Abstract
Zeolites and Metal Organic Frameworks (MOFs) have frequently been considered as “competitors” for the development of new advanced separation processes. The production of high quality gasoline is currently achieved through the energy demanding conventional Total Isomerization Process (TIP) that separates pentane and hexane isomers while not reaching yet the ultimate goal of a Research Octane Number (RON) higher than 92. Herein we demonstrate how an unprecedented synergistic action of two complementary benchmark materials of each family of porous solids, a commercially available zeolite, 5A and the bio-derived Al-dicarboxylate MOF MIL-160(Al), leads to a novel adsorptive process for octane upgrading of gasoline through an efficient separation of pentane and hexane isomer mixtures into fractions of low and high research octane number (RON). This innovative mixed bed adsorbent strategy encompasses a thermodynamically-driven separation of hexane isomers according to the degree of branching by MIL-160(Al) coupled to a steric rejection of pentane and hexane linear isomers by the molecular sieve zeolite 5A. The adsorptive separation ability of this MOF/zeolite duo was further evaluated under industrial operating conditions by sorption breakthrough and continuous cyclic experiments with a mixed bed of shaped adsorbents. Remarkably, at the industrially relevant temperature of 423 K, an ideal sorption hierarchy of low RON over high RON alkanes is achieved, i.e., n-hexane >> n-pentane >> 2-methylpentane > 3-methylpentane >>> 2,3-dimethylbutane > isopentane ≈ 2,2-dimethylbutane, and an exceptional ideal productivity of 1.14 mol.dm-3 is attained for a final high RON isomers product of 92, which corresponds to a substantial leap-forward when compared with existing processes.
Separation of branched alkane feeds by a synergistic action of zeolite and metal-organic framework
