Tailoring Copper Pillars to Prevent Physical Aging in Matrimid^® 5218 Carbon Molecular Sieve Membranes

Carbon molecular sieve membranes (CMSMs) provide a means to greatly improve gas separations. CMSMs have a pore size distribution comprising micropores and ultramicropores which provide high flux and high selectivity, enabling them to outperform polymeric membranes. CMSMs, however, suffer from physical aging that results from the collapse of the pores that severely reduces their gas permeability. Therefore, reducing physical aging of CMSMs is an important step in the development of these types of materials. In this work, a method for reducing physical aging through the incorporation of metal nanoparticles that serve as a structural scaffold for the membrane pore structure is presented. The pore structure in CMSMs is dependent upon the polymeric precursor, and thus the support system incorporated must be tailored. The copper nanoparticles were formed in situ from soluble, copper-based metal-organic polyhedra 18 (MOP-18) dispersed into Matrimid^® 5218, a low free volume polymer. The size (2 to 20 nm) and shape (sphere, rods) of the copper particles were refined by adjusting MOP-18 loading, pyrolysis temperature, and soaking time. The Cu-pillared Matrimid^® 5218 CMSMs from this work showed no decline in permeability or selectivity for methane (107 Barrer) and carbon dioxide (1785 Barrer) over a period of 21 d. The results suggest that tailored metal pillars can suppress physical aging in CMSMs, thereby enhancing their long-term stability and applicability in gas separations.