CN113105630A

CN113105630A - Solvent recovery process in polyphenylene sulfide production process flow

Info

Publication number: CN113105630A
Application number: CN202110401653.0A
Authority: CN
Inventors: 贺鹏勇; 马茂祥
Original assignee: Shenzhen Huaying New Material Co ltd
Current assignee: Shenzhen Huaying New Material Co ltd
Priority date: 2021-04-14
Filing date: 2021-04-14
Publication date: 2021-07-13
Anticipated expiration: 2041-04-14
Also published as: CN113105630B

Abstract

The invention provides a solvent recovery process in a polyphenylene sulfide production process flow, which adopts sodium sulfide dihydrate and p-dichlorobenzene as raw materials, takes N-methyl-2-pyrrolidone as a solvent, and produces polyphenylene sulfide resin through the process steps of dehydration, polycondensation and the like, wherein a filter cake is a mixture of solvents containing the polyphenylene sulfide resin, sodium chloride and NMP, and a filtrate is a mixture containing NMP and H₂Adding a certain amount of water-soluble acidic substance into the filtrate, converting the alkali metal organic acid salt in the filtrate into organic acid and alkali metal water-soluble salt-sodium chloride, removing the organic acid and water by reduced pressure evaporation, and then distilling, purifying and recovering the NMP solvent containing a small amount of water to obtain the NMP solvent with the purity of 99.96-99.98%.

Description

Solvent recovery process in polyphenylene sulfide production process flow

Technical Field

The invention relates to the technical field of recovery of high polymer materials, in particular to a solvent recovery process in a production process flow of polyphenylene sulfide resin.

Background

In U.S. patent numbers: 3354129 discloses a process for the production of polyarylene sulfides by polymerization of at least one polyhalo-substituted cyclic compound with an alkali metal sulfide in a reaction medium containing a polar organic solvent, which is incorporated herein by reference. Polyphenylene sulfide resin, hereinafter PAS is referred to as its abbreviation, a semi-crystalline polyphenylene sulfide polymer is an important industrial raw material, hereinafter PPS is referred to as its abbreviation, and its industrial production process is carried out by mixing the same amount of sodium sulfide, or a mixture of sodium hydrosulfide and sodium hydroxide in a molar ratio approximately equal to the molar ratio, with subsequently added P-DCB in cyclic amides such as: NMP/N-methyl pyrrolidone in a reaction medium.

In the production of polyphenylene sulfide resins, several preferred methods of recovering the reaction product of polyphenylene sulfide are employed in a process of refluxing and washing PPS with a solid filter cake impregnated with a starting solvent, wherein steam is introduced into the process of the PPS operation as a separated polymer solid substance, and the main purpose of the washing operation is to replace the starting solvent in the wet solid filter cake with a washing solvent, thereby washing out the solid substance which can be dissolved in the solid filter cake to the maximum extent, such as: multistage washing with a very large amount of washing solvent, with essentially no initial liquid solvent in the solid cake at the last stage of the washing operation, i.e. only washing solvent remaining in the cake, is economical to operate to the extent of washing, however, instead of completely replacing all of the initial liquid solvent with washing solvent, in the usual case, a small amount of initial liquid solvent remains in the solid cake after the washing operation.

The equipment installed for the reflux washing operation requires a suitable number of stages, typically 2 to 6 stages in the PPS washing operation scheme, to achieve a high desired, i.e., low level, ratio of the initial liquid solvent remaining in the filter cake at the last stage of the washing operation.

In the production process of polyphenylene sulfide resin, sodium sulfide and P-dichlorobenzene (P-DCB) are basically used as raw materials, in the process of polycondensation Production of Polyphenylene Sulfide (PPS) resin under the action of alkali metal cosolvent, NMP (N-methyl pyrrolidone) addition solution of alkali metal chloride is needed to complete polymerization reaction in the polymerization stage, compared with the cost of other raw materials, NMP and alkali metal cosolvent occupy equivalent price proportion, but NMP and cosolvent are not consumed theoretically in the production process of PPS, so that the key of reducing the production cost of PPS is that whether the NMP solvent can be recovered at a higher recovery rate or not.

After the polymerization reaction is finished, 50-60% of NMP can be recovered by a conventional method, but the rest 48-38% of NMP is combined with polyphenylene sulfide resin, an auxiliary agent and a byproduct sodium chloride and is wrapped in the polyphenylene sulfide resin, the auxiliary agent is an alkali metal organic acid salt dissolved in an NMP solvent, the melting point of the alkali metal organic acid salt is 200-204 ℃, the boiling point of the alkali metal organic acid salt is far higher than that of the NMP solvent, the alkali metal organic acid salt is extremely difficult to separate, the partial NMP cannot be recovered even under a vacuum condition, meanwhile, in the recovery process flow of the polyphenylene sulfide resin, a large amount of deionized water is needed to wash the polyphenylene sulfide resin, and further, the solvent to be recovered contains a large amount of water, sodium chloride and some organic.

In the U.S. Pat. No. 5711873, a process for recovering a solvent in the production of polyphenylene sulfide resin is disclosed, which uses a low boiling point solvent as a diluent of a reaction system, and although the addition of a low boiling point organic solvent to the reaction system is helpful for filtering the reaction mixture, and the low boiling point solvent is also easy to recover and purify, the requirement on the material of a polymerization reaction kettle is high, if the low boiling point organic solvent is added at a later stage of the reaction system, the pressure of the reaction kettle is increased, and at the same time, the reaction kettle is required to be kept above the designed bearing pressure at all times, which may cause serious accidents inadvertently.

In chinese patent No: 201110229729.2A process for recovering solvent from the production of polyphenyl thioether resin features that sodium sulfide and p-dichlorobenzene as raw materials are used to produce polyphenyl thioether resin through dewatering and polycondensation. After the polycondensation reaction is finished, the lithium chloride cosolvent is subjected to solid-liquid first-stage separation, then the solid-liquid first-stage separation is carried out, then a second-stage filtration, evaporation and further treatment are carried out by a single-screw evaporator, NMP crude solutions containing certain impurities are respectively obtained, the NMP solvent is further rectified and purified by a rectifying tower to obtain the NMP solvent with the purity of 99.98%, the NMP solvent is reused for synthesizing the polyphenylene sulfide resin, the recovery rate of the NMP solvent is 97-98.5%, the raw materials are saved, and the production cost of the PPS is reduced.

In chinese patent No: 201110066328. a solvent and catalyst recovery technique in the production of polyphenylene sulfide is introduced in X, after the polycondensation reaction is completed,adding 1-3mol/mol Na₂And S, using fresh NMP solvent as a diluent, enabling the reaction system to obtain another mixture under the dilution of NMP, and respectively obtaining a mixed solution containing NMP and water and a powdery mixture containing a cosolvent and a byproduct after the mixture is filtered, extracted, evaporated and further processed by a spiral evaporator. And (2) evaporating the mixed solution of NMP and water to remove water to obtain an NMP solvent containing certain impurities, further rectifying and purifying the NMP solvent by a rectifying tower to obtain the NMP solvent with the purity of 99.98%, and reusing the NMP solvent in the synthesis of the polyphenylene sulfide enzyme resin, wherein the recovery rate of the NMP solvent is 9698%, the purity of 99.9-99.98% and the recovery rate of 98-99% of the catalyst lithium chloride.

Disclosure of Invention

The invention provides a solvent recovery process in a polyphenylene sulfide production process flow, and aims to create a new method for recovering a solvent in polyphenylene sulfide production, so that NMP and a cosolvent which are remained in a solid solution form can be efficiently recovered, the production cost of PPS is reduced, and meanwhile, the purity of the NMP solvent is improved on the basis of shortening the recovery process flow, so that the level of a similar foreign recovery device is reached or exceeded.

The technical scheme adopted by the invention is as follows:

the invention adopts sodium sulfide and p-dichlorobenzene as raw materials, N-methyl-2-pyrrolidone (NMP for short) as solvent, and produces polyphenylene sulfide resin through the process steps of dehydration, polycondensation and the like, wherein the filter cake is a mixture of the polyphenylene sulfide resin, sodium chloride and the NMP solvent, and the filtrate is NMP, H and the like₂Adding a certain amount of water-soluble acidic substance into filtrate to convert the alkali metal organic acid salt in the filtrate into organic acid and alkali metal water-soluble salt-sodium chloride, and distilling and purifying the NMP solvent containing a small amount of water after removing the organic acid and the water by reduced pressure evaporation, wherein the NMP solvent recovery process comprises the following steps:

