A mixture separation system and method for separating a mixture comprising acrylonitrile, water and dimethyl sulfoxide

Abstract

The application discloses a mixture separation system and method containing acrylonitrile, water and dimethyl sulfoxide, and the separation system comprises a dividing wall column, a vertical layered tank, a reboiler and a polymerization inhibition protection unit. A vertical dividing wall plate is arranged in the dividing wall column, and the vertical dividing wall plate divides the internal space of the dividing wall column into a pre-fractionation section and a main column section. The main column section comprises a common rectification section at the upper portion, a side line extraction section at the middle portion and a common stripping section at the lower portion, and the middle portion of the main column section is the side line extraction section. A feeding port and a side line discharge port are arranged on the side surface of the dividing wall column, the feeding port is connected with the pre-fractionation section, the side line discharge port is connected with the side line extraction section, a crude distillate outlet is arranged at the top of the dividing wall column, and a dimethyl sulfoxide extraction outlet is arranged at the bottom of the dividing wall column.

Description

Technical Field

[0001] This invention relates to the field of separation equipment technology, and more specifically, to a separation system and method for a mixture containing acrylonitrile, water and dimethyl sulfoxide. Background Technology

[0002] Acrylonitrile-based carbon fiber is a high-grade fiber material with excellent properties such as high strength, high modulus, and high temperature resistance, playing an irreplaceable role in national economy, people's livelihood, and defense industry. In the carbon fiber preparation process, polymerization is a crucial component, using acrylonitrile as the monomer and dimethyl sulfoxide as the solvent. However, during polymerization, the monomer conversion rate is only 87%–90%, and unreacted monomers need to be removed in the post-treatment process of the polymerization solution. If unreacted monomers cannot be effectively recycled, it will affect production costs.

[0003] Currently, the most commonly used method for removing monomers and bubbles in carbon fiber production is the vacuum method. However, this method has some problems: acrylonitrile and water are azeotropic, and dimethyl sulfoxide is prone to decomposition during distillation. It is difficult to separate the material and reuse acrylonitrile monomers by distillation alone. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a separation system and method for a mixture containing acrylonitrile, water and dimethyl sulfoxide.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] This invention discloses a separation system for a mixture containing acrylonitrile, water, and dimethyl sulfoxide, comprising a partition column, a vertical separator, a reboiler, and a polymerization inhibition unit. The partition column has a vertical partition plate that divides its internal space into a pre-fractionation section and a main column section. The main column section includes an upper common rectification section, a middle side-stream collection section, and a lower common stripping section, with the side-stream collection section located in the middle. The partition column has a feed inlet and a side-stream outlet on its side. The feed inlet is connected to the pre-fractionation section, and the side-stream outlet is connected to the side-stream collection section. The top of the partition column has a crude distillate outlet, and the bottom of the partition column has a dimethyl sulfoxide collection outlet. The vertical separator includes a main section and a bottom section. The main section has an inlet and an overflow outlet on two opposite sides. The inlet of the vertical layered tank is connected to the crude distillate outlet at the top of the adjacent column, and a turbulence-inducing structure is fixedly installed inside the vertical layered tank. A condenser and a reflux tank are installed on the pipeline connecting the inlet of the vertical layered tank to the crude distillate outlet at the top of the adjacent column. The reboiler is installed at the bottom of the adjacent column. The polymerization inhibitor protection unit includes a polymerization inhibitor injection device, an online turbidity monitoring device, and an interlocking control module. The polymerization inhibitor injection device is connected to the pipeline connecting the feed inlet of the adjacent column, the reflux tank, and the overflow outlet of the vertical layered tank. The online turbidity monitoring device is installed on the outlet pipeline of the reboiler, the production pipeline of the dimethyl sulfoxide production outlet, and the downstream pipeline of the polymerization inhibitor injection device. The interlocking control module is electrically connected to the online turbidity monitoring device, the polymerization inhibitor injection device, and the reboiler electrical control mechanism.

[0007] Furthermore, the height of the vertical partition plate accounts for 50% to 65% of the total height of the partition column, the lower end of the vertical partition plate is 1 / 3 to 1 / 2 of the column height from the bottom of the column, the pre-fractionation section is equipped with 15 to 25 theoretical plates, the main column section is equipped with 30 to 45 theoretical plates, and the side stream outlet is located between the 25th and 35th theoretical plates.

[0008] Furthermore, the bottom end of the partition plate is provided with a gas phase distribution structure component for controlling the gas phase distribution ratio between the pre-fractionation section and the main column section. The gas phase distribution component is a fixed gas phase distribution plate or an adjustable gas phase distribution valve, and the gas phase distribution ratio is 0.40–0.55.

[0009] Furthermore, a liquid distributor is provided at the top of the vertical partition plate, with a liquid phase distribution ratio of 0.35–0.50.

[0010] Furthermore, the main body of the vertical stratified tank is a cylindrical cavity, the bottom section is a conical structure, and the turbulence-inducing structure is arranged inside the main body.

