JP2023081436A - Hydrogen recovering method, and recycling method - Google Patents

Abstract

A method for stably recovering hydrogen over a long period of time from exhaust gas containing hydrogen chloride and hydrogen, such as purge exhaust gas. SOLUTION: A hydrogen recovery method for obtaining hydrogen gas from which hydrogen chloride has been removed by contacting an exhaust gas containing hydrogen chloride and hydrogen with an alkaline aqueous solution, wherein the exhaust gas containing hydrogen chloride and hydrogen contains silanes. and the concentration of hydrogen chloride in the exhaust gas is 10 to 70% by mass, and the concentration of silanes is 0.1 to 5% by mass. [Selection diagram] Fig. 1

Description

TECHNICAL FIELD The present invention relates to a method for recovering and reusing hydrogen. More particularly, the present invention relates to a method for recovering hydrogen from an exhaust gas containing hydrogen chloride and hydrogen discharged during the production of polysilicon and a method for reusing the hydrogen obtained by the recovery method.

Various methods for producing silicon used as a raw material for semiconductors or wafers for photovoltaic power generation have been known for some time, and some of them are already in industrial use. For example, one of them is a method called the Siemens method, in which polysilicon is obtained by supplying a mixed gas of hydrogen and trichlorosilane to an electrically heated filament and depositing silicon on the filament by chemical vapor deposition. be. Exhaust gas discharged from the polysilicon manufacturing process by the Siemens method contains, in addition to hydrogen and unreacted trichlorosilane, silane compounds such as monosilane, monochlorosilane, dichlorosilane, and tetrachlorosilane, which are reaction by-products, and Contains hydrogen chloride, etc.

In the method for producing polysilicon by the Siemens method, each gas component contained in the exhaust gas is separated and recycled to the production of polysilicon. For example, in Patent Document 1, a process of cooling by-product hydrogen chloride-containing exhaust gas discharged from a polysilicon manufacturing process to a predetermined temperature or less to condense and remove a part of silanes, and treating the exhaust gas after the process with activated carbon through a layer to adsorb and remove silanes in the exhaust gas, and the step of passing the exhaust gas that has undergone the adsorption and removal step through an activated carbon layer with a specific average pore radius to adsorb and remove hydrogen chloride. A method for producing polysilicon is disclosed in which the hydrogen of the polysilicon is purified and recycled to the polysilicon production process.

The activated carbon layer in which hydrogen chloride is adsorbed and retained in the step of adsorbing and removing hydrogen chloride is desorbed using hydrogen as a purge gas, and then the purge exhaust gas containing hydrogen and the desorbed hydrogen chloride is used. is brought into contact with acid water such as hydrochloric acid in a scrubbing tower to absorb hydrogen chloride in the purge exhaust gas into the acid water, and then hydrogen chloride is recovered from the acid water.

In Patent Document 1, the exhaust gas discharged after the purge exhaust gas is brought into contact with acid water in the scrubbing tower is a gas containing hydrogen as a main component. Since it contains impurities such as (CH ₄ ) and phosphine (PH ₃ ), as well as a trace amount of hydrogen chloride contained in the water entrained from the scrubber, the exhaust gas cannot be used as a source of hydrogen in other reactions. It is considered difficult and has been discarded after proper treatment.

On the other hand, as the amount of polysilicon produced by the Siemens method increases, the exhaust gas emitted from the polysilicon production process is increasing. Since the ability of the activated carbon layer to adsorb and remove hydrogen chloride is limited, multiple activated carbon layers are used in parallel to cope with the increase in exhaust gas. However, as a large number of activated carbon layers are used, the number of times of regeneration treatment of the activated carbon layer in which hydrogen chloride is adsorbed and retained, that is, desorption of hydrogen chloride from the activated carbon layer using hydrogen as a purge gas is also increasing. The amount of purge exhaust gas emitted during the desorption of the gas has also increased, and establishment of a method for effectively reusing this exhaust gas has been desired. Since the activated carbon from which hydrogen chloride has been desorbed is reused to remove hydrogen chloride from the exhaust gas discharged from the polysilicon manufacturing process, hydrogen, which is also a component gas in the exhaust gas, is used as the purge gas. .

When hydrogen chloride is used as a purge gas to desorb the adsorbed hydrogen chloride from the activated carbon layer in which hydrogen chloride is adsorbed and retained, the discharged purge exhaust gas containing hydrogen chloride and hydrogen mainly contains hydrogen. As a method for reusing hydrogen from such exhaust gas, the purge exhaust gas is brought into contact with a hydrogen chloride absorbent to obtain hydrogen gas from which hydrogen chloride has been removed, and the hydrogen recovery step recovers hydrogen. A method for reusing hydrogen in the purge exhaust gas has been proposed, including a hydrogen supply step of compressing the hydrogen gas produced and supplying it as a hydrogen source for another step (see Patent Document 2).

JP-A-2006-131491 International publication WO2011/040214

In the above Patent Document 2, the removal of hydrogen chloride from the purge exhaust gas containing hydrogen chloride and hydrogen is mainly performed using an aqueous sodium hydroxide solution as the hydrogen chloride absorbing liquid and using a gas-liquid contact device such as a scrubber. ing. When hydrogen chloride is removed from the purge exhaust gas containing hydrogen chloride and hydrogen by the method described in Patent Document 2, solid deposition occurs near the piping supplying the purge exhaust gas containing hydrogen chloride and hydrogen. The present inventors' studies have revealed that long-term treatment may be difficult due to clogging.

The present invention has been made in view of the above situation. That is, an object of the present invention is to provide a method for stably recovering hydrogen from exhaust gas containing hydrogen chloride and hydrogen, such as purge exhaust gas, over a long period of time.

