Pré-tratamento de biomassa pelo método organosolv utilizando glicerol para obtenção de açúcares redutores

Abstract

The production of the cellulosic ethanol is not yet economically viable, the main obstacle is the intrinsic strength between the components of biomass. Therefore, a pretreatment needs to be carried out to break down lignocellulose and make carbohydrates available for the enzymatic hydrolysis and fermentation processes. In this context, the organosolv pretreatment with glycerol has been investigated. The use of glycerol is promising due to its economically and environmentally sustainable aspect. Organosolv pretreatment reactions with glycerol, applied to water hyacinth (Eichhornia crassipes), were performed with evaluation of the effects of the following variables: time (10-120 min), temperature (100-220 °C), solid/liquid ratio (1-6%), water percentage (0-40%), and cobalt ferrite (CoFe2O4) catalyst (0-10%). The objective was to optimize the process in order to maximize the yield of sugars in subsequent enzymatic hydrolysis. The optimized condition obtained using a 25-1 experimental design was as follows: time of 10 min, temperature of 220 °C, solid/liquid ratio of 6%, 0% water, and 0% catalyst, which resulted in 37% release of sugars. Others sources of iron were also tested (FeCl3 and FeSO4). Unlike CoFe2O4, these added iron salts presented activity, under the optimal condition. The use of FeSO4 and FeCl3 at 0.1 mol.L-1 increased the release of sugars to 41 and 51%, respectively. It was evident that the activity of the iron was determined by the form in which it was present. In view of this optimization, a factorial design 23 was carried out to investigate the synergism between particle size (<0.85 - > 2.0 mm), FeCl3 concentration (0.025- 0.175 mol.L-1 ) and temperature (160-220 ºC), in the deconstruction of water hyacinth, sugarcane bagasse, corn straw and green coconut shell. The analysis of the effects indicated that the type of lignocellulose interferes with the action of the variables, but an optimal condition in common (<0.85 mm; 0.025 mol.L-1 ; 220 ° C) was found, viable for using a small amount of catalyst. For water hyacinth, this new optimization, besides reducing the amount of FeCl3 used by 75%, increased the amount of glucose produced per 100 grams of fresh biomass by 64%, from 14 g / 100 g to 23 g / 100 g after 48 h of enzymatic hydrolysis, due to greater cellulose recovery in the pre-treated biomass. Biomasses pretreated with this combination of factors exhibited enzymatic digestibility greater than 93% after 48 h, reflecting an efficient reduction in recalcitrance, due to the high removal of hemicellulose, approximately 90%, related to the use of FeCl3 that favored its decomposition, also occurred considerable delignification. There was low formation of inhibitors in the hydrolyzate, indicating that it can be directly fermented. In liqueurs, fermentation can be carried out after the separation of acetic acid, and the lignin removed for them can be easily recovered only by centrifugation. Tests carried out in the optimum condition revealed that FeCl3 is more viable than HCl, and that after pre-treatment the biomass can be directly subjected to enzymatic hydrolysis without washing and moist. In addition, crude glycerol, after simple treatment, provided the same effectiveness as commercial glycerol.