Abstract: The dependent relationship between temperature and pressure of supercritical CO₂+EtOH+ CO+H₂ quaternary system in the pressure range from 5 to 11 MPa in densities of CO₂ ranging from 0.542 to 0.590 g/cm³ was investigated by the static visual method in a constant volume. The critical temperature and pressure were experimentally determined simultaneously. The molar fraction of ethanol is 0.2% and that of CO and H₂ whose molar ratio is 1;1 changes from 0 to 4%. The phase behavior of the hydroformylation of propylene in supercritical CO₂ was simulated. It was found that the addition of CO and H₂ could change the supercritical properties of the CO₂+EtOH+CO+H₂ quaternary system obviously. Its critical temperature decreases linearly while its critical pressure increases linearly with the increasing molar fraction of CO and H₂. It was also found that pressure of the quaternary system in definite density of CO₂ increases linearly with increasing temperature and the slopes of p-T lines were basically the same. Simultaneously, pressure of the same quaternary system increases linearly with the increasing molar fraction of CO and H₂ in definite temperature and the rates of change at different temperatures were almost identical.

Key words: Supercritical CO2+EtOH+CO+H2 quaternary system, Critical temperature, Critical pressure, p-T lines