Environment & Energy
Related: About this forumA Device For Air Capture of Carbon Dioxide Which Regenerates at Waste Heat Temperatures.
Events in the United States and Brazil - and in fact, practically everywhere else on Earth - in the last few years assure that every living being on Earth is going to face increasing catastrophe from climate change.
Coupled deliberate indifference by politicians, again notable in the US and Brazil, is the idiotic and unworkable misplaced but popular faith in so called "renewable energy" - which is neither "renewable" nor sustainable - that is often incorrectly described as "doing something" about climate change.
We are doing nothing about climate change.
Future generations will need therefore to find a way to clean up our mess, and do so with far reduced resources, because in our contempt for all future generations, we have been consuming vast amounts of resources for quixotic things like wind turbines and electric cars, as well as a lot of other consumer junk.
To clean up our mess, the only option for these future generations from whom we've stolen, well, everything will be - and it is an incredibly difficult engineering challenge - air capture of carbon dioxide.
About 7 years ago, a controversial but much discussed paper on the energetics and thermodynamics of air capture was published, which at least put the challenge in perspective. It is here: Economic and energetic analysis of capturing CO2 from ambient air, (House et al PNAS, 108, 51 2042820433, 2011). It drew a negative conclusion about the possibility of doing this, by exploring an estimations the costs of various technologies for doing this:
Advanced nuclear: $286/ton
IGCC CSS: $666/ton
Gas CC CCS: $388/ton
Wind (land): $369/ton
Wind Offshore: $598/ton
Solar PV: $1,030/ton
Solar Thermal: $686/ton
Biomass: $580/ton
Hydroelectricity: $299/ton.
It is possible to hydrogenate carbon dioxide to make gasoline. I covered this topic elsewhere (in a place where I was banned for telling the truth): How Much Gasoline Could Hydrogenation of ONE Coal Plant's Waste Produce?
Using a similar calculation of cost, I have calculated - using 2,4 dimethylpentane as the model gasoline compound - what the cost of the carbon atoms in gasoline might translate in familiar terms in the US, dollars per gallon. (Note this does not include the internal and external costs of producing hydrogen and thus is only a fraction of the real cost of gasoline would be in this case. These costs would be, respectively, using the figures above:
$2.32/gallon, $5.40/gallon $3.15/gallon $2.99/gallon $4.85/gallon $8.36/gallon $5.57/gallon $4.71/gallon $2.43/gallon.
The House paper has been criticized in the same journal on the grounds that the analysis relied on a narrow focus on technology.
Another paper in the same journal argued that air capture is essential; it MUST BE DONE.
I personally agree with the last paper's claim, if the future generations from whom we've stolen everything are to save anything left to be saved.
Thus I was entranced by a recent publication in one of my favorite scientific journals, this one: The Development and Validation of a Closed-Loop Experimental Setup for Investigating CO2 and H2O Coadsorption Kinetics under Conditions Relevant to Direct Air Capture (Jovanovic, Ng, and Yang, Ind. Eng. Chem. Res., 2018, 57 (42), pp 1398713998.
I have convinced myself that the only sustainable option for providing the energy for this extremely challenging engineering task is nuclear energy, although I'm not convinced that the "advanced nuclear" House describes is really suitable for the task. Few details are provided directly in the paper about the kind of nuclear energy that constitutes "advanced nuclear" in House's paper, but I suspect it involves an electricity intermediate energy form, which, in my view, is unnecessary and wasteful. Carbon dioxide and water splitting by thermochemical means involves high temperatures, and high temperatures, although increasing thermodynamic efficiency, imply the rejection of heat to the environment. To the extent that this waste heat can be partially captured to do useful things, like say, capture carbon dioxide and release it in a concentrated form available for use, it can be environmentally attractive. Hence my interest in the Jovanovic paper where the regeneration of the absorbent occurs at a relatively low temperature, 95C, temperatures which would be relatively accessible for very high temperature nuclear reactors being utilized to either split carbon dioxide or water or both.
