A new trichlorosilane distillation process

Abstract

The present invention provides a novel trichlorosilane distillation process, comprising a first-stage baffle distillation tower, a second-stage reaction distillation tower, and a third-stage baffle distillation tower connected in series. The process of the present invention innovatively applies the reaction distillation process intensification technology and two integrated energy-saving technologies, baffle distillation tower and differential pressure thermal coupling distillation, to the trichlorosilane purification process, thereby enhancing the separation strength of each stage of distillation tower. Compared with the traditional trichlorosilane distillation process, the process of the present invention has low energy consumption and small investment, and can effectively remove impurities such as boron, phosphorus, and carbon in trichlorosilane, so that the quality of the trichlorosilane product meets the preparation requirements of electronic-grade second-stage and above polysilicon.

Description

Technical Field

[0001] The present invention belongs to the field of chemical distillation, and more specifically, relates to a novel trichlorosilane distillation process in the process of preparing polysilicon. Background Art

[0002] Boron and phosphorus are donor impurities in polysilicon, which will change the conductivity type and resistivity of polysilicon. Generally speaking, the phosphorus content is higher than the boron content for N-type polysilicon, and vice versa for P-type polysilicon. However, their content must be very low, generally reaching ppb level (i.e. 10 -9 ) can meet the requirements of solar grade or electronic grade.

[0003] Carbon is an interstitial impurity in polysilicon, reducing its crystallinity and purity, affecting its optical and electrical properties. Furthermore, carbon acts as a nucleation center for oxygen atoms, promoting oxygen precipitation. Excessive oxygen precipitation can lead to lattice dislocation, ultimately significantly shortening the lifespan of polysilicon products.

[0004] As a fundamental raw material for polysilicon, the impurity content of trichlorosilane directly impacts the quality of the resulting polysilicon. Boron chloride, phosphorus chloride, and phosphorus oxychloride in trichlorosilane are the primary sources of boron and phosphorus impurities in polysilicon. Methyldichlorosilane, a significant source of carbon impurities in polysilicon, has a boiling point of 41.9°C and a relative volatility of only 1.16 compared to trichlorosilane. Conventional distillation is difficult to remove, requiring significant energy and equipment investment.

[0005] Traditional trichlorosilane purification processes often use a multi-stage distillation tower series process. First, multiple distillation towers are used to perform a rough separation of the trichlorosilane raw material. Then, the trichlorosilane obtained from the rough separation is further removed from light and heavy impurities to obtain a high-purity trichlorosilane product. The entire purification process usually includes 4 to 6 conventional distillation towers depending on the processing volume and the level of impurities.

[0006] The traditional trichlorosilane purification process can only remove some impurities with a relatively high volatility compared to trichlorosilane, and has poor removal ability for trace impurities such as boron, phosphorus, and carbon. In addition, the traditional trichlorosilane purification process has defects such as high energy consumption, large investment, and poor anti-interference ability, which cannot meet the current needs of energy conservation and consumption reduction.

[0007] Patent (CN 212467169 U) discloses a distillation recovery unit comprising a light-removal column, a first heavy-removal column, and a second heavy-removal column. The light-removal column, the first heavy-removal column, and the second heavy-removal column are connected in series, and the first heavy-removal column and the second heavy-removal column are connected in parallel. This improves the trichlorosilane purification capacity and output of the recovery distillation unit to a certain extent. Compared to the novel trichlorosilane distillation process proposed in this patent, this patent has higher energy consumption and poor impurity removal.

[0008] Dividing Wall Columns (DWCs) are a promising energy-saving device for the chemical industry. By placing a vertical baffle within a traditional distillation column, they can save up to 30% in investment and 40% in energy consumption, making them a promising device for energy conservation in the chemical industry. Furthermore, DWCs effectively prevent internal component backmixing, improving thermodynamic efficiency and reducing effective energy loss.

[0009] Reactive distillation (RD) combines chemical reaction and distillation separation to improve the conversion rate and yield of the reaction, thereby reducing investment and significantly reducing operating energy consumption.

