Recycling process of carbon fiber production waste liquid

Abstract

The invention discloses a carbon fiber production waste liquid recycling process, which comprises: (1) inputting a waste liquid containing acrylonitrile and dimethyl sulfoxide into an acrylonitrile recovery tower, controlling the pressure and the temperature, enabling acrylonitrile and a part of water to form a gas phase, and separating the gas phase from the tower top to obtain dimethyl sulfoxide and water at the tower bottom; (2) dimethyl sulfoxide and water at the bottom of the acrylonitrile recovery tower sequentially enter a first-stage dehydrating tower, a second-stage dehydrating tower and a third-stage dehydrating tower, water is discharged from the tops of the dehydrating towers, and dimethyl sulfoxide at the bottom of the tower is purified step by step until the concentration reaches 99.5% or above; and (3) the purified dimethyl sulfoxide enters a rectifying tower, the pressure and the temperature are controlled, dimethyl sulfoxide impurities exist at the tower bottom, dimethyl sulfoxide forms a gas phase, the gas phase is discharged through the tower top, and after condensation and recovery, a pure dimethyl sulfoxide product without impurities is obtained. The process is efficient, environment-friendly and energy-saving, and the recovery rate of acrylonitrile and dimethyl sulfoxide is high.

Description

Technical Field

[0001] This invention belongs to the field of fiber waste liquid recycling, specifically, it relates to a recycling process for waste liquid from carbon fiber production. Background Technology

[0002] Carbon fiber is a high-strength, high-modulus, high-performance fiber with a density less than one-quarter that of steel and a strength 7 to 9 times that of steel. It also possesses excellent properties such as high-temperature resistance, corrosion resistance, abrasion resistance, electrical conductivity, and thermal conductivity, making it widely used in aerospace, defense, new energy, automotive manufacturing, rail transportation, medical, and sporting goods industries. Polyacrylonitrile (PAN)-based carbon fiber refers to carbon fiber materials prepared by polymerizing acrylonitrile (AN) as the main raw material into PAN, followed by processes such as spinning, pre-oxidation, and carbonization. It accounts for over 90% of the total carbon fiber production.

[0003] High-quality, high-performance precursor fibers are essential for producing high-performance carbon fibers. The preparation process of PAN-based carbon fiber precursor fibers mainly consists of two parts: polymerization and spinning. Currently, most domestic carbon fiber companies use a one-step wet spinning process with dimethyl sulfoxide (DMSO) for precursor fiber preparation. In the production process of polyacrylonitrile (PAN) carbon fiber precursor fibers, especially in the one-step DMSO process, the waste liquid generated contains DMSO and acrylonitrile.

[0004] Acrylonitrile is a highly toxic compound, slightly soluble in water, and extremely toxic to microorganisms. It is one of the most toxic pollutants in environmental remediation, not only disrupting the ecological balance of aquatic bodies but also posing a significant threat to human health. Dimethyl sulfoxide (DMSO) is chemically stable, has good biocompatibility, and is a common universal solvent used in large quantities in PAN fiber production, but is easily depleted. The inherent toxicity of acrylonitrile to microorganisms, combined with the permeability of DMSO, results in highly toxic, poorly biodegradable, and slow-degrading organic wastewater from carbon fiber production. Furthermore, passive environmental treatment technologies such as biochemical and degradation methods suffer from high treatment costs and difficulties in environmentally friendly discharge.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The technical problem this invention aims to solve is to overcome the shortcomings of existing technologies and provide a recycling process for wastewater from carbon fiber production. This recycling process can efficiently recover acrylonitrile and dimethyl sulfoxide from carbon fiber production wastewater, achieving a recovery rate of 99.9% for acrylonitrile and 99.99% for dimethyl sulfoxide. Furthermore, the entire process has low steam consumption, VOC emissions from the production waste gas meet national standards, and wastewater discharge meets municipal wastewater treatment requirements. It is highly efficient, environmentally friendly, energy-saving, and achieves wastewater recycling and reuse.

