Vinylene carbonate production process and device
Through continuous production process and solid-liquid separation technology, the problems of low efficiency, high energy consumption and low yield in synthesis of vinyl carbonate are solved, and efficient and safe production of vinyl carbonate is achieved, and product purity and yield are improved.
Patent Information
- Application Number
- CN202510626934.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-15
- Publication Date
- 2025-08-15
AI Technical Summary
The existing vinyl carbonate synthesis process has problems such as low production efficiency, high energy consumption, high three wastes and low yields. Especially due to the increased safety hazards and side reactions caused by uneven exothermic reactions, polymer production affects purity and yield.
The continuous production process is adopted, through the continuous input and timely separation of solvents and tertiary amines, combined with solid-liquid separation devices and high-efficiency polymerization inhibitors, the control of reaction heat and the timely separation of materials are achieved, side reactions are reduced, and yields are improved.
It improves the production efficiency and yield of vinylene carbonate, reduces the production of three wastes, reduces energy consumption, and ensures production safety and product purity.
Smart Images
Figure CN120483953A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of lithium ion battery additives, and in particular relates to a continuous production process and device for vinylene carbonate. Background Art
[0002] Vinylene carbonate, with its high dielectric constant and low viscosity, is currently the most commonly used electrolyte additive. It can significantly improve the electrochemical performance of electrolytes, increasing coulombic efficiency and charge capacity retention. With the rapid development of new energy vehicles and energy storage in recent years, the importance of vinylene carbonate has become increasingly prominent.
[0003] Currently, the main principles of the industrial production methods of vinylene carbonate are similar. They all use vinylene carbonate as a raw material, react with chlorine under ultraviolet light to synthesize vinyl chloride carbonate; then, in an organic solvent, the vinyl chloride carbonate reacts with a tertiary amine to remove hydrogen chloride to produce crude vinylene carbonate; the obtained crude vinylene carbonate is then purified by distillation and crystallization to finally produce vinylene carbonate with higher purity.
[0004] Research has found that the reaction of tertiary amines with chloroethylene carbonate is a typical dehydrohalogenation reaction, but during the reaction process, the tertiary amine will cause the generated vinylene carbonate to further generate polymers, resulting in the loss of vinylene carbonate and a reduction in yield. In the prior art, the synthesis process of vinylene carbonate is mainly a kettle-type dropwise addition reaction, which is an intermittent operation. That is, a quantitative tertiary amine is added dropwise to a substrate previously composed of chloroethylene carbonate, a solvent, and a polymerization inhibitor, and the reaction is filtered after a period of time. The filtrate is subjected to precipitation and purification to obtain vinylene carbonate. Since the dechlorination reaction is a highly exothermic reaction, a violent and highly exothermic reaction will occur after the tertiary amine is added dropwise and accumulated to a certain amount, resulting in a "flyaway" phenomenon, which is prone to solvent boiling out of control and poses a great safety hazard. Therefore, it is difficult to increase the volume of the reactor. In addition, during the intermittent reaction process, the tertiary amine added dropwise in the early stage cannot be consumed in time, resulting in a large excess of tertiary amine in the reaction system relative to the product vinylene carbonate, which leads to instability of the vinylene carbonate, an increased probability of side reactions, and an increase in polymers, thereby resulting in a decrease in yield. The polymers produced by side reactions are viscous, tarry, or pitch-like, which further contaminate the reaction system, making filtration and post-processing of the reaction liquid difficult. This results in a reaction yield of only around 60%, low production efficiency, a high concentration of waste products, and high energy consumption. Particularly in the later stages of the crude distillation process, a large amount of asphalt-like polymer, with high viscosity, forms at the bottom of the crude distillation equipment. This not only affects the purity of the vinylene carbonate but also severely impairs the heat transfer efficiency of the distillation equipment's inner walls, making them difficult to clean. This ultimately reduces the overall heat transfer efficiency of the distillation process.
[0005] In addition, the existing industrial production process of vinylene carbonate accumulates a large amount of heat and has low production efficiency. At the same time, due to the long reaction time and the large amount of polymer generated, the yield of vinylene carbonate is low, which makes it difficult to meet the requirements of large-scale industrial production. Summary of the Invention
[0006] One of the problems to be solved by the present invention is that the traditional synthesis process of vinylene carbonate is mainly a kettle-type dropwise reaction, intermittent operation, low production efficiency, a lot of three wastes, high energy consumption and other problems;
[0007] The second problem to be solved by the present invention is that as the reaction proceeds, the generated polymer accumulates and wraps around the tertiary amine hydrochloride generated by the reaction, and adheres to the wall of the reactor. After the reaction is completed, the reactor is difficult to clean, and the cleaning solution will also cause an increase in the three wastes.
[0008] The third problem to be solved by the present invention is that the polymerization of vinylene carbonate itself and the reaction with excess tertiary amine result in a reduced yield of vinylene carbonate and a purity that does not meet the requirements.
[0009] The object of the present invention is to overcome the defects in the prior art and provide a production process and device for vinylene carbonate, which can improve production efficiency, reduce the generation of three wastes, reduce energy consumption and costs, reduce material polymerization, and improve the yield of vinylene carbonate products.
[0010] In order to solve one of the above problems, the technical solution adopted by the present invention is: improving the synthesis process design, eliminating the accumulation of reaction heat, reducing the number of equipment and the number of workers, thereby improving production efficiency, reducing the amount of three wastes generated, reducing energy consumption and costs, and improving the inherent safety of the process.
[0011] In order to solve the second problem mentioned above, the technical solution adopted by the present invention is: in the production process, the solvent and tertiary amine hydrochloride are separated in time. The relative density of tertiary amine hydrochloride is greater than that of the liquid, and it will be precipitated and separated from the reaction system, thereby reducing the occurrence of side reactions and improving the product yield.
[0012] In order to solve the third problem mentioned above, the technical solution adopted by the present invention is to use a solid-liquid separation device to perform solid-liquid separation and washing on the sinking tertiary amine hydrochloride slurry, and bring the vinylene carbonate product entrained in the tertiary amine hydrochloride slurry into an intermediate receiving tank, thereby improving the yield of vinylene carbonate; the tertiary amine hydrochloride filter residue enters the neutralization kettle, and at the same time, a high-efficiency polymerization inhibitor is added to the reaction system to prevent the polymerization of vinylene carbonate itself and the reaction with the tertiary amine, thereby further improving the yield.