[0011] Furthermore, the turbulence structure is a vertically arranged plate-like component located on the liquid flow path between the inlet and the overflow port. The horizontal distance between its liquid-facing plate surface and the inlet centerline is 4 to 10 times the inner diameter of the inlet nozzle. Two elongated oval grooves with their length along the vertical direction are opened on each of the two sides of the turbulence structure. The ratio of the total volume ΣVg of the four elongated oval grooves to the feed volume flow rate Qv of the vertical stratified tank is 10 to 60s. The groove length L1 of the elongated oval groove is 1 / 4 to 1 / 3 of the height of the turbulence structure, the groove width is 1 / 5 to 1 / 3 of the groove length, and the groove depth is 1 / 3 to 1 / 2 of the thickness of the turbulence structure. The two elongated oval grooves on the same side are arranged vertically at intervals. The net distance Sn between adjacent ends is 1 / 3 to 1 / 2 of the groove length L1 and is not less than the sum of twice the maximum fluctuation amplitude of the phase separation interface and 1 / 4 of the groove length L1. The steady-state phase separation interface of the vertical stratified tank is located in the plate surface area between the two elongated oval grooves.

[0012] A separation method based on a mixture separation system containing acrylonitrile, water, and dimethyl sulfoxide includes the following steps:

[0013] S1. Feed: The mixture containing acrylonitrile, water and dimethyl sulfoxide is fed into the pre-fractionation section of the partition tower at a feed temperature of 20-40℃.

[0014] S2. Vacuum distillation separation in a partition column: Control the operating pressure of the partition column to 10-30 kPa, preferably 15-20 kPa; control the top reflux ratio to 1-5, the side reflux ratio to 1-5, and do not set a reflux at the bottom of the column;

[0015] S3. Precise temperature control in segments: Top temperature 43-65℃, side stream extraction temperature 45-70℃, bottom temperature 120-145℃; bottom temperature is indirectly heated by steam or heat transfer oil, with multi-point temperature monitoring and online sulfide chromatography detection.

[0016] S4. Simultaneous extraction of three components: crude distillate is extracted from the top of the column, process water is extracted from the side stream, and dimethyl sulfoxide solvent is extracted from the bottom of the column.

[0017] S5. Top Distillate Phase Separation and Purification: The top distillate is sent to a vertical separator for gravity separation. The upper layer is used to extract high-purity acrylonitrile for reuse, and the lower aqueous phase is recycled and treated.

[0018] Furthermore, in step S2, the operating pressure of the partition column is 15-20 kPa, the gas phase distribution ratio of the partition column is maintained at 0.40-0.55, and the liquid phase distribution ratio is maintained at 0.35-0.50; when the gas phase distribution ratio increases, the liquid phase distribution ratio is simultaneously reduced to maintain a stable vapor-liquid ratio in the pre-fractionation section.

[0019] Furthermore, polymerization inhibitors are continuously added at three locations: the feed inlet connection line, the reflux tank connection line, and the overflow connection line. TEMPO-type polymerization inhibitors are used, specifically 4-HT polymerization inhibitors, and the concentration of the polymerization inhibitors is controlled at 10ppm to 50ppm.

[0020] Furthermore, the product purity indicators are as follows: the purity of acrylonitrile collected from the upper layer after stratification in the vertical stratification tank is ≥98.5wt%, the purity of process water collected from the side stream is ≥99.5wt%, and the purity of dimethyl sulfoxide collected from the bottom of the tower is ≥99.5wt%.

[0021] Furthermore, the bottom temperature control in step S3 adopts the following linkage mechanism: when the multi-point temperature monitoring device detects that the local temperature at the bottom of the column exceeds 145°C or the online sulfide chromatography detects dimethyl sulfoxide decomposition products, the reboiler heating power is reduced; when the online turbidity monitoring device detects that the turbidity exceeds 5 NTU, the interlock control module automatically increases the injection amount of the polymerization inhibitor dosing device and simultaneously reduces the reboiler heating power until the turbidity recovers to below 5 NTU.

[0022] The beneficial effects of this invention are: by using a single-tower design with a partitioned wall, pre-fractionation, distillation, stripping, and side-stream collection are integrated into one tower, reducing the number of heating and condensation cycles. Compared with the traditional three-tower series process, the energy consumption per unit product is reduced. By optimizing the operating pressure of the partitioned wall and the location of the side-stream collection, the azeotropic zone can be effectively avoided, achieving high-purity separation of acrylonitrile. Attached Figure Description

[0023] Fig. 1 This is a schematic diagram of one structure in this embodiment;

[0024] Fig. 2 This is a schematic diagram of one type of turbulence structure in this embodiment.

[0025] Reference numerals: 100, Divider column; 101, Feed inlet; 102, Side stream outlet; 103, Crude distillate outlet; 104, Dimethyl sulfoxide outlet; 110, Vertical partition plate; 120, Pre-fractionation section; 130, Main column section; 131, Common rectification section; 132, Side stream outlet section; 133, Common stripping section; 200, Vertical layered tank; 210, Elliptical head; 220, Main section; 221, Inlet; 222, Overflow outlet; 230, Conical structure; 240, Turbulence structure; 241, Groove; 300, Condenser; 400, Reflux tank. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] like Figs. 1-2 As shown, a separation system for a mixture containing acrylonitrile, water and dimethyl sulfoxide includes a partition tower 100, a vertical stratification tank 200, a condenser 300, a reflux tank, a reboiler and a polymerization inhibition protection unit.

[0028] A vertical partition plate 110 is installed inside the diverter column 100. This vertical partition plate 110 divides the internal space of the column longitudinally into two parallel channels: one side is the pre-fractionation section 120, and the other side is the main column section 130. The main column section 130 is further divided from top to bottom into an upper common rectification section 131, a middle side-stream extraction section 132, and a lower common stripping section 133.

