On novel processes for removing sulphur from refinery streams

Transition Metal Phosphide Nanoarchitectonics for Versatile Organic Catalysis

Transition metal phosphides (TMP) posses unique physiochemical, geometrical, and electronic properties, which can be exploited for different catalytic applications, such as photocatalysis, electrocatalysis, organic catalysis, etc. Among others, the use of TMP for organic catalysis is less explored and still facing many complex challenges, which necessitate the development of sustainable catalytic reaction protocols demonstrating high selectivity and yield of the desired molecules of high significance. In this regard, the controlled synthesis of TMP-based catalysts and thorough investigations of underlying reaction mechanisms can provide deeper insights toward practical achievement of desired applications. This review aims at providing a comprehensive analysis on the recent advancements in the synthetic strategies for the tailored and tunable engineering of structural, geometrical, and electronic properties of TMP. In addition, their unprecedented catalytic potential toward different organic transformation reactions is succinctly summarized and critically analyzed. Finally, a rational perspective on future opportunities and challenges in the emerging field of organic catalysis is provided. On the account of the recent achievements accomplished in organic synthesis using TMP, it is highly anticipated that the use of TMP combined with advanced innovative technologies and methodologies can pave the way toward large scale realization of organic catalysis.

Carbon‐Supported Potassium Hydride for Efficient Low‐Temperature Desulfurization

The industrial removal of organosulfur impurities from fossil fuels relies on transition‐metal‐based catalysts in harsh conditions (ca. 400 °C, up to 100 bar H₂), yet desulfurization (DS) of refractory alkyl dibenzothiophenes (DBTs) remains challenging. Here, we report that carbon‐supported potassium hydride (KH/C) enables efficient DS of DBTs in mild conditions, viz. >97 % conversion of DBTs is achieved at 165 °C in 3–6 h while the yields of respective biphenyls are 84–95 % by using only 15 % excess of KH per a C−S bond. In addition, KH/C allows to lower the concentration of 4,6‐Me₂DBT in the mesitylene solution from 1000 ppm to <3 ppm (165 °C, 20 h) and provides deoxygenation, denitrogenation and catalytic aromatic hydrogenation reactions. DS of various sulfur heterocycles by using KH/C, a transition‐metal‐free material based on earth abundant elements, is viable at low temperature and has prospects for the further development towards decentralized removal of organosulfur species from fossil fuels.

Assessment of the Oxidative Desulfurization of Middle Distillate Surrogate Fuels with Spectroscopic Techniques

The oxidative desulfurization of five (5) model sulfur compounds and eleven (11) surrogate blends was investigated using the hydrogen peroxide (H₂O₂)-acetic acid (CH₃COOH) system. Consequently, extractive desulfurization was carried out using conventional solvents. The model sulfur compounds, as well as the solvent, are present in petroleum middle distillates. The selection of the compounds was made so that they represent various kinds of sulfur compounds. The goal of this study was the implementation of a simple and economical oxidative and extractive system for the desulfurization of surrogate mixtures with an intermediate sulfur concentration 1% w/w, at the mild temperature of 70°C, and without the use of supplementary and assisting methods such as heterogeneous catalysis or ultrasound irradiation. The sulfur content was estimated using X-ray fluorescence. The progress of the oxidation reaction was monitored using liquid FT-IR. The solid sediments of the oxidation procedure were identified with solid-state FT-IR and ¹H NMR spectroscopy.

Insights to the oxidative desulfurization process of fossil fuels over organic and inorganic heterogeneous catalysts: advantages and issues

Strict environmental laws have been put in place around the world to reduce the amount of sulfur in the fuel to reduce the emissions of harmful gases from fuel combustion and improve air quality. Therefore, extensive researches have been undertaken to devise effective processes or to improve the desulfurization processes. Among the desulfurization processes, the oxidative desulfurization (ODS) process is a promising method to achieve very low and near-zero sulfur content of the fuel. In this process, sulfur compounds are converted to the corresponding sulfone by a catalyst and in the presence of an oxidant. The obtained compounds by polar solvents or adsorbents are removed from the fuel. In recent decades, extensive studies have been carried out on the catalysts used in the oxidative desulfurization process. In this review, a comprehensive survey has been performed on heterogeneous catalysts used in the oxidative desulfurization process. According to the reported researches, the heterogeneous catalysts used can be divided into five groups: ionic liquids, carbon materials, polyoxometalates, transition metal oxides stabilized on porous solid substrates, and metal-organic frameworks. The proposed mechanisms with different catalysts have also been studied in this work.

Ni-Based Nanoparticles on Mesoporous Silica Supports for Single-Stage Arsenic and Chlorine Removal during Diesel Fraction Hydrotreating

As- and Cl-containing impurities are highly detrimental to sulfided catalysts in hydrotreating processes. To prevent the irreversible loss of activity of the main sulfide catalysts by As and Cl contaminants, a protective double-layered guard bed catalyst is applied. Two types of mesoporous silica supports (SBA-15 and MCF) were used to obtain sorption-catalytic materials. The high specific surface area of the supports allowed for a significant increase in access to the active catalyst centers. The NiMo/SBA-15/Al₂O₃ and NiMg/MCF/Al₂O₃ sorption-catalytic materials demonstrated high activity and stability over 48 h for the simultaneous removal of As and Cl. The catalytic materials allowed for reducing the concentrations of As and Cl to less than 0.1 ppm in the diesel fraction under the following conditions: 5.0 MPa pressure, 2.0 h^-1 LHSV, 300 L/L H₂-to-substrate volume ratio, and 360 °C.

