A recovery system and method for dimethyl sulfoxide and dimethyl sulfoxide obtained thereby

Abstract

The application provides a dimethyl sulfoxide recovery system and a recovery method. The recovery system comprises a front dehydration tower, a solvent flash tank, a rear dehydration tower, a solvent refining tower and a heavy-removing flash tank. The recovery system is provided with the solvent flash tank and the heavy-removing flash tank, and the heavy-removing flash tank is provided with a different forced external circulation heating system. The solvent can be further recovered, and the solvent loss is reduced. The problems of high energy consumption, high solvent loss, low solvent recovery rate and low purity of recovered solvent in the solvent recovery process in the carbon fiber production process are solved, and the application prospect is wide.

Description

Technical Field

[0001] This invention belongs to the field of recycling technology, specifically relating to a dimethyl sulfoxide recycling system, recycling method, and the resulting dimethyl sulfoxide. Background Technology

[0002] Carbon fiber is a new type of reinforced and functional fiber material with high specific strength and high specific modulus. It is a high-tech product that developed rapidly in the 1960s. It possesses a range of comprehensive functions, including low density, heat resistance, chemical corrosion resistance, abrasion resistance, thermal shock resistance, electrical conductivity, thermal conductivity, radiation resistance, good damping, vibration reduction, and noise reduction. As a fiber, it also has flexibility and can be woven and spun. Its most prominent features are its high specific strength and high specific modulus. Resin-based composites reinforced with carbon fiber have a specific modulus five times higher than steel and aluminum alloys, and a specific strength more than three times higher. As an engineering structural material and ablation-resistant material, it can solve many key problems in engineering technology, leading to its widespread application in industrial fields such as wind power, building reinforcement, lightweight rail transit, and sucker rods, as well as civilian applications such as high-end sporting goods and medical devices.

[0003] Dimethyl sulfoxide (DMSO) is an important organic solvent, often referred to as a "universal solvent," with a wide range of applications. A large amount of DMSO is used as a spinning solvent in the production of carbon fiber, and the quality of the spinning solvent directly determines the performance of the precursor fiber and the carbon fiber itself. Since the concentration of DMSO in the process water discharged from the spinning unit during carbon fiber spinning is 20-30 wt%, directly discharging this process water would cause environmental pollution due to the DMSO in the water and would also result in the loss of a significant amount of DMSO, increasing raw material costs. Therefore, it is necessary to separate the water from the DMSO to recover and reuse both.

[0004] Chinese patent CN102225904A discloses a device and method for the recovery and purification of dimethyl sulfoxide (DMSO), comprising a primary dehydration tower, a scraped-film evaporator, a primary distillation intermediate tank, a secondary dehydration tower, and a DMSO purification tower. The primary dehydration tower is connected to the primary distillation intermediate tank, and the scraped-film evaporator is also connected to the primary distillation intermediate tank, followed by the secondary dehydration tower and the DMSO purification tower in sequence. The DMSO feedstock is divided into two streams: a low-concentration DMSO feedstock (DMSO content 2.0%–15.0%), which directly enters the primary dehydration tower to remove most of the water; and a high-concentration DMSO feedstock (DMSO content 22.0%–50.0%), which is depolymerized by the scraped-film evaporator and then fed together with the dehydrated low-concentration feedstock into the secondary dehydration tower. The top of the secondary dehydration tower is connected to a wastewater discharge line, and the bottom discharge line is connected to the feed line in the middle of the DMSO purification tower. The top of the DMSO purification tower is connected to the discharge line of the purified DMSO product. While this patent can separate water and DMSO, the separation relies primarily on a two-stage dehydration tower. The separated water and DMSO often fail to meet standards for direct reuse due to excessive impurities. Furthermore, the condensers in both the two-stage dehydration tower and the DMSO purification tower use chilled ethylene glycol, requiring a chilled water system for the recovery unit, which significantly increases investment and operating costs.

[0005] Chinese patent CN110054239A provides a method and apparatus for treating carbon fiber wastewater. The method includes the following steps: the carbon fiber wastewater is fed into a distillation tower to separate dimethyl sulfoxide (DMSO) and acrylonitrile; the separated acrylonitrile is fed into a polymerization reactor to undergo a polymerization reaction; and the separated dimethyl sulfoxide is fed into a rectification tower for purification. First, acrylonitrile and dimethyl sulfoxide in the carbon fiber wastewater are separated by distillation. The separated acrylonitrile is then subjected to self-polymerization, and the dimethyl sulfoxide is concentrated by rectification. This patent provides a method for separating process wastewater containing three components: acrylonitrile, DMSO, and water. However, the separated acrylonitrile, DMSO, and water cannot be directly reused. DMSO and water require subsequent purification processes to ensure reuse, while acrylonitrile is directly incinerated, which is a waste of raw materials.

[0006] Existing methods for recovering dimethyl sulfoxide (DMSO) have various problems, such as high energy consumption during solvent recovery, significant solvent loss, low solvent recovery rate, low purity of recovered solvent or water that cannot be directly reused, and large equipment investment. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention proposes a dimethyl sulfoxide recovery system and method, which can solve the problems of high energy consumption, significant solvent loss, low solvent recovery rate, and low purity of the recovered solvent during the solvent recovery process in carbon fiber production.

[0008] One objective of this invention is to provide a method for recovering dimethyl sulfoxide, comprising dehydrating a dimethyl sulfoxide-containing stream, flash evaporating a solvent, removing heavy metals, and refining the solvent to obtain dimethyl sulfoxide, specifically including the following steps:

[0009] Step 1. After the dimethyl sulfoxide-containing stream is dehydrated in the pre-dehydration tower, solvent flash evaporation is performed;

[0010] Step 2. The liquid phase component obtained by solvent flash evaporation is subjected to degravity flash evaporation treatment;

[0011] Step 3. The gaseous components obtained after the heavy removal flash evaporation treatment and the gaseous components obtained after solvent flash evaporation are fed into the post-dehydration tower for dehydration;

[0012] Step 4. The dimethyl sulfoxide component obtained from the bottom of the dehydration tower after dehydration is sent to the solvent purification tower for purification to obtain pure dimethyl sulfoxide.

