Investigations on Catalyst Stability and Product Isolation in the Extractive Oxidative Desulfurization of Fuels Using Polyoxometalates and Molecular Oxygen

Abstract

Our contribution adds important new insight to the recent finding that polyoxometalate catalysts, such as H8PV5Mo7O40 (HPA‐5), are very effective catalysts in the extractive oxidative desulfurization of fuels using molecular oxygen. Our contribution focuses on aspects of catalyst stability and deactivation caused by the accumulation of acidic products and intermediates, i. e. sulfuric acid, formic acid, acetic acid, sulfoacetic acid or 2‐sulfobenzoic acid. These compounds reduce the pH value of the aqueous catalyst phase during the course of the desulfurization reaction. At lower pH values, the higher V‐substituted species rearrange to lower V‐substituted species and VO2+. This rearrangement is responsible for a decreasing activity in extractive oxidative desulfurization. We show that formic acid, acetic acid, sulfoacetic acid and 2‐sulfobenzoic acid block active sites of the catalyst. Oxalic acid, in contrast, has been found to exert a remarkable positive effect on catalyst activity. The feasibility of catalyst recycling and efficient isolation of the decomposition products is demonstrated using four commercially available organic solvent nanofiltration membranes.

Kinetics of Triphase Extractive Oxidative Desulfurization of Benzothiophene with Molecular Oxygen Catalyzed by HPA‐5

“…For higher conversions (see Fig. b), the deviation of modeled and measured conversion is more pronounced, indicating product inhibition of HPA‐5 by the acids formed in period II . This is also observable in the parity plot in Fig.…”

“…Below a pH‐value of 1.1, the BT conversion linearly decreases. The change of the pH to lower values is due to the formation of sulfuric acid accompanied by other organic acids, which possibly inhibit the catalyst (Tab. and Fig.…”

Polyoxometalate Dicationic Ionic Liquids as Catalyst for Extractive Coupled Catalytic Oxidative Desulfurization

“…However, in addition to the harsh operation conditions, HDS is not effective for removing aromatic sulfur compounds and their derivatives with steric hindrance [11,12]. In this context, as a nonhydrodesulfurization technology that can achieve deep desulfurization of fuel oil under mild conditions, the ECODS process has become a main focus due to its simplicity and effectiveness [13][14][15][16]. Although various types of solvents and oxidants have been used in the desulfurization process, and also play an important role, the biggest challenge for a successful ECODS process is to use catalysts with high activity.…”

Heterogeneous Catalysts Containing an Anderson-Type Polyoxometalate for the Aerobic Oxidation of Sulfur-Containing Compounds

“…However, since an increasing part of the produced crude oil is of the heavy variety, there is a significant increase in the content of condensed thiophene derivatives, for which the hydrodesulfurization technology becomes ineffective, especially for dibenzothiophene (DBT) and its alkyl derivatives. , To increase the rate of hydrogenolysis of heteroaromatic compounds, the parameters of the process are tightened, including an increase in temperature and pressure in conjunction with the supply of excess hydrogen. This approach makes the hydrotreating technology unprofitable; therefore, special attention is paid to the development of alternative hydrogen-free desulfurization methods, including adsorptive desulfurization, , extraction desulfurization, , biodesulfurization, , and oxidative desulfurization. , The latter technique is considered the most promising one, because it can effectively cope with difficult sulfur compounds under relatively mild conditions (temperatures up to 150 °C, atmospheric pressure). This method is based on the oxidation of organosulfur compounds in the presence of an oxidizing agent and a catalyst to the corresponding sulfoxides and sulfones, followed by the removal of the polar products by simple adsorption or extraction methods.…”

“…This approach makes the hydrotreating technology unprofitable; therefore, special attention is paid to the development of alternative hydrogen-free desulfurization methods, including adsorptive desulfurization, 8,9 extraction desulfurization, 10,11 biodesulfurization, 12,13 and oxidative desulfurization. 14,15 The latter technique is considered the most promising one, because it can effectively cope with difficult sulfur compounds under relatively mild conditions (temperatures up to 150 °C, atmospheric pressure). This method is based on the oxidation of organosulfur compounds in the presence of an oxidizing agent and a catalyst to the corresponding sulfoxides and sulfones, followed by the removal of the polar products by simple adsorption or extraction methods.…”