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Release of sugars from lignocellulosic biomass by microwave plasma

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Sugar release for ethanol production from biomass

Using crops and crop residues to produce bioethanol conventionally requires highly inefficient enzymatic breakdown of biomass. EU-funded scientists developed microwave (MW) technology with unprecedented success in the breaking of tenacious chemical bonds.


The development of efficient ways to produce biofuels for the transport sector is a key pillar of the EU's programme to reduce dependence on fossil fuels and decrease the global climate impact associated with their combustion. First-generation biofuels that continue to provide the majority of bioethanol come from food crops requiring farmland and resources that could be used for other purposes. Production of bioethanol from lignocellulosic biomass (agricultural and forestry waste such as grasses and wood chips) yields so-called second-generation biofuels. However, it has proved quite challenging to extract the sugars for fermentation from their tightly bound lignin. No commercially operating biorefineries exist. At lab scale, biochemical conversion with enzymes (acid hydrolysis) produces very low yields and takes about two days. EU-funded scientists took a revolutionary step forward, putting the search for better enzymes to separate hemicellulose from lignin on the back burner. They developed a novel MW irradiation technique within the context of the project 'Release of sugars from lignocellulosic biomass by microwave plasma' (MICROGRASS). Grasses were chosen as the biomass of interest because their cultivation provides small and medium-sized enterprise (SME) farmers with the opportunity to utilise poor soil that is otherwise unfit for agricultural crops. The fully automated prototype demonstrated that the MW technology can effectively separate hemicellulose from lignin before saccharification (release of the fermentable sugars from the carbohydrates). It does not require any pre-processing of the biomass and the product is free from acids and other chemicals that must be removed following conventional biochemical conversion. This adds another processing step and increased energy consumption. The 'sugar soup' is produced at a fraction of the energy cost of conventional processing. MICROGRASS technology to exploit grass grown on land unfit for other crops as biofuels for the transport sector is expected to have major impact on SME farmers. In addition, it makes an important contribution to EU alternative and sustainable energy goals without conflicting with food production. Finally, it could have important benefits for the EU economy as a fast, efficient and less energy-intensive alternative to conventional processes to convert lignocellulosic biomass to bioethanol.

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