The inventors of the present invention have made intensive studies in view of the above problems. When the purge exhaust gas containing hydrogen chloride and hydrogen, in which the concentration of silanes in the purge exhaust gas is high, is kept in contact with an alkaline aqueous solution such as sodium hydroxide, solids precipitate and form layers near the supply port of the exhaust gas. confirmed. When this solid was analyzed, it was confirmed to be a solid composed of Si, O, H, and C.

Based on these findings, a method for suppressing clogging of the supply port due to stacking of solids near the exhaust gas supply port during contact between the purge exhaust gas and the alkaline aqueous solution was investigated. There is an upper limit to the concentration of silanes in the exhaust gas containing The present inventors have found that the clogging of the supply port due to this can be suppressed, and have completed the present invention.

That is, the first present invention is a method for recovering hydrogen by contacting an exhaust gas containing hydrogen chloride and hydrogen with an alkaline aqueous solution to obtain hydrogen gas from which hydrogen chloride has been removed, wherein the exhaust gas containing hydrogen chloride and hydrogen is obtained. contains silanes, the concentration of hydrogen chloride in the exhaust gas is 10 to 70% by mass, and the concentration of silanes is 0.1 to 5% by mass.

The method for recovering hydrogen according to the present invention can preferably adopt the following aspects.
(1) The contact between the exhaust gas containing hydrogen chloride and hydrogen and the alkaline aqueous solution is controlled by an alkaline aqueous solution supply pipe for supplying the alkaline aqueous solution, an exhaust gas supply pipe for supplying the exhaust gas containing hydrogen chloride and hydrogen, and an exhaust gas containing hydrogen chloride and hydrogen. A gas-liquid contactor having a discharge pipe for discharging hydrogen gas from which hydrogen chloride has been removed after contact with an alkaline aqueous solution, and the exhaust gas supply pipe supplies exhaust gas containing hydrogen chloride and hydrogen. an exhaust gas supply port, and at least one seal gas supply port arranged around the periphery of the exhaust gas supply port for supplying a seal gas inert to any of alkali, hydrogen chloride, and hydrogen. and supplying an exhaust gas containing hydrogen chloride and hydrogen from the exhaust gas supply port, and supplying the seal gas from the seal gas supply port.
(2) The sealing gas in (1) above is hydrogen gas, and the linear velocity of the hydrogen gas supplied from the sealing gas supply port is 10 to 50 Nm/s.
(3) The exhaust gas containing hydrogen chloride and hydrogen contains the purge exhaust gas containing hydrogen chloride and hydrogen obtained in the following steps.
(i) a hydrogen chloride adsorption step of adsorbing hydrogen chloride by passing exhaust gas discharged from the step of reacting hydrogen and trichlorosilane to produce polysilicon through an activated carbon layer; and (ii) hydrogen chloride is adsorbed and retained. hydrogen chloride desorption step of desorbing the adsorbed hydrogen chloride by passing hydrogen gas as a purge gas through the activated carbon layer; trichlorosilane is condensed and separated from the reaction product gas containing trichlorosilane, and the exhaust gas after trichlorosilane is condensed and separated is included.
(5) The exhaust gas containing hydrogen chloride and hydrogen condenses and separates the trichlorosilane from the reaction product gas containing trichlorosilane, which is produced by reacting metallic silicon, tetrachlorosilane, and hydrogen to form trichlorosilane, and separating the trichlorosilane. including exhaust gas after condensing and separating.
(6) including a dehydration step of dehydrating the hydrogen gas from which hydrogen chloride has been removed, obtained by any of the recovery methods described above;

A second aspect of the present invention is a method for reusing hydrogen by compressing the hydrogen obtained by any of the recovery methods described above and using the compressed hydrogen as a hydrogen source for another step.

Furthermore, the third aspect of the present invention includes a storage section for storing an alkaline aqueous solution, an exhaust gas supply pipe for supplying an exhaust gas containing hydrogen chloride and hydrogen, and hydrogen chloride after the exhaust gas containing hydrogen chloride and hydrogen is brought into contact with the alkaline aqueous solution. A gas-liquid contactor having a discharge pipe for discharging the removed hydrogen gas, wherein the exhaust gas supply pipe is arranged at an exhaust gas supply port for supplying the exhaust gas and on the outer periphery of the exhaust gas supply port, and the alkali, hydrogen chloride and The gas-liquid contactor is characterized by having at least one seal gas supply port for supplying a seal gas inert to any hydrogen.

According to the recovery method of the present invention, when the exhaust gas containing hydrogen chloride and hydrogen discharged from the polysilicon manufacturing process is brought into contact with the alkaline aqueous solution to remove hydrogen chloride from the exhaust gas, the vicinity of the supply port of the exhaust gas is clogged. can be suppressed, and hydrogen chloride can be stably removed over a long period of time. Although the details of the reason why the method of the present invention can suppress clogging are unknown, the present inventors speculate as follows.

That is, as described above, the exhaust gas containing hydrogen chloride discharged from the polysilicon manufacturing process contains silanes, and when the silanes come into contact with the alkaline aqueous solution, the Si—Cl bond of the silanes is broken. , hydrolysis with water in an alkaline aqueous solution to form Si—O bonds and generate hydrogen chloride. The generated hydrogen chloride is neutralized with the alkali in the alkali aqueous solution to form an alkali salt. The Si—H bond of silanes is oxidized by oxygen in the contact atmosphere or dissolved oxygen in the alkaline aqueous solution to form Si—O bonds and generate hydrogen. Under the contact _{atmosphere temperature} , _the hydrolysis reaction is much faster than the oxidation reaction _. (x, y, z, w are integers) is formed (this silica is assumed to be Si ₆ H ₆ O ₉ when the silane is trichlorosilane, for example). . The formed silica reacts with dissolved oxygen in the aqueous solution in an alkaline aqueous solution bath to convert Si—H bonds into Si—O bonds.

