System and method for recovering methane chloride from methyl chlorosilane synthesis tail gas

Abstract

The invention provides a system and method for recycling methane chloride from methyl chlorosilane synthesis tail gas. According to the method, 85%-90% of methane chloride in the methyl chlorosilane synthesis tail gas is recycled in a three-stage sectional type condensation mode. 90-95% of residual methane chloride is recovered through directional absorption of dichloromethane; and finally, residual methane chloride is recovered in a decompression analysis and reflux impurity removal mode, the total recovery rate of methane chloride is larger than or equal to 99%, the purity of methane chloride is larger than or equal to 99.5%, waste of methane chloride is greatly reduced, high recovery of methane chloride is achieved, and methane chloride can be directly reused in a methyl chlorosilane synthesis reaction.

Description

Technical Field

[0001] This invention belongs to the field of exhaust gas treatment technology, and relates to a system and method for recovering chloromethane from the exhaust gas of methylchlorosilane synthesis. Background Technology

[0002] Methylchlorosilane is a core monomer in the organosilicon industry. It is mainly prepared by the synthesis reaction of methylchlorosilane using silicon powder and chloromethane as raw materials.

[0003] In the preparation of methylchlorosilanes, chloromethane cannot be completely converted, resulting in tail gas containing small amounts of methylchlorosilane monomers such as dimethyldichlorosilane and trimethylchlorosilane, chloromethane, nitrogen, and hydrogen. Current methods for recovering this tail gas primarily involve single-stage condensation at -20 to -30°C. However, this only recovers approximately 85-90% of the chloromethane, leaving 10-15% emitted as non-condensable gas, resulting in a low recovery rate. Furthermore, the purity of the condensed chloromethane is easily affected by the methylchlorosilane monomers, failing to meet the purity requirement of ≥99.5% for the methylchlorosilane synthesis reaction. Consequently, the recovered chloromethane is insufficient for reuse in the methylchlorosilane synthesis reaction, leading to resource waste. Summary of the Invention

[0004] The purpose of this invention is to provide a system and method for recovering chloromethane from the tail gas of methylchlorosilane synthesis, so as to solve the problem of low purity of chloromethane recovered from the tail gas of existing methylchlorosilane synthesis.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: This application provides a method for recovering chloromethane from the tail gas of methylchlorosilane synthesis, the method comprising: The tail gas from the synthesis of methylchlorosilane is subjected to three-stage segmented condensation and gas-liquid separation to obtain condensate and non-condensable gas; the condensate is then distilled to obtain chloromethane. The non-condensable gas is absorbed by a packed absorption tower containing dichloromethane, resulting in non-condensable tail gas at the top of the tower and rich liquid at the bottom. After the rich liquid is desorbed in a desorption column at 40-60℃, lean liquid is obtained at the bottom of the column and desorption gas is obtained at the top of the column. The desorbed gas was dried by adsorption and then filtered to obtain chloromethane.

[0006] This application also provides a system for recovering monochloromethane from the tail gas of methylchlorosilane synthesis, comprising a deep condenser, a packed absorption tower, a stripping tower, an adsorption dryer, and a precision filter connected in sequence; the deep condenser is also connected to a condensate recovery tank.

[0007] The present invention has the following beneficial effects: (1) High recovery rate and high purity: In this application, a three-stage segmented condensation method is used to recover 85-90% of the monochloromethane in the tail gas of methylchlorosilane synthesis; 90-95% of the remaining monochloromethane is recovered through the directional absorption of dichloromethane; and finally, the remaining monochloromethane is recovered through depressurization and reflux to remove impurities, so as to achieve a total recovery rate of monochloromethane ≥99% and a purity of ≥99.5%, which greatly reduces the waste of monochloromethane and achieves high recovery of monochloromethane, which can be directly reused in the synthesis reaction of methylchlorosilane.