[0013] A production process for vinylene carbonate comprises the following steps:
[0014] S1: The solvent is continuously fed through the solvent preheater and into the reactor by controlling the flow rate through the solvent delivery pump and flow meter; when the solvent feed amount reaches a certain mass, warm water is introduced into the jacket of the reactor to preheat and keep the solvent warm;
[0015] When the solvent in the reactor reaches the reaction temperature, the flow rates are controlled by the solvent, ethylene chloride and tertiary amine delivery pumps and flow meters respectively, and the solvent, ethylene chloride and tertiary amine are continuously passed through the preheater and pipeline mixer at a certain flow rate and fed into the reactor from the feed port at the top of the reactor for dechlorination reaction. The reaction heat is removed by cooling water introduced into the jacket of the reactor and evaporation of the solvent in the reactor. The solvent in the reactor absorbs the reaction heat and evaporates, and is distilled out from the gas phase port at the top of the reactor. After being cooled by a circulating water and chilled water two-stage heat exchanger, it is received in a solvent receiving tank and recycled.
[0016] S2: The slurry in the reactor is continuously fed into the solid-liquid separation device through the slurry delivery pump from the discharge valve at the bottom of the reactor. The by-product tertiary amine hydrochloride generated by the reaction is separated from the reaction liquid in the solid-liquid separation device. The reaction liquid is discharged from the clear liquid outlet, and the slurry residue is discharged from the slurry residue outlet and enters the salt washing kettle or directly enters the neutralization kettle; a solvent is introduced into the salt washing kettle for stirring, and the slurry residue is beaten, dispersed, and washed, and then enters the next-stage solid-liquid separation device to separate the tertiary amine hydrochloride and the washing liquid, and is combined with the reaction liquid clear liquid separated by the previous-stage solid-liquid separation device, and fed into the intermediate receiving tank through a circulation pump, or returned to the reactor from the clear liquid inlet at the top or middle of the reactor to realize cyclic synthesis. After the reaction is complete, it is cut into the intermediate receiving tank for reception, and the slurry residue is discharged into the neutralization kettle;
[0017] S3: The reaction liquid and washing liquid after continuous or cyclic synthesis and complete reaction enter the intermediate receiving tank, and then undergo continuous distillation. The solvent is first separated and recovered through a desolventizing tower, a low-boiling tower, and a high-boiling tower, and then returned to S1 or S2 for synthesis or washing, and high-boiling substances are removed to obtain crude vinylene carbonate;
[0018] S4: The crude vinylene carbonate is purified by distillation in a primary distillation tower and a secondary distillation tower to obtain refined vinylene carbonate;
[0019] S5: The vinylene carbonate product is melt-crystallized and purified in a primary melt crystallizer and a secondary melt crystallizer, and finally a vinylene carbonate product with a purity of more than 99.99% is obtained and enters the vinylene carbonate product receiving tank;
[0020] S6: The tertiary amine hydrochloride slurry discharged from S2 enters the neutralization kettle, is neutralized by adding liquid alkali, and then transferred to the separator tank for stratification. The upper organic phase enters the dehydration tower of the recovery system for dehydration, and then enters the solvent recovery tower for distillation to recover the solvent, and the tertiary amine recovery tower for distillation to recover the tertiary amine. The recovered solvent can be returned to S1 or S2 for reuse, and the recovered tertiary amine can be reused in S1;
[0021] S7: The brine separated from the lower layer of the S6 separator tank passes through a single-effect or multi-effect evaporation system, and the evaporated wastewater enters the sewage treatment system for biochemical treatment; the salt slurry discharged by evaporation is transferred to the rotary kiln of the waste liquid incinerator for high-temperature calcination to remove organic matter, and the obtained sodium chloride is sold as a by-product or treated as general solid waste.
[0022] As a further technical solution, the tertiary amine is selected from N,N-dimethylethylamine, N,N-dimethyl-n-propylamine, N,N-dimethylisopropylamine, N,N-dimethylbutylamine, N,N-dimethylhexylamine, N,N-dimethylcyclohexylamine, N,N-dimethylaniline, diethylmethylamine, di-n-propylmethylamine, diisopropylmethylamine, triethylamine, triisopropylamine, tributylamine, pyridine, N-methylpyrrole, N-methylpyrrolidine, N-methylmorpholine, One or more combinations of N-methylpiperidine, imidazole, N-methylimidazole, N,N,N',N'-tetramethylethylenediamine, N,N,N',N'-tetramethylbutanediamine, N,N,N',N'-tetramethylhexanediamine, N,N'-dimethylpiperazine, pentamethyldiethylenetriamine, triethylenediamine, 1,5-diazabis[4.3.0]non-5-ene, and 1,8-diazabicyclo[5.4.0]undec-7-ene.
[0023] As a further technical solution, the solvent is a hydrocarbon, ether, ester, or nitrile compound, more typically selected from one or more mixtures of n-hexane, cyclohexane, n-heptane, petroleum ether, dichloromethane, dichloroethane, methyl propyl ether, ethyl propyl ether, methyl tert-butyl ether, n-propyl ether, isopropyl ether, ethyl formate, n-propyl formate, isopropyl formate, n-butyl formate, isobutyl formate, tert-butyl formate, methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, methyl propionate, ethyl propionate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and acetonitrile; the density of the solvent or mixed solvent at 25°C is less than 1.0.
[0024] As a further technical solution, the solvent contains 0.01 to 0.5% of a polymerization inhibitor, which is a combination of one or more of phenols, quinones, phenothiazines, phosphites, piperidinols, and piperidine nitrogen oxides. Typical polymerization inhibitors are one or more of hydroquinone, p-methoxyphenol, p-tert-butylcatechol, 2,6-di-tert-butyl-p-cresol, 2,5-di-tert-butylhydroquinone, phenothiazine, 2,2,6,6-tetramethyl-4-hydroxy-piperidine nitrogen oxide, tris(2,2,6,6-tetramethyl-4-oxy-piperidine nitrogen oxide) phosphite, and bis(2,2,6,6-tetramethyl-4-oxy-piperidine nitrogen oxide) sebacate.
