Device for synthesizing chloromethane

Abstract

The utility model provides a device for synthesizing methyl chloride. The device comprises a reaction unit and a reaction 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 utility model, 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 through 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] This application relates to the chemical industry, and more particularly to an apparatus for synthesizing chloromethane. Background Technology

[0002] Chloromethane (CH3Cl), also known as methyl chloride, has a certain anesthetic and pungent odor and is chemically reactive. Due to its unique chemical structure and properties, chloromethane has a wide range of applications in the chemical industry, including as a solvent, catalyst, and methylating agent. Specifically, the main application areas of chloromethane include the following:

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

[0004] In the pesticide industry: Chloromethane can be used as an intermediate in the production process of certain pesticides;

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

[0006] Refrigerant: Chloromethane can be used as one of the precursors for certain refrigerants.

[0007] Currently, the demand for chloromethane is increasing year by year, but its production process requires the use of toxic substances such as chlorine or hydrochloric acid. Coupled with the high energy consumption and pollution of the production process, its preparation technology needs further optimization. Therefore, developing a safe, environmentally friendly, and low-energy-consumption method for the synthesis of chloromethane has significant application value.

[0008] The synthesis methods for chloromethane are relatively mature, and currently mainly include methanol chlorination, methane chlorination, and methanol electrochemical chlorination. In current industrial production, the methanol chlorination process is the primary method used, and its reaction formula is as follows:

[0009] CH3OH + HCl → CH3Cl + H2O.

[0010] Furthermore, there are two process directions for methanol chlorination:

[0011] 1. Excess Hydrogen Chloride Method

[0012] The excess hydrogen chloride method refers to the synthesis of chloromethane using a methanol (mol):hydrogen chloride (mol) ratio of 1:(1.05–1.1). The excess hydrogen chloride ensures approximately 99% conversion of methanol during the reaction. This method requires zinc chloride (ZnCl2) or aluminum chloride (AlCl3) as a catalyst to achieve a high reaction rate. The process typically includes reaction, water washing, alkali washing, drying and purification, and compression liquefaction. Disadvantages of the excess hydrogen chloride method include complex separation and purification processes. Recovering and separating the excess hydrogen chloride increases the complexity and energy consumption of the production process. Inadequate recovery and treatment of excess hydrogen chloride can lead to excessive emissions, requiring additional investment in environmental protection facilities. Furthermore, approximately 70% of the steam heat in the excess hydrogen chloride method is consumed in hydrochloric acid desorption and deep desorption, with the remaining steam heat consumed in heating the reactants and catalyst post-treatment, thus highlighting its high energy consumption.

[0013] 2. Methanol Excess Method

[0014] The methanol excess method refers to the synthesis of chloromethane using a methanol (mol):hydrogen chloride (mol) ratio of (1.05–1.1):1. The excess methanol ensures approximately 99% conversion of hydrogen chloride during the reaction. This method generally does not use a catalyst, resulting in a slower reaction rate and requiring a larger reactor to provide sufficient residence time.

[0015] The conventional methanol excess process typically includes two-stage reaction and multi-step distillation to separate components such as chloromethane, hydrogen chloride, methanol, and water from the reactor. Excess methanol is separated, recovered, and reused. Hydrogen chloride and water are treated as waste hydrochloric acid. The chloromethane product, after purification by sulfuric acid absorption, needs to be pressurized by a compressor to raise its boiling point before condensing into a liquid. In the methanol excess process, approximately 60% of the steam heat is consumed in the reboiler of the methanol recovery tower, and approximately 35% of the steam heat is consumed in the vaporization of methanol before it enters the reactor. Utility Model Content

[0016] In response to the problems mentioned in the background art, this application provides an apparatus and method for synthesizing chloromethane. By optimizing the apparatus for synthesizing chloromethane, ultra-low energy consumption of the chloromethane synthesis apparatus is achieved.

[0017] One object of this invention is to provide an apparatus for synthesizing chloromethane, the apparatus comprising:

[0018] The reaction unit includes a methanol feeding unit and a reactor. The reactor includes a feed inlet and a discharge outlet. The methanol feeding unit is connected to the feed inlet of the reactor.