(1) under the condition of stirring speed of 10-50 rpm, adding 5-35 wt% of NMP, 1.5-3.5 wt% of sodium benzoate or sodium formate or sodium acetate or sodium propionate orAlkali metal organic acid salt of sodium butyrate, 10-25 wt% of sodium chloride and 36.5-71.5 wt% of wtH₂Adding 10-30L of hydrochloric acid or ammonium chloride water-soluble acidic liquid with the concentration of 3-8% v/v into the O mixed liquid at the flow rate of 0.3-0.8L/min, and inputting the mixed liquid into a 316L stainless steel jacket evaporation kettle when the pH value of the mixed liquid is measured to be 0-4 by an on-line acidimeter; in this case, the mixed liquid contains 10-30 wt% of NMP, 1.0-3.0 wt% of benzoic acid or formic acid or acetic acid or propionic acid or butyric acid organic acid, 10-22 wt% of sodium chloride, 0.3-0.8 wt% of excess water-soluble acidic liquid, 44.2-78.7 wt% of H₂O; if the water-soluble acidic liquid is ammonium chloride, NMP and H are contained₂Acidizing a mixed liquid of O, alkali metal organic salt and sodium chloride, wherein the mixed liquid contains 10-30 wt% of NMP, 11-28 wt% of sodium chloride and 44.2-78.7 wt% of wtH₂O, 0.3-0.8 wt% of excessive water-soluble acid; 1.0-3.0 wt% of ammonium benzoate or ammonium formate or ammonium acetate or ammonium propionate or ammonium butyrate;

(2) inputting the acidified mixed solution in the step (1) into a 200L 316L stainless steel jacket evaporation kettle, inputting heat conducting oil from the bottom of a jacket of the 316L stainless steel jacket evaporation kettle, outputting the heat conducting oil from the top of the jacket, and carrying out reaction on the heat conducting oil containing NMP and H₂Heating a mixed liquid of O, organic acid and sodium chloride, stirring the mixed liquid at a stirring speed of 30-80 rpm, starting a vacuum pump when the temperature reaches 60-90 ℃, allowing water vapor to flow out of the top of a 316L stainless steel jacket evaporation kettle, cooling the mixed liquid by a condenser arranged at the top, allowing the cooled mixed liquid to flow into a wastewater treatment process, treating the wastewater for recycling, introducing the mixed liquid into a solid-liquid separation centrifuge for separation when the solution in the 316L stainless steel jacket evaporation kettle is brown, detecting the viscosity of the mixed liquid to be 2.0-6.0 cPa.s by an in-line viscometer when crystals are crystallized and separated out, detecting the water content in the mixed liquid to reach 0.5-0.9 wt% by liquid chromatography, and introducing the solid into a recovery and drying device for sodium chloride, wherein the solid is light green sodium chloride containing a small amount of NMP and organic impurities; inputting the filtrate into an NMP solvent recovery rectifying tower;

(3) inputting the light green sodium chloride solid containing a small amount of NMP and organic impurities separated in the step (2) into a spiral dryer, and respectively configuring the front part, the middle part and the tail part of the spiral dryerA steam outlet with diameter phi of 60, the steam outlet is connected with the lower port of the condenser tube side, the upper outlet of the condenser tube side is connected with the inlet of the vacuum pump, the steam containing NMP evaporated from the spiral dryer is cooled by the condenser and then is input with NMP and H₂The method comprises the following steps of (1) acidifying and concentrating mixed liquid of O, alkali metal organic acid salt and sodium chloride, then rectifying the mixed liquid in a rectifying tower, inputting cooling water from a lower opening of a shell pass of a condenser, and outputting the cooling water from an upper opening of the shell pass of the condenser to a circulating water storage tank for recycling;

(4) separating the (2) to obtain mixed liquid containing NMP, inputting the mixed liquid from the middle part of a rectifying tower at an input speed of 2-8L/min, assembling a 20L glass jacket evaporator at the lower part of the rectifying tower, assembling a magnetic stirrer below the glass jacket evaporator, stirring the mixed liquid containing the NMP solvent which is not evaporated at a stirring speed of 30-60 rpm, inputting heat conduction oil from the bottom of a glass jacket expander, outputting the heat conduction oil from the top of the glass jacket evaporator, inputting the evaporated NMP steam into a condenser arranged at the top of the rectifying tower, inputting the NMP steam from a tube pass bottom inlet of the condenser, connecting a top outlet of the condenser with an inlet of a vacuum pump, cooling the NMP steam by the condenser, flowing out from the lower end of a tube pass of the condenser, detecting the NMP content to be 99.96-99.98% by a liquid chromatograph, inputting the NMP steam into a storage tank, returning unqualified NMP to a crude NMP tank for temporary, then inputting the mixture into an NMP rectifying tower for rectification and purification again; the cooling water of the condenser is input from the bottom inlet of the condenser shell pass, is output from the upper part of the condenser shell pass and flows into the circulating water storage tank, and is used after being cooled.

The process flow for recovering the polyphenylene sulfide resin production solvent has the following characteristics:

1. in the process of the invention, NMP and H are reduced₂Concentrating the mixed liquid of O, alkali metal salt of organic acid and sodium chloride to remove water, and adding NMP and H₂The mixed liquid of O, alkali metal organic acid salt and sodium chloride is acidified to reduce the viscosity of the concentrated mixed liquid, and analyzed to find that the mixed liquid contains NMP and H₂O, alkali metal organic acid salt and sodium chloride, namely sodium benzoate and sodium acetateSodium benzoate, sodium formate, sodium propionate and sodium butyrate, especially sodium benzoate and sodium butyrate, are gradually saturated with the evaporation of water, and at this time, NMP and H are not only contained₂The azeotropic point of the mixed liquid of O, alkali metal organic acid salt and sodium chloride is increased, and NMP and H are also added₂The viscosity of the mixed liquid of O, alkali metal organic acid salt and sodium chloride obviously increases the current of a stirring motor, repeated experiments show that proper addition of water-soluble acidic liquid is helpful for reducing the viscosity of the residual solution after concentration and dehydration, and analysis shows that after the water-soluble acidic liquid is added, NMP and H are contained₂In the mixed liquid of O, organic acid and sodium chloride, the organic acid, i.e. benzoic acid or formic acid or acetic acid or butyric acid or propionic acid, is removed along with the continuous evaporation of water, so that the content of NMP and H is reduced₂Viscosity of the mixed liquid of O and sodium chloride, and does not contain NMP and H₂The azeotropic point of the mixed liquid of O and sodium chloride is increased and the current of the stirring motor is kept stable, and this is mainly caused by the removal of low-boiling organic acids such as benzoic acid, formic acid, acetic acid, butyric acid, propionic acid, etc. by distillation of water.

2. In the process flow for recovering the polyphenylene sulfide resin production solvent, an online acidimeter is used for improving the production efficiency, and the aim is to reduce NMP and H₂The measurement times of the pH value of the mixed liquid of O, organic acid and sodium chloride can be simultaneously reduced by online detection, the addition of the water-soluble acidic liquid can be reduced, and NMP and H can be contained₂The acidification degree of the mixed liquid of O, organic acid and sodium chloride is effectively controlled, so that the production cost can be saved, the production efficiency can be improved, and if the hydrochloric acid is added excessively, the NMP solvent can be subjected to ring opening under the high-temperature condition, so that the recovery rate of the NMP solvent is reduced; if the addition amount of the hydrochloric acid is insufficient, the energy consumption of solvent recovery is increased.

3. In the process flow for recovering the polyphenylene sulfide resin production solvent, NMP and H are contained in order to save energy₂Mixing of O, organic acid and sodium chlorideIn the evaporation process after the liquid is acidified, the on-line viscosity detection is adopted, so that the content of NMP and H can be controlled₂The concentration of residual liquid after the water content of the mixed liquid of O, organic acid and sodium chloride and the organic acid are evaporated and removed can be effectively controlled to contain NMP and H₂The viscosity of the residual liquid after the mixed liquid moisture of O, organic acid and sodium chloride and the organic acid are evaporated and removed, and the input quantity of the heat conducting oil can be effectively controlled, so that the energy can be saved, the recovery efficiency of the NMP solvent can be improved, and the NMP and H are effectively controlled₂And (3) evaporating and removing the water content in the residual liquid after the mixed liquid water of the O, the organic acid and the sodium chloride and the organic acid are evaporated and removed.

4. In order to recover and obtain high-purity NMP, the invention acidifies NMP and H₂In the process of mixing O, alkali metal benzoate or acetate or formate or propionate or butyrate and sodium chloride, strong oxidizing acid or its strong oxidizing acid weak base salt is not used as much as possible, so that under the condition of strong oxidizing acid, especially under the condition of heating, the ring opening of NMP solvent can be implemented by using strong oxidizing acid, and this not only can reduce recovery rate of NMP solvent, but also can make the product after ring opening of NMP not be easily removed with evaporation of water₂The viscosity of the mixed liquid of O, organic acid and sodium chloride is reduced, and the ring opening rate of NMP solvent under strong acid condition is monitored by using an on-line acidimeter₂The pH value of the mixed liquid of O, organic acid and sodium chloride can be detected, so that NMP and H can be detected₂The pH value of the mixed liquid of O, organic acid and sodium chloride can be controlled, the addition amount of dilute hydrochloric acid or ammonium chloride can be controlled, and the content of NMP solvent containing NMP and H can be reduced₂The yield of the ring-opening reaction is generated in the process of evaporating and removing the water content of the mixed liquid of O, benzoic acid or formic acid or acetic acid or propionic acid or butyric acid organic acid and sodium chloride, along with the evaporation and removal of the water content, hydrochloric acid, benzoic acid and the like,hydrochloric acid, benzoic acid, etc. in the presence of NMP, H₂The concentration of the mixed liquid of O and sodium chloride is lower and lower, so that the ring-opening decomposition of the NMP solvent can be controlled, the recovery rate of the NMP solvent can be improved, and the production cost of the polyphenylene sulfide resin can be reduced.

