Abstract
AbstractIndustrial purification of propylene and ethylene requires cryogenic distillation and selective hydrogenation over palladium catalysts to remove propane, ethane and/or trace amounts of acetylene. Here, we report the excellent separation of equimolar mixtures of propylene/propane and ethylene/ethane, and of a 1/100 mixture of acetylene/ethylene by a highly robust microporous material, MFM‐520, under dynamic conditions. In situ synchrotron single crystal X‐ray diffraction, inelastic neutron scattering and analysis of adsorption thermodynamic parameters reveal that a series of synergistic host–guest interactions involving hydrogen bonding and π⋅⋅⋅π stacking interactions underpin the cooperative binding of alkenes within the pore. Notably, the optimal pore geometry of the material enables selective accommodation of acetylene. The practical potential of this porous material has been demonstrated by fabricating mixed‐matrix membranes comprising MFM‐520, Matrimid and PIM‐1, and these exhibit not only a high permeability for propylene (≈1984 Barrer), but also a separation factor of 7.8 for an equimolar mixture of propylene/propane at 298 K.
Highlights
Over 200 million tonnes of ethylene (C2H4) and propylene (C3H6) are produced from steam cracking of naphtha each year, consuming 0.3 % of the global energy production.[1]
While the adsorption capacity of C2H6 and C3H8 in MFM-520 decreases rapidly with the increasing temperatures, consistent with majority of reported adsorption isotherms for metal-organic framework (MOF), the variation of temperature has a much smaller effect on the uptake of C2H2, C2H4 and C3H6, in the low pressure region where only small changes are observed for C3H6 adsorption
By improving the permeability of Matrimid and the selectivity of PIM-1, the mixedmatrix membrane (MMM) based upon PIM-1/Matrimid/MFM-520 exhibits superior performance that surpasses the current upper bound for C3H6/C3H8 separation and compares favourably with other MOF-containing MMMs
Summary
Over 200 million tonnes of ethylene (C2H4) and propylene (C3H6) are produced from steam cracking of naphtha each year, consuming 0.3 % of the global energy production.[1]. Removal of acetylene by its partial hydrogenation to ethylene over supported palladium-catalysts is a widely used solution, but suffers from poor selectivity and very high cost.[4] By exploiting their active sites,[5] functional groups,[6,7] pore sizes[8] and geometry,[9] metal-organic framework (MOF) materials can show preferential adsorption of alkynes over alkenes,[6,9,10,11] and alkenes over alkanes.[5,8,12] MOFs incorporating open metal sites afford highly selective binding of unsaturated hydrocarbons, typically by forming a coordination complex; such systems are often sensitive to moisture and the regeneration of sorbent is not always straightforward.
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