Our contribution demonstrates a new way of fuel desulfurization, namely selective oxidation of organic S-compounds present in fuels to water-soluble sulfur compounds followed by in situ extraction of the latter into an aqueous phase. Different from common oxidative desulfurization (ODS) processes, we demonstrate a technique that converts sulfur compounds in fuel to a large extent to sulfate (60–70%) using oxygen as the oxidant and an aqueous H8PV5Mo7O40 (HPA-5) solution as the catalyst phase. Other water-soluble desulfurization products are sulfoacetic acid (SAA) with a share of 10–20%, 2-sulfobenzoic acid (2-SBA), and 2-(sulfooxy)­benzoic acid (2-SOBA), the latter two with a share of <10%. The new desulfurization method has been optimized for removing benzothiophene from isooctane, giving the best results with a degree of desulfurization of 99% applying 120 °C, 20 bar oxygen pressure, and 1000 rpm of 6 h reaction time using a volume water/oil ration of 10/1. Furthermore, we also successfully demonstrated the desulfurization of a domestic fuel oil with 973 ppmw sulfur content with a degree of desulfurization of 28% under nonoptimized conditions.

Our contribution describes the oxidative desulfurization of dibenzothiophene (DBT) from model oils using an aqueous H8PV5Mo7O40 (HPA-5) catalyst solution and molecular oxygen as the oxidant. In contrast to common oxidative desulfurization (ODS) protocols, the organic sulfur compound DBT is oxidized to water-soluble compounds, such as sulfuric acid (50–55%), sulfoacetic acid (20–25%), and sulfobenzoic acid (25–30%), which are extracted in situ into the aqueous catalyst phase. We describe the activating effect of oxalic acid on the ODS performance of the catalyst and propose a mechanism for the catalyst activation. Moreover, we report on the influence of various organic solvents, i.e., n-alkanes and aromatics, on the oxidative DBT removal. Remarkably, the rate of DBT oxidation and removal enhances with an increasing chain length of the alkane matrix, whereas aromatic compounds in the oil matrix inhibit the desulfurization rate. Moreover, we demonstrate that the aqueous catalyst phase can be reused at least 5 times without loss in catalytic performance.

In this contribution, we successfully apply our recently developed extractive catalytic oxidative desulfurization technology (ECODS) for the removal of different nitrogen-containing compounds (ECODN) from both gasoline and diesel fuels. Hereby, indole, 1-methylindole, 2-methylindole, 3-methylindole, quinoline, and quinaldine are completely removed from different model fuels under oxidative conditions, i.e., 120 °C and 20 bar oxygen, with the use of an aqueous HPA-5 catalyst solution within minutes. Indole and quinoline species are oxidized selectively to water-soluble compounds such as acetic acid (6−16%), formic acid (4−13%), and oxalic acid (0−4%), which are extracted in situ into the aqueous catalyst solution. Moreover, mainly carbon dioxide (71−86%) is formed in the gas phase. Our catalyst system is also very effective for denitrogenation at ambient conditions. In contrast to the removal of N-compounds at 120 °C and 20 bar oxygen, the reaction at 25 °C and atmospheric pressure produces solid Ncontaining compounds. By combining ECODS and ECODN in one vessel, desulfurization and denitrogenation of different model oils is possible in parallel. Interestingly, N-compounds present in the fuel are found to significantly promote the desulfurization reaction.

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.

The triphasic aerobic extractive desulfurization of benzothiophene (BT) using an aqueous H8[PV5Mo7O40] solution as catalyst and O2 as oxidant was investigated. A time‐resolved analysis of all reaction products in the gas, organic and aqueous phase, is given. The organic sulfur in BT is mainly converted to sulfuric acid. Mass transport limitations can be excluded. The reaction orders are 1 with regard to BT, and 0.5 both for HPA‐5 and O2. Calculated data derived from this mechanism with a power law kinetic approach show good agreement to the experimental data for conversions below 60 %. At higher BT conversions, significant deviations are found, suggesting that acidic products formed in the BT oxidation affect the catalyst and therefore the initial kinetics of the BT oxidation.