Chloromethane synthesis process without generation of byproduct hydrochloric acid

Abstract

The invention discloses a chloromethane synthesis process without generation of byproduct hydrochloric acid, which comprises the following steps: S1, hydrogen chloride and methanol are subjected to mixed reaction in a chloromethane reaction system, and a gas phase discharged from the chloromethane reaction system enters a hydrochloric acid separation system for primary washing separation; s2, returning one part of a liquid phase discharged from the hydrochloric acid separation system to the chloromethane reaction system, and enabling the other part of the liquid phase to enter a stripping tower for stripping separation; s3, the gas phase discharged from the hydrochloric acid separation system enters a hydrogen chloride washing system for secondary washing separation, the gas phase discharged from the hydrogen chloride washing system is condensed and then enters a chloromethane purification system, and one part of the liquid phase discharged from the hydrogen chloride washing system returns to the hydrogen chloride washing system for recycling; and the other part returns to the hydrochloric acid separation system to be recycled as a washing solution. The process has the advantages of simple process flow, high conversion efficiency, low energy consumption and few byproducts, and can generate better economic benefits and environmental benefits.

Description

Technical Field

[0001] The invention belongs to the technical field of organosilicon production technology, and specifically relates to a chloromethane synthesis process without producing by-product hydrochloric acid. Background Art

[0002] Chloromethane is an important chemical raw material for the production of organic silicon, methane chloride and other products. At present, the production technology of methane chloride at home and abroad is quite mature, the production capacity of a single machine has exceeded 40Kt / a, and the economic and technical indicators are also high. The mainstream production processes mainly include liquid phase catalytic method, gas-solid phase catalytic method and liquid phase non-catalytic method. Regardless of which of the above methods is used, the equation for preparing chloromethane is as follows: Main reaction: CH 3 OH + HCl → CH 3 Cl+H 2 O (1) Side reaction: 2CH 3 OH→CH 3 OCH 3 +H 2 O (2) CH 3 OCH 3 +HCl→CH 3 Cl+H 2 O (3) As the domestic chlorination industry develops towards high quality and environmental protection, in the process of preparing methyl chloride using the above-mentioned synthesis process, it is hoped that the process technology route for preparing methyl chloride will achieve the following technical indicators: first, high conversion efficiency, the conversion rate of methanol and hydrogen chloride put into the system is close to 100%; second, as few by-products as possible, the reaction product is as much as possible methyl chloride, reducing the formation of by-product dimethyl ether; third, as little hydrochloric acid as possible; the reaction produces water, and the amount is fixed. Water will absorb hydrogen chloride to form hydrochloric acid, and it is necessary to control as little hydrogen chloride as possible to be absorbed to form hydrochloric acid for discharge; fourth, high energy utilization rate, the reaction is an exothermic reaction, and the system needs to consider the comprehensive utilization of the reaction heat. In recent years, with the development and growth of the silicone industry, domestic research and development institutions and production enterprises have also carried out a lot of research and experimental work around the above four technical indicators for the existing chloroform production process technology. However, it still cannot fundamentally solve the problem of clean production of chloroform. In the actual production process of chloroform, there are still many problems such as long process flow, many auxiliary materials used, low conversion rate, high energy consumption, and discharge of by-products or hydrochloric acid.

[0003] For example, the publication number CN 103351274A discloses a process for synthesizing methyl chloride in a gas-liquid phase at low temperature and low pressure. The process flow is that gaseous hydrogen chloride and liquid methanol are sequentially subjected to synthesis reactions in at least four reaction vessels connected in series, and methyl chloride is synthesized at 60-85° C. and a pressure of no more than 0.1 MPa. The gaseous hydrogen chloride entrained in the synthesized gaseous methyl chloride reacts with liquid methane again, and the gaseous methyl chloride from which the gaseous hydrogen chloride has been removed is washed with water, washed with alkali and washed with acid according to the existing method, and methyl chloride is obtained after condensation and compression. The process adopts a multi-stage series reaction at low temperature and low pressure. Although the conversion rate is improved, the generation and emission of waste hydrochloric acid are not reduced, and the problem of clean production of methyl chloride still cannot be solved.

