A method for purifying hydrogen gas recycled in the production of polycrystalline silicon

Abstract

The present application belongs to the technical field of polycrystalline silicon industry, and particularly relates to a method for purifying hydrogen gas in polycrystalline silicon production. The method comprises the following steps: (1) cooling the reduction furnace tail gas to obtain condensate and recycled hydrogen gas containing borohydride and phosphine; the reduction furnace tail gas contains hydrogen, borohydride, phosphine and chlorosilane, and the condensate contains chlorosilane; (2) adding a chlorine supply agent to the condensate to obtain an absorbent; (3) contacting the absorbent with the recycled hydrogen gas containing borohydride and phosphine to obtain the recycled hydrogen gas which is preliminarily purified; and (4) purifying the recycled hydrogen gas which is preliminarily purified by an adsorbent to obtain the recycled hydrogen gas from which boron and phosphorus impurities are removed. The method reduces the introduction of reagents, has the advantages of environmental friendliness, no secondary pollution and the like, and is suitable for purifying recycled hydrogen gas in the production of electronic-grade polycrystalline silicon.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of polycrystalline silicon industry, and particularly relates to a method for purifying circulating hydrogen in polycrystalline silicon production. BACKGROUND

[0002] Polycrystalline silicon is an electronic material with a certain purity obtained by purifying industrial silicon through a series of physical and chemical reactions, and is the core raw material for manufacturing silicon polished wafers, solar cells and semiconductors, and is the most basic raw material in the information industry and new energy industry. The purity of polycrystalline silicon determines its application field. The solar-grade polycrystalline silicon used in photovoltaics generally has a purity of 6N-9N (i.e. 99.9999%-99.9999999%, and several 9s are several Ns). The electronic-grade polycrystalline silicon used in semiconductor production requires a purity of 11N, and the process is much more difficult than solar-grade polycrystalline silicon.

[0003] High-purity polycrystalline silicon has the characteristics of high technical barriers, great process difficulty and high danger level. The mainstream process at present is the improved method of the "Siemens method" invented by the German company Siemens. In this method, trichlorosilane is used as raw material, and trichlorosilane is reduced by circulating hydrogen in a reduction furnace to form polycrystalline silicon rods by vapor deposition on a silicon core. The main factors affecting the purity of the product of the improved Siemens method include the purity of trichlorosilane and circulating hydrogen. The purity of trichlorosilane can be controlled by means such as rectification / adsorption. However, the purity of circulating hydrogen is difficult to guarantee, especially the phosphorus and boron impurities contained in the circulating hydrogen are important bottlenecks that limit the further improvement of the quality of polycrystalline silicon.

[0004] The phosphorus and boron impurities in the circulating hydrogen are mainly phosphorus and boron hydrides formed by phosphorus and boron elements and hydrogen at high temperature. They are difficult to remove because their boiling points are low, and they accumulate in the circulating hydrogen, eventually affecting the quality of polycrystalline silicon. There are three main methods to remove such impurities at present. The first method is to oxidize them into oxidized state by an oxidizing adsorbent and remove them; the second method is to reduce the temperature of circulating hydrogen below the boiling point of the impurities by condensation to form condensate enrichment and then remove them from the system; the third method is to convert them into liquid-phase impurities in chlorosilane, and then remove them by rectification and adsorption. The common practice in the industry for purifying circulating hydrogen is to preliminarily separate and purify hydrogen in the tail gas by deep cooling and chlorosilane cold washing, and then to adsorb it by an activated carbon adsorption tower. However, this purification method is not ideal for the removal of phosphorus and boron hydride impurities.

[0005] To solve the problem of removing boron, phosphorus and other impurities in the circulating hydrogen, Chinese invention patent application CN113233420A discloses a method for hydrogen purification for electronic grade polysilicon production, the tail gas after the end of the CVD process is separated by a tail gas separation device, the crude purified hydrogen obtained after separation enters an activated carbon adsorption tower system for adsorption of phosphine, and then is treated by a CVD front hydrogen treatment system to obtain high-purity hydrogen, which is returned to the vapor deposition process system for reuse.

