(252e) Low-Temperature Chemical Looping Driven NOx Decomposition with Natural Gas Utilization | AIChE

(252e) Low-Temperature Chemical Looping Driven NOx Decomposition with Natural Gas Utilization


Mohapatra, P. - Presenter, The Ohio State University
Kumar, S., The Ohio State University
Cheng, Z., The Ohio State University
Fan, L. S., Ohio State University
Feilen, J. W., The Ohio State University
Nitrogen oxide (NOx) refers to the family of nitrogen and oxygen compounds including NO, NO2, N2O,
NO3, and N2O5, where the emission of NO and NO2 from several combustion processes remain a major
concern. These compounds are extremely harmful environmental pollutants and contribute significantly to
acid rain and the destruction of the polar ozone layer. Current catalytic and non-catalytic NOx
decomposition processes exhibit drawbacks such as the thermal instability, poor selectivity, poisoning by
acidic gases, and the requirement of high temperatures. Chemical looping NOx decomposition (CLND) is
an advanced process scheme that can address these concerns. This scheme is based on the second law of
thermodynamics which translates to the reduction of process irreversibility thereby enhancing the process
efficiency. Moreover, it provides an additional degree of freedom in process optimization of the operating
conditions for NOx decomposition reaction. The scheme employs a low temperature isothermal operation
which encompasses reduction of the carrier material utilizing the natural gas such as methane at 400°C
(reducer) and subsequent oxidation of the reduced carrier material by NOx at 400°C in the subsequent step
(oxidizer). This culminates in a NOx free pure N2 stream and methane combustion products (majorly CO2)
at the oxidizer and reducer, respectively. Novelty of the proposed process manifests in the form of selective
separation of NOx from a flue gas stream consisting of CO2, NOx, H2O as the presence of CO2 and H2O in
the stream is found to not affect the NOx uptake of the carrier, thereby enabling the purification of the flue
gas stream. Additionally, the process utilizes methane that is a greenhouse gas for regeneration and
produces a sequestration ready pure CO2 stream. The overall reaction is exothermic, and heat can be
extracted from the process to improve the process efficiency. A metal oxide, NiO is employed as the active
carrier material, wherein the material exists in the form of a crystalline phase. Furthermore, to increase the
dispersity of the active material and reduce sintering effect across redox cycles, five supports i.e., SiO2,
CeO2, Al2O3, TiO2 and ZrO2 are investigated. Besides, the best performing support is tested at different
concentrations to find the optimum support concentration. The supports chosen for the study varied by the
nature of active sites. Acidic support SiO2 exhibited the lowest NOx uptake owing to its weak interaction
with the NOx while basic support CeO2 is found comparatively better. Interestingly, the amphoteric supports
performed the best with Al2O3 performing significantly better than others. Experimental investigation of
the performance of carrier samples is conducted using a Thermogravimetric analyzer (TGA) and a fixed
bed reactor setup. Results indicate a NOx uptake of 412.5μg uptake per mg of the active material (NiO).
The morphological transformation and active material dispersion are investigated for all supports across
multiple redox cycles, using microscopy-assisted solid characterization. Additionally, XRD and BET
analyses are used to study the phase and surface area changes respectively for pre and post reaction samples.
DFT calculations are performed further to investigate the active sites and identify the possible reaction
pathway. The CLND process thus offers an opportunity for a low temperature NOx decomposition alongside
natural gas utilization in an economically viable and environmentally sustainable manner.

Key words: NOx decomposition, Chemical looping, Flue gas processing, Methane utilization, Oxygen
carrier, Environment