TABLE OF CONTENTS Conversion processes in the petroleum industry are generally used to:
Upgrade lower-value materials such as heavy residues to more valuable products such as naphtha and LPG. Naphtha is mainly used to supplement the gasoline pool, while LPG is used as a fuel or as a petrochemical feedstock.
Improve the characteristics of a fuel. For example, a lower octane naphtha fraction is reformed to a higher octane reformate product. The reformate is mainly blended with naphtha for gasoline formulation or extracted for obtaining aromatics needed for petrochemicals production.
Reduce harmful impurities in petroleum fractions and residues to control pollution and to avoid poisoning certain processing catalysts. For example, hydrotreatment of naphtha feeds to catalytic reformers is essential because sulfur and nitrogen impurities poison the catalyst.
Conversion processes are either thermal, where only heat is used to effect the required change, or catalytic, where a catalyst lowers the reaction activation energy. The catalyst also directs the reaction toward a desired product or products (selective catalyst).
Thermal cracking was the first process used to increase gasoline production. After the development of catalytic cracking, which improved yields and product quality, thermal cracking was given other roles in refinery operations. The three important thermal cracking techniques are coking, viscosity breaking, and steam cracking.
Steam cracking is of special importance as a major process designed specifically for producing light olefins. It is discussed separately later in this chapter.
Coking is a severe thermal cracking process designed to handle heavy...