[0006] In addition, Chinese invention patent application CN105293438A discloses a hydrogen purification method and device for preparing electronic grade polysilicon by improved Siemens method, which removes boron and phosphorus element impurities in the circulating hydrogen by using modified activated carbon and modified silica gel as adsorption reagents. Specifically, the circulating hydrogen is first introduced into a hydrogen cooler for cooling, and the hydrogen is cooled to 0-30 DEG C, enters a first adsorption reaction column, and adsorbs and removes impurities mainly containing boron elements. The circulating hydrogen after the first adsorption enters a hydrogen deep cooler, the hydrogen is cooled to -88 to -68 DEG C, enters a second adsorption reaction column, and adsorbs and removes impurities mainly containing phosphorus elements. The present application realizes the adsorption reaction of the circulating hydrogen to remove harmful impurities such as boron and phosphorus elements, greatly reduces the content of boron and phosphorus element impurities in the hydrogen, improves the quality of the circulating hydrogen, and makes it possible to stably produce electronic grade polysilicon by the improved Siemens method.

[0007] However, the above-mentioned processes only remove the boron and phosphorus element impurities in the circulating hydrogen by adsorption or adsorption reaction, the contact area between the impurities and the adsorbent is limited, and the single method has limited effect on removing the impurities.

[0008] Therefore, it is necessary to develop a method for efficiently purifying circulating hydrogen in polysilicon production. SUMMARY

[0009] The present application provides a method for purifying circulating hydrogen in polysilicon production, which converts boron and phosphorus impurities in the circulating hydrogen into liquid-phase impurities that are easier to handle at low temperature by using condensate obtained by reducing the temperature of the tail gas of the reducing furnace, and then removes them from the liquid phase by rectification or adsorption. The remaining small amount of impurities in the gas phase can be deeply removed after adsorption. The process is simple, has strong popularization, is environmentally friendly, and has no secondary pollution.

[0010] To achieve the above-mentioned purposes, the technical solutions adopted by the present application are as follows:

[0011] The present application provides a method for efficiently purifying circulating hydrogen in polysilicon production, which converts boron and phosphorus impurities in the circulating hydrogen into liquid-phase impurities that are easier to handle at low temperature by using condensate obtained by reducing the temperature of the tail gas of the reducing furnace, and then removes them from the liquid phase by rectification or adsorption. The remaining small amount of impurities in the gas phase can be deeply removed after adsorption. The process is simple, has strong popularization, is environmentally friendly, and has no secondary pollution.

[0012] (1) cooling the tail gas of the reduction furnace to separate a condensate and a recycled hydrogen gas containing boron hydride and phosphine; the tail gas of the reduction furnace mainly consists of hydrogen, boron hydride, phosphine and chlorosilane, and the condensate mainly consists of chlorosilane;

[0013] (2) adding a chlorine donor to the condensate to obtain an absorbent;

[0014] (3) contacting the absorbent with the recycled hydrogen gas containing boron hydride and phosphine to obtain a recycled hydrogen gas that is preliminarily purified;

[0015] (4) purifying the recycled hydrogen gas that is preliminarily purified by an adsorbent to obtain a recycled hydrogen gas from which boron and phosphorus impurities are removed.

[0016] Preferably, the chlorosilane in step (1) includes at least one of dichlorodihydrogen silane, trichlorohydrogen silane and silicon tetrachloride; and the proportion of the chlorosilane in the condensate is > 95%.

[0017] Preferably, the chlorine donor in step (2) includes one or more of hydrogen chloride, chlorine, hypochlorous acid and perchloric acid.

[0018] Preferably, the addition amount of the chlorine donor in step (2) is 0.05%-0.5% of the mass of the condensate, preferably 0.05%-0.2%.

[0019] Preferably, the temperature of the contacting reaction in step (3) is -90-0℃.

[0020] Preferably, the ratio of the use amount of the absorbent to the flow of the tail gas of the reduction furnace in step (3) is 0.5-5m 3 :1000m 3 / h, preferably 1-3m 3 :1000m 3 / h.

[0021] Preferably, in step (4), the adsorbent is an oxidizing adsorbent.

[0022] Further preferably, the oxidizing adsorbent is selected from one or more of oxidizing modified activated carbon, supported silica gel, supported alumina, supported molecular sieve and resin.

[0023] Preferably, the absorbent after the contacting reaction in step (3) is subjected to rectification or adsorption treatment and is recycled.

