Device and method for synthesizing chloromethane

Abstract

The invention provides a device and a method for synthesizing methyl chloride. The device comprises a reaction unit, a reaction unit and a control unit, wherein the reaction unit comprises a methanol feeding unit and a reactor; the hydrochloric acid separation unit comprises a hydrochloric acid separation tower, a compressor and a tower top condenser; the methanol recovery unit comprises a methanol recovery tower and a double-effect reboiler; and the chloromethane purification unit comprises a chloromethane separation tower. According to the invention, the compressor is additionally arranged to pressurize the tower top gas phase of the hydrochloric acid separation unit, so that the waste heat energy which is originally required to be removed by cooling water is changed into a heat source which can be directly used, and the reboiler and the methanol evaporator of the methanol recovery tower are directly heated. By recycling the heat energy, the consumption of steam and cooling water in the process flow is greatly reduced, and the ultralow energy consumption of the chloromethane synthesis device is realized.

Description

Technical Field

[0001] The present application relates to the field of chemical industry, and in particular to a device and method for synthesizing methyl chloride. Background Art

[0002] Methyl chloride (CH 3 Methyl chloride, also known as methyl chloride, has a certain anesthetic and pungent smell and active chemical properties. Due to its unique chemical structure and properties, methyl chloride is widely used in the chemical industry, including as a solvent, catalyst, methylating agent, etc. Specifically, the main application areas of methyl chloride include the following:

[0003] Pharmaceutical industry: Methyl chloride, as an important methylating agent, can be used to prepare a variety of drug molecules;

[0004] Pesticide industry: Methyl chloride can be used as an intermediate in the production process of some pesticides;

[0005] Synthetic materials: Methyl chloride can be used to produce high value-added chemicals such as silicone and silane;

[0006] Refrigerants: Methyl chloride can be used as a precursor for certain refrigerants.

[0007] At present, the demand for methyl chloride is increasing year by year, but its production process requires the use of toxic substances such as chlorine or hydrochloric acid. In addition, the production process is energy-intensive and highly polluting, and its preparation process needs to be further optimized. Therefore, the development of a safe, environmentally friendly, and low-energy methyl chloride synthesis method has important application value.

[0008] The synthesis methods of methyl chloride are relatively mature, and currently mainly include methanol chlorination, methane chlorination, methanol electrochemical chlorination, etc. The methanol chlorination production process is mainly used in actual industrial production, and its reaction formula is as follows:

[0009] CH 3 OH + HCl → CH 3 Cl+H 2 O.

[0010] Furthermore, the methanol chlorination method has two process directions:

[0011] 1. Excess hydrogen chloride method

[0012] The excess hydrogen chloride method refers to the process of synthesizing chloromethane, in which methanol (mol): hydrogen chloride (mol) = 1: (1.05 ~ 1.1) is reacted. Excess hydrogen chloride enables methanol to achieve a conversion rate of about 99% during the reaction. At the same time, in the process of synthesizing hydrogen chloride using the excess hydrogen chloride method, zinc chloride (ZnCl2) or aluminum chloride (AlCl3) is required as a catalyst to achieve a higher reaction rate. The process flow of the excess hydrogen chloride method generally includes process steps such as reaction, water washing, alkali washing, drying purification and compression liquefaction. The disadvantage of the excess hydrogen chloride method is that the separation and purification process is complicated. The recovery and separation of the excess hydrogen chloride will increase the complexity and energy consumption of the production process. The imperfect recovery and treatment of excess hydrogen chloride may cause waste gas emissions to exceed the standard, and additional investment in environmental protection facilities is required. In addition, about 70% of the steam heat in the excess hydrogen chloride method is consumed in hydrochloric acid analysis and deep desorption, and the remaining steam heat is consumed in the heating of the reaction materials and catalyst post-treatment, so there is still a pain point of high energy consumption.

[0013] 2. Methanol Excess Method

[0014] The methanol excess method refers to the process of synthesizing methyl chloride, in which the reaction is carried out at a ratio of methanol (mol): hydrogen chloride (mol) = (1.05-1.1): 1. Excess methanol enables the conversion rate of hydrogen chloride to be about 99% during the reaction. The methanol excess method generally does not use a catalyst, so the reaction speed is slow and a larger reactor is required to provide sufficient residence time.

[0015] The conventional methanol excess process generally includes two-stage reaction and multi-step distillation separation process steps to separate the components such as methyl chloride, hydrogen chloride, methanol, water, etc. from the reactor. The excess methanol is separated and recycled, and hydrogen chloride and water form waste hydrochloric acid and are discharged to the wastewater treatment unit. After the methyl chloride product is purified by sulfuric acid absorption, it is necessary to increase the pressure through a compressor to increase the boiling point and then condense it into a liquid. In the methanol excess method, about 60% of the steam heat is consumed in the reboiler of the methanol recovery tower, and about 35% of the steam heat is consumed in the vaporization of methanol before it enters the reactor. Summary of the invention

[0016] In response to the problems raised in the background technology, the present application provides a device and method for synthesizing methyl chloride. By optimizing the device for synthesizing methyl chloride, ultra-low energy consumption of the methyl chloride synthesis device is achieved.

[0017] An object of the present invention is to provide a device for synthesizing methyl chloride, comprising:

[0018] The reaction unit comprises a methanol feed unit and a reactor, wherein the reactor comprises a feed inlet and a discharge port, and the methanol feed unit is connected to the feed inlet of the reactor;

[0019] The hydrochloric acid separation unit comprises a hydrochloric acid separation tower, a compressor and a tower top condenser, wherein the hydrochloric acid separation tower comprises a first inlet, a first outlet located at the tower top and a second outlet located at the tower bottom; the discharge port of the reactor is connected to the first inlet; the first outlet is connected to the inlet of the compressor; the tower top condenser comprises a gas phase outlet and a liquid phase outlet; the inlet of the tower top condenser is connected to the methanol feed unit, and the tower top condenser is used to condense the material extracted from the compressor outlet and heat exchanged through the methanol feed unit;

