Solubility of carbon dioxide in cellulose acetate at elevated pressures

The solubility of carbon dioxide in symmetric (dense) cellulose 2.4‐acetate has been measured at temperatures from 0 to 70°C and pressures up to 45 atm. The polymer samples were prepared by slowly drying asymmetric reverse osmosis membranes. The solubility isotherms can be described satisfactorily up to 60°C by the “dual‐sorption” model for glassy polymers. The model cannot represent the experimental data above 60°C, possibly because of a second‐order transition in the polymer between 60 and 70°C. An analysis of the dual‐sorption parameters and of the heats of solution and “hole filling” suggests that the polymer samples contained a relatively large volume of microcavities. Gas solution appears to occur predominantly in microcavities, a large fraction of the penetrant moleculers being immobilized or partially immobilized. The solubilities obtained in this work are compared with similar data computed from time‐lag measurements of other investigators, and the validity of the dual‐sorption model is examined for the present case.