[0004] For example, the publication number CN 102234216A discloses a process for producing methyl chloride by a gas-liquid phase non-catalytic method. The general steps of the process are: methanol and excess hydrogen chloride enter the reactor from the lower part of the reactor after heat exchange, the reaction temperature is 120°C, the pressure is 1.06MPa, a distillation tower is located above the reactor, the reflux ratio of the distillation is controlled at 1-2, and the methyl chloride saturated with hydrogen chloride is separated. The unreacted methanol, dimethyl ether and water are returned to the reactor, and part of the reaction liquid enters the stripping tower to evaporate the dissolved chlorine. Organic substances such as methane and methanol, the azeotropic liquid containing hydrogen chloride discharged from the bottom of the tower can further absorb hydrogen chloride to become 32% HCl Hydrochloric acid, the gas separated from the top of the distillation tower is condensed, gas-liquid separated, refluxed, and a part of it enters the hydrogen chloride separation tower. The hydrogen chloride separated from the top of the tower is returned to the reactor, and the product methyl chloride is obtained in the bottom of the tower. Although this process also uses a hydrogen chloride separation tower to separate hydrogen chloride from methyl chloride, a large amount of waste acid is still generated during the reaction distillation of the distillation tower.

[0005] For example, the publication number CN111606776A discloses a liquid-phase catalyst-free synthesis of methyl chloride clean production process, the process of which is to introduce gaseous hydrogen chloride or a mixture of hydrochloric acid and methanol in a ratio of 10 to 25% into a main reactor for synthesis reaction, then introduce the methyl chloride at the outlet of the main reactor, unreacted hydrogen chloride and excess methanol mixed gas into the main reactor for synthesis reaction, the synthesized methyl chloride mixed gas is subjected to non-aqueous washing, freeze dehydration, dedimethyl ether removal, pressurization and condensation, and then the product is collected. The process adopts a liquid-phase non-catalytic reaction, and although no waste acid is ultimately produced, the hydrochloric acid normal desorption process is actually combined in the system, and the hydrochloric acid normal desorption requires a large amount of energy consumption, which will cause the problem of high energy consumption in the production process.

[0006] The publication number is CN115745733A, which discloses a chloromethane synthesis process. The process includes a reaction stage and a separation and liquefaction stage. In the reaction stage, gaseous hydrogen chloride, hydrochloric acid solution, and preheated gaseous methanol are used as raw materials, and the raw materials are passed into a primary reactor for synthesis reaction. The products of the primary reactor include synthesized chloromethane, water, unreacted hydrogen chloride, and a methanol mixed solution. Liquid methanol is added into a secondary reactor, and the chloromethane, water, hydrogen chloride, and methanol mixed solution in the primary reactor are passed into the secondary reactor for synthesis reaction. The products of the secondary reactor include synthesized chloromethane, water, dimethyl ether, unreacted hydrogen chloride, and a methanol mixed solution. The process adopts a liquid-phase non-catalytic two-stage reaction, and excessive addition of methanol reduces the generation of dimethyl ether. Afterwards, a hydrochloric acid separation tower is used in the separation and liquefaction stage to separate chloromethane, methanol, and hydrochloric acid, and then a methanol separation tower is used to separate methanol and wastewater. Although no waste acid is generated in the end, a large amount of energy consumption is still required in the process of separating methanol using the methanol separation tower, and the operating cost is high. The publication number is CN209555111U, which discloses a device for synthesizing hydrochloric acid without by-product from methyl chloride. The device has a primary reactor, a secondary reactor, an alcohol-water separator, and a methyl chloride gas tank. Although this method adopts a liquid-phase non-catalytic secondary reaction to improve the conversion efficiency of methyl chloride, the methyl chloride is washed by a water washing tower, and then a methanol separation tower is used to separate methanol and wastewater. As mentioned above, although no waste acid is produced in the methanol separation, the separation process still consumes a lot of energy.

[0007] In summary, the above-mentioned process methods have two major shortcomings: high process energy consumption and large amount of waste acid produced, resulting in high operating costs. Therefore, it is an objective need to develop a chloromethane synthesis process with a simple process flow, high conversion efficiency, low energy consumption, and few by-products. Summary of the invention

[0008] In order to solve the technical problems of high process energy consumption and waste acid generation in the background technology, the object of the present invention is to provide a chloromethane synthesis process with simple process flow, high conversion efficiency, low energy consumption and few by-products.