In addition, when the atmosphere of the composition is a basic atmosphere, the silica formed near the gas supply port rapidly polymerizes into a gel compound (-(Si _x H _y O _z C _w ) _n - water It is presumed that a hydrated substance (n is an integer) is formed (hereinafter referred to as gelation) and laminated in the vicinity of the gas supply port, blocking the supply port if contact is continued. However, when the ambient atmosphere is an acidic atmosphere, the initial polymerization rate of silica is slow, so silica can exist in a low-molecular and stable state. Therefore, when the concentration of silanes in the exhaust gas containing hydrogen chloride and silanes discharged from the polysilicon manufacturing process is a predetermined concentration (5% by mass) or less, the concentration of hydrogen chloride in the gas is a predetermined value. (10 to 70% by mass), the formation of silica in the vicinity of the gas supply port is carried out in an acidic atmosphere of hydrochloric acid, so that it does not polymerize, and the formed product is blown away by the gas flow, and as a result, the gas It is presumed that clogging in the vicinity of the supply port can be suppressed.

Thus, according to the present invention, it is possible to recover high-purity hydrogen from the exhaust gas containing hydrogen chloride and hydrogen discharged from the polysilicon manufacturing process and reuse it as a hydrogen source in other manufacturing processes. This can contribute to a significant reduction in disposal costs as well as a reduction in manufacturing costs.

1 is a schematic diagram showing an example of the configuration of a gas-liquid contactor of the present invention; FIG. 1 is a cross-sectional view showing an example of an exhaust gas supply pipe in the gas-liquid contactor of the present invention; FIG.

In the method for recovering hydrogen of the present invention, an exhaust gas containing hydrogen chloride and hydrogen is brought into contact with an alkaline aqueous solution to obtain hydrogen gas from which hydrogen chloride has been removed. It is characterized by containing silanes and hydrogen chloride. As described above, by using a gas with a relatively high concentration of hydrogen chloride as the exhaust gas, it is possible to prevent the vicinity of the exhaust gas supply port from being in a strongly basic atmosphere immediately after the exhaust gas containing hydrogen chloride and hydrogen is brought into contact with the alkaline aqueous solution. It is presumed that the clogging of the supply port can be suppressed by suppressing the gelation of silica in the vicinity of the supply port.

In this specification, unless otherwise specified, the notation "A to B" for numerical values A and B means "A or more and B or less". If a unit is attached only to the numerical value B in such notation, the unit is applied to the numerical value A as well. Hereinafter, the method for recovering hydrogen according to the present invention will be described in detail.

<Exhaust gas containing hydrogen chloride and hydrogen>
In the hydrogen recovery method of the present invention, the exhaust gas containing hydrogen chloride and hydrogen contains silanes, and the hydrogen chloride concentration in the exhaust gas is 10 to 70% by mass and the silane concentration is 0.1 to 5% by mass. It is characterized by using a certain exhaust gas.

If the content of hydrogen chloride contained in the exhaust gas is too high, increasing the size of the device for removing hydrogen chloride will increase the load on the device, and if it is too low, the silica gelation suppression effect will be reduced. Therefore, the range of 20 to 70% by mass is preferable, the range of 30 to 60% by mass is more preferable, and the range of 30 to 40% by mass is particularly preferable.

Specifically, the silanes contained in the exhaust gas include SiH ₄ , SiH ₃ Cl, SiH ₂ Cl ₂ , SiHCl ₃ , SiH ₂ Cl(CH ₃ ), SiHCl ₂ (CH ₃ ), SiHCl(CH ₃ ) _{2 ,} SiCl ₄ , and the like. These silanes may be contained singly, or a plurality of silanes may be mixed. When these silanes come into contact with an alkaline aqueous solution, they are hydrolyzed to form silica, and the resulting silica becomes a factor of gelation. A range of % by weight is preferred, a range of 1 to 4% by weight is more preferred, and a range of 2 to 4% by weight is particularly preferred.

Further, from the viewpoint of efficiently treating the exhaust gas, the molar ratio of hydrogen chloride and silanes in the exhaust gas used in the recovery method of the present invention is preferably in the range of hydrogen chloride / silanes = 1 to 100. The range of ∼80 is more preferable, and the range of 20 to 70 is particularly preferable.

Such hydrogen containing hydrogen chloride and silane hydrides include:
1. The purge exhaust gas (that is, the exhaust gas discharged from the step of reacting hydrogen and trichlorosilane to produce polysilicon) is passed through an activated carbon layer to adsorb hydrogen chloride, and the hydrogen chloride is adsorbed and retained. Exhaust gas obtained through hydrogen chloride desorption process to desorb adsorbed hydrogen chloride by passing hydrogen gas as purge gas through activated carbon layer)
2. 2. Exhaust gas after condensing and separating tetrachlorosilane from exhaust gas containing tetrachlorosilane which is a by-product of polysilicon production. 4. Exhaust gas after producing trichlorosilane by reacting metal silicon with hydrogen chloride and condensing and separating trichlorosilane. Exhaust gas after producing trichlorosilane by reacting metal silicon, tetrachlorosilane, and hydrogen, and condensing and separating trichlorosilane. The cooling temperature of the gas when condensing and separating tetrachlorosilane and trichlorosilane from the exhaust gas may be lower than the temperature at which tetrachlorosilane and trichlorosilane condense, and is appropriately determined in consideration of the cooling capacity of the cooling device. Generally, it is set at -10°C or lower, particularly -30°C or lower. The same applies to the pressure during condensation separation, which is usually set to 300 kPaG or higher, particularly 500 kPaG or higher. After tetrachlorosilane and trichlorosilane are condensed and separated in this way, the exhaust gas usually contains 95 to 99 mol % hydrogen, 100 to 6000 mol ppm hydrogen chloride, and 5000 to 50000 mol ppm silanes. ing. These exhaust gases may be used alone as the exhaust gas of the present invention, or may be mixed and used as the exhaust gas of the present invention. In addition, if the content of hydrogen chloride and silanes in these exhaust gases is not within the above range, for example, by mixing hydrogen chloride, silanes, or hydrogen into these exhaust gases, the content of hydrogen chloride and silanes can be reduced. may be appropriately prepared and used so that is within the above range. The contents of hydrogen, hydrogen chloride and silanes in the exhaust gas can be determined by analysis using gas chromatography or the like.

