A method and device for synthesizing methyl chloride gas by high-temperature washing

Abstract

The present invention relates to a method and device for washing chloromethane synthesis gas at high temperature. The chloromethane synthesis gas at 145 - 155 °C from the chloromethane synthesis kettle enters the chloromethane washing tower, where the condensate condensed by the methanol vaporizer in the chloromethane washing tower absorbs hydrogen chloride gas in the gas phase to form hydrochloric acid with a concentration of 18 - 21%, which is then transported to the chloromethane reaction kettle. The washed gas phase enters the methanol vaporizer as a recovered heat source. The present invention recovers hydrogen chloride in the gas phase through high-temperature washing and reuses it in the chloromethane reaction kettle, and forms dilute hydrochloric acid with a concentration of 2 - 3% after being cooled by the methanol vaporizer, effectively reducing the energy consumption of hydrogen chloride stripping; the heat of the chloromethane gas at 105 - 115 °C after high-temperature washing vaporizes methanol, making full use of the reaction heat generated by chloromethane synthesis and reducing the energy consumption of the device.

Description

Technical Field

[0001] The present invention belongs to the technical field of the treatment of chloromethane synthesis gas, and particularly relates to a method and a device for washing chloromethane synthesis gas at high temperature. Background Art

[0002] In the production of organosilicon, chloromethane is the main raw material. There are generally two production methods for the chloromethane synthesis process. One method is high-temperature reaction synthesis using an aqueous zinc chloride solution as a catalyst, and the other method is high-temperature reaction synthesis using a solid-phase catalyst. Each has its own advantages and disadvantages.

[0003] In the production of organosilicon, since hydrogen chloride is derived from the hydrolysis by-product of methylchlorosilane and contains a certain amount of siloxane, chloromethane, which is the raw material for synthesizing methylchlorosilane in organosilicon, generally adopts a wet synthesis technology.

[0004] Chloromethane synthesis equation:

[0005]

[0006] In the actual production process, generally, an excessive amount of hydrogen chloride is used to completely react the methanol in the system. Therefore, the actually controlled molar ratio in the production process is: HCl:CH 3 OH = 1.05 - 1.1:1. Therefore, the chloromethane tail gas contains excessive hydrogen chloride and water produced in the process of the process, and finally forms 10% - 20% dilute hydrochloric acid in the subsequent system.

[0007] In order to ensure the comprehensive utilization of chlorine resources and reduce pollutant emissions, production units generally adopt an analytical method for the dilute hydrochloric acid produced in the production process to strip out hydrogen chloride for reuse in chloromethane synthesis. In the stripping process, steam is required to re-distill hydrogen chloride and water, which is a high-energy-consuming process and has the defect of high energy consumption in hydrogen chloride recovery. Summary of the Invention

[0008] The present invention provides a method and a device for washing chloromethane synthesis gas at high temperature, which effectively reduce the energy consumption in the process of hydrogen chloride recovery.

[0009] The technical solution adopted by the present invention is as follows:

[0010] A method for washing chloromethane synthesis gas at high temperature includes the following steps: The chloromethane synthesis gas (chloromethane synthesis tail gas) at 145 - 155°C from the chloromethane synthesis kettle enters the chloromethane washing tower, and the condensate condensed by the methanol vaporizer in the chloromethane washing tower absorbs hydrogen chloride gas in the gas phase to form 18 - 21% hydrochloric acid, which is then transported to the chloromethane reaction kettle. The washed gas phase enters the methanol vaporizer as a recovered heat source.

[0011] The chloromethane synthesis gas of the present invention is washed at a high temperature (145 - 155 °C), and hydrogen chloride in the gas is absorbed to form hydrochloric acid, which is returned to the chloromethane reaction kettle. The gas after the high-temperature washing tower enters the methanol vaporizer to recover the waste heat in the gas phase. The vaporized methanol goes to chloromethane synthesis, and the chloromethane cooled by the methanol vaporizer goes to the next process.

[0012] Preferably, the temperature of the gas phase entering the methanol vaporizer is 100 - 120 °C.