[0007] To solve the above-mentioned technical problems, the basic concept of the technical solution adopted by the present invention is as follows:

[0008] This invention provides a process for recycling waste liquid from carbon fiber production, comprising:

[0009] (1) The waste liquid containing acrylonitrile and dimethyl sulfoxide is fed into the acrylonitrile recovery tower. The pressure and temperature are controlled. Acrylonitrile and some water form a gas phase and are separated at the top of the tower. The bottom of the tower contains dimethyl sulfoxide and water.

[0010] (2) The dimethyl sulfoxide and water at the bottom of the acrylonitrile recovery tower enter the first-stage dehydration tower, the second-stage dehydration tower, and the third-stage dehydration tower in sequence. The water is discharged from the top of the dehydration tower, and the dimethyl sulfoxide at the bottom of the tower is purified step by step to a concentration of more than 99.5%.

[0011] (3) The purified dimethyl sulfoxide enters the distillation column. The pressure and temperature are controlled. The bottom of the column contains dimethyl sulfoxide impurities. The dimethyl sulfoxide forms a gas phase and is discharged through the top of the column. After condensation and recovery, pure dimethyl sulfoxide without impurities is obtained with a purity of 99.97%.

[0012] The waste liquid containing acrylonitrile and dimethyl sulfoxide mainly originates from recovered polymerization solvents and spinning solvents. This invention utilizes the different boiling points of AN (acrylonitrile), DMSO (dimethyl sulfoxide), and H2O, employing distillation and evaporation to separate DMSO, AN, and H2O. Simultaneously, to prevent DMSO decomposition, part of the recovery process is carried out at a lower operating pressure, allowing for continuous operation at lower operating temperatures.

[0013] In a further embodiment, in step (1), the pressure in the acrylonitrile recovery tower is controlled at -80 to -95 kPa, the top temperature of the tower is 40℃-50℃, the reflux temperature is 50℃-60℃, and the reflux ratio is 0.8-1.5.

[0014] Wastewater containing acrylonitrile and dimethyl sulfoxide (DMSO content 30%-40%, acrylonitrile 1%-2%) is pumped into an acrylonitrile recovery tower, where acrylonitrile is separated from the mixed solution by vacuum distillation. Simultaneously, to prevent DMSO decomposition, the separation process is carried out at a lower operating temperature and to save energy; therefore, the separation process is performed under reduced pressure.

[0015] The liquid at the bottom of the acrylonitrile tower is heated by the reboiler at the bottom of the tower. Since the boiling point of acrylonitrile is 77.3℃, the acrylonitrile evaporates first. The acrylonitrile vapor at the top of the tower is condensed by the condenser at the top of the tower. After condensation, it enters the separator and is separated into layers by the difference in density between water and acrylonitrile. The upper layer of acrylonitrile overflows into a tank for storage, while the lower layer of water is discharged to wastewater for treatment.

[0016] In a further scheme, in step (1), acrylonitrile and some water form a gas phase at the top of the tower and are then cooled into a liquid. The liquid overflows into a separator for separation, with acrylonitrile as the upper layer and water as the lower layer, which are then recovered separately.

[0017] As a more concrete solution, in the acrylonitrile recovery tower, when the liquid level of the waste liquid entering the tower bottom reaches 50%, the vacuum system at the top of the tower starts working. When the pressure inside the tower reaches -70 to 80 kPa, low-pressure steam is introduced into the tower reboiler to gradually raise the temperature. Because of the high pressure inside the tower, when the temperature reaches 50°C to 60°C, the material containing acrylonitrile and water at the bottom of the tower begins to form a gas phase and rises to the top of the tower. A gas phase cooler is installed at the top of the tower. Through cooling, the gas phase forms a liquid and overflows into a separator. The separator has two overflow ports, one at the high point and one at the low point. When water and acrylonitrile flow into the separator, acrylonitrile, being lighter than water, floats to the top. The bottom layer is water, and the top layer is acrylonitrile. The acrylonitrile overflows from the upper overflow port into the acrylonitrile storage tank for recycling, while the water overflows from the lower overflow port into the water tank.

