Pretrattamento idrotermico di biomassa per la produzione di etanolo di seconda generazione

The experimental work was conducted during the Erasmus Student Exchange Program at the Université catholique de Louvain. It aimed to investigate the enhancing effect of hydrothermal pretreatments on the digestibility of lignocellulosic biomass, and consequently to the second generation bioethanol production potential. Among the available biomass pretreatments, the hydrothermal ones stand out for their low severity and simplicity. In this study three biomasses (wheat straw, salicornia and willow) were tested using 3 different solutions (deionized water, seawater and an alkali 4 % sodium carbonate solution) and 3 temperatures (150 °C, 180 °C, 200 °C). Specifically, during each reaction a mix of tested solution and biomass was heated under high pressure. The pretreatment enables the solubilization of hemicellulose and enhances the digestibility of the cellulosic component. The three biomasses underwent preliminary compositional analysis, based on the NREL standard laboratory protocols, and were then subjected to a hydrothermal pretreatment based on the defined experimental design. The experimental design, replicated two times, required 54 reactions from the combination of the 3 factors. After each reaction, the resulting slurry was then filtered and divided in liquid and solid fraction. Both fractions were analyzed for their dry matter, ash content and sugars content, through acid hydrolysis. Once obtained the data from the HPLC sugar analysis, a mass balance for each reaction was performed. The slurry underwent finally an enzymatic hydrolysis to degrade fibers to fermentable sugars. It was performed in a shaking incubator for 72 hours, using a commercial mix of cellulases, ß-glucosidases, and hemicellulase. The following sugar content HPLC analysis allowed the estimation of the enhancement, compared to untreated substrates, of cellulosic fraction digestibility. The ANOVA performed on the cellulosic fraction convertibility showed a significant improvement for the pretreated samples, compared to raw biomass, and confirmed the significance of reaction temperature in the mean comparison (p-value = 1.43*10-4). Biomass as well was observed being a significant factor (p-value = 0.0309), while the null hypothesis was not rejected for the different Solutions. No significant interaction among factors was found. The stoichiometric theoretical ethanol conversion was then applied to the sugars resulting from enzymatic hydrolysis, showing a bioethanol production enhancement, compared to raw materials, of 2.6 times for wheat straw, 2.4 times for willow and 1.9 times for salicornia. The outcomes in terms of sugar amounts showed an overall high variability, probably due to the slurry heterogeneity, which affected the precision of sampling; this determined a high standard deviation in the analysis' results. Moreover, the enzymatic hydrolysis results presented some outliers, probably due to the leaking of the solution from the tubes in the shake incubator. In conclusion, the hydrothermal pretreatment confirmed its moderate potential as a tool to enhance biomass digestibility and bioethanol production; the reaction temperature played an essential role. Despite the complexity of experimental operations, the sample size was too small and the variability too high to affirm which catalyzer responded better to the pretreatment. A more complex investigation should be carried out.