The Effect of Crosslinking on the Physical Aging of PTMSP Membranes

Abstract

For post-combustion CO2 capture, membranes with high permeability and relatively high CO2/N2 selectivity are favoured to compete with the commercial amine-based absorption technology. With the highest known CO2 permeability, poly(1-trimethylsilyl-1-propyne) (PTMSP) have gained a lot of attention for CO2 separation membranes. However, the significant physical aging of PTMSP membranes, due to the non-equilibrium free volume, leads to an undesirable permeability loss over time. In this work, in order to reduce the physical aging of PTMSP membrane, CO2-philic polyethyleneimine (PEI) was blended with PTMSP to introduce reaction sites for crosslinking. Subsequently, poly (ethylene glycol) diglycidyl ether (PEGDGE) was used to crosslink the PEI in the blend PTMSP/PEI membrane. Fabrication of PTMSP and PTMSP/ 10 w.t% PEI self-standing membranes was conducted and various characterization methods were applied in order to investigate the feasibility of the approach. FT-IR analysis confirmed the crosslinking reaction. The reaction mechanism between amino groups of branched PEI and epoxide groups of PEGDGE was discussed. Solvent resistance tests proved that crosslinking rendered insoluble membranes. The TGA results revealed that blending and crosslinking have little effect on the overall thermal stability and decomposition characteristics of PTMSP. The thermal stability proved satisfactory for uses in CO2 post-capture systems. DSC analysis was used to investigate the glass transition temperature (Tg) of the modified membranes. Glass transitions were not detectable for the modified membranes under applied experimental conditions. Physical aging was studied by means of single gas and mixed gas permeation tests over a period up to 3 months. The effect of membrane thickness was studied by using membranes with two thicknesses, 50 and 150 µm, respectively. After crosslinking, physical aging rate of the PTMSP membrane had been significantly reduced. Exhibiting the most reduced physical aging rate in this work, 150 µm crosslinked PTMSP membranes proved to be the optimal choice of material, maintaining a relatively high CO2 permeability (over 7000 Barrer) and moderate CO2/N2 selectivity (over 8).