So, as you may or may not know, I currently work as an organic chemist in the field of carbon capture and storage (CCS). It has come to my attention that not many of you actually know what CCS is so I thought I would take this opportunity, in my jet lagged state, to explain it. There are plenty of other people who have explained it much better than me so do also check out the literature.1, 2
“Carbon capture” refers to the capturing of carbon dioxide (CO2), usually from power station flue gases and “storage” is the storing of this captured CO2. So why do we want or need to capture and store carbon dioxide from places such as power stations? Fossil fuel combustion supplies more than 85% of energy for industrial activities and is therefore a huge greenhouse gas contributor. Coal will supply 28% of global energy by 2030, as part of a 57% increase in CO2 emissions. CCS is a way of reducing emissions and is considered a provisional system to allow a transition away from the use of fossil fuels [“World energy outlook” (International Energy Agency, Paris, 2007), http://www.iea.org. 2
There are many different methods for the capture of CO2. My research is in post-combustion carbon capture (PCCS) which, as the name suggests, allows the capture of CO2 after the combustion of the coal (or gas). There are also pre-combustion and oxy-fuel combustion processes which can be used (as shown in my very crude and simplified schemes below).3
Since it is what I research, I will only talk about PCCS, but the other CCS options are equally valid. The majority of PCCS research is in the use of amines to capture CO2, as these can form stable carbamates or bicarbonates with CO2. These salts can then be heated up to allow release of pure CO2, which can be sent off for storage, and the free amine, which is recycled.
There are many amines that can be used in carbon capture processes but mostly they are alkanolamines such as monoethanolamine (MEA) and N-methyldiethanolamine (MDEA) or hindered amines such as piperazine (PZ).
MEA MDEA PZ
There are currently lots of pilot plant projects where amines are being used to capture carbon dioxide. Hopefully soon there will be a full-scale demonstration project, and then fingers crossed, it will be commercialised.
Right, now onto storage… 5, 6
Storage (or sequestration) is very much a geologist’s problem and although I know more than the average person about it, I am in no way an expert. The theory is that the captured, pure CO2 can be stored in underground geological formations such as oil fields, gas fields and saline aquifers. The current trend is to use CO2 in enhanced oil recovery which allows previously unavailable oil to be retrieved. Similarly, CO2 can be used to obtain coal from unmineable coal seams. Saline aquifers, of which there are many, offer a large potential storage volume but relatively little is known about the effects of storing CO2 in them, particularly in relation to potential CO2 leakage. There is a great deal of research into all areas of storage and I do recommend looking at further literature if you wish to learn more.
I hope I have managed to inform you further on CCS. Although it is not a fix-all process, I believe CCS is necessary as a short term measure to reduce our carbon emissions and I hope a full-scale CCS project does go ahead very soon.
1 J. Gibbins, Energy Policy, 2008, 36, 4317–4322. 2 H. J. Herzog, Environ. Sci. Technol., 2001, 35, 148A–153A. 3 R. S. Haszeldine, Science, 2009, 325, 1647–52. 4 J. D. Figueroa et al, Int. J. Greenh. Gas. Con., 2008, 2, 9–20. 5 K. Michael et al, Int. J. Greenh. Gas. Con., 2010, 4, 659–667. 6 K. S. Lackner, Science, 2003, 300, 1677–8.