Mixed matrix formulations with MOF molecular sieving for key energy-intensive separations

Abstract

Membrane-based separations can improve energy efficiency and reduce the environmental impacts associated with traditional approaches. Nevertheless, many challenges must be overcome to design membranes that can replace conventional gas separation processes. Here, we report on the incorporation of engineered submicrometre-sized metal-organic framework (MOF) crystals into polymers to form hybrid materials that successfully translate the excellent molecular sieving properties of face-centred cubic (fcu)-MOFs into the resultant membranes. We demonstrate, simultaneously, exceptionally enhanced separation performance in hybrid membranes for two challenging and economically important applications: the removal of CO and HS from natural gas and the separation of butane isomers. Notably, the membrane molecular sieving properties demonstrate that the deliberately regulated and contracted MOF pore-aperture size can discriminate between molecular pairs. The improved performance results from precise control of the linkers delimiting the triangular window, which is the sole entrance to the fcu-MOF pore. This rational-design hybrid approach provides a general toolbox for enhancing the transport properties of advanced membranes bearing molecular sieve fillers with sub-nanometre-sized pore-apertures.

Molecularly Mixed Composite Membranes for Advanced Separation Processes

“…[1] Despite being eminently scalable,e xisting and emerging polymer membranes suffer from atradeoff between permeability and selectivity,which are among the defining performance metrics for membranes. [5] Perhaps driven by the early successes of MOF-based MMMs and the continued rapid development of novel porous materials,anincredible variety of new types of filler materials have recently been incorporated into MMMs,i ncluding COFs [6] and metal-organic polyhedrons (MOPs). [3] However,t he preparation of large-scale,d efect-free inorganic membranes suitable for industrial applications remains ac hallenge.M ixed matrix membranes (MMMs) incorporate inorganic filler materials (that is,t he discrete phase) into ap olymer (that is,t he continuous phase or the matrix) to boost the performance of the membranes while retaining the intrinsic scalability of polymer processing.…”

“…[2] Inorganic membranes such as zeolites and metal-organic frameworks (MOFs) have surpassed this tradeoff and have shown extraordinary separation performances in challenging molecular pairs. [5] Perhaps driven by the early successes of MOF-based MMMs and the continued rapid development of novel porous materials,anincredible variety of new types of filler materials have recently been incorporated into MMMs,i ncluding COFs [6] and metal-organic polyhedrons (MOPs). These materials have long been proposed to address the orthogonal issues associated with polymer membranes and inorganic membranes.…”

“…[3] However,t he preparation of large-scale,d efect-free inorganic membranes suitable for industrial applications remains ac hallenge.M ixed matrix membranes (MMMs) incorporate inorganic filler materials (that is,t he discrete phase) into ap olymer (that is,t he continuous phase or the matrix) to boost the performance of the membranes while retaining the intrinsic scalability of polymer processing. [5] Perhaps driven by the early successes of MOF-based MMMs and the continued rapid development of novel porous materials,anincredible variety of new types of filler materials have recently been incorporated into MMMs,i ncluding COFs [6] and metal-organic polyhedrons (MOPs). [4] Thea rea of MMMs originated with the study of the addition of zeolite materials to polymer phases before experiencing ar esurgence in research interest with the advent of metal-organic framework (MOF)-based MMMs.…”

Enhanced CO2/CH4 Separation Performance of a Mixed Matrix Membrane Based on Tailored MOF‐Polymer Formulations

“…The engineered fcu ‐MOFs have triangular windows as the sole entrance for guest molecules to the MOF pore system 15. Our previous work had demonstrated the good CO 2 /CH 4 separation performance of Y‐ fum ‐ fcu ‐MOF incorporated 6FDA‐DAM polyimide membrane at 35 °C (308 K) 16. In this work, we extend our investigation to show that controlling the temperature is a promising way to further fine‐tune the performance attributes of hybrid membranes.…”

“…The as‐synthesized micron‐sized Y‐ fum ‐ fcu ‐MOF crystals were nonideal to form MMMs directly, and thus a mild manual grinding method carrying out at ultralow temperature (e.g., −196 °C using liquid nitrogen) was applied to reduce the crystal sizes as described elsewhere 16. The submicron‐sized Y‐ fum ‐ fcu ‐MOF/THF suspension was added to the 6FDA‐DAM/THF solution to form a mixed‐matrix dope, which was then mixed thoroughly on a rolling mixer overnight.…”