Solvent rectification recovery system and rectification method for polyphenylene sulfide production

Abstract

The invention discloses a solvent rectification recovery system for polyphenylene sulfide production. The solvent rectification recovery system comprises an evaporation tower, a rectification tower, an evaporation tower feed preheater, an evaporation tower bottom reboiler, a rectification tower top condenser, a rectification tower bottom reboiler, a third-stage compressor, a second-stage compressor, a first-stage spraying tank, a second-stage spraying tank and a gas-liquid separation tank. According to the rectification method disclosed by the invention, heat in the system is fully used through heat integration and heat pump technologies in the system, and a large amount of additional steam consumption is saved and the operation cost is saved by consuming a small amount of electric energy.

Description

Technical Field

[0001] The present invention relates to the field of chemical energy conservation, and in particular to a solvent distillation recovery system and a distillation method for use in polyphenylene sulfide production. Background Art

[0002] Polyphenylene sulfide (PPS) is currently the world's most cost-effective specialty engineering plastic, known as the leading specialty engineering plastic, with excellent economic value and application prospects. The sodium sulfide method is currently the predominant method for industrial production of PPS. This method offers advantages such as abundant raw material resources, a short process path, good reproducibility during production, high yield, and high purity.

[0003] The back-end refining process of the sodium sulfide synthesis process for polyphenylene sulfide involves multiple distillation and evaporation steps, resulting in high energy consumption. Preliminary estimates indicate that energy consumption accounts for 20% to 30% of the production cost of polyphenylene sulfide. With the increasing market demand and production of polyphenylene sulfide, reducing energy consumption in the sodium sulfide synthesis process is a top priority for reducing production costs and enhancing its competitiveness in the global plastics market. Summary of the Invention

[0004] In view of the above-mentioned defects of the prior art, the purpose of the present invention is to provide a solvent distillation recovery system and a distillation method for polyphenylene sulfide production to solve the problems of high energy consumption and high operating costs of the existing process.

[0005] The objective of the present invention is achieved through such technical solution:

[0006] A solvent distillation recovery system for polyphenylene sulfide production, comprising: an evaporation tower, a distillation tower, an evaporation tower feed preheater, an evaporation tower bottom reboiler, a distillation tower top condenser, a distillation tower bottom reboiler, a three-stage compressor, a two-stage compressor, a first-stage spray tank, a second-stage spray tank, a gas-liquid separation tank, and a steam drum;

[0007] The evaporation tower is provided with an evaporation feed inlet, a first light component outlet is provided at the top of the tower, and a first heavy component extraction outlet is provided at the bottom of the tower; the outlet of the evaporation tower feed preheater is connected to the evaporation feed inlet of the evaporation tower; the outlet of the evaporation tower bottom reboiler is connected to the bottom of the evaporation tower;

[0008] The top of the distillation tower is provided with a distillation feed inlet, the top of the tower is provided with a second light component extraction outlet, the bottom of the tower is provided with a second heavy component extraction outlet, the inlet of the top condenser of the distillation tower is connected to the second light component extraction outlet through a pipeline; the outlet of the reboiler at the bottom of the distillation tower is connected to the bottom of the distillation tower through a pipeline;

[0009] The first light component extraction port at the top of the evaporation tower is connected to the distillation feed port of the distillation tower through a pipeline;

[0010] The second heavy component extraction outlet at the bottom of the distillation tower is connected to the shell side inlet of the evaporation tower feed preheater through a pipeline;

[0011] The outlets of the three-stage compressor and the two-stage compressor are connected to the inlet of the first-stage spray tank and the inlet of the second-stage spray tank respectively through pipelines;

[0012] The gas phase outlet of the first stage spray tank is divided into two paths through pipelines and respectively connected to the shell side inlet of the evaporator bottom reboiler and the inlet of the secondary compressor;

