Treatment method of waste viscous fluid in polyphenylene sulfide production process

Abstract

The invention belongs to the field of new chemical materials, and particularly relates to a method for treating waste viscous fluid in a polyphenylene sulfide production process, which comprises the following specific steps of: washing with a compound solvent, separating solid and liquid, precisely filtering, separating the solvent, evaporating and drying, refining NMP (N-Methyl Pyrrolidone) and the like. According to the method, the viscous liquid generated in the polymerization process is washed with the compound polar solvent, the high-value solvent NMP and the low-molecular polymer in the viscous liquid are extracted into a solvent system, the liquid phase is precisely filtered after solid-liquid separation, the low-molecular polymer is recycled, the filtrate is rectified and separated, the washing solvent is recycled, and the high-value solvent NMP and the low-molecular polymer are obtained. The refined NMP can be reused for polymerization reaction. According to the method, the problem that the viscous liquid of the device is difficult to treat is solved, meanwhile, the yield of the reaction aid N-methyl pyrrolidone is increased, the treatment difficulty of the solid waste salt is reduced, the recycling process is simple, and the method has the advantages of being low in resource occupancy rate, low in energy consumption and small in pollution.

Description

Technical Field

[0001] The invention relates to the field of new chemical material synthesis, and in particular to a method for treating waste viscous liquid in the production process of polyphenylene sulfide. Background Art

[0002] Polyphenylene sulfide is the most important type of polyarylene sulfide. It has excellent comprehensive properties and is the most cost-effective special engineering plastic in the world so far. It is known as the largest special engineering plastic and one of the eight major aerospace materials. With the rapid development of new energy vehicles, electronics and electrical, marine ships, and industrial protection industries, the market demand for PPS is increasing year by year.

[0003] At present, in terms of synthesis process routes, most companies use Philips sodium sulfide method or improve it on this basis. Only South Korea's SK uses melt polymerization. According to different catalytic processes, there are two process routes: lithium-free catalytic process and lithium chloride process, and both process routes have been industrialized. The two processes are different in the polymerization process, but are roughly similar in resin purification and solvent recovery systems.

[0004] In the production process of polyphenylene sulfide, abnormal reactions may occur due to process abnormalities or operational errors, which easily generate a large amount of production waste, most of which are viscous liquids of low-molecular polyphenylene sulfide, which are currently mostly treated as solid waste. In addition, in the solvent recovery device, viscous liquid will appear in the NMP distillation tower kettle. The composition of this part of viscous liquid is similar to that of viscous liquid produced by abnormal polymerization, mainly low-molecular polymers, salts, and NMP, of which the NMP content is more than 50%.

[0005] At present, in the production of polyphenylene sulfide, there is no report on the effective treatment of the above-mentioned viscous liquid involved. Most of them are disposed of in the form of solid waste or directly incinerated. The incineration method will waste the value of NMP and low molecular polymers in the viscous liquid, and the incineration of the gas phase will also cause new environmental problems. Some companies directly dry the viscous liquid, recover part of the NMP, and dispose of the rest as solid waste or incinerate it, but NMP has a high boiling point, the recovery rate of this method is low and the energy consumption is high, which is not economical. Therefore, how to better dispose of the polyphenylene sulfide viscous liquid, effectively reduce production costs, and improve resource utilization has become one of the problems that need to be solved in this field. Summary of the invention

[0006] Aiming at the problem that the waste viscous liquid in the production process of polyphenylene sulfide in the prior art cannot be effectively recycled and treated, the present invention provides a method for treating the waste viscous liquid in the production process of polyphenylene sulfide, wherein the waste viscous liquid is subjected to processes such as solvent washing, solid-liquid separation, precision filtration, solvent separation, evaporation and drying, and NMP vacuum distillation and refining, so as to improve the utilization rate of NMP and realize the recovery of low-molecular polyphenylene sulfide polymers, thereby reducing the cost of three wastes disposal, and has the characteristics of flexible and simple process, strong operability, low resource occupation rate, low energy consumption, and low pollution.