[0013] Preferably, the temperature of the chloromethane mixed gas from the chloromethane washing tower is reduced to 105 - 115 °C and enters the methanol vaporizer. Condensing heat is generated by the vaporization of methanol, and methanol is vaporized into methanol gas. Moisture and the remaining part of hydrogen chloride in the gas phase are condensed. Part of the condensate is used for absorbing hydrogen chloride in the chloromethane washing tower, and part is transported to the hydrogen chloride recovery device; the chloromethane after high-temperature washing and methanol cooling enters the subsequent device.

[0014] Preferably, the condensate is 2 - 3% dilute hydrochloric acid. By washing the chloromethane synthesis gas at a high temperature, the content of hydrogen chloride in the chloromethane synthesis tail gas is reduced. The chloromethane synthesis tail gas after high-temperature washing vaporizes methanol, so that the concentration of the dilute hydrochloric acid formed after the final chloromethane is cooled is reduced to 2 - 3%.

[0015] The 2 - 3% hydrochloric acid can be concentrated to 20% by multi-effect evaporation, and then hydrogen chloride is stripped and recycled to the chloromethane device, reducing the energy consumption of hydrogen chloride recovery.

[0016] Preferably, the vaporized methanol is transported to the chloromethane reaction kettle.

[0017] The present invention also provides a device for washing the chloromethane synthesis gas at a high temperature for the above method. The device includes a chloromethane washing tower and a methanol vaporizer. The chloromethane washing tower includes a chloromethane synthesis gas inlet, an air outlet, a liquid inlet, and a liquid outlet. The methanol vaporizer includes a chloromethane mixed gas inlet, a condensate outlet, a gas methanol outlet, a chloromethane outlet, and a liquid methanol inlet; the chloromethane synthesis gas inlet is connected to the chloromethane reaction kettle, the air outlet of the chloromethane washing tower is connected to the chloromethane mixed gas inlet, the condensate outlet of the methanol vaporizer is connected to the liquid inlet of the chloromethane washing tower, and the liquid outlet of the chloromethane washing tower is connected to the chloromethane reaction kettle.

[0018] Preferably, the chloromethane synthesis gas inlet is arranged at the lower part of the chloromethane washing tower, the air outlet of the chloromethane washing tower is arranged at the top of the chloromethane washing tower, the liquid inlet of the chloromethane washing tower is arranged at the upper part of the chloromethane washing tower, and the liquid outlet of the chloromethane washing tower is arranged at the bottom of the chloromethane washing tower.

[0019] Preferably, the condensate outlet of the methanol vaporizer is also connected to the hydrogen chloride recovery device.

[0020] Preferably, the gas methanol outlet of the methanol vaporizer is connected to the methyl chloride reactor, and the methyl chloride outlet of the methanol vaporizer is connected to the methyl chloride transfer pipeline.

[0021] Preferably, the methanol inlet of the methanol vaporizer is connected to the methanol liquid transfer pipeline.

[0022] The high-temperature washing process of methyl chloride in the present invention can be carried out by one tower or multiple towers.

[0023] The beneficial effects of the present invention are as follows:

[0024] (1) By high-temperature washing, hydrogen chloride in the gas phase is recovered and reused in the methyl chloride reactor. After being cooled by the methanol vaporizer, dilute hydrochloric acid with a concentration of 2-3% is formed, effectively reducing the energy consumption of hydrogen chloride stripping.

[0025] (2) The methanol is vaporized by the waste heat of the methyl chloride gas after high-temperature washing, making full use of the reaction heat generated by methyl chloride synthesis and reducing the energy consumption of the device. Description of the Drawings

[0026] Figure 1 is the process flow chart of the present invention;

[0027] Illustration: Methane washing tower 1, methanol vaporizer 2, methyl chloride synthesis gas inlet 3, gas outlet 4, liquid inlet 5, liquid outlet 6, methyl chloride mixture inlet 7, condensate outlet 8, gas methanol outlet 9, methyl chloride outlet 10, liquid methanol inlet 11, hydrogen chloride recovery device 12, methyl chloride transfer pipeline 13, methanol liquid transfer pipeline 14. Detailed Embodiments

[0028] The technical solutions of the present invention will be further specifically described below through examples. These examples are for the purpose of illustrating the present invention and are not intended to limit the present invention. All other examples obtained by those of ordinary skill in the art based on the examples in this application without creative efforts shall fall within the scope of protection of this application.

