Method and system for catalytic synthesis of chloromethane

Abstract

The invention belongs to the field of chloromethane synthesis, and particularly relates to a method and system for catalytically synthesizing chloromethane, and the method comprises the following steps: taking gaseous hydrogen chloride and gaseous methanol as raw materials, taking a compound of a zinc chloride aqueous solution and pyridine chloride salt as a catalyst, and preparing the chloromethane through a gas-liquid phase catalytic reaction in a double-kettle tandem reaction kettle. According to the method disclosed by the invention, the high-efficiency synthesis of chloromethane under the low-pressure state of 0.16-0.22 Mpa is realized, and the conversion rate of hydrogen chloride is up to 97% or above; according to the invention, less waste acid is generated, and the waste acid treatment pressure of a rear-end system is reduced.

Description

Technical Field

[0001] This invention belongs to the field of chloromethane synthesis, specifically relating to a method and system for catalytic synthesis of chloromethane. Background Technology

[0002] Chloromethane is a key raw material for the synthesis of organosilicon monomers, and its quality directly affects the dimethyl content in the crude organosilicon monomers. Currently, domestic chemical companies producing chloromethane typically use excess hydrogen chloride and methanol in a single-stage reactor, which increases operating costs for these companies.

[0003] Currently, the gas-liquid phase catalytic synthesis of chloromethane involves the catalytic conversion of hydrogen chloride gas and methanol gas into crude chloromethane in a reactor via a catalyst. The resulting crude chloromethane gaseous product contains water, unreacted hydrogen chloride and methanol, and impurities such as dimethyl ether produced as a side reaction. The crude chloromethane is then purified in a washing tower. The washed hydrogen chloride and methanol form a mixed solution that enters a dealcoholization tower, where it is heated to recover the dealcohol. The resulting waste hydrochloric acid solution is sent to a wastewater treatment plant. In single-reactor reactions, insufficient residence time of hydrogen chloride and methanol in the catalyst leads to a low hydrogen chloride conversion rate, resulting in a large amount of waste hydrochloric acid and impacting wastewater treatment costs, thus causing significant losses. To improve the hydrogen chloride conversion rate, methods typically involve increasing the methanol dosage or increasing the reactor pressure. However, increasing the methanol dosage leads to excessive dimethyl ether byproduct; increasing the reactor pressure results in higher energy consumption and increased system safety risks.

[0004] Chinese patent CN114605222B discloses a method for the efficient synthesis of chloromethane. This invention involves a multi-stage series reactor with an internal heat exchanger. The reaction is carried out in an aqueous solution of water, hydrogen chloride, and methanol by gradually adding excess hydrogen chloride and methanol. While this invention addresses the issues of excessive excess hydrogen chloride and dimethyl ether as a byproduct to some extent, it also presents problems such as high operating pressure, increased safety risks, and significant steam consumption due to the reactor's internal heater.

[0005] Chinese patent CN 115745733A discloses a process for synthesizing chloromethane, which involves a high-pressure dual-reactor series reaction method with excess methanol. While this invention can reduce the generation of waste acid and lower the energy consumption for chloromethane condensation and compression, it also suffers from high system pressure operation, high operational difficulty, increased leakage safety risks, and stringent equipment selection requirements, thus increasing equipment costs.

[0006] In summary, the existing methods for synthesizing chloromethane still have the following problems:

[0007] (1) Excessive amounts of hydrogen chloride and dimethyl ether byproduct;

[0008] (2) The reaction pressure is too high, which increases the safety risk;

[0009] (3) The feeding pressure of the device that provides the raw material hydrogen chloride should also be increased accordingly, which will increase the transportation cost;

[0010] (4) The system operates under high pressure, is difficult to operate, and has an increased risk of leakage. Summary of the Invention

[0011] The present invention aims to overcome the problems existing in the prior art by using a catalyst to improve the conversion rate of hydrogen chloride in a low-pressure reaction system, and finally achieve efficient synthesis of chloromethane under lower pressure conditions.

[0012] In a first aspect, the present invention provides a method for the catalytic synthesis of chloromethane, comprising the following steps:

[0013] Chloromethane was prepared by gaseous hydrogen chloride and gaseous methanol as raw materials, and a combination of zinc chloride aqueous solution and pyridine chloride salt as catalyst, through a gas-liquid phase catalytic reaction in a double-reactor series reactor.

[0014] Pyridine chloride is an ionic liquid. The inventors unexpectedly discovered that when combined with an aqueous solution of zinc chloride, it significantly improves the catalytic effect in the synthesis of chloromethane. This is likely because pyridine chloride can coordinate with compounds, thus providing activation centers for the reaction; simultaneously, pyridine chloride exhibits better solubility for hydrogen chloride and methanol.

