CN110563999A

CN110563999A - Aramid fiber solvent membrane extraction separation method

Info

Publication number: CN110563999A
Application number: CN201810573890.3A
Authority: CN
Inventors: 于品华; 孔凡敏; 王祥云
Original assignee: China Petrochemical Corp; Research Institute of Sinopec Nanjing Chemical Industry Co Ltd
Current assignee: China Petroleum and Chemical Corp; China Petrochemical Corp; Research Institute of Sinopec Nanjing Chemical Industry Co Ltd
Priority date: 2018-06-06
Filing date: 2018-06-06
Publication date: 2019-12-13

Abstract

A membrane extraction separation process for aramid fiber solvent, which adopts a hollow fiber membrane extractor to remove the solvent in PPTA washing water and simultaneously recover cosolvent and water, belongs to the technical field of polymer material synthesis. Filtering PPTA washing water, pumping the PPTA washing water into a shell pass of a membrane extractor by a solvent pump, injecting an extracting agent into a tube pass of the membrane extractor by the solvent pump, carrying out countercurrent mass transfer on the extracting agent and the PPTA washing water in the membrane extractor, transferring the solvent from a water phase to an extraction phase, and then removing the solvent from a solvent recovery system. After the raffinate phase is crystallized, water and cosolvent are respectively recycled. Compared with the prior common extraction method, the method avoids mutual pollution of the extracting agent and the solvent, has the advantages of low investment, low energy consumption and simple operation, and is particularly suitable for recovering the solvent in the PPTA resin synthesis washing water.

Description

Aramid fiber solvent membrane extraction separation method

Technical Field

An aramid fiber solvent membrane extraction separation process belongs to the field of polymer material synthesis, and is used for recovering a solvent and a cosolvent from an aramid fiber resin washing solvent.

Background

Poly-p-phenylene terephthalamide (PPTA) is an important polymer material and is generally prepared by low-temperature polycondensation of p-phenylene diamine and terephthaloyl chloride in an N-methylpyrrolidone (NMP) -calcium chloride system, wherein NMP is used as a solvent, and calcium chloride is used as a cosolvent. The hydrogen chloride produced during the polycondensation is neutralized by the addition of calcium oxide or calcium hydroxide. After the polycondensation reaction is completed, the PPTA resin is usually washed with water to remove residual solvent, cosolvent, and salt. The washing water therefore contains, in addition to water, also the N-methylpyrrolidone solvent, calcium chloride and unreacted starting materials and oligomers. Since NMP is expensive, a large amount of NMP solvent contained in the washing water is generally recovered to reduce production costs. At present, the recovery method of NMP in PPTA resin washing water is roughly divided into two methods: one is a vacuum distillation method and the other is an extraction method.

CN1445266A discloses a double-tower vacuum rectification refining method, washing water is firstly sent into a dehydration tower to be dehydrated under the vacuum degree of-0.88 ~ -0.095 MPa, then tower bottom solvent is sent into a recovery tower, NMP is recovered by rectification under the pressure of-0.09 ~ -0.098MPa, such as CN1112140, CN201089749Y, CN102268142B, CN101289548B and the like, on the basis of rectification or by changing evaporation equipment or changing evaporation sequence or adding auxiliary process and the like, and the problem of recovering NMP by a reduced pressure rectification method is that (1) the vacuum operation environment is large, the equipment investment is difficult to operate, (2) oligomers and cosolvent contained in mixed liquor are easy to block the rectification tower, the solvent in residual liquor is difficult to recover, and (3) a large amount of water is directly evaporated from the solvent, and the energy consumption is high.

CN101550233B discloses a solvent extraction method for recovering NMP, wherein washing water obtained by washing synthetic resin is extracted by adopting a halogenated hydrocarbon extractant, and then water obtained by stripping raffinate is used for washing resin, and the extractant is recycled; after the extraction phase is rectified and layered, the extractant and the water are recycled, and the obtained NMP crude product is recycled after being rectified and purified under reduced pressure. The extraction method avoids the step of vacuum distillation and water removal in double-tower distillation, and the energy consumption is greatly reduced. However, the following problems still remain: (1) the extractant has residue in raffinate phase, and a recovery procedure is required to be added; (2) the extraction phase contains certain water and needs to be dewatered; (3) NMP still needs rectification and refining under reduced pressure, and the equipment investment is large.

Aiming at the problems of the prior process for recovering the NMP solvent in PPTA washing water, the method for recovering the NMP solvent is necessary to be developed, which can overcome the defects of vacuum rectification and common extraction method simultaneously, so as to solve the problems of high energy consumption, large investment and solvent entrainment of the extraction method in the rectification method. One of the series of the invention adopts a membrane extraction method to replace a commonly used extraction mode, thereby fundamentally solving the problem of mutual pollution between an extracting agent and an extracted solution in the common extraction process.

