Solvent recovery method in polyphenylene sulfide resin production process

Abstract

The invention belongs to the field of chemical material treatment, and particularly relates to a solvent recovery method in a polyphenylene sulfide resin production process. According to the method, low polymers are cut firstly, then N-methyl pyrrolidone and p-dichlorobenzene in washing liquid are extracted and recovered, high-energy-consumption operation of direct water steaming is avoided, an extraction agent in a raffinate phase is recovered in a pervaporation mode, selective permeability of a membrane is utilized, and compared with steam stripping, the separation efficiency is high, the energy consumption is low, and the cost is low. The extraction agent is recovered in an azeotropic coupling steam stripping manner, so that on one hand, the energy consumption is reduced, and on the other hand, the problem of acidizing corrosion of a reboiler caused by heating rectification by using the reboiler is solved; the method comprises the following steps: carrying out reduced pressure supergravity rectification on residual components, recycling unreacted p-dichlorobenzene monomers, and then carrying out refining purification and other treatment operations on NMP, so that efficient recovery of the solvent NMP is realized, and the method has the characteristics of controllable process, high separation efficiency, low energy consumption, small pollution, high solvent purity and high yield.

Description

Technical Field

[0001] This invention belongs to the field of chemical material processing, and specifically relates to a solvent recovery method in the production process of polyphenylene sulfide resin. Background Technology

[0002] Currently, the conventional preparation method for polyphenylene sulfide (PPS) typically involves polymerizing p-dichlorobenzene with sodium sulfide in an NMP solvent system. The polymerized resin is then washed with water, dried, and packaged for storage. The washing liquid enters a solvent recovery system. The main components of the washing liquid are water, NMP, oligomers, salts, and unreacted monomers. The water content is approximately 45%-50%, the NMP content is approximately 40%-45%, the salt content is approximately 2%-5%, and other components account for approximately 1%-3%.

[0003] There are two main methods for treating washing liquid. The currently common method in the industry is direct distillation for dehydration, followed by vacuum distillation of NMP and drying of the salt before disposal as hazardous waste. Some research uses extraction for solvent recovery and purification. This involves first extracting NMP from the washing liquid with extractants such as chloroform, then recovering the extractant from the extract phase using distillation, and further recovering the extractant entrained in the raffinate phase via stripping. Compared to the first process, the extraction-solvent recovery method can improve the recovery rate of both NMP and extractant. However, wastewater treatment is more difficult, requiring the recovery of the extractant from the wastewater. Furthermore, recovering chloroform from the raffinate phase is energy-intensive. If distillation is used to recover chloroform, there is a significant problem of extractant residue in the column bottom. The extractant is prone to thermal decomposition and acidification, and the column bottom is susceptible to corrosion. Traditional extraction and distillation columns have low separation efficiency and require a high number of plates, resulting in a large overall investment.

[0004] Therefore, how to better treat polyphenylene sulfide washing liquid and more efficiently recover the solvent has become one of the urgent problems to be solved in this field. Summary of the Invention

[0005] To address the problems of high separation energy consumption and equipment corrosion in existing technologies, this invention provides a solvent recovery method in the production process of polyphenylene sulfide (PPS). The specific steps include oligomer removal, pH adjustment, continuous extraction, pervaporation treatment of the raffinate phase, azeotropic distillation of the extractant, ultragravity recovery of p-dichlorobenzene, and purification of N-methylpyrrolidone. First, the oligomers are removed. Then, a hydrophobic solvent is used to extract and recover N-methylpyrrolidone and p-dichlorobenzene from the washing liquid, avoiding the high energy consumption of direct water distillation. This invention uses pervaporation to recover the extractant from the raffinate phase. Compared to stripping, it utilizes the selective permeability of membranes, resulting in high separation efficiency and low energy consumption. Simultaneously, an azeotropic coupled stripping method is used to recover the extractant in the extraction phase, lowering the boiling point of the extractant. This reduces energy consumption and solves the problem of acidification and corrosion of the reboiler caused by heating distillation in the reboiler. The remaining components are subjected to depressurized high-gravity distillation to recover and reuse unreacted p-dichlorobenzene monomer. Then, NMP is purified and refined, achieving efficient recovery of solvent NMP. This reduces the problems of solvent decomposition, pipeline corrosion and blockage, low yield, and high energy consumption that exist in traditional processes. It features controllable process, high separation efficiency, low energy consumption, low pollution, high solvent purity, and high yield.