[0015] Further, the molar ratio of zinc chloride to pyridine chloride in the zinc chloride aqueous solution is 1:(0.4-0.7), preferably 1:(0.5-0.6); the concentration of the zinc chloride aqueous solution is 55wt%-70wt%.

[0016] Further, the pyridine chloride salt is at least one selected from N-butylpyridine chloride, N-allylpyridine chloride, 1-butyl-3-methylpyridine chloride, 1-hexyl-3-methylpyridine chloride, and 1-octyl-3-methylpyridine chloride.

[0017] Furthermore, the molar ratio of gaseous hydrogen chloride to gaseous methanol is (0.95~1):1.

[0018] Furthermore, in the method for catalytic synthesis of chloromethane, the steps include:

[0019] (S1) Reaction stage 1: The raw materials are fed into a primary reactor containing a catalyst to react and obtain the primary reaction product. During the reaction, the reaction temperature of the primary reactor is controlled at 140-160℃ by adjusting the preheating temperature of gaseous methanol, and the reaction pressure is 0.16-0.22MPa.

[0020] (S2) Reaction stage 2: The primary reaction product is fed into a secondary reaction vessel containing a catalyst to react and obtain the secondary reaction product, namely crude chloromethane; the reaction temperature in the secondary reaction vessel is controlled at 140-150℃ and the reaction pressure is 0.16-0.20 MPa.

[0021] (S3) Refining stage: The crude chloromethane is separated to remove impurities and obtain chloromethane.

[0022] Furthermore, in step (S1), the reaction temperature in the primary reactor is 145℃~155℃, and the reaction pressure is 0.19~0.20 MPa; and / or

[0023] In step (S2), the reaction temperature in the secondary reactor is 145℃~150℃ and the reaction pressure is 0.17~0.18Mpa.

[0024] Furthermore, the refining stage in step (S3) includes: feeding crude chloromethane into a water washing tower for washing; the chloromethane gas obtained after washing enters a drying tower from the top of the water washing tower, and after drying, it is condensed in a condenser to obtain liquid chloromethane; the alcohol-acid mixture obtained after washing enters a de-alcoholizing tower from the bottom of the water washing tower for distillation; the methanol obtained from distillation is discharged from the top of the tower and collected; and the waste hydrochloric acid remaining from distillation is discharged from the bottom of the tower to a wastewater treatment device.

[0025] Furthermore, the catalyst level is 35-55% of the total height of the reactor and 0.5-1.0 meters above the gas inlet; preferably, the catalyst level is 45-50% of the total height of the reactor.

[0026] In a second aspect, the present invention provides a system for implementing the above-described catalytic synthesis of chloromethane, comprising a primary reactor, a secondary reactor, and a purification system;

[0027] Both the primary reactor and the secondary reactor are equipped with top discharge ports. The primary reactor is connected to the secondary reactor through its top discharge port, and the secondary reactor is connected to the refining system through its top discharge port.

[0028] Furthermore, the refining system includes: a water washing tower, a drying tower, a condenser, a storage tank, a dealcoholization tower, and a tail gas absorption tower; the water washing tower is connected to the drying tower through its top outlet, and the drying tower is connected to the condenser and the storage tank in sequence; the water washing tower is connected to the dealcoholization tower through its bottom outlet; the dealcoholization tower is connected to the primary reactor through its top outlet, and the methanol obtained by distillation in the dealcoholization tower is sent to the primary reactor from its top outlet to continue participating in the synthesis reaction; the waste hydrochloric acid remaining after distillation in the dealcoholization tower is discharged from the bottom of the tower to the wastewater treatment device; the tail gas absorption tower absorbs all the vented tail gas in the system, and the harmless gas absorbed and treated is discharged into the atmosphere, while the liquid absorbed and treated is sent to the water washing tower for utilization.

[0029] Furthermore, the primary and secondary reactors are lined with steel and corrosion-resistant materials.

[0030] Thirdly, the present invention provides the use of a combination of zinc chloride aqueous solution and pyridine chloride as a catalyst in the preparation of chloromethane; preferably, the molar ratio of zinc chloride to pyridine chloride is 1:(0.4-0.7), more preferably 1:(0.5-0.6).

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] 1) In this invention, a combination of zinc chloride aqueous solution and pyridine chloride salt is used as a catalyst, and the synthesis reaction is carried out by two reactors in series, which realizes the efficient synthesis of chloromethane under low pressure of 0.16-0.22 MPa, with a hydrogen chloride conversion rate of over 97%.

