Page 91 - Synthetic Fuels Handbook

78 CHAPTER THREE

TABLE 3.4 Summary of Hydrocracking Process Operations
Conditions
Solid acid catalyst (silica-alumina with rare earth metals, various other options)
Temperature: 260–450°C (500–842°F) (solid/liquid contact)
Pressure: 1,000–6,000 psi hydrogen
Frequent catalysts renewal for heavier feedstocks
Gas oil: catalyst life up to 3 years
Heavy oil/tar sand bitumen: catalyst life less than 1 year
Feedstocks
Refractory (aromatic) streams
Coker oils
Cycle oils
Gas oils
Residua (as a full hydrocracking or hydrotreating option)
In some cases, asphaltic constituents (S, N, and metals) removed by deasphalting
Products
Lower molecular weight paraffins
Some methane, ethane, propane, and butane
Hydrocarbon distillates (full range depending on the feedstock)
Residual tar (recycle)
Contaminants (asphaltic constituents) deposited on the catalyst as coke or metals
Variations
Fixed bed (suitable for liquid feedstocks
Ebullating bed (suitable for heavy feedstocks)

Hydrotreating. Hydrotreating (Fig. 3.10) is carried out by charging the feed to the reac-
tor, together with hydrogen in the presence of catalysts such as tungsten-nickel sulfide,
cobalt-molybdenum-alumina, nickel oxide-silica-alumina, and platinum-alumina. Most
processes employ cobalt-molybdenum catalysts which generally contain about 10 percent
of molybdenum oxide and less than 1 percent of cobalt oxide supported on alumina. The
temperatures employed are in the range of 260 to 345°C (500–653°F), while the hydrogen
pressures are about 500 to 1000 psi.

Reactor High pressure Stripper
separator
Hydrogen
make-up Hydrogen recycle Fuel gas
Off gas

Unstabilized
light distillate

Feed
Desulfurized product
FIGURE 3.10 A distillate hydrotreater for hydrodesulfurization.