[0029] The side of the partition column 100 is provided with a feed inlet 101 and a side outlet 102. The feed inlet 101 is located in the lower middle part of the pre-fractionation section 120, corresponding to theoretical plates 5-20, and is used to introduce a mixture containing acrylonitrile, water, and dimethyl sulfoxide into the pre-fractionation section 120 for preliminary separation. The side outlet 102 is located in the side outlet section 132 of the main column section 130, corresponding to theoretical plates 25-35, and is used to extract the intermediate component, process water. The top of the partition column 100 is provided with a crude distillate outlet 103, used to extract the overhead vapor, which is mainly composed of acrylonitrile and water; the bottom is provided with a dimethyl sulfoxide outlet 104, used to extract the heavy component, dimethyl sulfoxide.

[0030] The height of the vertical partition plate 110 accounts for 50% to 65% of the total height of the partition column 100, and its lower end is 1 / 3 to 1 / 2 of the column height from the bottom of the column. The pre-fractionation section 120 is equipped with 15 to 25 theoretical plates, and the main column section 130 is equipped with 30 to 45 theoretical plates. A gas phase distribution structure component is provided at the bottom of the vertical partition plate 110 to control the gas phase distribution ratio between the pre-fractionation section 120 and the main column section 130. This gas phase distribution component 111 can be a fixed gas phase distribution plate or an adjustable gas phase distribution valve. The fixed gas phase distribution plate achieves fixed distribution through a preset opening area ratio.

[0031] The adjustable gas phase distribution valve achieves closed-loop regulation through a butterfly valve or louvered regulating valve in conjunction with a differential pressure sensor, controlling the gas phase distribution ratio between 0.40 and 0.55. A liquid distributor is installed at the top of the vertical partition plate 110 to control the liquid phase distribution ratio, with a recommended value of 0.35 to 0.50. When the acrylonitrile content in the input mixture increases, the gas phase distribution ratio increases, and the liquid phase distribution ratio is simultaneously decreased to maintain a stable vapor-liquid ratio in the pre-fractionation section. Specifically, based on the feed composition and separation requirements, the baseline parameters under the design conditions are determined through process simulation or calibration experiments: the baseline value of the gas phase distribution ratio VSR0 and the baseline value of the liquid phase distribution ratio LSR0. Pre-fractionation side vapor-liquid ratio baseline value:

[0032]

[0033] In the formula, L represents the total descending liquid phase flow rate above the adjacent column, and V represents the total ascending vapor phase flow rate below the adjacent column. The target value of the adjusted vapor phase distribution ratio, VSR, is obtained through differential pressure sensors or flow calculations. t Calculation and VSR t Matching liquid phase distribution ratio:

[0034]

[0035] In the formula, The decoupling index is taken as 0.5–1.0. When the vapor-phase distribution ratio increases, the vapor load on the pre-fractionation side increases. If the liquid-phase distribution ratio remains constant, the vapor-liquid ratio on the pre-fractionation side decreases, the liquid layer thins, and tends towards the dry plate. The liquid-phase distribution ratio is simultaneously reduced according to the above formula, causing a corresponding decrease in the liquid load on the pre-fractionation side, and the vapor-liquid ratio recovers to near the baseline value, maintaining a stable mass transfer state on the tray. Conversely, when the vapor-phase distribution ratio decreases, the liquid-phase distribution ratio increases simultaneously to prevent excessive liquid phase from causing flooding. The calculated LSR is then used to... t Apply boundary constraints: If LSR t If the value is greater than 0.50, then take the LSR. t It is 0.5; if LSR t If <0.35, then take LSR. t The value is 0.35. The LSR after limiting is... t The output is sent to the liquid distributor for appropriate adjustment.

[0036] Calculate the adjusted vapor-liquid ratio on the pre-fractionation side:

[0037]

[0038] Verify whether it satisfies:

[0039]

[0040] Here, coefficients 0.85 and 1.15 represent the lower and upper safety margins of the vapor-liquid ratio on the pre-fractionation side relative to the design baseline, respectively, corresponding to the empirical distance between the leakage point (dry plate point) and the flooding point in engineering practice. If the verification passes, the coordinated adjustment is completed; if it exceeds this range, an alarm is triggered, further adjustment of the vapor phase distribution ratio is suspended, and VSR0 and LSR0 are recalibrated after the system stabilizes.

[0041] The vertical separator 200 is used to perform gravity settling and stratification of the crude distillate collected from the top of the adjacent column 100 to overcome the azeotropic limitation of acrylonitrile and water. The vertical separator 200 includes an elliptical top head 210, a cylindrical main body section 220 in the middle, and a conical bottom structure 230. The main body section 220 has an inlet 221 and an overflow port 222 on two opposite sides. The inlet 221 is connected to the crude distillate outlet 103 at the top of the adjacent column 100 via a pipeline, and the overflow port 222 is used to discharge the upper acrylonitrile-rich phase. The conical bottom structure 230 facilitates the collection and discharge of the heavy phase medium.

[0042] The vertical stratification tank 200 is internally equipped with a turbulence-inducing structure 240, with two elongated oval grooves 241 on both sides. When material enters the container or there are fluctuations in the liquid level inside, the originally empty container is prone to turbulence, which can disrupt the stability of the static stratification. The newly added turbulence-inducing structure 240 acts like a baffle, buffering the flowing liquid phase, reducing the impact of the liquid flow, preventing the two phases that have already been separated from being mixed again, and helping the system reach a stable stratification state more quickly. Acrylonitrile and water are partially miscible systems, and mass transfer occurs at the interface between the two phases during static settling. Trace components that are not completely separated require time to migrate. The presence of the elongated oval grooves 241 creates multiple small residence zones within the container, prolonging the residence time of the liquid phase in these zones. This promotes the escape of trace amounts of dissolved acrylonitrile from the aqueous phase and the precipitation of trace amounts of water from the acrylonitrile phase, improving the final separation purity.

