Thermodynamics of hydroprocessing reactions

Cleaner fuels are vital in combating air pollution from automobile emissions. Legislation is being enacted in many countries mandating stringent sulfur and aromatics specifications for transportation fuels. One of the most versatile options to produce cleaner fuels is hydrotreating, and its role has been pivotal. Although hydrotreating has always been an important part of refinery operations, its role has been to remove objectionable elements such as sulfur and nitrogen from products of feedstocks by reacting them with hydrogen. In the past decade, hydrotreating capacity in the world refineries has been increasing at a steady rate as a response to the following three factors: (1) increasingly stringent environmental requirements for clean-burning fuels; (2) strong demand for transportation fuels and decreased demand for heavy fuel oil; and (3) the increased share of heavy and sour crudes (Ali, 1997). As a result, hydrotreating applications in refineries include a variety of streams, such as naphtha, light and heavy gas oils, and resids. These developments have brought hydrotreating to a level of economic importance matching catalytic cracking and reforming. Newer applications of hydrotreating include fluid catalytic cracking feed pretreatment, naphtha desulfurization and olefin saturation, deep desulfurization and dearomatization of straight-run and other middle distillate streams, and catalytic reformer feedstock pretreatment to obtain ultra-low-sulfur naphtha.