[0025] As a further technical solution, the mass ratio of the solvent, ethylene chloride and tertiary amine is 2.0-10.0:1.0:0.8-1.5; the reaction temperature is controlled at 50-100°C; the residence time of ethylene chloride and tertiary amine in the reactor is 1-12 hours to carry out the dechlorination reaction.
[0026] As a further technical solution, a temperature measuring device is provided on the pipes connecting the rear end of the preheater for the solvent, ethylene chloride, and tertiary amine and the front end of the pipeline mixer; temperature measuring devices are provided at the upper, middle, and lower parts of the reactor; and the temperature measuring device is interlocked with the flow meter in the DCS control room and controlled.
[0027] A vinylene carbonate production device comprises: a solvent delivery pump, a chloroethylene carbonate delivery pump, a tertiary amine delivery pump, a solvent preheater, a chloroethylene carbonate preheater, a tertiary amine preheater, a pipeline mixer, a reactor, a circulating water condenser, a chilled water condenser, a solvent receiving tank, an intermediate receiving tank, a solid-liquid separation device, a salt washing reactor, a desolventizing tower, a low-salt removal tower, a high-salt removal tower, a primary distillation tower, a secondary distillation tower, a primary melting crystallizer, a secondary melting crystallizer, and a vinylene carbonate finished product receiving tank, which are sequentially connected. The solid-liquid separation device is connected to a discharge valve at the bottom of the reactor, and a slag slurry discharge valve at the bottom of the solid-liquid separation device is sequentially connected to a neutralization reactor, a liquid caustic soda tank, a separator, a dehydration tower, a solvent recovery tower, a solvent tank, a tertiary amine recovery tower, and a tertiary amine tank.
[0028] As a further technical solution, a feed port is provided on the top of the reactor, which extends into the interior of the reactor and is connected to a liquid distributor, and the plane of the liquid distributor is installed and fixed parallel to the cross-section of the reactor; the feed port is connected to the pipeline from the pipeline mixer; a gas phase port is provided on the upper part of the reactor, which is connected to the circulating water condenser and the chilled water condenser, and a clear liquid inlet is also provided on the upper and middle parts of the cylinder wall of the reactor; a slurry discharge valve is provided at the bottom of the reactor, and the slurry discharge valve is an automatic switching valve, which is connected to the slurry inlet of the solid-liquid separation device; the clear liquid outlet of the solid-liquid separation device is connected to the circulation pump; the diameter of the central pipe is 100 to 2000 mm; the diameter of the outer cylinder wall of the reactor is 500 to 4000 mm, and the height of the cylinder is 1000 to 10000 mm; a jacket is provided on the outside of the reactor, through which a heat exchange medium passes, and the heat exchange medium includes but is not limited to steam, thermal oil, refrigerant, and circulating water.
[0029] As a further technical solution, the solid-liquid separation device can be selected from various devices with solid-liquid separation functions, such as centrifuge, plate and frame filter press, candle filter, zero-residue filter, bag filter, stacked membrane filter, rotary wheel filter press, disc filter, pressurized drum filter, dynamic cross-flow membrane filter, etc., and one or more units can be connected in parallel, or connected in parallel and then in multiple stages in series, and the two stages of solid-liquid separation devices are connected by a salt washing kettle; each solid-liquid separation device is provided with a slurry inlet, a clear liquid outlet and a slurry residue outlet, the slurry inlet of the first-stage solid-liquid separation device is connected to the reactor discharge valve, the slurry residue outlet is connected to the upper inlet of the salt washing kettle or directly connected to the neutralization kettle, the next-stage solid-liquid separation device is connected to the salt washing kettle outlet, the clear liquid outlet is connected to the circulation pump, and the slurry residue outlet is connected to the neutralization kettle.
[0030] Compared with the prior art, the present invention has the following beneficial effects:
[0031] 1. Process improvement: the conversion rate of ethylene chloride carbonate is ≥98%, and the total yield of vinylene carbonate relative to ethylene chloride carbonate is ≥70%, which greatly improves production efficiency and target product yield, reduces the generation of three wastes, and reduces energy consumption and labor costs.
[0032] 2. The boiling point of the solvent is lower than that of the tertiary amine, the relative density is less than 1.0, and the solubility of the tertiary amine hydrochloride is low, which is conducive to separation.
[0033] 3. Add special high-efficiency polymerization inhibitor to prevent material polymerization and improve product yield.
[0034] 4. The tertiary amine hydrochloride produced by the reaction has a high density and gradually sinks in the reactor. It is discharged into the solid-liquid separation device through the discharge valve at the bottom of the reactor. After solid-liquid separation and washing, the reaction liquid and the clear liquid of the washing liquid enter the intermediate receiving tank, and the solid slurry enters the neutralization kettle, realizing separation while reacting, maintaining homogeneous reaction, reducing side reactions, and improving product purity and yield.
[0035] 5. After separation, the tertiary amine hydrochloride residue directly enters the neutralization kettle to react with liquid alkali to replace the tertiary amine, thereby realizing tertiary amine recovery, with a short process and high efficiency. BRIEF DESCRIPTION OF THE DRAWINGS
[0036] Figure 1 This is a process flow chart for the continuous production of vinylene carbonate according to the present invention;
[0037] Figure 2 It is a structural diagram of a dynamic cross-flow membrane filter;
[0038] Figure 3 This is a schematic diagram of three dynamic cross-flow membrane filters connected in series and parallel.
[0039] Description of reference numerals:
[0040] A1, solvent preheater; A2, ethylene chlorocarbonate preheater; A3, tertiary amine preheater; Z1, solvent delivery pump; Z2, ethylene chlorocarbonate delivery pump; Z3, tertiary amine delivery pump; Z4, slurry delivery pump; Z5, washing solvent delivery pump; Z6, circulation pump; B, pipeline mixer; C, reactor; D1, circulating water condenser; D2, chilled water condenser; D3, condenser; D4, condenser; E, solvent receiving tank; Wm, primary solid-liquid separation device; X, salt washing tank; Wn, secondary solid-liquid separation device; F, intermediate receiving tank; G, desolventizing tower; H, low-pressure desolventizing tower; J, high-pressure desolventizing tower Tower; K1, primary distillation tower; K2, secondary distillation tower; M1, primary melt crystallizer; M2, secondary melt crystallizer; V, vinylene carbonate finished product receiving tank; N, neutralization kettle; N1, liquid caustic soda tank; P, separator tank; Q, dehydration tower; R, solvent recovery tower; R1, solvent tank; T, tertiary amine recovery tower; T1, tertiary amine tank; 10, liquid distributor; 11, feed inlet; 12, clear liquid inlet; 13, discharge valve; 14, gas phase port; 15, clear liquid inlet; 16, jacket; W1 and W4, slurry or slurry residue inlet; W2 and W5, clear liquid outlet; W3 and W6, slurry residue outlet. DETAILED DESCRIPTION
[0041] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. 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 making any creative efforts shall fall within the scope of protection of the present invention.
