CN113549198A - Method for preparing polylactic acid from lactic acid - Google Patents
Method for preparing polylactic acid from lactic acid Download PDFInfo
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- CN113549198A CN113549198A CN202110948906.6A CN202110948906A CN113549198A CN 113549198 A CN113549198 A CN 113549198A CN 202110948906 A CN202110948906 A CN 202110948906A CN 113549198 A CN113549198 A CN 113549198A
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- JVTAAEKCZFNVCJ-UHFFFAOYSA-N lactic acid Chemical compound CC(O)C(O)=O JVTAAEKCZFNVCJ-UHFFFAOYSA-N 0.000 title claims abstract description 262
- 239000004310 lactic acid Substances 0.000 title claims abstract description 131
- 235000014655 lactic acid Nutrition 0.000 title claims abstract description 131
- 229920000747 poly(lactic acid) Polymers 0.000 title claims abstract description 98
- 239000004626 polylactic acid Substances 0.000 title claims abstract description 98
- 238000000034 method Methods 0.000 title claims abstract description 32
- 230000002194 synthesizing effect Effects 0.000 claims abstract description 35
- 239000003054 catalyst Substances 0.000 claims abstract description 33
- 229920000642 polymer Polymers 0.000 claims abstract description 16
- 238000003786 synthesis reaction Methods 0.000 claims abstract description 10
- 230000015572 biosynthetic process Effects 0.000 claims abstract description 9
- XEKOWRVHYACXOJ-UHFFFAOYSA-N Ethyl acetate Chemical compound CCOC(C)=O XEKOWRVHYACXOJ-UHFFFAOYSA-N 0.000 claims description 33
- 238000010438 heat treatment Methods 0.000 claims description 32
- JVTAAEKCZFNVCJ-REOHCLBHSA-N L-lactic acid Chemical compound C[C@H](O)C(O)=O JVTAAEKCZFNVCJ-REOHCLBHSA-N 0.000 claims description 22
- KSBAEPSJVUENNK-UHFFFAOYSA-L tin(ii) 2-ethylhexanoate Chemical compound [Sn+2].CCCCC(CC)C([O-])=O.CCCCC(CC)C([O-])=O KSBAEPSJVUENNK-UHFFFAOYSA-L 0.000 claims description 21
- 238000003756 stirring Methods 0.000 claims description 20
- HEDRZPFGACZZDS-UHFFFAOYSA-N Chloroform Chemical compound ClC(Cl)Cl HEDRZPFGACZZDS-UHFFFAOYSA-N 0.000 claims description 18
- 239000002904 solvent Substances 0.000 claims description 15
- 238000004821 distillation Methods 0.000 claims description 13
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- 239000012974 tin catalyst Substances 0.000 claims description 10
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- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 claims description 9
- ZMXDDKWLCZADIW-UHFFFAOYSA-N N,N-Dimethylformamide Chemical compound CN(C)C=O ZMXDDKWLCZADIW-UHFFFAOYSA-N 0.000 claims description 9
- 239000005416 organic matter Substances 0.000 claims description 9
- LBLYYCQCTBFVLH-UHFFFAOYSA-N 2-Methylbenzenesulfonic acid Chemical compound CC1=CC=CC=C1S(O)(=O)=O LBLYYCQCTBFVLH-UHFFFAOYSA-N 0.000 claims description 8
- AFVFQIVMOAPDHO-UHFFFAOYSA-N Methanesulfonic acid Chemical compound CS(O)(=O)=O AFVFQIVMOAPDHO-UHFFFAOYSA-N 0.000 claims description 8
- XOLBLPGZBRYERU-UHFFFAOYSA-N tin dioxide Chemical compound O=[Sn]=O XOLBLPGZBRYERU-UHFFFAOYSA-N 0.000 claims description 8
- 239000003795 chemical substances by application Substances 0.000 claims description 7
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 claims description 6
- IAZDPXIOMUYVGZ-UHFFFAOYSA-N Dimethylsulphoxide Chemical compound CS(C)=O IAZDPXIOMUYVGZ-UHFFFAOYSA-N 0.000 claims description 6
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 claims description 6
- 239000000460 chlorine Substances 0.000 claims description 6
- 229910052801 chlorine Inorganic materials 0.000 claims description 6
- 238000002425 crystallisation Methods 0.000 claims description 6
- 230000008025 crystallization Effects 0.000 claims description 6
- JBTWLSYIZRCDFO-UHFFFAOYSA-N ethyl methyl carbonate Chemical compound CCOC(=O)OC JBTWLSYIZRCDFO-UHFFFAOYSA-N 0.000 claims description 6
- QJGQUHMNIGDVPM-UHFFFAOYSA-N nitrogen group Chemical group [N] QJGQUHMNIGDVPM-UHFFFAOYSA-N 0.000 claims description 6
- 229910052717 sulfur Inorganic materials 0.000 claims description 6
- 239000011593 sulfur Substances 0.000 claims description 6
