Photocatalytic oxidative of Keggin-type polyoxometalate ionic liquid for enhanced extractive desulfurization in binary deep eutectic solvents

Abstract

A series of novel binary deep eutectic solvents (DESs) composed of choline chloride (ChCl) and formic acid (HCOOH) with different molar ratios have been successfully synthesized and applied in extractive desulfurization (EDS). Keggin-type polyoxometallate ionic liquid [TTPh]3PW12O40 was prepared and used as catalyst to enhance the EDS capacity by means of photocatalytic oxidative process. Both of the DESs and [TTPh]3PW12O40 ionic liquid catalyst were characterized in detail by Fourier transform infrared spectroscopy spectra (FT-IR), elemental analysis, and X-ray photoelectron spectroscopy (XPS). It was found that the molar ratios of ChCl:HCOOH had a major impact on desulfurization performance, and the optimal desulfurization capacity 96.5% was obtained by ChCl/5HCOOH. Besides dibenzothiophene (DBT), the desulfurization efficiencies of 4-methylbenzothiophene (4-MDBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT), two kinds of DBT derivatives, were also investigated under the same experimental conditions. Moreover, the free radical scavenging experiments manifested that superoxide radical (O2−) and hole (h+) played important roles in the desulfurization system. After further analysis of the oxidation products by gas chromatography-mass spectrometry (GC–MS), the possible reaction mechanism was proposed. Thus, photocatalytic oxidative has been proved to be one of the efficient approaches for enhancing the extractive desulfurization performance in DES.