Submitted to: Energy and Fuels
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 24, 2009
Publication Date: March 18, 2009
Citation: Boateng, A.A. Response of the devolatilization process to the lignin concenration in alfalfa stems. 2009. Energy and Fuels. 23:2316-2318. Interpretive Summary: Legumes, like alfalfa, are potential energy crops that have been identified under the US-DOE biofuels feedstock groups. Alfalfa stems have considerable potential as a feedstock for bio-fuels and chemicals production because of the large alfalfa hay production, 50% of which is stem which, although relatively indigestible for feed purposes, can become a source of biomass already collected. However, the conversion of the biomass into energy and chemicals via the thermal route can be dependent upon the composition. The effect of the lignin content in alfalfa hay on the rate at which volatile gases evolve during slow heating in an inert atmosphere was investigated; a procedure which is fundamental to all thermal energy conversion processes. It was found that while the rate of gas evolution was inherently lignin content dependent, the effect was not significant within the normal range of lignin content of alfalfa stem especially at higher temperatures which industrial plants would normally operate. The result is contrary to the effect lignin has on bio-conversion such as fermentation. The findings are relevant today for researchers who are determining the potential of alfalfa stems as future energy feedstocks and will be useful in the future to breeders and producers of alfalfa as an energy crop.
Technical Abstract: The devolatilization of alfalfa stems with variable lignin content and within a narrow band of biological lignin range was carried out using a thermogravimetric analyzer (TGA). The samples were subjected to a full thermochemical conversion temperature range between ambient and 1100 degree C. The data was compared with similar evolution curves for pure cellulose and pure extracted lignin (alkali and organisolv). The pure cellulose, extracted lignin and the lignocellulosic alfalfa exhibited completely different evolution profiles with the cellulose and the lignin forming two boundary profiles within which lie all the lignified alfalfa stems. Within the biological lignin content studied that ranged between 13 and 20%, the amount devolatilized was higher with lower lignin content. However, the differences were small and depended on the heating rate. Lower heat rate showed more pronounced differences in volatile evolution in the rapid devolatilization temperature range (250-400 degree C) with the differences diminishing at higher heating rate.