Excess molar enthalpies for binary mixtures related to supercritical antisolvent precipitation: Carbon dioxide + N-methyl-2-pyrrolidone

An isothermal high-pressure flow calorimeter has been used to measure excess molar enthalpies ( H m E ) for mixtures of supercritical CO2 and N-methyl-2-pyrrolidone (NMP) under conditions of temperature and pressure typically used in supercritical CO2 antisolvent precipitation (SAS): 313.15 and 338.15 K and 9.48, 15.00 and 20.00 MPa. Mixtures showed exothermic mixing; excess molar enthalpies exhibited a minimum in the CO2-rich region. The effects of pressure and temperature on the excess molar enthalpy of CO2 + NMP are large. The lowest H m E values (≈−4500 J mol−1) were observed for mixtures at 338.15 K and 9.48 MPa. On the other hand, H m E at this condition of temperature and pressure varies linearly with CO2 mole fraction in the two-phase region where a gaseous and a liquid mixture of fixed composition are in equilibrium. These data were analyzed in terms of phase equilibria data and critical locus for CO2 + NMP and the related SAS experiments. Very exothermic excess molar enthalpies were obtained for conditions of temperature and pressure with marked coalescence phenomena for micro and submicro particles of tetracycline, amoxicillin and ampicillin produced by SAS. Excess molar enthalpies here reported and those previously measured at 298.15 K and 7.50, 10.60 and 12.60 MPa were correlated using the Soave–Redlich–Kwong and Peng–Robinson equations of state and the classical mixing rule with two binary interaction parameters.