(121d) Synthesis of Renewable Jet Fuel Range Cycloparaffins with Levulinic and Formic Acids

This research presents a production pathway for renewable cycloparaffinic fuel blendstocks for military and commercial jet fuels. Cycloparaffins are major constituents of jet fuel that provide beneficial properties to the fuel such as low freezing point, increased density, higher volumetric heating value, and enhanced operability. Both aromatics and cycloparaffins are known for contributing to elastomer swell which is an important fuel property required for the proper operation of aircraft fueling systems. Most efforts to produce bio-jet fuels have focused on producing straight-chain and branched-chain alkanes because of their higher energy densities. However, there is still a need for technologies to produce renewable cycloparaffins for sustainable full-performance military and commercial jet fuels.

In this work, jet fuel range cycloparaffins were synthesized with levulinic and formic acids which can be produced from lignocellulosic biomass. Using a novel non-catalytic thermochemical process a mixture of levulinate and formate salts was converted to synthetic crude Thermal DeOxygenation (TDO) oil in a pilot-scale continuous flow reactor at 450 °C and atmospheric pressure. The crude TDO oil has a broad boiling point range (75-550 °C), contains a very low oxygen content (< 5 wt %) and has high levels of monoaromatics and polyaromatics. Crude TDO oil was hydroprocessed using a commercial Ni/SiO₂-Al₂O₃ catalyst in a bench-scale continuous flow reactor. The hydrogenation reactions were carried out at 300 ℃ and 750 psig with an excess flow of hydrogen at 300 sccm. The feed flow rate was maintained at 0.3-0.5 mL/min with a corresponding weight hourly space velocity (WHSV) of 0.1 - 0.3 hr^-1. Hydrogenated TDO oil was distilled to produce jet fuel range (180-250 °C) hydrocarbons according to the American Society for Testing and Materials (ASTM) standards.

The jet fuel fraction (180-250 °C) of hydrotreated TDO oil has a 32.5 % mass recovery and mainly consists of 94 vol% cycloparaffins. The remainder of the jet fuel fraction consists of 5.73 vol% aromatics with trace n-paraffins and iso-paraffins. The cycloparaffins range from C₉-C₁₅ and consist of a mixture of monocycloparaffins (10 vol%), dicycloparaffins (78.47 vol%) and tricycloparaffins (5.52 vol%). The jet fuel range cycloparaffins have a very low freezing point (-70 °C) and low viscosity (3.9 mm²/s). The TDO oil jet fuel fraction is compliant with all ASTM 3699 specifications and meets MIL-DTL-83133H specifications with the exceptions of density, hydrogen content, and higher heating value. Based on the fuel properties the TDO oil cycloparaffinic fuel can be blended up to 50 % by volume with JP-8 as well as Jet-A and meet the specific fuel standards.