Mixed-matrix membranes containing metal-organic frameworks for gas separations.

摘要

Mixed-matrix membranes for gas separations were prepared using metal-organic framework 5 (MOF-5), copper metal-organic framework (Cu-MOF), and the soluble metal-organic polyhedra 18 (MOP-18) in MatrimidRTM. The MOF crystals were synthesized as nanocrystals and then activated to obtain high surface areas, comparable to the reported by the corresponding authors. It was found that depending on the organic character of the crystals, the dispersion of the additives in the polymer matrix is improved. MOF-5, having benzene diacetic acid as linker, was loaded up to 30% (w/w) in the polymer matrix and Cu-MOF, having two organic linkers (biphenyl diacetic acid and triethylenediamine), was loaded up to 80% (w/w). The most successful dispersion was achieved with MOP-18 with loadings of up to 80 wt%. Scanning electron microscopy revealed that the morphology of the membranes changed substantially with the types of MOF used. Membranes containing up to 30% (w/w) MOF-5 crystals showed the formation of polymer veins around the nanocrystals suggesting a strong interaction between the two materials. Membranes containing up to 80% (w/w) Cu-MOF crystals did not show the formation of polymer veins due to the improved dispersion of the Cu-MOF nanocrystals. The surface of the membrane showed however a zeolite membrane like morphology consisting of crystal aggregates. Membranes containing up to 80 wt% MOP-18 did not show a defined morphology nor aggregation and exhibited a smooth surface. Gas permeation with pure gases showed that membranes containing MOF-5 and Cu-MOF crystals have affinity for methane and that membranes containing MOP-18 are selective for propylene and methane. Owing to its large pore, membranes containing Cu-MOF showed high permeability values, in the order of hundred of Barrers for most of the gases tested.