Process and apparatus for recovering isopropyl alcohol, acrylonitrile and styrene from a solution of a polymeric polyol
By employing a dual-tower pressure swing distillation method, utilizing pressure difference and thermal coupling technology, the problem of inefficient water recovery from polymer polyol solutions was solved, achieving high recovery rate and stable operation.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- TIANJIN UNIV
- Filing Date
- 2026-04-28
- Publication Date
- 2026-07-10
AI Technical Summary
Existing technologies for dehydration and solvent recovery of polymer polyol solutions suffer from low solvent recovery rates and poor water removal, especially when the isopropanol content is high, resulting in poor phase separation and dehydration effects and increased production costs.
A dual-tower pressure swing distillation method is adopted, using acrylonitrile as an entrainer to separate the components in a reduced-pressure tower and a pressurized tower respectively. By controlling the pressure difference and thermal coupling, the efficient recovery of isopropanol, acrylonitrile and styrene can be achieved.
It achieves efficient moisture removal, improves the recovery rate of isopropanol, acrylonitrile and styrene, ensures operational stability and adaptability, and reduces production costs.
Smart Images
Figure CN122355869A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method and apparatus for dehydrating and recovering isopropanol, acrylonitrile and styrene from a polymer polyol solution, which has the advantages of high material recovery rate, good product quality, simple process and stable operation. Background Technology
[0002] Polymer polyols (POPs) possess high molecular weight, low volatility, low toxicity, and flexibility, enabling them to improve the performance of polyurethane foams and showing great potential for application in footwear manufacturing, automotive manufacturing, and construction engineering. POPs are polymeric, dispersed graft copolymer ethers obtained by graft polymerization of vinyl monomers in polyethers or other polyols. Taking the production of POPs from acrylonitrile and styrene as an example, isopropanol solvent needs to be added during the reaction. The resulting POP product contains not only a small amount of unreacted monomers but also solvent containing acrylonitrile, styrene, isopropanol, and a small amount of water. On the one hand, to reduce production costs, the organic matter in the solvent must be recovered; on the other hand, the water content in the recycled solvent must be kept within acceptable limits to avoid affecting the polymerization reaction. A common solvent recovery and dehydration method is multi-stage flash evaporation, which suffers from low solvent recovery rates and poor water removal, significantly increasing the production cost of POPs.
[0003] CN 221492406 U reports a scheme and apparatus for dehydration using a phase separator. The process involves passing a material containing water, styrene, acrylonitrile, POP residue, and isopropanol into a phase separator, where it separates into an oil phase and an aqueous phase based on density differences. The oil phase is recycled back to the POP polymerization unit, while the aqueous phase is discharged. However, the phase separation method employed is highly sensitive to the mixture composition. When the isopropanol content in the mixture is high, the phase separation and dehydration effect is poor, or even fails to separate, significantly limiting its application.
[0004] Hu et al. (Petrochemical Technology, 2025, 54(6):824-833) reported a conventional two-tower distillation method for recovering polymer polyol solutions. The method employs a two-tower process. Materials containing water, styrene, acrylonitrile, POP residue, and isopropanol enter the first distillation tower for separation. The top distillate mainly contains water, acrylonitrile, and isopropanol, while the bottom distillate mainly contains isopropanol, styrene, and POP monomers. The top distillate from the first distillation tower is sent to the second distillation tower. After cooling, the top distillate separates into an aqueous phase and an oil phase. The aqueous phase is discharged as wastewater, while the oil phase is returned to the second distillation tower as reflux. The bottom distillate from the second distillation tower contains isopropanol and acrylonitrile. However, the composition of the top distillate from the second distillation tower is in a non-separated phase region. If the phase separation effect of the top effluent from the second distillation tower is poor or non-separated, the process objective is difficult to achieve, and the rationality of the process needs further investigation.
[0005] CN 221815334 U reports a dehydration process combining distillation and pervaporation. The feed containing isopropanol and water first enters a first distillation column for separation. The top of the column contains an azeotrope of isopropanol and water. Part of the vapor phase at the top is directly cooled and refluxed, while the rest is sent to a membrane module. In the membrane module, water is selectively removed by differential vaporization. The crude isopropanol after dehydration enters a second distillation column, where the top contains a small amount of isopropanol and water azeotrope, and the bottom contains the isopropanol product. This method is effective for streams containing only isopropanol and water. However, if the feed is more complex, such as containing styrene, it is difficult to guarantee operational stability and dehydration efficiency. This is because styrene is highly reactive and prone to self-polymerization. Membrane separation often requires pressurized operation to increase the driving force, leading to high temperatures within the distillation column and potentially triggering styrene polymerization. Therefore, this method is not suitable for the recovery and dehydration of POP solutions.
