Catalytic Oxidative-Extractive Deep Desulfurization of Diesel Fuel by N-methyl-۲-pyrrolidone-Based Protic Acidic Ionic Liquids (PAILs)

Inexpensive and low-viscosity Protic Acidic Ionic Liquids (PAILs) of N-metheyl-۲-pyrrolidone formate, acetate, and propionate abbreviated as [Hnmp][HCOO], [Hnmp][CH۳COO] and [Hnmp][CH۳CH۲COO] respectively, were prepared and characterized by FT-IR and H-NMR. Deep oxidative and extractive desulfurization of a simulated oil and a real diesel containing ۱۰۰۰ ppmw sulfur were studied under the catalysis of the proposed PAILs without additional carboxylic acid and extraction solvent in the system. The desulfurization efficiency in this study was influenced by both amounts of PAILs and concentration of the produced peroxy acids from H۲O۲. Comparing to [Hnmp][HCOO], [Hnmp][CH۳COO] and [Hnmp][CH۳CH۲COO] had a relatively higher extraction ability however the weaker acidic properties of them resulted in a lower activation of H۲O۲ to produce peroxy acids and finally led to lower oxidative desulfurization (ODS) efficiency in the same condition. Additionally, the neutralization reaction may not be efficiently gone to the right hand by weaker acids. The effects of the main process variables were studied in detail. The highest desulfurization yield of ۹۷% for BT and ۹۹% for DBT and ۴,۶-DMDBT, were achieved using [Hnmp][HCOO] in the ODS system at a temperature of ۴۰ °C, H۲O۲/sulfur molar ratio of ۱۰, VPAIL/Voil of ۰.۲, and a reaction time of ۹۰ min. The immiscibility of the proposed PAILs in this study with the oil phase caused the easy separation of them after desulfurization. The possible ODS pathway was also proposed.

Keywords:

Oxidative desulfurization , Ionic liquid , Carboxylic acid , catalyst , Thiophenic compounds