Amorphous Silica-Alumina – Perspective Supports for Selective Hydrotreating of FCC Gasoline: Influence of Mg
FCC gasoline is one of the main components of blending gasoline. The main characteristics are high sulfur content (150-3500 ppm) and high octane numbers (92-93 points) . Hydrotreating of full FCC gasoline fraction on traditional CoMo/Al2O3 catalyst will result in inevitable octane number loss. Maximum permissible octane number loss after hydrotreating has not to exceed 1,5 point. Otherwise, hydrotreating FCC gasoline is ineligible for production of commercial gasoline with octane number more than 95.
There are two main reaction pathways during hydrotreating of FCC gasoline: desulfurization of sulfur compounds and hydrogenation of olefins. The second reaction results in octane number loss. The main problem is that both reactions proceed on the same active sites of CoMoS phase that is the active component of CoMo/Al2O3 catalysts. Investigation of FCC gasoline composition showed that most olefins had terminal double bond . Such olefins have the highest activity in hydrogenation. To decrease their reactivity, it is necessary to isomerize them into branched olefins with internal double bond . It can be achieved by creation of acid sites that differ from acid sites of CoMo/Al2O3 catalyst. One of the ways to achieve this goal is to use amorphous silica-alumina of different composition (for example, with an addition of alkaline metals).
In this paper, we propose catalysts with the supports that contain amorphous silica-alumina (ASA). Influence of ratios of Si/Al in ASA powders and ASA/binding agent in a support was studied. In addition, possibility of Mg addition into ASA and support was investigated. All catalysts were tested in hydrotreating of model fuels. The catalyst with the best activity and selectivity was tested in hydrotreating of FCC gasoline. Finally, it is shown that the catalyst provides the production of gasoline containing less than 10 ppm of sulfur with minimum octane loss (<1,5 point).