JP6698762B2 - Hydrogen gas recovery system and method for separating and recovering hydrogen gas - Google Patents

Description

The present invention relates to a hydrogen gas recovery system and a method for separating and recovering hydrogen gas, and more specifically,
TECHNICAL FIELD The present invention relates to a technique that separates and recovers hydrogen from a reaction exhaust gas of a polycrystalline silicon manufacturing apparatus using trichlorosilane as a raw material, and makes it possible to circulate and use highly purified hydrogen gas.

In the manufacturing process of polycrystalline silicon using trichlorosilane (HSiCl ₃ ) as a raw material, the reaction represented by the following formula mainly progresses, and polycrystalline silicon is generated according to formula 1.
HSiCl ₃ + H ₂ → Si + 3HCl (Equation 1)
HSiCl ₃ + HCl → SiCl ₄ + H ₂ (Equation 2)

When producing polycrystalline silicon by the Siemens method, the raw material gases trichlorosilane and hydrogen are brought into contact with a Torii type (inverted U-shaped) silicon core wire heated in the reactor, and the surface of the silicon core wire is polycrystalline silicon. Is vapor-deposited by a CVD (Chemical Vapor Deposition) method.

Since heating of the silicon core wire is performed by electric heating, carbon having high conductivity and heat resistance and less metal contamination is used for the member in the reactor. Such carbon members include, for example, a core wire holder for energizing a silicon core wire and a heater for initial heating for energizing a high-purity, high-resistance silicon core wire.

According to Non-Patent Document 1 ("New Carbon Industry" by Toshikazu Ishikawa and Tsuru Nagaoki), carbon is 900C
It is said to react with hydrogen at the above temperature. The carbon member in the reactor at the time of deposition of polycrystalline silicon becomes high temperature of 900° C. or higher by receiving heat conduction or radiant heat from the silicon core wire that is being electrically heated, so that hydrogen of the supply gas reacts with carbon, A small amount of methane is produced according to the following formula 3.
C + 2H ₂ → CH ₄ (Equation 3)

In addition to this reaction, trichlorosilane, which is a raw material gas, contains a small amount of methyldichlorosilane having a close boiling point, and therefore, these are decomposed into methane under the reaction conditions for depositing polycrystalline silicon (Patent Document 1 (Patent Document 1 No. 3727470)).

Therefore, in the reaction exhaust gas from the polycrystalline silicon manufacturing apparatus, in addition to tetrachlorosilane, hydrogen, a trace amount of hydrogen chloride (HCl) and unreacted trichlorosilane shown in the above formulas 1 and 2, a trace amount of methane is included. Will be included.

In addition to these, the reaction exhaust gas also contains trace amounts of monochlorosilane (SiH ₃ Cl) and dichlorosilane (SiH ₂ Cl ₂ ) as other by-product gases.

In the following, tetrachlorosilane, trichlorosilane, and dichlorosilane are collectively referred to as chlorosilanes, and the liquid thereof is referred to as a chlorosilane liquid.

By the way, when converting trichlorosilane to silicon by the Siemens method, the conversion rate is as low as several to 10%, so the amount of raw material gas supplied to the reactor is as large as 15 to 50 Nm ³ per kg of deposited silicon. I don't get. Most of the raw material gas supplied to the reactor is discharged from the reactor as a reaction exhaust gas, so that it is necessary to suppress the loss of the raw material gas in order to suppress the manufacturing cost. In other words, it is essential to collect the reaction exhaust gas, purify trichlorosilane and hydrogen to high purity, and supply the raw material gas to the polycrystalline silicon manufacturing apparatus again.

In such a hydrogen gas recovery system, generally, the reaction exhaust gas from the polycrystalline silicon manufacturing apparatus is first separated into hydrogen and other components by a hydrogen recovery circulation device directly connected to the polycrystalline silicon manufacturing apparatus, and this separated hydrogen is separated. It is recovered and again introduced into the polycrystalline silicon manufacturing apparatus. An example of such a system is, for example, Non-Patent Document 2 (“Showa 55-62 New Energy Comprehensive Development Agency Commissioned Business Results Report Solar Power Generation System Practical Technology Development Low Cost Silicon Experimental Purification Verification (Hydrogen Reduction of Chlorsilane Technological Development of Processes) General Edition"), Patent Document 2 (JP 2008-143775 A), Patent Document 3 (JP 2011-84422 A), etc. and are publicly known.