[0042] A production process for vinylene carbonate comprises the following steps:
[0043] S1: The solvent is continuously fed through the solvent preheater A1 and into the reactor C through the flow rate controlled by the solvent delivery pump Z1 and the flow meter; when the solvent feed amount reaches a certain mass, warm water is introduced into the jacket of the reactor C to preheat and keep the solvent warm;
[0044] When the solvent in the reactor C reaches the reaction temperature, the flow rates are controlled by the solvent, ethylene chloride and tertiary amine delivery pumps Z1, Z2, Z3 and flow meters respectively, and the solvent, ethylene chloride and tertiary amine are continuously passed through the preheaters A1, A2, A3 at a certain flow rate, and then merged into the pipeline mixer B, and input into the reactor C from the feed port 11 at the top of the reactor C for dechlorination reaction. The reaction heat is removed by the cooling water introduced into the jacket of the reactor C and the evaporation of the solvent in the reactor. The solvent in the reactor C absorbs the reaction heat and evaporates, and is distilled out from the gas phase port 14 at the top of the reactor C. After being cooled by the circulating water and chilled water two-stage heat exchangers D1 and D2, it is received by the solvent receiving tank E and recycled.
[0045] S2: The slurry in the reactor C is discharged from the discharge valve 13 at the bottom of the reactor C through the slurry delivery pump Z4, and is continuously input into the solid-liquid separator Wm from the slurry inlet W1 of the solid-liquid separator Wm. The tertiary amine hydrochloride by-product generated by the reaction is separated from the reaction liquid in the solid-liquid separator Wm, and the reaction liquid is discharged from the clear liquid outlet W2, and the slurry residue is discharged from the slurry residue outlet W3 and enters the salt washing kettle X; the solvent is continuously input into the salt washing kettle X to stir and disperse the slurry residue, and then enters the solid-liquid separator Wn from the slurry inlet of the next-level solid-liquid separator Wn to separate the tertiary amine hydrochloride from the washing liquid, and the clear washing liquid is discharged from the clear liquid outlet W5, combined with the reaction liquid clear liquid discharged from W2, and input into the intermediate receiving tank F through the circulation pump Z6; or returned to the reactor C from the clear liquid inlet 12 or 15 on the upper or middle part of the reactor C to realize circulation; the washed slurry residue is discharged from the slurry residue outlet W6 of the solid-liquid separator Wn into the neutralization kettle N;
[0046] S3: The reaction liquid after the continuous synthesis or cyclic synthesis reaction is transferred from the circulating pump Z6 to the intermediate receiving tank F, and then continuously distilled. The solvent is first separated and recovered by the desolventizing tower G, the low-boiling tower H, and the high-boiling tower J, and then returned to S1 or S2 for synthesis or washing, and the high-boiling substances are removed to obtain crude vinylene carbonate.
[0047] S4: The crude vinylene carbonate is distilled and purified in the primary distillation tower K1 and the secondary distillation tower K2 to obtain the refined vinylene carbonate;
[0048] S5: The vinylene carbonate product is melt-crystallized and purified in the primary melt crystallizer M1 and the secondary melt crystallizer M2 to obtain a vinylene carbonate product with a purity of more than 99.99%, which enters the vinylene carbonate product receiving tank V;
[0049] S6: The tertiary amine hydrochloride slurry discharged from S2 enters the neutralization kettle N, is neutralized by adding liquid caustic soda, and then transferred to the separator P for stratification. The upper organic phase enters the dehydration tower Q of the recovery system for dehydration, and then enters the solvent recovery tower R for distillation to recover the solvent, and the tertiary amine recovery tower T for distillation to recover the tertiary amine. The recovered solvent can be returned to S1 and reused in S2, and the recovered tertiary amine can be reused in S1;
[0050] S7: The brine separated from the lower layer of the S6 separator tank P passes through a single-effect or multi-effect evaporation system, and the evaporated wastewater enters the sewage treatment system for biochemical treatment; the salt slurry discharged by evaporation is transferred to the rotary kiln of the waste liquid incinerator for high-temperature calcination to remove organic matter, and the obtained sodium chloride is sold as a by-product or treated as general solid waste.
[0051] The tertiary amine is selected from N,N-dimethylethylamine, N,N-dimethyl-n-propylamine, N,N-dimethylisopropylamine, N,N-dimethylbutylamine, N,N-dimethylhexylamine, N,N-dimethylcyclohexylamine, N,N-dimethylaniline, diethylmethylamine, di-n-propylmethylamine, diisopropylmethylamine, triethylamine, triisopropylamine, tributylamine, pyridine, N-methylpyrrole, N-methylpyrrolidine, N-methylmorpholine, N-methylpiperidine , imidazole, N-methylimidazole, N,N,N',N'-tetramethylethylenediamine, N,N,N',N'-tetramethylbutanediamine, N,N,N',N'-tetramethylhexanediamine, N,N'-dimethylpiperazine, pentamethyldiethylenetriamine, triethylenediamine, 1,5-diazabis[4.3.0]non-5-ene, 1,8-diazabicyclo[5.4.0]undec-7-ene or one or more combinations thereof.
[0052] The solvent is a hydrocarbon, ether, ester, or nitrile compound, more typically selected from one or more mixtures of n-hexane, cyclohexane, n-heptane, petroleum ether, dichloromethane, dichloroethane, methyl propyl ether, ethyl propyl ether, methyl tert-butyl ether, n-propyl ether, isopropyl ether, ethyl formate, n-propyl formate, isopropyl formate, n-butyl formate, isobutyl formate, tert-butyl formate, methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, methyl propionate, ethyl propionate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and acetonitrile; the density of the solvent or mixed solvent at 25° C. is less than 1.0.
