Separation of Branched Alkanes Feeds by a Synergistic Action of Zeolite 5A and Metal-Organic Framework MIL-160(Al)
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The total isomerisation process (TIP) developed by the universal oil products (UOP) for upgrading the octane rating of light hydrocarbon fractions, especially mixed feedstocks containing pentane (C5) and hexane (C6) isomers, is among the first and most successful adsorption processes applied in the industry. Typically, the light naphtha, characterised by a low research octane number (RON, ≈70), undergoes an incomplete catalytic isomerisation that generates an effluent containing unconverted linear paraffins, mostly n-pentane (nC5; RON 61.7) and n-hexane (nC6; RON 30), mixed with their respective branched isomers, i.e., isopentane (iC5; RON 93.5), 2-methylpentane (2MP; RON 74.5), 3-methylpentane (3MP; RON 75.5), 2,2-dimethylbutane (22DMB; RON 94), and 2,3-dimethylbutane (23DMB; RON 105). After that, the output of the isomerisation reactor is fed into an adsorber packed with zeolite (LTA type) that behaves as a molecular sieve, adsorbing only the linear paraffins (which are then recycled to the catalytic reactor for further processing). This results in a final branched isomerate product with an average RON ≈87–90. However, with the actual TIP process, the monobranched hexanes 2MP and 3MP represent up to 30% of the final product composition, which is detrimental to the octane improvement of gasoline for RON values higher than 90. Accordingly, this work shows a novel adsorptive separation process, based on the synergistic action of the zeolite 5A and the MIL-160(Al) metal-organic framework (MOF), to efficiently fractionate C5/C6 alkane isomers according to classes of high RON (HRON – 22DMB, 23DMB, and iC5) and low RON (LRON – nC5, nC6, 2MP, and 3MP) compounds.
