Production of Jet Biofuels by Catalytic Hydroprocessing of Esters and Fatty Acids: A Review

Abstract

The transition from fossil to bio-based fuels is a requisite for reducing CO2 emissions in the aviation sector. Jet biofuels are alternative aviation fuels with similar chemical composition and performance of fossil jet fuels. In this context, the Hydroprocessing of Esters and Fatty Acids (HEFA) presents the most consolidated pathway for producing jet biofuels. The process for converting esters and/or fatty acids into hydrocarbons may involve hydrodeoxygenation, hydrocracking and hydroisomerization, depending on the chemical composition of the selected feedstock and the desired fuel properties. Furthermore, the HEFA process is usually performed under high H2 pressures and temperatures, with reactions mediated by a heterogeneous catalyst. In this framework, supported noble metals have been preferably employed in the HEFA process; however, some efforts were reported to utilize non-noble metals, achieving a similar performance of noble metals. Besides the metallic site, the acidic site of the catalyst is crucial for product selectivity. Bifunctional catalysts have been employed for the complete process of jet biofuel production with standardized properties, with a special remark for using zeolites as support. The proper design of heterogeneous catalysts may also reduce the consumption of hydrogen. Finally, the potential of enzymes as catalysts for intermediate products of the HEFA pathway is highlighted.

Multi-criteria decision analysis for the evaluation and screening of sustainable aviation fuel production pathways

“…Several researchers have also explored different renewable feedstock including vegetable oils, animal fats, and algal oils. 40 It should be emphasized that some edible oil crops are unsuitable for SAF production because of the food versus energy competition. Regardless, the choice of feedstock for HEFA is very important because it determines if an extra pre-treatment step is required as well as the quality of the fuel produced.…”

“…Also, the cracking and distillation steps could be avoided with feedstock containing mostly fatty acids with carbon chain length within the jet fuel range. 40 Highly unsaturated feedstock often needs an additional process to saturate the double or triple bonds of the corresponding fatty acids. These steps necessitate large amounts of hydrogen consumption at moderate pressure and temperature thereby improving the overall processing cost.…”

Catalytic Upgrading of Rice Straw Bio-Oil via Esterification in Supercritical Ethanol over Bimetallic Catalyst Supported on Rice Straw Biochar

“…The esterification process with a heterogenous solid catalyst alongside the HDO is seen as the best approach for upgrading bio-oil [14]. It is also important to note that esterification carried in the presence of a solid heterogeneous catalyst does not only catalyze the esterification reaction but also aids the deoxygenation of the esterified bio-oil, thereby further enhancing the calorific value of the upgraded fuel [16]. It is therefore not surprising that there has been increasing interest in the development in the enhancement of fast pyrolysis bio-oils through supercritical alcohol treatment, presenting an alternative to traditional techniques like HDO and catalytic cracking [17,18].…”

Butene-Rich Alkene Formation from 2,3-Butanediol through Dioxolane Intermediates

“…Renewably sourced C 3+ alkenes are key precursors for renewable fuel generation from fermentation products and are the primary objective of other alcohol conversion technologies including ethanol. , Dioxolanes are synthesized from BDO and a range of C 2 –C 8 aldehydes prior to converting them into alkene mixtures. Dioxolane conversion occurs over a bifunctional Cu/ZSM-5 catalyst previously identified for its catalytic functionality for gas-phase BDO-to-alkene conversion, adding to a growing literature on the development for bifunctional or multifunctional catalysts for sustainable catalysis applications. − Alkene product compositions are investigated as a function of the reaction temperature and dioxolane composition, the latter of which is controlled by the choice of aldehyde when synthesizing the dioxolane. The wider scale application of dioxolanes for renewable fuel generation is investigated using aldehydes derived from renewable sources to identify potential advantages in the BDO-derived alkene formation process.…”