In such a conventional hydrogen gas recovery system, first, chlorosilanes are condensed and separated, and then hydrogen chloride gas is absorbed and separated by a low-temperature chlorosilane solution, and finally, a small amount of residual chlorosilanes and hydrogen chloride are activated carbon. However, it is not configured for the purpose of actively removing methane contained in the exhaust gas.

When chlorosilanes and hydrogen chloride are adsorbed and separated by activated carbon, methane is also slightly adsorbed and removed by this activated carbon, but the concentration of methane in a large amount of hydrogen is extremely low at several hundred ppb to several ppm. The amount adsorbed by the activated carbon is extremely small, and in fact, it is supplied to the polycrystalline silicon manufacturing apparatus again with almost no removal. As a result, if the hydrogen recovery rate is increased,
Along with that, the methane concentration in the recovered hydrogen also rises.

When such recovered hydrogen is re-supplied to the polycrystalline silicon manufacturing apparatus, carbon, which is a constituent element of methane, is easily taken into the precipitated polycrystalline silicon (for example, see Patent Document 1), and This is a major obstacle to the production of pure polycrystalline silicon. Therefore, controlling the methane concentration in the recovered hydrogen is an important issue in producing high-purity polycrystalline silicon.

From such a point of view, as a measure against methane generation, surface treatment of the carbon member has been proposed in order to suppress the amount produced by the reaction between the carbon member and hydrogen in the reactor (see, for example, Patent Document 4 (Japanese Patent Laid-Open No. H05-18753). -213697) and Patent Document 5 (Japanese Patent Laid-Open No. 2009-62252)). However, since the surface treatment of the carbon member, which is a consumable material, is very expensive, the running cost is greatly increased, and even if the carbon member is subjected to the surface treatment, a slight amount of methane is generated, which is a raw material. Since methane is generated by thermal decomposition of a trace hydrocarbon compound contained in a certain trichlorosilane, it is necessary to remove methane from the reaction exhaust gas after all.

In addition, as measures against methane generation due to decomposition of hydrocarbon-containing impurities such as methyldichlorosilane contained in trichlorosilane, Patent Document 1 (Japanese Patent No. 3727470) describes:
There are reports on the control of the concentration of methane passing through the activated carbon adsorption layer and the average pore radius of activated carbon. However, the concentration of methane in the recovered hydrogen is as low as several hundreds of ppb to several ppm, and since methane has a property of being difficult to be adsorbed by activated carbon, the methane concentration in a large amount of recovered hydrogen is 1
In order to suppress the content to below ppm, an extremely large activated carbon filling tank is required on an industrial scale, which causes a problem of increasing equipment cost.

In addition, in Patent Document 6 (JP 2010-184831A), the residence time of the reaction exhaust gas in the condenser is lengthened, the dissolution of methane in chlorosilanes, which is a condensate, is promoted, and Methods for reducing methane concentration have been proposed. However, in this method, when the chlorosilanes that have absorbed methane are re-supplied to the reactor, the dissolved methane is also re-supplied to the reactor.

Patent No. 3727470 JP, 2008-143775, A JP, 2011-84422, A JP-A-5-213697 JP, 2009-62252, A JP, 2010-184831, A

"New Carbon Industry" by Toshikazu Ishikawa and Michiru Nagaoki "Fiscal 55-62 New Energy Development Agency Commissioned Business Results Report Solar Power Generation System Practical Technology Development Low-cost Silicon Experimental Refining Verification (Technology Development of Hydrogen Reduction Process for Chlorsilane) Summary Version" (Germany New Energy AIST (November 1988)

As described above, although the control of the methane concentration in the recovered hydrogen is an important issue in producing high-purity polycrystalline silicon, each of the conventional methods has its own drawbacks. Providing technology is desired.

The present invention has been made in view of the above problems, and an object thereof is to efficiently remove methane in a reaction exhaust gas from a polycrystalline silicon manufacturing process without a complicated system configuration. It is an object of the present invention to provide a technique that makes it possible to obtain highly pure polycrystalline silicon with few carbon impurities by purifying recovered hydrogen to a high degree of purity and supplying it to the polycrystalline silicon manufacturing process again.