[0043] Specifically, the turbulence structure 240 is a vertically arranged plate-shaped component, fixedly installed on the inner wall of the main body section 220, located on the liquid flow path between the inlet 221 and the overflow port 222, with its liquid-facing plate facing the outflow direction of the inlet 221. The horizontal distance L0 between the liquid-facing plate of the turbulence structure 240 and the centerline of the inlet 221 is 4 to 10 times the inner diameter D0 of the inlet 221 nozzle: the feed jet diffuses fully along the diffusion cone angle during its flow over this distance, and after the jet cross-sectional area expands to more than 5 times the inlet cross-sectional area, it impacts the center of the plate surface of the turbulence structure 240, resulting in a significant reduction in kinetic energy density. The remaining kinetic energy is dissipated by the plate surface, preventing the feed from directly impacting the phase interface or forming a short-circuit flow in the tank; if L0 is less than 4 times D0, the jet impacts the plate surface before it has fully diffused, and the reflected flow will mix the phase interface; if L0 is greater than 10 times D0, the jet impact position deviates from the center of the plate surface, and the buffering effect fails. The height of the turbulence structure 240 is 50% to 70% of the height of the main section 220, the top end is 50 to 100 mm above the highest operating liquid level, and a double phase flow gap with a height of 1 / 10 to 1 / 6 of the height of the main section 220 is left between the bottom end and the top end of the conical structure 230.

[0044] Two elongated oval grooves 241 are provided on each of the two sides of the turbulence structure 240. The length of the grooves is along the vertical direction, and the vertical center line of each groove coincides with the vertical center line of the plate surface. The length L1 of the elongated oval groove 241 is 1 / 4 to 1 / 3 of the height of the turbulence structure 240, the width W1 is 1 / 5 to 1 / 3 of the length L1, and the depth H1 is 1 / 3 to 1 / 2 of the thickness of the turbulence structure 240. The groove walls have a smooth arc transition. The ratio of the total volume ΣVg of the four elongated oval grooves 241 to the feed volumetric flow rate Qv of the vertical layered tank 200 is defined as the characteristic residence time tr of the groove zone. tr is controlled between 10 and 60 s. The lower limit of tr is greater than the migration relaxation time of trace components at the interface of the acrylonitrile-water partially miscible system, which is measured to be 2–6 s. This ensures that the liquid phase entering the low-flow-rate zone of the tank has sufficient time to complete the escape of trace acrylonitrile from the aqueous phase and the precipitation of trace water from the acrylonitrile phase. The upper limit of tr is less than 1 / 5 of the polymerization induction period of acrylonitrile at an operating temperature of 43–65 °C with 10–50 ppm 4-HT polymerization inhibitor. This polymerization induction period is not less than 300 s, ensuring that the liquid phase in the tank is completely renewed during the polymerization induction period, avoiding the retention, polymerization, adhesion, and blockage of acrylonitrile in the low-flow-rate zone of the groove. Therefore, the size of the elongated oval grooves 241 is not arbitrarily selected, but is a window defined by the constraints of the lower limit of mass transfer and the upper limit of polymerization in opposite directions.

[0045] Two elongated oval grooves 241 on the same side are arranged vertically at intervals. The distance between the bottom of the lower groove and the top of the upper groove and the corresponding end of the turbulence structure 240 is 1 / 10 to 1 / 8 of its height. The net distance Sn between adjacent ends of the two elongated oval grooves 241 is 1 / 3 to 1 / 2 of the groove length L1, and Sn is not less than twice the maximum fluctuation amplitude Δh of the phase separation interface and 1 / 4 of the groove length L1. In the installed state, the steady-state phase separation interface is located in the middle of the plate area between the two elongated oval grooves 241. Even if the phase separation interface fluctuates within the range of Δh, the distance between the interface and the end of either groove is still not less than 1 / 8 of the groove length L1. The light phase always flows through the upper residence area formed by the upper groove, and the heavy phase always flows through the lower residence area formed by the lower groove, avoiding interface fluctuations from intruding into the groove and causing cross-contamination between the two phases. The elongated oval grooves 241 on both sides of the turbulence structure 240 are arranged facing each other or staggered in the vertical direction, with an stagger distance of 1 / 4 to 1 / 2 of the groove length L1.

[0046] In this embodiment, the main body section 220 has an inner diameter of 800mm and a height of 1600mm; the inlet 221 has a DN40 connector; the turbulence structure 240 has a height of 1000mm, a thickness of 40mm, and a plate width of 350mm. The horizontal distance L0 between the liquid-facing plate and the centerline of the inlet 221 is 300mm, L0 / D0 = 7.5, the top is 80mm above the highest operating liquid level, and the bottom heavy phase flow gap height is 200mm. The elongated oval groove 241 has a groove length L1 of 320mm, a groove width W1 of 90mm, and a groove depth H1 of 15mm. The volume of a single groove is approximately 406cm³, and the total volume ΣVg of the four grooves is approximately 1.62L. The corresponding feed volumetric flow rate is 102~390kg / h, approximately 0.12~0.43m³ / h, and the characteristic residence time tr is 13~49s, which is within the 10~60s window. The bottom of the lower side trough is 100mm from the bottom of the turbulence structure 240, the net distance between the two troughs Sn is 160mm, and the top of the upper side trough is 100mm from the top. The maximum fluctuation amplitude Δh of the steady-state phase separation interface is 40mm, Sn=160mm=2Δh+L1 / 4, the interface is located in the middle of the net distance zone, and the distance from the ends of the two troughs is 80mm.

