CN114195632B - Terephthalic acid, preparation method thereof and method for recycling polyethylene terephthalate with high polymerization degree - Google Patents
Terephthalic acid, preparation method thereof and method for recycling polyethylene terephthalate with high polymerization degree Download PDFInfo
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- CN114195632B CN114195632B CN202111489678.7A CN202111489678A CN114195632B CN 114195632 B CN114195632 B CN 114195632B CN 202111489678 A CN202111489678 A CN 202111489678A CN 114195632 B CN114195632 B CN 114195632B
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- 239000005020 polyethylene terephthalate Substances 0.000 title claims abstract description 180
- 229920000139 polyethylene terephthalate Polymers 0.000 title claims abstract description 180
- KKEYFWRCBNTPAC-UHFFFAOYSA-N Terephthalic acid Chemical compound OC(=O)C1=CC=C(C(O)=O)C=C1 KKEYFWRCBNTPAC-UHFFFAOYSA-N 0.000 title claims abstract description 128
- -1 polyethylene terephthalate Polymers 0.000 title claims abstract description 62
- 238000006116 polymerization reaction Methods 0.000 title claims abstract description 57
- 238000000034 method Methods 0.000 title claims abstract description 56
- 238000002360 preparation method Methods 0.000 title abstract description 22
- 238000004064 recycling Methods 0.000 title abstract description 10
- LYCAIKOWRPUZTN-UHFFFAOYSA-N Ethylene glycol Chemical compound OCCO LYCAIKOWRPUZTN-UHFFFAOYSA-N 0.000 claims abstract description 179
- 238000006243 chemical reaction Methods 0.000 claims abstract description 137
- 229910052783 alkali metal Inorganic materials 0.000 claims abstract description 44
- 239000003513 alkali Substances 0.000 claims abstract description 33
- 150000001340 alkali metals Chemical class 0.000 claims abstract description 33
- 238000002156 mixing Methods 0.000 claims abstract description 28
- 239000002253 acid Substances 0.000 claims abstract description 27
- 150000003839 salts Chemical class 0.000 claims abstract description 21
- 238000006561 solvent free reaction Methods 0.000 claims abstract description 15
- 239000011734 sodium Substances 0.000 claims description 28
- 230000008569 process Effects 0.000 claims description 23
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 23
- 239000000203 mixture Substances 0.000 claims description 22
- 238000010438 heat treatment Methods 0.000 claims description 17
- 239000002585 base Substances 0.000 claims description 13
- 239000007788 liquid Substances 0.000 claims description 12
- 229920000642 polymer Polymers 0.000 claims description 10
- 229910052708 sodium Inorganic materials 0.000 claims description 9
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 claims description 4
- 238000004519 manufacturing process Methods 0.000 claims description 4
- 229910052700 potassium Inorganic materials 0.000 claims description 4
- QTBSBXVTEAMEQO-UHFFFAOYSA-M Acetate Chemical compound CC([O-])=O QTBSBXVTEAMEQO-UHFFFAOYSA-M 0.000 claims description 3
- BVKZGUZCCUSVTD-UHFFFAOYSA-M Bicarbonate Chemical compound OC([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-M 0.000 claims description 3
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 claims description 3
- BDAGIHXWWSANSR-UHFFFAOYSA-M Formate Chemical compound [O-]C=O BDAGIHXWWSANSR-UHFFFAOYSA-M 0.000 claims description 3
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims description 3
- 229910019142 PO4 Inorganic materials 0.000 claims description 3
- NBIIXXVUZAFLBC-UHFFFAOYSA-L Phosphate ion(2-) Chemical compound OP([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-L 0.000 claims description 3
- ZLMJMSJWJFRBEC-UHFFFAOYSA-N Potassium Chemical compound [K] ZLMJMSJWJFRBEC-UHFFFAOYSA-N 0.000 claims description 3
- 229920001577 copolymer Polymers 0.000 claims description 3
- NBIIXXVUZAFLBC-UHFFFAOYSA-M dihydrogenphosphate Chemical compound OP(O)([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-M 0.000 claims description 3
- 229920001519 homopolymer Polymers 0.000 claims description 3
- 229910052744 lithium Inorganic materials 0.000 claims description 3
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 claims description 3
- 239000010452 phosphate Substances 0.000 claims description 3
- 239000011591 potassium Substances 0.000 claims description 3
- 238000006460 hydrolysis reaction Methods 0.000 abstract description 28
- 239000003960 organic solvent Substances 0.000 abstract description 16
- 239000007810 chemical reaction solvent Substances 0.000 abstract description 13
- LLLVZDVNHNWSDS-UHFFFAOYSA-N 4-methylidene-3,5-dioxabicyclo[5.2.2]undeca-1(9),7,10-triene-2,6-dione Chemical compound C1(C2=CC=C(C(=O)OC(=C)O1)C=C2)=O LLLVZDVNHNWSDS-UHFFFAOYSA-N 0.000 abstract description 2
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 66
- VIQSRHWJEKERKR-UHFFFAOYSA-L disodium;terephthalate Chemical compound [Na+].[Na+].[O-]C(=O)C1=CC=C(C([O-])=O)C=C1 VIQSRHWJEKERKR-UHFFFAOYSA-L 0.000 description 38
- 238000001069 Raman spectroscopy Methods 0.000 description 35
- 238000001228 spectrum Methods 0.000 description 33
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 25
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 22
- 238000000354 decomposition reaction Methods 0.000 description 21
- 239000000126 substance Substances 0.000 description 21
- 230000000052 comparative effect Effects 0.000 description 20
- 230000002829 reductive effect Effects 0.000 description 17
- 230000007062 hydrolysis Effects 0.000 description 16
- 239000002244 precipitate Substances 0.000 description 16
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 14
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 14
- 239000002904 solvent Substances 0.000 description 14
- 239000000243 solution Substances 0.000 description 13
- IAZDPXIOMUYVGZ-UHFFFAOYSA-N Dimethylsulphoxide Chemical compound CS(C)=O IAZDPXIOMUYVGZ-UHFFFAOYSA-N 0.000 description 12
- 238000002844 melting Methods 0.000 description 11
- 230000008018 melting Effects 0.000 description 11
- 239000007787 solid Substances 0.000 description 11
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- 239000008213 purified water Substances 0.000 description 9
- 238000007792 addition Methods 0.000 description 8
- 238000009835 boiling Methods 0.000 description 8
- WOZVHXUHUFLZGK-UHFFFAOYSA-N dimethyl terephthalate Chemical compound COC(=O)C1=CC=C(C(=O)OC)C=C1 WOZVHXUHUFLZGK-UHFFFAOYSA-N 0.000 description 8
- 150000002148 esters Chemical class 0.000 description 7
- 239000011780 sodium chloride Substances 0.000 description 7
- YMWUJEATGCHHMB-UHFFFAOYSA-N Dichloromethane Chemical compound ClCCl YMWUJEATGCHHMB-UHFFFAOYSA-N 0.000 description 6
- 230000007423 decrease Effects 0.000 description 6
- LRUDDHYVRFQYCN-UHFFFAOYSA-L dipotassium;terephthalate Chemical compound [K+].[K+].[O-]C(=O)C1=CC=C(C([O-])=O)C=C1 LRUDDHYVRFQYCN-UHFFFAOYSA-L 0.000 description 6
- 239000000835 fiber Substances 0.000 description 6
- 238000003756 stirring Methods 0.000 description 6
- 230000002378 acidificating effect Effects 0.000 description 5
- 229910052500 inorganic mineral Inorganic materials 0.000 description 5
- 150000002500 ions Chemical class 0.000 description 5
- 238000005259 measurement Methods 0.000 description 5
- 239000011707 mineral Substances 0.000 description 5
- 230000036632 reaction speed Effects 0.000 description 5
- 238000010992 reflux Methods 0.000 description 5
- 159000000000 sodium salts Chemical class 0.000 description 5
- 230000008961 swelling Effects 0.000 description 5
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 description 4
- 239000003054 catalyst Substances 0.000 description 4
- 239000007795 chemical reaction product Substances 0.000 description 4
- 239000000155 melt Substances 0.000 description 4
- 125000001997 phenyl group Chemical group [H]C1=C([H])C([H])=C(*)C([H])=C1[H] 0.000 description 4
- 239000002994 raw material Substances 0.000 description 4
- 231100000331 toxic Toxicity 0.000 description 4
- 230000002588 toxic effect Effects 0.000 description 4
- 238000012795 verification Methods 0.000 description 4
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 description 3
- 101100494773 Caenorhabditis elegans ctl-2 gene Proteins 0.000 description 3
- 101100112369 Fasciola hepatica Cat-1 gene Proteins 0.000 description 3
- 101100005271 Neurospora crassa (strain ATCC 24698 / 74-OR23-1A / CBS 708.71 / DSM 1257 / FGSC 987) cat-1 gene Proteins 0.000 description 3
- 150000001298 alcohols Chemical class 0.000 description 3
- 239000007864 aqueous solution Substances 0.000 description 3
- 235000013361 beverage Nutrition 0.000 description 3
- 150000001875 compounds Chemical class 0.000 description 3
- 238000009826 distribution Methods 0.000 description 3
- 230000009969 flowable effect Effects 0.000 description 3
- 238000009998 heat setting Methods 0.000 description 3
