An experimental study of multilayered composite palladium membrane reactors for partial oxidation of methane to syngas

Abstract

Today only a small percentage of methane is used as a chemical feedstock to produce syngas that is a valuable feedstock for the production of higher hydrocarbons or methanol. Currently, the process extensively used in industry for the production of syngas is the steam reforming of methane in large furnaces. The reaction is industrially operated under strong conditions resulting in several undesirable consequences: sintering of the catalyst, danger of explosion, very high carbon deposition and the use of high-temperature resisting materials. A potential alternative technique to steam reforming processes for producing syngas is the partial oxidation of methane with oxygen, having over steam reforming the disadvantage that pure oxygen is required. Utilisation of air instead of pure oxygen is beneficial only if it can be performed by using a membrane reactor in which the membrane is permselective to oxygen. Another route to produce syngas using the partial oxidation of methane is offered by membrane reactors, i.e. engineering systems that combine the separation properties of membrane with the typical characteristics of catalytic reactions. It is well known that the use of dense palladium as membrane enables hydrogen product to permeate out through the membrane, shifting thereby conversions towards the values higher than thermodynamic equilibrium ones and providing pure hydrogen product. In fact, only hydrogen is allowed to permeate through dense palladium membranes. In this work five reactors are investigated with respect to the partial oxidation of methane. In particular, the performance of a traditional reactor (TR), three composite ceramic palladium membrane reactors (MRa, MRb and MRc), and a dense palladium membrane Reactor (PMR), all having the same geometrical dimensions and using the same Ni-based catalyst, are evaluated in terms of experimental results of methane conversion to syngas and in terms of hydrogen selectivity. A comparison between methane conversion at various temperatures and data in literature is also presented.