Biogas produced in landfills contains large amounts of methane (a potent greenhouse gas) and hence requires collection and treatment according to EPA regulations.
Cylindrical
NiMg/Ce0.6Zr0.4O2 pellet
catalysts with two different sizes (large, radius = 1.59 mm; small,
radius = 0.75 mm) were produced by extrusion of powder catalysts.
The small catalyst pellets had a higher specific surface area, pore
volume, average pore size, radial crush strength, and resistance to
breakage than the large pellets. Tri-reforming tests with surrogate
biogas were conducted at 3 bar and 882 °C, with the feed molar
ratios of CH4:CO2:air fixed at 1.0:0.7:0.95
and the H2O/CH4 molar feed ratio varied (0.35–1.16).
The small catalyst pellets exhibited lower internal mass-transfer
resistance and higher coking resistance compared to the large pellets.
CO2 conversion decreased and H2/CO molar ratio
increased with the increase of H2O/CH4 molar
feed ratio, which are consistent with the trends predicted by thermodynamic
equilibrium calculations. The results indicate that the NiMg/Ce0.6Zr0.4O2 catalyst pellets are promising
for commercial scale applications.
Correction for ‘Conversion of landfill gas to liquid fuels through a TriFTS (tri-reforming and Fischer–Tropsch synthesis) process: a feasibility study’ by Xianhui Zhao et al., Sustainable Energy Fuels, 2019, 3, 539–549.
Reduction of greenhouse gases is vital for the long-term environmental health of the planet. While there has been progress in reducing CO2 emissions at large point sources, a significant portion of the CO2 emitted each year in the United States is released from distributed sources, like cars, smaller factories, and farms. Direct capture of CO2 from ambient air is therefore necessary for the ultimate reduction of greenhouse gas emissions in the atmosphere. However, capturing the CO2 in ambient air presents a much greater challenge due to the dilute nature of the CO2, requiring different strategies than carbon capture from concentrated CO2 waste streams.
We are developing a novel process for the capture and containment of CO2 from air into a purified, concentrated CO2 stream that can be redirected for use as a feedstock for a wide variety of applications, including chemical manufacturing and syngas formation. This process involves the capture of CO2 in a concentrated KOH solution using a high-surface area air contactor to form potassium carbonate. The potassium carbonate is then efficiently electrolyzed in a hydrogen-assisted process to regenerate the CO2 at a low operating potential, increasing the electrical efficiency of the process while producing concentrated and purified CO2. In addition, water, hydrogen, and KOH are also regenerated as byproducts that can be recycled back into the CO2 capture and electrolysis processes, reducing both overall energy and chemical consumption.
Using a custom designed test stand and traditional electrolysis cell design, we have demonstrated voltage of <1.8 V at 100 mA/cm2 for potassium carbonate conversion to carbon dioxide at the anode, with concomitant H2 and KOH production at the cathode, based on potassium-selective ion exchange across the membrane. Furthermore, using a custom 3-compartment electrolysis flow cell and ion-selective membranes, we successfully demonstrated hydrogen-assisted carbonate electrolysis, with hydrogen consumption at the anode, hydrogen and KOH production at the cathode, and CO2 formation from potassium carbonate in an internal flow-through compartment, at 1.4 V at 50 mA/cm2. Further improvements in operating conditions and cell components and design should decrease the operating voltage significantly, to <1 V at 100 mA/cm2.
Acknowledgement: The project is financially supported by the Department of Energy’s ARPA-E Office under the Grant DE-AR0001495
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