Oxidative desulfurization of a model fuel using MoO3 nanoparticles supported on carbon nanotubes catalyst: Examine most significance variables, optimization, kinetics and thermodynamics study

Abstract

Molybdenum oxide nanoparticles MONP were dispersed on multiwall nanotubes MWNTs as an attempt to synthesize MONP/MWNTs catalyst, the synthesis method done by wet impregnation. The prepared catalyst was characterized by FTIR (Fourier –Transform Infrared Spectroscopy) and, XRD (X-ray diffraction), whilst the catalyst activity is done with catalytic oxidative desulfurization ODS reaction for oxidation dibenzothiophene DBT dissolved in heptane (model fuel) with hydrogen peroxide H2O2, in which catalyst activity investigation achieved via studying impact six from most affected variables on ODS reaction. The chosen variables are reaction temperature, contact time, sulfur initial sulfur concentration, stirring speed, oxidant/sulfur ratio and catalyst dosage, and then the studied variables were screened by application of Plackett-Burman design PBD to identify the more significant on response (DBT pollutant removal). DBT pollutant removal is referred to as sulfur removal efficiency. Analysis of variance ANOVA shows that the reaction temperature, oxidant/sulfur ratio, stirring speed, and sulfur initial concentration are the most significant from the chosen variables due to their F-values 37.60, 25.45, 11.62 and 6.71 respectively. Box –Behnken experimental design was used to complete the study the effect of the most significant more deeply on ODS reaction (sulfur removal efficiency),in which this part exhibited that sulfur removal efficiency at range between 51 and 93%, whilst the optimum sulfur removal efficiency was 96% at 70 °C,4.36, 957 rpm and 50 ppm for reaction temperature, oxidant/sulfur ration, stirring speed and initial sulfur concentration respectively. The study involves estimation of kinetics and thermodynamics parameters for ODS reaction; kinetics studying exhibited that ODS reaction followed pseudo-first-order reaction with activation energy (12.996 kJ/mol), while the thermodynamics study shows the low negative entropy change (-0.221 kJ /mol.K), positive enthalpy and free energy changes which confirm a high hydrate transition complex was formed.