Chemical technology news from across RSC Publishing.
Instant insight: Back in black
24 May 2007
Markus Antonietti, Arne Thomas and Maria Titirici discuss the hydrothermal carbonization of biomass - is it a solution to the CO2 problem?
Biomass can be converted to a form of carbon much like coal
The global atmospheric concentration of carbon dioxide (CO2) has increased markedly as a result of human activities since the industrial revolution. The inevitable impact on the world climate, recently announced by the IPCC (Intergovernmental Panel on Climate Change, see link below), has prompted intensive discussions from politics, industry and the scientific community about how to treat the CO2 problem.
The biggest carbon converter, with the highest efficiency to bind CO2 from the atmosphere, is biomass. Interestingly, the removal of just 8.5% of freshly produced biomass from active ecosystems would compensate for all the CO2 liberated from oil. Coal formation from biomass is one of the natural sinks that has been active in the past on the longest scale. Natural coalification of biomass takes place on a timescale of some hundred (peat) to hundred million (black coal) years. Due to its slowness, it is usually not considered in renewable energy exploitation schemes or as an active sink in CO2 cycles. Nevertheless, it is obvious that carbon fixation into coal is a lasting effort, as brown or black coal are practically not biodegradable. Thus, turning coal formation into an active element of carbon sequestration schemes would be very meaningful, but requires the acceleration of the underlying coalification processes.
Hydrothermal carbonization (HTC) can be such a process (see the reference below): HTC describes heating carbohydrate sources in water, e.g. biomass dispersions, in a closed reaction vessel for 4-24 h to temperatures around 200 °C. Upon dehydration of the carbohydrates, carbon with a chemical composition similar to brown coal is observed. Thus, HTC is an extremely simple, cheap and easily scalable process. Furthermore, it was shown that HTC of carbohydrates can yield interesting carbon micro- and nanostructures, such as carbon microspheres. Using suitable additives, carbon nanocables and fibres, porous carbon architectures and metal-carbon composite materials can be generated.
A variety of nanostructures and porous architectures can be made
In CO2 conversion schemes, HTC has a number of other practical advantages: once activated, HTC is a spontaneous, exothermic process, it liberates up to a third of the combustion energy stored in the carbohydrate throughout dehydration. Furthermore, HTC inherently requires wet starting products or biomass, as effective dehydration only occurs in the presence of water, plus the final carbon can be filtered easily from the reaction solution. This way, complicated drying schemes and costly isolation procedures can be avoided. In addition, most of the original carbon stays bound to the final structure. Carbon structures produced by this route-either for deposit or materials use-are therefore the most CO2-efficient.
In that sense, HTC can be seen as much more than just a technique for making carbon-rich substances.
Read the full Opinion article in issue 6 of New Journal of Chemistry.
Link to journal article
Back in the black: hydrothermal carbonization of plant material as an efficient chemical process to treat the CO2 problem?
Maria-Magdalena Titirici, Arne Thomas and Markus Antonietti, New J. Chem., 2007, 31, 787
Intergovernmental Panel on Climate Change
Read more from the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP).
External links will open in a new browser window