Solvent and salt recovery methods for polyphenylene sulfide synthesis waste liquid
By adjusting the pH and using a seed solution distillation method, the problem of efficient recovery of NMP and solid salts from polyphenylene sulfide synthesis waste liquid was solved, achieving the preparation of high-purity NMP and large-particle-size solid salts, avoiding reactor blockage, and supporting the stable operation of the polymerization reaction.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHANGHAI ZHONGHUA TECH CO LTD
- Filing Date
- 2024-12-30
- Publication Date
- 2026-06-30
AI Technical Summary
Existing technologies are insufficient for efficiently recovering NMP solvent from polyphenylene sulfide synthesis waste liquid and obtaining high-purity solid salts. Furthermore, the extractant is a toxic substance or is prone to clogging during the recovery process.
The concentration of NMP was controlled by adjusting the pH of the synthetic waste liquid to neutral, and the concentration and particle size of solid salt were controlled by mixing the seed solution with the waste liquid for distillation to avoid clogging. NMP and solid salt were recovered by centrifugation and drying.
It enables the recovery of high-purity NMP and the preparation of solid salts with large particle size and low organic content, avoiding the problem of vessel blockage and supporting continuous production.
Smart Images
Figure CN122302365A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method for solvent and salt recovery from polyphenylene sulfide synthesis waste liquid. Background Technology
[0002] In the sodium sulfide process for producing polyphenylene sulfide (PPS), 8-15 tons of NMP solvent are typically recycled for every 1 ton of PPS produced, while 1-1.5 tons of sodium chloride and 12-15 tons of wastewater are generated. The solid-liquid slurry containing PPS resin prepared after the polymerization reaction is separated and purified to obtain PPS resin and synthesis waste liquid. The solvent recovery system is a key factor for the continuous and stable production of PPS; reducing solvent loss and the energy consumption of the solvent recovery system can significantly reduce the production cost of PPS.
[0003] Therefore, there is a need to develop solvent and byproduct recovery processes for polyphenylene sulfide (PPS) production plants that require low investment, have low operating costs, high efficiency, good stability, and are easy to scale up. The main components of the synthesis wastewater are sodium chloride, solvent (N-methylpyrrolidone, NMP), and water, in addition to small amounts of oligomers and catalysts / auxiliaries. To improve the economics of PPS resin production, the synthesis wastewater needs to be utilized resourcefully, separating the NMP solvent for recycling and separating the sodium chloride byproduct to reduce the salinity of the wastewater.
[0004] Current technologies for recovering NMP from synthetic waste typically employ either distillation or extraction. Distillation results in viscous sodium chloride crystals that carry a significant amount of NMP; while extraction, with chloroform as a suitable extractant, is classified as a Group 2 precursor chemical, making industrial-scale production difficult to approve. Therefore, neither distillation nor extraction methods for separating byproduct salts and recovering solvents from synthetic waste offer efficient and non-toxic NMP recovery. Summary of the Invention
[0005] To overcome the shortcomings of existing technologies, such as the difficulty in efficiently recovering NMP from synthetic waste liquid, the high organic content of the recovered solid salt, or the use of toxic substances in the recovery process, a method for solvent and salt recovery from polyphenylene sulfide (PPS) synthesis waste liquid is provided. This invention can recover high-purity NMP and solid salt with larger particle size and lower organic content. Furthermore, it avoids the formation of sticky crystalline particles during the recovery process and prevents the nucleation of by-product salts during dehydration, thus avoiding the formation of a large number of small-diameter solid salt particles, preventing reactor blockage, and facilitating continuous production.
[0006] In this invention, the method for separating polyphenylene sulfide (PPS) by-product salts and recovering the solvent is located in the solvent recovery stage after the polymerization reaction. The PPS product has already been extracted from the reaction solution using existing methods. The purpose of this invention is to reduce the sodium chloride content in the recovered solvent and improve the purity and yield of the recovered solvent.
[0007] This invention provides a method for solvent and salt recovery from polyphenylene sulfide synthesis waste liquid, comprising the following steps:
[0008] S1. Adjust the pH of the synthetic waste liquid to neutral and control the concentration of NMP in the synthetic waste liquid to 10wt% to 60wt%, where wt% is the mass percentage of NMP in the synthetic waste liquid; then remove the oligomers to obtain the first solution; wherein, the synthetic waste liquid is a by-product waste liquid from the production of polyphenylene sulfide resin;
[0009] S2. The mixed solution formed by mixing the first solution and the seed solution is distilled to obtain a solid-liquid mixture; the volume ratio of the seed solution to the first solution is 1:(1-30); the seed solution includes a salt solution, and the solid content in the seed solution is 10wt% to 60wt%.
