A method for preparing dimethyl sulfoxide using a microreactor

Abstract

The present invention discloses a method for preparing dimethyl sulfoxide using a microreactor, which comprises pumping dimethyl sulfide and hydrogen peroxide into the microreactor respectively for reaction, controlling the reaction pressure by a back pressure valve at the outlet of the microreactor, and controlling the reaction temperature by a heat exchange system outside the microreactor; the microreactor is made of non-metallic material, and the heat exchange area per unit volume is ≥5000m 2 / m 3 The present invention uses a microreactor with a high heat exchange area per unit volume, which simplifies the process flow, reduces equipment investment costs, and reduces production costs; at the same time, it reduces the influence of the reaction on the transfer rate control, greatly shortens the reaction time, improves the reaction efficiency, and reduces energy consumption.

Description

Technical Field

[0001] The present invention relates to the technical field of organic synthesis, and in particular to a method for preparing dimethyl sulfoxide by using a microreactor. Background Art

[0002] Dimethyl sulfoxide (DMSO) is a sulfur-containing organic compound with high polarity, a high boiling point, good thermal stability, aprotic properties, and water miscibility. It is soluble in most organic compounds, including ethanol, propanol, benzene, and chloroform. It can be used as an organic solvent, reaction medium, and organic synthesis intermediate. DMSO is also used as a dyeing solvent for synthetic fibers, a pesticide additive, an antifreeze, a metal paint stripper, a degreasing agent, a capacitor dielectric, a rare metal extractant, and a sulfur dioxide absorbent.

[0003] Methods for preparing dimethyl sulfoxide from dimethyl sulfide include nitric acid oxidation, ozone oxidation, nitrogen dioxide, and hydrogen peroxide oxidation. Nitric acid oxidation, due to the use of excess nitric acid, is subject to severe equipment corrosion and requires large amounts of waste acid disposal. Currently reported conversion rates for ozone oxidation are only 26%-28%, making it unsuitable for industrial applications. The nitrogen dioxide method, a mature and widely used method both domestically and internationally, offers low production costs, but it carries significant project investment, environmental concerns, and the risk of accidents, leading to its gradual elimination. The hydrogen peroxide method, while more expensive than the nitrogen dioxide method, offers milder reaction conditions, a simpler process, and lower project investment. Furthermore, the hydrogen peroxide used reacts with water, which does not cause pollution. This makes it a cost-effective, resource-efficient, and environmentally friendly process.

[0004] Chinese patent CN114105840A discloses a method for preparing dimethyl sulfoxide (DMSO) from dimethyl sulfide. The method involves adding a mixed solution of dimethyl sulfide, water, and DMSO in a certain proportion to a high-aspect-ratio tower reactor filled with an activated alumina support. Hydrogen peroxide and dimethyl sulfide are then continuously introduced into the mixed solution to achieve continuous production of DMSO. This method is environmentally friendly, with high hydrogen peroxide conversion and DMSO yields. However, the process is complex and requires pre-filling of the support and mixed solution, increasing production costs.

[0005] Chinese patent CN114805145A discloses an apparatus and method for producing dimethyl sulfoxide (DMSO) using hydrogen peroxide to oxidize dimethyl sulfide. Dimethyl sulfide and hydrogen peroxide are pumped into a mixer, then sequentially fed into one to six tubular reactors at different temperatures to react and produce crude DMSO. This method further simplifies the process flow, but due to the limited mixing effect of the mixer, the reaction requires six tubular reactors, each with its own temperature control, increasing energy consumption.

[0006] Chinese patent CN114890924A discloses a method for the continuous production of dimethyl sulfoxide (DMSO). Dimethyl sulfide and hydrogen peroxide are first introduced into a membrane mixer for thorough mixing, and then introduced into a continuous flow microreactor to generate DMSO. This method utilizes the membrane mixer and continuous flow microreactor to improve the heat and mass transfer efficiency of the reaction, thereby increasing the conversion rate of the raw materials. However, the nano-membrane mixer increases the cost of the device, and hydrogen peroxide is more easily decomposed during mixing in the nano-membrane reactor. The generated oxygen reduces the reaction residence time, resulting in unstable product quality and a need for further improvement in yield.

[0007] In summary, the existing hydrogen peroxide method for preparing dimethyl sulfoxide has high production costs, large energy consumption and unstable product quality. Summary of the Invention

[0008] In order to solve the technical problems of high production cost, large energy consumption and unstable product quality in the existing hydrogen peroxide method for preparing dimethyl sulfoxide, the present invention provides a method for preparing dimethyl sulfoxide using a microreactor.