- 239000012535 impurity Substances 0.000 description 3
- 239000012263 liquid product Substances 0.000 description 3
- 239000000178 monomer Substances 0.000 description 3
- 229920003023 plastic Polymers 0.000 description 3
- 239000004033 plastic Substances 0.000 description 3
- 238000007086 side reaction Methods 0.000 description 3
- 238000012360 testing method Methods 0.000 description 3
- BYEAHWXPCBROCE-UHFFFAOYSA-N 1,1,1,3,3,3-hexafluoropropan-2-ol Chemical compound FC(F)(F)C(O)C(F)(F)F BYEAHWXPCBROCE-UHFFFAOYSA-N 0.000 description 2
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 2
- 238000001237 Raman spectrum Methods 0.000 description 2
- 230000009471 action Effects 0.000 description 2
- 238000005904 alkaline hydrolysis reaction Methods 0.000 description 2
- 230000008901 benefit Effects 0.000 description 2
- 238000007664 blowing Methods 0.000 description 2
- 239000006227 byproduct Substances 0.000 description 2
- BVKZGUZCCUSVTD-UHFFFAOYSA-N carbonic acid Chemical compound OC(O)=O BVKZGUZCCUSVTD-UHFFFAOYSA-N 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 238000012790 confirmation Methods 0.000 description 2
- 238000002425 crystallisation Methods 0.000 description 2
- 230000008025 crystallization Effects 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- NWJKPSLXLQLUTC-UHFFFAOYSA-N ethane-1,2-diol;sodium Chemical compound [Na].OCCO NWJKPSLXLQLUTC-UHFFFAOYSA-N 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 239000004744 fabric Substances 0.000 description 2
- 239000012634 fragment Substances 0.000 description 2
- 239000007789 gas Substances 0.000 description 2
- 230000009477 glass transition Effects 0.000 description 2
- 230000034659 glycolysis Effects 0.000 description 2
- WGCNASOHLSPBMP-UHFFFAOYSA-N hydroxyacetaldehyde Natural products OCC=O WGCNASOHLSPBMP-UHFFFAOYSA-N 0.000 description 2
- BDAGIHXWWSANSR-UHFFFAOYSA-N methanoic acid Natural products OC=O BDAGIHXWWSANSR-UHFFFAOYSA-N 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- BWHMMNNQKKPAPP-UHFFFAOYSA-L potassium carbonate Chemical compound [K+].[K+].[O-]C([O-])=O BWHMMNNQKKPAPP-UHFFFAOYSA-L 0.000 description 2
- 238000010298 pulverizing process Methods 0.000 description 2
- 238000000746 purification Methods 0.000 description 2
- 239000011541 reaction mixture Substances 0.000 description 2
- 229910000029 sodium carbonate Inorganic materials 0.000 description 2
- 230000003595 spectral effect Effects 0.000 description 2
- 239000002699 waste material Substances 0.000 description 2
- PWKNBLFSJAVFAB-UHFFFAOYSA-N 1-fluoro-2-nitrobenzene Chemical compound [O-][N+](=O)C1=CC=CC=C1F PWKNBLFSJAVFAB-UHFFFAOYSA-N 0.000 description 1
- XRBXGZZMKCBTFP-UHFFFAOYSA-N 4-(2,2-dihydroxyethoxycarbonyl)benzoic acid Chemical compound OC(O)COC(=O)C1=CC=C(C(O)=O)C=C1 XRBXGZZMKCBTFP-UHFFFAOYSA-N 0.000 description 1
- OSWFIVFLDKOXQC-UHFFFAOYSA-N 4-(3-methoxyphenyl)aniline Chemical compound COC1=CC=CC(C=2C=CC(N)=CC=2)=C1 OSWFIVFLDKOXQC-UHFFFAOYSA-N 0.000 description 1
- 229920000742 Cotton Polymers 0.000 description 1
- AEMRFAOFKBGASW-UHFFFAOYSA-M Glycolate Chemical compound OCC([O-])=O AEMRFAOFKBGASW-UHFFFAOYSA-M 0.000 description 1
- 239000004698 Polyethylene Substances 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 229910000147 aluminium phosphate Inorganic materials 0.000 description 1
- 238000003556 assay Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- QPKOBORKPHRBPS-UHFFFAOYSA-N bis(2-hydroxyethyl) terephthalate Chemical compound OCCOC(=O)C1=CC=C(C(=O)OCCO)C=C1 QPKOBORKPHRBPS-UHFFFAOYSA-N 0.000 description 1
- 125000003178 carboxy group Chemical group [H]OC(*)=O 0.000 description 1
- 238000002144 chemical decomposition reaction Methods 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 239000000356 contaminant Substances 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 125000004122 cyclic group Chemical group 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000010790 dilution Methods 0.000 description 1
- 239000012895 dilution Substances 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 239000012153 distilled water Substances 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 238000004880 explosion Methods 0.000 description 1
- 238000006446 extruder reaction Methods 0.000 description 1
- 239000012530 fluid Substances 0.000 description 1
- 238000005243 fluidization Methods 0.000 description 1
- 235000019253 formic acid Nutrition 0.000 description 1
- 230000036541 health Effects 0.000 description 1
- XLYOFNOQVPJJNP-ZSJDYOACSA-N heavy water Substances [2H]O[2H] XLYOFNOQVPJJNP-ZSJDYOACSA-N 0.000 description 1
- 239000000413 hydrolysate Substances 0.000 description 1
- 125000004356 hydroxy functional group Chemical group O* 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 230000000670 limiting effect Effects 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 230000000877 morphologic effect Effects 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
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- 239000002245 particle Substances 0.000 description 1
- 235000012736 patent blue V Nutrition 0.000 description 1
- 238000000053 physical method Methods 0.000 description 1
- 239000003495 polar organic solvent Substances 0.000 description 1
- 239000002798 polar solvent Substances 0.000 description 1
- 229910000027 potassium carbonate Inorganic materials 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 230000000750 progressive effect Effects 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 238000000550 scanning electron microscopy energy dispersive X-ray spectroscopy Methods 0.000 description 1
- 229940023144 sodium glycolate Drugs 0.000 description 1
- 229910001415 sodium ion Inorganic materials 0.000 description 1
- 239000011343 solid material Substances 0.000 description 1
- 239000007790 solid phase Substances 0.000 description 1
- 239000012265 solid product Substances 0.000 description 1
- 238000007711 solidification Methods 0.000 description 1
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- WROMPOXWARCANT-UHFFFAOYSA-N tfa trifluoroacetic acid Chemical compound OC(=O)C(F)(F)F.OC(=O)C(F)(F)F WROMPOXWARCANT-UHFFFAOYSA-N 0.000 description 1
- 238000005979 thermal decomposition reaction Methods 0.000 description 1
- 231100000419 toxicity Toxicity 0.000 description 1
- 230000001988 toxicity Effects 0.000 description 1
- JEJAMASKDTUEBZ-UHFFFAOYSA-N tris(1,1,3-tribromo-2,2-dimethylpropyl) phosphate Chemical compound BrCC(C)(C)C(Br)(Br)OP(=O)(OC(Br)(Br)C(C)(C)CBr)OC(Br)(Br)C(C)(C)CBr JEJAMASKDTUEBZ-UHFFFAOYSA-N 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
- C07C51/09—Preparation of carboxylic acids or their salts, halides or anhydrides from carboxylic acid esters or lactones
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
- C07C51/02—Preparation of carboxylic acids or their salts, halides or anhydrides from salts of carboxylic acids
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
- C07C51/41—Preparation of salts of carboxylic acids
- C07C51/412—Preparation of salts of carboxylic acids by conversion of the acids, their salts, esters or anhydrides with the same carboxylic acid part
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C63/00—Compounds having carboxyl groups bound to a carbon atoms of six-membered aromatic rings
- C07C63/14—Monocyclic dicarboxylic acids
- C07C63/15—Monocyclic dicarboxylic acids all carboxyl groups bound to carbon atoms of the six-membered aromatic ring
- C07C63/26—1,4 - Benzenedicarboxylic acid
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
- Separation, Recovery Or Treatment Of Waste Materials Containing Plastics (AREA)
- Polyesters Or Polycarbonates (AREA)
Abstract
The invention relates to the technical field of preparation of terephthalic acid, in particular to terephthalic acid, a preparation method thereof and a method for recycling polyethylene terephthalate with high polymerization degree. The preparation method of the terephthalic acid comprises the following steps: mixing molten high-polymerization-degree polyethylene terephthalate, alkali metal-containing strong alkali, alkali metal-containing weak acid salt and ethylene glycol for solvent-free reaction, wherein the amount of the ethylene glycol is less than 10% of the mass of the high-polymerization-degree polyethylene terephthalate. The preparation method can hydrolyze the ethylene terephthalate with high polymerization degree on the basis of not using an organic solvent as a reaction solvent, and improves the yield of terephthalic acid. In particular, the problems of safety and low reaction rate of the organic solvent in the economic hydrolysis reaction of PET can be improved, and particularly, the problems of low reaction rate of PET with high polymerization degree, which is difficult to react in PET bottles, and the like, are solved.
