(459d) Jet Fuels Production from Waste Cooking Oil Via Catalytic Transfer Hydrogenation

The progressive depletion of fossil fuels and the environmental impacts associated with such exploitation has fostered research on alternative and renewable fuel sources. Currently, the transportation sector, especially the aviation industry, relies on liquid hydrocarbon-based fuels which requires kerosene-range hydrocarbons with strict quality standards to power gas-turbine engines. These hydrocarbons can be obtained from renewable sources, such as triglycerides. Waste cooking oil (WCO) is a suitable renewable fuel and is not an edible source like virgin vegetable oil. It can represent a sustainable alternative feedstock as it is widely produced globally. Moreover, its use in jet fuels production converts waste into a valuable product resulting in a circular economy.

In this work, a novel process for jet fuels production from WCO (catalytic transfer hydrogenation (CTH)) is thoroughly investigated. CTH utilizes hydrogen-donating compounds and a suitable catalyst to release H₂ in situ which saturates and reduces triglyceride molecules. CTH is potentially beneficial relative to conventional hydrogenation because it avoids the handling of large quantities of H₂ gas at high operating pressures. Jet fuels production from WCO was investigated experimentally in a continuous-flow lab-scale fixed-bed reactor, using 2-propanol as hydrogen donor and a granular activated carbon catalyst. The experiments were carried out at low pressure (2 bar) and temperature (300-400°C). The reaction products were fully characterized using GC-MS. An optimum yield of 72 wt% liquid hydrocarbon products was obtained at 380°C.

Using the experimental results obtained in the lab, a detailed techno-economic analysis (TEA) and life cycle assessment (LCA) were performed to assess the profitability and environmental impacts of CTH. Both processes were simulated via Aspen Plus^® process simulation software to determine material and energy balances. For the LCA, a “well-to-pump” system boundary is used, incorporating all material and energy flows during resource extraction up to the delivered product (i.e. jet fuel). A functional unit of 1,000 ton-d^-1 WCO feedstock was employed for the life cycle inventory (LCI). Characterization factors were obtained from Argonne’s GREET model and SimaPro’s Ecoinvent database to determine three (3) key environmental impacts: (1) total energy use (including fossil and petroleum), (2) greenhouse gas (GHG) emissions, and (3) energy return-on-investment (EROI). For the TEA employing a 25-year life, cost information was collected to determine capital cost, direct cost, indirect cost, fixed operating cost, variable operating cost, and energy cost. Modeling results for this holistic system is benchmarked against a conventional hydrogenation process to fully capture the novel process’ overall sustainability.

The results of the analysis highlight that although both processes achieved comparable jet fuel/diesel product yields, CTH would require significantly lower capital and energetic costs. However, the cost of the 2-propanol feedstock might hinder the process profitability under current market scenarios. CTH’s “well-to-pump” total energy consumption is 25% lower than conventional hydrogenation, for all products and co-products. CTH also reflects a 35% GHG reduction compared to conventional hydrogenation. Both processes were highly-sensitive to the cost of 2-propanol. While the market price for 2-propanol is significantly variable, this study shows that CTH could potentially be a promising, greener and safer process for jet fuels production from WCO. This work demonstrated that with reduced feedstock supply costs, the tradeoff between environmental impacts and profitability of CTH-based jet fuels is achieved.