ROLE OF 1-BUTYL-3-METHYLIMIDAZOLIUM-HYDROXIDE IN PREVENTING SELECTIVITY LOSS OF ACETYLENE PARTIAL HYDROGENATION OVER PALLADIUM CATALYST

چکیده مقاله

Acetylene acts as a poison in high density grade polyethylene production by Ziegler-Natta catalyst and its removal from ethylene is an essential process. Industrially, the acetylene content can be decreased to less than 5 ppm by hydrogenation which is usually carried out in adiabatic packed bed reactors. Alumina supported catalysts with 0.01-0.1% by weight palladium are mostly used for the selective partial hydrogenation of acetylene in excess ethylene feed [1, 2].One of the important features of palladium catalyst is dissociative chemisorption of the reactants and migration of formed atomic hydrogen and carbon towards the bulk of palladium nanoparticles. Hydrogen absorption in presence of acetylene shows PdHxCn which can be assumed as two distinguishable phases of PdHx and PdCn. The ratio of these two phases alters acetylene hydrogenation rate and selectivity. As the result of subsurface phases formation, the acetylene hydrogenation activity and selectivity over palladium catalysts changes by aging towards higher activity and lower selectivity. Different promoters and additives are investigated to maintain selectivity of commercial catalysts over aging under constant stream and temperature