Reduced Aging in Carbon Molecular Sieve Membranes Derived from PIM-1 and MOP-18

Carbon molecular sieve membranes (CMSMs) commonly lose permeability over time due to the collapse of micropores. This decline in permeability, due to the densification of the membrane, is known as physical aging. CMSMs derived from polymers of intrinsic microporosity (PIM-1) are highly affected by physical aging, with declines in permeability greater than 60% over time. It is hypothesized that the densification of CMSMs derived from this high-free-volume polymer precursor is thermodynamically driven by the collapse of large unconnected graphene domains to reach a more stable conformation (i.e., graphite). This study describes a novel strategy to mitigate physical aging by pillaring the CMSM using copper nanoparticles. Highly soluble metal-organic polyhedra-18 (MOP-18) was introduced into PIM-1 with loadings up to 40 wt/wt to form a mixed-matrix membrane (MMM). Pyrolysis of the MMM at 550 degrees C resulted in the in situ formation of copper metal nanoparticles that acted as pillars for the graphene sheets within the CMSM, preventing the collapse of the micropores, thus minimizing the aging of the CMSM. Single gas permeation measurements of CO2 and CH4 were made on the pristine polymer-derived CMSM and the copper-pillared CMSM at 35 degrees C and 2 bar to confirm the membranes' resistance to physical aging. The CH4 permeability for the PIM-1 CMSM decreased by similar to 60%, from 64 to 27 Barrers, over a period of 7 days, while the copper-pillared PIM-1 CMSM remarkably showed essentially no decline in CH4 permeability. This research demonstrates a general approach to reducing physical aging in CMSMs.