[0019] Hydrochloric acid separation unit: includes a hydrochloric acid separation tower, a compressor, and a top condenser. The hydrochloric acid separation tower includes a first inlet, a first outlet at the top of the tower, and a second outlet at the bottom of the tower. The discharge port of the reactor is connected to the first inlet. The first outlet is connected to the inlet of the compressor. The top condenser includes a gas phase outlet and a liquid phase outlet. The inlet of the top condenser is connected to the methanol feed unit. The top condenser is used to condense the material collected from the compressor outlet and heat-exchanged by the methanol feed unit.

[0020] The methanol recovery unit includes a methanol recovery tower and a double-effect reboiler. The methanol recovery tower includes a second inlet, a reboiler reflux inlet, a third outlet at the top of the tower, and a fourth outlet at the bottom of the tower. The second outlet of the hydrochloric acid separation tower is connected to the second inlet, and 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, providing heat to the methanol recovery tower. Simultaneously, the outlet of the double-effect reboiler is also connected to the methanol feed unit, providing heat to the methanol feed unit. The outlet of the compressor is simultaneously connected to both the methanol feed unit and the inlet of the double-effect reboiler. The material collected from the compressor outlet is used to provide heat to both the methanol feed unit and the double-effect reboiler.

[0021] Chloromethane purification unit: includes a chloromethane separation tower, which has 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 condenser at the top of the hydrochloric acid separation unit is connected to the third inlet of the chloromethane separation tower.

[0022] Further, 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, wherein 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 of the reaction in 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 reactor is 10 wt.%-20 wt.%, and / or the concentration of the hydrochloric acid solution in the secondary reactor is 6 wt.%-16 wt.%.

[0024] Furthermore, the methanol feed unit includes a methanol buffer tank, a methanol preheater, a methanol double-effect heater, and a methanol evaporator connected in sequence. The inlet of the methanol buffer tank is connected to the sixth outlet of the chloromethane separation tower. The source of methanol in the methanol buffer tank includes at least methanol drawn from the bottom of the chloromethane separation tower. The methanol preheater, the methanol double-effect heater, and the methanol evaporator are all heat exchangers. Methanol in the methanol buffer tank can enter the methanol preheater, the methanol double-effect heater, and the methanol evaporator in sequence to exchange heat 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 from the material extracted from the fourth outlet is used to exchange heat 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 from 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 a portion of the heat from the material collected at the compressor outlet exchanges heat with the methanol in the methanol evaporator.

[0028] Furthermore, the hydrochloric acid separation unit also includes a separator, which is disposed 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. 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. 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 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 chloromethane purification unit also includes a sulfuric acid absorption tower, a chloromethane condenser, and a chloromethane product buffer tank. The sulfuric acid absorption tower includes a fourth inlet, a seventh outlet at the top of the tower, and an eighth outlet at the bottom of the tower. The fifth outlet of the chloromethane separation tower is connected to the fourth inlet, the seventh outlet is connected to the inlet of the chloromethane condenser, and the outlet of the chloromethane condenser is connected to the inlet of the chloromethane product buffer tank. The eighth outlet is used to discharge solid waste.

[0032] Another object of this invention is to provide a method for synthesizing chloromethane, the method utilizing the apparatus described above, the method comprising the following steps:

[0033] In the reaction unit: the raw material hydrogen chloride and gaseous methanol supplied by the methanol feed unit react in the reactor, and the products generated by the reaction include chloromethane, unreacted hydrogen chloride and methanol, water and dimethyl ether produced by the reaction;

[0034] In the hydrochloric acid separation unit: the products generated by the reaction unit enter the hydrochloric acid separation tower through the first inlet. After being distilled by the hydrochloric acid separation tower, the gaseous material separated from the first outlet at the top of the hydrochloric acid separation tower includes gaseous methanol, chloromethane, and dimethyl ether. The material collected from the second outlet at the bottom of the tower includes dilute hydrochloric acid and methanol. The gaseous material is compressed by a compressor connected to the hydrochloric acid separation tower and then divided into two streams, which are sent to the methanol feed unit and the double-effect reboiler, respectively, to heat the methanol in the methanol feed unit and to serve as a heat source for the double-effect reboiler.

