Otimização do uso de pré-tratamento alcalino, ácido, líquido iônico e oxidativo para conversão de resíduos de coco em açúcares fermentescíveis

Abstract

Coconut (Cocos nucifera L) is a very important fruit for the food and chemical industries, although its processing generates large amounts of waste. To minimize this problem, the waste consisting of green coconut shells is abundant and renewable, and its use has provoked a growing interest in the production of fermentable sugars. The present study aims to evaluate the effect of the conditions of four different pretreatments on the structure of the residual biomass of the coconut shell to maximize the conversion to these sugars. The optimization was carried out according to the DCCR 22 planning, varying the experimental conditions of time and temperature, respectively of each pre-treatment, peroxide (2.59 -5.41 h) and (33.79- 76.21 ° C), alkaline (0.59 - 3.41 h) and (33.79 - 76.21 ° C) and acid (0.29-1.71 h) e (105.86 - 134.14 ° C), for pretreatment with Ionic Liquid (LI) was carried out with the following conditions (2 h; 100 ° C; 4 h, 120 ° C; 6 h, 140 ° C) for reducing sugars production and total lignin removal after acid hydrolysis by Response Surface Methodology (RSM). The highest yielding sugar yield (70%) was when the coconut shell residue underwent alkaline pretreatment for 2 hours at 76.21 °C, a considerable increase considering the gross biomass (32.2%). The highest lignin removal rate was recorded when hydrogen peroxide (55 °C and 4 h) solutions and alkaline (70 °C and 3 h) were used. Acid pretreatment allowed for reasonable sugar (58.1%) production and considerable increase in lignin content (44.1%). The Ionic Liquid (IL) did not increase the sugar contents. At the end of the processes, the pretreated biomasses were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR), to verify the effect of the various pretreatments on the structure of the lignocellulosic biomass. The XRD, SEM and FTIR performed in the pre-treatments are in agreement with the biomass chemical composition, with changes in the structure of the after the application of the pre-treatments adopted. Biomass crystallinity increased based on pretreatment severity, following the order of the following treatments: alkaline> peroxide> IL> acid.