[0009] The present invention discloses a chloromethane synthesis process without producing by-product hydrochloric acid, comprising the following steps: S1: Hydrogen chloride and methanol are mixed and reacted in an equimolar ratio in a methyl chloride reaction system, and the gas phase discharged from the methyl chloride reaction system enters a hydrochloric acid separation system for a washing and separation; S2: A portion of the liquid phase discharged from the hydrochloric acid separation system is returned to the methyl chloride reaction system to participate in the mixed reaction, and the other portion enters the stripping tower for stripping separation. The gas phase discharged from the top of the stripping tower enters the hydrochloric acid separation system for washing and separation. A portion of the liquid phase discharged from the bottom of the stripping tower is heated by a falling film evaporator and returned to the stripping tower for recycling, and the other portion is returned to the methyl chloride reaction system to participate in the mixed reaction; S3: The gas phase discharged from the hydrochloric acid separation system enters the hydrogen chloride washing system for secondary washing and separation. The gas phase discharged from the hydrogen chloride washing system is condensed in the condenser and then enters the methyl chloride purification system for purification to obtain the methyl chloride product. The condensed waste water discharged from the condenser enters the reflux tank and a part of it enters the sewage treatment system for purification, and the other part is pressurized and heated before entering the hydrogen chloride washing system for recycling as washing liquid. A part of the liquid phase discharged from the hydrogen chloride washing system is returned to the hydrogen chloride washing system for recycling as reflux liquid, and the other part is returned to the hydrochloric acid separation system for recycling as washing liquid.

[0010] Compared with the traditional chloromethane synthesis process, the advantages of this process are: First, when methane and hydrogen chloride react in the methyl chloride reaction system, the reaction heat of methanol and hydrogen chloride and the steam heat of the stripping tower are used to separate the gas phase entering the hydrochloric acid separation system into gas and liquid, so that the reaction heat and steam heat waste heat can be fully utilized, which can reduce the energy consumption of the hydrochloric acid separation system and the hydrogen chloride washing system, thereby reducing the operating cost; Secondly, a hydrogen chloride washing system is used to circulate and wash the gas phase discharged from the hydrochloric acid separation system, and hydrogen chloride and methanol entrained in the gas phase can be washed and recovered, thereby reducing the HCl content in the condensed wastewater. The HCl content in the condensed wastewater is less than 1%, and the condensed wastewater directly enters the wastewater treatment, which reduces the difficulty of wastewater treatment and saves production costs. At the same time, the condensed wastewater generated by the condenser is pressurized and heated and then returned to the hydrogen chloride washing system for recycling. No waste acid is generated in the production process, which avoids the phenomenon of waste acid discharge, and solves the problem of clean production in the methyl chloride synthesis process; Third, a stripping tower is used to separate the liquid phase at the bottom of the hydrogen chloride separation system. The gas phase at the top of the stripping tower enters the hydrogen chloride separation system to continue the reaction, and the liquid phase at the bottom enters the methyl chloride synthesis system to react. The two-stage cycle is used to enhance the mass transfer and heat transfer reaction, which not only makes the reaction more complete and significantly improves the conversion rate of methanol and hydrogen chloride, but also ensures the stability of the reaction process, effectively reduces the generation of by-products hydrochloric acid and dimethyl ether, and has fewer by-products in the reaction process, which is conducive to improving the product quality of methyl chloride; In summary, this process has the advantages of simple process flow, high conversion efficiency, low energy consumption, and few by-products. It can produce good economic and environmental benefits and is easy to promote and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a structural schematic diagram of the present invention; In the figure: 1-chloromethane reaction system, 2-hydrochloric acid separation system, 3-hydrogen chloride washing system, 4-chloromethane purification system, 5-condenser, 6-reflux tank, 7-stripping tower, 8-falling film evaporator, 9-wastewater treatment system. DETAILED DESCRIPTION

[0012] The present invention is further described below in conjunction with the embodiments and accompanying drawings, but the present invention is not limited in any way. Any changes or substitutions made based on the teachings of the present invention belong to the protection scope of the present invention. Example 1