[0007] The main idea of ​​the present invention is: A low-boiling point polar solvent A that is miscible with the polymerization solvent system NMP and has low solubility in salt is used as a compounding solvent in a certain ratio with NMP. The main function of the low-boiling point polar solvent A in the compounding solvent is to wash and replace NMP from the waste viscous liquid as much as possible; and the addition of NMP in the compounding solvent is to reduce the interfacial tension between the low-boiling point polar solvent A and the waste viscous liquid on the one hand, and to help the oligomers to be stripped from the waste viscous liquid and enter the solvent system on the other hand. Through process design, the waste viscous liquid is treated with a compounding solvent, and then the solvent is recycled by filtration, distillation and other means. Low molecular polymers can enter the low molecular recovery device to increase the added value of the product, solving the problem of waste viscous liquid treatment and realizing the maximum utilization of resources.

[0008] The waste viscous liquid used in the present invention can come from the bottom liquid of the NMP recovery tower of the recovery device in the polyphenylene sulfide production process, specifically from the bottom liquid of the NMP recovery tower of the polyphenylene sulfide preparation process by the sodium sulfide method, and its components include NMP, low molecular weight polyphenylene sulfide resin (molecular weight 1000-20000) and sodium chloride, etc., but the present invention is not limited to the waste viscous liquid, as long as the component content of the waste viscous liquid is within the above range, the method of the present invention can be used for treatment. In addition, even if some waste viscous liquids (such as waste viscous liquids produced by abnormal synthesis processes) also contain p-dichlorobenzene, they are also suitable for treatment by this method.

[0009] The method for treating waste viscous liquid in the production process of polyphenylene sulfide provided by the present invention comprises the following specific steps: (1) Washing with a compound solvent: Wash the waste viscous liquid with a compound solvent; extract NMP and low molecular weight polymers in the waste viscous liquid into the solvent system, and filter to obtain filtrate A and salt-containing filter cake A.

[0010] The compound solvent is a compound of N-methylpyrrolidone (NMP) and a low-boiling point polar solvent A, and the mass ratio of N-methylpyrrolidone to the low-boiling point polar solvent A is 1:(1-9); the mass of the compound solvent added is 1-3 times the mass of the waste viscous liquid; Preferably, the low boiling point polar solvent A is one or more of chlorinated alkanes, ketones, and alcohols; the chlorinated alkanes are dichloromethane and / or chloroform; the alcohols are methanol and / or ethanol; the ketones are one or more of acetone, butanone, and pyrrolidone. The low boiling point polar solvent A can be compounded with multiple solvents, which can be recovered and reused by distillation in subsequent processes.

[0011] Preferably, the washing is carried out with stirring at 25-35° C., with a stirring rate of 50-150 r / min, more preferably 80-100 r / min, and a washing time of 10-50 min, more preferably 20-40 min.

[0012] (2) Precision filtration of filtrate A: Precision filtration is performed on the filtrate A obtained in step (1) with a filtration accuracy of 5-10 μm to obtain filtrate B and filter cake B; The obtained filter cake B is mainly low molecular weight polymers of polyphenylene sulfide (about 90% of low molecular weight polymers of polyphenylene sulfide, and the rest is solvent residue), which can be sent to a low molecular weight polyphenylene sulfide recovery device or process for recycling; the main components of the filtrate B are NMP, solvent A and a small amount of salt.

[0013] (3) Distillation separation of filtrate B: filtrate B is subjected to distillation treatment, and the heating temperature of the tower bottom is controlled at 110-160°C during the distillation treatment. A low-boiling point polar solvent A is obtained from the top of the distillation tower, and NMP concentrate is obtained from the bottom of the distillation tower; Preferably, the NMP concentrate obtained in step (3) is subjected to vacuum distillation purification, wherein the tower top pressure of the vacuum distillation purification is 2-5 KPa, the tower bottom temperature is 110-135° C., and the NMP collected liquid is collected from the tower top. The purity of the NMP collected liquid can reach more than 99%.