[0020] Methanol recovery unit: comprising a methanol recovery tower and a double-effect reboiler, wherein the methanol recovery tower comprises a second inlet, a reboiler reflux inlet, a third outlet located at the top of the tower and a fourth outlet located at the bottom of the tower; the second outlet of the hydrochloric acid separation tower is connected to the second inlet, the fourth outlet is connected to the inlet of the double-effect reboiler, the outlet of the double-effect reboiler is connected to the reboiler reflux inlet, and is used to provide heat to the methanol recovery tower, and the outlet of the double-effect reboiler is also connected to the methanol feed unit, and is used to provide heat to the methanol feed unit; the outlet of the compressor is connected to the methanol feed unit and the inlet of the double-effect reboiler at the same time, and the material extracted from the compressor outlet is used to provide heat to the methanol feed unit and the double-effect reboiler at the same time;

[0021] The methyl chloride purification unit comprises a methyl chloride separation tower, which comprises a third inlet, a fifth outlet at the top of the tower and a sixth outlet at the bottom of the tower; the gas phase outlet of the top condenser of the hydrochloric acid separation unit is connected to the third inlet of the methyl chloride separation tower.

[0022] Furthermore, the reactor comprises: a primary reactor and a secondary reactor, the outlet of the primary reactor is connected to the inlet of the secondary reactor; the raw materials in the primary reactor comprise hydrogen chloride and gaseous methanol, the molar ratio of methanol to hydrogen chloride is (0.95-1):1, and the hydrogen chloride comprises gaseous hydrogen chloride and hydrochloric acid solution; the raw materials in the secondary reactor comprise liquid methanol and the product after the reaction of the primary reactor; the feed molar ratio of total methanol to total hydrogen chloride in the two reactors is (1.05-1.1):1.

[0023] Furthermore, the concentration of the hydrochloric acid solution in the primary reaction kettle is 10wt.%-20wt.%, and / or the concentration of the hydrochloric acid solution in the secondary reaction kettle is 6wt.%-16wt.%.

[0024] Furthermore, the methanol feed unit comprises a methanol buffer tank, a methanol preheater, a methanol double-effect heater and a methanol evaporator which are connected in sequence, the inlet of the methanol buffer tank is connected to the sixth outlet of the chloromethane separation tower, and the source of the methanol in the methanol buffer tank includes at least the methanol extracted from the bottom of the chloromethane separation tower; the methanol preheater, the methanol double-effect heater and the methanol evaporator are all heat exchangers, and the methanol in the methanol buffer tank can enter the methanol preheater, the methanol double-effect heater and the methanol evaporator in sequence to realize heat exchange, and enter the reactor in the form of gaseous methanol.

[0025] Furthermore, the fourth outlet of the methanol recovery tower is simultaneously connected to the inlet of the methanol preheater, and at least part of the heat of the material extracted from the fourth outlet is used to achieve heat exchange with the methanol in the methanol preheater.

[0026] Furthermore, the outlet of the double-effect reboiler is also connected to the inlet of the methanol double-effect heater, so that at least part of the heat of the material extracted from the double-effect reboiler is exchanged with the methanol in the methanol double-effect heater.

[0027] Furthermore, the outlet of the compressor is also connected to the inlet of the methanol evaporator, and at least part of the heat of the material extracted from the outlet of the compressor is exchanged with the methanol in the methanol evaporator.

[0028] Furthermore, the hydrochloric acid separation unit also includes a stratifier, which is arranged between the hydrochloric acid separation tower and the methanol recovery tower and connects the second outlet of the hydrochloric acid separation tower and the second inlet of the methanol recovery tower.

[0029] Furthermore, the methanol recovery unit also includes a methanol recovery condenser and a methanol recovery tower reflux tank, and the methanol recovery tower also includes a first methanol reflux inlet; the third outlet of the methanol recovery tower is connected to the inlet of the methanol recovery condenser, the outlet of the methanol recovery condenser is connected to the inlet of the methanol recovery tower reflux tank, and the outlet of the methanol recovery tower reflux tank is simultaneously connected to the first methanol reflux inlet and the inlet of the methanol buffer tank.

[0030] Furthermore, the device in the hydrochloric acid separation unit also includes a top cooler and a top reflux tank, and the hydrochloric acid separation tower also includes a second methanol inlet; the liquid phase outlet of the top condenser is connected to the inlet of the top cooler, the outlet of the top cooler is connected to the inlet of the top reflux tank, and the outlet of the top reflux tank is connected to the second methanol inlet of the hydrochloric acid separation tower.

[0031] Furthermore, the methyl chloride purification unit also includes a sulfuric acid absorption tower, a methyl chloride condenser and a methyl chloride product buffer tank, the sulfuric acid absorption tower includes a fourth inlet, a seventh outlet located at the top of the tower and an eighth outlet located at the bottom of the tower; the fifth outlet of the methyl chloride separation tower is connected to the fourth inlet, the seventh outlet is connected to the inlet of the methyl chloride condenser, and the outlet of the methyl chloride condenser is connected to the inlet of the methyl chloride product buffer tank; the eighth outlet is used to discharge solid waste.

[0032] Another object of the present invention is to provide a method for synthesizing methyl chloride, in which the apparatus as described above is utilized, and the method comprises the following steps:

[0033] In the reaction unit: the raw material hydrogen chloride and the gaseous methanol provided by the methanol supply unit react in a reactor, and the products generated by the reaction include methyl chloride, unreacted hydrogen chloride and methanol, and water and dimethyl ether generated by the reaction;

[0034] In the hydrochloric acid separation unit: the product generated by the reaction of the reaction unit enters the hydrochloric acid separation tower from the first inlet, and after being distilled by the hydrochloric acid separation tower, the gaseous materials separated from the first outlet at the top of the hydrochloric acid separation tower include gaseous methanol, methyl chloride and dimethyl ether, and the materials extracted from the second outlet at the bottom of the tower include dilute hydrochloric acid water and methanol; the gaseous materials are compressed by a compressor connected to the hydrochloric acid separation tower, and then divided into two streams and sent to the methanol feed unit and the double-effect reboiler respectively, and are respectively used to heat the methanol in the methanol feed unit and as a heat source for the double-effect reboiler;

[0035] In the methanol recovery unit: the material extracted from the second outlet at the bottom of the hydrochloric acid separation tower enters from the second inlet of the methanol recovery tower, and after distillation by the methanol recovery tower, gaseous methanol is extracted from the third outlet at the top of the tower, and solid waste is extracted from the fourth outlet at the bottom of the tower; wherein the heat of distillation in the methanol recovery tower comes from the double-effect reboiler, and the heat of the double-effect reboiler comes from the gaseous material compressed by the compressor;

[0036] In the methyl chloride purification unit: the crude gaseous methyl chloride coming out of the top condenser of the hydrochloric acid separation tower enters the methyl chloride separation tower, and after distillation by the methyl chloride separation tower, methyl chloride and dimethyl ether are produced from the fifth outlet at the top of the tower, and methanol is produced from the sixth outlet at the bottom of the tower.

