Reaction-Devolatilization Coupling for Lactide Synthesis: Process Development and Influence Factor Analysis

To address the challenges of low reaction efficiency, poor product yield, and severe racemization during the depolymerization of lactic acid oligomers to lactide, this study proposes a proprietary wiped-film depolymerization reactor featuring enhanced heat and mass transfer, coupled with a cyclic depolymerization process. The reactor enables efficient integration of the critical control reaction with the devolatilization step. Results demonstrate that rapid depolymerization can be achieved at reduced temperatures, thereby simultaneously minimizing racemization and enhancing product yield, with lactide yields reaching 85.0% or above and meso-lactide content controlled within 6.0%. Furthermore, for the continuous cyclic depolymerization process, the effects of four key parameters—reaction temperature, molecular weight of lactic acid oligomers, vacuum degree, and catalyst concentration—on product yield and quality were systematically investigated to determine the optimal operating conditions. By modulating the catalyst addition protocol, the accumulation rate of the catalyst in the recycle loop was effectively reduced, and the maximum lactide yield reached 89.5%. The operational flexibility of the unit was significantly improved compared to conventional stirred-tank depolymerization processes, providing technical support for the continuous and stable production of lactide.