[0010] Pressure-Swing Thermally Coupled Distillation (PSTCD) refers to a technology that adjusts the operating pressure of a distillation column to match the condenser and reboiler loads between two or more distillation columns, thereby achieving heat exchange between column equipment and reducing energy consumption. Summary of the Invention

[0011] In order to solve the problem that the trichlorosilane purification process in the prior art has poor removal ability of trace impurities such as boron, phosphorus and carbon, while further reducing energy consumption and equipment investment, the present invention provides a novel trichlorosilane distillation process.

[0012] This process applies two integrated energy-saving technologies, namely reactive distillation process intensification technology and baffle distillation tower and differential pressure thermal coupling distillation, to the trichlorosilane purification process. While achieving high-purity separation of trichlorosilane, it has the significant advantages of low investment and low energy consumption, greatly improving the competitiveness of polysilicon products.

[0013] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions.

[0014] A novel trichlorosilane distillation process comprises a first-stage baffle distillation tower, a second-stage reactive distillation tower, and a third-stage baffle distillation tower connected in series. The process is characterized by comprising the following steps:

[0015] A. Trichlorosilane raw material enters the middle of the primary baffle distillation tower, the distillate from the tower flows into the upper part of the secondary reactive distillation tower, the side-line silicon tetrachloride flows into the silicon tetrachloride product storage tank, and the bottom liquid flows into the heavy component impurity storage tank;

[0016] B. Chlorine enters the middle of the secondary reactive distillation tower, the vapor phase at the top of the tower goes to the tail gas treatment section, and the bottom liquid enters the middle of the tertiary partition distillation tower;

[0017] C. The distillate from the top of the three-stage partition distillation tower flows into the low-boiling storage tank, the high-purity trichlorosilane from the side line flows into the trichlorosilane product storage tank, and the bottom liquid of the tower flows into the high-boiling storage tank.

[0018] The first-stage partition plate distillation tower and the third-stage partition plate distillation tower can use packing, tower tray or a packing-tower tray composite form. The second-stage reaction distillation tower uses tower tray, wherein the packing is high-efficiency plate corrugated packing or double-layer wire mesh packing, and the tower tray is a sieve plate tray, a fixed valve tray or a floating valve tray.

[0019] The primary baffled distillation tower has a common distillation section height of 4 to 20 meters, a baffle section height of 10 to 40 meters, and a common stripping section height of 4 to 15 meters. The tower body is made of carbon steel, and the tower internals are made of 304 stainless steel. The reflux-feed ratio is 0.5:2 to 1, the operating temperature is 75 to 140°C, and the operating pressure is 0.4 to 0.5 MPa. The primary baffled distillation tower can produce a silicon tetrachloride product with a purity of 99% to 99.9% from the side stream, and remove heavy impurities in the silicon tetrachloride from the bottom of the tower.

[0020] The secondary reactive distillation tower has a rectifying section height of 2 to 5 meters, a reaction section height of 5 to 10 meters, and a stripping section height of 8 to 15 meters. The rectifying and stripping sections are constructed of a composite material of carbon steel and stainless steel, the reaction section is constructed of organic glass, and the tower internals are constructed of 316L stainless steel. The tower operates at a reflux ratio of 40 to 120:1, an operating temperature of -15 to 80°C, and an operating pressure of 0.15 to 0.25 MPa. The secondary reactive distillation tower removes exhaust gas generated by the reaction from the top of the tower.

[0021] The three-stage baffled distillation tower has a common distillation section height of 10 to 20 meters, a baffle section height of 15 to 30 meters, and a common stripping section height of 5 to 10 meters. The tower body is made of a carbon steel and stainless steel composite material, and the tower internals are made of 316L stainless steel. The reflux feed ratio is 3:6 to 1, the operating temperature is 30 to 85°C, and the operating pressure is 0.1 to 0.25 MPag. The three-stage baffled distillation tower removes low-boiling and high-boiling substances from trichlorosilane, and a high-purity trichlorosilane product with a boron and phosphorus content of 0.1 to 0.01 ppbw (6N to 9N) is obtained in the side line. The boron and phosphorus content is 0.1 to 0.01 ppbw, and the carbon impurity content is less than 0.1 ppmw. The quality of the obtained trichlorosilane product meets the production requirements of electronic-grade secondary polysilicon and above.

