Trichlorosilane synthesis tail gas pressure swing adsorption recovery system and method

Abstract

The application discloses a trichlorosilane synthesis tail gas pressure swing adsorption recovery system and method, wherein the recovery system is used for adsorbing and regenerating hydrogen chloride / chlorosilane and nitrogen / hydrogen through two adsorption units respectively, and high-purity hydrogen is obtained at the tail; the adsorption unit comprises at least two adsorption towers, pressure balance between the towers is realized, and the desorption is realized through power provided by a vacuum pump, thereby realizing the recovery and utilization of two mixed gases and high-purity hydrogen, and improving the economic value of tail gas by-product recovery and utilization.

Description

Technical Field

[0001] This invention relates to the field of gas recovery technology, specifically to a pressure swing adsorption system and method for recovering trichlorosilane synthesis tail gas. Background Technology

[0002] The tail gas from the synthesis of trichlorosilane contains a large amount of mixed gases such as hydrogen chloride, chlorosilane, hydrogen, and nitrogen. Traditional treatment methods involve absorbing the tail gas with water or alkali before discharging it into the atmosphere, or simply compressing and condensing it for reuse, or using adsorption and condensation systems for reuse. These methods either generate a lot of wastewater during treatment, putting significant pressure on environmental protection, or fail to fully recover and reuse the gas, causing a vicious cycle of impurities within the system, resulting in low efficiency of the trichlorosilane synthesis system.

[0003] Patent document CN207745676U discloses a system for recovering and treating the tail gas from the synthesis of trichlorosilane. The system involves a first-stage adsorption treatment of the tail gas, where the desorbed hydrogen chloride and chlorosilanes are condensed and reused. Hydrogen and nitrogen then enter a second-stage adsorption stage, with the nitrogen and hydrogen chloride being emitted into the air. The hydrogen is then pressurized and reused, achieving a purity of 99.9%. This method preheats the raw gas and then uses multi-stage pressure selective adsorption. The condensation of the desorbed chlorosilanes results in high energy consumption, and the emitted nitrogen and chlorosilane gases pose environmental problems.

[0004] Therefore, it is necessary to propose a pressure swing adsorption recovery system for trichlorosilane synthesis tail gas to solve the problems of high energy consumption and incomplete recovery in the existing trichlorosilane synthesis tail gas adsorption and recovery technology. Summary of the Invention

[0005] This invention provides a pressure swing adsorption (PSA) recovery system and method for trichlorosilane synthesis tail gas, which solves the problems of high energy consumption and incomplete recovery in the adsorption and recovery of trichlorosilane synthesis tail gas in the prior art.

[0006] To achieve the above objectives, the present invention provides the following solution:

[0007] A pressure swing adsorption (PSA) recovery system for trichlorosilane synthesis tail gas includes a feed pipe, a first recovery section, and a second recovery section; wherein:

[0008] The first recovery section includes a first adsorption unit and a first recovery unit; the second recovery section includes a second adsorption unit, a second recovery unit, and a third recovery unit;

[0009] The feed pipe and the first recovery unit are respectively connected to the feed end of the first adsorption unit; the discharge end of the first adsorption unit and the feed end of the second recovery unit are respectively connected to the feed end of the second adsorption unit; the third recovery unit is connected to the discharge end of the second adsorption unit; the first adsorption unit and the second adsorption unit are each equipped with at least two adsorption towers connected in parallel; the first recovery unit and the second recovery unit are each equipped with a vacuum pump.

[0010] The first adsorption unit is used to adsorb hydrogen chloride and chlorosilane, and the second adsorption unit is used to adsorb nitrogen and hydrogen.

[0011] Furthermore, both the first adsorption unit and the second adsorption unit are provided with three or more adsorption towers connected in parallel.

[0012] Furthermore, the feed end of the second adsorption unit is equipped with a deoxygenator.

[0013] Preferably, the feed end of the second adsorption unit is further provided with a heat exchanger; the feed end and discharge end of the deoxidizer correspond to the medium channel and material channel connected to the heat exchanger, respectively.

[0014] Furthermore, the feed end of the second adsorption unit is provided with a condenser and a gas-liquid separator connected together, and the gas phase discharge end of the gas-liquid separator is connected to the feed end of the second adsorption unit.

[0015] Furthermore, the first recycling section also includes a first circulation pipe connected in parallel with the first recycling unit; the discharge end of the first circulation pipe is connected to the feed pipe, and a compressor is provided on the first circulation pipe.

