A new apparatus to measure the vapour-liquid equilibria of low-volatility compounds with near-critical carbon dioxide. Experimental and modelling results for carbon dioxide+n-butanol, +2-butanol, +2-butyl acetate and +vinyl acetate systems

摘要

A new apparatus has been developed for the experimental determination of vapour-liquid equilibria in systems containing low-volatility compounds and near-critical carbon dioxide. The apparatus combines the advantages of the gas saturation method with those of a circulation method. An air-lift-functioning draft tube is used in the centre of the equilibrium cell to increase contact time between solute and solvent. The apparatus is tested by measuring the vapour-liquid equilibrium (VLE) of the system CO2+1-butanol at 313.2 and 333.2 K and at pressures up to 11 MPa. For the systems CO2+2-butanol, CO2+vinyl acetate and CO2+2-butyl acetate, VLE data were measured at pressures up to 10 MPa and at the temperatures of 303.2, 313.2 and 333.2 K. The measured mole fractions of the low-volatility compound in carbon dioxide have an accuracy better than 3%. The solubility isotherms were modelled using the PRSV EOS with Wong-Sandler mixing rules and the LCVM model. It is shown that the solubility of the low-volatility compounds in carbon dioxide can be predicted well with the PRSV-WS EOS (NRTL-GE-model) using the fit parameters obtained from bubble point measurements. The PRSV-WS predicts the solubilities better than the LCVM model (t-mPR EOS with an adapted UNIFAC-GE-model).