Organic Chemists Contribute to Renewable Energy
Background - Why is this important?
“Biofuels play an essential role in reducing the carbon emissions from transportation.The development of ‘drop in’ fuels produced from lignocellulosic raw materials will increase both the availability of biofuels and the sustainability of the biofuel industry”
Adrian Higson - Energy Consultant
Biofuels are either liquid or gaseous fuel. They can be produced from any source that can be replenished rapidly, e.g. plants, agricultural crops and municipal waste. Current biofuels are produced from sugar and starch crops such as wheat and sugar cane, which are also part of the food chain.
One of the key targets for energy researchers is a sustainable route to biofuels from non-edible lignocellulosic (plant) biomass, such as agricultural wastes, forestry residues or purpose grown energy grasses. These are examples of so-called advanced biofuels.
Current biofuels, such as ethanol, have a lower energy content (volumetric energy density) compared with conventional hydrocarbon fuels, petroleum and natural gas. The aim is to produce fuels that have a high carbon content and therefore have a higher volumetric energy density. This can be achieved by chemical reactions that remove oxygen atoms from biofuel chemical compounds. This process produces a so called 'drop-in biofuel', i.e. a fuel that can be blended directly with existing hydrocarbon fuels that have similar combustion properties.
What did the organic chemists do?
Efficient synthesis of renewable fuels remains a challenging and important line of research. Levulinic acid and furfural are examples of potential ’platform molecules’, i.e. molecules that can be produced from biomass and converted into biofuels. Levulinic acid can be produced in high yield (>70%) from inedible hexose bio-polymers such as cellulose, which is a polymer of glucose and the most common organic compound on Earth. Furfural has been produced industrially for many years from pentose-rich agricultural wastes and can also act as a platform molecule.
Recent reports have highlighted the use of organic chemistry to convert platform molecules like levulinic acid and furfural into potential advanced biofuels. Specifically, changing parts of the molecules that are responsible for their structure and function. This process is called ‘functional group interconversion’ and is part of the basic toolkit of organic chemistry. For example, researchers have described a process for converting levulinic acid into so-called 'valeric biofuels'. One of these biofuels, ethyl valerate, is claimed to be a possible advanced bio-gasoline molecule with several advantages over bio-ethanol.
A second method to create hydrocarbons involves Dumesic's approach1 via a decarboxylation of gamma-valerolactone, which can be produced in one step from levulinic acid by hydrogenation.
Generating a hydrocarbon from 2-methylfuran
Corma’s synthesis2 is one of the more recent and ingenious examples of C5 or C6 decomposition products being used as precursors to biofuel molecules. This method generates a C15 hydrocarbon molecule from furfural via a molecule called, 2-methylfuran (a C5 molecule). The key step in this process is an acid catalysed, water mediated trimerisation of 2-methylfuran to give a trimer. A catalysed hydrogenation was then used to deoxygenate this trimer resulting in the C15 hydrocarbon. This molecule is a potential bio-diesel molecule with advantages over first generation bio-diesels both in terms of fuel quality and sustainability.
What is the impact?
Biodiesel is likely to be the second most important biofuel after ethanol in the short to medium term. Global production of biodiesel is expected to increase from 11 billion litres to reach 24 billion litres by 2017. For organic chemists, there are significant opportunities associated with further developing energy crops and producing advanced biofuels from new sources such as algae, industrial or post-consumer waste.
1 J Q Bond, D M Alonso, D Wang, R M West and J A Dumesic, Science, 2010, 327, 1110
2 A Corma, O de la Torre, M Renz and N Villandier, Angew. Chem. Int. Ed., 2011, 50, 2375
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Contact and Further Information
Dr Anne Horan
Programme Manager, Life Sciences
Royal Society of Chemistry, Thomas Graham House, Science Park, Milton Road, Cambridge, CB4 0WF
Tel: 01223 432699