[0006] The main technical concept of this invention is: Wash water has a complex composition and high water content, making direct evaporation costly. Furthermore, salt can easily precipitate from the bottom of the distillation column during the later stages, corroding or clogging pipes. Additionally, after water distillation, NMP purification is necessary. NMP is easily decomposed under salt and high temperatures, and the light decomposition products mix with the NMP at the top of the column, while the condensed heavy components form a gel with salt and residual oligomers, corroding and clogging heat exchangers. This invention employs a coupled approach of extraction, pervaporation, azeotropic distillation, high-gravity distillation, and vacuum distillation to extract the effective components from water. Then, the effective components are separated from low-boiling-point solvents at low temperature and high efficiency, achieving high-purity, high-yield, and low-energy recovery of NMP and p-dichlorobenzene from wash water.

[0007] In the pervaporation process, the extractant in the raffinate phase is vaporized on the permeate side of the pervaporation unit by selectively permeating the membrane, and then recovered by condensation. Azeotropic distillation is used to treat and recover the extractant phase. The azeotropic distillation is coupled with stripping, and steam is directly injected into the lower part of the azeotropic distillation column, eliminating the need for a reboiler, reducing heat loss in the reboiler, and improving energy utilization. At the same time, after stripping, the main components of the residue in the column bottom are NMP and condensate, which improves the problem of severe residue and acidification of extractant in the column bottom caused by extractant in the residue in conventional methods. It also improves the problem of extractant residue in the column bottom acidification and corrosion at high temperature. The heat transfer efficiency is higher, and energy consumption is effectively reduced and the thermal decomposition of extractant and corrosion of the equipment walls are inhibited.

[0008] The polyphenylene sulfide washing solution used in this invention is derived from a polyphenylene sulfide purification and washing device (i.e., a device used in the polyphenylene sulfide resin purification process to wash NMP, salts, and other substances from the resin with water). In the embodiments of this invention, the washing solution has the following mass composition: water content of approximately 45.2%, NMP content of approximately 47.9%, salt content of approximately 5.2%, p-dichlorobenzene content of approximately 0.9%, and oligomer content (the oligomer molecular weight is mostly between 2000 and 10000) of approximately 0.8%.

[0009] The solvent recovery method in the production process of polyphenylene sulfide resin provided by this invention comprises the following specific steps: 1) Oligomer removal: The polyphenylene sulfide washing solution is settled in a settling tank equipped with a filter to retain oligomers; Preferably, the settling tank is equipped with a three-layer filter screen of 80 mesh, 200 mesh and 80 mesh, and a precision filter with a filtration accuracy of 200 to 300 mesh is installed at the outlet of the settling tank. Because of their higher density relative to water, oligomers can settle in settling tanks, removing more than 95% of them. The retained oligomers can be sent to an oligomer crosslinking device for washing and crosslinking, and then sold as crosslinked products.

[0010] 2) pH adjustment: The clear liquid from step 1) where oligomers were removed was placed in a pH adjustment tank for pH adjustment, and the pH was controlled at 6-7 to avoid solvent decomposition due to excessively high or low pH. The pH adjustment can be achieved using various commonly used pH adjusters in the art, such as hydrochloric acid solutions and sodium hydroxide solutions of different concentrations.

[0011] 3) Continuous extraction: The solution with pH 6-7 obtained in step 2) and the extractant are continuously extracted in an extraction tower. The extraction tower is a plate tower with a theoretical number of 5-10 plates, to obtain the light phase at the top of the tower and the oil phase at the bottom of the tower. Preferably, the extractant is selected from haloalkanes, and the extractant mass: solution mass = 1 to 3:1. The haloalkanes are selected from one or more of dichloromethane, trichloromethane, and carbon tetrachloride (chloroform).