[0006] There is currently no good solution for the dehydration and recovery of polymer polyol solutions. Dehydration at the expense of yield will greatly increase the production cost of POP. It is necessary to develop a targeted recovery solution based on the physical properties of the process stream to maximize the recovery rate of organic matter while ensuring the dehydration rate. Summary of the Invention
[0007] To address the shortcomings of existing technologies, this invention employs a dual-tower pressure swing distillation method to remove water from the polymer polyol (POP) recovery solution and recover isopropanol, acrylonitrile, and styrene.
[0008] The technical features of this invention are as follows: (1) The azeotropic composition of acrylonitrile and water is greatly affected by pressure, as shown in Table 1. At 50 kPaA, the water content in the azeotrope of acrylonitrile and water is 0.126 wt, while at 500 kPaA, the water content in the azeotrope of acrylonitrile and water is 0.208 wt. Therefore, acrylonitrile in the system is used as an entrainer, and two towers with different pressures are set up. A stream containing water and styrene is obtained in the bottom of the vacuum tower, and an isopropanol-rich stream without water is obtained in the bottom of the pressurized tower, which mainly consists of isopropanol and acrylonitrile, thereby achieving the purpose of raw material dehydration; (2) In order to avoid styrene polymerization at high temperature in the pressurized tower and to ensure continuous and stable operation, the styrene content in the stream distilled from the vacuum tower to the pressurized tower is minimized, and most of the styrene is collected from the bottom of the vacuum tower; (3) In order to recover styrene as much as possible, the bottom of the pressurized tower is cooled and separated into an aqueous phase and an oil phase after cooling. The oil phase is a styrene-rich stream, mainly consisting of styrene and isopropanol. The aqueous phase is wastewater containing a small amount of organic matter.
[0009] Table 1. Relationship between acrylonitrile-water azeotropic composition and pressure
[0010] Pressure / kPaA Temperature ℃ Acrylonitrile wt water wt 50.0 52.97 0.874 0.126 101.3 71.37 0.849 0.151 200.0 91.35 0.825 0.175 500.0 122.47 0.792 0.208
[0011] To achieve the above objectives, the technical solution of the present invention is as follows:
[0012] A method for dehydrating a polymer polyol solution to recover isopropanol, acrylonitrile, and styrene; comprising the following steps:
[0013] 1) The recovered solution from the POP synthesis section and the circulating liquid from the pressurization tower enter the vacuum tower for separation. The distillate from the top of the vacuum tower is isopropanol, acrylonitrile and water, which are sent to the pressurization tower. The bottom product of the vacuum tower is isopropanol, styrene and water. After cooling and phase separation, it is divided into an aqueous phase and an oil phase. The oil phase is a styrene-rich stream that is sent back to the POP synthesis section, and the aqueous phase is discharged as wastewater.
[0014] The recovered solution from the POP synthesis section and the circulating liquid from the pressurized tower enter the vacuum distillation tower for separation. Due to the low pressure in the vacuum distillation tower, the water content in the acrylonitrile-water azeotrope is low, while the high pressure in the pressurized tower results in a high water content in the acrylonitrile-water azeotrope. Therefore, a portion of water is collected from the bottom of the pressurized tower to balance the difference in azeotropic composition, thus achieving the purpose of water separation. The distillate from the top of the vacuum distillation tower is isopropanol, acrylonitrile, and water, which is sent to the pressurized tower. The bottom of the vacuum distillation tower is isopropanol, styrene, and water, which, after cooling and phase separation, separate into an aqueous phase and an oil phase. The oil phase is a styrene-rich stream, mainly consisting of styrene and isopropanol, and is returned to the POP synthesis section. The aqueous phase is discharged as wastewater.
[0015] 2) The material from the vacuum tower is separated in the pressurization tower. Part of the condensate from the top gas of the pressurization tower is sent back to the pressurization tower as reflux, and the other part is recycled back to the vacuum tower. The bottom product is an isopropanol-rich stream, including isopropanol, acrylonitrile and a small amount of water, which is sent back to the POP synthesis section.
