In general, refineries aim to maximize the amount of gasoline produced. To accomplish this, a number of processes have been created to convert other kinds of hydrocarbons into gasoline. For example, cracking takes the long carbon chains of heavy gas oil and breaks them into shorter-chain hydrocarbons, including gasoline.
The kind of cracking process used will determine the mix of end products. Fluid catalytic cracking yields mostly gasoline and diesel, as well as some light gases. Hydrocracking yields kerosene instead of diesel.
Fluid catalyst - As the name implies, fluid catalytic cracking uses a free-flowing catalyst to help break apart molecules of heavy gas oil. The catalyst is actually a fine, slick powder that causes bonds within the hydrocarbon chain to snap. Once the process is complete, the contents of the reaction chamber are spun into a cyclone that separates the heavier catalyst from the lighter hydrocarbons so that the catalyst can be reused.
Hydrocracking - This process uses hydrogen and pressure combined with a solid catalyst to break apart longer hydrocarbon chains. Because the catalyst is fixed in place, there is no need for an additional step to separate the catalyst from the cracked product.
Hydrogen not used in the cracking process is cycled back through the system. This is just one example of the efficient reuse of resources within the refinery.»next