[0053] The solvent contains 0.01 to 0.5% of a polymerization inhibitor, which is a combination of one or more of phenols, quinones, phenothiazines, phosphites, piperidinols, and piperidine nitrogen oxides. Typical polymerization inhibitors are a combination of one or more of hydroquinone, p-methoxyphenol, p-tert-butylcatechol, 2,6-di-tert-butyl-p-cresol, 2,5-di-tert-butylhydroquinone, phenothiazine, 2,2,6,6-tetramethyl-4-hydroxy-piperidine nitrogen oxide, tris(2,2,6,6-tetramethyl-4-oxy-piperidine nitrogen oxide) phosphite, and bis(2,2,6,6-tetramethyl-4-oxy-piperidine nitrogen oxide) sebacate.
[0054] The mass ratio of solvent, ethylene chlorocarbonate and tertiary amine is 2.0-10.0:1.0:0.8-1.5; the reaction temperature is controlled at 50-100° C.; the residence time of ethylene chlorocarbonate and tertiary amine in the reaction kettle (C) is 1-12 hours to carry out dechlorination reaction.
[0055] Temperature measuring devices are installed on the pipes connecting the rear ends of the preheaters A1, A2, and A3 for the solvent, ethylene chloride, and tertiary amine, and the front end of the pipeline mixer B; temperature measuring devices are installed at the top, middle, and bottom parts of the reactor; the temperature measuring devices are interlocked and controlled with the flow meter in the DCS control room.
[0056] A vinylene carbonate production device, comprising: a solvent delivery pump Z1, a vinylene carbonate delivery pump Z2, a tertiary amine delivery pump Z3, a solvent preheater A1, a vinylene carbonate preheater A2, a tertiary amine preheater A3, a pipeline mixer B, a reactor C, a circulating water condenser D1, a chilled water condenser D2, a solvent receiving tank E, solid-liquid separation devices Wm and Wn, a salt washing reactor X, an intermediate receiving tank F, a desolventizing tower G, a low-liquid desalting tower H, a high-liquid desalting tower J, a primary distillation tower K1, a secondary distillation tower K2, a primary melt crystallizer M1, a secondary melt crystallizer M2, and a vinylene carbonate finished product receiving tank V, and the devices are connected in a process sequence. The feed inlet W1 of the solid-liquid separation device Wm is connected to the discharge valve 13 at the bottom of the reactor C; the slurry discharge outlet W3 of the solid-liquid separation device Wm is connected to the salt washing kettle X, or directly connected to the neutralization kettle; the slurry outlet of the salt washing kettle is connected to the secondary solid-liquid separation device Wn; the slurry discharge outlet W6 of the solid-liquid separation device Wn is connected to the neutralization kettle N, and then to the separator P, dehydration tower Q, solvent recovery tower R, solvent receiving tank R1, tertiary amine recovery tower T, tertiary amine receiving tank T1, and are connected in the order of the process; the clear liquid outlets W2 and W5 of the solid-liquid separation devices Wm and Wn are connected to the circulation pump Z6; the circulation pump Z6 is connected to the intermediate receiving tank F and the reactor C.
[0057] The top of the reactor C is provided with a feed port 11, the feed port 11 pipe extends into the interior of the reactor C, and is connected to a liquid distributor 10, so that the feed liquid is evenly distributed along the cross section of the reactor C and added to the reactor C; the feed port 11 is connected to the pipeline mixer B; the upper part of the reactor C is provided with a gas phase port 14, which is connected to the circulating water condenser D1 and the chilled water condenser D2; the upper part of the cylinder of the reactor C is also provided with a clear liquid inlet 12, which is connected to the circulating pump W6; the bottom of the reactor C is provided with a discharge valve 13, the discharge valve 13 is an automatic switching valve, which is connected to the slurry inlet W1 of the solid-liquid separation device Wm; the upper and middle parts of the reactor C are provided with filtrate inlets 12 and 15, which are connected to the circulation pump W6; the diameter of the liquid distributor 10 is 100-2000 mm; the diameter of the cylinder of the reactor C is 500-4000 mm, and the height of the cylinder is 1000-10000 mm; the outside of the reactor C is provided with a jacket, through which a heat exchange medium passes, and the heat exchange medium includes but is not limited to steam, thermal oil, refrigerant, and circulating water.
[0058] The solid-liquid separation devices Wm and Wn include but are not limited to centrifuges, plate and frame filter presses, candle filters, zero-residue filters, bag filters, laminated membrane filters, rotary filter presses, disc filters, pressurized drum filters, dynamic cross-flow membrane filters and other devices with solid-liquid separation functions. The solid-liquid separation devices Wm and Wn are connected in series, and Wm and Wn are one or more connected in parallel. Wm and Wn are provided with slurry or slurry residue inlets W1 and W4, clear liquid outlets W2 and W5, and slurry residue outlets W3 and W6. The slurry inlet W1 is connected to the discharge valve 13, W3 is connected to the upper inlet of the salt washing kettle X or directly connected to the neutralization kettle N, W4 is connected to the outlet of the salt washing kettle X, W2 and W5 are connected to the circulation pump, and W6 is connected to the neutralization kettle N.
[0059] Example
[0060] This embodiment is used to illustrate a continuous production process flow chart of vinylene carbonate according to the present invention. Figure 1 shown.
[0061] This embodiment is used to illustrate a vinylene carbonate production device according to the present invention. Figure 1 The dimensions of the production device of this embodiment are as follows: the diameter of the reactor C is 1600 mm, the head is elliptical, the height of the cylinder is 2400 mm, the diameter of the liquid distributor 10 inside the reactor C is 800 mm, and the liquid distributor 10 is located 200 mm above the upper cross section of the cylinder of the reactor C.
[0062] This embodiment is used to illustrate that in a vinylene carbonate production device according to the present invention, a dynamic cross-flow membrane filter is selected as a solid-liquid separation device. The schematic diagram is as follows: Figure 2 As shown; three dynamic cross-flow membrane filters with a filtration area of 15 m2 are connected in series and parallel. The first-level solid-liquid separation device uses two dynamic cross-flow membrane filters Wm-1 and Wm-2 in parallel, and then connected in series with a second-level solid-liquid separation device dynamic cross-flow membrane filter Wn. The series-parallel diagram is shown as follows Figure 3 shown.