From the introduction to the Jovanovic paper:
The paper is rather detailed and involved, but it may be useful to look at the pictures to get a feel for it:
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IRGA stands for infrared gas analysis. CSTR = continuous stirred-tank reactor
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experiments compared in Figure
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Some excerpts from the text:
with qj (t) calculated from the temporal gas-phase species balance
where nj(t) and msorb represent the instantaneous sorbate amount in the gas phase within the closed-loop and mass of sorbent, respectively. The sorbate amount present in the gasphase can be determined using the ideal gas law if the sorbate mole fraction xj and the system pressure P, volume V, and temperature T are all known. Assuming the CSTR flow pattern in the tank and the plug flow through the reminder of the loop, xj is assumed uniform throughout the entire closed-loop. However, the pressure and temperature both vary within the loop due to the pressure drop in pipes, gas compression by the pump, and the lack of temperature control outside of the tank. To account for these nonuniformities in P and T, the closedloop was divided in several compartments as described in section S5 of the SI to calculate nj(t) as
where R is the universal gas constant and subscript i designates different compartments involved in the analysis. Note that the calculations of nj(0) and nj,(t) do not account for the exact same compartments, because the sorbate mixture bypassed the sorbent bed before the adsorption (see SI)...
...and...
the tracer material balance for the CSTR condition, that is, assumption that the CO2 composition in the tank is uniform and equal to that at the tank outlet, reduces to
In eqs 4 and 5, ntank designates the total amount contained within the tank and subscripts in and out indicate the quantities at the inlet and the outlet of the tank, respectively.
From the conclusion:
...The setup presented in this work can be readily implemented to determine the adsorption kinetics on other sorbents developed for similar applications as well as kinetics of some gas?solid catalytic or noncatalytic reactions. The design and validation methodologies presented in this paper can serve as a reference for the development of batch experimental setups for measuring adsorption/reaction kinetics free of the intrusions by heat and mass transfer.
The turn of events surrounding climate change are depressing because, in my opinion, even many of the people who get remain hostile to the only viable solution which necessarily will involve nuclear energy, but also require huge advancements in chemical technology and chemical and materials science engineering.
I will be gone from this planet soon enough, and I do not really expect, at my age, that things will really get better, but if they do, the work performed and published here, and thousands of examples more like it, written by scientists working in relative obscurity and enduring some popular contempt, will lead the way.
That it exists makes me feel a little better.
Have a wonderful weekend.
defacto7
(13,485 posts)Bringing promising ideas back to the forefront is encouraging, for what that's worth.
NNadir
(33,545 posts)...since the oceans continuously extract and concentrate carbon dioxide in the form of carbonate, bicarbonate and solvated CO2.
Quite possibly the most promising research for quick application is the work of Dr. Heather Willauer at the Naval Research Laboratory whose work for the US Navy has involved making jet fuel on nuclear powered aircraft carriers from seawater.
It's an electrolytic process, which to my mind makes it inferior to other processes, but the concept of using seawater to make fuels is excellent.
The work is partially described here: Extraction of Carbon Dioxide and Hydrogen from Seawater by an Electrolytic Cation Exchange Module (E-CEM) Part V: E-CEM Effluent Discharge Composition as a Function of Electrode Water Composition.
There is a tremendous amount of research devoted to the removal of carbon dioxide from air. We often don't think of this but much of the driving force for the high energy density of dangerous fossil fuels is connected with entropy.
This is the reverse endothermic (and therefore thermodynamically unfavorable) reaction for the combustion of 2,4-dimethylpentane, a known constituent of gasoline and other liquid fuels derived from dangerous fossil fuels:
7 CO2 + 8 H2O -> C7H16 + 11 O2.
Not only does this reaction involve the investment of heat energy, but 15 gaseous molecules, including seven that are highly dilute are converted into one concentrated liquid molecule and 11 gas molecules. Many degrees of freedom are lost, and thus the product side is lower entropy than the reactant side. The seven carbon dioxide molecules have also been subject to the entropy of mixing. Thus the free energy input is rather high, but lower for seawater than for air.
An interesting thing about Willauer's scheme is that it results, temporarily, in a highly basic fraction which can extract even more carbon dioxide from the air from mildly basic (still) seawater.
Here's a brief video involving her:
The video is lacking a discussion of the energy source to drive this, which is nuclear energy, and the interviewer is somewhat scientifically illiterate since he's referring to it as a "source of energy" which it isn't, and which she is not correcting him. It is not a source of energy; it is an energy storage system.
She is discussing as a system for use in war; but there is no intrinsic reason that it cannot be a system for use in peace.