Síntese e caracterização de carvão ativado do resíduo do cacau (Theobroma cacao) para a remoção de furfural

Abstract

In view of the environmental problems caused by fossil fuels, along with the large disposal of agroindustrial residues, technologies have been developed for the generation of bioproducts (ethanol, xylose and arabinose) with high added value. Such generation is carried out through the reuse of lignocellulosic materials, since these present significant amounts of sugars used later in the fermentation process. Acid hydrolysis is a chemical pretreatment aimed to reduce crystallinity by breaking the lignocellulosic matrix, allowing the fermentable monomers to be accessible to biological attack. Under severe operating conditions, hydrolysis with dilute acid can generate compounds undesirable to the fermentation process, such as furfural. To reduce the inhibitory effect of furfural in the pre-hydrolyzed pineapple crown liquor, activated charcoal was produced from the cocoa residue carbonization process. Initially, the cocoa residue underwent a chemical treatment process with 85% phosphoric acid at a 1:2 ratio (biomass/acid) for two hours at 80 °C. Subsequently, the chemically treated residue underwent a carbonization process and physical activation with water vapor. The chemical changes suffered by the material were determined by surface area analysis (BET), thermogravimetric analysis (TGA) and pH at zero charge point (pHPCz). The surface area found was 577.8 m2.g-1 and the pHPCZ = 5.0 was acidic. The thermogravimetric analysis showed four stages of significant mass loss corresponding to water vaporization, decomposition of cellulose, hemicellulose and lignin, and the appearance of ash. The adsorption studies showed a maximum furfural removal capacity at a rate of 200 rpm and an optimal adsorbent mass to solution volume ratio of 12 g. L-1. The adsorbent-adsorbate equilibrium time was reached in 300 min and the pseudo-first model was the best represented, having an R2 of 0.987. Three pretreatment conditions with sulfuric acid on the pineapple crown were used, varying the time (30, 60 and 90 min), temperature (105, 115 and 125 ⁰C) and reagent concentration (1, 2 and 3%). They were established from an experimental 23 factorial design with three repetitions at the central point. With the best conditions (90 min, 125 °C, 1%), the hydrolysis of the pineapple crown showed a high production of fermentable sugars (21.28 g. L-1) and acceptable concentration of inhibitors, generating a suitable liquor for fermentation.