Oxidative coupling of methane over a La₂O₃/CaO catalyst. Optimization of reaction conditions in a bubbling fluidized‐bed reactor

Abstract

Oxidative coupling of methane over a La2O3/CaO catalyst was investigated in laboratory‐scale fluidized‐bed reactors (ID = 5 and 7 cm) in the following range of reaction conditions: T = 700 – 880°C, P CH 4 = 41 – 72 kPa and P O 2 = 6 – 29 kPa. The maximum C2+ selectivity and yield amounted to 73.8% (T = 800°C, X CH 4 = 13.1%, Y C 2+ = 9.7%) and 16.0% (T = 840°C, X CH 4 = 34.0%, S C 2+ = 47.2%), respectively. Axial gas concentration profiles revealed that C2+ selectivity was not only influenced by oxidative consecutive reactions, but also by steam reforming of ethylene. When diluting the catalytic bed (mcat = 145 g) with quartz (m siO 2 = 200 and 400 g), a slight decrease of the selectivity (1–2%) was observed. The dilution of the feed gas with nitrogen only led to only a small increase (< 2%) of the C2+ selectivity.

Reaction Engineering Simulations of Oxidative Coupling of Methane in a Circulating Fluidized-Bed Reactor

“…However, the selectivity of 35.1% at this point is significantly lower than the maximum selectivity of 64.8 % (T = 800 C, CH 4 /O 2 = 10). The predicted dependencies of methane conversion, C 2+ selectivity and yield on temperature and feed-gas composition are qualitatively the same as obtained in the polytropic fixedbed [2] and bubbling-bed reactor [5,31]. The highest yield of Y C2+ = 11.7% which was obtained at CH 4 /O 2 = 3 and T = 800 C is lower compared to the yields obtained in the laboratory-scale fixed-bed (Y C2+,max.…”

Performance of an internally circulating fluidized‐bed reactor for the catalytic oxidative coupling of methane

“…The average attrition rate for the La203/Ca0 catalyst in the ICFB reactor estimated from the difference between the initial mass of the catalytic bed (60 g) and the bed mass after 12 hours of operation amounted to 0.31 g/h. This value is much higher than the entrainment rate (0.02 g/h) in a bubbling fluidized-bed reactor (Mleczko et al, 1996a). The comparison of these two values indicates that mechanical stability of the catalyst might be a serious problem which limits the application of the ICFB reactor.…”

“…a La2031Ca0 catalyst (Mleczko et al, 1996a), a LilSnlMgO catalyst (Santos et al, 1995) or a (Sro 125Mgo.,,5)C03 catalyst (Do et al, 1994), C2+ yields above 15% or even slightly higher have been reported. C2+ selectivities and yields obtained in fluidized-bed reactors were comparable and under certain conditions even better than in fixed beds (Follmer et al, 1988;Do et al, 1995;Mleczko et al, 1996a). However, lower selectivities and yields have also been reported (e.g.…”

“…This material is one of the most active and selective catalysts proposed for the OCM reaction. In experimental studies in a micro-catalytic fixed bed (Becker and Baerns, 1991), in a polytropic fixed bed (Schweer et al, 1994) and in a bubbling fluidized bed (Mleczko et al, 1996a), C , , yields up to 16% were obtained. The reported investigations aimed at elucidation of the optimal hydrodynamic conditions with respect to high C2 selectivity and yield as well as temperature control.…”

Reactor material and gas dilution effects on the performance of miniplant-scale fluidized-bed reactors for oxidative coupling of methane

“…It is important to mention that the reactor scale described in literatures of OCM fluidized-bed reactors using Na-Mn-W/SiO 2 catalytic system so far are smaller than in this study (1200 ml reactor of this study). Mleczko et al studied a fluidized-bed reactor with inner diameter (ID) of 7 cm containing La 2 O 3 /CaO catalyst [15] which is the largest scale of fluidized-bed reactor in open literatures of OCM research. However, their research focused on a reactor with ID of 5 cm [16] and the larger one with 7 cm ID was just reported for concentration of gas in different heights, because gas sampling was easier in a reactor with wider diameter.…”