[0013] Preferably, the operating steps are as follows: Aqueous, dimethyl sulfoxide (DMSO), and heavy component streams are mixed with pH-adjusting streams and fed into a pre-dehydration tower. Pure water streams are obtained at the top of the tower, and a stream containing aqueous, DMSO, and heavy component streams is obtained at the bottom and fed into a solvent flash tank. The aqueous and DMSO streams obtained at the top of the solvent flash tank are fed into a post-dehydration tower, and the DMSO and heavy component streams obtained at the bottom of the solvent flash tank are fed into a de-heavy flash tank. The aqueous and DMSO streams obtained at the top of the post-dehydration tower are fed into the pre-dehydration tower, and the DMSO stream obtained at the bottom of the post-dehydration tower is fed into a solvent purification tower. Pure DMSO streams are obtained at the top of the solvent purification tower. The DMSO stream obtained at the top of the de-heavy flash tank is fed into the post-dehydration tower, and the heavy component stream obtained at the bottom of the de-heavy flash tank is discharged from the separation system.

[0014] Preferably,

[0015] In the above recovery method, the dimethyl sulfoxide stream in step 1 is subjected to a weak alkalinization treatment before entering the dehydration unit; the alkaline solution used for the weak alkalinization treatment is selected from at least one of sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution, and potassium carbonate solution; the pH of the alkaline solution used for the weak alkalinization treatment is 10-14, preferably 11-14; the pH of the dimethyl sulfoxide stream after the weak alkalinization treatment is 7.01-10, preferably 7.1-9;

[0016] The solvent flash evaporation in step 1 employs at least one set of forced external circulation heating;

[0017] The heavy fraction obtained after the de-gravity flash evaporation treatment in step 2 is separated out of the recycling system;

[0018] The components obtained from the top of the post-dehydration tower after dehydration in step 3 are transported to the pre-dehydration tower.

[0019] The de-gravity flash evaporation in step 2 employs at least two sets of forced external circulation heating, including forced external circulation heating of low-viscosity fluid and forced external circulation heating of high-viscosity fluid. Specifically, the vaporization fraction of the material subjected to forced external circulation heating of low-viscosity fluid is less than or equal to 25 wt%, preferably less than or equal to 20 wt%; the viscosity of the low-viscosity fluid is 1.8–500 cp, preferably 10–500 cp; the vaporization fraction of the material subjected to forced external circulation heating of high-viscosity fluid is less than or equal to 20 wt%, preferably less than or equal to 15 wt%; the viscosity of the high-viscosity fluid is 500–30000 cp, preferably 500–25000 cp.

[0020] In the above recycling method, the dimethyl sulfoxide stream in step 1 contains dimethyl sulfoxide and other impurities, including water and heavy components. By mass percentage, the dimethyl sulfoxide content in the dimethyl sulfoxide stream is 20-30%, the heavy component content is 50-200 PPM, and the water content is 70-80%. The heavy components mainly contain acrylonitrile derivatives, which mainly include acrylonitrile polymers, polyacrylonitrile, and acrylonitrile spinning waste filaments.

[0021] In step 1, the water content in the dimethyl sulfoxide mixture obtained at the bottom of the pre-dehydration tower after dehydration is 0.01–40%, preferably 0.1–35%. The pre-dehydration tower cuts some of the water in the dimethyl sulfoxide mixture to the bottom stream, thereby significantly reducing the solvent content in the water collected from the top of the tower. The purity meets the requirements for direct reuse, and the impurity content in the pure water stream is less than 1 PPB. On the other hand, the pre-dehydration tower only needs to ensure that the water component at the top of the tower is qualified, without the need for precise cutting of both water and solvent components. This greatly reduces the difficulty of operation and has strong practical industrial application value.

[0022] In step 3, the mass percentage of dimethyl sulfoxide (DMSO) in the dimethyl sulfoxide mixture obtained at the top of the dehydration tower after dehydration is 0.01–40%, preferably 0.1–35%. The dehydration tower partially cuts the DMSO solvent to the top stream, significantly reducing the water content in the solvent collected from the bottom. The purity of the DMSO obtained at the top of the solvent purification tower meets the requirements for direct reuse, and the impurity content in the pure DMSO stream is below 5 PPM. Furthermore, the dehydration tower only needs to ensure the solvent components at the bottom are qualified, without requiring precise cutting of both water and solvent components, thus greatly reducing operational difficulty and possessing strong practical industrial application value.

[0023] In the above recycling methods,

[0024] The operating pressure of the aforementioned pre-dehydration tower is 10–200 kPaA, preferably 10–180 kPaA;

[0025] The operating temperature at the top of the aforementioned dehydration tower is 30–150°C, preferably 45–120°C;

[0026] The operating pressure of the post-dehydration tower is 2-15 kPaA, preferably 2-12 kPaA;

[0027] The operating temperature at the top of the post-dehydration tower is 30–100°C, preferably 40–85°C;

[0028] The solvent purification tower operates at a pressure of 2–14 kPaA, preferably 2–12 kPaA;

[0029] The operating temperature at the top of the solvent refining tower is 60–150°C, preferably 75–125°C;

[0030] The vaporization fraction of the solvent flash tank with forced external circulation heating is less than or equal to 30 wt%, preferably less than or equal to 26 wt%.

[0031] The second objective of this invention is to provide a dimethyl sulfoxide recovery system, characterized in that the dimethyl sulfoxide is recovered using the above-described dimethyl sulfoxide recovery method.

[0032] Specifically, the recovery system includes a pre-dehydration tower, a solvent flash tank, a de-gravity flash tank, a post-dehydration tower, and a solvent refining tower connected in sequence.

[0033] The solvent flash tank is connected to the top of the post-dehydration tower; the solvent flash tank is equipped with at least one forced external circulation heating system. The vaporization fraction of the solvent flash tank's forced external circulation heating system is less than or equal to 30 wt%, preferably less than or equal to 26 wt%. The operating pressure of the solvent flash tank is determined by the operating pressure of the post-dehydration tower. Because the gas phase at the top of the solvent flash tank is directly connected to the post-dehydration tower, the operating pressure of the solvent flash tank only needs to be slightly higher than the pressure at the inlet of the post-dehydration tower. The solvent flash tank's top stream enters the post-dehydration tower directly in gaseous form, which significantly reduces the energy consumption of both the solvent flash tank and the post-dehydration tower, and saves on equipment investment. The solvent flash tank used in this invention avoids the problem of reboiler operation difficulties under high vacuum conditions, allowing for flexible adjustment of the reboiler feed flow rate and vaporization fraction, adapting to various operating conditions.

