Some of the products of the catalytic cracking, or cat cracking, unit are the feed stocks for the alkylation, or alky, unit. The gases, or light ends, produced in the cat cracking unit consist partly of olefins. Olefins are valuable because they have a relatively high octane number, but they are also unstable. In addition, the vapor pressure of some of the light end olefins is too high to meet vapor pressure specifications for motor fuel. It is possible to increase the stability and lower the vapor pressure of the olefins while also increasing the octane number. One way to do this is by reacting the
olefins with isobutane. The process designed for this reaction is alkylation.