<Recovery of hydrogen>
In the recovery method of the present invention, the exhaust gas containing hydrogen chloride and hydrogen is brought into contact with an alkaline aqueous solution. Specific examples of alkaline aqueous solutions include alkaline aqueous solutions in which alkalis such as sodium hydroxide, potassium hydroxide and calcium hydroxide are dissolved.

The method for contacting the exhaust gas containing hydrogen chloride and hydrogen with the alkaline aqueous solution is not particularly limited as long as the exhaust gas and the alkaline aqueous solution are sufficiently contacted and the hydrogen chloride in the exhaust gas can be removed. A gas-liquid contact method can be employed. As the gas-liquid contact method, specifically, a method of forcibly forming a gas-liquid mixed flow of the exhaust gas and an alkaline aqueous solution by an ejector or the like; a method of spraying an alkaline aqueous solution on the exhaust gas flow by a scrubber or the like; and a method of directly blowing the exhaust gas into the liquid phase. Among the above gas-liquid contact methods, a method such as a scrubber in which an alkaline aqueous solution is sprayed on the exhaust gas stream is preferable because the exhaust gas that has come into contact with the alkaline aqueous solution can be easily discharged and the apparatus is simple. This gas-liquid contacting apparatus can be used alone, can be used by connecting gas-liquid contacting methods in series, or can be used in combination with a plurality of gas-liquid contacting methods.

The temperature at which the flue gas containing hydrogen chloride and hydrogen is brought into contact with the alkaline aqueous solution is not particularly limited, and may be appropriately determined in consideration of the ability of the gas-liquid contactor to be used. However, if the temperature is too high, the alkali and the like from the alkaline aqueous solution are likely to diffuse and tend to be entrained in the exhaust gas from which hydrogen chloride has been removed. Therefore, the temperature at which the exhaust gas containing hydrogen chloride and hydrogen is brought into contact with the alkaline aqueous solution is preferably in the range of 10 to 60°C.

Further, when the exhaust gas containing hydrogen chloride and hydrogen is brought into contact with the alkaline aqueous solution in the gas-liquid contact method, the exhaust gas supply pipe for supplying the exhaust gas containing hydrogen chloride and hydrogen supplies the exhaust gas containing hydrogen chloride and hydrogen. and at least one seal gas supply port arranged around the periphery of the exhaust gas supply port for supplying a seal gas inert to any of alkali, hydrogen chloride, and hydrogen. It is preferable to use a supply pipe, supply exhaust gas containing hydrogen chloride and hydrogen from the exhaust gas supply port, and supply the seal gas from the seal gas supply port. The flue gas supplied from the flue gas supply pipe produces silica when it comes into contact with the alkaline aqueous solution, but it can be efficiently dispersed in the gas-liquid contactor by the seal gas supplied together, and silica gels. It is possible to improve the effect of suppressing

At least one sealing gas supply port is required along the outer periphery of the exhaust gas supply port, but it is also possible to have a multi-pipe structure with two or more sealing gas supply ports.

The seal gas supplied from the seal gas supply port is not particularly limited as long as it is inert in the contact atmosphere between the exhaust gas containing hydrogen chloride and hydrogen and the alkaline aqueous solution. Specific examples of the seal gas include hydrogen gas, nitrogen gas, argon gas, etc. From the viewpoint of reusing recovered hydrogen gas, which will be described later, it is preferable to use hydrogen gas as the seal gas. The supply rate of the seal gas should be sufficient to efficiently disperse the generated silica. For example, a linear velocity of 10 to 50 Nm/s for the hydrogen gas supplied from the seal gas supply port is sufficient. The linear velocity of the seal gas supplied from this seal gas supply port is sufficient if the linear velocity of the seal gas discharged from each seal gas supply port is within the above range when the seal gas supply port is a multi-pipe. . Also, the linear velocity of the seal gas discharged from the outer supply port may be adjusted to be higher than the linear velocity of the seal gas discharged from the inner supply port.