[0022] The novel trichlorosilane distillation process introduces differential pressure thermal coupling technology, which increases the operating pressure of the first-stage baffle distillation tower to improve the "grade" of the top steam, and uses it as a heat source to exchange heat with the liquid phase in the bottom of the third-stage baffle distillation tower, thereby reducing energy consumption in the trichlorosilane distillation process.

[0023] The difference between the top steam temperature of the first-stage partition distillation tower and the bottom liquid temperature of the third-stage partition distillation tower must be greater than 15°C.

[0024] The free radical rearrangement reaction involved in the secondary reactive distillation tower is:

[0025]

[0026] Cl2 acts as a chlorine radical donor, and methyldichlorosilane reacts with chlorine to produce methyltrichlorosilane (boiling point 66.4°C) through photochlorination. This reaction selectively converts the low-boiling-point methyldichlorosilane in trichlorosilane into the high-boiling-point methyltrichlorosilane through photochlorination, which is then removed.

[0027] The ratio of methyldichlorosilane to chlorine in the raw materials of the secondary reaction distillation tower is 1:3-8, the reaction temperature is 50-80°C, the ultraviolet wavelength is 300-450nm, and the reaction time is 20-30s. Under these conditions, the conversion rate of methyldichlorosilane can reach 99%-99.99%.

[0028] When the production scale is expanded, in order to facilitate operation, the first-stage baffle distillation tower, the second-stage reaction distillation tower, and the third-stage baffle distillation tower can be designed as two towers or multiple towers. In the multiple-tower situation, the operating pressure of the first-stage baffle distillation tower can be changed to facilitate thermal coupling and reduce energy consumption.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] This process innovatively integrates two energy-saving technologies, reactive distillation process intensification and baffled distillation towers and differential pressure thermally coupled distillation, into the trichlorosilane purification process, enhancing the separation strength of each distillation tower. Compared to traditional trichlorosilane distillation processes, this process offers lower energy consumption and investment, and effectively removes impurities such as boron, phosphorus, and carbon from trichlorosilane, ensuring that the trichlorosilane product quality meets the requirements for the production of electronic-grade Class II polysilicon and above. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The present invention will be further described below with reference to the accompanying drawings:

[0032] Attachment Figure 1 Schematic diagram of the novel trichlorosilane distillation process according to the present invention, wherein:

[0033] 1. First-stage baffle distillation tower, 2. Second-stage reactive distillation tower, 3. Third-stage baffle distillation tower. DETAILED DESCRIPTION

[0034] To make the objectives, technical solutions and advantages of the present invention more clearly understood, the method of the present invention is described below with reference to the accompanying drawings and specific embodiments, but the accompanying drawings and specific embodiments do not constitute a limitation to the present invention.

[0035] Example 1:

[0036] The mixed raw materials for the trichlorosilane distillation process in Example 1 come from a cold hydrogenation reactor. Table 1 shows the feed composition, and the feed flow rate is 180,000 kg / h:

[0037]

[0038] A novel trichlorosilane distillation process comprises a first-stage baffle distillation tower 1, a second-stage reactive distillation tower 2 and a third-stage baffle distillation tower 3 which are sequentially connected in series.

[0039] A. Trichlorosilane feedstock enters the middle of the primary baffled distillation tower 1, the overhead distillate flows into the upper part of the secondary reactive distillation tower 2, the side-line silicon tetrachloride flows into the silicon tetrachloride product storage tank, and the tower bottom liquid flows into the heavy component impurity storage tank;

[0040] B. Chlorine enters the middle of the secondary reactive distillation tower 2, the vapor phase at the top of the tower goes to the tail gas treatment section, and the bottom liquid enters the middle of the tertiary partition distillation tower 3;

[0041] C. The distillate from the top of the three-stage partition distillation tower 3 flows into the low-boiling storage tank, the high-purity trichlorosilane from the side line flows into the trichlorosilane product storage tank, and the bottom liquid of the tower flows into the high-boiling storage tank.

