Wanna Talk Sequestration? One Route: Carbon Dioxide In USE.

[NNadir]

Let's face the facts. Long term carbon dioxide sequestration in geological formations is garbage thinking, literally, since by definition disposal for the long term is a dump and dumps involve garbage.

Garbage thinking is clearly unsustainable and uneconomic. If you have to pay, especially a lot of money, disposal fees, you will resist doing so, particularly in our current culture of "me first" greed. On the other hand, if you can make something believed to be waste into an important industrial or otherwise commercial product, then, well, everybody wins.

We can say, I think, a lot of bad things - if we want to do so - about the chemical giant BASF, but BASF has pioneered many chemical technologies on which all of humanity has become dependent. Without the contributions of BASF, the modern technological infrastructure, for better or worse, would simply not exist.

As a corporate policy - and I am not sufficiently familiar with the company to remark on corporate practice - BASF has a practice it calls in corporate speak, Verbund, which is the German word for "integration" or "interlinking." In a purely chemical sense, stripped of the other parts, this means the elimination of waste products by finding a use for all side products.

I favor banning all dangerous fossil fuels. They are not acceptable in any sense of the word. But reality calls for a phase out of them since nobody here or elsewhere, with a few exceptions, is willing to become impoverished for the environment. Indeed it is very arguable that the worst factor in environmental degradation is, in fact, poverty. So I'm thinking about what might drive a phase out, and how it might be accomplished and what we can do to ameliorate the huge problems in the transition phase.

I have been trying to use this holiday period to catch up on some reading and to outline some processes for the extraction of certain classes of materials, and I have been focusing in the last week or so on what may become a miracle solvent, specifically, carbon dioxide.

Whether people realize it or not, one of the biggest environmental risks we face today involves the use of solvents, many of which are petroleum based and many of which, like the halooalkanes that have been a long term plague from the semiconductor industry, are extremely persistant and toxic compounds that contaminate water, land and air around the world.

For instance, the solvent dichloroethane is produced in tens of millions ton quantities, as is the solvent perchloroethylene, dry cleaning fluid, which is found in almost all ground water, surface water, and predictably rain in the United States.

The kinds of solvents are replacable by supercritical carbon dioxide.

There is an explosion in the chemical literature of work now involving the replacement of these solvents with supercritical carbon dioxide, a form of the compound that is neither a liquid nor a gas, but an intermediate state that exists at high pressures just above room temperature.

The use for this stuff is remarkable. Although its lack of polarity makes it a poor solvent for most metals, the addition of small amounts of complexing agents like diethyldithiolatocarbamate, tributyl phosphate, and simple organic carboxylic acids makes it possible to extract metals and organic materials both in a remediation or production standpoint. Indeed the flexibility of these systems is such that remediation can become production, thus expanding the Verbund principle. In the last hours I have read about these kinds of processes for the use of extraction of gold cyanide complexes, lead, copper, zinc, uranium, rhodium, ruthenium maleic acid, oxalic acid, a variety of organic acids and esters, including those used a food products,

This is the kind of thing in which we should be investing heavily. Wanna sink money into environmental R&D? This might well be a winner.

The fact is that carbon dioxide used as a solvent must be stored, and the storage by nature involves sequestration, monitored sequestration, as opposed to dumping.

The carbon dioxide dumps everyone talks about are merely trying to sweep a big problem under the rug, dumping responsibility on future generations who will have more than just cause to hate us already.

How much carbon dioxide can we sequester through use? A lot, not enough to make dangerous fossil fuels sustainable, but enough to help. Potentially these applications could easily, as an off the cuff impression and without a systematic analysis, involve one or two billion tons a year, since many more toxic solvents are used on a hundred million ton scale.

The dangerous fossil fuel culture currently dumps somewhere on the order of 30 billion tons of carbon dioxide a year into its favorite dump, the planetary atmosphere.

I'm trying to cut down on the time I waste on blogging - a push pull affair of a sort of mutual agreement - but my increasing cynicism about blogging not withstanding, it seems a worthwhile thing to throw out for people to think about.