[0010] S3. Separate the solid-liquid mixture to obtain NMP and solid salt respectively.
[0011] In step S1 of the present invention, by adjusting the pH and NMP content of the synthetic waste liquid, the oligomers can be separated from the mixture in advance, thus avoiding the formation of sticky crystalline particles during the crystallization process.
[0012] In step S2 of the present invention, the concentration of solid salt in the distillation equipment is controlled by adjusting the volume ratio of the seed solution to the first solution and the solid content in the seed solution, thereby avoiding the problem of solid salt nucleation caused by the excessively fast dehydration rate of the solution due to the distillation process, which could lead to blockage of the vessel.
[0013] In some embodiments, in step S1, the raw materials for producing polyphenylene sulfide resin include sodium sulfide polyhydrate, p-dichlorobenzene, and NMP.
[0014] In some embodiments, in step S1, the synthetic waste liquid comprises water, NMP, solid salt, and oligomers.
[0015] The oligomers referred to here are polymers with relatively small molecular weights that are produced as a byproduct during the synthesis of polyphenylene sulfide.
[0016] In a specific embodiment, the solid salt includes a salt that is insoluble in NMP but soluble in water, such as sodium chloride.
[0017] In a specific embodiment, the synthetic waste liquid contains 10wt% to 80wt% water, 10wt% to 90wt% NMP, 0.1wt% to 15wt% sodium chloride, and 0.1wt% to 10wt% oligomers, where wt% is the mass percentage of each component in the synthetic waste liquid.
[0018] In some embodiments, in step S1, the concentration of NMP in the synthetic waste liquid is controlled to be 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt%, or 60 wt%.
[0019] In some embodiments, in step S1, the method for removing oligomers includes centrifugation; preferably, the equipment for centrifugation includes a horizontal centrifuge.
[0020] In some embodiments, in step S1, the reagent used to control the concentration of the NMP includes water.
[0021] In this invention, "adjusting the pH of the synthetic waste liquid to neutral" means adjusting the pH of the synthetic waste liquid to 7±0.5.
[0022] In some embodiments, in step S1, the reagent used to adjust the pH of the synthetic waste liquid includes hydrochloric acid.
[0023] In step S2 of the present invention, water in the mixed solution can be quickly removed by distillation; the resulting solid-liquid mixture is a dehydrated NMP-salt solid-liquid mixture.
[0024] In step S2 of the present invention, the seed solution can be prepared using commercially available materials or using the solid salt separated in step S3 of this scheme.
[0025] In some embodiments, in step S2, the distillation apparatus includes a crystallization evaporator.
[0026] In this invention, by introducing a seed solution during the distillation process, crystallization can be kept within the crystal growth range, preventing nucleation explosions and the formation of a large number of small-diameter salt particles, thereby avoiding reactor blockage and facilitating continuous production.
[0027] In some embodiments, in step S2, the distillation includes atmospheric distillation or vacuum distillation.
[0028] In a specific embodiment, the temperature of the atmospheric distillation is 101–150°C.
[0029] In a specific embodiment, the temperature of the vacuum distillation is 50–100°C.
[0030] The atmospheric distillation mentioned above refers to distillation carried out at the same pressure as the ambient air pressure.
[0031] In a specific embodiment, the pressure of the vacuum distillation is 0.01 to 0.101 MPa.
[0032] In particular, when vacuum distillation is used, the boiling point of water is lowered by reducing the system pressure, allowing water to evaporate at a low temperature and reducing the cost of heating operations. In specific operations, when the pressure is constant, the solution is heated to a temperature higher than the boiling point of water. When the heating temperature of the crystallization evaporator is constant, the system pressure is reduced so that the boiling point of water is lower than the temperature inside the crystallization evaporator.
[0033] In step S2 of the present invention, since the mixed solution being distilled contains seed crystals, as water evaporates during the distillation process, the salt dissolved in the solution will precipitate from the solution and grow on the surface of the seed crystals, causing the seed crystals in the solution to grow into large solid salt particles. However, when there are no seed crystals or the seed crystal content is low, as water evaporates during the distillation process, the salt dissolved in the solution will nucleate and form a large number of individual small-diameter crystals, causing blockage of the vessel.