[0042] The primary baffled distillation tower 1 utilizes three 5-meter sections of high-efficiency structured corrugated packing in the common distillation section, 50 fixed-valve trays in the baffle section, and 10 fixed-valve trays in the common stripping section. The tower body is constructed of carbon steel, and the tower internals are constructed of 304 stainless steel. The reflux-feed ratio is 1.18:1, the operating pressure is 0.45 MPaig, the tower top operating temperature is 90.4°C, and the reboiler temperature is 127°C. The primary baffled distillation tower 1 can produce a silicon tetrachloride product with a purity of 99.9% by weight from a side stream, and heavy impurities in the silicon tetrachloride are removed from the bottom of the tower.

[0043] The secondary reactive distillation tower 2 utilizes 50 sieve trays, with the rectifying and stripping sections constructed of a composite material of carbon steel and stainless steel. The reaction section utilizes organic glass, and the tower internals utilize 316L stainless steel. The tower has a reflux ratio of 60:1, an operating pressure of 0.2 MPa, a top operating temperature of -10°C, and a reboiler temperature of 67.6°C. The secondary reactive distillation tower 2 removes the tail gas generated by the reaction from the top of the tower.

[0044] The three-stage baffled distillation tower 3 uses three 5-meter sections of high-efficiency structured corrugated packing in the common distillation section, four 5-meter sections of high-efficiency structured corrugated packing in the baffle section, and one 5-meter section of high-efficiency structured corrugated packing in the common stripping section. The tower body is made of carbon steel, and the tower internals are made of 316L stainless steel. The reflux-feed ratio is 4.84:1, the operating pressure is 0.2 MPag, the tower top operating temperature is 41.3°C, and the reboiler temperature is 73.5°C. The three-stage baffled distillation tower 3 removes low-boiling and high-boiling substances from trichlorosilane, and a high-purity trichlorosilane product of 99.99999% (7N) is obtained in the side stream. The boron and phosphorus impurity contents are 0.098 ppbw, and the carbon impurity content is 0.0032 ppmw. The quality of the resulting trichlorosilane product meets the production requirements of electronic-grade Class II polysilicon and above.

[0045] The novel trichlorosilane distillation process introduces differential pressure thermal coupling technology. By increasing the operating pressure of the first-stage baffle distillation tower 1 to 0.45 MPag, the "grade" of the overhead steam is improved, and the overhead steam is used as a heat source to exchange heat with the liquid phase in the bottom of the third-stage baffle distillation tower 3, thereby reducing energy consumption during the trichlorosilane distillation process.

[0046] The difference between the top steam temperature of the first-stage partition plate distillation tower 1 and the bottom liquid temperature of the third-stage partition plate distillation tower 3 is 16.9°C.

[0047] The ratio of methyldichlorosilane to chlorine in the raw materials of the secondary reaction distillation tower 2 is 1:5, the reaction temperature is 59-64° C., the ultraviolet wavelength is 365 nm, the reaction time is 25 seconds, and the conversion rate of methyldichlorosilane can reach 99.99%.

[0048] The 0.4 MPa steam consumption of the novel trichlorosilane distillation process from the cold hydrogenation reactor feed described in Example 1 is 0.56 t (steam) / t (TCS).