[0034] The top of the de-weight flash tank is connected to the post-dehydration tower; the de-weight flash tank is equipped with at least two sets of forced external circulation heating systems; the forced external circulation heating systems configured in the de-weight flash tank include a low-viscosity fluid forced external circulation heating system and a high-viscosity fluid forced external circulation heating system. The vaporization fraction of the material in the low-viscosity fluid forced external circulation heating system of the de-weight flash tank is less than or equal to 25 wt%, preferably less than or equal to 20 wt%; the vaporization fraction of the material in the high-viscosity fluid forced external circulation heating system of the de-weight flash tank is less than or equal to 20 wt%, preferably less than or equal to 15 wt%. The viscosity of the low-viscosity fluid is 1.8–500 cp, preferably 10–500 cp; the viscosity of the high-viscosity fluid is 500–30000 cp, preferably 500–25000 cp. The forced external circulation heating system for low-viscosity fluids is mainly used when there is a large amount of solvent and the viscosity of the fluid in the deweighting flash tank is low. Low-viscosity fluids circulate at high speeds, resulting in a high vaporization rate and rapid solvent evaporation. The heat exchanger is a standard heat exchanger; forced external circulation heating causes solvent vaporization, continuously recovering the solvent and reducing its concentration in the deweighting flash tank, thus increasing the polymer concentration within the solvent. The forced external circulation heating system for high-viscosity fluids is used when there is a large polymer content and high fluid viscosity in the deweighting flash tank. High-viscosity fluids circulate at slower speeds, resulting in a lower vaporization rate and slower solvent evaporation. The heat exchanger tubes can be equipped with mixing components to enhance heat and mass transfer, ensuring uniform heating of the high-viscosity fluid and avoiding localized overheating and uneven heating caused by the decreased heat transfer coefficient due to high viscosity. Forced external circulation heating further vaporizes the solvent, increasing and concentrating the polymer concentration, thus further recovering the solvent and reducing solvent loss. In the de-gravity flash evaporator, an online viscometer can be used to monitor the fluid viscosity in real time. Based on the fluid viscosity value, either a forced external circulation heating system for low-viscosity fluids or a forced external circulation heating system for high-viscosity fluids can be selected. In the later stages of de-gravity flash evaporation, the solvent content in the fluid gradually decreases, and the fluid viscosity gradually increases. When it reaches 30,000 cp, it meets the discharge requirements.

[0035] The operating pressure of the de-weight flash tank is determined by the operating pressure of the subsequent dehydration tower. Since the gas phase at the top of the de-weight flash tank is directly connected to the subsequent dehydration tower, the operating pressure of the de-weight flash tank only needs to be slightly higher than the pressure at the feed inlet of the subsequent dehydration tower, so that the material at the top of the de-weight flash tank enters the subsequent dehydration tower directly in the form of gas.

[0036] In the above-mentioned recovery system, all the top condensers of the distillation columns use inexpensive circulating cooling water as the refrigerant, instead of using more expensive and costly chilled water. This technology has broad adaptability and practical industrial application value.

[0037] A third objective of this invention is to provide a dimethyl sulfoxide solvent, obtained using the aforementioned dimethyl sulfoxide recovery method or system. The impurity content in the dimethyl sulfoxide solvent is less than 5 PPM by mass percentage.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] 1. The recovery method provided by this invention has the advantages of low energy consumption, small solvent loss, high solvent recovery rate, and high purity of recovered solvent.

[0040] 2. This invention does not require the use of circulating chilled water as a refrigerant, is inexpensive, requires less investment, has wide technical adaptability, and has practical industrial application value;

[0041] 3. This invention uses a deweight flash tank to deweight the fluid and is equipped with different forced external circulation heating systems, which can further recover the solvent and reduce solvent loss;

[0042] 4. In this invention, the pre-dehydration tower and post-dehydration tower do not require precise separation of water and solvent components, which greatly reduces the difficulty of operation and has strong practical industrial application value. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of a dimethyl sulfoxide recovery system. Figure 1 The symbols are as follows:

[0044] 1. Contains water, dimethyl sulfoxide, and heavy components.

[0045] 2. pH adjustment of the material (using an alkaline solution for weak alkalinization treatment)

[0046] 3. Pure water logistics (top discharge logistics from the front dehydration tower)

[0047] 4. Stream containing water, dimethyl sulfoxide, and heavy components (bottom discharge stream from the pre-dehydration tower)

[0048] 5. Solvent flash tank bottom discharge logistics

[0049] 6 Solvent flash tank external circulation heater feed flow

[0050] 7. Solvent flash tank external circulation heater discharge material flow

[0051] 8 containing dimethyl sulfoxide and heavy components

[0052] 9. Stream containing water and dimethyl sulfoxide (top discharge stream from solvent flash tank)

[0053] 10. Stream containing water and dimethyl sulfoxide (top discharge stream from the post-dehydration tower)

[0054] 11. Dimethyl sulfoxide-containing stream (bottom discharge stream from the post-dehydration tower)

[0055] 12% pure dimethyl sulfoxide (top discharge from solvent refining tower)

[0056] 13. Solvent Refining Tower Bottom Discharge Flow

[0057] 14 Top discharge logistics of the de-gravity flash evaporator

[0058] 15 De-gravity flash tank bottom discharge logistics

[0059] 16. De-weighting flash tank external circulation heater - booster pump feed material flow

[0060] 17. De-gravity flash tank external circulation heater - feed flow

[0061] 18 De-weighting flash tank external circulation heater - discharge logistics

[0062] 19. De-weighting flash tank, external circulation heater, booster pump, and feed logistics.