[0008] (2) Low solvent loss: During the desorption process, the volatility of dichloromethane is reduced by reducing the pressure and controlling the temperature. At the same time, dichloromethane is recovered by reflux, so that the solvent content in the desorption gas is ≤0.5%, the lean liquid recycling rate is ≥98%, and the solvent loss is ≤0.3% / cycle. Attached Figure Description

[0009] Figure 1 This is a schematic diagram of the system for recovering chloromethane from the tail gas of methylchlorosilane synthesis, provided in an embodiment of this application. Symbolic representation: 1-Deep condenser, 2-Condensate recovery tank, 3-Packed absorption tower, 4-Lean solution tank, 5-Lean solution pump, 6-Analysis tower, 7-Reboiler, 8-Tail gas condenser, 9-Adsorption dryer, 10-Precision filter. Detailed Implementation

[0010] This application provides a method for recovering chloromethane from the tail gas of methylchlorosilane synthesis, the method comprising: S01: The tail gas from the synthesis of methylchlorosilane is condensed and separated into condensate and non-condensable gas in a three-stage segmented process; the condensate is then distilled to obtain chloromethane.

[0011] The tail gas from the synthesis of methylchlorosilane is pressurized by a compressor and then undergoes a three-stage segmented condensation process to form a gas-liquid mixture. Specifically, the pressurized tail gas undergoes a first-stage condensation using ambient temperature circulating water, a second-stage condensation using -15℃ ethylene glycol, and a third-stage deep condensation using a deep condenser. The third-stage deep condensation operates at a pressure of 0.8-1.2 MPa, a temperature of -40 to -60℃, and a residence time of 10-20 seconds.

[0012] The gas-liquid mixture after deep condensation is separated into condensate and non-condensable gas by a gas-liquid separator. The condensate is mainly composed of ≥95% chloromethane, with the remainder being a small amount of methylchlorosilane monomers; the non-condensable gas mainly contains 5-15% chloromethane, 70-80% nitrogen, and 5-15% hydrogen.

[0013] In this embodiment of the application, the condensate is fed into a distillation column and distilled under the conditions of a distillation pressure of 0.8-1.2 MPa and a distillation column bottom temperature of 40-60°C to obtain monochloromethane with a purity of ≥99.0%, which is temporarily stored in the condensate recovery tank 2.

[0014] In the embodiments of this application, gas-liquid separation is performed using a conventional gas-liquid separator, as long as gas-liquid separation can be achieved.

[0015] S02: The non-condensable gas is absorbed by a packed absorption tower containing dichloromethane, resulting in non-condensable tail gas at the top of the tower and rich liquid at the bottom.

[0016] The non-condensable gas is fed into a packed absorption tower, using dichloromethane with a purity ≥99.8% as the absorbent, at an absorption temperature of 0-15℃, an absorption pressure of 0.2-0.5MPa, and a liquid-to-gas ratio of 5-15L / m³. 3 The absorption tower absorbs chloromethane at an empty gas velocity of 0.2-0.5 m / s, producing a non-condensable tail gas at the top and a rich liquid at the bottom. The rich liquid contains 15-25% chloromethane by mass. The non-condensable tail gas mainly consists of nitrogen, hydrogen, and ≤0.1% chloromethane, and can be directly vented or incinerated. The packed absorber uses 250Y ceramic corrugated packing.

[0017] S03: After the rich liquid is desorbed by the desorption tower at 40-60℃, the lean liquid is obtained at the bottom of the tower and the desorption gas is obtained at the top of the tower.

[0018] The rich liquor is fed into a stripping column, where stripping is performed under conditions of stripping pressure of 0.05-0.15 MPa, stripping temperature of 40-60℃, and reflux ratio of 1-3:1. Lean liquor is obtained at the bottom of the column, and stripping gas is obtained at the top. The lean liquor contains ≤0.8% (w / w) of monochloromethane, with the remainder being dichloromethane. The stripping gas is mainly monochloromethane, with a dichloromethane content ≤0.5%.

[0019] In this embodiment, the stripping column is a plate stripping column with 15-25 trays. During the stripping process, the reflux liquid is condensed dichloromethane, which is refluxed to the upper tray of the stripping column.

[0020] To achieve the recovery and utilization of dichloromethane, in this application, the lean liquid is cooled to 0-15℃ and then filtered using a filter with a filtration accuracy of 0.5μm. Finally, the filtered filtrate is recycled to the packed absorption tower.

[0021] S04: The desorbed gas is dried by adsorption and then filtered to obtain chloromethane.