[0049] Example 2:

[0050] The similarities between the distillation process provided in this embodiment and the distillation process provided in Example 1 are not described in detail here, and only the differences from Example 1 are described here. The differences between the distillation process provided in this embodiment and the distillation process provided in Example 1 are:

[0051] The mixed raw materials for the trichlorosilane distillation process in Example 2 come from the synthesis reactor. Table 2 shows the feed composition, and the feed flow rate is 5812.5 kg / h:

[0052]

[0053] The primary baffled distillation tower 1 utilizes a 4-meter high-efficiency structured corrugated packing in the public distillation section, 60 fixed-valve trays in the baffle section, and 20 fixed-valve trays in the public stripping section. The tower body is constructed of carbon steel, and the tower internals are constructed of 304 stainless steel. The reflux-to-feed ratio is 1.94:1, the operating pressure is 0.5 MPaig, the tower top operating temperature is 94.9°C, and the reboiler temperature is 136.5°C. The primary baffled distillation tower 1 can produce a silicon tetrachloride product with a purity of 99.1 wt% from a side stream, and heavy impurities in the silicon tetrachloride are removed from the bottom of the tower.

[0054] The secondary reactive distillation tower 2 utilizes 50 sieve trays, with the rectifying and stripping sections constructed of a composite material of carbon steel and stainless steel. The reaction section utilizes organic glass, and the tower internals utilize 316L stainless steel. The tower has a reflux ratio of 107:1, an operating pressure of 0.2 MPa, a top operating temperature of 47.5°C, and a reboiler temperature of 68.5°C. The secondary reactive distillation tower 2 removes the tail gas generated by the reaction from the top of the tower.

[0055] The three-stage baffled distillation tower 3 uses two 5-meter sections of high-efficiency structured corrugated packing in the common distillation section, five 5-meter sections of high-efficiency structured corrugated packing in the baffle section, and one 5-meter section of high-efficiency structured corrugated packing in the common stripping section. The tower body is made of carbon steel, and the tower internals are made of 316L stainless steel. The reflux-feed ratio is 3.02:1, the operating pressure is 0.15 MPa, the tower top operating temperature is 60.6°C, and the reboiler temperature is 79.8°C. The three-stage baffled distillation tower 3 removes low-boiling and high-boiling substances from trichlorosilane, and a high-purity trichlorosilane product of 99.999999% (8N) is obtained in the side stream. The boron and phosphorus impurity contents are 0.043 ppbw, and the carbon impurity content is 0.0005 ppmw. The quality of the resulting trichlorosilane product meets the production requirements of electronic-grade secondary polysilicon and above.

[0056] The novel trichlorosilane distillation process introduces differential pressure thermal coupling technology. By increasing the operating pressure of the first-stage baffle distillation tower 1 to 0.5 MPag, the "grade" of the overhead steam is improved, and the overhead steam is used as a heat source to exchange heat with the liquid phase in the bottom of the third-stage baffle distillation tower 3, thereby reducing energy consumption during the trichlorosilane distillation process.

[0057] The difference between the top steam temperature of the first-stage partition plate distillation tower 1 and the bottom liquid temperature of the third-stage partition plate distillation tower 3 is 15.1°C.

[0058] The ratio of methyldichlorosilane to chlorine in the raw materials of the secondary reaction distillation tower 2 is 1:5.6, the reaction temperature is 67.3-67.5° C., the ultraviolet wavelength is 365 nm, the reaction time is 25 seconds, and the conversion rate of methyldichlorosilane can reach 99.9%.

[0059] The unit steam consumption at 0.4 MPa for the novel trichlorosilane distillation process from the feed of the synthesis reactor described in Example 2 is 0.272 t (steam) / t (TCS).

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A novel trichlorosilane distillation process comprises a first-stage baffled distillation tower, a second-stage reactive distillation tower, and a third-stage baffled distillation tower connected in series. The process increases the operating pressure of the first-stage baffled distillation tower to improve the "grade" of the overhead vapor, which serves as a heat source for heat exchange with the bottom liquid of the third-stage baffled distillation tower, thereby reducing energy consumption during the trichlorosilane distillation process. The process is characterized by: The steps include: A. Trichlorosilane raw material enters the middle of the primary baffle distillation tower, the distillate from the tower flows into the upper part of the secondary reactive distillation tower, the side-line silicon tetrachloride flows into the silicon tetrachloride product storage tank, and the bottom liquid flows into the heavy component impurity storage tank; B. Chlorine is introduced into the middle of the secondary reaction distillation tower, and a photochlorination reaction of methyldichlorosilane and chlorine occurs in the tower; the vapor phase at the top of the tower is sent to the tail gas treatment section, and the bottom liquid of the tower flows into the middle of the three-stage partition distillation tower; C. The distillate from the top of the three-stage partition distillation tower flows into the low-boiling storage tank, the high-purity trichlorosilane from the side line flows into the trichlorosilane product storage tank, and the bottom liquid of the tower flows into the high-boiling storage tank.

