3.2 Petrochemical processing

Following distillation of petroleum into the major fractions (gasoline C₅ up to 95 °C, naphtha 75–175 °C, kerosine 175–225 °C), the naphtha cut is subjected to cracking to yield smaller, double bonded molecules. The reaction is conducted at high temperatures (400–800 °C), but under low pressure using steam for cracking. This process can yield monomers directly, such as ethylene (C₂), propylene (C₃) and butadiene (C₄), but often further reactions are required to add other elements such as oxygen and chlorine. Since cracked naphthas are complex mixtures, expensive separation procedures are needed for the co-products.