Guard bed catalysts for silicon removal during hydrotreating of middle distillates

Abstract

The influence of textural characteristics of NiMo/Al2O3 on silicon capacity and hydrotreating activity has been investigated so as to develop guard-bed catalyst for silicon removal from middle distillates. Series of NiMo/Al2O3 catalysts with a specific surface area from 150 to 210 m2/g and an average pore diameter from 21.1 to 10.5 nm have been synthesized. The difference in textural characteristics has been achieved by variation of aging time and temperature of hydrothermal treatment of boehmites. The boehmites, supports and catalysts were studied by various physico-chemical methods: XRD, nitrogen adsorption-desorption, IR spectroscopy, UV–vis, 1H NMR, 27Al NMR, XPS, SEM, HRTEM. Catalysts were tested in hydrotreating of diesel fuel contaminated with decamethylcyclopentasiloxane as a model silicon compound. It is shown that the increase in aging time and temperature of hydrothermal treatment of initial boehmites results in the decrease of OH groups concentration per 1 g of an alumina support. The increase of the OH groups content leads to higher silicon capacity, while HDS activity of catalysts decreases. The study of catalysts surface after reaction showed that Si located on a support surface and did not cover directly active component particles. However, its location on the support near edges of active component particles could result in the decrease of HDS activity due to limited accessibility of the active sites.