Phase equilibrium (solid-liquid-gas) in polyethyleneglycolcarbon dioxide systems

Phase equilibria (solid-liquid-gas) for polyethyleneglycol (with molar masses 1500, 4000, 8000 and 35 000 g mol -1) and carbon dioxide mixtures were determined. It was found that the S-L-V lines in P-T projection for all polyethyleneglycols studied show a temperature minimum and a temperature maximum. These phenomena have not been reported previously in the literature. If a reduced temperature (obtained by dividing the temperature of the solid-liquid transition under pressure by the melting point of PEG at 1 bar) is introduced, the S-L transition of all binary systems are represented by one line. The solubility of CO2 in liquid polyethyleneglycols is influenced by pressure and temperature, and is almost independent of the molecular mass of polyethyleneglycol. In a P-T projection, the vapour-liquid equilibrium is represented by a straight line if isopleths are plotted as a function of the reduced temperature. By combining the P-Tred projections of the S-L and L-V transitions, one master diagram can obtained which is valid for all binary mixtures of polyethyleneglycol and CO2 in the pressure and temperature range investigated.