In order to solve the above problems, a hydrogen gas recovery system according to the present invention is a hydrogen gas recovery system for separating and recovering hydrogen gas from a reaction exhaust gas from an apparatus for producing polycrystalline silicon using trichlorosilane as a raw material. , A: a condensing separator for condensing and separating chlorosilanes from the reaction exhaust gas containing hydrogen from the polycrystalline silicon manufacturing process; B: a compressor for compressing the reaction exhaust gas containing hydrogen, which has passed through the condensing separator. : Absorption device that passes through the compression device the reaction exhaust gas containing hydrogen with an absorbing liquid to absorb and separate hydrogen chloride; D: Methane and hydrogen chloride contained in the reaction exhaust gas containing hydrogen passed through the absorption device , And a first adsorption device comprising an adsorption tower filled with activated carbon for adsorbing and removing a part of chlorosilanes, and E:
A second adsorption device comprising an adsorption tower filled with synthetic zeolite that adsorbs and removes methane contained in the reaction exhaust gas containing hydrogen, which has passed through the first adsorption device, and F: is discharged from the second adsorption device. A gas line for recovering the purified hydrogen gas having a reduced methane concentration is provided.

Preferably, the synthetic zeolite packed in the second adsorption device has a molecular ratio (SiO ₂ /Al ₂ O ₃ ) of silica (SiO ₂ ) and alumina (Al ₂ O ₃ ) as main components of 2 or more. It is 30 or less.

Further, preferably, the synthetic zeolite, as a cation, sodium, potassium,
It contains a cation of any of calcium, magnesium, barium, and lithium.

In one aspect, the first adsorption device includes a plurality of adsorption towers filled with the activated carbon.

Moreover, in one aspect, the second adsorption device includes a plurality of adsorption columns filled with the synthetic zeolite.

Further, in one aspect, a gas line that uses the hydrogen gas purified by the second adsorption device as a carrier gas at the time of regeneration of an adsorption tower provided in at least one of the first adsorption device and the second adsorption device. Is equipped with.

Further, in an aspect, the hydrogen gas purified by the second adsorption device is used as a carrier gas at the time of regeneration of an adsorption tower provided in the second adsorption device, and the exhaust gas at the time of regeneration of the adsorption tower is A gas line used as a carrier gas at the time of regeneration of the adsorption tower included in the first adsorption device is provided.

The method for separating and recovering hydrogen gas according to the present invention is a method for separating and recovering hydrogen gas from a reaction exhaust gas from a device for producing polycrystalline silicon from trichlorosilane as a raw material, using the above-mentioned hydrogen gas recovery system, The methane concentration in the hydrogen gas is refined to 1 ppm or less and recovered by the second adsorption device.

Preferably, the concentration of hydrogen chloride in the hydrogen gas is set to 100 pp by the first adsorption device.
mv or less and chlorosilane concentration is purified to 100 ppmv or less.

Further, it is preferable that the pressure inside the adsorption tower provided in the second adsorption device is 0.3 M when regenerating.
Perform at PaA or less.

According to the present invention, methane in the reaction exhaust gas from the polycrystalline silicon manufacturing process is efficiently removed without a complicated system configuration and the recovered hydrogen is highly purified. By supplying it to the manufacturing process, a technique is provided that enables to obtain high-purity polycrystalline silicon with few carbon impurities.

It is a block diagram for explaining an example of composition of a hydrogen gas recovery system of the present invention. It is a block diagram for explaining other examples of composition of a hydrogen gas recovery system of the present invention. It is a block diagram for explaining other examples of composition of a hydrogen gas recovery system of the present invention.

  Hereinafter, modes for carrying out the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram for explaining a configuration example of a hydrogen gas recovery system of the present invention.
In the example shown in this figure, a condensation separation device (A) for condensing and separating chlorosilanes from a reaction exhaust gas containing hydrogen from a polycrystalline silicon manufacturing process, and a reaction exhaust gas containing hydrogen that has passed through the condensation separation device (A). Via a compressor (B) for compressing hydrogen chloride, a absorber (C) for contacting the reaction exhaust gas containing hydrogen with the absorber through the compressor (B) to absorb and separate hydrogen chloride, and an absorber (C). Adsorption device (D) comprising an adsorption tower filled with activated carbon for adsorbing and removing a part of methane, hydrogen chloride, and chlorosilanes contained in the reaction exhaust gas containing hydrogen, and a first adsorption device The gas was discharged from the second adsorption device (E), which comprises an adsorption tower filled with a synthetic zeolite that adsorbs and removes methane contained in the reaction exhaust gas containing hydrogen, which has passed through (D), and the second adsorption device (E). A hydrogen gas recovery system is constituted by the gas line (F) for recovering the purified hydrogen gas having a reduced methane concentration.