[0037] Furthermore, the reactor comprises a primary reactor and a secondary reactor, the outlet of the primary reactor is connected to the inlet of the secondary reactor; the raw materials in the primary reactor comprise hydrogen chloride and gaseous methanol, the molar ratio of methanol to hydrogen chloride is (0.95-1):1, and the hydrogen chloride comprises gaseous hydrogen chloride and hydrochloric acid solution; the raw materials in the secondary reactor comprise liquid methanol and the product after the reaction of the primary reactor; the feed molar ratio of total methanol to total hydrogen chloride in the two reactors is (1.05-1.1):1.

[0038] Furthermore, the concentration of the hydrochloric acid solution in the primary reaction kettle is 10wt.%-20wt.%, and / or the concentration of the hydrochloric acid solution in the secondary reaction kettle is 6wt.%-16wt.%.

[0039] Furthermore, the reaction pressure in the primary reactor (1) and the secondary reactor (2) is 2.5-3 barg, and the reaction temperature is 120-130°C.

[0040] Furthermore, the gaseous material extracted from the first outlet of the hydrochloric acid separation tower includes methanol, methyl chloride and dimethyl ether. After being compressed by the compressor, the pressure of the gaseous material is 9-11 barg and the temperature is 160-175°C; the gaseous material is divided into two streams, one of which accounts for 10-20% of the total flow of the gaseous material and is sent to the methanol feed unit to heat the methanol; the other stream accounts for 80-90% of the total flow of the gaseous material and is sent to the double-effect reboiler as a heat source for the double-effect reboiler.

[0041] Furthermore, the fourth outlet of the methanol recovery tower is connected to the inlet of the methanol preheater, and at least part of the material extracted from the fourth outlet enters the methanol preheater to heat the methanol therein.

[0042] Furthermore, the outlet of the double-effect reboiler is connected to the inlet of the methanol double-effect heater, and at least part of the material produced from the double-effect reboiler enters the methanol double-effect heater to heat the methanol therein.

[0043] Furthermore, the outlet of the compressor is connected to the inlet of the methanol evaporator, and at least part of the material extracted from the outlet of the compressor enters the methanol evaporator and heats the methanol therein.

[0044] Furthermore, the methanol recovery unit also includes a methanol recovery condenser and a methanol recovery tower reflux tank, and the methanol recovery tower also includes a first methanol reflux inlet; the third outlet of the methanol recovery tower is connected to the inlet of the methanol recovery condenser, the outlet of the methanol recovery condenser is connected to the inlet of the methanol recovery tower reflux tank, and the outlet of the methanol recovery tower reflux tank is simultaneously connected to the first methanol reflux inlet and the inlet of the methanol buffer tank.

[0045] The present invention has at least the following beneficial effects:

[0046] The present invention optimizes the device for synthesizing methyl chloride, and changes the pressurized liquefaction of pure methyl chloride in the conventional methanol excess method methyl chloride synthesis process to pressurizing the gas phase at the top of the hydrochloric acid separation unit. The waste heat energy that originally needs to be removed by cooling water is converted into a heat source that can be directly used to directly heat the reboiler of the methanol recovery tower and the methanol evaporator. The recycling of this heat energy greatly reduces the consumption of steam and cooling water in the process flow. While achieving ultra-low energy consumption cost production of the methyl chloride synthesis device, it also provides an excellent solution for the green and sustainable development of enterprises and society.

[0047] In addition, the present invention connects a compressor to the rear end of the hydrochloric acid separation tower for pressurization, so that the pressure of the reaction system only needs to maintain the power of the reactor and the hydrochloric acid separation tower, so there is no need to maintain a pressure of more than 3 bar in the reactor (the pressure required to be reached by the conventional methanol excess method). The pressure of the primary reactor and the secondary reactor is maintained at 2.5 bar to maintain the normal operation of the system. The reaction temperature corresponding to such pressure is about 120°C. At this temperature, the hydrochloric acid reaction liquid contained in the reactor will not corrode the inner wall of the reactor (the corrosion temperature of the enamel reactor at a hydrochloric acid solution concentration of 15wt.% is 125°C), thereby reducing the cost of replacing equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The drawings herein are incorporated into the specification and constitute a part of this specification, illustrate embodiments consistent with the present application, and together with the specification are used to explain the technical solutions of the present application.

[0049] Figure 1 The present invention is a schematic diagram of the structure of the device for synthesizing methyl chloride provided by the present invention.

[0050] Reference numerals:

[0051] A primary reactor (1), a secondary reactor (2), a hydrochloric acid separation tower (3), a compressor (4), a double-effect reboiler (5), a methanol recovery tower (6), a methanol recovery tower condenser (7), a methanol recovery tower reflux tank (8), a methanol preheater (9), a methanol double-effect heater (10), a methanol evaporator (11), a tower top condenser (12), a tower top cooler (13), a tower top reflux tank (14), a chloromethane separation tower (15), a chloromethane separation tower reboiler (16), a chloromethane separation tower bottom cooler (17), a sulfuric acid absorption tower (18), a chloromethane condenser (19), a chloromethane product buffer tank (20), a methanol buffer tank (21), and a stratifier (22). DETAILED DESCRIPTION

[0052] The embodiment of the present application provides a device and method for synthesizing methyl chloride. The preferred embodiments of the present application are described below in conjunction with the drawings of the specification. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present application, and are not used to limit the present application. In addition, the embodiments and features in the embodiments of the present application can be combined with each other if there is no conflict.

