Catalytic dehydrogenation of hydrocarbons in palladium composite membrane reactors

Different methods for the preparation of hydrogen permselective palladium composite membranes on asymmetric ceramic and porous stainless-steel tubes were tested. Electroless plating, electroplating, chemical and physical vapor deposition, as well as high velocity oxy-fuel spraying were investigated. Electroless plating was confirmed to be a suitable method for coating ceramic supports. Promising methods for the preparation of composite palladium-steel membranes are high velocity oxy-fuel spraying and a combined method of electroplating and electroless plating. Successfully coated membranes were employed for hydrogen separation in lab-scale membrane reactors during,the dehydrogenation of ethylbenzene to styrene and propane to propylene. In both cases, the removal of hydrogen significantly increased the olefin yield, as compared to the corresponding conventional packed-bed reactor results. A relative increase of styrene: yield above 15% was observed using a palladium-ceramic membrane. The relative increase of propylene yield was close to 18% for the same type of membrane. Employing a stainless steel-based membrane even further increased the yield of propylene. However, in contrast to the virtually defect-fret ceramic-based membranes, a certain amount of other components passed the palladium-steel membrane along with hydrogen, amounting to roughly 20% of the total exit gas flow. (C) 2000 Elsevier Science B.V. All rights reserved.