Description
Technical Field
The invention relates to the technical field of preparation of terephthalic acid, in particular to terephthalic acid, a preparation method thereof and a method for recycling polyethylene terephthalate with high polymerization degree.
Background
In order to realize chemical recycling of polyethylene terephthalate (hereinafter abbreviated as "PET"), it is necessary to break molecular chains in a high-temperature and high-pressure environment by using a glycol (hereinafter abbreviated as "EG") solvent to complete depolymerization; or in an acidic or alkaline environment, in a polar solvent such as alcohols, etc.
At this time, if PET is smaller thanWhen the polymerization degree is not high, the following three methods (equation 1) are mainly used.
The method comprises the following steps: as shown in (a) of (reaction 1), a process for producing dimethyl terephthalate (DMT) by decomposition in a methanol solvent by methanol decomposition. An amount of an organic solvent, such as dimethyl sulfoxide (DMSO), methylene chloride (Dichloromethane), etc., is mixed to promote swelling of the PET so that the reaction is completed under weak conditions.
The second method is as follows: as shown in (b) of [ reaction scheme 1], it is relatively easy to decompose terephthalic acid disodium salt (TRA-Na 2) and Ethylene Glycol (EG) by hydrolysis with an alkaline substance such as NaOH in a polar organic solvent, and TPA-Na2 is easily converted to terephthalic acid (TPA) by the action of an acid. The process is widely applied to the fields of recycling polyethylene terephthalate fiber garbage, PET cloth reduction processing and the like. It is considered that a large amount of hydrolysis can be accomplished by adding an organic solvent for swelling molecular chains (e.g., DMSO) and by heat generated when an alkaline substance is dissolved in an alcohol. In this case, in the case of a fiber or a packaging material having a low degree of polymerization of PET, some of the fibers can be hydrolyzed even if the fibers cannot be hydrolyzed completely, but in the case of a PET bottle or the like having a high degree of polymerization, the degree of hydrolysis is very small because of the poor swelling effect of DMSO.
The third method is as follows: as shown in (c) of (reaction formula 1), ethylene Glycol (EG) is used as a solvent to carry out glycolysis of PET under high temperature and high pressure conditions to decompose the PET into dihydroxyethyl terephthalate (BHET) and an oligomer state, which is a method for recycling PET waste, which has been most widely used since a long time ago, by PET manufacturing enterprises. These reaction products can be mixed again into the polymerization process for PET polymerization. In this case, a method of recycling PET waste with little contamination in PET production is mainly used. This is because, when PET is polymerized, if the purity of the raw material is not high, the polymer is degraded, so that a high purity raw material is used, but when PET is regenerated using a PET bottle or the like, it is difficult to clean up the contaminants adhering to PET, and it is difficult to extract the obtained oligomer with high purity.
Therefore, the above-mentioned methods are all methods in which an organic solvent is used as a reaction solvent and then a decomposition reaction is carried out, and are applicable to PET having a low degree of polymerization and a relatively loose molecular chain state, but are hardly applicable to products having a high degree of polymerization of more than iv=0.75 dl/g and tightly packed molecular chains, such as PET bottles, due to solid-phase polymerization and heat setting (HEATSETTING) treatment. In practice, PET bottle pulverized materials (pulverized materials such as mineral water bottles and beverage bottles) are mixed in a weight ratio such that solid materials account for about 30%, and when alkali hydrolysis is performed in a high-pressure reaction tube with an alcohol solvent, reflux is performed at a reaction pressure of 3 to 5bar and an alcohol boiling temperature, and stirring is vigorously performed. Even if the hydrolysis reaction was performed for one week in this way, there was 20% of PET residues. In particular to a heat-resistant PET bottle for beverages, the production process comprises a heat setting process which is much stronger than the primary blowing process of a common mineral water bottle, namely a secondary blowing process, has high molecular weight and higher degree of tightness of molecular chains required for crystallization, so that alkali hydrolysis is more difficult to carry out than the common mineral water bottle. These materials are also difficult to dissolve in the powerful solvents such as Hexafluoroisopropanol (HFIP) and trifluoroacetic acid (TFA) used in the assay PETIV, and even leave considerable amounts of undissolved material, so that more undissolved residue is produced when ordinary hydrolysis is performed. The surface of these residues is swelled by the solvent and then is coagulated like cake, and is stuck to the inner wall of the reactor and the stirrer, as a result, the reactor can not work or the discharge port of the reactor is blocked, and normal discharge is difficult. Alcohols used as common hydrolysis solvents, such as methanol, ethanol, etc., have similar hydrolysis results even with differences in solvent polarity, and the addition of swelling organic solvents (DMSO, CH 2Cl2), etc., at a unit% level, has not significantly improved the results.
It is clear that when PET having a high degree of polymerization is hydrolyzed by a known method, hydrolysis starts at a part of the surface, but the PET cannot be further decomposed to the inside due to the high degree of polymerization, and swelling occurs only at the surface. After the surface becomes tacky like a gel, the PET chips stick together even with vigorous stirring, stick to the inner wall of the reactor and the stirrer, etc. over time, and even the reaction product sticks to it, forming cake-like hard lumps. As a result, the acid and alkali substances cannot further penetrate into the reaction vessel, and the decomposition reaction rate is greatly reduced, so that the normal reaction cannot be performed. There is a method of minimizing this phenomenon, namely, pulverizing PET as much as possible, but it is difficult to physically pulverize PET at normal temperature because PET is highly amorphous. Particularly, PET bottles are difficult to pulverize into powder, and therefore are cut into small pieces as much as possible for use. Generally, plastic products are pulverized by a liquid nitrogen ultra-low temperature pulverizer or a ball mill, and although the pulverizing effect of crystalline polymers or polymers having high hardness is good, PET is difficult to pulverize because of its high degree of amorphism. In addition, the difficulty is greater for the high polymerization PET, and the crushing method is meaningless from the economic point of view.
For the above reasons, PET having a high polymerization degree has not been almost economically and practically recycled, and a main recycling method is to simply melt-spin and spin the PET after washing and drying to obtain low-grade fibers such as cotton and staple fibers.
In summary, the chemical decomposition of PET with a high degree of polymerization has the following problems:
(1) In the traditional method, a toxic and flammable low-boiling point organic solvent is used as a reaction solvent, and in order to realize the rapid reaction, the heating and pressurizing reaction is also carried out. The most common solvents used for alkaline hydrolysis are alcohols such as ethanol and methanol, which are toxic to the skin and eyes, although to different extents, and have low boiling point, strong volatility, flammability, strong steam toxicity, and risk of explosion.
(2) If EG is depolymerized, cyclic oligomers harmful to the human body, BHT and other substances are produced, and if PET for mineral water and food containers is produced again, health risks may be raised. Specifically, when hydrolysis is performed by adding a swelling organic solvent such as DMSO or CH 2Cl2, it is necessary to re-separate these substances after the reaction, and it is difficult to obtain a high-purity monomer product because of by-products. To obtain a high purity product, a high level of purification equipment is required. In addition, the end product of the decomposition is not TPA, but rather dimethyl terephthalate (DMT), and impurities such as various monomers and oligomers including TPA are formed. In this case, purification is hardly possible, and it is not useful as a raw material for PET polymerization requiring ultra-high purity.
