A Simple Process for the Dimerization and Cross-Coupling of Isoprene and Myrcene to High-Performance Jet and Diesel Blendstocks
Josanne–Dee Woodroffe, Benjamin G. Harvey
Abstract
Three high-energy density fuels were generated in a one-pot reaction from the [4+4]-cyclodimerization and cross-coupling of isoprene and myrcene using a homogeneous iron pyridineimine (PDI) catalyst. The resulting mixture of C10, C15, and C20 regio- and chemoselectively synthesized cyclooctadienes was fractionally distilled to yield three fractions. The isolated cyclic hydrocarbons were then hydrogenated, and the fuel properties were evaluated as potential jet and diesel blendstocks. F-1 was composed primarily of 1,4-dimethylcyclooctane (DMCO) and small quantities of 2,6-dimethyloctane (DMO), the latter from the hydrogenation of unreacted myrcene. F-2 was composed of the cross-product of isoprene and myrcene (MPCO), while F-3 consisted of myrcene dimers (BMCO). F-1 and F-2 exhibited an ∼6% higher density, 2.0–2.4 and 8.5–10% higher gravimetric and volumetric net heats of combustion, respectively, than the lower limits of Jet-A. F-3 exhibited a 1.7% higher gravimetric heat of combustion than Diesel #2 and an outstanding derived cetane number (DCN) of 51. Blends of F-2 and F-3 up to 50% by volume with DMO and Diesel #2 were prepared, focusing on blends that met the −40 °C kinematic viscosity requirement (<12.0 mm2/s) for Jet-A or the required 40 °C kinematic viscosity of Diesel #2 (2.1–4.1 mm2/s). The eight-membered cyclic hydrocarbons described herein are highly attractive due to the efficient catalytic process employed in their synthesis and the ability to produce the substrates from sustainable feedstocks. These blendstocks are aromatic-free, zero-sulfur fuel additives that have the potential to deliver enhanced performance compared to Jet-A and Diesel #2 while reducing the carbon footprint of the transportation sector.