[0053] Example 1

[0054] refer to Figure 1 This embodiment provides a device for synthesizing methyl chloride, which includes: a reaction unit, a hydrochloric acid separation unit, a methanol recovery unit and a methyl chloride purification unit.

[0055] Specifically, the raw material gaseous methanol in the present invention comes from the methanol buffer tank (21), the methanol buffer tank (21), the methanol preheater (9), the methanol double-effect heater (10) and the methanol evaporator (11) are connected in sequence, and the gaseous methanol is extracted from the outlet of the methanol evaporator (11) and used as a raw material to enter the reaction unit.

[0056] The reaction unit comprises a primary reactor (1) and a secondary reactor (2), the outlet of the primary reactor is connected to the inlet of the secondary reactor (2), the outlet of the secondary reactor (2) is connected to the first inlet of the hydrochloric acid separation tower (3), the first outlet at the top of the hydrochloric acid separation tower (3) is connected to a compressor (4), the outlet of the compressor (4) is connected to two routes through pipelines, one of which is connected to the double-effect reboiler (5), and the double-effect reboiler (5) is connected to the methanol double-effect heater (10); the other route is connected to the methanol evaporator (11).

[0057] The second outlet at the bottom of the hydrochloric acid separation tower (3) is connected to the second inlet of the methanol recovery tower (6). The double-effect reboiler (5) is connected to the methanol recovery tower (6) as a heat source. The third outlet at the top of the methanol recovery tower (6) is connected to the inlet of the methanol recovery condenser (7), and the outlet of the methanol recovery tower condenser (7) is connected to the inlet of the methanol recovery tower reflux tank (8), and the outlet of the methanol recovery tower reflux tank (8) is simultaneously connected to the first methanol reflux inlet and the inlet of the methanol buffer tank (21). The fourth outlet at the bottom of the methanol recovery tower (6) is connected to the inlet of the double-effect reboiler (5), and the outlet of the double-effect reboiler (5) is not only connected to the reboiler reflux inlet, but also connected to the methanol double-effect heat exchanger (10). The fourth outlet is also connected to the methanol preheater (9).

[0058] The methanol evaporator (11) and the methanol double-effect heater (10) are both connected to the tower top condenser (12); one stream of the tower top gaseous material at the outlet of the compressor (4) is heat exchanged through the methanol evaporator (11), and the other stream is heat exchanged through the double-effect reboiler (5) and the methanol double-effect heater (10); after the heat exchange, the two streams of material are combined and enter the tower top condenser (12) for condensation; the liquid phase outlet of the tower top condenser (12) is connected to the inlet of the tower top cooler (13); the outlet of the tower top cooler (13) is connected to the inlet of the tower top reflux tank (14); and the outlet of the tower top reflux tank (14) is connected to the second methanol inlet of the hydrochloric acid separation tower (3).

[0059] The gas phase outlet of the top condenser (12) is connected to the third inlet of the chloromethane separation tower (15), the fifth outlet of the top of the chloromethane separation tower (15) is connected to the fourth inlet of the sulfuric acid absorption tower (18), the seventh outlet of the sulfuric acid absorption tower (18) is connected to the downstream at one end, and the high-purity chloromethane gas is directly used by the downstream, the other end of the seventh outlet is connected to the inlet of the chloromethane condenser (19), the outlet of the chloromethane condenser (19) is connected to the inlet of the chloromethane product buffer tank (20), and the eighth outlet is used to discharge solid waste. The sixth outlet at the bottom of the chloromethane separation tower (15) is connected to the inlet of the chloromethane bottom cooler (17), and the outlet of the chloromethane bottom cooler (17) is connected to the inlet of the methanol buffer tank (21).

[0060] Preferably, the hydrochloric acid separation unit further comprises a stratifier (22), wherein the stratifier (22) is arranged between the hydrochloric acid separation tower (3) and the methanol recovery tower (6), and connects the second outlet of the hydrochloric acid separation tower (3) and the second inlet of the methanol recovery tower (6).

[0061] Furthermore, in order to ensure that the methanol temperature at the outlet of the methanol evaporator (11) can meet the reaction requirements when the flow pressure and temperature at the outlet of the compressor (4) fluctuate during start-up and shutdown, the present invention can also add a methanol vaporizer heated by steam as heat supplement at the downstream of the methanol side of the methanol evaporator (11) according to the needs of actual production. The steam pipeline of the methanol vaporizer is equipped with an automatic regulating valve and connected to the DCS system. At the same time, a bypass pipeline is arranged beside the pipeline from the compressor (4) to the methanol evaporator (11), and the bypass pipeline is also equipped with an automatic regulating valve and connected to the DCS system. A temperature sensor is arranged on the methanol pipeline at the outlet of the methanol evaporator (11) and connected to the DCS system. When the temperature sensor detects that the temperature is lower than the set value, the DCS system automatically opens and adjusts the steam regulating valve of the methanol vaporizer and closes the automatic regulating valve of the bypass pipeline of the methanol evaporator (11), thereby increasing the steam flow to provide more heat source; when the temperature sensor detects that the temperature is higher than the set value, the DCS system automatically opens and adjusts the automatic regulating valve of the bypass pipeline of the methanol evaporator (11) and closes the steam regulating valve of the methanol vaporizer, thereby reducing the flow of the compressor (4) outlet material through the methanol evaporator (11) to reduce the supply of heat source.

[0062] Example 2

[0063] This embodiment provides a process for synthesizing methyl chloride, which comprises a reaction unit, a hydrochloric acid separation unit, a methanol recovery unit and a methyl chloride purification unit. Figure 1 , the following reaction processes are realized in each unit:

[0064] (1) Reaction unit: Binding Figure 1 The reaction unit comprises a primary reactor (1) and a secondary reactor (2) connected in series, wherein the raw materials in the primary reactor (1) comprise gaseous hydrogen chloride (raw material B), hydrochloric acid solution (raw material C) and gaseous methanol, wherein the gaseous methanol is gaseous methanol formed after being heated by a methanol preheater (9), a methanol double-effect heater (10) and a methanol evaporator (11). In the primary reactor (1), methanol and hydrogen chloride (herein, hydrogen chloride comprises raw material B and raw material C) are reacted at a molar ratio of (0.95-1):1. The product generated by the reaction is then introduced into the secondary reactor (2) through a pipeline, and at the same time, methanol of about 10% of the amount of methanol added in the primary reactor (1) is added to the secondary reactor (2) in advance, and after the reaction in the secondary reactor (2), about 5% of hydrogen chloride in the reaction system can be reduced to about 1% of hydrogen chloride. The molar ratio of total methanol to total hydrogen chloride feed in the two reactors is (1.05-1.1):1.

