Transition Metal (Zn(II), Co(II), Cu(II), Ni(II)) Complexes for the Removal of Acidic Sulfur Impurities from Hydrocarbon Fuel

The review addresses the main approaches to desulfurization of hydrocarbon products by adsorption methods. Examples of the use of various supports (metal-organic frameworks, various porous carbons, silica, and alumina) for the removal of acidic sulfur components from gas and liquid hydrocarbons are presented. Modification of the supports with transition metals, oxides, salts, and complex compounds to remove hydrogen sulfide and thiols from hydrocarbon raw materials is substantiated. The environmental friendliness and lower energy consumption for the use of silica gel modified with Zn(II), Co(II), Ni(II), and Cu(II) carboxylates to refine hydrocarbon fuel are demonstrated. A comparison of the theoretical calculations (DFT) with experimental results attests to good agreement between the data. The choice of the parameters for silica gel surface modification with metal carboxylates is discussed, including pore size of the support, time and power of the ultrasonic treatment for the support impregnation with solutions of complexes, optimal concentration of transition metal complexes, effect of the geometry of complexes on their adsorption and on the absorption of acidic sulfur components, and so on. According to quantum chemical calculations and experimental results, metal sulfides are formed as the final products of reactions of both hydrogen sulfide and thiols with metal carboxylates. Zinc pivalate is proposed as the most promising modifier for silica, which not only efficiently removes sulfur impurities, but also gives rise to nontoxic zinc sulfide supported on silica gel.