[0035] In the methanol recovery unit: the material collected from the second outlet at the bottom of the hydrochloric acid separation tower enters the second inlet of the methanol recovery tower, and after being distilled by the methanol recovery tower, gaseous methanol is collected from the third outlet at the top of the tower, and solid waste is collected from the fourth outlet at the bottom of the tower; wherein the heat of the distillation of 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 chloromethane purification unit: the crude chloromethane gaseous product from the top condenser of the hydrochloric acid separation tower enters the chloromethane separation tower. After distillation in the chloromethane separation tower, chloromethane and dimethyl ether are collected from the fifth outlet at the top of the tower, and methanol is collected from the sixth outlet at the bottom of the tower.

[0037] Furthermore, the reactor comprises a primary reactor and a secondary reactor, with the outlet of the primary reactor 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 of the reaction in 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 reactor is 10 wt.%-20 wt.%, and / or the concentration of the hydrochloric acid solution in the secondary reactor is 6 wt.%-16 wt.%.

[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℃.

[0040] Furthermore, the gaseous material extracted from the first outlet of the hydrochloric acid separation tower includes methanol, chloromethane, 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 stream accounts for 10-20% of the total flow rate 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 rate 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 is drawn from the fourth outlet into 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 is drawn from the double-effect reboiler into 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 a portion of the material collected from the compressor outlet enters the methanol evaporator to heat the methanol therein.

[0044] Furthermore, the methanol recovery unit also includes a methanol recovery condenser and a methanol recovery tower reflux tank. 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. 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] This utility model has at least the following beneficial effects:

[0046] This invention optimizes the apparatus for synthesizing chloromethane by replacing the pressurized liquefaction of pure chloromethane in the conventional methanol excess method with pressurization of the overhead vapor phase in the hydrochloric acid separation unit. Waste heat energy, which previously required removal via cooling water, is transformed into a directly usable heat source, directly heating the reboiler and evaporator of the methanol recovery tower. This recycling of heat energy significantly reduces steam and cooling water consumption in the process. While achieving ultra-low energy consumption and cost production in the chloromethane synthesis unit, it also provides an excellent solution for the green and sustainable development of enterprises and society.

[0047] Furthermore, this 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. Therefore, it is not necessary to maintain a pressure of more than 3 bar in the reactor (the pressure required by the conventional methanol excess method). The pressure of the primary and secondary reactors can be maintained at 2.5 bar to maintain the normal operation of the system. The reaction temperature corresponding to this 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 (the initial corrosion temperature of the enamel reactor at a hydrochloric acid solution concentration of 15 wt.% is 125°C), thereby reducing the cost of equipment replacement. Attached Figure Description

[0048] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the specification, serve to explain the technical solutions of this application.

[0049] Figure 1 A schematic diagram of the apparatus for synthesizing chloromethane provided by this utility model.

[0050] Figure label:

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

[0052] This application provides an apparatus and method for synthesizing chloromethane. Preferred embodiments of this application are described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of this application. Furthermore, the embodiments and features described herein can be combined with each other unless otherwise specified.

[0053] Example 1

[0054] refer to Figure 1 This embodiment provides an apparatus for synthesizing chloromethane, which includes a reaction unit, a hydrochloric acid separation unit, a methanol recovery unit, and a chloromethane purification unit.

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

[0056] The reaction unit includes 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 the compressor (4). The outlet of the compressor (4) is connected to two pipelines. One pipeline is connected to the double-effect reboiler (5), which is connected to the methanol double-effect heater (10). The other pipeline 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). The outlet of the methanol recovery tower condenser (7) is connected to the inlet of the methanol recovery tower reflux tank (8). 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). The outlet of the double-effect reboiler (5) is connected not only to the reboiler reflux inlet but also 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 top condenser (12). One stream of the gaseous material from the top of the compressor (4) passes through the methanol evaporator (11) for heat exchange, and the other stream passes through the double-effect reboiler (5) and the methanol double-effect heater (10) for heat exchange. After heat exchange, the two streams of material are combined and enter the top condenser (12) for condensation. The liquid phase outlet of the top condenser (12) is connected to the inlet of the top cooler (13). The outlet of the top cooler (13) is connected to the inlet of the top reflux tank (14). The outlet of the 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 at the top of the chloromethane separation tower (15) is connected to the fourth inlet of the sulfuric acid absorption tower (18). The seventh outlet at the top of the sulfuric acid absorption tower (18) is connected downstream, and high-purity chloromethane gas is directly supplied to 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). 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). 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 includes a separator (22), which is disposed 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, to ensure that the methanol temperature at the outlet of the methanol evaporator (11) meets the reaction requirements during start-up and shutdown, and when the flow rate, pressure, and temperature at the compressor (4) outlet fluctuate, this invention can also add a steam-heated methanol vaporizer downstream of the methanol side of the methanol evaporator (11) as a heat supplement, according to actual production needs. 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 set next to the pipeline from the compressor (4) to the methanol evaporator (11), and this bypass pipeline is also equipped with an automatic regulating valve and connected to the DCS system. A temperature sensor is installed 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 line of the methanol evaporator (11) to increase the steam flow and 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 line of the methanol evaporator (11) and closes the steam regulating valve of the methanol vaporizer, thereby reducing the flow of the material from the compressor (4) outlet through the methanol evaporator (11) to reduce the supply of heat source.