[0065] The purpose of the reaction unit is to react hydrogen chloride and methanol, and the products generated by the reaction include methyl chloride, unreacted hydrogen chloride and methanol, water generated by the reaction, dimethyl ether, etc. The reaction pressure in the primary reactor (1) and the secondary reactor (2) is 2.5-5 barg, and the reaction temperature is 120-150°C. Further, the reaction pressure in the primary reactor (1) and the secondary reactor (2) is 2.5-3 barg, and the reaction temperature is 120-130°C. The concentration of the hydrochloric acid solution in the primary reactor (1) is 10wt.% to 20wt.%, and the concentration of the hydrochloric acid solution in the secondary reactor (2) is 6wt.% to 16wt.%. In the present invention, the raw material hydrogen chloride in the primary reactor (1) is slightly excessive in order to fully react the gaseous methanol in the primary reactor (1), thereby reducing the production of by-product dimethyl ether and increasing the yield of the product methyl chloride. The secondary reactor (2) is provided with a slight excess of methanol in the present invention in order to make the hydrogen chloride in the secondary reactor (2) react as completely as possible, improve the conversion rate of hydrogen chloride, reduce the workload of the system for discharging waste acid, reduce the amount of solid waste discharged, and realize green production.

[0066] (2) Hydrochloric acid separation unit: combined Figure 1 , the product from the secondary reactor (2) enters the hydrochloric acid separation tower (3) from the first inlet at the bottom of the tower. After being rectified by the hydrochloric acid separation tower (3), the components of the gaseous material separated from the first outlet at the top of the tower mainly include part of methanol, methyl chloride and dimethyl ether. After the above gaseous material is compressed by the compressor (4) connected to the hydrochloric acid separation tower (3), the pressure reaches 9-11 barg and the temperature reaches 160-175°C. The purpose of the hydrochloric acid separation tower (3) in the present invention is to separate methyl chloride, dimethyl ether and dilute hydrochloric acid water, and the components at the top of the tower are methyl chloride, part of methanol and dimethyl ether. The second outlet at the bottom of the tower produces dilute hydrochloric acid water and part of methanol. The operating pressure of the hydrochloric acid separation tower (3) is 2-4 barg, the operating temperature at the top of the tower is 75-90°C, and the operating temperature at the bottom of the tower is 105-125°C.

[0067] Furthermore, in the present invention, the gas phase components compressed by the compressor (4) are divided into two streams: one stream is used as a heat source to heat and vaporize the methanol in the methanol evaporator (11); the other stream is used as a heat source to heat the double-effect reboiler (5) of the methanol recovery tower (6), and a part of the residual heat is used to heat the methanol double-effect heater (10). One stream of the tower top gas phase material at the outlet of the compressor (4) is heat exchanged through the methanol evaporator (11), and the other stream is heat exchanged through the double-effect reboiler (5) and the methanol double-effect heater (10), and then combined after heat exchange and enter the tower top condenser (12) for condensation. Among them, the chloroform and dimethyl ether with lower boiling points enter the rear end chloroform separation tower (15) in the form of gas phase, and the methanol with higher boiling point is condensed and enters the tower top cooler (13) for further cooling. The temperature of the cooled methanol is about 30-50°C, and the condensate enters the tower top reflux tank (14) and then returns to the hydrochloric acid separation tower (3) as reflux. For example, a flow rate of about 10-20% of the gas phase at the top of the tower is used as a heat source to heat and vaporize the methanol in the methanol evaporator (11); another flow rate of about 80-90% of the gas phase at the top of the tower is used as a heat source to heat the double-effect reboiler (5) of the methanol recovery tower (6). When the gas phase material leaves the double-effect reboiler (5), the temperature is reduced to about 130-135°C, and the remaining heat is used to heat the methanol in the methanol double-effect heater (10) again. The temperature of the heated gas phase material is reduced to about 80-85°C, so that the thermal energy of the gas phase material is fully utilized.

[0068] In addition to fully circulating heat energy, the invention connects the compressor (4) from the rear end of the hydrochloric acid separation tower to increase pressure, and another function is that in the conventional methanol excess method, the pressure of the reaction system needs to maintain the power of two reactors and multiple distillation towers, so the reaction pressure must be maintained above 3 bar, and the corresponding reaction temperature must be above 130° C. At this time, the hydrochloric acid in the reactor will corrode the inner wall of the reactor, because the corrosion temperature of the enamel reactor at a hydrochloric acid solution concentration of 15wt.% is 125° C. The invention connects the compressor (4) from the rear end of the hydrochloric acid separation tower to increase pressure, so that the pressure of the reaction system only needs to maintain the power of the reactor and the hydrochloric acid separation tower, that is, the pressure of the reactor is maintained at 2.5 bar to maintain the normal operation of the system, and the reaction temperature corresponding to such pressure is about 120° C. At this temperature, the hydrochloric acid reaction solution contained in the reactor will not corrode the inner wall of the reactor, thereby reducing the equipment cost.

[0069] (3) Methanol recovery unit: combined Figure 1The material containing methanol, water and unreacted hydrogen chloride is extracted from the second outlet at the bottom of the hydrochloric acid separation tower (3) in the form of liquid. The liquid material passes through a separator (22) connected to the hydrochloric acid separation tower (3) to remove the organic layer (hydrocarbon) that may exist therein, and then enters the methanol recovery tower (6) from the second inlet located in the middle of the methanol recovery tower (6). After being distilled in the methanol recovery tower (6), the gaseous methanol is evaporated from the third outlet at the top of the tower and enters the methanol recovery tower condenser (7) connected thereto. The condensed methanol enters the methanol recovery tower reflux tank (8). A part of the methanol entering the methanol recovery tower reflux tank (8) is refluxed into the methanol recovery tower (6) as reflux liquid, and the rest enters the methanol buffer tank (21) connected thereto as output.

