Method and system for preparing lactic acid by using biological fermentation technology to produce high-yield and high-optical purity lactide

Abstract

The invention relates to the fields of fermentation biology and biodegradable materials, and in particular relates to a method and a system for preparing lactic acid by using a biological fermentationtechnology to produce high-yield and high-optical purity lactide. The method comprises the following steps: 1, inoculating lactic acid zymophyte (lactobacillus rhamnosus with the preservation numberof CGMCC No.19507) into a fermentation culture medium for lactic acid fermentation to obtain a lactic acid fermentation liquid, separating the lactic acid fermentation liquid to obtain an L-lactic acid raw material, and carrying out a pre-polycondensation reaction on lactic acid under a first polymerization condition to obtain a lactic acid prepolymer with a polymerization degree of less than 5 and a gas phase containing lactic acid; under a second polymerization condition, carrying out condensation polymerization on the lactic acid prepolymer in a falling-film reactor to obtain a lactic acidoligomer with a polymerization degree of 10 or below; and depolymerizing the lactic acid oligomer under the action of a catalyst to obtain a lactide-containing product. By utilizing the method and thesystem provided by the invention, the high-optical purity lactide can be obtained, and the yield is high.

Description

technical field [0001] The invention relates to the fields of fermentation biology and biodegradable materials, in particular to a method and system for producing lactic acid with high yield and high-gloss pure lactide by using biological fermentation technology. Background technique [0002] Under the background of global plastic restrictions, new biodegradable polylactic acid materials are attracting more and more attention, and the annual consumption is increasing. Statistics from the European Bioplastics Association show that the production capacity of degradable materials is growing at a rate of nearly 20% per year, but its demand is growing at a rate of 30%, and the supply of products has been in short supply for a long time. The synthesis of bio-based polylactic acid generally uses glucose with high DE value as raw material to produce high-gloss pure lactic acid through biological fermentation, and then undergoes steps such as dehydration concentration, condensation r...

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Problems solved by technology

[0003] The purpose of the present invention is to overcome the problems of low light purity and low yield of lactide prepared by the lactide production process in the prior art, and to provide a method for producing lactic acid with high yield and high light pure lactide by using biological fermentation technology. The method and system of ester, using the method and system of the present invention, can obtain high light pure lactide, and the yield is high

[0004] The inventors of the present invention have found that the reason why the yield and optical purity of lactide cannot be effectively improved in the prior art is that 1) in the prior art, lactic acid oligomers are usually obtained by one-step polycondensation, but the polymerization cannot be effectively obtained by one-step polycondensation lactic acid oligomers with a degree of 5-10, resulting in low efficiency of subsequent reactions and more by-products; 2) in the existing process, in order to obtain good reactivity, it is usually necessary to effectively dehydrate lactic acid (including the lactic acid carried by itself) water and the water generated by the polycondensation reaction), and the lactide product generated by the depolymerization reaction is evaporated in time, and in order to obtain a good effect of water and lactide evaporation, it is generally achieved by increasing the system temperature and reducing the system pressure However, many side reactions will occur under high temperature and low pressure, such as carbonization and oxidation of lactic acid oligomers, racemization and even decomposition of lactide, resulting in low lactide yield and optical purity

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