The oxidative coupling of methane with cofeeding of ethane

Abstract

The oxidative coupling of methane with cofeeding of ethane was investigated experimentally both in the absence and in the presence of a Sn/Li/MgO catalyst. Cofeeding ethane in the absence of catalyst results in a higher total radical concentration, explaining the strong increase of the observed feed conversions. The hydrogen-peroxy radical-concentration increase is more pronounced than the corresponding methyl radical concentration increase, resulting in a lower selectivity. The combined effect of feed conversion and selectivity is beneficial for inlet ethane-to-methane ratios lower than 4 mol%. Ethane cofeeding results in a slight increase of the oxygen conversion in the presence of a Sn/Li/ MgO catalyst. This can be accounted for by a mechanism in which both the hydrogen abstraction from the hydrocarbon and the regeneration of the active sites are kinetically significant. The corresponding decrease of methane conversion results from competition between methane and the more reactive ethane for these sites. The addition of ethane does not result in a beneficial effect on conversions to ethane or C2.

Irreducible Mass-Transport Limitations during a Heterogeneously Catalyzed Gas-Phase Chain Reaction: Oxidative Coupling of Methane

“…In the axial direction the interstitial hydrogen-peroxy concentration keeps increasing due to the increase in the ethane concentration. It was shown by Chen et al (1994a) that increasing the ethane concentration leads to higher propagation rates in the branched-chain gas-phase reaction mechanism. This leads to increasing the total radical concentrations and, hence, to an increasing importance of the nonselective gas-phase reactions.…”

Kinetics of a Gas-Phase Chain Reaction Catalyzed by a Solid: The Oxidative Coupling of Methane over Li/MgO-Based Catalysts

“…Note that eq 4 is the sum of 2 times reaction 5 and reaction 1 in Table 2. Chen et al (1994b) discussed experiments in which ethane was added to the feed stream and showed that regeneration of active sites through water desorption is not a potentially instantaneous reaction. TAP experiments (Mallens, 1996) showed that the catalyst contains a pool of hydrogen atoms probably in the form of hydroxy groups.…”

“…This way of presenting a complex reaction network was developed by Temkin (1971) and allows a straightforward calculation of the net production rates of the components involved in the catalytic reactions. The set of catalytic reactions, shown in Table 2, is coupled to the gas-phase branched-chain reaction network reported by Chen et al (1994b). The complete kinetic model thus contains 10 catalytic and 39 gasphase reactions in which 13 molecules, 10 radicals, and 5 surface components are involved.…”

“…Several routes for direct CO x formation on the catalyst surface were proposed in the literature. McCarty (1992) Lines: calculated using the heterogeneous reactor model equations of Couwenberg et al (1996) and the heterogeneous reactions of Table 2 with corresponding kinetic parameters of Table 3 coupled to the gas-phase reaction network of Chen et al (1994b Aparicio et al (1991) mentioned the reversible adsorption of a methyl radical on O * , leading to a methoxy species. This methoxy species subsequently leads to carbon dioxide through a series of steps which are potentially infinitely fast.…”

“…The kinetic model consists of elementary catalytic reactions coupled to the gas-phase reaction network reported by Chen et al (1994b). The considered catalytic reactions are based on kinetic experiments and on information provided by pulse experiments performed on a TAP setup (Gleaves et al, 1988;Mallens et al, 1995) and steady-state transient isotopic kinetic (SSTIKA) experiments (Nibbelke et al 1995) on the same catalyst.…”