In the light of depleting fossil resources, biomass is gaining renewed interest as a source of renewable carbon, which can be used for energy and chemicals. The production of biofuels such as ethanol, palm oil and bio-diesel has come under criticism for its likely competition with food. These production systems need either huge areas of monocultures or use some parts of plant material such as the carbohydrate fraction only for fermentation to produce ethanol. Other technologies such as fast pyrolysis offer the advantage of using whole plant material for the production of so called 'bio-oils', which adheres to the condensates of the pyrolysis process.
Bio-oils are complex mixture of various molecules with different polarities. Their content of monomers, oligomers and water depend not only on the pyrolysis conditions but also on the characteristics of the feedstock. In order to broaden the palette of feedstocks to be considered, 12 agricultural waste types from annual plants were comparatively pyrolyzed in a laboratory fluidized-bed reactor against white wood from beech wood. Agricultural wastes such as wheat straw, wheat grains, whole corn plants (cobs, stems, leaves) were used untreated, whereas corn, rape, barley, oat, sorghum, whole plant silage, and winter peas were used after silage. Moreover, press cakes from hemp seeds and flax seeds were also investigated.
Pyrolysis temperature was kept constant at 475 °C. The residence time was varied and set to 1 or 2 s. Organic yields were highest with beech wood (55 wt.%) and lowest with flax seeds (13 wt.%). Detailed quantitative GC/MS analyses of the bio-oils were carried out. In total, 44 components were used for the comparison of the feedstocks. The components were grouped into distinct chemical categories such as organic acids, aldehydes, aromatics, furans, guaiacols, ketones, phenols, pyrans, anhydrosugars, and syringols. Interestingly, sorghum silage gave similar bio-oil composition compared to beech wood. Corn silage gave superior results in comparison to whole plant material. Other properties of the bio-oils such as pH and elemental composition were also determined.
Dietrich Meier and Jens Markgraf, "COMPARATIVE FAST PYROLYSIS OF AGRICULTURAL RESIDUES FOR USE IN BIOREFINERIES" in "Bioenergy - II: Fuels and Chemicals from Renewable Resources", Eds, ECI Symposium Series, Volume P10 (2009). http://dc.engconfintl.org/bioenergy_ii/25