CN114805766A - Method for preparing PBT (polybutylene terephthalate) from PBT and waste PET (polyethylene terephthalate) polyester or/and PET-PBT mixed polyester thereof - Google Patents
Method for preparing PBT (polybutylene terephthalate) from PBT and waste PET (polyethylene terephthalate) polyester or/and PET-PBT mixed polyester thereof Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
- C08G63/02—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds
- C08G63/12—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds derived from polycarboxylic acids and polyhydroxy compounds
- C08G63/16—Dicarboxylic acids and dihydroxy compounds
- C08G63/18—Dicarboxylic acids and dihydroxy compounds the acids or hydroxy compounds containing carbocyclic rings
- C08G63/181—Acids containing aromatic rings
- C08G63/183—Terephthalic acids
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
- C08G63/78—Preparation processes
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J11/00—Recovery or working-up of waste materials
- C08J11/04—Recovery or working-up of waste materials of polymers
- C08J11/10—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation
- C08J11/18—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation by treatment with organic material
- C08J11/22—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation by treatment with organic material by treatment with organic oxygen-containing compounds
- C08J11/24—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation by treatment with organic material by treatment with organic oxygen-containing compounds containing hydroxyl groups
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2367/00—Characterised by the use of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Derivatives of such polymers
- C08J2367/02—Polyesters derived from dicarboxylic acids and dihydroxy compounds
Abstract
The invention relates to a method for preparing PETG (polyethylene terephthalate glycol) from waste PET (polyethylene terephthalate) polyester or/and PET-PBT (polyethylene terephthalate-polybutylene terephthalate) mixed polyester, which comprises the following steps of: depolymerization: melting waste PET polyester or/and PET-PBT mixed polyester into a melt, adding depolymerization liquid, and depolymerizing in a depolymerization kettle to obtain BHET and BHBT monomers; the depolymerization liquid comprises BDO and/or EG; primary ester exchange: performing ester exchange reaction on BHET and BHBT monomers and methanol to obtain DMT solution, and purifying and refining the DMT solution to obtain refined DMT; and (3) secondary ester exchange: carrying out ester exchange reaction on the refined DMT and BDO to obtain BHBT; polycondensation: BHBT is polycondensed to produce PBT polymer. The invention improves the utilization rate of PBTPET polyester and the mixing range of the regenerated PBT and PET; the produced PBT product has stable and uniform performance; the indexes such as intrinsic viscosity, molecular weight distribution, color value, melting point and the like are excellent, and the requirements of market spinning grade and the like are met.
Description
Technical Field
The invention relates to waste alcohol ester utilization, in particular to a method for preparing PBT (polybutylene terephthalate) by using PBT and waste PET (polyethylene terephthalate) polyester or/and PET-PBT mixed polyester.
Background
The existing PBT products in the market at present mainly adopt a PTA method production process, wherein PTA and BDO (1, 4-butanediol) are subjected to esterification reaction to form a BHBT monomer; then the BHBT monomer is polycondensed to produce the macromolecular chain PBT polymer.
The PTA raw material is mainly derived from a petrochemical base, so that the carbon emission in the whole acquisition process is relatively large, and primary resources are mainly consumed. Meanwhile, various derivative products prepared from the PBT raw material cannot be recycled fully after use, for example, PBT, PET mixed polyester or PBT polyester waste products in the market cannot be degraded after consumption, so that the recycling rate is low. Part of methods for physical melting are available in recycling, but have the defects that the product performance cannot meet the high-end spinning requirement, and the color is darker. This results in waste PBT, PET mixed polyester or PBT polyester, which can not be recycled efficiently, and causes waste of such waste textile and industrial product resources.
Disclosure of Invention
In view of the above problems, the application provides a method for preparing PBT by effectively utilizing waste PET and/or PBT polyester, and the process improves the utilization rate of PBT and PET polyester and the mixing range of regenerated PBT and PET; the produced PBT product has stable and uniform performance; the indexes such as intrinsic viscosity, molecular weight distribution, color value, melting point and the like are excellent, and the requirements of market spinning grade and the like are met.
The application firstly provides a method for preparing PBT by using waste PET and/or PBT polyester, which comprises the following steps:
depolymerization: melting waste PET polyester or/and PET-PBT mixed polyester into a melt, adding depolymerization liquid, and depolymerizing in a depolymerization kettle to obtain BHET and BHBT monomers;
primary ester exchange: performing ester exchange reaction on BHET and BHBT monomers and methanol to obtain DMT solution, and purifying and refining the DMT solution to obtain refined DMT;
and (3) secondary ester exchange: the refined DMT and BDO are subjected to ester exchange reaction to obtain BHBT
Polycondensation: BHBT is polycondensed to produce PBT polymer.