[0009] The technical solution adopted in the present invention is:

[0010] A method for preparing dimethyl sulfoxide using a microreactor comprises pumping dimethyl sulfide and hydrogen peroxide into the microreactor for reaction, controlling the reaction pressure by a back pressure valve at the outlet of the microreactor, controlling the reaction temperature by a heat exchange system outside the microreactor, and collecting the reaction product at the outlet of the back pressure valve to obtain dimethyl sulfoxide; the microreactor is made of non-metallic material, and has a heat exchange area per unit volume of ≥2000 m 2 / m 3 .

[0011] A microreactor is a device that allows reactants to continuously flow, react, and exchange heat within a tiny channel. In a narrow sense, the channel size of a microreactor is generally within 1000 μm, in order to achieve a sufficiently short diffusion distance between molecules, high mass transfer efficiency, large specific surface area, and high heat exchange efficiency. The heat exchange area per unit volume of a microreactor is 2 / rm 2 / m 3 , where r is the channel radius, and both the heat transfer coefficient and the mass transfer coefficient are inversely proportional to r. Therefore, selecting a small channel can increase the heat exchange area per unit volume of the microreactor, enhance the heat and mass transfer efficiency of the microreactor, and reduce the influence of transfer rate control on strong exothermic and fast reactions. The present invention uses a microreactor with a high heat exchange area per unit volume to pass the raw materials dimethyl sulfide and hydrogen peroxide under pressure into the microreactor, and controls the reaction temperature, residence time, and reaction pressure to obtain high-quality dimethyl sulfoxide without the need for enhanced mixing using membrane mixers, micromixers, static mixers, etc., thereby simplifying the process flow.

[0012] During experiments, the inventors unexpectedly discovered that using a microreactor made of metals such as Fe, Ti, Cu, and Ni resulted in a higher dimethyl sulfone content in the reaction product, indicating an increase in side reactions during the reaction. This is likely because hydrogen peroxide becomes more reactive when in contact with metals, increasing the reaction rate with dimethyl sulfide and concentrating the heat release, leading to an increase in side reactions. Therefore, the present invention opted for a microreactor made of non-metallic materials.

[0013] Preferably, the microreactor is made of silicon carbide, ceramic, polytetrafluoroethylene or glass.

[0014] Preferably, the heat exchange area per unit volume of the microreactor is ≥5000m 2 / m 3 , and ≤40000m 2 / m 3 If the inner diameter of the channel is too small, on the one hand, the manufacturing difficulty increases and the equipment investment cost is high; on the other hand, the pressure drop during the reaction process increases, the reactant flow rate can only be very small, and the output is reduced.

[0015] Preferably, the feed molar ratio of dimethyl sulfide to hydrogen peroxide is 1:0.8-1.5, more preferably, the feed molar ratio is 1:0.95-1.05.

[0016] Conventional methods typically use an excess of hydrogen peroxide to increase the conversion of dimethyl sulfide. However, in actual industrial production, the reaction product must be separated into a main product (dimethyl sulfoxide) and a by-product (dimethyl sulfone) by distillation. Excess hydrogen peroxide in the reaction product will continue to react with dimethyl sulfoxide during the distillation stage to form dimethyl sulfone, resulting in a reduced dimethyl sulfoxide yield. Therefore, the present invention selects a similar ratio of dimethyl sulfide to hydrogen peroxide to improve conversion and dimethyl sulfoxide yield.

[0017] Preferably, the reaction temperature in the microreactor is 30-100° C., and the reaction pressure is 0-5 MPa. More preferably, the reaction temperature is 35-80° C., and the reaction pressure is 0.5-4 MPa.

[0018] If the reaction temperature is too low, a long reaction time is required, the reaction is incomplete, the conversion rate is low, and during the stage of separating the main product and by-products, unreacted dimethyl sulfide and hydrogen peroxide continue to undergo a highly exothermic reaction, and the accumulation of reaction heat poses an explosion risk; if the reaction temperature is too high and exceeds the boiling point of the reactants, the reaction residence time is difficult to control and the yield is reduced.

[0019] Preferably, the residence time of the reactants in the microreactor is 0.001 to 1000 s, more preferably, the residence time is 0.01 to 300 s.

[0020] The reaction residence time is closely related to the reaction temperature. A lower reaction temperature requires a longer reaction time, while a higher reaction temperature requires a shorter reaction time.

[0021] Preferably, the hydrogen peroxide is an aqueous solution with a mass concentration of 5% to 60%. More preferably, the mass concentration of the hydrogen peroxide aqueous solution is 15% to 50%, thereby improving the reaction efficiency and the stability of the reaction product.