- TXUICONDJPYNPY-UHFFFAOYSA-N (1,10,13-trimethyl-3-oxo-4,5,6,7,8,9,11,12,14,15,16,17-dodecahydrocyclopenta[a]phenanthren-17-yl) heptanoate Chemical compound C1CC2CC(=O)C=C(C)C2(C)C2C1C1CCC(OC(=O)CCCCCC)C1(C)CC2 TXUICONDJPYNPY-UHFFFAOYSA-N 0.000 claims description 4
- OQBLGYCUQGDOOR-UHFFFAOYSA-L 1,3,2$l^{2}-dioxastannolane-4,5-dione Chemical compound O=C1O[Sn]OC1=O OQBLGYCUQGDOOR-UHFFFAOYSA-L 0.000 claims description 4
- 229930182843 D-Lactic acid Natural products 0.000 claims description 4
- JVTAAEKCZFNVCJ-UWTATZPHSA-N D-lactic acid Chemical compound C[C@@H](O)C(O)=O JVTAAEKCZFNVCJ-UWTATZPHSA-N 0.000 claims description 4
- 229910021626 Tin(II) chloride Inorganic materials 0.000 claims description 4
- QDHFHIQKOVNCNC-UHFFFAOYSA-N butane-1-sulfonic acid Chemical compound CCCCS(O)(=O)=O QDHFHIQKOVNCNC-UHFFFAOYSA-N 0.000 claims description 4
- 229940022769 d- lactic acid Drugs 0.000 claims description 4
- PNOXNTGLSKTMQO-UHFFFAOYSA-L diacetyloxytin Chemical compound CC(=O)O[Sn]OC(C)=O PNOXNTGLSKTMQO-UHFFFAOYSA-L 0.000 claims description 4
- CCIVGXIOQKPBKL-UHFFFAOYSA-M ethanesulfonate Chemical compound CCS([O-])(=O)=O CCIVGXIOQKPBKL-UHFFFAOYSA-M 0.000 claims description 4
- FYAQQULBLMNGAH-UHFFFAOYSA-N hexane-1-sulfonic acid Chemical compound CCCCCCS(O)(=O)=O FYAQQULBLMNGAH-UHFFFAOYSA-N 0.000 claims description 4
- 229940098779 methanesulfonic acid Drugs 0.000 claims description 4
- WLGDAKIJYPIYLR-UHFFFAOYSA-N octane-1-sulfonic acid Chemical compound CCCCCCCCS(O)(=O)=O WLGDAKIJYPIYLR-UHFFFAOYSA-N 0.000 claims description 4
- KCXFHTAICRTXLI-UHFFFAOYSA-N propane-1-sulfonic acid Chemical compound CCCS(O)(=O)=O KCXFHTAICRTXLI-UHFFFAOYSA-N 0.000 claims description 4
- 235000011150 stannous chloride Nutrition 0.000 claims description 4
- 239000001119 stannous chloride Substances 0.000 claims description 4
- -1 sulfonic acid compound Chemical class 0.000 claims description 4
- 150000003460 sulfonic acids Chemical class 0.000 claims description 4
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 3
- FXHOOIRPVKKKFG-UHFFFAOYSA-N N,N-Dimethylacetamide Chemical compound CN(C)C(C)=O FXHOOIRPVKKKFG-UHFFFAOYSA-N 0.000 claims description 3
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 claims description 3
- 230000001476 alcoholic effect Effects 0.000 claims description 3
- JALQQBGHJJURDQ-UHFFFAOYSA-L bis(methylsulfonyloxy)tin Chemical compound [Sn+2].CS([O-])(=O)=O.CS([O-])(=O)=O JALQQBGHJJURDQ-UHFFFAOYSA-L 0.000 claims description 3
- 230000001376 precipitating effect Effects 0.000 claims description 3
- 239000002253 acid Substances 0.000 claims description 2
- 239000000126 substance Substances 0.000 claims 3
- 230000018044 dehydration Effects 0.000 claims 1
- 238000006297 dehydration reaction Methods 0.000 claims 1
- 239000002994 raw material Substances 0.000 abstract description 14
- 238000002360 preparation method Methods 0.000 abstract description 8
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- WSFSSNUMVMOOMR-UHFFFAOYSA-N Formaldehyde Chemical compound O=C WSFSSNUMVMOOMR-UHFFFAOYSA-N 0.000 description 18
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 8
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- 238000005259 measurement Methods 0.000 description 6
- 239000000843 powder Substances 0.000 description 6
- 238000001226 reprecipitation Methods 0.000 description 6
- JJTUDXZGHPGLLC-UHFFFAOYSA-N lactide Chemical compound CC1OC(=O)C(C)OC1=O JJTUDXZGHPGLLC-UHFFFAOYSA-N 0.000 description 4
- 238000006068 polycondensation reaction Methods 0.000 description 4
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 3
- LSNNMFCWUKXFEE-UHFFFAOYSA-M Bisulfite Chemical compound OS([O-])=O LSNNMFCWUKXFEE-UHFFFAOYSA-M 0.000 description 2
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- RDOXTESZEPMUJZ-UHFFFAOYSA-N anisole Chemical compound COC1=CC=CC=C1 RDOXTESZEPMUJZ-UHFFFAOYSA-N 0.000 description 2
- 229920000704 biodegradable plastic Polymers 0.000 description 2
- 238000009835 boiling Methods 0.000 description 2
- 230000000052 comparative effect Effects 0.000 description 2
- 150000001875 compounds Chemical class 0.000 description 2
- MHDVGSVTJDSBDK-UHFFFAOYSA-N dibenzyl ether Chemical compound C=1C=CC=CC=1COCC1=CC=CC=C1 MHDVGSVTJDSBDK-UHFFFAOYSA-N 0.000 description 2