[0022] The desorbed gas was fed into an adsorption dryer, using 3A molecular sieve as the adsorbent. Adsorption drying was carried out at an adsorption temperature of 20-30℃ and an adsorption pressure of 0.1-0.3MPa to remove moisture from the desorbed gas, ensuring a water content ≤5ppm. After adsorption drying, the desorbed gas was filtered through a precision filter with a filtration accuracy of 0.1μm to obtain monochloromethane with a purity ≥99.5%. This monochloromethane, temporarily stored in condensate recovery tank 2, can be combined and reused in the synthesis reaction of methylchlorosilanes. Based on the above-described method for recovering chloromethane from the tail gas of methylchlorosilane synthesis, this application also provides a system for recovering chloromethane from the tail gas of methylchlorosilane synthesis. This system includes a deep condenser 1, a packed absorption tower 3, a stripping tower 6, an adsorption dryer 9, and a precision filter 10 connected in sequence. The deep condenser 1 is also connected to a condensate recovery tank 2, as shown in the attached diagram. Figure 1 As shown. In addition, the bottom of the stripping column 6 is connected in sequence to the lean liquid tank 4 and the lean liquid pump 5, and the bottom of the stripping column 6 is also equipped with a reboiler 7; a tail gas condenser 8 is also provided between the top of the stripping column 6 and the adsorption dryer 9.

[0023] The technical solution of the present invention will be further explained and described below through specific embodiments.

[0024] Example 1 This application provides a method for recovering chloromethane from the tail gas of methylchlorosilane synthesis, the method comprising: S101: The tail gas from the synthesis of methylchlorosilane is compressed and boosted by a compressor, then undergoes first-stage condensation via ambient temperature circulating water, followed by second-stage condensation via -15℃ ethylene glycol, and finally deep condensation for 15 seconds at a pressure of 0.8 MPa and a temperature of -50℃. The gas-liquid mixture after deep condensation is separated by a gas-liquid separator to obtain condensate and non-condensable gas. The condensate is mainly composed of 96% chloromethane, with the remainder being small amounts of methylchlorosilane monomers; the non-condensable gas mainly contains 7% chloromethane, 75% nitrogen, and 18% hydrogen. The condensate is fed into a distillation column for distillation at a pressure of 0.8 MPa and a bottom temperature of 50℃ to obtain chloromethane with a purity of 99.2% and a yield of 85 kg / h.

[0025] S102: Non-condensable gas is fed into a packed absorption tower filled with ceramic corrugated packing, using 99.8% pure dichloromethane as the absorbent, at an absorption temperature of 10℃, an absorption pressure of 0.5MPa, and a liquid-to-gas ratio of 10L / m³. 3Under the condition of an empty tower gas velocity of 0.3 m / s, chloromethane is absorbed, resulting in non-condensable tail gas at the top of the tower and rich liquid at the bottom. The rich liquid contains 20% chloromethane by mass. The non-condensable tail gas mainly consists of nitrogen, hydrogen, and chloromethane with a content ≤0.1%. This non-condensable tail gas can be directly vented or incinerated.

[0026] S103: The rich solution is fed into the stripping column and stripped under the conditions of stripping pressure of 0.1 MPa, stripping temperature of 55℃, and reflux ratio of 2:1. Lean solution is obtained at the bottom of the column, and stripping gas is obtained at the top. The lean solution contains 0.6% (w / w) of monochloromethane, with the remainder being dichloromethane. The dichloromethane content in the stripping gas is 0.3%. After cooling the lean solution to 10℃, it is filtered using a filter with a filtration precision of 0.5 μm. Finally, the filtered filtrate is recycled to the packed absorption column.

[0027] S104: The desorbed gas is fed into an adsorption dryer, using 3A molecular sieve as the adsorbent. Adsorption drying is carried out at an adsorption temperature of 25℃ and an adsorption pressure of 0.2MPa to remove moisture from the desorbed gas and reduce its water content to 4ppm. After adsorption drying, the desorbed gas is filtered through a precision filter with a filtration accuracy of 0.1μm to obtain chloromethane with a purity of 99.8% and a yield of 14.5kg / h.

[0028] Calculations show that the total recovered yield of chloromethane is 99.5 kg / h, the recovery rate is 99.5%, and the lean liquor recycling rate is 98.5%.

