Low-byproduct methyl mercaptan synthesis process

Abstract

The invention provides a low-byproduct methyl mercaptan synthesis process. The byproduct of dimethyl sulfide is inevitably generated in the process of generating methyl mercaptan from hydrogen sulfide and methanol. The method comprises the following steps: filling a thioether conversion catalyst at the front end, introducing methyl sulfide with a large proportion of hydrogen sulfide ratio, connecting a multi-stage methyl mercaptan synthesizer in series at the rear end, supplementing and introducing methanol, reacting excessive hydrogen sulfide at the front end with methanol to generate methyl mercaptan, gradually heating the multi-stage methyl mercaptan synthesizer from front to back, filling a high-selectivity catalyst in the methyl mercaptan synthesizer at the front end, the last-stage methyl mercaptan synthesizer is filled with a high-conversion-rate catalyst, hydrogen sulfide is slightly insufficient, and hydrogen sulfide is basically consumed. According to the designed methyl mercaptan synthesis process, the byproduct of dimethyl sulfide is reduced, the amount of tail gas is reduced, compression and recycling of hydrogen sulfide are avoided, gas-liquid entrainment is reduced while energy consumption is reduced, condensation of the product is facilitated, and the yield of methyl mercaptan is increased.

Description

Technical Field

[0001] This invention relates to the field of methanethiol production, specifically to a multi-stage tandem process for thioether conversion and methanethiol synthesis, achieving low by-product production of methanethiol and a reduction in the amount of synthesis tail gas. Background Technology

[0002] Methanethiol, as an important organic synthesis intermediate, has wide applications in materials, pesticides, and pharmaceuticals. It can be used to synthesize methionine, fenthion, permethrin, prochloraz, dimethyl disulfide, etc., and is also an important source of intermediates such as methanesulfonyl chloride and methylthiopropanol.

[0003] The synthesis of methanethiol (CH3SH) is mainly based on differences in raw materials and reaction routes. Currently, the most widely used industrial method is the hydrogen sulfide-methanol method, while auxiliary routes such as the thiourea-dimethyl sulfate method also exist. Traditional methanethiol synthesis processes inevitably produce dimethyl sulfide as a byproduct. Dimethyl sulfide, a colorless to pale yellow transparent and volatile liquid, is an important organic intermediate and solvent, widely used in the fields of dimethyl sulfoxide and dimethyl sulfone.

[0004] Chinese invention patent application CN114591205A discloses a combined production process of methanethiol and dimethyl sulfide. Most methanethiol synthesis processes inevitably produce dimethyl sulfide as a byproduct. The catalyst is crucial in methanethiol synthesis, and its performance directly affects the feed conversion rate, product selectivity, and reaction conditions. Therefore, in a sluggish sulfide market with no downstream sulfide products, developing a simple, reliable, and low-byproduct methanethiol synthesis process is of great significance. Furthermore, methanethiol production processes typically require an excess of hydrogen sulfide, resulting in a large volume of synthesis tail gas. Reducing the tail gas volume will decrease gas-liquid entrainment, facilitating the condensation and collection of downstream products, and avoiding the need for tail gas recompression and reuse, thus achieving cost reduction and efficiency improvement. Summary of the Invention

[0005] The purpose of this invention is to address the issue of thioether byproducts in existing methanethiol processes by providing a low-byproduct methanethiol synthesis process that employs a thioether-to-thiol converter at the front end and a multi-stage methanethiol synthesizer at the back end.

[0006] A process for synthesizing methanethiol with low by-product yield includes the following steps: (1) Hydrogen sulfide and by-product dimethyl sulfide are fed into a sulfide converter and reacted under the action of a sulfide conversion catalyst to convert part of the dimethyl sulfide into methanethiol. (2) The output gas of the sulfide converter and gaseous methanol are fed into a multi-stage methanethiol synthesizer connected in series. Under the action of the methanethiol synthesis catalyst, hydrogen sulfide reacts with methanol to generate methanethiol, and methanethiol is produced as a byproduct. (3) The output gas of the final stage methanethiol synthesizer is condensed and distilled to obtain methanethiol product, and the separated by-product methyl sulfide is returned to the sulfide converter for recycling.

