ABSTRACT
The hydrocracking processes described in the literature are designed to upgrade a variety of petroleum feedstocks, such as vacuum gas oils, straight run gas oils, coker gas oils, deasphalted oils, FCC cycle oils, thermally cracked stocks, straight run and cracked naphthas, by adding hydrogen and cracking to a desired boiling range. The particular products are liquefied petroleum gas (LPG), light naphtha, heavy naphtha, jet fuel, diesel fuel, heating oil, petrochemical feedstocks, FCC feedstock, ethylene cracker feedstock, and lube oil base stock. Hydrogen addition is accomplished by a metal function on the hydrocracking catalyst. The catalyst adds hydrogen to organic sulfur, nitrogen, and oxygen compounds to form H2S, NH3, and H20, respectively. In addition, the catalyst saturates olefins and multiring aromatics. Part of the hydrogen addition function of the hydrocracking process is sometimes done in a separate reactor with hydrotreating catalyst. Cracking is accomplished by an acidic catalyst function. In general, the cracking catalyst function selectively converts high-boiling hydrocarbons to products in the desired boiling range of naphtha, jet fuel, or diesel fuel. The product boiling range can be controlled by a combination of process variables and catalyst modifications. The following parameters determine product distribution:
1. Process configuration (i.e., single-stage, two-stage, once-through, etc.) 2. Feed/recycle ratio 3. Fractionation cut point 4. Conversion level 5. Catalyst type
In general, the hydrocracking process operating conditions are: 300-450°C (570-840°F) catalyst bed temperature, 85-200 bar (1250-2915 psi) pressure, 0.5-2.5 hr-1 liquid hourly space velocity, 505-1685 nm3/m3 (3000-10,000 scf/b) hydrogen-to-oil ratio, 200-590 nm3/m3 (1200-3500 scf/b) hydrogen consumption. Due to high hydrogen partial pressures and the use of dual function catalysts, the rate of catalyst coking and deactivation is very low, resulting in on-stream cycle lengths of several years.