<Gas liquid contact device>
The gas-liquid contactor for carrying out the hydrogen recovery method of the present invention includes an alkaline aqueous solution supply pipe for supplying an alkaline aqueous solution, an exhaust gas supply pipe for supplying an exhaust gas containing hydrogen chloride and hydrogen, and hydrogen chloride and hydrogen. A gas-liquid contactor having a discharge pipe for discharging hydrogen gas from which hydrogen chloride has been removed after exhaust gas and an alkaline aqueous solution are contacted, wherein the exhaust gas supply pipe comprises an exhaust gas supply port for supplying the exhaust gas and the exhaust gas supply. It is preferable to have at least one seal gas supply port arranged on the periphery of the port and supplying a seal gas inert to all of alkali, hydrogen chloride and hydrogen. FIG. 1 is a schematic diagram showing an example of the configuration of the gas-liquid contactor of the present invention. The gas-liquid contactor 1 includes a gas-liquid contact tower 10, an exhaust gas supply pipe 20 for supplying the exhaust gas to the gas-liquid contact tower 10, an alkaline aqueous solution supply pipe 40 for supplying an alkaline aqueous solution, and a hydrogen gas discharge for discharging hydrogen gas. It consists of a tube 50 . In FIG. 1, the alkaline aqueous solution and the exhaust gas are supplied from the tower top. As described above, the exhaust gas supply pipe 20 includes an exhaust gas supply port 21 for supplying the exhaust gas into the gas-liquid contact tower 10 and a It has a seal gas supply port 22 which is arranged on the outer periphery and supplies a seal gas inert to all of alkali, hydrogen chloride and hydrogen. As shown in FIG. 2B, the exhaust gas supply pipe 20 may have a multi-pipe structure having a first seal gas supply port 23 and a second seal gas supply port 24 on the outer periphery of the exhaust gas supply port 21 . In the case of a multi-tube structure, it may be appropriately set to double, triple, or the like.

In the gas-liquid contactor of the present invention, since the alkaline aqueous solution supplied to the gas-liquid contact tower 10 is accumulated in the lower part of the tower, a pump 44 and an alkaline aqueous solution discharge pipe 43 for discharging the alkaline aqueous solution may be provided. Further, the alkaline aqueous solution supply pipe 40 may be configured to circulate and supply the discharged alkaline aqueous solution to the gas-liquid contact tower 10, and an alkaline aqueous solution supply pipe 42 for replenishing the discharged alkaline aqueous solution may be provided. In addition, a filler 30 may be provided inside the gas-liquid contact tower 10 from the viewpoint of promoting the reaction between the exhaust gas and the alkaline aqueous solution. Specific examples of fillers include irregular fillers such as Rachschilling and ordered fillers such as plastic nets.

<Dehydration process>
Hydrogen gas from which hydrogen chloride has been removed can be obtained by the recovery method of the present invention. The obtained hydrogen gas is sufficiently high-purity hydrogen gas to be reused as a hydrogen source in other processes. It may contain an extremely small amount of components (alkali, etc.). If these components are a problem in other manufacturing processes, hydrogen gas is used for the purpose of removing these components derived from the aqueous alkaline solution before compressing the hydrogen gas discharged after contact with the aqueous alkaline solution. It is preferable to provide a dehydration step for dehydrating the

As a means for removing moisture in the hydrogen gas, it is possible to employ a known removal means. Specifically, means for removing moisture by condensing it by cooling hydrogen gas, means for removing moisture by passing hydrogen gas through a layer filled with a desiccant such as molecular sieves, and passing it through a mist separator. is mentioned. In addition, these moisture removing means can be used alone, similar moisture removing means can be connected in series, and a plurality of moisture removing means can be used in combination. By providing this dehydration step, the water content in the hydrogen gas can be reduced to about 100 to 500 ppm.

<Step of separating residual silanes>
In addition, a very small amount of silanes may be present in the hydrogen gas from which the hydrogen chloride has been removed. Among the silanes contained, most of the silanes are separated from the hydrogen gas in the water in the hydrogen chloride absorbing liquid or in the dehydration step. However, some (particularly when the silanes contain SiH ₄ (monosilane)) did not react with water and were entrained in the hydrogen gas, and were vented from the dissolved oxygen in the alkaline aqueous solution during the subsequent steps. By-products such as silica are produced by reacting with oxygen, and the produced by-products are scattered, which may cause clogging of compressors, pipes, and the like.

Therefore, the hydrogen gas from which the hydrogen chloride has been removed is brought into contact with a silane scavenger, and then the silane scavenger entrained in the hydrogen gas is separated from the hydrogen gas to remove silanes or by-products derived from silanes. Separating and removing silanes from hydrogen by dissolving or suspending them in a silane scavenger is a preferred operation. In the present invention, the silane scavenger means the silanes such as monosilane, monochlorosilane, dichlorosilane, tetrachlorosilane, and trichlorosilane, decomposition products thereof, and by-products derived from these silanes dissolved or suspended. It enables separation from hydrogen gas.

The silane scavenger is inert to hydrogen and can dissolve or suspend silanes, decomposition products thereof, and by-products derived therefrom. It may be determined as appropriate in consideration of the type and material of the compressor in the latter stage. Examples include organic solvents and oils. Specifically, organic solvents such as hexane, heptane, alcohol, and acetone are preferably used as the organic solvent. Examples of the oil include lubricating oils such as paraffin oil, naphthene oil, halogenated hydrocarbon oil, and silicone oil used in the oil-cooled compressor. Specifically, there are "KB-310-46" (manufactured by Kobe Steel, Ltd.) and "Daphne Alpha Screw 32" (manufactured by Idemitsu Kosan Co., Ltd.).
This silane scavenger can be used alone or as a mixture of multiple organic solvents and oils.

Specifically, the contact method includes a method of spraying the silane scavenger with hydrogen gas and contacting it; a method of supplying hydrogen gas into the silane scavenger and contacting it; and the like. As mentioned above, it is also possible to bring hydrogen gas and lubricating oil into contact in an oil-cooled compressor. When using a compressor that does not use lubricating oil, it is necessary to remove the silane scavenger in advance before supplying it to the compressor.