[0012] 4) Pervaporation: The light phase at the top of the extraction tower mainly consists of water, salt and trace amounts of extractant (i.e., raffinate phase). It is sent to the pervaporation unit for pervaporation treatment to recover the extractant from the wastewater. Then, the wastewater after recovering the extractant is sent to the biological wastewater system for biological treatment. The extractant content in the light phase at the top of the extraction tower undergoing pervaporation is 0.1-1% by mass; the temperature of the pervaporation feed liquid side is 45℃-55℃, the pervaporation pressure is 2-6KPa (absolute pressure), and the condensation temperature is -5 to -10℃.

[0013] Recovering the extractant reduces waste, but its presence can hinder subsequent wastewater treatment and harm the microbial agents used in wastewater treatment.

[0014] The pervaporation device is a commonly used pervaporation membrane separation device in the art, comprising a feed pretreatment system, a membrane module array with built-in composite membranes, a low-temperature condensation system connected to the permeate side of the membrane modules, and a vacuum system connected to the outlet of the condensation system. The pervaporation device contains 2 to 5 composite membrane modules connected in series. These composite membrane modules can be selected from various existing membrane modules available in pervaporation devices, such as PDMS / PVDF composite membranes, with each PDMS / PVDF composite membrane module having an area of ​​40 to 90 m². 2 .

[0015] 5) Azeotropic distillation recovery of extractant: The bottom oil phase (i.e., the extractant phase) obtained in step 3) is fed into an azeotropic distillation column. The main components of the bottom oil phase are extractant, NMP, p-dichlorobenzene, trace amounts of water and trace amounts of salt. A combination of steam stripping and azeotropic distillation is used. The bottom temperature of the azeotropic distillation column is 105-110℃, the top temperature is 50-80℃, and the steam injection temperature is 180℃-200℃. The steam flow rate is adjusted flexibly in real time according to the amount of oil phase. For example, the flow rate can be determined through pre-experimentation and is not specifically limited. The azeotropic distillation column is fed with steam from the bottom of the column and discharged from the product vapor outlet at the top of the column. It is a conventional piece of equipment in the field. The material obtained at the top of the azeotropic distillation column, mainly composed of extractant and water, is sent to the collection tank for stratification. The upper layer of water can be reused for washing polyphenylene sulfide resin, while the lower layer is the extractant, which can be recycled for continuous extraction processes. The bottom liquid of the azeotropic distillation column mainly consists of stripping condensate, NMP, p-dichlorobenzene, and trace amounts of salt. The bottom material is subsequently sent to a high gravity distillation column. Azeotropic distillation columns simultaneously perform steam stripping and azeotropic distillation, combining the characteristics of azeotropic distillation. On the one hand, the latent heat of steam can be effectively utilized, and on the other hand, the investment in reboilers is reduced. At the same time, the azeotropic relationship between steam condensate and extractant can lower the boiling point of the components to be separated in the stripping column. The principle of water and extractant incompatibility is used to recover the extractant. The combination of these two methods achieves the recovery of low-boiling-point extractant.

[0016] 6) Recovering p-dichlorobenzene by gravity: The bottom liquid from the azeotropic distillation column in step 5) is fed into a gravity distillation column for gravity distillation. Water and p-dichlorobenzene are obtained at the top of the column. After being cooled to 40-60°C in the cooler at the top of the column, p-dichlorobenzene and water separate into layers in the reflux tank connected to the top of the column because they are immiscible. The lower layer of p-dichlorobenzene can be directly reused as a reaction monomer in the polyphenylene sulfide (PPS) production process, while the upper layer of aqueous phase can be used for washing and reuse of PPS. The equipment used for gravity distillation (gravity distillation column and reflux tank) is a complete set of conventional equipment that has been maturely applied in this field. Preferably, the rotational speed of the supergravity distillation column is in the range of 200 to 1000 r / min, the bottom temperature is 105 to 120℃, the top temperature is 90 to 110℃, the top pressure is 2 to 10 kPa (absolute pressure), and the steam temperature is 180℃ to 200℃. The steam flow rate is flexibly adjusted in real time according to the amount of oil phase. For example, the flow rate can be determined through pre-experiment and is not particularly limited. In a high gravity distillation column, high gravity distillation and vacuum distillation can be coupled. The liquid in the bottom of the high gravity distillation column mainly contains NMP, trace amounts of salt and oligomers, and is sent to the NMP purification column for further processing.

