This paperpublished in Nature seems to demonstrate how carbon can be extracted from the air using Cerium and other liquid metals. It looks very interesting, but could a more knowledgeable Doper please translate it into something rather simpler?
In theory could we just hook up some solar panels around Meteor Crater and let the collected carbon fill it?
As you note, it demonstrates a way of turning CO2 basically to bits of carbonaceous matter through the use of a catalyzing agent and some electricity. And at room temperatures, which is nice.
There are other methods to do similar things, and the issue remains the same - does the method scale up efficiently or at all? And what other engineering challenges are there to make it economic (one off the top of my head - how to gather and concentrate the CO2 about the electrodes)?
The paper doesn’t address practicality. It demonstrates a method that works at least in small scale. That’s important as a potential first step but there are several giant leaps ahead.
The concentration issue is a big one in any carbon-capture scheme. I read about them all the time, but every one of them does the experiment in a high CO[sub]2[/sub] environment. Most do it in pure carbon dioxide gas, although I saw one not too long ago that did it in a flue (exhaust pipe for a natural gas burner). That one was actually kinda, sorta, but probably not really practical. (It’d have been better just to do whatever (heating, I think) without burning the natural gas in the first place.)
The thing is, the amount of CO[sub]2[/sub] in the air is about 400 ppm, which is a very low concentration. Just consider how many fans you’d need to run for how long just to run a single ton of the gas through whatever capturing device you have. And that’s just the first step to capturing. So unless someone comes up with a magical capturing device, it’s not practical.
If I’ve read the article correctly (and I’m not sure that I have, hence this thread!) this technology looks to be something you can just leave out in the open, periodically skimming off the carbon. And if that period is once per hour or once per day then that’s fine. You’re still reducing atmospheric CO2.
There’s the teenie-weenie problem that their solution requires the conversion of CO2 back into C and O2. And their method even, potentially, could be very efficient at doing it. So their energy requirement really isn’t that much of a biggie…
The article also mentions that CO (carbon monoxide) is also produced, in amounts that vary with the bias applied to the liquid metal. In fact they tout it as an advantage as CO is used in a number of industrial processes. But since CO isn’t real human-friendly (plus I thought is a worse greenhouse gas than CO2) I don’t think open puddles of Cerium oxide alloyed liquid metal is the solution.
Ya gotta start somewhere. If scientists can come up with an electrochemical process, it gives the engineers something to work with in the attempt to make a practical solution. The key here is that the paper is describing a catalytic process which operates at a reasonable temperature and bias (voltage) level. Without the basic research we got nothing.
ETA: Possibly something like this would work in conjunction with methods currently envisioned concentrate CO2 for underground sequestration, except instead of storing the CO2 underground (where is can eventually leak back into the atmosphere) it gets converted into a stable solid.
”Somewhere” has to be a point at which the energy balance of sequestering carbon dioxide exceeds the peoduction of it, and the process can be scaled to a level where practical reductions in net corban dioxide levels can be achieved. dtilque is correct that the 0.04% level of CO[SUB]2[/SUB] at sea level makes sequestration in air about as effective as swatting at knats. It would probably be more effective to extract CO[SUB]2[/SUB] from the oceans provided you have some power source that does not produce net carbon dioxide emissions (presumably photovoltaic solar), but the scale on which this would need to be developed would dwarf all existing macroengineering projects by orders of magnitude.
In other words, looking to such ‘geoengineering’ concepts to save us from shortsightedness is just about as plausible as expecting gifts from Santa Claus and the Easter Bunny. Actual, realizable changes in energy policy that move to minimize atmospheric carbon production while looking toward ultimately sustainable solutions are really the only practical approach to mitigate global climate change. Unfortunately, such solutions are not as simple and appeasing as the handwaving technomagic of sucking CO[SUB]2[/SUB] out of the air, but they could actually be implemented starting now without waiting for a miracle to spontaneously occur beyond global leaders agreeing to put the health and security of the world ahead of nationalistic interests.
Stranger
It’s not that carbon can’t be captured by whatever means. It’s that it can’t be captured in amounts significant enough to make a difference.
For example, there’s a Swiss company (mentioned in that link) that has a plant that captures 900 tons a year. As described here, it would take 250,000 of these plants to capture a mere 1% of the CO[sub]2[/sub] emitted worldwide.
