METHOD AND SYSTEM FOR CONTINUOUSLY PREPARING LACTIDE BY STEP CONTROL

The present invention belongs to the technical field of biodegradable materials. Disclosed are a method and a system for continuously preparing lactide by step control. The method comprises: (1) reacting a lactic acid oligomer and a depolymerization catalyst in a first depolymerization reaction unit to obtain a first liquid-phase material; (2) circulating the first liquid-phase material in a second depolymerization reaction unit for reaction until the molecular weight of the liquid-phase material is higher than 6,000 to obtain a second liquid-phase material; (3) circulating the second liquid-phase material in a third depolymerization reaction unit for reaction until the molecular weight of the liquid-phase material is higher than 10,000; and (4) collecting gas-phase crude lactide from the first depolymerization reaction unit, the second depolymerization reaction unit and the third depolymerization reaction unit, and then purifying same. The present invention achieves the high-efficiency depolymerization of a lactic acid oligomer, reduces the racemization degree of lactide and the coking carbonization probability of the substrate, and ensures the conversion rate of the lactic acid oligomer and the system stability throughout the whole reaction process.