[0029] The experimental methods described in the examples are all conventional methods unless otherwise specified; the percentages involved are all mass percentages unless otherwise specified; the reagents and materials can be obtained from commercial sources unless otherwise specified.

[0030] Refer to Figure 1, A device for washing and synthesizing methyl chloride gas at high temperature, comprising a methyl chloride washing tower 1 and a methanol vaporizer 2. The methyl chloride washing tower includes a methyl chloride synthesis gas inlet 3, an air outlet 4, a liquid inlet 5 and a liquid outlet 6. The methanol vaporizer includes a methyl chloride mixed gas inlet 7, a condensate outlet 8, a gaseous methanol outlet 9, a methyl chloride outlet 10 and a liquid methanol inlet 11. The methyl chloride synthesis gas inlet 3 is connected to a methyl chloride reaction kettle. The air outlet 4 of the methyl chloride washing tower is connected to the methyl chloride mixed gas inlet 7. The condensate outlet 8 of the methanol vaporizer is connected to the liquid inlet 5 of the methyl chloride washing tower. The liquid outlet 6 of the methyl chloride washing tower is connected to the methyl chloride reaction kettle.

[0031] The methyl chloride synthesis gas inlet 3 is arranged at the lower part of the methyl chloride washing tower. The air outlet 4 of the methyl chloride washing tower is arranged at the top of the methyl chloride washing tower. The liquid inlet 5 of the methyl chloride washing tower is arranged at the upper part of the methyl chloride washing tower. The liquid outlet 6 of the methyl chloride washing tower is arranged at the bottom of the methyl chloride washing tower.

[0032] The condensate outlet 8 of the methanol vaporizer is also connected to a hydrogen chloride recovery device 12. The gaseous methanol outlet 9 of the methanol vaporizer is connected to the methyl chloride reaction kettle. The methyl chloride outlet 10 of the methanol vaporizer is connected to a methyl chloride conveying pipeline 13. The methanol inlet 11 of the methanol vaporizer is connected to a methanol liquid conveying pipeline 14.

[0033] The methyl chloride synthesis gas (methyl chloride tail gas) from the methyl chloride reaction kettle contains a mixture of methyl chloride, methanol, methyl ether, hydrogen chloride, water, etc., with a temperature of 145°C to 155°C. It enters the methyl chloride washing tower, and the condensate condensed by the methanol vaporizer in the methyl chloride washing tower absorbs hydrogen chloride gas in the gas phase. Since 20% hydrochloric acid is a constant-boiling acid, and the hydrogen chloride partial pressure on the hydrochloric acid is relatively low while the water vapor partial pressure is relatively high, at high temperature, the hydrogen chloride in the methyl chloride is washed into the liquid phase to form 20% hydrochloric acid, which is transported to the methyl chloride reaction kettle by a transfer pump. The washed gas phase (methyl chloride mixed gas) enters the methanol vaporizer to recover heat.

[0034] The temperature of the methyl chloride mixed gas from the methyl chloride washing tower drops to 105 - 115°C and enters the methanol vaporizer to recover heat. Condensing heat is generated by the vaporization of methanol, and methanol is vaporized into methanol gas. The water and the remaining part of hydrogen chloride in the gas phase are condensed. Part of the condensate is used for absorbing hydrogen chloride in the high-temperature washing tower, and part is transported to the hydrogen chloride recovery device. The vaporized methanol is transported to the methyl chloride reaction kettle.

[0035] The methyl chloride after high-temperature washing and methanol cooling enters the subsequent device.

