A process for the production of dimethyl sulfoxide

Abstract

The application discloses a high-purity dimethyl sulfoxide production method and belongs to the technical field of dimethyl sulfoxide production. The method comprises the following steps: hydrogen sulfide concentration: taking methanol washing acid gas containing hydrogen sulfide as raw material, adopting a two-stage chemical absorption and desorption process with MDEA solution as absorbent to prepare hydrogen sulfide gas with a concentration greater than or equal to 92%; dimethyl sulfide synthesis: mixing the prepared hydrogen sulfide gas with methanol according to a molar ratio of 0.5-0.75:1, performing gas phase catalytic dehydration reaction under the action of a catalyst at 380 DEG C, and obtaining dimethyl sulfide after separation and rectification; dimethyl sulfoxide synthesis: oxidizing nitrogen monoxide output from a circulation pipe with oxygen to generate nitrogen dioxide, performing oxidation reaction of the nitrogen dioxide and the dimethyl sulfide in a sulfoxide reactor, and obtaining dimethyl sulfoxide after light removal, gas stripping and rectification of the reaction product; and the top of the sulfoxide reactor is communicated with the circulation pipe. The method has high safety and can obtain products with high purity.

Description

Technical Field

[0001] This invention belongs to the field of dimethyl sulfoxide production technology, and in particular relates to a method for producing dimethyl sulfoxide. Background Technology

[0002] Dimethyl sulfoxide is a sulfur-containing organic compound with the molecular formula […]. Dimethyl sulfoxide (DMSO) is a colorless, odorless, and transparent liquid at room temperature. It is a hygroscopic and flammable liquid. DMSO possesses high polarity, a high boiling point, good thermal stability, is aprotic, and miscible with water. It is soluble in most organic compounds, including ethanol, propanol, benzene, and chloroform, and is known as a "universal solvent." It is widely used in synthetic fibers, pharmaceuticals, pesticides, electronics, carbon fiber, and aerospace industries, and is an important fine chemical raw material.

[0003] Currently, the industrial production process of dimethyl sulfoxide mainly uses methyl sulfide as a raw material through an oxidation reaction. The main methods for synthesizing methyl sulfide include the dimethyl sulfate method, the carbon disulfide method, and the hydrogen sulfide method. Among these, the dimethyl sulfate method has high production costs and produces a large amount of sulfate as a byproduct; the carbon disulfide method has high raw material costs; and the hydrogen sulfide method uses desulfurized and recovered hydrogen sulfide as a raw material, offering a significant cost advantage and is currently the mainstream methyl sulfide production process. The main methods for oxidizing methyl sulfide to prepare dimethyl sulfoxide include the nitric acid oxidation method, the hydrogen peroxide oxidation method, and the nitrogen dioxide oxidation method. The nitric acid oxidation method has low purification efficiency and produces a large amount of nitrate as a byproduct; the hydrogen peroxide oxidation method has high raw material costs and high steam consumption; and the nitrogen dioxide oxidation method has low production costs and is currently the most widely used method.

[0004] The nitrogen dioxide oxidation method can be found in the method disclosed in application CN202110548997.4, "A Production Apparatus and Process for Electronic Grade Dimethyl Sulfoxide." This method uses methanol and hydrogen sulfide as raw materials to prepare refined sulfide. The refined sulfide, oxygen, and nitrogen dioxide are then fed into an oxidation tower for excess oxidation, generating acidic crude sulfoxide. Excess oxygen and nitrogen dioxide are stripped out in a stripping tower, and the mixture is neutralized with alkali to obtain salt-containing sulfoxide. Finally, the salt-containing sulfoxide is continuously vacuum concentrated in an evaporator, and the vapor phase enters a dehydration tower. After dehydration, the bottom liquid is discharged into a concentrated sulfoxide tank to obtain electronic grade dimethyl sulfoxide with a single metal ion concentration ≤10 ppb. However, this method has the following problems: 1. Concentrating combustible methyl sulfide, oxidizers oxygen and nitrogen dioxide inside the oxidation tower poses a serious explosion hazard.

[0005] 2. Using alkali neutralization to remove nitrogen dioxide from the product results in the presence of nitrate impurities in the product, affecting the purity and quality of the product.