Different from the prior art, the technical scheme provides a process method for efficiently recycling waste PET polyester or/and PET-PBT mixed polyester by chemical cycle. The waste polyester raw material of PBT (polybutylene terephthalate) \ PET (polyethylene terephthalate) is depolymerized and decomposed into PBT (bis-hydroxybutyl terephthalate) and PET (bis-hydroxyethyl terephthalate)) monomers; then carrying out ester exchange reaction with methanol to generate intermediate molecular DMT (dimethyl terephthalate); purifying the generated DMT; carrying out esterification reaction on the purified refined DMT and BDO (1, 4-butanediol) to obtain a BHBT monomer; then the BHBT monomer is polycondensed to produce the macromolecular chain PBT polymer. The process method of the invention improves the utilization rate of the PBT-PET polyester and the mixing range of the regenerated PBT and the PET; the produced PBT product has stable and uniform performance; the indexes such as intrinsic viscosity, molecular weight distribution, color value, melting point and the like are excellent, and the requirements of market spinning grade and the like are met.
Preferably, the depolymerization step is carried out continuously using two or more depolymerization vessels connected in series.
Preferably, the depolymerization step adds a depolymerization solution comprising BDO and/or EG; the mass ratio of BDO to PBT is 1-6: 2; the mass ratio of EG to PET is 1-6: 2.
Preferably, the temperature of the EG added into the depolymerization kettle is 190-200 ℃.
Preferably, in the depolymerization step, a depolymerization catalyst is added in an amount of 0.1 to 5 wt% of a depolymerization mixture (the depolymerization mixture includes the melt and the depolymerization liquid).
Preferably, the depolymerization catalyst is zinc acetate and potassium carbonate.
Preferably, in the depolymerization step, the depolymerization kettle is subjected to nitrogen pressure sealing in the depolymerization process, and the pressure of the nitrogen pressure sealing is controlled to be 0-0.2 MPa.
Preferably, the depolymerization step comprises a first depolymerization kettle, a second depolymerization kettle and a third depolymerization kettle which are arranged in series.
Preferably, the liquid levels of the first depolymerization kettle and the second depolymerization kettle are controlled to be 60%.
The application also provides a PBT polymer which is prepared by adopting the preparation method.
Different from the prior art, the technical scheme provides a process method for efficiently recycling waste PET/PBT mixed polyester or PBT polyester raw materials. The waste polyester raw material of PBT (polybutylene terephthalate) \ PET (polyethylene terephthalate) is depolymerized and decomposed into PBT (bis-hydroxybutyl terephthalate) and PET (bis-hydroxyethyl terephthalate)) monomers; then carrying out ester exchange reaction with methanol to generate intermediate molecular DMT (dimethyl terephthalate); purifying the generated DMT; carrying out esterification reaction on the purified refined DMT and BDO (1, 4-butanediol) to obtain a BHBT monomer; then the BHBT monomer is polycondensed to produce the macromolecular chain PBT polymer. The process method of the invention improves the utilization rate of the PBT-PET polyester and the mixing range of the regenerated PBT and the PET; the produced PBT product has stable and uniform performance; the indexes such as intrinsic viscosity, molecular weight distribution, color value, melting point and the like are excellent, and the requirements of market spinning grade and the like are met.
The above description of the present invention is only an overview of the technical solutions of the present application, and in order to make the technical solutions of the present application more clearly understood by those skilled in the art, the present invention may be further implemented according to the content of the text of the specification, and in order to make the above objects, other objects, features, and advantages of the present application more easily understood, the following description is given with reference to the detailed embodiments of the present application.
Detailed Description
In order to explain technical contents, structural features, and objects and effects of the technical means in detail, the following detailed description is given with reference to specific embodiments.
In order to explain in detail possible application scenarios, technical principles, practical embodiments, and the like, the following detailed description is given with reference to specific embodiments. The embodiments described herein are merely for more clearly illustrating the technical solutions of the present application, and therefore, the embodiments are only used as examples, and the scope of the present application is not limited thereby.
Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase "an embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or related to other embodiments specifically defined. In principle, in the present application, the technical features mentioned in the embodiments can be combined in any manner to form a corresponding implementable technical solution as long as there is no technical contradiction or conflict.
Unless defined otherwise, technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the use of relational terms herein is intended only to describe particular embodiments and is not intended to limit the present application.