[0016] Furthermore, the second recovery section also includes a second circulation pipe connected in parallel with the second recovery unit; the discharge end of the second circulation pipe is connected to the discharge end of the first adsorption unit, and a compressor is provided on the second circulation pipe.

[0017] Furthermore, the first recovery unit is equipped with two condensers at the output end of the vacuum pump, and a compressor is located between the condensers.

[0018] Another objective of this invention is to provide a method for recovering trichlorosilane synthesis tail gas via pressure swing adsorption, comprising the following steps:

[0019] S1. The tail gas from the synthesis of trichlorosilane is discharged after being adsorbed by hydrogen chloride and chlorosilane in the first adsorption unit;

[0020] S2. In step S1, the tail gas obtained is adsorbed by nitrogen and hydrogen in the second adsorption unit, and high-purity hydrogen is discharged.

[0021] The first adsorption unit and the second adsorption unit are each provided with at least two adsorption towers connected in parallel;

[0022] In step S1, hydrogen chloride and chlorosilane are adsorbed and then subjected to pressure equalization and desorption to obtain hydrogen chloride and chlorosilane. The desorption process is powered by a vacuum pump.

[0023] After adsorbing nitrogen and hydrogen in step S2, nitrogen and hydrogen are obtained by equalization and desorption. The desorption process is powered by a vacuum pump.

[0024] Furthermore, in step S2, oxygen is first removed, and then the liquid phase is removed by condensation, while the gaseous components enter the second adsorption unit for adsorption.

[0025] Compared with the prior art, the beneficial effects of the present invention include, but are not limited to:

[0026] 1. The trichlorosilane synthesis tail gas adsorption unit provided by the present invention uses parallel absorption towers to achieve pressure equalization, combined with a vacuum pump to provide desorption power, thereby reducing energy consumption; and through multi-stage absorption, the trichlorosilane synthesis tail gas is separated into a hydrogen chloride / chlorosilane mixture, a hydrogen-nitrogen mixture, and high-purity hydrogen, thereby achieving full recovery and utilization of the tail gas and improving the economic value of tail gas by-product recovery and utilization.

[0027] 2. The trichlorosilane synthesis tail gas adsorption and recovery system provided by this invention can improve the adsorption utilization rate by setting up a circulation system, and the high-purity hydrogen yield can reach more than 85%. In addition, by first adsorbing hydrogen chloride / chlorosilane, removing oxygen, and then adsorbing hydrogen-nitrogen mixture, the purity of hydrogen chloride / chlorosilane can reach 99%, and the content of hydrogen chloride / chlorosilane in hydrogen-nitrogen mixture is less than 15 ppm, which can be used for the resynthesis of trichlorosilane. The purity of high-purity hydrogen can reach 5N and above, which can maximize the utilization of by-products. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the pressure swing adsorption recovery system for the trichlorosilane synthesis tail gas described in this invention.

[0029] The markings in the diagram are as follows: 10, Feed pipe; 11, Circulation pipe one; 12, Desorption pipe one; 20, Tail gas output pipe; 21, Deoxygenated feed pipe; 22, Deoxygenated discharge pipe; 23, Gas phase output pipe; 24, Circulation pipe two; 25, Desorption pipe two; 100, First recovery unit; 200, Second recovery unit; 300, Third recovery unit; E1, Heat exchanger; E2, Condenser one; E3, Condenser two; E4, Condenser three; F1, Valve one; F2, Valve two; F3, Valve three; F4, Valve four; F5, Valve five; F6, Valve six; P1 Compressor 1, Compressor 2; Compressor 3, Compressor 4; Compressor 5; Compressor 6; R1, Deaerator; T1, First Adsorption Unit; T2, Second Adsorption Unit; V1, Buffer Tank 1; V2, Buffer Tank 2; V3, Buffer Tank 3; V4, Buffer Tank 4; V5, Buffer Tank 5; V6, Buffer Tank 6; V7, Buffer Tank 7; V8, Buffer Tank 8; V9, Buffer Tank 9; V10, Buffer Tank 10; V11, Buffer Tank 11; VP1, Vacuum Pump 1; VP2, Vacuum Pump 2; X1, Gas-Liquid Separator. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] It should be understood that the terms "upper", "lower", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention.

[0032] It should also be noted that, unless otherwise explicitly specified and limited, terms such as "connected," "connected," and "set up" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two components or the interaction between two components. The terms "a," "b," "c," etc., are only for the convenience of distinguishing similar or identical elements and do not imply a specific order or numbering. These terms should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms in the present invention can be understood according to the specific circumstances.