[0016] The material from the vacuum distillation tower is separated in the pressurization tower. Due to the high pressure in the pressurization tower, the acrylonitrile-water azeotrope has a high water content, while the pressure in the vacuum distillation tower is low, resulting in a low water content in the acrylonitrile-water azeotrope. Therefore, a portion of acrylonitrile is collected from the bottom of the tower to balance the difference in azeotrope composition. Part of the condensate from the overhead gas in the pressurization tower is refluxed back to the pressurization tower, while the other part is recycled back to the vacuum distillation tower. The bottom feed is an isopropanol-rich stream, mainly consisting of isopropanol, acrylonitrile, and a small amount of water, which is sent back to the POP synthesis section.
[0017] 3) The pressure reducing tower and the pressure increasing tower are thermally coupled. The top gas of the pressure increasing tower heats the reboiler of the pressure reducing tower, and the heating medium of the reboiler of the pressure increasing tower is low-pressure steam.
[0018] The pressure at the top of the pressure reducing tower is 20~80 kPaA, and the pressure at the top of the pressurizing tower is 200~500 kPaA.
[0019] The pressure reducing tower and the pressure boosting tower are thermally coupled, with the pressure reducing tower reboiler and the pressure boosting tower condenser coupled into one device, and the heating medium of the pressure reducing tower reboiler is the top gas of the high-pressure tower.
[0020] The phase separation process employs a high-efficiency phase separator, which contains multiple layers of corrugated phase separation plates.
[0021] The phase splitter operates at a temperature of 0~70℃.
[0022] The theoretical number of plates in the pressure reducing tower is 15-50; the theoretical number of plates in the pressure increasing tower is 10-50.
[0023] The aforementioned pressure reducing tower reboiler and pressurizing tower hot reboiler are thermosiphon type reboilers.
[0024] The water content in the recycled solution from the POP production section is 1% to 20%.
[0025] The apparatus for dehydrating and recovering isopropanol, acrylonitrile, and styrene from a polymer polyol solution according to the present invention is characterized by mainly comprising a vacuum tower 1, a pressurized tower condenser 2, a vacuum tower reboiler 3, a phase separator 4, a pressurized tower 5, a pressurized tower reboiler 6, and a vacuum pump 7; the recovered solution from the POP production section is connected to the feed of the vacuum tower 1; the vapor phase outlet from the top of the vacuum tower 1 is connected to the feed of the vacuum tower condenser 2; the condensate outlet from the vacuum tower condenser 2 is divided into two streams, one connected to the vacuum tower 1 and the other connected to the pressurized tower 5; the tail gas from the vacuum tower condenser 2 is connected to the vacuum pump 7; the bottom of the vacuum tower 1 has... Two streams of material are discharged, one connected to the reboiler 3 of the vacuum distillation tower and the other connected to the phase separator 4; the tube-side discharge of the reboiler of the vacuum distillation tower is connected to the vacuum distillation tower 1; the phase separator has a discharge, one connected to the styrene-rich stream and the other connected to the wastewater, with the styrene-rich stream being recycled back to the POP synthesis section; the overhead gas discharge of the pressurized tower 5 is connected to the shell side of the reboiler 3 of the vacuum distillation tower, and the discharge of the reboiler 3 of the vacuum distillation tower is divided into two streams, one connected to the vacuum distillation tower 1 and the other to the pressurized tower 5; the bottom of the pressurized tower 5 has two discharges, one connected to the reboiler 6 of the pressurized tower and the other being an isopropanol-rich stream, which is recycled back to the POP synthesis section.
[0026] This invention employs a dual-tower pressure swing distillation method to remove water from a polymer polyol (POP) recovery solution, recovering isopropanol, acrylonitrile, and styrene. The recovery solution from flash distillation in the POP production section enters a vacuum distillation tower 1 for separation. The overhead gas from the vacuum distillation tower mainly consists of isopropanol, acrylonitrile, and water. After condensation in the vacuum distillation tower condenser 2, it is divided into two streams: one is sent as reflux to the vacuum distillation tower 1, and the other is sent to the pressurization tower 5. The tail gas from the vacuum distillation tower condenser 2 is sent to a vacuum pump 7, and the tail gas from the vacuum pump 7 is discharged as waste gas. The top pressure of the vacuum distillation tower 1 is 20~80 kPaA, and the top pressure of the pressurization tower 5 is 200~500 kPaA. The theoretical plate number of the vacuum distillation tower 1 is 15~50; the theoretical plate number of the pressurization tower 5 is 10~50. Preferably, the top pressure of the vacuum distillation tower 1 is 40~60 kPaA, and the preferred top pressure of the pressurization tower 5 is 200~300 kPaA. The preferred theoretical plate number for a pressure reducing tower is 15-30; the preferred theoretical plate number for a pressure increasing tower is 10-30.