In the description of the present application, the term "and/or" is a expression for describing a logical relationship between objects, meaning that three relationships may exist, for example a and/or B, meaning: there are three cases of A, B, and both A and B. In addition, the character "/" herein generally indicates that the former and latter associated objects are in a logical relationship of "or".
In this application, terms such as "first" and "second" are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions.
Without further limitation, in this application, the use of "including," "comprising," "having," or other similar expressions in phrases and expressions of "including," "comprising," or "having," is intended to cover a non-exclusive inclusion, and such expressions do not exclude the presence of additional elements in a process, method, or article that includes the recited elements, such that a process, method, or article that includes a list of elements may include not only those elements but also other elements not expressly listed or inherent to such process, method, or article.
As is understood in the examination of the guidelines, the terms "greater than", "less than", "more than" and the like in this application are to be understood as excluding the number; the expressions "above", "below", "within" and the like are understood to include the present numbers. In addition, in the description of the embodiments of the present application, "a plurality" means two or more (including two), and expressions related to "a plurality" similar thereto are also understood, for example, "a plurality of groups", "a plurality of times", and the like, unless specifically defined otherwise.
The PET is polyethylene terephthalate, is the most main variety in thermoplastic polyester, and is commonly called polyester resin. The chemical formula of PET is (C) 10 H 8 O 4 ) n The polyester belongs to crystalline saturated polyester, is a milky white or light yellow polymer with high crystallinity, and has smooth and glossy surface; melting point: 250 ℃ and 260 ℃ and the viscosity is 0.6-0.7.
The PBT in the application is polybutylene terephthalate; it is a milky translucent to opaque, semicrystalline thermoplastic polyester having high heat resistance. PBT is not resistant to strong acid and strong base, can resist organic solvent, is combustible, is decomposed at high temperature, and has a monomer melting point: the viscosity is 1.0-1.2 at 233 ℃.
The BHET is ethylene terephthalate, also called dihydroxyethyl terephthalate; the melting point of the monomer is 110 ℃; the dimer melting point is 169-170 ℃, and the trimer melting point is 200-202 ℃.
The BHBT in the application is dibutylene glycol terephthalate.
DMT described herein is dimethyl terephthalate, a colorless orthorhombic crystal; melting point 140.6 ℃; a boiling point of 283 ℃; relative density 1.084; a refractive index 1.4752; insoluble in water, soluble in ether and hot ethanol.
BDO described herein is 1, 4-butanediol having the formula C 4 H 10 O 2 And the molecular weight is 90.12. The appearance is colorless or light yellow oily liquid. Flammable, 20.1 ℃ freezing point, 1.4461 refractive index. BDO is dissolved in methanol, ethanol and acetone, and is slightly soluble in ether.
EG described herein is ethylene glycol. Has a chemical formula of (CH) 2 OH) 2 Is the simplest diol. The ethylene glycol is colorless, odorless and sweetLiquid, with low toxicity to animals, ethylene glycol is miscible with water and acetone, but has low solubility in ethers, and the boiling point is 197.4 ℃.
The method mainly recycles waste products mainly comprising PBT, and also recycles waste products mixed by PBT and PET; molecular chains of PBT and PET polymers are butanediol ester and glycol ester, and the PBT and PET polymers are easy to carry out depolymerization reaction with butanediol or glycol; and even if benzene rings are generated, one end of the benzene ring is glycol ester, the other end of the benzene ring is butanediol ester, DMT can be generated by reaction with methanol in the subsequent ester exchange step, and byproducts are ethylene glycol and butanediol.
After waste PBT is depolymerized into monomers, the waste PBT is subjected to ester exchange reaction with methanol to generate dimethyl terephthalate, and by utilizing the characteristic of easy purification of the dimethyl terephthalate, a regenerated raw material is provided for the subsequent process of utilizing the dimethyl terephthalate to reproduce PET, PBT and DMT to produce diversified products, and the consumption of the terephthalic acid or dimethyl terephthalate directly produced by petroleum is reduced.
The application firstly provides a method for preparing PETG from waste PET polyester or/and PET-PBT mixed polyester, which comprises the following steps:
depolymerization: melting waste PET polyester or/and PET-PBT mixed polyester into a melt, adding depolymerization liquid, and depolymerizing in a depolymerization kettle to obtain BHET and BHBT monomers; the depolymerization liquid comprises BDO and/or EG; primary ester exchange: performing ester exchange reaction on BHET and BHBT monomers and methanol to obtain DMT;
and (3) secondary ester exchange: carrying out ester exchange reaction on DMT and BDO to obtain BHBT;
polycondensation: BHBT is polycondensed to produce PBT polymer.