5. In the process of synthesizing the polyphenylene sulfide resin, in order to adjust the molecular weight distribution coefficient of the polyphenylene sulfide resin, after the heat preservation at 255 ℃, a certain molecular weight and molecular weight distribution coefficient regulator sodium benzoate or sodium formate or sodium acetate or sodium propionate or sodium butyrate is added.

6. In the recovery process of the NMP solvent, sodium chloride crystals are separated out from a tan solution, and the sodium chloride crystals are in a light green solid in the air after solid-liquid separation, and become a light reddish brown solid after being oxidized by the air, and become a tan solid after being dried by a spiral dryer.

7. In the process of recovering the NMP solvent, a small amount of the polyphenylene sulfide resin enters the solvent containing NMP and H through the filter screen in the process of filtering the polyphenylene sulfide resin₂In the mixed liquid of O, the alkali metal organic acid salt and sodium chloride, the polyphenylene sulfide resin is not dissolved in water and NMP solvent, and the amount is small, so that the polyphenylene sulfide resin can be ignored.

8. The composition of the mixed liquid of the present invention was measured using an Agilent1200 liquid chromatograph and a GC7900 gas chromatograph.

The process flow of the invention is briefly described as follows:

under a certain stirring condition, adding NMP and H₂In the evaporation kettle of the mixed liquid of O, alkali metal organic acid salt and sodium chloride, water-soluble acidic liquid with certain concentration is added in a flowing line manner, and NMP and H are contained under the monitoring of a linear acidimeter₂Controlling the pH value of the mixed liquid of O, organic acid and sodium chloride within the range of 0-4, and immediately adding NMP and H₂Stirring the mixed liquid of O, organic acid and sodium chloride under magnetic forceUnder the stirring of the stirrer, the water, the excessive water-soluble acidic liquid and the benzoic acid or formic acid or acetic acid or propionic acid or butyric acid generated by acidification are evaporated to remove water, and the water and the acetic acid or the propionic acid or the butyric acid are mixed with NMP and H₂Continuously concentrating mixed liquid of O, organic acid and sodium chloride, continuously increasing the concentration of system materials, under the monitoring of an linear viscometer, when the viscosity of the system reaches 2.0-6.0 cPa.s, the liquid in the system is changed into brown, and when sodium chloride crystals are separated out, performing solid-liquid centrifugal separation on the materials in the system, oxidizing solid substances by air to be light green, inputting the solid substances into a sodium chloride recovery process, and inputting filtrate into an NMP solvent recovery process.

Inputting light green solid sodium chloride containing small amount of NMP solvent, water, formic acid or acetic acid or propionic acid or butyric acid and other insoluble organic substances which are possibly generated after acidification treatment into a spiral dryer for drying, cooling and recovering the NMP solvent and water, and mixing with NMP, H and water₂And mixing the mixed liquid of O, alkali metal organic acid salt and sodium chloride, and then recovering the NMP solvent.

The mixed liquid containing NMP is obtained by solid-liquid separation and is input from the middle part of the rectifying tower at a certain input speed, the lower part of the rectifying tower is provided with a glass jacket evaporator, a magnetic stirrer is arranged below the glass jacket evaporator, and the magnetic stirrer is arranged at a certain stirring speed, stirring the unevaporated mixed liquid containing NMP solvent, inputting heat-conducting oil from the bottom of glass jacket evaporator, outputting from the top of glass jacket evaporator, inputting the evaporated NMP steam into condenser arranged on the top of rectifying tower, inputting from the inlet at the bottom of tube pass of condenser, connecting the outlet at the top of condenser with the inlet of vacuum pump, cooling the NMP steam by condenser, flowing out from the lower end of the condenser tube side, detecting the NMP content of 99.96-99.98% wt by a liquid chromatograph, inputting into an NMP storage tank, returning unqualified NMP to an NMP crude product tank for temporary storage, and inputting into an NMP rectifying tower for rectification and purification again; the cooling water of the condenser is input from the bottom inlet of the condenser shell pass, is output from the upper part of the condenser shell pass and flows into the circulating water storage tank, and is used after being cooled.

Detailed Description

Example 1

(1) To 100L of a mixture containing 15% by weight of NMP, 1.5% by weight of sodium benzoate, 10% by weight of sodium chloride, 73.5% by weight of wtH at a stirring speed of 10rpm₂Adding 30L of hydrochloric acid solution with the concentration of 3% v/v into the mixed liquid of O, and inputting the mixed liquid into a 316L stainless steel jacket evaporation kettle when the pH value of the mixed liquid is 4 measured by an on-line acidimeter; at this time, the mixed liquid contained 10% by weight of NMP, 11% by weight of sodium chloride, 0.3% by weight of excess hydrochloric acid, 77.7% by weight of H₂O, 1.0% wt benzoic acid;

(2) inputting the acidified mixed solution in the step (1) into a 200L 316L stainless steel jacket evaporation kettle, inputting heat-conducting oil from the bottom of a jacket of the 316L stainless steel jacket evaporation kettle, outputting the heat-conducting oil from the top of the jacket, and carrying out reaction on the heat-conducting oil containing NMP and H₂Heating a mixed liquid of O, benzoic acid and sodium chloride, stirring the mixed liquid at a stirring speed of 30rpm, starting a vacuum pump when the temperature reaches 60 ℃, enabling water vapor to flow out of the top of a 316L stainless steel jacket evaporation kettle, cooling the mixed liquid by a condenser arranged at the top, flowing into a wastewater treatment process, treating the wastewater for recycling, inputting the residual mixed liquid into a solid-liquid separation centrifuge for separation when a solution in the 316L stainless steel jacket evaporation kettle is changed into tan and crystals are separated out, measuring the viscosity of the mixed liquid to be 6.0cPa.s by an online viscometer, and detecting the water content in the mixed liquid to reach 0.5 wt% by liquid chromatography, and inputting the residual mixed liquid into a recovery and drying device of sodium chloride, wherein the solid is light green sodium chloride containing a small amount of NMP and organic impurities; inputting the filtrate into an NMP solvent recovery rectifying tower;

(3) inputting the light green sodium chloride solid containing a small amount of NMP and organic impurities separated in the step (2) into a spiral dryer, respectively configuring a phi 60 steam outlet at the front part, the middle part and the tail part of the spiral dryer, connecting the outlet with the lower opening of a condenser tube side, connecting the upper outlet of the condenser tube side with the inlet of a vacuum pump, cooling the steam containing NMP evaporated from the spiral dryer by a condenser, and inputting the steam containing NMP and H₂Acidifying and concentrating the mixed liquid of O, sodium benzoate and sodium chloride, then rectifying the mixed liquid in a rectifying tower, inputting cooling water from the lower opening of the shell pass of the condenser, and outputting the cooling water from the upper opening of the shell pass of the condenser to a circulating water storage tank for recycling;

(4) the mixed liquid containing NMP obtained by the separation in the step (2) is input from the middle part of the rectifying tower at the input speed of 2L/min, A20L glass jacketed evaporator was fitted at the lower part of the rectification column, a magnetic stirrer was fitted below the glass jacketed evaporator, and the stirring speed was 30rpm, stirring the unevaporated mixed liquid containing NMP solvent, inputting heat-conducting oil from the bottom of glass jacket evaporator, outputting from the top of glass jacket evaporator, inputting the evaporated NMP steam into condenser arranged on the top of rectifying tower, inputting from the inlet at the bottom of tube pass of condenser, connecting the outlet at the top of condenser with the inlet of vacuum pump, cooling the NMP steam by condenser, flows out from the lower end of the condenser tube side, and after the NMP content is detected to be 99.96 percent wt by a liquid chromatograph, the NMP solvent recovery for this experiment was 97.69% by transferring to the NMP storage tank.

Example 2

(1) To 100L of a solution containing 35% by weight of NMP, 3.5% by weight of sodium benzoate, 25% by weight of sodium chloride, 36.5% by weight of wtH at a stirring speed of 50rpm₂Adding 10L of hydrochloric acid solution with the concentration of 8% v/v into the mixed liquid of O, and inputting the mixed liquid into a 316L stainless steel jacket evaporation kettle when the pH value of the mixed liquid is 0 by using an on-line acidimeter; at this time, the mixed liquid contained 30% by weight of NMP, 22% by weight of sodium chloride, 0.8% by weight of excess hydrochloric acid, 44.2% by weight of H₂O, 3.0% wt benzoic acid;

(2) inputting the acidified mixed solution in the step (1) into a 200L 316L stainless steel jacketed evaporation kettle, inputting heat-conducting oil from the bottom of a jacket of the 316L stainless steel jacketed evaporation kettle, outputting the heat-conducting oil from the top of the jacket, and carrying out treatment on the heat-conducting oil containing NMP and H₂Heating the mixed liquid of O, benzoic acid and sodium chloride, stirring the mixed liquid at a stirring speed of 80rpm, starting a vacuum pump when the temperature reaches 90 ℃, enabling water vapor to flow out of the top of a 316L stainless steel jacket evaporation kettle, cooling the mixed liquid by a condenser arranged at the top, flowing into a wastewater treatment process, recycling the treated mixed liquid, measuring the viscosity of the mixed liquid to be 2.0cPa.s by an on-line viscometer when the solution in the 316L stainless steel jacket evaporation kettle is changed into tan and crystal is separated out, and inputting the residual mixed liquid into a solid phase chromatography when the water content in the mixed liquid reaches 0.9 wt% by liquid chromatography-a liquid separation centrifuge for separation, the solid being light green sodium chloride containing small amounts of NMP and organic impurities, to be fed to a sodium chloride recovery drying unit; inputting the filtrate into an NMP solvent recovery rectifying tower;