[0047] The turbulence structure 240 is arranged inside the main body section 220. By forming a meandering flow path to extend the liquid phase flow path, it plays a role in turbulence buffering, increasing the residence time at the phase interface, optimizing the flow field distribution and eliminating flow dead zones, thereby enhancing the gravity settling separation effect of acrylonitrile and water.

[0048] Condenser 300 is installed on the pipeline connecting the inlet 221 of vertical separator 200 to the crude distillate outlet 103 at the top of the adjacent column 100, and is used to condense the overhead vapor into a liquid phase. A reflux tank is connected to condenser 300 and is used to temporarily store the condensate. The reflux tank is equipped with a reflux line connected to the top of the adjacent column 100; part of the condensate is returned to the top of the column as reflux, and the remainder is sent to the vertical separator 200 for stratification.

[0049] The reboiler is installed at the bottom of the adjacent column 100 and uses indirect heating with steam or thermal oil to provide rising steam to the column. The heating temperature of the reboiler is controlled between 132℃ and 148℃ to ensure that the bottom temperature of the column is maintained within the range of 120℃ to 145℃, which is strictly below the decomposition temperature of dimethyl sulfoxide.

[0050] The polymerization inhibition protection unit includes a polymerization inhibitor dosing device, an online turbidity monitoring device, and an interlocking control module.

[0051] The polymerization inhibitor injection device is connected to the feed inlet of the adjacent tower, the reflux tank, and the overflow outlet of the vertical stratified tank, respectively, to achieve continuous polymerization inhibitor injection at three key locations: before feeding, at the top of the tower for reflux, and before product extraction. The polymerization inhibitor used is 4-HT, and the concentration is controlled at 10ppm to 50ppm.

[0052] Online turbidity monitoring devices are installed on the outlet pipeline of the reboiler, the outlet pipeline of the dimethyl sulfoxide outlet 104, and the downstream pipeline of the polymerization inhibitor injection device to monitor the generation of polymer particles in real time.

[0053] The interlock control module is electrically connected to the online turbidity monitoring device, the polymerization inhibitor dosing device, and the electrical control mechanism of the reboiler. When the online turbidity monitoring device detects that the turbidity exceeds 5 NTU, the interlock control module triggers an alarm, increases the injection rate of the polymerization inhibitor dosing device, and simultaneously reduces the heating power of the reboiler until the turbidity returns to below 5 NTU.

[0054] Example 1

[0055] The condensate from the production of PAN-based carbon fibers after partial depolymerization is separated. The feed contains 1 wt% acrylonitrile, and the three components of acrylonitrile, water, and dimethyl sulfoxide (DMSO) need to be separated simultaneously. The feed composition is 1 wt% acrylonitrile, 55 wt% water, and 44 wt% DMSO. The feed temperature is 20℃, and the feed flow rate is 3000 kg / h. The operating pressure is 15–20 kPa; the top temperature is 52–58℃; the side stream temperature is 55–63℃; and the bottom temperature is 128–140℃. The top reflux ratio is 3, and the side stream reflux ratio is 2. The bottom is indirectly heated by steam at a temperature of 132–142℃. The condenser cooling medium is circulating cooling water with an inlet temperature of 28–30℃. The vapor-phase distribution ratio (VSR) is 0.40–0.55, and the liquid-phase distribution ratio (LSR) is 0.35–0.50.

[0056] The flow rate of the crude distillate from the top of the column is 102–108 kg / h, with an acrylonitrile content of 27.8–29.5 wt%, a water content of 70.0–71.8 wt%, and a dimethyl sulfoxide content of ≤0.1 wt%. The crude distillate from the top of the column is fed into a vertical separatory tank. Utilizing the liquid-phase equilibrium characteristics of the partially miscible acrylonitrile and water phases, combined with the structural optimization effects of the tank's meandering flow path, turbulence buffering, and extended phase interface residence time, gravity-induced stratification is achieved. The lighter acrylonitrile phase is enriched in the upper layer, while the heavier aqueous phase settles in the lower layer, without being restricted by the atmospheric pressure azeotropic system.

[0057] The product specifications after separation in the vertical separation tank are as follows: Acrylonitrile phase flow rate 28–30 kg / h, purity 98.4–98.8 wt%, water impurities 1.2–1.6 wt%, no dimethyl sulfoxide detected, can be directly recycled in the PAN polymerization process. Aqueous phase flow rate 72.0–78.0 kg / h, purity 96–98 wt%, containing trace dissolved acrylonitrile 2.0–4.0 wt%, can be sent to subsequent water treatment or returned to the system for recycling.

[0058] The side outlet has a flow rate of 1580-1590 kg / h, a water content of 99.5-99.9 wt%, a trace acrylonitrile content of ≤0.05 wt%, and a dimethyl sulfoxide content of 0.1-0.5 wt%. It can be used directly as process makeup water or discharged after treatment to meet standards.