[0006] 3. Oxidation towers generate large amounts of nitric oxide and unreacted nitrogen dioxide. These gases cannot be directly released into the atmosphere and need to be absorbed by sodium hydroxide solution to prevent environmental pollution. In the absorption tower, nitrogen oxides react with sodium hydroxide to ultimately produce a mixed salt solution of sodium nitrite and sodium nitrate, resulting in a large amount of nitrates that are difficult to treat and pose significant environmental pressure. Summary of the Invention

[0007] To address the issues of low safety and low purity in existing technologies, this invention provides a method for producing dimethyl sulfoxide. To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first aspect of this invention provides a method for producing dimethyl sulfoxide, comprising the following steps: Hydrogen sulfide concentration: Using methanol washing acid gas containing hydrogen sulfide as raw material, a two-stage chemical absorption and desorption process with MDEA solution as absorbent is used to prepare hydrogen sulfide gas with a concentration of greater than or equal to 92%. Synthesis of dimethyl sulfide: The prepared hydrogen sulfide gas is mixed with methanol at a molar ratio of 0.5~0.75:1, and then... A gas-phase catalytic dehydration reaction was carried out at 380℃ under the action of a catalyst, and distillation was performed to obtain dimethyl sulfide. Dimethyl sulfoxide synthesis: Nitric oxide and oxygen from the circulation tube are oxidized in a nitrogen dioxide reactor to produce nitrogen dioxide. Nitric oxide and dimethyl sulfide are then oxidized in a sulfoxide reactor. The reaction product is subjected to light removal, stripping, and distillation to obtain dimethyl sulfoxide. The nitric oxide produced in the sulfoxide reactor is recycled back to the nitrogen dioxide reactor via a circulation tube.

[0008] The beneficial effects of this invention are: 1. In this method, the top of the sulfoxide reactor is connected to the circulation pipe. During the synthesis of dimethyl sulfoxide, oxygen is not required, and the entire process has high safety performance.

[0009] 2. Nitric oxide, one of the products of dimethyl sulfoxide synthesis, re-enters the oxidation cycle to obtain the raw materials for dimethyl sulfoxide synthesis. Theoretically, the entire process only consumes oxygen. By circulating within the system, costs are reduced.

[0010] 3. This method uses light component removal, gas stripping, and distillation to purify the low-purity dimethyl sulfoxide synthesized from dimethyl sulfoxide, thereby improving the purity of the obtained dimethyl sulfoxide.

[0011] 4. The method in this scheme only produces dimethyl sulfoxide and nitric oxide in the sulfoxide reactor. The nitric oxide can be directly recycled without tail gas treatment and no nitrate is produced, which is beneficial to the environment. Attached Figure Description

[0012] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 This is a schematic diagram of the absorption and desorption equipment used in the hydrogen sulfide concentration stage of this invention.

[0014] The attached figure labels are named as follows: 11. Primary absorption tower; 12. Secondary absorption tower; 21. First lean-rich liquid heat exchanger; 22. Second lean-rich liquid heat exchanger; 31. Primary regeneration tower; 32. Secondary regeneration tower. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0016] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0017] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other.

[0018] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0019] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use, or the orientation or positional relationship commonly understood by those skilled in the art. They are only used for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. In addition, the terms "first," "second," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0020] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0021] This invention discloses a method for producing dimethyl sulfoxide, which includes three core procedures: hydrogen sulfide concentration, dimethyl sulfide synthesis, and dimethyl sulfoxide synthesis.

[0022] When concentrating hydrogen sulfide, methanol washing gas containing hydrogen sulfide is used as raw material, and a two-stage chemical absorption and desorption process using MDEA solution as absorbent is employed to prepare hydrogen sulfide gas with a concentration of ≥92%.

[0023] This step employs two sets of absorption and desorption equipment, such as... Figure 1 As shown, each absorption and desorption unit includes an absorption tower, a lean-rich liquid heat exchanger, and a regeneration tower. Specifically, this step includes steps S11 to S14.

[0024] Step S11: Primary absorption is performed using a primary absorption tower 11. During primary absorption, the raw material enters from the bottom of the primary absorption tower and flows upward, while the lean MDEA solution enters from the top of the primary absorption tower and flows downward. In this process, the gas and liquid come into full counter-current contact. The lean solution selectively absorbs hydrogen sulfide from the raw material gas to form a rich solution, while the unabsorbed carbon dioxide and other components are discharged from the top of the primary absorption tower. After the entrained liquid is separated by a gas-liquid separator, the solution is sent outside the boundary to recover carbon dioxide.