Disclosure of Invention

The invention aims to provide a membrane extraction separation method for aramid fiber solvent, which separates an extracting agent from an extracted phase by adopting a membrane extractor, not only efficiently recovers NMP, but also avoids mutual pollution of the extracting agent and the extracted phase.

The invention is realized by the following steps: the aramid fiber solvent membrane extraction separation process comprises the steps of filtering PPTA washing water containing water, a cosolvent, a solvent and a small amount of unreacted monomers to remove impurities and crystals, and then feeding the PPTA washing water into a membrane extractor; in the membrane extractor, the solvent is removed by countercurrent contact of the extractant and the washing water.

Generally, aramid fiber washing water containing water, a solvent, a cosolvent, a small amount of PPTA resin and unreacted monomers is filtered to remove most of solid impurities, and then the aramid fiber washing water is pumped into a shell pass of a membrane extractor through a solvent pump, meanwhile, an extractant from an extractant tank is pumped into a tube pass of the membrane extractor through the solvent pump, the extractant and the aramid fiber washing water are in countercurrent contact for mass transfer in the membrane extractor, the solvent in the washing water is extracted to enter an extraction phase, and the water and the cosolvent are left in a raffinate phase. The raffinate phase after solvent removal from the shell pass of the membrane extractor mainly comprises water and cosolvent, the main components are directly fed into a crystallizer, the cosolvent is separated out and separated from water after cooling crystallization, the water and the cosolvent are simultaneously recycled, and the extract phase is fed into a solvent recovery system.

The solvent in the PPTA washing water is mother liquor containing the solvent, a cosolvent, water and trace oligomers, which is generated by multi-stage water washing in the process of synthesizing the PPTA resin by low-temperature solution polycondensation.

The solvent is one or more of N-methyl pyrrolidone (NMP), N-ethyl pyrrolidone and hexamethylene phosphoric triamide.

The cosolvent is mainly alkali metal salt, generally calcium chloride, lithium chloride, stannic chloride and magnesium chloride.

The trace oligomer refers to monomer and PPTA resin which do not participate in reaction.

The structure of the membrane extractor is hollow fiber type, and the hollow fiber membrane material adopts a polytetrafluoroethylene microporous membrane.

In the practical operation of the membrane extractor, the liquid trend is that an extracting agent passes through a tube side, a PPTA washing solvent passes through a shell side, and the extracting agent and the PPTA washing solvent are in countercurrent contact mass transfer.

The extractant refers to dichloromethane, chloroform, trichloroethylene, dichloroethylene and tetrachloroethylene, and dichloromethane and chloroform are preferred.

The advantages and the achieved effects of the invention are as follows: a process for extracting and separating aramid fibres by solvent membrane features that the hydrophobic microporous membrane is used to separate the extracted phase from the extracted phase, and the solute in the extracted phase is dissolved and diffused in the extracted phase in the countercurrent contact procedure. Compared with common stirring or centrifugal extraction, the extraction agent and the extracted phase are not macroscopically mixed, so that the mutual pollution is reduced, the recovery rate of the solute is effectively improved, and the loss of the extraction agent is reduced. The cosolvent and water in the raffinate phase are recycled after crystallization and separation. Is particularly suitable for recycling the solvent in the PPTA synthesis industry.

Drawings

FIG. 1 is a schematic diagram of a process flow of the aramid fiber solvent membrane extraction separation of the embodiment.

In the figure, 1 is a filter, 2 is a solvent pump 1, 3 is a membrane extractor, 4 is an extractant tank, and 5 is a solvent pump 2, 6 is a crystallizer.

Detailed Description

The invention is described in further detail below with reference to the figures and examples.

The process flow of the aramid fiber solvent membrane extraction separation of the following examples is shown in the attached figure 1.

Example 1

The washing solvent composed of N-methyl pyrrolidone (NMP), calcium chloride, water, oligomer and the like is stored in a storage tank, solid impurities are removed by filtration, and the washing solvent is pumped into the shell side of a membrane extractor by a solvent pump. The extracting agent adopts trichloromethane, the extracting agent in the extracting agent storage tank is injected into the tube side of the membrane extractor by a solvent pump, and the solvent in the washing water completes mass transfer to the extracting agent in the membrane extractor. The extract phase is sent to a solvent recovery system, and the residual rate of NMP in the raffinate phase is less than 0.5 percent (mass percentage concentration) through detection. Recovering cosolvent CaCl from raffinate phase in membrane extractor by crystallization₂And then, respectively recycling the water and the cosolvent.

