Technology

Generic Selective Hydrogenation Technology is selected when details about Selective Hydrogenation Technology employed are not available.

The most common Steam Cracker Selective Hydrogenation applications include Acetylenes/Diolefins removal form C₂'s and C₃'s, Vinyl Acetylene and Butadiene Removal from C₄'s and Diolefin Removal from C₅+ Pyrolysis Liquids. 

In the Petroleum Refining industry where gross Hydroprocessing is practised to make cleaner Fuels, the most common Selective Hydrogenation applications are for the removal of Diolefins from either a C₄ or C₅ Olefin stream.

The Catalyst technology applied to the treating of the C₄ and heavier streams is similar if not the same for both industry segments. Even though Base Metal Catalysts are used at times for Selective Hydrogenation, the majority of applications are based around the use of a Palladium Catalyst. 

The most frequently used Reactor System for Selective Hydrogenation applications is a Fixed-Bed system with Hydrogen and liquid always co-current but with flow direction (down-flow vs up-flow) being the major question. Even for the Process in which a substantial exotherm is experienced, a Fixed-Bed Reactor with attendant Product Recycle is preferred over a Tubular Design for its simplicity in loading, in normal operation and in lower initial capital cost. The primary criterion for choosing flow direction in a Selective Hydrogenation Reactor System with liquid and vapour mixed at the Reactor Inlet conditions is gas/liquid molar ratio entering the Reactor System. Intimate mixing of Hydrogen and Reactants at the point of reaction for each level in the Reactor Bed is essential to making the best use of the Palladium Catalyst as well as providing good Two-Phase Flow Distribution.

Source: Ronald G McClung and Steve Novalany, Oct 2002, Choosing a selective hydrogenation system, Digital Refining.