(3) The more critical problem is that the decomposition of (a), (b) and (c) of (equation 1) is hardly caused in the high polymerization degree PET having iv=0.75 dl/g or more. Of the high polymerization degree PET with iv=0.75 dl/g or more, the most representative product is PET mineral water bottle; the PET heat-resistant bottle for the beverage is more difficult to decompose due to higher crystallization degree; the high strength yarn of PET tire ring and the like which need stronger mechanical property reaches IV=1.0 to 1.2dl/g.
In view of this, the present invention has been made.
Disclosure of Invention
The invention aims to provide terephthalic acid, a preparation method thereof and a method for recycling polyethylene terephthalate with high polymerization degree. The preparation method provided by the embodiment of the invention can hydrolyze the ethylene terephthalate with high polymerization degree on the basis of not using an organic solvent as a reaction solvent, and improves the yield of terephthalic acid. In particular, the problems of safety and low reaction rate of the organic solvent in the economic hydrolysis reaction of PET can be improved, and particularly, the problems of low reaction rate of PET with high polymerization degree, which is difficult to react in PET bottles, and the like, are solved.
The invention is realized in the following way:
in a first aspect, the present invention provides a process for producing terephthalic acid comprising: mixing molten high-polymerization-degree polyethylene terephthalate, alkali metal-containing strong alkali, alkali metal-containing weak acid salt and ethylene glycol for solvent-free reaction, wherein the amount of the ethylene glycol is less than 10% of the mass of the high-polymerization-degree polyethylene terephthalate.
In an alternative embodiment, the method comprises: mixing and melting polyethylene terephthalate with high polymerization degree and first alkali containing alkali metal to form first molten liquid, mixing the first molten liquid, second alkali containing alkali metal, weak acid salt and ethylene glycol, and then carrying out multi-stage heating;
Wherein the dosage of the first strong base and the dosage of the second strong base which is 5-10% of the weight of the high-polymerization degree polyethylene terephthalate are 2-2.5 times equivalent of the high-polymerization degree polyethylene terephthalate; the dosage of the weak acid salt is 0.1-0.5 times equivalent of the polyethylene terephthalate with high polymerization degree; the dosage of the ethylene glycol is 0.1 to 0.3 times equivalent of the polyethylene terephthalate with high polymerization degree.
In an alternative embodiment, the method comprises: and simultaneously adding the polyethylene terephthalate with high polymerization degree and the first strong base into a continuous extruder to melt to form the first molten liquid, adding the mixture of the second strong base, the weak acid salt and the ethylene glycol into the inner position of the continuous extruder where the first molten liquid is located, and then carrying out multi-stage heating in different reaction areas of the continuous extruder.
In an alternative embodiment, the temperature at which the first melt is formed is 100-180 ℃, and the temperature at which the mixture is added is 150-230 ℃; the temperature at this time does not mean the temperature of the mixture itself, but means that the temperature of the internal position of the continuous extruder where the first melt is located is 150 to 230 ℃ when the mixture is added;
preferably, the multi-stage heating comprises: heating at 180-230deg.C, heating at 180-200deg.C, and heating at 150-180deg.C;
preferably, the pressure is no higher than 3 normal atmospheres, preferably 2.5 to 3 normal atmospheres, throughout the process of producing the terephthalic acid.
In an alternative embodiment, the method comprises: post-treating alkali metal terephthalate formed by solvent-free reaction;
preferably, the post-treatment comprises: the alkali metal terephthalate is mixed with water, filtered and centrifuged, and then acid is added.
In an alternative embodiment, the high degree of polymerization polyethylene terephthalate has a polymer greater than Preferably greater than
Preferably, the polymer of the high degree of polymerization polyethylene terephthalate is selected from homopolymers or copolymers.
In an alternative embodiment, the alkali metal is selected from any one of lithium, sodium and potassium.
In an alternative embodiment, the weak acid salt includes any one of carbonate, bicarbonate, phosphate, hydrogen phosphate, dihydrogen phosphate, acetate, and formate.
In a second aspect, the present invention provides a terephthalic acid prepared by the method for preparing terephthalic acid according to any one of the previous embodiments.
In a third aspect, the present invention provides a process for recovering polyethylene terephthalate having a high degree of polymerization, comprising the process for producing terephthalic acid according to any one of the preceding embodiments.
The invention has the following beneficial effects: the invention can rapidly hydrolyze the materials which are difficult to hydrolyze by the traditional method through solvent-free reaction under the condition of not using toxic organic solvent as reaction solventThe above PET with high polymerization degree can be used for preparing high-purity terephthalic acid with high yield and safety.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the embodiments will be briefly described below, it being understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and other related drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic process diagram of a solvent-free reaction according to an embodiment of the present invention;
FIG. 2 is a morphological cross-sectional view of a screw of an extruder provided by an embodiment of the present invention;
FIG. 3 is a Raman spectrometer spectrum of a high polymerization degree PET used in an embodiment of the present invention;
FIG. 4 is a Raman spectrometer spectrum of a standard substance of terephthalic acid sodium salt provided by the embodiment of the invention;
FIG. 5 is a Raman spectrometer spectrum of a terephthalic acid standard substance provided by an embodiment of the invention;
FIG. 6 is a Raman spectrometer spectrum of the terephthalic acid sodium salt prepared in example 1 provided in the example of the present invention;
FIG. 7 is a Raman spectrometer spectrum of terephthalic acid prepared in example 1 provided in the examples of the present invention;
FIG. 8 is a Raman spectrometer spectrum of the terephthalic acid sodium salt prepared in comparative example 1 provided in the example of the present invention;
FIG. 9 is a Raman spectrometer spectrum of the terephthalic acid sodium salt prepared in comparative example 2 provided in the example of the present invention;
FIG. 10 is a Raman spectrometer spectrum of the terephthalic acid sodium salt prepared in comparative example 3 provided in the example of the present invention;
FIG. 11 is a Raman spectrometer spectrum of the terephthalic acid sodium salt prepared in comparative example 4 provided in the example of the present invention;
FIG. 12 is a Raman spectrometer spectrum of terephthalic acid prepared in comparative example 5 provided in the present invention;
FIG. 13 is a Raman spectrometer spectrum of the terephthalic acid sodium salt prepared in comparative example 6 provided in the example of the present invention;
FIG. 14 is a Raman spectrometer spectrum of the terephthalic acid sodium salt prepared in comparative example 7 provided in the example of the present invention;
FIG. 15 is a Raman spectrometer spectrum of terephthalic acid prepared in comparative example 8 provided in the present invention;
FIG. 16 is a Raman spectrometer spectrum of the potassium terephthalate salt prepared in example 2 provided in the examples of the present invention;
FIG. 17 is a Raman spectrometer spectrum of terephthalic acid prepared in example 2 provided in the present invention;
FIG. 18 is a 500-fold NaSEM-EDS profile of verification example 2 provided in an example of the present invention;
FIG. 19 is a 500-fold NaSEM-EDS profile of verification example 1 provided in an example of the present invention;
FIG. 20 is a graph showing the relationship between the temperature and vapor pressure of EG provided by an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below. The specific conditions are not noted in the examples and are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.
The embodiment of the invention provides a preparation method of terephthalic acid, which comprises the following steps: mixing molten high-polymerization-degree polyethylene terephthalate, alkali containing alkali metal, weak acid salt of the alkali metal and ethylene glycol for solvent-free reaction, wherein the amount of the ethylene glycol is less than 10% of the mass of the high-polymerization-degree polyethylene terephthalate.
Specifically, the conventional decomposition reaction is a decomposition reaction performed by pouring an organic solvent such as ethanol or methanol or the like as a reaction solvent into a reactor, but there are problems. In the embodiment of the invention, PET is melted, and the melted PET is not only a reaction substance, but also plays a role similar to a solvent, and does not actually add an organic solvent as a reaction solvent, and then a solvent-free continuous decomposition reaction is carried out. Catalyst levels of ethylene glycol, alkali containing strong base of alkali, weak acid salts of the alkali are added based on the use of molten PET. NaOH is used as an example of alkali containing alkali metal, and NaOH and a salt of weak acid (carbonic acid) (sodium carbonate) thereof are poured. After hydrolysis of PET, the reaction was carried out according to [ equation 2] to give terephthalic acid disodium salt (TPA-Na 2) and ethylene glycol, with the concentration of Na + gradually decreasing and the hydrolysis reaction rate gradually slowing down. However, if Na 2CO3 is a weak acid salt of Na +, it will dissolve into EG to produce more Na +, and the concentration of Na + released by NaOH will increase further to produce more NaO-C 2H4 -ONa. Thereby preventing the Na + concentration from decreasing due to the hydrolysis reaction of PET and ensuring the reaction speed to be kept at a faster level.