[0018] At this point, the bottom of the acrylonitrile recovery tower contains dimethyl sulfoxide and water, with an acrylonitrile content of less than 0.001%. The acrylonitrile is then pumped into the primary dehydration tower for water removal and purification.

[0019] In this invention, the water removal process consists of a three-stage (triple-effect) dehydration tower. Each dehydration tower utilizes the different boiling points of DMSO and water to separate and discharge water from the solution, thereby increasing the concentration of DMSO. The first-stage dehydration tower operates at atmospheric pressure, while the second and third-stage dehydration towers operate under reduced pressure to lower the boiling point of DMSO. In this invention, the first-stage dehydration tower operates at positive pressure, which can provide a heat source for the subsequent two towers.

[0020] In a further step, in step (2), the primary dehydration tower is operated at atmospheric pressure, with a pressure of 1-20 kPa, a top temperature of 85-95℃, a bottom temperature of 95-105℃, and a reflux ratio of 1-1.5.

[0021] Preferably, after purification in a primary dehydration tower, the concentration of dimethyl sulfoxide at the bottom of the tower reaches more than 40%.

[0022] As a more specific approach, the material enters the primary dehydration tower, which is an atmospheric pressure tower. When the feed reaches 50% of the bottom liquid level, the bottom pump is turned on to circulate the material to the reboiler for heating. When the temperature reaches 100 degrees Celsius, the water in the bottom of the tower turns into steam. The steam rises to the top pipe of the tower and is discharged into the cooler, where it turns into liquid and is discharged into wastewater. At this point, the concentration of dimethyl sulfoxide at the bottom of the tower is about 40%. The material at the bottom of the tower is pumped to the secondary dehydration tower for further dehydration and purification.

[0023] In a further step, in step (2), a pressure reduction operation is performed in the secondary dehydration tower, with a pressure of -90Kpa to -100Kpa, a tower top temperature of 55℃-60℃, a tower bottom temperature of 65℃-70℃, and a reflux ratio of 0.8-1.3.

[0024] Preferably, after purification in a two-stage dehydration tower, the concentration of dimethyl sulfoxide at the bottom of the tower reaches 65%-75%.

[0025] As a more specific approach, the pressure of the secondary dehydration tower is -90 kPa to -100 kPa. Low-pressure steam is introduced into the reboiler to heat the secondary dehydration tower. When the gas volume is large, the reflux flow rate at the top of the tower is increased to reduce the steam volume, ensuring that dimethyl sulfoxide is not evaporated. The water vapor is cooled by a cooler at the gas outlet at the top of the tower to form water which is discharged into the wastewater tank. When the concentration of dimethyl sulfoxide in the tower reaches 65%-75%, it is pumped to the tertiary dehydration tower for purification through the bottom pump.

[0026] In a further embodiment, in step (2), the material is preheated by a preheater and then enters the first-stage dehydration tower. The heat source of the preheater comes from the steam condensate of the reboiler at the bottom of the first-stage dehydration tower. The gas phase at the top of the first-stage dehydration tower flows through the reboiler of the second-stage dehydration tower to heat the bottom liquid of the second-stage dehydration tower.

[0027] In a further step, in step (2), a pressure reduction operation is performed in the three-stage dehydration tower, with a pressure of -90Kpa to -100Kpa, a tower top temperature of 40℃-50℃, a tower bottom temperature of 110℃-120℃, and a reflux ratio of 0.8-1.3.

[0028] Preferably, after purification by a three-stage dehydration tower, the concentration of dimethyl sulfoxide at the bottom of the tower reaches 99.5% or higher.

[0029] As a more specific solution, the three-stage dehydration tower is a negative pressure tower with a controlled pressure of -90 kPa to -100 kPa. Low-pressure steam is passed to the reboiler to heat the three-stage dehydration tower. The temperature is controlled by the reflux rate and vacuum degree. When the temperature reaches 110℃-120℃, the water turns into a gas phase and enters the cooler at the top of the tower for cooling before being discharged into the wastewater tank. At this time, the concentration of dimethyl sulfoxide at the bottom of the tower is 99.5%, but it contains some impurities and needs to be filtered. Therefore, it is pumped to the distillation tower through the bottom pump.