[0033] 2) The present invention generates less waste acid, which reduces the pressure on the back-end system to process waste acid.

[0034] 3) In this invention, there is no need to heat or cool the materials in the first reactor through external equipment, making full use of the heat released by the synthesis reaction, and controlling the temperature inside the reactor by adjusting the preheating temperature of the raw materials, which greatly reduces energy consumption. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the system for the catalytic synthesis of chloromethane in Example 1.

[0036] In the attached diagram, 1-primary reactor, 2-secondary reactor, 3-water washing tower, 4-drying tower, 5-condenser, 6-storage tank, 7-dehydroethanolating tower, and 8-tail gas absorption tower. Detailed Implementation

[0037] To further understand the present invention, the following description of the present invention is provided in conjunction with embodiments. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the present invention.

[0038] Example 1

[0039] This embodiment provides a method such as Figure 1 The system shown includes: a primary reactor 1, a secondary reactor 2, a water washing tower 3, a drying tower 4, a condenser 5, a storage tank 6, a dealcoholization tower 7, and a tail gas absorption tower 8;

[0040] Both the primary reactor 1 and the secondary reactor 2 are equipped with top discharge ports. The primary reactor 1 is connected to the secondary reactor 2 through its top discharge port, and the top discharge port of the secondary reactor 2 is connected to the water washing tower 3.

[0041] The water washing tower 3 is connected to the drying tower 4 through its top outlet. The drying tower 4 is connected to the condenser 5 and the storage tank 6 in sequence. The water washing tower 3 is connected to the deethanolination tower 7 through its bottom outlet. The deethanolination tower 7 is connected to the primary reactor 1 through its top outlet. The methanol obtained by the distillation treatment in the deethanolination tower 7 is sent to the primary reactor 1 through its top outlet to continue to participate in the synthesis reaction. The waste hydrochloric acid remaining after the distillation treatment in the deethanolination tower is discharged from the bottom of the tower to the wastewater treatment device. The tail gas absorption tower absorbs all the vented tail gas in the system. The harmless gas absorbed and treated is discharged into the atmosphere. The liquid absorbed and treated is sent to the water washing tower for utilization.

[0042] This embodiment also provides a method for catalytic synthesis of chloromethane in the above system, comprising the following steps:

[0043] (S1) Reaction Stage 1: Gaseous hydrogen chloride and preheated gaseous methanol are introduced into a primary reactor 1 containing a catalyst to react and obtain primary reaction products, which include synthesized chloromethane, water, unreacted hydrogen chloride, and a mixed gas of methanol. During the reaction, the reaction temperature of the primary reactor 1 is controlled at 143±1℃ by adjusting the preheating temperature of the gaseous methanol, and the pressure of the primary reactor 1 is 0.18MPa. The liquid level of the catalyst in the primary reactor 1 is controlled at 40% of the total height of the reactor and 0.5 meters above the gas inlet.

[0044] The molar ratio of gaseous hydrogen chloride to preheated gaseous methanol is 0.95:1;

[0045] The catalyst is a mixture of a 65 wt% aqueous solution of zinc chloride and N-butylpyridine chloride, wherein the molar ratio of zinc chloride to pyridine chloride is 1:0.4.

[0046] (S2) Reaction Stage 2: The primary reaction product is fed into a secondary reactor containing a catalyst for synthesis to obtain the secondary reaction product, namely crude chloromethane. The secondary reaction product includes synthesized chloromethane, water, dimethyl ether, unreacted hydrogen chloride, and a mixed gas of methanol. The temperature of the primary reactor 2 is controlled at 141±1℃, and the pressure is maintained at 0.16MPa. The catalyst level in the secondary reactor 2 is controlled at 40% and is 0.5 meters above the gas inlet.

[0047] The catalyst is a mixture of a 65 wt% aqueous solution of zinc chloride and N-butylpyridine chloride, wherein the molar ratio of zinc chloride to pyridine chloride is 1:0.5.

[0048] (S3) Refining stage: The crude chloromethane is fed into a water washing tower for washing. The chloromethane gas obtained after washing enters the drying tower from the top of the water washing tower. After drying, it is condensed in the condenser to obtain liquid chloromethane. The alcohol-acid mixture obtained after washing enters the de-alcoholizing tower from the bottom of the water washing tower for distillation. The methanol obtained from distillation is discharged from the top of the tower and collected. The waste hydrochloric acid product remaining from distillation is discharged from the bottom of the tower to the wastewater treatment device.

[0049] After the reaction was completed, the conversion rate of hydrogen chloride was measured to be 97.1%.

