Effect of temperature and pressure on gas transport in ethyl cellulose membrane

A homogeneous dense ethyl cellulose (EC) membrane has been prepared by a solution casting technique with chloroform as solvent and characterized by wide-angle X-ray diffraction, differential scanning calorimetry, and tensile tester. Permeating characteristics of five pure gases through the membrane has been described in detail. The permeability, diffusivity, solubility, and their selectivities of oxygen, nitrogen, carbon dioxide, methane and hydrogen through the membrane have been measured by a change in operating temperature and upstream pressure in a time-lag apparatus. A continuously enhanced permselectivity for gas pairs of carbon dioxide/methane, and hydrogen/nitrogen, an enhanced diffusivity selectivity for gas pairs of oxygen/nitrogen, carbon dioxide/methane, as well as a decreased permeability and diffusivity for five pure gases, have been observed with decreasing the operating temperature. The solubility of five gases in the EC membrane increases with decreasing temperature. The solubility selectivity does not vary nearly with operating temperature. Especially, the permeability, diffusivity, solubility, and their selectivities in the EC membrane almost maintain constant with changing the upstream pressure. The highest oxygen/nitrogen, carbon dioxide/methane, and hydrogen/nitrogen selectivity coefficients were, respectively, equal to 4.27, 14.7, and 19.5. A relationship between the diffusivity and effective molecule diameter of the gases across the EC membrane was discussed. The gas solubility in the membrane is believed to be a linear function of the critical temperature of the gases.