[0017] 7) N-methylpyrrolidone purification: The liquid in the bottom of the supergravity distillation column in step 6) is transferred to the NMP purification column. The NMP is distilled under reduced pressure in the NMP purification column to collect NMP from the top of the column. The liquid in the bottom of the NMP purification column mainly contains a small amount of oligomers, salt and NMP solvent, and is sent to step 1) to repeat the above solvent recovery treatment. Preferably, the pressure at the top of the NMP refining column is 2–10 kPa (absolute pressure), the temperature at the bottom of the column is 110–120°C, and the temperature at the top of the column is 98–115°C. The NMP collected from the top of the NMP purification column has a purity of ≥99.5%. By repeatedly processing the solvent using the above-described solvent recovery method, NMP can be fully recovered, with a yield of over 98% throughout the entire process.

[0018] In summary, compared with existing technologies, the technical solution adopted in this invention solves the problems of high energy consumption, low solvent recovery rate, and pipeline blockage and corrosion during operation, achieving an NMP recovery purity of 99.9% and a recovery rate of 99%. It also reduces the difficulty of solid waste salt treatment and features low resource consumption, low energy consumption, and minimal pollution.

[0019] The use of pervaporation to treat the raffinate reduces energy consumption and effectively inhibits the thermal decomposition of the extractant, thus providing corrosion protection for the equipment. For the recovery of the extractant, an azeotropic distillation coupled with steam injection is used, eliminating the need for a reboiler and resulting in higher heat transfer efficiency. By using a combination of pervaporation and azeotropic distillation for stripping, the raffinate and extract phases are treated and recovered separately, effectively solving the problems of high energy consumption and high-temperature acidification and corrosion of the extractant in the bottom of the tower. Attached Figure Description

[0020] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0021] The technical solution of the present invention will be further described below with reference to specific embodiments. These embodiments are only used to illustrate the technical solution of the present invention in more detail and should not be construed as limiting the scope of protection of the present invention.

[0022] All the devices used are common and conventional devices in the field and can be purchased through market channels.

[0023] Unless otherwise specified, all substances and materials used are commercially available products.

[0024] The pervaporation apparatus used is a commonly used pervaporation membrane separation device in this field, including a feed pretreatment system, a membrane module array with built-in PDMS / PVDF composite membrane modules, a low-temperature condensation system connected to the permeate side of the membrane modules, and a vacuum system connected to the outlet of the condensation system. The pervaporation apparatus contains two PDMS / PVDF composite membrane modules connected in series, each with an area of ​​55 m². 2 .

[0025] The polyphenylene sulfide washing liquid processed in the following examples is the washing liquid produced by the device in the polyphenylene sulfide resin purification process that washes NMP, salt and other substances in the resin with water. Its mass composition is basically as follows: water content about 45.2%, NMP content about 47.9%, salt content about 5.2%, p-dichlorobenzene content about 0.9%, and oligomer content about 0.8%.

[0026] In the following examples and comparative examples, organic components (such as NMP and p-dichlorobenzene) were detected by gas chromatography (flame ionization detector), low molecular weight polymers were detected by gravimetric method, salt content was detected by ash method, and water was quantitatively analyzed by gas chromatography (thermal conductivity detector).

[0027] Example 1: A solvent recovery method in the production process of polyphenylene sulfide resin, such as... Figure 1 As shown, the specific steps are as follows: 1) Oligomer removal: The polyphenylene sulfide washing solution is settled in a settling tank equipped with a filter to retain oligomers. The flow rate of the polyphenylene sulfide washing solution is 10 t / h. The settling tank is equipped with a three-layer filter screen of 80 mesh, 200 mesh and 80 mesh, and a precision filter with a filtration accuracy of 300 mesh is installed at the outlet of the settling tank. Because of their higher density relative to water, oligomers can settle in settling tanks, removing more than 95% of them. The retained oligomers can be sent to an oligomer crosslinking device for washing and crosslinking, and then sold as crosslinked products.