[0033] In the following embodiments, the composition and volume percentage of the trichlorosilane synthesis tail gas are as follows: 50-60% hydrogen, 10-15% hydrogen chloride, 10-15% nitrogen, and the balance being chlorosilane.

[0034] like Figure 1 As shown, in one embodiment, a pressure swing adsorption (PSA) recovery system for trichlorosilane synthesis tail gas is provided, comprising a connected feed pipe 10, a first recovery section, and a second recovery section; wherein:

[0035] The first recovery section includes a first adsorption unit T1 and a first recovery unit 100; the second recovery section includes a second adsorption unit T2, a second recovery unit 200 and a third recovery unit 300; the first adsorption unit T1 is used to adsorb hydrogen chloride and chlorosilane, and the second adsorption unit T2 is used to adsorb nitrogen and hydrogen.

[0036] Specifically, the left end of the feed pipe 10 is connected to the buffer tank V1, and the right end is connected to the bottom of the first adsorption unit T1. The feed pipe 10 has a valve F1. The bottom of the first adsorption unit T1 is provided with a desorption pipe 12 connected to the first recovery unit 100. The desorption pipe 12 is provided with a valve F2. The first recovery unit 100 includes a buffer tank V6, a vacuum pump VP1, and a buffer tank V8 arranged in sequence.

[0037] The top exhaust outlet of the first adsorption unit T1 is connected to the bottom of the second adsorption unit T2. The bottom of the second adsorption unit T2 is provided with a desorption pipe 25 connected to the second recovery unit 200. A valve 6F6 is provided on the desorption pipe 25. The second recovery unit 200 includes a buffer tank 10V10, a vacuum pump 2VP2, a buffer tank 11V11, and a compressor 6P6 connected in sequence.

[0038] The top exhaust outlet of the second adsorption unit T2 is connected to the third recovery unit 300, which includes buffer tank four V4, compressor two P2 and buffer tank five V5 connected in sequence.

[0039] In the above embodiments, the first adsorption unit T1 and the second adsorption unit T2 are each equipped with two or more adsorption towers connected in parallel to facilitate adsorption / desorption and pressure equalization. The first recovery unit 100 is equipped with a vacuum pump VP1, and the second recovery unit 200 is equipped with a vacuum pump VP2, which are used to provide desorption power. Specifically, after the trichlorosilane synthesis tail gas enters the system through the feed pipe 10, it is adsorbed by hydrogen chloride and chlorosilane in one absorption tower of the first adsorption unit T1. The remaining unadsorbed gas enters the second adsorption unit T2. During this process, after one absorption tower in the first adsorption unit T1 adsorbs hydrogen chloride and chlorosilane to saturation, it releases pressure to the other parallel adsorption towers to achieve pressure equalization. When the pressure drops to a certain range, valve F2 is opened, and vacuum pump VP1 is started to provide desorption power. The hydrogen chloride and chlorosilane adsorbed in the first adsorption unit T1 enter the first recovery unit 100 under negative pressure to obtain hydrogen chloride and chlorosilane. Unadsorbed gas from the outlet of the first adsorption unit T1 enters the second adsorption unit T2. One absorption tower adsorbs nitrogen and hydrogen. The remaining unadsorbed gas enters the third recovery unit 300 to obtain high-purity hydrogen. After adsorption to a certain pressure in the second adsorption unit T2, the pressure is released to the other parallel towers. Then, valve F6 is opened, and vacuum pump VP2 is started to desorb and obtain nitrogen and hydrogen.

[0040] In the above embodiments, the recovery system separates the trichlorosilane synthesis tail gas into a hydrogen chloride / chlorosilane mixture, a hydrogen-nitrogen mixture, and high-purity hydrogen through multiple processes, achieving full recovery and utilization of the tail gas. Specifically, the hydrogen chloride / chlorosilane mixture can be used for the resynthesis of trichlorosilane, the hydrogen-nitrogen mixture can be used for ammonia synthesis, and the high-purity hydrogen can be output as a single product, maximizing the utilization of tail gas byproducts.

[0041] In the above embodiments, the first adsorption unit T1 is filled with a common 15A molecular sieve adsorbent for adsorbing hydrogen chloride and chlorosilanes; the second adsorption unit T2 is filled with a common 3A molecular sieve adsorbent for adsorbing nitrogen and hydrogen. Specifically, the molecular sieves mentioned above are all molecular sieves synthesized from aluminosilicate composites.