[0030] In a further step, in step (3), a pressure reduction operation is performed in the distillation column, with a pressure of -90Kpa to -100Kpa, a column top temperature of 90℃ to 100℃, and a column bottom temperature of 99℃ to 105℃.

[0031] Preferably, after purification by a distillation column, the concentration of dimethyl sulfoxide reaches 99.97% or higher.

[0032] As a more specific solution, the distillation column is a negative pressure column with a pressure of -90 kPa to -100 kPa. When the temperature reaches 90-100 degrees Celsius, dimethyl sulfoxide forms a gas phase and is discharged into the condenser through the gas phase port at the top of the column. It overflows into the dimethyl sulfoxide recovery tank. The dimethyl sulfoxide concentration is above 99.5% and contains no impurities, so it can be reused. The bottom of the distillation column contains dimethyl sulfoxide impurities, which are pumped to the dryer through the bottom of the column to evaporate the dimethyl sulfoxide impurities, thereby maximizing recovery and saving materials.

[0033] A distillation column provides a two-phase flow for gas-liquid mass transfer. The feed is introduced into the middle of the column; the liquid in the feed descends along with the liquid from the upper section, while the vapor in the feed rises along with the vapor from the lower section. Throughout the distillation column, the vapor and liquid phases flow countercurrently for mass transfer. The more volatile components in the liquid phase enter the vapor phase, while the less volatile components in the vapor phase transfer to the liquid phase. The reboiler at the bottom of the column partially vaporizes the liquid, allowing the vapor to rise along the column; the remaining liquid is the bottom product. The condenser at the top of the column partially condenses the vapor; some of the condensate returns to the bottom as reflux, and the remaining distillate is the top product. The section above the feed inlet further concentrates the more volatile components in the rising vapor; this is called the rectification section. The section below the feed inlet extracts the more volatile components from the descending liquid; this is called the stripping section. The combination of these two sections allows for more complete separation of the two components in the liquid mixture, producing a product of the desired purity.

[0034] In a further embodiment, in step (1), the waste liquid containing acrylonitrile and dimethyl sulfoxide has a dimethyl sulfoxide content of 10%-40% and an acrylonitrile content of 1%-2%.

[0035] In a further embodiment, the wastewater discharged from the recycling process contains less than 100 ppm of dimethyl sulfoxide and 0 ppm of acrylonitrile.

[0036] By adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art.

[0037] 1. The recycling process of this invention can efficiently recover acrylonitrile and dimethyl sulfoxide (DMSO) from carbon fiber production wastewater. The acrylonitrile recovery rate can reach 99.9%, and the DMSO recovery rate can reach 99.99%. Furthermore, the entire process has low steam consumption, and the discharged wastewater contains less than 100 ppm of DMSO and less than 0 ppm of acrylonitrile, meeting municipal wastewater treatment standards. The VOCs emissions from the production exhaust gas meet national standards. The recovered acrylonitrile concentration reaches 99%, meeting recycling standards, and the DMSO purity reaches over 99.97%. Therefore, this recycling process is efficient, environmentally friendly, energy-saving, and achieves wastewater recycling and reuse.

[0038] 2. The water removal process of this invention consists of a three-stage (triple-effect) dehydration tower. Each distillation tower utilizes the different boiling points of DMSO and water to separate and discharge water from the solution, thereby increasing the concentration of DMSO. The first-stage dehydration tower operates at atmospheric pressure, while the second and third-stage dehydration towers operate under reduced pressure to lower the boiling point of DMSO. This combination of atmospheric and reduced pressure operation not only achieves efficient water removal but also improves the recovery rate of dimethyl sulfoxide.

[0039] 3. In the recycling process of the present invention, the vapor evaporated at the top of the primary dehydration tower is used to heat the solution at the bottom of the secondary dehydration tower, and the steam condensate is used to heat the feed, so as to fully recycle the heat energy and hot water generated in the production and reduce the energy consumption of the production. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below in conjunction with the embodiments of the present invention. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0041] Detection method:

[0042] Method for determining the content of acrylonitrile and dimethyl sulfoxide: Dimethyl sulfoxide is completely separated from other impurities under set conditions by gas chromatography, and then quantitative analysis is performed by area normalization method.

