Systematic investigation of methods to suppress membrane plasticization during CO2 permeation at supercritical conditions

The suppression of CO2-induced plasticization in polyimide membranes at supercritical conditions up to 120 bar is investigated. Three approaches (polymer blending, thermal treatments and chemical crosslinking) known from relatively low-pressure applications are applied and their effectiveness to suppress membrane plasticization at high CO2 pressures and under supercritical conditions is systematically identified. CO2 sorption measurements reveal that especially Henry sorption promotes plasticization and that the corresponding Henry sorption parameter (k(D)) correlates with the d-spacing and T-g of the membranes. A lower d-spacing and higher T-g results in a reduced k(D) parameter and thus a higher resistance to plasticization. A high interchain rigidity is required to suppress plasticization at the highly plasticizing liquid-like CO2 densities. Chemical and thermo-oxidative crosslinking results in the largest decrease in interchain mobility and therefore shows the highest resistance to plasticization, but also a significantly lower permeability. Thermally treating the membranes in N-2 retains a high permeability, while still displaying significant plasticization resistance. Polymer blending does increase the plasticization resistance, but strongly reduces the permeability. All three methods manage to suppress plasticization at supercritical conditions, but crosslinking offers superior plasticization resistance. However, proper tailoring strategies are required to combine a high plasticization resistance with a high permeability.

Automated summary

This study investigates the suppression of CO2-induced plasticization in polyimide membranes under supercritical conditions. Three methods (polymer blending, thermal treatments, and chemical crosslinking) known from low-pressure applications are applied and their effectiveness in suppressing membrane plasticization at high CO2 pressures is identified. Chemical and thermo-oxidative crosslinking provides the highest resistance to plasticization but also lowers permeability, while thermal treatments in N-2 retain high permeability with significant plasticization resistance. Polymer blending increases plasticization resistance but strongly reduces permeability. Crosslinking offers superior plasticization resistance, but tailored strategies are needed to balance this with permeability.