[0062] Example 2

[0063] This embodiment provides a process for synthesizing chloromethane, which includes a reaction unit, a hydrochloric acid separation unit, a methanol recovery unit, and a chloromethane purification unit. Figure 1 The following reaction processes are implemented in each unit:

[0064] (1) Reaction unit: Combination Figure 1 The reaction unit comprises a primary reactor (1) and a secondary reactor (2) connected in series. The raw materials in the primary reactor (1) include 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 (here, hydrogen chloride includes raw material B and raw material C) react at a molar ratio of (0.95-1):1. The product generated by the reaction is then piped into the secondary reactor (2). At the same time, methanol of approximately 10% of the amount of methanol added in the primary reactor (1) is added to the secondary reactor (2) in advance. After the reaction in the secondary reactor (2), the hydrogen chloride in the reaction system can be reduced from approximately 5% to approximately 1%. The total methanol to total hydrogen chloride feed molar ratio in the two reactors is (1.05-1.1):1.

[0065] The objective of the reaction unit is to react hydrogen chloride and methanol, producing products including chloromethane, unreacted hydrogen chloride and methanol, water, and dimethyl ether. 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 10 wt.% to 20 wt.%, and the concentration of the hydrochloric acid solution in the secondary reactor (2) is 6 wt.% to 16 wt.%. In this invention, the primary reactor (1) is set with a slight excess of hydrogen chloride to ensure that the gaseous methanol is fully reacted within the primary reactor (1), thereby reducing the production of the byproduct dimethyl ether and increasing the yield of the product chloromethane. In this invention, the methanol in the secondary reactor (2) is slightly excessive 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 amount of waste acid discharged from the system, reduce the amount of solid waste discharged, and achieve 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) through the first inlet at the bottom of the tower. After distillation in the hydrochloric acid separation tower (3), the gaseous material separated from the first outlet at the top of the tower mainly consists of some methanol, chloromethane, and dimethyl ether. After being compressed by the compressor (4) connected to the hydrochloric acid separation tower (3), the pressure of the gaseous material reaches 9-11 barg and the temperature reaches 160-175℃. The purpose of the hydrochloric acid separation tower (3) in this invention is to separate chloromethane, dimethyl ether, and dilute hydrochloric acid water. The components at the top of the tower are chloromethane, some methanol, and dimethyl ether, while the second outlet at the bottom of the tower produces dilute hydrochloric acid water and some 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℃, and the operating temperature at the bottom of the tower is 105-125℃.

[0067] Furthermore, in this invention, the gaseous components compressed by the compressor (4) are divided into two streams: one stream serves as a heat source to heat and vaporize the methanol in the methanol evaporator (11); the other stream serves as a heat source to heat the double-effect reboiler (5) of the methanol recovery tower (6), and some residual heat is used to heat the methanol double-effect heater (10). One stream of the gaseous material at the top of the tower from the compressor (4) passes through the methanol evaporator (11) for heat exchange, and the other stream passes through the double-effect reboiler (5) and the methanol double-effect heater (10) for heat exchange. After heat exchange, they are combined and enter the top condenser (12) for condensation. Among them, the chloromethane and dimethyl ether with lower boiling points enter the chloromethane separation tower (15) at the rear end in gaseous form, and the methanol with higher boiling points enters the top cooler (13) for further cooling after condensation. The temperature of the cooled methanol is about 30-50°C. The condensate enters the top reflux tank (14) and then returns to the hydrochloric acid separation tower (3) as reflux. For example, a flow 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 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 drops to about 130-135°C. The remaining heat is used to reheat the methanol in the methanol double-effect heater (10). The temperature of the heated gas phase material drops 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 pressurization function of the compressor (4) connected to the rear end of the hydrochloric acid separation tower in this invention also has another function. In the conventional methanol excess method, the pressure of the reaction system needs to maintain the power of two reactors and multiple distillation towers. Therefore, 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 15 wt.% is 125°C. The pressurization function of the compressor (4) connected to the rear end of the hydrochloric acid separation tower in this invention makes the pressure of the reaction system only need to maintain the power of the reactor and the hydrochloric acid separation tower. That is, the pressure of the reactor can be 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, thereby reducing the equipment cost.