[0013] The methyl chloride synthesis process without by-product hydrochloric acid production described in this embodiment 1 comprises the following steps: S1: Hydrogen chloride and methanol are mixed and reacted in an equimolar ratio in a methyl chloride reaction system 1, methanol is in a liquid phase or a gas phase, the gas phase discharged from the methyl chloride reaction system 1 enters a hydrochloric acid separation system 2 for a washing separation, the gas phase discharged from the methyl chloride reaction system 1 includes methyl chloride, hydrogen chloride, methanol, dimethyl ether and water, the methyl chloride mixed reaction system 1 includes 1 to 3 reactors connected in series, the liquid phase of each stage of the reactor is connected, the reactors can be powered step by step by a pump, or the potential difference can be used for gravity transport of chlorine, the gas phase between each stage of the reactor is connected to the hydrochloric acid separation system 2 through a pipeline, the temperature of the methyl chloride reaction system 1 is controlled at 105°C, and the pressure is controlled at 105°C. At 0.1MPa, in order to improve the conversion rate of the chloromethane reaction system, the hydrochloric acid separation system 2 is a hydrochloric acid separation tower, the hydrochloric acid separation tower adopts a packed tower, the tower bottom temperature is controlled at 105°C, the tower top temperature is controlled at 105°C, and the pressure is controlled at 0.1MPa. The liquid phase discharged from the chloromethane reaction system 1 is an azeotropic acid containing HCl, and the azeotropic acid concentration is about 20%. In order to improve the conversion rate of the chloromethane reaction system 1, the liquid phase discharged from the chloromethane reaction system 1 enters the stripping tower 7 for stripping separation, reducing the liquid phase storage capacity in the chloromethane reaction system 1 and improving the conversion rate of hydrogen chloride and methanol; S2: A portion of the liquid phase discharged from the hydrochloric acid separation system 2 is returned to the methyl chloride reaction system 1 to participate in the mixed reaction, and the other portion enters the stripping tower 7 for stripping separation. The liquid phase discharged from the bottom of the hydrochloric acid separation system 2 is waste water that absorbs hydrogen chloride, methanol and dimethyl ether. This can ensure the stability of the methyl chloride reaction system 1 and improve the conversion rate of the reaction. The gas phase discharged from the top of the stripping tower 7 enters the hydrochloric acid separation system 2 for washing and separation. The stripping tower 7 adopts a packed tower, the tower bottom temperature is controlled to be greater than 120°C, the tower top temperature is controlled to be 105°C, and the pressure needs to be higher than that of the hydrochloric acid separation system 2. 0.05MPa or more, the gas phase discharged from the stripping tower 7 is mainly methyl chloride and methanol, the liquid phase discharged from the bottom of the stripping tower 7 is hydrochloric acid, the concentration is constant boiling acid under the operating temperature and pressure, the constant boiling acid concentration is 21-22%, the concentration is higher than the hydrochloric acid concentration of the methyl chloride reaction system 1, a part of the liquid phase discharged from the bottom of the stripping tower 7 is heated by the falling film evaporator 8 and returned to the stripping tower 7 for recycling, and the other part is returned to the methyl chloride reaction system 1 to participate in the mixed reaction. In order to improve the efficiency of washing and separation, a part of the liquid phase discharged from the bottom of the stripping tower 7 is returned to the hydrochloric acid separation system 2 as a washing liquid for recycling; S3: The gas phase discharged from the hydrochloric acid separation system 2 enters the hydrogen chloride washing system 3 for secondary washing and separation. The hydrogen chloride washing system 3 is a washing tower. The washing tower adopts a packed tower. The kettle temperature is controlled at 105°C, the tower top temperature is controlled at 105°C, and the pressure is controlled at 0.1MPa. The gas phase discharged from the top of the hydrochloric acid separation system 2 is methyl chloride and a small amount of methanol and dimethyl ether. After washing and separation in the hydrogen chloride washing system 3, the methanol and dimethyl ether in the methyl chloride can be completely separated. The gas phase discharged from the hydrogen chloride washing system 3 is condensed in the condenser 5 and then enters the methyl chloride purification system 4 for purification to obtain the methyl chloride product. The gas phase discharged from the top of the hydrogen chloride washing system 3 is methyl chloride. The circulating water is used in the condenser 5 to cool the incoming gas phase. The gas phase outlet temperature of the condenser 5 is controlled at 40°C. The condensed waste water discharged from the condenser 5 enters the reflux tank 6 and a part of it enters the sewage treatment system 9 for purification. The HCl content in the wastewater discharged from the condenser 5 is very low, less than 1%. The other part is pressurized and heated before entering the hydrogen chloride washing system 3 for recycling as washing liquid. The wastewater discharged from the reflux tank 6 is first heated by a pressure pump and then by a steam heater. The wastewater replenishment amount entering the hydrogen chloride washing system 1 after heating is 1m 3 / h, a part of the liquid phase discharged from the hydrogen chloride washing system 3 is returned to the hydrogen chloride washing system 3 for recycling as reflux liquid, and the other part is returned to the hydrochloric acid separation system 2 for recycling as washing liquid. The liquid phase discharged from the bottom of the hydrogen chloride washing system 3 is waste water that absorbs a small amount of methanol and dimethyl ether. The liquid phase discharged from the bottom of the hydrogen chloride washing system 3 is returned to the hydrogen chloride washing system 3 and the hydrochloric acid separation system 2 for recycling, which can reduce the discharge of waste acid, save water resources and reduce energy consumption.