[0029] Example 2 This application provides a method for recovering chloromethane from the tail gas of methylchlorosilane synthesis, the method comprising: S201: The tail gas from the synthesis of methylchlorosilane is compressed and boosted by a compressor, then undergoes first-stage condensation via ambient temperature circulating water, followed by second-stage condensation via -15℃ ethylene glycol, and finally deep condensation for 12 seconds at a pressure of 0.85 MPa and a temperature of -45℃. The gas-liquid mixture after deep condensation is separated by a gas-liquid separator to obtain condensate and non-condensable gas. The condensate is mainly composed of 96.5% chloromethane, with the remainder being small amounts of methylchlorosilane monomers; the non-condensable gas mainly contains 6% chloromethane, 79% nitrogen, and 15% hydrogen. The condensate is fed into a distillation column for distillation at a pressure of 1.2 MPa and a bottom temperature of 40℃ to obtain chloromethane with a purity of 99.1% and a yield of 68 kg / h.

[0030] S202: Non-condensable gas is fed into a packed absorption tower filled with ceramic corrugated packing, using 99.9% pure dichloromethane as the absorbent, at an absorption temperature of 8℃, an absorption pressure of 0.5MPa, and a liquid-to-gas ratio of 8L / m³. 3 Under the condition of an empty tower gas velocity of 0.2 m / s, chloromethane is absorbed, resulting in non-condensable tail gas at the top of the tower and rich liquid at the bottom. The rich liquid contains 18% chloromethane by mass. The non-condensable tail gas mainly consists of nitrogen, hydrogen, and chloromethane with a content ≤0.1%. This non-condensable tail gas can be directly vented or incinerated.

[0031] S203: The rich solution is fed into the stripping column and stripped under the conditions of stripping pressure of 0.08 MPa, stripping temperature of 50℃, and reflux ratio of 1.5:1. Lean solution is obtained at the bottom of the column, and stripping gas is obtained at the top. The lean solution contains 0.4% (w / w) of monochloromethane, with the remainder being dichloromethane. The stripping gas contains 0.4% dichloromethane. After cooling the lean solution to 15℃, it is filtered using a filter with a filtration precision of 0.5 μm. Finally, the filtered filtrate is recycled to the packed absorption column.

[0032] S204: The desorbed gas is fed into an adsorption dryer, using 3A molecular sieve as the adsorbent. Adsorption drying is carried out at an adsorption temperature of 20℃ and an adsorption pressure of 0.3MPa to remove moisture from the desorbed gas and reduce its water content to 5ppm. After adsorption drying, the desorbed gas is filtered through a precision filter with a filtration accuracy of 0.1μm to obtain chloromethane with a purity of 99.6% and a yield of 9.2kg / h.

[0033] Calculations show that the total recovered yield of chloromethane is 77.2 kg / h, with a recovery rate of 99.0% and a lean liquor recycling rate of 98.2%.

[0034] Example 3 This application provides a method for recovering chloromethane from the tail gas of methylchlorosilane synthesis, the method comprising: S301: The tail gas from the synthesis of methylchlorosilane is compressed and boosted by a compressor, then undergoes first-stage condensation via ambient temperature circulating water, followed by second-stage condensation via -15℃ ethylene glycol, and finally deep condensation for 10 seconds at a pressure of 1.2 MPa and a temperature of -60℃. The gas-liquid mixture after deep condensation is separated by a gas-liquid separator to obtain condensate and non-condensable gas. The condensate is mainly composed of 96% chloromethane, with the remainder being small amounts of methylchlorosilane monomers; the non-condensable gas mainly contains 12% chloromethane, 80% nitrogen, and 8% hydrogen. The condensate is fed into a distillation column for distillation at a pressure of 0.8 MPa and a bottom temperature of 60℃ to obtain chloromethane with a purity of 99.2% and a yield of 72 kg / h.

[0035] S302: Non-condensable gas is fed into a packed absorption tower filled with ceramic corrugated packing, using 99.9% pure dichloromethane as the absorbent, at an absorption temperature of 15℃, an absorption pressure of 0.2MPa, and a liquid-to-gas ratio of 5L / m³. 3 Under the condition of an empty tower gas velocity of 0.5 m / s, chloromethane is absorbed, resulting in non-condensable tail gas at the top of the tower and rich liquid at the bottom. The rich liquid contains 20% chloromethane by mass. The non-condensable tail gas mainly consists of nitrogen, hydrogen, and chloromethane with a content ≤0.1%. This non-condensable tail gas can be directly vented or incinerated.