[0024] Compared with the prior art, the present application has the following beneficial effects:

[0025] (1) the present application can more efficiently convert the boron and phosphine in the circulating hydrogen into boron and phosphine chlorides by contacting the condensate containing chlorine and chlorosilane with the boron and phosphine in the circulating hydrogen;

[0026] (2) the present application is carried out at low temperature, which is conducive to the conversion of boron and phosphine into boron and phosphine chlorides, and the reaction degree is higher, so that the boron and phosphine are less likely to enter the circulating hydrogen, the purity of the purified circulating hydrogen is higher, and the reaction efficiency can be increased by 50%-90%;

[0027] (3) the present application has good combination with the existing adsorption and rectification processes, and can be better matched with the original equipment to realize the recycling of the condensate and reduce the production cost while purifying the circulating hydrogen;

[0028] (4) the present application has the advantages of simple process, less introduction of reagents, environmental friendliness, no secondary pollution, etc., and is suitable for the purification of circulating hydrogen in the field of electronic-grade polysilicon production. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The present application is a process flow diagram for efficiently purifying circulating hydrogen in polysilicon production. DETAILED DESCRIPTION

[0030] It is worth noting that the raw materials used in the present application are ordinary commercially available products, and their sources are not specifically limited. The following non-limiting examples can enable those skilled in the art to more fully understand the present application, but do not limit the present application in any way.

[0031] The following reagents are commonly used in industry and are commercially available.

[0032] Example 1

[0033] A method for purifying circulating hydrogen in polysilicon production, as shown in the flowchart. Figure 1 The flowchart.

[0034] The circulating hydrogen at the outlet of the reduction furnace is used as the experimental flue gas. The circulating hydrogen contains hydrogen, chlorosilane, a small amount of silicon powder, boron and phosphorus impurities, etc. After stepwise cooling, chlorosilane liquid and gas are obtained. The gas obtained is contacted with chlorosilane liquid containing or adding chlorine donor at low temperature, which can transfer a large amount of impurities in the gas phase to the liquid phase. After further adsorption, high-purity circulating hydrogen can be obtained. The specific experimental conditions and steps are as follows:

[0035] (1) The reduction furnace tail gas is cooled by air and water at 7℃ to obtain a condensate mainly containing chlorosilane and a gas phase mainly containing hydrogen. The actual flue gas conditions of the reduction furnace tail gas are as follows: flue gas flow 3000m 3hydrogen chloride was added to the chlorosilane-containing condensate of step (1) in an amount of 0.1% of the mass of the condensate to obtain an absorbent;

[0036] (2) Hydrogen chloride was added to the chlorosilane-containing condensate of step (1) in an amount of 0.1% of the mass of the condensate to obtain an absorbent;

[0037] (3) The 3m 3 of absorbent and the recycled hydrogen gas containing boron and phosphorus hydrides were subjected to contact reaction at -35°C to convert the boron and phosphorus impurity hydrides into chlorides to obtain the recycled hydrogen gas that was preliminarily purified;

[0038] (4) The recycled hydrogen gas that was preliminarily purified was subjected to purification by honeycomb activated carbon to obtain the high-purity recycled hydrogen gas; the removal efficiencies of boron and phosphorus hydrides at the outlet were 41% and 52% respectively (average yield in three times) ;

[0039] (5) The absorbent after reaction can be recycled after regeneration by heating in a regenerator.

[0040] Example 2

[0041] This example is directed to the influence of reaction temperature on removal performance. The reducing furnace tail gas containing boron and phosphorus hydrides was subjected to stepwise cooling by air cooling and water cooling, and the cooled condensate and recycled hydrogen gas were subjected to contact reaction in a reactor to obtain the recycled hydrogen gas that was preliminarily purified. The solvent after absorption can be recycled after regeneration by heating in a regenerator. The recycled hydrogen gas that was preliminarily purified was subjected to purification by activated carbon to obtain the high-purity recycled hydrogen gas. The main parameters are as follows:

[0042] (1) The reducing furnace tail gas was subjected to stepwise cooling by air cooling and 7°C water cooling to obtain liquid mainly containing chlorosilane and gas phase mainly containing hydrogen. The actual flue gas conditions of the reducing furnace tail gas were as follows: flue gas flow 3000m 3 / h, pressure 1.38 MPa, boron and phosphorus hydride concentrations 37 ppm and 50 ppm respectively;

[0043] (2) Hydrogen chloride was added to the chlorosilane-containing condensate of step (1) in an amount of 0.1% of the mass of the condensate to obtain an absorbent;

[0044] (3) The 3m 3 of absorbent and the recycled hydrogen gas containing boron and phosphorus hydrides were subjected to contact reaction at -45°C to convert the boron and phosphorus impurity hydrides into chlorides to obtain the recycled hydrogen gas that was preliminarily purified;

[0045] (4) The recycled hydrogen gas that was preliminarily purified was subjected to purification by activated alumina balls to obtain the high-purity recycled hydrogen gas; the removal efficiencies of boron and phosphorus hydrides at the outlet were 47% and 53% respectively (average yield in three times) ;

[0046] (5) The absorbent after reaction can be recycled after regeneration in the regenerator.

[0047] Example 3

[0048] This embodiment is directed to the influence of the absorbent on the removal performance. The reduction furnace tail gas containing boron and phosphine is gradually cooled by air cooling and water cooling, and the condensed liquid and the circulating hydrogen obtained by cooling are contacted in the reactor to obtain the preliminary purified circulating hydrogen. The solvent after absorption can be recycled after regeneration in the regenerator. Then the preliminary purified circulating hydrogen is purified by activated carbon to obtain high-purity circulating hydrogen. The main parameters are as follows:

[0049] (1) The reduction furnace tail gas is gradually cooled by air cooling and 7°C water cooling to obtain liquid mainly containing chlorosilane and gas phase mainly containing hydrogen. The actual flue gas conditions of the reduction furnace tail gas are as follows: flue gas flow is 3000 m 3 / h, pressure is 1.8 MPa, and the concentrations of boron and phosphine are 40 ppm and 57 ppm, respectively;

[0050] (2) Hydrogen chloride and hypochlorous acid are added to the condensed liquid containing chlorosilane in step (1), and the addition amounts of hydrogen chloride and hypochlorous acid are 0.05% and 0.05% of the mass of the condensed liquid, respectively, to obtain an absorbent;

[0051] (3) The absorbent of 5 m 3 and the circulating hydrogen containing boron and phosphine are contacted at -45°C to convert the boron and phosphine impurities into chlorides to obtain the preliminary purified circulating hydrogen;

[0052] (4) The preliminary purified circulating hydrogen is purified by Y-type molecular sieve to obtain high-purity circulating hydrogen; the removal efficiencies of boron and phosphine are 68% and 75% (three times average yield), respectively;

[0053] (5) The absorbent after reaction can be recycled after regeneration in the regenerator.

[0054] Example 4

[0055] This embodiment is directed to the influence of the reaction temperature on the removal performance. The reduction furnace tail gas containing boron and phosphine is gradually cooled by air cooling and water cooling, and the condensed liquid and the circulating hydrogen obtained by cooling are contacted in the reactor to obtain the preliminary purified circulating hydrogen. The solvent after absorption can be recycled after regeneration in the regenerator. Then the preliminary purified circulating hydrogen is purified by activated carbon to obtain high-purity circulating hydrogen. The main parameters are as follows:

[0056] (1) The reduction furnace tail gas is gradually cooled by air cooling and 7°C water cooling to obtain liquid mainly containing chlorosilane and gas phase mainly containing hydrogen. The actual flue gas conditions of the reduction furnace tail gas are as follows: flue gas flow is 3000 m 3 / h, and pressure is 1.8 MPa;

[0057] (2) Hydrogen chloride and hypochlorous acid are added to the condensate containing chlorosilane in step (1), and the addition amounts of hydrogen chloride and hypochlorous acid are 0.05% and 0.05% of the mass of the condensate, respectively, to obtain an absorbent;

[0058] (3) The absorbent of 5 m 3 and the recycled hydrogen gas containing boron and phosphorus hydrides are contacted at -80°C to convert the boron and phosphorus impurity hydrides into chlorides, and the recycled hydrogen gas after preliminary purification is obtained;

[0059] (4) The recycled hydrogen gas after preliminary purification is purified by a honeycomb activated carbon to obtain high-purity recycled hydrogen gas; the removal efficiencies of boron and phosphorus hydrides at the outlet are 76% and 83% (three-time average yield), respectively;

[0060] (5) The absorbent after reaction can be recycled after regeneration in a regenerator.