It is also understood that in the embodiment of the present invention, although ethylene glycol is added, it is not used as a reaction solvent, and if it is used as a reaction solvent initially, the amount of ethylene glycol added should be 200% of the polyethylene terephthalate with high polymerization degree, and in the embodiment of the present invention, the function of the added amount of ethylene glycol is not to dissolve the reaction substance, but a catalyst. That is, the initially added EG reacts with alkali metal to form an alkali metal salt (e.g., sodium glycolate) that catalyzes a more uniform and rapid reaction. In addition, EG is a reaction product produced by the decomposition reaction of PET, and its action corresponds to a diluted solution for reducing the viscosity of unreacted molten PET, and is not a reaction solvent because EG is not externally added in order to promote the reaction. If a large amount of EG is initially added (i.e., as a reaction solvent), the main reaction is adversely affected due to the glycolysis phenomenon occurring in the side reaction.
Reaction formula 2:
Na2CO3→2Na+Co3 -2 (1)
2NaOH+HO-C2H4-OH→NaO-C2H4ONa+2H2O (2)
PET+NaOC2H4-ONa→Na-TPANa+HO-C2H4OH (3)。
In the decomposition reaction adopted in the embodiment of the invention, an organic solvent which is inflammable and harmful to human bodies is not used as a reaction solvent, but the solvent-free reaction is carried out by melting PET and alkali containing alkali metals (such as KOH, naOH and the like) and adding alkali metal salt and glycol which are equivalent to catalysts. The advantage of solvent-free reactions is that they have no harmful compounds which are independent of the reaction and are present only as solvents, and they have very good results in terms of safety, reaction rate and speed.
In terms of the reaction rate, the concentration dilution caused by the reaction solvent is avoided, and the reaction between the reaction substances directly occurs (namely, the reaction concentration is 100%), so that the reaction speed is faster than that when the solvent is used, the side reaction is less, and the impurities are obviously reduced. However, there is a problem in that, when such solvent-free reaction is performed, the melt viscosity of PET is far higher than that of a general organic solvent reaction, so that it is difficult to mix the reaction materials in a batch reactor. A very effective way to solve the above problems is to use a mixing device such as an extruder as a reactor. It is also important that the reaction rate be increased by lowering the reaction temperature and melt viscosity when the reaction is carried out with an extruder.
Specifically, in the embodiment of the invention, a continuous extruder is adopted for melting, solvent-free reaction and the like. The extruder is the most common continuous reactor. The extruder may combine the screws it uses into something else in the form of a screw. That is, the equipment characteristics can be set according to the reaction conditions such as the temperature and pressure of the reaction zone, and since it is continuous, a high yield can be obtained with a small apparatus. Of course, when a high efficiency twin screw extruder is used, it can react faster and in higher yield than a single screw extruder due to its higher mixing efficiency.
Further, referring to fig. 1, the continuous extruder has 5 reaction zones, with different feeds being added and different reactions being carried out in the 5 different reaction zones. First, the polyethylene terephthalate with high polymerization degree is fed into a continuous reactor in the form of an extruder, i.e., into the reaction zone 1, and then heated and pressurized to prepare the flowable polyethylene terephthalate, i.e., the molten polyethylene terephthalate with high polymerization degree.
Preferably, the alkali metal-containing first strong base is added simultaneously with the addition of the high-polymerization degree polyethylene terephthalate, wherein the amount of the first strong base is 5 to 10% by weight of the high-polymerization degree polyethylene terephthalate, and the polymer of the high-polymerization degree polyethylene terephthalate is larger thanPreferably greater thanThe polymer of the polyethylene terephthalate with high polymerization degree is selected from homopolymers or copolymers.
In this case, the screws of the extruder are not of the same screw structure as a whole, but are structured to conform to the characteristics of each reaction zone as shown in fig. 2. Adopts a structure which meets the reaction purpose of a reaction zone 1 (PET feeding) - > a reaction zone 2 (NaOH mixing) - > a reaction zone 3 (1 time reaction) - > a reaction zone 4 (2 time reaction) - > a reaction zone 5 (discharging).
Then, a mixture of a second alkali, a weak acid salt of an alkali metal and ethylene glycol is added to the internal position of the continuous extruder where the first melt is located, namely a reaction zone 2, and then the molten polyethylene terephthalate and the mixture are subjected to multi-stage heating in the extruder in different reaction zones of the continuous extruder to perform solvent-free reaction, so as to prepare alkali metal terephthalate.
In order to keep the lower reaction temperature and improve the mixing effect, the embodiment of the invention adopts a method of pouring alkali twice. First, when PET is fed into a continuous reactor (extruder) for the first time, a small amount of alkali (e.g., naOH) is mixed, and 1 hydrolysis reaction occurs, so that the average molecular weight of PET decreases and the melting temperature decreases. Meanwhile, the additive is mixed with a small amount of EG generated, the viscosity is further reduced, the reaction condition is milder, and the decomposition reaction is easier to control. Then, the main decomposition reaction was carried out, and the mixture comprising the alkali metal base, the alkali metal salt of weak acid and ethylene glycol was fed to the mixing zone (reaction zone 2) of the continuous reactor having a reaction temperature of 2 times or less in sufficient amount. Even if the feed amount is excessive, the PET viscosity is reduced after 1 time of hydrolysis, and the mixing becomes easier. Namely, the second alkali, the first alkali and the alkali metal-containing alkali are all the same alkali. The alkali containing alkali is divided into two times, and in order to distinguish the time of addition, the embodiment of the invention is named as a second alkali and a first alkali.
Further, the amount of the second strong base is 2 to 2.5 times equivalent weight of the polyethylene terephthalate with high polymerization degree; the dosage of the weak acid salt is 0.1-0.5 times equivalent of the polyethylene terephthalate with high polymerization degree; the dosage of the ethylene glycol is 0.1 to 0.3 times equivalent of the polyethylene terephthalate with high polymerization degree. The alkali metal is selected from any one of lithium, sodium and potassium. The weak acid salt can be carbonate or bicarbonate formed by alkali metal and carbonic acid; can be phosphate, hydrogen phosphate or dihydrogen phosphate formed by alkali metal and phosphoric acid; the catalyst may be acetate formed by alkali metal and acetic acid or formate formed by alkali metal and formic acid. The alkali metal in the strong base and the alkali metal in the weak acid salt are the same alkali metal.
Further, when the temperature of each reaction zone in the extruder is set, thermal characteristics of PET, that is, glass transition temperature (Tg: about 70 ℃), melting point (Tm: about 250 to 260 ℃ in general), boiling point of EG (b.p: 197 ℃ C., 1 standard atmospheric pressure) and the like are most considered, and if pressure is generated, these temperatures naturally differ from ordinary temperature.
Details of each reaction zone are as follows:
The first reaction zone is a PET feeding zone, and the conveyed PET solid chips are converted into fluid objects under the heat and pressure of the screw and the block, and pushed forward. In this case, if only PET is fed, it is necessary to raise the temperature to the melting temperature in order to fluidize PET, and the melt viscosity is too high. To ensure the supply and fluidization, alkali is mixed in the fed PET in an amount of 5-10% by weight, and the hydrolysis reaction is carried out 1 time while the fed PET is fed, so that the melting point and viscosity can be reduced, and the feeding becomes easier.
In addition, the form of the extruder screw is also important. Generally, a screw having a larger pitch is used as the particle diameter of the raw material to be fed is larger. In order to ensure that the PET bottle fragments can be smoothly fed, the screw adopts a larger screw pitch when common PET fragments are used. At this time, the initial temperature of the PET-supplying region, i.e., the reaction region 1, is maintained between the glass transition temperature (Tg) and the melting point (Tm) of PET, typically 100-180℃so that the PET melts when 1 decomposition is performed. This ensures that sufficient mixing with 2 feeds of base is possible in the second mixing zone, reaction zone 2.
The second reaction zone 2 is a mixing zone. In this case, the screw is designed to mix the flowable PET and the alkali pushed from the feed zone and to increase the mixing efficiency. First, a mixture was prepared by mixing a small amount of EG with a slightly larger equivalent ratio of alkali (e.g., naOH, KOH) and a weak acid salt of an alkali metal (e.g., na 2CO3、K2CO3, etc.). As a result, EG and alkali MOH (M: alkali metal) react to form a metalloglycolate as shown in the following (equation 3). In addition, a part of the metal salt M 2CO3 is dissociated into M + ions and CO 3 -2 ions, and all of these ions are in a mixed state. At this time, the amount of M + ions is about 10 to 20% more than the equivalent ratio.