2. A novel trichlorosilane distillation process according to claim 1, characterized in that: The first-stage partition plate distillation tower and the third-stage partition plate distillation tower can use packing, tower tray or a packing-tower tray composite form. The second-stage reaction distillation tower uses tower tray, wherein the packing is high-efficiency plate corrugated packing or double-layer wire mesh packing, and the tower tray is a sieve plate tray, a fixed valve tray or a floating valve tray.

3. A novel trichlorosilane distillation process according to claim 1, characterized in that: The first-stage baffle distillation tower has a common distillation section height of 4-20 m, a baffle section height of 10-40 m, and a common stripping section height of 4-15 m. The tower body is made of carbon steel, the tower internals are made of 304 stainless steel, the reflux-feed ratio is 0.5:2-1, the operating temperature is 75-140° C., and the operating pressure is 0.4-0.5 MPa. The first-stage baffle distillation tower can obtain a silicon tetrachloride product with a purity of 99%-99.9% from a side line, and remove heavy component impurities in the silicon tetrachloride from the tower bottom.

4. A novel trichlorosilane distillation process according to claim 1, characterized in that: The distillation section height of the secondary reaction distillation tower is 2-5m, the reaction section height is 5-10m, and the stripping section height is 8-15m. The tower bodies of the distillation section and the stripping section are made of carbon steel and stainless steel composite materials, the reaction section is made of organic glass material, the tower internals are made of 316L stainless steel, the reflux ratio is 40-120:1, the operating temperature is -15-80°C, and the operating pressure is 0.15-0.25MPag. The secondary reaction distillation tower can remove the tail gas generated by the reaction from the top of the tower.

5. A novel trichlorosilane distillation process according to claim 1, characterized in that: The three-stage baffle distillation tower has a common distillation section height of 10-20 m, a baffle section height of 15-30 m, and a common stripping section height of 5-10 m. The tower body is made of a composite material of carbon steel and stainless steel, the tower internals are made of 316L stainless steel, the reflux-feed ratio is 3:6-1, the operating temperature is 30-85° C., and the operating pressure is 0.1-0.25 MPag. The three-stage baffle distillation tower removes low-boiling and high-boiling substances from trichlorosilane, and a high-purity trichlorosilane product with a purity of 99.9999%-99.9999999% (6N-9N) can be obtained in a side line. The boron and phosphorus contents are 0.1-0.01 ppbw, and the carbon impurity content is less than 0.1 ppmw. The quality of the obtained trichlorosilane product meets the preparation requirements of electronic-grade secondary polysilicon and above.

6. A novel trichlorosilane distillation process according to claim 1, characterized in that: The difference between the top steam temperature of the first-stage partition distillation tower and the bottom liquid temperature of the third-stage partition distillation tower must be greater than 15°C.

7. A novel trichlorosilane distillation process according to claim 1, characterized in that: The ratio of methyldichlorosilane to chlorine in the raw materials of the secondary reaction distillation tower is 1:3-8, the reaction temperature is 50-80°C, the ultraviolet wavelength is 300-450nm, and the reaction time is 20-30s. Under these conditions, the conversion rate of methyldichlorosilane can reach 99%-99.99%.

8. A novel trichlorosilane distillation process according to claim 1, characterized in that: When the production scale is expanded, in order to facilitate operation, the first-stage baffle distillation tower, the second-stage reaction distillation tower, and the third-stage baffle distillation tower can be designed as two towers or multiple towers. In the multiple-tower situation, the operating pressure of the first-stage baffle distillation tower can be changed to facilitate thermal coupling and reduce energy consumption.

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