[0070] Furthermore, the pressure of the methanol recovery tower (6) is 0.5-2 barg, the top temperature is 70-85° C., and the bottom temperature is 110-130° C. The goal of the methanol recovery unit is to recover about 5 wt.% of methanol in the waste hydrochloric acid water.

[0071] (4)Methyl Chloride Purification Unit: Combined Figure 1 , the crude gaseous chloromethane from the top condenser (12) of the hydrochloric acid separation tower (3) enters the chloromethane separation tower (15) from the third inlet, and the components of the crude gaseous chloromethane mainly include chloromethane, methanol and dimethyl ether. The purpose of the chloromethane separation tower (15) in the present invention is to separate methanol and chloromethane. The chloromethane separation tower reboiler (16) is heated by steam. The component extracted from the sixth outlet at the bottom of the tower is methanol, which enters the methanol buffer tank (21) after being cooled by the chloromethane separation tower bottom cooler (17), and then enters the reaction system again as a raw material. The fifth outlet at the top of the tower extracts chloromethane and dimethyl ether, enters the sulfuric acid absorption tower (18) and reacts with the fresh sulfuric acid at the top of the tower in the tower, removes impurities such as dimethyl ether and water in the product, and extracts a high-purity chloromethane gaseous product at the seventh outlet at the top of the tower. The gaseous methyl chloride product can be directly produced for use in the downstream system, or it can be cooled in a methyl chloride cooler (19) and then enter a methyl chloride buffer tank (20), with part of it entering a methyl chloride separation tower (15) as reflux and the rest produced as a liquid product.

[0072] A process for synthesizing methyl chloride is described above. Another object of the present invention is to make full use of the heat generated in the system for synthesizing methyl chloride, thereby reducing energy consumption and production costs. Specifically, the present invention optimizes the methyl chloride process flow. Based on the MVR heat pump distillation technology, the pressurized liquefaction of pure methyl chloride in the conventional methanol excess method methyl chloride synthesis process is changed to pressurization in the top gas phase of the hydrochloric acid separation unit. MVR is the abbreviation of mechanical vapor recompression technology. MVR technology consumes a small amount of compressor compression work at the cost of upgrading a large amount of low-grade waste heat carried by secondary steam to high-grade for reuse, so it is also called MVR heat pump technology. In the present invention, MVR heat pump technology is combined with the traditional distillation production process, and a compressor (4) is connected to the top outlet of the hydrochloric acid separation tower (3) to pressurize the top gas phase of the hydrochloric acid separation unit, thereby fully recovering the heat of the top vapor and reducing the consumption of cold and hot utilities in the distillation system.

[0073] The following is a further explanation and analysis of the heat generated and utilized between the various units in the system for synthesizing methyl chloride:

[0074] The introduction of conventional methanol excess method is shown in the background technology section. Since the pressure of the reaction system needs to maintain the power of two sets of reactors and multiple sets of distillation towers, the reaction pressure must be maintained above 3 bar, and the corresponding reaction temperature must be above 130 ° C. The water produced by the reaction is heated and evaporated by the heat generated by the reaction and the heat provided by the additional steam, and then enters the hydrochloric acid separation tower together with other reaction components. In the conventional methanol excess method, because the top of the hydrochloric acid separation tower needs to condense the condensable methanol component into a liquid, if it is not condensed, more methanol will be sent to the chloromethane tower in the back, increasing the load of the chloromethane separation tower. If it is further taken to the sulfuric acid absorption tower, more sulfuric acid will be consumed to remove the methanol that affects the quality of the chloromethane product. Therefore, a large amount of heat must be removed in the hydrochloric acid separation unit to achieve the condensation of methanol. The conventional method is to use a large amount of methanol reflux to remove it through the top condensation cooler, which causes a very huge waste of energy. In addition, the compressor design of the conventional methanol excess method is after the purification of chloromethane, and the heat generated by compression needs additional cooling water to remove, which also causes energy waste here.

[0075] In view of the problem of energy waste in the conventional methanol excess method, the present invention optimizes the synthesis process based on the MVR heat pump distillation technology, uses a compressor (4) to compress the material with high heat at the top of the tower, further increases the temperature of the material to about 175°C, and the heat carried by the compressed material is used to provide the methanol recovery tower reboiler and methanol evaporator that have a particularly high heat demand. Specifically, in the present invention, the gas phase components compressed by the compressor (4) are divided into two streams: one stream is used as a heat source to heat and vaporize the methanol in the methanol evaporator (11); the other stream is used as a heat source to heat the double-effect reboiler (5) of the methanol recovery tower (6), and a part of the waste heat is provided to the methanol double-effect heater (10) for heating. In the actual production process, each reactor and distillation tower and other equipment are correspondingly equipped with a temperature sensor, and the temperature of the entire system is monitored by the temperature sensor. The distribution of these two heat streams is regulated according to the actual heat required by each part of the system.

[0076] In the reaction unit, in the conventional methanol excess method, about 35% of the total heat of the system is consumed in the vaporization of methanol before it enters the primary reactor (1). In the present invention, no external steam heat is needed to vaporize the methanol entering the primary reactor (1). The methanol (about 30° C.) from the methanol buffer tank (21) enters the methanol preheater (9), the methanol double-effect heater (10) and the methanol evaporator (11) in sequence through the pipeline, and the methanol is heated in each stage. In the present invention, the heat for heating the methanol in each stage comes from the following parts: the waste water with a temperature of about 115° C. coming out of the bottom of the methanol recovery tower (6) is used to preheat the methanol (about 30° C.) from the methanol buffer tank (21), so that the temperature of the methanol is increased from 30° C. to about 45° C. Then, the residual heat (about 130° C.) of the material after heating in the double-effect reboiler (5) of the methanol recovery tower (6) is used to further heat the methanol in the methanol double-effect heater (10), so that the methanol temperature rises from 45° C. to about 110° C. Finally, the material at about 175° C. from the compressor (4) is directly heated in the methanol evaporator (11), so that the temperature of the methanol rises to about 135° C. Thus, the temperature requirement for adding methanol to the primary reactor (1) and achieving normal reaction can be met without using additional steam.