[0007] The feed molar ratio of hydrogen sulfide to dimethyl sulfide entering the sulfide converter is ≥3:1. Preferably, the hydrogen sulfide:dimethyl sulfide feed molar ratio is 3:1 to 10:1. The reaction temperature of the sulfide converter and the multi-stage methanethiol synthesizer is 200℃ to 380℃, the reaction pressure is 0.7MPa to 1.3MPa, and the gas hourly space velocity is 500 h⁻¹. -1 Up to 3000 h -1 .

[0008] The sulfide converter and the methanethiol synthesizer are connected in series. The series connection can include multiple stages of sulfide converters and methanethiol synthesizers. The reaction gas in the sulfide converter directly enters the methanethiol synthesizer, while gaseous methanol is simultaneously transported into the methanethiol synthesizer.

[0009] The multi-stage methanethiol synthesizer has at least n stages, where n≥2. The methanol feed rate of the first-stage methanethiol synthesizer satisfies the following molar ratio: (total molar feed rate of hydrogen sulfide - 1 / 2 × total molar feed rate of dimethyl sulfide) / molar feed rate of methanol = 2.2 to 6.0.

[0010] The ratio of the methanol feed rate to the molar amount of unreacted hydrogen sulfide in the previous stage to the methanol feed rate to the second to n-1 stage methanethiol synthesizers is 1.2 to 5; the ratio of the methanol feed rate to the molar amount of unreacted hydrogen sulfide in the previous stage to the methanol feed rate to the nth stage methanethiol synthesizer is 0.95:1 to 1:1.

[0011] The methanethiol synthesizer is filled with a methanethiol synthesis catalyst, preferably ZSM-5@SiO2 supported with 5-20% tungsten oxide and 2.5-10% potassium oxide.

[0012] The catalyst is synthesized by impregnating purchased ZSM-5@SiO2 with an equal volume of potassium hydroxide solution with a mass concentration of 2.5-10%, drying at 120°C, and calcining at 500°C for 5 hours to obtain a ZSM-5@SiO2 catalyst loaded with potassium oxide. The ZSM-5@SiO2 catalyst loaded with potassium oxide was impregnated with an equal volume of ammonium tungstate solution with a mass concentration of 5-20%, dried at 120°C and calcined at 500°C for 5 hours to obtain a ZSM-5@SiO2 catalyst loaded with 5-20% tungsten oxide and 2.5-10% potassium oxide.

[0013] In the multi-stage methanethiol synthesizer, the high-loaded ZSM-5@SiO2 to the low-loaded ZSM-5@SiO2 catalyst is sequentially loaded from front to back.

[0014] In the above scheme, the output gas of the final stage methanethiol synthesizer is condensed and distilled to obtain methanethiol product, and the separated by-product dimethyl sulfide is returned to the sulfide converter for recycling.

[0015] In the above scheme, hydrogen sulfide and dimethyl sulfide are introduced into a sulfide converter, where they react under the action of a sulfide conversion catalyst to convert part of the dimethyl sulfide into methanethiol.

[0016] The sulfide converter is filled with a sulfide conversion catalyst, which is preferably supported on a γ-alumina carrier with 0.1-1% cerium oxide and 0.5-2% cobalt oxide.

[0017] The catalyst is synthesized by impregnating purchased γ-alumina with an equal volume of 0.1-1% cerium nitrate solution, drying at 120°C and calcining at 500°C for 5 hours to obtain a γ-alumina supported catalyst with cerium oxide. A γ-alumina supported catalyst loaded with cerium oxide was impregnated with an equal volume of a 0.5-2% cobalt nitrate solution, dried at 120°C and calcined at 500°C for 5 hours to obtain a γ-alumina supported catalyst loaded with 0.1-1% cerium oxide and 0.5-2% cobalt oxide.

