Methyl chloride production process

Abstract

The invention relates to a production process of methane chloride. The production process comprises the following steps: introducing HCl gas and a first part of methanol in a molar ratio of (0.95-1.1): 1 into parallel first-stage reactors to carry out first-stage reaction; introducing the primary gas-phase reaction product and a second part of methanol into a secondary reactor for secondary reaction, wherein the molar ratio of the second part of methanol to the HCl gas is (0.05-0.5): 1; the second-stage gas-phase reaction product enters a rectifying section to be rectified, methyl chloride mixed gas obtained at the top is sequentially condensed through a condenser and carried-out methyl alcohol liquid drops are removed through a demister, condensate and a crude methyl chloride product are obtained, and the condensate flows back to the rectifying section; tower bottoms of the rectifying section enter the stripping section to be subjected to stripping treatment, stripping gas obtained at the top of the stripping section is fed into the rectifying section, tower bottoms obtained at the bottom of the stripping section are fed into the reboiler to generate vaporized gas and are fed into the stripping section, and the ratio of the tower bottoms discharged as sewage to the tower bottoms fed into the reboiler is (2-5): 1.

Description

Technical Field

[0001] The invention belongs to the field of methyl chloroethane synthesis technology, and specifically relates to a methyl chloroethane production process. Background Art

[0002] Methyl chloride is an important chemical raw material that can be used to produce chemical products such as organosilicon and glyphosate. In China, the preparation process of methyl chloride is mainly liquid phase catalysis and gas-solid phase catalysis. Among them, the single-stage HCl conversion rate of methyl chloride synthesis reaction is usually less than 95%. When treating the obtained mixed gas, it is usually necessary to use deacidification, dealcoholization, dimethyl ether removal and other devices for treatment, and a large amount of hydrochloric acid-containing wastewater, alkali-containing waste liquid and waste sulfuric acid containing organic impurities are generated. Therefore, the goal of improving methyl chloride synthesis technology is not only to increase the conversion rate of methanol and hydrogen chloride and reduce the impurity content, but also to reduce acid-containing and alkali-containing waste liquid, which is also a requirement of current technological development.

[0003] The reaction equation involved in the production of methyl chloride is as follows:

[0004] Main reactions:

[0005] CH3OH+HCl——CH3Cl+H2O

[0006] Main side effects:

[0007] 2CH3OH——(CH3)2O+H2O

[0008] (CH3)2O+2HCl——CH3OH+H2O.

[0009] The reaction equation involved in the purification of chloromethane is as follows:

[0010]

[0011] Chinese patent CN114605222B discloses a method for efficiently synthesizing methyl chloride, wherein the synthesis device used comprises a series of reactors, wherein an internal plug-in heat exchanger is arranged inside the reactor; an aqueous phase solution is added inside each reactor, wherein the aqueous phase solution is composed of water, hydrogen chloride and methanol; hydrogen chloride gas and methanol gas are introduced into the first reactor in the series reactor according to the material flow direction; methanol gas and gas materials discharged from the upstream adjacent reactor are introduced into the remaining reactors of the series reactor until the last reactor reacts, and the reaction ends. This method helps to improve the HCl conversion rate, but the disadvantages are that the system pressure drop increases, the HCl feed pressure requirement increases, the size of the reaction equipment is limited by conventional glass-lined firing tools, and although the step-by-step series connection of multiple reactors improves the efficiency of methyl chloride synthesis, the capacity utilization rate is low.

[0012] Chinese patent application CN113548941A discloses a reaction packing tower for methyl chloride production, including a tower body, a methanol vapor, a hydrogen chloride inlet, a discharge port and an emptying port are provided at the bottom of the tower, a reflux port is provided at the top of the tower, the discharge port is connected to a reflux pump provided externally, the reflux pump circulates the discharge from the bottom of the tower to the top of the tower for reflux, and the tower body is divided into two sections of upper and lower packings, a methanol vapor side line feed port is provided between the two sections of packings, and a methanol evaporator is provided on the methanol vapor feed line. It can effectively improve the gas-liquid mass transfer efficiency, reduce the generation of by-products, and improve the hydrochloric acid conversion rate. This method is similar to the above-mentioned multi-stage horizontal reactor series mode, but the methyl chloride synthesis reaction is carried out in an electrolyte solution, and the tower reactor has a low space-time yield.

