Obtención de bioetanol de segunda generación a partir de vainas de fréjol (Phaseolus vulgaris L.)

Abstract

With the development of renewable energies, agro-industrial waste has been considered as a rich source of cellulose to be used as raw material, in order to obtain second-generation biofuels as an alternative to reduce the consumption of petroleum-derived fuels. This work aims to obtain bioethanol using bean pods (Phaseolus vulgaris L.). First, bean pods were characterized where the main chemical composition was 36.47% cellulose, 28,25% hemicellulose, 6.69% lignin, moisture 6,66%, and ash 6,86%. To obtain bioethanol, a conditioning of the sample was carried out through a process of drying, grinding and sieving, which is subjected to an alkaline pretreatment of 121 °C, for 60 min and 0,5% sodium hydroxide, then hydrolysis was performed. acid to achieve the conversion of cellulose to simple sugars. By using a complete factorial design with two levels and three variables and with the Minitab 19 program, a standard matrix was generated where the effect of time, temperature and concentration of sulfuric acid on the response variable was evaluated. In this stage of decomposition to total sugars, the best results were obtained with the conditions of 120 °C, for 60 min and 3% sulfuric acid, resulting in 29,836 g/L of total sugars. The hydrolyzed liquid was subjected to a fermentation process (6 h, 35 °C, pH 3,5 and 150 rpm) in a stirred tank bioreactor, simultaneously the ethanol concentration was determined by the Winnick method, the highest concentration of ethanol that was obtained was 7 g/L, the data obtained fitted the modified Gompertz kinetic model satisfactorily with a high coefficient of determination R2 >0.98. Finally, the liquid obtained after separating the yeast was distilled to obtain 7,89 g/L of ethanol. Keywords: Bean pods, total sugars, fermentation, modified Gompertz model.