[0063] 20 De-weighting flash tank external circulation heater two feed logistics

[0064] 21. De-weighting flash tank external circulation heater II. Discharge logistics

[0065] 22 including reorganized logistics

[0066] A front dehydration tower

[0067] B Solvent Flash Evaporator

[0068] C solvent flash tank external circulation booster pump

[0069] D Solvent Flash Tank External Circulation Heater

[0070] E Post-dehydration tower

[0071] F Solvent Purification Tower

[0072] G De-weighting Flash Tank

[0073] H De-weighting flash tank external circulation heater - booster pump

[0074] J-type deweight flash tank external circulation heater II booster pump

[0075] K-Deweight Flash Tank External Circulation Heater II

[0076] L-type de-weighting flash tank external circulation heater Detailed Implementation

[0077] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0078] The raw materials used and their sources in the examples are as follows:

[0079] Alkaline compounds in pH-adjusted logistics: Commercially available sodium hydroxide is used.

[0080] The testing methods used in this embodiment are as follows:

[0081] Determination of essential moisture and dimethyl sulfoxide: Refractometer was used for determination.

[0082] Determination of trace moisture and dimethyl sulfoxide: Gas chromatography was used for determination;

[0083] Polymer determination: The determination was performed by weighing.

[0084] Test method for vaporization fraction: Measured using a vaporization fraction detector;

[0085] Method for calculating the recovery rate of dimethyl sulfoxide:

[0086] Recovery rate = (Dimethyl sulfoxide in stream 1 - Dimethyl sulfoxide discharged from the system in stream 22) / Dimethyl sulfoxide in stream 1 * 100%

[0087]

Example 1

[0088] The dimethyl sulfoxide recovery system and recovery method provided by the present invention will be described below with reference to the accompanying drawings.

[0089] like Figure 1As shown, the dimethyl sulfoxide (DMSO) recovery system includes a pre-dehydration tower A, a solvent flash tank B, a de-heavy flash tank G, a post-dehydration tower E, and a solvent purification tower F connected in sequence. The aqueous, DMSO, and heavy component stream 1 is mixed with pH-adjusted stream 2 (sodium hydroxide solution with pH 13) to obtain a DMSO stream with pH 10, which is then fed into the pre-dehydration tower A. At the top of the pre-dehydration tower A, a pure water stream 3 is obtained, and at the bottom, a stream containing aqueous, DMSO, and heavy components 4 is obtained and fed into the solvent flash tank B. The aqueous and DMSO stream 9 obtained from the top of the solvent flash tank B is fed into the post-dehydration tower E, and the DMSO and heavy component stream 8 obtained from the bottom of the solvent flash tank B is fed into the de-heavy flash tank G. The external circulation heater D of the solvent flash tank B is fed by the external circulation booster pump C, and the vaporized stream 7 enters the upper part of the solvent flash tank. The aqueous and dimethyl sulfoxide stream 10 obtained from the top of the post-dehydration tower E is sent to the pre-dehydration tower A, and the dimethyl sulfoxide stream 11 obtained from the bottom of the post-dehydration tower E is sent to the solvent purification tower F. The pure dimethyl sulfoxide stream 12 obtained from the top of the solvent purification tower F and the stream 13 containing a small amount of heavy components obtained from the bottom are discharged from the separation system continuously or intermittently at a low flow rate, or they can be sent to the de-heavy flash evaporator to flash and recover the solvent. The dimethyl sulfoxide-containing stream 14 obtained from the top of the heavy-duty flash tank G is sent to the dehydration tower E, and the heavy-duty stream 22 obtained from the bottom of the heavy-duty flash tank G is sent out of the separation system. The external circulation heater L of the heavy-duty flash tank G (a forced external circulation heating system for low-viscosity fluids) is fed by the external circulation booster pump H of the heavy-duty flash tank G, and the vaporized stream 18 enters the upper part of the heavy-duty flash tank G. The external circulation heater K of the heavy-duty flash tank G (a forced external circulation heating system for high-viscosity fluids) is fed by the external circulation booster pump J of the heavy-duty flash tank G, and the vaporized stream 21 enters the upper part of the heavy-duty flash tank G. The fluid viscosity is monitored in real time using an online viscometer inside the deweighting flash tank. When the fluid viscosity is 50 cp, heater L and booster pump H are turned on. When the fluid viscosity reaches 5000 cp, heater K and booster pump J are turned on. In the later stage of deweighting flash evaporation, the solvent content in the fluid gradually decreases, and the fluid viscosity gradually increases. When it reaches 30000 cp, it meets the discharge requirements.

[0090] Taking a 100-ton-level carbon fiber production unit as an example, the process water produced by the unit contains 75 wt% water, 25 wt% solvent, and 150 PPM polymer by weight percentage.

[0091] like Figure 1 As shown, the operating pressure of the front dehydration tower is 10 kPaA, and the corresponding operating temperature at the top of the front dehydration tower is 45.7℃; the operating pressure of the rear dehydration tower is 2 kPaA, and the corresponding operating temperature at the top of the rear dehydration tower is 46.6℃; the operating pressure of the solvent purification tower is 2 kPaA, and the corresponding operating temperature at the top of the solvent purification tower is 80.1℃.

[0092] By weight percentage, water accounts for 0.07% in filtrate 4, and dimethyl sulfoxide accounts for 33.34% in filtrate 10.

[0093] By weight percentage, the vaporization rate of Logistics 7 was 25.9%, Logistics 18 was 19.5%, and Logistics 21 was 14.0%.

[0094] The reboiler in the full separation process consumes 565.3 kW. The dimethyl sulfoxide recovery rate is >99.96%, the water recovery rate is >99.96%, the impurity content of the pure water stream 3 from the top of the pre-dehydration tower is <1 PPB, and the impurity content of the pure dimethyl sulfoxide stream 12 from the top of the solvent purification tower is 2268 PPB, which is less than 1 PPM. The purity of both the pure water stream and the pure dimethyl sulfoxide stream meets the direct reuse index of ≤200 PPM and can be directly reused.

[0095]

Example 2

[0096] The recycling system and operating procedures in Example 2 are the same as those in Example 1, with the specific operating conditions as follows:

[0097] like Figure 1 As shown, the operating pressure of the front dehydration tower is 10 kPaA, and the corresponding operating temperature at the top of the front dehydration tower is 45.7℃; the operating pressure of the rear dehydration tower is 2 kPaA, and the corresponding operating temperature at the top of the rear dehydration tower is 46.6℃; the operating pressure of the solvent purification tower is 2 kPaA, and the corresponding operating temperature at the top of the solvent purification tower is 80.1℃.

