Reaction Kinetics of MoCo/Al2O3-Meso-ZSM-5 Catalyst for Ultra-Deep Hydrodesulfurization of Diesel Fuel

Series of Mo-Co type catalysts were supported on Al2O3, Al2O3-meso-ZSM-5-Al2O3-typical-ZSM-5 and tested in the hydrodesulfurization (HDS) of straight-run diesel feedstocks. The materials were characterized by N2 physisorption, X-ray diffraction, scanning electron microscopy, NH3 adsorption and temperature-programmed desorption, and Py-adsorbed IR spectra. The dynamics of the main steps in the HDS reaction were calculated, and seven lumped kinetic equations were established containing reaction pathways of hydrogenation (HYD), direct desulfurization (DDS) and alkyl transfer on the catalyst. The Levenberg-Marquardt (LM) algorithm method was used then to solve the resulting differential equations. The results showed that the HDS activity of C12-ZSM5 was highest because it had large VP and DP, and moderate acid content, which could improve the alkyl transfer activity and the macromolecular sulfide diffusion. By increasing the operating temperatures, the sulfur removal through the alkyl transfer route on C12-ZSM5 catalyst significantly increased, and the removal of sulfur content through alkyl transfer at 400 °C and 4.0 MPa or 6.0 MPa was 86 or 88%, respectively. Furthermore, the increase of sulfur removal confirmed that the alkyl transfer route was dominant at a deep HDS level at a high operating temperature.