Rational Design of Caprolactam-Based Deep Eutectic Solvents for Extractive Desulfurization of Diesel Fuel and Mechanism Study

Abstract

Deep eutectic solvents (DESs) are considered novel alternatives compared to organic solvents and ionic liquids. However, the low extractive efficiency of fuel oil has limited its wide application in desulfurization of diesel fuel. In this work, a series of caprolactam-based DESs were prepared using caprolactam as a hydrogen bond donor (HBD) and tetrabutylammonium halides as hydrogen bond acceptors (HBAs). By screening different halide anions and molar ratios of HBD and HBA, the DES tetrabutylammonium bromide/caprolactam (TBAB/CPL = 1:2) showed the highest desulfurization efficiency with the Nernst partition coefficient of 5.04, which was much higher than those of most metal-free DESs and ILs. The desulfurization efficiency could reach as high as 96.6% after a two-stage extraction. Finally, the extraction mechanism was investigated systematically using 1H nuclear magnetic resonance and Fourier transform infrared spectroscopies. Then, a density functional theory study suggested that hydrogen bonding and C–H···π interaction between DES and dibenzothiophene accounted for the higher desulfurization efficiency, enabling DES to effectively remove dibenzothiophene from the model fuels.

Designing Low-Cost, Green, and Recyclable Deep Eutectic Solvents for Selective Separation and Recovery of Valuable Metals from Spent Li-Ion Batteries

“…To verify the properties of the as-prepared UC13-DESs and UC13-FA2.4-DESs, FT-IR spectroscopy investigated the variation of intermolecular interactions and functional groups between CPL, UR, and FA (Figure a,b). The UR molecules, − CPL molecules, , and FA molecules , of characteristic absorption peaks are shown in the Supporting Information (3.1). Nearly all the characteristic peaks of functional groups belonging to CPL and UR were still retained in UC13-DESs, suggesting that no new substances were generated .…”

“…To solve the bottleneck mentioned above of DESs in cyclic leaching, it is necessary to introduce a new type of hydrogen bond receptor (HBAs) to replace ChCl in organic acid-based DESs. Meanwhile, the amides, as excellent solvents and extractants, − are a veritable component, which can be used as HBD in the preparation of DES. Given the stability of the solvent and the persistence of the cycle leaching, cyclic lactam (e.g., caprolactam, CPL) is more prominent and competitive among all the amides.…”

Extractive Desulfurization in Microchannel Contactors Using Deep Eutectic Solvents: Optimization Using Central Composite Design (CCD) and Flow Pattern Mapping

“…DESs are capable of removing sulfur compounds such as thiophene (Th), benzothiophene (BT), DBT, and 4-6-dimethyldibenzothiophene (4-6-DMDBT) in the EDS process. 21−23 Xu et al 24 screened different halide anions as HBA and investigated the effect of HBA and HBD molar ratios on desulfurization. According to their results, the highest sulfur removal was achieved using tetrabutylammonium bromide and caprolactam with a 1:2 molar ratio.…”

“…Xu et al screened different halide anions as HBA and investigated the effect of HBA and HBD molar ratios on desulfurization. According to their results, the highest sulfur removal was achieved using tetrabutylammonium bromide and caprolactam with a 1:2 molar ratio.…”

Hydrocarbon Extraction with Ionic Liquids

“…The DES showed a desulfurization efficiency of up to 65% within a single cycle within 10 min of ultrasonic extraction at 80 °C of synthesis temperature, 37 °C of extraction temperature, and a molar ratio of 3:1. DESs as extractants exhibited remarkable potential for EDS for the prerefining or postrefining of flow cutting during crude oil distillation.Caprolactam-based DESs were designed and synthesized by mixing tetrabutylammonium halides (F − , Cl − , Br − , and I − ) as HBAs and caprolactam (CPL) as an HBD for EDS from a model diesel fuel of a mixture of DBT, MDBT, DMDBT, and ndodecane 425. The halogen-based anions of HBAs influenced the EDS efficiency.…”