Cyclic l-lactide synthesis from lignocellulose biomass by biorefining with complete inhibitor removal and highly simultaneous sugars assimilation.

Abstract

Cyclic chiral lactide is the monomer chemical for polymerization of high molecular weight polylactic acid (PLA). The synthesis of cyclic l-lactide starts from poly-condensation of l-lactic acid to a low molecular weight prepolymer and then depolymerized to cyclic l-lactide. Lignocellulose biomass is the most promising carbohydrate feedstock for lactic acid production, but the synthesis of cyclic l-lactide from l-lactic acid produced from lignocellulose has so far not been successful. The major barriers are the impurities of residual sugars and inhibitors in the crude cellulosic l-lactic acid product. Here we show a successful cyclic l-lactide synthesis from cellulosic l-lactic acid by lignocellulose biorefining with complete inhibitor removal and coordinated sugars assimilation. The removal of inhibitors from lignocellulose pretreatment was accomplished by biodetoxification using a unique fungus Amorphotheca resinae ZN1. The nonglucose sugars were completely and simultaneously assimilated at the same rate with glucose by the engineered l-lactic acid bacterium Pediococcus acidilactici. The l-lactic acid production from wheat straw was comparable to that from corn starch with high optical pure (99.6%), high l-lactic acid titer (129.4 g/L), minor residual total sugars (~2.2 g/L), and inhibitors free. The cyclic l-lactide was successfully synthesized from the regularly purified l-lactic acid and verified by detailed characterizations. This study paves the technical foundation of carbon-neutral production of biodegradable PLA from lignocellulose biomass.