Separation method and application of mixture containing acrylonitrile and water and separation device of mixture containing acrylonitrile, water and dimethyl sulfoxide

Abstract

The invention relates to a separation method and application of a mixture containing acrylonitrile and water and a separation device of a mixture containing acrylonitrile, water and dimethyl sulfoxide. The method comprises the following steps: a, carrying out first rectification on a mixture to obtain a first heavy component material flow and a first gas phase material flow; b, condensing the first gas-phase material flow, and carrying out oil-water separation to obtain an oil-rich phase and a water-rich phase; c, carrying out membrane separation on the water-rich phase to obtain a dehydrated circulating liquid and water; d, circulating the dehydration circulating liquid back to the first gas phase material flow condensate; e, carrying out second rectification on at least part of the oil-rich phase to obtain an acrylonitrile side product, a second heavy component material flow and a second gas phase material flow; in the mixture, the content of acrylonitrile is less than or equal to 50wt%, and the content of water is less than or equal to 10wt%. According to the present invention, with the rectification coupling oil-water separation technology and the membrane separation technology, the recycling of the high-purity acrylonitrile product can be achieved on the basis of ensuring the relatively simple process.

Description

Technical Field

[0001] The present invention relates to the technical field of PAN-based carbon fiber preparation, and specifically relates to a separation method and application of a mixture containing acrylonitrile and water and a separation device for a mixture containing acrylonitrile, water and dimethyl sulfoxide. Background Art

[0002] Acrylonitrile-based carbon fibers have characteristics such as light weight, high strength, high modulus, and high temperature resistance in a non-oxidizing atmosphere, and are widely used in the national defense industry. Removal of monomer and degassing are important steps in the preparation process of PAN-based carbon fibers. In the polymerization process of carbon fiber production using DMSO as a solvent in the preparation process of PAN-based carbon fibers, the polymerization solution contains unreacted AN monomers, and the polymerization product coming out of the polymerization kettle must be de-monomerized; there will be bubbles in the spinning solution during polymerization or transportation, and larger bubbles will cause interruption, deformation, and breakage of the spinning filament through the spinneret holes. Therefore, the bubbles and residual monomers in the spinning solution must be completely removed before spinning.

[0003] The polymerization process generally uses vacuum for de-monomerization and degassing. The residual monomer AN needs to be removed under vacuum conditions to reduce the monomer residual amount in the polymerization solution to 100 - 300 PPM to become the spinning polymerization stock solution. In the condensate of de-monomerization and degassing of PAN-based carbon fibers, there are relatively large amounts of dimethyl sulfoxide, acrylonitrile, and trace amounts of water. However, acrylonitrile and water form an azeotrope, and dimethyl sulfoxide is prone to decomposition during the rectification process. It is difficult to achieve the separation of this stock material and the reuse of acrylonitrile monomer solely by rectification.

[0004] During the preparation process of carbon fibers, although the total amount of the condensate of de-monomerization and degassing of PAN-based carbon fibers is not large, due to the presence of acrylonitrile, if it cannot be reasonably recovered and utilized, acrylonitrile entering the emission system will cause serious environmental protection problems. There are currently no relevant reports or patents on the separation and recovery of dimethyl sulfoxide and acrylonitrile in the condensate of de-monomerization and degassing of PAN-based carbon fibers, which is a new attempt. Summary of the Invention

[0005] The purpose of the present invention is to overcome the problem of difficult recovery of acrylonitrile existing in the prior art, and provide a separation method and application of a mixture containing acrylonitrile and water and a separation device for a mixture containing acrylonitrile, water and dimethyl sulfoxide. This method has the characteristics of high acrylonitrile recovery purity, simple process, and low energy consumption.