(4) the mixed liquid containing NMP obtained by the separation in the step (2) is input from the middle part of the rectifying tower at the input speed of 8L/min, A20L glass jacketed evaporator was fitted at the lower part of the rectification column, a magnetic stirrer was fitted below the glass jacketed evaporator, and the stirring speed was 60rpm, stirring the unevaporated mixed liquid containing NMP solvent, inputting heat-conducting oil from the bottom of glass jacket evaporator, outputting from the top of glass jacket evaporator, inputting the evaporated NMP steam into condenser arranged on the top of rectifying tower, inputting from the inlet at the bottom of tube pass of condenser, connecting the outlet at the top of condenser with the inlet of vacuum pump, cooling the NMP steam by condenser, flows out from the lower end of the condenser tube side, and after the NMP content is detected to be 99.98 percent wt by a liquid chromatograph, the NMP solvent recovery for this experiment was 97.47% after being transferred to the NMP storage tank.

Comparative example 1

(1) 100L of a mixture containing 15% by weight of NMP, 1.5% by weight of sodium benzoate, 10% by weight of sodium chloride, 73.5% by weight of wtH were stirred at 10rpm₂The mixed liquid of O is input into a 316L stainless steel jacket evaporation kettle, the pH value of the mixed liquid is measured to be 9.3 by an on-line acidimeter, the heat-conducting oil is input from the bottom of the jacket of the 316L stainless steel jacket evaporation kettle, and is output from the top of the jacket, and the mixed liquid containing NMP and H is subjected to heat treatment₂Heating a mixed liquid of O, sodium benzoate and sodium chloride, stirring the mixed liquid at a stirring speed of 30rpm, starting a vacuum pump when the temperature reaches 60 ℃, enabling water vapor to flow out of the top of a 316L stainless steel jacket evaporation kettle, cooling the mixed liquid by a condenser arranged at the top, flowing into a wastewater treatment process, treating the wastewater for recycling, inputting the residual mixed liquid into a solid-liquid separation centrifuge for separation when a solution in the 316L stainless steel jacket evaporation kettle is changed into tan and crystals are separated out, measuring the viscosity of the mixed liquid to be 33.1cPa.s by an on-line viscometer, and detecting the water content in the mixed liquid to reach 0.5 percent by weight by liquid chromatography, wherein the solid is light green sodium chloride containing a small amount of NMP and organic impurities, and inputting the solid into a sodium chloride recovery and drying device; inputting the filtrate into an NMP solvent recovery rectifying tower;

(2) inputting the light green sodium chloride solid containing a small amount of NMP and organic impurities separated in the step (1) into a spiral dryer, respectively configuring a phi 60 steam outlet at the front part, the middle part and the tail part of the spiral dryer, connecting the outlet with the lower opening of a condenser tube side, connecting the upper outlet of the condenser tube side with the inlet of a vacuum pump, cooling the steam containing NMP evaporated from the spiral dryer by a condenser, and inputting the steam containing NMP and H₂Acidifying and concentrating the mixed liquid of O, sodium benzoate and sodium chloride, then rectifying the mixed liquid in a rectifying tower, inputting cooling water from the lower opening of the shell pass of the condenser, and outputting the cooling water from the upper opening of the shell pass of the condenser to a circulating water storage tank for recycling;

(3) the mixed liquid containing NMP obtained by the separation in the step (1) is input from the middle part of the rectifying tower at the input speed of 2L/min, A20L glass jacketed evaporator was fitted at the lower part of the rectification column, a magnetic stirrer was fitted below the glass jacketed evaporator, and the stirring speed was 30rpm, stirring the unevaporated mixed liquid containing NMP solvent, inputting heat-conducting oil from the bottom of glass jacket evaporator, outputting from the top of glass jacket evaporator, inputting the evaporated NMP steam into condenser arranged on the top of rectifying tower, inputting from the inlet at the bottom of tube pass of condenser, connecting the outlet at the top of condenser with the inlet of vacuum pump, cooling the NMP steam by condenser, flows out from the lower end of the condenser tube side, and after the NMP content is detected to be 99.16 percent wt by a liquid chromatograph, unqualified NMP is returned to the NMP crude tank for temporary storage, and the recovery rate of NMP solvent in the experiment is 95.73%.

Example 3

(1) Under the condition of stirring speed of 10-50 rpm, 100L of the mixed solution contains 20 wt% of NMP, 2.0 wt% of sodium formate, 17.3 wt% of sodium chloride and 60.7 wt% of wtH₂Adding 26L hydrochloric acid liquid with the concentration of 3.6% v/v into the mixed liquid of O, and inputting into a 316L stainless steel jacket evaporation kettle when the pH value of the mixed liquid is 0.35 measured by an on-line acidimeter; at this time, the mixed liquid contained 18.6% by weight of NMP, 15.61% by weight of sodium chloride, 0.4% by weight of excess hydrochloric acid, 63.76% by weight of H₂O, 1.63% wt formic acid;

(2) inputting the acidified mixed solution in the step (1) into a 200L 316L stainless steel jacketed evaporation kettle, inputting heat-conducting oil from the bottom of a jacket of the 316L stainless steel jacketed evaporation kettle, outputting the heat-conducting oil from the top of the jacket, and carrying out treatment on the heat-conducting oil containing NMP and H₂Heating mixed liquid of O, formic acid and sodium chloride, stirring the mixed liquid at a stirring speed of 43rpm, starting a vacuum pump when the temperature reaches 71 ℃, enabling water vapor to flow out of the top of a 316L stainless steel jacket evaporation kettle, cooling the mixed liquid by a condenser arranged at the top, flowing into a wastewater treatment process, treating the wastewater for recycling, inputting the residual mixed liquid into a solid-liquid separation centrifuge for separation when the solution in the 316L stainless steel jacket evaporation kettle is changed into tan and crystals are separated out, measuring the viscosity of the mixed liquid to be 3.1cPa.s by an online viscometer, and detecting the water content in the mixed liquid to reach 0.7 wt% by liquid chromatography, wherein the solid is light green sodium chloride containing a small amount of NMP and organic impurities, and inputting the solid into a sodium chloride recovery and drying device; inputting the filtrate into an NMP solvent recovery rectifying tower;

(3) inputting the light green sodium chloride solid containing a small amount of NMP and organic impurities separated in the step (2) into a spiral dryer, respectively configuring a phi 60 steam outlet at the front part, the middle part and the tail part of the spiral dryer, connecting the outlet with the lower opening of a condenser tube side, connecting the upper outlet of the condenser tube side with the inlet of a vacuum pump, cooling the steam containing NMP evaporated from the spiral dryer by a condenser, and inputting the steam containing NMP and H₂O, formic acidAcidifying and concentrating the mixed liquid of sodium and sodium chloride, and then rectifying the mixed liquid in a rectifying tower, wherein cooling water is input from the lower opening of the shell side of the condenser and output from the upper opening of the shell side of the condenser to a circulating water storage tank for recycling;

(4) the mixed liquid containing NMP obtained by the separation in the step (2) is input from the middle part of the rectifying tower at the input speed of 4.3L/min, A20L glass jacketed evaporator was fitted at the lower part of the rectification column, a magnetic stirrer was fitted below the glass jacketed evaporator, and the stirring speed was 41rpm, stirring the unevaporated mixed liquid containing NMP solvent, inputting heat-conducting oil from the bottom of glass jacket evaporator, outputting from the top of glass jacket evaporator, inputting the evaporated NMP steam into condenser arranged on the top of rectifying tower, inputting from the inlet at the bottom of tube pass of condenser, connecting the outlet at the top of condenser with the inlet of vacuum pump, cooling the NMP steam by condenser, flows out from the lower end of the condenser tube side, and after the NMP content is detected to be 99.97 percent wt by a liquid chromatograph, the NMP solvent recovery from this experiment was 97.82% by transferring to the NMP storage tank.