[0043] Analysis steps

[0044] 1. Adjust the instrument according to the chromatographic operating conditions listed in Table 1, and prepare for sample injection analysis after stabilization. Other chromatographic columns and operating conditions that can achieve the same degree of separation can also be used.

[0045] 2. The chromatographic column should be aged before its first use.

[0046] 3. Accurately pipette 0.5 μL of sample and inject it into the chromatograph, then record the chromatogram.

[0047] Table 1

[0048] chromatographic column Capillary column (DB-FFAP) Column specifications 60m×320um×0.5um carrier gas Nitrogen Septum purging / (mL / min) 3 Column flow rate (mL / min) 1.5 Carrier gas saving rate (mL / min) 20 Flow split ratio 50:1 Inlet temperature 200 Column temperature / ℃ 160 Detector temperature / °C 300 Hydrogen flow rate (mL / min) 30 Airflow rate (mL / min) 400 Purging rate (mL / min) 25 Injection volume / μL 0.4

[0049] Example 1

[0050] (1) Wastewater containing acrylonitrile and dimethyl sulfoxide (30% dimethyl sulfoxide, 1% acrylonitrile) is pumped into the acrylonitrile recovery tower. When the liquid level in the tower bottom reaches 50%, the vacuum system at the top of the tower starts working. When the pressure inside the tower reaches -83 kPa, the reboiler is supplied with low-pressure steam to gradually raise the temperature of the tower. When the temperature reaches 51°C, the material containing acrylonitrile and water at the bottom of the tower begins to form a gas phase and rises to the top of the tower. The top of the tower has a gas phase outlet to a cooler, where cooling water condenses the gas phase into liquid, which overflows into a separator. The separator has two overflow outlets, one at a high point and one at a low point. When water and acrylonitrile flow into the separator, acrylonitrile, being lighter than water, floats at the top. The bottom is water, and the top is acrylonitrile. The acrylonitrile overflows from the upper overflow outlet into the acrylonitrile storage tank for recycling, while the water overflows from the lower overflow outlet into the water tank. The recovery rate and concentration of the recovered acrylonitrile are measured.

[0051] The bottom product of the acrylonitrile recovery tower is an aqueous solution of DMSO with an acrylonitrile content of less than 0.001%. It is then pumped by the bottom pump of the acrylonitrile recovery tower into the primary dehydration tower for the next step.

[0052] (2) The primary dehydration tower operates at atmospheric pressure. The bottom solution from the acrylonitrile recovery tower is preheated by the primary preheater (E598) and the secondary preheater (E530) of the distillation tower before being fed into the primary dehydration tower. When the feed reaches 50% of the bottom liquid level, the bottom pump is turned on to circulate the solution to the reboiler for heating. When the solution is heated to 100 degrees Celsius, the water in the bottom of the tower turns into steam. The mixed liquid vapor generated by the reboiler at the bottom of the tower undergoes countercurrent contact and separation of vapor and liquid into DMSO and water in the primary dehydration tower. The top temperature is 85°C, the bottom temperature is 105°C, and the reflux ratio is 1.4.

[0053] The steam from the reboiler is condensed and flows to the condensate tank, then pumped by the condensate pump to the E530 to preheat the feed to the primary dehydration tower, thus recovering and reusing the heat energy. The vapor from the top of the primary dehydration tower flows through the secondary dehydration tower reboiler to heat the bottom liquid, serving as a heat source for the secondary distillation tower reboiler to reduce energy consumption. Part of the condensate from the top of the tower is refluxed, while the other part is pumped to wastewater treatment. The material at the bottom of the tower with a dimethyl sulfoxide concentration of 40% is pumped to the secondary dehydration tower for further dehydration and purification.

