Phase behaviour of L-lactide in supercritical carbon dioxide at high pressures

The solid-fluid and the liquid-vapour equilibria for the binary system carbon dioxide + L-lactide were determined in the temperature range 275-355 K and in the pressure range 10-80 MPa. This system shows the type of phase behaviour characterized by two branches of the solid L-lactide + liquid + vapour curve ended with first and second critical endpoints. In this study only the high-temperature branch of the three-phase curve was determined. The second critical end point (solid L-lactide + liquid = vapour) was found at 323.0 K and 30.3 MPa. The liquid-vapour equilibria were modelled with the Peng-Robinson equation of state coupled with the classical mixing rules. For the calculations L-lactide critical temperature, critical pressure and acentric factor were estimated from the Joback-Lyndersen group contribution method. (c) 2008 Elsevier B.V. All rights reserved.