[0063] This embodiment is used to illustrate a vinylene carbonate production device according to the present invention. The salt washing kettle X is a 500L reactor with stirring and a jacket. The jacket is filled with 70°C warm water to keep the washing liquid warm.
[0064] The process flow for the continuous production of vinylene carbonate according to the present invention is described as follows:
[0065] S1: A mixed organic solvent of isopropyl ether and methyl acetate in a volume ratio of 2:1, in which 0.3% 2,5-di-tert-butylhydroquinone and 0.1% p-methoxyphenol as a polymerization inhibitor are dissolved, is heated to 60°C in preheater A1 via delivery pump Z1 and then fed into reactor C. A cumulative input of 2700 kg is then stopped before feeding Z1.
[0066] Pass 70°C warm water into the jacket of reactor C and maintain the temperature of the organic solvent in reactor C at 60-65°C;
[0067] Open the discharge valve 13, start the dynamic cross-flow membrane filters Wm-1, Wm-2, and Wn, and start the stirring and circulation pump Z6 of the salt washing kettle X pre-added with 100L of washing solvent isopropyl ether, and pump the solvent into the reactor C from the clear liquid inlet 12 of the reactor C for circulation;
[0068] The ethylene chlorocarbonate and triethylamine delivery pumps were started simultaneously at flow rates of 180 kg / h and 160 kg / h, respectively, and preheated to 60°C via preheaters A2 and A3, respectively. The ethylene chlorocarbonate and triethylamine were then combined and fed into the reactor C from the feed port 11 via the pipeline mixer B and evenly sprinkled into the reactor C via the liquid distributor 10. The triethylamine hydrochloride generated by the dechlorination reaction precipitated from the reactants, forming particles that gradually sank.
[0069] The reaction is exothermic. On the one hand, the solvent evaporates and evaporates from the gas phase port 14 on the top of the reactor C. It is cooled by condensers D1 and D2, received by the solvent receiving tank E, and refluxed into the reactor C. The evaporation rate and reflux flow of the solvent are controlled by the liquid level gauge in the reactor C. At the same time, the steam flow or cooling water flow of the jacket of the reactor C is controlled according to the temperature feedback in the reactor C to maintain the temperature of the reactants in the reactor C at 60-70°C.
[0070] S2: The reaction solution slurry carrying triethylamine hydrochloride is discharged from the discharge valve 13 of the reactor C at a flow rate of 2000 kg / h and is simultaneously discharged into the dynamic cross-flow membrane filters Wm-1 and Wm-2. At the same time, isopropyl ether is continuously added to the salt washing kettle X at a flow rate of 200 kg / h; the triethylamine hydrochloride slurry discharged from the slurry outlets Wm-1 and Wm-2 enters the salt washing kettle, the slurry of triethylamine hydrochloride is washed and dispersed, the bottom valve opening is controlled by the liquid level gauge on the salt washing kettle X, and the triethylamine hydrochloride slurry in the salt washing kettle is input into the dynamic cross-flow membrane filter Wn; the reaction solution and the washing liquid clear liquid separated from the first-level dynamic cross-flow membrane filter Wm-1, Wm-2 and the second-level dynamic cross-flow membrane filter Wn are combined together and returned to the reactor C from the clear liquid inlet 12 on the top of the reactor C by the circulating pump Z6 for a circulation reaction; the slurry of triethylamine hydrochloride is discharged into the neutralization kettle N through the slurry outlet W6 of the slurry dynamic cross-flow membrane filter Wn;
[0071] Ethylene chlorocarbonate and triethylamine were carried and stopped charging simultaneously after 5 hours, continued insulation reaction 5 hours, carried out gas chromatographic analysis from the recycle pump Z6 outlet sampling, and the ethylene chlorocarbonate content dropped to 0.23% after deducting methyl acetate and isopropyl ether solvent peak in the reaction solution that merges and the washings, showed that dechlorination reaction was complete basically; Open the feed valve of intermediate receiving tank F, the clear liquid inlet valve on the closed reactor C, the reaction solution that reacted completely is input intermediate receiving tank F by recycle pump Z6; Simultaneously the feed rate of ethylene chlorocarbonate and triethylamine is transferred to 135kg / h, 120kg / h respectively, start mixed solvent feed pump Z1 simultaneously, the feed rate of mixed solvent is transferred to 330kg / h, the flow of reactor C discharge valve is transferred to 585kg / h, carries out continuous synthesis; Carry out gas chromatographic analysis from the recycle pump Z6 outlet sampling, and the ethylene chlorocarbonate content is controlled at 0.5% after deducting methyl acetate and isopropyl ether solvent peak in the reaction solution that merges and the washings.
[0072] S3: The reaction liquid and washing liquid received in the intermediate receiving tank F are continuously distilled, and the solvent mixture of methyl acetate and isopropyl ether is removed through a desolventizing tower G, low-boiling substances such as triethylamine and solvent are removed through a low-boiling tower H, and high-boiling polymers are removed through a high-boiling tower J to obtain crude vinylene carbonate. Gas chromatography analysis shows a vinylene carbonate content of 93.2%;
[0073] S4: The crude vinylene carbonate obtained in S3 is continuously distilled through a primary distillation tower K1 and a secondary distillation tower K2 to obtain refined vinylene carbonate. Gas chromatography analysis shows that the purity of the vinylene carbonate is 99.63%.
[0074] S5: The refined vinylene carbonate product is sequentially passed through the primary melt crystallizer of M1 and the secondary melt crystallizer of M2 for melt crystallization to obtain the finished vinylene carbonate product. Gas chromatography analysis shows that the purity of the vinylene carbonate reaches 99.996%.
[0075] S6: 32% liquid caustic soda is added dropwise to the neutralization kettle N to allow triethylamine hydrochloride to react slowly with the added sodium hydroxide solution until the triethylamine hydrochloride reacts completely. The mixture is then transferred to a separatory tank P for stratification. The upper layer is an organic phase containing isopropyl ether and triethylamine, which is sequentially distilled and separated through a dehydration tower Q, a solvent recovery tower P, and a tertiary amine recovery tower Q. The recovered isopropyl ether has a purity of 99.1% and a moisture content of 162 ppm; the recovered triethylamine has a purity of 99.4% and a moisture content of 196 ppm, which can be fully reused in S1 and S2.