[0034] In some embodiments, in step S2, the salt in the seed solution is derived from the solid salt in step S3 or from commercially available salt; the solvent in the salt solution is derived from the water obtained by distillation in step S2 or from deionized water supplied by the factory.
[0035] The process of preparing the seed crystal solution can be carried out in a dissolving vessel.
[0036] In some embodiments, in step S2, the salt solution in the seed solution is a sodium chloride solution; preferably, the sodium chloride solution is a saturated sodium chloride solution.
[0037] In some embodiments, in step S2, the seed solution further includes NMP, which is derived from the NMP in step S3.
[0038] Preferably, the method for preparing the seed solution includes: mixing a saturated sodium chloride solution with NMP, wherein the mixing stirring speed is 10 to 1000 rpm.
[0039] In step S2 of the present invention, the solid content in the seed solution refers to the percentage of the dry weight of the salt in the seed solution to the mass of the liquid exiting the seed reactor; wherein, the solid in the seed solution may be small-grained salt seed crystals with a typical particle size of 5±1μm.
[0040] In some embodiments, in step S2, the solid content in the seed solution is 10 wt%, 20 wt%, 40 wt%, or 60 wt%.
[0041] In some embodiments, in step S2, the volume ratio of the seed solution to the first solution is 1:1, 1:10, 1:20, or 1:30.
[0042] In some implementations, step S3 includes centrifugal separation.
[0043] In some embodiments, step S3 further includes post-treatment of the solid salt after the separation step; the post-treatment includes drying under a nitrogen atmosphere; the drying temperature is 50-150°C.
[0044] One method is to use nitrogen drying to remove residual solvents on the surface of solid salt particles during solid-liquid separation (sedimentation filtration).
[0045] In some embodiments, in step S3, the purity of NMP is 99% or higher, where % represents the mass content of NMP in the product liquid.
[0046] In some embodiments, in step S3, the solid salt includes sodium chloride.
[0047] In some embodiments, in step S3, the particle size of the solid salt is 150 μm to 450 μm.
[0048] In some embodiments, in step S3, the organic content in the solid salt is less than 200 ppm, where ppm is the mass content of organic matter in the solid salt.
[0049] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.
[0050] The reagents and raw materials used in this invention are all commercially available.
[0051] The positive and progressive effects of this invention are as follows:
[0052] 1. This invention can recover high-purity NMP, specifically, the purity of NMP can reach over 99%;
[0053] 2. The present invention can produce solid salt with larger particle size and lower organic content. The solid salt particles have less residual organic matter and organic solvent on their surface, so that the solid salt crystals obtained in this application do not have the problem of crystal viscosity.
[0054] 3. No sticky crystalline particles will be formed during the recycling process, and the nucleation of by-product salts during dehydration can be avoided, thus preventing the formation of a large number of small-diameter solid salt particles, thereby avoiding the blockage of the reactor and facilitating continuous production. Attached Figure Description
[0055] Figure 1 This is a process flow diagram of the method in Embodiment 1 of this application. Detailed Implementation
[0056] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.
[0057] The content ranges of components in the synthetic waste liquids of Examples 1-4 and Comparative Examples 1-5 of this application are shown in Table 1:
[0058] Table 1 shows the component content in the synthetic waste liquid of each embodiment and comparative example.
[0059]
[0060] Example 1
[0061] This embodiment discloses a method for solvent and salt recovery from polyphenylene sulfide synthesis waste liquid. Figure 1 This is a process flow diagram of the method in this embodiment; the method includes the following steps:
[0062] a. Add hydrochloric acid aqueous solution to the synthetic waste liquid containing 45wt% NMP to adjust the pH value to neutral. During this process, the NMP content in the synthetic waste liquid is diluted to 40wt%, where wt% is the mass percentage of NMP in the synthetic waste liquid.
[0063] b. The above liquid is centrifuged using a horizontal centrifuge to separate the oligomers;
[0064] c. The mixture of the centrifuged residue and the seed solution is fed into a crystallization evaporator. The seed solution is a sodium chloride solution with a solid content of 20 wt% and containing NMP with a small particle size (5 ± 1 μm). Under the conditions of an absolute pressure of 0.01 MPa and a temperature of 60 °C, the above mixture is subjected to vacuum distillation to remove water. The water is condensed and recovered at the top of the crystallization evaporator. The NMP-salt solid-liquid mixture is collected from the bottom of the crystallization evaporator.