In this system, first, a reaction exhaust gas from a polycrystalline silicon manufacturing apparatus (not shown) is supplied to a condensation separation device (A), and chlorosilanes are condensed and separated (S101). This condensation separation step is not only for preventing gas from liquefying inside the compression device (B) in the next step so as not to damage the equipment, but also for adsorption removal using the first adsorption device (D) in the next step. It is provided to reduce the heat load in the process, and by this condensation and separation process, a part of chlorosilanes contained in hydrogen in the reaction exhaust gas is removed and recovered outside the system.

Specifically, the reaction exhaust gas from the polycrystalline silicon manufacturing apparatus is cooled and a part of chlorosilanes is excluded from the reaction exhaust gas. The cooling temperature may be equal to or lower than the temperature at which chlorosilanes do not condense under the pressure after compression in the compression step using the compression device (B). Therefore, the cooling temperature may be -10°C or lower, preferably -20°C or lower.

In the compression step (S102) using the compression device (B) following the condensation/separation step (S101), the pressure of the exhaust gas after condensation is increased to the pressure necessary for sending/circulating the exhaust gas to the subsequent step. The reaction exhaust gas compressed here contains not only hydrogen but also unseparated chlorosilanes, monosilane, hydrogen chloride, nitrogen and methane, and also a trace amount of carbon monoxide and carbon dioxide.

In the step of absorbing and separating hydrogen chloride using the absorber (C) subsequent to the compression step (S102), a step of absorbing chlorosilanes and hydrogen chloride contained in the reaction exhaust gas into the absorbing liquid (
S103) and the step of distilling hydrogen chloride (S104) are appropriately repeated to remove hydrogen chloride from the reaction exhaust gas and recover it outside the system.

The absorption device (C) includes a hydrogen chloride absorption unit that executes step S103 and a hydrogen chloride distillation unit that executes step S104, and the absorption liquid mainly composed of liquid chlorosilanes from the hydrogen chloride distillation unit absorbs hydrogen chloride. When the reaction exhaust gas is supplied to the section and comes into gas-liquid contact with the absorption liquid, chlorosilanes and hydrogen chloride in the reaction exhaust gas are absorbed by the absorption liquid.

Although not shown in the figure, the hydrogen chloride absorbing section is provided with a packing or a tray that allows efficient gas-liquid contact. Further, for efficient absorption, it is preferable to perform gas-liquid contact at low temperature and high pressure. Specifically, it is preferable that the temperature is −30° C. to −60° C. and the pressure is 0.4 MPa to 2 MPa.

The reaction exhaust gas containing hydrogen as a main component, from which chlorosilanes and hydrogen chloride have been removed in the absorption device (C), is introduced into the first adsorption device (D) including an adsorption tower filled with activated carbon. Here, unseparated chlorosilanes, monosilane, and hydrogen chloride are adsorbed and removed by passing through a packed bed of activated carbon, and then recovered or discarded outside the system (S105). On the other hand, since methane has a property that it is difficult to be adsorbed by activated carbon, most of it is removed by adsorption, but most of it is not adsorbed and is discharged from the adsorption device (D). Nitrogen, carbon monoxide, carbon dioxide,
Similar to methane.

It is preferable that the first adsorption device (D) includes a plurality of adsorption towers filled with activated carbon.
When a plurality of adsorption towers are provided, while regenerating one adsorption tower, exhaust gas is supplied to another adsorption tower, and the activated carbon adsorption step (S105) can be continuously executed without interruption. .. The activated carbon as the adsorbent is, for example, a coconut shell or petroleum pitch-based molded product, and can have an average pore radius of, for example, 5 μm to 20 μm. Further, for efficient adsorption, it is preferable to carry out at low temperature and high pressure. Specifically, the temperature is -30°C to +100°C.
It is preferably -10°C to +50°C, and the pressure is preferably 0.4 MPa to 2 MPa.

Regeneration (desorption) of activated carbon is efficient at high temperatures and low pressures, so the pressure should first be -0.1 MPa
The pressure is reduced to +0.2 MPa or less and then heated to a temperature of 80°C to 300°C, preferably 1
The temperature is 40°C to 200°C. During the regeneration, hydrogen is aerated as a carrier gas to desorb adsorbed chlorosilanes, monosilane, hydrogen chloride, methane, nitrogen, carbon monoxide, and carbon dioxide. The desorbed gas may be used in another process, or may be recovered by returning it to the absorber (C) used in the previous step or discarded.