[0013] The gas phase outlet of the second-stage spray tank is connected to the left inlet of the drum through a pipeline, the added steam is connected to the upper inlet of the drum through a pipeline, and the outlet of the drum is connected to the shell side inlet of the bottom reboiler of the distillation tower through a pipeline;

[0014] The liquid phase outlets of the first-stage spray tank and the second-stage spray tank are connected to the inlet of the gas-liquid separation tank through pipelines; the shell-side outlets of the bottom reboiler of the evaporation tower and the bottom reboiler of the distillation tower are connected to the inlet of the gas-liquid separation tank through pipelines;

[0015] The gas phase outlet pipeline of the gas-liquid separation tank is connected to the inlet of the first-stage spray tank. The liquid phase outlet pipeline of the gas-liquid separation tank is divided into three routes and respectively connected to the inlet of the top condenser of the distillation tower, the inlet of the first-stage spray tank, and the inlet of the second-stage spray tank. The outlet pipeline of the top condenser of the distillation tower is connected to the inlet of the third-stage compressor.

[0016] Furthermore, the bottom extraction pipeline of the evaporation tower is connected to the tube side inlet of the bottom reboiler of the evaporation tower, and the tube side outlet of the bottom reboiler of the evaporation tower is connected to the bottom reflux port of the evaporation tower through a pipeline.

[0017] Furthermore, the bottom extraction pipeline of the distillation tower is connected to the tube side inlet of the bottom reboiler of the distillation tower, and the tube side outlet of the bottom reboiler of the distillation tower is connected to the bottom reflux port of the distillation tower through a pipeline.

[0018] A distillation method for a solvent recovery system in polyphenylene sulfide production comprises preheating a mixed liquid generated in the polyphenylene sulfide production process to 80-90°C in an evaporation tower feed preheater and feeding the mixed liquid to the bottom of the evaporation tower. The evaporation tower kettle temperature is controlled at 110-125°C, and the operating pressure is controlled at 0.3-0.5 bar. After separation, a mixed liquid of methyl pyrrolidone (NMP) and water containing salt is produced at the bottom of the evaporation tower, and a mixed vapor of NMP, water, and paradichlorobenzene is produced at the top of the evaporation tower and enters a distillation tower.

[0019] The liquid phase at the bottom of the evaporation tower is heated by the bottom reboiler, and the gas phase flows back into the evaporation tower;

[0020] The temperature of the distillation tower kettle is controlled at 160-175°C, and the operating pressure is controlled at 0.3-0.5 bar. After separation, a mixture of water and p-dichlorobenzene is produced at the top of the distillation tower, and high-purity NMP is obtained at the bottom of the distillation tower. The gas phase at the top of the distillation tower is condensed in the top condenser, and part of the liquid phase is refluxed into the distillation tower. The liquid phase at the bottom of the distillation tower is heated in the bottom reboiler, and the gas phase is refluxed into the distillation tower.

[0021] The water vapor at the outlet of the top condenser of the distillation tower, after cooling, enters the three-stage compressor for compression and pressure increase, and the pressure is increased to 2.5~3.0bar. The compressed high-temperature and high-pressure supersaturated water vapor enters the first spray tank and is sprayed with condensed water from the heat pump gas-liquid separation tank. The obtained liquid returns to the heat pump gas-liquid separation tank for reuse. Part of the saturated water vapor after spraying goes to the reboiler at the bottom of the evaporation tower to replace the external steam as a heating heat source, and the other part enters the secondary compressor for compression and pressure increase, and the pressure is increased to 10.0~10.5b The compressed high-temperature and high-pressure supersaturated water vapor enters the second-stage spray tank and is sprayed by the condensed water from the heat pump gas-liquid separation tank. The obtained liquid returns to the heat pump gas-liquid separation tank for reuse. The saturated water vapor after spraying goes to the reboiler at the bottom of the distillation tower to replace a part of the external steam as a heating heat source. The condensed water obtained by condensing the water vapor compressed and heated by the three-stage compressor in the reboiler at the bottom of the evaporation tower and the condensed water obtained by condensing the water vapor compressed and heated by the two-stage compressor in the reboiler at the bottom of the distillation tower are both returned to the heat pump gas-liquid separation tank to realize a closed-loop cycle.