[0065] d. The above NMP-salt solid-liquid mixture is centrifuged using a horizontal centrifuge to remove the solid salt from the solution, and the remaining liquid is the solvent NMP;
[0066] e. A portion of the centrifuged solid salt is mixed with the water removed in step c in a dissolving vessel to prepare a saturated salt solution, and the remaining portion is dried with hot nitrogen to become a solid salt by-product.
[0067] f. Input the saturated salt solution from step e and a portion of the NMP solution obtained from step d into the seed crystal reactor to prepare a small-particle-size salt seed crystal solution with a solid content of 20 wt%.
[0068] g. The small-particle-size salt seed solution from step f is used as the seed solution for step c. It is then fed into the circulating evaporation crystallizer at a volume ratio of 1:10 with the residual liquid after centrifugation in step b for the growth of salt crystals during the dehydration process.
[0069] This method will not cause vessel blockage and can recover NMP with a purity of 99.5%, which meets the requirements; the particle size of the solid salt by-product is 351±95μm, the particle size is uniform, and its organic matter content is less than 50ppm.
[0070] Example 2
[0071] This embodiment discloses a method for solvent and salt recovery from polyphenylene sulfide synthesis waste liquid, which includes the following steps:
[0072] a. Add hydrochloric acid aqueous solution to the synthetic waste liquid containing 65wt% NMP to adjust the pH value to neutral. During this process, the NMP content in the synthetic liquid is diluted to 60wt%, where wt% is the mass percentage of the NMP in the synthetic waste liquid.
[0073] b. The above liquid is centrifuged using a horizontal centrifuge to separate the oligomers;
[0074] c. The mixture of the centrifuged residue and the seed solution is sent to a crystallization evaporator. The seed solution is a sodium chloride solution with a solid content of 40 wt% and a small particle size of (5 ± 1 μm). Under the conditions of atmospheric pressure and temperature of 120 °C, the above mixture is subjected to atmospheric pressure distillation to remove water. The water is condensed and recovered at the top of the crystallization evaporator. The bottom of the crystallization evaporator is a NMP-salt solid-liquid mixture.
[0075] d. The above NMP-salt solid-liquid mixture is centrifuged using a horizontal centrifuge to remove the solid salt from the solution, and the remaining liquid is the solvent NMP;
[0076] e. A portion of the centrifuged solid salt is mixed with the water removed in step c in a dissolving vessel to prepare a saturated salt solution, and the remaining portion is dried with hot nitrogen to become a solid salt by-product.
[0077] f. Input the saturated salt solution from step e into the seed crystal reactor to prepare a small-particle-size salt seed crystal solution with a solid content of 40 wt%.
[0078] g. The small-particle-size salt seed solution from step f is used as the seed solution for step c. It is then fed into the circulating evaporation crystallizer at a volume ratio of 1:20 with the residual liquid after centrifugation in step b for the growth of salt crystals during the dehydration process.
[0079] This method will not cause vessel blockage and can recover NMP with a purity of 99%, which meets the requirements; the particle size of the solid salt by-product is 225±68μm, the particle size is uniform, and the organic matter content is less than 200ppm.
[0080] Example 3
[0081] This embodiment discloses a method for solvent and salt recovery from synthetic waste liquid, which includes the following steps:
[0082] a. Add hydrochloric acid aqueous solution to the synthetic waste liquid containing 15wt% NMP to adjust the pH value to neutral. During this process, the NMP content in the synthetic liquid is diluted to 10wt%, where wt% is the mass percentage of NMP in the synthetic waste liquid.
[0083] b. The above liquid is centrifuged using a horizontal centrifuge to separate the oligomers;
[0084] c. The mixture of the centrifuged residue and the seed solution is fed into a crystallization evaporator. The seed solution is a sodium chloride solution with a solid content of 10 wt% and containing NMP with a small particle size (5 ± 1 μm). Under the conditions of an absolute pressure of 0.05 MPa and a temperature of 90 °C, the above mixture is subjected to vacuum distillation to remove water. The water is condensed and recovered at the top of the crystallization evaporator. The NMP-salt solid-liquid mixture is collected from the bottom of the crystallization evaporator.
