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.
Oxidative coupling of methane to C2+ hydrocarbons
over a Zr/La/Sr catalyst was investigated in
an atmospheric-pressure shallow fluidized-bed reactor (i.d. = 5 cm;
H
mf = 1.4−3.2 cm) at
temperatures between 800 and 880 °C. The catalyst was
mechanically and catalytically stable,
but its fluidizability was limited; agglomeration and channeling
occurred. The highest C2+ yield
amounted to 18.0% (X
CH
4
= 36.5%, S
C
2+
=
49.4%) and 17.2% (X
CH
4
= 36.6%, S
C
2+
=
46.9%) for the
diluted (p
O
2
= 17 kPa,
p
CH
4
= 41.5 kPa,
p
N
2
= 41.5 kPa) and
undiluted feed (p
O
2
=
28 kPa,
p
CH
4
= 72 kPa), respectively. These yields are among the highest ones
reported in the open literature
for OCM in fluidized beds. In the whole investigated temperature
range higher selectivities
and yields were obtained upon reducing partial pressures of methane and
oxygen but keeping
their ratio constant
(p
CH
4
/p
O
2
= 2.5). An increased gas velocity (from
u/u
mf = 6 to 10) or
bed
height (from 1.4 to 3.2 cm) resulted in a drop of C2+
selectivity.
The catalytic oxidation of fluorene to 9-fluorenone in a fluidized-bed reactor was investigated by modeling of the reactor and simulation of its performance. The "Bubble Assemblage Model" of Kato and Wen, the "Bubbling Bed Model" of Kunii and Levenspiel and the "Countercurrent Backmixing Model" of Potter were applied. From a comparison of simulation results obtained by the various fluidized-bed models and a fixed-bed model conclusions were drawn about the influence of interphase mass transfer and gas backmixing on the conversion of fluorene and selectivity of 9-fluorenone formation. Furthermore, the dependence of conversion and selectivity on temperature and hydrodynamic conditions was investigated. In particular, the implications of a change of hydrodynamic conditions for scale-up were analysed. The highest yield of 9-fluorenone predicted for a bench-scale fluidized bed amounted to 88% (XF = 97v0, SNON = 91 Yo). This yield was lower than in a fixed-bed reactor ( YNON = 92%, XF = 99%, SNON = 93%). A further drop of the yield was predicted when scaling-up from a bench-scale reactor to a commercial size unit ( Y N o N = %YO, XF = 86%, SNON = 63%).
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