Since the silane scavenger is usually entrained in the hydrogen gas in contact with the silane scavenger, by separating the entrained silane scavenger from the hydrogen gas, it can be supplied as a hydrogen source in other manufacturing processes. As a method for separating the entrained silane scavenger, it is possible to adopt a known separation method. Specifically, separation means such as a demister, an oil mist filter, activated carbon, etc. are employed.

<Use as a hydrogen source for other processes>
By removing hydrogen chloride from the exhaust gas, the hydrogen chloride in the exhaust gas can be almost completely removed. As a result, the exhaust gas becomes sufficiently high-purity hydrogen gas to be reused as a hydrogen source for other processes described later. However, since the pressure of the exhaust gas becomes almost the same as the atmospheric pressure by contacting with the alkaline aqueous solution, when supplying the obtained hydrogen gas from which hydrogen chloride has been removed as a hydrogen source for other processes, hydrogen should not be used. It must be compressed by means of compression.

The means for compressing hydrogen is not particularly limited, and known compression means can be employed. Specific examples of such compression means include centrifugal compressors, turbo compressors such as axial compressors, reciprocating compressors, diaphragm compressors, screw compressors, and volumetric compressors such as rotary compressors. be done. In addition, it is possible to suitably use either an oil-cooled type compressor that operates while injecting lubricating oil into the compression section of the compressor, or an oil-free type compressor that does not use lubricating oil. Among these compression means, a screw compressor is particularly suitable in that hydrogen gas can be compressed efficiently. Specific examples of lubricating oils used in oil-cooled compressors include paraffinic oils, naphthenic oils, halogenated hydrocarbon oils, and silicone oils.

When an oil-cooled compression means is employed, after the hydrogen gas is compressed, the lubricating oil is separated from the hydrogen gas and supplied as a hydrogen source in other manufacturing processes. The method for separating the lubricating oil from the compressed hydrogen gas is not particularly limited as long as it can separate the lubricating oil, and known separating means can be employed. Specifically, separation means such as a demister, an oil mist filter, and activated carbon are employed as such separation means.

The compression pressure of the hydrogen gas is not particularly limited as long as it can be used as a hydrogen source in other processes, and may be appropriately determined in consideration of the hydrogen supply capacity to the manufacturing equipment in other processes. Generally, it is sufficient to compress the hydrogen gas until the pressure of the compressed hydrogen gas reaches 200 to 600 kPaG. A series of compression means compress the hydrogen gas so that it can be supplied as a source of hydrogen in other manufacturing processes.

The hydrogen gas recovered from the exhaust gas containing hydrogen chloride and hydrogen by the method of the present invention is sufficiently high-purity hydrogen gas and can be reused as a hydrogen source for other processes. For example, it is reacted (hydrolysis and oxidation reaction) with waste liquid silane (a silane mixture consisting of various silanes) on an oxyhydrogen flame. It can be used as a hydrogen source in other processes, such as a hydrogen source when producing hydrogen.

EXAMPLES The present invention will be further described below with reference to Examples, but the present invention is not limited to these Examples.

<Exhaust gas containing hydrogen chloride and hydrogen>
Exhaust gas containing hydrogen chloride and hydrogen used in the following examples and comparative examples was prepared by the following method.

Exhaust Gas A: Purge Exhaust Gas Polysilicon was deposited at a deposition temperature of 1100° C. using a well-known Siemens method bell jar and flowing a mixed gas having a molar ratio of 10 of hydrogen and trichlorosilane. The gas discharged from the bell jar was condensed at -50°C under a pressure of 700 kPaG to separate trichlorosilane. The uncondensed gas after separation is passed through an adsorption tower (filled tower filled with activated carbon having an average particle diameter of 3 to 5 mm and a BET specific surface area of 1100 m ² /g and maintained at 10° C.) at a space velocity (SV) of 10 h ⁻¹ . , components other than hydrogen in the gas were removed by adsorption to obtain a recovered hydrogen gas A. As a result of analyzing the average purity of the obtained recovered hydrogen gas A by gas chromatography (thermal conductivity detector (TCD), hydrogen is 99.99 mol%, hydrogen chloride and silanes are below the detection limit (10 ppm mol or less Next, the packed column was maintained at 200° C., hydrogen gas was passed through at a space velocity (SV) of 1 h ⁻¹ to desorb the adsorbed components, and the discharged gas was collected in a drum. , to obtain an exhaust gas A. As a result of analyzing the purity of the exhaust gas A similarly by gas chromatography, the concentrations of hydrogen, hydrogen chloride, dichlorosilane, trichlorosilane, and tetrachlorosilane were 31.5, 65.0, and 0, respectively. .3, 3.1 and 0.13 mass %.

Exhaust gas B: Exhaust gas after producing trichlorosilane and condensing and separating trichlorosilane A fluidized bed of metallic silicon is formed in a known trichlorosilane synthesis furnace, and the temperature in the fluidized bed is 300 ° C., and the gas is dispersed in the lower part of the fluidized bed. Hydrogen chloride gas was flowed through the plate to produce trichlorosilane. The gas discharged from the synthesis furnace was condensed at −30° C. under a pressure of 700 kPaG to separate trichlorosilane.
Alternatively, a fluidized bed of metallic silicon is formed in a known tetrachlorosilane reduction furnace, and at a temperature of 500° C. in the fluidized bed, a mixed gas of tetrachlorosilane and hydrogen is caused to flow from a gas distribution plate below the fluidized bed to produce tetrachlorosilane. Preparation of trichlorosilane by reduction was carried out. The gas discharged from the reduction furnace was condensed at −20° C. under a pressure of 700 kPaG to separate trichlorosilane.

