LOW METHANE SELECTIVITY USING CO/MNO CATALYSTS FOR THE FISCHER-TROPSCH REACTION - EFFECT OF INCREASING PRESSURE AND CO-FEEDING ETHENE

CO hydrogenation using cobalt/manganese oxide catalysts is described and discussed. These catalysts are known to give low methane selectivity with high selectivity to C-3 hydrocarbons at moderate reaction conditions (GHSV < 500 h(-1), < 600 kPa). In this study the effect of reaction conditions more appropriate to industrial operation are investigated. CO hydrogenation at 1-2 MPa using catalyst formulations with Co/Mn = 0.5 and 1.0 gives selectivities to methane that are comparable to those observed at lower pressures. At the higher pressure the catalyst rapidly deactivates, a feature that is not observed at lower pressures. However, prior to deactivation rates of CO + CO2 conversion > 8 mol/l-catalyst h can be observed. Go-feeding ethene during CO hydrogenation is investigated by the reaction of (CO)-C-13-(C2H4)-C-12-H-2 mixtures and a significant decrease in methane selectivity is observed but the hydrogenation of ethene is also a dominant reaction. The results show that the co-fed ethene can be molecularly incorporated but in addition it can generate a C-1 species that can react further to form methane and higher hydrocarbons.