[0098] By weight percentage, water accounts for 0.07% in filtrate 4, and dimethyl sulfoxide accounts for 33.34% in filtrate 10.

[0099] By weight percentage, the vaporization rate of Logistics 7 was 20.7%, the vaporization rate of Logistics 18 was 15.0%, and the vaporization rate of Logistics 21 was 10.0%.

[0100] The reboiler in the full separation process consumes 565.3 kW. The dimethyl sulfoxide recovery rate is >99.96%, and the water recovery rate is >99.96%. The impurity content of the pure water stream 3 from the top of the pre-dehydration tower is <1 PPB, and the impurity content of the pure dimethyl sulfoxide stream 12 from the top of the solvent purification tower is 2284 PPB, which is less than 1 PPM. The purity of both the pure water stream and the pure dimethyl sulfoxide stream meets the direct reuse index of ≤200 PPM and can be directly reused.

[0101]

Example 3

[0102] The recycling system and operating procedures in Example 3 are the same as those in Example 1, with the specific operating conditions as follows:

[0103] like Figure 1As shown, the operating pressure of the front dehydration tower is 10 kPaA, and the corresponding operating temperature at the top of the front dehydration tower is 45.7℃; the operating pressure of the rear dehydration tower is 2 kPaA, and the corresponding operating temperature at the top of the rear dehydration tower is 46.6℃; the operating pressure of the solvent purification tower is 2 kPaA, and the corresponding operating temperature at the top of the solvent purification tower is 80.1℃.

[0104] By weight percentage, water accounts for 0.07% in filtrate 4, and dimethyl sulfoxide accounts for 33.34% in filtrate 10.

[0105] By weight percentage, the vaporization rate of Logistics 7 was 15.6%, the vaporization rate of Logistics 18 was 10.2%, and the vaporization rate of Logistics 21 was 6.3%.

[0106] The reboiler in the full separation process consumes 565.3 kW. The dimethyl sulfoxide recovery rate is >99.96%, and the water recovery rate is >99.96%. The impurity content of the pure water stream 3 from the top of the pre-dehydration tower is <1 PPB, and the impurity content of the pure dimethyl sulfoxide stream 12 from the top of the solvent purification tower is 2284 PPB, which is less than 1 PPM. The purity of both the pure water stream and the pure dimethyl sulfoxide stream meets the direct reuse index of ≤200 PPM and can be directly reused.

[0107]

Example 4

[0108] The recycling system and operating procedures in Example 4 are the same as those in Example 1, with the specific operating conditions as follows:

[0109] like Figure 1 As shown, the operating pressure of the front dehydration tower is 10 kPaA, and the corresponding operating temperature at the top of the front dehydration tower is 45.7℃; the operating pressure of the rear dehydration tower is 2 kPaA, and the corresponding operating temperature at the top of the rear dehydration tower is 46.6℃; the operating pressure of the solvent purification tower is 2 kPaA, and the corresponding operating temperature at the top of the solvent purification tower is 80.1℃.

[0110] By weight percentage, water accounts for 0.07% in filtrate 4, and dimethyl sulfoxide accounts for 33.34% in filtrate 10.

[0111] By weight percentage, the vaporization rate of Logistics 7 was 10.4%, Logistics 18 was 6.1%, and Logistics 21 was 3.2%.

[0112] The reboiler in the full separation process consumes 565.2 kW. The dimethyl sulfoxide recovery rate is >99.96%, and the water recovery rate is >99.96%. The impurity content of the pure water stream 3 from the top of the pre-dehydration tower is <1 PPB, and the impurity content of the pure dimethyl sulfoxide stream 12 from the top of the solvent purification tower is 2285 PPB, which is less than 1 PPM. The purity of both the pure water stream and the pure dimethyl sulfoxide stream meets the direct reuse index of ≤200 PPM and can be directly reused.

[0113]

Example 5

[0114] The recycling system and operating procedures in Example 5 are the same as those in Example 1, with the specific operating conditions as follows:

[0115] like Figure 1 As shown, the operating pressure of the front dehydration tower is 10 kPaA, and the corresponding operating temperature at the top of the front dehydration tower is 45.7℃; the operating pressure of the rear dehydration tower is 2 kPaA, and the corresponding operating temperature at the top of the rear dehydration tower is 46.6℃; the operating pressure of the solvent purification tower is 2 kPaA, and the corresponding operating temperature at the top of the solvent purification tower is 80.1℃.

[0116] By weight percentage, water accounts for 0.07% in filtrate 4, and dimethyl sulfoxide accounts for 33.34% in filtrate 10.

[0117] By weight percentage, the vaporization rate of Logistics 7 was 5.2%, the vaporization rate of Logistics 18 was 3.3%, and the vaporization rate of Logistics 21 was 2.5%.

[0118] The reboiler in the full separation process consumes 565.2 kW. The dimethyl sulfoxide recovery rate is >99.96%, the water recovery rate is >99.96%, the impurity content of the pure water stream 3 from the top of the pre-dehydration tower is <1 PPB, and the impurity content of the pure dimethyl sulfoxide stream 12 from the top of the solvent purification tower is 2284 PPB, which is less than 1 PPM. The purity of both the pure water stream and the pure dimethyl sulfoxide stream meets the direct reuse index of ≤200 PPM and can be directly reused.

[0119]

Example 6

[0120] The recycling system and operating procedure in Example 6 are the same as those in Example 1, with the specific operating conditions as follows:

[0121] like Figure 1 As shown, the operating pressure of the front dehydration tower is 10 kPaA, and the corresponding operating temperature at the top of the front dehydration tower is 45.7℃; the operating pressure of the rear dehydration tower is 2 kPaA, and the corresponding operating temperature at the top of the rear dehydration tower is 46.6℃; the operating pressure of the solvent purification tower is 2 kPaA, and the corresponding operating temperature at the top of the solvent purification tower is 80.1℃.

[0122] By weight percentage, water accounts for 0.07% in filtrate 4, and dimethyl sulfoxide accounts for 33.34% in filtrate 10.

[0123] By weight percentage, the vaporization rate of Logistics 7 is 1.5%, the vaporization rate of Logistics 18 is 1.0%, and the vaporization rate of Logistics 21 is 0.9%.

