CSIRO makes CO2 "sponge"

[Dr Mordrid]

CSIRO = Commonwealth Scientific and Industrial Research Organisation (Australia)

http://www.csiro.au/en/portals/media/csiro-solar-sponge-soaks-up-co2-emissions.aspx

CSIRO 'solar sponge' soaks up COâ‚‚ emissions

CSIRO scientists have created a 'solar sponge' which captures and then releases carbon dioxide using the power of natural sunlight – as published today in scientific journal Angewandte Chemie.

The breakthrough presents a new way to recycle CO2 emissions using renewable energy. The 'sponge' which is made from a new smart material called a MOF - metal organic framework - adsorbs carbon dioxide, but when exposed to sunlight, instantaneously releases it.

Known as dynamic photo-switching, this capture-and-release method is extremely energy efficient and only requires UV light to trigger the release of CO2 after it has been captured from the mixture of exhaust gases.

Dr Matthew Hill, who was awarded a 2012 Eureka Prize for his MOF research and led the CSIRO group conducting this research, said: "The capture and release process can be compared to soaking up water with a sponge and then wringing it out. When UV light hits the material its structure bends and twists and stored gas is released."

"This is an exciting development for carbon capture because concentrated solar energy can be used instead of further coal-based energy to drive the process," he added.

The traditional process for carbon dioxide capture has been to use liquid absorbers such as amines to remove flue gases at a coal-fired power station before they are released into the atmosphere. They are then heated to release the CO2 which is then stored and can be re-used. This process can consume as a much as 30 per cent of a power plant's production capacity.

MOFs absorb as much as a litre of nitrogen gas in just one gram of material. This is possible because MOFs have the surface area of a football field in just one gram, meaning that gases can be soaked up like a sponge to all of the internal surfaces within.

In their paper titled 'Dynamic Photo-Switching in Metal Organic Frameworks as a Route to Low Energy Carbon Dioxide Capture and Release' CSIRO researchers show that when exposed to concentrated UV light the MOF sponge instantaneously releases up to 64 per cent of absorbed CO2.

Lead researcher and author of the paper, Richelle Lyndon, who is also a Monash University student, said: "The MOFs are impregnated with light-responsive azobenzene molecules which react to UV light and trigger the release of CO2. It is this reaction, and the material's ability to bend and flex, which makes the material we have created so unique."
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[Brian Ellis]

Let's look at some figures.

Man-made CO2 fossil fuel emissions total 26 billion tonnes/year. = 26 trillion kg = ~23 trillion l

Assuming 1 g/l of MOF, this would require 23 trillion g (the re-usability apparently diminishes to 64% per go) = 23 trillion g of nanoparticles = 23 million tonnes. Even if we capture only 10% of our emissions, we are still needing quantities of nanoparticles in the order of a million tonnes.

I suggest that the energy required to manufacture such a quantity may require the production of more CO2 than it could absorb in a lifetime.

Then there is the UV energy required to release the CO2 for sequestration. No mention is made of this. Many years ago, I directed a printed circuit factory, where we used film photoresists using azocinnemates. These triggered the release of radicals which started the polymerisation of a methacrylate monomer when exposed to a high-intensity UV light source. I experimentally tried to use sunlight to achieve the same effect. It required a full week's exposure to summer sun to produce a result equivalent to 60 sec of exposure in the lab. By analogy, I suggest their azobenzoates would release radicals that would initiate the release of the absorbed CO2. Notice the use of the term 'concentrated' UV. I therefore postulate the 'free' unconcentrated UV from the sun would require thousands of km^2 to slowly release of the CO2.

Worse, the article talks about N2 absorption, as well as CO2. If this 'sponge' is not specific to one gas, then the process is practically useless because it would be necessary to use monoethanolamine (MEA) separation to concentrate the CO2 to sequestrable purities. In that case, use the MEA in the first place and forget the intermediate MOFs!

This is an interesting development and probably good academic research BUT, as proposed in the article, it has no practical application, at this stage, IMO.

As a PS, I can't help but compare this with the, also Australian, research into the catalytic photolysis of water to produce hydrogen. This also requires a concentrated UV light source. The energy used to produce the UV is ~10,000 times greater than the thermal energy obtained by burning the resultant hydrogen!