Hydrotreating of oil fractions

Catalytic hydrotreating represents a fundamental process in modern petroleum refining operations. It allows removing hydrocarbon contaminants, such as sulfur, nitrogen, oxygen, and metals, saturating aromatic rings and olefins, and breaking high molecular weight molecules into lighter compounds. Due to its flexibility, the process can be employed to upgrade a variety of petroleum streams, ranging from naphtha to vacuum residues, or even full-range crude oils. Conventional hydrotreating is typically used as a pretreatment step to provide suitable quality feeds for conversion processes, such as reforming, catalytic cracking, and hydrocracking, and also as a finishing step to produce transportation fuels that meet ecological standards. Over the years, hydrotreating has also been gaining acceptance in the primary upgrading of heavy and extra-heavy crude oils to produce the so-called synthetic crudes. Among all the available hydrotreating reactor technologies, fixed-bed reactors are the most frequently used in the petroleumindustry. In such systems, both gas and liquid flow cocurrently down through a catalyst bed in trickle-flow regime. Modeling and simulation of hydrotreating becomes a challenging task due to the complex interaction of numerous physical and chemical processes: vapor-liquid equilibrium, gas-liquid and liquid-solid mass transfer of reactants and products, diffusion inside the catalyst particle, vast reaction networks, and catalyst deactivation. The purpose of this chapter is to provide a comprehensive overview of the hydrotreating process. It covers general aspects such as process chemistry, reaction kinetics, and thermodynamics, but it also presents more process-oriented topics including process variables, reactor characteristics, and reactor modeling and simulation.