Detection and elimination of trace d‐lactic acid in lignocellulose biorefining chain: Generation, flow, and impact on chiral lactide synthesis

Abstract

High chiral purity of lactic acid is a crucial indicator for the synthesis of chiral lactide as the primary intermediate chemical for ring‐open polymerization of high molecular weight polylactic acid (PLA). Lignocellulose biomass is the most promising carbohydrate feedstock for commercial production of PLA, but the presence of trace d‐lactic acid in the biorefinery chain adversely affects the synthesis and quality of chiral lactide. This study analyzed the fingerprint of trace d‐lactic acid in the biorefinery chain and found that the major source of d‐lactic acid comes from lignocellulose feedstock. The naturally occurring lactic acid bacteria and water‐soluble carbohydrates in lignocellulose feedstock provide the necessary conditions for d‐lactic acid generation. Three strategies were proposed to eliminate the generation pathway of d‐lactic acid, including reduction of moisture content, conversion of water‐soluble carbohydrates to furan aldehydes in pretreatment, and conversion to l‐lactic acid by inoculating engineered l‐lactic acid bacteria. The natural reduction of lactic acid content in lignocellulose feedstock during storage was observed due to the lactate oxidase‐catalyzed oxidation of l‐ and d‐lactic acids. This study provided an important support for the production of cellulosic l‐lactic acid with high chiral purity.