Synthesis of renewable jet and diesel fuels from 2-ethyl-1-hexene

Abstract

An efficient method for the selective dimerization of the renewable feedstock, 2-ethyl-1-hexene, to a complex mixture of C₁₆H₃₂ hydrocarbons has been developed. To optimize the process, the activity of a variety of strongly acidic heterogeneous catalysts was investigated. Montmorillonite K-10 and sulfated zirconia readily isomerized 2-ethyl-1-hexene to a mixture of the cis- and trans isomers of 3-methyl-2-heptene and 3-methyl-3-heptene, but were inactive for the dimerization of 2-ethyl-1-hexene at temperatures up to 116 °C. In contrast, the cation exchange resins Amberlyst-15 and Nafion, readily dimerized 2-ethyl-1-hexene at elevated temperatures. For both sets of catalysts, the degree of hydration strongly affected the rate of isomerization/dimerization. After hydrogenation over PtO₂ and fractional distillation, saturated dimer mixtures could be isolated in up to 90% yield. The dimers have a density of 0.78 g mL⁻¹ and a freezing point <−60 °C, suggesting that they can be blended with renewable or conventional jet fuels, without adversely affecting the overall density and low temperature viscosity of the mixtures.