Low-pressure liquid-phase synthesis and separation method for chloromethane

Abstract

The invention discloses a low-pressure liquid-phase synthesis and separation method of chloromethane, which comprises the following steps: vaporizing methanol and circulating rich methanol to form methanol steam, feeding one part of the methanol steam and all hydrogen chloride gas into a 1 # microbubble generator, forming a large number of microbubbles in a 1 # reactor, and carrying out a chloromethane synthesis reaction; the gas phase after the reaction and the residual methanol steam enter a 2 # micro-bubble generator together, a large number of micro-bubbles are formed in a 2 # reactor, and a chloromethane synthesis reaction is further carried out; cooling a gas phase after the reaction is completed by a first-stage cooler, enabling a liquid phase to flow back to the 2 # reactor, and enabling the gas phase to enter a second-stage cooler; and the gas phase after secondary cooling enters a chloromethane rectifying tower, and the liquid phase enters a methanol recovery tower. A traditional catalyst does not need to be used; meanwhile, synthesis of chloromethane can be completed at low temperature and low pressure, and large-scale design of the reactor is facilitated; the concentration of hydrogen chloride in the discharged waste liquid is 1t; and no extra hydrochloric acid refining is needed, and the product can be directly sent to a wastewater treatment device.

Description

Technical Field

[0001] The invention relates to the technical field of methane chloride, and in particular to a low-pressure liquid phase synthesis and separation method for methyl chloride. Background Art

[0002] Methyl chloride (CH3Cl) is an important organic chemical raw material, widely used in many fields. It is a colorless, transparent, volatile liquid with a pungent odor. As an important intermediate raw material in the production of organosilicon, the quality and production cost of methyl chloride directly affect the quality, production cost and energy consumption of organosilicon products. In recent years, with the development of the organosilicon industry and the further improvement of the country's requirements for energy consumption and product quality in the organosilicon industry, the development and application of advanced technologies for new organosilicon plants and the energy-saving transformation of existing organosilicon plants are imminent.

[0003] At present, in the field of organic silicon, the chloromethane synthesis technology mainly adopts the liquid phase catalytic method, that is, the raw materials methanol and hydrogen chloride (HCl) gas enter the chloromethane reactor, and the bubbling reaction is carried out in the homogeneous catalyst solution (usually 70%wt~80%wt ZnCl2 solution) to generate chloromethane, and a small amount of side reaction occurs to generate dimethyl ether. The main reaction equation is as follows:

[0004] CH3OH+HCl→CH3Cl+H2O

[0005] 2CH3OH→CH3OCH3+H2O

[0006] CH3OCH3+HCl→CH3OH+CH3Cl

[0007] In order to inhibit the side reactions and reduce the formation of dimethyl ether, an excess of HCl is usually added to the system. As a result, the excess HCl will be brought into the subsequent acid and alkali washing systems to produce a large amount of alcohol-containing hydrochloric acid. The energy consumption required to separate methanol and purify HCl is high, which increases operating costs. Summary of the invention

[0008] The purpose of the present invention is to solve the above technical problems and to provide a low-pressure liquid phase synthesis and separation method for methyl chloride, so as to reduce the concentration of hydrochloric acid in the waste liquid, and to directly send the waste water to the waste water treatment device without the need for additional hydrochloric acid refining, thereby achieving the purpose of energy saving and consumption reduction and reducing product costs.

[0009] To achieve the above-mentioned purpose, the present invention provides a low-pressure liquid phase synthesis and separation method of methyl chloride. Methanol and circulating rich methanol are vaporized in a methanol vaporizer to form methanol vapor. A part of the methanol vapor enters a No. 1 microbubble generator together with all the hydrogen chloride gas, and a large number of microbubbles are formed in the No. 1 reactor, and a methyl chloride synthesis reaction occurs; the gas phase after the reaction is completed enters a No. 2 microbubble generator together with the remaining methanol vapor, and a large number of microbubbles are formed in the No. 2 reactor, and a further methyl chloride synthesis reaction occurs; the gas phase after the reaction is cooled by a primary cooler, and the liquid phase flows back to the No. 2 reactor, and the gas phase goes to a secondary cooler; the gas phase after the secondary cooling enters a methyl chloride distillation tower, and the liquid phase enters a methanol recovery tower.