[0077] In addition to making full use of system heat and reducing energy consumption in the reaction unit and the hydrochloric acid separation unit, the present invention also achieves the same effect in the methanol recovery unit. Specifically, the heat source of the methanol recovery tower (6) comes from the double-effect reboiler (5). Part of the liquid material extracted from the bottom of the tower is pumped into the double-effect reboiler (5), heated and evaporated, and returned to the tower. The rest passes through the methanol preheater (9) and is discharged as a solid waste system. The liquid material mainly includes wastewater containing 2% hydrochloric acid and a trace amount of methanol. The steam consumption of the reboiler of the conventional methanol excess method methanol recovery tower (6) accounts for about 60% of the entire chloroform device. The present invention uses the material compressed from the compressor (4) as a heat source to heat the bottom material to 120°C through the double-effect reboiler (5) and then returns to the tower to vaporize, thereby realizing the reboiling function, which saves a lot of steam compared to the conventional methanol excess method.

[0078] The present invention utilizes MVR heat pump distillation technology to fully utilize the heat generated by this part of compression. Compared with the conventional methanol excess method, the present invention does not increase the additional equipment cost. After preliminary calculation, only the power consumption of the compressor increases by 12%.

[0079] The present invention optimizes the process flow of synthesizing chloromethane, and realizes ultra-low energy consumption during the production of chloromethane synthesis device by using MVR heat pump distillation technology. By arranging a compressor at the rear end of the hydrochloric acid separation unit, the reaction heat, compression heat and steam heat are fully utilized, and it is no longer necessary to use a large amount of steam as the heat source of the methanol recovery tower reboiler and the methanol evaporator, which greatly reduces the consumption of steam in the process flow. Specifically, from the two aspects of saving production costs and reducing equipment costs, the present invention has achieved unexpected technical effects.

[0080] 1. Save production costs

[0081] Table 1 shows the energy consumption and cost comparison of different methods for synthesizing methyl chloride.

[0082] Table 1

[0083]

[0084] Note: The above data comes from production practice, journal articles and Aspen plus V14

[0085] For a chloromethane synthesis unit with an annual output of 350,000 tons, the present invention can save 75 million yuan per year compared with the hydrogen chloride excess process, and can save 23 million yuan per year compared with the conventional methanol excess process.

[0086] 2. Provides low-cost equipment options

[0087] As mentioned above, in the conventional methanol excess method, since the pressure of the reaction system needs to maintain the power of two reactors and multiple distillation towers, the pressure must be maintained above 3 bar, so the corresponding reaction temperature must be above 130°C. Since the concentration of the hydrochloric acid solution in the primary reactor (1) is 10wt.% to 20wt.%, if the reactor is made of enamel material, there will be a corrosion rate of more than 0.1mm per year, which is easy to cause damage to the reactor and cause leakage to cause safety accidents. If corrosion-resistant bricks are used for corrosion protection in a reactor with a volume similar to that of an enamel reactor, the effective volume of the reactor will be reduced. As mentioned above, since the methanol excess method has no catalyst and the reaction rate is slow, a large-volume reactor is required to provide sufficient residence time. Therefore, the enterprises currently using the conventional methanol excess process, corresponding to the 350,000 tons of chloromethane synthesis unit, all use a 6-meter diameter, 350 cubic meter reactor, and corrosion-resistant bricks are used in the reactor for corrosion protection, but such equipment is difficult to transport by conventional roads. At the same time, the cost of corrosion-resistant bricks for corrosion protection is very high, reaching more than 40% of the construction cost of the chloromethane unit. Due to the above factors, there are very few companies in China that currently use the conventional methanol excess method.

[0088] Since the present invention uses a compressor (4) to pressurize the gas phase of the hydrochloric acid separation tower (3), the pressure of the reaction system only needs to maintain the power of the reactor and the hydrochloric acid separation tower (3), so no pressure above 3 bar is required. The normal operation of the system can be maintained by maintaining the pressure of the reactor at 2.5 bar. Such a pressure corresponds to a temperature of the primary reactor (1) of about 120°C. At this temperature, the enamel material can withstand any concentration of hydrochloric acid, thereby solving the corrosion problem. In response to the reaction volume problem, multiple sets of small reactors (domestic manufacturers already have 135 cubic meters of enamel reactors) can be connected in parallel. According to calculations, the cost of using multiple sets of small reactors is only one-fifth of that of using large reactors with corrosion-resistant bricks. The use of the present invention can greatly promote the use of the methanol excess method in methyl chloride synthesis equipment.

[0089] Those skilled in the art will appreciate that the accompanying drawings are merely schematic diagrams of a preferred embodiment, and the modules or processes in the accompanying drawings are not necessarily required for implementing the present application.

[0090] The serial numbers of the above-mentioned embodiments of the present application are for description only and do not represent the advantages or disadvantages of the embodiments.

[0091] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

Claims

1. A device for synthesizing methyl chloride, characterized in that: The device comprises: The reaction unit comprises a methanol feed unit and a reactor, wherein the reactor comprises a feed inlet and a discharge port, and the methanol feed unit is connected to the feed inlet of the reactor; The hydrochloric acid separation unit comprises a hydrochloric acid separation tower, a compressor and a tower top condenser, wherein the hydrochloric acid separation tower comprises a first inlet, a first outlet located at the tower top and a second outlet located at the tower bottom; the discharge port of the reactor is connected to the first inlet; the first outlet is connected to the inlet of the compressor; the tower top condenser comprises a gas phase outlet and a liquid phase outlet; the inlet of the tower top condenser is connected to the methanol feed unit, and the tower top condenser is used to condense the material extracted from the compressor outlet and heat exchanged through the methanol feed unit; Methanol recovery unit: comprising a methanol recovery tower and a double-effect reboiler, wherein the methanol recovery tower comprises a second inlet, a reboiler reflux inlet, a third outlet located at the top of the tower and a fourth outlet located at the bottom of the tower; the second outlet of the hydrochloric acid separation tower is connected to the second inlet, the fourth outlet is connected to the inlet of the double-effect reboiler, the outlet of the double-effect reboiler is connected to the reboiler reflux inlet, and is used to provide heat to the methanol recovery tower, and the outlet of the double-effect reboiler is also connected to the methanol feed unit, and is used to provide heat to the methanol feed unit; the outlet of the compressor is connected to the methanol feed unit and the inlet of the double-effect reboiler at the same time, and the material extracted from the compressor outlet is used to provide heat to the methanol feed unit and the double-effect reboiler at the same time; The methyl chloride purification unit comprises a methyl chloride separation tower, which comprises a third inlet, a fifth outlet at the top of the tower and a sixth outlet at the bottom of the tower; the gas phase outlet of the top condenser of the hydrochloric acid separation unit is connected to the third inlet of the methyl chloride separation tower.

