A process for producing monochloromethane

Abstract

This invention relates to a process for producing chloromethane, comprising: introducing HCl gas with a molar ratio of 0.95-1.1:1 and a first portion of methanol into a parallel primary reactor for a primary reaction; introducing the primary gas-phase reaction product and the second portion of methanol into a secondary reactor for a secondary reaction, wherein the molar ratio of the second portion of methanol to HCl gas is 0.05-0.5:1; introducing the secondary gas-phase reaction product into a rectification section for rectification treatment, wherein the chloromethane mixture obtained at the top is successively condensed by a condenser and a demister to remove the carried-out methanol droplets, thereby obtaining condensate and crude chloromethane product, wherein the condensate is refluxed back to the rectification section; the bottom liquid of the rectification section is introduced into a stripping section for stripping treatment, wherein the stripping gas obtained at the top of the stripping section is sent to the rectification section, and the bottom liquid obtained at the bottom of the stripping section is sent to a reboiler to generate vaporized gas, which is then sent to the stripping section, wherein the ratio of the bottom liquid discharged as wastewater to the bottom liquid sent to the reboiler is 2-5:1.

Description

Technical Field

[0001] This invention belongs to the field of monochloromethane synthesis processes, and specifically relates to a monochloromethane production process. Background Technology

[0002] Chloromethane is an important chemical raw material used in the production of organosilicon, glyphosate, and other chemical products. In China, the main processes for chloromethane preparation are liquid-phase catalysis and gas-solid-phase catalysis. The single-stage HCl conversion rate in the chloromethane synthesis reaction is typically below 95%. The resulting mixed gas usually requires treatment using equipment for acid removal, alcohol removal, and dimethyl ether removal, generating large amounts of wastewater containing hydrochloric acid, alkaline wastewater, and waste sulfuric acid containing organic impurities. Therefore, in addition to increasing the conversion rates of methanol and hydrogen chloride and reducing impurity content, reducing acidic and alkaline wastewater is also a current technological development requirement for improving chloromethane synthesis technology.

[0003] The reaction formulas involved in the production of monochloromethane are as follows:

[0004] Main reaction:

[0005] CH3OH + HCl → CH3Cl + H2O

[0006] Main side reactions:

[0007] 2CH3OH——(CH3)2O+H2O

[0008] (CH3)2O+2HCl——CH3OH+H2O.

[0009] The reaction equations involved in the purification of chloromethane are as follows:

[0010]

[0011] Chinese patent CN114605222B discloses a method for efficiently synthesizing chloromethane. The synthesis apparatus includes reactors connected in series, each equipped with an internal heat exchanger. An aqueous solution consisting of water, hydrogen chloride, and methanol is added to each reactor. Hydrogen chloride and methanol gas are introduced into the first reactor in the material flow direction. Methanol gas and the gaseous material discharged from the upstream adjacent reactor are introduced into the remaining reactors in the series until the last reactor has reacted, at which point the reaction ends. This method helps improve HCl conversion rate. However, it has disadvantages such as increased system pressure drop, higher HCl feed pressure requirements, and limitations in reactor size due to the constraints of conventional glass-lined fabrication tools. While the series connection of multiple reactors improves chloromethane synthesis efficiency, it results in low capacity utilization.

[0012] Chinese patent application CN113548941A discloses a packing tower for the production of chloromethane, comprising a tower body, a methanol vapor and hydrogen chloride inlet, a discharge port, and an vent port at the bottom of the tower, and a reflux port at the top of the tower. The discharge port is connected to an external reflux pump, which circulates the material from the bottom of the tower back to the top. The tower body is divided into upper and lower packing sections, with a methanol vapor side-line inlet located between the two sections. Methanol evaporators are installed along the methanol vapor feed line. This method effectively improves gas-liquid mass transfer efficiency, reduces by-product generation, and increases hydrochloric acid conversion rate. This method is similar to the multi-stage horizontal reactor series configuration described above; however, the chloromethane synthesis reaction is carried out in an electrolyte solution, resulting in a lower space-time yield for the tower reactor.

[0013] Chinese patent application CN113582811A discloses a deacidification process for chloromethane synthesis gas. It uses a packed tower as the deacidification tower and methanol as the deacidification agent. By adding a condenser at the top of the deacidification tower, the tower becomes a multi-stage separator, improving deacidification efficiency and reducing the water content in the treated synthesis gas. This method offers significant advantages over water washing. However, its disadvantages include the need for additional equipment to remove the methanol carried over from the top of the tower, and a high methanol content in the bottom wastewater.

