What is hydrotreating and why is it necessary?

Hydrotreating uses hydrogen to remove sulfur, nitrogen, and metals from petroleum fractions without significantly cracking the molecules. Sulfur forms H2S, nitrogen forms NH3. Operating conditions: 300-400C, 30-100 bar hydrogen pressure, over Co-Mo or Ni-Mo catalyst on alumina support. Also saturates olefins and some aromatics. Necessary because: environmental regulations limit sulfur in fuels (diesel <10 ppm), sulfur poisons downstream catalysts (FCC, reformer), nitrogen and metals also harm catalysts, and product stability improves. Different units for different feeds: naphtha hydrotreater, kerosene hydrotreater, diesel hydrotreater, VGO hydrotreater. Each optimized for feed characteristics and product requirements.