[0022] Furthermore, the liquid phase at the bottom of the distillation tower is heated by a bottom reboiler, and the gas phase is refluxed into the distillation tower. The liquid phase is extracted to obtain NMP with a mass fraction greater than 99.5% and is fed into the evaporation tower feed preheater to preheat the feed to recover part of the energy. The evaporation tower feed preheater is heated by the high-purity NMP obtained at the bottom of the distillation tower, and the temperature of the NMP entering the evaporation tower feed preheater is 160-175°C.

[0023] Furthermore, the reboiler at the bottom of the evaporation tower is also heated by an indirect heat pump assisted distillation system, using water vapor as a heat source, and the temperature of the water vapor entering the reboiler at the bottom of the evaporation tower is 120-135°C;

[0024] Furthermore, the distillation tower bottom reboiler is also heated by an indirect heat pump assisted distillation system, using water vapor as a heat source, and the temperature of the water vapor entering the evaporation tower bottom reboiler is 170-185°C.

[0025] Furthermore, the distillation tower top condenser uses the liquid water in the indirect heat pump-assisted distillation system as a cold source to recover the latent heat of the distillation tower top steam, and the temperature of the liquid water entering the distillation tower top condenser is 50-70°C.

[0026] Furthermore, when the saturated water vapor generated by spraying the second-stage spray tank with the condensed water from the heat pump gas-liquid separation tank and directed to the reboiler at the bottom of the distillation tower is insufficient, the shortfall is supplemented by external steam.

[0027] Furthermore, the liquid phase at the bottom of the evaporator is heated by the bottom reboiler, and the liquid phase is extracted and sent to the desalination section for further treatment; the gas phase at the top of the distillation tower is condensed by the top condenser, and part of the liquid phase is extracted from the top of the distillation tower and enters the subsequent recovery link.

[0028] Due to the adoption of the above technical solution, the present invention has the following advantages:

[0029] In the existing technical solution, the condenser at the top of the distillation tower is cooled by low-temperature water, and the reboiler at the bottom of the evaporation tower and the distillation tower is heated by steam. The low-temperature energy of the tower bottom cannot be effectively utilized, resulting in energy waste and high energy consumption. The low-temperature refrigerant is generated by a refrigeration unit, and the refrigeration unit is directly cooled by circulating water, resulting in waste of low-grade waste heat and consumption of circulating water. The present invention realizes the co-generation of cold and heat through heat integration and heat pump technology within the system, and the low-grade heat is fully utilized. At the same time, the cold capacity of the tower bottom is recovered, and by consuming a small amount of electricity, a large amount of external steam consumption is saved, thereby achieving the purpose of energy saving and consumption reduction.

[0030] Other advantages, objects and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art based on an examination of the following or may be learned from the practice of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of the structure of the solvent distillation recovery system used in the production of polyphenylene sulfide in the embodiment.

[0032] In the figure: T1-evaporation tower; T2-distillation tower; E1-evaporation tower feed preheater; E2-evaporation tower bottom reboiler; E3-distillation tower top condenser E3; E4-distillation tower bottom reboiler E4; C1-three-stage compressor; C2-two-stage compressor; C3-three-stage compressor; V1-first stage spray tank; V2-second stage spray tank; V3-gas-liquid separation tank; V4-steam drum. DETAILED DESCRIPTION

[0033] The present invention will be further described below with reference to the embodiments.

