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Thu Aug 15, 2019, 10:59 PM

Molecular Modeling of the Degradation of a Potential Direct Air CO2 Capture Resin.

The paper I'll discuss in this post is this one: Direct Air Capture of CO2 with an Amine Resin: A Molecular Modeling Study of the Deactivation Mechanism by CO2 (Buijs, Ind. Eng. Chem. Res. 2019, 58, 14705−14708)

It is increasingly obvious that we haven't got a practical clue about how to address climate change, since the popular answer, so called "renewable energy" may be soaking up tons of money on a trillion dollar scale, but it has done nothing at all to even slow the increase in the rate of accumulations of the dangerous fossil fuel waste carbon dioxide, the 2nd derivative, and even less to prevent the deaths of seven million people each year from air pollution.

As of 2019, the rate of growth of carbon dioxide concentrations in the planetary atmosphere is hovering around 2.4 ppm/year. In the 20th century, according to the records at the Mauna Loa carbon dioxide observatory operating since the late 1950's, it was (according to monthly data) around 1.3 ppm/year.

Solar. Wind. Blah. Blah. Blah.

Somehow, in the bizarre universe of people at a Trumpian intellectual level for moral and intellectual dishonesty, there are actually people who carry on more about the collapse of a uranium tailings dam in a remote region of New Mexico, which apparently killed no one, with zero attention to the aforementioned annual deaths from air pollution, or for that matter, similar coal mining tailing dam collapses all over the world while we wait for the grand so called "renewable energy" nirvana that did not come, is not here, and will not come.

By the way, about those steel towers for all those wind turbines that will be landfill in 20 years, they're made of steel and to make steel one needs to mine, um, coal.

In the 21st century the fastest growing source of energy on the planet has been coal.

Solar. Wind. Blah. Blah. Blah.

You can actually get people to cheer for this outcome.

As a result of this unconscionable selective attention, future generations are totally screwed; not only will they need to clean up all the toxic electronic waste generated in the useless solar and electric car fantasies, but they will need to clean up the planetary atmosphere that has been greatly degraded because so called "renewable energy" did not work, is not working, and will not work.

For the last 10 years or so, recognizing that there is no political will either on the right or on the left to do what is necessary to address climate change, even to slow it or merely stop its acceleration, represented by a celebration of ignorance throughout the spectrum, I have been considering the very difficult engineering question of how to remove carbon dioxide from the planetary atmosphere, which seems to me to be remotely feasible, but only if we have access to huge amounts of cheap energy, since we need to not only find a way to remove the carbon from the atmosphere, but also to have a place to put it (or better use it), and well as huge amounts of energy to overcome the entropy we have left for people who are infants today.

There are sophisticated arguments in great abundance in the primary scientific literature about this topic, one area of discussion being direct air capture (often abbreviated DAC), of which I am not personally a great fan, although I can certainly imagine some esoteric approaches by which some of this can be practiced, albeit not a tremendously significant scale.

The paper referenced here, which is rather short, examines a case that the author plainly suggests will not work, although the outcome does suggest another possibility for useful organic synthesis using carbon dioxide as a starting material.

From the introductory text:

Direct air capture of CO2 (DAC CO2) will become an unavoidable option and tool for CO2 capture (and utilization) in general, as small point (transport, residential) emissions of CO2 account for more than 40% of the U.S. CO2 emissions.1,2 In 2012 the polymeric resin Lewatit R VP OC 1065 was reported as a promising material for direct air capture of CO2 with respect to aspects like rate of CO2 uptake, limited H2O uptake, CO2 capacity, and CO2 desorption under favorable conditions and energy requirements.2,3 In 2017, a molecular modeling study was reported wherein the CO2 capturing reactions of the polymeric resin Lewatit R VP OC 1065 were identified and quantitatively described in accordance with experimental data.4 In 2017, Yu et al.,5 reported significant oxidative degradation above 70 °C in air and, surprisingly, above 120 °C degradation in concentrated dry CO2. Both types of deactivation in principle are detrimental for its practical application. Thus, determination of the reaction mechanisms of both types of deactivation is of utmost importance. In this molecular modeling study, various reactions on the resin in the presence of CO2 are investigated. Oxidative degradation reactions will be reported separately.

I am not immediately familiar with the structure of this commercial resin, but I'm guessing that it is an arylalkyl amine of some kind; it is clearly an amine from the context. There may be proprietary issues here.

This is an in silico study:

All molecular modeling studies were performed using Wave function’s Spartan ’18 suite.6 Molecular mechanics (MMFF) was used to explore the physisorption complexes of CO2 with the previously obtained model for Lewatit R VP OC 1065, the saturated trimer of 4-aminomethyl vinylbenzene.4 Results obtained with molecular mechanics were used as starting structures for various quantum chemical calculations wherein physisorption and particularly chemical reactions were investigated further. All structures were fully optimized using density functional theory (DFT) B3LYP/6-31-G*. Transition states were identified and characterized using their unique imaginary vibrational frequency or internal reaction coordinate (IRC).9 Reaction enthalpies and activation barriers were calculated using total energies and enthalpy corrections. Entropy corrections were generally not used because of the huge simplifications of the QM-systems. However, in some specific cases the entropy contribution is explicitly mentioned.

Here are the graphics from the paper, suggesting the structure of the resin, generally shown edge on, with a few exceptions showing aromatic rings.

Figure 1. CO2 physisorption complex of the carbamic acid amine (a), the transition state of the CO2 capturing reaction (b), and the bis carbamic acid (c). Display: ball and spoke; B3LYP/6-31G*.

Figure 2. Bis carbamic acid complex (a), the bis carbamic acid prereaction complex (b), the transition state for isocyanate formation (c), and the product carbamic acid isocyanate H2O complex (d). Display: ball and spoke; B3LYP/6-31G*.

Figure 3. Amine isocyanate complex (a), the transition state for H2O catalyzed amine to isocyanate addition (b), the (enol) urea H2O complex (c). Display: ball and spoke; B3LYP/6-31G*.

Figure 4. The transition state for CO2 catalyzed formation of an isocyanate (a) and the transition state for CO2 catalyzed addition of an amine to a carbamic acid. Display: ball and spoke; B3LYP/6-31G*.

B3LYP/6-31G refers to the basis orbital set in the DFT calculations.

Apparently the degradation pathway in this model seems to involve the formation of isocyanates which further react to give ureas.

I personally am always interested in the formation of isocyanates without the use of phosgene, and if nothing else, this paper is of interest in this regard. To the extent that urethanes and polyureas and polycarbonates are synthesized with a carbon dioxide starting material they are effectively sequestered.

This mechanism as described here, in terms of a DAC resin, suggests that this resin will prove as useless for air capture, ultimately generating large amounts of plastic waste, already an intractable problem, much as electronic waste, to which all those shiny solar cells will become in 20 years is an intractable problem.

At least, as opposed to the solar fantasy, this direct air capture will never become sexy and the subject as much wishful thinking as the solar energy scam is proving to be.

From my perspective, direct air capture, as opposed to other more (it seems to me) workable processes seems unlikely to be spectacularly successful, although load leveling by using compressed air, with waste heat being recovered and utilized to minimize energy losses associated with temporary energy storage, said heat available from the output of combined cycle nuclear plants and/or fission products being utilized from used nuclear fuels, may offer some tools available to the generations we have screwed with pure contempt.

Although such processing offers the possibility of addressing and destroying halogenated greenhouse gases, nitrogen oxides and ozone, the effect is likely to be small.

Have a nice day tomorrow.

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