Low-Carbon Aviation Fuel Through the Alcohol to Jet Pathway

The aviation industry is seeking economical and technically viable approaches to providing sustainable alternatives to petroleum-based jet fuel. For example, the Federal Aviation Administration (FAA) Destination 2025 (FAA 2025) has a goal to develop cleaner jet fuels, explore new ways to meet environmental and energy goals, and foster development towards one billion gallons of renewable jet fuel for aviation use by 2018. Alternative jet fuels via Fischer–Tropsch (F–T) and hydrotreated vegetable oils (HEFA) have already been approved for use in jet fuel blends of up to 50%. Other conversion processes, such as alcohol to jet (ATJ), are in various stages of development. This chapter focuses on opportunities for production of jet fuel blend components through an ethanol intermediate via a number of processing routes. These are then compared to conversion routes through other oxygenated intermediates, such as higher alcohols (eg, butanol). Higher alcohols provide technically simple conversion chemistry routes to jet blend components, but are currently produced in small quantities (relative to fuels) for the chemical market. Ethanol on the other hand is widely produced as both a fuel and a chemical and has an established distribution infrastructure. Furthermore, renewable ethanol volumetric yields via fermentation surpass those of higher alcohols. Ethanol conversion processes can produce both paraffinic and cyclic molecules. However, the conversion pathway from ethanol through ethylene is more challenging than from higher alcohol-derived olefins. Mixed oxygenated intermediates can also belong in the ATJ category, but are not yet at the same stage of development as alcohols. The major market drivers for producing alternative jet fuel components, including ATJ, are climate change, cost stability, and national security. Biologically derived ATJ fuels can provide significant climate change benefits by reducing CO2 life cycle emissions, possibly exceeding 80%. In addition, they produce lower levels of sulphur oxides and particulate matter. Because jet fuel accounts for 40% of an airline’s operating costs, reducing price fluctuations associated with petroleum is another significant driver. Finally, dependence on foreign oil could be minimized using alternative fuels. As a result of these drivers, government agencies as well as the private sector have set aggressive targets to increase their consumption of alternative fuels. In addition to targets, the government has provided favourable policies to incentivize alternative aviation fuel use. Carbon taxes abroad and potentially in the United States will drive up prices of petroleum-based fuels, making alternative fuels more competitive. Government incentives in the form of renewable fuel credits are expected to further improve alternative fuel viability. Energy Information Agency (EIA) projections suggest there may be a significant surplus of ethanol over that required for gasoline blending, potentially filling 4% of jet fuel demand in 2020. EIA projections also suggest there is a positive price differential between ethanol intermediate and jet fuel in future scenario projections, unless oil prices drop to the Low Oil Case. Ethanol currently has a price and market share advantage over other alcohols, such as butanol. However, development of ethanol to jet technology lags butanol to jet technology. Reported production costs for raw ethanol, projected ethanol supplies over that needed for gasoline blending, and the presence of existing infrastructure all suggest that ethanol is a viable intermediate for the production of alternative jet fuel components.