[0014] Chinese patent CN106748632B discloses a clean production method for synthesizing chloromethane, including the following steps: 1) Chloromethane synthesis step, where crude chloromethane is synthesized from gaseous hydrogen chloride and gaseous methanol; 2) Waste heat recovery step: the crude chloromethane is discharged after heat exchange with liquid methanol and cooled by a heat exchanger; the liquid methanol is heated by a heat exchanger to form gaseous methanol, which is then used as raw material gas to participate in the reaction in step 1); 3) Deacidification tower step: the crude chloromethane is deacidified; 4) Absorption tower purification step; 5) Pressurized, extractive distillation and etherification step; 6) Dilute acid water film concentration step. This method has a wider pressure range for hydrogen chloride and methanol, and uses a combination of a deacidification tower and an absorption tower (methanol as washing liquid) to remove HCl and water. However, as mentioned earlier, the residence time of HCl in the liquid phase of the tower reactor is short, resulting in low space-time yield and limited production capacity. Summary of the Invention

[0015] In view of this, the purpose of this invention is to address the deficiencies in the prior art by providing a chloromethane production process. The chloromethane production process of this invention solves at least one of the technical problems in existing chloromethane production processes, such as low HCl conversion rate, high chloride ion content in wastewater, and limited volume of key reaction equipment. It can realize continuous production of chloromethane with high production efficiency and environmental friendliness.

[0016] The objective of this invention is achieved through the following technical solutions.

[0017] This invention provides a process for producing monochloromethane, wherein the monochloromethane production process includes the following steps:

[0018] S100. HCl gas and a first portion of methanol are introduced into parallel primary reactors to carry out a primary reaction, and a primary gaseous reaction product is obtained from the top of each primary reactor, wherein the molar ratio of HCl gas to the first portion of methanol is 0.95-1.1:1.

[0019] S200. The primary gas phase reaction product and the second portion of methanol are introduced into a secondary reactor to carry out a secondary reaction, and the secondary gas phase reaction product is obtained from the top of the secondary reactor, wherein the molar ratio of the second portion of methanol to the HCl gas is 0.05-0.5:1.

[0020] S300. The secondary gas-phase reaction product is fed into a deacidification tower for deacidification treatment. The deacidification tower includes a rectification section and a stripping section. The stripping section is equipped with an external reboiler. The deacidification treatment includes:

[0021] S310. The secondary gas phase reaction product enters the rectification section for rectification treatment. A chloromethane mixture is obtained at the top of the rectification section and a bottom liquid is obtained at the bottom of the rectification section. The chloromethane mixture is condensed by a condenser and the methanol droplets carried by it are removed by a demister in sequence to obtain condensate and crude chloromethane product. The condensate is refluxed to the rectification section.

[0022] S320. The bottom liquid of the rectification section enters the stripping section for stripping treatment. The stripping gas obtained at the top of the stripping section is sent to the rectification section for rectification treatment. The bottom liquid obtained at the bottom of the stripping section is sent to the reboiler to generate vaporized gas and sent to the stripping section. A drain port is provided at the bottom of the stripping section to discharge part of the bottom liquid as wastewater. Preferably, the weight ratio of the bottom liquid discharged as wastewater to the bottom liquid sent to the reboiler is 2-5:1.

[0023] The monochloromethane production process of this invention features high HCl and methanol conversion rates, low chloride ion content in wastewater, low tail gas volume, and low energy consumption. It is not limited by the volume of key reaction equipment, enabling continuous monochloromethane production with high efficiency and environmental friendliness. Specifically, this invention employs a parallel primary reactor followed by a series secondary reactor, achieving highly efficient monochloromethane synthesis even under conditions of limited reaction equipment size. This improves HCl conversion while ensuring production capacity, making it particularly suitable for monochloromethane synthesis in organosilicon production processes. Furthermore, this invention utilizes specific deacidification processes—distillation and stripping—resulting in low water content in the crude monochloromethane product and low chloride ion content in the wastewater, effectively reducing chlorine loss during monochloromethane production and contributing to environmental friendliness. This invention proposes that using methanol for reflux at the top of the rectification section can effectively remove water and HCl from the secondary gas-phase reaction products, resulting in a chloromethane mixture at the top of the rectification section and a bottom liquid containing unreacted HCl and methanol at the bottom. This bottom liquid is then stripped to allow the methanol to return to the rectification column without the need for additional vaporized methanol. This not only recovers methanol from the wastewater but also allows the HCl to continue reacting with methanol in the rectification and stripping sections, effectively reducing chlorine loss during chloromethane production. The resulting wastewater has a low chloride ion content and is environmentally friendly.

[0024] According to the chloromethane production process provided by the present invention, a catalyst solution and / or an aqueous HCl solution are independently added to each of the primary reactor and the secondary reactor.

[0025] In this invention, the catalyst solution can be an aqueous solution of ZnCl2 and / or FeCl3. Using an aqueous solution of ZnCl2 and / or FeCl3 as the catalyst solution promotes the reaction. It is believed that adding aqueous solutions of ZnCl2, FeCl3, etc., can increase the Cl... - The residence time in the reactor and the azeotropic point of the reaction liquid are used to improve the space-time yield of the reaction. In some embodiments, the concentration of the aqueous ZnCl2 and / or FeCl3 solution can be 50-80% by weight, for example, 75% by weight.

[0026] The present invention also found that aqueous solutions of ZnCl2 and / or FeCl3 may be carried into wastewater along with the water produced in the reaction, polluting the environment. Therefore, in some embodiments, aqueous solutions of HCl are independently added to both the primary reactor and the secondary reactor. The concentration of the aqueous HCl solution can be 5-30% by weight, preferably 10-20% by weight.