Reaction formula 3:
HO-CH2CH2-OH+2M++20H-→MO-CH2CH2-OM+H2O
The mixture was quantitatively pushed into the mixing zone of the main extruder with a gear pump or a2 nd feeding extruder and thoroughly mixed with the flowable PET. In reaction zone 2, the temperature starts below PETTm and then gets lower and lower to near the end of reaction zone 2, bringing the temperature to around 200 ℃. As the mobile PET flows into reaction zone 2 through the end of reaction zone 1, the Tm of the PET decreases due to 1 hydrolysis. This temperature factor and 1 hydrolysis results in a decrease in molecular weight and thus a decrease in viscosity, and by properly adjusting the temperature of reaction zone 2, the tangential force of mixing is maintained, allowing the PET and mixture to be thoroughly mixed. In the reaction zone 2, the two reaction substances are mixed, a partial reaction further occurs, but the completion of the reaction is completed in the third reaction zone 3 and the fourth reaction zone 4, and a screw structure capable of improving the mixing efficiency is adopted.
At the end of the reaction zone 2, the temperature of the reaction mass is adjusted to about 150-200 ℃ and the reaction mass can enter the next reaction zone 3.
Reaction zone 3 is the zone where 1 reaction occurs, as shown in [ equation 4], where the reaction of PET with the metallo glycolate occurs, and where most of the alkaline hydrolysis reaction of PET occurs.
Reaction formula 4:
At this time, the screw will use a structure with a narrower pitch than the feed zone to ensure the reaction pressure and continuously push the reaction mass forward. Even if other plastics such as PP, PE and PS are mixed in the decomposition reaction of PET, the decomposition reaction is not affected, and the other plastics are not involved in the reaction, and remain as they are, and can be removed by a physical method. When the most common alkaline substance NaOH is used, the product consists of disodium terephthalate and EG, but is not completely hydrolyzed to a mixture with PET in the oligomeric state.
The initial reaction temperature of the reaction zone 3 is 150-200 ℃ from the reaction zone 2, the temperature is increased by 20-30 ℃, and the hydrolysis reaction rate is improved to the maximum extent. The temperature is kept at 180 to 230 ℃, the melt viscosity reduced by the decrease in molecular weight of PET due to the reaction is kept unchanged, and the vapor pressure of EG produced is kept at a level as low as possible.
The reaction zone 4 is a zone for carrying out 2 times of reaction, the initial temperature is 180-230 ℃, the temperature is reduced to 180-200 ℃, and the reaction rate is improved to the maximum extent by prolonging the residence time. As a result of the reaction at the end of the reaction zone 4, the PET is almost completely converted into monomers, a small amount of residues are oligomers, the viscosity is very low, and the viscosity and pressure are kept unchanged by adjusting the temperature.
The fifth reaction zone 5 is a discharge zone, and the temperature is reduced to about 150-180 ℃. The major components of the solid product are alkali metal salts of terephthalic acid (abbreviated as "TPA" throughout), partially incompletely decomposed PET and oligomers, and the liquid product comprises EG and alkali metal glycolate. These products are discharged in the form of a mixture. At this time, the discharge temperature is reasonably regulated, the vapor pressure of the liquid product EG is reduced, the liquid product EG is stably discharged, and the bumping phenomenon caused by the vapor pressure of EG does not occur. The discharged material was cooled to become a solid, and then pulverized into powder.
The reaction temperature provided by the embodiment of the invention is also realized in a short time lower than the melting temperature of PET, so that byproducts generated by thermal decomposition are hardly existed, and only high-purity hydrolysate can be obtained. Most importantly, no toxic low-boiling point organic solvent with high fire hazard is used, so that the process safety is greatly improved.
Further, in the whole process of preparing the terephthalic acid, not only the temperature setting has an influence on the reaction rate, the mixing reaction rate of the reaction speed and the like, but also the adjustment of the pressure. The reaction temperature is preferably kept as low as possible throughout the reaction. Because only then can the impurity that the side reaction produced be reduced, reaction pressure drops, and the reaction is more easily adjusted. After melting PET is started, a weak acid salt of an alkali and its alkali metal of [ reaction formula 2] is mixed into the melted PET, and the molecular weight is drastically reduced as the hydrolysis reaction speed increases. The reaction results in the formation of TPA-Na2 and EG, where TPA-Na2 is formed as a solid powder and EG is a liquid. Wherein TPA-Na2 has a boiling point of 392.4℃at 1 atm, and is very stable to temperature. But EG has a boiling point of 197℃at 1 normal atmospheric pressure, preferably at low temperature. This is because EG produced during hydrolysis is homogeneously mixed with molten PET only if the EG remains in a liquid state and is not vaporized, and a part of EG becomes Na-OC 2H4 O-Na, thereby further promoting hydrolysis.
Fig. 20 is a graph showing the relationship between the EG temperature and the vapor pressure, and it is clear from fig. 20 that a higher pressure than the vapor pressure is required to maintain EG in a liquid state at a specific temperature. For example, EG has a boiling point of 197℃at 1 normal atmospheric pressure, and a vapor pressure of 760mmHg. At a melting temperature of 260 ℃ for PET, the vapor pressure is about 4000mmHg (about 5.3 atmospheres gauge) and at this temperature, the reaction pressure should be maintained at a level above 5.3 atmospheres gauge in order to maintain EG in the liquid state.
In the actual process, when EG starts to be produced by decomposition of PET, the molecular weight of PET is drastically reduced, and PET can be kept in a molten state even when the reaction temperature is 20 to 30 ℃ lower than 260 ℃. However, the EG vapor pressure is less than 2000mmHg, so that the high pressure of 5.3 atmospheres or more is not required, and the EG can be kept in a liquid state only by keeping the reaction pressure of 2.5-3 standard atmospheres, thereby keeping the rapid hydrolysis reaction speed. Thus, the pressure is not higher than 3 normal atmospheres, preferably 2.5 to 3 normal atmospheres, throughout the process of producing the terephthalic acid.
After the solvent-free reaction is completed, the alkali metal terephthalate formed is mixed with water, filtered and centrifuged, and then acid is added to react to form high-purity terephthalic acid.
The inventive examples utilize raman spectroscopy to confirm the products of each process of the reaction. The raman spectrometer can directly measure the molecular structure of the solid sample without pretreatment process, thereby directly confirming the reaction degree of each product in the embodiment of the invention. In addition, the molecular weight change of PET was measured by IV and the degree of distribution of alkali metal (e.g., sodium) was determined by SEM-EDX to confirm the mixing performance of the extruder.
First, raman reference spectra of the compounds at each stage were measured.
The reaction provided by the embodiment of the invention is subjected to the process of PET-TPA-Na-TPA, and the characteristic of the maximum molecular structure change is as follows.
The most representative structure of PET is benzene ring and ester carboxyl (estercarbonyl) c=o, as shown in (fig. 3), with a benzene ring peak at 1601cm -1 and a large peak of ester at 1714cm -1. This peak becomes smaller as the ester bond of PET is converted to TPA-Na, and thus the amount of PET decomposed can be determined.
Sodium terephthalate (TPA-Na) is converted into sodium hydroxy acid C-O-Na by the decomposition of the ester structure, and after this conversion, as shown in FIG. 4, the peak of benzene ring is at the same position, but the peak of ester at 1714cm -1 gradually disappears and the peak of sodium hydroxy acid at 1123cm -1 gradually increases.
TPA exhibits the following characteristics: h ions replace Na ions by pouring acid into TPA-Na, and finally become hydroxy acid-COOH. As a result, as shown in FIG. 5, the sodium hydroxy acid peak at 1123cm -1 disappeared, a new sodium hydroxy acid peak was generated at 823cm -1, and the benzene ring peak was slightly shifted and appeared at 1617cm -1.
Based on this basic raman spectrum, the compounds obtained during the test were compared and confirmed.
In a second aspect, the present invention provides a terephthalic acid prepared by the method for preparing terephthalic acid according to any one of the previous embodiments.
In a third aspect, the present invention provides a process for recovering polyethylene terephthalate having a high degree of polymerization, comprising the process for producing terephthalic acid according to any one of the preceding embodiments.
The features and capabilities of the present invention are described in further detail below in connection with the examples.
Example 1
The embodiment of the invention provides a preparation method of terephthalic acid, which comprises the following steps:
first, a terephthalic acid sodium salt is prepared:
PET bottle chips of more than iv=0.83 dl/g and NaOH in a weight ratio of 5% were thoroughly mixed and fed using a twin screw extruder having 5 reaction zones (temperature adjustment zone), and then a mixture was prepared by mixing 30% NaOH (mass relative to PET), 5% Na 2CO3 (mass relative to PET) and 10% EG (mass relative to PET) using a second-stage extruder, and fed into the extruder reaction zone 2, to prepare terephthalic acid sodium salt.