[0010] Reactor 1# and reactor 2# are equipped with microbubble generator 1# and microbubble generator 2# respectively. Through micro-interface strengthening technology, the interface area per unit volume and the mass-energy transfer efficiency are improved, so that the reaction can be carried out under low pressure without a catalyst, which can reduce the large amount of dimethyl ether generated by traditional catalytic reactions. At the same time, low pressure and low temperature make the design conditions of the reactor milder.

[0011] Furthermore, the top vapor of the chloromethane distillation tower is condensed by the top condenser of the distillation tower and then enters the reflux tank of the distillation tower, and the crude chloromethane is sent to the downstream process for purification and compression as a gas phase product; the liquid phase is pressurized by the distillation tower reflux pump and then sent back to the chloromethane distillation tower; part of the liquid at the bottom of the chloromethane distillation tower is heated by the distillation tower reboiler and then returned to the chloromethane distillation tower, and part of the liquid is sent to the methanol recovery tower.

[0012] Furthermore, the top steam of the methanol recovery tower is condensed by the top condenser of the recovery tower and then enters the reflux tank of the recovery tower. A small amount of gas phase is sent to the downstream process for treatment as process waste gas. The liquid phase is pressurized by the reflux pump of the recovery tower and partly sent back to the methanol recovery tower, and partly enters the No. 1 reactor as circulating rich methanol; part of the liquid at the bottom of the methanol recovery tower is heated by the reboiler of the recovery tower and then returned to the methanol recovery tower, and part of the liquid is sent to the sewage treatment device as waste liquid.

[0013] Furthermore, the molar ratio of hydrogen chloride to methanol vapor entering the 1# microbubble generator is 1.1:1 to 1.3:1; the generation of by-product dimethyl ether can be effectively suppressed by the participation of excess hydrogen chloride in the reaction.

[0014] Furthermore, the operating pressure of the No. 1 reactor is 0.1-0.3 MPag, and the operating temperature is 100-140°C.

[0015] Furthermore, the volume ratio of the methanol vapor entering the 2# microbubble generator to the methanol vapor entering the 1# microbubble generator is 2:3 to 3:17. Excess methanol participating in the reaction can effectively convert the unreacted HCl gas in the 1# reactor and reduce the concentration of HCl in the final waste liquid.

[0016] Furthermore, the operating pressure of the 2# reactor is 0.1-0.3 MPag and the operating temperature is 100-130°C.

[0017] Furthermore, the operating pressure of the methyl chloride distillation tower is 0.1-0.25 MPag. On the one hand, high-purity methyl chloride (>99% wt) can be separated through distillation, reducing the difficulty of downstream separation and purification; on the other hand, an acid-containing alcohol solution can be separated for the next step of methanol recovery.

[0018] Furthermore, the operating pressure of the methanol recovery tower is 0.05-0.2 Mpag. On the one hand, the methanol-rich (containing chloromethane-4%wt) can be separated and recycled back to the reaction system by distillation, thereby reducing the loss of chloromethane; on the other hand, the waste liquid can be separated, and the HCl concentration in the waste liquid is <3%wt, and the methanol concentration is <500ppmw. The waste liquid can be directly sent to a sewage treatment device for treatment.

[0019] Furthermore, the bottom of the 1# reactor is connected to the 2# reactor through a pipeline.

