(305f) Nanocomposite Molecular Sieve Membranes for the Separation of C4 Olefins

C4 mono and di-olefins (e.g., 1-butene, isobutene and 1,3-butadiene) are important chemicals for the manufacture of a wide range of polymers and materials. Their purification is currently performed by the energy-intensive extraction and distillation processes. Incorporating membranes into the existing separation schemes can potentially result in substantial energy savings. However, the membrane materials that have been explored for the separation of C4 olefins, which mainly include facilitated transport and polymer membranes, have not demonstrated adequate separation efficiency or stability. Here, we report the synthesis of nanocomposite molecular sieve membranes capable of separating C4 olefins based on the sub-ångström differences in their molecular sizes and shapes. The membrane structure consists of zeolitic imidazolate frameworks (ZIF) deposited inside an inorganic matrix through a vapor-phase synthesis approach. The ZIF phase possesses well-defined micropores and enhanced framework rigidity due to their confinement by the inorganic matrix. C4 single gas permeances through the membrane are strongly dependent on their kinetic diameters and/or molecular conformations, showing a diffusion-dominating permeation mechanism for the nanocomposite membranes. Due to the molecular sieving effect and enhanced structural stability, the membranes were found to be effective and stable in separating multi-component C4 hydrocarbon mixtures under varied conditions (e.g., feed pressure, feed composition, temperature, etc.). Adsorption results will be correlated with the membrane permeation data to further understand the separation mechanism.