The twin screw extruder is electrically heated and water cooled to regulate temperature and may be vacuum cleaned to produce gas. The ratio of the length to the diameter of the screw is 40:1.
At this time, the temperatures of reaction zone 1, reaction zone 2, reaction zone 3, reaction zone 4 and reaction zone 5 were set to 160℃180℃220℃200℃170℃respectively. The total pressure was below 3 atmospheres. The number of revolutions of the screw was adjusted so that the residence time of PET in the extruder was about 10 minutes.
The sodium terephthalate that completed the reaction was cooled. When this was examined, as shown in FIG. 6, a large peak appears at 1123cm -1, and an ester peak at 1714cm -1 is significantly smaller, and only a trace is visible, as shown in FIG. 6.
Secondly, preparing terephthalic acid;
100g of the sodium terephthalate salt thus prepared was dissolved in 1L of purified water, and the solution was stirred to dissolve it completely. After about 10 minutes, the aqueous solution was filtered with filter paper. The solid filtered through the filter paper was put into 1L purified water again, and was completely dissolved by stirring. After 10 minutes, the solid was again filtered through a filter paper, and the undissolved portion was dried and weighed to give 2g, which means that the conversion reaction rate of PET to TPA-Na2 in this example was about 98%. 1L of the 2-time filtrate and 1L of the 1-time filtrate were combined together. A small amount of hydrochloric acid was mixed into 2L of the filtrate, and the mixture was stirred well to measure acidity (pH value). The addition of hydrochloric acid was continued until the acidity of the solution was slightly acidic (ph=about 4.5). White precipitates were then formed, and the precipitates were filtered with filter paper, washed with purified water 2 times, and dried to prepare terephthalic acid.
The prepared terephthalic acid is detected, the detection result is shown in fig. 7, and compared with the raman spectrometer spectrum of the standard substance TPA in fig. 5, the dried white precipitate is TPA.
Example 2
The embodiment of the invention provides a preparation method of terephthalic acid, which comprises the following steps:
first, a potassium terephthalate salt is prepared:
A potassium terephthalate was produced in the same manner as in example 1, except that the PET bottle chips of more than iv=0.83 dl/g and KOH in a weight ratio of 5% were thoroughly mixed by a twin screw extruder, fed 1 st time, and then a second-stage extruder was used, except that 35% KOH (mass relative to PET), 5% K 2CO3 (mass relative to PET) and 10% EG (mass relative to PET) were fed 2 nd time.
The raman spectrometer spectrum of the prepared potassium terephthalate salt is shown in fig. 16. Fig. 16 shows almost the same raman spectrum as that of terephthalic acid sodium salt, but shows some difference in peak intensity ratio and the like.
Secondly, preparing terephthalic acid;
100g of the potassium terephthalate prepared above was dissolved in 1L of purified water, and the solution was stirred to dissolve the potassium terephthalate completely. After about 10 minutes, the aqueous solution was filtered with filter paper. The solid filtered through the filter paper was put into 1L purified water again, and was completely dissolved by stirring. After 10 minutes, the undissolved solids were dried and weighed to give 4g, which means that the conversion of PET to TPA-K2 was about 96%. 1L of the 2-time filtrate and 1L of the 1-time filtrate were combined together. A small amount of hydrochloric acid was mixed into 2L of the filtrate, and the mixture was stirred well to measure acidity (pH value). The addition of hydrochloric acid was continued until the acidity of the solution was slightly acidic (ph=about 4.5). White precipitates were then formed, and the precipitates were filtered with filter paper, washed with purified water 2 times, and dried to prepare terephthalic acid.
The raman spectrometer spectrum of the terephthalic acid obtained by the preparation method is shown in fig. 17, and compared with the raman spectrometer spectrum of the standard substance TPA in fig. 5, the result shows that the dried white precipitate is TPA.
Comparative example 1
Preparation of terephthalic acid sodium salt
Sodium terephthalate (TPA-Na 2) was prepared by reacting PET bottle chips with iv=0.83 dl/g with NaOH using a twin screw extruder with 5 reaction zones (temperature adjustment zone). The twin screw extruder is electrically heated and water cooled to regulate temperature and may be vacuum cleaned to produce gas. The ratio of the length to the diameter of the screw is 40:1.
NaOH was mixed homogeneously with PET chips in a weight ratio of 5% and fed into an extruder. At this time, the temperatures of reaction zone 1, reaction zone 2, reaction zone 3, reaction zone 4 and reaction zone 5 were set to 160℃180℃220℃200℃170℃respectively. The number of revolutions of the screw was adjusted so that the residence time of PET in the extruder was about 10 minutes.
The sodium terephthalate that completed the reaction was cooled. The IV measurement result of the prepared terephthalic acid sodium salt is 0.51dl/g, and the Raman spectrometer spectrum is shown in FIG. 8. The IV was reduced from 0.83dl/g to 0.51dl/g, indicating that the decomposition reaction was to some extent. In addition, as can be seen from the raman spectrometer spectrum of fig. 8, a small peak appears at 1123cm -1, because PET is partially decomposed, producing terephthalic acid sodium salt (TPA-Na 2).
Comparative example 2
Preparation of terephthalic acid sodium salt
A sodium salt of terephthalic acid was produced in the same manner as in example 1, except that a mixture of PET bottle chips with iv=0.83 dl/g and NaOH in a weight ratio of 15% was fed into a twin screw extruder. The raman spectrometer spectrum of the sodium salt of terephthalic acid that completed the reaction is shown in fig. 9. As can be seen from fig. 9, a very large peak appears at 1123cm -1, the PET ester peak at 1714cm -1 is almost halved, less than 1123cm -1; the Intensity (Intensity) of the two peaks was about 1.2 times the peak at 1123cm -1 representing the amount of sodium terephthalate (TPA-Na 2).
Comparative example 3
Preparation of terephthalic acid sodium salt
A sodium salt of terephthalic acid was produced in the same manner as in comparative example 1, except that a mixture of PET bottle chips mixed with iv=0.83 dl/g and NaOH in a weight ratio of 30% was fed into a twin screw extruder. The raman spectrometer spectrum of the sodium salt of terephthalic acid that completed the reaction is shown in fig. 10. As can be seen from FIG. 10, a very large peak appears at 1123cm -1, the PET ester peak at 1714cm -1 is greatly reduced to about 1/16 of the peak at 1123cm -1.
Comparative example 4
Preparation of terephthalic acid sodium salt
PET bottle chips of more than iv=0.83 dl/g and NaOH in a weight ratio of 5% were thoroughly mixed using a twin screw extruder, fed 1 st time, and then sodium terephthalate was prepared in the same manner as in example 1, except that a mixture of 30% NaOH and 15% EG fed 2 nd time was used. The raman spectrometer spectrum of the sodium salt of terephthalic acid that completed the reaction is shown in fig. 11. As can be seen from fig. 11, a very large peak appears at 1123cm -1, the PET ester peak is greatly reduced at 1714cm -1, the intensity is reduced to about 1/18 of the peak at 1123cm -1, but still undigested PET remains.
Comparative example 5
Preparation of terephthalic acid
100G of the sodium terephthalate salt obtained in comparative example 4 was dissolved in 1L of purified water, and the solution was completely dissolved by stirring. After about 10 minutes, the aqueous solution was filtered with filter paper. The solid filtered through the filter paper was put into 1L purified water again, and was completely dissolved by stirring. After 10 minutes, the undissolved solid was dried and weighed to give 13g, which means that the conversion of PET to TPA-Na was about 87%. 1L of the 2-time filtrate and 1L of the 1-time filtrate were combined together. A small amount of hydrochloric acid was mixed into 2L of the filtrate, and the mixture was stirred well to measure acidity (pH value). The addition of hydrochloric acid was continued until the acidity of the solution was slightly acidic (ph=about 4.5). White precipitates were then formed, and the precipitates were filtered with filter paper, washed with purified water 2 times, and dried to prepare terephthalic acid.
The raman spectrometer spectrum measurement results of the terephthalic acid obtained are shown in fig. 12. Comparing with the raman spectrometer spectrum of the standard substance TPA of fig. 5, it can be seen from the results that the white solid substance prepared is TPA.
