Technical term in chemistry and petroleum refining for breaking down large hydrocarbon molecules into smaller ones by heat and pressure, often in the presence of a catalyst.
Cracking is used to produce gasoline from heavy oil.
蒸留 is general distillation; 分解蒸溜法 specifically refers to destructive distillation or cracking where chemical decomposition occurs.
Compound of 分解 (decomposition) + 蒸溜 (distillation) + 法 (method). The spelling 蒸溜 is a variant of 蒸留.