[0050] Example 2

[0051] The system provided in this embodiment is the same as that in Embodiment 1.

[0052] This embodiment also provides a method for catalytic synthesis of chloromethane in the above system, comprising the following steps:

[0053] (1) Gaseous hydrogen chloride and preheated gaseous methanol are introduced into a primary reactor 1 containing a catalyst to carry out a synthesis reaction, and a primary reaction product is obtained. The primary reaction product includes synthesized chloromethane, water, unreacted hydrogen chloride, and a mixed gas of methanol. During the reaction, the reaction temperature of the primary reactor 1 is controlled at 150±1℃ by adjusting the preheating temperature of the gaseous methanol, and the pressure of the primary reactor 1 is 0.20MPa. The liquid level of the catalyst in the primary reactor 1 is controlled at 45% of the total height of the reactor and 0.5 meters above the gas inlet.

[0054] The molar ratio of gaseous hydrogen chloride to preheated gaseous methanol is 0.98:1;

[0055] The catalyst is a mixture of a 60 wt% aqueous solution of zinc chloride and N-allylpyridine chloride, wherein the molar ratio of zinc chloride to pyridine chloride is 1:0.5.

[0056] (2) The primary reaction product is fed into a secondary reaction vessel containing a catalyst for synthesis reaction to obtain the secondary reaction product, namely crude chloromethane. The secondary reaction product includes the synthesized chloromethane, water, dimethyl ether, unreacted hydrogen chloride, and methanol mixed gas. The temperature of the primary reaction vessel 2 is controlled at 147±1℃ and the pressure is maintained at 0.18MPa. The catalyst level in the secondary reaction vessel 2 is controlled at 50% and is 0.5 meters above the gas inlet.

[0057] The catalyst is a mixture of a 60 wt% aqueous solution of zinc chloride and N-butylpyridine chloride, wherein the molar ratio of zinc chloride to pyridine chloride is 1:0.6.

[0058] (3) The crude chloromethane is fed into a water washing tower for washing. The chloromethane gas obtained after washing enters the drying tower from the top of the water washing tower. After drying, it is condensed in the condenser to obtain liquid chloromethane. The alcohol-acid mixture obtained after washing enters the de-alcoholizing tower from the bottom of the water washing tower for distillation. The methanol obtained from distillation is discharged from the top of the tower and collected. The waste hydrochloric acid product remaining from distillation is discharged from the bottom of the tower to the wastewater treatment device.

[0059] After the reaction was completed, the conversion rate of hydrogen chloride was measured to be 98.4%.

[0060] Example 3

[0061] The system provided in this embodiment is the same as that in Embodiment 1.

[0062] This embodiment also provides a method for catalytic synthesis of chloromethane in the above system, comprising the following steps:

[0063] (1) Gaseous hydrogen chloride and preheated gaseous methanol are introduced into a primary reactor 1 containing a catalyst to carry out a synthesis reaction, and a primary reaction product is obtained. The primary reaction product includes synthesized chloromethane, water, unreacted hydrogen chloride, and a mixed gas of methanol. During the reaction, the reaction temperature of the primary reactor 1 is controlled at 155±1℃ by adjusting the preheating temperature of the gaseous methanol, and the pressure of the primary reactor 1 is 0.21MPa. The liquid level of the catalyst in the primary reactor 1 is controlled at 45% of the total height of the reactor and 0.5 meters above the gas inlet.

[0064] The molar ratio of gaseous hydrogen chloride to preheated gaseous methanol is 1:1;

[0065] The catalyst is a mixture of a 55 wt% aqueous solution of zinc chloride and 1-butyl-3-methylpyridine chloride, wherein the molar ratio of zinc chloride to pyridine chloride is 1:0.6.

[0066] (2) The primary reaction product is fed into a secondary reaction vessel containing a catalyst to carry out a synthesis reaction, thereby obtaining a secondary reaction product, namely crude chloromethane. The secondary reaction product includes synthesized chloromethane, water, dimethyl ether, unreacted hydrogen chloride, and a mixed gas of methanol. The temperature of the primary reaction vessel 2 is controlled at about 147±1℃, and the pressure is maintained at 0.19MPa. The catalyst level in the secondary reaction vessel 2 is controlled at 50%, and is 0.5 meters above the gas inlet.

[0067] The catalyst is a mixture of a 55 wt% aqueous solution of zinc chloride and N-butylpyridine chloride, wherein the molar ratio of zinc chloride to pyridine chloride is 1:0.7.

