CN-122007105-A - Method for cleaning liquid crystal polyester reaction kettle

Abstract

A cleaning method of a liquid crystal polyester reaction kettle belongs to the technical field of cleaning of high polymer material production equipment. The method comprises the steps of adding a cleaning composition A into a reaction kettle from which liquid crystal polyester is discharged, wherein the cleaning composition A comprises alkali metal hydroxide and dihydric alcohol with the boiling point of more than 150 ℃, heating the cleaning composition A to the temperature of 10-30 ℃ higher than the boiling point of the dihydric alcohol, carrying out reflux cleaning, discharging and collecting cleaning waste liquid, adding a cleaning composition B into the reaction kettle, wherein the cleaning composition B is by-product acetic acid in the production process of the liquid crystal polyester, carrying out heat reflux cleaning, discharging pickling waste liquid after the cleaning is finished, washing with water, carrying out reduced pressure distillation treatment on the discharged and collected cleaning waste liquid, neutralizing the distilled kettle residual liquid to a pH value of 2-5, and separating out polymer monomers and recycling. The method has the advantages of reducing energy consumption, lowering comprehensive cleaning cost, reducing wastewater discharge, having excellent cleaning effect on the adherents on the inner wall of the reaction kettle and the fractionating column, and lowering production cost.

Inventors

• Song Juye
• ZHANG FENGSHOU
• WANG LUQIAN
• WANG YUANCHAO
• MA XINYUAN
• YANG ZHENG

Assignees

• 苏州纤美达材料科技有限公司
• 平顶山纤美达材料科技有限公司

Dates

Publication Date

20260512

Application Date

20260327

Claims (10)

1. 1. A cleaning method of a liquid crystal polyester reaction kettle is characterized by comprising the following steps: A) Alkali alcohol cleaning, namely adding a cleaning composition A into a reaction kettle from which liquid crystal polyester is discharged, wherein the cleaning composition A comprises alkali metal hydroxide and dihydric alcohol with the boiling point of more than 150 ℃, the mass concentration of the alkali metal hydroxide is 5-10%, heating the cleaning composition A to the temperature of 10-30 ℃ above the boiling point of the dihydric alcohol, carrying out reflux cleaning, discharging and collecting cleaning waste liquid; B) Acid washing, namely adding a cleaning composition B into the reaction kettle cleaned in the step A), wherein the cleaning composition B is byproduct acetic acid in the production process of the liquid crystal polyester, and the mass concentration of the byproduct acetic acid is more than or equal to 90 percent; c) Washing, namely adding deionized water into the reaction kettle subjected to the acid washing in the step B), and heating, refluxing and cleaning; D) Recovering the dihydric alcohol, namely carrying out reduced pressure distillation treatment on the cleaning waste liquid discharged and collected in the step A), wherein the distillation vacuum degree is-0.095 MPa to-0.05 MPa, and the distillation temperature is 80-150 ℃, and recovering the dihydric alcohol; e) And D) monomer recovery, namely neutralizing the residual liquid of the kettle obtained in the step D) to a pH value of 2-5, separating out polymer monomers and recovering.
2. 2. The method for cleaning a liquid crystal polyester reactor according to claim 1, wherein the mass concentration of the alkali metal hydroxide in the step A) is 6-8%, the cleaning temperature is 15-25 ℃ above the boiling point of dihydric alcohol, and the reflux cleaning time is 3-5 hours.
3. 3. The method for cleaning a liquid crystal polyester reactor according to claim 1 or 2, wherein the dihydric alcohol with a boiling point of more than 150 ℃ is one or more of ethylene glycol, 1, 2-propylene glycol, 1, 3-propylene glycol, 1, 4-butanediol, 1, 5-pentanediol and 1, 6-hexanediol, and the alkali metal hydroxide is sodium hydroxide and/or potassium hydroxide.
4. 4. The method for cleaning a liquid crystal polyester reactor according to claim 1, wherein the mass concentration of the byproduct acetic acid in the step B) is 95-98%, the temperature of the heating reflux cleaning is 105-115 ℃ and the time is 1.5-2.5 hours.
5. 5. The method for cleaning a liquid crystal polyester reactor according to claim 1, wherein the washing step in the step C) is repeated 1 to 3 times.
6. 6. The method for cleaning a liquid crystal polyester reactor according to claim 1, wherein the vacuum degree of reduced pressure distillation in the step D) is-0.09 MPa to-0.06 MPa, and the distillation temperature is 90-140 ℃.
7. 7. The method for cleaning a liquid crystal polyester reactor according to claim 1, wherein the neutralization in the step E) is performed by using hydrochloric acid until the pH value is 3-4.
8. 8. The method of claim 1, wherein the polymer monomer in the step E) comprises one or more of p-hydroxybenzoic acid, 2-hydroxy-6-naphthoic acid, 4' -dihydroxybiphenyl, terephthalic acid and isophthalic acid.
9. 9. The method for cleaning a liquid crystal polyester reactor according to any one of claims 1 to 8, wherein the liquid crystal polyester reactor comprises a reactor body, and a stirrer, a fractionating column, a condenser and auxiliary equipment thereof which are matched with the reactor body.
10. 10. The method for cleaning a liquid crystal polyester reactor according to claim 9, wherein the auxiliary equipment comprises an alkaline alcohol cleaning unit, an acid washing unit, a water washing unit, a dihydric alcohol recovery unit and a monomer recovery unit which are connected with the reactor body.

