Kinetics of the catalytic hydrogenation of oxygen and its application to a process for deoxygenation of refinery gases
A literature survey shows the detrimental effect of oxygen in refinery gases for various processes, and the need for a deoxygenation process. The present work has been confined to gases containing hydrogen sulfide, as is the case with shale gas. Several of the intermediate or side reactions that are likely to occur have been studied separately and rate equations have been determined, indicating the most probable reaction mechanism. From these results the mechanism of the total reaction including all components has been postulated, and it has been shown that a critical oxygen concentration is likely to ; exist. Below this concentration, water is the i9Utt ^ 7 only reaction product and the life time of the catalyst is very long. Above this concentration, on the other hand, sulfur is formed as a by-product and the catalyst is deactivated by capillary condensation of this sulfur. This hypothesis has been verified by tests with shale gas. Various catalysts have been tested, and it has been shown that a cobalt molybdenum alumina catalyst has outstanding properties. Besides the composition, the pore structure also is important, wider pores giving a higher critical oxygen concentration. The chemical structure of the cobalt molybdenum alumina catalyst is unknown, but preliminary tests have shown that the alumina is not an inert carrier, but forms a part of the active catalyst. Cobalt and molybdenum are probably not adsorbed on the surface of alumina crystallites but are homogeneously distributed. The results have been utilized for a technical process for deoxygenation of shale gas containing 1 — 2 % oxygen in a plant with a capacity of 20 000 m3/h.