(705a) Production of Unblended, "Drop-in," Renewable Jet Fuel

Early research attempts to produce a fully on-spec, 100 percent non-petroleum jet fuel revealed that not all of the fuel specifications criteria could be achieved from some alternative fuel feedstocks. Appropriate aromatic levels proved to be particularly elusive although most other spec limits were easily achievable. As somewhat of a compromise, these low-aromatic fuels were blended with fuels derived from petroleum feedstocks thereby meeting the demanding requirements for military aircraft. These alternatively derived fuels were thus subsequently certified by the Air Force for fleet use when blended 50/50 with their petroleum-derived counterparts. While this was a significant achievement supporting the goal of making the US Air Force less dependent on petroleum fuels, especially those derived from foreign petroleum resources, the ultimate objective of being able to operate on a fully-alternatively sourced fuel remained unfulfilled.

In response to this need, Applied Research Associates, Inc. (ARA) developed the Catalytic Hydrothermolysis (CH) process. The CH process converts renewable oils from plants and algae into “Renewable, Aromatic, Drop-in” (Readi) fuels known as ReadiJet. These fuels are designed to be ready to use, without blending, in turbine engines designed to operate on petroleum-based fuels.

The CH process followed by mild hydrotreating and distillation converts the feed triglycerides into high-density aromatic, cycloparaffin, and isoparaffin hydrocarbons that are are essentially identical to the hydrocarbons in Jet A fuels from petroleum. ARA produced 1750 gallons of CH oil from Canola oil; this oil included hydrocarbons ranging from C₆ to C₃₆. It was a dark green liquid with a Total Acid Number (TAN) of 115 mg KOH/g. The density was 878 kg/m³, which was consistent with a feedstock containing a mixture of alkanes, olefins, and more dense organic acids, polycyclics, and aromatics. The CH Oil was delivered to the Air Force’s Assured Aerospace Fuel Research Facility (AAFRF) located at Wright Patterson Air Force Base for mild hydrotreating in the AAFRF hydrotreating unit. Conversion was achieved by passing CH Oil over a proprietary sulfided-metal catalyst at elevated pressures and temperatures. Recycled hydrogen, along with makeup fresh hydrogen, was fed co-currently with the CH oil. TAN was the operational quality control measure used to gauge hydrotreating efficiency. The TAN of the product jet fuel ranged from 0 to 0.006 mg KOH/g (which is below the 0.1 mg KOH/g limit established for Jet A and below the ≤ 0.015 mg KOH/g limit set in MIL-DTL-83133G for JP-8).

Downstream of the reactors, the pressure was reduced and the naphtha was removed by processing the naphtha/jet/diesel mixture through a nine-stage Fractionator Column operated at 35 psia. The jet fraction was separated from the diesel-range remnant using a four-stage Vacuum Column operated at 7 psia.  A composite sample of the 525 gallons of renewable jet was analyzed for the 24 pass/fail requirements included in the Jet A specification. It met all the requirements except conductivity, which is typical for hydrotreated fuel and is addressed by incorporating a conductivity additive.

In addition, the Air Force Research Laboratory conducted a series of Tier II Compatibility Tests on the composite ReadiJet sample. This series of tests included the JP-8 specification, Extended Chemical & Physical Analysis (lubricity evaluation, low temperature properties, polar species, and dissolved metals); Initial Material Compatibility Evaluation (fuel-effected swell and the fuel solvency of o-ring and fuel system materials); Experimental Thermal Stability Evaluation (thermal deposit tendencies and oxidation profile at elevated temperatures) as well as viscosity versus temperature (fuels viscosity at 40°C and -40°C).

This paper will present details on the CH process, hydrotreating, and fractionation into naphtha, jet, and diesel-range remnant splits, as well as a comparison of the ReadiJet properties against the requirements for Jet A and Tier II fuel compatibility.   

Public Release Case No. : 88ABW-2013-023