[0034] Example 1:

[0035] like Figure 1As shown, the solvent distillation recovery system used in the production of polyphenylene sulfide includes an evaporation tower T1, a distillation tower T2, an evaporation tower feed preheater E1, an evaporation tower bottom reboiler E2, a distillation tower top condenser E3, a distillation tower bottom reboiler E4, a three-stage compressor C1, a two-stage compressor C2, a first-stage spray tank V1, a second-stage spray tank V2, a gas-liquid separation tank V3, and a steam drum V4.

[0036] Evaporation tower T1 has a raw liquid feed inlet, equipped with an evaporation tower feed preheater E1. The tube-side outlet of evaporation tower feed preheater E1 is connected to the feed inlet of evaporation tower T1 via a pipeline. Evaporation tower T1 has a light component outlet at the top and a heavy component outlet at the bottom. The bottom extraction pipeline of evaporation tower T1 is connected to the tube-side inlet of evaporation tower bottom reboiler E2, and the tube-side outlet of evaporation tower bottom reboiler E2 is connected to the bottom reflux port of evaporation tower T1 via a pipeline. Evaporation tower T1 is equipped with an evaporation tower bottom reboiler E2 at the bottom of evaporation tower T1, and the light component outlet at the top of evaporation tower T1 is connected to the inlet of distillation tower T2 via a pipeline.

[0037] Rectifier T2 has a light component extraction port at the top and a heavy component extraction port at the bottom. Rectifier T2 is equipped with an overhead condenser E3 at the top and a bottom reboiler E4 at the bottom. The bottom extraction line of Rectifier T2 is connected to the tube-side inlet of Reboiler E4, and the tube-side outlet of Reboiler E4 is connected to the bottom reflux port of Rectifier T2 via a pipeline.

[0038] The outlets of the three-stage compressor C1 and the two-stage compressor C2 are connected to the spray tanks V1 and V2 respectively through pipelines. The gas phase outlet of the first-stage spray tank V1 is divided into two by a pipeline and connected to the shell side inlet of the evaporator bottom reboiler E2 and the inlet of the two-stage compressor C2 respectively. The gas phase outlet of the second-stage spray tank V2 is connected to the left inlet of the drum V4 through a pipeline, and the additional steam is connected to the upper inlet of the drum V4 through a pipeline. The outlet of the drum V4 is connected to the shell side inlet of the distillation tower bottom reboiler E4 through a pipeline. The spray tanks V1 and V 2 are connected to the inlet of the gas-liquid separation tank V3 through a pipeline; the shell-side outlets of the evaporator bottom reboiler E2 and the distillation tower bottom reboiler E4 are connected to the inlet of the gas-liquid separation tank V3 through a pipeline, the gas phase outlet pipeline of the gas-liquid separation tank V3 is connected to the inlet of a spray tank V1, and the liquid phase outlet pipeline of the gas-liquid separation tank V3 is divided into three routes and respectively connected to the inlets of the distillation tower top condenser E3, spray tanks V1 and V2, and the outlet pipeline of the distillation tower top condenser E3 is connected to the inlet of the three-stage compressor C1.

[0039] Example 2:

[0040] The solvent distillation recovery method used in the production of polyphenylene sulfide is as follows:

[0041] The mixed liquid (containing NMP, water, p-dichlorobenzene, NaCl, LiCl, etc.) produced during the polyphenylene sulfide production process is preheated to 80-90°C in the evaporation tower feed preheater E1 and then fed into the bottom of the evaporation tower T1. The tower bottom temperature is controlled at 110-125°C and the operating pressure is controlled at 0.3-0.5 bar. After separation, a mixed liquid of methyl pyrrolidone (NMP) and water containing salt is produced at the bottom of the tower, and a mixed vapor of NMP, water and p-dichlorobenzene is produced at the top of the tower and enters the distillation tower T2.

