Hydrotreating

Hydrotreating is a refinery process in which petroleum fractions are reacted with hydrogen in the presence of a catalysts to remove sulfur, nitrogen, oxygen, and metals, and to saturate unsaturated hydrocarbons. The main goal is to improve product quality, meet specifications, and prepare feeds for downstream processes such as hydrocracking and catalytic reforming.

Common feedstocks include naphtha, kerosene, diesel, vacuum gas oil, and residual oils. The process uses sulfided transition-metal catalysts, typically molybdenum or tungsten compounds promoted with cobalt or nickel on an alumina-based support (often described as CoMoS or NiMoS catalysts). These catalysts are usually conducted in fixed-bed or slurry configurations, with hydrogen recycled to maintain a reducing environment.

Key reactions include hydrodesulfurization (HDS), converting organosulfur compounds to hydrogen sulfide; hydrodenitrogenation (HDN), removing nitrogen as ammonia; hydrodeoxygenation (HDO), removing oxygen from oxygenates; and hydrogenation or saturation of aromatics to cycloalkanes. Demetallization (HDM) removes metals from heavier feeds at higher severity. Operating conditions vary by feed and target product but generally involve elevated temperatures (roughly 250–400°C) and substantial hydrogen partial pressure (often tens of bar to over 100 bar), with moderate space velocities.

Hydrotreating reduces impurities and stabilizes products, enabling lighter process streams and enabling downstream units. By removing sulfur, nitrogen, and metals, it also lowers corrosion risk and catalyst poisoning in subsequent operations and reduces sulfur emissions in end-use fuels, contributing to environmental compliance. Hydrotreating is usually distinguished from hydrocracking by its emphasis on impurity removal and saturation rather than extensive molecular cracking.