Conversion and Processing of Vacuum Gas Oils
Moving to the vacuum distillation column, the vacuum distillates, light vacuum gas oil (LVGO) and heavy vacuum gas oil (HVGO) can be processed by some advanced FCC processes. However, hydrocracking is more frequently used to convert LVGO and HVGO into light and middle distillates, using particular catalysts and hydrogen. Similar to LCO, the LVGO and HVGO fractions from vacuum distillation tend to be highly aromatic. Catalytic hydrocracking combines hydrogenation and cracking to handle feedstocks that are heavier than those that can be processed by FCC, because of excessive coke deposition on the catalyst in the absence of hydrogen. Middle distillates (e.g., kerosene and diesel fuel) are the principal products of hydrocracking. In addition to light and middle distillates, hydrocracking also produces light distillates and LPG, as shown in Figure 3.7.
HVGO can also be used as a feedstock to produce lubricating oil base stock, through a sequence of solvent extraction processes to remove aromatic hydrocarbons by furfural extraction, and to remove long-chain paraffins by dewaxing (Figure 3.8).