A process for the preparation of dimethyl disulfide

Abstract

The application discloses a preparation method of dimethyl disulfide, which comprises the following steps: (1) introducing methyl mercaptan into a fixed bed loaded with a catalyst to generate a decomposition reaction; (2) separating a mixture into a liquid product and a gas mixture after the reaction is completed; and (3) pressurizing and refining the obtained gas mixture to separate methyl mercaptan for recycling. The dimethyl disulfide compound can be obtained by using the one-step method, sulfur is not needed to be added in the process, hydrogen sulfide is not generated after the reaction is completed, the operation is simple, the method is green and environment-friendly, and has a good market prospect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of chemical synthesis and separation and purification, and particularly relates to a preparation method of dimethyl disulfide. BACKGROUND

[0002] Dimethyl disulfide (hereinafter referred to as DMDS) is a yellowish transparent liquid with a foul odor. It is insoluble in water and can be mixed with ethanol, diethyl ether and acetic acid. The relative density is 1.0625, the boiling point is 109.7℃, the melting point is -85℃, the flash point is 24℃, and the explosion limit is 1.1-16%. It cannot coexist with strong alkali, strong oxidant and strong reducing agent. Dimethyl disulfide is commonly used as a solvent and can also be used as a main raw material for producing methylsulfonyl chloride and methylsulfonic acid. It is also used as a sulfiding agent for gasoline hydrogenation catalysis, a coking inhibitor for oil refining devices and a soil fumigant. It can also be used as an intermediate for synthesizing organophosphorus insecticide fenthion, benzoxime and p-methylthio phenol. In addition, GB2760-1996 regulations allow the use of dimethyl disulfide as a food flavoring. Therefore, dimethyl disulfide is a high-value-added product.

[0003] The main methods for synthesizing disulfide compounds are as follows: first, dimethyl sulfate method, that is, sodium sulfide is reacted with dimethyl sulfate to obtain the product, which has the problem of toxic raw materials that are difficult to obtain; second, methanethiol oxidation method, that is, methanethiol is reacted with an oxidizing agent to obtain the product, and common oxidizing agents include hydrogen peroxide, sodium perchlorate and potassium permanganate, which has the problem of violent reaction and large heat release, and the safety risk in the production process is extremely high; and third, methanol sulfuration method, that is, methanol, hydrogen sulfide and sulfur are reacted or methanethiol is directly sulfided with sulfur to obtain the product, which has the problems of extremely low threshold of methanethiol and generation of highly toxic hydrogen sulfide, and the odor is difficult to control in the production process, and the environmental and safety problems are prominent.

[0004] Therefore, it is of great commercial value to develop a green and environmentally friendly dimethyl disulfide synthesis technology. SUMMARY

[0005] The present application provides a preparation method of dimethyl disulfide, which does not need to add sulfur during the process, does not produce hydrogen sulfide after the reaction, is simple to operate, green and environmentally friendly, and has a good market prospect.

[0006] To achieve the above-mentioned purposes, the present application provides the following technical solutions:

[0007] A preparation method of dimethyl disulfide, comprising the following steps:

[0008] (1) passing methanethiol into a fixed bed filled with a catalyst to occur a decomposition reaction;

[0009] (2) After the reaction is completed, the mixture is gas-liquid separated to obtain a liquid product and a gas mixture;

[0010] (3) The obtained gas mixture is pressurized and refined to separate methyl mercaptan for recycling.

[0011] The chemical reaction equation is as follows:

[0012]

[0013] Preferably, the fixed bed of step (1) is filled with a catalyst and is infiltrated with dimethyl disulfide throughout the fixed bed.

[0014] The catalyst of step (1) is a mixture of an alkaline earth metal oxide and aluminum oxide, the alkaline earth metal is one or more of magnesium oxide, calcium oxide, strontium oxide and barium oxide, preferably magnesium oxide; the mass ratio of the alkaline earth metal to aluminum oxide is (0.01-0.5):1, preferably (0.05-0.1):1; the function of the catalyst is mainly to improve the selectivity of the product dimethyl disulfide.

[0015] The preparation method of the catalyst comprises the following steps:

[0016] Aluminum oxide is weighed and placed in a container, an aqueous solution of alkaline earth metal chloride is added, stirred and filtered to obtain a solid, and the compounded catalyst is obtained after calcination.

[0017] Preferably, the stirring time is 1-48h; the calcination temperature is 400-800℃, and the calcination time is 10-48h.