[0027] According to the chloromethane production process provided by the present invention, the feed into the primary reactor and the secondary reactor is bubbled into the catalyst solution and / or HCl aqueous solution. In this invention, the bubbling feeding method ensures thorough mixing of HCl and methanol. The chloromethane gas produced in the reaction also leaves the liquid surface in the form of bubbles and enters the upper gas phase space.

[0028] According to the chloromethane production process provided by the present invention, the first portion of methanol is vaporized methanol, and the second portion of methanol is liquid methanol, preferably liquid methanol preheated by an economizer. Using liquid methanol as the second portion of methanol in this invention facilitates effective measurement and adjustment of the proportions, reducing deviations.

[0029] In some embodiments, in step S100, HCl gas and the first portion of methanol are bubbled into a parallel primary reactor for a primary reaction; and in some embodiments, in step S200, the primary gas phase reaction product and the second portion of methanol are fed into a secondary reactor for a secondary reaction.

[0030] According to the chloromethane production process provided by the present invention, the conditions for the first-stage reaction include: a temperature of 115-160℃ and a pressure of 0.1-0.5 MPaG; and a residence time of HCl of 1-5 h; and / or the conditions for the second-stage reaction include: a temperature of 110-155℃ and a pressure of 0.05-0.45 MPaG; and a residence time of HCl of 3-15 h.

[0031] In this invention, the pressure expressed in "MPaG" is gauge pressure, which is pressure excluding atmospheric pressure.

[0032] In some embodiments, the temperatures of the first-order reaction and the second-order reaction are each independently 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, 150°C, 155°C, 160°C, or a range thereof.

[0033] In some embodiments, the pressure in the secondary reactor is typically lower than the pressure in the primary reactor, preferably 0.02-0.2 MPa lower, more preferably 0.04-0.15 MPa, for example, 0.02 MPa, 0.03 MPa, 0.04 MPa, 0.05 MPa, 0.06 MPa, 0.07 MPa, 0.08 MPa, 0.09 MPa, 0.1 MPa, 0.12 MPa, 0.15 MPa, or a range thereof.

[0034] In some embodiments, the pressure of the first-order reaction can be 0.1 MPaG, 0.15 MPaG, 0.2 MPaG, 0.25 MPaG, 0.3 MPaG, 0.35 MPaG, 0.38 MPaG, 0.4 MPaG, 0.45 MPaG, 0.5 MPaG, or a range thereof.

[0035] In some embodiments, the pressure of the second-order reaction can be within the range of 0.05 MPaG, 0.08 MPaG, 0.1 MPaG, 0.15 MPaG, 0.2 MPaG, 0.25 MPaG, 0.27 MPaG, 0.3 MPaG, 0.35 MPaG, 0.37 MPaG, 0.4 MPaG, or a combination thereof.

[0036] In some specific embodiments, the primary reactor and the secondary reactor each contain an independently added catalyst solution. The conditions for the primary reaction include: a temperature of 140-160°C, a pressure of 0.1-0.2 MPaG, and a residence time of 2-3.5 h; and / or the conditions for the secondary reaction include: a temperature of 140-155°C, a pressure of 0.05-0.1 MPaG, and a residence time of 8-15 h.

[0037] In some specific embodiments, an aqueous HCl solution is independently added to both the primary and secondary reactors. The conditions for the primary reaction include: a temperature of 120-150°C, a pressure of 0.38-0.5 MPaG, and a residence time of 2-3.5 h; and / or the conditions for the secondary reaction include: a temperature of 115-145°C, a pressure of 0.27-0.4 MPaG, and a residence time of 8-15 h. Under these conditions, the bottom liquid (wastewater) in the stripping section has a reduced HCl content.

[0038] According to the monochloromethane production process provided by the present invention, the number of parallel primary reactors is 2-5, preferably 2-3.

[0039] According to the chloromethane production process provided by the present invention, the HCl conversion rate of the first-stage reaction is 85%-95%, and / or the HCl conversion rate of the second-stage reaction is 95%-99.5%.

[0040] According to the chloromethane production process provided by the present invention, the molar ratio of the HCl gas to the first portion of methanol is 0.95-1.05:1, preferably 1-1.05:1.

[0041] According to the chloromethane production process provided by the present invention, the molar ratio of the second portion of methanol to the HCl gas can be 0.05:1, 0.08:1, 0.1:1, 0.12:1, 0.15:1, 0.18:1, 0.2:1, 0.25:1, 0.3:1, 0.35:1, 0.4:1, 0.45:1, 0.5:1, or a range thereof. In some embodiments, the molar ratio of the second portion of methanol to the HCl gas is 0.05-0.15:1.

[0042] According to the chloromethane production process provided by the present invention, the first portion of methanol is vaporized methanol, and the second portion of methanol is liquid methanol, preferably liquid methanol preheated by an economizer. Using liquid methanol as the second portion of methanol in this invention facilitates effective measurement and adjustment of the proportions, reducing deviations.

[0043] According to the chloromethane production process provided by the present invention, the primary reactor and the secondary reactor are each independently vertical or horizontal reactors, and the feeding method can be top or bottom; the present invention does not have any particular limitations in this regard. Furthermore, the material can be glass-lined or other acid-resistant linings.

