James H Clark, Green Chemistry Centre of Excellence, University of York, York YO10 5DD, UK
The future success of many biorefineries is likely to depend on obtaining fuel, chemical and material value from biomass. The use of low environmental impact green chemical technologies will help ensure that those products are genuinely and verifiably green and sustainable as is likely to be required from new and future standards imposed in many regions1.
The extraction of valuable chemicals from biomass could form the initial processing step of many future biorefineries. We have shown that wax products with numerous applications, can be extracted from crop and other by-products including wheat and barley straws, timber residues and grasses, using supercritical carbon dioxide – a green chemical technology that allows the production of products with no solvent residues 2. The extracted residues can subsequently be used in applications including construction as well as in bioprocessing.
Microwaves are a green chemical technology increasingly used to pyrolyse biomass: they provide direct heating and uniform distribution of heat which in turn allow better control over the process and significant energy savings. We have been shown that low-temperature microwave activation of biomass can lead to remarkably high quality oils, and oils and solids with very interesting and useful chemical properties. By combining continuous extraction with microwave irradiation an aqueous phase can be separated leaving the oils cleaner, less acidic and with lower quantities of other contaminants such as alkali metals. These oils have great potential as feedstocks for making chemical products as well as for blending into transport fuels 3. Our microwave technology can also be tuned to produce bio-chars with calorific values and physical properties that make them suitable for co-firing with coal in power-stations.
The use of green chemical technologies such as CO2 extraction and microwave-assisted decomposition will enable us to move towards zero-waste production as well as offering a much wider range of products in future biorefineries.
1. Clark, J.H. et al The integration of green chemistry into future biorefineries, BioFpr, 2009, 3, 72-90.
2. Clark, J.H. et al, Generation, capture and utilization of industrial carbon dioxide, ChemSusChem., 2010, 3, 306-322.
3. Clark, J.H et al, The preparation of high-grade bio-oils through the controlled, low temperature microwave activation of wheat straw, Bioresource Technology, 2009, 100, 6064–6068.