[0020] This technical solution has the following beneficial effects:

[0021] 1) The present invention adds a secondary reactor, which can further convert a large amount of unreacted HCl in the primary reactor into methyl chloride, thereby improving the total conversion rate of HCl and reducing the concentration of HCl in the waste liquid, meeting the acceptance requirements of the downstream wastewater treatment device, and avoiding the increase in energy consumption and material consumption caused by secondary treatment;

[0022] 2) The present invention improves the interface area per unit volume and the mass-energy-mass transfer efficiency through micro-interface strengthening technology, so that the reaction can be carried out at low pressure without a catalyst, which can reduce the generation of a large amount of dimethyl ether caused by traditional catalytic reactions. At the same time, low pressure and low temperature make the design conditions of the reactor more moderate, which is conducive to the large-scale design of the reactor;

[0023] 3) The present invention adopts a two-tower process of a chloromethane rectification tower and a methanol recovery tower, which can obtain chloromethane with higher purity, achieve the purpose of recovering methanol and chloromethane, and reduce material loss; at the same time, the concentration of hydrogen chloride in the discharged waste liquid is less than 3%wt, and no additional hydrochloric acid refining is required, and it can be directly sent to the wastewater treatment device. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the system structure of the present invention.

[0025] Among them, 1-methanol vaporizer, 2-1# microbubble generator, 3-1# reactor, 4-2# microbubble generator, 5-2# reactor 6-primary cooler, 7-secondary cooler, 8-chloromethane distillation tower, 9-distillation tower top condenser, 10-distillation tower reflux tank, 11-distillation tower reflux pump, 12-distillation tower reboiler, 13-methanol recovery tower, 14-recovery tower top condenser, 15-recovery tower reflux tank, 16-recovery tower reflux pump, 17-recovery tower reboiler. DETAILED DESCRIPTION

[0026] The present invention is further described below by examples in combination with the accompanying drawings.

[0027] Example 1

[0028] After methanol and circulating rich methanol are gasified, 80% of methanol vapor enters the 1# microbubble generator together with all hydrogen chloride gas, and the molar ratio of hydrogen chloride to methanol vapor is 1.1:1. A large number of microbubbles are formed in the 1# reactor, and a chloromethane synthesis reaction occurs. The reactor pressure is 0.25MPag and the temperature is 130°C. Unreacted HCl enters the 2# microbubble generator along with the gas phase of the 1# reactor and the remaining 20% ​​methanol vapor, forming a large number of microbubbles in the 2# reactor, further converting the unreacted HCl into chloromethane. The reactor pressure is 0.2MPag and the temperature is 115°C.

[0029] The reaction product gas from the 2# reactor is cooled to 112°C by the primary cooler, and the cooled liquid phase is returned to the 2# reactor to maintain the liquid level of the 1# reactor and the 2# reactor stable. The gas phase is further cooled by the secondary cooler, and the cooled methanol-rich liquid goes to the lower part of the methanol recovery tower, and the gas phase enters the chloromethane distillation tower. The operating pressure of the chloromethane distillation tower is 0.15MPag. The gas phase at the top of the tower is condensed by the top condenser of the distillation tower and enters the reflux tank of the distillation tower. The crude chloromethane (chloromethane>99.4%wt, dimethyl ether<0.4%wt) is sent to the downstream process for purification and compression as a gas phase product, and the liquid phase is pressurized by the distillation tower reflux pump and sent back to the chloromethane distillation tower. The methanol-rich liquid at the bottom of the chloromethane distillation tower is partially extracted and sent to the methanol recovery tower. The operating pressure of the methanol recovery tower is 0.1MPag. The gas at the top of the tower is condensed by the recovery tower top condenser and then enters the recovery tower reflux tank. A small amount of non-condensable gas is sent to the downstream device for treatment as waste gas. The liquid phase is sent back to the methanol recovery tower after being pressurized by the recovery tower reflux pump. Part of it enters the No. 1 reactor as circulating rich methanol; part of the liquid at the bottom of the methanol recovery tower is sent to the sewage treatment device as waste liquid (HCl concentration <2%wt).

[0030] The total HCl conversion rate is >99.2%, the methanol conversion rate is >99.2%, and the byproduct dimethyl ether / product methyl chloride is <0.4%.