[0076] S7: The brine separated from the lower layer of the separator tank P passes through a three-effect evaporation system, and the evaporated wastewater enters the sewage treatment system for biochemical treatment; the salt slurry discharged by evaporation is transferred to the rotary kiln of the solid waste incinerator for high-temperature calcination to remove organic matter, and the obtained sodium chloride is sold as a by-product or treated as general solid waste.
[0077] The present invention provides a vinylene carbonate production process and apparatus, which can not only effectively improve the purity and yield of the product and stabilize the product characteristics, but also reduce equipment investment and labor costs, lower production energy consumption, and have low production costs, and can be applied to the large-scale production of vinylene carbonate.
[0078] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. The above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.
Claims
1. A process for producing vinylene carbonate, characterized in that: The following steps are involved: S1: The solvent is continuously fed through the solvent preheater A1 and into the reactor C through the flow rate controlled by the solvent delivery pump Z1 and the flow meter; when the solvent feed reaches a certain mass, warm water is introduced into the jacket of the reactor C to preheat and keep the solvent warm; When the solvent in the reactor C reaches the reaction temperature, the flow rates are controlled by the solvent, ethylene chloride and tertiary amine delivery pumps Z1, Z2, Z3 and flow meters respectively, and the solvent, ethylene chloride and tertiary amine are continuously passed through the preheaters A1, A2, A3 and the pipeline mixer B at a certain flow rate, and are input into the reactor C from the feed port 11 at the top of the reactor C for dechlorination reaction. The reaction heat is removed by the cooling water introduced into the jacket of the reactor C and the evaporation of the solvent in the reactor. The solvent in the reactor C absorbs the reaction heat and evaporates, and is distilled out from the gas phase port 14 at the top of the reactor C. After being cooled by the circulating water and chilled water two-stage heat exchangers D1 and D2, it is received by the solvent receiving tank E and recycled. S2: The slurry in the reactor C is continuously fed into the solid-liquid separation device W through the slurry delivery pump Z4 from the discharge valve 13 at the bottom of the reactor C and from the feed port W1 of the solid-liquid separation device Wm. The by-product tertiary amine hydrochloride generated by the reaction is separated from the reaction liquid in the solid-liquid separation device Wm and discharged from the clear liquid outlet W2. The slurry residue is discharged from the slurry residue outlet W3 and enters the salt washing kettle X. The washing solvent is fed into the salt washing kettle X from the solvent inlet on the salt washing kettle. Under the stirring provided by the salt washing kettle X, the slurry residue and the solvent are evenly dispersed, and the slurry residue is washed. The washed slurry is then discharged from the discharge port of the salt washing kettle and input into the solid-liquid separator Wn through the feed port W4 of the solid-liquid separator Wn to separate the tertiary amine hydrochloride and the washing liquid. The clear liquid of the washing liquid is combined with the clear liquid from the clear liquid outlet W5 of the solid-liquid separator W2 and input into the intermediate receiving tank F through the circulation pump Z6, or returned to the reactor C from the clear liquid inlet 12 or 15 at the upper or middle part of the reactor C to realize circulation; the slurry residue is discharged into the neutralization reactor N from the slurry residue outlet W3 or W6 of the solid-liquid separator Wm and Wn; S3: After the continuous or cyclic reaction is completed and the reaction liquid and washing liquid are separated by the solid-liquid separation devices Wm and Wn, they are transported from the clear liquid outlets W2 and W5 through the circulation pump Z6 to the intermediate receiving tank F, and then continuously distilled. The solvent is first separated and recovered by the desolventizing tower G, the low-boiling tower H, and the high-boiling tower J, and then returned to S1 or S2 for synthesis or washing, and the high-boiling substances are removed to obtain crude vinylene carbonate; S4: The crude vinylene carbonate is distilled and purified in the primary distillation tower K1 and the secondary distillation tower K2 to obtain the refined vinylene carbonate; S5: The vinylene carbonate product is melt-crystallized in the primary melt crystallizer M1 and the secondary melt crystallizer M2 to obtain a vinylene carbonate product with a purity of more than 99.99%, which enters the vinylene carbonate product receiving tank V; S6: The tertiary amine hydrochloride slurry discharged from S2 enters the neutralization kettle N, is neutralized by adding liquid caustic soda, and then transferred to the separator P for stratification. The upper organic phase enters the dehydration tower Q of the recovery system for dehydration, and then enters the solvent recovery tower R for distillation to recover the solvent, and the tertiary amine recovery tower T for distillation to recover the tertiary amine. The recovered solvent can be returned to S1 and reused in S2, and the recovered tertiary amine can be reused in S1; S7: The brine separated from the lower layer of the S6 separator tank P passes through a single-effect or multi-effect evaporation system, and the evaporated wastewater enters the sewage treatment system for biochemical treatment; the salt slurry discharged by evaporation is transferred to the rotary kiln of the waste liquid incinerator for high-temperature calcination to remove organic matter, and the obtained sodium chloride is sold as a by-product or treated as general solid waste.
2. A vinylene carbonate production device, characterized in that: The production device comprises: a solvent delivery pump Z1, a chloroethylene carbonate delivery pump Z2, a tertiary amine delivery pump Z3, a solvent preheater A1, a chloroethylene carbonate preheater A2, a tertiary amine preheater A3, a pipeline mixer B, a reactor C, a circulating water condenser D1, a chilled water condenser D2, a solvent receiving tank E, solid-liquid separation devices Wm and Wn, a salt washing reactor X, an intermediate receiving tank F, a desolventizing tower G, a low-salting tower H, a high-salting tower J, a primary distillation tower K1, a secondary distillation tower K2, a primary melting crystallizer M1, a secondary melting crystallizer M2, and a vinylene carbonate finished product receiving tank V, and the like are connected in a process sequence; the solid-liquid separation device Wm is connected to the solid-liquid separation device Wn; the solid-liquid separation device Wm is connected to the solid-liquid separation device Wn; the solid-liquid separation device Wn is connected to the solid-liquid separation device Wm; the solid-liquid separation device Wn is connected to the solid-liquid separation device Wm; the solid-liquid separation device Wn is connected to the solid-liquid separation device Wm; the solid-liquid separation device Wn is connected to the solid-liquid separation device Wm; the solid-liquid separation device Wn is connected to the solid-liquid separation device Wm; the solid-liquid separation device Wn is connected to the solid-liquid separation device Wn; the solid-liquid separation device Wm is connected to the solid-liquid separation device Wn ... The feed port W1 is connected to the discharge valve 13 at the bottom of the reactor C; the slurry discharge outlet W3 of the solid-liquid separation device Wm is connected to the salt washing kettle X, or directly connected to the neutralization kettle; the slurry outlet of the salt washing kettle is connected to the secondary solid-liquid separation device Wn; the slurry discharge outlet W6 of the solid-liquid separation device Wn is connected to the neutralization kettle N, and then connected to the separator P, dehydration tower Q, solvent recovery tower R, solvent receiving tank R1, tertiary amine recovery tower T, tertiary amine receiving tank T1, and in the order of the process; the clear liquid outlets W2 and W5 of the solid-liquid separation devices Wm and Wn are connected to the circulation pump Z6; the circulation pump Z6 is connected to the intermediate receiving tank F and the reactor C.