[0014] The process flow of the present embodiment 1 is simple, which can not only make full use of the heat generated by the reaction heat and the steam heat, reduce the energy consumption of the hydrochloric acid separation system 2 and the hydrogen chloride washing system 3, and reduce the operating cost, but also can wash and recover the methanol, hydrogen chloride, etc. entrained in the methyl chloride, which can greatly reduce the HCl content in the wastewater, and the HCl content in the wastewater is less than 1%. No waste acid is generated during the production process, which avoids the phenomenon of waste acid discharge, solves the problem of clean production in the methyl chloride synthesis process, and significantly improves the conversion rate of methanol and hydrogen chloride. There are few by-products in the reaction process, which effectively improves the product purity of methyl chloride, and can obtain better economic and environmental benefits. Example 2

[0015] The methyl chloride synthesis process without by-product hydrochloric acid production described in this embodiment 2 comprises the following steps: S1: Hydrogen chloride and methanol are mixed and reacted in an equimolar ratio in a methyl chloride reaction system 1, methanol is in a liquid phase or a gas phase, the gas phase discharged from the methyl chloride reaction system 1 enters a hydrochloric acid separation system 2 for a washing separation, the gas phase discharged from the methyl chloride reaction system 1 includes methyl chloride, hydrogen chloride, methanol, dimethyl ether and water, the methyl chloride mixed reaction system 1 includes 1 to 3 reactors connected in series, the liquid phase of each reactor is connected, the reactors can be powered step by step by a pump, or the potential difference can be used to gravity transport chlorine, the gas phase between each reactor is connected to the hydrochloric acid separation system 2 through a pipeline, the temperature of the methyl chloride reaction system 1 is controlled at 112°C, and the pressure is controlled at 112°C. At 0.2MPa, in order to improve the conversion rate of the chloromethane reaction system, the hydrochloric acid separation system 2 is a hydrochloric acid separation tower, the hydrochloric acid separation tower adopts a packed tower, the tower bottom temperature is controlled at 112°C, the tower top temperature is controlled at 112°C, and the pressure is controlled at 0.2MPa. The liquid phase discharged from the chloromethane reaction system 1 is an azeotropic acid containing HCl, and the azeotropic acid concentration is about 20%. In order to improve the conversion rate of the chloromethane reaction system 1, the liquid phase discharged from the chloromethane reaction system 1 enters the stripping tower 7 for stripping separation, reducing the liquid phase storage capacity in the chloromethane reaction system 1 and improving the conversion rate of hydrogen chloride and methanol; S2: A part of the liquid phase discharged from the hydrochloric acid separation system 2 is returned to the methyl chloride reaction system 1 to participate in the mixed reaction, and the other part enters the stripping tower 7 for stripping separation. The liquid phase discharged from the bottom of the hydrochloric acid separation system 2 is waste water that absorbs hydrogen chloride, methanol and dimethyl ether. This can ensure the stability of the methyl chloride reaction system 1 and improve the conversion rate of the reaction. The gas phase discharged from the top of the stripping tower 7 enters the hydrochloric acid separation system 2 for washing and separation. The stripping tower 7 adopts a packed tower, the tower bottom temperature is controlled to be greater than 120°C, the tower top temperature is controlled to be 112°C, and the pressure needs to be higher than that of the hydrochloric acid separation system 2. 0.05MPa or more, the gas phase discharged from the stripping tower 7 is mainly methyl chloride and methanol, the liquid phase discharged from the bottom of the stripping tower 7 is hydrochloric acid, the concentration is constant boiling acid under the operating temperature and pressure, the constant boiling acid concentration is 21-22%, the concentration is higher than the hydrochloric acid concentration of the methyl chloride reaction system 1, a part of the liquid phase discharged from the bottom of the stripping tower 7 is heated by the falling film evaporator 8 and returned to the stripping tower 7 for recycling, and the other part is returned to the methyl chloride reaction system 1 to participate in the mixed reaction. In order to improve the efficiency of washing and separation, a part of the liquid phase discharged from the bottom of the stripping tower 7 is returned to the hydrochloric acid separation system 2 as a washing liquid for recycling; S3: The gas phase discharged from the hydrochloric acid separation system 2 enters the hydrogen chloride washing system 3 for secondary washing and separation. The hydrogen chloride washing system 3 is a washing tower. The washing tower adopts a packed tower. The kettle temperature is controlled at 112°C, the tower top temperature is controlled at 112°C, and the pressure is controlled at 0.2MPa. The gas phase discharged from the top of the hydrochloric acid separation system 2 is methyl chloride and a small amount of methanol and dimethyl ether. After washing and separation in the hydrogen chloride washing system 3, the methanol and dimethyl ether in the methyl chloride can be completely separated. The gas phase discharged from the hydrogen chloride washing system 3 is condensed in the condenser 5 and then enters the methyl chloride purification system 4 for purification to obtain the methyl chloride product. The gas phase discharged from the top of the hydrogen chloride washing system 3 is methyl chloride. The circulating water is used in the condenser 5 to cool the incoming gas phase. The gas phase outlet temperature of the condenser 5 is controlled at 50°C. The condensed waste water discharged from the condenser 5 enters the reflux tank 6 and a part of it enters the sewage treatment system 9 for purification. The HCl content in the wastewater discharged from the condenser 5 is very low, less than 1%. The other part is pressurized and heated before entering the hydrogen chloride washing system 3 for recycling as washing liquid. The wastewater discharged from the reflux tank 6 is first heated by a pressure pump and then by a steam heater. The wastewater replenishment amount entering the hydrogen chloride washing system 1 after heating is 2m 3 / h, a part of the liquid phase discharged from the hydrogen chloride washing system 3 is returned to the hydrogen chloride washing system 3 for recycling as reflux liquid, and the other part is returned to the hydrochloric acid separation system 2 for recycling as washing liquid. The liquid phase discharged from the bottom of the hydrogen chloride washing system 3 is waste water that absorbs a small amount of methanol and dimethyl ether. The liquid phase discharged from the bottom of the hydrogen chloride washing system 3 is returned to the hydrogen chloride washing system 3 and the hydrochloric acid separation system 2 for recycling, which can reduce the discharge of waste acid, save water resources and reduce energy consumption.