[0068] (3) The crude chloromethane is fed into a water washing tower for washing. The chloromethane gas obtained after washing enters the drying tower from the top of the water washing tower. After drying, it is condensed in the condenser to obtain liquid chloromethane. The alcohol-acid mixture obtained after washing enters the de-alcoholizing tower from the bottom of the water washing tower for distillation. The methanol obtained from distillation is discharged from the top of the tower and collected. The waste hydrochloric acid product remaining from distillation is discharged from the bottom of the tower to the wastewater treatment device.

[0069] After the reaction was completed, the conversion rate of hydrogen chloride was measured to be 97.8%.

[0070] Comparative Example 1

[0071] The rest is the same as in Example 1, except that the catalyst is a 65wt% aqueous solution of zinc chloride and N-butylpyridine chloride is not added.

[0072] After the reaction was completed, the conversion rate of hydrogen chloride was measured to be 88.5%.

[0073] The above detailed description is a specific description of one of the feasible embodiments of the present invention. This embodiment is not intended to limit the patent scope of the present invention. All equivalent implementations or modifications that do not depart from the present invention should be included within the scope of the technical solution of the present invention.

Claims

1. A method for catalytic synthesis of chloromethane, characterized in that, Includes the following steps: Chloromethane was prepared by gaseous hydrogen chloride and gaseous methanol as raw materials, and a mixture of zinc chloride aqueous solution and pyridine chloride salt as catalyst, through a gas-liquid phase catalytic reaction in a double-reactor series reactor.

2. The method according to claim 1, characterized in that, The molar ratio of zinc chloride to pyridine chloride in the zinc chloride aqueous solution is 1:(0.4-0.7), preferably 1:(0.5-0.6); the concentration of the zinc chloride aqueous solution is 55wt%-70wt%.

3. The method according to claim 1, characterized in that, The pyridine chloride salt is at least one of N-butylpyridine chloride, N-allylpyridine chloride, 1-butyl-3-methylpyridine chloride, 1-hexyl-3-methylpyridine chloride, and 1-octyl-3-methylpyridine chloride.

4. The method according to claim 1, characterized in that, The molar ratio of gaseous hydrogen chloride to gaseous methanol is (0.95~1):

1.

5. The method according to claim 1, characterized in that, The method for catalytic synthesis of chloromethane includes the following steps: (S1) Reaction stage 1: The raw materials are fed into a primary reactor containing a catalyst to react and obtain the primary reaction product. During the reaction, the reaction temperature of the primary reactor is controlled at 140-160℃ by adjusting the preheating temperature of gaseous methanol, and the reaction pressure is 0.16-0.22MPa. (S2) Reaction stage 2: The primary reaction product is fed into a secondary reaction vessel containing a catalyst to react and obtain the secondary reaction product, namely crude chloromethane; the reaction temperature in the secondary reaction vessel is controlled at 140-150℃ and the reaction pressure is 0.16-0.20 MPa. (S3) Refining stage: The crude chloromethane is separated to remove impurities and obtain chloromethane.

6. The method according to claim 5, characterized in that, In step (S1), the reaction temperature in the primary reactor is 145℃~155℃, and the reaction pressure is 0.19~0.20 MPa; and / or In step (S2), the reaction temperature in the secondary reactor is 145℃~150℃ and the reaction pressure is 0.17~0.18Mpa.

7. The method according to claim 5, characterized in that, The refining stage in step (S3) includes: feeding crude chloromethane into a water washing tower for washing; the chloromethane gas obtained after washing enters a drying tower from the top of the water washing tower, and after drying, it is condensed in a condenser to obtain liquid chloromethane; the alcohol-acid mixture obtained after washing enters a de-alcoholizing tower from the bottom of the water washing tower for distillation; the methanol obtained from distillation is discharged from the top of the tower and collected; the remaining product of distillation, waste hydrochloric acid, is discharged from the bottom of the tower to a wastewater treatment device.

8. The method according to claim 1, characterized in that, The catalyst level is 35-55% of the total height of the reactor and 0.5-1.0 meters above the gas inlet; preferably, the catalyst level is 45-50% of the total height of the reactor.

9. A system for implementing the method of claim 1, characterized in that, Includes a primary reactor, a secondary reactor, and a purification system; Both the primary reactor and the secondary reactor are equipped with top discharge ports. The primary reactor is connected to the secondary reactor through its top discharge port, and the secondary reactor is connected to the refining system through its top discharge port.

10. The use of a combination of zinc chloride aqueous solution and pyridine chloride as a catalyst in the preparation of chloromethane; preferably, the molar ratio of zinc chloride to pyridine chloride is 1:(0.4-0.7).

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