[0014] Preferably, the low boiling point polar solvent A obtained in step (3) can be used to prepare a composite solvent for recycling, and the collected NMP liquid obtained can be used to prepare a composite solvent for recycling, or can be sent to the polymerization unit of the polyphenylene sulfide production process; part of it can also be used to prepare a composite solvent and part of it can be sent to the polymerization unit, and the kettle residue at the bottom of the tower in step (3) can be treated as the waste viscous liquid in step (1).

[0015] Preferably, the filtrate B is distilled by intermittent distillation, and the intermittent distillation is atmospheric distillation or vacuum distillation. The tower top pressure during vacuum distillation is 2-5 KPa. The intermittent distillation treatment of the filtrate B in step (3) is based on the fact that the treatment volume is not large and the intermittent distillation is used to achieve the effect of solvent recovery in order to save project investment. The method is also applicable to continuous distillation.

[0016] Preferably, if the waste viscous liquid contains p-dichlorobenzene, after collecting the low-boiling polar solvent A by atmospheric distillation, the p-dichlorobenzene is collected by vacuum distillation, the top pressure is controlled at 2-5 KPa, the bottom of the tower is controlled at 100-115°C, the purity of the recovered p-dichlorobenzene is ≥99%, and the residual NMP is ≤1%. Since NMP is a co-solvent for the polymerization unit p-dichlorobenzene, the recovered p-dichlorobenzene contains a small amount of NMP and can be directly returned to the polymerization device for reuse.

[0017] (4) Treatment of the salt-containing filter cake A: The salt-containing filter cake A obtained in step (1) is washed with a low-boiling point polar solvent A of the same type as in step (1), and filtered to obtain a filtrate C and a filter cake C.

[0018] Preferably, the mass of the low-boiling point polar solvent A used to wash the salt-containing filter cake A in step (4) is 0.5-1 times the mass of the compound solvent added in step (1); the purity of the low-boiling point polar solvent A in the obtained filtrate C is ≥98%, and can be directly used as the low-boiling point polar solvent A for the preparation of the compound solvent without separation.

[0019] (5) Salt recovery: The filter cake C obtained in step (4) is dried at 80-120° C. for 30-50 min to obtain refined salt whose main component is sodium chloride, wherein the purity of the sodium chloride is ≥99%.

[0020] The refined salt obtained in step (5) can be sent to a salt recovery device.

[0021] Preferably, in step (5), condensation is performed during the drying process, and the solvent volatilized during the drying process is collected by condensation, and the collected solvent is used as the low-boiling point polar solvent A again for the preparation of the composite solvent.

[0022] Preferably, the waste viscous liquid in step (1) is the bottom viscous liquid of the solvent recovery device in the polyphenylene sulfide synthesis process, the discharge rate of the bottom viscous liquid can be 0.1 t / h, or it is the kettle viscous waste liquid generated by the abnormal polymerization process.

[0023] In summary, compared with the prior art, the technical solution adopted by the present invention can realize the comprehensive utilization of the viscous liquid resources of the polyphenylene sulfide production device, recover NMP and low molecular weight polyphenylene sulfide resin in the viscous liquid, and the solid salt can be treated in the salt treatment device to obtain a by-product salt with higher purity. Through this technical solution, the purity of the recovered NMP reaches 99.5%, the residual NMP in the salt is less than 500ppm, and the purity of the sodium chloride salt reaches 99% under low temperature drying at 90°C. The scheme of the present invention can realize the recycling and reuse of NMP and low molecular weight polymers, while solving the problem of viscous liquid treatment, and at the same time improving the yield of the reaction aid N-methylpyrrolidone, reducing the difficulty of solid waste salt treatment, and has the characteristics of low resource occupancy, low energy consumption, low pollution, simple process and easy operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a flow chart for the treatment of waste viscous liquid in the production process of polyphenylene sulfide. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] The waste viscous liquid in the polyphenylene sulfide sodium sulfide synthesis process treated in the following embodiments comes from the bottom liquid of the NMP recovery tower. Its composition is measured by mass and includes 60-70 wt% NMP, 3-5 wt% low molecular weight polyphenylene sulfide resin (molecular weight 1000-20000) and 25-37 wt% sodium chloride. Other by-products are negligible and have no effect on this treatment method.