The main reactions of the depolymerization step are:
PBT+BDO＝BHBT
HOC 4 H 8 O(-CO-C 6 H 4 -COOC 4 H 8 O-)nH+(n-1)HOC 4 H 8 OH→nHOC 4 H 8 OCO-C 6 H 4 -COOC 4 H 8 OH
PET+EG＝BHET
HOC 2 H 4 O(-CO-C 6 H 4 -COOC 2 H 4 O-)nH+(n-1)HOC 2 H 4 OH→nHOC 2 H 4 OCO-C 6 H 4 -COOC 2 H 4 OH
wherein, the EG ethylene glycol side reaction:
2HOC 2 H 4 OH→HOC 2 H 4 OC 2 H 4 OH+H 2 O
HOC 2 H 4 OH→CH 3 CHO+H 2 O
BDO butanediol side reaction:
HO(CH 2 ) 4 OH→THF+H 2 O
a first ester exchange step:
BHET+MA→DMT+EG
nHOC 2 H 4 OCO-C 6 H 4 -COOC 2 H 4 OH+2nCH 3 OH→nCH 3 OCO-C 6 H 4 -COOCH 3 +2nHOC 2 H 4 OH
BHBT+MA→DMT+BDO
nHOC 4 H 8 OCO-C 6 H 4 -COOC 4 H 8 OH+2nCH 3 OH→nCH 3 OCO-C 6 H 4 -COOCH 3 +2nHOC 4 H 8 OH
second transesterification
CH 3 OOC-C 6 H 4 -COOCH3+HOC 4 H 8 OH→HOC 4 H 8 OCO-C 6 H 4 -COOC 4 H 8 OH+2CH 3 OH
Polycondensation:
nHOC 4 H 8 OCO-C 6 H 4 -COOC 4 H 8 OH→HOC 4 H 8 O(-CO-C 6 H 4 -COOC 4 H 8 O-)nH+(n-1)HOC 4 H 8 OH
dimethyl terephthalate (DMT) is transesterified with 1, 4-butanediol to form dibutylene terephthalate, which is polycondensed to form polybutylene terephthalate.
The secondary ester exchange method adopts excessive proportion of 1, 4-butanediol, the molar ratio of DMT to 1, 4-butanediol is 1: 1.3-1.7, the reaction temperature is about 200 ℃, the reaction equilibrium is favorable to the direction of generating the dibutylene glycol terephthalate, and the occurrence of side reaction can be reduced.
The second-step polycondensation reaction is carried out at a temperature of about 250 ℃ and 260 ℃ under a reduced pressure of 0.1-1mm Hg.
Different from the prior art, the technical scheme provides a process method for efficiently recycling waste PET polyester or/and PET-PBT mixed polyester by chemical cycle. The waste polyester raw material of PBT (polybutylene terephthalate) \ PET (polyethylene terephthalate) is depolymerized and decomposed into PBT (bis-hydroxybutyl terephthalate) and PET (bis-hydroxyethyl terephthalate)) monomers; then carrying out ester exchange reaction with methanol to generate intermediate molecular DMT (dimethyl terephthalate); purifying the generated DMT; carrying out esterification reaction on the purified refined DMT and BDO (1, 4-butanediol) to obtain a BHBT monomer; then a BHBT monomer polycondensation reaction is adopted to produce a macromolecular chain PBT polymer. The process method of the invention improves the utilization rate of the PBT-PET polyester and the mixing range of the regenerated PBT and the PET; the produced PBT product has stable and uniform performance; the indexes such as intrinsic viscosity, molecular weight distribution, color value, melting point and the like are excellent, and the requirements of market spinning grade and the like are met.
Preferably, the melting of the waste PET polyester or/and PET-PBT mixed polyester into the melt also comprises the steps of removing impurities, preparing the sorted raw materials into aggregate particles, melting and extruding the aggregate particles through a screw rod, and finally forming the melt. The method comprises the following specific steps:
1. the impurity removal comprises the steps of collecting waste PET polyester or/and PET-PBT mixed polyester and carrying out sorting work, and comprises the step of removing foreign matters such as metal in the raw materials.