[0124] The reboiler in the full separation process consumes 565.3 kW. The dimethyl sulfoxide recovery rate is >99.96%, and the water recovery rate is >99.96%. The impurity content of the pure water stream 3 from the top of the pre-dehydration tower is <1 PPB, and the impurity content of the pure dimethyl sulfoxide stream 12 from the top of the solvent purification tower is 2285 PPB, which is less than 1 PPM. The purity of both the pure water stream and the pure dimethyl sulfoxide stream meets the direct reuse index of ≤200 PPM and can be directly reused.

[0125] [Examples 1] to [Examples 6] By changing the vaporization fraction of materials 7, 18, and 21 while keeping other parameters unchanged, it can be seen that the change in vaporization fraction has little impact on energy consumption, recovery rate, and the purity of pure water and pure dimethyl sulfoxide materials. This is because the total amount of material to be vaporized is constant. The change in vaporization fraction only affects the flow rate into the external circulation heater and does not significantly change the load on the external circulation heater. If the vaporization fraction is too low, the external circulation volume will increase exponentially, which will increase the flow rate of the external circulation heater booster pump, thereby correspondingly increasing operating costs and equipment investment.

[0126]

Example 7

[0127] The recycling system and operating procedure in Example 7 are the same as those in Example 3, and the specific operating conditions are as follows:

[0128] like Figure 1 As shown, the operating pressure of the front dehydration tower is 30 kPaA, and the corresponding operating temperature at the top of the front dehydration tower is 69.1℃; the operating pressure of the rear dehydration tower is 4 kPaA, and the corresponding operating temperature at the top of the rear dehydration tower is 40.2℃; the operating pressure of the solvent purification tower is 4 kPaA, and the corresponding operating temperature at the top of the solvent purification tower is 95.1℃.

[0129] By weight percentage, water accounts for 1.04% in filtrate 4 and dimethyl sulfoxide accounts for 3.24% in filtrate 10.

[0130] By weight percentage, the vaporization rate of Logistics 7 was 15.6%, the vaporization rate of Logistics 18 was 10.2%, and the vaporization rate of Logistics 21 was 6.3%.

[0131] The reboiler in the full separation process consumes 547.7 kW. The dimethyl sulfoxide recovery rate is >99.96%, and the water recovery rate is >99.96%. The impurity content of the pure water stream 3 from the top of the pre-dehydration tower is <1 PPB, and the impurity content of the pure dimethyl sulfoxide stream 12 from the top of the solvent purification tower is 0.26 PPM, which is less than 1 PPM. The purity of both the pure water stream and the pure dimethyl sulfoxide stream meets the direct reuse index of ≤200 PPM and can be directly reused.

[0132]

Example 8

[0133] The recycling system and operating procedure in Example 8 are the same as those in Example 3, with the specific operating conditions as follows:

[0134] like Figure 1 As shown, the operating pressure of the front dehydration tower is 60 kPaA, and the corresponding operating temperature at the top of the front dehydration tower is 86.0℃; the operating pressure of the rear dehydration tower is 6 kPaA, and the corresponding operating temperature at the top of the rear dehydration tower is 56.6℃; the operating pressure of the solvent purification tower is 6 kPaA, and the corresponding operating temperature at the top of the solvent purification tower is 104.6℃.

[0135] By weight percentage, water accounts for 8.81% in filtrate 4 and dimethyl sulfoxide accounts for 12.54% in filtrate 10.

[0136] By weight percentage, the vaporization rate of Logistics 7 was 15.6%, the vaporization rate of Logistics 18 was 10.2%, and the vaporization rate of Logistics 21 was 6.3%.

[0137] The reboiler in the full separation process consumes 570.2 kW. The dimethyl sulfoxide recovery rate is >99.96%, the water recovery rate is >99.96%, the impurity content of the pure water stream 3 from the top of the pre-dehydration tower is <1 PPB, and the impurity content of the pure dimethyl sulfoxide stream 12 from the top of the solvent purification tower is 0.85 PPM, which is less than 1 PPM. The purity of both the pure water stream and the pure dimethyl sulfoxide stream meets the direct reuse index of ≤200 PPM and can be directly reused.

[0138]

Example 9

[0139] The recycling system and operating procedure in Example 9 are the same as those in Example 3, with the specific operating conditions as follows:

[0140] like Figure 1 As shown, the operating pressure of the front dehydration tower is 90 kPaA, and the corresponding operating temperature at the top of the front dehydration tower is 96.8℃; the operating pressure of the rear dehydration tower is 8 kPaA, and the corresponding operating temperature at the top of the rear dehydration tower is 65.5℃; the operating pressure of the solvent purification tower is 8 kPaA, and the corresponding operating temperature at the top of the solvent purification tower is 111.7℃.

[0141] By weight percentage, water accounts for 15.82% in filtrate 4 and dimethyl sulfoxide accounts for 17.68% in filtrate 10.

[0142] By weight percentage, the vaporization rate of Logistics 7 was 15.6%, the vaporization rate of Logistics 18 was 10.2%, and the vaporization rate of Logistics 21 was 6.3%.

[0143] The reboiler in the full separation process consumes 611.3 kW. The dimethyl sulfoxide recovery rate is >99.96%, the water recovery rate is >99.96%, the impurity content of the pure water stream 3 from the top of the pre-dehydration tower is <1 PPB, and the impurity content of the pure dimethyl sulfoxide stream 12 from the top of the solvent purification tower is 0.47 PPM, which is less than 1 PPM. The purity of both the pure water stream and the pure dimethyl sulfoxide stream meets the direct reuse index of ≤200 PPM and can be directly reused.

[0144]

Example 10

[0145] The recycling system and operating procedure in Example 10 are the same as those in Example 3, with the specific operating conditions as follows:

[0146] like Figure 1 As shown, the operating pressure of the front dehydration tower is 130 kPaA, and the corresponding operating temperature at the top of the front dehydration tower is 107.2℃; the operating pressure of the rear dehydration tower is 10 kPaA, and the corresponding operating temperature at the top of the rear dehydration tower is 72.6℃; the operating pressure of the solvent purification tower is 10 kPaA, and the corresponding operating temperature at the top of the solvent purification tower is 117.4℃.