[0022] Beneficial effects of the present invention:

[0023] 1. The present invention selects a microreactor made of non-metallic materials to avoid concentrated heat release in the metal-catalyzed hydrogen peroxide reaction and effectively reduce the generation of the by-product dimethyl sulfone.

[0024] 2. The present invention uses a microreactor with a high heat exchange area per unit volume, which simplifies the process flow, reduces equipment investment costs, and reduces production costs; at the same time, it reduces the influence of the reaction on the transfer rate control, greatly shortens the reaction time, improves the reaction efficiency, and reduces energy consumption.

[0025] 3. The present invention reduces the generation of dimethyl sulfone as a by-product during the product distillation process and improves the yield of dimethyl sulfoxide by adopting a feeding method with a slightly excessive amount of dimethyl sulfide.

[0026] 4. The present invention adopts a back pressure valve to stably control the reaction pressure, effectively reducing the decomposition of hydrogen peroxide, allowing the reaction process to proceed in a steady state, and improving the stability of product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The present invention is a simplified process flow diagram of the dimethyl sulfoxide synthesis process. DETAILED DESCRIPTION

[0028] The present invention will be further described below with reference to specific examples to facilitate understanding of the present invention, but the present invention is not limited thereto.

[0029] The raw materials used in the following examples and comparative examples are: dimethyl sulfide, AR grade, 99%, Shanghai Jizhi Biochemical Technology Co., Ltd.; aqueous hydrogen peroxide, industrial grade, Jiangsu Yangnong Chemical Co., Ltd.

[0030] The reaction products obtained in the examples and comparative examples were analyzed for their composition using a Fuli 9790 II gas chromatograph; the gas chromatograph detection conditions were:

[0031] The chromatographic column is MEGA-5, 30m*0.92mm*0.25um, air is used as the carrier gas, and the flow rate is 100mL·min -1The injection port temperature was 260°C, the initial column box temperature was 60°C, maintained for 3 min, and then increased at 20°C min -1 Raise to 250℃, maintain for 3 minutes, detector temperature 260℃, splitless injection, injection volume 2.0uL.

[0032] Example 1

[0033] ginseng Figure 1 Dimethyl sulfide and hydrogen peroxide were pumped into a tee with an inner diameter of 1 / 16 inch by a high-pressure constant flow pump, mixed, and then entered the microreactor for reaction. The reaction temperature was controlled at 35°C by the temperature control system, and the reaction pressure was controlled at 0.2 MPa by the back pressure valve. The reactants stayed in the microreactor for 300 seconds, and the reaction products were collected at the outlet of the back pressure valve. The obtained reaction products were distilled at 100°C to remove unreacted dimethyl sulfide and water, and the obtained samples were sent to the Fuli 9790Ⅱ gas chromatograph for analysis of the content of each component. The analysis results are shown in Table 1.

[0034] The feed molar ratio of dimethyl sulfide to hydrogen peroxide is 1:1.03, the mass concentration of the hydrogen peroxide aqueous solution is 45%, the microreactor is made of silicon carbide, and the heat exchange area per unit volume is 5000m 2 / m 3 .

[0035] Example 2

[0036] Dimethyl sulfide and hydrogen peroxide were pumped into a tee with an inner diameter of 1 / 16 inch by a high-pressure constant flow pump, mixed, and then entered into a microreactor for reaction. The reaction temperature was controlled at 70°C by a temperature control system, and the reaction pressure was controlled at 2 MPa by a back pressure valve. The reactants stayed in the microreactor for 0.8 s, and the reaction products were collected at the outlet of the back pressure valve. The obtained reaction products were distilled at 100°C to remove unreacted dimethyl sulfide and water, and the obtained samples were sent to a Fuli 9790Ⅱ gas chromatograph for analysis of the content of each component. The analysis results are shown in Table 1.

[0037] The feed molar ratio of dimethyl sulfide to hydrogen peroxide is 1:0.97, the mass concentration of the hydrogen peroxide aqueous solution is 20%, the microreactor is made of ceramic, and the heat exchange area per unit volume is 10000m 2 / m 3 .

[0038] Example 3

[0039] Dimethyl sulfide and hydrogen peroxide were pumped into a tee with an inner diameter of 1 / 16 inch by a high-pressure constant flow pump, mixed, and then entered into a microreactor for reaction. The reaction temperature was controlled at 80°C by a temperature control system, and the reaction pressure was controlled at 4 MPa by a back pressure valve. The reactants stayed in the microreactor for 0.08 s, and the reaction products were collected at the outlet of the back pressure valve. The obtained reaction products were distilled at 100°C to remove unreacted dimethyl sulfide and water, and the obtained samples were sent to a Fuli 9790Ⅱ gas chromatograph for analysis of the content of each component. The analysis results are shown in Table 1.

