Avaliação do potencial de uso de resíduos do processamento de frutas na produção de etanol 2G

Abstract

The search for other sources of energy has encouraged the development of research and innovation in the production of biofuels, such as the second generation ethanol. Biomass from agricultural residues has advantages such as reuse, solves the disposal problem and also offers a low cost of production. In this context, this paper evaluates the best pretreatment (acid, alkaline and hydrothermal) waste from processing fruits (orange, passion fruit and soursop) to obtain bioethanol. The waste collected, stored at -20°C were thawed at room temperature, sanitized in 100 ppm sodium hypochlorite for 15 min and dried in an oven with air circulation at 55 ± 5°C until constant weight, ground and subsequently on a knife mill type Willye 30 mesh and packed in airtight plastic bottles at room temperature. Determinations of lipid, protein, moisture, ash, fiber, pectin and carbohydrate were performed. Pretreatments were designed according to experimental design where, for the acid, time 15 to 120 min, Cacid from 1 to 5% and Cbiomass 1 to 9%. For the alkali, it was used the same conditions as the acid, changing only the Cbasis, from 0.5 to 2.5%. For the hydrothermal only Cbiomass and time were evaluated. As answers, the mass yield, the amount of total reducing sugars (TRS) and total soluble solids in the liquid fraction. For the enzymatic hydrolysis it was employed cellulase Sigma-Aldrich in a 2:1 by enzyme mL:g pretreated biomass in 60 mL of 50 mM citrate buffer at 50°C and 100 rpm, evaluating the concentration of total reducing sugars. In ethanol fermentation, was used the hydrolyzate complemented with mineral solution and the yeast Saccharomyces cerevisiae, the main responses analyzed were ethanol concentration and yield of fermentation. The waste orange, passion fruit and soursop higher content of sugar in the liquor pretreatment occurred in the acid using low biomass concentration and longer pretreatment (65%), whereas at higher acid concentrations was sugars decreased, probably because undergo degradation. In alkaline pretreatment, was lower than the saccharification acid pretreatment (35%) and lower yields mass, indicating that some component of the lignocellulosic matrix was solubilized lignin probably characteristic of alkaline treatments. In hydrothermal there was the lowest saccharification liquor from both the pretreatment and in the enzymatic hydrolysis, possibly because the time and temperature used were not effective in destroying the lignocellulosic matrix. In enzymatic hydrolysis, alkali was more efficient than the acid, achieving, in the best conditions, around 35% of ART, except for the residue of passion fruit (<10% hydrolysis for the three pre-treatments), suggesting negative relationship between the amount of pectin and action of cellulases. The yield of fermentation behaved differently among trials for obtaining pre-treatment acid with shorter (15 minutes) the highest rates, while for these alkaline and hydrothermal stood in a longer time (120 min) pretreatment. These observations suggest that in the case of residual soursop optimizations must be carried out using lower heating times and higher biomass concentrations. However, for the orange peel and passion fruit residue, the intermediate condition seems to be more appropriate, and more efficient enzyme complexes and the presence of enzymes that break down pectin.