[0018] In some preferred embodiments, a thioether converter is provided before the multi-stage methanethiol synthesizer, so that hydrogen sulfide feedstock can continuously enter the thioether converter during the continuous process.

[0019] The methanethiol synthesis process provided by this invention utilizes a multi-stage reactor series, increasing production while fully utilizing hydrogen sulfide. Compared to parallel reactors, where each synthesizer generates excessive hydrogen sulfide in the tail gas, this invention significantly reduces the amount of hydrogen sulfide in the tail gas. The front-end sulfide converter, combined with the staged temperature gradient and segmented loading of specific performance catalysts in the methanethiol synthesizer, achieves a sulfide byproduct of less than 1.5%, essentially zero sulfide byproduct. The highly selective catalyst at 300°C achieves a methanethiol selectivity greater than 90%. (The byproduct sulfide is circulated and converted within the system; the dynamic balance between the sulfide byproduct from methanethiol synthesis and the sulfide-to-thiol conversion achieves zero sulfide recovery, equivalent to zero byproduct. The highly selective catalyst at 300°C achieves a methanethiol selectivity greater than 90%.) Attached Figure Description Figure 1 This is a diagram of a low-by-product methanethiol synthesis process apparatus according to the present invention. In the diagram, 1. sulfide converter, 2. primary methanethiol synthesizer, 3. secondary methanethiol synthesizer, 4. tertiary methanethiol synthesizer, 5. condensation system, and 6. distillation system. Detailed Implementation

[0020] The present invention will be further illustrated below through embodiments. It should be noted that the given embodiments should not be construed as limiting the scope of protection of the present invention. Non-essential improvements and adjustments made to the present invention by those skilled in the art based on the content of the present invention should still fall within the scope of protection of the present invention.

[0021] Example 1 A diagram of a low-by-product methanethiol synthesis process unit, wherein the methanethiol feed line and the hydrogen sulfide feed line are combined and enter the sulfide converter 1 via a static mixer; The outlet pipeline of the sulfide converter 1 is combined with the gaseous methanol feed pipeline and enters the first-stage methanethiol synthesizer 2 through a static mixer. The outlet pipeline of the first-stage methanethiol synthesizer 2 is combined with the gaseous methanol feed pipeline and enters the second-stage methanethiol synthesizer 3 through a static mixer. The outlet pipeline of the second-stage methanethiol synthesizer 3 is combined with the gaseous methanol feed pipeline and enters the third-stage methanethiol synthesizer 4 through a static mixer. The outlet pipeline of the three-stage methanethiol synthesizer 4 is connected to the condensation system 5. Condensation system 5 is connected to distillation system 6; One branch of the distillation system 6 is connected to the methanethiol discharge pipeline, and the other branch is connected to the dimethyl sulfide discharge pipeline.

[0022] Example 2 Using a portion of the apparatus from Example 1 (i.e., the experiment was conducted in sulfide converter 1), the molar ratio of hydrogen sulfide to dimethyl sulfide feed was 5:1. The converter 1 was loaded with a conversion catalyst consisting of 0.2% cerium oxide and 1% cobalt oxide supported on a γ-alumina carrier. The conversion temperature was 300°C, the reaction pressure was 1 MPa, and the volume hourly space velocity (VHSV) based on the catalyst bed volume was 1000 h⁻¹. -1 The sulfide conversion rate was 52.3%, and the methanethiol selectivity was 98.2%.