[0069] (3) Methanol recovery unit: combined with Figure 1The material containing methanol, water, and unreacted hydrogen chloride is collected as a liquid from the second outlet at the bottom of the hydrochloric acid separation tower (3). After the liquid material passes through the separator (22) connected to the hydrochloric acid separation tower (3) to remove any organic layer (hydrocarbons) that may be present, it enters the methanol recovery tower (6) through the second inlet located in the middle of the methanol recovery tower (6). After distillation in the methanol recovery tower (6), the gaseous methanol is distilled out from the third outlet at the top of the tower and enters the methanol recovery tower condenser (7) connected to it. The condensed methanol enters the methanol recovery tower reflux tank (8). A portion of the methanol entering the methanol recovery tower reflux tank (8) is returned to the methanol recovery tower (6) as reflux liquid, and the remainder is produced and enters the methanol buffer tank (21) connected to it.

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

[0071] (4) Chloromethane purification unit: combined Figure 1 The crude chloromethane gaseous product from the top condenser (12) of the hydrochloric acid separation tower (3) enters the chloromethane separation tower (15) through the third inlet. The components of the crude chloromethane gaseous product mainly include chloromethane, methanol, and dimethyl ether. The purpose of the chloromethane separation tower (15) in this invention is to separate methanol and chloromethane. The reboiler (16) of the chloromethane separation tower is heated by steam. The component collected from the sixth outlet at the bottom of the tower is methanol, which is cooled by the bottom cooler (17) of the chloromethane separation tower and then enters the methanol buffer tank (21), and then enters the reaction system again as a raw material. The component collected from the fifth outlet at the top of the tower is chloromethane and dimethyl ether, which enter the sulfuric acid absorption tower (18) and react with the fresh sulfuric acid at the top of the tower to remove impurities such as dimethyl ether and water from the product. High-purity chloromethane gaseous product is collected from the seventh outlet at the top of the tower. The gaseous chloromethane product can be directly extracted for use in downstream systems, or it can be cooled by a chloromethane cooler (19) and then enter a chloromethane buffer tank (20). Part of it is refluxed into the chloromethane separation tower (15), and the rest is extracted as a liquid product.

[0072] The above describes a process for synthesizing chloromethane. Another objective of this invention is to fully utilize the heat generated in the chloromethane synthesis system, thereby reducing energy consumption and production costs. Specifically, this invention optimizes the chloromethane process flow. Based on MVR heat pump distillation technology, the pressurized liquefaction of pure chloromethane in the conventional methanol excess method chloromethane synthesis process is replaced by pressurization of the gas phase at the top of the hydrochloric acid separation unit. MVR is short for Mechanical Vapor Recompression. MVR technology uses a small amount of compressor compression work to raise the large amount of low-grade waste heat carried by secondary vapor to a high grade for reuse, hence it is also called MVR heat pump technology. In this invention, MVR heat pump technology is combined with the traditional distillation production process. A compressor (4) is connected to the top outlet of the hydrochloric acid separation tower (3) to pressurize the gas phase at the top 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 chloromethane:

[0074] For an introduction to the conventional methanol excess process, please refer to the background section. Because the reaction system pressure needs to maintain the power of two reactors and multiple distillation columns, the reaction pressure must be maintained above 3 bar, corresponding to a reaction temperature above 130°C. The water produced in the reaction is heated and evaporated by the heat generated by the reaction and the heat provided by additional steam, and then enters the hydrochloric acid separation column along with other reaction components. In the conventional methanol excess process, the top of the hydrochloric acid separation column needs to condense the condensable methanol components into liquid. If condensation is not achieved, more methanol will be sent to the downstream chloromethane column, increasing the load on the chloromethane separation column. If it is further carried to the sulfuric acid absorption column, more sulfuric acid will be consumed to remove 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 methanol condensation. The conventional method uses a large amount of methanol reflux to remove it through the top condenser, resulting in significant energy waste. Furthermore, the compressor design in the conventional methanol excess process is located after chloromethane purification, and the heat generated by compression requires additional cooling water removal, which also leads to energy waste.

