Oxidative Desulfurization

“There is nothing more difficult to take in hand, more perilous to conduct or more uncertain in its success than to take the lead in the introduction of a new order of things.” -- Niccolo Machiavelli (Italian writer and statesman, Florentine patriot, author of 'The Prince', 1469-1527)
“Do you suppose I could buy back my introduction to you?” -- Groucho Marx (American Comedian, Actor and Singer, 1890-1977)

Oxidative desulfurization is a hot topic in the desulfurization arena.  The introduction to this research article explains why.

BONUS: You can download the full text at no charge.

///////
Chemical Engineering Journal, 283 (2016) 89–96
Efficient oxidative desulfurization of diesel fuel using amide-based ionic liquids
a School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, People’s Republic of China
b Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin University, Tianjin 300072, People’s Republic of China
c National Engineering Research Centre of Distillation Technology, Tianjin University, Tianjin 300072, People’s Republic of China
Abstract
A series of Brønsted acidic ionic liquids having a protonated amide- or lactam-based cation were synthesized and investigated as extractants and catalysts in the extraction combined with oxidative desulfurization (ECODS) of both model oil and diesel fuel, with hydrogen peroxide (H2O2, 30 wt%) as oxidant. Each of them showed obvious removal of benzothiophene (BT) and dibenzothiophene (DBT) in model oil. Among them, [HCPL][TFA] exhibited the best performance by completely removing BT and DBT in a short time. The detailed structure and conformation of [HCPL][TFA] were investigated by 1H NMR and FTIR as well as theoretical calculation. HCPL+ cation was verified to exist in an enol form, which was supposed to contribute to high desulfurization performance by improving the formation of peroxides. In the end, two kinds of diesel were used to evaluate its desulfurization performance. [HCPL][TFA] can reduce the S-content of real hydrogenated diesel from 659.7 ppm to 8.62 ppm with 98.69% S-removal efficiency after two ECODS processes. Furthermore, the total S-content of straight-run diesel fuel was reduced to 89.36 ppm from 11,034 ppm with a similar S-removal rate. The results of GC-PFPD before and after each ECODS process indicated that almost all the original S-compounds in diesel had been converted to their corresponding oxidation products. The desulfurization performance was actually restricted by extraction capability.
Introduction
In the recent years, worldwide environmental regulations toward transportation fuels have been increasingly strict in order to reduce the air pollution and related public health impacts [1]. S-compounds in diesel fuel are converted into SOx when combusted and further reduce combustion efficiency and increase emission of particulates [1–3]. Many countries mandated stringent legislation to cut diesel fuel S-content down to 10 ppm, which put forth a critical challenge to the refinery industry [1]. The traditional hydrodesulfurization (HDS) is a high-pressure, high-temperature catalytic process which can remove various types of sulfur compounds by converting organic sulfur to hydrogen sulfide gas. However, when the deep desulfurization of diesel fuel is needed, HDS is less effective for removing heterocyclic S-compounds such as benzothiophene (BT), dibenzothiophene (DBT) and their derivatives [4]. Due to this reason, many groups have been engaged in the exploitation of non-HDS technologies, such as extraction [5,6], oxidation [7–10] and adsorption [11–14]. Among these non-HDS methods, extraction combined with oxidative desulfurization (ECODS) using ionic liquid is regarded as one of the most promising after that, compared with imidazolium- or pyridinium-based ionic liquids. In this work, eight amide-based ionic liquids were synthesized and listed in Fig. 1. The desulfurization performance of these low-cost ionic liquids was first evaluated under the same conditions for the oxidation of BT and DBT in model oil for a preliminary screening. The influence of cation structure and anion types were discussed. Among the ionic liquids, [HCPL][TFA] performed the best by completely converting BT and DBT. Thus, a more detailed assessment of its performance was conducted. Some important factors of desulfurization processes were investigated, such as reaction temperature, the ratio of O/S, the amount of IL and reusability. In order to explain the mechanism, the structure and conformation of [HCPL][TFA] was studied. Amide-based ionic liquids were reported to exist in two forms, namely, the keto form and the enol form [36]. So the structure of [HCPL][TFA] was characterized by 1H NMR and FTIR and further investigated theoretically by means of DFT methods with the Gaussian 09 program package. A supposed mechanism was then put forward to explain the outstanding desulfurization performance of [HCPL][TFA]. Finally, ECODS was applied to both hydrogenated diesel and straight-run diesel, and the evolution of total S-content and speciation of S-compounds after each step were measured.
Free Full Text Source:  https://www.researchgate.net/profile/Huawei_Yang2/publication/281589730_Efficient_oxidative_desulfurization_of_diesel_fuel_using_amide-based_ionic_liquids/links/55eeeff008ae0af8ee1af74b.pdf
//////