- USIUVYZYUHIAEV-UHFFFAOYSA-N diphenyl ether Chemical compound C=1C=CC=CC=1OC1=CC=CC=C1 USIUVYZYUHIAEV-UHFFFAOYSA-N 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 239000000155 melt Substances 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 230000008018 melting Effects 0.000 description 2
- WWZKQHOCKIZLMA-UHFFFAOYSA-M octanoate Chemical compound CCCCCCCC([O-])=O WWZKQHOCKIZLMA-UHFFFAOYSA-M 0.000 description 2
- 238000007151 ring opening polymerisation reaction Methods 0.000 description 2
- 231100000331 toxic Toxicity 0.000 description 2
- 230000002588 toxic effect Effects 0.000 description 2
- WSQZNZLOZXSBHA-UHFFFAOYSA-N 3,8-dioxabicyclo[8.2.2]tetradeca-1(12),10,13-triene-2,9-dione Chemical compound O=C1OCCCCOC(=O)C2=CC=C1C=C2 WSQZNZLOZXSBHA-UHFFFAOYSA-N 0.000 description 1
- CTQNGGLPUBDAKN-UHFFFAOYSA-N O-Xylene Chemical compound CC1=CC=CC=C1C CTQNGGLPUBDAKN-UHFFFAOYSA-N 0.000 description 1
- 229920002472 Starch Polymers 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 229910002092 carbon dioxide Inorganic materials 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 229920006238 degradable plastic Polymers 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 238000000855 fermentation Methods 0.000 description 1
- 230000004151 fermentation Effects 0.000 description 1
- 231100000171 higher toxicity Toxicity 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- VUZPPFZMUPKLLV-UHFFFAOYSA-N methane;hydrate Chemical compound C.O VUZPPFZMUPKLLV-UHFFFAOYSA-N 0.000 description 1
- UZKWTJUDCOPSNM-UHFFFAOYSA-N methoxybenzene Substances CCCCOC=C UZKWTJUDCOPSNM-UHFFFAOYSA-N 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
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- 229920005586 poly(adipic acid) Polymers 0.000 description 1
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- 239000007790 solid phase Substances 0.000 description 1
- RCIVOBGSMSSVTR-UHFFFAOYSA-L stannous sulfate Chemical compound [SnH2+2].[O-]S([O-])(=O)=O RCIVOBGSMSSVTR-UHFFFAOYSA-L 0.000 description 1
- 235000019698 starch Nutrition 0.000 description 1
- 239000008107 starch Substances 0.000 description 1
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- 229910000375 tin(II) sulfate Inorganic materials 0.000 description 1
- 239000008096 xylene Substances 0.000 description 1
Images
Classifications
-
- 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
- C08G63/06—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds derived from hydroxycarboxylic acids
Abstract
The invention provides a method for preparing polylactic acid from lactic acid, which comprises three steps of: synthesizing low-polymer lactic acid; synthesizing and purifying lactic acid; and (3) synthesizing polylactic acid. According to the invention, lactic acid is prepolymerized to obtain oligomeric lactic acid, and the oligomeric lactic acid is not easy to be pumped away compared with lactic acid during the synthesis of polylactic acid, so that the loss of raw materials is reduced, and the yield of the product is improved. According to the invention, after low polymeric lactic acid is synthesized, purified lactic acid is synthesized and then polylactic acid is synthesized in two steps, so that the preparation method can ensure the purity of the finally prepared polylactic acid, and meanwhile, the two-step synthesis can also ensure the activity of the catalyst, ensure the increase of the molecular weight of the polylactic acid and synthesize a product with relatively high molecular weight.
Description
Technical Field
The invention relates to the technical field of high polymer materials, in particular to a method for preparing polylactic acid from lactic acid.
Background
At present, main raw materials of the mainstream degradable plastics are PLA (polylactic acid) and PBAT (poly adipic acid and butylene terephthalate copolymer). PBAT belongs to petroleum-based biodegradable plastics, has a mature industrial chain, good use performance and economy, is one of the most widely used degradable materials in the market in the research of the current biodegradable plastics, but finally has the degradation capability in the nature to be observed.
