Transhydrogenation of pentane with 1,5- and 2,4-hexadiene over CrO x /Al 2 O 3
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ORIGINAL ARTICLE
Transhydrogenation of pentane with 1,5‑ and 2,4‑hexadiene over CrOx/Al2O3 Mustapha D. Garba1 · S. David Jackson1 Received: 20 October 2020 / Accepted: 9 November 2020 © The Author(s) 2020
Abstract Transhydrogenation of pentane (P) and 1,5-hexadiene (1,5HD) and pentane and 2,4-hexadiene (2,4HD) was studied over a CrOx/alumina catalyst at 523–773 K. Thermodynamic stability differences between the conjugated (2,4-hexadiene) and non-conjugated (1,5-hexadiene) isomers indicated that transhydrogenation was favoured between pentane and 1,5-hexadiene but not pentane and 2,4-hexadiene (+ ve ∆G). At 773 K a significantly enhanced alkene yield was observed for the P/1,5HD system, clearly showing the effect of transhydrogenation. The yield of alkenes was ~ 50% and included alkylated and isomerized alkenes. Alkylation and isomerization were significant reactions under reaction conditions. Pentane was shown to affect the chemistry of 1,5HD and vice versa with the conversion of pentane significantly enhanced at all reaction temperatures, indicating a molecular interaction between the reactants even when transhydrogenation was not obvious. In contrast, no effect on the conversion of pentane was observed when the co-feed was 2,4HD. An unexpected effect of pentane on 2,4HD conversion was observed, with all reactions of cis-2,4-hexadiene (including alkylation and isomerization) being completely inhibited at low reaction temperatures (573 K and 523 K) by the presence of pentane, suggesting that pentane competes for the same sites as cis-2,4-hexadiene. Transhydrogenation activity between pentane and 1,5-hexadiene was less obvious at the lower reaction temperature, which appeared to be a kinetic effect. Direct hydrogenation of 1,5-hexadiene revealed that 1,5HD sampled the same hydrogen population for hydrogenation and transhydrogenation. Comparisons of transhydrogenation of 1-hexyne, 1,5-hexadiene, and 2,4-hexadiene with pentane have revealed significant differences in the adsorption and reaction chemistry of the three isomers. Keywords Transhydrogenation · Dehydrogenation · Hydrocarbons · Hexadienes · CrOx/Al2O3 catalyst
Introduction It is well known that hydrocarbon feedstock streams, such as naphtha, LPG, or gas oil are cracked in a furnace to produce mixtures of hydrocarbons of varying molecular weight and functionality [1–6]. To optimise the value-added converting low-value, cracked hydrocarbons (e.g., alkanes) into valued distillate products is important. Although transhydrogenation is not a new technology for the production of olefins and Electronic supplementary material The online version of this article (https://doi.org/10.1007/s13203-020-00259-3) contains supplementary material, which is available to authorized users. * S. David Jackson [email protected] 1
Centre for Catalysis Research, School of Chemistry, University of Glasgow, Glasgow G12 8QQ, Scotland, UK
other valuable petroleum distillate products, there has been limited scientific attention toward the invention. The transhydro