[0085] d. The above NMP-salt solid-liquid mixture is centrifuged using a horizontal centrifuge to remove the solid salt from the solution, and the remaining liquid is the solvent NMP;
[0086] e. A portion of the centrifuged solid salt is mixed with the water removed in step c in a dissolving vessel to prepare a saturated salt solution, and the remaining portion is dried with hot nitrogen to become a solid salt by-product.
[0087] f. Input the saturated salt solution from step e and a portion of the NMP solution obtained from step d into the seed crystal reactor to prepare a small-particle-size salt seed solution with a content of 10 wt%.
[0088] g. The small-particle-size salt seed solution from step f is used as the seed solution for step c. It is fed into the circulating evaporation crystallizer at a volume ratio of 1:1 with the residual liquid after centrifugation in step b for the growth of salt crystals during the dehydration process.
[0089] This method will not cause vessel blockage and can recover NMP with a purity of 99%, which meets the requirements; the particle size of the solid salt by-product is 337±91μm, the particle size is uniform, and the organic matter content is less than 100ppm.
[0090] Example 4
[0091] This embodiment discloses a method for solvent and salt recovery from synthetic waste liquid, which includes the following steps:
[0092] a. Add hydrochloric acid aqueous solution to the synthetic waste liquid containing 22wt% NMP to adjust the pH value to neutral. During this process, the NMP content in the synthetic liquid is diluted to 20wt%, where wt% is the mass percentage of NMP in the synthetic waste liquid.
[0093] b. The above liquid is centrifuged using a horizontal centrifuge to separate the oligomers;
[0094] c. The mixture of the centrifuged residue and the seed solution is fed into a crystallization evaporator. The seed solution is a sodium chloride solution with a solid content of 60 wt% and containing NMP with a small particle size (5 ± 1 μm). Under the conditions of an absolute pressure of 0.06 MPa and a temperature of 95 °C, the above mixture is subjected to vacuum distillation to remove water. The water is condensed and recovered at the top of the crystallization evaporator. The NMP-salt solid-liquid mixture is collected from the bottom of the crystallization evaporator.
[0095] d. The above NMP-salt solid-liquid mixture is centrifuged using a horizontal centrifuge to remove the solid salt from the solution, and the remaining liquid is the solvent NMP;
[0096] e. A portion of the centrifuged solid salt is mixed with the water removed in step c in a dissolving vessel to prepare a saturated salt solution, and the remaining portion is dried with hot nitrogen to become a solid salt by-product.
[0097] f. Input the saturated salt solution from step e and a portion of the NMP solution obtained from step d into the seed crystal reactor to prepare a small-particle-size salt seed solution with a content of 60 wt%.
[0098] g. The small-particle-size salt seed solution from step f is used as the seed solution for step c. It is fed into the circulating evaporation crystallizer at a volume ratio of 1:30 with the residual liquid after centrifugation in step b for the growth of salt crystals during the dehydration process.
[0099] This method will not cause vessel blockage and can recover NMP with a purity of 99%, which meets the requirements; the particle size of the solid salt by-product is 272±82μm, the particle size is uniform, and the organic matter content is less than 150ppm.
[0100] Comparative Example 1
[0101] This comparative example discloses a method for solvent and salt recovery from synthetic waste liquid, which includes the following steps:
[0102] a. Do not add acid to adjust the pH of the synthesis waste liquid to maintain its alkalinity. Instead, add water directly to adjust the NMP content in the synthesis liquid to 20%.
[0103] b. The above liquid was centrifuged using a horizontal centrifuge, and no oligomer precipitate was found.
[0104] c. The residual liquid after centrifugation is sent to a crystallization evaporator. Under the conditions of atmospheric pressure and temperature of 120℃, the residual liquid after centrifugation is subjected to atmospheric pressure distillation to remove water. The water is recovered by condensation, and the NMP-salt solid-liquid mixture is collected from the bottom of the tower.
[0105] d. In this embodiment, the salt solid in the evaporator is viscous and has difficulty flowing in the pipeline, causing blockage of the crystallization evaporator and making subsequent separation impossible.
[0106] Solid salt was extracted from the evaporation vessel, and the organic matter adsorbed on the surface of the solid salt was removed. The particle size was measured to be 25±21μm.
[0107] Comparative Example 2
[0108] This comparative example discloses a method for solvent and salt recovery from synthetic waste liquid, which includes the following steps:
[0109] a. Add hydrochloric acid aqueous solution to the synthetic waste liquid containing 32wt% NMP to adjust the pH value to neutral. During this process, the NMP content in the synthetic liquid is diluted to 30wt%, where wt% is the mass percentage of the NMP in the synthetic waste liquid.
