Abstract
At high temperatures, the oxidative coupling of methane (OCM) is an attractive approach for catalytic conversion of methane into value-added chemicals. Experiments with a Pt/Al2O3-coated catalytic honeycomb monolith were conducted with varying CH4/O2 ratios, N2 dilution at atmospheric pressure, and very short contact times. The reactor was modeled by a multiscale approach using a parabolic two-dimensional flow field description in the monolithic channels coupled with a heat balance of the monolithic structure, and multistep surface reaction mechanisms as well as elementary-step, gas phase reaction mechanisms. The contribution of heterogeneous and homogeneous reactions, both of which are important for the optimization of C2 products, is investigated using a combination of experimental and computational methods. The oxidation of methane, which takes place over the platinum catalyst, causes the adiabatic temperature increase required for the generation of CH3 radicals in the gas phase, which are essential for the formation of C2 species. Lower CH4/O2 ratios result in higher C2 selectivity. However, the presence of OH radicals at high temperatures facilitates subsequent conversion of C2H2 at a CH4/O2 ratio of 1.4. Thereby, C2 species selectivity of 7% was achieved at CH4/O2 ratio of 1.6, with 35% N2 dilution.
Highlights
Methane, the main component of natural gas, is burnt for heating purposes but is an important chemical feedstock for the production of syngas by steam reforming, dry reforming, and partial oxidation [1]
In order to investigate the role of the surface and gas-phase chemistry under oxidative coupling over Pt, simulation studies of experiments were conducted by a two-dimensional flow field description of a single channel of the catalytic monolith using DETCHEMCHANNEL [21,22]
Varying the reaction conditions during experiments revealed that low N2 dilution and higher space velocity favors the formation of C2 species
Summary
The main component of natural gas, is burnt for heating purposes but is an important chemical feedstock for the production of syngas by steam reforming, dry reforming, and partial oxidation [1]. Oxidative coupling of methane (OCM) was first introduced in 1982 by Keller and Bhasin [3] for the production of C2 products—namely, C2 H4 and C2 H6 —in the presence of metal catalysts at atmospheric pressure and temperatures in the range of 700–1300 K. The main challenge of the process is the achievement of high C2 product selectivity at high methane conversion. Most of the catalysts investigated for OCM are oxides of pure or modified transition metals [4], IA or IIA group elements [5], Mn/Na2 WO4 /SiO2 catalysts [6], or Li/MgO catalysts [7] in the temperature range 1000–1100 K. Other wellknown catalysts for OCM are La-doped catalysts such as LaAlO3 [8], La2 O3 /CeO2 [9], and
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