Synthesis of morpholine-based ionic liquids for extractive desulfurization of diesel fuel

Abstract

Extractive desulfurization with ionic liquids has attracted significant attention from a growing number of scientists due to the current environmental restrictions on fuel. Protic ionic liquids (PILs) were synthesized via equimolar neutralization of morpholine and formic-based compounds. The obtained PILs were characterized by Fourier transform infrared and 1H NMR spectroscopy and used as a promoter for the room temperature deep desulfurization of model oil and commercial B0S500 diesel. Extractive desulfurization of the model oil in n-octane showed that the alkyl chain length of the ionic liquid [Nmorph]+[HCOO]- does not enhance the efficiency of dibenzothiophene (DBT) removal. Regardless, the [Morph]+[HCOO]- IL is the most promising candidate for extractive desulfurization. The best results were obtained using multistage extraction (n = 3) and a 1:1 volume ratio, resulting in a 99.44% removal rate of sulfur compounds. For commercial B0S500 diesel, extraction time significantly influenced the removal of sulfur species. For samples with multistage extraction and a 1:1 volume ratio, [Morph]+[HCOO]- removed approximately 47.48% of the sulfur-containing compounds. The recycling study of [Morph]+[HCOO]- suggests that the IL remains active for up to three operating cycles without losing efficiency.