What is hydrocracking and how does it differ from FCC?

Hydrocracking cracks heavy hydrocarbons in the presence of hydrogen and catalyst. Operating conditions: 350-450C, high pressure (100-200 bar), with bifunctional catalyst (acid and metal functions). Products: naphtha, jet fuel, diesel - high quality with low sulfur and aromatics. Differences from FCC: higher hydrogen consumption but better product quality, more flexible feed processing (can handle poor quality feeds), produces more middle distillates (jet, diesel) vs. gasoline, operates at high pressure with hydrogen, no coke production (hydrogen prevents coking). Hydrocracking is preferred when maximizing diesel/jet production and processing heavy or high-sulfur feeds. Higher capital and operating cost than FCC.