12 February 2015

Chemical composition of plant biomass and energy use

In a rapidly changing world, and faced with the challenges of green growth and climate change, the wide availability and sustainability of plant biomass give it significant potential as a source of energy and bioproducts.

CRA-W has further developed its work on the chemical composition of fibrous plant species and their suitability for energy uses. This study has been carried out in the context of two projects: BIOETHA2 (Moerman Act) and ENERBIOM (INTERREG IVa ‘Greater Region’ cross-border project) and a thesis by B. Godin. The research has looked at the production  of high-fibre (cellulose and hemicellulose) fibrous plant biomass such as miscanthus, switchgrass, fibre sorghum, fibre maize, pasture, cereal straw and hemp. Selecting suitable plant species for plant-to-energy applications requires a sound knowledge of their chemical composition and convertibility to biomethane or bioethanol by fermentation or their suitability for use as a solid fuel.

We have developed an analytical method for fibre determination which is suited to the plant biomass-to-energy field. The method has been implemented with the aid of a charged aerosol detector (CAD) funded under the Moerman Act. We have shown that this method enables cellulose, hemicellulose and hemicellulose composition to be determined with a high degree of accuracy. By analysing a great many types of biomass we found out that the diversity of their chemical composition can be structured into biomass groups that not only have similar properties and fibre content but also have common phylogenetic origins. To reduce the analytical costs we selected three routinely analysed parameters (cellulose, hemicellulose and mineral content) as sufficient to predict the suitability of the biomass for the different biomass-to-energy conversions. It finally appears that gross per hectare energy productivity depends first and foremost on the crops’ dry matter productivity, far more than on their changing chemical composition during growth or the growing conditions (sites, years, varieties, levels of nitrogen fertilisation).
The lessons we have learned from this research can also be used in connection with converting plant biomass into bioproducts by biorefining. This type of research is carried on by CRA-W in the context of the BioThermoRaf postdoctoral project funded under the Moerman Act.

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