An overview of conventional and alternative technologies for the production of ultra-low-sulfur fuels

Environmental concerns have given a great deal of attention for the production of ultra-low-sulfur fuels. The conventional hydrodesulfurization (HDS) process has high operating cost and also encounters difficulty in removing sulfur compound with steric hindrance. Consequently, various research efforts have been made to overcome the limitation of conventional HDS process and exploring the alternative technologies for deep desulfurization. The alternative processes being explored for the production of ultra-low-sulfur content fuel are adsorptive desulfurization (ADS), biodesulfurization (BDS), oxidative desulfurization (ODS), and extractive desulfurization (EDS). The present article provided the comprehensive information on the basic principle, reaction mechanism, workability, advantages, and disadvantages of conventional and alternative technologies. This review article aims to provide valuable insight into the recent advances made in conventional HDS process and alternative techniques. For deep desulfurization of liquid fuels, integration of conventional HDS with an alternative technique is also proposed.

Effect of Mono-, Di-, and Triethylene Glycol on the Activity of Phosphate-Doped NiMo/Al2O3 Hydrotreating Catalysts

The effect of glycols on the catalytic properties of phosphate-doped NiMo/Al2O3 catalysts in the hydrotreating of straight-run gas oil (SRGO) was studied. The NiMo(P)/Al2O3 catalysts were prepared using ethylene glycol (EG), diethylene glycol (DEG), and triethylene glycol (TEG) as additives. The organic agent was introduced into the aqueous impregnation solution obtained by the dissolving of MoO3 in H3PO4 solution, followed by Ni(OH)2 addition. The Raman and UV–Vis studies show that the impregnation solution contains diphosphopentamolybdate HxP2Mo5O23(6−x)− and Ni(H2O)62+, and that these ions are not affected by the presence of glycols. When the impregnation solution comes in contact with the γ-Al2O3 surface, HxP2Mo5O23(6−x)− is decomposed completely. The catalysts were characterized by Raman spectroscopy, low-temperature N2 adsorption, X-ray photoelectron spectroscopy, and transmission electron microscopy. It is shown that the sulfide catalysts prepared with glycols display higher activity in the hydrotreating of straight-run gas oil than the NiMoP/Al2O3 catalyst prepared without the additive. The hydrodesulfurization and hydrodenitrogenation activities depend on the glycol type and are decreased in the following order: NiMoP-DEG/Al2O3 > NiMoP-EG/Al2O3 > NiMoP-TEG/Al2O3 > NiMoP/Al2O3. The higher activity of NiMoP-DEG/Al2O3 can be explained with the higher dispersion of molybdenum on the surface of the catalyst in the sulfide state.

Transfer of hydrosulfide from thiols to iron(ii): a convenient synthetic route to nonheme diiron(ii)–hydrosulfide complexes

The synthesis and reactivity of an unprecedented nonheme diiron(ii)–hydrosulfide complex via Fe(ii) mediated C–S bond cleavage of thiols.

Heterogeneously Catalyzed Aerobic Oxidation of Sulfides with a BaRuO3 Nanoperovskite

A rhombohedral BaRuO₃ nanoperovskite, which was synthesized by the sol-gel method using malic acid, could act as an efficient heterogeneous catalyst for the selective oxidation of various aromatic and aliphatic sulfides with molecular oxygen as the sole oxidant. BaRuO₃ showed much higher catalytic activities than other catalysts, including ruthenium-based perovskite oxides, under mild reaction conditions. The catalyst could be recovered by simple filtration and reused several times without obvious loss of its high catalytic performance. The catalyst effect, ¹⁸O-labeling experiments, and kinetic and mechanistic studies showed that substrate oxidation proceeds with oxygen species caused by the solid. The crystal structure of ruthenium-based oxides is crucial to control the nature of the oxygen atoms and significantly affects their oxygen transfer reactivity. Density functional theory calculations revealed that the face-sharing octahedra in BaRuO₃ likely are possible active sites in the present oxidation in sharp contrast to the corner-sharing octahedra in SrRuO₃, CaRuO₃, and RuO₂. The superior oxygen transfer ability of BaRuO₃ is also applicable to the quantitative conversion of dibenzothiophene into the corresponding sulfone and gram-scale oxidation of 4-methoxy thioanisole, in which 1.20 g (71% yield) of the analytically pure sulfoxide could be isolated.