[0027] The detection method of NMP is: firstly dissolve the sample with a certain amount of deionized water, and then use liquid chromatography to perform trace detection of NMP in the dissolved system.

[0028] The detection method of sodium chloride is: dissolve the sample in a certain amount of deionized water, and analyze and detect it by silver nitrate titration.

[0029] Example 1 A method for treating waste viscous liquid in the production process of polyphenylene sulfide, the treatment process is as follows Figure 1 As shown, the specific steps are as follows.

[0030] (1) Washing with a composite solution: First, 1000 g of NMP and 2000 g of acetone were weighed, and the NMP and acetone were mixed into 3000 g of a composite solvent; then, 1000 g of the waste viscous liquid was weighed, and the composite solvent and the waste viscous liquid were mixed, and the mixture was mixed at 25° C. and a stirring rate of 80 r / min for 10 min, and then filtered to obtain a filtrate A and a salt-containing filter cake A.

[0031] (2) Precision filtration of filtrate A: filtrate A is subjected to precision filtration with a filtration accuracy of 5 μm to obtain filtrate B and filter cake B, wherein filter cake B is mainly low molecular weight polymer of polyphenylene sulfide and can be sent to a recovery device of low molecular weight polyphenylene sulfide for recycling.

[0032] (3) Distillation and separation of filtrate B: filtrate B is distilled by atmospheric intermittent distillation, the bottom temperature of the tower is heated to 150° C. and heating is stopped, and acetone with a purity of more than 99.51% is collected from the top of the tower. The obtained acetone can be reused to prepare a composite solvent or used in other processes. In this embodiment, the acetone obtained in step (3) is used to prepare a composite solvent; Obtain NMP concentrate from the bottom of the distillation tower; perform vacuum distillation to purify the NMP concentrate, the pressure at the top of the refining tower is 2 KPa, the temperature at the bottom of the tower is 112°C, the purity of the NMP collected at the top of the tower is 99.95%, the residual liquid in the kettle is sent to step (1) for treatment as a waste viscous liquid, the NMP collected liquid can be prepared with a compound solvent for recycling, or it can be sent to the polymerization unit of the polyphenylene sulfide production process.

[0033] (4) Treatment of the salt-containing filter cake A: The salt-containing filter cake A obtained in step (1) was washed with 2000 g of acetone, and filtrated to obtain filtrate C and filter cake C; The mass content of NMP in filtrate C was 0.07%, and the mass content of acetone was 99.92% (the remaining 0.01% was salt and other unknown impurities). Filtrate C was returned for the preparation of compound solvent.

[0034] (5) Salt recovery: The filter cake C obtained in step (4) is evaporated and dried at 90°C for 50 min. A condenser is set on the evaporation and drying system to collect the acetone solvent volatilized during the evaporation and drying process. The collected acetone has a purity of 99.93% and can be used for the preparation of a composite solvent. After evaporation and drying, refined salt whose main component is sodium chloride is obtained. The mass content of sodium chloride in the obtained refined salt is 99.22% after testing. No NMP residue is detected in the refined salt. The obtained refined salt can be sent to a salt recovery device.

[0035] Example 2 A method for treating waste viscous liquid in the production process of polyphenylene sulfide, the treatment process is as follows Figure 1 As shown, the specific steps are as follows.