[0016] The process flow of this embodiment 2 is simple, which not only enables the heat generated by the reaction heat and steam heat to be fully utilized, reduces the energy consumption of the hydrochloric acid separation system 2 and the hydrogen chloride washing system 3, and reduces the operating cost, but also can wash and recover the methanol, hydrogen chloride, etc. entrained in the methyl chloride, which can greatly reduce the HCl content in the wastewater, and the HCl content in the wastewater is less than 1%. No waste acid is generated during the production process, which avoids the phenomenon of waste acid discharge, solves the problem of clean production in the methyl chloride synthesis process, and significantly improves the conversion rate of methanol and hydrogen chloride. There are few by-products in the reaction process, which effectively improves the product purity of methyl chloride, and can obtain better economic and environmental benefits. Example 3

[0017] The methyl chloride synthesis process without by-product hydrochloric acid production described in this embodiment 3 comprises the following steps: S1: Hydrogen chloride and methanol are mixed and reacted in an equimolar ratio in a methyl chloride reaction system 1, methanol is in a liquid phase or a gas phase, the gas phase discharged from the methyl chloride reaction system 1 enters a hydrochloric acid separation system 2 for a washing separation, the gas phase discharged from the methyl chloride reaction system 1 includes methyl chloride, hydrogen chloride, methanol, dimethyl ether and water, the methyl chloride mixed reaction system 1 includes 1 to 3 reactors connected in series, the liquid phase of each stage of the reactor is connected, the reactors can be powered step by step by a pump, or the potential difference can be used for gravity transport of chlorine, the gas phase between each stage of the reactor is connected to the hydrochloric acid separation system 2 through a pipeline, the temperature of the methyl chloride reaction system 1 is controlled at 120°C, and the pressure is controlled at 120°C. At 0.3MPa, in order to improve the conversion rate of the chloromethane reaction system, the hydrochloric acid separation system 2 is a hydrochloric acid separation tower, the hydrochloric acid separation tower adopts a packed tower, the tower bottom temperature is controlled at 120°C, the tower top temperature is controlled at 115°C, and the pressure is controlled at 0.3MPa. The liquid phase discharged from the chloromethane reaction system 1 is an azeotropic acid containing HCl, and the azeotropic acid concentration is about 20%. In order to improve the conversion rate of the chloromethane reaction system 1, the liquid phase discharged from the chloromethane reaction system 1 enters the stripping tower 7 for stripping separation, reducing the liquid phase storage capacity in the chloromethane reaction system 1 and improving the conversion rate of hydrogen chloride and methanol; S2: A part of the liquid phase discharged from the hydrochloric acid separation system 2 is returned to the methyl chloride reaction system 1 to participate in the mixed reaction, and the other part enters the stripping tower 7 for stripping separation. The liquid phase discharged from the bottom of the hydrochloric acid separation system 2 is waste water that absorbs hydrogen chloride, methanol and dimethyl ether. This can ensure the stability of the methyl chloride reaction system 1 and improve the conversion rate of the reaction. The gas phase discharged from the top of the stripping tower 7 enters the hydrochloric acid separation system 2 for washing and separation. The stripping tower 7 adopts a packed tower, the tower bottom temperature is controlled to be greater than 120°C, the tower top temperature is controlled to be 120°C, and the pressure needs to be higher than that of the hydrochloric acid separation system 2. 