The Removal of Benzothiophene from Model Diesel on NaY and NiY Zeolites: Equilibrium and Kinetic Studies

This work investigates the adsorption of sulfur compounds in model fuel (benzothiophene dissolved in n-octane) on NaY and NiY zeolites from the points of adsorption equilibrium and kinetics. The crystal structures, textural properties and chemical compositions of zeolites were characterized by XRD, N2 physisorption and ICP-AES, respectively. The adsorption of sulfur from model diesel was processed in a batch experiment on NaY and NiY zeolites, and the effects of adsorption temperature and adsorption time on adsorption capacity were investigated. The experimental isotherm data were fitted using Langmuir, Freundlich and Toth models. The pseudo-first order, pseudo-second order, pseudo-n order and intra-particle diffusion models were applied to fit the kinetic data and determine the adsorption mechanism. It is observed from the correlation coefficient (R2) that Toth model is more appropriate to depict the isotherm equilibrium adsorption process and the sulfur uptake process follows the pseudo-n order rate expression on NaY and NiY zeolites. The diffusion study indicated that the adsorption of benzothiophene is controlled by two steps. Moreover, the results of the relative error (RE) analysis further confirm the conclusion of the kinetic study. Thermodynamic studies demonstrated that the adsorption process is exothermal and spontaneous. The equilibrium adsorption sulfur capacities are 20.66 and 28.21 mgS˙g−1 on NaY and NiY zeolites at 50 °C, respectively.

Effect of calcium formate as an additive on desulfurization in power plants

SO₂ in flue gas needs to be eliminated to alleviate air pollution. As the quality of coal decreases and environmental standard requirements become more stringent, the high-efficiency desulfurization of flue gas faces more and more challenges. As an economical and environmentally friendly solution, the effect of calcium formate as an additive on desulfurization efficiency in the wet flue gas desulfurization (WFGD) process was studied for the first time. Improvement of the desulfurization efficiency was achieved with limited change in pH after calcium formate was added into the reactor, and it was found to work better than other additives tested. The positive effects were further verified in a power plant, which showed that adding calcium formate could promote the dissolution of calcium carbonate, accelerate the growth of gypsum crystals and improve the efficiency of desulfurization. Thus, calcium formate was proved to be an effective additive and can potentially be used to reduce the amount of limestone slurry required, as well as the energy consumption and operating costs in industrial desulfurization.

Palladium islands on iron oxide nanoparticles for hydrodesulfurization catalysis

Deposition of thin Pd islands on iron oxide nanoparticles results in a 4-fold activity enhancement in HDS and suppresses cracking.

Biodesulphurization of gasoline by Rhodococcus erythropolis supported on polyvinyl alcohol

A new biodesulphurization (BDS) method has been considered using Rhodococcus erythropolis supported on polyvinyl alcohol (PVA) for BDS of thiophene as a gasoline sulphur model compound in n-hexane as the solvent, subsequently this biocatalyst has been applied to BDS of gasoline samples. The obtained results according to UV-Spectrophotometer analysis at 240 nm showed that 97·41% of thiophene at the optimum condition of primary concentration 80 mg l^-1 , pH = 7, by 0·1 g of biocatalyst in 30°C and after 20 h of contact time has been degraded. These optimum conditions have been applied to gasoline BDS and the biodegradation of gasoline thiophenic compounds have been investigated by gas chromatography-mass spectrometry (GC-MS). According to GC-MS, thiophene and its 2-methyl, 3-methyl and 2- ethyl derivatives had acceptable biodegradation efficiencies of about 26·67, 21·03, 23·62% respectively. Also, benzothiophene that has been detected in a gasoline sample had 38·89% biodegradation efficiency at optimum conditions, so biomodification of PVA by R. erythropolis produces biocatalysts with an active metabolism that facilitates the interaction of bacterial strain with gasoline thiophenic compounds. The morphology and surface functional groups of supported R. erythropolis on PVA have been investigated by scanning electron microscope (SEM) and FT-IR spectroscopy respectively. SEM images suggest some regular layered shape for the supported bacteria. FT-IR spectra indicate a desirable interaction between bacterial cells and polymer supports. Also, the recovery of biocatalyst has been investigated and after three times of using in BDS activity, its biocatalytic ability had no significant decreases.

SIGNIFICANCE AND IMPACT OF THE STUDY

The biomodification of polyvinyl alcohol by Rhodococcus erythropolis described herein produces a new biocatalyst which can be used for significantly reducing the thiophenic compounds of gasoline and other fossil fuels. The immobilization process is to increase the biodegradation efficiency of cells and accelerating the biodesulphurization process.

Corrosion properties of steel in 1-butyl-3-methylimidazolium hydrogen sulfate ionic liquid systems for desulfurization application

The corrosivity of [BMIM]HSO₄-based systems for desulfurization applications were investigated by weight loss and surface analyses.

Enhancement of the selective hydrodesulfurization performance by adding cerium to CoMo/γ-Al2O3 catalysts

CoMo/CeO₂–Al₂O₃ catalysts were prepared with high catalytic performance. The content of CeO₂ is the key to adjusting the morphology of MoS₂. The catalytic activity and selectivity are closely related to the sulfidation of the Mo species.

Influence of a porous MOF support on the catalytic performance of Eu-polyoxometalate based materials: desulfurization of a model diesel

An aluminum 2-aminoterephthalate based metal–organic framework material was used to prepare highly efficient heterogeneous catalysts in desulfurization processes.