[0018] Preferably, the decomposition reaction temperature is 60-100℃, preferably 70-85℃.

[0019] Preferably, the decomposition reaction pressure is 0-10.0MPaG, preferably 0.1-1.0MPaG.

[0020] Preferably, the volume space velocity of the decomposition reaction is 0.1-2h -1 , preferably 0.2-0.5h -1 .

[0021] The gas-liquid separation temperature of step (2) is 0-20℃, preferably 5-10℃, and the pressure is consistent with the pressure of the fixed bed reactor.

[0022] The gas mixture obtained in step (3) is a mixture of hydrogen and methyl mercaptan, which is separated by pressurized refining. The refining temperature is 30-100℃, preferably 40-80℃; the refining pressure is 0.5-10.0MPaG, preferably 1-5.0MPaG.

[0023] The beneficial effects of the present application are:

[0024] First, no sulfur is added in the process, so that the raw material cost is reduced, and there is no elemental sulfur residue in the product, and the quality is high;

[0025] Second, the reaction does not produce hydrogen sulfide, a highly toxic substance,

[0026] Third, the process is simple to operate, environmentally friendly, and has good market prospects. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 Process flow chart for the preparation method described in Example 1;

[0028] Among them, 1 is a fixed bed reactor, 2 is a gas-liquid separator, 3 is a refining tower, and 4 is a raw material storage tank. DETAILED DESCRIPTION

[0029] The methyl mercaptan, calcium oxide, magnesium oxide and aluminum oxide used in the present application are purchased from Shanghai Titan Technology Co., Ltd.

[0030] In the present application, the content and purity of each component are tested and calculated by the external standard method of high performance liquid chromatograph (Shimadzu LC-20AD), and the conversion rate is calculated based on the content of the product; the liquid chromatography conditions are as follows: chromatographic column: Waters XSelect HSS T3, 4.6 μm x 250 mm; sample size: 2-10 μL, adjusted according to the sample; column temperature: 40℃; flow rate: 1 mL / min; detector: ultraviolet detector (UV), detection wavelength: 254-400 nm; mobile phase: acetonitrile / 0.1% phosphoric acid aqueous solution; when measuring the sample, first establish a liquid phase external standard curve with pure product, and calculate the mass fraction (content) of each detected substance based on the linear relationship between concentration and liquid phase peak area.

[0031] The height-diameter ratio of the fixed bed reactor in the present application is 10, the diameter is 50 mm, and the particle size of the catalyst is 2 mm, so as to ensure that the pressure drop of the fixed bed bed layer is within the normal range, and at the same time, the wall effect along the radial direction of the bed layer is eliminated.

[0032] The preparation method of the catalyst with different content of alkaline earth metal in the present application is as follows: 100g of aluminum oxide is weighed and placed in a 500mL three-necked flask, a certain mass and concentration of alkaline earth metal chloride aqueous solution is added, stirred for 24h, filtered to obtain a solid, and then calcined at 500℃ in a muffle furnace for 24h to obtain an aluminum oxide catalyst compounded with different alkaline earth metals. Different alkaline earth metal compounded aluminum oxide catalysts are prepared according to the types and amounts of alkaline earth metals, including but not limited to the mixed catalysts in the following table:

[0033]

[0034]

[0035] Example 1

[0036] Under the atmosphere of nitrogen, the fixed bed 1 filled with catalyst, which is the mixture of MgO and Al2O3 with the mass ratio of 0.05:1, is passed through with the flow rate of 100g / h of methyl mercaptan. The temperature of the reactor is controlled at 70℃, the reaction pressure is 0.1MPaG, and the volume space velocity of the reactor is 0.2h -1 The methyl mercaptan is allowed to react under the action of the catalyst to generate dimethyl disulfide and hydrogen. After the reaction system is stable, the conversion rate of the raw material is analyzed to be 99%, the selectivity of the product dimethyl disulfide is 80.5%, and the selectivity of methyl hydrogen disulfide is 19.5%. The obtained gas mixture is passed into the gas-liquid separator 2, the mixture is cooled, the temperature of the system is controlled at 5℃, and the pressure is 0.1MPaG, which is consistent with the reaction end pressure. The mixture of methyl hydrogen disulfide and dimethyl disulfide is separated and sent to the refining tower 3. The hydrogenation refining is carried out at the pressure of 1.0MPaG and the temperature of 40℃. The methyl hydrogen disulfide with the purity of 99.5% and 0.5% of methyl mercaptan are obtained at the top of the tower, and the part of the product can be sent to the upstream raw material methyl mercaptan storage tank 4 for recycling. The product dimethyl disulfide is obtained at the bottom of the tower, and the bottom product is collected and analyzed, and the specific composition is shown as follows (all compositions are mass percentages, %):

[0037] DMDS, % DMTS, % CH3SH, % CH3SSH, % CH4, % 99.8 0.1 0.03 0.05 0.02

[0038] As shown in the above table, the dimethyl disulfide with the purity of >99% can be obtained by the present application, and no high-toxic hydrogen sulfide is generated, the process is green and environmentally friendly, and has good commercial application prospect.