[0036] S303: The rich solution is fed into the stripping column, where stripping is performed under the conditions of a stripping pressure of 0.15 MPa, a stripping temperature of 40°C, and a reflux ratio of 3:1. Lean solution is obtained at the bottom of the column, and stripping gas is obtained at the top. The lean solution contains 0.6% (w / w) of monochloromethane, with the remainder being dichloromethane. The dichloromethane content in the stripping gas is 0.4%. After cooling the lean solution to 12°C, it is filtered using a filter with a filtration precision of 0.5 μm. Finally, the filtered filtrate is recycled to the packed absorption column.

[0037] S304: The desorbed gas is fed into an adsorption dryer, using 3A molecular sieve as the adsorbent. Adsorption drying is carried out at an adsorption temperature of 30℃ and an adsorption pressure of 0.1MPa to remove moisture from the desorbed gas and reduce its water content to 5ppm. After adsorption drying, the desorbed gas is filtered through a precision filter with a filtration accuracy of 0.1μm to obtain chloromethane with a purity of 99.5% and a yield of 8.5kg / h.

[0038] Calculations show that the total recovered yield of chloromethane is 80.5 kg / h, with a recovery rate of 99.3% and a lean liquor recycling rate of 98.4%.

[0039] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for recovering chloromethane from tail gas during methylchlorosilane synthesis, characterized in that, include: The tail gas from the synthesis of methylchlorosilane is subjected to three-stage segmented condensation and gas-liquid separation to obtain condensate and non-condensable gas; the condensate is then distilled to obtain chloromethane. The non-condensable gas is absorbed by a packed absorption tower containing dichloromethane, resulting in non-condensable tail gas at the top of the tower and rich liquid at the bottom. After the rich liquid is desorbed in a desorption column at 40-60℃, lean liquid is obtained at the bottom of the column and desorption gas is obtained at the top of the column. The desorbed gas was dried by adsorption and then filtered to obtain chloromethane.

2. The method for recovering chloromethane from the tail gas of methylchlorosilane synthesis according to claim 1, characterized in that, The three-stage segmented condensation includes: a first stage of ambient temperature circulating water condensation, a second stage of -15℃ ethylene glycol condensation, and a third stage of deep condensation, wherein the pressure of deep condensation is 0.8-1.2MPa, the temperature is -40~-60℃, and the residence time is 10-20s.

3. The method for recovering chloromethane from the tail gas of methylchlorosilane synthesis according to claim 1, characterized in that, The distillation pressure is 0.8-1.2 MPa, and the distillation column temperature is 40-60℃.

4. The method for recovering chloromethane from the tail gas of methylchlorosilane synthesis according to claim 1, characterized in that, The absorption conditions of the packed absorption tower are: absorption temperature 0-15℃, absorption pressure 0.2-0.5MPa, and liquid-to-gas ratio 5-15L / m³. 3 The air velocity in the empty tower is 0.2-0.5 m / s.

5. The method for recovering chloromethane from the tail gas of methylchlorosilane synthesis according to claim 1, characterized in that, The analytical conditions of the analytical tower are: 15-25 trays, analytical pressure of 0.05-0.15 MPa, and reflux ratio of 1-3:

1.

6. The method for recovering chloromethane from the tail gas of methylchlorosilane synthesis according to claim 1, characterized in that, The desorbed gas is adsorbed and dried using 3A molecular sieves at an adsorption temperature of 20-30℃ and an adsorption pressure of 0.1-0.3MPa.

7. The method for recovering chloromethane from the tail gas of methylchlorosilane synthesis according to claim 1, characterized in that, The lean solution is cooled to 0-15°C, filtered through a filter with a filtration accuracy of 0.5μm, and then circulated back into the packed absorption tower.

8. The method for recovering chloromethane from the tail gas of methylchlorosilane synthesis according to claim 1, characterized in that, The desorbed gas, after being adsorbed and dried, is filtered using a filter with a filtration accuracy of 0.1 μm.

9. A system for recovering chloromethane from tail gas during methylchlorosilane synthesis, characterized in that, It includes a deep condenser (1), a packed absorption tower (3), a desorption tower (6), an adsorption dryer (9), and a precision filter (10) connected in sequence; the deep condenser (1) is also connected to a condensate recovery tank (2).

10. The system for recovering chloromethane from the tail gas of methylchlorosilane synthesis according to claim 9, characterized in that, The bottom of the analytical column (6) is connected in sequence to the lean liquid tank (4) and the lean liquid pump (5), and the bottom of the analytical column (6) is also equipped with a reboiler (7); a tail gas condenser (8) is also provided between the top of the analytical column (6) and the adsorption dryer (9).

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