[0040] The feed molar ratio of dimethyl sulfide to hydrogen peroxide is 1:1, the mass concentration of the hydrogen peroxide aqueous solution is 27%, the microreactor is made of polytetrafluoroethylene, and the heat exchange area per unit volume is 20000m 2 / m 3 .

[0041] Example 4

[0042] Dimethyl sulfide and hydrogen peroxide were pumped into a tee with an inner diameter of 1 / 16 inch by a high-pressure constant flow pump, mixed, and then entered into a microreactor for reaction. The reaction temperature was controlled at 50°C by a temperature control system, and the reaction pressure was controlled at 1 MPa by a back pressure valve. The reactants stayed in the microreactor for 30 seconds, and the reaction products were collected at the outlet of the back pressure valve. The obtained reaction products were distilled at 100°C to remove unreacted dimethyl sulfide and water, and the obtained samples were sent to a Fuli 9790Ⅱ gas chromatograph for analysis of the content of each component. The analysis results are shown in Table 1.

[0043] The feed molar ratio of dimethyl sulfide to hydrogen peroxide is 1:1, the mass concentration of the hydrogen peroxide aqueous solution is 40%, the microreactor is made of glass, and the heat exchange area per unit volume is 40000m 2 / m 3 .

[0044] Example 5

[0045] Dimethyl sulfide and hydrogen peroxide were pumped into a tee with an inner diameter of 1 / 16 inch by a high-pressure constant flow pump, mixed, and then entered into a microreactor for reaction. The reaction temperature was controlled at 50°C by a temperature control system, and the reaction pressure was controlled at 1 MPa by a back pressure valve. The reactants stayed in the microreactor for 30 seconds, and the reaction products were collected at the outlet of the back pressure valve. The obtained reaction products were distilled at 100°C to remove unreacted dimethyl sulfide and water, and the obtained samples were sent to a Fuli 9790Ⅱ gas chromatograph for analysis of the content of each component. The analysis results are shown in Table 1.

[0046] The feed molar ratio of dimethyl sulfide to hydrogen peroxide is 1:1, the mass concentration of the hydrogen peroxide aqueous solution is 40%, the microreactor is made of glass, and the heat exchange area per unit volume is 2000m 2 / m3 .

[0047] Comparative Example 1

[0048] Dimethyl sulfide and hydrogen peroxide were pumped into a tee with an inner diameter of 1 / 16 inch by a high-pressure constant flow pump, mixed, and then entered into a microreactor for reaction. The reaction temperature was controlled at 70°C by a temperature control system. The reactants stayed in the microreactor for 0.8s. The reaction products were collected at the outlet of the microreactor and the obtained reaction products were distilled at 100°C to remove unreacted dimethyl sulfide and water. The obtained samples were sent to a Fuli 9790Ⅱ gas chromatograph for analysis of the content of each component. The analysis results are shown in Table 1.

[0049] The feed molar ratio of dimethyl sulfide to hydrogen peroxide is 1:0.97, the mass concentration of the hydrogen peroxide aqueous solution is 20%, the microreactor is made of ceramic, and the heat exchange area per unit volume is 10000m 2 / m 3 .

[0050] Comparative Example 2

[0051] Dimethyl sulfide and hydrogen peroxide were pumped into a tee with an inner diameter of 1 / 16 inch by a high-pressure constant flow pump, mixed, and then entered into a microreactor for reaction. The reaction temperature was controlled at 35°C by a temperature control system, and the reaction pressure was controlled at 0.2 MPa by a back pressure valve. The reactants stayed in the microreactor for 300 seconds, and the reaction products were collected at the outlet of the back pressure valve. The obtained reaction products were distilled at 100°C to remove unreacted dimethyl sulfide and water, and the obtained samples were sent to a Fuli 9790Ⅱ gas chromatograph for analysis of the content of each component. The analysis results are shown in Table 1.

[0052] The feed molar ratio of dimethyl sulfide to hydrogen peroxide is 1:1.03, the mass concentration of the hydrogen peroxide aqueous solution is 45%, the microreactor is made of stainless steel 316L, and the heat exchange area per unit volume is 5000m 2 / m 3 .