[0006] To achieve the above purpose, the first aspect of the present invention provides a separation method for a mixture containing acrylonitrile and water, the method comprising:

[0007] a. Subject the mixture to a first rectification to obtain a first heavy component stream and a first gas-phase stream;

[0008] b. Condense the first gas-phase stream and send it for oil-water separation to obtain an oil-rich phase and a water-rich phase;

[0009] c. Perform membrane separation on the water-rich phase to obtain a dehydrated recycle liquid and water;

[0010] d. Recycle the dehydrated recycle liquid back to the condensate of the first gas-phase stream;

[0011] e. Subject at least part of the oil-rich phase to a second rectification to obtain a side-stream product of acrylonitrile, a second heavy-component stream, and a second gas-phase stream;

[0012] In the mixture, the content of acrylonitrile is ≤ 50 wt%, and the content of water is ≤ 5 wt%.

[0013] The second aspect of the present invention provides an application of the separation method in the preparation of PAN-based carbon fiber.

[0014] The third aspect of the present invention provides a separation device for a mixture containing acrylonitrile, water, and dimethyl sulfoxide. The device includes: a first separation unit for enriching dimethyl sulfoxide; a first condensation unit connected to the gas-phase outlet of the first separation unit; a liquid separation unit connected to the outlet of the first condensation unit; the liquid separation unit is provided with an oil-phase outlet and a water-phase outlet, and the oil-phase outlet is provided with a reflux ratio distributor so that part of the oil-phase material is refluxed to the first separation unit, and the other part of the oil-phase material is sent to the second separation unit; a membrane separation member is provided at the water-phase outlet of the liquid separation storage tank, and the non-permeate phase outlet is connected to the liquid separation unit; a second separation unit connected to the oil-phase discharge port of the liquid separation unit, and a side-stream outlet is provided between the feed port and the bottom of the second separation tower for separating and obtaining high-purity acrylonitrile; and a second condensation unit provided at the gas-phase outlet of the second separation unit.

[0015] Through the above technical solutions, the present invention has the following advantages:

[0016] By coupling rectification with oil-water separation technology and membrane separation technology, the present invention can realize the recovery and utilization of high-purity acrylonitrile products on the basis of ensuring a relatively simple process. Description of the Drawings

[0017] Figure 1 It is a schematic diagram of the separation device and process of a preferred embodiment of the present invention.

[0018] Description of the Reference Numerals

[0019] T1, the first separation tower; 5, oil-phase material;

[0020] E1, the first condenser; 6, water-phase material;

[0021] V1, the liquid separation storage tank; 7, the components at the top of T2;

[0022] T2, the second separation column; 8, condensate at the top of T2;

[0023] R1, membrane separation system; 9, the second light fraction;

[0024] 1, de - single - component and de - foam condensate; 10, separated product;

[0025] 2, the first heavy component; 11, the second heavy component;

[0026] 3, components at the top of T1; 12, separated aqueous phase;

[0027] 4, the first light fraction; 13, dehydrated circulating liquid. Detailed implementation mode

[0028] In the ranges disclosed herein, the endpoints and any values of the ranges are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0029] In the present invention, unless otherwise stated, the orientation terms such as "upper, lower, left, right" generally refer to the upper, lower, left, and right shown in the reference drawings; "inner, outer" refer to the inner and outer of the contour of each component itself.

[0030] In the present invention, unless otherwise specified, "bottom of the column" refers to the position from 90 - 100% of the container from top to bottom; "top of the column" refers to the position from 0 - 10% of the container from top to bottom; "upper part" refers to the position from 0 - 30% of the container from top to bottom; "middle part" refers to the position from 30 - 70% of the container from top to bottom.

[0031] The present invention provides a method for separating a mixture containing acrylonitrile and water, the method comprising: a. performing a first rectification on the mixture to obtain a first heavy - component stream and a first gas - phase stream; b. condensing the first gas - phase stream and then sending it for oil - water separation to obtain an oil - rich phase and a water - rich phase; c. performing membrane separation on the water - rich phase to obtain a dehydrated circulating liquid and water; d. recycling the dehydrated circulating liquid back into the condensate of the first gas - phase stream; e. performing a second rectification on at least a part of the oil - rich phase to obtain a side - line product of acrylonitrile, a second heavy - component stream, and a second gas - phase stream;

[0032] In the mixture, the content of acrylonitrile ≤ 50 wt%, and the content of water ≤ 10 wt%.

