Our world has entirely too much carbon dioxide. Millions of tons of carbon dioxide gas are emitted from car engines and from coal-fired power plants, and the gas goes up into the atmosphere where it serves to heat up the planet surface – the dreaded greenhouse gas effect. What can be done about this? As far as Nature is concerned, the primary “drain” that sucks carbon dioxide from the atmosphere is plantlife, or “biomass” in the parlance of many scientists. Plants take in carbon dioxide gas and, through a sequence of chemical transformations, use the carbon present to build useful plant structures such as cell walls. Plants, then, represent a “sink” for carbon, specifically the carbon found in carbon doxide.
This role of plants is doubly valuable as opposed to methods which only reduce the release of carbon dioxide, plants can remediate and reduce carbon dioxide which has already been released to the atomosphere. This helps to address the problem of the large buildup of CO2 that has been carelessly released over the past fifty years. The trick for using plants – biomass – as a “sink” for carbon dioxide is that we can’t afford for the plants to be burned when they are at the end of their lifecycle. Burning the plants would simply oxidize all the carbon in the biomass and rerelease all of the carbon dioxide that the plant had retained over its lifetime. Another method of disposal is needed, one which keeps all of the carbon locked in and doesn’t allow it to be rereleased as carbon dioxide gas.
Scientists report in the New Journal of Chemistry that they have now developed such a method. It’s based on an existing, natural process. One of the possible fates of biomass in the wild is the slow transformation to coal. This process can normally take several hundred million years to complete, unaided. However, the process can be dramatically sped up in the laboratory by heating the plant material in a closed vessel for 24 hours at a temperature of about 200 degrees Celsius. This process, called hydrothermal carbonization, dehydrates all of the plant material and yields a material very similiar to coal. The oxygen present in the plant is not converted to carbon dioxide but rather leaves the reaction vessel as part of water molecules.
This chemical process has many advantages. To start with, once it has been started, it is a spontaneous (exothermic) process, meaning that no outside heat is necessary to maintain the reaction temperature of 200 degrees. This provides immense energy cost savings. Also, the plant material does not have to be dried beforehand, as the process tolerates water just fine. This removes the need for complicated and costly drying steps. All of these factors combined make the carbonization of biomass an attractive process for removing carbon dioxide. The plants suck up the gas from the atmosphere and transform it into parts of their plant structure; this process then turns that carbon directly into coal, locking it into a form which doesn’t pollute the atmosphere and which doesn’t contribute to global warming. Coal is pure, concentrated carbon, and is a valuable building block for many organic materials; it can also simply be buried, becoming the ultimate “graveyard” for greenhouse gases.
The source of this article can be found at: http://www.rsc.org/Publishing/Journals/NJ/article.asp?doi=b616045j