[0025] Step S12: Primary regeneration is performed using a primary regeneration tower 31. During primary regeneration, the rich MDEA solution at the bottom of the primary absorption tower 11 is heated by the first lean-rich solution heat exchanger 21 before entering the primary regeneration tower 31 for regeneration. The lean MDEA solution flowing out from the bottom of the primary regeneration tower 31 is cooled and circulated back into the primary absorption tower 11 after being heated by the first lean-rich solution heat exchanger 21. During this process, the primary regeneration tower 31 is heated and regenerated under 0.3MPa low-pressure steam. The regeneration gas at the top of the tower is cooled and condensed by an acid gas condenser. The condensate is returned to the primary regeneration tower, and the crude hydrogen sulfide non-condensable gas flows out from the top and enters the secondary absorption tower.

[0026] Step S13: Secondary absorption is carried out using a secondary absorption tower 12. The crude hydrogen sulfide flowing out from the top of the primary regeneration tower 31 enters the lower part of the secondary absorption tower 12, and the lean MDEA solution enters from the upper part of the secondary absorption tower 12.

[0027] Step S14: Secondary regeneration is performed using a secondary regeneration tower 32. The rich MDEA solution at the bottom of the secondary absorption tower 12 is regenerated after heat exchange in the second lean-rich solution heat exchanger 22. The lean MDEA solution flowing out from the bottom of the secondary regeneration tower 32 is cooled and circulated back into the secondary absorption tower 12 after heat exchange in the second lean-rich solution heat exchanger 22. Hydrogen sulfide gas with a concentration of ≥92% is obtained from the top.

[0028] The principle of second-order absorption desorption is the same as that of first-order absorption, and will not be elaborated here.

[0029] In this step, MDEA solution is used as the absorbent. The raw gas does not need to be compressed, resulting in low operating costs. MDEA solution is chemically stable, non-toxic, non-degradable, and has low solvent loss, making it recyclable.

[0030] In the synthesis of dimethyl sulfide, the prepared hydrogen sulfide gas is mixed with methanol at a molar ratio of 0.5~0.75:1. A gas-phase catalytic dehydration reaction is carried out under the action of a catalyst, and dimethyl sulfide is obtained after separation and distillation.

[0031] This step uses hydrogen sulfide gas obtained from the hydrogen sulfide concentration step and methanol as raw materials to synthesize dimethyl sulfide via a methanol-hydrogen sulfide gas-phase catalytic dehydration method. Specifically, this step includes steps S21 to S23.

[0032] Step S21: Pretreatment of raw materials. Hydrogen sulfide gas and methanol are mixed at a molar ratio of 0.5~0.75:1, and after preheating, vaporization and superheating, it is used as the raw material gas for the synthesis dehydration reactor.

[0033] The hydrogen sulfide gas used in this step is preferably hydrogen sulfide from industrial by-product acid gas, or hydrogen sulfide prepared from sulfur by-products of industrial desulfurization units. Compared to existing methods such as the carbon disulfide method and the dimethyl sulfate method, this method significantly reduces raw material costs.

[0034] Step S22: Perform gas-phase catalytic reaction. The feed gas is fed into a fixed-bed tubular dehydration reactor, and the reactor tubes are filled with... The catalyst is heated by molten salt between tubes, and the reaction temperature is controlled at 380℃ to carry out a gas-phase catalytic dehydration reaction. Molten salt is pumped into the dehydration reactor cylinder via a molten salt tank and a molten salt pump for heat exchange, removing the heat of reaction. The temperature of the molten salt is maintained at 360-380℃. After heat exchange with the raw material gas via a molten salt heat exchanger and vaporization via a vaporizer, the molten salt flows back to the molten salt tank, realizing molten salt circulation and heat recovery of reaction.

[0035] In this process, the molten salt circulates through the molten salt tank, molten salt pump, molten salt heat exchanger, and vaporizer, thereby recovering the heat of reaction and preheating and vaporizing the raw material gas.