[0042] In a preferred embodiment, in order to improve adsorption and regeneration efficiency, the first adsorption unit T1 and the second adsorption unit T2 preferably have three or more absorption towers connected in parallel, and are provided with a pressure equalization channel and a desorption channel (not shown in the figure) connected to the first recovery unit 100; so that at least one absorption tower is in the absorption state, at least one absorption tower is in the desorption and regeneration state, and at least one tower is used for pressure equalization operation.

[0043] In a preferred embodiment, to improve gas purity, a deoxygenation and liquid phase removal device is also provided. Specifically, the top output pipeline of the first adsorption unit T1 is sequentially connected to buffer tank two V2, compressor one P1, and buffer tank three V3; the top of buffer tank three V3 is connected to the tube-side input end of heat exchanger E1, the tube-side output end of heat exchanger E1 is connected to deoxygenator R1, the output end of deoxygenator R1 is connected to the shell-side input end of heat exchanger E1, the shell-side output end of E1 is connected to condenser one E1, gas-liquid separator X1, and valve four F4, and further connected to the feed end of the second adsorption unit T2. On the one hand, the gas output from the top of the first adsorption unit T1 undergoes self-heating after deoxygenation by heat exchanger E1 and deoxygenator R1, removing oxygen and carbon dioxide while reducing energy consumption; on the other hand, the purity of the mixed gas is improved after condensation by condenser one E1.

[0044] In the above embodiments, the deaerator R1 is a common catalytic deaerator, whose main component is palladium metal catalyst, which can reduce oxygen and carbon dioxide to below 3 ppm.

[0045] In a preferred embodiment, the bottom of the first adsorption unit T1 is further provided with a circulation pipe 11 connected to a buffer tank 1V1. The circulation pipe 11 is equipped with a valve 3F3, a buffer tank 9V9, and a compressor 5P5. When the pressure in the first adsorption unit T1 is equalized to a certain level (e.g., 2 bar), some gas is re-entered into the buffer tank 1V1 through the circulation pipe 11 for re-absorption, thereby improving adsorption efficiency. Similarly, the bottom of the second adsorption unit T2 is further provided with a circulation pipe 24 connected to a buffer tank 3V3. The circulation pipe 24 is equipped with a valve 5F5 and a compressor 3P3. When the pressure in the second adsorption unit T2 is equalized, some gas is re-entered into the buffer tank 3V3 through the circulation pipe 24 for re-absorption. The high-purity hydrogen produced by this system can achieve a yield of over 85%, demonstrating a significant increase in product added value.

[0046] In a preferred embodiment, the first recovery unit 100 further includes a buffer tank V7, a condenser E3, a compressor P4, and a condenser E4 disposed at the output end of the vacuum pump VP1. The gas exiting the vacuum pump VP1 generates heat, which is condensed and cooled by the condenser E3. After being compressed by the compressor P4 and condensed by the condenser E4, a hydrogen chloride / chlorosilane mixture is obtained, and the nitrogen and hydrogen impurity content can be reduced to below 1%.

[0047] In the above embodiments, under any operating condition, at least one tower in the first adsorption unit T1 and the second adsorption unit T2 is in the adsorption process, while the other towers are in regeneration and pressure equalization. Taking the second adsorption unit T2 as an example, when the gas enters the first adsorption tower through valve four F4 and becomes saturated, the pressure is released to the other towers through the inter-tower valve (not shown in the figure). After the pressure reaches 6 bar, the pressure in the first adsorption tower is released through valve five F5 to the compressor three P3 for pressurization, and then partially circulated back to the buffer tank three V3 to improve the purity and recovery rate of the product hydrogen. When the pressure in the adsorption tower is released to 0 bar, valve five F5 is closed and valve six F6 is opened to release the pressure in the tower to the V0110 buffer tank 10. After the pressure is taken down to -0.8 bar by vacuum pump two VP2, one adsorption cycle ends. The gas exiting vacuum pump VP2 is pressurized by buffer tank XI (V11) and then pressurized to 200 bar by compressor VI (P6). The hydrogen-nitrogen mixture is then loaded into the tube bundle truck and can be transported to the upstream synthetic ammonia plant. The hydrogen chloride and chlorosilane impurities in this hydrogen-nitrogen mixture are as low as 15 ppm. In addition, the residual product gas from the second adsorption unit T2 is pressurized by buffer tank IV (V4) and then pressurized to 200 bar by compressor II (P2). It then enters buffer tank V (P5) and is finally loaded into the high-purity hydrogen tube bundle truck for sale as 5N electronic-grade hydrogen.