[0044] In this invention, both the primary reactor and the secondary reactor are equipped with heaters to control the reaction temperature. The heaters used can be built-in coil heaters, scalpel heaters, or external reboilers or jackets.

[0045] According to the chloromethane production process provided by the present invention, in step S310, the secondary gas-phase reaction product enters the rectification section from the lower part of the rectification section, and / or the condensate is refluxed to the upper part of the rectification section.

[0046] According to the monochloromethane production process provided by the present invention, in step S310, the water content in the crude monochloromethane product is less than 0.1% by weight, preferably 0.01-0.08% by weight, for example 0.02-0.06% by weight; the methanol content is less than 0.1% by weight, for example 0.01-0.08% by weight; and the dimethyl ether content is less than 0.8% by weight, for example 0.05-0.5% by weight.

[0047] According to the monochloromethane production process provided by the present invention, in step S310, the conditions for the distillation treatment include: bottom temperature of 80-150℃, bottom pressure of 0.05-0.45MPaG, and theoretical plate number of 15-25.

[0048] In some embodiments, the bottom temperature of the distillation process in step S310 can be 80°C, 90°C, 100°C, 105°C, 110°C, 115°C, 120°C, 130°C, 140°C, 150°C or a range thereof.

[0049] In some embodiments, the bottom pressure of the distillation process in step S310 is within the range of 0.05 MPaG, 0.075 MPaG, 0.1 MPaG, 0.15 MPaG, 0.2 MPaG, 0.25 MPaG, 0.3 MPaG, 0.35 MPaG, 0.4 MPaG, 0.45 MPaG, or a combination thereof.

[0050] Similarly, in some embodiments, the top temperature of the distillation process in step S310 can be 60-90°C, for example, 60°C, 70°C, 80°C, 90°C or a range thereof.

[0051] According to the monochloromethane production process provided by the present invention, the temperature of the condensate in step S310 can be 20-40°C.

[0052] According to the chloromethane production process provided by the present invention, in step S310, the demister can achieve a demisting efficiency of over 99.3% for removing methanol droplets.

[0053] According to the monochloromethane production process provided by the present invention, the amount of condensate refluxed to the rectification section in step S310 can be determined based on the quality of the crude monochloromethane product and the conditions of the rectification section. Excess condensate can be returned to the methanol feed buffer tank as methanol feedstock. In some embodiments, the condensate reflux rate is 8-15 t / h, preferably 9-12 t / h, relative to the HCl gas flow rate of 10 t / h in the first-stage reaction.

[0054] According to the monochloromethane production process provided by the present invention, in step S320, the conditions for the distillation treatment include: bottom temperature of 110-160℃, bottom pressure of 0.05-0.5MPaG, and theoretical plate number of 15-30.

[0055] In some embodiments, the bottom temperature of the distillation process in step S320 can be 110°C, 120°C, 130°C, 140°C, 150°C, 160°C or a range thereof.

[0056] In some embodiments, the bottom pressure of the distillation process in step S320 can be a range of 0.05 MPaG, 0.06 MPaG, 0.07 MPaG, 0.08 MPaG, 0.09 MPaG, 0.1 MPaG, 0.15 MPaG, 0.2 MPaG, 0.25 MPaG, 0.3 MPaG, 0.35 MPaG, 0.4 MPaG, 0.45 MPaG, 0.5 MPaG, or a combination thereof.

[0057] Similarly, in some embodiments, the top temperature of the distillation process in step S320 can be 90-120°C, for example, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C or a range thereof.

[0058] According to the monochloromethane production process provided by the present invention, the temperature of the vaporized gas in step S320 is 120-160°C.

[0059] According to the monochloromethane production process provided by the present invention, in step S320, the weight ratio of the bottom liquid discharged as wastewater to the bottom liquid fed into the reboiler can be 2:1, 3:1, 4:1, 5:1 or a range thereof, for example, 4-5:1.

[0060] According to the monochloromethane production process provided by the present invention, step S320 further includes exchanging heat between the bottom liquid discharged as wastewater and the liquid methanol feedstock to recover heat energy.

[0061] According to the monochloromethane production process provided by the present invention, the monochloromethane production process further includes: S400, feeding the crude monochloromethane product into a sulfuric acid tower for treatment to remove dimethyl ether and methanol, thereby obtaining liquid monochloromethane product and tail gas.

[0062] In some embodiments, the sulfuric acid tower is equipped with a built-in demister at the top. Crude chloromethane product enters the sulfuric acid tower from the bottom, and concentrated sulfuric acid enters the sulfuric acid tower from below the built-in demister and comes into countercurrent contact with the crude chloromethane product to treat the crude chloromethane product.

[0063] The amount of sulfuric acid added to the sulfuric acid tower can be determined based on the content of impurities such as dimethyl ether and methanol in the crude chloromethane product. In some embodiments, the molar ratio of the added sulfuric acid to impurities in the crude chloromethane product (e.g., dimethyl ether and methanol impurities) is 1.5-6:1, preferably 2-4:1, for example, 3:1. In this invention, using excess sulfuric acid allows for sufficient reaction with dimethyl ether and methanol, thereby reducing the impurity content in the chloromethane product and obtaining a pure chloromethane product. Furthermore, compared to the traditional water washing deacidification process, the alcohol washing deacidification process used in this invention results in a product with lower water content, and sulfuric acid consumption can be reduced by approximately 2-3 times.

