Mixed matrix membranes with A polymer of intrinsic microporosity

Membrane processes for high volume applications, such as carbon dioxide capture from flue gases, require materials with high permeability and good selectivity. However, it is well known that high permeability is generally associated with poor selectivity, as illustrated by double logarithmic "Robeson" plots of selectivity against permeability.1 "Mixed matrix" or "nanocomposite" membranes offer the prospect of a synergistic enhancement in performance. In the context of the "DoubleNanoMem" European project, a wide variety of nanofillers have been utilised with the polymer of intrinsic microporosity PIM-1 (Fig. 1a), which itself operates at the current upper bound of performance for a number of important gas pairs.1,2 A range of porous crystalline materials, including inorganic molecular sieves and metal-organic frameworks, have been incorporated into PIM-1, enabling the effects of different kinds of filler to be investigated. Here, representative results are presented for PIM-1 with three metal organic frameworks (MOFs): ZIF-8, HKUST-1 and MIL-101. The zeolitic imidazolate framework ZIF-8 (Fig. 1b) has a sodalite structure with 1.16 nm diameter cavities accessible through 0.34 nm sized windows. HKUST-1 contains a three-dimensional system of 0.95 nm size channels (Fig. 1c). MIL-101 has both large cages (3.4 nm cavity with ca. 1.6 nm windows) and small cages (2.9 nm cavity with 1.2 nm windows) (Fig. 1d).