrogen varying from 50% to 95%, according to the H⁺ / As ratio applied (as illustrated in FIG. 2), with a flow rate of the mixture leaving the cell of at least 3 l / h. The drying stage, consisting of the refrigerant 27 and a molecular sieve 30, makes it possible to obtain a mixture almost free of water, any additional drying which can be carried out on the membrane 30. The essential objective of the membrane is to concentrate the arsine in the mixture obtained at the membrane outlet. Experiments have shown that from highly variable mixtures such as those mentioned above, it was possible to concentrate the mixture in arsine at the membrane outlet to contents of at least 99.5% in hydrogen, this with flow rates at the membrane outlet of the order of 1 l / h of pure arsine (the flow rate of the mixture at 99.5 being slightly higher). The use of a post-concentration step by membrane making it possible to obtain details on the content of arsine produced of the order of 0.1%, but also excellent stability of this concentration over time.

Claims (20)

Method for generating arsine electrolytically from an electrochemical cell (12) which has a cathode (7) supplied with H⁺ and AsO₂⁻ ions, where two competing reactions occur, respectively producing arsine and hydrogen gas, and an anode (3), where a reaction source of H⁺ ions takes place, characterized in that the ratio of the H⁺ / As concentrations to the cathode (7) is controlled and kept constant. Method according to claim 1, characterized in that the control of the H⁺ / As ratio is obtained by the following steps: a) The electrochemical cell is separated into two compartments, anodic and cathodic, using a cationic membrane (11), thus allowing the control of the material flows inside the cell; b) circulation of the fluid supplying the cathode compartment is sufficiently high to obtain a conversion rate of arsenic at the cathode of less than 10%; c) The cathode compartment is supplied with H⁺ and AsO₂⁻ ions by a reserve of As₂O₃ (8), which is swept away by an acid solution (19). Method for generating arsine electrolytically according to one of claims 1 or 2, characterized in that the cathode (7) is produced from a material which promotes the arsine formation reaction to the detriment of the arsenic reaction hydrogen. Method according to one of claims 1 to 3, characterized in that the cathode (7) consists of lead, or copper on which a deposit of bismuth, lead, thallium or even cadmium has been carried out. Method according to one of claims 1 to 4, characterized in that the H⁺ / As ratio is maintained between 0.7 and 1.5, preferably between 0.75 and 1.25. Method according to one of claims 1 to 5, characterized in that the mixture of hydrogen and arsine produced at the cathode (7) is subjected to a subsequent separation step on a membrane module (32), so as to obtain a higher arsine concentration at the outlet of the module than in said mixture. Method according to claim 6, characterized in that the permeate side of the membrane is evacuated. Method according to claim 6, characterized in that a permeate-side sweep of the membrane is carried out, using a gas having a low permeation of the permeate towards the interior of the membrane, such as nitrogen or SF6. Method according to one of claims 6,7,8, characterized in that before its arrival on the membrane module (32), the mixture produced at the cathode (7) undergoes at least one drying operation, on a device such as '' a Peltier refrigerant (27) or a molecular sieve (30), or a combination of these two means, and if necessary, at least one filtering operation on a particle filter (31). Device for generating arsine by electrolytic means, particularly suitable for implementing the method according to one of claims 1 to 9, characterized in that it comprises at least: - An electrochemical cell (12) where a cathode (7) is supplied supplied with H⁺ and AsO₂⁻ ions, where two competing reactions take place, producing respectively arsine and hydrogen gas, and an anode (3), where a reaction source of H⁺ ions takes place; and - A cationic membrane (11) separating the electrochemical cell into two compartments, anodic and cathodic; and - Means for supplying the cathode compartment with H⁺ and AsO₂⁻ ions, comprising a saturator (8) constituted by a reserve of As₂O₃, which is swept away by an acid solution (19). Device according to claim 10, characterized in that the saturator (8) is located between the electrochemical cell (12) and the storage tank (10) of the acid solution (19) supplying the cathode compartment. Device according to claim 10, characterized in that the saturator (8) is located inside the storage tank (10) of the acid solution supplying the cathode compartment, within said acid solution (19). Device according to one of Claims 10 to 12, characterized in that the cathode (7) is produced from a material which promotes the reaction for the formation of arsine to the detriment of the reaction for the formation of hydrogen. Device according to claim 13, characterized in that the cathode (7) consists of lead, or copper on which a deposit of bismuth, lead, thallium or even cadmium has been carried out. Device according to one of claims 10 to 14, characterized in that it comprises, downstream of the electrochemical cell, a membrane module (32), on which the arsine / hydrogen mixture produced at the cathode (7) undergoes a step separation, so as to obtain a higher arsine concentration at the outlet of the module than in said mixture. Device according to claim 15, characterized in that the membrane module is connected to means making it possible to carry out a vacuum on the permeate side of the membrane. Device according to claim 15, characterized in that the membrane module is connected to a gas source, making it possible to carry out a permeate-side sweep of the membrane using this gas, which has a low permeation of the permeate towards the inside the membrane, such as nitrogen or SF6 Device according to one of Claims 15 to 17, characterized in that it comprises, upstream of the membrane module, at least one device for drying the mixture produced at the cathode, and if necessary, at least one particle filter ( 31). Device according to one of claims 10 to 18, characterized in that the anode compartment is of the planar electrode type supplied with acid solution, where the electrolysis of water takes place. Device according to one of claims 10 to 18, characterized in that the anode compartment is of the gas diffusion electrode type, supplied with hydrogen, where the oxidation of hydrogen occurs.

Images