8-02: Recent achievements in the production of fuel ethanol from sugarcane bagasse

Phosphoric acid has been identified as an attractive catalyst for the steam treatment of sugarcane bagasse as well as other lignocellulosic materials. In this work, sugarcane bagasse was collected directly from an industrial crusher and submitted to a phosphoric acid-catalysed steam explosion using a 10-L batch reactor.  Pretreatment was carried out at different temperatures, times and acid loadings using a central composite design in which the selected response variables were glucose recovered for fermentation in substrate hydrolysates and ethanol produced in bench-scale SSF experiments. Acid impregnation along with high pressure steaming produced steam-treated substrates with low hemicellulose contents and easily extractable lignin that were highly accessible to enzymatic hydrolysis using the Cellic CTec 2 preparation (Novozymes), which had a catalytic performance much better than that of a Celluclast 1.5L/Novozym 188 mixture under equivalent enzyme loadings. Hydrolysis experiments at higher substrate concentrations of 20wt% were also assessed for the best substrate of the central composite design. SSF was carried out in shake flask incubators with both washed and unwashed pretreated materials at 8wt% using 0.01mL of enzyme/g of dry substrate and baker’s yeast for glucose fermentation. The pretreatment water-solubles were not identified as inhibitory to enzymatic hydrolysis but their effect on fermentation yields varied depending on their composition. Organic acids and dehydration by-products were monitored in these assays by chromatography and capillary electrophoresis and this allowed for the identification of critical fermentation inhibitors for the successful conversion of cellulose to fuel ethanol. Supported by: EU FP7 Programme (http://www.canebiofuel.org), Fundação Araucária, CNPq, CAPES.