Aldehyde-Assisted Aerobic-Oxidative Desulfurization of HDS Diesel Fuels by a Highly Effective Heterogeneous V-Substituted Keggin-Type Semiorganic Catalyst: Modeling of Experimental Design and Mechanistic and Kinetic Insights

Aldehyde-assisted aerobic oxidative desulfurization (AODS) of model and real hydrodesulfurization (HDS) diesel fuels were examined by using a newly synthesized V-substituted Keggin-type semi-organic catalyst, (2-H2NC5H4NH)(5)[PV2W10O40]1/2(C5H5N)2H(2)O ((AP)(5)PWV2), as the heterogeneous catalyst and benzaldehyde (PhCHO) as a sacrificial reductant. At first, a modeling of experimental design (DOE) was conducted by using the Taguchi orthogonal array (L9 OA) method to determine the most substantial parameters that synergically improved the AODS process in model diesel oil. Many trials were conducted at an air-flow rate of 20 mL min(-1), where the effect of the selected controllable process parameters, dibenzothiophene (DBT)/catalyst (rho(C),mol/mol), PhCHO/DBT (rho(A), mol/mol), temperature (theta, degrees C), and time (t, min), was examined in terms of standard average and signal-to-noise ratio. Results showed that the sulfur-removal efficiency (RSE) selected as a performance evaluation characteristic was significantly influenced by rho(C) and rho(A) ratios, which achieved 100% under the following predicted optimum factors: rho(C) = 10 mol/mol, rho(A) = 12 mol/mol, theta = 60 degrees C, and t = 90 min. Then, AODS of real HDS diesel fuel with 1511 ppm of total sulfur was run at the optimum factors considering the same O-2/(AP)(5)PWV2/PhCHO system. As a result, the desulfurized oil reached 61 ppm of sulfur, corresponding to 96% RSE. Thus, a satisfactory catalytic performance of (AP)(5)PWV2 was proven, as was its recovery and reuse without loss of activity in five consecutive AODS reaction cycles. Finally, mechanistic and kinetic investigations revealed that the AODS reaction was suggested to proceed via an unbranched radical chain mechanism and followed a first-order kinetic. This finding novelty affords not only a mathematical model to predict the optimum controllable parameters for an efficient green ultradeep AODS process for industrial use but also a prominent alternative to future research concerns of oxidative catalysis applications using V-substituted heteropoly potent catalysts for both fuel oils and real gas condensate.