[0036] (1) Washing with a composite solution: First, weigh 500 g of NMP and 1500 g of ethanol, and prepare 2000 g of a composite solvent with the NMP and ethanol; then weigh 800 g of the waste viscous liquid, mix the composite solvent and the waste viscous liquid, mix them at 25°C at a stirring rate of 80 r / min for 10 min, and then filter to obtain a filtrate A and a salt-containing filter cake A.

[0037] (2) Precision filtration of filtrate A: filtrate A is subjected to precision filtration with a filtration accuracy of 10 μm to obtain filtrate B and filter cake B, wherein filter cake B is mainly low molecular weight polymer of polyphenylene sulfide and can be sent to a recovery device of low molecular weight polyphenylene sulfide for recycling.

[0038] (3) Distillation and separation of filtrate B: filtrate B is distilled by intermittent distillation at normal pressure, the bottom temperature of the tower is heated to 160°C and heating is stopped, and ethanol with a purity of more than 99.49% is collected from the top of the tower. The obtained ethanol can be reused to prepare a composite solvent or used in other processes. In this embodiment, the ethanol obtained in step (3) is used to prepare a composite solvent; Obtain NMP concentrate from the bottom of the distillation tower; perform vacuum distillation to purify the NMP concentrate, the pressure at the top of the refining tower is 4 KPa, the temperature at the bottom of the tower is 116°C, the purity of the NMP collected at the top of the tower is 99.97%, the residual liquid in the kettle is sent to step (1) for treatment as a waste viscous liquid, the NMP collected liquid can be prepared with a compound solvent for recycling, or it can be sent to the polymerization unit of the polyphenylene sulfide production process.

[0039] (4) Treatment of the salt-containing filter cake A: rinse the salt-containing filter cake A obtained in step (1) with 1000 g of ethanol, and obtain filtrate C and filter cake C after filtration; The NMP content in the filtrate C was analyzed and detected to be 0.09%, and the ethanol content was 99.91%. The filtrate C was returned for preparing the compound solvent.

[0040] (5) Salt recovery: The filter cake C obtained in step (4) is evaporated and dried at 90°C for 30 min. A condenser is set on the evaporation and drying system to collect the ethanol solvent volatilized during the evaporation and drying process. The collected ethanol has a purity of 99.98% and can be used for the preparation of a composite solvent. After evaporation and drying, refined salt whose main component is sodium chloride is obtained. The sodium chloride content of the obtained refined salt is 99.19% and the residual NMP is 288 ppm. The obtained refined salt can be sent to a salt recovery device.

[0041] Example 3 A method for treating waste viscous liquid in the production process of polyphenylene sulfide, the treatment process is as follows Figure 1 As shown, the specific steps are as follows.

[0042] (1) Washing with a composite solution: First, 200 g of NMP and 1800 g of acetone were weighed, and the NMP and acetone were mixed to prepare 2000 g of a composite solvent; then 750 g of the waste viscous liquid was weighed, and the composite solvent and the waste viscous liquid were mixed, and the mixture was mixed at 25° C. and a stirring rate of 80 r / min for 10 min, and then filtered to obtain a filtrate A and a salt-containing filter cake A.

[0043] (2) Precision filtration of filtrate A: filtrate A is subjected to precision filtration with a filtration accuracy of 5 μm to obtain filtrate B and filter cake B, wherein filter cake B is mainly low molecular weight polymer of polyphenylene sulfide and can be sent to a recovery device of low molecular weight polyphenylene sulfide for recycling.