[0042] Evaporation tower T1 is a packed tower consisting of a rectification section and a stripping section. High-efficiency packing is used for separation, and the bottom temperature is 110-125°C. High-purity NMP is drawn from the bottom of rectification tower E2 to heat the evaporation tower feed preheater E1. The temperature of the NMP entering the evaporation tower feed preheater E1 is between 160-175°C. The bottom reboiler E2 is heated by an indirect heat pump-assisted distillation system using steam as the heat source. The temperature of the steam entering the evaporation tower reboiler E2 is between 120-135°C.

[0043] The overhead vapor phase from evaporation tower T1 enters distillation tower T2, where the bottom temperature is controlled at 160-175°C and the operating pressure is controlled at 0.3-0.5 bar. After separation, a mixture of water and paradichlorobenzene is produced overhead, while NMP is obtained at the bottom. The overhead vapor phase from distillation tower T2 is condensed in overhead condenser E3, with a portion of the liquid phase refluxed back into the tower. The remaining liquid phase (containing water and paradichlorobenzene) is withdrawn from the top of the tower for subsequent recovery. The bottom liquid phase is heated in bottom reboiler E4, where the vapor phase refluxes back into the tower. The withdrawn liquid phase, yielding NMP with a mass fraction greater than 99.5%, is fed to the evaporation tower feed preheater E1 to preheat the feed and recover some energy.

[0044] Distillation tower T2 is a packed tower, divided into two sections: the rectifying section and the stripping section, utilizing high-efficiency packing for separation. The overhead condenser E3 utilizes liquid water from an indirect heat pump-assisted distillation system as a cooling source to recover the latent heat of the overhead steam. The temperature of the liquid water entering E3 is between 50°C and 70°C. The bottom reboiler E4 is heated by an indirect heat pump-assisted distillation system using water vapor as a heat source. The temperature of the water vapor entering E4 is between 170°C and 185°C.

[0045] The indirect heat pump assisted distillation system uses water as the working medium for closed-loop circulation. The heated water vapor at the outlet of the top condenser E3 of the distillation tower enters the first compression system. After compression and heat increase by the three-stage compressor C1, the pressure rises to 2.5-3.0 bar. The compressed high-temperature and high-pressure supersaturated water vapor enters the first spray tank V1 and is sprayed with condensed water from the heat pump gas-liquid separation tank V3. The obtained liquid returns to the heat pump gas-liquid separation tank V3 for reuse. Part of the saturated water vapor after spraying goes to the reboiler E2 at the bottom of the evaporator to replace the external steam as the heating heat source, and the other part enters the second compression system. After compression and heat increase by the secondary compressor C2, the pressure rises. The pressure reaches as high as 10.0-10.5 bar, and the compressed high-temperature and high-pressure supersaturated water vapor enters the second-stage spray tank V2, and is sprayed by the condensed water from the heat pump gas-liquid separation tank V3. The obtained liquid returns to the heat pump gas-liquid separation tank V3 for reuse. The saturated water vapor after spraying goes to the reboiler E4 at the bottom of the distillation tower to replace a part of the external steam as a heating heat source, and the unsupplemented part is supplemented by the external steam. The condensed water obtained by condensing the heated water vapor compressed by the three-stage compressor C1 and condensing in the reboiler E2 at the bottom of the evaporation tower and the condensed water obtained by condensing the heated water vapor compressed by the two-stage compressor C2 and condensing in the reboiler E4 at the bottom of the distillation tower are both returned to the heat pump gas-liquid separation tank V3 to realize a closed-loop cycle.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should all be included in the scope of the claims of the present invention.