[0059] The dimethyl sulfoxide (DMSO) outlet has a flow rate of 1312–1319 kg / h, a DMSO purity of 99.5–99.9 wt%, and a total impurity of trace water plus acrylonitrile ≤0.5 wt%. No sulfide decomposition products were detected, and the thermal stability is controllable. It can be directly reused in the PAN polymerization dissolution process.

[0060] The total output of the three phases is matched with the total feed to achieve material balance. The reboiler heat load is 3300-3400 kW, and the condenser cooling load is 3030-3080 kW. Compared with the traditional three-tower series process, the energy consumption per unit product is reduced by 35%-40%, and the energy saving rate under typical operating conditions is 38.4%.

[0061] In this embodiment, the top reflux ratio is controlled at 3, and the side reflux ratio is controlled at 2. Under these reflux ratio conditions, the acrylonitrile concentration in the acrylonitrile-water mixture at the top of the column is effectively controlled at around 28.5 wt%, ensuring a moderate top product and providing a suitable concentration window for gravity settling in the subsequent vertical separator. If the top reflux ratio drops below 1, the acrylonitrile concentration at the top will increase to over 35 wt%, leading to a decrease in the density difference between the two phases in the vertical separator and a decline in separation efficiency. If the top reflux ratio is increased to over 5, although the acrylonitrile concentration at the top can be further reduced, the reboiler heat load will increase to over 3800 kW, resulting in a significant increase in energy consumption. Therefore, a top reflux ratio of 3 and a side reflux ratio of 2 are the preferred operating points in this embodiment.

[0062] Example 2

[0063] A high-acrylonitrile feed mixture was separated. The feed composition was 8 wt% acrylonitrile, 50 wt% water, and 42 wt% dimethyl sulfoxide. The feed temperature was 25°C, and the feed flow rate was 3000 kg / h. The operating pressure was 16–20 kPa, the top temperature was 53–61°C, the side stream temperature was 56–64°C, and the bottom temperature was 130–142°C. The top reflux ratio was 4, and the side stream reflux ratio was 3. The bottom heating method was indirect steam heating at a temperature of 132–148°C. The condenser cooling medium was circulating cooling water with an inlet temperature of 28–30°C.

[0064] Polymerization inhibitor system: 4-HT polymerization inhibitor is used, and it is continuously added at three points: the feed line, the top reflux tank, and the stratified settling tank, with the concentration controlled at 10-50 ppm.

[0065] The flow rate of the crude distillate from the top of the column is 375–390 kg / h, with an acrylonitrile content of 60.0–62.0 wt%, a water content of 38.0–40.0 wt%, and a dimethyl sulfoxide content of ≤0.1 wt%. The crude distillate from the top of the column is sent to a vertical separator for gravity settling and stratification.

[0066] The product specifications after separation in the vertical separation tank are as follows: Acrylonitrile phase flow rate 238–242 kg / h, purity 98.5–98.9 wt%, water impurities 1.1–1.5 wt%, no dimethyl sulfoxide detected, can be directly recycled in the PAN polymerization process. Aqueous phase flow rate 130–152 kg / h, purity 96.2–97.8 wt%, containing trace dissolved acrylonitrile 2.2–3.8 wt%, can be sent to subsequent water treatment or returned to the system for recycling.

[0067] The side outlet has a flow rate of 1350–1370 kg / h, a water content of 99.5–99.9 wt%, a trace acrylonitrile content of ≤0.05 wt%, and a dimethyl sulfoxide content of 0.1–0.4 wt%. It can be directly used as process makeup water or discharged after treatment to meet standards.

[0068] The dimethyl sulfoxide (DMSO) outlet flow rate is 1245–1255 kg / h, and the DMSO purity is 99.6–99.9 wt%. Trace amounts of water and total acrylonitrile impurities are ≤0.4 wt%. Online sulfide chromatography analysis showed no sulfide decomposition products, and the thermal stability is controllable, allowing for direct reuse in the PAN polymerization dissolution process.

[0069] The total output of the three phases is matched with the total feed to achieve material balance. The reboiler heat load is 3700-3800kW, and the condenser cold load is 3400-3500kW. Compared with the traditional three-tower series process, the energy consumption per unit product is reduced by 35%-39%, and the energy-saving effect remains stable under high acrylonitrile feed conditions.

[0070] After 720 hours of continuous operation, the purity fluctuations of each product were controlled within ±1.0%; there were no over-temperature points in the tower, no dimethyl sulfoxide decomposition byproducts were detected, and there was no polymer blockage in the trays, pipelines, and reboiler. The unit is highly adaptable to fluctuations in the composition of high acrylonitrile feed and operates stably.

[0071] Because the acrylonitrile content in the feed increased from 1.0 wt% to 8.0 wt% in this embodiment, the overhead product volume increased significantly. To ensure the separation efficiency at the top of the column and control the acrylonitrile concentration within a suitable stratification range, the overhead reflux ratio was increased from 3 to 4, and the side stream reflux ratio was increased from 2 to 3. Sufficient reflux liquid was provided at the top of the column for washing to prevent acrylonitrile from prematurely penetrating to the side stream; sufficient liquid phase was provided for reflux in the side stream to maintain the aqueous phase purity ≥99.5 wt%. If the reflux ratio of Example 1 were maintained, the acrylonitrile concentration at the top of the column would increase to over 65 wt%, increasing the viscosity of the light phase in the vertical stratification tank, prolonging the stratification time, and reducing the processing efficiency.