PLA (polylactic acid) is a material prepared from lactic acid obtained by starch fermentation (or chemical synthesis) as a basic raw material. PLA has the characteristics of biodegradability, reproducibility, good biocompatibility, high mechanical strength, easy processing and the like. PLA can be decomposed into carbon dioxide and water in nature, has no pollution to the ecological environment, and belongs to a green environment-friendly polymer. The PLA synthesis methods can be broadly classified into two types, one is a direct polycondensation method, which includes a melt polycondensation method and a solution azeotropic polymerization method, wherein the melt polycondensation is a polymerization reaction occurring at a temperature above the melting point of the polymer, and has the advantage that the obtained product is pure, and does not require a separation medium, but it is difficult to obtain polylactic acid having a high molecular weight and a high melting point simply by melt polymerization. The solution azeotropic polymerization method can obtain a product with a higher molecular weight, but the method needs to introduce a solvent with a higher boiling point, such as xylene, diphenyl ether, anisole, dibenzyl ether and the like, which have higher toxicity, thereby influencing the environment and further limiting the application of polylactic acid products. Another class is the ring opening polymerization of lactide. Chinese patent CN1068011C discloses a method for preparing polylactic acid by lactide melt/solid phase polycondensation, which adopts the ring-opening polymerization method of lactide, but needs to recrystallize the raw material lactide many times and then polymerize, otherwise, polylactic acid with high molecular weight cannot be obtained, and the cost is high.
Disclosure of Invention
In view of the above, the present invention provides a method for preparing polylactic acid from lactic acid, wherein the prepared polylactic acid product has stable purity, high yield and relatively high molecular weight by improving the preparation method.
In order to solve the technical problems, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a method for preparing polylactic acid from lactic acid, the method comprising:
s1: synthesizing low-polymer lactic acid: heating lactic acid at the temperature of 110-180 ℃ for 4-8 h under the pressure of 0.01-10 Kpa to synthesize oligomeric lactic acid;
s2: synthesizing and purifying lactic acid: adding 0.1-2.0 wt.% of catalyst into the low-polymerization lactic acid synthesized in S1 under the pressure of 0.1-10 Kpa, reacting at 200-260 ℃ for 2-20 h, and adding a crystallizing agent for crystallizing after the reaction is finished to obtain purified lactic acid;
s3: and (3) synthesizing polylactic acid: heating the purified lactic acid synthesized in the step S2 at a temperature of 90-110 ℃ under a pressure of 0.1-10 Kpa, adding 0.1-2.0 wt.% of catalyst, and heating and stirring the mixture of the purified lactic acid and the catalyst for 0.5-1 h; after stirring, the temperature is raised to 150-180 ℃, then the temperature is gradually reduced, and the temperature is reduced to 120-140 ℃ for heat preservation until the polylactic acid is obtained after complete distillation.
Further, the lactic acid includes at least one of L-lactic acid and D-lactic acid.
Further, before synthesizing the low-polymer lactic acid, the lactic acid needs to be dehydrated, and the method for removing the moisture comprises the following steps: distilling for 1-10 h at 60-160 ℃.
Further, the catalysts described in S2 and S3 include tin-based catalysts, and composite catalysts of sulfonic acid-based compounds.
Further, the tin catalyst comprises stannous chloride, stannic oxide, stannous acetate, stannic acid, stannous octoate, stannous oxalate, stannous methanesulfonate;
the sulfonic acid compounds comprise methanesulfonic acid, toluenesulfonic acid, ethanesulfonic acid, propanesulfonic acid, butanesulfonic acid, hexanesulfonic acid and octanesulfonic acid.
Further, the crystallizing agent in S2 includes ethyl acetate.
Further, in S3, the temperature is raised to 150-180 ℃ at the heating rate of 1-5 ℃/min, then the temperature is gradually reduced, and the temperature is reduced to 120-140 ℃ for heat preservation and distillation for 2-20 h.
Further, the polylactic acid synthesized in S3 needs to be dissolved and precipitated to obtain further purified polylactic acid.
Further, the solvent for dissolving the polylactic acid comprises sulfur-containing organic matters, nitrogen-containing organic matters and chlorine-containing organic matters; the solvent for precipitating the polylactic acid comprises an ester solvent or an alcohol solvent;
wherein the sulfur-containing organic matter comprises dimethyl sulfoxide; the nitrogen-containing organic matter comprises N, N-dimethylformamide, N-dimethylacetamide or N-methylpyrrolidone; the chlorine-containing organic matter comprises chloroform and dichloromethane; the ester solvent comprises ethyl acetate; the alcoholic solvent includes methanol.
In a second aspect, the present invention provides a polylactic acid, which is prepared by the above method.