[0028] 2) pH control: The clear liquid from step 1) where oligomers were removed was placed in a pH adjustment tank for pH adjustment. The pH was controlled at 6-7 using sodium hydroxide solution or hydrochloric acid solution to avoid solvent decomposition due to excessively high or low pH.

[0029] 3) Continuous extraction: The solution obtained in step 2) and the extractant are subjected to continuous countercurrent extraction in an extraction tower with a theoretical plate number of 5. The extractant is 10 t / h chloroform, resulting in a light phase at the top of the tower and an oil phase at the bottom.

[0030] 4) Pervaporation: The light phase at the top of the extraction tower mainly consists of water, salt and trace amounts of extractant, with chloroform content at 0.12% (mass concentration). This light phase at the top of the tower is sent to a pervaporation unit for pervaporation to recover the extractant from the solvent. Then, the wastewater after recovering the extractant is sent to a biological wastewater system for biological treatment. The feed liquid temperature was 50℃, the permeation pressure was 3 kPa, the condensation temperature was -8℃, and the chloroform content in the treated water was 106 ppm.

[0031] 5) Extractant Azeotropic Distillation Recovery: The bottom oil phase obtained in step 3) is fed into an azeotropic distillation column. The main components of the bottom oil phase are extractant, NMP, p-dichlorobenzene, trace amounts of water and trace amounts of salt. The bottom temperature of the azeotropic distillation column is 106°C, and the top temperature is 71°C. Steam is fed into the bottom of the azeotropic distillation column at a temperature of 183°C. The material obtained at the top of the azeotropic distillation column, mainly composed of extractant and water, is sent to the collection tank for stratification. The upper layer of water can be reused for washing polyphenylene sulfide resin (the upper aqueous phase contains trace amounts of chloroform, which does not affect its use as washing water). The lower layer is the extractant chloroform, which is returned to the extraction process for recycling in the continuous extraction process. The bottom liquid at the bottom of the column mainly consists of stripping condensate, NMP, p-dichlorobenzene, and trace amounts of salt. The bottom liquid is subsequently sent to a high gravity distillation column.

[0032] 6) Recovering p-dichlorobenzene by gravity: The bottom liquid of the azeotropic distillation in step 5) is fed into a gravity distillation column for gravity distillation. Water and p-dichlorobenzene are obtained at the top of the column. After cooling to 50°C, p-dichlorobenzene and water are separated into layers in a reflux tank connected to the top of the gravity distillation column. The lower layer of p-dichlorobenzene can be directly reused as a reaction monomer in the polyphenylene sulfide production process, and the upper aqueous phase can be returned to the polyphenylene sulfide resin purification unit for the purification process of washing polyphenylene sulfide. The rotational speed of the supergravity distillation column is 200 r / min, the bottom temperature is 109℃, the top temperature is 94℃, the top pressure is 3 kPa (absolute pressure), and the steam temperature is 183℃. In a high gravity distillation column, high gravity distillation and vacuum distillation are coupled. The liquid in the bottom of the high gravity distillation column mainly contains NMP, trace amounts of salt and oligomers, and is sent to the NMP purification column for further processing.

[0033] 7) N-methylpyrrolidone purification: The liquid in the bottom of the supergravity distillation column in step 6) is transferred to the NMP purification column. The NMP is distilled under reduced pressure in the NMP purification column, and NMP with a purity of 99.93% is collected from the top of the column. The liquid in the bottom of the NMP purification column mainly contains a small amount of oligomers, salt and NMP solvent. It is sent to the front end of the settling tank in step 1) to repeat the above solvent recovery treatment in order to improve the NMP recovery rate. The NMP refining column has a top pressure of 4.6 kPa (absolute pressure), a bottom temperature of 118°C, and a top temperature of 113°C.

[0034] Through the above process, p-dichlorobenzene with a purity of 99.92% and NMP product with a purity of 99.93% were obtained. 4.75 t / h of NMP product was obtained from the top of the tower, with a yield of 99.09%.

