COBALT-BASED FISCHER-TROPSCH CATALYST PERFORMANCE IN THE PRESENCE OF NITROGEN AND CARBON-DIOXIDE

A cobalt, thoria, magnesia-on-silica catalyst was investigated for conversion of syngases produced using straight air and oxygen-enriched air from PSA and membrane separation as feeds to a partial oxidation reactor. Additional quantities of nitrogen present were not detrimental to the subsequent FTS with no evidence for the formation of nitrogen-containing by-products, and higher levels of catalyst activity being maintained due to retardation of cobalt sintering. When the syngas contained higher levels of carbon dioxide, selectivity to methane was increased, most probably due to some carbon dioxide hydrogenation. This effect could be reversed by operation at increased pressure which reduced methane selectivity, most probably due to the conversion of some carbon dioxide to carbon monoxide and its subsequent incorporation into the FTS.