Fiber Supported Amino Acidate Functionalized Ionic Liquid Gels for Direct Air CO2 Capture.

[NNadir]

The paper I'll discuss in this post is this one: Hollow Fiber-Type Facilitated Transport Membrane Composed of a Polymerized Ionic Liquid-Based Gel Layer with Amino Acidate as the CO2 Carrier (Hideto Matsuyama et al. Ind. Eng. Chem. Res. 2020, 59, 5, 2083-2092)

This paper caught my eye because it has in its introductory text a "by 2100" statement that's quite different than all those I've been hearing my whole adult life about so called "renewable energy." I first started hearing these when I was effectively a child - since I was a gullible sort well into my twenties - about how "by 2000" we'd live in a renewable energy nirvana.

We don't.

The fastest growing source of energy on this planet in this century has been coal, despite all the "coal is dead" rhetoric that flies around among the other distortions one hears in these times of the celebration of the lie, Trumpian and otherwise. So called "renewable energy" remains what it has been since the early 20th century (when its abandonment was nearly complete), a trivial form of energy.

One doesn't see much blunt realism, even in the primary scientific literature, but this paper has it. To wit, from the introductory text:

Because of the high use of fossil fuels, atmospheric CO2 has increased from 280 ppm in 1800 to over 400 ppm today.(1?3) In the worst-case scenario, atmospheric CO2 concentrations will be in the range 535–983 ppm by 2100, and in the near future, the risk of climate change is expected to rise significantly.(3?6) About half of the CO2 emissions are from large point sources such as fossil fuel-fired power plants, cement manufacturing plants, and chemical plants. CO2 capture from large point sources is important to keep the atmospheric CO2 concentration constant. However, CO2 capture from large point sources is not enough because the other half originates from smaller distributed sources including residential and commercial heating and cooling as well as daily land transportation.(7) Therefore, development of a technology to capture CO2 from small sources and decrease CO2 concentration in atmosphere has been desired.

I have put in bold the realistic statement.

It's realistic because we are no where near close to doing anything effective to address climate change. We'd rather prattle on endlessly about Fukushima - without recognizing that almost all of the people in the area of the failed reactors who died were killed by seawater and not radiation - than we would have a serious discussion of what the destruction of the entire planetary atmosphere might mean.

980 ppm sounds reasonable to me. In my lifetime, I've seen an increase of over 100 ppm, and despite the trillions thrown at so called "renewable energy" the rate of increase (the second derivative) is rising and accelerating (the third derivative).

I have been studying and thinking about direct air capture for sometime to dream that something will be available for future generations to clean up the mess we left for them because, well, we need our cars, and we need our vacations, and we need our suburbs, etc, etc.

Fugettaboutit.

The technical stuff from the paper:

The introduction continues thus:

Direct air capture (DAC) is broadly defined as the direct extraction of CO2 from ambient air.(7) In recent years, many efforts have been made to develop materials and processes to realize DAC. Because DAC processes are not location-specific, the development of a compact CO2 capture system that can be installed anywhere is desired. In addition, current air capture deals with an extremely low CO2 concentration of ?400 ppm, about 350 times lower than that found in typical coal-fired power plant flue gas. Therefore, physical separation methods, such as physical sorption and membrane separations based on the conventional solution-diffusion mechanism, are not suitable for DAC. Separation methods using chemical reactions, for example, chemical sorption and facilitated transport-based membrane separation, are effective due to the effective recovery of CO2 at low CO2 partial pressure.
However, CO2 desorption requires high temperatures, which increases equipment costs and energy consumption. On the other hand, the membrane technology does not require high temperatures for CO2 separation, and energy-efficient processes can be established. In particular, facilitated transport membranes (FTMs) are suitable for capturing CO2 from gases with low CO2 concentration, such as those found in closed spaces (0.5–0.6% of CO2) as well as flue gases (approximately 10–15% of CO2). Therefore, FTMs are suitable for DAC applications.

FTMs are functional membranes that contain a chemical compound called a CO2 carrier.(8?24) The CO2 carrier can selectively and reversibly absorb CO2 by a chemical reaction. Therefore, FTMs have an extremely high CO2 permeability, even at low CO2 partial pressure.(8?12,16?24) Sarma Kovvali et al. reported that FTMs consisting of polyamidoamine in a porous hydrophilized polyvinylidene fluoride flat membrane showed CO2 permeability of 4100 barrer [1 barrer = 1 × 10–10 cm3 (STP) cm/(cm2 s cmHg)] at a CO2 partial pressure of 0.26 cmHg for completely humidified CO2/N2 mixed gas at room temperature.(10) Chen et al. also reported that FTMs containing glycine–Na–glycerol had CO2 permeability of more than 3000 barrer at CO2 partial pressure of 0.5 cmHg under relative humidity exceeding 70% at room temperature (23 ± 2 °C).(8)...