[0048] In a comparative embodiment, swapping the order of the first adsorption unit T1 and the second adsorption unit T2 could affect the adsorption effect and the overall operation. The specific reasons are as follows: chlorosilane molecules are the largest; if nitrogen is adsorbed first, it becomes difficult to select a suitable adsorbent, and the nitrogen desorbed gas will contain chlorosilanes, rendering the desorbed gas unusable. Furthermore, the metal catalyst used in the deaerator R1 can be poisoned by hydrogen chloride and chlorosilanes. Therefore, it is necessary to use the first adsorption unit T1 to adsorb hydrogen chloride / chlorosilanes first, followed by the second adsorption unit T2 to adsorb nitrogen / hydrogen, in order to improve the purity of the by-product recovered gas and enhance the reliability of the system operation.

[0049] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A pressure swing adsorption (PSA) recovery system for trichlorosilane synthesis tail gas, characterized in that, Includes a feed pipe (10), a first recovery section, and a second recovery section; wherein: The first recovery section includes a first adsorption unit (T1) and a first recovery unit (100); the second recovery section includes a second adsorption unit (T2), a second recovery unit (200), and a third recovery unit (300). The feed pipe (10) and the first recovery unit (100) are respectively connected to the feed end of the first adsorption unit (T1), the discharge end of the first adsorption unit (T1) and the feed end of the second recovery unit (200) are respectively connected to the feed end of the second adsorption unit (T2), and the third recovery unit (300) is connected to the discharge end of the second adsorption unit (T2); the first adsorption unit (T1) and the second adsorption unit (T2) are respectively provided with at least two or more adsorption towers connected in parallel; the first recovery unit (100) and the second recovery unit (200) are respectively provided with vacuum pumps; The first adsorption unit (T1) is used to adsorb hydrogen chloride and chlorosilane, and the second adsorption unit (T2) is used to adsorb nitrogen and hydrogen. The feed end of the second adsorption unit (T2) is provided with a deoxidizer (R1), a heat exchanger (E1), a condenser (E2), and a gas-liquid separator (X1) connected in sequence; the feed end and the discharge end of the deoxidizer (R1) are respectively connected to the medium channel and the material channel of the heat exchanger (E1); the gas phase discharge end of the gas-liquid separator (X1) is connected to the feed end of the second adsorption unit (T2); The output end of the first adsorption unit (T1) is connected to the medium channel of the heat exchanger (E1) via a buffer tank (V2). The first recycling section also includes a circulation pipe (11) connected in parallel with the first recycling unit (100); the outlet end of the circulation pipe (11) is connected to the feed pipe (10). The second recycling section also includes a second circulation pipe (24) connected in parallel with the second recycling unit (200); the discharge end of the second circulation pipe (24) is connected to the second buffer tank (V2); The first recovery unit (100) includes a buffer tank six (V6), a vacuum pump one (VP1), a condenser two (E3), a compressor four (P4), and a condenser three (E4) connected in series. The second recovery unit (200) includes a buffer tank ten (V10), a vacuum pump two (VP2), and a buffer tank eleven (V11) connected in series.

2. The recycling system according to claim 1, characterized in that, Both the first adsorption unit (T1) and the second adsorption unit (T2) are equipped with three or more adsorption towers connected in parallel.

3. The recycling system according to claim 1, characterized in that, A compressor is provided on the circulation pipe (11).

4. The recycling system according to claim 1, characterized in that, A compressor is provided on the second circulation pipe (24).

5. The method for recovering trichlorosilane synthesis tail gas using the recovery system according to any one of claims 1-4, characterized in that, The steps are as follows: S1. The tail gas from the synthesis of trichlorosilane is discharged after being adsorbed by hydrogen chloride and chlorosilane in the first adsorption unit (T1); S2. The exhaust gas obtained in step S1 is subjected to adsorption of nitrogen and hydrogen in the second adsorption unit (T2), and high-purity hydrogen is discharged. The first adsorption unit (T1) and the second adsorption unit (T2) are each provided with at least two adsorption towers connected in parallel; In step S1, hydrogen chloride and chlorosilane are adsorbed and then subjected to pressure equalization and desorption to obtain hydrogen chloride and chlorosilane. The desorption process is powered by a vacuum pump. After adsorbing nitrogen and hydrogen in step S2, nitrogen and hydrogen are obtained by equalization and desorption. The desorption process is powered by a vacuum pump.

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