[0072] Comparative Example 1

[0073] A conventional three-tower series process—a light-light component removal tower, an azeotropic distillation tower, and a solvent recovery tower—was used to process the same feed as in Example 1. The light-light component removal tower operated at atmospheric pressure, removing acrylonitrile and water from the top and yielding a product containing dimethyl sulfoxide and water at the bottom. The azeotropic distillation tower operated under pressure, using an extractant or pressurization to alter the azeotropic composition and separate acrylonitrile and water. The solvent recovery tower operated under reduced pressure to recover dimethyl sulfoxide.

[0074] The second column yielded acrylonitrile at the top, with a flow rate of 28.0 kg / h and a purity of 96.5 wt%. Due to the azeotropic limitation of acrylonitrile-water, even with pressurized distillation, the purity of the acrylonitrile at the top of the second column could not overcome the azeotropic composition limitation, resulting in a final product purity of only 96.5 wt%, below 98.5 wt%. Water was collected from the bottom of the second column, with a flow rate of 1580.0 kg / h and a purity of 98.5 wt%. Dimethyl sulfoxide was collected from the bottom of the third column, with a flow rate of 1310.0 kg / h and a purity of 98.8 wt%.

[0075] Tests revealed trace amounts of sulfide decomposition products in the dimethyl sulfoxide at the bottom of the third column. This was because the temperature at the bottom of the column reached 160°C, exceeding the thermal stability temperature range of DMSO, which led to the thermal decomposition of some DMSO.

[0076] The total heat load of the three-tower reboiler is 5400 kW. The total cooling load of the three-tower condenser is 4950 kW.

[0077]

[0078] The total heat load of the reboiler in the single-tower system of the adjacent tower is reduced compared to the traditional three-tower series system, significantly lowering operating costs. The purity of acrylonitrile and dimethyl sulfoxide (DMSO) is improved. By controlling the bottom temperature of the tower and using online sulfide chromatography, no sulfide decomposition products were detected in DMSO; whereas in the traditional process, the bottom temperature of the third tower reaches as high as 160℃, leading to the thermal decomposition of DMSO and the generation of sulfides.

[0079] Comparative Example 2

[0080] Using the same system and process conditions as in Example 1, the difference was that the depth H1 of the oblong groove 241 was increased from 15mm to 30mm, the total volume ΣVg of the four grooves was approximately 3.25L, and the characteristic residence time tr was approximately 98s, exceeding the upper limit of the 10-60s window. After 720 hours of continuous operation, a polymer adhesion layer of 0.3-0.5mm was detected on the inner wall of the oblong groove 241, requiring shutdown and cleaning. After separation in the vertical separation tank, the purity of the acrylonitrile phase decreased from 98.4-98.8wt% to 97.2wt%. This indicates that after the characteristic residence time tr exceeded the upper limit, the residence time of acrylonitrile in the low flow rate zone of the groove approached its polymerization induction period, resulting in delayed polymerization, which both blocked the groove and reduced the purity of the separation.

[0081] Comparative Example 3

[0082] Using the same system and process conditions as in Example 1, the difference lies in that the depth H1 of the oblong groove 241 is reduced from 15 mm to 5 mm, the total volume ΣVg of the four grooves is approximately 0.54 L, and the characteristic residence time tr is approximately 5 s, which is below the lower limit of the 10–60 s window. After separation in the vertical separation tank, the water impurity content of the acrylonitrile phase increased from 1.2–1.6 wt% to over 2.5 wt%, and the purity of the acrylonitrile phase decreased to below 97%. This indicates that when the characteristic residence time tr is below the lower limit, the liquid phase mass transfer time in the groove residence area is insufficient, and trace amounts of water cannot be fully separated from the acrylonitrile phase, resulting in a significant decrease in the purity of the separation.

[0083] Comparative Example 4

[0084] Using the same system and process conditions as in Example 1, the difference lies in that the net distance Sn between adjacent ends of the two elongated oval grooves 241 on the same side is reduced from 160 mm to 60 mm. Sn is less than twice the maximum fluctuation amplitude Δh (40 mm) of the phase separation interface and one-quarter of the groove length L1 (160 mm). During operation, the phase separation interface fluctuations repeatedly invade the residence area of ​​the upper elongated oval groove 241, and the aqueous phase is carried into the light phase. The purity fluctuation amplitude of the acrylonitrile phase increases from ±0.2% to ±1.0%, requiring a longer settling time to restore stable stratification. This indicates that when the net distance Sn does not meet the requirement of Sn≥2Δh+L1 / 4, the residence area of ​​the groove cannot maintain isolation from the fluctuating phase interface, and the cross-contamination between the two phases is aggravated.

[0085] The comparison between Example 1 and Comparative Examples 2 to 4 shows that the ratio of the total volume of the elongated groove 241 to the feed flow rate, and the dimensional relationship between the net distance between the two elongated grooves 241 and the phase interface fluctuation amplitude, together define the effective working window of the residence area in the vertical stratified tank. When within this window, the effects of turbulence buffering and extended phase interface residence time work synergistically, resulting in high acrylonitrile phase purity and no polymer adhesion during long-term operation. When outside this window, insufficient mass transfer, stagnant polymerization, or phase interface cross-contamination will occur, confirming the rationality of the above-mentioned dimensional parameters.