The reaction exhaust gas containing hydrogen as a main component, which is obtained by removing chlorosilanes, monosilane, and hydrogen chloride in the first adsorption device (D), is a second adsorption device (E) composed of an adsorption tower filled with synthetic zeolite.
Will be introduced to. In this adsorption device (E), the reaction exhaust gas is passed through the packed bed of synthetic zeolite to adsorb and remove methane, nitrogen, carbon monoxide, and carbon dioxide that could not be removed by the activated carbon in the previous step (S106). .

The second adsorption device (E) also preferably includes a plurality of adsorption columns filled with synthetic zeolite. When a plurality of adsorption towers are provided, while regenerating one adsorption tower, exhaust gas is supplied to another adsorption tower, and the synthetic zeolite adsorption step (S106) can be continuously executed without interruption. it can. Further, for efficient adsorption, it is preferable to carry out at low temperature and high pressure. Specifically, the temperature is −30° C. to +100° C., preferably −10° C. to +50° C., and the pressure is preferably 0.4 MPa to 2 MPa.

The synthetic zeolite used as the adsorbent is selected to have a high dilute methane adsorption capacity. Preferably, the molecular ratio of silica (SiO ₂ ) and alumina (Al ₂ O ₃ ) which are the main components (
A synthetic zeolite having a SiO ₂ /Al ₂ O ₃ content of ₂ or more and 30 or less is used. Further, such a synthetic zeolite preferably contains, as a cation, any cation of sodium, potassium, calcium, magnesium, barium, and lithium.

Specific examples of the synthetic zeolite suitable for use in the present invention include silica (SiO ₂ ) and alumina (Al ₂ O ₃ ) having a molecular ratio (SiO ₂ /Al ₂ O ₃ ) of 2 to 4 and a main cation. Is Ca, Zeolum (registered trademark) SA-600A (Tosoh Corp.) having an X-type crystal structure, and a molecular ratio (SiO ₂ /Al ₂ O ₃ ) of 15 to 20 and K as a cation. Examples of the zeolite include Mg and Ba and have a ferrierite-type crystal structure. In hydrogen gas with a methane partial pressure of 5 to 10 ppm, the amount of adsorbed methane is very large, and specifically, it is several tens of times that of activated carbon (average pore radius 8Å) described in Patent Document 1. Since it is very large, the methane adsorption device (E
) Can be miniaturized.

The regeneration (desorption) of the synthetic zeolite is efficient at high temperature and low pressure as in the case of activated carbon, and the pressure inside the adsorption column during regeneration is preferably 0.3 MPaA or less. For example, first, the pressure is reduced to −0.1 MPa to +0.2 MPa or less, and then heated to 30° C.
According to the above-mentioned two-step procedure of flowing hydrogen as a carrier gas while maintaining the temperature at ˜200° C., or by simply reducing the pressure to −0.1 MPa to +0.2 MPa or less without heating and then flowing the carrier gas without heating. Can be easily removed.

The desorption gas may be used in another process, or as a desorption carrier gas for the activated carbon adsorber (D) described above, or it may be discarded.

2 and 3 are block diagrams for explaining another configuration example of the hydrogen gas recovery system of the present invention.

In the embodiment shown in FIG. 2, the hydrogen gas purified by the second adsorption device (E) is used in at least one of the first adsorption device (D) and the second adsorption device (E). A gas line (G1, G2) used as a carrier gas during regeneration is provided.

In the embodiment shown in FIG. 3, hydrogen gas purified by the second adsorption device (E)
Used as a carrier gas during regeneration of the adsorption tower included in the adsorption device (E), and the exhaust gas during regeneration of the adsorption tower used as a carrier gas during regeneration of the adsorption tower included in the first adsorption device (D). The gas line (G1, G2) is provided.

In any of the hydrogen gas recovery systems illustrated in FIGS. 1 to 3, the second adsorption device (
According to E), the methane concentration in hydrogen gas is refined to 1 ppm or less and recovered.

