Another CO2 to Fuels Approach
Researchers at Columbia University’s Lenfest Center for Sustainable Energy, in collaboration with Risø National Laboratory for Sustainable Energy, DTU, are investigating the high-temperature co-electrolysis of CO2 and H2O using solid oxide electrolysis cells (SOECs) to produce a syngas for conversion into liquid hydrocarbon fuels. _GCC
The idea of "re-cycling" CO2 back into a fuel -- skipping the middleman of photosynthesis -- continues to be popular in certain scientific circles. This approach involves the co-electrolysis of H20 with CO2 to create an H2/CO syngas, which can be further processed into liquid hydrocarbon fuels.
The Lenfest/Risø team notes that high temperature electrolysis makes very efficient use of electricity and heat (near-100% electricity-to-syngas efficiency), provides high reaction rates (no need for precious metal catalysts), and the syngas produced can be catalytically converted to hydrocarbons in well-known fuel synthesis reactors (e.g. Fischer-Tropsch). There is no need for a separate reverse water-gas shift reactor to produce syngas, and the waste heat from exothermic fuel synthesis is useful in the process.
An analysis of the system energy balance presented by Christopher Graves at the May conference showed a 70% electricity to hydrocarbon fuel efficiency. Using solar photovoltaic energy at 10-20% efficiency, that would result in an overall 7-14% solar energy to liquid fuel efficiency, he said.
Their analysis of the economics of a co-electrolysis-based synthetic fuel production process, including CO2 air capture (earlier post) and Fischer-Tropsch fuel synthesis, determined that the price of electricity needed to produce competitive synthetic gasoline (at $2/gal wholesale) is $0.02 - $0.03 per kWh. _GCC
The Columbia / Riso approach involves the use of Ni/YSZ based solid oxide cells for co-electrolysis. This high temperature approach is somewhat similar to the STEP process being developed by George Washington U. and Howard U. researchers, for the explicit purpose of splitting CO2 for purposes of reduction of atmospheric CO2 levels. The STEP process provides the option of turning atmospheric CO2 into solid carbon for easy sequestration, or turning CO2 into CO for conversion to liquid fuels -- as in the Columbia / Riso approach pictured above.
Al Fin engineers and atmospheric scientists are uncertain where the large quantities of CO2 required to make these processes economical will be obtained. If political activists are successful in shutting down large-scale coal and other hydrocarbon power generation processes, CO2 could become rather scarce. (the atmosphere possesses only 0.04% CO2)
The plant life of Earth evolved, for the most part, under conditions of much higher levels of atmospheric CO2, and conditions of much more "acidic" oceans than at present. The planet's natural systems are, if anything, starved for CO2. If political activists ever grow beyond their greedy scamming stage of carbon scheme and tax grifting -- if they become efficacious at carbon reduction despite themselves -- planet Earth
...In other words, we know that the planet can thrive at higher temperatures and higher levels of CO2 than at present -- because it has done so many times before, for prolonged periods of time. We do not know what may happen if humans -- out of a fanatical fear of a trace gas -- push levels of CO2 far below where natural homeostasis would have placed them. Particularly if Milankovitch cycles and other natural triggers of cooler climate happen to coincide with such sanctimonious human meddling. Earth life can be hurt badly if CO2 levels are pushed too low.