[0035] Example 2: A solvent recovery method in the production process of polyphenylene sulfide resin, the method is basically the same as that in Example 1, the difference being: The flow rate of the polyphenylene sulfide washing solution is 8 t / h, and the flow rate of the extractant chloroform is 12 t / h. The temperature on the liquid side of the pervaporation unit is 55℃, and the pressure is 2KPa. The bottom temperature of the azeotropic distillation column is 109℃, and the top temperature is 79℃. The rotational speed of the supergravity distillation column is 300 r / min, the bottom temperature is 115℃, the top temperature is 103℃, and the top pressure is 5 kPa (absolute pressure). The NMP refining column has a top pressure of 3.1 kPa (absolute pressure), a bottom temperature of 116°C, and a top temperature of 104°C.

[0036] Through the above process, p-dichlorobenzene with a purity of 99.93% and NMP product with a purity of 99.92% were obtained. 3.81 t / h of NMP product was obtained from the top of the tower, with a yield of 99.35%.

[0037] Example 3: A solvent recovery method in the production process of polyphenylene sulfide resin, the method is basically the same as that in Example 1, the difference being: The flow rate of the polyphenylene sulfide washing solution is 8 t / h, and the flow rate of the extractant chloroform is 20 t / h. The temperature of the liquid side during pervaporation is 45℃, and the pressure on the pervaporation side is 2KPa. The bottom temperature of the azeotropic distillation column is 105℃, and the top temperature is 56℃. The rotational speed of the supergravity distillation column is 600 r / min, the bottom temperature is 108℃, the top temperature is 92℃, and the top pressure is 2.8 kPa (absolute pressure). The NMP refining column has a top pressure of 2.2 kPa (absolute pressure), a bottom temperature of 110.4℃, and a top temperature of 98℃.

[0038] Through the above process, p-dichlorobenzene with a purity of 99.72% and NMP product with a purity of 99.94% were obtained. 3.81 t / h of NMP product was obtained from the top of the tower, with a yield of 99.36%.

[0039] The reason for the decrease in the purity of dichlorobenzene is that the amount of extractant added was relatively large, the temperature of the bottom of the azeotropic distillation column was relatively low, and chloroform was not completely removed, which affected its purity, but did not affect its reuse.

[0040] Example 4: A solvent recovery method in the production process of polyphenylene sulfide resin. The method is basically the same as that in Example 1, except that: The flow rate of the polyphenylene sulfide washing solution is 6 t / h, and the flow rate of the extractant chloroform is 18 t / h. The temperature of the liquid side during pervaporation is 55℃, the pressure on the pervaporation side is 6KPa, and the condensation temperature is -5℃. The bottom temperature of the azeotropic distillation column is 107℃, and the top temperature is 74℃. The rotational speed of the supergravity distillation column is 800 r / min, the bottom temperature is 112℃, the top temperature is 96℃, and the top pressure is 3.2 kPa (absolute pressure). The NMP refining column has a top pressure of 2.7 kPa (absolute pressure), a bottom temperature of 113°C, and a top temperature of 99.3°C.

[0041] Through the above process, p-dichlorobenzene with a purity of 99.89% and NMP product with a purity of 99.92% were obtained. 2.86 t / h of NMP product was obtained from the top of the tower, with a yield of 99.43%.

[0042] The treatment method of Comparative Example 1 is basically the same as that of Example 1, except that the stripping evaporation method is used to treat the raffinate phase and recover the extractant. The raffinate phase is passed into the stripping tower for treatment. Water and extractant are collected from the top of the stripping tower. After the water and extractant are allowed to stand and separate into layers, they are separated and recovered. The remaining wastewater is sent to the biological sewage system for treatment.

[0043] The stripping tower used has a bottom temperature of 106℃, a top temperature of 71℃, a pressure of 0.15 MPa(G) (gauge pressure), and 5 theoretical plates.