[0036] Step S23: Product separation and purification. The reaction gas is cooled and condensed after waste heat recovery. The non-condensable gas is washed with methanol and then sent to an off-site sulfur recovery unit for treatment. The liquid phase yields crude dimethyl sulfide and water. The crude dimethyl sulfide is separated by liquid-liquid separation and sent to a distillation column for further distillation to obtain purified dimethyl sulfide, which is then sent to the dimethyl sulfoxide synthesis process. Methanethiol, a byproduct, is separated from the distillation column bottom. Wastewater generated from separation and distillation is treated by removing hydrogen sulfide and then sent to an off-site wastewater treatment plant.

[0037] The byproduct of this step, methanethiol, can be absorbed by alkaline solution to produce a 20% wt sodium methanethiol solution for sale, thereby improving the comprehensive utilization rate of resources and further reducing production costs. Alternatively, it can be reacted in the gas phase to generate dimethyl sulfide, which can then be returned to the dehydration reactor as raw material for recycling after passing through a vaporizer, thus reducing raw material consumption.

[0038] Using this method, the purity of the refined methyl sulfide obtained is ≥99.5%.

[0039] During the synthesis of dimethyl sulfoxide, nitric oxide and oxygen from the circulation tube are oxidized in a nitrogen dioxide reactor to produce nitrogen dioxide. Nitrogen dioxide and dimethyl sulfide are then oxidized in a sulfoxide reactor. The reaction product is then subjected to light removal, stripping, and distillation to obtain dimethyl sulfoxide. The nitric oxide produced in the sulfoxide reactor is recycled back to the nitrogen dioxide reactor via the circulation tube.

[0040] This step uses dimethyl sulfide synthesized from dimethyl sulfide as a raw material and employs a stepwise oxidation process to prepare dimethyl sulfoxide. This avoids direct contact between oxygen and dimethyl sulfide, eliminating the risk of explosion. Simultaneously, the nitrogen dioxide removal method is improved to prevent the formation of nitrate impurities in the product. Specifically, this step includes steps S31 to S33.

[0041] Step S31: Preparation of nitrogen dioxide. Nitric oxide, a byproduct of the dimethyl sulfide oxidation reaction, flows directly into the circulation pipe, where it is pressurized by a blower and then fed with oxygen. reactor, The heat of reaction in the reactor is removed by circulating water. The reactor temperature is controlled at around 100℃, and the following reaction occurs: The generated nitrogen dioxide is fed into the sulfoxide reactor according to the specified ratio via a flow meter.

[0042] Step S32: Oxidation of dimethyl sulfide. Refined dimethyl sulfide is pumped from the buffer tank into the sulfoxide reactor, where it undergoes an oxidation reaction with nitrogen dioxide in full contact with the nitrogen dioxide. The heat of reaction is removed by circulating water, and the temperature of the sulfoxide reactor is controlled at around 60°C to produce crude dimethyl sulfoxide and nitric oxide. The nitric oxide flows out from the top of the sulfoxide reactor and is circulated through the circulation pipe to step S31. The nitrogen oxide is oxidized again in the reactor to nitrogen dioxide, thus achieving the recycling of nitric oxide.

[0043] Step S33: Purification with dimethyl sulfoxide. Specifically, this step involves the sequential removal of light components, stripping, and distillation.

[0044] Light nitrogen removal: The crude dimethyl sulfoxide product from the sulfoxide reactor is fed into the light nitrogen removal tower to remove the dissolved nitrogen dioxide. The removed nitrogen dioxide is then pressurized by a blower and recycled back to the sulfoxide reactor to continue participating in the dimethyl sulfide oxidation reaction.

[0045] Specifically, the reaction product, crude dimethyl sulfoxide, is pumped into the top of the light component removal tower via a feed pump. The first reboiler at the bottom of the light component removal tower is heated with low-pressure steam (0.2-0.4 MPaG saturated steam). The gas from the top of the light component removal tower enters the tail gas condenser, and the condensate in the tail gas condenser is returned to the top of the light component removal tower. The non-condensable nitrogen dioxide in the tail gas condenser is pressurized and recycled to the sulfoxide reactor to continue participating in the dimethyl sulfide oxidation reaction. The bottom liquid after the removal of light components is pumped from the bottom of the light component removal tower and sent to the stripping tower. The pressurized circulation here uses a blower or a Venturi ejector.

[0046] For example, if 0.3 MPaG saturated steam is used, the corresponding temperature is 143°C.