[0023] Example 3 Using a portion of the apparatus from Example 1 (i.e., the experiment was conducted in the primary methanethiol synthesizer 2), hydrogen sulfide passed through the sulfide converter 1, and then entered the primary methanethiol synthesizer 2 at a hydrogen sulfide to methanol feed molar ratio of 4:1. The catalyst was ZSM-5@SiO2 supported on 20% tungsten oxide and 10% potassium oxide. The synthesis temperature was 300°C, the reaction pressure was 1 MPa, and the volume hourly space velocity (VHSV) based on the catalyst bed volume was 1000 h⁻¹. -1 The methanol conversion rate was 90.2%, the methanethiol selectivity was 98.4%, and the methanethiol yield was 88.8%. The tail gas contained 98.3% hydrogen sulfide, 1% methanethiol, 0.1% dimethyl sulfide, 0.1% methane, 0.3% carbon dioxide, and 0.2% dimethyl ether.

[0024] Example 4 Using a portion of the apparatus from Example 1 (i.e., the experiment was conducted in the secondary methanethiol synthesizer 3), hydrogen sulfide sequentially passed through the sulfide converter 1 and the primary methanethiol synthesizer 2, and then entered the secondary methanethiol synthesizer 3 at a hydrogen sulfide to methanol feed molar ratio of 2:1. The catalyst packed in this secondary methanethiol synthesizer 3 was ZSM-5@SiO2 supported with 15% tungsten oxide and 7.5% potassium oxide. The synthesis temperature was 340°C, the reaction pressure was 1 MPa, and the volume hourly space velocity (VHSV) based on the catalyst bed volume was 1000 h⁻¹. -1 The methanol conversion rate was 96.3%, the methanethiol selectivity was 94.2%, and the methanethiol yield was 90.7%. The tail gas contained 95.1% hydrogen sulfide, 2% methanethiol, 0.5% dimethyl sulfide, 0.4% methane, 1.2% carbon dioxide, and 0.8% dimethyl ether.

[0025] Example 5 Using a portion of the apparatus from Example 1 (i.e., the experiment was conducted in the three-stage methanethiol synthesizer 4), hydrogen sulfide passed through the sulfide converter 1, the first-stage methanethiol synthesizer 2, and the second-stage methanethiol synthesizer 3, and then entered the three-stage methanethiol synthesizer 4 at a hydrogen sulfide to methanol feed molar ratio of 0.98:1. The catalyst packed was ZSM-5@SiO2 supported on 10% tungsten oxide and 5% potassium oxide. The synthesis temperature was 360°C, the reaction pressure was 1 MPa, and the volume hourly space velocity (VHSV) based on the catalyst bed volume was 1000 h⁻¹. -1 The methanol conversion rate was 99.8%, the methanethiol selectivity was 72.8%, and the methanethiol yield was 72.7%. The tail gas contained 1% hydrogen sulfide, 4% methanethiol, 1% dimethyl sulfide, 18% methane, 52% carbon dioxide, and 24% dimethyl ether.

[0026] Example 6 Using the scheme of Example 3, the sulfide converter 1 and the primary methanethiol synthesizer 2 are connected in series. The synthesis gas from the primary methanethiol synthesizer 2 is condensed by the condensation system 5 and then distilled by the distillation system 6. The resulting by-product sulfide and hydrogen sulfide are fed into the sulfide converter 1. The converter is packed with a conversion catalyst consisting of 0.2% cerium oxide and 1% cobalt oxide supported on a γ-alumina carrier. The temperature is 300°C, the reaction pressure is 1 MPa, and the volume hourly space velocity (VHSV) based on the total volume of the catalyst bed is 1000 h⁻¹. -1 The methanol conversion rate is 90.5%, the methanethiol selectivity is 99.5%, and the methanethiol yield is 90%. The tail gas contains 98.6% hydrogen sulfide, 0.8% methanethiol, 0.1% methane, 0.3% carbon dioxide, and 0.2% dimethyl ether.

