Wednesday, December 30, 2009

UOP Patents New Class of Nanoporous Membranes for Dramatically Enhanced Gas Separation

UOP LLC (Des Plaines, IL) earned U. S. Patent 7,637,983 for new nano metal-organic framework (MOF)-polymer mixed matrix membranes (MOF-MMMs)  that show “dramatically enhanced gas separation permeability performance for CO2 removal from natural gas.”   

Gas separation processes with membranes have undergone a major evolution since the introduction of the first membrane-based industrial hydrogen separation process about two decades ago. The design of new materials and efficient methods will further advance the membrane gas separation processes within the next decade.

The gas transport properties of many glassy and rubbery polymers have been measured, driven by the search for materials with high permeability and high selectivity for potential use as gas separation membranes. Unfortunately, an important limitation in the development of new membranes for gas separation applications is a well-known trade-off between permeability and selectivity. By comparing the data of hundreds of different polymers, Robeson demonstrated that selectivity and permeability seem to be inseparably linked to one another, in a relation where selectivity increases as permeability decreases and vice versa.

Despite concentrated efforts to tailor polymer structure to improve separation properties, current polymeric membrane materials have seemingly reached a limit in the tradeoff between productivity and selectivity.  UOP inventors have overcome some of those limitation with a new class of nanoporous gas separation membranes.

According to inventors Chunqing Liu, Beth McCulloch,  Stephen T. Wilson, Annabelle I. Benin  and Mark E. Schott, metal-organic framework (MOF)-polymer mixed matrix membranes (MOF-MMMs) were prepared by dispersing high surface area MOFs (e.g. IRMOF-1) into a polymer matrix (e.g. Matrimid 5218). The MOFs allow the polymer to infiltrate the pores of the MOFs, which improves the interfacial and mechanical properties of the polymer and in turn affects permeability.

Pure gas permeation tests show the incorporation of 20 wt-% of IRMOF-1 in Matrimid 5218 polyimide matrix results in 280% improvement in CO2  permeability without a loss of CO2/CH4 selectivity compared to those of the pure Matrimid 5218 membrane. This type of MOF-MMMs has significantly improved gas separation performance with dramatically CO2  permeability (>35 barrer) and higher than 29 CO2/CH4 selectivity at C. under 100 psig pressure, which are attractive candidates for practical gas separation applications such as CO2 removal from natural gas.

The inventors found the new type of metal-organic framework (MOF)-polymer or metal-organic polyhedra (MOP)-polymer MMM achieves significantly enhanced gas separation performance compared to that of cellulose acetate membranes.

U. S. Patent 7,637,983 describes the design and preparation of  UOP’s new class of metal-organic framework (MOF)-polymer MMMs containing high surface area MOF (or IRMOF or MOP, all referred to as "MOF" herein) as fillers. These MMMs incorporate the MOF fillers possessing micro- or meso-pores into a continuous polymer matrix. The MOF fillers have highly porous crystalline zeolite-like structures and exhibit behavior analogous to that of conventional microporous materials such as large and accessible surface areas and interconnected intrinsic micropores.

Moreover, these MOF fillers may reduce the hydrocarbon fouling problem of the polyimide membranes due to their relatively larger pore sizes compared to those of zeolite materials. The polymer matrix can be selected from all kinds of glassy polymers such as polyimides (e.g., Matrimid 5218 sold by Ciba Geigy), polyetherimides (e.g., Ultem 1000 sold by General Electric), cellulose acetates, polysulfone, and polyethersulfone.

These MOF-polymer MMMs combine the properties of both the continuous polymer matrix and the dispersed MOF fillers. Pure gas separation experiments on these MMMs show dramatically enhanced gas separation permeability performance for CO2 removal from natural gas (i.e., 2-3 orders of magnitude higher permeability than that of the continuous Matrimid 5218 polymer matrix without a loss of CO2 over CH4 selectivity). These separation results suggest that these new membranes are attractive candidates for practical gas separation applications such as CO2 removal from natural gas.

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