| Resumo: |
For biofuels production, the recovery of lignocellulosic feedstock is seen as a promising alternative, both from environmental and economic point of views. Among the lignocellulosic biomasses most important in Brazil, sugarcane straw plays a prominent position regarding the production of second generation ethanol (E2G), due to its great availability in the field. One of the main challenges involving the production of second generation ethanol is to obtain high conversion rates of polysaccharides into fermentable sugars, in the hydrolysis step. A solid knowledge is an important pre-requisite to optimize the conversion of lignocellulosic biomass into ethanol. In this context, the aim of this work is to study the kinetics of the enzymatic hydrolysis of cellulose from hydrothermally pretreated sugarcane straw (HPS) (195oC, 10 min e 200 rpm) and hydrothermally pretreated followed by alkaline pretreatment (NaOH 4% w/v, 30 min, 121oC). The influence of process variables as stirring speed, pH, temperature and, concentration of substrate and enzyme was evaluated. Experiments using HPS were carried out in Erlenmeyers (50oC, pH 5, 5 FPU.gcellulose -1 e 10% solids m/v) with shaking from 0 to 300 rpm. Then, the influences of pH and temperature were analyzed. Initially, the pH was ranged from 3 to 7 and afterwards, the temperature was varied from 40 to 60oC. After determining and setting the ideal conditions of agitation, pH and temperature, it was studied the effect of substrate and enzyme concentration for both pretreated and delignified biomass. In order to verify the effect of substrate concentration, solid load was varied in a range of 2.5 to 10.0% (w/v), in initial velocity and long term assays. Enzyme concentration (Cellic®CTec2 Novozymes S/A) was varied from 275 to 5,000 FPU.Lsolution -1 (5 to 80 FPU.gcellulose -1), with solid load settled at 10% (w/v). Finally, it was possible to fit Michaelis-Menten (MM), modified MM, with and without competitive inhibition by glucose, and Chrastil model. For HPS, modified MM model with inhibition (suitable for heterogeneous system, with high resistance to diffusion) was fitted. For alkaline delignified HPS pseudo-homogeneous and modified MM models were fitted. The Chrastil model was also used to fit long term assays for both pretreated biomass. The fitted models were able to identifying key features of the hydrolysis process, and, therefore, useful within the perspective of engineering bioreactors. |
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