[0027] Example 7 Using the scheme of Example 4, the sulfide converter 1 and the secondary methanethiol synthesizer 3 are connected in series. The synthesis gas from the secondary methanethiol synthesizer 3 is condensed by the condensation system 5 and then distilled by the distillation system 6. The resulting by-product sulfide and hydrogen sulfide are fed into the sulfide converter 1. The conversion catalyst is a γ-alumina support loaded with 0.2% cerium oxide and 1% cobalt oxide. The temperature is 300°C, the reaction pressure is 1 MPa, and the volume hourly space velocity based on the total volume of the catalyst bed is 1000 h⁻¹. -1 The methanol conversion rate was 95.3%, the methanethiol selectivity was 96.8%, and the methanethiol yield was 92.3%. The tail gas contained 96.1% hydrogen sulfide, 1.1% methanethiol, 0.1% dimethyl sulfide, 0.5% methane, 1.3% carbon dioxide, and 0.9% dimethyl ether.

[0028] Example 8 The primary methanethiol synthesizer 2, secondary methanethiol synthesizer 3, and tertiary methanethiol synthesizer 4 are connected in series. Hydrogen sulfide passes through the sulfide converter 1, and then enters the primary methanethiol synthesizer 2 at a hydrogen sulfide to methanol feed molar ratio of 5:1. The catalyst is ZSM-5@SiO2 supported on 20% tungsten oxide and 10% potassium oxide. The synthesis temperature is 300℃, the reaction pressure is 1 MPa, and the volume hourly space velocity (VHSV) based on the total catalyst bed volume is 1000 h⁻¹. -1 .

[0029] Synthesis gas from primary methanethiol synthesizer 2 enters secondary methanethiol synthesizer 3, which is packed with ZSM-5@SiO2 catalyst supported on 15% tungsten oxide and 7.5% potassium oxide. It is supplemented with 3 equivalents of methanol. The synthesis temperature is 340℃, the reaction pressure is 1 MPa, and the volume hourly space velocity (VHSV) based on the total catalyst bed volume is 1000 h⁻¹. -1 .

[0030] Syngas from the secondary methanethiol synthesizer 3 enters the tertiary methanethiol synthesizer 4, which is packed with a catalyst of ZSM-5@SiO2 supported on 10% tungsten oxide and 5% potassium oxide, supplemented with 1 equivalent of methanol. The synthesis temperature is 360℃, the reaction pressure is 1MPa, and the volume hourly space velocity (VHSV) based on the total catalyst bed volume is 1000h. -1 This unit achieves a methanol conversion rate of 96.8%, a methanethiol selectivity of 93.2%, and a methanethiol yield of 90.2%. The tail gas contains 2% hydrogen sulfide, 4.2% methanethiol, 0.8% dimethyl sulfide, 18% methane, 52% carbon dioxide, and 23% dimethyl ether.

[0031] Example 9 Using the scheme of Example 4, the molar ratio of hydrogen sulfide to methanol feed was adjusted to 1:1, the methanol conversion rate was 97.3%, the methanethiol selectivity was 78.2%, and the methanethiol yield was 76.1%. The tail gas contained 2.6% hydrogen sulfide, 4.2% methanethiol, 1.5% dimethyl sulfide, 17.3% methane, 51.2% carbon dioxide, and 23.2% dimethyl ether.

[0032] Example 10 The sulfide converter 1, primary methanethiol synthesizer 2, secondary methanethiol synthesizer 3, and tertiary methanethiol synthesizer 4 are connected in series. Following the scheme of Example 8, the synthesis gas from the tertiary methanethiol synthesizer 4 is condensed by condensation system 5 and then distilled by distillation system 6. The resulting byproduct sulfide, along with hydrogen sulfide, is fed into the sulfide converter 1. The converter catalyst is a γ-alumina support loaded with 0.2% cerium oxide and 1% cobalt oxide. The reaction temperature is 300°C, the reaction pressure is 1 MPa, and the volume hourly space velocity (VHSV) based on the total catalyst bed volume is 1000 h⁻¹. -1 This unit achieves a methanol conversion rate of 98.2%, a methanethiol selectivity of 96.2%, and a methanethiol yield of 94.5%. The tail gas contains 1.8% hydrogen sulfide, 4.2% methanethiol, 18.3% methane, 52.2% carbon dioxide, and 23.5% dimethyl ether.