[0031] Example 2

[0032] After methanol and circulating rich methanol are gasified, 70% of methanol vapor enters the 1# microbubble generator together with all hydrogen chloride gas, the molar ratio of hydrogen chloride to methanol vapor is 1.2:1, a large number of microbubbles are formed in the 1# reactor, and methyl chloride synthesis reaction occurs, the reactor pressure is 0.3MPag, and the temperature is 135°C. Unreacted HCl enters the 2# microbubble generator along with the gas phase of the 1# reactor and the remaining 30% methanol vapor, forming a large number of microbubbles in the 2# reactor, further converting the unreacted HCl into methyl chloride, the reactor pressure is 0.25MPag, and the temperature is 120°C.

[0033] The reaction product gas from the 2# reactor is cooled to 115°C by the primary cooler, and the cooled liquid phase is returned to the 2# reactor to maintain the liquid level of the 1# reactor and the 2# reactor stable. The gas phase is further cooled by the secondary cooler, and the cooled methanol-rich liquid goes to the lower part of the methanol recovery tower, and the gas phase enters the chloromethane distillation tower. The operating pressure of the chloromethane distillation tower is 0.2MPag. The gas phase at the top of the tower is condensed by the top condenser of the distillation tower and enters the reflux tank of the distillation tower. The crude chloromethane (chloromethane>99.3%wt, dimethyl ether<0.5%wt) is sent to the downstream process for purification and compression as a gas phase product, and the liquid phase is pressurized by the distillation tower reflux pump and sent back to the chloromethane distillation tower. The methanol-rich liquid at the bottom of the chloromethane distillation tower is partially extracted and sent to the methanol recovery tower. The operating pressure of the methanol recovery tower is 0.15MPag. The gas at the top of the tower is condensed by the recovery tower top condenser and then enters the recovery tower reflux tank. A small amount of non-condensable gas is sent to the downstream device for treatment as waste gas. The liquid phase is sent back to the methanol recovery tower after being pressurized by the recovery tower reflux pump. Part of it enters the No. 1 reactor as circulating rich methanol; part of the liquid at the bottom of the methanol recovery tower is sent to the sewage treatment device as waste liquid (HCl concentration <2%wt).

[0034] The total HCl conversion rate is >99.4%, the methanol conversion rate is >99.4%, and the byproduct dimethyl ether / product methyl chloride is <0.5%.

[0035] Example 3

[0036] After methanol and circulating rich methanol are gasified, 60% of methanol vapor enters the 1# microbubble generator together with all hydrogen chloride gas, the molar ratio of hydrogen chloride to methanol vapor is 1.3:1, a large number of microbubbles are formed in the 1# reactor, and methyl chloride synthesis reaction occurs, the reactor pressure is 0.2MPag, and the temperature is 125°C. Unreacted HCl enters the 2# microbubble generator along with the gas phase of the 1# reactor and the remaining 40% methanol vapor, forming a large number of microbubbles in the 2# reactor, further converting the unreacted HCl into methyl chloride, the reactor pressure is 0.15MPag, and the temperature is 110°C.

[0037] The reaction product gas from the 2# reactor is cooled to 105°C by the primary cooler, and the cooled liquid phase is returned to the 2# reactor to maintain the liquid level of the 1# reactor and the 2# reactor stable. The gas phase is further cooled by the secondary cooler, and the cooled methanol-rich liquid goes to the lower part of the methanol recovery tower, and the gas phase enters the chloromethane distillation tower. The operating pressure of the chloromethane distillation tower is 0.1MPag. The gas phase at the top of the tower is condensed by the top condenser of the distillation tower and enters the reflux tank of the distillation tower. The crude chloromethane (chloromethane>99.3%wt, dimethyl ether<0.5%wt) is sent to the downstream process for purification and compression as a gas phase product, and the liquid phase is pressurized by the distillation tower reflux pump and sent back to the chloromethane distillation tower. The methanol-rich liquid at the bottom of the chloromethane distillation tower is partially extracted and sent to the methanol recovery tower. The operating pressure of the methanol recovery tower is 0.1MPag. The gas at the top of the tower is condensed by the recovery tower top condenser and then enters the recovery tower reflux tank. A small amount of non-condensable gas is sent to the downstream device for treatment as waste gas. The liquid phase is sent back to the methanol recovery tower after being pressurized by the recovery tower reflux pump. Part of it enters the No. 1 reactor as circulating rich methanol; part of the liquid at the bottom of the methanol recovery tower is sent to the sewage treatment device as waste liquid (HCl concentration <2%wt).

