Patent ID: 7488783

Claim:
A process for the production and purification of lactide, wherein, staffing from an aqueous solution of lactic acid or lactic acid derivatives, the stages comprise: a) evaporation of free water and a portion of the water of constitution until oligomers having a molecular mass of between 400 and 2000 amu, a total acidity as lactic acid equivalent of between 119 and 124.5% and an optical purity, expressed as L-lactic acid, of between 90 and 100% are obtained; b) feeding a mixture comprising a depolymerization catalyst and the oligomers obtained in step a) to a depolymerization reactor to produce: b1) a lactide-rich vapor phase, and b2) an oligomer-rich liquid residue; c) selective condensation of the lactide-rich vapor with recovery, in the liquid form, of a crude lactide product freed from the volatile compounds; d) melt crystallization of the crude lactide product to produce: d1) a purified lactide fraction having a residual acidity of less than 10 meq/kg, a water content of less than 200 ppm, a total lactide content of 99-99.9% and a meso-lactide content of less than 1%; and d2) at least a first residual fraction having a lactide content comprise between 35 and 80%; and e) separating the purified lactide from the step d1) and the at least first residual fraction from the step d2); and f) aqueous treatment of said at least first residual fraction from the step d2) of melt crystallization, consisting of: f1) extractive and controlled crystallization of the residue fractions in an aqueous medium, with control of the geometry of crystals formed and with segregation of a lactide suspension towards a solid phase and of impurities towards a liquid phase to carry out aqueous extraction of the impurities; f2) separation of the suspension of crystals formed in step e1) from the liquid phase and then draining to separate a wet cake rich in lactide crystals from a liquid phase depleted in lactide and laden with impurities; and f3) drying the wet cake to provide prepurified lactide obtained from said at least first residual fraction of said step d2).