Example 4

(1) Under the condition of stirring speed of 10-50 rpm, the 100L of the aqueous dispersion contains 25.6 wt% of NMP, 2.1 wt% of sodium acetate, 21.4 wt% of sodium chloride and 36.5-71.5% of wtH₂Adding 29L of hydrochloric acid solution with the concentration of 4.6% v/v into the mixed liquid of O, inputting the mixed liquid into a 316L stainless steel jacket evaporation kettle when the pH value of the mixed liquid is 1.3 measured by an on-line acidimeter; at this time, the mixed liquid contained 21.4% by weight of NMP, 20.34% by weight of sodium chloride, 0.6% by weight of excess hydrochloric acid, 55.9% by weight of H₂O, 1.76% wt acetic acid;

(2) inputting the acidified mixed solution in the step (1) into a 200L 316L stainless steel jacket evaporation kettle, inputting heat-conducting oil from the bottom of a jacket of the 316L stainless steel jacket evaporation kettle, outputting the heat-conducting oil from the top of the jacket, and carrying out heat treatment on the heat-conducting oil containing NMP and H₂Heating the mixed liquid of O, acetic acid and sodium chloride, stirring the mixed liquid at a stirring speed of 56rpm, starting a vacuum pump when the temperature reaches 73.6 ℃, enabling water vapor to flow out of the top of a 316L stainless steel jacket evaporation kettle, cooling the water vapor by a condenser arranged at the top, flowing into a wastewater treatment process, recycling the treated water, and when the 316L stainless steel jacket evaporation kettle is cooled, enabling the water vapor to flow into a 316L stainless steel jacket evaporation kettleThe solution in the evaporation kettle is changed into brown, when crystals are separated out, the viscosity of the mixed liquid is measured to be 4.3cPa.s by an on-line viscometer, when the water content in the mixed liquid is detected to reach 0.7 wt% by liquid chromatography, the residual mixed liquid is input into a solid-liquid separation centrifuge for separation, the solid is light green sodium chloride containing a small amount of NMP and organic impurities, and the input is input into a recovery and drying device of the sodium chloride; inputting the filtrate into an NMP solvent recovery rectifying tower;

(3) inputting the light green sodium chloride solid containing a small amount of NMP and organic impurities separated in the step (2) into a spiral dryer, respectively configuring a phi 60 steam outlet at the front part, the middle part and the tail part of the spiral dryer, connecting the outlet with the lower opening of a condenser tube side, connecting the upper outlet of the condenser tube side with the inlet of a vacuum pump, cooling the steam containing NMP evaporated from the spiral dryer by a condenser, and inputting the steam containing NMP and H₂Acidifying and concentrating the mixed liquid of O, sodium acetate and sodium chloride, then rectifying the mixed liquid in a rectifying tower, inputting cooling water from the lower opening of the shell pass of the condenser, and outputting the cooling water from the upper opening of the shell pass of the condenser to a circulating water storage tank for recycling;

(4) the mixed liquid containing NMP obtained by the separation in the step (2) is input from the middle part of the rectifying tower at the input speed of 5L/min, A20L glass jacketed evaporator was fitted at the lower part of the rectification column, a magnetic stirrer was fitted below the glass jacketed evaporator, and the stirring speed was 44rpm, stirring the unevaporated mixed liquid containing NMP solvent, inputting heat-conducting oil from the bottom of glass jacket evaporator, outputting from the top of glass jacket evaporator, inputting the evaporated NMP steam into condenser arranged on the top of rectifying tower, inputting from the inlet at the bottom of tube pass of condenser, connecting the outlet at the top of condenser with the inlet of vacuum pump, cooling the NMP steam by condenser, flows out from the lower end of the condenser tube side, and after the NMP content is detected to be 99.98 percent wt by a liquid chromatograph, the NMP solvent recovery for this experiment was 97.61% after being transferred to the NMP storage tank.

Comparative example 2

(1) 100L of a mixture containing 35% by weight of NMP, 3.5% by weight of sodium formate, 25% by weight of sodium chloride, 36.5% by weight of sodium chloride are stirred at 50rpmtH₂Inputting the mixed liquid of O into a 316L stainless steel jacket evaporation kettle; the pH value of the mixed liquid measured by an on-line acidimeter is 9.9, the heat-conducting oil is input from the bottom of a jacket of a 316L stainless steel jacket evaporation kettle and output from the top of the jacket, and the mixed liquid containing NMP and H is subjected to reaction₂Heating a mixed liquid of O, sodium formate and sodium chloride, stirring the mixed liquid at a stirring speed of 80rpm, starting a vacuum pump when the temperature reaches 90 ℃, enabling water vapor to flow out of the top of a 316L stainless steel jacket evaporation kettle, cooling the mixed liquid by a condenser arranged at the top, flowing into a wastewater treatment process, treating the wastewater for recycling, inputting the residual mixed liquid into a solid-liquid separation centrifuge for separation when a solution in the 316L stainless steel jacket evaporation kettle is changed into tan and crystals are separated out, measuring the viscosity of the mixed liquid to be 13.9cPa.s by an online viscometer, detecting the water content in the mixed liquid to reach 0.9 wt% by liquid chromatography, and inputting the residual mixed liquid into a recovery and drying device of sodium chloride, wherein the solid is light green sodium chloride containing a small amount of NMP and organic impurities; inputting the filtrate into an NMP solvent recovery rectifying tower;

(2) inputting the light green sodium chloride solid containing a small amount of NMP and organic impurities separated in the step (1) into a spiral dryer, respectively configuring a phi 60 steam outlet at the front part, the middle part and the tail part of the spiral dryer, connecting the outlet with the lower opening of a condenser tube side, connecting the upper outlet of the condenser tube side with the inlet of a vacuum pump, cooling the steam containing NMP evaporated from the spiral dryer by a condenser, and inputting the steam containing NMP and H₂Acidifying and concentrating the mixed liquid of O, sodium formate and sodium chloride, then rectifying the mixed liquid in a rectifying tower, inputting cooling water from the lower opening of the shell pass of a condenser, and outputting the cooling water from the upper opening of the shell pass of the condenser to a circulating water storage tank for recycling;

(3) the mixed liquid containing NMP obtained by the separation in the step (1) is input from the middle part of the rectifying tower at the input speed of 8L/min, A20L glass jacketed evaporator was fitted at the lower part of the rectification column, a magnetic stirrer was fitted below the glass jacketed evaporator, and the stirring speed was 60rpm, stirring the unevaporated mixed liquid containing NMP solvent, inputting heat-conducting oil from the bottom of glass jacket evaporator, outputting from the top of glass jacket evaporator, inputting the evaporated NMP steam into condenser arranged on the top of rectifying tower, inputting from the inlet at the bottom of tube pass of condenser, connecting the outlet at the top of condenser with the inlet of vacuum pump, cooling the NMP steam by condenser, flowing out from the lower end of the condenser tube side, detecting the NMP content of 99.13 wt% by a liquid chromatograph, unqualified NMP is returned to the NMP crude tank for temporary storage, and the recovery rate of NMP solvent in the experiment is 96.72%.

Example 5

(1) 100L of a mixture containing 30.1% wt of NMP, 2.7% wt of sodium propionate, 23.1% wt of sodium chloride, 47.1% wt of WtH at a stirring speed of 43rpm₂Adding 18L of 8% v/v ammonium chloride solution into the mixed liquid of O, and inputting the mixed liquid into a 316L stainless steel jacket evaporation kettle when the pH value of the mixed liquid is 1.5 measured by an on-line acidimeter; at this time, the mixed liquid contained 28.3% by weight of NMP, 24.3% by weight of sodium chloride, 0.5% by weight of excess ammonium chloride, and 44.7% by weight of H₂O, 2.2% wt ammonium propionate;

(2) inputting the acidified mixed solution in the step (1) into a 200L 316L stainless steel jacketed evaporation kettle, inputting heat-conducting oil from the bottom of a jacket of the 316L stainless steel jacketed evaporation kettle, outputting the heat-conducting oil from the top of the jacket, and carrying out treatment on the heat-conducting oil containing NMP and H₂Heating a mixed liquid of O, ammonium propionate and sodium chloride, stirring the mixed liquid at a stirring speed of 57rpm, starting a vacuum pump when the temperature reaches 80.3 ℃, enabling water vapor to flow out of the top of a 316L stainless steel jacket evaporation kettle, cooling the mixed liquid by a condenser arranged at the top, flowing into a wastewater treatment process, recycling the wastewater after treatment, inputting the residual mixed liquid into a solid-liquid separation centrifuge for separation when the solution in the 316L stainless steel jacket evaporation kettle is changed into tan and crystal is separated out, measuring the viscosity of the mixed liquid to be 2.3cPa.s by an online viscometer, and measuring the water content in the mixed liquid to be 0.5 wt% by liquid chromatography, and inputting the residual mixed liquid into a recovery and drying device of sodium chloride, wherein the solid is light green sodium chloride containing a small amount of NMP and organic impurities; inputting the filtrate into an NMP solvent recovery rectifying tower;

(3) inputting the light green sodium chloride solid containing a small amount of NMP and organic impurities separated in the step (2) into a spiral dryer, and respectively configuring a steam outlet with phi 60 at the front part, the middle part and the tail part of the spiral dryerThe outlet is connected with the lower port of the condenser tube pass, the upper outlet of the condenser tube pass is connected with the inlet of the vacuum pump, and the vapor containing NMP evaporated from the spiral dryer is cooled by the condenser and then is input with NMP and H₂After acidification and concentration, the mixed liquid of O, sodium propionate and sodium chloride is rectified in a rectifying tower, cooling water is input from the lower opening of the shell pass of the condenser and is output to a circulating water storage tank from the upper opening of the shell pass of the condenser for recycling;

(4) the mixed liquid containing NMP obtained by the separation in the step (2) is input from the middle part of the rectifying tower at the input speed of 7L/min, A20L glass jacketed evaporator was fitted at the lower part of the rectification column, a magnetic stirrer was fitted below the glass jacketed evaporator, and the stirring speed was 39rpm, stirring the unevaporated mixed liquid containing NMP solvent, inputting heat-conducting oil from the bottom of glass jacket evaporator, outputting from the top of glass jacket evaporator, inputting the evaporated NMP steam into condenser arranged on the top of rectifying tower, inputting from the inlet at the bottom of tube pass of condenser, connecting the outlet at the top of condenser with the inlet of vacuum pump, cooling the NMP steam by condenser, flows out from the lower end of the condenser tube side, and after the NMP content is detected to be 99.97 percent wt by a liquid chromatograph, the NMP solvent recovery for this experiment was 97.74% by volume when transferred to the NMP storage tank.