[0027] The outlet of vacuum distillation tower 1 contains isopropanol, styrene, and water. After cooling, it separates into an aqueous phase and an oil phase in phase separator 4. The oil phase is a styrene-rich stream, mainly composed of styrene and isopropanol, and is sent back to the POP synthesis section. The aqueous phase is discharged as wastewater. The phase separator is a high-efficiency phase separator with multiple corrugated phase separation plates. The operating temperature of phase separator 4 is 0~70℃. Preferably, the operating temperature of phase separator 4 is 40~60℃.
[0028] The material from vacuum distillation tower 1 is separated in pressurization tower 5. The overhead gas from pressurization tower 5 serves as a heat source to heat the reboiler 3 of the vacuum distillation tower. Part of the condensate is returned to pressurization tower 5 as reflux, while the other part is recycled back to vacuum distillation tower 1. The bottom stream of pressurization tower 5, rich in isopropanol and mainly composed of isopropanol, acrylonitrile, and a small amount of water, is sent back to the POP synthesis section. The heating medium in pressurization tower reboiler 6 is low-pressure steam. Both vacuum distillation tower reboiler 3 and pressurization tower 6 are thermosiphon reboilers.
[0029] The beneficial effects of this invention are as follows:
[0030] This invention relates to a method and apparatus for dehydrating and recovering isopropanol, acrylonitrile, and styrene from a polymer polyol solution. The method employs a dual-tower pressure swing distillation process to remove water from the polymer polyol recovery solution and recover isopropanol, acrylonitrile, and styrene. The recovery solution from the POP (Polypropylene Open-Package) production section enters a vacuum distillation tower for separation. The distillate from the vacuum distillation tower is isopropanol, acrylonitrile, and water, which is sent to a pressurization tower. The bottom product from the vacuum distillation tower is isopropanol, styrene, and water, which, after cooling, separates into an aqueous phase and an oil phase. The oil phase, consisting of styrene and isopropanol, is returned to the POP synthesis section, while the aqueous phase is discharged as wastewater. The material from the vacuum distillation tower is further separated in the pressurization tower. The overhead gas from the pressurization tower is used as a heat source to heat the bottom product of the vacuum distillation tower. Part of the condensate is returned to the pressurization tower as reflux, and the other part is recycled back to the vacuum distillation tower. The bottom product from the pressurization tower is isopropanol, acrylonitrile, and a small amount of water, which is returned to the POP synthesis section.
[0031] This invention fully utilizes the physical properties of the system and employs a dual-tower pressure swing distillation method to remove water from the polymer polyol (POP) recovery solution, recovering isopropanol, acrylonitrile, and styrene. It can simultaneously obtain isopropanol-rich and styrene-rich streams, which can help control the ratio of POP polymer reactants. It removes water while avoiding high-temperature polymerization of styrene, and has the advantages of high material recovery rate, strong raw material adaptability, high water removal rate, and stable operation.
[0032] The feed to this unit is a recovered solution from the POP synthesis section. This technology separates the feed into a styrene-rich stream in a vacuum distillation tower and an isopropanol-rich stream in a pressurization tower. Both are used as the outputs of this unit, meeting the following specifications: isopropanol-rich stream water content <0.2 wt%; styrene-rich stream water content <0.3 wt%; water removal rate >98%; isopropanol recovery rate >99%; acrylonitrile recovery rate >99.5%; styrene recovery rate >99.5%. Furthermore, this design does not have a bottleneck in scaling up the unit's processing capacity and is suitable for production units of different scales. Attached Figure Description
[0033] Figure 1 Schematic diagram of the process for recovering isopropanol, acrylonitrile, and styrene from polymer polyol recovery solution via dehydration.
