Excess molar enthalpies of (carbon dioxide+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

Abstract

The excess molar enthalpies H m Eof { xCO 2+ (1 − x)CH 3(OCH 2CH 2) n OCH 3}, 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 Ebehaviour. The values of H m Eof 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 Eobserved at T= 308.15 K and p= 7.5 MPa are due to the proximity to the critical point of CO 2. In contrast to the behaviour of ethylene glycol dimethyl ether mixtures, for which (∂ H m E/∂ p) Tx is positive, the pressure dependence of H m Efor 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 (∂ H m E/∂ p) Tx .