Separation of branched alkanes feeds by a synergistic action of zeolite and metal-organic framework

Zeolites and metal-organic frameworks (MOFs) are considered as “competitors” for new separation processes. The production of high-quality gasoline is currently achieved through the total isomerization process that separates pentane and hexane isomers while not reaching the ultimate goal of a research octane number (RON) higher than 92. This work demonstrates how a synergistic action of the zeolite 5A and the MIL-160(Al) MOF leads to a novel adsorptive process for octane upgrading of gasoline through an efficient separation of isomers. 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 linear isomers by the molecular sieve zeolite 5A. Their adsorptive separation ability is further evaluated under real 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, together with a productivity of 1.14 mol dm−3 and a high RON of 92, which is a leap-forward compared with existing processes.The authors acknowledge Fundação para a Ciência e Tecnologia (FCT, Portugal) and ERDF under Programme PT2020 to 1) José A. C. Silva under Project ref. POCI01-0145-FEDER-016517 (PTDC/QEQPRS/ 3599/2014), 2) CIMO (UID/AGR/00690/2020), (3) LSRE-LCM (POCI-01-0145-FEDER006984), and (4) Adriano Henrique from the individual research grant SFRH/BD/148525/2019. The authors also acknowledge Ivan M. C. Pinto for the measurement of the single component isotherms shown in Figure S20 in the Supporting Information, Kristin Gleichmann and Chemiewerk Bad Koestritz GmbH for kindly providing the binder-free beads of zeolite 5A used in this work, Ben Slater from IMAP for the proofreading of the manuscript, and Dr. Jong San Chang from KRICT for his helpful discussions.The computational work was performed using HPC resources from GENCI-CINES (Grant A0100907613).