[0034] The components include: 1. Pressure reducing tower; 2. Pressure reducing tower condenser; 3. Pressure reducing tower reboiler; 4. Phase separator; 5. Pressure increasing tower; 6. Pressure increasing tower reboiler; and 7. Vacuum pump. Detailed Implementation
[0035] Specific embodiments of the present invention Figure 1Further description, but the scope of the invention is not limited thereto. The recovered solution from flash distillation in the POP production section enters a vacuum distillation tower for separation. The distillate from the vacuum distillation tower is isopropanol, acrylonitrile, and water, which is sent to a pressurization tower. The bottom product from the vacuum distillation tower is isopropanol, styrene, and water, which, after cooling, separates into an aqueous phase and an oil phase. The oil phase is a styrene-rich stream, mainly composed of styrene and isopropanol, and is sent back to the POP synthesis section. The aqueous phase is discharged as wastewater. The material from the vacuum distillation tower is separated in the pressurization tower. The overhead gas from the pressurization tower is used as a heat source to heat the bottom product of the vacuum distillation tower. Part of the condensate is sent back to the pressurization tower as reflux, and the other part is recycled back to the vacuum distillation tower. The bottom product is an isopropanol-rich stream, mainly composed of isopropanol, acrylonitrile, and a small amount of water, which is sent back to the POP synthesis section.
[0036] Example 1:
[0037] The recovered solution from the flash distillation of the POP production section has a flow rate of 2000 kg / h and a water content of 9%. It enters the vacuum distillation tower 1 for separation. The vacuum distillation operation pressure is 60 kPa, and the theoretical plate number is 30. The overhead gas from the vacuum distillation tower mainly consists of isopropanol, acrylonitrile, and water, with a styrene content of <1 ppm. After condensation in the vacuum distillation tower condenser 2, the overhead gas is divided into two streams. The condenser condensation temperature is 60℃. One stream is sent as reflux to the vacuum distillation tower 1, and the other stream is sent to the pressurization tower 5. The tail gas from the vacuum distillation tower condenser 2 is sent to the vacuum pump 7, and the tail gas from the vacuum pump 7 is discharged as waste gas.
[0038] The outlet of vacuum distillation tower 1 contains isopropanol, styrene, and water. After cooling, it is separated into an aqueous phase and an oil phase in phase separator 4, which operates at 40°C. The oil phase consists of styrene and isopropanol with a water content of 0.26 wt%, and is returned to the POP synthesis section. The aqueous phase is discharged as wastewater, containing 5 wt% organic matter.
[0039] The material from vacuum distillation tower 1 is separated in pressurization tower 5, with an operating pressure of 300 kPa and a theoretical plate number of 30. The overhead gas from pressurization tower 5 serves as a heat source to heat reboiler 3 in vacuum distillation tower 1. A portion of the condensate is returned to pressurization tower 5 as reflux, while the remainder is recycled back to vacuum distillation tower 1. The bottom product of pressurization tower 5 consists of isopropanol, acrylonitrile, and a small amount of water (0.18 wt%), which is sent back to the POP synthesis section. The heating medium in reboiler 6 is low-pressure steam at a pressure of 0.4 MPaA, with a steam flow rate of 6300 kg / h. Both reboilers 3 and 6 are thermosiphon reboilers.
[0040] The feed to this unit is a recovered solution from the POP synthesis section. This technology separates the solutions, producing a styrene-rich stream in a vacuum distillation tower and an isopropanol-rich stream in a pressurization tower. Both are the outputs of this unit. In this embodiment, the water removal rate is 98.2%; the isopropanol recovery rate is 99.05%; the acrylonitrile recovery rate is 99.6%; and the styrene recovery rate is 99.6%.
[0041] Example 2:
[0042] The recovered solution from the flash distillation of the POP production section has a flow rate of 1000 kg / h and a water content of 5%. It enters the vacuum distillation tower 1 for separation. The vacuum distillation operation pressure is 20 kPa, and the theoretical plate number is 15. The overhead gas from the vacuum distillation tower mainly consists of isopropanol, acrylonitrile, and water, with a styrene content of <1.5 ppm. After condensation in the vacuum distillation tower condenser 2, the overhead gas is divided into two streams. The condenser condensation temperature is 40℃. One stream is sent as reflux to the vacuum distillation tower 1, and the other stream is sent to the pressurization tower 5. The tail gas from the vacuum distillation tower condenser 2 is sent to the vacuum pump 7, and the tail gas from the vacuum pump 7 is discharged as waste gas.
[0043] The outlet of vacuum distillation tower 1 contains isopropanol, styrene, and water. After cooling, it is separated into an aqueous phase and an oil phase in phase separator 4, which operates at 50°C. The oil phase consists of styrene and isopropanol with a water content of 0.28 wt%, and is returned to the POP synthesis section. The aqueous phase is discharged as wastewater, containing 5.5 wt% organic matter.