The technical scheme of the invention has the following beneficial effects:
the invention provides a method for preparing polylactic acid from lactic acid, which comprises the following steps: s1: synthesizing low-polymer lactic acid: heating lactic acid at the temperature of 110-180 ℃ for 4-8 h under the pressure of 0.1-10 Kpa to synthesize oligomeric lactic acid; s2: synthesizing and purifying lactic acid: adding 0.1-2.0 wt.% of catalyst into the low-polymerization lactic acid synthesized in S1 under the pressure of 0.1-10 Kpa, reacting at 200-260 ℃ for 2-20 h, and adding a crystallizing agent for crystallizing after the reaction is finished to obtain purified lactic acid; s3: and (3) synthesizing polylactic acid: heating the purified lactic acid synthesized in the step S2 at a temperature of 90-110 ℃ under a pressure of 0.1-10 Kpa, adding 0.1-2.0 wt.% of catalyst, and heating and stirring the mixture of the purified lactic acid and the catalyst for 0.5-1 h; after stirring, the temperature is raised to 150-180 ℃, then the temperature is gradually reduced, and the temperature is reduced to 120-140 ℃ for heat preservation until the polylactic acid is obtained after complete distillation.
According to the invention, lactic acid is prepolymerized to obtain oligomeric lactic acid, and the oligomeric lactic acid is not easy to be pumped away compared with lactic acid during the synthesis of polylactic acid, so that the loss of raw materials is reduced, and the yield of the product is improved. According to the invention, after low polymeric lactic acid is synthesized, purified lactic acid is synthesized and then polylactic acid is synthesized in two steps, so that the preparation method can ensure the purity of the finally prepared polylactic acid, and meanwhile, the two-step synthesis can also ensure the activity of the catalyst, ensure the increase of the molecular weight of the polylactic acid and synthesize a product with relatively high molecular weight. In addition, the preparation method provided by the invention does not need to use toxic solvents and the like, the production safety is high, and the prepared polylactic acid product is wide in application and not limited.
Drawings
FIG. 1 is a flow chart of the preparation of polylactic acid from lactic acid.
Detailed Description
For a further understanding of the invention, reference will now be made to the preferred embodiments of the invention in conjunction with the following examples, but it will be understood that the description is intended to illustrate the features and advantages of the invention further, and not to limit the invention.
In a first aspect, the present invention provides a method for preparing polylactic acid from lactic acid, the method comprising:
s1: synthesizing low-polymer lactic acid: heating lactic acid at the temperature of 110-180 ℃ for 4-8 h under the pressure of 0.1-10 Kpa to synthesize oligomeric lactic acid;
s2: synthesizing and purifying lactic acid: adding 0.1-2.0 wt.% of catalyst into the low-polymerization lactic acid synthesized in S1 under the pressure of 0.1-10 Kpa, reacting at 200-260 ℃ for 2-20 h, and adding a crystallizing agent for crystallizing after the reaction is finished to obtain purified lactic acid;
s3: and (3) synthesizing polylactic acid: heating the purified lactic acid synthesized in the step S2 at a temperature of 90-110 ℃ under a pressure of 0.1-10 Kpa, adding 0.1-2.0 wt.% of catalyst, and heating and stirring the mixture of the purified lactic acid and the catalyst for 0.5-1 h; after stirring, the temperature is raised to 150-180 ℃, then the temperature is gradually reduced, and the temperature is reduced to 120-140 ℃ for heat preservation until the polylactic acid is obtained after complete distillation.
The preparation method provided by the invention can be divided into three steps, wherein the first step is to perform prepolymerization and synthesize oligomeric lactic acid by taking lactic acid as a raw material; secondly, low-polymer lactic acid is used as a raw material, and the low-polymer lactic acid is catalyzed and synthesized to purify the lactic acid under the action of a catalyst; and the third step is to synthesize polylactic acid by secondary crystallization with purified lactic acid as raw material under the action of catalyst. The synthesis procedure is shown in FIG. 1. In the invention, lactic acid is prepolymerized to obtain oligomeric lactic acid, and the reason for prepolymerizing is as follows: the reaction for synthesizing polylactic acid is a low-pressure reaction, and the lactic acid can be pumped out while dehydrating, so that the loss of raw materials can be caused, and the yield of the product is reduced. And lactic acid is prepolymerized to obtain a prepolymer, so that the boiling point of the lactic acid can be improved, the lactic acid is not easy to be pumped away compared with the lactic acid during the synthesis of the polylactic acid, the loss of raw materials is reduced, and the yield of the product is improved. After low polymeric lactic acid is synthesized, a catalyst is added to synthesize and purify the lactic acid. According to the invention, polylactic acid is not directly synthesized after low polymeric lactic acid is synthesized, and purified lactic acid is synthesized first and then the polylactic acid is synthesized in two steps, so that the preparation method can ensure the purity of the finally prepared polylactic acid, and meanwhile, the two-step synthesis can also ensure the activity of the catalyst, ensure the increase of the molecular weight of the polylactic acid, and synthesize a product with higher relative molecular weight. In addition, the preparation method provided by the invention does not need to use toxic solvents and the like, the production safety is high, and the prepared polylactic acid product is wide in application and not limited.
In some embodiments of the invention, the lactic acid comprises at least one of L-lactic acid, D-lactic acid. The raw material for synthesizing the polylactic acid in the invention is selected from L-lactic acid or D-lactic acid, preferably L-lactic acid, and the purity of the lactic acid raw material is more than 90 wt.%.