[0110] b. The above liquid is centrifuged using a horizontal centrifuge to separate the oligomers;
[0111] c. The mixture of the centrifuged residue and the seed solution is fed into a crystallization evaporator. The seed solution is a sodium chloride solution with a solid content of 1 wt% and containing NMP with a small particle size (5 ± 1 μm). Under the conditions of an absolute pressure of 0.04 MPa and a temperature of 85 °C, the above mixture is subjected to vacuum distillation to remove water. The water is condensed and recovered at the top of the crystallization evaporator. The bottom of the crystallization evaporator yields an NMP-salt solid-liquid mixture.
[0112] d. The above NMP-salt solid-liquid mixture solution is centrifuged using a horizontal centrifuge to remove the solid salt from the solution, and the remaining liquid is the solvent NMP;
[0113] e. Prepare a saturated salt solution in a dissolving vessel by mixing a portion of the centrifuged solid salt with the water removed in step c, and dry the remaining portion with hot nitrogen to obtain a solid salt by-product.
[0114] f. Input the saturated salt solution from step e and the NMP solution obtained from step d into the seed crystal reactor to prepare a small-particle-size salt seed crystal solution with a solid content of 1 wt%.
[0115] g. The small-particle-size salt seed solution from step f is used as the seed solution for step c. It is then fed into the circulating evaporation crystallizer at a volume ratio of 1:10 with the residual liquid after centrifugation in step b for the growth of salt crystals during the dehydration process.
[0116] In this situation, solid salt particles nucleate and explode within the crystallization evaporator, causing blockage. The solid salt in the evaporator is extracted, and the organic matter adsorbed on its surface is removed. The particle size is measured to be 43±38 μm.
[0117] Comparative Example 3
[0118] This comparative example discloses a method for solvent and salt recovery from synthetic waste liquid, which includes the following steps:
[0119] a. Add hydrochloric acid aqueous solution to the synthetic waste liquid containing 75wt% NMP to adjust the pH value to neutral. During this process, the NMP content in the synthetic liquid is diluted to 65wt%, where wt% is the mass percentage of NMP in the synthetic waste liquid. The NMP content is not further adjusted.
[0120] b. The above liquid is centrifuged using a horizontal centrifuge to separate the oligomers;
[0121] c. The mixture of the centrifuged residue and the seed solution is fed into a crystallization evaporator. The seed solution is a sodium chloride solution with a solid content of 20 wt% and containing NMP with a small particle size (5 ± 1 μm). Under the conditions of an absolute pressure of 0.03 MPa and a temperature of 75 °C, the above mixture is subjected to vacuum distillation to remove water. The water is condensed and recovered at the top of the crystallization evaporator. The NMP-salt solid-liquid mixture is collected from the bottom of the crystallization evaporator.
[0122] d. The above NMP-salt solid-liquid mixture solution is centrifuged using a horizontal centrifuge to remove the solid salt from the solution, and the remaining liquid is the solvent NMP;
[0123] e. A portion of the centrifuged solid salt is mixed with the water removed in step c in a dissolving vessel to prepare a saturated salt solution, and the remaining portion is dried with hot nitrogen to become a solid salt by-product.
[0124] f. Input the saturated salt solution from step e and the portion of NMP solution obtained from step d into the seed crystal reactor to prepare a small-particle-size salt seed solution with a content of 20 wt%.
[0125] g. The small-particle-size salt seed solution from step f is used as the seed solution for step c. It is then fed into the circulating evaporation crystallizer at a volume ratio of 1:0.1 with the residual liquid after centrifugation in step b for the growth of salt crystals during the dehydration process.
[0126] In this situation, solid salt particles nucleate and explode within the crystallization evaporator, causing blockage. The solid salt in the evaporator is extracted, and the organic matter adsorbed on its surface is removed. The particle size is measured to be 66±60 μm.
[0127] Comparative Example 4
[0128] This comparative example discloses a method for solvent and salt recovery from synthetic waste liquid, which includes the following steps:
[0129] a. Add hydrochloric acid aqueous solution to the synthetic waste liquid containing 55wt% NMP to adjust the pH value to neutral. During this process, the NMP content in the synthetic waste liquid is diluted to 50wt%, where wt% is the mass percentage of NMP in the synthetic waste liquid.
