OP-II-3

PP-III-45REACTOR FOR THE DEPOLYMERISATION OF OLIGOLACTIC ACIDMulyashov S.A., Sirovski F.S., Beksaev S.G., Kolbakov V.V.OU Nordbiochem, Estonia, e-mail: lab-tos@mail.ruCurrently polylactic acid (PLA) is one of the most promising biodegradablepolymers due to the unique set of its valuable performance properties. PLA ismanufactured from lactic acid obtained by microbial carbohydrate wastefermentation. Unfortunately, the wide use of PLA i.e. for packaging is restricted byhigher production costs as compared to polythene, etc.PLA is obtained by the following reaction chain: lactic acid oligolactate cyclic dimer (lactide) polylactide. The contribution of the lactide synthesis step tothe overall production costs is quite significant. Depolymerisation is the most crucialstep in lactide synthesis. Increasing the process temperature to 250 °C shifts theoligomer – monomer equilibrium to the right as desired, however the rate of sidereactions such as racemisation, dehydration and thermal degradation is significantlyincreased above 210 °C. These side reactions decrease the quality of the finishedproduct. The issue could be resolved intensifying heat and mass transfer anddecreasing reactant residence time at high temperatures.This could be achieved by carrying out depolymerisation in the vacuumevaporator with the low temperature evaporation zone. Melted oligomer with thetemperature ≤210 °C is fed into the tubular heater where its temperature is brieflyraised to 220-260 °C. Then it flows into the low temperature evaporation zone. Thesharp pressure drop results in intensive lactide evaporation and its efficient removal.The simulation of the process allowed us to calculate the heater, reactant residencetime and lactide concentration in the melt prior to evaporation. The real experimentswere run on a pilot plant and optimal operation parameters were determined.522