This chapter explores catalytic reforming and isomerization. Catalytic reforming of heavy naphtha and isomerization of light naphtha constitute a very important source of products having high octane numbers, which are key components in the production of gasoline. Environmental regulations limit on the benzene content in gasoline. If benzene is present in the final gasoline it produces carcinogenic material on combustion. Elimination of benzene forming hydrocarbons, such as hexane will prevent the formation of benzene, and this can be achieved by increasing the initial point of heavy naphtha. These light paraffinic hydrocarbons can be used in an isomerization unit to produce high octane number isomers. Catalytic reforming is the process of transforming C₇–C₁₀hydrocarbons with low octane numbers to aromatics and iso-paraffins which have high octane numbers. It is a highly endothermic process requiring large amounts of energy. The process can be operated in two modes: a high severity mode to produce mainly aromatics (80–90 vol%) and a middle severity mode to produce high octane gasoline (70% aromatics content). Isomerization is a mildly exothermic reaction and leads to the increase of an octane number. It is a process in which light straight chain paraffins of low RON (C₆, C₅, and C₄) are transformed with proper catalyst into branched chains with the same carbon number and high octane numbers.

This chapter explores thermal cracking and coking in the process of petroleum refining. Thermal cracking is the cracking of heavy residues under severe thermal conditions. The liquid products of this process are highly olefinic, aromatic, and have high sulfur content. They require hydrogen treatment to improve their properties. Coking is the process of carbon rejection from the heavy residues producing lighter components lower in sulfur, since most of the sulfur is retained in the coke. The thermal treatment of hydrocarbons follows a free radical mechanism where cracking reactions take place in the initiation step. The reactions in the final step result in the formation of heavy fractions and products like coke. There are three classes of industrial thermal cracking processes. (1) Mild cracking (as in visbreaking) in which mild heating is applied to crack the residue just enough to lower its viscosity and also to produce some light products; (2) Delayed coking in which moderate thermal cracking converts the residue into lighter products, leaving coke behind; (3) The final process involves severe thermal cracking: part of the coke is burned and used to heat the feed in the cracking reactor, as in fluid coking. In other version of the process, steam is used to gasify most of the coke (flexicoking).

Hydroconversion is a term used to describe all different processes in which hydrocarbon reacts with hydrogen. It includes hydrotreating, hydrocracking, and hydrogenation. The term hydrotreating is used to describe the process of the removal of sulfur, nitrogen, and metal impurities in the feedstock by hydrogen in the presence of a catalyst. Hydrotreating units are needed in the refinery to clean streams from material such as sulfur, nitrogen, or metals harmful to the catalysts. That is why they are located before the reformer, hydrocracker and fluidized catalytic cracking. They are also needed to adjust the final product specification for various streams, such as light naphtha, kerosene and low sulphur fuel oils. Hydrocracking is the process of catalytic cracking of feedstock to products with lower boiling points by reacting them with hydrogen. Hydrocracking is a catalytic hydrogenation process in which high molecular weight feedstocks are converted and hydrogenated to lower molecular weight products. The catalyst used in hydrocracking is a bifunctional one. It is composed of a metallic part, which promotes hydrogenation, and an acid part, which promotes cracking. Hydrogenation removes impurities in the feed such as sulphur, nitrogen, and metals. It is used when aromatics are saturated by hydrogen to the corresponding naphthenes. Cracking will break bonds, and the resulting unsaturated products are consequently hydrogenated into stable compounds. Furthermore, the use of the hydroconversion technique depends on the type of feedstock and the desired products.