Catalytic cracking, general conditions

Cracking is effected by one of three general methods thermal cracking, catalytic cracking, or hydrocracking. Each process has its own characteristics concerning operating conditions and product compositions. 

Some other industrial processes are or have been carried out under supercritical conditions even though the fact may not have been generally recognized. For example, McKee and Parker pointed out in 1928 that some oil cracking processes performed industrially at the time occurred above the critical temperature of the reaction mixtures [151]. These processes have since been replaced by lower temperature catalytic cracking methods. Other historical industrial processes which probably involved supercritical phases include the synthesis of melamine [152] from dicyanodiamide, N2 and NH3, and the alkylation of aniline by methanol [152]. 

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