1.1 absorbing iron substances by multi-ring strong magnet;
1.2 picking out foreign matters which are obviously capable of being sorted and are not iron non-raw materials by a flat conveyer belt;
1.3, filtering and conveying to remove small-grained sandstone and other foreign matters through tiling;
2. preparing the sorted raw materials into aggregate
2.1, removing impurities, and conveying the raw materials to a material gathering machine for crushing and grain gathering;
2.2 conveying the aggregate to a feeding bin for continuous conveying to a raw material feeding bin;
3. the agglomerated material is melt extruded through a screw to form a melt:
3.1, setting the temperatures of the zones of the screw respectively and raising the temperature to the set temperature, wherein the temperature range is 240-290 ℃;
3.2 continuously feeding the aggregate to melt and extrude into a melt;
4. the melt can be subjected to primary melt filtration to filter out metals and foreign matters which cannot be decomposed at 220-290 ℃;
4.1 heating the melt filter to 285 ℃, wherein the melt filter is used for standby;
4.2 the melt can directly enter a depolymerization kettle after being filtered to finish the melt conveying process;
in the depolymerization step, the depolymerization kettle utilizes a melt feeding form to improve the depolymerization efficiency.
Preferably, the depolymerization step is carried out continuously using two or more depolymerization vessels connected in series. The depolymerization kettle adopts two or three kettles for continuous depolymerization. Is more beneficial to improving the proportion of 1-4 oligomers, can achieve 98-99 percent of completion rate, and has high-efficiency depolymerization and low side reaction.
Preferably, the depolymerization step adds a depolymerization solution comprising BDO and/or EG; the mass ratio of BDO to PBT is 1-6: 2; the mass ratio of EG to PET is 1-6: 2.
Preferably, the temperature of the EG added into the depolymerization kettle is 190-200 ℃.
Preferably, in the depolymerization step, a depolymerization catalyst is added in an amount of 0.1 to 5 wt% of the depolymerization mixture (the depolymerization mixture includes the melt and the depolymerization liquid).
Preferably, the depolymerization catalyst is zinc acetate and potassium carbonate.
Preferably, in the depolymerization step, the depolymerization kettle is subjected to nitrogen pressure sealing in the depolymerization process, and the pressure of the nitrogen pressure sealing is controlled to be 0-0.2 MPa.
Preferably, the depolymerization step comprises a first depolymerization kettle, a second depolymerization kettle and a third depolymerization kettle which are arranged in series. The three kettles are continuously depolymerized, so that continuous feeding and discharging can be realized, and the mass production is facilitated; three-kettle continuous depolymerization can optimize the reaction temperature, the reaction residence time and the pressure of each kettle, effectively reduce the generation of side reactions such as dehydration of EG (ethylene glycol) BDO (butanediol) and the like, and simultaneously improve the proportion of depolymerized oligomer monomers; is more beneficial to improving the proportion of 1-4 oligomers, can achieve 98-99% of completion rate, and has high-efficiency depolymerization and low side reaction.
Preferably, the liquid level of the first depolymerization kettle and the liquid level of the second depolymerization kettle are controlled to be 60%.
After the first depolymerization kettle continuously feeds materials to reach 60% of liquid level, continuously discharging materials, and keeping the liquid level in the first depolymerization kettle constant at 60% of liquid level; continuously feeding the discharged monomer solution into a second depolymerization kettle; and after the liquid level of the second depolymerization kettle reaches 60 percent of the liquid level, continuously discharging, keeping the liquid level in the second depolymerization kettle constant at 60 percent of the liquid level, and continuously feeding discharged monomer solution into a third depolymerization kettle. In the third depolymerization vessel, the pressure and temperature are adjusted so as to obtain the ratio of the depolymerization oligomer monomer in the total solution.
After the respective set pressure of the three depolymerization kettles reaches, the pressure is adjusted by the regulating valve at the top of the tower, so that the pressure in the kettles is ensured to be balanced; meanwhile, the released gas is separated by a separation tower, and the tower bottom can be returned to a depolymerization kettle to ensure the proportion of depolymerization liquid; the top of the tower is mainly low-boiling components and is removed from the system.
The three kettles are continuously depolymerized, so that continuous feeding and continuous discharging can be realized, and the mass production is facilitated; the three-kettle continuous depolymerization can optimize the reaction temperature, the residence time of the feeding reaction and the pressure of each kettle, effectively reduce the generation of side reactions such as dehydration of EG (ethylene glycol) BDO (butanediol) and the like, and simultaneously improve the proportion of depolymerized oligomer monomers.
Preferably, the reaction temperature of the first depolymerization kettle is set to 190-. The retention time is the set volume/discharge flow rate; in this embodiment, the set volume is 60% of the tank volume; in other embodiments, the set volume may be adjusted as desired.
