EXPERIMENTAL AND MOLECULAR-DYNAMICS SIMULATED EXCESS-ENTHALPIES AND SOLUBILITIES OF NEOPENTANE IN SUPERCRITICAL CARBON-DIOXIDE

Excess enthalpies were measured as a function of composition for mixtures of neopentane in supercritical CO2 at two temperatures (310 and 313.15 K) slightly above the critical temperature of pure CO2 and at three pressures (6.29, 8.36, and 10.44 MPa) spanning the pure CO2 critical pressure. The excess enthalpies were extremely pressure dependent, ranging from very large exothermic values at the lowest pressure to endothermic values at the highest pressure. Excess enthalpies at these same conditions were calculated from molecular-dynamics simulations treating neopentane as a spherical Lennard-Jones fluid and CO2 as both a single- and two-site Lennard-Jones fluid. Both models correctly predict the strong pressure dependence of the excess enthalpy. The simulated and experimental values agree well over the entire range of conditions studied if the Lennard-Jones unlike energy parameter is regressed from a single experimental datum. © 1990.