Excess molar enthalpies of (carbon dioxide plus ethylene glycol dimethyl ether or 2-methoxyethyl ether) 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)CH3(OCH2CH2)(n)OCH3}, where n = 1 (ethylene glycol dimethyl ether) and n = 2 (2-methoxyethyl ether) were measured at the temperatures 298.15 K and 308.15 K and pressures (7.5, 10.0, and 12.5) MPa. No (vapour + liquid) phase boundaries were observed from the H-m(E) behaviour. The values of H-m(E) of all the mixtures are negative over the entire composition, temperature, and pressure range. An analysis using the Peng-Robinson equation with a composition-dependent interaction parameter confirms that the large negative values of H-m(E) observed at T = 308.15 K and p = 7.5 MPa are due to the proximity to the critical point of CO2. In contrast to the behaviour of ethylene glycol dimethyl ether mixtures, for which (partial derivative H-m(E)/partial derivative p)(T,x) is positive, the pressure dependence of H-m(E) for the 2-methoxyethyl ether mixtures became negative in the solvent-rich region at T = 298.15 K. The Peng-Robinson equation reproduces the main features observed,but fails to predict the reversal in (partial derivative H-m(E)/partial derivative p)(T,x). (C) 1996 Academic Press Limited