[0013] Chinese patent application CN113582811A discloses a deacidification process for methyl chloride synthesis gas, which uses a packed tower as a deacidification tower, methanol as a deacidification agent, and adds a partial condenser at the top of the deacidification tower, so that the deacidification tower becomes a multi-stage separator, thereby improving the deacidification efficiency and reducing the water content in the treated synthesis gas. The deacidification method provided by this method has obvious advantages over water washing, but the disadvantage is that the methanol carried out from the top of the tower needs to be removed by additional equipment, and the methanol content of the tower bottom wastewater is relatively high.

[0014] Chinese patent CN106748632B discloses a clean production method for synthesizing chloromethane, including the following steps: 1) chloromethane synthesis step, using gaseous hydrogen chloride and gaseous methanol to synthesize crude chloromethane; 2) waste heat recovery step: crude chloromethane is heat exchanged with liquid methanol by a heat exchange device and discharged after cooling; liquid methanol is heated by a heat exchange device to form gaseous methanol as raw material gas to enter step 1) to participate in the reaction; 3) deacidification tower deacidification step: deacidify the crude chloromethane; 4) absorption tower refining step; 5) pressurization, extraction distillation and deetherification step; 6) dilute acid water film concentration step. In this method, the pressure adaptability range of hydrogen chloride and methanol is wider, and HCl and water are removed by combining a deacidification tower with an absorption tower (methanol as a washing liquid). However, as mentioned above, the residence time of HCl in the liquid phase of the tower reactor is short, the time-space yield is low, and the production capacity is limited. Summary of the invention

[0015] In view of this, the purpose of the present invention is to provide a chloromethane production process in view of the defects existing in the prior art. The chloromethane production process of the present invention solves at least one technical problem of low HCl conversion rate, high chloride ion content in wastewater, and limited volume of key reaction equipment in the existing chloromethane production process, and can realize continuous production of chloromethane with high production efficiency and environmental friendliness.

[0016] The objectives of the present invention are achieved through the following technical solutions.

[0017] The present invention provides a chloromethane production process, wherein the chloromethane production process comprises the following steps:

[0018] S100, introducing HCl gas and the first part of methanol into parallel primary reactors for primary reaction, and obtaining a primary gas phase reaction product 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;

[0019] S200, introducing the primary gas-phase reaction product and the second portion of methanol into a secondary reactor for a secondary reaction, and obtaining a secondary gas-phase reaction product 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, sending the secondary gas phase reaction product to a deacidification tower for deacidification treatment, wherein the deacidification tower comprises a rectifying section and a stripping section, wherein the stripping section is provided with an external reboiler, and the deacidification treatment comprises:

[0021] S310, the secondary gas phase reaction product enters the distillation section for distillation treatment, a chloromethane mixed gas is obtained at the top of the distillation section, and a bottom liquid is obtained at the bottom of the distillation section. The chloromethane mixed gas is sequentially condensed by a condenser and the methanol droplets carried by the demister are removed to obtain a condensate and a chloromethane crude product, and the condensate is refluxed to the distillation section;

[0022] S320, the bottom liquid of the distillation section enters the stripping section for stripping treatment, the stripping gas obtained at the top of the stripping section is sent to the distillation section for distillation 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, and a sewage outlet is set at the bottom of the stripping section to discharge part of the bottom liquid as sewage. Preferably, the weight ratio of the bottom liquid discharged as sewage to the bottom liquid sent to the reboiler is 2-5:1.

