Hydroprocessing of heavy petroleum feeds: Tutorial

Abstract

The world wide trends in crude oil supply indicate a declining availability of conventional crudes, which has been offset by increasing volume of heavy crudes. For the latter, the yield of liquid fractions can be increased by upgrading the distillation residues. A number of thermal processes (e.g., visbreaking, delayed-, fluidand flexi-coking), so-called carbon rejecting processes, have been used on a commercial scale for several decades [1,2]. Heavy feeds can also be upgraded by hydroprocessing, so-called hydrogen addition option [3,4]. This requires the presence of hydrogen and an active catalyst. Compared with thermal processes, hydroprocessing operations are more flexible, giving higher yields of liquid fractions. An optimum of hydroprocessing operation can be achieved by properly matching the type of reactor and catalyst with the properties of heavy feeds. Several types of catalytic reactors, i.e., fixed-, movingand ebullated-bed reactors are available commercially. In spite of some similarities, hydroprocessing of heavy feeds differs markedly from that of light feeds. This results from the presence of high molecular weight asphaltenic molecules and organometallic compounds in the former. Then, the catalyst design has to take this fact into consideration. Special attention has to be paid to the textural properties of catalysts, such as pore diameter and pore volume. These parameters have to be optimized to ensure adequate surface area. The size and shape of catalyst particles are important for the efficient operation as well. An active catalyst for hydroprocessing of heavy feeds has to be resistant to deactivation by coke and metal deposits.