[0033] The present invention can realize the recycling of high-purity acrylonitrile products on the basis of ensuring relatively simple processes by coupling rectification with oil-water separation technology and membrane separation technology.

[0034] In the present invention, the contents of acrylonitrile and water in the mixture containing acrylonitrile and water need to meet the requirements of rectification and membrane separation. Generally, the content of acrylonitrile ≥ 2 wt%, preferably ≥ 5 wt%; the content of water ≥ 1 wt%.

[0035] In the present invention, there is no particular requirement for the type of the second component. According to a preferred embodiment of the present invention, the first heavy component stream contains at least one of dimethyl sulfoxide (DMSO), N,N-dimethylacetamide (DMAc), and sodium thiocyanate (NaSCN), preferably dimethyl sulfoxide, and at this time, dimethyl sulfoxide with a purity ≥ 98 wt% can be obtained.

[0036] According to a preferred embodiment of the present invention, the content of acrylonitrile in the mixture ≤ 30 wt%, and the content of water ≤ 5 wt%.

[0037] According to a preferred embodiment of the present invention, in step e, the rich oil phase is recycled back to step a for the first rectification, and the recycling ratio (the ratio of the amount recycled back to the first rectification to the amount sent to the second rectification) is 0.1 - 10.

[0038] According to a preferred embodiment of the present invention, in step e, after the second gas-phase stream is condensed, part of it is recycled back to the condensate of the first gas-phase stream, and part of it is recycled back to step e for the second rectification. The mass ratio of the amount recycled back to the condensate of the first gas-phase stream to the amount recycled back to step e for the second rectification is 0.1 - 10.

[0039] According to a preferred embodiment of the present invention, the conditions of the first rectification include: at least 8 theoretical plates.

[0040] According to a preferred embodiment of the present invention, the conditions of the first rectification include: the operating pressure is 7 - 25 kPa, preferably 10 - 15 kPa.

[0041] According to a preferred embodiment of the present invention, the conditions of the first rectification include: the bottom temperature is 100 - 140 °C, preferably 110 - 125 °C.

[0042] According to a preferred embodiment of the present invention, the conditions for condensing the first gas-phase stream include: the temperature does not exceed 38 °C, preferably does not exceed 25 °C, and more preferably does not exceed 15 °C.

[0043] According to a preferred embodiment of the present invention, the conditions for membrane separation include: the temperature of the membrane module is 10 - 65°C, preferably 35 - 55°C; the operating pressure on the permeate side is 0 - 20 kPa, preferably 5 - 15 kPa; preferably, the temperature of the membrane condenser is -15 - 30°C, preferably -10 - 20°C.

[0044] According to a preferred embodiment of the present invention, the conditions for the second rectification include: the number of theoretical plates is 10 - 30.

[0045] According to a preferred embodiment of the present invention, the conditions for the second rectification include: the operating pressure is 40 - 80 kPa, preferably 50 - 70 kPa.

[0046] According to a preferred embodiment of the present invention, the conditions for the second rectification include: the bottom temperature of the column is 50 - 70°C, preferably 55 - 65°C.

[0047] According to a preferred embodiment of the present invention, the conditions for the second rectification include: the reflux ratio is 1 - 10, preferably 2 - 5.

[0048] According to a preferred embodiment of the present invention, the conditions for the second rectification include: the temperature difference between the side - stream product extraction temperature of acrylonitrile and the bottom temperature of the column does not exceed 5°C, preferably does not exceed 3°C.

[0049] The present invention provides an application of the separation method in the preparation of PAN - based carbon fiber for the separation and recovery of dimethyl sulfoxide and acrylonitrile in the condensate of PAN - based carbon fiber for removing monomers and de - foaming.