Comparative example 6
Preparation of terephthalic acid sodium salt by ethanol solvent
A stirrer, thermometer, reflux cooler and heating mantle were mounted on a 1 liter four port round bottom beaker. 100 g PET bottle chips with IV=0.83 dl/g, 30 ml ethylene glycol sodium salt, 40 g sodium hydroxide, 600ml ethanol were added. The temperature of the heating mantle was raised until the ethanol boiled, and the stirrer was started to reflux, and the reaction was carried out for about 10 hours. After the reaction, the reaction mixture was filtered through a 100-mesh sieve, and the unreacted PET bottle chips were filtered out and then wiped with 100ml of pure ethanol. The unreacted material was dried and then weighed, resulting in 23g. This means that the decomposition reaction rate of PET with a high polymerization degree is only about 77%.
The milky white reaction solution containing the white precipitate from which the unreacted PET chips had been removed was filtered with filter paper to obtain a white precipitate. The white precipitate was washed 3 times with methanol and then dried to prepare terephthalic acid sodium salt.
The obtained terephthalic acid sodium salt was dissolved in water, and the spectral results of the measurement with a raman spectrometer are shown in fig. 13. Comparing the spectrum with the Raman spectrometer spectrum of the standard substance terephthalic acid sodium salt in fig. 4, and confirming that the component is terephthalic acid sodium salt.
Comparative example 7
Preparation of terephthalic acid sodium salt by ethanol solvent
A stirrer, thermometer, reflux cooler and heating mantle were mounted on a 1 liter four port round bottom beaker. Cut 100 g of bright PET cloth pieces, 30 ml of ethylene glycol sodium salt, 40 g of sodium hydroxide, 600ml of ethanol were added with iv=0.55 dl/g. The temperature of the heating mantle was raised until the ethanol boiled, and the stirrer was started to reflux, and the reaction was carried out for about 1 hour. After the reaction, the reaction mixture was filtered through a 100-mesh sieve, and the unreacted PET bottle chips were filtered out and then wiped with 100ml of pure ethanol. The unreacted material was not filtered off at all. This means that the decomposition reaction rate of PET having a low degree of polymerization in the middle was almost 100%.
The milky white reaction solution containing the white precipitate from which the unreacted substances had been removed was filtered with a filter paper to obtain a white precipitate. The white precipitate was washed 3 times with methanol and then dried to prepare terephthalic acid sodium salt.
The obtained terephthalic acid sodium salt was dissolved in water, and the spectral results of the measurement with a raman spectrometer are shown in fig. 14. Comparing the spectrum with the Raman spectrometer spectrum of the standard substance terephthalic acid sodium salt in fig. 4, and confirming that the component is terephthalic acid sodium salt.
Comparative example 8
Preparation of terephthalic acid
100G of sodium terephthalate obtained in comparative example 7 was poured into a 2 liter beaker, and 1.5 liter of distilled water was poured thereinto and stirred to be completely dissolved. Then, hydrochloric acid was added little by little and stirred well until the solution became weakly acidic (ph=about 4.5). A white precipitate then appears. The precipitate was filtered through filter paper and dried to prepare terephthalic acid.
The raman spectrometer spectrum of the prepared terephthalic acid is shown in fig. 15, and the component is confirmed to be terephthalic acid by comparison with the raman spectrometer spectrum of the standard substance of fig. 5.
Verification example 1
Confirmation test for confirming degree of alkali powder mixing Using NaCl
Under the same test conditions as in example 1, 10% by weight NaCl powder was mixed with PET. The effluent was cooled at normal temperature, and after solidification, SEM-EDS results measured at 500 times are shown in FIG. 19, where Na (sky blue) and C (red) elements from PET are well mixed without large agglomerates, indicating uniform powder distribution of NaCl. This shows that when feeding PET, a small amount of NaOH is mixed and added into a part of the total amount of NaOH at the 1 st time, and then the feeding is carried out at the 2 nd time, namely the progressive hydrolysis reaction, so that the viscosity of PET is slowly reduced and the mixture is more uniform. This illustrates why NaOH is more uniformly and better reacted in two additions than in one addition.
Verification example 2
Confirmation experiment for confirming degree of alkali powder mixing Using NaCl
Under the same reaction conditions as in comparative example 3, 10% by weight of NaCl powder was mixed with PET. The effluent was cooled to room temperature, and SEM-EDS measurements at 500 times were performed, as shown in FIG. 18. Na (green) derived from NaCl and C (red) derived from PET are not sufficiently mixed, and there are many lumps. This is because too much NaOH is added at a time to cause too severe hydrolysis reaction, and the PET viscosity difference at each position is large and the variation is uneven, which means that the powder distribution of NaCl is uneven. This indicates that the mixing during the mixing was insufficient when NaOH was fed at one time under the twin screw extruder operating conditions used in the experiments.
The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (11)
1. A process for producing terephthalic acid, comprising: mixing molten high-polymerization-degree polyethylene terephthalate, alkali metal-containing strong alkali, alkali metal weak acid salt and ethylene glycol for solvent-free reaction, wherein the amount of the ethylene glycol is 10% of the mass of the high-polymerization-degree polyethylene terephthalate; the pressure is 2.5-3 standard atmospheric pressures in the whole process of preparing the terephthalic acid;
The mixing is carried out in a solvent-free reaction mode, namely polyethylene terephthalate with high polymerization degree and first alkali containing alkali metal are simultaneously added into a continuous extruder to be melted to form first molten liquid, then a mixture containing second alkali metal, weak acid salt and ethylene glycol is added into the inner position of the continuous extruder where the first molten liquid is located, and then multi-stage heating is carried out in different reaction areas of the continuous extruder;
Wherein the dosage of the first strong base is 5-10% of the weight of the high-polymerization degree polyethylene terephthalate, and the mass of the second strong base is 30% or 35% of the weight of the high-polymerization degree polyethylene terephthalate; the mass of the weak acid salt is 5% of that of the polyethylene terephthalate with high polymerization degree.
2. The method of claim 1, wherein the first melt is formed at a temperature of 100-180 ℃ and the mixture is added at a temperature of 150-230 ℃.
3. The method of claim 1, wherein the multi-stage heating comprises: heating at 180-230deg.C, heating at 180-200deg.C, and heating at 150-180deg.C.
4. The method of manufacturing according to claim 1, comprising: the alkali metal terephthalate formed by the solvent-free reaction is subjected to a post-treatment.
5. The method of claim 1, wherein the post-treatment comprises: the alkali metal terephthalate is mixed with water, filtered and centrifuged, and then acid is added.
6. The method of claim 1, wherein the high degree of polymerization polyethylene terephthalate polymer is greater than 0.75 ㎗/g.
7. The method of claim 1, wherein the high degree of polymerization polyethylene terephthalate polymer is greater than 0.80 ㎗/g.
8. The method of claim 1, wherein the polymer of high-polymerization polyethylene terephthalate is selected from the group consisting of homopolymers and copolymers.
9. The method according to claim 1, wherein the alkali metal is selected from any one of lithium, sodium and potassium.
10. The method of claim 1, wherein the weak acid salt comprises any one of carbonate, bicarbonate, phosphate, hydrogen phosphate, dihydrogen phosphate, acetate, and formate.
11. A process for recovering polyethylene terephthalate having a high degree of polymerization, comprising the process for producing terephthalic acid according to any one of claims 1 to 10.
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| JPH09286744A (en) * | 1996-04-23 | 1997-11-04 | Res Inst For Prod Dev | Method for recovering terephthalic acid and ethylene glycol from polyethylene terephthalate |
| EP1134211A1 (en) * | 2000-02-29 | 2001-09-19 | Massimo Broccatelli | Method of recovering chemical species by depolymerization of poly(ethylene terephthalate) and related use |
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| US6706843B1 (en) * | 1999-10-22 | 2004-03-16 | Teijin Limited | Method for separating and recovering dimethyl terephthalate and ethylene glycol from polyester waste |
| CN1390826A (en) * | 2002-07-24 | 2003-01-15 | 重庆大学 | Process for depolymerizing waste polyester |
| CN108658758B (en) * | 2018-07-18 | 2021-05-11 | 南京道港贸易有限公司 | Preparation method of terephthaloyl chloride, terephthaloyl chloride and application, preparation method of p-phenylenediamine and p-phenylenediamine |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JPH09286744A (en) * | 1996-04-23 | 1997-11-04 | Res Inst For Prod Dev | Method for recovering terephthalic acid and ethylene glycol from polyethylene terephthalate |
| EP1134211A1 (en) * | 2000-02-29 | 2001-09-19 | Massimo Broccatelli | Method of recovering chemical species by depolymerization of poly(ethylene terephthalate) and related use |
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