Hydrocracking in Petroleum Processing

Abstract

Hydrocracking is a flexible catalytic refining process that can upgrade a large variety of petroleum fractions. Hydrocracking is commonly applied to upgrade the heavier fractions obtained from the distillation of crude oils, including residue. The process adds hydrogen which improves the hydrogen to carbon ratio of the net reactor effluent, removes impurities like sulfur to produce a product that meets the environmental specifications, and converts the heavy feed to a desired boiling range. The chemistry involves the conversion of heavy molecular weight compounds to lower molecular weight compounds through carbon-carbon bond breaking and hydrogen addition. The main products have lower boiling points, are highly saturated, and generally range from heavy diesel to light naphtha. Hydrocracking processes are designed for, and run at, a variety of conditions. The process design will depend on many factors such as feed type, desired cycle length, and the desired product slate. Hydrocracking is a process that is suitable to produce products that meet or exceed all of the present environmental regulations. Hydrocracking reactions proceed through a bifunctional mechanism. Two distinct types of catalytic sites are required to catalyze the steps in the reaction sequence. The cracking and isomerization reactions take place on the acidic support. The acid can be an amorphous silica alumina or a zeolite. The metals provide the hydrogenation function. The metals are typically noble metal (palladium, platinum) or non-noble metal sulfides from group VIA (molybdenum, tungsten) and group VIIA (cobalt, nickel).

Catalyst manufacturing can be done by a variety of methods. The method chosen represents a balance between the manufacturing cost and the degree to which the desired chemical and physical properties are achieved. Many companies are involved in the licensing of the process and the production of a variety of hydrocracking catalysts.