[0147] By weight percentage, water accounts for 21.32% in filtrate 4 and dimethyl sulfoxide accounts for 22.25% in filtrate 10.

[0148] By weight percentage, the vaporization rate of Logistics 7 was 15.6%, the vaporization rate of Logistics 18 was 10.2%, and the vaporization rate of Logistics 21 was 6.3%.

[0149] The reboiler in the full separation process consumes 629.4 kW. The dimethyl sulfoxide recovery rate is >99.96%, the water recovery rate is >99.96%, the impurity content of the pure water stream 3 from the top of the pre-dehydration tower is <1 PPB, and the impurity content of the pure dimethyl sulfoxide stream 12 from the top of the solvent purification tower is 0.63 PPM, which is less than 1 PPM. The purity of both the pure water stream and the pure dimethyl sulfoxide stream meets the direct reuse index of ≤200 PPM and can be directly reused.

[0150]

Example 11

[0151] The recycling system and operating procedures in Example 11 are the same as those in Example 3, with the specific operating conditions as follows:

[0152] like Figure 1 As shown, the operating pressure of the front dehydration tower is 180 kPaA, and the corresponding operating temperature at the top of the front dehydration tower is 117.0℃; the operating pressure of the rear dehydration tower is 12 kPaA, and the corresponding operating temperature at the top of the rear dehydration tower is 82.4℃; the operating pressure of the solvent purification tower is 11 kPaA, and the corresponding operating temperature at the top of the solvent purification tower is 119.9℃.

[0153] By weight percentage, water accounts for 24.67% of filtrate 4, and dimethyl sulfoxide accounts for 33.36% of filtrate 10.

[0154] By weight percentage, the vaporization rate of Logistics 7 was 15.6%, the vaporization rate of Logistics 18 was 10.2%, and the vaporization rate of Logistics 21 was 6.3%.

[0155] The reboiler in the full separation process consumes 673.5 kW. The dimethyl sulfoxide recovery rate is >99.96%, the water recovery rate is >99.96%, the impurity content of the pure water stream 3 from the top of the pre-dehydration tower is <1 PPB, and the impurity content of the pure dimethyl sulfoxide stream 12 from the top of the solvent purification tower is 0.38 PPM, which is less than 1 PPM. The purity of both the pure water stream and the pure dimethyl sulfoxide stream meets the direct reuse index of ≤200 PPM and can be directly reused.

[0156]

Example 12

[0157] The recycling system and operating procedures in [Example 12] are the same as those in [Example 3], and the specific operating conditions are as follows:

[0158] like Figure 1 As shown, the operating pressure of the front dehydration tower is 180 kPaA, and the corresponding operating temperature at the top of the front dehydration tower is 117.0℃; the operating pressure of the rear dehydration tower is 12 kPaA, and the corresponding operating temperature at the top of the rear dehydration tower is 79.9℃; the operating pressure of the solvent purification tower is 11 kPaA, and the corresponding operating temperature at the top of the solvent purification tower is 119.9℃.

[0159] By weight percentage, water accounts for 29.05% in filtrate 4 and dimethyl sulfoxide accounts for 28.59% in filtrate 10.

[0160] By weight percentage, the vaporization rate of Logistics 7 was 15.6%, the vaporization rate of Logistics 18 was 10.2%, and the vaporization rate of Logistics 21 was 6.3%.

[0161] The reboiler in the full separation process consumes 690.3 kW. The dimethyl sulfoxide recovery rate is >99.96%, the water recovery rate is >99.96%, the impurity content of the pure water stream 3 from the top of the pre-dehydration tower is <1 PPB, and the impurity content of the pure dimethyl sulfoxide stream 12 from the top of the solvent purification tower is 0.41 PPM, which is less than 1 PPM. The purity of both the pure water stream and the pure dimethyl sulfoxide stream meets the direct reuse index of ≤200 PPM and can be directly reused.

[0162] As can be seen from Examples 7-12 above, as the operating pressure of the recovery system gradually increases, the reboiler energy consumption of the entire separation process gradually increases. However, due to the gradual increase in operating pressure, the temperature difference between the heat exchanger at the top of the column and the circulating cooling water gradually increases, and the size of the heat exchanger at the top of the column gradually decreases, which will correspondingly reduce equipment investment. In addition, the impurity content of the pure dimethyl sulfoxide stream 12 discharged from the top of the solvent refining column gradually decreases.

[0163] Comparative Example 1

[0164] According to the method described in Chinese Patent CN102225904A, dimethyl sulfoxide (DMSO) separation is performed. The impurity content in both the separated water and DMSO is greater than 500 PPM, and the DMSO recovery rate is between 95% and 98%. Therefore, it cannot be directly reused and requires additional equipment to purify the water and DMSO. The energy consumption of the reboiler in the entire process is comparable to that of the present invention, but due to the need for an additional chilled water system, the investment is approximately 20% greater than that of the present invention.

[0165] Comparative Example 2

[0166] According to the method described in Chinese patent CN 110054239A, dimethyl sulfoxide was separated. The impurity content in both the separated water and dimethyl sulfoxide was greater than 500 PPM. The recovery rate of dimethyl sulfoxide was between 92% and 96%, which means it could not be directly reused. Additional equipment was needed to purify the water and dimethyl sulfoxide.

[0167] As can be seen from the above embodiments, compared with Comparative Examples 1 and 2, the dimethyl sulfoxide recovery method provided in Examples 1 to 12 of the present invention has lower energy consumption, less solvent loss, higher solvent recovery rate, and higher purity of recovered solvent. The recovered dimethyl sulfoxide solvent can be directly reused. Moreover, the present invention does not require the use of circulating chilled water as a refrigerant, is inexpensive, requires less investment, has wide technical adaptability, and has practical industrial application value.