[0044] Compared to Comparative Example 1, this example uses pervaporation to treat the residual extractant in the raffinate phase. The main difference lies in utilizing the selective permeability of the membrane, allowing the organic solvent to selectively permeate through the membrane. Then, under heat and negative pressure, the organic solvent evaporates on the membrane, achieving efficient separation. Comparative Example 1, operating under the same conditions using evaporative stripping, requires 3-5 tons of steam to process 1 ton of raffinate phase, with negligible power consumption and an estimated cost of approximately 720-1200 yuan / ton. Example 1, using pervaporation, consumes only 0.2-0.5 tons of steam to process 1 ton of raffinate phase, with power consumption of approximately 8KW-10KW and a processing cost of approximately 53.6-127 yuan / ton, showing a significant cost reduction.

[0045] Comparative Example 2 uses a method that is basically the same as that of Example 1, except that a conventional distillation column is used in conjunction with a conventional reboiler to recover the extractant from the extract phase. The temperature of the column bottom is 155°C, the temperature of the column top is 61°C, and the pressure is 0.18 MPa(G) (gauge pressure). The liquid residue in the column bottom is about 0.5%-1.5% (mass concentration) of extractant.

[0046] For the recovery of extractant from the extract phase, distillation is the commonly considered solution. However, in operation, firstly, a reboiler is required for indirect heat exchange, and secondly, extractant residues remain at the bottom of the distillation column, which are easily decomposed at high temperatures, corroding pipes and heat exchangers.

[0047] In Example 1, azeotropic distillation coupled with steam stripping is used. On the one hand, it can reduce the heat of evaporation required to recover the extractant. On the other hand, steam is directly injected from the bottom of the column. The main components of the column bottom are NMP and water, which solves the problem of extractant acidification.

[0048] Compared with Example 1, Comparative Example 2 increased energy consumption by about 20% when processing the same amount of washing liquid under the same conditions, and there was about 0.89% (mass concentration) of extractant residue in the bottom liquid of the column. In contrast, the extractant content in the bottom liquid of Example 1 was ≤100ppm, which greatly improved the acid corrosion problem.

[0049] Comparative Example 3 uses a similar treatment method to Example 1, except that a conventional distillation column is used instead of a supergravity distillation column. The conventional distillation column has a bottom temperature of 145°C, a top temperature of 104°C, a pressure of 3 kPa, and steam is introduced at the bottom with a temperature of 183°C. The steam flow rate is determined through a preliminary experiment. The theoretical number of plates is 20, the column height is about 15 meters, and the reflux ratio is 2.

[0050] Example 1 utilizes high-gravity technology to generate powerful centrifugal force through a high-speed rotating packed bed, tearing the liquid into extremely thin liquid films, filaments, and droplets, significantly increasing the gas-liquid contact area and turnover rate. Compared to conventional distillation equipment, it has a smaller footprint, a mass transfer efficiency approximately 20 times higher, and features low reflux ratio and low energy consumption. Comparative Example 3, under the same conditions, requires 0.3-0.5 tons of steam to process 1 ton of mixed organic solution after extractant removal; Example 1, using high-gravity vacuum distillation, with the same theoretical plate number, a column height of approximately 3 meters, a reflux ratio of 0.5, and a top pressure of 3 kPa, requires only 0.15-0.25 tons of steam to process 1 ton of mixed organic solution after extractant removal, demonstrating significant energy savings and investment benefits.

[0051] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any equivalent substitutions or modifications made by those skilled in the art within the spirit and principle of the present invention without any creative effort should be included within the protection scope of the present invention.

