Research progress on one-step green and efficient production of lactide from lactic acid

Polylactic acid (PLA) and other biodegradable materials have the potential to replace petroleum-based materials as the mainstream option. As a synthetic monomer for PLA, the purity and cost of lactide (LD) seriously restrict the production scale and application range of PLA. This article analyzes the reasons affecting the purity of LD from the aspects of reaction mechanism, catalyst, and LD purification method based on the one-step production process of LD. It is pointed out that bimolecular nucleophilic substitution reactions (SN2) and the ester-semiacetal tautomerization is a possible mechanism for causing racemization reactions. Comparing the differences of various purification methods, it is suggested that the melting crystallization method and distillation method are expected to become the mainstream LD purification processes. The gas-phase one-step method has the potential to become the mainstream process for LD production in the future due to its advantages of simple process, high product purity, and low energy consumption. The key is to design high-stability, high-selectivity, and high-conversion-rate catalysts.