41 C Cracking(裂解) When a mixture of alkanes from the gas oil C12 and higher) fraction is heated at very high temperatures(--500oC)in the presence of a variety of catalysts, the, the molecules break apart and rearrange to smaller, more highly branched alkanes containing 5-10 carbon atoms. This process is called catalytic cracking(催化裂解). Cracking can also be done in the absence of a catalyst- called thermal cracking(热裂解)4.1 C Cracking (裂解） When a mixture of alkanes from the gas oil (C12 and higher) fraction is heated at very high temperatures (--500 oC) in the presence of a variety of catalysts, the, the molecules break apart and rearrange to smaller, more highly branched alkanes containing 5-10 carbon atoms. This process is called catalytic cracking (催化裂解）. Cracking can also be done in the absence of a catalyst--- called thermal cracking (热裂解）