(562ao) Selective Oxygen Reduction Using Methane for CO2 Purification from a Simulated Flue Gas

Catalytic Oxygen
Reduction using Methane for CO₂ Purification from a Simulated Flue
Gas

Andrew Kuhn¹, Zhitao Chen¹,
Yongqi Lu² and Hong Yang¹*

¹University of Illinois Urbana Champaign,
Urbana, IL 61801 (USA)

²Prairie Research Institute, Champaign,
IL 61801 (USA)

*hy66@illinois.edu

Introduction. Efficient sequestration of carbon
dioxide (CO₂) from flue gas generated from fossil fuel sources
remains a critical endeavor due to the link between rising global temperatures
and increasing atmospheric CO₂ concentrations. State of the art
oxy-combustion practices both increase the energy efficiency and maximize the
effluent purity for coal and natural gas power plants (>85% CO₂,
dry basis).[1]
Streams with 95% CO₂ purity can be utilized in Enhanced Oil Recovery
or chemically-upgraded to value-added chemicals such as methanol. One of the
main impurities, oxygen gas (O₂), prevents the direct utilization of
these streams due to undesirable oxidation reactions. Because of selectivity
challenges and the energy requirement, traditional separation technologies
(i.e. membranes and distillation) are unpromising. A new process must be
developed that is both energy efficient and
technologically practical. Here, we propose to catalytically reduce O₂
from a simulated flue gas stream to produce high purity CO₂.[2]
Methane was used as the primary reducing gas due to its availability and high
energy density (CH₄ + 2O₂à CO₂
+ 2H₂O). In
order to purify flue gas, both the oxygen conversion and selectivity to CO₂
must approach 100% because of the tight specifications for O₂
and carbon monoxide (CO). Here, we study palladium-based (Pd) catalyst systems as
benchmark catalysts for the purification of CO₂ from flue gas. Three
variables to increase the activity of the model Pd system were conducted: the metal
loading, the oxygen-methane feed ratio, and the usage of a copper-based (Cu)
oxygen scavenger sequentially after the Pd bed. This novel approach to purify
and capture CO₂ is achieved by careful material design.

Results and Discussion. Pd catalysts were made
by impregnating the precursor onto gamma alumina (γ-Al₂O₃).
The performance of the catalysts was tested using an
in-house ambient fix-bed reactor system. The CO₂ feed composition
was set at 85% (balance: CH₄ and O₂ at various ratios).
The product compositions were measured (on a dry basis) by gas chromatography.
The temperature was varied from 300 to 600 ºC. Using this fixed bed reactor system,
the Pd catalytic materials were tested for oxygen conversion, selectivity to CO₂,
and product CO₂ purity. A stoichiometric feed to be optimal for all
catalysts. A summary of the activity of three materials is shown in Figure 1. Notably, the Pd then copper-adsorber (Pd+Cu)
yielded the highest in all three categories. Additionally, we discuss the
outlook for using non-precious metal catalysts to achieve the performance metrics.

Figure
2. Oxygen conversion,
selectivity to CO₂, and product CO₂ purity for 1% Pd/Al₂O₃
(Pd1), 1% Pd/Al₂O₃ (Pd4), and the sequential beds containing
1% Pd/Al₂O₃ and 13% Cu/Al₂O₃ (Pd+Cu).
Ambient pressure. 450 °C. Feed: 50 mL/min (85% CO₂, 10% O₂,
and 5% CH₄). WHSV: 60,000 hr^-1.

.

References

1.         Buhre,
B.J.P., et al., Oxy-fuel combustion technology for coal-fired power
generation. Progress in Energy and Combustion Science, 2005. 31(4):
p. 283-307.

2.         Kuhn, A.N.,
et al., Sequential Oxygen Reduction and Adsorption for Carbon Dioxide
Purification for Flue Gas Applications. Energy Technology. 0(0).