[0050] The present invention provides a separation device for a mixture containing acrylonitrile, water and dimethyl sulfoxide, which device includes: a first separation unit for the enrichment of dimethyl sulfoxide; a first condensation unit connected to the gas - phase outlet of the first separation unit; a liquid - separation unit connected to the outlet of the first condensation unit; the liquid - separation unit is provided with an oil - phase outlet and a water - phase outlet, and the oil - phase outlet is provided with a reflux - ratio distributor so that part of the oil - phase material is refluxed to the first separation unit and the other part of the oil - phase material is sent to the second separation unit; the water - phase outlet of the liquid - separation storage tank is provided with a membrane separation component, and the non - permeate - phase outlet is connected to the liquid - separation unit; a second separation unit connected to the oil - phase discharge port of the liquid - separation unit, and a side - stream discharge port is provided between the feed inlet and the bottom of the second separation column for separating and obtaining high - purity acrylonitrile; and a second condensation unit provided at the gas - phase outlet of the second separation unit; preferably, the extraction end of the second condenser is respectively connected to the liquid - separation unit and the second separation unit.

[0051] As Figure 1 , the present invention provides a device and process of a preferred embodiment:

[0052] The device includes: a first separation tower T1, a first condenser E-1, a liquid separation storage tank V-1, a second separation tower T2, and a second condenser E-2 that are connected in sequence; the liquid separation storage tank V-1 is a storage tank coupled with oil-water separation, and its internal structure can be selected from a folded baffle type, a hydrocyclone separation type, and / or a liquid-liquid two-phase separator structure containing coalescing filler materials; the first separation tower includes a rectifying section, where one end of the rectifying section is connected to a heating kettle with stirring or a heating section, and the other end is connected to the first condenser E-1. The first condenser is connected to the top of the liquid separation storage tank; multiple folding plates are arranged in the intermediate liquid separation storage tank, and the liquid separation storage tank is provided with an oil phase outlet and a water phase outlet; the oil phase outlet of the liquid separation storage tank includes a reflux ratio distributor, so that part of the material is refluxed to the top of the first separation tower, and the other part of the material is taken out and then connected to the feed inlet of the second separation tower; a membrane separation system is arranged at the water phase outlet of the liquid separation storage tank, and the non-permeate phase outlet is connected to the top of the liquid separation storage tank V-1. A second condenser is provided at the top of the second separation tower, and the extraction end of the second condenser is connected to the top of the liquid separation storage tank V-1; a side line discharge port is provided between the feed inlet and the bottom of the second separation tower;

[0053] The process includes:

[0054] The raw material degassed and de-bubbled condensate 1 enters the first separation tower T1, and the first heavy component 2 is separated from the bottom of the tower. The components 3 at the top of the T1 tower enter the condenser E-1 and are condensed to obtain the first light fraction 4. The first light fraction 4 enters the liquid separation storage tank V1, and the aqueous phase material 6 is separated from the water phase outlet of the liquid separation storage tank V1; the aqueous phase material 6 enters the membrane separation system R1, and after separating the separated aqueous phase 12, the dehydrated circulating liquid 13 returns to the liquid separation storage tank V1. The oil phase material 5 separated from the oil phase outlet of the liquid separation storage tank V1, part of it is taken out as the raw material for the T2 tower and enters the second separation tower T2, and the other part is recycled back to the first separation tower T1; part of the components 7 at the top of the T2 tower (the second light fraction 9) is returned to the liquid separation storage tank V1 after being condensed from the top of the second separation tower T2, and the other part is recycled back to the T2 tower. The separated product 10 is taken out from the side line of the second separation tower T2, and the second heavy component 11 is taken out from the bottom of the tower.

[0055] The present invention will be described in detail below through embodiments. In the following embodiments, the water content parameter is measured by a moisture meter, and parameters such as DMSO and acrylonitrile content are measured by gas chromatography; unless otherwise specified, the raw materials are commercially available products.