0.05MPa or more, the gas phase discharged from the stripping tower 7 is mainly methyl chloride and methanol, the liquid phase discharged from the bottom of the stripping tower 7 is hydrochloric acid, the concentration is constant boiling acid under the operating temperature and pressure, the constant boiling acid concentration is 21-22%, the concentration is higher than the hydrochloric acid concentration of the methyl chloride reaction system 1, a part of the liquid phase discharged from the bottom of the stripping tower 7 is heated by the falling film evaporator 8 and returned to the stripping tower 7 for recycling, and the other part is returned to the methyl chloride reaction system 1 to participate in the mixed reaction. In order to improve the efficiency of washing and separation, a part of the liquid phase discharged from the bottom of the stripping tower 7 is returned to the hydrochloric acid separation system 2 as a washing liquid for recycling; S3: The gas phase discharged from the hydrochloric acid separation system 2 enters the hydrogen chloride washing system 3 for secondary washing and separation. The hydrogen chloride washing system 3 is a washing tower. The washing tower adopts a packed tower. The kettle temperature is controlled at 120°C, the tower top temperature is controlled at 120°C, and the pressure is controlled at 0.3MPa. The gas phase discharged from the top of the hydrochloric acid separation system 2 is methyl chloride and a small amount of methanol and dimethyl ether. After washing and separation in the hydrogen chloride washing system 3, the methanol and dimethyl ether in the methyl chloride can be completely separated. The gas phase discharged from the hydrogen chloride washing system 3 is condensed in the condenser 5 and then enters the methyl chloride purification system 4 for purification to obtain the methyl chloride product. The gas phase discharged from the top of the hydrogen chloride washing system 3 is methyl chloride. The condenser 5 uses circulating water to cool the incoming gas phase. The gas phase outlet temperature of the condenser 5 is controlled at 60°C. The condensed waste water discharged from the condenser 5 enters the reflux tank 6 and a part of it enters the sewage treatment system 9 for purification. The HCl content in the wastewater discharged from the condenser 5 is very low, less than 1%. The other part is pressurized and heated before entering the hydrogen chloride washing system 3 for recycling as washing liquid. The wastewater discharged from the reflux tank 6 is first heated by a pressure pump and then by a steam heater. The wastewater replenishment amount entering the hydrogen chloride washing system 1 after heating is 3m 3 / h, a part of the liquid phase discharged from the hydrogen chloride washing system 3 is returned to the hydrogen chloride washing system 3 for recycling as reflux liquid, and the other part is returned to the hydrochloric acid separation system 2 for recycling as washing liquid. The liquid phase discharged from the bottom of the hydrogen chloride washing system 3 is waste water that absorbs a small amount of methanol and dimethyl ether. The liquid phase discharged from the bottom of the hydrogen chloride washing system 3 is returned to the hydrogen chloride washing system 3 and the hydrochloric acid separation system 2 for recycling, which can reduce the discharge of waste acid, save water resources and reduce energy consumption.

[0018] The process flow of this embodiment 3 is simple, which not only enables the heat generated by the reaction heat and steam heat to be fully utilized, reduces the energy consumption of the hydrochloric acid separation system 2 and the hydrogen chloride washing system 3, and reduces the operating cost, but also can wash and recover the methanol, hydrogen chloride, etc. entrained in the methyl chloride, which can greatly reduce the HCl content in the wastewater, and the HCl content in the wastewater is less than 1%. No waste acid is generated during the production process, which avoids the phenomenon of waste acid discharge, solves the problem of clean production in the methyl chloride synthesis process, and significantly improves the conversion rate of methanol and hydrogen chloride. There are few by-products in the reaction process, which effectively improves the product purity of methyl chloride, and can obtain better economic and environmental benefits.