[0044] (3) Distillation and separation of filtrate B: filtrate B is distilled by intermittent distillation at normal pressure, the bottom temperature of the tower is heated to 130°C and heating is stopped, and acetone with a purity of more than 99.73% is collected from the top of the tower. The obtained acetone can be reused to prepare a composite solvent or used in other processes. In this embodiment, the acetone obtained in step (3) is used to prepare a composite solvent; Obtain NMP concentrate from the bottom of the distillation tower; perform vacuum distillation to purify the NMP concentrate, the top pressure of the refining tower is 5 KPa, the bottom temperature is 118°C, the purity of the NMP collected at the top of the tower is 99.96%, the kettle residue is sent to step (1) for treatment as a waste viscous liquid, the NMP collected liquid can be prepared with a compound solvent for recycling, or it can be sent to the polymerization unit of the polyphenylene sulfide production process.

[0045] (4) Treatment of the salt-containing filter cake A: The salt-containing filter cake A obtained in step (1) was washed with 2000 g of acetone, and filtrated to obtain filtrate C and filter cake C; The NMP content in the filtrate C was analyzed and detected to be 0.05%, and the acetone content was 99.95%. The filtrate C was returned for preparing the compound solvent.

[0046] (5) Salt recovery: The filter cake C obtained in step (4) is evaporated and dried at 100°C for 40 min. A condenser is set on the evaporation and drying system to collect the acetone solvent volatilized during the evaporation and drying process. The collected acetone has a purity of 99.95% and can be used for the preparation of a composite solvent. After evaporation and drying, refined salt whose main component is sodium chloride is obtained. The sodium chloride content of the obtained refined salt is 99.39% after testing. No NMP residue is detected in the refined salt. The obtained refined salt can be sent to a salt recovery device.

[0047] Example 4 A method for treating waste viscous liquid in the production process of polyphenylene sulfide, the treatment process is as follows Figure 1 As shown, the specific steps are as follows.

[0048] (1) Washing with a composite solution: First, weigh 500 g of NMP and 500 g of acetone, and prepare 1000 g of a composite solvent with the NMP and acetone; then weigh 1000 g of the waste viscous liquid, mix the composite solvent and the waste viscous liquid, mix them at 25°C at a stirring rate of 80 r / min for 10 min, and then filter to obtain a filtrate A and a salt-containing filter cake A.

[0049] (2) Precision filtration of filtrate A: filtrate A is subjected to precision filtration with a filtration accuracy of 5 μm to obtain filtrate B and filter cake B, wherein filter cake B is mainly low molecular weight polymer of polyphenylene sulfide and can be sent to a recovery device of low molecular weight polyphenylene sulfide for recycling.

[0050] (3) Distillation and separation of filtrate B: filtrate B is distilled by intermittent distillation at normal pressure, the bottom temperature of the tower is heated to 140°C and heating is stopped, and acetone with a purity of more than 99.61% is collected from the top of the tower. The obtained acetone can be reused to prepare a composite solvent or used in other processes. In this embodiment, the acetone obtained in step (3) is used to prepare a composite solvent; Obtain NMP concentrate from the bottom of the distillation tower; perform vacuum distillation to purify the NMP concentrate, the pressure at the top of the refining tower is 3.5 KPa, the temperature at the bottom of the tower is 115°C, the purity of the NMP collected at the top of the tower is 99.93%, the residual liquid in the kettle is sent to step (1) for treatment as a waste viscous liquid, the NMP collected liquid can be prepared with a compound solvent for recycling, or it can be sent to the polymerization unit of the polyphenylene sulfide production process.

[0051] (4) Treatment of the salt-containing filter cake A: The salt-containing filter cake A obtained in step (1) was washed with 1000 g of acetone, and filtrated to obtain a filtrate C and a filter cake C; The NMP content in the filtrate C was analyzed and detected to be 0.11%, and the acetone content was 99.89%. The filtrate C was returned for preparing the compound solvent.