[drm604]

1. Some questions.

Not criticism, just curiosity.

Is that one or two billion tons a year cumulative? Would we be adding that much more each year, or replacing it? Is it cleanable and reusable? (Obviously it can somehow be cleaned, filtered or whatever, but is it economical to do so?)

What is the carbon footprint from doing this? Gathering, compressing, retaining, recycling - how much of a carbon footprint does all this entail? Is it more or less than that of current solvent usage?

[NNadir]

2. These are good questions.

In answer to the first one, it is almost certainly the case that a plateau would be reached. How high that plateau is, is difficult to say.

It would certainly be in the range of billions of tons.

The other uses of carbon dioxide are refrigeration - it's actually an excellent refrigerant, although not as efficient as the much more environmentally obnoxious fluorocarbons - and as a oxidizing reagent in a very important reaction known as the Boudouard reaction and related reactions.

Examples of use as an oxidizing reagent are C + CO₂ <-> 2 CO.

Carbon monoxide is a starting material for syn gas, a mixture of CO and H₂. In theory, this reaction could be used to replace all of the world's petroleum, including that used for synthetic purposes. In this way every piece of plastic on earth could become a sequestering device, albeit with the well known environmental drawbacks of plastics.

Another, maybe more interesting variant of this reaction is of the form:

C_xH_y + CO₂ <-> zCO + wH₂. Most commonly this reaction is currently performed with methane, CH₄, but it applicable in many other situations, including waste plastics, waxes and oils.

This reaction can be driven further with the water shift reaction, a very important industrial reaction already, to produce pure hydrogen: CO + H₂O <-> CO₂ + H₂. In this case, carbon dioxide is a catalyst for the production of hydrogen from alkanes or superalkanes like polymers.

The use of carbon dioxide as an oxidant will continuously consume carbon dioxide assuming a reductant is available. One possible reductant is the electron itself, which is, in theory, available from electricity. Another is hydrogen which can be made in a variety of (energy consuming) ways. Others include biomass and wastes dumped up to now in various places around the world.

Carbon dioxide is also useful for synthetic chemical reactions of many types, for example, the production of acetic acid from methane: CH₄ + CO₂ <-> CH₃COOH.

There is a thermodynamic penalty for capturing carbon dioxide. It's the elephant on the table no matter whether one is dumping carbon dioxide in the atmosphere or into some imagined waste dump/geological formation or using it in industrial processes. Your point is well taken.

If one obtains the energy to address this thermodynamic penalty in clean ways, say nuclear energy, the net effect is to reduce the carbon dioxide concentration in the international waste dump, our atmosphere.

All of these approaches are the subject of a vast amount of research world wide. This is, of course, a good thing, although it's all coming in under the radar. Basically, personally I think about this stuff all the time.

Again, your questions are excellent, and I thank you for asking them.

[wtmusic]

3. Apparently practical as a dry-cleaning agent at 90°F and 1000psi:

"Supercritical carbon dioxide (SCD) can be used instead of PERC (perchloroethylene) or other undesirable solvents for dry-cleaning. Supercritical carbon dioxide sometimes intercalates into buttons, and, when the SCD is depressurized, the buttons pop, or break apart. Detergents that are soluble in carbon dioxide improve the solvating power of the solvent."

http://en.wikipedia.org/wiki/Supercritical_fluid

(Of course instead of Chevron, you're going up against Dow Chemical now).

Once the CO2 is used as a solvent does it return to the atmosphere as CO2?

"Garbage thinking is clearly unsustainable and uneconomic." I'm reminded of one time I naively asked my Dad (who grew up in Depression-era rural Wisconsin) where they dumped their garbage. His answer: "We didn't have any garbage."

[NNadir]

4. Because of the cost of separations, it is easier to recover the CO2 by transfer to a tank.

That's the beauty of it.

The dirt + detergent is isolated during depressurization, probably as a small amount of mass.