[0047] Stripping: The liquid from the light-removal tower is fed into the stripping tower to further remove residual nitrogen dioxide, ensuring that the product is free of nitrogen oxide impurities.

[0048] Specifically, the liquid in the stripping column enters the column from the top, while nitrogen gas enters from the bottom. The two gases come into countercurrent contact within the column: crude dimethyl sulfoxide (DMSO) flows from top to bottom, while nitrogen gas passes through the liquid phase from bottom to top. Through stripping, trace amounts of nitrogen dioxide and other impurities dissolved in the crude product are carried out. The stripped crude DMSO flowing out from the bottom of the column is pumped out by the stripping column bottom liquid pump and sent to the distillation column.

[0049] Distillation: The liquid in the stripping column is fed into the distillation column, and the top of the column yields refined dimethyl sulfoxide. The high-boiling-point substances produced in the bottom of the column are sent to the outside for recovery, realizing comprehensive resource utilization.

[0050] Specifically, the stripping column bottom liquid enters the middle section of the distillation column. The second reboiler at the bottom of the distillation column is heated by low-pressure steam, specifically saturated steam at 0.2~0.4 MPaG. The DMSO vapor distilled from the top of the distillation column is condensed in the condenser, which is cooled by cooling water. A portion of the DMSO condensate flowing from the bottom of the condenser is returned to the top of the distillation column as reflux; the other portion is collected and sent to the product tank. The distillation column bottom liquid is pumped out using a bottom liquid transfer pump, and high-boiling-point substances are sent for off-site recovery, achieving comprehensive resource utilization.

[0051] This step involves refluxing a portion of the DMSO condensate back into the top of the distillation column, supplying the column with descending liquid that comes into countercurrent contact with rising vapor, thereby achieving repeated mass transfer and separation of the components in the mixture and improving the purity of DMSO.

[0052] The purified dimethyl sulfoxide obtained by distillation is cooled by a product cooler and then sent to a DMSO buffer tank for storage to obtain the final product.

[0053] The dimethyl sulfoxide product prepared using the process of this invention is a high-end, high-purity product, with quality exceeding the superior grade indicators of the national standard GB / T21395-2008. Specific indicators are as follows:

[0054] To facilitate understanding of this solution, examples are provided below based on the above process methods.

[0055] With Low-temperature methanol washing acid gas is used as raw material with a flow rate of 1540 Nm³ / h. MDEA solution is used as absorbent and the process is carried out through a two-stage absorption and desorption process. The gas and liquid are in countercurrent contact in the first-stage and second-stage absorption towers. The rich liquid is regenerated under the heating of 0.3 MPa low-pressure steam. The top of the second-stage regeneration tower yields a gas with a hydrogen sulfide concentration of 93%, which is then pressurized by a compressor and sent to the dimethyl sulfide synthesis process. The lean MDEA solution is recycled. This process consumes 2.1 kg of composite MDEA amine solution, 105 kWh of electricity, and 6.65 t of 0.3 MPa steam per hour.

[0056] The 93% concentration hydrogen sulfide was mixed with industrial methanol at a molar ratio of 0.6:1. This industrial methanol met the superior grade indicators of the GB338-2011 standard. After preheating, vaporization, and superheating, the mixture was fed into a fixed-bed tubular dehydration reactor. The dehydration reactor was filled with... The catalyst has a diameter of 3×5~10mm and a crushing resistance of ≥130N / piece. The reaction temperature is 380℃, the molten salt temperature between tubes is 370℃, and the molten salt is recycled to recover the heat of reaction. After the reaction gas is condensed, it is separated into liquid and liquid. The crude sulfide is purified by distillation in a light and heavy removal tower to obtain refined methyl sulfide with a purity of 99.8%, with an hourly output of 1.06t. The by-product methanethiol is absorbed by alkaline solution to obtain a 20%wt sodium methanethiol solution with an hourly output of 0.77t.