Claims

1. A method for recovering dimethyl sulfoxide, comprising: subjecting a dimethyl sulfoxide-containing stream to a dehydration treatment, a solvent flashing, a heavy component removal treatment, and a solvent refining to obtain dimethyl sulfoxide, wherein the dimethyl sulfoxide-containing stream is subjected to a weak alkalization treatment before the dehydration treatment. The method for recovering dimethyl sulfoxide specifically comprises the following steps: Step 1. Subjecting the dimethyl sulfoxide-containing stream to a dehydration treatment in a front dehydration tower, and then subjecting the stream to a solvent flashing; Step 2. Subjecting the liquid-phase component obtained in the solvent flashing to a heavy component removal flashing treatment; Step 3. Subjecting the gas-phase component obtained in the heavy component removal flashing treatment and the gas-phase component obtained in the solvent flashing to a dehydration treatment in a rear dehydration tower; Step 4. Subjecting the dimethyl sulfoxide-containing component obtained at the bottom of the rear dehydration tower to a solvent refining in a solvent refining tower to obtain pure dimethyl sulfoxide. The solvent flashing in Step 1 is subjected to at least one set of forced external circulation heating, and the stream subjected to the forced external circulation heating in the solvent flashing has a vaporization fraction of 30 wt% or less; the heavy component removal flashing in Step 2 is subjected to at least two sets of forced external circulation heating, and the forced external circulation heating in the heavy component removal flashing includes low-viscosity fluid forced external circulation heating and high-viscosity fluid forced external circulation heating, the stream subjected to the low-viscosity fluid forced external circulation heating has a vaporization fraction of 25 wt% or less, and the stream subjected to the high-viscosity fluid forced external circulation heating has a vaporization fraction of 20 wt% or less; and the solvent refining tower has a top operating temperature of 60-150℃. 2.The method for recovering dimethyl sulfoxide according to claim 1, wherein the dimethyl sulfoxide-containing stream in Step 1 is subjected to a weak alkalization treatment before being subjected to the dehydration treatment; and / or the heavy component stream obtained after the heavy component removal flashing treatment in Step 2 is separated and discharged; and / or the component obtained at the top of the rear dehydration tower in Step 3 is sent to the front dehydration tower. 3.The method for recovering dimethyl sulfoxide according to claim 2, wherein the alkaline solution used in the weak alkalization treatment is at least one selected from the group consisting of sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution, and potassium carbonate solution; and / or the alkaline solution used in the weak alkalization treatment has a pH of 10-14; and / or the dimethyl sulfoxide-containing stream after the weak alkalization treatment has a pH of 7.01-10. 4.The method for recovering dimethyl sulfoxide according to claim 3, wherein the alkaline solution used in the weak alkalization treatment has a pH of 11-14; and / or the dimethyl sulfoxide-containing stream after the weak alkalization treatment has a pH of 7.1-9. 5.The method for recovering dimethyl sulfoxide according to claim 1, wherein the low-viscosity fluid has a viscosity of 1.8-500 cp; and / or the high-viscosity fluid has a viscosity of 500-30000 cp. 6.The method for recovering dimethyl sulfoxide according to claim 5, wherein the low-viscosity fluid has a viscosity of 10-500 cp; and / or the stream subjected to the low-viscosity fluid forced external circulation heating has a vaporization fraction of 20 wt% or less; and / or the high-viscosity fluid has a viscosity of 500-25000 cp; and / or ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The vaporization fraction of the solvent flash forced external circulation heating stream is less than or equal to 26wt%.

7. The recovery method according to claim 1, wherein, The dimethyl sulfoxide stream in step 1 contains dimethyl sulfoxide and other impurities, and the other impurities include water and heavy components; and / or, The mass percentage of water in the dimethyl sulfoxide mixture obtained from the bottom of the pre-dehydration tower in step 1 is 0.01-40%; and / or, The mass percentage of dimethyl sulfoxide in the dimethyl sulfoxide mixture obtained from the top of the post-dehydration tower in step 3 is 0.01-40%.

8. The recovery method according to claim 7, wherein, The mass percentage of water in the dimethyl sulfoxide mixture obtained from the bottom of the pre-dehydration tower in step 1 is 0.1-35%; and / or, The mass percentage of dimethyl sulfoxide in the dimethyl sulfoxide mixture obtained from the top of the post-dehydration tower in step 3 is 0.1-35%.

9. The recovery method according to claim 7, wherein, In step 1, the mass percentage of dimethyl sulfoxide in the dimethyl sulfoxide stream is 20-30%, the mass percentage of heavy components is 50-200 PPM, and the mass percentage of water is 70-80%.

10. The recovery method according to claim 1, wherein, The operating pressure of the pre-dehydration tower is 10-200 KPaA; and / or, The operating temperature at the top of the pre-dehydration tower is 30-150℃; and / or, The operating pressure of the post-dehydration tower is 2-15 KPaA; and / or, The operating temperature at the top of the post-dehydration tower is 30-100℃; and / or The operating pressure of the solvent refining tower is 2-14 KPaA.

11. The recovery method according to claim 10, wherein, The operating pressure of the pre-dehydration tower is 10-180 KPaA; and / or, The operating temperature at the top of the pre-dehydration tower is 45-120℃; and / or, The operating pressure of the post-dehydration tower is 2-12 KPaA; and / or, The operating temperature at the top of the post-dehydration tower is 40-85℃; and / or The operating pressure of the solvent refining tower is 2-12 KPaA; and / or, The operating temperature at the top of the solvent refining tower is 75-125℃; and / or, The vaporization fraction of the solvent flash forced external circulation heating stream is less than or equal to 26wt%.

12. A dimethyl sulfoxide recovery system characterized by, The dimethyl sulfoxide recovery method according to any one of claims 1-11 is used to recover dimethyl sulfoxide.

13. The recycling system of claim 12, wherein, The recovery system comprises a pre-dehydration tower, a solvent flash tank, a heavy component removal flash tank, a post-dehydration tower and a solvent refining tower connected in sequence.

14. The recovery system according to claim 13, wherein, The top of the solvent flash tank is communicated with the post-dehydration tower; and / or, The solvent flash tank is provided with at least one set of forced external circulation heating system; and / or, The top of the heavy component removal flash tank is communicated with the post-dehydration tower; and / or, The heavy component removal flash tank is provided with at least two sets of forced external circulation heating system.

15. The recovery system according to claim 14, wherein, The forced external circulation heating system of the heavy flash tank arrangement includes a low viscosity fluid forced external circulation heating system and a high viscosity fluid forced external circulation heating system.

16. The dimethyl sulfoxide recovery system of any one of claims 12-15, wherein, The obtained dimethyl sulfoxide solvent has impurity content less than 5 PPM in terms of mass percentage.

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