[0039] Example 2

[0040] Under the atmosphere of nitrogen, the fixed bed 1 filled with catalyst, which is the mixture of MgO and Al2O3 with the mass ratio of 0.1:1, is passed through with the flow rate of 100g / h of methyl mercaptan. The temperature of the reactor is controlled at 60℃, the reaction pressure is 1.0MPaG, and the volume space velocity of the reactor is 2h -1The methyl mercaptan is allowed to react in the presence of the catalyst to produce dimethyl disulfide and hydrogen. When the reaction system is stable, the conversion rate of the raw material is 98.0%, the selectivity of the product dimethyl disulfide is 81.5%, and the selectivity of methyl hydrosulfide is 18.5%. The obtained gas mixture is introduced into a gas-liquid separator 2, the mixture is cooled, the system temperature is controlled at 0°C, and the pressure is 1 MPaG, which is consistent with the pressure at the reaction end. The mixture of methyl hydrosulfide and dimethyl disulfide is separated and sent to a refining tower 3. Hydrogenation refining is carried out at a pressure of 1.0 MPaG and a temperature of 50°C. The purity of the methyl hydrosulfide obtained at the top of the tower is 99.5%, and the purity of the methyl mercaptan is 0.5%. The product can be sent to the upstream raw material methyl mercaptan storage tank 4 for recycling. The product dimethyl disulfide is obtained at the bottom of the tower, and the composition of the collected product at the bottom of the tower is as follows (all compositions are mass percentages, %):

[0041] DMDS, % DMTS, % CH3SH, % CH3SSH, % CH4, % 99.5 0.4 0.04 0.05 0.01

[0042] Example 3

[0043] A flow of methyl mercaptan at a rate of 100 g / h is passed through a fixed bed 1 filled with a catalyst, which is a mixture of CaO and Al2O3, with a mass ratio of CaO to Al2O3 of 0.08:1, under a nitrogen atmosphere. The temperature of the reactor is controlled at 80°C, the reaction pressure is 3.0 MPaG, and the volume space velocity of the reactor is 1.6 h -1 The methyl mercaptan is allowed to react in the presence of the catalyst to produce dimethyl disulfide and hydrogen. When the reaction system is stable, the conversion rate of the raw material is 98.0%, the selectivity of the product dimethyl disulfide is 81.5%, and the selectivity of methyl hydrosulfide is 18.5%. The obtained gas mixture is introduced into a gas-liquid separator 2, the mixture is cooled, the system temperature is controlled at 0°C, and the pressure is 1 MPaG, which is consistent with the pressure at the reaction end. The mixture of methyl hydrosulfide and dimethyl disulfide is separated and sent to a refining tower 3. Hydrogenation refining is carried out at a pressure of 1.0 MPaG and a temperature of 50°C. The purity of the methyl hydrosulfide obtained at the top of the tower is 99.5%, and the purity of the methyl mercaptan is 0.5%. The product can be sent to the upstream raw material methyl mercaptan storage tank 4 for recycling. The product dimethyl disulfide is obtained at the bottom of the tower, and the composition of the collected product at the bottom of the tower is as follows (all compositions are mass percentages, %):

