Title : Beneficial effect of glycols on the activity of NiMoP/Al2 O3 hydrotreating catalysts
The sulfided Co(Ni)Mo/Al2 O3 catalysts are widely used in the refineries for hydrotreating process of petroleum distillates. To improve the catalytic activity of the sulfide catalysts in hydrodesulfurization (HDS) reaction different approaches are used. Addition of ethylene glycol (EG), diethylene glycol (DEG) or triethylene glycol (TEG), in particular, to aqueous impregnation solution of the active component precursors of the catalysts on preparation step allows synthesizing more active HDS catalysts. It was supposed that the presence of glycols prevents the interaction between supported active component and alumina, which contributes to the formation of an oxide precursor with a high ratio of Co(Ni)/Mo. In current work the effect of EG, DEG and TEG on the catalytic properties of phosphatedoped NiMo/Al2 O3 catalysts in the hydrotreating of the straight-run gas oil (SRGO) was compared. The NiMo(P)/Al2 O3 catalysts were prepared using ethylene glycol, diethylene glycol and triethylene glycol as additive. The organic agent was introduced into the aqueous impregnation solution obtained by the dissolving of MoO3 in H3 PO4 solution, followed by Ni(OH)2 addition. The support was γ-Al2 O3 in the form of granules with a trefoil-shaped cross section and a size of 1.2 mm (BET surface area 235 m2 g−1, pore volume 0.79 cm3 g−1, average pore diameter 13.4 nm). The Raman and UV–Vis studies show that the impregnation solution contains diphosphopentamolybdate Hx P2 Mo5 O23 (6-x)- and Ni(H2 O)6 2+ and that these ions are not affected by the presence of glycols. When the impregnation solution comes into contact with the γ-Al2 O3 surface Hx P2 Mo5 O23 (6-x)- is decomposed completely.
The catalysts were characterized by Raman spectroscopy, low-temperature N2 adsorption, X-ray photoelectron spectroscopy and transmission electron microscopy. The catalysts contained approximately the same amount of Mo (13.1-13.4 wt.%) with the Ni/Mo molar ratios of 0.4. According to the XPS data Mo dispersion in the terms of Mo/Al ratio is increased after glycol addition in the following order: NiMoP/Al2 O3 < NiMoP-TEG/Al2 O3 < NiMoP-EG/Al2 O3 < NiMoP-DEG/Al2 O3 . The catalytic properties of the NiMoP/Al2 O3 , NiMoP-EG/Al2 O3 , NiMoP-DEG/Al2 O3 and NiMoPTEG/Al2 O3 catalysts were investigated in the hydrotreating of SRGO (from Urals crude oil) in a trickle-bed down-flow reactor at temperature of 330-340°C under hydrogen pressure of 3.5 MPa, H2 /feedstock ratio of 300 Nm3 /m3 with liquid hourly space velocity of 2 h–1 after in-situ sulfidation procedure. The sulfur content in the feedstock and hydrogenated products was measured on a Lab-X 3500SCl energy dispersive X-ray fluorescence analyzer (Oxford Instruments) and on an ANTEK 9000NS analyzer (for products containing less than 100 ppm S). It is shown that the sulfide catalysts prepared with glycols display higher activity in the hydrotreating of SRGO than the NiMoP/Al2 O3 catalyst prepared without the additive. The hydrodesulfurization and hydrodenitrogenation activities depend on the glycol type and are decreased in the following order: NiMoP-DEG/Al2 O3 > NiMoP-EG/Al2 O3 > NiMoP-TEG/Al2 O3 > NiMoP/Al2 O3 . The higher activity of NiMoP-DEG/Al2 O3 can be explained with the higher dispersion of molybdenum on the surface of the catalyst in the sulfided state.
The work was supported by the Ministry of Education and Science of the Russian Federation, project ? 14.575.21.0128, unique identification number RFMEFI57517X0128.
Audience Take Away:
- Addition of glycols to impregnation solution allows creating more active NiMoP/Al2 O3 catalyst in hydrodesulfurization and hydrodenitrogenation reactions due to the improved dispersion of Mo on the surface of sulfide catalysts.
- Both Mo dispersion in the terms of Mo/Al ratio and HDS and HDN activity of catalysts in SRGO hydrotreating are decreased in the following order: NiMoP-DEG/Al2 O3 > NiMoP-EG/Al2 O3 > NiMoP-TEG/Al2 O3 > NiMoP/Al2 O3.
- Preparation of NiMoP/Al2 O3 catalyst using molybdenum (VI) trioxide and nickel (II) hydroxide as precursors of active phase is more environmentally friendly due to the absence of any emissions during heat treatment of the catalyst (for example, using of nickel (II) nitrate as precursor results in NO2 emissions).