In some embodiments of the present invention, the lactic acid is dehydrated before the synthesis of the oligomeric lactic acid by: distilling for 1-10 h at 60-160 ℃. In the present invention, the lactic acid raw material is distilled under normal pressure without adding a catalyst, since it is necessary to remove water before synthesizing the low-polymerized lactic acid. Alternatively, the moisture may be removed by other means, such as by inert gas purging, etc.
In some embodiments of the present invention, the catalysts described in S2 and S3 include tin-based catalysts, and composite catalysts of sulfonic acid-based compounds.
In some embodiments of the invention, the tin-based catalyst comprises stannous chloride, stannic oxide, stannous acetate, stannic octanoate, stannous oxalate, stannous methanesulfonate; the sulfonic acid compounds comprise methanesulfonic acid, toluenesulfonic acid, ethanesulfonic acid, propanesulfonic acid, butanesulfonic acid, hexanesulfonic acid and octanesulfonic acid.
The catalyst selected in the invention is a tin catalyst, and the tin catalyst can be used alone or a composite catalyst of the tin catalyst and a sulfonic acid compound. Wherein the tin catalyst comprises stannous chloride, stannic oxide, stannous acetate, stannic octanoate, stannous oxalate and stannous sulfate; the sulfonic acid compounds comprise methanesulfonic acid, toluenesulfonic acid, ethanesulfonic acid, propanesulfonic acid, butanesulfonic acid, hexanesulfonic acid and octanesulfonic acid. Preferably, the composite catalyst comprises a tin catalyst and a sulfonic acid compound, wherein the molar ratio of the sulfonic acid compound to the tin catalyst in the composite catalyst is 1: 10-10: 1.
in some embodiments of the invention, the crystallization agent in S2 comprises ethyl acetate.
In some embodiments of the invention, the temperature in S3 is raised to 150-180 ℃ at a heating rate of 1-5 ℃/min, then gradually reduced, and the temperature is reduced to 120-140 ℃ for heat preservation and distillation for 2-20 h.
In some embodiments of the present invention, the polylactic acid synthesized in S3 is further dissolved and precipitated to obtain further purified polylactic acid.
In some embodiments of the present invention, the solvent that dissolves the polylactic acid comprises sulfur-containing organics, nitrogen-containing organics, chlorine-containing organics; the solvent for precipitating the polylactic acid comprises an ester solvent or an alcohol solvent;
wherein the sulfur-containing organic matter comprises dimethyl sulfoxide; the nitrogen-containing organic matter comprises N, N-dimethylformamide, N-dimethylacetamide or N-methylpyrrolidone; the chlorine-containing organic matter comprises chloroform and dichloromethane; the ester solvent comprises ethyl acetate; the alcoholic solvent includes methanol.
In a second aspect, the present invention provides a polylactic acid, which is prepared by the above method.
The invention is further illustrated by the following specific examples.
The molecular weight of the finally prepared L-polylactic acid is measured by adopting a viscosity-average method, and the calculation of the viscosity-average molecular weight adopts the following formula: [ eta ]]＝1.04*10-4Mη 0.75(ii) a Wherein [ eta ]]Is a characteristic viscosity, MηIs the viscosity average molecular weight.
Example 1
(1) Synthesizing low-polymer lactic acid: 200g of L-lactic acid was taken and distilled at 80 ℃ to remove water. Then heating lactic acid at 110 ℃ for 8h under the pressure of 0.1Kpa to synthesize oligomeric lactic acid;
(2) synthesizing and purifying lactic acid: adding 0.1 wt.% of catalyst stannous octoate into the low-polymerization lactic acid synthesized in the step (1) under the pressure of 0.1Kpa, reacting for 2 hours at 200 ℃, and adding 1 wt.% of ethyl acetate for crystallization after the reaction is finished to obtain purified lactic acid;
(3) and (3) synthesizing polylactic acid: heating the purified lactic acid synthesized in step (2) at a temperature of 90 ℃ under a pressure of 0.1Kpa, adding 0.1 wt.% of catalyst stannous octoate, and heating and stirring the mixture of the purified lactic acid and the stannous octoate for 0.5 h; after stirring, the temperature is raised to 150 ℃, then the temperature is gradually reduced, and the temperature is reduced to 120 ℃ for heat preservation until the polylactic acid is obtained after complete distillation.
(4) After the polylactic acid powder is obtained, chloroform is added for dissolution, and then formaldehyde is added for re-precipitation. Finally obtaining the purified L-polylactic acid.
As a result of measurement and calculation, the yield of the L-polylactic acid prepared in this example was 85%, and the viscosity-average molecular weight was about 62000.