[0023] The chloromethane production process of the present invention has high HCl and methanol conversion rates, low chloride ion content in sewage, low tail gas volume, low energy consumption, is not limited by the volume of key reaction equipment, can achieve continuous production of chloromethane, high production efficiency, and is environmentally friendly. In particular, the present invention adopts a parallel primary reactor and then connects it in series with a secondary reactor, which can achieve efficient chloromethane synthesis reaction under the condition of limited processing size of the reaction equipment, which can not only improve the conversion rate of HCl, but also ensure production capacity, and is particularly suitable for the synthesis of chloromethane in the organosilicon production process. Further, the present invention adopts a specific deacidification process-rectification treatment and stripping treatment, the water content in the chloromethane crude product is low, the chloride ion content in the sewage is low, and the chlorine loss in the chloromethane production process is effectively reduced, and it is environmentally friendly. The present invention believes that methanol is used for circulation reflux at the top of the distillation section, so that water and HCl in the secondary gas phase reaction product can be effectively removed, a chloromethane mixed gas is obtained at the top of the distillation section, and a bottom liquid is obtained at the bottom of the distillation section. The bottom liquid contains unreacted HCl and methanol. The bottom liquid is subjected to stripping treatment to return the methanol in the bottom liquid to the distillation tower without the need to additionally add vaporized methanol. Not only can the methanol in the wastewater be recovered, but the contained HCl can also continue to react with the methanol in the distillation section and the stripping section, so that the chlorine loss in the chloromethane production process is effectively reduced, the chloride ion content in the sewage is low, and the process is environmentally friendly.

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

[0025] In the present invention, the catalyst solution may be an aqueous solution of ZnCl2 and / or FeCl3. An aqueous solution of ZnCl2 and / or FeCl3 is used as a catalyst solution to promote the reaction. It is believed that adding aqueous solutions such as ZnCl2 and FeCl3 can increase the Cl - The residence time in the reactor and the azeotropic point of the reaction solution, thereby improving the reaction space-time yield. In some embodiments, the concentration of the ZnCl2 and / or FeCl3 aqueous solution can be 50-80 wt %, for example, 75 wt %.

[0026] The present invention also found that the ZnCl2 and / or FeCl3 aqueous solution may be brought into sewage along with the water produced by the reaction, polluting the environment. Therefore, in other embodiments, the primary reactor and the secondary reactor are each independently added with an HCl aqueous solution. The concentration of the HCl aqueous 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 in the primary reactor and the secondary reactor is bubbled into the catalyst solution and / or the HCl aqueous solution. In the present invention, the bubbling feeding method is adopted to make the HCl and methanol fully mixed. The chloromethane gas generated by the reaction also leaves the liquid surface in the form of bubbles and enters the gas phase space at the top.

[0028] According to the monochloromethane production process provided by the present invention, the first part of methanol is vaporized methanol, and the second part of methanol is liquid methanol, preferably liquid methanol preheated by an economizer. In the present invention, liquid methanol is used as the second part of methanol, which is convenient for effective measurement and ratio adjustment, and reduces deviation.

[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 passed into a secondary reactor for a secondary reaction.

[0030] According to the monochloromethane production process provided by the present invention, the conditions of the primary reaction include: temperature of 115-160° C., pressure of 0.1-0.5 MPaG; residence time of HCl of 1-5 h; and / or, the conditions of the secondary reaction include: temperature of 110-155° C., pressure of 0.05-0.45 MPaG; residence time of HCl of 3-15 h.

[0031] In the present invention, the pressure expressed in "MPaG" is a gauge pressure, that is, a pressure excluding atmospheric pressure.

[0032] In some embodiments, the temperature of the primary reaction and the secondary 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 composed 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, 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 composed thereof.

[0034] In some embodiments, the pressure of the primary reaction may be in a range of 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 combination thereof.

[0035] In some embodiments, the pressure of the secondary reaction can be in a 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, a catalyst solution is independently added to the primary reactor and the secondary reactor, and the conditions of the primary reaction include: temperature of 140-160°C, pressure of 0.1-0.2 MPaG, and residence time of 2-3.5 h; and / or the conditions of the secondary reaction include: temperature of 140-155°C, pressure of 0.05-0.1 MPaG, and residence time of 8-15 h.

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

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

[0039] According to the monochloromethane production process provided by the present invention, 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%.

[0040] According to the process for producing monochloromethane provided by the present invention, the molar ratio of the HCl gas to the first part of methanol is 0.95-1.05:1, preferably 1-1.05:1.

[0041] According to the monochloromethane production process provided by the present invention, the molar ratio of the second part 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 part of methanol to the HCl gas is 0.05-0.15:1.