The only practical means of carbon sequestration from air is at point of emission by adsorption (referred to as carbon capture and sequestration (CCS)), where it is concentrated enough to do so efficiently. To get a sense of scale, human activity puts about 400 GT of CO[SUB]2[/SUB] in the atmosphere per year, which at current rates represents a net increase of about 2 ppm per annum. Terrestrial plant life absorbs roughly 25% of this, and the oceans absorb somewhere between 20% to 30% (which increases acidification that causes all sorts of havoc with marine biosystems). There are concepts for extracting CO[SUB]2[/SUB] mid-ocean where concentrations are higher than air using automated solar-powered plants or bioengineered mechanisms but nothing that is going to be ready for production scale deployment within the next couple of decades. We’d literally have to build and power tens of millions of the kind of plant described in the link above to offset even current emissions, much less absorb the excess CO[SUB]2[/SUB] resident in the atmosphere from human activity before average atmospheric temperature rise exceeds 2 °C.
Of course, none of this addresses feedback cycles in which heating releases CO[SUB]2[/SUB] from thawing permafrost or methane from ocean clathrates, release from increased forest burning (both natural and clearcutting), and methane release from large scale animal production. In short, relying on some technomagical solution to pull carbon dioxide out of open air and reverse the effects of anthropogenically produced atmospheric carbon is not practical for the foreseeable future.
Stranger
** Carbon Dioxide Emissions Rise to 2.4 Million Pounds Per Second **
Experiments in controlled laboratory conditions are interesting and even exciting, but how does the method being studied translate to a volume of air equal to that of the earth’s? In other words, when considering how much new CO2 is belched into the atmosphere every day by our wayward species, how many of these cleansers would be needed just to balance that out alone much less reduce it?
Pursuing these kinds of solutions is certainly far better than doing nothing at all but, to me, it is akin to eating and doing whatever you want until you get sick and then trying to invent a pill to make you well. We need to address the root cause, the massive burning of fossil fuels, because I can’t at this point envision any kind of filters/cleaners that could possibly keep up with the volume of CO2 streaming into the atmosphere every day much less reduce what is already there.
Consider a 1% reduction in CO[sub]2[/sub] production from cement production –> 25,000,000 tons per year. Which research avenue do you want to go down?
I’m not sure I understand this. Producing cement releases CO[sub]2[/sub] in copious amounts. Some, but not all, of if is reabsorbed when the cement cures. So are you suggesting we stop or drastically reduce the production of cement? If so, how?
When you say this, do you mean an increase of 2 ppm per annum AFTER plant life and ocean absorption?
I believe the point that Grey is making is that a transition to lower carbon footprint types of concrete would have a greater impact at much lower cost than attempting to scale this CCS system for capturing CO[SUB]2[/SUB] out of the air, notwithstanding the carbon footprint for having to construct hundreds of thousands of CCS plants.
In general, a sensible energy and atmospheric carbon mitigation strategy would focus on the practicable near term ways to reduce carbon emissions, e.g. eliminating coal and fuel oil in favor of natural gas and biofuel where possible, investing in scalable renewables where it is cost effective to do so to further offset carbon emissions, enacting and enforcing energy efficient building codes and appliances, improving transportation efficiency and associated emissions with electric or alternative sustainable fuel, while investing research into next generation full burnup nuclear fission power production that doesn’t require the energy intenstive enrichment of natural uranium and wasteful once-through cycle extracting only a few percent of potential energy which produces long lived actinides. Expecting some magical technology to come along and just turn back the clock with a figurative flick of a switch is the ultimate “Hail Mary” solution which does not appear to be on the horizon in any feasible form.
Stranger
If we want to remove enough carbon from the air to remain at a steady state, we would need to sequester more than five tonnes per person on Earth per year. What could we do with all that reduced carbon? Maybe it could be converted into strong, tough carbon allotropes for building materials. That would be one way to cut the CO2 production associated with concrete.
Of course this technology hasn’t been invented yet.
Engineered wood buildings are becoming more popular, that would reduce CO2 production from concrete.
Stranger made my point, but let me expand on it.
Dramatic, swinging for the chandelier technology is not going to help in any meaningful way. If you want to reduce CO[sub]2[/sub] in the atmosphere then you need to not put any there in the first places especially when CO[sub]2[/sub] is such a pain in the ass to rip apart.
So spend $5 million on a tentative lab/science experiment or $50 million to nail down a better temperature profile for creating cement that reduces CO[sub]2[/sub] emissions by a lowly 1%? The $50 Million is a better investment.
Now don’t get me wrong, new techniques may evolve into legitimate approaches to CO[sub]2[/sub] reduction but their value is currently marginal.
Though on reflection I just restated Stranger’s post so… ah well. 
I agree, but surely research into the subject is worthwhile anyway?