[0044] The material from vacuum distillation tower 1 is separated in pressurization tower 5, with an operating pressure of 200 kPa and a theoretical plate number of 50. The overhead gas from pressurization tower 5 serves as a heat source to heat reboiler 3 in vacuum distillation tower 1. A portion of the condensate is returned to pressurization tower 5 as reflux, while the remainder is recycled back to vacuum distillation tower 1. The bottom product of pressurization tower 5 consists of isopropanol, acrylonitrile, and a small amount of water (0.19 wt%), which is returned to the POP synthesis section. The heating medium in reboiler 6 is low-pressure steam at a pressure of 0.4 MPaA, with a steam flow rate of 2500 kg / h. Both reboilers 3 and 6 are thermosiphon reboilers.
[0045] The feed to this unit is a recovered solution from the POP synthesis section. This technology separates the solutions, producing a styrene-rich stream in a vacuum distillation tower and an isopropanol-rich stream in a pressurization tower. Both are the outputs of this unit. In this embodiment, the dehydration rate is 98.4%; the isopropanol recovery rate is 99.04%; the acrylonitrile recovery rate is 99.55%; and the styrene recovery rate is 99.7%.
[0046] Example 3:
[0047] The recovered solution from the flash evaporation in the POP production section has a flow rate of 500 kg / h and a water content of 1%. It enters vacuum tower 1 for separation, with a vacuum operating pressure of 80 kPa and a theoretical plate number of 50. The overhead gas from the vacuum tower mainly consists of isopropanol, acrylonitrile, and water, with a styrene content of <1 ppm. After condensation in vacuum tower condenser 2, the overhead gas is divided into two streams at a condensation temperature of 60°C. One stream is sent as reflux to vacuum tower 1, and the other is sent to pressurization tower 5. The tail gas from vacuum tower condenser 2 is sent to vacuum pump 7, and the tail gas from vacuum pump 7 is discharged as waste gas.
[0048] The outlet of vacuum distillation tower 1 contains isopropanol, styrene, and water. After cooling, it is separated into an aqueous phase and an oil phase in phase separator 4, which operates at 60°C. The oil phase consists of styrene and isopropanol with a water content of 0.21 wt%, and is returned to the POP synthesis section. The aqueous phase is discharged as wastewater, containing 5.1 wt% organic matter.
[0049] The material from vacuum distillation tower 1 is separated in pressurization tower 5, with an operating pressure of 500 kPa and a theoretical plate number of 15. The overhead gas from pressurization tower 5 serves as a heat source to heat reboiler 3 in vacuum distillation tower 1. A portion of the condensate is returned to pressurization tower 5 as reflux, while the remainder is recycled back to vacuum distillation tower 1. The bottom product of pressurization tower 5 consists of isopropanol, acrylonitrile, and a small amount of water (0.15 wt%), which is sent back to the POP synthesis section. The heating medium in reboiler 6 is low-pressure steam at a pressure of 0.4 MPaA, with a steam flow rate of 1500 kg / h. Both reboilers 3 and 6 are thermosiphon reboilers.
[0050] The feed to this unit is a recovered solution from the POP synthesis section. This technology separates the solutions, producing a styrene-rich stream in a vacuum distillation tower and an isopropanol-rich stream in a pressurization tower. Both are the outputs of this unit. In this embodiment, the water removal rate is 99%; the isopropanol recovery rate is 99.05%; the acrylonitrile recovery rate is 99.7%; and the styrene recovery rate is 99.8%.
[0051] The embodiments of the present invention have been described above in conjunction with the accompanying drawings. The present invention is not limited to the above description, and various changes can be made according to the purpose of the invention. All modifications, combinations, simplifications, equivalent substitutions, etc., made in accordance with the spirit and principle of the implementation of the technical solution of the present invention should be considered equivalent substitution modes. As long as they meet the purpose of the invention and do not deviate from the technical principle and inventive concept of the present invention, they should be included within the protection scope of the present invention.
