Systematic investigation of the effects of temperature and pressure on gas transport through polyurethane/poly(methylmethacrylate) phase-separated blends

Polyurethane (PU) and polyurethane-poly (methyl methacrylate) (PMMA) blend membranes were used in gas separation studies. The effects of blend composition, temperature, and pressure on the permeability, diffusivity, and solubility of CO2, H-2, O-2, CH4, and N-2 were investigated. The separation factors of some gas pairs were also evaluated. Positron annihilation lifetime spectroscopy was applied to assess free volume changes as a function of blend composition and temperature. Free volume size increases by approximately 30% with increasing temperature from 10 to 40 degrees C for all blends studied. The permeability of all gases decreases by approximately 55% with the addition of 30 wt% of PMMA. The permeation process is governed by diffusion, except that Of CO2, In relation to the behavior of gas transport as a function of temperature, some important observations are W CO2 presents the lowest permeation activation energy value (28 kJ/mol), and (ii) gas pair selectivity increases at low temperatures and is high for gas pairs that present differences in permeation activation energies as high as 15 kJ/mol for the CO2/CH4 gas pair. Furthermore, the study with pressure variations shows that: (i) at elevated pressure, the PU and the blend membrane permeability to CO2 and H-2 increases by approximately 35%, and (ii) oxygen-to-nitrogen selectivity increases with pressure as a consequence of the decrease in the permeability to nitrogen in the case of the 30%-PMMA blend. (C) 2007 Elsevier B.V. All rights reserved.