Preferably, a concentration step is further included between the depolymerization and the first transesterification: depolymerizing the obtained mixed solution of BHET and BHBT, concentrating excessive depolymerized liquid in the mixed solution, and recycling the solvent;
1. dilute monomer BHET and BHBT solution, and a concentration tower is used for removing partial butanediol and ethylene glycol of excessive solution during depolymerization;
2. the concentration tower is separated under the working condition of negative pressure of 10-30 KPa; circularly heating the tower bottom liquid at 160-180 ℃, condensing and collecting the butanediol and the ethylene glycol at the tower top, and recycling; and continuously conveying the mixture to a concentrated monomer storage tank for the next working procedure by on-line monitoring of the tower bottom density.
Preferably, the method further comprises the following steps of purifying and refining DMT between the first transesterification step and the second transesterification step:
DMT purification: the DMT generated after the first transesterification reaction is cleaned by methanol to remove most of the color; wherein, the solvent with heavier color is recycled by towers; the method specifically comprises the following steps:
1. carrying out periodic operations of filter pressing, cleaning and re-filter pressing on the DMT solution produced by the ester exchange reaction for the first time for 1-4 times by using positive pressure filter pressing equipment; washing the DMT filter cake with a methanol solution; the press filtrate is subjected to utilization and recovery treatment of each process; the filter press uses stirring frequency conversion to control speed for fully stirring, so that the color, EG and the like in the DMT solution are fully dissolved with methanol, and then the mixture is subjected to filter pressing;
2. carrying out negative pressure of 10-101KPa on the filter cake subjected to filter pressing, and volatilizing, dealcoholizing and drying crude DMT at the temperature of 25-100 ℃; and (5) condensing and collecting the volatile alcohol by using chilled water, and recycling the volatile alcohol.
DMT refining: extracting the dried crude DMT in a distillation kettle to obtain refined DMT;
distilling by using a DMT distillation still, a rectifying tower, a constant-temperature trap, a vacuum system and other equipment to rectify the DMT intermediate product; the refined DMT is directly stored in a DMT storage tank in liquid state, thus being beneficial to the use of the secondary ester exchange step.
Preferably, in the polycondensation step, a heat stabilizer is added, and the heat stabilizer comprises one or more of phosphoric acid, phosphorous acid, trimethyl phosphate, triethyl phosphate and triphenyl phosphate. Trimethyl phosphate is preferred. The polycondensation reaction temperature is 250-260 ℃, and a heat stabilizer is added to avoid the high-temperature decomposition of the PBT polymer.
The application also provides a PBT polymer which is prepared by adopting the preparation method.
Different from the prior art, the technical scheme provides a process method for efficiently recycling waste PET/PBT mixed polyester or PBT polyester raw materials. The waste polyester raw material of PBT (polybutylene terephthalate) \ PET (polyethylene terephthalate) is depolymerized and decomposed into PBT (bis-hydroxybutyl terephthalate) and PET (bis-hydroxyethyl terephthalate)) monomers; then carrying out ester exchange reaction with methanol to generate intermediate molecular DMT (dimethyl terephthalate); purifying the generated DMT; carrying out esterification reaction on the purified refined DMT and BDO (1, 4-butanediol) to obtain a BHBT monomer; then the BHBT monomer is polycondensed to produce the macromolecular chain PBT polymer. The process method of the invention improves the utilization rate of the PBT-PET polyester and the mixing range of the regenerated PBT and the PET; the produced PBT product has stable and uniform performance; the indexes such as intrinsic viscosity, molecular weight distribution, color value, melting point and the like are excellent, and the requirements of market spinning grade and the like are met.
Example 1: 100kg of regenerated PBT slice produced by using variegated leftover materials and raw materials
1. Depolymerization:
100kg of variegated scrap after impurity removal containing PET (50.5 wt%) and PBT (36 wt%); preparing aggregate material by an aggregate machine system; melting and extruding the aggregate screw to form a melt; the melt is filtered by a melt filter and then is conveyed into a first depolymerization kettle; 100kg of depolymerization liquid including 55kg of EG, 45kg of BDO and 2g of depolymerization catalyst zinc acetate are additionally metered into the first depolymerization kettle, and the temperature of the EG in the first depolymerization kettle is kept at 190-200 ℃.