What follows is a number of references to publications in which various scientific groups discussed the utility of amino acids for CO2 capture.

The authors not however, that the thickness of layers and the viscosity of amino acid solutions are a limitation. They here suggest a supported membrane consisting of hollow fibers to support an amino acidate (an ionic amino acid species). (This is, by the way, sort of similar to what goes on in biological systems for transporting CO2. Biological systems are quite good at CO2 capture from the air.)

The authors write:

In this study, we developed an FTM with a hollow fiber structure by forming a gel layer on the inner wall of a hollow fiber-type support membrane. The gel layer was composed of a polymer network having an amino acid anion derived from an ionic liquid-based monomer. Because ionic liquids are types of organic salts, their chemical structures can be easily designed and tailored by organic synthesis. We can easily introduce a polymerizable functional group into the molecule of the ionic liquid. By using such a polymerizable ionic liquid monomer, a polymer having the properties of the ionic liquid monomer can be synthesized. Furthermore, the characteristics of the ionic liquid can be freely adjusted by selecting a combination of a cation and an anion. The characteristics of the polymerized ionic liquid (PIL) can also be controlled by exchanging the counter ions. In this study, we introduced amino acid anion in our developed PIL-based gel layer by anion-exchange. We prepared hydrogel particles having a PIL network by polymerizing 1-vinyl-3-ethylimidazolium bromide ([Veim][Br]). The counter anion was then substituted with an amino acid to introduce CO2 carrier properties to the gel particles. The obtained poly(vinylethylimidazolium amino acid) (poly([Veim][AA]) gel particles were deposited on the inner surface of a hollow fiber membrane. The performance of the developed FTMs was evaluated at low CO2 partial pressure to demonstrate the potential of the developed FTM for DAC applications.

Ionic liquids are comprised of organic ions that are positively charged and organic ions that are negatively charged. (Sometimes one of the ions will not be organic, but most often they are.) These are not entirely new compounds. Stable organic ions have been known for a very long time. Brains, among other organs, function because of the organic ion choline, which is positively charged, and many choline based ionic liquids are known. These ionic salts are remarkable because, as the name implies, they can be liquid at, below or slightly above room temperature. They are a positively huge area of research.

Some pictures from the text to illuminate the authors approach in which they polymerize a fairly well known class of organic cations, alkyl imidazolium cations, and then do ion exchange with the resulting resin, exchanging a bromine ion for a glycinate anion, derived from the simplest amino acid, glycine:



The caption:

Figure 1. Scheme of poly([Veim][Gly]) gel particle synthesis.

The caption:

Figure 2. Schematic illustrations of (a) gel layer formation apparatus, (b) gas permeation cell for the hollow fiber-type membrane, and (c) composite membrane composed of a poly([Veim][Gly]) layer and a hollow fiber-type PSf support membrane.

The caption:

Figure 4. Size of the fully swollen hydrogel particle composed of a poly([Veim][Br]) network. (a) Optical microscope image of the gel particle suspended in water and (b) particle size distribution measured using a laser diffraction particle size analyzer.

The caption:

Figure 5. SEM images of the hollow fiber-type FTM with the gel layer on the inner surface of the porous PSf support membrane: (a) whole image and (b) cross-section of the gel layer formed on the inner surface of the support.

The separation between nitrogen and carbon dioxide - the important point since air is mostly nitrogen - as a function of gel layer thickness is shown:



The caption:

Figure 6. Relationship between (a) CO2 and (b) N2 permeances and gel layer thickness.

(A GPU is a unit of gas permeance that has a unit of volume of a gas at standard temperature and pressure (STP) per unit of surface area of the permeating surface, per second per unit of pressure). The unit is sometimes denoted the "Barrer." )

Subsequent diagrams will make better sense with this bit of text:

It was considered that the substance that blocked the pores of the support membrane would be the [Veim][Gly] derivatives. The PSf support membrane used in this study had a skin layer. Therefore, poly([Veim][Gly]) having a molecular weight of more than 50 kDa or more would not penetrate the pores of the support membrane. Thus, by removing the [Veim][Gly] derivatives having molecular weights lower than 50 kDa from the gel particle suspension for the poly([Veim][Gly]) layer formation, the formation of the diffusion resistance layer could be prevented in the support membrane. In order to remove the [Veim][Gly] derivatives, we dialyzed the gel particle suspension.

