The world patent WO 2004 0 14889 published by Brussels Biotechnology Company (be) on February 3, 2004 reported the preparation of polylactic acid, and its independent rights included the following contents: (1) lactic acid was prepared by the following methods: (a) the molecular weight of lactic acid or lactic acid derivative solution was 400-2000, and the total equivalent acidity of lactic acid was/kloc-. (b) adding oligomer and depolymerization catalyst into the depolymerization reactor to prepare a gas phase rich in lactic acid and a liquid phase rich in oligomer; (c) condensing the gas phase to obtain liquid crude lactic acid; (d) extracting and crystallizing crude lactic acid; (e) separating and discharging the crystals to obtain a wet cake rich in lactic acid crystals; (f) drying the wet cake to obtain pre-purified lactic acid; (g) crystallizing and pre-purifying lactic acid to obtain purified lactic acid with residual acidity lower than 65438+/-00 meq/kg, water content lower than 200ppm and racemic lactic acid content lower than 65438+/-0%; (2) Polymerizing the lactic acid obtained above to obtain polylactic acid.
Patent WO 2004 057008-A 1 published by BOTELHO T et al. in 2004 reported a preparation method of polylactic acid, which can be used as candy packaging material mainly through fermentation. The specific method reported in its example is: heating the culture medium (45 1) (containing whey, milk protein, inorganic salts, semi-gloss amino acids and other nutrients) to 70℃. Lactobacillus helveticus (99g) and flavor protease (RTM) (a) (26.5g) (26.5g) were added. Batch fermentation for 9 hours, supplemented with fresh broth containing whey, lactose and flavor protease (RTM). Adjust the pH to 5.75 with ammonia water, control the biological density to 7-8%, and continuously ventilate during the fermentation, with the aeration rate of 1 liter/minute. During the fermentation period of 34 days, the dilution rate was 0. 1.5-0.3/ hour. The content of lactic acid in wastewater is 4%, and the yield is12g/l hour when the dilution rate is 0.3/ hour ... The effluent of lactic acid is separated by ion exchange resin and chelating agent, and then it is subjected to continuous electrodialysis twice, and the recovery rate is 85-90%.
The U.S. patent US 2003 158360 published by HANZSCH BERND et al. on Aug. 2, 2003/KLOC-0 reported a preparation method of polylactic acid, which included the following steps: fermenting starch agricultural products to obtain lactic acid, ultra-purifying lactic acid through ultrafiltration, nanofiltration and/or electrodialysis, concentrating lactic acid, preparing prepolymer, cyclizing and depolymerizing to obtain dibasic lactic acid, purifying dibasic lactic acid, and.
JP 2002 300898, published by Shimadzu Corp on Jun. 65438+1Oct. 65438+May, 2002, reported a method for producing lactic acid and polylactic acid. The specific method is as follows: ammonium lactate is synthesized into lactate; ⑵ Poly (lactic acid) prepolymer with average molecular weight less than15000 mol.wt was synthesized from poly (lactic acid) ester in the presence of catalyst other than butyl tin. (3) depolymerizing polylactic acid to obtain lactic acid; The method also includes ring-opening the lactic acid polymer to prepare polylactic acid.
Patent WO 2002 6089 1-A published on aug. 8, 2002 by SHIMADZU CORP, OHARA H, TOYOTA JIDOSHA KK, ITO M and sawas reported the preparation method of lactic acid and polylactic acid for producing biodegradable plastics. An example of this patent reports the following method: the L- ammonium lactate obtained by fermentation is 90- 100. Removing the water in the reaction at 65438 020℃; Ethyl lactate purified by distillation was polycondensed at 65438 060℃ in the presence of octyl tin, and ethanol was removed. The obtained reaction solution was distilled at 200℃ to obtain lactic acid with a yield of 99.2%. Lactic acid was prepared by polymerizing lactic acid in the presence of octyl tin. Japanese patent JP 200 1 published on Aug.21reported the preparation of polylactic acid by using hydrolase instead of organometallic catalyst.