Hydroprocessing Units Similarities and Differences

As shown in Table 2, the extent of conversion is the most significant difference between hydrotreating and hydrocracking. In this context, the term conversion is defined as the difference in amount of unconverted oil between feed and product divided by the amount of unconverted oil in the feed. Unconverted oil is defined as material that boils above a specified temperature. For vacuum gas oil (VGO), a typical specified temperature is 650°F (343°C). Conversion in hydrotreaters is less than 15 wt%, while conversion in hydrocrackers and mild hydrocrackers exceeds 20 wt%. 

332°C) generates biphenyl (492.6°F, 255.9°C). This reaetion does not break any carbon-to-earbon bonds, but it does convert a molecule that boils above 600°F (315.5°C) into one that boils below 600°F (315.5°C). 

In hydrotreaters, conversion due to the removal of sulfur, nitrogen and oxygen usually is less than 15 wt%. 

HGO = heavy gas oil HCO = FCC heavy cycle oil VBGO = visbreaker gas oil CGO = coker gas oil 

Hydrotreating and hydrocracking differ in other ways. For a given amount of feed, hydrocrackers use more catalyst and operate at higher pressures. They also use different catalysts. Because they make large amounts of light products, hydrocracker fractionation sections must be more complex. In some hydrocrackers, unconverted oil from the fiactionation section is recycled, either back to the front of the unit or to a separate cracking reactor. 

---