Fuel oil products extractive denitrogenation by protonated L-proline/xylitol-based deep eutectic solvent – An environmentally friendly approach

Concerns about the environment and strict regulations on emissions have led to a growing demand for creative solutions to decrease nitrogen oxide (NOx) emissions from combustion processes. In this study, we introduce a new approach for the removal of N-containing organic compounds from fuels (denitrogenation), based on experiments using a model fuel containing pyridine. In this work, an environmentally friendly and sustainable Natural Deep Eutectic Solvents (NADES), based on L-proline protonated by HCl and xylitol (L-prol/xyl) with an acidic character, were used, for the first time, for this purpose. A central composite design was used for the optimization of the process; the best effectiveness was obtained for 0.5 g of L-proline NADES, a time of extraction of 2 h, and a temperature of 40 °C used for treatment of 5 mL of model fuel. As a result, the study revealed high denitrogenation effectiveness, resulting in 100 % removal of pyridine in a single-stage extraction. Additionally, L-proline-based NADESs showed three successful regeneration cycles. Furthermore, Fourier-transform infrared spectroscopy (FTIR) and Density Functional Theory (DFT) confirmed the interaction mechanism between DESs and nitrogen compound (pyridine), explaining the phenomena responsible for the obtained high effectiveness of the extraction process. Finally, utilizing L-proline-based NADES has facilitated the establishment of environmentally friendly solvents for removing nitrogen compounds from fuel.