Synthetic zeolite has a high adsorption capacity for non-polar methane having a small molecular diameter, and further for methane in a dilute concentration range of several hundreds of ppb to several ppm, but desorption of highly polar hydrogen chloride and chlorosilanes is difficult. is there. Therefore, once hydrogen chloride or chlorosilanes are adsorbed, the adsorbability of methane decreases thereafter. Therefore, it is necessary to control the concentrations of hydrogen chloride and chlorosilanes in the gas introduced into the synthetic zeolite adsorption device (E).

Specifically, it is preferable that both the hydrogen chloride concentration and the chlorosilane concentration be 100 ppmv or less. It is more preferably 10 ppm or less, further preferably 0.1 ppm
Below.

Basically, the activated carbon adsorbing device (D) in the previous step is designed or operated so that the hydrogen chloride and chlorosilanes are not more than the above concentration, but just in case, it is introduced into the synthetic zeolite adsorbing device (E). It is desirable to monitor the concentration of hydrogen chloride and chlorosilanes in the gas.

Concentration monitoring methods include an in-line infrared absorption analyzer, a method in which part of the gas is absorbed in water and the ion concentration, conductivity, etc. are continuously monitored, or the gas is absorbed in a phenolphthalein liquid and the color is monitored. A simple method of confirming the change of If the concentration of hydrogen chloride or chlorosilanes exceeds the specified level, take measures such as switching the activated carbon adsorption tower.

Also, when initially packing the synthetic zeolite in the packed column, it is necessary to consider the adsorption of water in the outside air. Since water also has a strong polarity and cannot be easily desorbed, dew point is -10°C or lower, preferably-
It is necessary to be careful to fill the container controlled at 60°C or lower with a gas whose dew point is controlled while ventilating.

A filter for collecting fine zeolite powder is provided at the gas outlet of the synthetic zeolite adsorption device (E). A filter having an opening of 10 μm or less is provided in order to prevent the formed fine powder from collapsing due to the initial filling and the pressure fluctuation during use and the generated fine powder from flowing out to the subsequent step.

[Example 1]
Chlorosilanes, monosilane, and hydrogen chloride were separated from the reaction exhaust gas of the polycrystalline silicon manufacturing apparatus, and recovered hydrogen containing 0.5 ppm of methane was introduced into the synthetic zeolite packed bed to adsorb and remove methane.

As the methane adsorbent, a φ1.5 mm pellet-shaped zeolite of ferrierite type crystal containing silica and alumina having a molecular ratio of 17 (SiO ₂ /Al ₂ O ₃ ) and cations of K, Mg and Ba was used. The size of the filling tank is 22 mm in inner diameter φ and 1,500 mm in height H. The methane concentration in the gas at the gas inlet and the gas outlet of the synthetic zeolite filling tank was analyzed by gas chromatography (detector FID, lower limit of quantification 0.01 ppm). The breakthrough was the time when 1/10 of the introduced methane concentration was detected at the outlet. The saturated adsorption amount was the time when the concentration of 98% or more of the introduced methane was detected at the outlet.

For desorption, hydrogen was flowed as a carrier gas to the saturated and adsorbed synthetic zeolite. Desorption was completed when the methane concentration at the packed bed outlet was confirmed to be 0.01 ppm or less.

The results are shown in Table 1A (adsorption) and Table 1B (desorption) together with the experimental conditions. Adsorption and desorption were repeated, and the saturated adsorption amount of methane in the 10th adsorption was 1,620 μg, and the amount of carrier hydrogen required for regeneration was 900 NL. There was no difference between the results of the first adsorption and the tenth adsorption, and it was confirmed that desorption was performed without any problem.

Polycrystalline silicon was produced by the Siemens method using recovered hydrogen obtained by adsorbing and refining methane.
The carbon concentration in the polycrystalline silicon was 0.04 ppma or less. Carbon concentration analysis is 607.5c at 80K as described in SEMI MF1391-0704.
It was calculated from the absorption coefficient of the m ⁻¹ infrared absorption spectrum. The carbon in the polycrystalline silicon produced from recovered hydrogen (methane concentration 0.5 ppm), which was not subjected to methane removal, was 0.
It was 15 ppma.

[Comparative Example 1]
Under the same conditions as in Example 1, the adsorbent was activated carbon (average pore radius 1 described in Patent Document 1
Adsorption removal and desorption of methane were carried out with a particle size of 2 Å or less, specifically, an average pore size of 8 Å, a specific surface area of 550 to 600 m ² /g, coconut shell, and pellet molding.