2. The device according to claim 1, characterized in that The reactor comprises: A primary reactor and a secondary reactor, wherein the outlet of the primary reactor is connected to the inlet of the secondary reactor; The raw materials in the primary reactor include hydrogen chloride and gaseous methanol, the molar ratio of methanol to hydrogen chloride is (0.95-1):1, and the hydrogen chloride includes gaseous hydrogen chloride and hydrochloric acid solution; The raw materials in the secondary reactor include liquid methanol and the product after the reaction of the primary reactor; The feed molar ratio of total methanol to total hydrogen chloride in the two reactors is (1.05-1.1):

1.

3. The device according to claim 1, characterized in that The methanol feed unit comprises a methanol buffer tank, a methanol preheater, a methanol double-effect heater and a methanol evaporator which are connected in sequence; The inlet of the methanol buffer tank is connected to the sixth outlet of the chloromethane separation tower, and the source of the methanol in the methanol buffer tank includes at least the methanol extracted from the bottom of the chloromethane separation tower; The methanol preheater, methanol double-effect heater and methanol evaporator are all heat exchangers. The methanol in the methanol buffer tank can enter the methanol preheater, methanol double-effect heater and methanol evaporator in sequence to achieve heat exchange and enter the reactor in the form of gaseous methanol.

4. The device according to claim 3, characterized in that The fourth outlet of the methanol recovery tower is simultaneously connected to the inlet of the methanol preheater, and at least part of the heat of the material extracted from the fourth outlet is used to achieve heat exchange with the methanol in the methanol preheater.

5. The device according to claim 3, characterized in that The outlet of the double-effect reboiler is also connected to the inlet of the methanol double-effect heater, so that at least part of the heat of the material extracted from the double-effect reboiler is exchanged with the methanol in the methanol double-effect heater.

6. The device according to claim 3, characterized in that The outlet of the compressor is also connected to the inlet of the methanol evaporator, and at least part of the heat of the material extracted from the outlet of the compressor is exchanged with the methanol in the methanol evaporator.

7. The device according to claim 3, characterized in that The methanol recovery unit further comprises a methanol recovery condenser and a methanol recovery tower reflux tank, and the methanol recovery tower further comprises a first methanol reflux inlet; The third outlet of the methanol recovery tower is connected to the inlet of the methanol recovery condenser, the outlet of the methanol recovery condenser is connected to the inlet of the methanol recovery tower reflux tank, and the outlet of the methanol recovery tower reflux tank is simultaneously connected to the first methanol reflux inlet and the inlet of the methanol buffer tank.

8. The device according to claim 1, characterized in that The methyl chloride purification unit also includes a sulfuric acid absorption tower, a methyl chloride condenser and a methyl chloride product buffer tank, wherein the sulfuric acid absorption tower includes a fourth inlet, a seventh outlet located at the top of the tower and an eighth outlet located at the bottom of the tower; The fifth outlet of the methyl chloride separation tower is connected to the fourth inlet, the seventh outlet is connected to the inlet of the methyl chloride condenser, the outlet of the methyl chloride condenser is connected to the inlet of the methyl chloride product buffer tank; the eighth outlet is used to discharge solid waste.

9. A method for synthesizing methyl chloride, characterized in that: The method utilizes the device according to any one of claims 1 to 8, and the method comprises the following steps: In the reaction unit: the raw material hydrogen chloride and the gaseous methanol provided by the methanol supply unit react in a reactor, and the products generated by the reaction include methyl chloride, unreacted hydrogen chloride and methanol, and water and dimethyl ether generated by the reaction; In the hydrochloric acid separation unit: the product generated by the reaction of the reaction unit enters the hydrochloric acid separation tower from the first inlet, and after being distilled by the hydrochloric acid separation tower, the gaseous materials separated from the first outlet at the top of the hydrochloric acid separation tower include gaseous methanol, methyl chloride and dimethyl ether, and the materials extracted from the second outlet at the bottom of the tower include dilute hydrochloric acid water and methanol; the gaseous materials are compressed by a compressor connected to the hydrochloric acid separation tower, and then divided into two streams and sent to the methanol feed unit and the double-effect reboiler respectively, and are respectively used to heat the methanol in the methanol feed unit and as a heat source for the double-effect reboiler; In the methanol recovery unit: the material extracted from the second outlet at the bottom of the hydrochloric acid separation tower enters from the second inlet of the methanol recovery tower, and after distillation by the methanol recovery tower, gaseous methanol is extracted from the third outlet at the top of the tower, and solid waste is extracted from the fourth outlet at the bottom of the tower; wherein the heat of distillation in the methanol recovery tower comes from the double-effect reboiler, and the heat of the double-effect reboiler comes from the gaseous material compressed by the compressor; In the methyl chloride purification unit: the crude gaseous methyl chloride coming out of the top condenser of the hydrochloric acid separation tower enters the methyl chloride separation tower, and after distillation by the methyl chloride separation tower, methyl chloride and dimethyl ether are produced from the fifth outlet at the top of the tower, and methanol is produced from the sixth outlet at the bottom of the tower.

10. The method according to claim 9, characterized in that The gaseous material extracted from the first outlet of the hydrochloric acid separation tower includes methanol, methyl chloride and dimethyl ether. After being compressed by the compressor, the pressure of the gaseous material is 9-11 barg and the temperature is 160-175°C; The gas phase material is divided into two streams, one stream accounts for 10-20% of the total flow of the gas phase material and is sent to the methanol feed unit to heat the methanol; the other stream accounts for 80-90% of the total flow of the gas phase material and is sent to the double-effect reboiler as a heat source for the double-effect reboiler.

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