[0052] (5) Salt recovery: The filter cake C obtained in step (4) is evaporated and dried at 120° C. for 30 min. A condenser is set on the evaporation and drying system to collect the acetone solvent volatilized during the evaporation and drying process. The collected acetone has a purity of 99.92% and can be used for the preparation of a composite solvent. After evaporation and drying, refined salt whose main component is sodium chloride is obtained. The sodium chloride content of the obtained refined salt is 99.25% and the residual NMP is 378 ppm. The obtained refined salt can be sent to a salt recovery device.

[0053] Example 5 A method for treating waste viscous liquid in the production process of polyphenylene sulfide.

[0054] The processing flow is as follows Figure 1 As shown, the waste viscous liquid is the waste viscous liquid produced by the abnormal polyphenylene sulfide process, which includes NMP, low molecular weight polyphenylene sulfide resin, sodium chloride and p-dichlorobenzene, wherein the mass content of NMP is 55%-60%, the content of p-dichlorobenzene is 1%-10%, and the rest is oligomers and salts.

[0055] The overall treatment process in this embodiment is the same as that in Embodiment 1, with the only difference being that in step (3), after intermittent distillation at normal pressure and collection of acetone, intermittent distillation at reduced pressure is then performed and p-dichlorobenzene is collected. The tower top pressure is controlled at 2 kPa and the tower bottom is controlled at 100° C. The p-dichlorobenzene recovered has a purity of ≥99% and a residual NMP of ≤1%. Since NMP is a co-solvent for the p-dichlorobenzene in the polymerization unit, the p-dichlorobenzene recovered contains a small amount of NMP and can be returned to the polymerization device for reuse. Subsequently, the NMP is recovered in the same manner as in Embodiment 1.

[0056] Example 6 A method for treating waste viscous liquid in the production process of polyphenylene sulfide.

[0057] The processing flow is as follows Figure 1 As shown, the waste viscous liquid is the waste viscous liquid produced by the abnormal polyphenylene sulfide process, which includes NMP, low molecular weight polyphenylene sulfide resin, sodium chloride and p-dichlorobenzene, wherein the mass content of NMP is 55%-60%, the content of p-dichlorobenzene is 1%-10%, and the rest is oligomers and salts.

[0058] The overall treatment process in this embodiment is the same as that in Embodiment 5, with the only difference being that in step (3), after intermittent distillation at normal pressure and collection of acetone, intermittent distillation at reduced pressure is then performed and p-dichlorobenzene is collected. The tower top pressure is controlled at 5 kPa and the tower bottom is controlled at 115° C. The purity of the recovered p-dichlorobenzene is ≥99%, and the residual NMP is ≤1%. Since NMP is a co-solvent for the polymerization unit p-dichlorobenzene, the recovered p-dichlorobenzene contains a small amount of NMP and can be returned to the polymerization device for reuse. Subsequently, the NMP is recovered in the same manner as in Embodiment 1.

[0059] In summary, it can be seen that the scheme of the present invention realizes the recycling and reuse of NMP and low-molecular polymers, solves the problem of treating viscous liquid, improves the yield of reaction aid N-methylpyrrolidone, reduces the difficulty of treating solid waste salt, and has the characteristics of low resource occupancy rate, low energy consumption, low pollution, simple process and easy operation.

[0060] The above embodiments enable those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for treating waste viscous liquid in the production process of polyphenylene sulfide, characterized in that: The specific steps are as follows: (1) Washing with a compound solvent: Wash the waste viscous liquid with a compound solvent; extract NMP and low molecular weight polymers in the waste viscous liquid into the solvent system, and filter to obtain filtrate A and salt-containing filter cake A; The compound solvent is a compound of N-methylpyrrolidone and a low-boiling point polar solvent A, and the mass ratio of the N-methylpyrrolidone to the low-boiling point polar solvent A is 1:(1-9); (2) Precision filtration of filtrate A: Precision filtration is performed on the filtrate A obtained in step (1) with a filtration accuracy of 5-10 μm to obtain filtrate B and filter cake B; (3) Distillation separation of filtrate B: filtrate B is subjected to distillation treatment, and the heating temperature of the tower bottom is controlled at 110-160°C during the distillation treatment. A low-boiling point polar solvent A is obtained from the top of the distillation tower, and NMP concentrate is obtained from the bottom of the distillation tower; (4) Treatment of the salt-containing filter cake A: washing the salt-containing filter cake A obtained in step (1) with a low-boiling point polar solvent A of the same type as in step (1), and filtering to obtain a filtrate C and a filter cake C; (5) Salt recovery: The filter cake C obtained in step (4) is dried at 80-120° C. for 30-50 min to obtain refined salt whose main component is sodium chloride.