[0075] To address the energy waste problem in conventional methanol excess methods, this invention optimizes the synthesis process based on MVR heat pump distillation technology. A compressor (4) is used to compress the high-heat material at the top of the column, further increasing its temperature to approximately 175°C. The heat carried by the compressed material is then used to supply the methanol recovery tower reboiler and methanol evaporator, which have particularly high heat requirements. Specifically, in this invention, the gaseous components compressed by the compressor (4) are divided into two streams: one stream serves as a heat source to heat and vaporize the methanol in the methanol evaporator (11); the other stream serves as a heat source to heat the double-effect reboiler (5) of the methanol recovery tower (6), and some residual heat is supplied to the methanol double-effect heater (10) for heating. In actual production, each reactor and distillation column is equipped with a temperature sensor to monitor the temperature of the entire system. The distribution of these two heat streams is adjusted according to the actual heat requirements of each part of the system.

[0076] In the conventional methanol excess method, approximately 35% of the total system heat is consumed in the vaporization of methanol before it enters the primary reactor (1). However, in this invention, no external steam heat is required to vaporize the methanol entering the primary reactor (1). Methanol (approximately 30°C) from the methanol buffer tank (21) enters the methanol preheater (9), the methanol double-effect heater (10), and the methanol evaporator (11) sequentially through pipelines, achieving methanol heating at each stage. The heat for heating methanol in each stage of this invention comes from the following sources: approximately 115°C wastewater from the bottom of the methanol recovery tower (6) is used to preheat the methanol (approximately 30°C) from the methanol buffer tank (21), raising the methanol temperature from 30°C to approximately 45°C. Then, the residual heat (approximately 130°C) from the material is further heated in the methanol double-effect heater (10) using the double-effect reboiler (5) of the methanol recovery tower (6), raising the methanol temperature from 45°C to approximately 110°C. Finally, the material at approximately 175°C from the compressor (4) is directly heated in the methanol evaporator (11), raising the methanol temperature to approximately 135°C. Thus, the temperature requirements for adding methanol to the primary reactor (1) and achieving normal reaction can be met with virtually no additional steam consumption.

[0077] In addition to fully utilizing the system heat and reducing energy consumption in the reaction unit and hydrochloric acid separation unit, this 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). A portion of the liquid material collected from the bottom of the tower is pumped into the double-effect reboiler (5), heated and evaporated, and then returned to the tower. The remainder passes through the methanol preheater (9) and is discharged from the system as solid waste. This liquid material mainly includes wastewater containing 2% hydrochloric acid and trace amounts of methanol. In the conventional methanol excess method, the steam consumption of the reboiler in the methanol recovery tower (6) accounts for about 60% of the entire chloromethane plant. In contrast, this invention uses the material compressed by the compressor (4) as a heat source to heat the material at the bottom of the tower to 120°C through the double-effect reboiler (5) and then vaporize it before returning it to the tower, thus achieving the reboil function. This saves a large amount of steam compared to the conventional methanol excess method.

[0078] This invention utilizes MVR heat pump distillation technology to fully utilize the heat generated during compression. Compared to the conventional methanol excess method, this invention does not increase equipment costs; preliminary calculations show only a 12% increase in compressor power consumption.

[0079] This invention optimizes the process flow for synthesizing chloromethane, achieving ultra-low energy consumption in the chloromethane synthesis unit by utilizing MVR heat pump distillation technology. By installing a compressor at the downstream end of the hydrochloric acid separation unit, the heat of reaction, heat of compression, and heat of steam are fully utilized, eliminating the need for large amounts of steam as a heat source for the methanol recovery tower reboiler and methanol evaporator, thus significantly reducing steam consumption in the process flow. Specifically, this invention achieves unexpected technical benefits in both saving production costs and reducing equipment costs.