[0042] According to the monochloromethane production process provided by the present invention, the first part of methanol is vaporized methanol, and the second part of methanol is liquid methanol, preferably liquid methanol preheated by an economizer. In the present invention, liquid methanol is used as the second part of methanol, which is convenient for effective measurement and ratio adjustment, and reduces deviation.

[0043] According to the monochloromethane production process provided by the present invention, the primary reactor and the secondary reactor are independently vertical or horizontal reactors, and the feeding method can be top or bottom, and the present invention has no special restrictions on this. In addition, the material can be glass lining or other acid-resistant lining.

[0044] In the present invention, the primary reactor and the secondary reactor are provided with a heater to control the reaction temperature. The heater used can be a built-in coil heater, a bayonet heater, or an external reboiler or a jacket.

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

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

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

[0048] In some embodiments, the bottom temperature of the distillation treatment 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 treatment in step S310 is 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 range composed thereof.

[0050] Similarly, in some embodiments, the top temperature of the distillation treatment in step S310 can be 60-90° C., for example, 60° C., 70° C., 80° C., 90° C. or a range composed 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 monochloromethane production process provided by the present invention, in step S310, the demister can achieve a demister efficiency of more than 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 distillation section in step S310 can be determined according to the quality of the crude monochloromethane product and the conditions of the distillation section. The excess condensate can be returned to the methanol feed buffer tank as methanol material. In some embodiments, the reflux amount of the condensate is 8-15 t / h, preferably 9-12 t / h, relative to the flow rate of 10 t / h of HCl gas in the primary reaction.

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

[0055] In some embodiments, the bottom temperature of the distillation treatment 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 treatment in step S320 can be 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 range composed thereof.

[0057] Similarly, in some embodiments, the top temperature of the distillation treatment 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 composed 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, the weight ratio of the bottom liquid discharged as wastewater in step S320 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 sewage and the liquid methanol raw material to recover heat energy.

[0061] According to the methyl chloroform production process provided by the present invention, the methyl chloroform production process further comprises: S400, sending the crude methyl chloroform product to a sulfuric acid tower for treatment to remove dimethyl ether and methanol, and obtaining a liquid methyl chloroform product and tail gas.

[0062] In some embodiments, the sulfuric acid tower is provided with a built-in demister at the top, the crude methyl chloride 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 contacts with the crude methyl chloride product in countercurrent to treat the crude methyl chloride product.

[0063] The amount of sulfuric acid added to the sulfuric acid tower can be determined according to the content of impurities such as dimethyl ether and methanol in the crude monochloromethane product. In some embodiments, the molar ratio of the added sulfuric acid to the impurities (such as dimethyl ether and methanol impurities) contained in the crude monochloromethane product in terms of dimethyl ether equivalent is 1.5-6:1, preferably 2-4:1, for example, 3:1. In the present invention, excessive sulfuric acid is used to fully react with dimethyl ether and methanol, thereby reducing the impurity content in the product monochloromethane to obtain a pure monochloromethane product. In addition, compared with the traditional water washing and deacidification process, the alcohol elution and deacidification process selected in the present invention has a low water content in the top product, and the sulfuric acid consumption can be reduced by about 2 to 3 times.

[0064] In step S400, a liquid-phase methyl chloride product is obtained by the following method: the methyl chloride product obtained from the top of the sulfuric acid tower and subjected to demisting treatment is pressurized and liquefied to obtain a liquid-phase methyl chloride product.

[0065] In step S400, the dilute sulfuric acid obtained from the bottom of the sulfuric acid tower is sent to a sulfuric acid regeneration device for treatment to obtain 96% concentrated sulfuric acid for recycling.