Example 6

(1) 100L of a mixture containing 28.6% wt of NMP, 2.3% wt of sodium butyrate, 19.6% wt of sodium chloride and 59.5% wt of H at a stirring speed of 43rpm₂Adding 30L of 6% v/v ammonium chloride solution into the mixed liquid of O, and inputting the mixed liquid into a 316L stainless steel jacket evaporation kettle when the pH value of the mixed liquid is 0.8 measured by an on-line acidimeter; at this time, the mixed liquid contained 26.5% by weight of NMP, 23.9% by weight of sodium chloride, 0.7% by weight of excess ammonium chloride, and 46.93% by weight of H₂O, 1.97% wt ammonium butyrate;

(2) inputting the acidified mixed solution in the step (1) into a 200L 316L stainless steel jacket evaporation kettle, inputting heat-conducting oil from the bottom of a jacket of the 316L stainless steel jacket evaporation kettle, outputting the heat-conducting oil from the top of the jacket, and carrying out heat treatment on the heat-conducting oil containing NMP and H₂Heating the mixed liquid of O, butyric acid and sodium chloride, stirring the mixed liquid at a stirring speed of 73rpm, and cooling the mixed liquidWhen the temperature reaches 73.4 ℃, starting a vacuum pump, allowing water vapor to flow out of the top of a 316L stainless steel jacket evaporation kettle, cooling the water vapor by a condenser arranged at the top, allowing the water vapor to flow into a wastewater treatment process, treating the wastewater for recycling, when the solution in the 316L stainless steel jacket evaporation kettle is changed into tan and crystals are separated out, measuring the viscosity of the mixed liquid to be 5.1cPa.s by an online viscometer, detecting the water content in the mixed liquid to reach 0.7 wt% by liquid chromatography, inputting the residual mixed liquid into a solid-liquid separation centrifuge for separation, wherein the solid is green sodium chloride containing a small amount of NMP and organic impurities, and inputting the solid into a shallow sodium chloride recovery and drying device; inputting the filtrate into an NMP solvent recovery rectifying tower;

(3) inputting the light green sodium chloride solid containing a small amount of NMP and organic impurities separated in the step (2) into a spiral dryer, respectively configuring a phi 60 steam outlet at the front part, the middle part and the tail part of the spiral dryer, connecting the outlet with the lower opening of a condenser tube side, connecting the upper outlet of the condenser tube side with the inlet of a vacuum pump, cooling the steam containing NMP evaporated from the spiral dryer by a condenser, and inputting the steam containing NMP and H₂After acidification and concentration, the mixed liquid of O, sodium butyrate and sodium chloride is input into a rectifying tower for rectification, cooling water is input from the lower opening of the shell pass of a condenser and is output from the upper opening of the shell pass of the condenser to a circulating water storage tank for recycling;

(4) the mixed liquid containing NMP obtained by the separation in the step (2) is input from the middle part of the rectifying tower at the input speed of 5L/min, A20L glass jacketed evaporator was fitted at the lower part of the rectification column, a magnetic stirrer was fitted below the glass jacketed evaporator, and stirring speed of 36rpm, stirring the unevaporated mixed liquid containing NMP solvent, inputting heat-conducting oil from the bottom of glass jacket evaporator, outputting from the top of glass jacket evaporator, inputting the evaporated NMP steam into condenser arranged on the top of rectifying tower, inputting from the inlet at the bottom of tube pass of condenser, connecting the outlet at the top of condenser with the inlet of vacuum pump, cooling the NMP steam by condenser, flows out from the lower end of the condenser tube side, and after the NMP content is detected to be 99.96 percent wt by a liquid chromatograph, the NMP solvent recovery for this experiment was 97.71% after being transferred to the NMP storage tank.

Comparative example 3

(1) To 100L of a mixture containing 15% by weight of NMP, 1.5% by weight of sodium formate, 10% by weight of sodium chloride, 73.5% by weight of wtH at a stirring speed of 10rpm₂Adding 36L of 8% v/v ammonium chloride solution into the mixed liquid of O, measuring the pH value of the mixed liquid to be-0.3 by using an on-line acidimeter, and inputting the mixed liquid into a 316L stainless steel jacket evaporation kettle; at this time, the mixed liquid contained 12.7% by weight of NMP, 10.7% by weight of sodium chloride, 0.8% by weight of excess ammonium chloride, 74.47% by weight of H₂O, 1.33% wt. ammonium formate;

(2) inputting the acidified mixed solution in the step (1) into a 200L 316L stainless steel jacketed evaporation kettle, inputting heat-conducting oil from the bottom of a jacket of the 316L stainless steel jacketed evaporation kettle, outputting the heat-conducting oil from the top of the jacket, and carrying out treatment on the heat-conducting oil containing NMP and H₂Heating the mixed liquid of O, ammonium formate and sodium chloride, stirring the mixed liquid at a stirring speed of 30rpm, starting a vacuum pump when the temperature reaches 60 ℃, enabling water vapor to flow out of the top of a 316L stainless steel jacket evaporation kettle, cooling the mixed liquid by a condenser arranged at the top, flowing into a wastewater treatment process, treating the wastewater for recycling, inputting the residual mixed liquid into a solid-liquid separation centrifuge for separation when the solution in the 316L stainless steel jacket evaporation kettle is changed into tan and crystals are crystallized and separated, measuring the viscosity of the mixed liquid to be 7.3cPa.s by an online viscometer, and detecting the water content in the mixed liquid to reach 0.5 percent by weight by liquid chromatography, wherein the solid is light green sodium chloride containing a small amount of NMP and organic impurities, and inputting the residual mixed liquid into a sodium chloride recovery and drying device; inputting the filtrate into an NMP solvent recovery rectifying tower;

(3) inputting the light green sodium chloride solid containing a small amount of NMP and organic impurities separated in the step (2) into a spiral dryer, respectively configuring a phi 60 steam outlet at the front part, the middle part and the tail part of the spiral dryer, connecting the outlet with the lower opening of a condenser tube side, connecting the upper outlet of the condenser tube side with the inlet of a vacuum pump, cooling the steam containing NMP evaporated from the spiral dryer by a condenser, and inputting the steam containing NMP and H₂Acidifying and concentrating the mixed liquid of O, sodium formate and sodium chloride, rectifying in rectifying tower, and introducing cooling water from the lower opening of condenser shell sideThe upper opening of the shell pass of the condenser is output to a circulating water storage tank for recycling;

(4) separating the liquid mixture containing NMP obtained in the step (2), inputting the liquid mixture from the middle part of a rectifying tower at an input speed of 2L/min, assembling a 20L glass jacket evaporator at the lower part of the rectifying tower, assembling a magnetic stirrer below the glass jacket evaporator, stirring the liquid mixture containing the NMP solvent which is not evaporated at a stirring speed of 30rpm, inputting heat conducting oil from the bottom of a glass jacket expander, outputting the heat conducting oil from the top of the glass jacket evaporator, inputting the evaporated NMP steam into a condenser arranged at the top of the rectifying tower, inputting the evaporated NMP steam from a tube pass bottom inlet of the condenser, connecting a top outlet of the condenser with an inlet of a vacuum pump, cooling the NMP steam by the condenser, flowing out from the lower end of a tube pass of the condenser, detecting the NMP content to be 98.98 wt% by a liquid chromatograph, returning the unqualified NMP to a crude NMP temporary storage tank, wherein the recovery rate of the NMP solvent in the experiment is 95, the mixed liquid evaporated after acidification was examined and NMP ring-opening compound was found to be present.

