Separation performance of poly(urethane–urea) membranes in the separation of C2 and C3 hydrocarbons from methane

Abstract

In this research, the effects of changing the polyol, disocyanate, and chain extender used in synthesized polyurethane membranes on gas permeability are investigated. The membranes are synthesized using PTMG, PPG, PCL as polyol; IPDI, HDI, TDI as diisocyanate; and BDO, BDA as chain extender in a 1/3/2 and 1/2/1M ratio of polyol/diisocyanate/chain extender. The results obtained from Fourier transfer infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) confirmed that changing the polyol type from PPG to PTMG and PCL leads to more phase interaction. Furthermore, changing the diisocyanate group from aromatic to aliphatic and from cyclic aliphatic to linear aliphatic leads to an increase in phase separation of hard and soft segments which cause the packing density of hard segment due to the enhancement of the hydrogen bonding. In addition, changing a chain extender from a diol one to a diamine leads to an increase in phase separation of hard and soft segments.Permeation experiments reveal that the larger, more condensable gases are more permeable than light ones in more rubbery polymers; and, the selectivity of polyurethane as a rubbery polymer is dominated by solubility. On the other hand, by enhancement of the microphase separation of hard and soft segments, the rubbery behavior and permeability of condensable gases increase along with their selectivity. Overall, polymers based on the PPG polyol show maximum permeability because of their higher rubbery property due to its higher phase separation. The results of permeability tests indicate high permeability, up to 200Barrer (1Barrer=1×10−10 [cm3(STP) cm/cm2scmHg]), and high selectivity for propane with respect to methane (C3H8/CH4: 5.47).