The effect of dilution of the catalyst bed on its heat-transfer characteristics in oxidative coupling of methane

The dilution of the catalyst bed was tested as one of the possible ways to improve the heat-transfer characteristics of a fixed-bed catalytic oxidative coupling of methane. The small-scale and scaled-up laboratory units with silica and stainless-steel reactors were applied. Both the temperature profiles and product concentrations profiles along the catalyst beds were determined. It was demonstrated that the process proceeds practically to its end in the peak area. Applying Li/MgO as a catalyst and varying the amounts of quartz chips or α-Al₂O₃ as diluents, it was observed that the dilution with limited amounts of diluent led to the lower and wider local temperature peaks (hot-spots) moved towards the exit from the bed. No changes in the conversions, selectivity and yields were observed at short time on stream. The dilution of the catalyst bed makes the heat removal easier and the catalyst bed more effectively used. The important requirement for the diluent should be its inertness towards both the reactants and the catalyst. It was confirmed that the presence of quartz stimulated the deactivation of Li/MgO, whereas a fused α-Al₂O₃ was shown to be almost inactive during several hours.