[0054] (3) The secondary dehydration tower operates under reduced pressure. The solution from the primary dehydration tower is fed from the bottom. The bottom solution is partially circulated by the bottom pump to the reboiler of the secondary dehydration tower, where it is heated by steam from the top of the primary dehydration tower. The steam generated by heating separates into DMSO and water through vapor-liquid contact with the reflux liquid from the top of the tower. The water vapor from the top of the tower is condensed by the condenser of the secondary distillation tower and then discharged into the wastewater treatment plant. The non-condensable gases at the top of the secondary dehydration tower are removed by the vacuum jet system of the secondary dehydration tower, and the vacuum degree of the secondary dehydration tower is controlled. The pressure is -90 kPa, the top temperature is 58°C, the bottom temperature is 70°C, and the reflux ratio is 0.9.

[0055] (4) The three-stage dehydration tower operates under reduced pressure. The DMSO solution from the two-stage dehydration tower is fed from the bottom of the tower. The bottom solution is circulated to the reboiler by the bottom pump for heating. The steam generated by heating separates into DMSO and water through vapor-liquid contact with the reflux liquid from the top of the tower. The water vapor at the top of the tower is condensed by the condenser and discharged into the wastewater system. The non-condensable gases at the top of the three-stage dehydration tower are removed by a vacuum jet system, and the vacuum level of the three-stage dehydration tower is controlled; the pressure is -90 kPa, the top temperature is 45°C, the bottom temperature is 110°C, and the reflux ratio is 0.8. The solution concentration at the bottom of the three-stage dehydration tower is 99.5%, and it is pumped to the dimethyl sulfoxide distillation tower for purification.

[0056] (5) The dimethyl sulfoxide (DMSO) distillation column operates under reduced pressure. A DMSO aqueous solution from the three-stage dehydration column is fed from the middle of the column. The bottom liquid is circulated to the reboiler by a bottom pump for heating. When the temperature reaches 100°C, DMSO vaporizes. The DMSO vapor comes into contact with the reflux liquid from the top of the column, further purifying the DMSO. The DMSO vapor at the top of the column is condensed by a condenser and enters the storage tank as the finished product. Non-condensable gases from the top condenser are removed by the distillation column injection system, which controls the vacuum level of the distillation column; the pressure is -90 kPa, the top temperature is 95°C, and the bottom temperature is 105°C.

[0057] The purity of the dimethyl sulfoxide product was 99.97%, and the recovery rate was 99.9%.

[0058] Examples 2-5

[0059] Referring to the methods and steps of Example 1, the process parameters of Examples 2-5 are as follows.

[0060] Table 2

[0061]

[0062]

[0063] Comparative Example 1

[0064] The difference between this comparative example and Example 1 is that the operation process in the primary dehydration tower is missing, and the acrylonitrile recovery tower bottom pump transports the product to the secondary dehydration tower for the next step.

[0065] The advantage of this process over other processes lies in the design and use of the primary dehydration tower. The primary dehydration tower is a positive pressure tower, with a reboiler at the bottom providing the heat source for evaporation. The steam evaporated at the top heats the bottom of the secondary dehydration tower (equivalent to the reboiler at the bottom of the secondary dehydration tower). This design increases the circulation and evaporation volume of the material between the primary and secondary dehydration towers. The two distillation towers share a single steam heater, saving 0.5 tons of steam per hour.

[0066] The index results of Examples 1-5 are shown in the table below.

[0067] Table 3

[0068]

[0069]

[0070] Results analysis:

[0071] Using the recycling methods described in Examples 1-5 of this invention, acrylonitrile and dimethyl sulfoxide in carbon fiber production wastewater can be efficiently recovered. The recovery rate of acrylonitrile can reach 99.9%, and the recovery rate of dimethyl sulfoxide can reach 99.99%. The content of dimethyl sulfoxide in the discharged wastewater is less than 100 ppm, and the content of acrylonitrile is 0 ppm. Therefore, waste liquid can be recycled and reused efficiently, environmentally friendly, and energy-savingly.

