Guy Desgrandchamps

A kinetic study of the oxidative coupling of methane over a BaCO3 / La2On(CO3)3-n catalyst: I. Determination of a global reaction scheme and the influence of heterogeneous and homogeneous reactions

Abstract It is shown that ethane is a primary, while ethylene is a secondary OCM product. CO and CO2 are primary products from each of these hydrocarbons. The surface of the BaCO3/La2On(CO3)3-n catalyst initiates the reactions of both CH4, C2H6 and C2H4 with oxygen, and is active for CO2 and H2O formation. However, at higher temperatures, gas phase reactions are of increasing importance for the product distribution, and at 800°C, the conversion of C2H6 and C2H4 with oxygen is equally rapid without a catalyst. C2H6 and, especially, C2H4 are more easily oxidized than CH4. The catalyst surface is the main source for CO2 formation, while CO is formed mainly in the gas phase. The kinetic parameters corresponding to each of the reactions in the OCM scheme have been determined. It has been shown that secondary reactions are of little importance when starting from a CH4/O2/Inert feed at 680°C. However, at 720°C a significant part of the oxidation products are formed via secondary oxidation of ethane and ethylene. The primary C2 selectivity was found to increase with increasing temperature.

A comparative study of coprecipitated BaCO3/La2On(CO3)rn catalysts for the oxidative coupling of methane

Abstract Coprecipitated catalyst systems containing BaCO3 and La2On(CO3)m (n≥1.5) with La/Ba = 0.05-10 were tested for catalytic activity, selectivity and stability in the oxidative coupling of methane reaction (OCM). Maximum C2+ selectivities of 78% and C2+ yields of 11% were obtained. The results show that La is the more active cation component of the system. The presence of BaCO3 in the system leads to decreasing crystal size of the La phases, and to higher C2+ selectivities at equal methane conversions. Life time tests showed that the Ba- La-containing catalysts were quite stable. Na impurities in the system lead to larger crystals in the La phases, and to less selective and less stable catalysts for the OCM reaction. Na is lost during reaction.

Oxidative coupling of methane - Ageing tests of a La-Sr catalyst

Abstract Ageing tests of a La-Sr based catalyst have been performed at 870°C, at different apparent contact times, with a feed of the same composition. They show that this catalyst deactivates only very slightly with time on stream. The most sensitive indicator for an ageing phenomenon is the oxygen conversion. Apparently the rate of ageing is so higher as the contact time is shorter. The explanations for this result are based on a first order relationship for the oxygen conversion.