[0057] The refined methyl sulfide was fed into the sulfoxide reactor at a flow rate of 1.06 t / h, while simultaneously... The nitrogen dioxide generated in the reactor is fed into the sulfoxide reactor according to the specified ratio. The temperature of the sulfoxide reactor is controlled at 60°C. The dimethyl sulfide reacts with the nitrogen dioxide to produce crude dimethyl sulfoxide and nitric oxide. The nitric oxide is then recycled to... The reactor reacts with 180 Nm³ / h of oxygen at 100°C to generate nitrogen dioxide, which is then recycled. Crude dimethyl sulfoxide is then sent to a distillation column for distillation after nitrogen dioxide removal by a light-removal column and a stripping column. The purified dimethyl sulfoxide product is obtained at the top of the column, with an hourly output of 1.25 t.

[0058] The final product underwent quality testing, and the results were as follows: dimethyl sulfoxide content 99.98%, crystallization point 18.35℃, acid value 0.008 mg (KOH) / g, transmittance (400nm) 99.2%, water and other impurities mass fraction 0.02%, color 8 Hazen units, and total metal ion content 8 PPb. All indicators met the product specifications set by this invention and the national standard electronic grade indicators.

[0059] In this embodiment, the entire unit operates continuously and stably without any safety accidents, exhibiting high raw material utilization and low emissions of waste gas, wastewater, and solid waste. Specifically, waste gas: only a small amount of process waste gas containing H2S and CO2 is discharged during the hydrogen sulfide purification process of waste acid gas, with an emission rate of 7 Nm3 / h; wastewater: process wastewater containing methanol, 0.2 t / h; waste liquid: distillation column bottom liquid containing dimethyl sulfone and heavy components, with an emission rate of 0.08 t / h. The products can be directly supplied to high-end fields such as electronics and carbon fiber, resulting in significant economic and environmental benefits.

[0060] This method employs a stepwise oxidation process, where nitric oxide is oxidized to nitrogen dioxide, and nitrogen dioxide is then oxidized to dimethyl sulfoxide to produce dimethyl sulfoxide. These two reactions occur in separate reactors, avoiding direct contact between oxygen and the flammable dimethyl sulfoxide, thus fundamentally eliminating the explosion hazards inherent in traditional processes. Furthermore, it allows for the reuse of nitric oxide, the oxidation product of dimethyl sulfoxide. Theoretically, the entire process consumes only oxygen. By circulating within the system, costs are reduced.

[0061] This method employs a two-stage process of light oxide removal and gas stripping to recover nitrogen dioxide and avoid the generation of nitrate impurities in the product. The final product has a purity of ≥99.98% and a crystallization point of ≥18.30℃. All indicators are superior to the national standard for superior grade products and can meet the usage requirements of high-end fields such as electronics, carbon fiber, and military aerospace.

[0062] The method of this scheme seamlessly connects the three processes of hydrogen sulfide concentration, dimethyl sulfide synthesis, and dimethyl sulfoxide synthesis. Each process adopts continuous operation, the process parameters are controllable, the equipment selection is reasonable, and the equipment is stable in operation and convenient in maintenance, making it suitable for large-scale industrial application.

[0063] The method described in this plan generates no large amount of harmful waste residue during the production process. Wastewater is sent to a professional wastewater treatment plant after hydrogen sulfide removal, and non-condensable gas is sent to a sulfur recovery unit for treatment. Nitrogen dioxide and nitric oxide are recycled, which reduces the emission of nitrogen oxides and complies with national energy and environmental protection policies and industrial development requirements.

[0064] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for producing dimethyl sulfoxide, characterized in that, Includes the following steps: Hydrogen sulfide concentration: Using methanol washing acid gas containing hydrogen sulfide as raw material, a two-stage chemical absorption and desorption process with MDEA solution as absorbent is used to prepare hydrogen sulfide gas with a concentration of greater than or equal to 92%. Dimethyl sulfide synthesis: The prepared hydrogen sulfide gas is mixed with methanol at a molar ratio of 0.5~0.75:1, and heated and vaporized to obtain feed gas. The feed gas is sent to a fixed-bed tubular dehydration reactor. The dehydration reactor tubes are filled with γ-Al2O3 catalyst, and molten salt is used to transfer heat between the tubes. The reaction temperature is controlled at 380℃. Molten salt is sent into the dehydration reactor cylinder through a molten salt tank and a molten salt pump for heat exchange, removing the heat of reaction. The molten salt temperature is maintained at 360~380℃. After heat exchange with the feed gas through a molten salt heat exchanger and vaporization of methanol through a vaporizer, the molten salt is returned to the molten salt tank. The reaction gas in the dehydration reactor is condensed to obtain liquid dimethyl sulfide and water. The dimethyl sulfide and water are separated and distilled to obtain dimethyl sulfide. Dimethyl sulfoxide synthesis: Nitric oxide from the circulation pipe is oxidized with oxygen in a nitrogen dioxide reactor to produce nitrogen dioxide. Nitric dioxide is then oxidized with dimethyl sulfide in a sulfoxide reactor. The reaction product is subjected to light sulfide removal, stripping, and distillation to obtain dimethyl sulfoxide. The nitric oxide produced in the sulfoxide reactor is recycled back to the nitrogen dioxide reactor via a circulation pipe. The reaction product, after light component removal, stripping, and distillation, yields dimethyl sulfoxide, specifically: The product from the sulfoxide reactor is fed into a light-removal tower to remove dissolved nitrogen dioxide. The liquid from the light nitrogen removal tower is fed into the stripping tower to remove residual nitrogen dioxide; The liquid in the stripping column is fed into the distillation column, and the dimethyl sulfoxide product is output from the top of the distillation column.