[0066] In some specific embodiments, the methyl chloride production process further includes: S500, sending the tail gas containing methyl chloride, methanol, and dimethyl ether from the sulfuric acid regeneration device and the methyl chloride in the condenser tail gas into a venting absorption tower, and absorbing it with fresh methanol and then entering a secondary reactor for reaction, so as to improve 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 (more than 98.5%), no new impurities are introduced, the chloride ion content in the sewage is low, the tail gas volume is small, the energy consumption is low, the production cost is low, and the environment is friendly; (2) The chloromethane production process of the present invention is not limited by the volume of key reaction equipment, and the continuous production of chloromethane can be achieved, and the production efficiency is high; (3) The chloromethane production process of the present invention has low sulfuric acid consumption, and the output of the by-product dilute sulfuric acid is low. The dilute sulfuric acid can also be recycled and regenerated and recycled in the sulfuric acid absorption tower, and no waste sulfuric acid is generated, which is environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1 The figure is a schematic flow diagram of an embodiment of a process for producing methyl chloride according to the present invention. DETAILED DESCRIPTION

[0069] The present invention will be further described below in conjunction with specific embodiments, but they do not constitute any limitation to the present invention.

[0070] Unless otherwise specifically stated, the raw materials used in the present invention can be homemade or commercially available, and the present invention is not particularly limited thereto.

[0071] Example 1

[0072] Reference Figure 1 , the production process of methyl chloride is as follows.

[0073] 1. First-order reaction

[0074] HCl gas and the first part of vaporized methanol are blown into two parallel primary reactors in a 75 wt% ZnCl2 aqueous solution (catalyst) for primary reaction, and a primary gas phase reaction product is obtained from the top of each primary reactor. Wherein, based on each primary reactor, the flow rate of HCl gas is 5000 kg / h, and the flow rate of vaporized methanol is 4255 kg / h; the molar ratio of HCl gas to the first part of vaporized methanol is 1.03:1, and the conditions of the primary reaction are as follows: pressure 0.128 MPaG, temperature 155±2°C, HCl residence time of about 2 hours, and HCl conversion rate of about 89%.

[0075] 2. Secondary reaction

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

[0077] 3. Deacidification treatment

[0078] 3.1 Distillation treatment

[0079] The secondary gas phase reaction product is sent to the economizer for heat exchange and then enters the distillation section for distillation treatment. A chloromethane mixed gas is obtained at the top of the distillation section, and a bottom liquid is obtained at the bottom of the distillation section. The chloromethane mixed gas is condensed by a condenser to obtain a condensate and a chloromethane crude product, and the condensate is refluxed to the distillation section. The distillation treatment conditions are as follows: the tower bottom temperature is 105°C, the tower bottom pressure is 0.075MPaG, the tower top temperature is 70°C; the theoretical plate number is 22; the condensate reflux rate is 9t / h, and the temperature is 23°C; the water content in the chloromethane crude product is about 0.05% by weight, the methanol content is about 0.06% by weight, and the dimethyl ether content is about 0.3% by weight; the HCl content in the bottom liquid of the distillation section is about 3% by weight, and the methanol content is about 4.5% by weight.

[0080] 3.2 Distillation treatment

[0081] The bottom liquid of the rectifying section enters the stripping section for stripping treatment, the gas obtained at the top of the stripping section is sent to the rectifying section for rectification treatment, the bottom liquid of the stripping section is sent to the reboiler to generate vaporized gas and sent to the stripping section, a sewage outlet is set at the bottom of the stripping section, and the bottom liquid of the tower is discharged through the sewage outlet. The conditions of the stripping treatment are as follows: the tower bottom temperature is 119°C, the tower bottom pressure is 0.095MPaG, the tower top temperature is 105°C; the theoretical plate number is 18; the weight ratio of the discharged bottom liquid to the bottom liquid sent to the reboiler is 5, and the vaporized gas temperature is 123°C; the HCl content in the sewage is about 2.6% by weight, and the methanol content is about 0.02% by weight.

[0082] Example 2

[0083] Reference Figure 1 , the production process of methyl chloride is as follows.

[0084] 1. First-order reaction

[0085] HCl gas and the first part of vaporized methanol are blown into 3 parallel primary reactors in a 20 wt% HCl aqueous solution for primary reaction, and a primary gas phase reaction product is obtained from the top of each primary reactor. Wherein, based on each primary reactor, the flow rate of HCl gas is 5000 kg / h, the flow rate of vaporized methanol is 4255 kg / h; the molar ratio of HCl gas to the first part of vaporized methanol is 1.03:1, and the conditions of the primary reaction are as follows: pressure 0.45 MPaG, temperature 145±2°C, HCl residence time 2.3 h, and HCl conversion rate is about 90.6%.