[0130] b. The above liquid is centrifuged using a horizontal centrifuge to separate the oligomers;
[0131] c. The mixture of the centrifuged residue and the seed solution is fed into a crystallization evaporator. The seed solution is a sodium chloride solution with a solid content of 80 wt% and containing NMP with a small particle size (5 ± 1 μm). Under the conditions of atmospheric pressure and temperature of 140 °C, the above mixture is subjected to atmospheric pressure distillation to remove water. The water is condensed and recovered at the top of the crystallization evaporator. The bottom of the crystallization evaporator yields an NMP-salt solid-liquid mixture.
[0132] d. The above NMP-salt solid-liquid mixture solution is centrifuged using a horizontal centrifuge to remove the solid salt from the solution, and the remaining liquid is the solvent NMP;
[0133] e. Prepare a saturated salt solution in a dissolving vessel by mixing a portion of the centrifuged solid salt with the water removed in step c, and dry the remaining portion with hot nitrogen to obtain a solid salt by-product.
[0134] f. Input the saturated salt solution from step e and a portion of the NMP solution obtained from step d into the seed crystal reactor to prepare a small-particle-size salt seed solution with a content of 80 wt%.
[0135] g. The small-particle-size salt seed solution from step f is used as the seed solution for step c. It is then fed into the circulating evaporation crystallizer at a volume ratio of 1:10 with the residual liquid after centrifugation in step b for the growth of salt crystals during the dehydration process.
[0136] In this situation, the viscous salt solid in the evaporator column is difficult to flow in the pipes, causing blockage of the crystallization evaporator and preventing subsequent separation. The solid salt in the evaporator is extracted, and the organic matter adsorbed on the surface of the solid salt is removed. The particle size is measured to be 36±31 μm.
[0137] Comparative Example 5
[0138] This comparative example discloses a method for solvent and salt recovery from synthetic waste liquid, which includes the following steps:
[0139] a. Add hydrochloric acid aqueous solution to the synthetic waste liquid containing 60wt% NMP to adjust the pH value to neutral. During this process, the NMP content in the synthetic waste liquid is diluted to 55wt%, where wt% is the mass percentage of NMP in the synthetic waste liquid.
[0140] b. The above liquid is centrifuged using a horizontal centrifuge to separate the oligomers;
[0141] c. The residual liquid after centrifugation is sent to a crystallization evaporator. Under the conditions of an absolute pressure of 0.01 MPa and a temperature of 55°C, the residual liquid after centrifugation is subjected to vacuum distillation to remove water. The water is condensed and recovered at the top of the crystallization evaporator. The NMP-salt solid-liquid mixture is collected from the bottom of the crystallization evaporator.
[0142] d. The above NMP-salt solid-liquid mixture solution is centrifuged using a horizontal centrifuge to remove the solid salt from the solution, and the remaining liquid is the solvent NMP;
[0143] If no seed solution is added during the distillation and dehydration process, solid salt particles will explode and nucleate in the crystallization evaporator, causing blockage.
[0144] Example 1
[0145] In this embodiment, the sodium chloride crystal samples of Examples 1-4 and Comparative Examples 1-5 were tested using a laser particle size analyzer (the laser particle size analyzer was a Mastersizer 3000+ Ultra laser particle size analyzer manufactured by Malvern Panaco). The particle size results are shown in Table 2.
[0146] Table 2. Sizes of the product salts recovered by the methods in each embodiment and comparative example.
[0147] Sodium chloride crystal sample name Typical particle size, μm Example 1 351±95 Example 2 225±68 Example 3 337±91 Example 4 272±82 Comparative Example 1 25±21 Comparative Example 2 43±38 Comparative Example 3 66±60 Comparative Example 4 36±31 Comparative Example 5 52±46
[0148] It can be seen that the sodium chloride crystals recovered in Examples 1-4 have a large particle size, all above 200 μm; while the sodium chloride crystals recovered in Comparative Examples 1 and 4 have a smaller particle size and a larger particle size distribution after solvent removal, which can easily cause blockage of the crystallization evaporator.