The first depolymerization kettle, the second depolymerization kettle and the third depolymerization kettle are connected in series for continuous depolymerization, continuous feeding and discharging are carried out, and the liquid levels of the first depolymerization kettle and the second depolymerization kettle are controlled to be 60 percent, so that BDO and EG added in the depolymerization reaction are in an excessive state and can fully carry out a main reaction with a melt, but the retention time of the excessive BDO and EG in the depolymerization kettle is limited, and the probability of occurrence of side reactions is reduced. And (3) carrying out nitrogen pressure sealing in the depolymerization process of the depolymerization kettle, wherein the pressure of the nitrogen pressure sealing is controlled to be 0-0.2 MPa.
The reaction temperature of the first depolymerization kettle was 205 ℃, the reaction pressure was 151kpa, and the residence time was 80 minutes.
The reaction temperature of the second depolymerization kettle is 200 ℃, the reaction pressure is 120kpa, and the retention time is 60 minutes;
the reaction temperature of the third depolymerization kettle was 190 ℃, the reaction pressure was 110ka, and the residence time was 40 minutes.
Through the arrangement, most of PET and PBT in the melt are depolymerized in the first depolymerization kettle, and the depolymerization temperature and pressure are gradually reduced in the second and third depolymerization kettles, so that residual PBT and PET can be depolymerized, and the increase of EG and BDO side reactions caused by long-time high temperature and high pressure is avoided.
The main reactions of the depolymerization step are:
PBT+BDO＝BHBT
HOC 4 H 8 O(-CO-C 6 H 4 -COOC 4 H 8 O-)nH+(n-1)HOC 4 H 8 OH→nHOC 4 H 8 OCO-C 6 H 4 -COOC 4 H 8 OH
PET+EG＝BHET
HOC 2 H 4 O(-CO-C 6 H 4 -COOC 2 H 4 O-)nH+(n-1)HOC 2 H 4 OH→nHOC 2 H 4 OCO-C 6 H 4 -COOC 2 H 4 OH
ethylene glycol side reaction:
2HOC 2 H 4 OH→HOC 2 H 4 OC 2 H 4 OH+H 2 O
HOC 2 H 4 OH→CH 3 CHO+H 2 O
side reaction of butanediol:
HO(CH 2 ) 4 OH→THF+H 2 O
2. concentration:
depolymerizing the obtained mixed solution of BHET and BHBT, concentrating the mixed solution by using a concentration tower to remove excessive ethylene glycol and butanediol, circularly heating the tower bottom liquid at 160-180 ℃, condensing and collecting the butanediol and ethylene glycol at the tower top, and recycling the butanediol and ethylene glycol; the concentration tower is separated under the working condition of negative pressure of 10-30 KPa; a mixed solution of concentrated BHET and BHBT was obtained.
3. Primary ester exchange:
the concentrated BHET and BHBT mixed solution is subjected to ester exchange with methanol to obtain DMT, EG and BDO: the reaction formula is as follows:
BHET+MA→DMT+EG
nHOC 2 H 4 OCO-C 6 H 4 -COOC 2 H 4 OH+2nCH 3 OH→nCH 3 OCO-C 6 H 4 -COOCH 3 +2nHOC 2 H 4 OH
BHBT+MA→DMT+BDO
nHOC 4 H 8 OCO-C 6 H 4 -COOC 4 H 8 OH+2nCH 3 OH→nCH 3 OCO-C 6 H 4 -COOCH 3 +2nHOC 4 H 8 OH
DMT purification step: the weight of the obtained crude DMT (steam oven dried) was 95.6 kg;
washing DMT generated after the first transesterification reaction by using methanol to remove most of color; wherein, the solvent with heavier color is recycled by towers; specifically comprises
Carrying out periodic operations of filter pressing, cleaning and re-filter pressing on the DMT solution produced by the ester exchange reaction for the first time for 1-4 times by using positive pressure filter pressing equipment; washing the DMT filter cake with a methanol solution, and utilizing and recycling the filter pressing liquid in each process; the filter press uses stirring frequency conversion to control speed for fully stirring, so that the color, EG and the like in the DMT solution are fully dissolved with methanol, and then the mixture is subjected to filter pressing; and (3) carrying out negative pressure of 10-101KPa on the filter cake subjected to filter pressing, and volatilizing, dealcoholizing and drying crude DMT at the temperature of 25-100 ℃. And various volatile alcohols in the purification step are condensed and collected by chilled water and are recycled.
DMT refining step: the amount of fine DMT liquid collected in the tank was 74.5 liters.
And (3) putting the dried crude DMT into a distillation kettle to extract into fine DMT. Distilling by using a DMT distillation still, a rectifying tower, a constant-temperature trap, a vacuum system and other equipment to rectify the DMT intermediate product; the refined DMT is directly stored in a DMT storage tank in liquid state.