Claims

1. A solvent distillation recovery system for polyphenylene sulfide production, characterized in that: include: Evaporation tower, distillation tower, evaporation tower feed preheater, evaporation tower bottom reboiler, distillation tower top condenser, distillation tower bottom reboiler, three-stage compressor, two-stage compressor, first-stage spray tank, second-stage spray tank, gas-liquid separation tank, steam drum; The evaporation tower is provided with an evaporation feed inlet, a first light component outlet is provided at the top of the tower, and a first heavy component extraction outlet is provided at the bottom of the tower; the outlet of the evaporation tower feed preheater is connected to the evaporation feed inlet of the evaporation tower; the outlet of the evaporation tower bottom reboiler is connected to the bottom of the evaporation tower; The top of the distillation tower is provided with a distillation feed inlet, the top of the tower is provided with a second light component extraction outlet, the bottom of the tower is provided with a second heavy component extraction outlet, the inlet of the top condenser of the distillation tower is connected to the second light component extraction outlet through a pipeline; the outlet of the reboiler at the bottom of the distillation tower is connected to the bottom of the distillation tower through a pipeline; The first light component extraction port at the top of the evaporation tower is connected to the distillation feed port of the distillation tower through a pipeline; The second heavy component extraction outlet at the bottom of the distillation tower is connected to the shell side inlet of the evaporation tower feed preheater through a pipeline; The outlets of the three-stage compressor and the two-stage compressor are connected to the inlet of the first-stage spray tank and the inlet of the second-stage spray tank respectively through pipelines; The gas phase outlet of the first stage spray tank is divided into two paths through pipelines and respectively connected to the shell side inlet of the evaporator bottom reboiler and the inlet of the secondary compressor; The gas phase outlet of the second-stage spray tank is connected to the left inlet of the drum through a pipeline, the added steam is connected to the upper inlet of the drum through a pipeline, and the outlet of the drum is connected to the shell side inlet of the bottom reboiler of the distillation tower through a pipeline; The liquid phase outlets of the first-stage spray tank and the second-stage spray tank are connected to the inlet of the gas-liquid separation tank through pipelines; the shell-side outlets of the bottom reboiler of the evaporation tower and the bottom reboiler of the distillation tower are connected to the inlet of the gas-liquid separation tank through pipelines; The gas phase outlet pipeline of the gas-liquid separation tank is connected to the inlet of the first-stage spray tank. The liquid phase outlet pipeline of the gas-liquid separation tank is divided into three routes and respectively connected to the inlet of the top condenser of the distillation tower, the inlet of the first-stage spray tank, and the inlet of the second-stage spray tank. The outlet pipeline of the top condenser of the distillation tower is connected to the inlet of the third-stage compressor.

2. The solvent distillation recovery system for polyphenylene sulfide production according to claim 1, characterized in that: The bottom extraction pipeline of the evaporation tower is connected to the tube side inlet of the bottom reboiler of the evaporation tower, and the tube side outlet of the bottom reboiler of the evaporation tower is connected to the bottom reflux port of the evaporation tower through a pipeline.

3. The solvent distillation recovery system for polyphenylene sulfide production according to claim 1, characterized in that: The bottom extraction pipeline of the distillation tower is connected to the tube side inlet of the bottom reboiler of the distillation tower, and the tube side outlet of the bottom reboiler of the distillation tower is connected to the bottom reflux port of the distillation tower through a pipeline.