[0038] The total HCl conversion rate is >99.0%, the methanol conversion rate is >99.0%, and the byproduct dimethyl ether / product methyl chloride is <0.5%.

Claims

1. A low-pressure liquid phase synthesis and separation method of methyl chloride, characterized in that: The synthesis and separation method specifically comprises the following steps: methanol and circulating rich methanol are vaporized in a methanol vaporizer (1) to form methanol vapor; a part of the methanol vapor enters a No. 1 microbubble generator (2) together with the whole hydrogen chloride gas to react in a No. 1 reactor (3); the gas phase after the reaction is completed enters a No. 2 microbubble generator (4) together with the remaining methanol vapor to react in a No. 2 reactor (5); the gas phase after the reaction is cooled in a primary cooler (6), the liquid phase flows back to the No. 2 reactor (5), and the gas phase goes to a secondary cooler (7); the gas phase after the secondary cooling enters a chloromethane distillation tower (8), and the liquid phase enters a methanol recovery tower (13).

2. The low-pressure liquid phase synthesis and separation method of methyl chloride according to claim 1, characterized in that: The top vapor of the chloromethane distillation tower (8) is condensed by the distillation tower top condenser (9) and then enters the distillation tower reflux tank (10), the gas phase is the crude chloromethane product, and the liquid phase is pressurized by the distillation tower reflux pump (11) and then sent back to the chloromethane distillation tower (8); part of the liquid at the bottom of the chloromethane distillation tower (8) is heated by the distillation tower reboiler (12) and then returned to the chloromethane distillation tower (8), and part of the liquid is sent to the methanol recovery tower (13).

3. The low-pressure liquid phase synthesis and separation method of methyl chloride according to claim 1, characterized in that: The top steam of the methanol recovery tower (13) is condensed by the recovery tower top condenser (14) and then enters the recovery tower reflux tank (15). The gas phase is the process waste gas. The liquid phase is pressurized by the recovery tower reflux pump (16) and then partly sent back to the methanol recovery tower (13), and partly enters the No. 1 reactor (3) as circulating rich methanol; part of the liquid at the bottom of the methanol recovery tower (13) is heated by the recovery tower reboiler (17) and then returned to the methanol recovery tower (13), and part of the liquid is discharged as waste liquid.

4. The low-pressure liquid phase synthesis and separation method of methyl chloride according to claim 1, characterized in that: The molar ratio of hydrogen chloride to methanol vapor entering the 1# microbubble generator (2) is 1.1:1 to 1.3:

1.

5. The low-pressure liquid phase synthesis and separation method of methyl chloride according to claim 1, characterized in that: The operating pressure of the No. 1 reactor (3) is 0.1-0.3 MPag, and the operating temperature is 100-140°C.

6. The low-pressure liquid phase synthesis and separation method of methyl chloride according to claim 1, characterized in that: The volume ratio of the methanol vapor entering the 2# microbubble generator (4) to the methanol vapor entering the 1# microbubble generator (2) is 2:3 to 3:

17.

7. The low-pressure liquid phase synthesis and separation method of methyl chloride according to claim 1, characterized in that: The operating pressure of the No. 2 reactor (5) is 0.1-0.3 MPag and the operating temperature is 100-130°C.

8. The low-pressure liquid phase synthesis and separation method of methyl chloride according to claim 1, characterized in that: The operating pressure of the methyl chloride distillation tower (8) is 0.1-0.25 MPag.

9. The low-pressure liquid phase synthesis and separation method of methyl chloride according to claim 1, characterized in that: The operating pressure of the methanol recovery tower (13) is 0.05-0.2 MPag.

10. The low-pressure liquid phase synthesis and separation method of methyl chloride according to claim 1, characterized in that: The bottom of the No. 1 reactor (3) is connected to the No. 2 reactor (5) through a pipeline.

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