Mitigating of Thin-Film Composite PTMSP Membrane Aging by Introduction of Porous Rigid and Soft Branched Polymeric Additives

This work was focused on the mitigation of physical aging in thin-film composite (TFC) membranes (selective layer similar to 1 mu m) based on polymer intrinsic microporosity (PTMSP) by the introduction of both soft, branched polyethyleneimine (PEI), and rigid, porous aromatic framework PAF-11, polymer additives. Self-standing mixed-matrix membranes of thicknesses in the range of 20-30 mu m were also prepared with the same polymer and fillers. Based on 450 days of monitoring, it was observed that the neat PTMSP composite membrane underwent a severe decline of its gas transport properties, and the resultant CO2 permeance was 14% (5.2 m(3) (STP)/(m(2)center dot h center dot bar)) from the initial value measured for the freshly cast sample (75 m(3) (STP)/(m(2)center dot h center dot bar)). The introduction of branched polyethyleneimine followed by its cross-linking allowed to us to improve the TFC performance maintaining CO2 permeance at the level of 30% comparing with day zero. However, the best results were achieved by the combination of porous, rigid and soft, branched polymeric additives that enabled us to preserve the transport characteristics of TFC membrane as 43% (47 m(3) (STP)/(m(2)center dot h center dot bar) after 450 days) from its initial values (110 m(3) (STP)/(m(2)center dot h center dot bar)). Experimental data were fitted using the Kohlrausch-Williams-Watts function, and the limiting (equilibrium) values of the CO2 and N-2 permeances of the TFC membranes were estimated. The limit value of CO2 permeance for neat PTMSP TFC membrane was found to be 5.2 m(3) (STP)/(m(2)center dot h center dot bar), while the value of 34 m(3)(STP)/(m(2)center dot h center dot bar) or 12,600 GPU was achieved for TFC membrane containing 4 wt% cross-linked PEI, and 30 wt% PAF-11. Based on the N-2 adsorption isotherms data, it was calculated that the reduction of the free volume was 1.5-3 times higher in neat PTMSP compared to the modified one. Bearing in mind the pronounced mitigation of physical aging by the introduction of both types of fillers, the developed high-performance membranes have great potential as support for the coating of an ultrathin, selective layer for gas separation.

Automated summary

This study aimed to mitigate the physical aging in thin-film composite (TFC) membranes based on polymer intrinsic microporosity (PTMSP) by introducing polymer additives, including soft, branched polyethyleneimine (PEI) and rigid, porous aromatic framework PAF-11. The results showed that the introduction of cross-linked PEI improved the TFC performance, maintaining a CO2 permeance level of 30%. However, the best results were achieved by combining porous, rigid, and soft polymeric additives, which preserved the transport characteristics of the TFC membrane at 43% after 450 days.