EXCESS-ENTHALPIES OF (CARBON-DIOXIDE PLUS PROPYLENE CARBONATE OR N-METHYL-EPSILON-CAPROLACTAM OR 1-FORMYL PIPERIDINE) AT THE TEMPERATURES 298.15 K AND 308.15 K AND PRESSURES FROM 7.5 MPA TO 12.5 MPA

The excess molar enthalpies H-m(E) of [xCO(2) + (1 - x){C4H6O3 (propyl ene carbonate) or C7H13NO (N-methyl-epsilon-caprolactam) or C6H11NO (1 -formyl piperidine)}] were measured at the temperatures 298.15 K and 3 08.15 K and pressures (7.5, 10.0, and 12.5) MPa. (Vapour + liquid) pha se boundaries were determined from the H(m)(E)s. The excess enthalpies for all of the mixtures are negative over the entire composition, tem perature, and pressure range. Large changes in the values of H-m(E) we re observed near the critical temperature and pressure of carbon dioxi de. The Peng-Robinson equation of state with a composition-dependent i nteraction parameter was used to model the behaviour of H-m(E). At low x the Peng-Robinson equation provided a satisfactory fit for all mixt ures studied over the full range of pressures and temperatures. For {x CO(2) + (1 - x)C4H6O3}, the predicted H-m(E) values for x > 0.5 were m ore negative than the experimental results. The fits to the other mixi ng curves were somewhat better, but show similar discrepancies at T = 308.15 K and p = 7.5 MPa. (C) 1995 Academic Press Limited