[0086] 2. Secondary reaction

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

[0088] 3. Deacidification treatment

[0089] 3.1 Distillation treatment

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

[0091] 3.2 Distillation treatment

[0092] The bottom liquid of the rectifying section enters the stripping section for stripping treatment, the gas obtained at the top of the stripping section is sent to the rectifying section for rectification treatment, the bottom liquid of the stripping section is sent to the reboiler to generate vaporized gas and sent to the stripping section, a sewage outlet is set at the bottom of the stripping section, and the bottom liquid of the tower is discharged through the sewage outlet. The conditions of the stripping treatment are as follows: the tower bottom temperature is 140°C, the tower bottom pressure is 0.36MPaG, the tower top temperature is 115°C; the theoretical plate number is 22; the weight ratio of the discharged bottom liquid to the bottom liquid sent to the reboiler is 3, and the vaporized gas temperature is 140°C; the HCl content in the sewage is about 1.2% by weight, and the methanol content is about 0.02% by weight.

[0093] Example 3

[0094] Reference Figure 1 This example is used to illustrate the post-treatment of the crude methyl chloride product.

[0095] The crude methyl chloroethane product in Example 1 is sent to a demister to remove the methanol droplets carried out, and the demister efficiency is 99.5%. Then the crude methyl chloroethane product is sent to a sulfuric acid absorption tower to remove water, dimethyl ether and methanol impurities. The molar ratio of sulfuric acid addition to dimethyl ether and methanol (converted into an equal amount of dimethyl ether) is 3:1. A demister is provided inside the sulfuric acid absorption tower to remove sulfuric acid droplets. The demister efficiency reaches more than 99.5%, and pure methyl chloroethane gas is obtained. After pressurized condensation, pure methyl chloroethane liquid is obtained.

[0096] Comparative Example 1

[0097] 1. Chloromethylation reaction

[0098] HCl gas and vaporized methanol are blown into 3 parallel primary reactors in a 20 wt% HCl aqueous solution for primary reaction, and a gas phase reaction product is obtained from the top of each primary reactor. The flow rate of HCl gas is 5000 kg / h, and the flow rate of vaporized methanol is 4255 kg / h for each primary reactor; the molar ratio of HCl gas to the first part of vaporized methanol is 1.03:1. Chloromethylation The reaction conditions were as follows: pressure 0.45 MPaG, temperature 145±2°C, HCl residence time 2.3 h, and HCl conversion rate of about 90.6%.

[0099] 2. Deacidification

[0100] 2.1 Distillation treatment

[0101] The gas phase reaction product is sent to the economizer for heat exchange and then enters the deacidification tower for treatment. A chloromethane mixed gas is obtained at the top and a bottom liquid is obtained at the bottom. The chloromethane mixed gas is condensed by a condenser to obtain a condensate and a chloromethane crude product. The condensate is refluxed to the deacidification tower. The deacidification treatment conditions are as follows: a bottom temperature of 120°C, a bottom pressure of 0.43MPaG, a top temperature of 83°C; a theoretical plate number of 22; a condensate reflux rate of 20t / h, and a temperature of 40°C; the water content of the chloromethane crude product is about 0.03% by weight, the methanol content is about 0.08% by weight, and the dimethyl ether content is about 0.15% by weight; the HCl content in the bottom liquid is about 17.4% by weight, and the methanol content is about 6% by weight.

[0102] 2.2 Distillation treatment

[0103] The bottom liquid of the rectifying section enters the stripping section for stripping treatment, the gas obtained at the top of the stripping section is sent to the rectifying section for rectification treatment, the bottom liquid of the stripping section is sent to the reboiler to generate vaporized gas and sent to the stripping section, a sewage outlet is set at the bottom of the stripping section, and the bottom liquid of the tower is discharged through the sewage outlet. The conditions of the stripping treatment are as follows: the tower bottom temperature is 155°C, the tower bottom pressure is 0.45MPaG, the tower top temperature is 120°C; the theoretical plate number is 22; the weight ratio of the discharged bottom liquid to the bottom liquid sent to the reboiler is 3, and the vaporized gas temperature is 155°C; the HCl content in the sewage is 18% by weight, and the methanol content is 0.03% by weight.