2. The method for treating waste viscous liquid according to claim 1, characterized in that: The mass of the composite solvent added in step (1) is 1-3 times the mass of the waste viscous liquid; the low-boiling point polar solvent A is one or more of chlorinated alkanes, ketones, and alcohols; the chlorinated alkanes are dichloromethane and / or chloroform; the alcohols are methanol and / or ethanol; and the ketones are one or more of acetone, butanone, and pyrrolidone.

3. The method for treating waste viscous liquid according to claim 1, characterized in that: The washing in step (1) is carried out with stirring at 25-35°C, a stirring rate of 50-150 r / min, and a washing time of 10-50 min.

4. The method for treating waste viscous liquid according to claim 1 or 3, characterized in that: The washing stirring rate in step (1) is 80-100 r / min, and the washing time is 20-40 min.

5. The method for treating waste viscous liquid according to claim 1, characterized in that: The NMP concentrated liquid obtained in step (3) is subjected to vacuum distillation refining, wherein the tower top pressure of the vacuum distillation refining is 2-5 KPa, the tower bottom temperature is 110-135°C, and the NMP collected liquid is collected from the tower top; in step (3), the filtrate B is distilled by intermittent distillation, and the intermittent distillation is atmospheric distillation or vacuum distillation, wherein the tower top pressure during the vacuum distillation is 2-5 KPa.

6. The method for treating waste viscous liquid according to claim 1 or 5, characterized in that: The low boiling point polar solvent A obtained in step (3) is used to prepare a composite solvent for recycling, and the NMP collected liquid obtained is used to prepare a composite solvent for recycling or sent to the polymerization unit of the polyphenylene sulfide production process; the kettle residue at the bottom of the tower in step (3) is treated as the waste viscous liquid in step (1).

7. The method for treating waste viscous liquid according to claim 1, characterized in that: The mass of the low-boiling-point polar solvent A used to wash the salt-containing filter cake A in step (4) is 0.5-1 times the mass of the compound solvent added in step (1); the obtained filtrate C is used as the low-boiling-point polar solvent A for the preparation of the compound solvent.

8. The method for treating waste viscous liquid according to claim 1, characterized in that: In step (5), condensation is performed during the drying process, and the solvent volatilized during the drying process is collected by condensation, and the collected solvent is used as the low-boiling point polar solvent A for the preparation of the composite solvent.

9. The method for treating waste viscous liquid according to claim 1, characterized in that: The waste viscous liquid in step (1) is the bottom viscous liquid of the solvent recovery device in the polyphenylene sulfide synthesis process, which contains NMP, low molecular weight polyphenylene sulfide resin and sodium chloride.

10. The method for treating waste viscous liquid according to claim 1, characterized in that: The waste viscous liquid in step (1) is a waste viscous liquid generated by an abnormal polyphenylene sulfide process, which contains NMP, low molecular weight polyphenylene sulfide resin, sodium chloride and p-dichlorobenzene. At this time, in step (3), after intermittent distillation at normal pressure and collecting the low boiling point polar solvent A, intermittent distillation at reduced pressure is performed and p-dichlorobenzene is collected, and the top pressure of the tower for collecting p-dichlorobenzene is controlled at 2-5 Kpa, and the bottom temperature of the tower is controlled at 100-115°C.

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