Potential uses of Cassava Bagasse for Bioenergy Generation by Pyrolysis and Copyrolysis with a Lignocellulosic Waste

L. GUREVICH; P. BONELLI; A. L. CUKIERMAN

Handbook on Cassava: Production, Potential Uses and Recent Advances

Nova Science Publishers

Lugar: New York; Año: 2017; p. 335 - 356

Cassava Manihot esculenta bagasse is a fibrous by-product generated in the tuber processing. After washing and peeling, the cassava is grated and then water is added in order to extract the starch. The mixture is filtered such that a rich starch solution and a wetsolid residue can be separated. This slurry, known as bagasse, comprises up to 20% of the weight of the processed cassava. In addition, as the extraction of starch from cassava is less efficient than those based on processing of potato or maize, the bagasse contains around 50-70% of starch on a dry basis. As ithas no important use, with the exception of animal feed, the bagasse is usually rejected to water courses increasing the environmental pollution. Therefore,several strategies are being studied to find useful applications for this by-product. Pyrolysis of the bagasse and copyrolysis, namely the thermal degradation of mixtures of the bagasse and lignocellulosic biomass in inert atmosphere, could be an appealing possibility to employ this waste in order to generate green energy and/or other value-added products. In particular, growing attention is paid to the liquid products arising from pyrolysis/copyrolysis,commonly known as bio-oils, since they show many of the advantages of liquid fuels, such as inexpensive storage and transportation, and high energy density.In this scenario, the processes of pyrolysis of cassava starch, the major constituent of dry cassava bagasse, and of copyrolyisis of the starch with peanut hulls, an abundant lignocellulosic residue, were studied by performing experiments in a fixed-bed reactor at different process temperatures (400ºC - 600ºC). Thepyrolysis of the starch led to a higher maximum yield of bio-oils that took place at a lower temperature than the copyrolysis (57 wt% at 400ºC vs. 49wt% at 500ºC). Physichochemical characterization of the three kinds ofpyrolysis/copyrolysis products with emphasis on the bio-oils was carried outmainly by proximate and ultimate analyses, Karl-Fischer titration, Fourier-transform infrared spectroscopy, N2 adsorption, scanning electronic microscopy,and gas chromatography (GC-TCD and GC-MS). While the pyrolysis of the starchresulted in bio-oils with less nitrogen content, the copyrolysis producedbio-oils with lower content of oxygen and higher carbon percent. Water contentof the bio-oils increased with rising process temperatures and it was lower forthe liquids resulting from the pyrolysis of the starch. Also, the bio-oilsarising from the pyrolysis of the starch presented more sugar compounds andfewer phenols. Besides, the pyrolysis of the starch led to a lower yield ofsolid products (bio-chars) than the copyrolysis. They showed greater higher heating values (up to 35 MJ/kg) than those arising from the latter process inagreement with their larger carbon content and lower presence of ash. In addition, the bio-chars produced at the highest process temperaturepresented an incipient pore development, suggesting their possible use as rough adsorbents or as intermediary for further upgrading to activated carbons.Furthermore, the pyrolysis of cassava starch and copyrolysis with peanut hulls generated gases, principally CO2, CO, CH4 and H2,that could help to sustain the processes.