Measurement and modelling of high-pressure phase equilibria in the systems polyethyleneglycol (PEG)–propane, PEG–nitrogen and PEG–carbon dioxide

Phase equilibria in the binary polymer–gas systems polyethyleneglycol (PEG)–propane, PEG–nitrogen and PEG–carbon dioxide have been investigated. The experiments were performed for PEG with molecular weights of 200, 1500, 4000 and 8000 g/mol in a temperature range of 50 to 120°C and a pressure range from 5 to 300 bar using a static-analytical method. It was found that carbon dioxide dissolves much better in PEG than does propane or nitrogen. With rising temperature the PEG–carbon dioxide miscibility gap increases, whereas the miscibility gaps of the PEG–propane and the PEG–nitrogen systems decrease. The influence of the polymer molecular weight on the gas solubility is almost negligible for PEG 1500 to PEG 8000. The behaviour of the small PEG 200 deviates significantly due to strong endgroup influence. The gas solubilities in the polymers are correlated with the SAFT equation of state. The influence of temperature and of PEG molecular weight is represented satisfactorily.