Claims

1. A process for synthesizing methanethiol with low by-product yield, characterized in that, Includes the following steps: (1) Hydrogen sulfide and by-product dimethyl sulfide are fed into a sulfide converter and reacted under the action of a sulfide conversion catalyst to convert part of the dimethyl sulfide into methanethiol. (2) The output gas of the sulfide converter and gaseous methanol are fed into a multi-stage methanethiol synthesizer connected in series. Under the action of the methanethiol synthesis catalyst, hydrogen sulfide reacts with methanol to generate methanethiol, and methanethiol is produced as a byproduct. (3) The output gas of the final stage methanethiol synthesizer is condensed and distilled to obtain methanethiol product, and the separated by-product methyl sulfide is returned to the sulfide converter for recycling.

2. The process according to claim 1, characterized in that, The feed molar ratio of hydrogen sulfide to dimethyl sulfide entering the sulfide converter is ≥3:

1. The reaction temperature of the sulfide converter and the multi-stage methanethiol synthesizer is 200℃ to 380℃, the reaction pressure is 0.7MPa to 1.3MPa, and the gas hourly space velocity is 500 h⁻¹. -1 Up to 3000 h -1 .

3. The process according to claim 1, characterized in that, The multi-stage methanethiol synthesizer has at least n stages, where n≥2. The methanol feed rate of the first-stage methanethiol synthesizer satisfies the following molar ratio: (total molar feed rate of hydrogen sulfide - 1 / 2 × total molar feed rate of dimethyl sulfide) / molar feed rate of methanol = 2.2 to 6.

0.

4. The process according to claim 3, characterized in that, The ratio of the methanol feed rate to the molar amount of unreacted hydrogen sulfide in the previous stage to the methanol feed rate to the second to n-1 stage methanethiol synthesizers is 1.2 to 5; the ratio of the methanol feed rate to the molar amount of unreacted hydrogen sulfide in the previous stage to the methanol feed rate to the nth stage methanethiol synthesizer is 0.95:1 to 1:

1.

5. The process according to claim 1, characterized in that, The methanethiol synthesis catalyst uses ZSM-5@SiO2 as the core support and is loaded with 5 wt% to 20 wt% tungsten oxide and 2.5 wt% to 10 wt% potassium oxide.

6. The process according to claim 1, characterized in that, In the multi-stage methanethiol synthesizer, methanethiol synthesis catalysts with active component loadings decreasing sequentially from front to back are loaded. The reaction temperature of the multi-stage methanethiol synthesizer increases progressively from front to back, with a temperature range of 300°C to 370°C.

7. The process according to any one of claims 1-6, characterized in that, The output gas from the final stage methanethiol synthesizer is condensed and distilled to obtain methanethiol product, and the separated byproduct dimethyl sulfide is returned to the sulfide converter for recycling.

8. The process according to claim 7, characterized in that, Hydrogen sulfide and dimethyl sulfide are passed into a sulfide converter, where they react under the action of a sulfide conversion catalyst to convert part of the dimethyl sulfide into methanethiol.

9. The process according to claim 8, characterized in that, The sulfide conversion catalyst is supported on γ-alumina and loaded with 0.1 wt% to 1 wt% cerium oxide and 0.5 wt% to 2 wt% cobalt oxide.

10. An apparatus for implementing the low-byproduct methanethiol synthesis process according to any one of claims 1-9, characterized in that, include: A sulfide converter (1), at least two stages of methanethiol synthesizer, a condensation system (5) and a distillation system (6) are connected in series. The distillation system (6) is provided with a methanethiol product outlet and a methanethiol outlet. The methanethiol outlet is connected to the feed inlet of the sulfide converter (1) through a pipeline to form a methanethiol circulation loop. The sulfide converter (1) is equipped with feed lines for hydrogen sulfide and dimethyl sulfide; Each stage of the methanethiol synthesizer is equipped with a gaseous methanol feed line before its inlet.

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