[0044] DMDS, % DMTS, % CH3SH, % CH3SSH, % CH4, % 99.6 0.3 0.02 0.06 0.02

[0045] Example 4

[0046] Under nitrogen atmosphere, the methanethiol with a flow rate of 100 g / h was passed through the fixed bed 1 packed with catalyst, which was a mixture of SrO and Al2O3 with a mass ratio of 0.05:1. The reactor temperature was controlled at 90°C, the reaction pressure was 5.0 MPaG, and the volume space velocity of the reactor was 1.0 h -1 The methanethiol reacted under the action of the catalyst to generate dimethyl disulfide and hydrogen. After the reaction system was stable, the conversion rate of the raw material was 98.9% and the selectivity of the product dimethyl disulfide was 80.3% and the selectivity of methyl hydrogen disulfide was 19.7% through sampling analysis. The obtained gas mixture was passed into the gas-liquid separator 2, the mixture was cooled, the system temperature was controlled at 15°C, and the pressure was 5 MPaG, which was consistent with the reaction end pressure. The mixture of methyl hydrogen disulfide and dimethyl disulfide was separated and sent to the refining tower 3. The hydrogenation refining was carried out at a pressure of 7.0 MPaG and a temperature of 90°C. The purity of the methyl hydrogen disulfide obtained at the top of the tower was 99.0% and 1.0% of methanethiol, which could be sent to the upstream raw material methanethiol storage tank 4 for recycling. The product dimethyl disulfide was obtained at the bottom of the tower, the tower bottom product was collected and analyzed, and the specific composition was as follows (all compositions were mass percentages, %):

[0047] DMDS, % DMTS, % CH3SH, % CH3SSH, % CH4, % 99.4 0.5 0.02 0.04 0.04

[0048] Example 5

[0049] Under nitrogen atmosphere, the methanethiol with a flow rate of 100 g / h was passed through the fixed bed 1 packed with catalyst, which was a mixture of SrO and Al2O3 with a mass ratio of 0.05:1. The reactor temperature was controlled at 90°C, the reaction pressure was 5.0 MPaG, and the volume space velocity of the reactor was 1.0 h -1 The methanethiol reacted under the action of the catalyst to generate dimethyl disulfide and hydrogen. After the reaction system was stable, the conversion rate of the raw material was 98.9% and the selectivity of the product dimethyl disulfide was 80.3% and the selectivity of methyl hydrogen disulfide was 19.7% through sampling analysis. The obtained gas mixture was passed into the gas-liquid separator 2, the mixture was cooled, the system temperature was controlled at 15°C, and the pressure was 5 MPaG, which was consistent with the reaction end pressure. The mixture of methyl hydrogen disulfide and dimethyl disulfide was separated and sent to the refining tower 3. The hydrogenation refining was carried out at a pressure of 7.0 MPaG and a temperature of 90°C. The purity of the methyl hydrogen disulfide obtained at the top of the tower was 99.0% and 1.0% of methanethiol, which could be sent to the upstream raw material methanethiol storage tank 4 for recycling. The product dimethyl disulfide was obtained at the bottom of the tower, the tower bottom product was collected and analyzed, and the specific composition was as follows (all compositions were mass percentages, %):

[0050] DMDS, % DMTS, % CH3SH, % CH3SSH, % CH4, % DMDS, % DMTS, % CH3SH, % CH3SSH, % CH4, % 99.5 0.3 0.05 0.09 0.06

Claims

1. A method for preparing dimethyl disulfide, comprising the following steps: (1) Methanethiol is introduced into a fixed bed packed with catalyst, and a decomposition reaction occurs; (2) After the reaction is complete, the mixture is separated into liquid and gas to obtain a liquid product and a gas mixture; (3) The resulting gas mixture is purified by pressurization to separate out methanethiol for recycling; the catalyst in step (1) is a mixture of alkaline earth metal oxide and aluminum oxide, wherein the alkaline earth metal is one or more of magnesium oxide, calcium oxide, strontium oxide and barium oxide.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the alkaline earth metal to aluminum oxide is (0.01-0.5):

1.

3. The preparation method according to claim 1, characterized in that, Weigh aluminum oxide and place it in a container. Add an aqueous solution of alkaline earth metal chloride to the solution, stir, and filter to obtain a solid. After calcination, a compound catalyst is obtained.

4. The preparation method according to claim 3, characterized in that, The stirring time is 1-48 hours; the calcination temperature is 400-800℃; and the calcination time is 10-48 hours.

5. The preparation method according to any one of claims 1-4, characterized in that, The decomposition reaction temperature is 60-100℃; and / or, the decomposition reaction pressure is 0-10.0 MPaG; and / or, the volume hourly space velocity (VHSV) of the decomposition reaction is 0.1-2 h⁻¹. -1 .

6. The preparation method according to any one of claims 1-4, characterized in that, The gas-liquid separation temperature in step (2) is 0-20℃.

7. The preparation method according to any one of claims 1-4, characterized in that, The gas mixture obtained in step (3) is a mixture of hydrogen and methanethiol. The two are separated by pressure purification. The purification temperature is 30-100℃ and the purification pressure is 0.5-10.0 MPaG.

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