3. A process for producing vinylene carbonate according to claim 1, characterized in that: The tertiary amine is selected from N,N-dimethylethylamine, N,N-dimethyl-n-propylamine, N,N-dimethylisopropylamine, N,N-dimethylbutylamine, N,N-dimethylhexylamine, N,N-dimethylcyclohexylamine, N,N-dimethylaniline, diethylmethylamine, di-n-propylmethylamine, diisopropylmethylamine, triethylamine, triisopropylamine, tributylamine, pyridine, N-methylpyrrole, N-methylpyrrolidine, N-methylmorpholine, N-methylpiperidin, One or more combinations of 1,5-diazabis[4.3.0]non-5-ene and 1,8-diazabicyclo[5.4.0]undec-7-ene.
4. A process for producing vinylene carbonate according to claim 1, characterized in that: The solvent is a hydrocarbon, ether, ester, or nitrile compound, more typically selected from one or more mixtures of n-hexane, cyclohexane, n-heptane, petroleum ether, dichloromethane, dichloroethane, methyl propyl ether, ethyl propyl ether, methyl tert-butyl ether, n-propyl ether, isopropyl ether, ethyl formate, n-propyl formate, isopropyl formate, n-butyl formate, isobutyl formate, tert-butyl formate, methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, methyl propionate, ethyl propionate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and acetonitrile; the density of the solvent or mixed solvent at 25° C. is less than 1.
0.
5. A process for producing vinylene carbonate according to claim 1, characterized in that: The solvent contains 0.01 to 0.5% of a polymerization inhibitor, which is a combination of one or more of phenols, quinones, phenothiazines, phosphites, piperidinols, and piperidine nitrogen oxides. Typical polymerization inhibitors are hydroquinone, p-methoxyphenol, p-tert-butylcatechol, 2,6-di-tert-butyl-p-cresol, 2,5-di-tert-butylhydroquinone, phenothiazine, 2,2,6,6-tetramethyl-4-hydroxy-piperidine nitrogen oxide, tris(2,2,6,6-tetramethyl-4-oxy-piperidine nitrogen oxide) phosphite, and bis(2,2,6,6-tetramethyl-4-oxy-piperidine nitrogen oxide) sebacate.
6. A process for producing vinylene carbonate according to claim 1, characterized in that: The mass ratio of the solvent, ethylene chlorocarbonate and tertiary amine is 2.0-10.0:1.0:0.8-1.5; the reaction temperature is controlled at 50-100° C.; the ethylene chlorocarbonate and tertiary amine stay in the reactor C for 1-12 hours to carry out the dechlorination reaction.
7. A process for producing vinylene carbonate according to claim 1, characterized in that: Temperature measuring devices are provided on the pipelines connecting the rear ends of the preheaters A1, A2, and A3 for the solvent, ethylene chloride, and tertiary amine and the front end of the pipeline mixer B; temperature measuring devices are provided at the upper, middle, and lower parts of the reactor C; the temperature measuring devices are interlocked and controlled with the flow meter in the DCS central control room.
8. The vinylene carbonate production device according to claim 2, characterized in that: The top of the reactor C is provided with a feed port 11, the feed port 11 pipe extends into the interior of the reactor C, and is connected to a liquid distributor 10, so that the feed liquid is evenly distributed along the cross section of the reactor C and added to the reactor C; the feed port 11 is connected to the pipeline mixer B; the upper part of the reactor C is provided with a gas phase port 14, which is connected to the circulating water condenser D1 and the chilled water condenser D2; the upper part of the cylinder of the reactor C is also provided with a clear liquid inlet 12, which is connected to the circulating pump W6; the bottom of the reactor C is provided with a slurry discharge valve 13, the slurry discharge valve 13 is connected to the circulating water condenser D1 and the chilled water condenser D2. Valve 13 is an automatic switching valve, connected to the slurry inlet W1 of the solid-liquid separation device Wm; filtrate inlets 12 and 15 are provided at the upper and middle parts of the reactor C, which are connected to the circulation pump W6; the diameter of the liquid distributor 10 is 100 to 2000 mm; the diameter of the cylinder of the reactor C is 500 to 4000 mm, and the height of the cylinder is 1000 to 10000 mm; the outside of the reactor C is provided with a jacket 16, through which heat exchange medium passes, and the heat exchange medium includes but is not limited to steam, thermal oil, refrigerant, and circulating water.
9. The vinylene carbonate production device according to claim 2, characterized in that: The solid-liquid separation devices Wm and Wn include but are not limited to centrifuges, plate and frame filter presses, candle filters, zero-residue filters, bag filters, laminated membrane filters, rotary filter presses, disc filters, pressurized drum filters, dynamic cross-flow membrane filters and other devices with solid-liquid separation functions. The solid-liquid separation devices Wm and Wn are connected in series, and Wm and Wn are one or more connected in parallel. Wm and Wn are provided with slurry or slurry residue inlets W1 and W4, clear liquid outlets W2 and W5, and slurry residue outlets W3 and W6. The slurry inlet W1 is connected to the discharge valve 13, W3 is connected to the inlet of the salt washing kettle X or directly connected to the neutralization kettle N, W4 is connected to the outlet of the salt washing kettle X, W2 and W5 are connected to the circulation pump, and W6 is connected to the neutralization kettle N.