OP-II-3

PP-I-40PACKED ABSORBER FOR THE ISOLATION OF L-LACTIDEMulyashov S.A. 1 , Sirovski F.S. 2 , Grechishkina O.S. 3 and Kolbakov V.V. 43 D.I. Mendeleev Univercity of Chemical Technology of Russia, Moscow, Russia,e-mail: olgrech@ hotmail.com1,2,4 OU Nordbiochem, Estonia, e-mail: vambola@nordbiochtm.comThe production of biodegradable polymers is based on polylactic acid (PLA). Thisacid is produced by polymerisation of a cyclic dimer that in turn is obtained frommicrobial L-acid. The known process of PLA manufacture comprises the synthesis ofan oligomer with molecular mass around 1000-5000 Daltons with its subsequentdepolymerisation. This reaction is carried out at 190-220 °C and residual pressure10-15 mm Hg giving also the considerable amount of side-products. The partial yieldof the desired product (L-lactide) could be increased by dropping thedepolymerisation temperature and respectively reaction pressure to 1-3 mm Hg.Unfortunately, under these conditions the complete removal of L-lactide with m.p. 97°C out of the gas phase becomes virtually impossible. The traces of L-lactide arefound all along the vacuum line as well as in the vacuum pumps themselves and theequipment operation is seriously compromised. The issue could be solved usingpacked absorbers.We have run several simulations of the packed absorber operation usingChemCad software. The plant included the depolymerisation reactor (a 70 l volumestirred jacketed tank) and the packed absorber installed on the vacuum line. Thereactor temperature was maintained in the range 160-260 °C. The regimes of thereactor and absorber operations were synchronised. It was shown that washing byaromatic solvents ensures virtually complete removal of L-lactide from the gas phase.292