Isoprene and C₅ Olefins Production by Oxidative Dehydrogenation of Isopentane

Abstract

The current limited availability of isoprene and isoamylenes (methyl butenes), which are the feedstock for a variety of petrochemical processes, could be boosted by converting the isopentane contained in the same refinery C 5 -fractions from which they are obtained. The oxidative dehydrogenation (ODH) of isopentane to isoprene and isoamylenes for this purpose has been studied very little to date. We present here a study of this reaction on oxide catalysts, using oxygen as an oxidant, without any dopant in the feed. After a broad catalyst formulations screening, a V-Mg oxide catalyst (15 wt % V 2 O 5 ) was selected to study the influence of the reaction parameters (temperature, residence time, and feed composition). Selectivity values of ca. 25% to isoprene, and 70% to isoprene plus isomylenes, could be attained under selected reaction conditions. These results are promising for the direct conversion of the branched C 5 -hydrocarbons fraction to isoprene.

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“…This demonstrates that phosphate modification of CNTs is beneficial to inhibit the formation of CO x in the ODH of isopentane. As depicted in Figure 2, the selectivity of all catalysts could not reach 100 % when the conversion was extrapolated to 0, indicating a reaction network with parallel and consecutive hydrocarbon combustions (Scheme ) 12. 14 Figure 2 b–d shows the selectivities towards mono‐olefins, diolefins, and CO x versus the isopentane conversion over the different catalysts.…”

“… Product selectivity versus isopentane conversion obtained by variation of reaction temperature, with V‐Mg‐O as a reference (Supporting Information, Figure S1) 12. Reaction conditions: 5P‐oCNTs, 200 mg; 3P‐oCNTs, 100 mg; 0.5P‐oCNTs and 1P‐oCNTs, 50 mg; oCNTs, 20 mg; 2.4 % isopentane (i‐C 5 H 12 ), O 2 /i‐C 5 H 12 =2, 16.7 mL min −1 , 623–673 K. a) Total dehydrogenation selectivity.…”

“…Numerous studies reveal that the molar ratio of combustion/dehydrogenation (hydrocarbon; HC) products (CO x /HC) in ODH reactions increases with the chain length of reactants. This tendency is summarized in Figure 1:7–12 it is more difficult to suppress the formation of CO x during ODH of isopentane than during ODH of lower alkanes (C2–C4). On the other hand, there is increased demand for C5 olefins and diolefins from dehydrogenation of C5 paraffins for use in resins, elastomers, and fine chemicals 12.…”

“…On the other hand, there is increased demand for C5 olefins and diolefins from dehydrogenation of C5 paraffins for use in resins, elastomers, and fine chemicals 12. Unfortunately, there are only few studies on the dehydrogenation of C5 alkanes, and most of these use metal oxide catalysts: under oxidative conditions, the selectivity towards the dehydrogenation products is lower than 65 % 12…”

“… Product distributions during ODH reactions of alkanes (C2–C5) over V‐Mg‐O catalysts. ▪: ethane [7–8] ; ⧫: propane [9] ; ▴: butane [10] , ▪: n ‐pentane [11] ; •: isopentane 12…”