Example 7

(1) To 100L of a solution containing 22% by weight of NMP, 3.3% by weight of sodium acetate, 23.7% by weight of sodium chloride, 51% by weight of wtH at a stirring speed of 23rpm₂Adding 29L of 7% v/v ammonium chloride solution into the O mixed liquid, and inputting the mixed liquid into a 316L stainless steel jacket evaporation kettle when the pH value of the mixed liquid is 3.6 measured by an on-line acidimeter; at this time, the mixed liquid contained 19.2% by weight of NMP, 20.3% by weight of sodium chloride, 0.3% by weight of excess ammonium chloride, and 57.2% by weight of H₂O, 3.0% wt ammonium acetate;

(2) inputting the acidified mixed solution in the step (1) into a 200L 316L stainless steel jacketed evaporation kettle, inputting heat-conducting oil from the bottom of a jacket of the 316L stainless steel jacketed evaporation kettle, outputting the heat-conducting oil from the top of the jacket, and carrying out treatment on the heat-conducting oil containing NMP and H₂Heating the mixed liquid of O, ammonium acetate and sodium chloride, stirring the mixed liquid at a stirring speed of 61rpm, starting a vacuum pump when the temperature reaches 83.8 ℃, enabling water vapor to flow out of the top of a 316L stainless steel jacket evaporation kettle, cooling the water vapor by a condenser arranged at the top, flowing into a wastewater treatment process, recycling the treated water, and changing the solution in the 316L stainless steel jacket evaporation kettle into brown,when crystals are crystallized and precipitated, the viscosity of the mixed liquid is 3.31cPa.s measured by an on-line viscometer, and when the water content in the mixed liquid reaches 0.6 wt% through liquid chromatography, the rest mixed liquid is input into a solid-liquid separation centrifuge for separation, the solid is light green sodium chloride containing a small amount of NMP and organic impurities, and the solid is input into a recovery and drying device of the sodium chloride; inputting the filtrate into an NMP solvent recovery rectifying tower;

(4) the mixed liquid containing NMP obtained by the separation in the step (2) is input from the middle part of the rectifying tower at the input speed of 3.7L/min, A20L glass jacketed evaporator was fitted at the lower part of the rectification column, a magnetic stirrer was fitted below the glass jacketed evaporator, and the stirring speed was 48rpm, stirring the unevaporated mixed liquid containing NMP solvent, inputting heat-conducting oil from the bottom of glass jacket evaporator, outputting from the top of glass jacket evaporator, inputting the evaporated NMP steam into condenser arranged on the top of rectifying tower, inputting from the inlet at the bottom of tube pass of condenser, connecting the outlet at the top of condenser with the inlet of vacuum pump, cooling the NMP steam by condenser, flows out from the lower end of the condenser tube side, and after the NMP content is detected to be 99.96wt by a liquid chromatograph, the NMP solvent recovery from this experiment was 97.95% by volume when transferred to the NMP storage tank.

Example 8

(1) 100L of a mixture containing 30.3% by weight of NMP, 2.6% by weight of sodium benzoate, 14.6% by weight of sodium chloride, 52.5% by weight of wtH at a stirring speed of 47rpm₂Adding into mixed liquid of O30L of 3v/v ammonium chloride solution, and when the pH value of the mixed liquid is 3.4 measured by an on-line acidimeter, inputting the mixed liquid into a 316L stainless steel jacket evaporation kettle; at this time, the mixed liquid contained 25.7% by weight of NMP, 18.7% by weight of sodium chloride, 0.4% by weight of excess ammonium chloride, and 54.2% by weight of H₂O, 1.0% wt. ammonium benzoate;

(2) inputting the acidified mixed solution in the step (1) into a 200L 316L stainless steel jacketed evaporation kettle, inputting heat-conducting oil from the bottom of a jacket of the 316L stainless steel jacketed evaporation kettle, outputting the heat-conducting oil from the top of the jacket, and carrying out treatment on the heat-conducting oil containing NMP and H₂Heating a mixed liquid of O, ammonium benzoate, acetic acid and sodium chloride, stirring the mixed liquid at a stirring speed of 57rpm, starting a vacuum pump when the temperature reaches 86.4 ℃, enabling water vapor to flow out of the top of a 316L stainless steel jacket evaporation kettle, cooling the mixed liquid by a condenser arranged at the top, flowing into a wastewater treatment process, and recycling the treated mixed liquid, when a solution in the 316L stainless steel jacket evaporation kettle is changed into tan and crystal is crystallized and separated, measuring the viscosity of the mixed liquid to be 4.7cPa.s by using an in-line viscometer, and detecting the water content in the mixed liquid to reach 0.8 wt% by using a liquid chromatography, inputting the rest mixed liquid into a solid-liquid separation centrifuge for separation, wherein the solid is light green sodium chloride containing a small amount of NMP and organic impurities, and inputting the mixed liquid into a sodium chloride recovery and drying device; inputting the filtrate into an NMP solvent recovery rectifying tower;

(4) the mixed liquid containing NMP obtained by the separation in the step (2) is input from the middle part of the rectifying tower at the input speed of 7.1L/min, A20L glass jacketed evaporator was fitted at the lower part of the rectification column, a magnetic stirrer was fitted below the glass jacketed evaporator, and the stirring speed was 52rpm, stirring the unevaporated mixed liquid containing NMP solvent, inputting heat-conducting oil from the bottom of glass jacket evaporator, outputting from the top of glass jacket evaporator, inputting the evaporated NMP steam into condenser arranged on the top of rectifying tower, inputting from the inlet at the bottom of tube pass of condenser, connecting the outlet at the top of condenser with the inlet of vacuum pump, cooling the NMP steam by condenser, flows out from the lower end of the condenser tube side, and after the NMP content is detected to be 99.97 percent wt by a liquid chromatograph, the NMP solvent recovery for this experiment was 97.71% after being transferred to the NMP storage tank.

Example 9

(1) 100L of a mixture containing 30.1% wt of NMP, 2.7% wt of sodium propionate, 23.1% wt of sodium chloride, 47.1% wt of WtH at a stirring speed of 43rpm₂Adding 18L of hydrochloric acid solution with the concentration of 8% v/v into the mixed liquid of O, and inputting the mixed liquid into a 316L stainless steel jacket evaporation kettle when the pH value of the mixed liquid is 1.5 measured by an on-line acidimeter; at this time, the mixed liquid contained 28.3% by weight of NMP, 24.3% by weight of sodium chloride, 0.5% by weight of excess hydrochloric acid, 44.7% by weight of H₂O, 2.2% wt propionic acid;

(2) inputting the acidified mixed solution in the step (1) into a 200L 316L stainless steel jacketed evaporation kettle, inputting heat-conducting oil from the bottom of a jacket of the 316L stainless steel jacketed evaporation kettle, outputting the heat-conducting oil from the top of the jacket, and carrying out treatment on the heat-conducting oil containing NMP and H₂Heating the mixed liquid of O, propionic acid and sodium chloride, stirring the mixed liquid at a stirring speed of 57rpm, starting a vacuum pump when the temperature reaches 80.3 ℃, enabling water vapor to flow out of the top of a 316L stainless steel jacket evaporation kettle, cooling the mixed liquid by a condenser arranged at the top, flowing into a wastewater treatment process, recycling the wastewater after treatment, inputting the residual mixed liquid into a solid-liquid separation centrifuge for separation when the solution in the 316L stainless steel jacket evaporation kettle is changed into tan and crystal is separated out, measuring the viscosity of the mixed liquid to be 2.3cPa.s by an online viscometer, and measuring the water content in the mixed liquid to reach 0.5 percent by weight by liquid chromatography, and inputting the residual mixed liquid into a recovery and drying device of sodium chloride, wherein the solid is light green sodium chloride containing a small amount of NMP and organic impurities; the filtrate is fed into NMP solventA rectifying tower is collected;

(3) inputting the light green sodium chloride solid containing a small amount of NMP and organic impurities separated in the step (2) into a spiral dryer, respectively configuring a phi 60 steam outlet at the front part, the middle part and the tail part of the spiral dryer, connecting the outlet with the lower opening of a condenser tube side, connecting the upper outlet of the condenser tube side with the inlet of a vacuum pump, cooling the steam containing NMP evaporated from the spiral dryer by a condenser, and inputting the steam containing NMP and H₂After acidification and concentration, the mixed liquid of O, sodium propionate and sodium chloride is rectified in a rectifying tower, cooling water is input from the lower opening of the shell pass of the condenser and is output to a circulating water storage tank from the upper opening of the shell pass of the condenser for recycling;

(4) the mixed liquid containing NMP obtained by the separation in the step (2) is input from the middle part of the rectifying tower at the input speed of 7L/min, A20L glass jacketed evaporator was fitted at the lower part of the rectification column, a magnetic stirrer was fitted below the glass jacketed evaporator, and the stirring speed was 39rpm, stirring the unevaporated mixed liquid containing NMP solvent, inputting heat-conducting oil from the bottom of glass jacket evaporator, outputting from the top of glass jacket evaporator, inputting the evaporated NMP steam into condenser arranged on the top of rectifying tower, inputting from the inlet at the bottom of tube pass of condenser, connecting the outlet at the top of condenser with the inlet of vacuum pump, cooling the NMP steam by condenser, flows out from the lower end of the condenser tube side, and after the NMP content is detected to be 99.98 percent wt by a liquid chromatograph, the NMP solvent recovery for this experiment was 97.73% by transferring to the NMP storage tank.