[0053] Table 1 Test results of examples and comparative examples

[0054] sample Conversion rate of dimethyl sulfide (%) Dimethyl sulfoxide selectivity (%) Example 1 100 99.4 Example 2 99.6 99.7 Example 3 99.9 99.6 Example 4 99.8 99.4 Example 5 89.1 93.7 Comparative Example 1 88.5 92.2 Comparative Example 2 100 93.8

[0055] As can be seen from Table 1, when dimethyl sulfide is in excess, hydrogen peroxide reacts completely, dimethyl sulfoxide selectivity is high, and less dimethyl sulfoxide is generated as a by-product; Comparative Example 1, compared with Example 2, does not use a back pressure valve, and the dimethyl sulfide conversion rate and dimethyl sulfoxide selectivity both decrease, indicating that the present invention uses a back pressure valve to stably control the reaction pressure, reduce the generation of side reactions, and improve the dimethyl sulfoxide selectivity. Compared with Example 1, Comparative Example 2 changes the microreactor material from silicon carbide to stainless steel 316L, the dimethyl sulfide conversion rate remains unchanged, and the dimethyl sulfoxide selectivity decreases from 99.4% to 93.8%, indicating that the by-product dimethyl sulfone is generated in large quantities. These results may be due to the enhanced dual oxidation activity under the catalysis of metal Fe, the concentrated heat release of the reaction, and the increase in side reactions. Compared with Example 5, Example 4 changes the heat exchange area per unit volume of the microreactor from 40,000 m 2 / m 3 becomes 2000m 2 / m 3 , the dimethyl sulfide conversion rate and dimethyl sulfoxide selectivity both dropped significantly, indicating that selecting a microreactor with a high unit volume heat exchange area can effectively improve the heat and mass transfer efficiency of the reactor, so that the reaction is not affected by the transfer rate control, and the reactant conversion rate is improved; at the same time, the high unit volume heat exchange area can also instantly remove the heat generated by the reaction and reduce the occurrence of side reactions.

[0056] Compared to the best results in the example of Chinese patent CN114890924A, which showed a dimethyl sulfide conversion rate of 99.5% and a dimethyl sulfoxide selectivity of 99.3%, Examples 1-4 of the present invention all achieved these levels, and the reaction time was significantly shortened, indicating that the present invention achieved a higher quality product without the use of a membrane mixer to enhance mixing. These results demonstrate the technical advancement of the present invention's microreactor with a high heat exchange area per unit volume. In summary, the results obtained in the examples and comparative examples show that the method provided by the present invention overcomes the shortcomings of the prior art and has the advantages of a simple process flow, automated continuous operation, low investment cost, stable product quality, and high yield.

[0057] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the same. Although the present invention has been described in detail with reference to preferred embodiments, persons skilled in the art should understand that the specific implementation methods of the present invention may still be modified or some technical features may be replaced by equivalents without departing from the spirit of the technical solutions of the present invention. All of these should fall within the scope of the technical solutions claimed for protection by the present invention.

Claims

1. A method for preparing dimethyl sulfoxide using a microreactor, characterized in that: include: Dimethyl sulfide and hydrogen peroxide are pumped into the microreactor respectively for reaction, the reaction pressure is controlled by the back pressure valve at the outlet of the microreactor, the reaction temperature is controlled by the heat exchange system outside the microreactor, and the reaction product is collected at the outlet of the back pressure valve to obtain dimethyl sulfoxide; the material of the microreactor is non-metallic material, and the heat exchange area per unit volume is ≥5000m 2 / m 3 , and ≤40000m 2 / m 3 ; The material of the microreactor is silicon carbide, ceramic, polytetrafluoroethylene or glass; The feed molar ratio of dimethyl sulfide to hydrogen peroxide is 1:0.8-1.

5.

2. A method for preparing dimethyl sulfoxide using a microreactor according to claim 1, characterized in that, The feed molar ratio of dimethyl sulfide to hydrogen peroxide is 1:0.95-1.

1.

3. A method for preparing dimethyl sulfoxide using a microreactor according to claim 1, characterized in that, The reaction temperature in the microreactor is 30-100° C., and the reaction pressure is 0-5 MPa.

4. The method for preparing dimethyl sulfoxide using a microreactor according to claim 1, wherein The residence time of the reactants in the microreactor is 0.001 to 1000 s.

5. A method for preparing dimethyl sulfoxide using a microreactor according to claim 4, characterized in that: The residence time is 0.01 to 300 seconds.

6. The method for preparing dimethyl sulfoxide using a microreactor according to claim 1, wherein: The hydrogen peroxide is in the form of an aqueous solution with a mass concentration of 5% to 60%.

7. The method for preparing dimethyl sulfoxide using a microreactor according to claim 6, wherein: The mass concentration of the hydrogen peroxide aqueous solution is 15% to 50%.

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