[0061] Example 5

[0062] This example is to study the effect of the amount of absorbent on the removal performance. The reduction furnace tail gas containing boron and phosphorus hydrides is gradually cooled by air cooling and water cooling to obtain condensate and recycled hydrogen gas, which are contacted in a reactor to obtain recycled hydrogen gas after preliminary purification. The solvent after absorption can be recycled after regeneration in a regenerator. The recycled hydrogen gas after preliminary purification is purified by activated carbon to obtain high-purity recycled hydrogen gas. The main parameters are as follows:

[0063] (1) The reduction furnace tail gas is gradually cooled by air cooling and 7°C water cooling to obtain liquid mainly containing chlorosilane and gas phase mainly containing hydrogen. The actual flue gas conditions of the reduction furnace tail gas are as follows: flue gas flow is 3000 m 3 / h, and pressure is 1.8 MPa;

[0064] (2) Hydrogen chloride is added to the condensate containing chlorosilane in step (1), and the addition amount of hydrogen chloride is 0.07% of the mass of the condensate, to obtain an absorbent;

[0065] (3) The absorbent of 3 m 3 and the recycled hydrogen gas containing boron and phosphorus hydrides are contacted at -45°C to convert the boron and phosphorus impurity hydrides into chlorides, and the recycled hydrogen gas after preliminary purification is obtained;

[0066] (4) The high purity recycled hydrogen gas is obtained by purifying the preliminary purified recycled hydrogen gas with honeycomb activated carbon. The removal efficiency of boron and phosphine is 35% and 55% respectively (average yield for three times).

[0067] (5) The absorbent after reaction can be recycled after being regenerated by heating in the regenerator.

[0068] Finally, it should be noted that the above content is only used to illustrate the technical solutions of the present application, and is not a limitation on the scope of protection of the present application. Simple modifications or equivalent replacements of the technical solutions of the present application made by those skilled in the art do not deviate from the essence and scope of the technical solutions of the present application.

Claims

1. A method for purifying hydrogen gas circulated in the production of polycrystalline silicon, characterized by, The method comprises the following steps: (1) cooling the tail gas of the reduction furnace to separate a condensate and a circulating hydrogen gas containing boron hydride and phosphorus hydride; the tail gas of the reduction furnace mainly comprises hydrogen, boron hydride, phosphorus hydride and chlorosilane, and the condensate mainly comprises chlorosilane; (2) adding a chlorine supply agent to the condensate to obtain an absorbent; (3) contacting the absorbent with the circulating hydrogen gas containing boron hydride and phosphorus hydride to obtain a preliminarily purified circulating hydrogen gas; (4) purifying the preliminarily purified circulating hydrogen gas by an adsorbent to obtain a circulating hydrogen gas from which boron and phosphorus impurities are removed; The temperature of the contacting reaction in step (3) is -90-0℃.

2. The method of claim 1, wherein, The chlorosilane in step (1) comprises at least one of dichlorodihydrogen silicon, trichlorohydrogen silicon and silicon tetrachloride; the proportion of the chlorosilane in the condensate is >95%.

3. The method of claim 1, wherein, The chlorine supply agent in step (2) comprises one or more of hydrogen chloride, chlorine, hypochlorous acid and perchloric acid.

4. The method of claim 1, wherein, The addition amount of the chlorine supply agent in step (2) is 0.05%-0.5% of the mass of the condensate.

5. The method of claim 1, wherein, The ratio of the amount of the absorbent used in step (3) to the flow rate of the reducing furnace flue gas is 1-20 s -1 .

6. The method of claim 1, wherein, In step (4), the adsorbent is a porous adsorbent.

7. The method of claim 6, wherein, The adsorbent is selected from one or more of porous modified activated carbon, supported silica gel, supported alumina, supported molecular sieve and resin.

8. The method of claim 1, wherein, The absorbent after the contacting reaction in step (3) is subjected to rectification or adsorption treatment and is recycled.

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