Example 2

The washing solvent composed of N-ethyl pyrrolidone, lithium chloride, water, oligomer and the like is stored in a storage tank, solid impurities are removed through filtration, and the washing solvent is pumped into the shell side of a membrane extractor through a solvent pump. The extractant adopts dichloromethane, the extractant in the extractant storage tank is injected into the tube side of the membrane extractor by a solvent pump, and the mass transfer of the solvent in the washing water to the extractant is completed in the membrane extractor. The extract phase is sent to a solvent recovery system, and the residue rate of the N-ethyl pyrrolidone in the raffinate phase is detected to be less than 0.7 percent (mass percentage concentration). After the raffinate phase in the membrane extractor is crystallized to recover the cosolvent lithium chloride, water and the cosolvent are respectively recycled.

Example 3

The washing solvent composed of N-methyl pyrrolidone, magnesium chloride, water, oligomer and the like is stored in a storage tank, solid impurities are removed through filtration, and the washing solvent is pumped into the shell side of a membrane extractor through a solvent pump. The extractant is dichloroethane, the extractant in the extractant storage tank is injected into the tube side of the membrane extractor by a solvent pump, and the mass transfer of the solvent in the washing water to the extractant is completed in the membrane extractor. The extract phase is sent to a solvent recovery system, and the residue rate of the N-methyl pyrrolidone in the raffinate phase is detected to be less than 0.6 percent (mass percentage concentration). After the raffinate phase in the membrane extractor is crystallized to recover the cosolvent magnesium chloride, water and the cosolvent are respectively recycled.

Example 4

The washing solvent composed of N-ethyl pyrrolidone, tin chloride, water, oligomer and the like is stored in a storage tank, solid impurities are removed through filtration, and the washing solvent is pumped into the shell side of a membrane extractor through a solvent pump. The extractant is trichloroethylene, the extractant in the extractant storage tank is injected into the tube side of the membrane extractor by a solvent pump, and the mass transfer of the solvent in the washing water to the extractant is completed in the membrane extractor. The extract phase is sent to a solvent recovery system, and the residue rate of the N-ethyl pyrrolidone in the raffinate phase is detected to be less than 0.8 percent (mass percentage concentration). After the raffinate phase in the membrane extractor is crystallized to recover the cosolvent tin chloride, water and the cosolvent are respectively recycled.

Claims

1. A membrane extraction separation method for aramid fiber solvent is characterized in that PPTA washing water containing water, cosolvent, solvent and a small amount of unreacted monomers is filtered to remove impurities and crystals, and then enters a membrane extractor; in the membrane extractor, the solvent is removed by countercurrent contact of the extractant and the washing water.

2. The aramid fiber solvent membrane extraction separation method as claimed in claim 1, wherein the extract phase in the membrane extractor is sent to a solvent recovery system, the raffinate phase in the membrane extractor is an aqueous solution containing a cosolvent, and the solid cosolvent and water are recycled after crystallization.

3. The aramid fiber solvent membrane extraction separation method as claimed in claim 1, wherein the structural form of the membrane extractor is a hollow fiber type.

4. The aramid fiber solvent membrane extraction separation method as claimed in claim 3, wherein the membrane material type of the membrane extractor is polytetrafluoroethylene microporous membrane.

5. The aramid fiber solvent membrane extraction separation method as claimed in claim 1 or 2, characterized in that the extractant in the membrane extractor passes through the tube side, the PPTA washing water passes through the shell side, and the two are countercurrent mass transfer.

6. The aramid fiber solvent membrane extraction separation method according to claim 1, characterized in that the solvent is one or more of N-methyl pyrrolidone (NMP), N-ethyl pyrrolidone, hexamethylene phosphoric triamide.

7. The method for extracting and separating the aramid fiber solvent film as claimed in claim 1, wherein the extractant is one or more selected from dichloromethane, chloroform, dichloroethylene, trichloroethylene and tetrachloroethane.

8. The method for separating aramid fiber from solvent by membrane extraction as claimed in claim 7, wherein the extractant is dichloromethane, chloroform, trichloroethylene, dichloroethylene or tetrachloroethylene.

9. The method for separating aramid fiber solvent by membrane extraction as claimed in claim 8, wherein the extractant is dichloromethane or chloroform.

10. The aramid fiber solvent membrane extraction separation method as claimed in claim 1, wherein the cosolvent is calcium chloride, lithium chloride, tin chloride or magnesium chloride.