Claims

1. A method for solvent recovery during the production of polyphenylene sulfide resin, characterized in that, The specific steps are as follows: 1) Oligomer removal: The polyphenylene sulfide washing solution is settled in a settling tank equipped with a filter to retain oligomers; 2) pH adjustment: The clear liquid from step 1) where oligomers were removed was placed in a pH adjustment tank for pH adjustment, and the pH was controlled at 6-7; 3) Continuous extraction: The solution obtained in step 2) and the extractant are continuously extracted in an extraction tower; 4) Pervaporation: The light phase at the top of the extraction tower is fed into the pervaporation unit for pervaporation treatment to recover the extractant in the wastewater. The wastewater after recovering the extractant is sent to the plant's biochemical wastewater system for biochemical treatment. 5) Azeotropic distillation recovery of extractant: The bottom oil phase obtained in step 3) is fed into an azeotropic distillation column; the material obtained at the top of the azeotropic distillation column is sent to the collection tank for stratification. The water in the upper layer is used for washing polyphenylene sulfide resin, and the extractant in the lower layer is recycled for continuous extraction process; the bottom liquid of the azeotropic distillation column is subsequently sent to a high gravity distillation column. 6) Recovering p-dichlorobenzene by gravity: The bottom liquid of the azeotropic distillation column in step 5) is fed into the gravity distillation column for gravity distillation. Water and p-dichlorobenzene are obtained at the top of the gravity distillation column. After cooling to 40-60℃, p-dichlorobenzene and water are separated in a reflux tank connected to the top of the gravity distillation column. The lower p-dichlorobenzene is reused as a reaction monomer in the polyphenylene sulfide production process, and the upper aqueous phase is used for washing polyphenylene sulfide. 7) Refining of N-methylpyrrolidone: The liquid in the bottom of the supergravity distillation column in step 6) is transferred to the NMP refining column, where it is distilled under reduced pressure to collect NMP from the top of the column. The liquid in the bottom of the NMP refining column is then sent to step 1) to repeat the solvent recovery process described above.

2. The solvent recovery method in the production process of polyphenylene sulfide resin according to claim 1, characterized in that: The polyphenylene sulfide washing solution is derived from a polyphenylene sulfide purification and washing device.

3. The solvent recovery method in the production process of polyphenylene sulfide resin according to claim 1, characterized in that: The settling tank is equipped with a three-layer filter screen of 80 mesh, 200 mesh and 80 mesh, and a precision filter with a filtration accuracy of 200 to 300 mesh is installed at the outlet of the settling tank; the oligomers obtained are sent to the oligomer crosslinking device for washing and crosslinking.

4. The solvent recovery method in the production process of polyphenylene sulfide resin according to claim 1, characterized in that: The extractant is selected from haloalkanes, and the extractant mass: solution mass = 1 to 3:

1. The haloalkanes are selected from one or more of dichloromethane, trichloromethane, and carbon tetrachloride. The extraction tower is a plate tower with 5 to 10 theoretical plates.

5. The solvent recovery method in the production process of polyphenylene sulfide resin according to claim 1, characterized in that: The pervaporation device is a pervaporation membrane separation device, comprising a feed pretreatment system, a membrane module array with built-in composite membranes, a low-temperature condensation system connected to the permeate side of the membrane modules, and a vacuum system connected to the outlet of the condensation system. The pervaporation device contains 2 to 5 composite membrane modules connected in series. Each composite membrane module is a PDMS / PVDF composite membrane, and the area of ​​each PDMS / PVDF composite membrane module is 40 to 90 m². 2 ; The extractant content in the light phase at the top of the extraction tower undergoing pervaporation is 0.1-1% by mass; the temperature of the pervaporation feed liquid side is 45℃-55℃, the pervaporation pressure is 2-6Kpa, and the condensation temperature is -5 to -10℃.

6. The solvent recovery method in the production process of polyphenylene sulfide resin according to claim 1, characterized in that: The bottom temperature of the azeotropic distillation column is 105-110℃, the top temperature is 50-80℃, and the injected steam temperature is 180℃-200℃. The azeotropic distillation column receives steam from the bottom and discharges it from the product vapor outlet at the top of the column.

7. The solvent recovery method in the production process of polyphenylene sulfide resin according to claim 1, characterized in that: The rotational speed of the supergravity distillation column is in the range of 200 to 1000 r / min, the bottom temperature is 105 to 120℃, the top temperature is 90 to 110℃, the top pressure is 2 to 10 kPa, and the steam temperature is 180℃ to 200℃.

8. The solvent recovery method in the production process of polyphenylene sulfide resin according to claim 1, characterized in that: The NMP refining column has a top pressure of 2–10 kPa, a bottom temperature of 110–120°C, and a top temperature of 98–115°C.

Images