hydrodemetallization

Hydrodemetallization (HDM) is a petroleum refining process that removes metallic contaminants, primarily nickel and vanadium, from heavy feedstocks through catalytic hydrogen treating at elevated temperature and pressure. The goal is to reduce metals levels in the oil before downstream processing, protecting catalysts used in desulfurization and cracking and improving overall upgrading performance.

HDM is carried out in hydroprocessing units that typically use sulfided NiMo or CoMo catalysts on supports such as alumina. The feeds are contacted with hydrogen under high pressure, at temperatures generally in the 350–420 C range and under substantial hydrogen partial pressures. The process is often operated in fixed-bed reactors in one or more zones and is commonly integrated with other hydroprocessing steps, such as desulfurization and denitrogenation.

Mechanistically, metal-containing compounds in heavy feeds (including porphyrin complexes and metal-bearing asphaltenes) are broken down under hydrogenation conditions. The metallic elements are converted into metal sulfides and tend to deposit on the catalyst, contributing to the deactivation of sites. A portion of metals may also be removed as solids that are carried away with the hydroprocessed products, though most metals are retained within the spent catalyst matrix. Effective HDM reduces the metal loading of the feed entering downstream units and mitigates catalyst poisoning in subsequent hydrocracking and desulfurization steps.

Applications and significance: HDM is used to upgrade high-metal-content residues and viscous feeds from various crude sources, making them more processable and less prone to fouling or rapid deactivation of downstream catalysts. It is commonly performed in conjunction with other hydroprocessing steps as part of resid upgrading strategies.

See also: hydrodesulfurization, hydrodenitrogenation, hydrocracking, resid upgrading.