Claims
1. A method for dehydrating and recovering isopropanol, acrylonitrile, and styrene from a polymer polyol solution; characterized in that, Includes the following steps: 1) The recovered solution from the POP synthesis section and the circulating liquid from the pressurization tower enter the vacuum tower for separation. The distillate from the top of the vacuum tower is isopropanol, acrylonitrile and water, which are sent to the pressurization tower. The bottom product of the vacuum tower is isopropanol, styrene and water. After cooling and phase separation, it is divided into an aqueous phase and an oil phase. The oil phase is a styrene-rich stream that is sent back to the POP synthesis section, and the aqueous phase is discharged as wastewater. 2) The material from the vacuum tower is separated in the pressurization tower. Part of the condensate from the top gas of the pressurization tower is sent back to the pressurization tower as reflux, and the other part is recycled back to the vacuum tower. The bottom product is an isopropanol-rich stream, including isopropanol, acrylonitrile and a small amount of water, which is sent back to the POP synthesis section. 3) The pressure reducing tower and the pressure increasing tower are thermally coupled. The top gas of the pressure increasing tower heats the reboiler of the pressure reducing tower, and the heating medium of the reboiler of the pressure increasing tower is low-pressure steam.
2. The method for dehydrating and recovering isopropanol, acrylonitrile, and styrene from a polymer polyol solution as described in claim 1; characterized in that, The pressure at the top of the pressure reducing tower is 20~80 kPaA, and the pressure at the top of the pressurizing tower is 200~500 kPaA.
3. The method for dehydrating and recovering isopropanol, acrylonitrile, and styrene from a polymer polyol solution as described in claim 1; characterized in that, The pressure reducing tower and the pressure boosting tower are thermally coupled. The reboiler of the pressure reducing tower and the condenser of the pressure boosting tower are coupled into one device. The heating medium of the reboiler of the pressure reducing tower is the top gas of the high pressure tower.
4. The method for dehydrating and recovering isopropanol, acrylonitrile, and styrene from a polymer polyol solution as described in claim 3; characterized in that, The phase separation process uses a high-efficiency phase separator, which contains multiple layers of corrugated phase separation plates.
5. The method for dehydrating and recovering isopropanol, acrylonitrile, and styrene from a polymer polyol solution as described in claim 4; characterized in that, The phase splitter operates at a temperature of 0~70℃.
6. The method for dehydrating and recovering isopropanol, acrylonitrile, and styrene from a polymer polyol solution as described in claim 1; characterized in that, The theoretical number of plates for a pressure reducing tower is 15~50; the theoretical number of plates for a pressure increasing tower is 10~50.
7. The method for dehydrating and recovering isopropanol, acrylonitrile, and styrene from a polymer polyol solution as described in claim 1; characterized in that, The reboiler of the pressure reducing tower and the hot reboiler of the pressurizing tower are thermosiphon type reboilers.
8. The method for dehydrating and recovering isopropanol, acrylonitrile, and styrene from a polymer polyol solution as described in claim 1; characterized in that, The water content in the recycled solution from the POP production section is 1% to 20%.
9. The apparatus for dehydrating and recovering isopropanol, acrylonitrile, and styrene from a polymer polyol solution according to claim 1; characterized in that, The main components include a vacuum distillation tower 1, a pressurized tower condenser 2, a vacuum distillation tower reboiler 3, a phase separator 4, a pressurized tower 5, a pressurized tower reboiler 6, and a vacuum pump 7. The recovered solution from the POP production section is connected to the feed of vacuum distillation tower 1. The vapor discharge from the top of vacuum distillation tower 1 is connected to the feed of vacuum distillation tower condenser 2. The condensate discharge from vacuum distillation tower condenser 2 is divided into two streams, one connected to vacuum distillation tower 1 and the other to pressurized tower 5. The tail gas from vacuum distillation tower condenser 2 is connected to vacuum pump 7. The bottom of vacuum distillation tower 1 has two discharge streams, one of which is connected to vacuum distillation tower reboiler 3. One stream is connected to phase separator 4; the tube-side outlet of the reboiler of the vacuum distillation tower is connected to vacuum distillation tower 1; the phase separator has an outlet, one stream is connected to the styrene-rich stream, and the other stream is connected to the wastewater. The styrene-rich stream is recycled back to the POP synthesis section; the top gas outlet of the pressurization tower 5 is connected to the shell side of the reboiler 3 of the vacuum distillation tower. The outlet of the reboiler 3 of the vacuum distillation tower is divided into two streams, one connected to vacuum distillation tower 1 and the other to pressurization tower 5; the bottom of the pressurization tower 5 has two outlets, one connected to the reboiler 6 of the pressurization tower and the other is an isopropanol-rich stream, which is recycled back to the POP synthesis section.