[0056] Example 1

[0057] In Figure 1 the device shown below is carried out:

[0058] The polyacrylonitrile-based carbon fiber de-singling and degassing condensate with an acrylonitrile content of 10wt%, a water content of 2wt% and a dimethyl sulfoxide content of 88% enters the first separation tower as the raw material to be separated, and is distilled under the conditions of 25kPa and a bottom temperature of 133°C. The gas phase material at the top of the first separation tower enters the condenser E-1, and the condensation temperature does not exceed 33°C. The condensed first light fraction enters the liquid separation storage tank with a baffle, and the water phase material enters the membrane separation system with an operating pressure of 15kPa and a membrane separation component temperature maintained at 55°C; after separating the separated water phase, the dehydrated circulating liquid returns to the liquid separation storage tank V1.

[0059] 50wt% of the oil phase material separated from the oil phase outlet of the separation storage tank V1 enters the second separation tower comprising 10 theoretical plates from 40% volume, and is distilled under the conditions of 80kPa, tower bottom temperature of 70°C and reflux ratio of 2. The remaining non-distilled gas phase material enters the condenser E-2 with a condensation temperature not exceeding 35°C, and is discharged from the side line 2 theoretical plates above the tower bottom of the tower T2. The temperature difference between the side line temperature and the tower bottom temperature is controlled to be ≤3°C. The side line fraction is the recovered acrylonitrile monomer product.

[0060] After analysis, the DMSO content in the first heavy component was 98.7wt%, the acrylonitrile content was 0.3wt%, and the remainder was mainly water; the acrylonitrile product extracted from the T2 side line had a purity of 99.6% and a water content of 0.4wt%.

[0061] Example 2

[0062] exist Figure 1 In the device shown:

[0063] The polyacrylonitrile-based carbon fiber deaeration and degassing condensate with an acrylonitrile content of 10wt%, a water content of 2wt% and a dimethyl sulfoxide content of 88% enters the first separation tower as the raw material to be separated, and is distilled under the conditions of 20kPa and a bottom temperature of 129°C. The gas phase material at the top of the first separation tower enters the condenser E-1, and the condensation temperature does not exceed 25°C. The condensed first light fraction enters the liquid separation storage tank with a baffle, and the water phase material enters the membrane separation system with an operating pressure of 10kPa and a membrane separation component temperature maintained at 46°C; after separating the separated water phase, the dehydrated circulating liquid returns to the liquid separation storage tank V1.

[0064] 50wt% of the oil phase material separated from the oil phase outlet of the separation storage tank V1 enters the second separation tower comprising 15 theoretical plates from 30% volume, and is distilled under the conditions of 70kPa, tower bottom temperature of 66°C and reflux ratio of 5. The remaining non-distilled gas phase material enters the condenser E-2 with a condensation temperature not exceeding 30°C, and is discharged from the side line 2 theoretical plates above the tower bottom of the tower T2. The temperature difference between the side line temperature and the tower bottom temperature is controlled to be ≤2°C. The side line fraction is the recovered acrylonitrile monomer product.

[0065] After analysis, the content of DMSO in the first heavy component is 98.9 wt%, the content of acrylonitrile is 0.1 wt%, and the balance is mainly water; the purity of the acrylonitrile product taken from the side line of T2 is 99.7%, and the water content is 0.3 wt%.

[0066] Example 3

[0067] In Figure 1 the device shown:

[0068] The polyacrylonitrile-based carbon fiber degassing and defoaming condensate with an acrylonitrile content of 10 wt%, a water content of 2 wt%, and a dimethyl sulfoxide content of 88% enters the first separation column as the raw material to be separated. Distillation is carried out under the conditions of 15 kPa and a column bottom temperature of 120 °C. The gas-phase material at the top of the first separation column enters condenser E-1, and the condensation temperature does not exceed 15 °C. The condensed first light fraction enters a baffle-equipped liquid separation storage tank, and the aqueous-phase material enters a membrane separation system with an operating pressure of 10 kPa and a membrane separation module temperature maintained at 46 °C; after separating the separated aqueous phase, the dehydrated circulating liquid returns to the liquid separation storage tank V1.