[0064] In step S400, the liquid-phase chloromethane product is obtained by pressurizing and liquefying the chloromethane product obtained from the top of the sulfuric acid tower after demisting treatment to obtain the liquid-phase chloromethane product.

[0065] In step S400, dilute sulfuric acid obtained from the bottom of the sulfuric acid tower is sent to the sulfuric acid regeneration unit for processing to obtain 96% concentrated sulfuric acid, which is then recycled.

[0066] In some specific implementations, the chloromethane production process further includes: S500, feeding the chloromethane containing chloromethane, methanol, and dimethyl ether from the tail gas of the sulfuric acid regeneration unit and the chloromethane in the condenser tail gas into a venting absorption tower, and absorbing it with fresh methanol before entering the secondary reactor for reaction, thereby improving the utilization rate of the raw material methanol.

[0067] The present invention has the following advantages: (1) In the chloromethane production process of the present invention, the conversion rate of HCl and methanol is high (above 98.5%), no new impurities are introduced, the chloride ion content in the wastewater is low, the tail gas volume is small, the energy consumption is low, the production cost is low, and the environment is environmentally friendly; (2) The chloromethane production process of the present invention is not limited by the volume of key reaction equipment, and can realize the continuous production of chloromethane with high production efficiency; (3) The chloromethane production process of the present invention has low sulfuric acid consumption and low by-product dilute sulfuric acid output. It can also choose to recycle and regenerate dilute sulfuric acid and use it in the sulfuric acid absorption tower. No waste sulfuric acid is generated, which is environmentally friendly. Attached Figure Description

[0068] Figure 1 This is a schematic flow chart of one embodiment of the monochloromethane production process according to the present invention. Detailed Implementation

[0069] The present invention will be further described below with reference to specific embodiments, but this does not constitute any limitation on the present invention.

[0070] Unless otherwise specified, all raw materials used in this invention can be prepared in-house or commercially available, and this invention does not impose any particular limitations on them.

[0071] Example 1

[0072] Reference Figure 1 The production process of monochloromethane is as follows.

[0073] 1. First-order reaction

[0074] HCl gas and partially vaporized methanol were bubbled into two parallel primary reactors containing a 75% by weight ZnCl2 aqueous solution (catalyst) for a first-stage reaction. The primary gaseous reaction products were obtained from the top of each primary reactor. Specifically, for each primary reactor, the flow rate of HCl gas was 5000 kg / h, and the flow rate of vaporized methanol was 4255 kg / h; the molar ratio of HCl gas to partially vaporized methanol was 1.03:1. The conditions for the first-stage reaction were: pressure 0.128 MPaG, temperature 155 ± 2 °C, HCl residence time approximately 2 h, and HCl conversion rate approximately 89%.

[0075] 2. Second-order reaction

[0076] The primary gas-phase reaction products from two primary reactors were combined and then introduced into a secondary reactor along with a second portion of liquid methanol in a 75% by weight ZnCl2 aqueous solution (catalyst) for a secondary reaction. The secondary gas-phase reaction product was obtained from the top of the secondary reactor. The flow rate of the second portion of vaporized methanol was 850 kg / h, and the molar ratio of the second portion of vaporized methanol to HCl gas was 0.1:1. The conditions for the secondary reaction were as follows: pressure 0.08 MPaG, temperature 148 ± 2 °C, HCl residence time approximately 9 h, and HCl conversion rate approximately 98.5%.

[0077] 3. Deacidification treatment

[0078] 3.1 Distillation Process

[0079] The secondary gas-phase reaction products are sent to the economizer for heat exchange and then enter the rectification section for rectification. A chloromethane mixture is obtained at the top of the rectification section, and a bottom liquid is obtained at the bottom. The chloromethane mixture is condensed in a condenser to obtain condensate and crude chloromethane product. The condensate is refluxed back to the rectification section. The rectification conditions are as follows: bottom temperature 105℃, bottom pressure 0.075 MPaG, top temperature 70℃; theoretical plate number 22; condensate reflux flow rate 9 t / h, temperature 23℃; the crude chloromethane product contains approximately 0.05% water, 0.06% methanol, and 0.3% dimethyl ether; the bottom liquid in the rectification section contains approximately 3% HCl and 4.5% methanol.

[0080] 3.2 Distillation Processing

[0081] The bottom liquid from the rectification section enters the stripping section for stripping. The gas obtained at the top of the stripping section is sent to the rectification section for rectification. The bottom liquid from the stripping section is sent to the reboiler to generate vaporized gas, which is then sent back to the stripping section. A drain outlet is provided at the bottom of the stripping section to discharge the bottom liquid. The stripping conditions are as follows: bottom temperature 119℃, bottom pressure 0.095MPaG, top temperature 105℃; theoretical plate number 18; weight ratio of discharged bottom liquid to bottom liquid sent to the reboiler 5; vaporized gas temperature 123℃; HCl content in the wastewater is approximately 2.6 wt%, and methanol content is approximately 0.02 wt%.