The results are shown in Table 2A (adsorption) and Table 2B (desorption) together with the experimental conditions. The saturated adsorption amount of methane was 68 μg, and the amount of carrier hydrogen required for regeneration was 48 NL.

The amount of methane adsorbed on the activated carbon does not reach 1/20 of that of the synthetic zeolite shown in Example 1. Also, the hydrogen unit required for desorption (total carrier amount/total treated gas amount in the table) is economically inferior because activated carbon requires 1.5 times that of synthetic zeolite. Polycrystalline silicon was produced by the Siemens method using recovered hydrogen obtained by adsorption purification of methane as a raw material. The carbon concentration in the crystal was 0.04 ppma or less, as in Example 1.

INDUSTRIAL APPLICABILITY The present invention provides a technology capable of efficiently removing methane in a reaction exhaust gas from a polycrystalline silicon manufacturing process without using a complicated system configuration and achieving highly purified recovered hydrogen.

A Condensation/separation device B Compressor C Absorption device D First adsorption device E Second adsorption device F, G1, G2 gas line

Claims (8)

A hydrogen gas recovery system for separating and recovering hydrogen gas from a reaction exhaust gas from an apparatus for producing polycrystalline silicon using trichlorosilane as a raw material,
A: a condensing separator for condensing and separating chlorosilanes from the reaction exhaust gas containing hydrogen from the polycrystalline silicon manufacturing process,
B: a compression device that compresses the reaction exhaust gas containing hydrogen, which has passed through the condensation separation device,
C: an absorption device that makes the reaction exhaust gas containing hydrogen that has passed through the compression device contact with an absorption liquid to absorb and separate hydrogen chloride;
D: a first adsorption device comprising an adsorption tower filled with activated carbon for adsorbing and removing a part of methane, hydrogen chloride, and chlorosilanes contained in the reaction exhaust gas containing hydrogen that has passed through the absorption device,
E: a second adsorption device comprising an adsorption tower filled with synthetic zeolite that adsorbs and removes methane contained in the reaction exhaust gas containing hydrogen, which has passed through the first adsorption device,
F: a gas line for collecting the purified hydrogen gas with a reduced methane concentration discharged from the second adsorption device ,
The synthetic zeolite packed in the second adsorption device has a molecular ratio (SiO ₂ /Al ₂ O ₃ ) of silica (SiO ₂ ) and alumina (Al ₂ O ₃ ) as main components of ₂ to 4, and is positive. Zeolite having an X-type crystal structure whose ion is Ca, or a ferrierite-type crystal having a molecular ratio (SiO ₂ /Al ₂ O ₃ ) of 15 to 20 and containing cations K, Mg, and Ba Is a zeolite with a structure,
A hydrogen gas recovery system characterized in that   The hydrogen gas recovery system according to claim 1, wherein the first adsorption device includes a plurality of adsorption towers filled with the activated carbon.   The hydrogen gas recovery system according to claim 1, wherein the second adsorption device includes a plurality of adsorption towers filled with the synthetic zeolite.   A gas line is provided, which uses the hydrogen gas purified by the second adsorption device as a carrier gas at the time of regeneration of an adsorption tower provided in at least one of the first adsorption device and the second adsorption device. Item 2. The hydrogen gas recovery system according to Item 1.   The hydrogen gas purified by the second adsorption device is used as a carrier gas during regeneration of the adsorption tower included in the second adsorption device, and the exhaust gas during regeneration of the adsorption column is included in the first adsorption device. The hydrogen gas recovery system according to claim 1, further comprising a gas line used as a carrier gas when the adsorption tower is regenerated. A method for separating and recovering hydrogen gas from a reaction exhaust gas from a device for producing polycrystalline silicon using trichlorosilane as a raw material,
Using the hydrogen gas recovery system according to any one of claims 1 to 5 ,
A method for separating and recovering hydrogen gas, wherein the methane concentration in the hydrogen gas is purified to 1 ppm or less and recovered by the second adsorption device. The method for separating and recovering hydrogen gas according to claim 6 , wherein the first adsorption device purifies the hydrogen chloride concentration in the hydrogen gas to 100 ppmv or less and the chlorosilane concentration to 100 ppmv or less. The method for separating and recovering hydrogen gas according to claim 6 , wherein the pressure in the tower during regeneration of the adsorption tower provided in the second adsorption device is 0.3 MPaA or less.