What is there to say about carbon capture and storage?

In December last year I spotted a kind of interesting thing in my Facebook feed: A post from Chalmers University of Technology describing how a few of their researchers, together with some other researchers from Stockholm University, had developed a new, promising material for carbon capture and storage (CCS). I found this interesting partly for materials science reasons and partly because by and large, I hear surprisingly little about CCS technology in general. Other technologies associated with reducing carbon dioxide emissions, like rechargeable batteries, fuel cells and biofuels, get substantially more attention. So what is there to say about CCS?

The idea behind CCS is to separate out carbon dioxide from a mix of gases, like the flue gases from coal- and oil-fired power plants, and thereby stop it from entering the atmosphere. Instead the carbon dioxide is taken away and stored. The ocean floor and certain types of bedrock are seen as promising storage sites, and countries like Norway are conducting tests where carbon dioxide from natural gas fields are stored in the bedrock of the ocean floor around the original deposits. All steps in this process are of course associated with technical challenges, costs and risks - for example, if the carbon dioxide escapes from its long-term storage it will both negate the benefits of capturing it in the first place and potentially harm people and the nearby environment. According to a review paper from 2018, published in the Royal Society of Chemistry journal Energy and Enviromental Science, attempts to use CCS have frequently turned out more expensive and time-consuming than expected, partly due to installation costs and the need to build up infrastructure. Successful applications of CCS, on the other hand, offer the possibility of large and rapid reductions of carbon dioxide emissions.

The new material presented by the Chalmers researchers is supposed to be used in the carbon capturing step. To understand what problem they are trying to solve we can return to the review paper linked above. Among many other things, it describes how current CCS technology relies on aqueous solutions of chemicals to separate out carbon dioxide from other gases. This process has been used for a long time to separate out carbon dioxide from natural gas and thereby get a cleaner and better natural gas product to burn, but it can be adapted for exhaust or flue gases from for example power plants. Unfortunately, the carbon capturing in itself consumes extra energy since the carbon dioxide, once captured, also has to be extracted from the aqueous solution so that it can be transported away. This may be accomplished by heating the solution or changing the pressure. Additionally, many of these chemical solutions are toxic and in higher concentrations also corrosive, which can cause problems both with wear and tear and in the case of an accident where the solution leaks out.

One way to get around this problem would be to develop solid materials that can selectively absorb carbon dioxide. These could, apart from the lower risk of leakages, potentially be easier to install in existing plants and factories and also require less energy during the extraction of the captured carbon dioxide. The paper published by the Chalmers researchers presents one such material, consisting of two component parts. One component is a porous network of gelatin and cellulose (yes, cellulose as in wood, although it has been processed into a different form) which gives the material structure and rigidity while still being porous enough to easily let gases like carbon dioxide pass through. The other component is a powder of the mineral zeolite, which consists of silicon and aluminium atoms and also has a structure full of large holes. Carbon molecules can attach themselves to the surface of this aluminium-silicon mineral, and thanks to the porous structure there is a lot of surface for them to attach to. This makes it a good carbon capture material.

The combination of zeolites, gelatin and cellulose in the new material is supposed to make it easy to handle and install, cheap, and also mostly biodegradable. It could therefore be part of the development of cheaper and more easily applicable CCS technology, which in turn might lead to wider use and more attention for CCS. Of course, this connects to the other question that comes up when CCS is actually discussed, namely if that is what we want. Something that separates CCS from technologies that receive more attention, like fuel cells and renewables, is that the latter two have a clear role in a society that has transitioned away from fossil fuels. CCS, on the other hand, is all about still producing carbon dioxide but not actually letting it out. The interest, or lack of interest, in CCS is influenced by if this is seen as a delay or obstacle to a necessary transition away from producing carbon dioxide or as a way to reduce carbon dioxide emissions faster than this transition can take place. There seems to be quite a few things to say about carbon capture and storage - from different perspectives.