ASTM International has approved and published a sixth pathway for the production of sustainable aviation fuel (SAF). The latest annex to the SAF specification, D7566, establishes criteria for the production and use of catalytic hydrothermolysis jet fuel (CHJ), a type of synthetic kerosene.

Catalytic hydrothermolysis to jet fuel. Wang et al.

The standard provides that CHJ fuel, which was developed by Applied Research Associates (ARA), may be blended at up to 50% by volume with conventional jet fuel.

The specification was approved and published with support from the Commercial Aviation Alternative Fuels Initiative (CAAFI).

In the CHJ process (also called hydrothermal liquefaction), clean free fatty acid (FFA) oil from the processing of waste oils or energy oils is combined with preheated feed water and then passed to the CH reactor. There, under very high temperature and pressure conditions, a single phase is formed consisting of FFA and supercritical water (SCW) wherein the FFAs are cracked, isomerized, and cyclized into paraffin, isoparaffin, cycloparaffin, and aromatic compounds.

The CH crude oil produced by the CH conversion process contains thousands of isomers distributed over the entire boiling range of jet and diesel fuels.

The treated products, ranging from 6–28 carbon numbers, contain n-alkanes, iso-alkanes, cyclo-alkanes, and aromatics, require a fractionation step for separation to naphtha, jet fuel, and diesel fuel.

Research has shown that through the CH process, biojet fuels can be produced from a variety of triglyceride-based feedstocks such as soybean oil, jatropha oil, camelina oil, carinata oil, and tung oil.

Resources

• Evaluation of ARA Catalytic Hydrothermolysis (CH) Fuel

• Wei-Cheng Wang, Ling Tao, Jennifer Markham, Yanan Zhang, Eric Tan, Liaw Batan, Ethan Warner, and Mary Biddy (2016) “Review of Biojet Fuel Conversion Technologies”