Stéphane Lamaudière

Chemical characteristics and biofuels potentials of various plant biomasses: influence of the harvesting date.

BACKGROUND An optimal valorization of plant biomasses to produce biofuels requires a good knowledge of the available contents and molecular composition of the main chemical components, which changes with the harvesting date. Therefore, we assessed the influence of harvesting date on the chemical characteristics of various energy crops in the context of their conversion to biofuels. RESULTS We showed that the biomass chemical composition, enzymatic digestible organic matter, bioethanol and thermal energy production potential for each species are impacted by the harvesting date. The proportion of enzymatically digestible organic matter decreases as the harvesting date is delayed. This is related to the increase in cellulose and lignin contents. The suitability of the biomasses for bioethanol production increases with harvest stage, as the total carbohydrates content increases. The suitability of the biomasses as a source of thermal energy increases according to the harvesting date as the proportion of organic matter increases and the content of mineral compounds decreases. For all investigated energy conversions, the best harvesting period is autumn, because the significantly higher crop dry matter yield largely compensates for the sometimes slightly less favorable chemical characteristics. CONCLUSION While the biomass composition of energy crops changes with harvest stage, the dry biomass yield per unit area is the main factor that controls the total amount of chemical components, digestible organic matter, bioethanol and thermal energy that can be expected to be harvested per unit area. The biomass compositions presented in this paper are essential to investigate their suitability for bioenergy conversion.

Evolution of Main Chemical Components Content and Monosaccharidic Content of Hemicelluloses in Several Lignocellulosic Grass Crops Grown under Different Crop Husbandry Conditions

Cellulose and hemicelluloses are the most abundant structural polysaccharide in nature. Their optimal valorization in lignocellulose-based biorefineries requires a good knowledge of the contents available in various biomasses, and of their molecular composition. The composition and more specifically the monosaccharidic content (cellulosic glucan, xylan, arabinan, mannan, galactan and hemicellulosic glucan) were analyzed in several lignocellulosic grass crops: switchgrass (Panicum virgatum L.), tall fescue (Festuca arundinacea Schreb.), cocksfoot-alfalfa association (Dactylis glomerata L.-Medicago sativa L.). Cellulose and hemicelluloses contents were in the range 20.8-33.3 and 14.5-32.6 g (100gDM)-1, respectively, with lignin, total soluble sugars, proteins, and ash contents around 2.9-7.8, 2.0-21.7, 5.7-17.2 and 4.3-16.3 g (100gDM)-1, respectively. The main hemicellulosic components were, by order of decreasing importance, xylan 8.3-23.2 g (100gDM)-1, arabinan 2.12-4.10 g (100gDM)-1, hemicellulosic glucan 1.36-3.42 g (100gDM)-1, galactan 0.63-2.31 g (100gDM)-1 and mannan 0.27-1.08 g (100gDM)-1. Plant species and harvest cycle has the most significant influence on the structural polysaccharide composition, while the influences of cultivar and nitrogen fertilization were only rarely significant.