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GWU team suggests C2CNT carbon nanotube composites could amplify reduction of GHG emissions

A team of researchers at George Washington University led by Prof. Stuart Licht reports that the addition of carbon nanotubes (CNTs) produced from CO2 by low-energy C2CNT (CO2 to CNT) molten electrolysis (earlier post) to materials such as concrete or steel not only forms composites with significantly better properties, but amplifies the reduction of CO2. Their paper is published in the journal Materials Today Sustainability.

Licht

Massive carbon dioxide avoidance by the addition of carbon nanotubes synthesized from CO2 to CNT-composites. (A) Carbon mitigation with CNT-cement. (B) Carbon mitigation with CNT-Al. The latter (B) includes a cascade effect due to virgin Al’s large carbon footprint, triggering larger CNT-composite induced CO2 emission elimination. In the figure "ton" refers to metric tonne and CNT, carbon nanotube. Licht et al.


The focus of their study was the theoretical calculations of greenhouse gas CO2 reductions using CNT composite structural materials when formed with CNTs made from CO2, rather than conventional high-CO2-emissive production techniques such as CVD.

The C2CNT production is achieved at a fraction of the current cost of manufacturing nanotubes and results in a cost of carbon savings in the materials production significantly below the current cost of carbon mitigation. Furthermore, the removed CO2 is permanently stored, unlike, other methods like the production of fuels or seltzer water that re-release CO2 when the product is used.

In this discovery of the C2CNT-composite process, carbon nanotubes are produced by electrolysis at low cost consuming, rather than releasing, CO2, and then mixed with the structural material. Approximately 4 tonnes of CO2 is absorbed in this process for every tonne of carbon nanotubes produced.

This then avoids several hundred tonnes of CO2 by replacing structural materials with CNT composites. For example, a 2-tonne cement block with 0.001 tonne of CNTs has the same strength as a 3-tonne block without CNTs.

The 1-tonne cement avoided eliminates its CO2 production emission. Specifically, a 0.048 wt% CNT-cement composite eliminates 840 tonne of CO2/tonne CNT. CO2 is thus eliminated from the anthropogenic carbon cycle at less than $1 per tonne.

High carbon footprint materials such as aluminum trigger larger CO2 composite elimination effects. One ton of CNT can avoid:

  • 4400 tons of CO2 in aluminum production,
  • 2750 tons of CO2 in titanium production,
  • 1800 tons of CO2 in magnesium production, or
  • 300 tons of CO2 steel production.

The new C2CNT-composite process would allow, for example, the entire greenhouse gas emission of a fossil fuel power plant to be offset with a small, onsite C2CNT plant producing carbon nanotubes.

Resources

  • S. Licht, X. Liu, G. Licht, X. Wang, A. Swesi, D. Chan (2019) “Amplified CO2 reduction of greenhouse gas emissions with C2CNT carbon nanotube composites,” Materials Today Sustainability, doi: 10.1016/j.mtsust.2019.100023.

Comments

mahonj

That is very cool. You create carbon nanotubes from waste co2 exhaust gases, and then use the CNTs to reinforce the concrete or steel, and as a result, need less of it in the first place.

Sweet - (assuming it works and scales).

(Or you could just make the CNTs to get the CO2 out of the exhaust stream)

Is this not a very big deal ?

GdB

There is a huge market for transport if it can be made small enough, perhaps starting with big trucks.

Engineer-Poet

I have to agree:  this is a very big deal.  If you can make already-light things like aluminum cans (and the F150) even lighter, you not only save material, you also save all the lifetime costs of moving the saved weight around.

If the standby cost of keeping the electrolysis systems ready can be held down far enough, this could be a good way to use unreliable energy from PV and wind to make a valuable product and sequester carbon in the process.  This appears to be far better than hydrogen for that purpose.

SJC

The is BIG stuff, if this pans out it could change a lot.

Roger Brown

Let us consider this scheme from the viewpoint of total CO2 emissions. I will consider concrete and aluminum only. I would have included steel in this analysis but some of the numbers I need are behind a pay wall. From the figure included with this article we can conclude CNT reinforcement will reduce CO2 emission from concrete and aluminum by 31% and 27% respectively simply by virtue of the fact that less material needs to be produced to carry out a given mechanical function.

In addition some amount of CO2 will be sequestered by production of CNT from CO2. From a global emissions standpoint one might as well assume that this CO2 comes directly from the production of the associated material. That is we can assume that the CO2 for CNT reinforcement of concrete comes from concrete production and the CO2 for aluminum reinforcement comes from aluminum production. Making this assumption the CO2 reductions for concrete and aluminum production become 31.1% and 27.03% respectively.

If we wish to achieve a net zero carbon economy the remaining emissions (more than 2/3 in each case) must be eliminated by carbon capture and storage. As for the CO2 emissions from other fossil sources (e.g. electricity generation, passenger and freight transportation, space and water heating, industrial process heating, etc.) nothing whatsoever has been accomplished.

Engineer-Poet

Roger, you're right as far as you go.  But consider this twist:

There is nothing in cement production which requires combustion.  It would be no real difficulty to use off-peak electricity to drive the calcination reaction and produce nearly pure CO2.  If more electricity was used to turn CO2 into the CNTs for reinforcement, and the rest sequestered, the process proper would be carbon-neutral.  It would be slightly carbon-negative over time as the alkaline cement carbonated itself.

The production of aluminum runs exclusively on electricity.  The current process generates strong GHGs including tetrafluoromethane, but I suspect that it can be destroyed by reaction with sodium hydroxide to make sodium fluoride, CO2 and water.  Turn the CO2 into CNTs and recycle them as anode elements; recycle the NaF as solute for aluminum production.

All you need for this is a carbon-free source of electric power, and nuclear energy is just the ticket.  Build it out using said CNT-reinforced cement until you've served at least the base load and mid-load, then use the overnight excess to make the concrete and CNTs.

I suspect there might be massive carbon sequestration possibilities with cellulose.  (I hope) We all know about engineered wood products, but I suspect that CNT-reinforced cellophane might be able to improve the properties in a number of ways.  This might go double if e.g. acetylization of the cellulose renders it largely immune to rot.  Use this to make structural elements and clad them in cement or gypsum skins for fireproofing.  Voila, you have turned construction into a net carbon sink.

That's just the beginning, I'm sure you can think of more.

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