And (3) secondary ester exchange: 50kg of BDO and 44g of tetrabutyl titanate serving as a catalyst were added into 74.5L of DMT to perform transesterification, and the temperature of the secondary transesterification was controlled at 200 ℃.
Performing ester exchange reaction on DMT and BDO in a reaction kettle to obtain BHBT
CH 3 OOC-C 6 H 4 -COOCH3+HOC 4 H 8 OH→HOC 4 H 8 OCO-C 6 H 4 -COOC 4 H 8 OH+2CH 3 OH
10g of thermal stabilizer trimethyl phosphate is added into the BHBT monomer obtained by the secondary ester exchange, polycondensation reaction is carried out at the temperature of 250-260 ℃, and the kettle is gradually vacuumized until the pressure is reduced to 0.5mmHg, thus obtaining the PBT polymer.
BHBT is polycondensed in a reaction kettle to generate PBT polymer
n HOC 4 H 8 OCO-C 6 H 4 -COOC 4 H 8 OH→HOC 4 H 8 O(-CO-C 6 H 4 -COOC 4 H 8 O-)nH+(n-1)HOC 4 H 8 OH
After the secondary esterification reaction is finished, methanol is generated by collecting the esterification reaction, the result of vacuumizing is achieved, and the polycondensation reaction of BHBT is catalyzed; after the polycondensation reaction is complete, the PBT is weighed to yield 79.5kg (about 2-5% residual pot).
In example 1, 79.5KG of the regenerated PBT was obtained by depolymerization of 100KG of the agglomerated material, transesterification to DMT, and polycondensation to BDO; the product has the analytical indexes of 1.03 viscosity, 223.2 melting point, 4.8B value, 29 carboxyl end groups and white color quality; the index is excellent, and the requirements of market spinning grade and the like are met.
Meanwhile, the EG \ BDO \ methanol used in the technical scheme can be recycled, so that the process cost is reduced.
Finally, it should be noted that, although the above embodiments have been described in the text of the specification of the present application, the scope of the patent protection of the present application is not limited thereby. All technical solutions which are generated by replacing or modifying the equivalent structure or the equivalent flow according to the content described in the specification of the present application based on the substantial idea of the present application, and which directly or indirectly implement the technical solutions of the above embodiments in other related technical fields, are included in the scope of patent protection of the present application.
Claims (10)
1. A method for preparing PBT by using waste PET polyester or/and PET-PBT mixed polyester is characterized by comprising the following steps:
depolymerization: melting waste PET polyester or/and PET-PBT mixed polyester into a melt, adding depolymerization liquid, and depolymerizing in a depolymerization kettle to obtain BHET and BHBT monomers; the depolymerization liquid comprises BDO and/or EG;
primary ester exchange: performing ester exchange reaction on BHET and BHBT monomers and methanol to obtain DMT solution, and purifying and refining the DMT solution to obtain refined DMT;
and (3) secondary ester exchange: carrying out ester exchange reaction on the refined DMT and BDO to obtain BHBT;
polycondensation: BHBT is polycondensed to produce PBT polymer.
2. The process of claim 1, wherein the depolymerization step is carried out in a continuous depolymerization step using two or more depolymerization vessels in series.
3. The process for preparing PBT according to claim 1, wherein the mass ratio of BDO to PBT is 1-6: 2; the mass ratio of EG to PET is 1-6: 2.
4. The process for preparing PBT according to claim 3, wherein the temperature of EG added to the depolymerization kettle is 190-200 ℃.
5. The process of claim 1, wherein the depolymerization step, adding a depolymerization catalyst, the depolymerization catalyst being added in an amount of 0.1 to 5 wt% of the depolymerization mixture; the depolymerization mixture includes the melt and the depolymerization liquid.
6. The process of making PBT according to claim 4, wherein said depolymerization catalyst is zinc acetate and potassium carbonate.
7. The process for preparing PBT according to claim 1, wherein in the depolymerization step, the depolymerization tank is subjected to a nitrogen pressure lock during depolymerization.
8. The process for preparing PBT according to claim 2, wherein in the depolymerization step, the depolymerization tank comprises a first depolymerization tank, a second depolymerization tank, and a third depolymerization tank arranged in series.
9. The process for preparing PBT according to claim 8, wherein the liquid levels of the first depolymerization kettle and the second depolymerization kettle are controlled to be 60%.
10. A PBT polymer, characterized in that it has been produced by a process for producing PBT according to any of claims 1-9.
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