The caption:

Figure 7. Concentration of the dialyzed organic carbon from the poly([Veim][Br]) gel particles suspension as a function of time. The error bars represent the standard error of four measurements.

The molecular weight distribution was determined by old fashioned GPC (Size exclusion chromatography) and not something like MALS. (Multiangle light scattering) It's good as a first approximation.

Some results of the dialysis:



The caption:

Figure 8. SEM–EDS line scans of hollow fiber-type membranes with a poly([Veim][Br]) layer on the inner surface of a PSf support membrane. The poly([Veim][Br]) layer were formed using gel particle suspension dialyzed for (a) 0, (b) 3, (c) 9, and (d) 64 h. Upper SEM image displays the position of the line scan and lower EDS plot shows the relative bromide content along the line scan.

The caption:

Figure 9. Relationships between CO2 and N2 permeances of the composite membranes and (a) dialysis time of the poly([Veim][Br]) gel particle suspension and (b) depth of the diffusion resistance layer formed in the PSf support membrane determined from the EDS results. The plots are experimental data; black circles are CO2 permeances, and white squares are N2 permeances. The gas permeation test was performed at 50 °C using CO2/N2 mixed gas with 1 kPa of CO2 partial pressure and 80% of relative humidity. The total pressure of the feed and sweep gases was atmospheric pressure. The solid lines in (b) are results calculated as per the resistance model. The error bars represent the standard error of the following numbers of the experimental data: 54 times for no dialysis conditions, 4 times for 3 and 9 h dialysis conditions, and 3 times for 20 and 64 h dialysis conditions.

The caption:

Figure 10. Illustration of the assumed pore structure with the diffusion resistance. A 1 ?m-thick poly([Veim][Gly]) gel layer is formed on the surface of the PSf support membrane. Diffusion resistance layer of the [Veim][Gly] monomer is impregnated in the pores near the surface (gray colored zone).

And now the important stuff, the selectivity:



The caption:

Figure 11. Relationships between the CO2 and N2 permeances of the composite FTM and (a) CO2 partial pressure difference and (b) temperature. The used composite FTM for this investigation was prepared using the poly([Veim][Gly]) gel particle suspension after dialysis for 30 h.

The conclusion:

In this work, we developed a hollow fiber-type CO2 separation membrane composed of a gel layer of PIL with glycine as the CO2 carrier and a PSf support membrane. An approximately 1 ?m thick gel layer was formed on the inner surface of the PSf support membrane via filtration of a suspension of gel particles with a poly([Veim][Gly]) network at constant pressure followed by the drying of the deposited gel layer. The gel layer showed high CO2 permeance based on the facilitated transport mechanism. The mixed gas CO2 permeance and CO2/N2 selectivity of the developed membrane at a partial pressure of CO2 is 0.1 kPa with 80% of relative humidity at 30 °C being about 1400 GPU and more than 2000, respectively. In addition, improvement of the CO2 permeance could be expected by preventing the formation of a diffusion resistance layer inside the support membrane. Because the developed hollow fiber-type membrane has a large specific surface area, it can be also expected that a membrane module with high volume efficiency could be produced using the developed membrane. The good CO2 permeance and CO2/N2 selectivity at very low CO2 partial pressure and the hollow fiber-type structure of the developed membrane could aid in the realization of a compact CO2 separation process for DAC applications.

These are dark times, and in dark times, sometimes it relieves the pain to recognize that for all that is, there are also things - good things - that are possible.

We have left our children nothing but disaster, except, in the cases like the work of scientists like these, perhaps some tools that they might use to dig out of the graves we have dug for them.

Have a nice TGIF day tomorrow.

[Karadeniz]

1. Thanks!❤ I didn't read when it may be available.

[NNadir]

2. This technology most likely will never approach industrialization, not in our lifetimes anyway.

The reality is this:

Carbon dioxide is not considered that valuable a commodity, and in any case, we have no interest in the environment.

There are plenty of streams of carbon dioxide that are far more concentrated by air, mostly dangerous fossil fuel waste, which is simply dumped into the atmosphere along with other things that kill people.

We are leaving this legacy of waste for all future generations; however we are also leaving them some valuable knowledge, assuming that our fondness for ignorance does not lead to an event that is the equivalent of burning the library at Alexandria.

This technology will be valuable in another time, but isn't so now, or at least I cannot think of an application that would make the only thing about which we care, money.