Efficient conversion of pure and mixed terpene feedstocks to high density fuels

A series of high density renewable fuels has been synthesized through selective dimerization of α-pinene, camphene, limonene, and crude turpentine using the heterogeneous catalysts Nafion, Nafion SAC-13, and Montmorillonite K-10. Terpene dimers are produced in up to 90% yield depending on the feedstock. The preferred catalyst, Nafion SAC-13, could be recovered by simple filtration and reused up to eight times without any significant decrease in activity. The fuels produced by this process have net heats of combustion ranging from 137,000 to 142,000 btu/gal which are comparable to the tactical missile fuel JP-10. Fuels derived from both α-pinene and camphene have similar viscosities, densities, and net heats of combustion due to isomerization of α-pinene to camphene prior to dimerization. In contrast, limonene dimers exhibit a much lower density and viscosity due to their ring opened structures. DSC analysis of the dimer fuels revealed freezing points of −54, −52, and −78 °C for dimers derived from camphene, α-pinene, and limonene, respectively. Empirical results and a terpene adsorption study suggest that the dimerization reaction proceeds through initial coordination of α-pinene to catalytic sites followed by cross-coupling with camphene. The ultra-performance renewable fuels described in this work have potential applications as significant components of jet, diesel, and tactical fuels.