Efficient pyridinium-based ionic liquid for deep oxidative desulfurization of model oil

Abstract

The present research work reports the synthesis of a pyridinium-based ionic liquid (IL) 1-butyl-4-methylpyridinium benzoate [BMPy][(C6H5)COO]. Full characterization of [BMPy][(C6H5)COO] was then performed using 1H NMR, 13C NMR, FTIR, TGA, and elemental analysis. [BMPy][(C6H5)COO] was firstly applied in the extractive desulfurization (EDS) of a model oil consisting of dibenzothiophene (DBT) and dodecane (1000 ppm), where 63.1% DBT-removal efficiency was revealed under optimum conditions of 60 °C, 90 min, and a mass ratio of 1:1 (IL/model oil). To further improve the efficiency of DBT-removal, [BMPy][(C6H5)COO] was subsequently employed in oxidative desulfurization (ODS), where it acted as an extractant with H2O2 as an oxidant. Successfully, 98.9% of DBT was removed at 60 °C and within 90 min using an equal mass ratio of IL/model oil and molar ratio (8) of O/S. Moreover, [BMPy][(C6H5)COO] could be regenerated and recycled for five consecutive runs while retaining approximately the same ODS efficiency. A mechanism of ODS using [BMPy][(C6H5)COO] was proposed. The π–π interactions between IL's structure and DBT were suggested to be the driving force behind the extraction power of [BMPy][(C6H5)COO]. Furthermore, recommendations for future research directions of ODS using ILs were introduced. Finally, a comparison of ODS results for [BMPy][(C6H5)COO] and different pyridinium-based ILs for various model oils was conducted where [BMPy][(C6H5)COO] showed to be a competitive and promising type of pyridinium-based IL for use in the ODS processes.