Low-energy-consumption electrochemical CO2 capture driven by biomimetic phenazine derivatives redox medium - ScienceDirect

[Greg Rau]

https://www.sciencedirect.com/science/article/abs/pii/S0306261919318069
“To reduce the energy consumption of CO2-capture methods, proton carriers can be used to drive the CO2 capture in a pH-swing way via the proton coupled electron transfer (PCET) reactions, which are electrochemically regenerable by electrolysis, surpassing the energy-intensive thermal regeneration of traditional monoethanolamine (MEA) absorption method in terms of energy efficiency. However, the low solubility of PCET organics limits its CO2 capture capacity and thus the application. We develop a low energy consuming, high-capacity CO2-capture cell using a phenazine-based organic as the proton carrier as the PCET redox medium, which has high proton capacity and fast PCET kinetics. The quasi-reversible redox-PCET of the phenazine derivative effectively swings the pH of NaHCO3/Na2CO3 aqueous electrolyte at the cathode and the anode, which work as the CO2 absorption/desorption half-cell respectively. This electrochemical CO2-capture cell with an optimal derivative (7,8-dihydroxyphenazine-2-sulfonic acid, noted as DHPS) demonstrates a 95.8% average current efficiency at 10 mA cm−2 and a superior low-electrolysis energy consumption of 0.49 GJ per ton of CO2.”


GR Relevant to CDR?

[Ronal Larson]

Greg and List:

My answer to your (below) relevance question for biochar is potentially “yes”.  “Potentially" because I have requested but not yet read the full article - and I have only a little experience along these lines.  The reason for some enthusiasm is the abstract's report of needing only " 0.49 GJ per ton of CO2”.   Biochar operations can now have income from a) the char and b) the thermal energy release accompanying all biochar production.  This paper offers the possibility of c) a third income stream - if the pyrolysis operation can provide the needed .49 GJ.

One tonne of input biomass can supply about 18 GJ of energy.   If combusted there would be about 1.8 Gt of CO2 produced (using the molecular weight ratio of 44/12 = 3.67 and that biomass is about half carbon by weight.  Because most of the biomass weight in (high energy density) hydrogen appears as water in the exiting hot gas stream (and not in the char), about half of the initial 18 GJ is in the CO2-containing gas stream that this paper is using as its source of pure CO2.  

That gas stream (from one tonne of biomass) contains pretty close to 1 Gt CO2 and 9 GJ (maybe 10 GJ) of thermal energy.   The ratio of .49 GJ to 9 GJ is about 0.055  -  close to a minimum present stated efficiency of Peltier thermoelectric devices (see Wiki).   

One market could be for beverage companies - who apparently now often locate close to a fossil fuel group that can supply CO2.  The biochar approach could presumably compete when the fossil carbon is taxed.  The beverage company can then have income from biochar while seeing low costs for needed thermal energy and clean CO2.

This is not to claim that the chemistry involved removes atmospheric carbon.  Only that it helps the economics for the half (or a bit more) of the biomass carbon that ends up as biochar.  It also potentially avoids the generation of CO2 from fossil sources.

I’ve checked with one biochar equipment manufacturer who says it sounds interesting.

Ron

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