[0069] 50 wt% of the oil-phase material separated from the oil-phase outlet of the liquid separation storage tank V1 enters the second separation column containing 15 theoretical plates at 40% of the volume. Distillation is carried out under the conditions of 60 kPa, a column bottom temperature of 60 °C, and a reflux ratio of 3. The remaining non-distilled gas-phase material enters condenser E-2 with a condensation temperature not exceeding 35 °C, and side-line discharging is carried out at one theoretical plate above the column bottom of the T2 column, controlling the temperature difference between the side-line temperature and the column bottom temperature to be ≤1 °C. The side-line drawn fraction is the recovered acrylonitrile monomer product.

[0070] After analysis, the content of DMSO in the first heavy component is 99.0 wt%, the content of acrylonitrile is 0.01 wt%, and the balance is mainly water; the purity of the acrylonitrile product taken from the side line of T2 is 99.8%, and the water content is 0.2 wt%.

[0071] Example 4

[0072] In Figure 1 the device shown:

[0073] The degassed condensate of polyacrylonitrile-based carbon fiber with an acrylonitrile content of 10 wt%, a water content of 2 wt%, and a dimethyl sulfoxide content of 88% enters the first separation column as the feedstock to be separated. Distillation is carried out at 9 kPa and a bottom temperature of 118 °C. The vapor-phase material at the top of the first separation column enters condenser E-1, and the condensation temperature does not exceed 12 °C. The first light fraction after condensation enters a hydrocyclone separation storage tank, and the aqueous-phase material enters a membrane separation system with an operating pressure of 10 kPa and a membrane separation module temperature maintained at 46 °C. After separating the separated aqueous phase, the dehydrated circulating liquid returns to the hydrocyclone separation storage tank.

[0074] 50 wt% of the oil-phase material separated from the oil-phase outlet of the liquid separation storage tank enters the second separation column with 25 theoretical plates at 40% of the volume. Distillation is carried out at 50 kPa, a bottom temperature of 57 °C, and a reflux ratio of 10. The remaining non-distilled vapor-phase material enters condenser E-2 with a condensation temperature not exceeding 20 °C. Side-stream withdrawal is carried out at 2 theoretical plates above the bottom of column T2, and the temperature difference between the side-stream temperature and the bottom temperature is controlled to be ≤1 °C. The side-stream withdrawn fraction is the recovered acrylonitrile monomer product.

[0075] After analysis, the DMSO content in the first heavy fraction is 99.8 wt%, the acrylonitrile content is not detected, and the balance is mainly water; the purity of the acrylonitrile product withdrawn from the side-stream of T2 is 99.8%, and the water content is 0.2 wt%.

[0076] Example 5

[0077] In Figure 1 the device shown below:

[0078] The degassed condensate of polyacrylonitrile-based carbon fiber with an acrylonitrile content of 10 wt%, a water content of 2 wt%, and a dimethyl sulfoxide content of 88% enters the first separation column as the feedstock to be separated. Distillation is carried out at 7 kPa and a bottom temperature of 105 °C. The vapor-phase material at the top of the first separation column enters condenser E-1, and the condensation temperature does not exceed 10 °C. The first light fraction after condensation enters a liquid separation storage tank with coalescing material, and the aqueous-phase material enters a membrane separation system with an operating pressure of 5 kPa and a membrane separation module temperature maintained at 35 °C. After separating the separated aqueous phase, the dehydrated circulating liquid returns to liquid separation storage tank V1.

[0079] 50 wt% of the oil-phase material separated from the oil-phase outlet of liquid separation storage tank V1 enters the second separation column with 20 theoretical plates at 50% of the volume. Distillation is carried out at 40 kPa, a bottom temperature of 52 °C, and a reflux ratio of 1. The remaining non-distilled vapor-phase material enters condenser E-2 with a condensation temperature not exceeding 20 °C. Side-stream withdrawal is carried out at 2 theoretical plates above the bottom of column T2, and the temperature difference between the side-stream temperature and the bottom temperature is controlled to be ≤3 °C. The side-stream withdrawn fraction is the recovered acrylonitrile monomer product.

[0080] After analysis, the DMSO content in the first heavy component is 97 wt%, and the balance is mainly water; the purity of the acrylonitrile product drawn from the side line of T2 is 99.6%, and the water content is 0.4 wt%.