Claims

1. A chloromethane synthesis process without producing by-product hydrochloric acid, characterized in that: The following steps are involved: S1: Hydrogen chloride and methanol are mixed and reacted in an equimolar ratio in a methyl chloride reaction system (1), and the gas phase discharged from the methyl chloride reaction system (1) enters a hydrochloric acid separation system (2) for a washing and separation. S2: a portion of the liquid phase discharged from the hydrochloric acid separation system (2) is returned to the methyl chloride reaction system (1) to participate in the mixed reaction, and another portion enters the stripping tower (7) for stripping separation. The gas phase discharged from the top of the stripping tower (7) enters the hydrochloric acid separation system (2) for washing and separation. A portion of the liquid phase discharged from the bottom of the stripping tower (7) is heated by the falling film evaporator (8) and then returned to the stripping tower (7) for recycling. The other portion returns to the methyl chloride reaction system (1) to participate in the mixed reaction. S3: The gas phase discharged from the hydrochloric acid separation system (2) enters the hydrogen chloride washing system (3) for secondary washing and separation. The gas phase discharged from the hydrogen chloride washing system (3) is condensed in the condenser (5) and then enters the methyl chloride purification system (4) for purification to obtain a methyl chloride product. The condensed waste water discharged from the condenser (5) enters the reflux tank (6) and a part of it enters the sewage treatment system (9) for purification. The other part is then pressurized and heated and then enters the hydrogen chloride washing system (3) for recycling as a washing liquid. A part of the liquid phase discharged from the hydrogen chloride washing system (3) is returned to the hydrogen chloride washing system (3) for recycling as a reflux liquid, and the other part is returned to the hydrochloric acid separation system (2) for recycling as a washing liquid.

2. A chloromethane synthesis process without by-product hydrochloric acid production according to claim 1, characterized in that: A portion of the liquid phase discharged from the bottom of the stripping tower 7 is returned to the hydrochloric acid separation system (2) for recycling.

3. A chloromethane synthesis process without by-product hydrochloric acid production according to claim 1, characterized in that: The liquid phase discharged from the methyl chloride reaction system (1) enters a stripping tower (7) for stripping separation.

4. A chloromethane synthesis process without by-product hydrochloric acid production according to claim 1, characterized in that: The methyl chloride mixed reaction system (1) comprises 1 to 3 reaction kettles connected in series. The temperature of the methyl chloride reaction system 1 is controlled at 105 to 120° C., and the pressure is controlled at 0.1 to 0.3 MPa.

5. A chloromethane synthesis process without by-product hydrochloric acid production according to claim 1, characterized in that: The hydrochloric acid separation system (2) is a hydrochloric acid separation tower. The hydrochloric acid separation tower adopts a packed tower. The bottom temperature is controlled at 105-120°C, the top temperature is controlled at 105-115°C, and the pressure is controlled at 0.1-0.3MPa.

6. A chloromethane synthesis process without by-product hydrochloric acid production according to claim 1, characterized in that: The hydrogen chloride washing system (3) is a washing tower, which is a packed tower. The kettle temperature is controlled at 105-120°C, the tower top temperature is controlled at 105-120°C, and the pressure is controlled at 0.1-0.3MPa.

7. A chloromethane synthesis process without by-product hydrochloric acid production according to claim 1, characterized in that: The wastewater discharged from the reflux tank (6) is first heated by a pressure pump and then heated by a steam heater. The wastewater replenishment amount entering the hydrogen chloride washing system (1) after heating is 1 to 3 m 3 / h.

8. A chloromethane synthesis process without by-product hydrochloric acid production according to claim 1, characterized in that: Circulating water is used in the condenser (5) to cool the incoming gas phase, and the gas phase outlet temperature of the condenser (5) is controlled at 40 to 60°C.

9. A chloromethane synthesis process without by-product hydrochloric acid production according to claim 1, characterized in that: The stripping tower (7) is a packed tower, the bottom temperature is controlled to be greater than 120°C, the top temperature is controlled to be between 105°C and 120°C, and the pressure needs to be higher than that of the hydrochloric acid separation system (2) by more than 0.05 MPa.

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