The uncondensed gas after condensing and separating trichlorosilane was collected in a drum and mixed in the drum to obtain an exhaust gas B. As a result of analyzing the purity of the exhaust gas B by gas chromatography in the same manner as the exhaust gas A, the concentrations of hydrogen, hydrogen chloride, dichlorosilane, trichlorosilane, and tetrachlorosilane were 70.0, 0.3, 3.0, and 22, respectively. .0 and 4.7% by mass.

<Gas liquid contact device>
In the following examples and comparative examples, the gas-liquid contactor shown in FIG. 1 was used. In the gas-liquid contact tower, a 10% by mass sodium hydroxide aqueous solution is sprayed downward from the top of the tower, descends in the tower and accumulates in a liquid tank at the bottom of the tower, and the liquid in the liquid tank is circulated to the top of the tower with a pump. In this method, a packing material (Lachschilling) is provided in the middle stage of the column. The gas from the gas drum is discharged downward from the flue gas supply pipe provided inside the sodium hydroxide supply port at the top of the contact tower through a gas supply pipe of a double-pipe structure (the structure of (a) in FIG. 2). , the gas from the gas drum was released from the inner tube, and hydrogen gas for sealing was released from the outer tube. The inner diameter of the sodium hydroxide supply port was 200 mm, the inner diameter of the outer tube of the double tube was 125 mm, the inner diameter of the inner tube was 100 mm, and the clearance between the inner diameter of the outer tube and the outer diameter of the inner tube was 10 mm. Hydrogen gas was used as the seal gas.

<Example 1>
The exhaust gas A is used as the exhaust gas containing hydrogen chloride and hydrogen, supplied to the gas-liquid contactor at a flow rate of 400 Nm ³ /h and a gas linear velocity of 15 Nm/s, and hydrogen gas is jetted as a sealing gas at a linear velocity of 20 Nm/s. bottom. The gas linear velocity in the tower was 3 Nm/s, and the gas-liquid contact time was about 1 second. The circulation amount of the aqueous sodium hydroxide solution was 20 m ³ /h. The discharged gas was dehydrated using a mist separator having a mist separation efficiency of removing 100% of mist with a diameter of 100 μm or more, and then compressed through an oil-cooled screw compressor to obtain hydrogen gas.

Even if the operation was continued for 3 months under the above conditions, no clogging of the exhaust gas supply port occurred. After the end of operation, an open inspection of the tower top of the gas-liquid contactor revealed that a thin layer of silica had formed on the surface of the inner tube near the exhaust gas supply port, but the layer thickness was such that it could be operated throughout the year. . The average purity of the recovered hydrogen gas was 99.99 mol % for hydrogen, and below the detection limit (10 ppm mol or below) for hydrogen chloride and silanes.

<Comparative Example 1>
As the exhaust gas containing hydrogen chloride and hydrogen, except that the exhaust gas B was used, hydrogen gas was recovered in the same manner as in Example 1. After 10 days of operation, the exhaust gas supply port was clogged. The supply of the exhaust gas B to the gas-liquid contactor was stopped, and the exhaust gas B was sent to the detoxification equipment. After completion of the operation, an open inspection of the top of the gas-liquid contactor revealed that a silica laminate had formed around the supply port of the flue gas supply port.

<Example 2>
The exhaust gas B is used as the exhaust gas containing hydrogen chloride and hydrogen, and the hydrogen gas and the hydrogen chloride gas are mixed at a flow rate ratio of exhaust gas B: hydrogen: hydrogen chloride = 1: 6: 0.2 to produce hydrogen. , hydrogen chloride, dichlorosilane, trichlorosilane, and tetrachlorosilane with concentrations of 63.2, 33.0, 0.4, 2.8, and 0.6% by mass were prepared to clean the exhaust gas. When hydrogen gas was recovered in the same manner as in Example 1, no clogging of the flue gas supply port occurred even after the operation was continued for 3 months. After the end of the operation, an open inspection of the top of the gas-liquid contactor revealed that silica layers thicker than those in Example 1 were deposited on the surface of the outer and inner tubes near the supply port of the flue gas supply port. Met. The average purity of the recovered hydrogen gas was 99.99 mol % for hydrogen, and below the detection limit (10 ppm mol or below) for hydrogen chloride and silanes.

<Comparative Example 2>
The exhaust gas B is used as the exhaust gas containing hydrogen chloride and hydrogen, and the hydrogen gas and the hydrogen chloride gas are mixed at a flow rate ratio of exhaust gas B: hydrogen: hydrogen chloride = 1: 9: 0.04 to produce hydrogen. , hydrogen chloride, dichlorosilane, trichlorosilane, and tetrachlorosilane with concentrations of 89.6, 6.6, 0.4, 2.8, and 0.6% by mass were prepared to clean the exhaust gas. , When hydrogen gas was recovered in the same manner as in Example 1, after 35 days of operation, the exhaust gas supply port was clogged. sent to the abatement facility. After completion of the operation, an open inspection of the top of the gas-liquid contactor revealed that a silica laminate had formed around the supply port of the flue gas supply port.

<Comparative Example 3>
The exhaust gas B is used as the exhaust gas containing hydrogen chloride and hydrogen, and the hydrogen gas and the hydrogen chloride gas are mixed at a flow rate ratio of exhaust gas B: hydrogen: hydrogen chloride = 1: 1.5: 0.1. , hydrogen, hydrogen chloride, dichlorosilane, trichlorosilane, and tetrachlorosilane having concentrations of 52.6, 38.6, 0.9, 6.6, and 1.4% by mass were prepared to clean the exhaust gas. Except for this, when hydrogen gas was recovered in the same manner as in Example 1, the exhaust gas supply port was clogged after 57 days of operation. B was sent to the abatement facility. After completion of the operation, an open inspection of the top of the gas-liquid contactor revealed that a silica laminate had formed around the supply port of the flue gas supply port.