[0081] Example 6

[0082] In Figure 1 the device shown below:

[0083] A mixed liquid with an acrylonitrile content of 10 wt%, a water content of 2 wt%, and an N,N-dimethylacetamide content of 88% enters the first separation column as the raw material to be separated, and is rectified under the conditions of 7 kPa and a tower bottom temperature of 105 °C. The gas-phase material at the top of the first separation column enters condenser E-1, and the condensation temperature does not exceed 10 °C. The condensed first light fraction enters a baffle-equipped liquid separation storage tank, and the aqueous-phase material enters a membrane separation system with an operating pressure of 15 kPa and a membrane separation module temperature maintained at 55 °C; after separating the separated aqueous phase, the dehydrated circulating liquid returns to the liquid separation storage tank V1.

[0084] 50 wt% of the oil-phase material separated from the oil-phase outlet of the liquid separation storage tank V1 enters the second separation column containing 10 theoretical plates at 40% of the volume, and is rectified under the conditions of 80 kPa, a tower bottom temperature of 70 °C, and a reflux ratio of 2. The remaining non-rectified gas-phase material enters condenser E-2 with a condensation temperature not exceeding 35 °C, and side-line discharge is carried out at 2 theoretical plates above the bottom of the T2 column, controlling the temperature difference between the side-line temperature and the tower bottom temperature to be ≤ 3 °C. The side-line drawn fraction is the recovered acrylonitrile monomer product.

[0085] After analysis, the N,N-dimethylacetamide content in the first heavy component is 98.8 wt%, the acrylonitrile content is 0.2 wt%, and the balance is mainly water; the purity of the acrylonitrile product drawn from the side line of T2 is 99.6%, and the water content is 0.4 wt%.

[0086] Comparative Example 1

[0087] The polyacrylonitrile-based carbon fiber degassing condensate with an acrylonitrile content of 10 wt%, a water content of 2 wt%, and a dimethyl sulfoxide content of 88% enters the first separation column as the raw material to be separated, and is rectified under the conditions of 25 kPa and a tower bottom temperature of 133 °C. The gas-phase material at the top of the first separation column enters condenser E-1, and the condensation temperature does not exceed 33 °C. The condensed first light fraction enters a baffle-equipped liquid separation storage tank, and no membrane separation treatment is carried out.

[0088] 50 wt% of the oil-phase material separated from the oil-phase outlet of the liquid separation storage tank V1 enters the second separation column with 10 theoretical plates at 40% of the volume. Distillation is carried out under the conditions of 80 kPa, a column bottom temperature of 70 °C, and a reflux ratio of 2. The remaining non-distilled gas-phase material enters the condenser E-2 with a condensation temperature not exceeding 35 °C. Side-stream discharge is carried out at 2 theoretical plates above the column bottom of the T2 column, and the temperature difference between the side-stream temperature and the column bottom temperature is controlled to be ≤ 3 °C. The side-stream fraction is the recovered acrylonitrile monomer product.

[0089] After analysis, the DMSO content in the first heavy component is 95.7 wt%, the acrylonitrile content is 0.3 wt%, and the balance is mainly water; the purity of the acrylonitrile product obtained by side-stream discharge from T2 is 98.6%, and the water content is 1.4 wt%. Moreover, the acrylonitrile content in the aqueous-phase material discharged from the liquid separation storage tank reaches more than 4%, becoming a high-concentration waste liquid, bringing greater environmental protection pressure.

[0090] Comparative Example 2

[0091] Same as Example 1, except that a mixed waste liquid with an acrylonitrile content of 55 wt%, a water content of 15 wt%, and a dimethyl sulfoxide content of 30 wt% is used as the raw material to be separated.

[0092] After analysis, the DMSO content in the first heavy component is 96.7 wt%, the acrylonitrile content is 0.5 wt%, and the balance is mainly water; the purity of the acrylonitrile product obtained by side-stream discharge from T2 is 98.7%, and the water content is 1.3 wt%.

