What the fuck? I'm pretty smart, but I have zero knowledge on this thing.
For fixed-bed hydrocracking units, proper feedstock preparation is necessary to minimize catalyst poisoning and give high yields and a long catalyst life. Many hydrocracking units use a hydrotreating reactor before the hydrocracking reactors to convert organic sulfur and nitrogen compounds to hydrogen sulfide and ammonia to prevent reduction of hydrocracking catalyst activity and deterioration of yield structure. During a run, the reactor temperatures are gradually increased to maintain a constant severity of operation (constant degree of sulfur or nitrogen removal or constant conversion level). Increasing the reaction temperature increases the cracking rates faster than the hydrogenation rates, and more of the feed is cracked to gases and coke. This results in lower yields of desirable products and less profitable operations.