[0082] Example 2

[0083] Reference Figure 1 The production process of monochloromethane is as follows.

[0084] 1. First-order reaction

[0085] HCl gas and partially vaporized methanol were bubbled into three parallel primary reactors containing a 20% by weight HCl aqueous solution for a first-stage reaction. The first-stage gaseous reaction products were obtained from the top of each reactor. Specifically, for each primary reactor, the flow rate of HCl gas was 5000 kg / h, and the flow rate of vaporized methanol was 4255 kg / h; the molar ratio of HCl gas to partially vaporized methanol was 1.03:1. The conditions for the first-stage reaction were: pressure 0.45 MPaG, temperature 145 ± 2 °C, HCl residence time 2.3 h, and HCl conversion rate approximately 90.6%.

[0086] 2. Second-order reaction

[0087] The primary gas-phase reaction products from three primary reactors were combined and then introduced into a secondary reactor along with a second portion of liquid methanol in a 12% by weight HCl aqueous solution for a secondary reaction. The secondary gas-phase reaction product was obtained from the top of the secondary reactor. The flow rate of the second portion of vaporized methanol was 850 kg / h, and the molar ratio of the second portion of vaporized methanol to HCl gas was 0.1:1. The conditions for the secondary reaction were as follows: pressure 0.37 MPaG, temperature 130 ± 2 °C, HCl residence time 11.7 h, and HCl conversion rate approximately 99.3%.

[0088] 3. Deacidification treatment

[0089] 3.1 Distillation Process

[0090] The secondary gas-phase reaction products are sent to the economizer for heat exchange and then enter the rectification section for rectification. A chloromethane mixture is obtained at the top of the rectification section, and a bottom liquid is obtained at the bottom. The chloromethane mixture is condensed in a condenser to obtain condensate and crude chloromethane product. The condensate is refluxed back to the rectification section. The rectification conditions are as follows: bottom temperature 115℃, bottom pressure 0.35 MPaG, top temperature 80℃; theoretical plate number 22; condensate reflux flow rate 18 t / h, temperature 40℃; the crude chloromethane product contains approximately 0.03% by weight of water, 0.05% by weight of methanol, and 0.1% by weight of dimethyl ether; the bottom liquid in the rectification section contains approximately 1.4% by weight of HCl and 3.7% by weight of methanol.

[0091] 3.2 Distillation Processing

[0092] The bottom liquid from the rectification section enters the stripping section for stripping. The gas obtained at the top of the stripping section is sent to the rectification section for rectification. The bottom liquid from the stripping section is sent to the reboiler to generate vaporized gas, which is then sent back to the stripping section. A drain outlet is provided at the bottom of the stripping section to discharge the bottom liquid. The stripping conditions are as follows: bottom temperature 140℃, bottom pressure 0.36 MPaG, top temperature 115℃; theoretical plate number 22; weight ratio of discharged bottom liquid to bottom liquid sent to the reboiler 3; vaporized gas temperature 140℃; HCl content in the wastewater is approximately 1.2 wt%, and methanol content is approximately 0.02 wt%.

[0093] Example 3

[0094] Reference Figure 1 This embodiment illustrates the post-processing of crude chloromethane.

[0095] The crude chloromethane product from Example 1 was fed into a demister to remove the methanol droplets carried over, with a demister efficiency of 99.5%. Then, the crude chloromethane product was fed into a sulfuric acid absorption tower to remove water, dimethyl ether, and methanol impurities. The molar ratio of sulfuric acid added to dimethyl ether and methanol (converted to an equal amount of dimethyl ether) was 3:1. The sulfuric acid absorption tower was equipped with a demister to remove sulfuric acid droplets, with a demister efficiency of over 99.5%, resulting in pure chloromethane gas. After pressurization and condensation, pure chloromethane liquid was obtained.

[0096] Comparative Example 1

[0097] 1. Chloromethane reaction

[0098] HCl gas and vaporized methanol were bubbled into three parallel primary reactors containing a 20% by weight HCl aqueous solution for a first-stage reaction. The gaseous reaction products were obtained from the top of each primary reactor. Specifically, for each primary reactor, the flow rate of HCl gas was 5000 kg / h, and the flow rate of vaporized methanol was 4255 kg / h; the molar ratio of HCl gas to the first portion of vaporized methanol was 1.03:1. Chloromethanization The reaction conditions were as follows: pressure 0.45 MPaG, temperature 145 ± 2℃, residence time of HCl 2.3 h, and HCl conversion rate approximately 90.6%.

[0099] 2. Deacidification treatment

[0100] 2.1 Distillation treatment

[0101] The gaseous reaction products are sent to an economizer for heat exchange and then to a deacidification tower for processing. A chloromethane mixture is obtained at the top, and a bottom liquid is obtained at the bottom. The chloromethane mixture is condensed in a condenser to obtain condensate and crude chloromethane product. The condensate is refluxed back to the deacidification tower. The deacidification conditions are as follows: bottom temperature 120℃, bottom pressure 0.43 MPaG, top temperature 83℃; theoretical number of trays 22; condensate reflux flow rate 20 t / h, temperature 40℃; the crude chloromethane product contains approximately 0.03% by weight of water, 0.08% by weight of methanol, and 0.15% by weight of dimethyl ether; the bottom liquid contains approximately 17.4% by weight of HCl and 6% by weight of methanol.