Claims
1. A method for solvent recovery and salt recovery of polyphenylene sulfide synthesis waste liquid, characterized by, It includes the following steps: S1. Adjust the pH of the synthetic waste liquid to neutral and control the concentration of NMP in the synthetic waste liquid to 10wt%~60wt%, where wt% is the mass percentage of NMP in the synthetic waste liquid; then remove the oligomers to obtain the first solution; The synthetic waste liquid is a by-product waste liquid from the production of polyphenylene sulfide resin; S2. The mixed solution formed by mixing the first solution and the seed solution is distilled to obtain a solid-liquid mixture; The volume ratio of the seed solution to the first solution is 1:(1-30); the seed solution includes a salt solution, and the solid content in the seed solution is 10wt% to 60wt%. S3. Separate the solid-liquid mixture to obtain NMP and solid salt respectively.
2. The solvent recovery and salt recovery method of the polyphenylene sulfide synthesis waste liquid according to claim 1, characterized in that, Step S1 satisfies one or two of the following conditions: ①The raw materials for producing polyphenylene sulfide resin include sodium sulfide polyhydrate, p-dichlorobenzene and NMP; ②The synthetic waste liquid contains water, NMP, solid salt and oligomers.
3. The solvent recovery and salt recovery method of the polyphenylene sulfide synthesis waste liquid according to claim 2, characterized by, Step S1 satisfies one or two of the following conditions: ①The solid salts include salts that are insoluble in NMP but soluble in water, such as sodium chloride; ② In the synthetic waste liquid, the water content is 10wt% to 80wt%, the NMP content is 10wt% to 90wt%, the solid salt content is 0.1wt% to 15wt%, and the oligomer content is 0.1wt% to 10wt%, where wt% is the mass percentage of each component in the synthetic waste liquid.
4. The solvent recovery and salt recovery method of the polyphenylene sulfide synthesis waste liquid according to claim 1, characterized in that, Step S1 satisfies one or more of the following conditions: ① The concentration of NMP in the synthetic waste liquid is controlled to be 10wt%, 20wt%, 30wt%, 40wt%, 50wt%, or 60wt%; ②The method for removing oligomers includes centrifugal separation; preferably, the equipment for centrifugal separation includes a horizontal centrifuge; ③ The reagent used to control the concentration of NMP in the synthetic waste liquid includes water; ④ The reagents used to adjust the pH of the synthetic waste liquid include hydrochloric acid.
5. The solvent recovery and salt recovery method of the polyphenylene sulfide synthesis waste liquid according to claim 1, wherein Step S2 satisfies one or more of the following conditions: ①The distillation equipment includes a crystallization evaporator; ②The distillation includes atmospheric distillation or vacuum distillation; Preferably, the temperature of the atmospheric distillation is 101–150°C; Preferably, the temperature of the vacuum distillation is 50–100°C; Preferably, the pressure of the vacuum distillation is 0.01 to 0.101 MPa.
6. The solvent recovery and salt recovery method of the polyphenylene sulfide synthesis waste liquid according to claim 1, wherein Step S2 satisfies one or more of the following conditions: ① In the seed solution, the salt in the salt solution comes from the solid salt in step S3 or commercially available salt; the solvent in the salt solution comes from the water obtained by distillation in step S2 or deionized water provided by the factory. ② In the seed solution, the salt solution is a sodium chloride solution; preferably, the sodium chloride solution is a saturated sodium chloride solution; ③The seed solution further includes NMP, which is derived from the NMP in step S3.
7. The solvent recovery and salt recovery method of the polyphenylene sulfide synthesis waste liquid according to claim 1, wherein Step S2 satisfies one or more of the following conditions: ①The solid content in the seed solution is 10wt%, 20wt%, 40wt%, or 60wt%; ②The volume ratio of the seed solution to the first solution is 1:1, 1:10, 1:20 or 1:
30.
8. The solvent recovery and salt recovery method of the polyphenylene sulfide synthesis waste liquid according to claim 1, wherein, Step S3 satisfies one or two of the following conditions: ①The separation method includes centrifugal separation; ②After the separation step, the solid salt is further subjected to post-treatment; the post-treatment includes drying under a nitrogen atmosphere; the drying temperature is 50-150°C.
9. The solvent recovery and salt recovery method of the polyphenylene sulfide synthesis waste liquid according to claim 1, wherein, In step S3, the purity of NMP is 99% or higher.
10. The solvent recovery and salt recovery method of the polyphenylene sulfide synthesis waste liquid according to claim 1, wherein Step S3 satisfies one or more of the following conditions: ①The solid salt includes sodium chloride; ②The particle size of the solid salt is 150μm~450μm; ③ The organic matter content in the solid salt is less than 200 ppm, where ppm is the mass content of organic matter in the solid salt.