Modelagem matemática das etapas de pré-tratamento hidrotérmico e hidrólise enzimática da palha da cana-de-açúcar

Abstract

The production of ethanol from lignocellulosic biomass, such as sugarcane straw, requires the inclusion of additional process steps to release the sugars (monomers, glucose and xylose) that will later be converted into ethanol via the fermentative pathway. The first of these two steps, known as the pretreatment step, promotes the disruption of the cell wall, reducing biomass recalcitrance through the removal or modification of lignin, an increase in surface area and porosity, as well as a decrease in cellulose crystallinity. These modifications aim to make cellulose and hemicellulose more accessible to the enzymes used in the second step of the process, enzymatic hydrolysis. The objective of this work was to implement, in the Scilab software, phenomenological mathematical models that could describe the hydrothermal pretreatment and enzymatic hydrolysis steps of sugarcane straw. Once the temperature (T) and time (t) parameters for the hydrothermal pretreatment stage had been defined, linear regression models were fitted to estimate the severity factor (SF) and the mass yield (MY). Based on this information, the composition of the solid fraction of the pretreated biomass can be obtained by integrating the differential equations resulting from the mass balances of the components released from the biomass during the pretreatment process. All degradation kinetics are assumed to be first order. Subsequently, the composition of the solid fraction is used as input for the enzymatic hydrolysis model, which, once the reaction time and the concentration of the enzymatic extract are provided, estimates the composition of sugars (glucose and xylose) in the liquid fraction. The experimental data used to fit the models were obtained from experiments carried out by the research group of the Laboratory for the Development and Automation of Bioprocesses (LaDABio) and of the Laboratory of Biochemical Engineering (LEB), both in Department of Chemical Engineering, Federal University of São Carlos. According to the results of this study, splitting the cellulose and hemicellulose into reactive and non-reactive parts optimised the description of their degradation profile during pretreatment. Moreover, the graphical method produced promising results for the severity factor estimation, with relative errors of less than 5% for each condition. Regarding enzymatic hydrolysis, the simplified model more accurately characterised the experimental data than the detailed model. Taken together, the most appropriate scenario for the hydrothermal pre-treatment of sugarcane straw is operating at an isothermal temperature of 195 °C for 10 minutes.