[0086] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A separation system for a mixture containing acrylonitrile, water, and dimethyl sulfoxide, characterized in that, The system includes a partition column, a vertical separator, a reboiler, and a polymerization inhibitor unit. The partition column has a vertical partition plate that divides its internal space into a pre-fractionation section and a main column section. The main column section has a side-stream collection section in the middle. The partition column has a feed inlet and a side-stream outlet on its side. The feed inlet connects to the pre-fractionation section, and the side-stream outlet connects to the side-stream collection section. The top of the partition column has a crude distillate outlet, and the bottom has a dimethyl sulfoxide collection outlet. The vertical separator includes a main section and a bottom section. The main section has an inlet and an overflow outlet on opposite sides. The inlet of the vertical separator is connected to the crude distillate outlet at the top of the partition column. The interior of the vertical separator... A fixed turbulence-inducing structure is installed; a condenser and a reflux tank are installed on the pipeline connecting the inlet of the vertical stratified tank to the crude distillate outlet at the top of the partition tower; the reboiler is installed at the bottom of the partition tower; the polymerization inhibitor protection unit includes a polymerization inhibitor injection device, an online turbidity monitoring device, and an interlocking control module. The polymerization inhibitor injection device is connected to the pipeline connecting the feed inlet of the partition tower, the reflux tank, and the overflow outlet of the vertical stratified tank. The online turbidity monitoring device is installed on the outlet pipeline of the reboiler, the production pipeline of the dimethyl sulfoxide production outlet, and the downstream pipeline of the polymerization inhibitor injection device. The interlocking control module is electrically connected to the online turbidity monitoring device, the polymerization inhibitor injection device, and the reboiler electrical control mechanism.

2. The separation system for a mixture containing acrylonitrile, water, and dimethyl sulfoxide according to claim 1, characterized in that, The height of the vertical partition plate accounts for 50% to 65% of the total height of the partition column. The lower end of the vertical partition plate is 1 / 3 to 1 / 2 of the column height from the bottom of the column. The pre-fractionation section is equipped with 15 to 25 theoretical plates, the main column section is equipped with 30 to 45 theoretical plates, and the side stream outlet is located between the 25th and 35th theoretical plates.

3. The separation system for a mixture containing acrylonitrile, water, and dimethyl sulfoxide according to claim 1, characterized in that, The bottom of the partition plate is equipped with a gas phase distribution structure component for controlling the gas phase distribution ratio between the pre-fractionation section and the main column section, with a gas phase distribution ratio of 0.40–0.

55.

4. The separation system for a mixture containing acrylonitrile, water, and dimethyl sulfoxide according to claim 1, characterized in that, A liquid distributor is installed at the top of the vertical partition plate, with a liquid phase distribution ratio of 0.35–0.

50.

5. The separation system for a mixture containing acrylonitrile, water, and dimethyl sulfoxide according to claim 1, characterized in that, The main body of the vertical stratified tank is a cylindrical cavity, and the bottom section is a conical structure. The turbulence structure is arranged inside the main body.

6. A separation method, based on the mixture separation system containing acrylonitrile, water and dimethyl sulfoxide as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Feed: The mixture containing acrylonitrile, water and dimethyl sulfoxide is fed into the pre-fractionation section of the partition tower at a feed temperature of 20-40℃. S2. Vacuum distillation separation in the partition column: control the operating pressure of the partition column to 10-30 kPa; control the top reflux ratio to 1-5 and the side reflux ratio to 1-5. S3. Precise temperature control in segments: Top temperature 43-65℃, side stream extraction temperature 45-70℃, bottom temperature 120-145℃; S4. Simultaneous extraction of three components: crude distillate is extracted from the top of the column, process water is extracted from the side stream, and dimethyl sulfoxide solvent is extracted from the bottom of the column. S5. Top Distillate Phase Separation and Purification: The top distillate is sent to a vertical separator for gravity separation. The upper layer is used to extract high-purity acrylonitrile for reuse, and the lower aqueous phase is recycled and treated.

7. The separation method according to claim 6, characterized in that, In step S2, the operating pressure of the partition tower is 15-20 kPa, the gas phase distribution ratio of the partition tower is maintained at 0.40-0.55, and the liquid phase distribution ratio is maintained at 0.35-0.

50.

8. The separation method according to claim 6, characterized in that, Add polymerization inhibitor continuously at three locations: the pipeline connected to the inlet, the pipeline connected to the reflux tank, and the pipeline connected to the overflow outlet, controlling the concentration of the polymerization inhibitor to be between 10 ppm and 50 ppm.

9. The separation method according to claim 6, characterized in that, The purity indicators for the products are as follows: the purity of acrylonitrile collected from the upper layer after stratification in the vertical stratification tank is ≥98.5wt%, the purity of process water collected from the side stream is ≥99.5wt%, and the purity of dimethyl sulfoxide collected from the bottom of the tower is ≥99.5wt%.

10. The separation method according to claim 6, characterized in that, In step S3, the bottom temperature control adopts the following linkage mechanism: multi-point temperature monitoring and online sulfide chromatography detection are provided at the bottom of the column. When the multi-point temperature monitoring device detects that the local temperature at the bottom of the column exceeds 145°C or the online sulfide chromatography detects dimethyl sulfoxide decomposition products, the reboiler heating power is reduced. When the online turbidity monitoring device detects that the turbidity exceeds 5 NTU, the interlock control module automatically increases the injection volume of the polymerization inhibitor dosing device and simultaneously reduces the reboiler heating power until the turbidity recovers to below 5 NTU.

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