[0104] 18% dilute hydrochloric acid cannot be directly used for sewage treatment and needs to be outsourced.

[0105] Comparative Example 2

[0106] 1. First-order reaction

[0107] HCl gas and the first part of vaporized methanol are blown into two parallel primary reactors in a 75 wt% ZnCl2 aqueous solution (catalyst) for primary reaction, and a primary gas phase reaction product is obtained from the top of each primary reactor. Wherein, based on each primary reactor, the flow rate of HCl gas is 5000 kg / h, and the flow rate of vaporized methanol is 4255 kg / h; the molar ratio of HCl gas to the first part of vaporized methanol is 1.03:1, and the conditions of the primary reaction are as follows: pressure 0.128 MPaG, temperature 155±2°C, HCl residence time of about 2 hours, and HCl conversion rate of about 89%.

[0108] 2. Secondary reaction

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

[0110] 3. Deacidification treatment

[0111] 3.1 Distillation treatment

[0112] The secondary gas phase reaction product is sent to the economizer for heat exchange and then enters the distillation section for distillation treatment. Figure 1 Water is added from the lower liquid of the top condenser to supplement the reflux liquid, a chloromethane mixed gas is obtained at the top, and a bottom liquid is obtained at the bottom. The chloromethane mixed gas is condensed by the condenser to obtain a condensate (water) and a crude chloromethane product. The condensate is refluxed to the distillation section, and the bottom liquid is sent to the reboiler to generate vaporized gas and sent to the distillation section to supplement heat. A sewage outlet is set at the bottom of the distillation section, and the bottom liquid is discharged through the sewage outlet. The conditions for the distillation treatment are as follows: tower bottom temperature is 110°C, tower bottom pressure is 0.07MPaG, tower top temperature is 80°C; the theoretical plate number is 22; the condensate reflux rate is 9t / h, and the temperature is 40°C; the ratio of the discharged bottom liquid to the bottom liquid fed into the reboiler is 3:1, and the vaporized gas temperature is 122°C; the water content in the crude monochloromethane product is 3% by weight, the methanol content is 0.24% by weight, and the dimethyl ether content is 0.32% by weight; the HCl content in the bottom liquid of the distillation section is 3% by weight, and the methanol content is 3.5% by weight.

[0113] 3.2 Distillation treatment

[0114] The bottom liquid of the rectifying section enters the stripping section for stripping treatment, the gas obtained at the top of the stripping section is sent to the rectifying section for rectification treatment, the bottom liquid of the stripping section is sent to the reboiler to generate vaporized gas and sent to the stripping section, a sewage outlet is set at the bottom of the stripping section, and the bottom liquid of the tower is discharged through the sewage outlet. The conditions of the stripping treatment are as follows: the tower bottom temperature is 119°C, the pressure is 0.095MPaG, the tower top temperature is 110°C; the theoretical plate number is 18; the ratio of the discharged bottom liquid to the bottom liquid sent to the reboiler is 5, and the vaporized gas temperature is 123°C; the HCl content in the sewage is 3% by weight, and the methanol content is 0.02% by weight.

[0115] It can be seen from Example 1 and Comparative Example 2 that, compared with Comparative Example 1 in which water is used as the coolant in the distillation treatment, under substantially the same distillation conditions, in Example 1 in which methanol is used as the coolant for reflux, the crude methyl chloride product has a significantly lower water content and a better separation effect.

[0116] It can be seen from Examples 1 and 2 that the bottom liquid (waste water) of the stripping section of Example 2 has a reduced HCl content, and the crude monochloromethane product of the rectification section has a lower dimethyl ether content.

[0117] It can be seen from Example 2 and Comparative Example 1 that, compared with Comparative Example 1 using a primary reaction, the HCl content in the bottom liquid of the rectification section of Example 2 is significantly reduced. In addition, in order to control the water content in the crude methyl chloride product at the same level (0.03 wt %), the amount of condensate required is less, the pressure is low, and the operation is more convenient.