[0093] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for separating a mixture containing acrylonitrile and water, characterized in that, the method comprises: a. subjecting the mixture to a first rectification to obtain a first heavy component stream and a first gas-phase stream; b. condensing the first gas-phase stream and sending it for oil-water separation to obtain an oil-rich phase and a water-rich phase; c. subjecting the water-rich phase to membrane separation to obtain a dehydrated recycle liquid and water; d. recycling the dehydrated recycle liquid back into the condensate of the first gas-phase stream; e. subjecting at least a part of the oil-rich phase to a second rectification to obtain a side-stream product of acrylonitrile, a second heavy component stream and a second gas-phase stream; In the mixture, the content of acrylonitrile is ≤ 50 wt%, and the content of water is ≤ 10 wt%.

2. The separation method according to claim 1, wherein, the first heavy component stream contains at least one of dimethyl sulfoxide, N,N-dimethylacetamide, sodium thiocyanate, preferably dimethyl sulfoxide.

3. The separation method according to claim 1 or 2, wherein, in the mixture, the content of acrylonitrile is ≤ 30 wt%, and the content of water is ≤ 5 wt%.

4. The separation method according to any one of claims 1-3, wherein, in step e, a part of the oil-rich phase is recycled back to step a for the first rectification, and the recycling ratio is 0.1-10; and / or after the second gas-phase stream is condensed, a part of it is recycled back into the condensate of the first gas-phase stream, and a part of it is recycled back to step e for the second rectification, and the mass ratio of the amount recycled back into the condensate of the first gas-phase stream to the amount recycled back to step e for the second rectification is 0.1-10.

5. The separation method according to any one of claims 1-4, wherein, the conditions of the first rectification include: at least 8 theoretical plates; and / or the operating pressure is 7-25 kPa, preferably 10-15 kPa; and / or the bottom temperature is 100-140 °C, preferably 110-125 °C.

6. The separation method according to any one of claims 1-5, wherein, the conditions for condensing the first gas-phase stream include: the temperature does not exceed 38 °C, preferably does not exceed 25 °C, more preferably does not exceed 15 °C.

7. The separation method according to any one of claims 1-6, wherein, the conditions of the membrane separation include: the temperature of the membrane module is 10-65 °C, preferably 35-55 °C; the operating pressure on the permeate side is 0-20 kPa, preferably 5-15 kPa.

8. The separation method according to any one of claims 1-7, wherein, the conditions of the second rectification include: 10-30 theoretical plates; and / or the operating pressure is 40-80 kPa, preferably 50-70 kPa; and / or the bottom temperature is 50-70 °C, preferably 55-65 °C; and / or the reflux ratio is 1-10, preferably 2-5; and / or the temperature difference between the side-stream product extraction temperature of acrylonitrile and the bottom temperature does not exceed 5 °C, preferably does not exceed 3 °C.

9. Application of the separation method according to any one of claims 1-8 in the preparation of PAN-based carbon fibers.

10. A separation device for a mixture containing acrylonitrile, water and dimethyl sulfoxide, characterized in that, the device comprises: The first separation unit is used for the enrichment of dimethyl sulfoxide; The first condensation unit communicated with the gas phase outlet of the first separation unit; The liquid separation unit communicated with the discharge port of the first condensation unit; the liquid separation unit is provided with an oil phase outlet and an aqueous phase outlet, and a reflux ratio distributor is arranged at the oil phase outlet, so that part of the oil phase material is refluxed to the first separation unit, and the other part of the oil phase material is sent to the second separation unit; a membrane separation part is arranged at the aqueous phase outlet of the liquid separation storage tank, and the non-permeate phase outlet is communicated with the liquid separation unit; The second separation unit communicated with the oil phase discharge port of the liquid separation unit, and a side line discharge port is arranged between the feed inlet and the bottom of the second separation tower for separating and obtaining high-purity acrylonitrile; And the second condensation unit arranged at the gas phase outlet of the second separation unit; Preferably, the extraction end of the second condenser is respectively communicated with the liquid separation unit and the second separation unit.

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