4. A distillation method for a solvent recovery system in the production of polyphenylene sulfide, characterized in that: The mixed liquid produced in the polyphenylene sulfide production process is preheated to 80-90°C in the evaporation tower feed preheater and then fed to the bottom of the evaporation tower. The evaporation tower kettle temperature is controlled at 110-125°C and the operating pressure is controlled at 0.3-0.5 bar. After separation, a mixture of methyl pyrrolidone (NMP) and water containing salt is produced at the bottom of the evaporation tower, and a mixed vapor of NMP, water and p-dichlorobenzene is produced at the top of the evaporation tower and enters the distillation tower. The liquid phase at the bottom of the evaporation tower is heated by the bottom reboiler, and the gas phase flows back into the evaporation tower; The temperature of the distillation tower kettle is controlled at 160-175°C, and the operating pressure is controlled at 0.3-0.5 bar. After separation, a mixture of water and p-dichlorobenzene is produced at the top of the distillation tower, and high-purity NMP is obtained at the bottom of the distillation tower. The gas phase at the top of the distillation tower is condensed in the top condenser, and part of the liquid phase is refluxed into the distillation tower. The liquid phase at the bottom of the distillation tower is heated in the bottom reboiler, and the gas phase is refluxed into the distillation tower. The water vapor at the outlet of the top condenser of the distillation tower, after cooling, enters the three-stage compressor for compression and pressure increase, and the pressure is increased to 2.5~3.0bar. The compressed high-temperature and high-pressure supersaturated water vapor enters the first spray tank and is sprayed with condensed water from the heat pump gas-liquid separation tank. The obtained liquid returns to the heat pump gas-liquid separation tank for reuse. Part of the saturated water vapor after spraying goes to the reboiler at the bottom of the evaporation tower to replace the external steam as a heating heat source, and the other part enters the secondary compressor for compression and pressure increase, and the pressure is increased to 10.0~10.5b The compressed high-temperature and high-pressure supersaturated water vapor enters the second-stage spray tank and is sprayed by the condensed water from the heat pump gas-liquid separation tank. The obtained liquid returns to the heat pump gas-liquid separation tank for reuse. The saturated water vapor after spraying goes to the reboiler at the bottom of the distillation tower to replace a part of the external steam as a heating heat source. The condensed water obtained by condensing the water vapor compressed and heated by the three-stage compressor in the reboiler at the bottom of the evaporation tower and the condensed water obtained by condensing the water vapor compressed and heated by the two-stage compressor in the reboiler at the bottom of the distillation tower are both returned to the heat pump gas-liquid separation tank to realize a closed-loop cycle.

5. The distillation method for a solvent recovery system in polyphenylene sulfide production according to claim 4, characterized in that: The liquid phase at the bottom of the distillation tower is heated by a bottom reboiler, and the gas phase refluxes into the distillation tower. The liquid phase is extracted to obtain NMP with a mass fraction greater than 99.5%. The NMP is fed into an evaporation tower feed preheater to preheat the feed to recover some energy. The evaporation tower feed preheater is heated by the high-purity NMP obtained from the bottom of the distillation tower. The temperature of the NMP entering the evaporation tower feed preheater is 160-175°C.

6. The distillation method for a solvent recovery system in polyphenylene sulfide production according to claim 4, characterized in that: The reboiler at the bottom of the evaporation tower is also heated by an indirect heat pump auxiliary distillation system, using water vapor as a heat source, and the temperature of the water vapor entering the reboiler at the bottom of the evaporation tower is 120-135°C.

7. The distillation method for a solvent recovery system in polyphenylene sulfide production according to claim 4, characterized in that: The reboiler at the bottom of the distillation tower is also heated by an indirect heat pump auxiliary distillation system, using water vapor as a heat source, and the temperature of the water vapor entering the reboiler at the bottom of the evaporation tower is 170-185°C.

8. The distillation method for a solvent recovery system in polyphenylene sulfide production according to claim 4, characterized in that: The top condenser of the distillation tower uses the liquid water in the indirect heat pump-assisted distillation system as a cold source to recover the latent heat of the steam at the top of the distillation tower. The temperature of the liquid water entering the top condenser of the distillation tower is 50-70°C.

9. The distillation method for a solvent recovery system in polyphenylene sulfide production according to claim 4, characterized in that: When the saturated water vapor generated by spraying the second-stage spray tank with the condensed water from the heat pump gas-liquid separation tank and going to the reboiler at the bottom of the distillation tower is insufficient, the shortfall is supplemented by external steam.

10. The distillation method for a solvent recovery system in polyphenylene sulfide production according to claim 4, characterized in that: After the liquid phase at the bottom of the evaporator is heated by the bottom reboiler, the liquid phase is extracted and sent to the desalination section for further treatment; after the gas phase at the top of the distillation tower is condensed by the top condenser, part of the liquid phase is extracted from the top of the distillation tower and enters the subsequent recovery link.

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