Deep hydrodesulfurization of gas oils with high sulfur content: Experiment and kinetic modeling

Abstract

The hydrodesulfurization of straight-run gas oils (SRGO-HS) with high content of sulfur (about 2 wt%) and its mixture with light coker gas oil (CGO) has been studied over CoMo/Al2O3 catalyst using a trickle bed down-flow reactor at the 335–365 °C, H2/HC − 300 Nm3/m3, LHSV − 0.8–2.5 h−1 and 3.5–5.1 MPa. The possibility of ultra-low sulfur diesel (<10 ppmS) production using feedstocks with sulfur content exceeding 2 wt% was demonstrated under conditions simulating industrial one. To predict the effect of process parameters on the amount of sulfur in products four kinetic models with different insight into the reactivity of individual S-containing compounds were considered. The first model is simplified kinetics based on power law rate equations, taking into account overall sulfur content, the second group includes LHHW type rate equations. The models 3 and 4 take into consideration the difference in the reactivity of sulfur-containing components. Model 3 classifies the total sulfur into two subgroups Se (easy reactive compounds) and Sr (refractory sulfur compounds - dibenzothiophene and its derivatives). In Model 4 the group Sr is divided into three more subgroups. Kinetic rate parameters i.e. frequency factors, apparent activation energies, and adsorption enthalpies, were estimated by fitting the experimental data obtained using the SRGO-HS/CGO feedstock to the models. All kinetic models predicted the experimentally determined conversions of sulfur with a relatively good accuracy (±20%). The kinetic models were verified by comparing the simulation results with the experimental data obtained using the other oil fractions (SRGO-LS) with lower content of sulfur (1.05 wt%). A better agreement was observed between the experiments and prediction by models 3 and 4.