Adsorptive denitrogenation of model fuel with silica gel†

Abstract

Utilization of wet waste to produce renewable fuels, including aviation fuel, is key to a sustainable energy portfolio. Currently, hydrothermal liquefaction (HTL) and subsequent hydrotreating steps can successfully produce drop-in fuels which meet standards for gasoline and diesel. A remaining obstacle for development of sustainable aviation fuels (SAF) is the presence of nitrogen containing compounds (NCCs). Aviation fuels have more stringent regulations on permissible concentrations of NCCs, which have been associated with fuel instability for use in jet engines and the emission of harmful pollutants into the environment. Currently, NCCs are removed through the hydrodenitrogenation (HDN) process, which requires severe operating conditions along with significant H₂ and energy consumption, resulting in yield lost due to cracking. Alternatively, adsorptive denitrogenation (ADN) is being investigated as a more energy efficient process. This work achieved over 99% nitrogen removal, supported by computational work showing nitrogen adsorption correlates with surface acidity. Among the adsorbents screened, silica gel exhibited high adsorption capacity of 150 mg g⁻¹ for pyridine and 80 mg g⁻¹ for indole, coupled with impressive regeneration performance through thermal treatment. The recyclability of the silica gel showed good adsorption efficiency of NCCs for up to five cycles. This research demonstrates mechanism of nitrogen removal using adsorption technologies for future waste-derived aviation fuel.