[0036] The present invention reduces the hydrogen chloride content in the methyl chloride synthesis gas by high-temperature washing the methyl chloride synthesis gas. After high-temperature washing, the methyl chloride mixed gas vaporizes methanol, so that the concentration of the dilute hydrochloric acid formed after the final cooling of methyl chloride is reduced to 2-3%, effectively reducing the energy consumption of hydrogen chloride stripping. In addition, the waste heat of the methyl chloride mixed gas after high-temperature washing vaporizes methanol, making full use of the reaction heat generated by methyl chloride synthesis and reducing the energy consumption of the device.

[0037] In the present invention, the methyl chloride synthesis gas is subjected to high-temperature washing to absorb hydrogen chloride in the gas to form hydrochloric acid and return it to the methyl chloride reaction kettle. The gas after the high-temperature washing tower enters the methanol vaporizer to recover the waste heat in the gas phase. The vaporized methanol goes to methyl chloride synthesis, and the methyl chloride cooled by the methanol vaporizer goes to the next process.

[0038] Industrial Case 1

[0039] Methyl chloride is synthesized by the method of excessive hydrogen chloride. Generally, the molar control amount of hydrogen chloride is 1.05-1.1. Finally, after cooling by the post-system, 20% hydrochloric acid is formed.

[0040] When the high-temperature washing is not used to recover hydrogen chloride and directly reuse it to the methyl chloride synthesis process, according to the methyl chloride production capacity of 100,000 tons / year, the quantity of by-product hydrochloric acid is:

[0041] 10 / 50.5*18 / 0.8 = 44,500 tons / year

[0042] Quantity of excessive hydrogen chloride: 44,500*0.2 = 8900 t / year

[0043] In the existing process of hydrochloric acid analysis, the steam consumption per ton of hydrogen chloride analysis is: 6.5 t steam / t hydrogen chloride.

[0044] By using the method of the present invention, the quantity of steam consumed by hydrochloric acid analysis is reduced annually: 6.5 t*8900 = 57,900 tons / year;

[0045] Calculated at the steam price of 180 yuan / ton, the steam saved annually is:

[0046] 57,900*180 = 10.42 million yuan.

[0047] Industrial Case 2

[0048] When the waste heat after high-temperature washing is not used for methanol vaporization, according to the methyl chloride production capacity of 100,000 tons / year, the quantity of by-product hydrochloric acid is:

[0049] 10 / 50.5*32 = 63,400 tons / year

[0050] Vaporization latent heat of methanol: 37.39 KJ / mol = 8.94 kcal / mol = 0.28 kcal / g = 279.53 kcal / kg

[0051] Vaporization latent heat of steam (0.6 MPa): 495.5 kcal / kg

[0052] By using the method of the present invention, the annual steam savings: 6.34 * 279.53 / 495.5 = 35,700 tons of steam;

[0053] Calculated at the steam price of 180 yuan / ton, the annual steam savings are:

[0054] 35,700 * 180 = 6,426,000 yuan.

[0055] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for washing methyl chloride synthesis gas at high temperature, characterized in that it comprises the following steps: The methyl chloride synthesis gas at 145 - 155 °C coming out of the methyl chloride synthesis kettle enters the methyl chloride washing tower, and the condensate condensed by the methanol vaporizer in the methyl chloride washing tower absorbs hydrogen chloride gas in the gas phase to form hydrochloric acid with a concentration of 18 - 21%, which is transported to the methyl chloride reaction kettle. The washed gas phase enters the methanol vaporizer as a recovered heat source; The temperature of the methyl chloride mixed gas from the methyl chloride washing tower is reduced to 105 - 115 °C and enters the methanol vaporizer. Condensation heat is generated by the vaporization of methanol, and methanol is vaporized into methanol gas. The water and the remaining part of hydrogen chloride in the gas phase are condensed. Part of the condensate is used for absorbing hydrogen chloride in the methyl chloride washing tower, and part is transported to the hydrogen chloride recovery device; The methyl chloride after high-temperature washing and methanol cooling enters the subsequent device; The condensate is dilute hydrochloric acid with a concentration of 2 - 3%.

2. The method for washing methyl chloride synthesis gas at high temperature according to claim 1, characterized in that: The vaporized methanol is transported to the methyl chloride reaction kettle.

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