[0080] 1. Save production costs

[0081] Table 1 shows a comparison of energy consumption and cost for synthesizing chloromethane using different methods.

[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, this invention can save 75 million yuan per year compared to the hydrogen chloride excess process and 23 million yuan per year compared to the conventional methanol excess process.

[0086] 2. Provides low-cost equipment selection options.

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

[0088] Because this invention uses a compressor (4) to pressurize the system starting from 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), thus eliminating the need for a pressure above 3 bar. Maintaining a reactor pressure of 2.5 bar is sufficient to maintain normal system operation. This pressure corresponds to a temperature of approximately 120°C in the primary reactor (1), at which temperature the enamel material can withstand any concentration of hydrochloric acid, thus solving the corrosion problem. Regarding the reaction volume, multiple small reactors (domestic manufacturers can already produce 135 cubic meter enamel reactors) can be connected in parallel. Calculations show that the cost of using multiple small reactors is only one-fifth of that of using corrosion-resistant bricks in a large reactor. The application of this invention can greatly promote the use of the methanol excess method in chloromethane synthesis plants.

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

[0090] The sequence numbers of the embodiments in this application are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0091] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. An apparatus for synthesizing chloromethane, characterized in that, The device includes: The reaction unit includes a methanol feeding unit and a reactor. The reactor includes a feed inlet and a discharge outlet. The methanol feeding unit is connected to the feed inlet of the reactor. Hydrochloric acid separation unit: includes a hydrochloric acid separation tower, a compressor, and a top condenser. The hydrochloric acid separation tower includes a first inlet, a first outlet at the top of the tower, and a second outlet at the bottom of the tower. The discharge port of the reactor is connected to the first inlet. The first outlet is connected to the inlet of the compressor. The top condenser includes a gas phase outlet and a liquid phase outlet. The inlet of the top condenser is connected to the methanol feed unit. The top condenser is used to condense the material collected from the compressor outlet and heat-exchanged by the methanol feed unit. The methanol recovery unit includes a methanol recovery tower and a double-effect reboiler. The methanol recovery tower includes a second inlet, a reboiler reflux inlet, a third outlet at the top of the tower, and a fourth outlet at the bottom of the tower. The second outlet of the hydrochloric acid separation tower is connected to the second inlet, and 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, providing heat to the methanol recovery tower. Simultaneously, the outlet of the double-effect reboiler is also connected to the methanol feed unit, providing heat to the methanol feed unit. The outlet of the compressor is simultaneously connected to both the methanol feed unit and the inlet of the double-effect reboiler. The material collected from the compressor outlet is used to provide heat to both the methanol feed unit and the double-effect reboiler. Chloromethane purification unit: includes a chloromethane separation tower, which has 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 condenser at the top of the hydrochloric acid separation unit is connected to the third inlet of the chloromethane separation tower.

2. The apparatus according to claim 1, characterized in that, The reactor includes: 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, wherein 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 products from the reaction in 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 apparatus according to claim 1, characterized in that, The methanol feed unit includes a methanol buffer tank, a methanol preheater, a methanol double-effect heater, and a methanol evaporator 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 methanol in the methanol buffer tank includes at least methanol drawn from the bottom of the chloromethane separation tower; The methanol preheater, methanol double-effect heater, and methanol evaporator are all heat exchangers. Methanol in the methanol buffer tank can enter the methanol preheater, methanol double-effect heater, and methanol evaporator in sequence to exchange heat and enter the reactor in the form of gaseous methanol.

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

5. The apparatus 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 from the material extracted from the double-effect reboiler is exchanged with the methanol in the methanol double-effect heater.

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

7. The apparatus according to claim 1, characterized in that, The hydrochloric acid separation unit also includes a separator, which is disposed between the hydrochloric acid separation tower and the methanol recovery tower, and is connected to the second outlet of the hydrochloric acid separation tower and the second inlet of the methanol recovery tower.

8. The apparatus according to claim 3, characterized in that, The methanol recovery unit further includes a methanol recovery condenser and a methanol recovery tower reflux tank, and the methanol recovery tower further 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.

9. The apparatus according to claim 1, characterized in that, 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.

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

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