[0102] 2.2 Distillation Process

[0103] The bottom liquid from the rectification section enters the stripping section for stripping. The gas obtained at the top of the stripping section is sent to the rectification section for rectification. The bottom liquid from the stripping section is sent to the reboiler to generate vaporized gas, which is then sent back to the stripping section. A drain outlet is provided at the bottom of the stripping section to discharge the bottom liquid. The stripping conditions are as follows: bottom temperature 155℃, bottom pressure 0.45MPaG, top temperature 120℃; theoretical plate number 22; weight ratio of discharged bottom liquid to bottom liquid fed into the reboiler 3; vaporized gas temperature 155℃; HCl content 18% by weight, methanol content 0.03% by weight in the wastewater.

[0104] 18% dilute hydrochloric acid cannot be directly used in wastewater treatment and must be outsourced for processing.

[0105] Comparative Example 2

[0106] 1. First-order reaction

[0107] HCl gas and partially vaporized methanol were bubbled into two parallel primary reactors containing a 75% by weight ZnCl2 aqueous solution (catalyst) for a first-stage reaction. The primary gaseous reaction products were obtained from the top of each primary reactor. Specifically, for each primary reactor, the flow rate of HCl gas was 5000 kg / h, and the flow rate of vaporized methanol was 4255 kg / h; the molar ratio of HCl gas to partially vaporized methanol was 1.03:1. The conditions for the first-stage reaction were: pressure 0.128 MPaG, temperature 155 ± 2 °C, HCl residence time approximately 2 h, and HCl conversion rate approximately 89%.

[0108] 2. Second-order reaction

[0109] The primary gas-phase reaction products from two primary reactors were combined and then introduced into a secondary reactor along with a second portion of liquid methanol in a 75% by weight ZnCl2 aqueous solution (catalyst) for a secondary reaction. The secondary gas-phase reaction product was obtained from the top of the secondary reactor. The flow rate of the second portion of vaporized methanol was 850 kg / h, and the molar ratio of the second portion of vaporized methanol to HCl gas was 0.1:1. The conditions for the secondary reaction were as follows: pressure 0.08 MPaG, temperature 148 ± 2 °C, HCl residence time 9 h, and HCl conversion rate approximately 98.5%.

[0110] 3. Deacidification treatment

[0111] 3.1 Distillation Process

[0112] The secondary gas-phase reaction products are sent to the economizer for heat exchange and then enter the rectification section for rectification, according to... Figure 1 Water is added from the bottom of the condenser at the top of the column to replenish the reflux liquid. A chloromethane mixture is obtained at the top, and a bottom liquid is obtained at the bottom. The chloromethane mixture is condensed by the condenser to obtain condensate (water) and crude chloromethane product. The condensate is refluxed to the rectification section, and the bottom liquid is sent to the reboiler to generate vaporized gas, which is then sent to the rectification section to replenish heat. A drain port is set at the bottom of the rectification section to discharge the bottom liquid. The distillation conditions are as follows: bottom temperature 110℃, bottom pressure 0.07MPaG, top temperature 80℃; theoretical plate number 22; condensate reflux flow rate 9t / h, temperature 40℃; ratio of discharged bottom liquid to bottom liquid fed into reboiler 3:1; vaporization gas temperature 122℃; the crude chloromethane product contains 3% water, 0.24% methanol, and 0.32% dimethyl ether; the bottom liquid in the rectification section contains 3% HCl and 3.5% methanol.

[0113] 3.2 Distillation Processing

[0114] The bottom liquid from the rectification section enters the stripping section for stripping. The gas obtained at the top of the stripping section is sent to the rectification section for rectification. The bottom liquid from the stripping section is sent to the reboiler to generate vaporized gas, which is then sent back to the stripping section. A drain outlet is provided at the bottom of the stripping section to discharge the bottom liquid. The stripping conditions are as follows: bottom temperature 119℃, pressure 0.095MPaG, top temperature 110℃; theoretical plate number 18; ratio of discharged bottom liquid to bottom liquid sent to the reboiler 5; vaporized gas temperature 123℃; HCl content 3% by weight, methanol content 0.02% by weight in the wastewater.

[0115] As can be seen from Example 1 and Comparative Example 2, compared with Comparative Example 1, which uses water as a coolant in the distillation process, under essentially the same distillation conditions, Example 1, which uses methanol as a coolant for reflux, has a significantly lower water content in the crude chloromethane product and exhibits better separation performance.

[0116] As can be seen from Examples 1 and 2, the bottom liquid (wastewater) of the stripping section in Example 2 has a reduced HCl content, and the crude chloromethane product in the rectification section has a lower dimethyl ether content.

[0117] As can be seen from Example 2 and Comparative Example 1, compared with Comparative Example 1 which uses a first-order reaction, the bottom liquid of the rectification section in Example 2 has a significantly lower HCl content. Furthermore, to control the water content in the crude chloromethane product at the same level (0.03% by weight), less condensate is required, the pressure is lower, and the operation is easier.

