(771e) CO2 As a “Soft” Oxidant for Syngas Production Via Chemical Looping

CO₂
as a “Soft” Oxidant for Syngas Production via Chemical Looping

Amey More,
Saurabh Bhavsar, Charlie Hansen and Götz Veser

 Department of
Chemical Engineering, University of Pittsburgh, Pittsburgh, PA

Abstract:

‘Chemical
Looping Combustion’ is a clean combustion technology, which enables fossil fuel
combustion with inherent CO₂ capture based on the cyclic oxidation
and reduction of an oxygen carrier. While most efforts in chemical looping (CL)
are focused on combustion, we previously demonstrated the application of the “CL
principle”—the periodic oxidation and reduction of a metal oxide to couple two
independent redox reactions—to the activation of CO₂ via reduction
to CO [1]. In the present contribution, we investigate and compare CO₂
activation via CL in two different operating modes: In the first scheme, CO₂
reduction is coupled with CH₄ oxidation by using mixtures of Fe and
Ni (as alloys or simple physical mixtures) to produce CO and syngas product
streams [2]. In the second operating scheme, monometallic Ni carriers are
utilized to catalytically crack CH₄, producing pure H₂ streams.
The solid carbon deposits are then burnt off with CO₂, overall
producing separate CO and H₂ product streams.

Supported
metal oxide carriers were synthesized, and a combination of thermo-gravimetric
analysis (TGA), X-ray diffraction (XRD), and electron microscopy (TEM) was used
to identify structure-reactivity correlations for systematic carrier design. Gas
phase conversions and selectivities were determined
in periodic fixed bed reactor operation. We find that Fe-Ni alloys can indeed
show good activity towards both methane activation and CO₂
reduction, and that the weak oxidant CO₂ allows controlled oxidation
of Fe–Ni alloys, which enables selective oxidation of CH₄ to syngas.
 Remarkably, a simple physical mixture of
Fe and Ni far exceeds the reactivity of an equivalent alloy carrier, which can
be traced back to a synergistic gas-phase coupling between the two carrier
fractions.  For the second proposed
scheme, we find a strong dependence on the support material, which affects particle
size and distribution of the active metal species. Overall, our investigations demonstrate
the potential of CO₂ as a “soft” oxidant which enables selective oxidation
reactions via novel, intensified chemical looping processes.

[1]
M. Najera, et al, Chem. Eng. Res. Des.
89 (2011) 1533; Bhavsar, et al, Chem.
Eng. Technol. 35 (2012) 1281; S. Bhavsar and G. Veser, Energy Fuels 27 (2013) 2073;  
A. More, S. Bhavsar, and G. Veser. Energy
Technology (2016) AOP.
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