Oxidative coupling of methane in a bubbling fluidized bed reactor

Abstract

The oxidative coupling of methane to higher hydrocarbons (C2+) was studied in a bubbling fluidized bed reactor between 700°C and 820°C, and with partial pressures of methane from 40 to 70 kPa and of oxygen from 2 to 20 kPa; the total pressure was ca 100 kPa. CaO, Na2CO3/CaO and PbO/γ‐Al2O3 were used as catalytic materials. C2+ selectivity depends markedly on temperature and oxygen partial pressure. The optimum temperature for maximizing C2+ selectivity varies between 720 and 800°C depending on the catalyst. Maximum C2+ selectivities were achieved at low oxygen and high methane partial pressures and amounted to 46% for CaO (T = 780°C; PCH4 = 70 kPa; PO2 = 5 kPa), 53% for Na2CO3/CaO (T = 760°C; PCH4 = 60 kPa; PO2 = 6 kPa) and 70% for PbO/γ‐Al2O3 (T = 720°C; PCH4 = 60 kPa; PO2 = 5 kPa). Maximum yields were obtained at low methane‐to‐oxygen ratios; they amounted to 4.5% for CaO (T = 800°C; PCH4 = 70 kPa; PO2 = 12 kPa), 8.8% for Na2CO3/CaO (T = 820°C; PCH4 = 60 kPa; PO2 = 20 kPa) and 11.3% for PbO/γ‐Al2O3 (T 2= 800°C; PCH4 = 60 kPa; PO2 = 20 kPa).

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

“…In comparison to catalysts investigated in previous studies e.g. PbO/y-A1203, CaO, Na203/Ca0, NaOH/CaO and Na2S04/Ca0 (Andorfet al, 1991;Baerns et al, 1993;Andorf and Baerns, 1991), high selectivities to H2 (SHz I 42%) and high CO/CO, ratios (CO/CO, I 0.39) were observed. H2 selectivity was calculated as the proportion of molecular H2 to total amount of hydrogen abstracted from the reacted methane.…”

“…Among various catalysts exhibiting high C2+ selectivities La2O3/CaO seems to be very promising for large scale operation of the OCM reaction due to its favourable catalytic and mechanical properties. Similarly as in micro-catalytic fixed-bed reactors higher yields were obtained compared to PbO/y-Alz03, CaO and NaOH/CaO which were investigated previously (see Andorf et al, 1991). The highest C2+ yield of 16% belongs to the highest values reported in the open literature for well fluidizable catalysts and an undiluted feed (PcH 2 60 kPa; for review see Mleczko and Baerns, 1995).…”

“…The effect of the bed dilution with an inert material on C2+ selectivity and yield was tested by adding quartz particles. In the previous studies (Andorf and Baerns, 1991) quartz was found to be inert for the OCM reaction. In order to minimize the effect of the dilution on hydrodynamics of the fluidized-bed, particles with the same diameter as the catalyst were applied.…”

“…However, in some cases lower selectivities were reported (Edwards et al, 1990). Moreover, not all selective OCM catalysts were fluidizable (Baerns et al, 1993;Andorf and Baerns, 1991;.…”

“…In a preceding paper (Andorf et al, 1991) the results obtained in a bubbling-bed reactor using PbOly-Al203, NazC03/Ca0 and CaO catalysts were reported. Some *Author to whom correspondence should be addressed.…”