Claims

1. A process for the production of chloromethane, wherein, The monochloromethane production process comprises the following steps: S100, feeding HCl gas and a first part of methanol into parallel primary reactors for primary reactions, and obtaining primary gas phase reaction products from the top of each primary reactor, wherein the molar ratio of the HCl gas to the first part of methanol is 0.95-1.1:1; S200, feeding the primary gas phase reaction products and a second part of methanol into a secondary reactor for secondary reactions, and obtaining secondary gas phase reaction products from the top of the secondary reactor, wherein the molar ratio of the second part of methanol to the HCl gas is 0.05-0.5:1; S300, feeding the secondary gas phase reaction products into a deacidification tower for deacidification treatment, the deacidification tower comprising a rectification section and a stripping section, the stripping section being provided with an external reboiler, and the deacidification treatment comprising: S310, the secondary gas phase reaction products entering the rectification section for rectification treatment, monochloromethane mixed gas being obtained from the top of the rectification section, and tower bottom liquid being obtained from the bottom of the rectification section, the monochloromethane mixed gas being condensed in sequence by a condenser and removing methanol droplets carried by a demister to obtain condensate and monochloromethane crude product, and the condensate flowing back to the rectification section; S320, the tower bottom liquid of the rectification section entering the stripping section for stripping treatment, stripping gas obtained from the top of the stripping section being fed into the rectification section for rectification treatment, tower bottom liquid obtained from the bottom of the stripping section being fed into the reboiler to generate vaporization gas and fed into the stripping section, and a blowdown port being provided at the bottom of the stripping section to discharge part of the tower bottom liquid as sewage.

2. The chloromethane production process of claim 1, wherein, The primary reactors and the secondary reactor are each independently added with a catalyst solution and / or an HCl aqueous solution.

3. The chloromethane production process of claim 2, wherein, The catalyst solution is an aqueous solution of ZnCl2 and / or FeCl3; And / or, the concentration of the HCl aqueous solution is 5-30% by weight.

4. The chloromethane production process of claim 3, wherein, The concentration of the aqueous solution of ZnCl2 and / or FeCl3 is 50-80% by weight; And / or, the concentration of the HCl aqueous solution is 10-20% by weight.

5. The chloromethane production process according to any one of claims 2-4, wherein, The conditions of the primary reactions include a temperature of 115-160℃, a pressure of 0.1-0.5 MPaG, and a residence time of HCl of 1-5h; and / or the conditions of the secondary reactions include a temperature of 110-155℃, a pressure of 0.05-0.45 MPaG, and a residence time of HCl of 3-15h.

6. The chloromethane production process of claim 5, wherein, The primary reactors and the secondary reactor are each independently added with an HCl aqueous solution, the conditions of the primary reactions include a temperature of 120-150℃, a pressure of 0.38-0.5 MPaG, and a residence time of 2-3.5h; and / or the conditions of the secondary reactions include a temperature of 115-145℃, a pressure of 0.27-0.4 MPaG, and a residence time of 8-15h.

7. The chloromethane production process of claim 5, wherein, The catalyst solution is added independently in the primary reactor and the secondary reactor, the conditions of the primary reaction include: temperature 140-160℃, pressure 0.1-0.2 MPaG, residence time 2-3.5h; and / or the conditions of the secondary reaction include: temperature 140-155℃, pressure 0.05-0.1 MPaG, residence time 8-15h.

8. The chloromethane production process according to any one of claims 1-4, wherein, The number of the parallel primary reactors is 2-5. And / or, the HCl conversion rate of the primary reaction is 85%-95%, and / or the HCl conversion rate of the secondary reaction is 95%-99.5%.

9. The chloromethane production process of claim 8, wherein, The number of the parallel primary reactors is 2-3.

10. The chloromethane production process according to any one of claims 1-4, wherein, The molar ratio of the HCl gas to the first part of methanol is 0.95-1.05:1; and / or the molar ratio of the second part of methanol to the HCl gas is 0.05-0.15:

1.

11. The chloromethane production process of claim 10, wherein, The molar ratio of the HCl gas to the first part of methanol is 1-1.05:

1.

12. The chloromethane production process according to any one of claims 1-4, wherein, In step S310, the conditions of the rectification treatment include: column bottom temperature 80-150℃, column bottom pressure 0.05-0.45 MPaG, theoretical plate number 15-25; And / or, the overhead temperature of the rectification treatment in step S310 is 60-90℃.

13. The chloromethane production process according to any one of claims 1-4, wherein, In step S320, the conditions of the stripping treatment include: column bottom temperature 110-160℃, column bottom pressure 0.05-0.5 MPaG, theoretical plate number 15-30; And / or, the overhead temperature of the stripping treatment in step S320 is 90-120℃.

14. The chloromethane production process according to any one of claims 1-4, wherein, The temperature of the vaporization gas in step S320 is 120-160℃; and / or, the weight ratio of the column still liquid discharged as waste water to the column still liquid sent into the reboiler is 4-5:1.

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