2. The method for producing dimethyl sulfoxide according to claim 1, characterized in that, The secondary chemical absorption and desorption process using MDEA solution as the absorbent is as follows: A primary absorption tower (11) is used for primary absorption. The raw material enters from the bottom of the primary absorption tower (11) and flows from bottom to top. The lean MDEA solution enters from the top of the primary absorption tower (11) and flows from top to bottom. A primary regeneration tower (31) is used for one regeneration. The rich MDEA solution at the bottom of the primary absorption tower (11) is heated by the first lean rich solution heat exchanger (21) and then enters the primary regeneration tower (31) for regeneration. The lean MDEA solution flowing out from the bottom of the primary regeneration tower (31) is cooled and circulated back to the primary absorption tower (11) after being heated by the first lean rich solution heat exchanger (21). A secondary absorption tower (12) is used for secondary absorption. The crude hydrogen sulfide flowing out from the top of the primary regeneration tower (31) enters the lower part of the secondary absorption tower (12), while the lean MDEA solution enters from the upper part of the secondary absorption tower (12). A secondary regeneration tower (32) is used for secondary regeneration. The rich MDEA solution at the bottom of the secondary absorption tower (12) is regenerated by the second lean-rich solution heat exchanger (22). The lean MDEA solution flowing out from the bottom of the secondary regeneration tower (32) is cooled and circulated back to the secondary absorption tower (12) after being reheated by the second lean-rich solution heat exchanger (22). The top of the tower produces hydrogen sulfide gas with a concentration greater than or equal to 92%.

3. The method for producing dimethyl sulfoxide according to claim 1, characterized in that, The process of removing dissolved nitrogen dioxide further includes: The nitrogen dioxide is fed into the sulfoxide reactor for recycling.

4. The method for producing dimethyl sulfoxide according to claim 1, characterized in that, The removal of light weights is as follows: The product from the sulfoxide reactor is fed into the light-light-removal tower. The first reboiler at the bottom of the light-light-removal tower is heated with steam, wherein the steam is saturated steam with a strength of 0.2~0.4 MPaG. The gas at the top of the light-light-removal tower enters the tail gas condenser. The condensate in the tail gas condenser is returned to the top of the light-light-removal tower. The non-condensable gas nitrogen dioxide in the tail gas condenser is pressurized and then recycled to the sulfoxide reactor.

5. The method for producing dimethyl sulfoxide according to claim 1, characterized in that, The gas stripping is: The crude dimethyl sulfoxide, after being stripped of light components, enters the tower from the top. Nitrogen gas is introduced into the bottom of the tower to remove impurities dissolved in the dimethyl sulfoxide through gas action.

6. The method for producing dimethyl sulfoxide according to claim 1, characterized in that, The distillation is as follows: The crude dimethyl sulfoxide after stripping enters the middle of the distillation column. The second reboiler at the bottom of the distillation column is heated with steam, which is saturated steam at 0.2~0.4 MPaG. The dimethyl sulfoxide vapor distilled from the top of the distillation column enters the condenser of the distillation column and is condensed. Part of it is returned to the top of the distillation column as reflux; the other part is collected to obtain dimethyl sulfoxide. The condenser of the distillation column is cooled with cooling water.

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