<Example 3>
The structure of the exhaust gas supply pipe of the gas-liquid contactor is a triple pipe structure ((b) structure in FIG. 2, the inner diameter of the outer pipe is 150 mm, the inner diameter of the middle pipe is 125 mm, the inner diameter of the inner pipe The clearance between the inner diameter and the outer diameter of the middle tube is 10 mm, and the clearance between the inner diameter of the middle tube and the outer diameter of the inner tube is 10 mm). Hydrogen gas was recovered in the same manner as in the example, except that hydrogen gas was ejected as a seal gas at a linear velocity of 20 Nm/s. As a result of open inspection of the tower top of the gas-liquid contactor after the end of the operation, silica thinner than that in Example 1 was laminated near the supply port of the exhaust gas supply pipe. The average purity of the recovered hydrogen gas was 99.99 mol % for hydrogen, and below the detection limit (10 ppm mol or below) for hydrogen chloride and silanes.

REFERENCE SIGNS LIST 1 gas-liquid contactor 10 gas-liquid contact tower 20 exhaust gas supply pipe 21 exhaust gas supply port 22 seal gas supply port 23 first seal gas supply port 24 second seal gas supply port 30 filler 40 alkaline aqueous solution supply pipe 41 alkaline aqueous solution Supply pipe 42 Alkaline aqueous solution supply pipe 43 Alkaline aqueous solution discharge pipe 44 Pump 50 Hydrogen gas discharge pipe

Claims (9)

A method for recovering hydrogen by contacting an exhaust gas containing hydrogen chloride and hydrogen with an alkaline aqueous solution to obtain hydrogen gas from which hydrogen chloride has been removed,
The exhaust gas containing hydrogen chloride and hydrogen contains silanes, the concentration of hydrogen chloride in the exhaust gas is 10 to 70% by mass, and the concentration of silanes is 0.1 to 5% by mass. A method for recovering hydrogen. The contact between the exhaust gas containing hydrogen chloride and hydrogen and the alkaline aqueous solution,
an alkaline aqueous solution supply pipe for supplying an alkaline aqueous solution;
an exhaust gas supply pipe for supplying an exhaust gas containing hydrogen chloride and hydrogen;
and a gas-liquid contactor having a discharge pipe for discharging hydrogen gas from which hydrogen chloride has been removed after contact between the exhaust gas containing hydrogen chloride and hydrogen and the alkaline aqueous solution,
an exhaust gas supply port through which the exhaust gas supply pipe supplies an exhaust gas that supplies an exhaust gas containing hydrogen chloride and hydrogen;
an exhaust gas supply pipe having at least one seal gas supply port disposed around the periphery of the exhaust gas supply port and supplying a seal gas inert to any of alkali, hydrogen chloride, and hydrogen;
2. The method for recovering hydrogen according to claim 1, wherein the exhaust gas containing hydrogen chloride and hydrogen is supplied from the exhaust gas supply port, and the seal gas is supplied from the seal gas supply port. 3. The method for recovering hydrogen according to claim 2, wherein the sealing gas is hydrogen gas, and the hydrogen gas supplied from the sealing gas supply port has a linear velocity of 10 to 50 Nm/s. The method for recovering hydrogen according to any one of claims 1 to 3, wherein the exhaust gas containing hydrogen chloride and hydrogen includes a purge exhaust gas containing hydrogen chloride and hydrogen obtained in the following steps.
(1) A hydrogen chloride adsorption step in which hydrogen chloride is adsorbed by passing exhaust gas discharged from the step of reacting hydrogen and trichlorosilane to produce polysilicon through an activated carbon layer, and (2) hydrogen chloride is adsorbed and retained. Hydrogen chloride desorption step to desorb the adsorbed hydrogen chloride by passing hydrogen gas as a purge gas through the activated carbon layer After the exhaust gas containing hydrogen chloride and hydrogen condenses and separates the trichlorosilane from the reaction product gas containing trichlorosilane in which hydrogen chloride is reacted with metallic silicon to produce trichlorosilane, and trichlorosilane is condensed and separated. The method for recovering hydrogen according to any one of claims 1 to 4, wherein the exhaust gas of The exhaust gas containing hydrogen chloride and hydrogen condenses and separates the trichlorosilane from the reaction product gas containing trichlorosilane, which is produced by reacting metal silicon, tetrachlorosilane, and hydrogen to produce trichlorosilane, and the trichlorosilane is condensed and separated. 6. The method for recovering hydrogen according to any one of claims 1 to 5, wherein the exhaust gas after being treated is included. A method for recovering hydrogen, comprising a dehydration step of dehydrating the hydrogen gas from which hydrogen chloride has been removed, obtained by the recovery method according to any one of claims 1 to 6. A method for reusing hydrogen by compressing the hydrogen obtained by the recovery method according to any one of claims 1 to 7 and using it as a hydrogen source for other steps. an alkaline aqueous solution supply pipe for supplying an alkaline aqueous solution;
A gas-liquid contactor having an exhaust gas supply pipe for supplying exhaust gas containing hydrogen chloride and hydrogen, and a discharge pipe for discharging hydrogen gas from which hydrogen chloride has been removed after contact between the exhaust gas containing hydrogen chloride and hydrogen and the alkaline aqueous solution. There is
The exhaust gas supply pipe comprises an exhaust gas supply port for supplying the exhaust gas and a seal gas supply port disposed around the periphery of the exhaust gas supply port for supplying a seal gas inert to any of alkali, hydrogen chloride and hydrogen. A gas-liquid contactor comprising at least one.

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