Claims

1. A process for producing methyl chloride, wherein: The monochloromethane production process comprises the following steps: S100, introducing HCl gas and the first part of methanol into parallel primary reactors for primary reaction, and obtaining a primary gas phase reaction product 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, introducing the primary gas-phase reaction product and the second portion of methanol into a secondary reactor for a secondary reaction, and obtaining a secondary gas-phase reaction product 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; S300, sending the secondary gas phase reaction product to a deacidification tower for deacidification treatment, wherein the deacidification tower comprises a rectifying section and a stripping section, wherein the stripping section is provided with an external reboiler, and the deacidification treatment comprises: S310, the secondary gas phase reaction product enters the distillation section for distillation treatment, a chloromethane mixed gas is obtained at the top of the distillation section, and a bottom liquid is obtained at the bottom of the distillation section. The chloromethane mixed gas is sequentially condensed by a condenser and the methanol droplets carried by the demister are removed to obtain a condensate and a chloromethane crude product, and the condensate is refluxed to the distillation section; S320, the bottom liquid of the distillation section enters the stripping section for stripping treatment, the stripping gas obtained at the top of the stripping section is sent to the distillation section for distillation 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, and a sewage outlet is set at the bottom of the stripping section to discharge part of the bottom liquid as sewage.

2. The process for producing methyl chloride according to claim 1, wherein: A catalyst solution and / or an aqueous HCl solution are added independently to the primary reactor and the secondary reactor; Preferably, the catalyst solution is an aqueous solution of ZnCl2 and / or FeCl3, and the concentration of the aqueous solution of ZnCl2 and / or FeCl3 is preferably 50-80 wt%; Preferably, the concentration of the HCl aqueous solution is 5-30 wt %, preferably 10-20 wt %.

3. The process for producing methyl chloride according to claim 2, wherein: The conditions of the primary reaction include: temperature of 115-160° C., pressure of 0.1-0.5 MPaG, and residence time of HCl of 1-5 h; and / or the conditions of the secondary reaction include: temperature of 110-155° C., pressure of 0.05-0.45 MPaG, and residence time of HCl of 3-15 h.

4. The process for producing methyl chloride according to claim 3, wherein: HCl aqueous solution is added to the primary reactor and the secondary reactor independently, and the conditions of the primary reaction include: temperature of 120-150° C., pressure of 0.38-0.5 MPaG, and residence time of 2-3.5 h; and / or the conditions of the secondary reaction include: temperature of 115-145° C., pressure of 0.27-0.4 MPaG, and residence time of 8-15 h.

5. The process for producing methyl chloride according to claim 3, wherein: Catalyst solution is added to each of the primary reactor and the secondary reactor independently, and the conditions of the primary reaction include: temperature of 140-160°C, pressure of 0.1-0.2MPaG, and residence time of 2-3.5h; and / or the conditions of the secondary reaction include: temperature of 140-155°C, pressure of 0.05-0.1MPaG, and residence time of 8-15h.

6. The process for producing methyl chloride according to any one of claims 1 to 5, wherein: The number of the parallel primary reactors is 2-5, preferably 2-3; 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%.

7. The process for producing methyl chloride according to any one of claims 1 to 5, wherein: The molar ratio of the HCl gas to the first portion of methanol is 0.95-1.05:1, preferably 1-1.05:1; and / or the molar ratio of the second portion of methanol to the HCl gas is 0.05-0.15:

1.

8. The process for producing methyl chloride according to any one of claims 1 to 5, wherein: In step S310, the conditions of the distillation treatment include: tower bottom temperature 80-150°C, tower bottom pressure 0.05-0.45MPaG, theoretical plate number 15-25; And / or, the tower top temperature of the distillation treatment in step S310 is 60-90°C.

9. The process for producing methyl chloride according to any one of claims 1 to 5, wherein: In step S320, the conditions of the stripping treatment include: tower bottom temperature 110-160°C, tower bottom pressure 0.05-0.5MPaG, theoretical plate number 15-30; And / or, the tower top temperature of the distillation treatment in step S320 is 90-120°C.

10. The process for producing methyl chloride according to any one of claims 1 to 5, wherein: The temperature of the vaporized gas in step S320 is 120-160° C.; and / or the weight ratio of the bottom liquid discharged as sewage to the bottom liquid fed into the reboiler is 4-5:1.

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