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A 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 20428–20433, 2011). It drew a negative conclusion about the possibility of doing this, by exploring an estimations the costs of various technologies for doing this:
CO2 cost per ton (House PNAS 108 51 20428–20433 2011):
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.
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 13987–13998.
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:
Over the past decades, the emission of CO2 to the atmosphere has been increasing at an alarming rate. To mitigate the resulting adverse greenhouse-effect, significant effort has been dedicated to the sequestration of CO2 from large anthropogenic point-sources such as fossil fuel-based power plants.1 However, in order to reduce the CO2 concentration in the atmosphere to the target of 350 ppm,2 it appears necessary to also capture a part of the CO2 already dispersed in the atmosphere as a product of fossil fuel combustion in the transportation sector.3 Compared to the atmospheric CO2 removal methods such as afforestation, increase of cloud alkalinity, and promotion of phytoplankton growth in the oceans, it has been suggested that direct air capture (DAC) poses the lowest risk to radical ecosystem alteration.4 Furthermore, the success at efficient, large-scale CO2 capture from air may provide a source of a clean syngas exploiting process concepts under development for (i) combined CO2 and H2O splitting5 or (ii) reverse water gas shifting of renewable H2 6 that compete with the biomass gasification for commercially viable production of renewable transportation fuels.7
The paper is rather detailed and involved, but it may be useful to look at the pictures to get a feel for it:
The caption:
Figure 1. Schematic diagram of the CLDB setup. The sections outlined by the (blue) dashed and (green) dash-dotted lines represent the gas/sorbate supply manifold and the closed-loop test-rig, respectively. The (red) dotted lines indicate the gas flow direction during the adsorption experiments.
The caption:
Figure 2. (a) Disassembled and (b) assembled sample holder with the gas flow direction indicated by the yellow arrows and main components as follows: (1) PTFE gasket, (2) sorbent bed, (3) coiled stainless steel tube, (4) thermocouple, (5) upper flange, (6) KF clamp, (7) lower flange.
The caption:
Figure 3. Schematic of the tracer study setup.
The caption:
Figure 4. Comparison between the experimental and calculated CO2 mole fractions at the outlet of the tank assuming CSTR flow pattern. The zoom-in plots in panels b and c indicate error bars determined by the accuracy of the IRGAout.
IRGA stands for infrared gas analysis. CSTR = continuous stirred-tank reactor
The caption:
Figure 5. CO2 equilibrium loadings measured in TGA and CLDB setup under T = 35 °C. The solid line represents the Toth adsorption isotherm (eq 13) fitted to the TGA-determined equilibrium loadings.
The caption:
Figure 6. Effect of gas flow rate on the (a) CO2 and (b) H2O uptake profiles obtained with 30 mg of the sorbent under Tads = 30 °C, xCO2,0 = 1000 ppm, and RHads,0 = 50%. Larger fluctuations seen in Figure 6b are attributed to the inherently larger noise in xH2O measured with the IRGA.
The caption:
Figure 7. Sorbent bed temperature profiles recorded during the
experiments compared in Figure
experiments compared in Figure
The caption:
Figure 8. Amine-functionalized NFCs with the particle diameters of (a) 10 mm, (b) 4?5 mm, and (c) 1?2 mm
.
The caption:
Figure 9. Effect of sorbent particle diameter on (a) CO2 and (b) H2O uptake profiles obtained with 69 mg of the sorbent under ṅ = 0.074 mol· min?1, Tads = 25 °C, xCO2,0 = 6000 ppm, and RHads,0 = 50%.
The caption:
Figure 10. Sorbent bed temperature profiles recorded during the experiments compared in Figure 9. Note: the temperature of the dp = 10 mm particle was recorded with the thermocouple inserted into the sorbent particle while the remaining temperature sets were recorded with the thermocouple placed between the sorbent particles
The caption:
Figure 11. Leakage induced-relative errors of (a) CO2 and (b) H2O uptakes. The gray areas indicate the range of interest where adsorption kinetics are extracted.
Some excerpts from the text:
2.4. Data Analysis. The species j has an instantaneous adsorption rate rj (t) represented by the time derivative of the mass specific sorbate molar loading qj (t)
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)...
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 mixing of the gas in the tank was assessed by imposing a continuous tracer input into the tank and then comparing the experimental CO2 tracer mole fractions at the outlet of the tank with those calculated based on the assumption that the gas in the tank was perfectly mixed (CSTR condition). As the experimentally observed uniformity of the gas temperature and pressure within the tank implied that
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.
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:
This paper presents development of a closed-loop setup for dynamic CO2 and H2O coadsorption on amine-functionalized NFC under conditions relevant to direct air capture. The setup, based on a differential sorbent bed placed outside of a perfectly gas mixing tank, allows for measuring the coadsorption kinetics in the absence of external heat and mass transfer effects that are commonly encountered in thermogravimetric analyzers and packed-bed reactors...
...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 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.
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