Example 2
(1) Synthesizing low-polymer lactic acid: 200g of L-lactic acid was taken and distilled at 80 ℃ to remove water. Then heating lactic acid at 110 ℃ for 8h under the pressure of 0.1Kpa to synthesize oligomeric lactic acid;
(2) synthesizing and purifying lactic acid: adding 0.5 wt.% of catalyst stannous octoate into the low-polymerization lactic acid synthesized in the step (1) under the pressure of 1Kpa, reacting for 2 hours at 240 ℃, and adding 1 wt.% of ethyl acetate after the reaction is finished to crystallize to obtain purified lactic acid;
(3) and (3) synthesizing polylactic acid: heating the purified lactic acid synthesized in step (2) at a temperature of 90 ℃ under a pressure of 1Kpa, adding 0.5 wt.% of catalyst stannous octoate, and heating and stirring the mixture of the purified lactic acid and the stannous octoate for 0.5 h; after stirring, the temperature is increased to 160 ℃, then the temperature is gradually reduced, and the temperature is reduced to 130 ℃ for heat preservation until the polylactic acid is obtained after complete distillation.
(4) After the polylactic acid powder is obtained, chloroform is added for dissolution, and then formaldehyde is added for re-precipitation. Finally obtaining the purified L-polylactic acid.
As a result of measurement and calculation, the yield of the L-polylactic acid produced in this example was 83%, and the viscosity-average molecular weight was about 70000.
Example 3
(1) Synthesizing low-polymer lactic acid: 200g of L-lactic acid was taken and distilled at 80 ℃ to remove water. Then heating lactic acid at 160 ℃ for 6h under the pressure of 0.1Kpa to synthesize oligomeric lactic acid;
(2) synthesizing and purifying lactic acid: adding 0.5 wt.% of catalyst stannous octoate into the low-polymerization lactic acid synthesized in the step (1) under the pressure of 10Kpa, reacting for 2 hours at 260 ℃, and adding 1 wt.% of ethyl acetate after the reaction is finished to crystallize to obtain purified lactic acid;
(3) and (3) synthesizing polylactic acid: heating the purified lactic acid synthesized in step (2) at a temperature of 90 ℃ under a pressure of 10Kpa, adding 2 wt.% of catalyst stannous octoate, and heating and stirring the mixture of the purified lactic acid and the stannous octoate for 0.5 h; after stirring, the temperature is increased to 180 ℃, then the temperature is gradually reduced, and the temperature is reduced to 140 ℃ for heat preservation until the polylactic acid is obtained after complete distillation.
(4) After the polylactic acid powder is obtained, chloroform is added for dissolution, and then formaldehyde is added for re-precipitation. Finally obtaining the purified L-polylactic acid.
As a result of measurement and calculation, the L-polylactic acid produced in this example had a yield of 80% and a viscosity-average molecular weight of about 67000.
Example 4
(1) Synthesizing low-polymer lactic acid: 200g of L-lactic acid was taken and distilled at 80 ℃ to remove water. Then heating lactic acid at 160 ℃ for 6h under the pressure of 0.1Kpa to synthesize oligomeric lactic acid;
(2) synthesizing and purifying lactic acid: adding 1 wt.% of stannous octoate and toluenesulfonic acid composite catalyst (the molar ratio of stannous octoate to toluenesulfonic acid is 1: 1) into the low-polymerization lactic acid synthesized in the step (1) under the pressure of 10Kpa, reacting at 260 ℃ for 2h, and adding 1 wt.% of ethyl acetate for crystallization after the reaction is finished to obtain purified lactic acid;
(3) and (3) synthesizing polylactic acid: heating the purified lactic acid synthesized in the step (2) at a temperature of 90 ℃ under a pressure of 10Kpa, adding 1 wt.% of a composite catalyst of stannous octoate and toluene sulfonic acid (the molar ratio of the stannous octoate to the toluene sulfonic acid is 1: 1), and heating and stirring the mixture of the purified lactic acid and the stannous octoate for 0.5 h; after stirring, the temperature is increased to 180 ℃, then the temperature is gradually reduced, and the temperature is reduced to 140 ℃ for heat preservation until the polylactic acid is obtained after complete distillation.
(4) After the polylactic acid powder is obtained, chloroform is added for dissolution, and then formaldehyde is added for re-precipitation. Finally obtaining the purified L-polylactic acid.
As a result of measurement and calculation, the L-polylactic acid prepared in this example had a yield of 80% and a viscosity-average molecular weight of about 75000.
Comparative example 1
(1) 200g of L-lactic acid was taken and distilled at 80 ℃ to remove water.
(2) Synthesizing and purifying lactic acid: adding 0.5 wt.% of catalyst stannous octoate into the lactic acid raw material in the step (1) under the pressure of 1Kpa, reacting for 2 hours at 240 ℃, and adding 1 wt.% of ethyl acetate for crystallization after the reaction is finished to obtain purified lactic acid;
(3) and (3) synthesizing polylactic acid: heating the purified lactic acid synthesized in step (2) at a temperature of 90 ℃ under a pressure of 1Kpa, adding 0.5 wt.% of catalyst stannous octoate, and heating and stirring the mixture of the purified lactic acid and the stannous octoate for 0.5 h; after stirring, the temperature is increased to 160 ℃, then the temperature is gradually reduced, and the temperature is reduced to 130 ℃ for heat preservation until the polylactic acid is obtained after complete distillation.
(4) After the polylactic acid powder is obtained, chloroform is added for dissolution, and then formaldehyde is added for re-precipitation. Finally obtaining the purified L-polylactic acid.