Comparative example 4

(1) 100L of a mixture containing 30.1% wt of NMP, 2.5% wt of sodium butyrate, 18.6% wt of sodium chloride, 48.9% wt of WtH, with a stirring speed of 43rpm₂Adding 13L of hydrochloric acid solution with the concentration of 13% v/v into the mixed liquid of O, inputting the mixed liquid into a 316L stainless steel jacket evaporation kettle when the pH value of the mixed liquid is measured to be-0.1 by an on-line acidimeter; at this time, the mixed liquid contained 28.4% by weight of NMP, 2.1% by weight of butyric acid, 20.6% by weight of sodium chloride, 0.5% by weight of excess hydrochloric acid, 48.4% by weight of H₂O；

(2) The acidified mixed solution of (1) was introduced into 3 of 200LThe 16L stainless steel jacket evaporation kettle, the heat-conducting oil is input from the bottom of the jacket of the 316L stainless steel jacket evaporation kettle, the heat-conducting oil is output from the top of the jacket, and the heat-conducting oil is used for carrying out heat exchange on the heat-conducting oil containing NMP and H₂Heating the mixed liquid of O, butyric acid and sodium chloride, stirring the mixed liquid at a stirring speed of 63rpm, starting a vacuum pump when the temperature reaches 76.1 ℃, enabling water vapor to flow out of the top of a 316L stainless steel jacket evaporation kettle, cooling the mixed liquid by a condenser arranged at the top, flowing into a wastewater treatment process, recycling the treated mixed liquid, inputting the residual mixed liquid into a solid-liquid separation centrifuge for separation when the solution in the 316L stainless steel jacket evaporation kettle is changed into tan and crystal is separated out, measuring the viscosity of the mixed liquid to be 13.7cPa.s by an online viscometer, and measuring the water content in the mixed liquid to reach 0.7 wt% by liquid chromatography, wherein the solid is light green sodium chloride containing a small amount of NMP and organic impurities, and inputting the solid into a sodium chloride recovery and drying device; inputting the filtrate into an NMP solvent recovery rectifying tower;

(3) inputting the light green sodium chloride solid containing a small amount of NMP and organic impurities separated in the step (2) into a spiral dryer, respectively configuring a phi 60 steam outlet at the front part, the middle part and the tail part of the spiral dryer, connecting the outlet with the lower opening of a condenser tube side, connecting the upper outlet of the condenser tube side with the inlet of a vacuum pump, cooling the steam containing NMP evaporated from the spiral dryer by a condenser, and inputting the steam containing NMP and H₂Acidifying and concentrating the mixed liquid of O and sodium chloride, and then rectifying the mixed liquid in a rectifying tower, wherein cooling water is input from the lower opening of the shell side of the condenser and output from the upper opening of the shell side of the condenser to a circulating water storage tank for recycling;

(4) separating the liquid mixture containing NMP obtained in the step (2), inputting the liquid mixture from the middle part of a rectifying tower at the input speed of 6L/min, assembling a 20L glass jacket evaporator at the lower part of the rectifying tower, assembling a magnetic stirrer below the glass jacket evaporator, stirring the liquid mixture containing the NMP solvent which is not evaporated at the stirring speed of 49rpm, inputting heat conducting oil from the bottom of a glass jacket expander, outputting the heat conducting oil from the top of the glass jacket evaporator, inputting the evaporated NMP steam into a condenser arranged at the top of the rectifying tower, inputting the evaporated NMP steam from a tube pass bottom inlet of the condenser, connecting a top outlet of the condenser with an inlet of a vacuum pump, cooling the NMP steam by the condenser, flowing out from the lower end of a tube pass of the condenser, returning unqualified NMP to a crude NMP temporary storage tank after the NMP content is detected to be 98.93 percent by a liquid chromatograph, wherein the recovery rate of the NMP solvent in the experiment is 95, the mixed liquid evaporated after acidification was examined and NMP ring-opening compound was found to be present.

Claims

1. A solvent recovery process in the production process flow of polyphenylene sulfide adopts sodium sulfide dihydrate and p-dichlorobenzene as raw materials, N-methyl-2-pyrrolidone as a solvent, and polyphenylene sulfide resin is synthesized and produced through the process steps of dehydration, polycondensation and the like, and is characterized in that: wherein the filter cake is a mixture of polyphenylene sulfide resin, sodium chloride and NMP solvent, and the filtrate is NMP and H₂Adding a certain amount of water-soluble acidic substance into the filtrate, converting the alkali metal organic acid salt in the filtrate into organic acid and alkali metal water-soluble salt-sodium chloride, removing the organic acid and water by reduced pressure evaporation, and then distilling and purifying the NMP solvent containing a small amount of water to recover the NMP solvent used for synthesizing the polyphenylene sulfide resin; the NMP solvent recovery process flow comprises the following steps:

(1) adding NMP and H to 100L at a stirring speed of 10-50 rpm₂Adding 10-30L of water-soluble acidic liquid with the concentration of 3-8% v/v into a mixed liquid of O, alkali metal organic acid salt and sodium chloride at the flow rate of 0.3-0.8L/min, and inputting the mixed liquid into a 316L stainless steel jacket evaporation kettle when the pH value of the mixed liquid is measured to be 0-4 by using an on-line acidimeter;

(2) inputting the acidified mixed solution obtained in the step (1) into a 200L 316L stainless steel jacket evaporation kettle, inputting heat conducting oil from the bottom of a jacket of the 316L stainless steel jacket evaporation kettle, and outputting the heat conducting oil from the top of the jacket to the evaporation kettle containing NMP and H₂Heating the mixed liquid of O, organic acid and sodium chloride, stirring the mixed liquid at a stirring speed of 30-80 rpm, starting a vacuum pump when the temperature reaches 60-90 ℃, allowing water vapor to flow out of the top of a 316L stainless steel jacket evaporation kettle, cooling the mixture by a condenser arranged at the top,flowing into a wastewater treatment process, treating and recycling, wherein when a solution in a 316L stainless steel jacket evaporation kettle is changed into brown, when crystals are separated out, the viscosity of the mixed liquid is measured to be 2.0-6.0 cPa.s by an online viscometer, and when the water content in the mixed liquid reaches 1.5-1.8% by weight by liquid chromatography, inputting the mixed liquid into a solid-liquid separation centrifuge for separation, and inputting light green sodium chloride solid containing a small amount of NMP and organic impurities into a sodium chloride recovery and drying device; inputting the filtrate into an NMP solvent recovery rectifying tower;

(3) inputting the light green sodium chloride solid containing a small amount of NMP and organic impurities separated in the step (2) into a spiral dryer, respectively configuring a phi 60 steam outlet at the front part, the middle part and the tail part of the spiral dryer, connecting the outlet with the lower opening of a condenser tube pass, connecting the upper outlet of the condenser tube pass with the inlet of a vacuum pump, cooling the steam containing NMP evaporated from the spiral dryer by a condenser, and inputting the steam containing NMP and H₂The method comprises the following steps of (1) acidifying and concentrating mixed liquid of O, alkali metal organic acid salt and sodium chloride, then inputting the mixed liquid into a rectifying tower for rectification, inputting cooling water from a lower opening of a shell pass of a condenser, outputting the cooling water from an upper opening of the shell pass of the condenser to a circulating water storage tank, and recycling the cooling water;

(4) inputting the mixed liquid containing NMP obtained by the separation in the step (2) from the middle part of a rectifying tower at an input speed of 2-8L/min, assembling a 20L glass jacket evaporator at the lower part of the rectifying tower, assembling a magnetic stirrer below the glass jacket evaporator, stirring the mixed liquid containing the NMP solvent which is not evaporated at a stirring speed of 30-60 rpm, inputting heat conduction oil from the bottom of the glass jacket expander, outputting the heat conduction oil from the top of the glass jacket evaporator, inputting the evaporated NMP steam into a condenser arranged at the top of the rectifying tower, inputting the NMP steam from a tube pass bottom inlet of the condenser, connecting a top outlet of the condenser with an inlet of a vacuum pump, cooling the NMP steam by the condenser, flowing out from the lower end of a tube pass of the condenser, detecting the NMP content to be 99.96-99.98% wt by a liquid chromatograph, inputting the NMP into a NMP storage tank, returning the unqualified NMP to a crude product temporary storage tank, and then inputting the water into an NMP rectifying tower for rectification and purification again, inputting cooling water of a condenser from an inlet at the bottom of a shell pass of the condenser, outputting the cooling water from the upper part of the shell pass of the condenser, flowing into a circulating water storage tank, and cooling the water for reuse.

2. The solvent recovery process in the polyphenylene sulfide production process flow according to claim 1, characterized in that: the water-soluble acidic liquid is hydrochloric acid and ammonium chloride aqueous solution.

3. The solvent recovery process in the polyphenylene sulfide production process flow according to claim 1, characterized in that: the alkali metal organic acid salt is sodium benzoate, sodium formate, sodium acetate, sodium propionate and sodium butyrate; the organic acid is benzoic acid, formic acid, acetic acid, propionic acid or butyric acid.

4. The solvent recovery process in the polyphenylene sulfide production process flow according to claim 1, characterized in that: the composition contains NMP and H₂The mixed liquid of O, alkali metal organic acid salt and sodium chloride contains 15-35 wt% of NMP, 1.5-3.5 wt% of alkali metal organic acid salt, 10-25 wt% of sodium chloride and 36.5-71.5 wt% of wtH₂O。

5. The solvent recovery process in the polyphenylene sulfide production process flow according to claim 1, characterized in that: the composition contains NMP and H₂The acidified mixed liquid of O, alkali metal organic acid salt and sodium chloride contains 10-30 wt% of NMP, 11-28 wt% of sodium chloride and 44.2-78.7 wt% of wtH₂O and 0.3-0.8 wt% of excessive water-soluble acid.

6. The solvent recovery process in the polyphenylene sulfide production process flow according to claim 2, characterized in that: when the water-soluble acidic liquid is ammonium chloride, the mixed liquid contains ammonium benzoate, ammonium formate, ammonium acetate, ammonium propionate and ammonium butyrate; the content is 1.0-3.0 wt%.