Description

Method for cleaning liquid crystal polyester reaction kettle Technical Field The invention belongs to the technical field of cleaning of high polymer material production equipment, and particularly relates to a cleaning method of a liquid crystal polyester reaction kettle. Background The liquid crystal polyester (Liquid Crystal Polymer, LCP) is widely applied to the fields of electronics, aerospace, precision instruments and the like due to the excellent heat resistance, solvent resistance and mechanical strength. The liquid crystal polyester is generally produced by adopting a melt polycondensation method, and raw materials comprise aromatic hydroxycarboxylic acid (such as p-hydroxybenzoic acid and 2-hydroxy-6-naphthoic acid), aromatic diol (such as 4,4' -dihydroxybiphenyl), aromatic dicarboxylic acid (such as terephthalic acid and isophthalic acid) and the like, and the raw materials undergo polymerization reaction at a high temperature (280-350 ℃). A common technical problem exists in the production process of the liquid crystal polyester, namely that after the polymerization reaction is finished, part of the polymer can adhere to the surfaces of the inner wall of the reaction kettle, the stirrer, the fractionating column and other parts to form residues. These residues are difficult to remove by conventional solvent washing due to the excellent solvent resistance of the liquid crystalline polyesters. If the polymer is not cleaned, residues can be carbonized to form impurities due to long-term high temperature in the next polymerization reaction, so that the color and whiteness of the product are seriously affected, and the polymer is especially used in the application fields of fibers, films and the like with high requirements on quality. In view of the above problems, various cleaning methods have been proposed in the prior art. US5762718 discloses a process for reducing black spots in thermotropic liquid crystal polymers by continuously using triethylene glycol, ethylene glycol and water for washing, which adopts a three-step washing process, and sequentially uses triethylene glycol (TEG), ethylene Glycol (EG) and water for washing a reaction kettle, but the process needs to be carried out at a high temperature (TEG washing temperature 330-355 ℃), so that the energy consumption is high, the TEG price is high, and the washing cost is high. CN101812385A discloses a cleaning composition comprising (a) a glycol, (B) an amine, and (C) a compound selected from cyclic esters, amides, and sulfoxides, wherein the content of component (B) is 5 to 40% by weight, the content of component (C) is 5 to 30% by weight, both relative to the total weight of the cleaning composition, and a method of cleaning a liquid crystalline polyester production device using the same. Can be cleaned at 190-240 ℃, but still needs to use various organic solvents, and does not involve waste liquid recycling. CN103289835A discloses a cleaning composition and a method for cleaning production equipment by using the same, wherein the cleaning composition comprises (a) alcohol, (b) a strong polar compound selected from amide, sulfoxide and the like and (c) alkali metal hydroxide, wherein the component (a) accounts for 40-80% of the total volume of the cleaning composition, and the component (b) accounts for 20-60% of the total volume. Specifically, a cleaning composition containing a low boiling point alcohol (methanol, ethanol, etc.), a strongly polar compound (DMSO, DMF, etc.), and an alkali metal hydroxide can be cleaned at a temperature lower than 100 ℃ and the whiteness value of the product is used as an index for evaluating the cleaning effect, but the low boiling point alcohol used is highly volatile, has a large potential safety hazard, and does not involve recycling of resources as such. The existing situation is that (1) the cleaning waste liquid is directly discharged, which not only causes environmental pollution but also causes resource waste, (2) the by-products in the production process are not considered for cleaning, the economical efficiency is poor, and (3) the cleaning step is single, and the cleaning effect on the complex structure parts such as the fractionating column is limited. Aiming at the technical problems, the method has positive significance for exploring a liquid crystal polyester reaction kettle cleaning method integrating efficient cleaning and resource recovery, so that residues on the inner wall of the reaction kettle and a fractionating column can be thoroughly removed, and cleaning solvents and polymer monomers can be recovered to realize the technical measure of resource recycling. Disclosure of Invention The invention aims to provide a cleaning method of a liquid crystal polyester reaction kettle, which has the advantages of low cleaning temperature, energy consumption saving, low cost of used solvents, obvious cost reduction, recycling of cleaning waste liquid, resource saving, environment pollution p