[0072] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A process for recycling waste liquid from carbon fiber production, characterized in that, Recycling processes include: (1) The waste liquid containing acrylonitrile and dimethyl sulfoxide is fed into the acrylonitrile recovery tower. The pressure and temperature are controlled. Acrylonitrile and some water form a gas phase and are separated at the top of the tower. The bottom of the tower contains dimethyl sulfoxide and water. (2) The dimethyl sulfoxide and water at the bottom of the acrylonitrile recovery tower enter the first-stage dehydration tower, the second-stage dehydration tower, and the third-stage dehydration tower in sequence. The water is discharged from the top of the dehydration tower, and the dimethyl sulfoxide at the bottom of the tower is purified step by step. (3) The purified dimethyl sulfoxide enters the distillation column, and the pressure and temperature are controlled. The bottom of the column contains dimethyl sulfoxide impurities, and the dimethyl sulfoxide forms a gas phase and is discharged through the top of the column. After condensation and recovery, pure dimethyl sulfoxide without impurities is obtained.

2. The recycling process for carbon fiber production waste liquid according to claim 1, characterized in that, In step (1), the pressure in the acrylonitrile recovery tower is controlled at -80 to -95 kPa, the tower top temperature is 40℃-50℃, the reflux temperature is 50℃-60℃, and the reflux ratio is 0.8-1.

5.

3. The recycling process for carbon fiber production waste liquid according to claim 1 or 2, characterized in that, In step (1), acrylonitrile and some water form a gas phase at the top of the tower, which is then cooled into a liquid and overflows into a separator for separation. The upper layer is acrylonitrile and the lower layer is water, which are then recovered separately.

4. The recycling process for carbon fiber production waste liquid according to any one of claims 1-3, characterized in that, In step (2), the primary dehydration tower is operated at atmospheric pressure, with a pressure of 1-20 kPa, a top temperature of 88-98℃, a bottom temperature of 90-100℃, and a reflux ratio of 1-1.

5. Preferably, after purification in a primary dehydration tower, the concentration of dimethyl sulfoxide at the bottom of the tower reaches more than 40%.

5. The recycling process for carbon fiber production waste liquid according to any one of claims 1-4, characterized in that, In step (2), a pressure reduction operation is performed in the secondary dehydration tower, with a pressure of -90Kpa to -100Kpa, a tower top temperature of 55℃-65℃, a tower bottom temperature of 65℃-70℃, and a reflux ratio of 0.8-1.

3. Preferably, after purification in a two-stage dehydration tower, the concentration of dimethyl sulfoxide at the bottom of the tower reaches 65%-75%.

6. The recycling process for carbon fiber production waste liquid according to any one of claims 1-5, characterized in that, In step (2), the material is preheated by the preheater and then enters the first-stage dehydration tower. The heat source of the preheater comes from the steam condensate of the heat exchanger at the bottom of the tower. The gas phase at the top of the first-stage dehydration tower flows through the reboiler of the second-stage dehydration tower to heat the bottom liquid of the second-stage dehydration tower.

7. The recycling process for carbon fiber production waste liquid according to any one of claims 1-6, characterized in that, In step (2), a depressurization operation is performed in the three-stage dehydration tower, with a pressure of -90Kpa to -100Kpa, a tower top temperature of 40℃-50℃, a tower bottom temperature of 110℃-120℃, and a reflux ratio of 0.8-1.3; preferably, after purification in the three-stage dehydration tower, the concentration of dimethyl sulfoxide at the bottom of the tower reaches more than 99.5%.

8. The recycling process for carbon fiber production waste liquid according to any one of claims 1-7, characterized in that, In step (3), a pressure reduction operation is performed in the distillation column, with a pressure of -90Kpa to -100Kpa, a top temperature of 90℃ to 100℃, and a bottom temperature of 99℃ to 105℃. Preferably, after purification by a distillation column, the concentration of dimethyl sulfoxide reaches 99.97% or higher.

9. The recycling process for carbon fiber production waste liquid according to any one of claims 1-8, characterized in that, In step (1), the waste liquid containing acrylonitrile and dimethyl sulfoxide has a dimethyl sulfoxide content of 10%-40% and an acrylonitrile content of 1%-2%.

10. The recycling process for carbon fiber production waste liquid according to any one of claims 1-9, characterized in that, The wastewater discharged from the recycling process contains less than 100 ppm of dimethyl sulfoxide and less than 0 ppm of acrylonitrile.

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