The L-polylactic acid prepared in this example was found to have a yield of 65% by measurement and calculation and a viscosity average molecular weight of about 57000.
Comparative example 2
(1) Synthesizing low-polymer lactic acid: 200g of L-lactic acid was taken and distilled at 80 ℃ to remove water. Then heating lactic acid at 110 ℃ for 8h under the pressure of 0.1Kpa to synthesize oligomeric lactic acid;
(2) and (3) synthesizing polylactic acid: heating the low-polymerized lactic acid synthesized in the step (1) at a temperature of 90 ℃ under a pressure of 1Kpa, adding 0.5 wt.% of catalyst stannous octoate, and heating and stirring the mixture of the purified lactic acid and the stannous octoate for 0.5 h; after stirring, the temperature is increased to 160 ℃, then the temperature is gradually reduced, and the temperature is reduced to 130 ℃ for heat preservation until the polylactic acid is obtained after complete distillation.
(3) After the polylactic acid powder is obtained, chloroform is added for dissolution, and then formaldehyde is added for re-precipitation. Finally obtaining the purified L-polylactic acid.
As a result of measurement and calculation, the yield of the L-polylactic acid prepared in this example was 73%, and the viscosity-average molecular weight was about 50000.
Unless defined otherwise, technical or scientific terms used herein shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention belongs. The use of "first," "second," and similar terms in the present application do not denote any order, quantity, or importance, but rather the terms are used to distinguish one element from another. The terms "connected" or "coupled" and the like are not restricted to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "upper", "lower", "left", "right", and the like are used merely to indicate relative positional relationships, and when the absolute position of the object being described is changed, the relative positional relationships are changed accordingly.
While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (10)
1. A method for preparing polylactic acid from lactic acid, which is characterized by comprising the following steps:
s1: synthesizing low-polymer lactic acid: heating lactic acid at the temperature of 110-180 ℃ for 4-8 h under the pressure of 0.01-10 Kpa to synthesize oligomeric lactic acid;
s2: synthesizing and purifying lactic acid: adding 0.1-2.0 wt.% of catalyst into the low-polymerization lactic acid synthesized in S1 under the pressure of 0.1-10 Kpa, reacting at 200-260 ℃ for 2-20 h, and adding a crystallizing agent for crystallizing after the reaction is finished to obtain purified lactic acid;
s3: and (3) synthesizing polylactic acid: heating the purified lactic acid synthesized in the step S2 at a temperature of 90-110 ℃ under a pressure of 0.1-10 Kpa, adding 0.1-2.0 wt.% of catalyst, and heating and stirring the mixture of the purified lactic acid and the catalyst for 0.5-1 h;
after stirring, the temperature is raised to 150-180 ℃, then the temperature is gradually reduced, and the temperature is reduced to 120-140 ℃ for heat preservation until the polylactic acid is obtained after complete distillation.
2. The method of claim 1, wherein the lactic acid comprises at least one of L-lactic acid and D-lactic acid.
3. The method of claim 1, wherein the lactic acid is dehydrated before the synthesis of the low-polymer lactic acid, and the dehydration is performed by: distilling for 1-10 h at 60-160 ℃.
4. The method of claim 1, wherein the catalysts used in S2 and S3 include a tin catalyst, a tin catalyst complex with a sulfonic acid compound.
5. The method for preparing polylactic acid from lactic acid according to claim 4, wherein the tin catalyst comprises stannous chloride, stannic oxide, stannous acetate, stannic acid, stannous octoate, stannous oxalate, stannous methanesulfonate;
the sulfonic acid compounds comprise methanesulfonic acid, toluenesulfonic acid, ethanesulfonic acid, propanesulfonic acid, butanesulfonic acid, hexanesulfonic acid and octanesulfonic acid.
6. The method of claim 1, wherein the crystallization agent in S2 comprises ethyl acetate.
7. The method for preparing polylactic acid from lactic acid according to claim 1, wherein the temperature in S3 is raised to 150-180 ℃ at a heating rate of 1-5 ℃/min, then gradually lowered, and then the temperature is lowered to 120-140 ℃ for heat preservation and distillation for 2-20 h.
8. The method of claim 1, wherein the polylactic acid synthesized in S3 is further dissolved and precipitated to obtain further purified polylactic acid.
9. The method for preparing polylactic acid from lactic acid according to claim 9, wherein the solvent for dissolving the polylactic acid comprises sulfur-containing organic substances, nitrogen-containing organic substances, chlorine-containing organic substances; the solvent for precipitating the polylactic acid comprises an ester solvent or an alcohol solvent;
wherein the sulfur-containing organic matter comprises dimethyl sulfoxide; the nitrogen-containing organic matter comprises N, N-dimethylformamide, N-dimethylacetamide or N-methylpyrrolidone; the chlorine-containing organic matter comprises chloroform and dichloromethane; the ester solvent comprises ethyl acetate; the alcoholic solvent includes methanol.
10. A polylactic acid produced by the method according to any one of claims 1 to 9.
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