Pré-tratamento do bagaço do fruto da palma de óleo com solução aquosa de ácido acético

Abstract

The pretreatment of oil palm fruit bagasse (PFB) with aqueous acetic acid solution (AcOH) and the use of pressure, in order to obtain sugars (glucose, xylose, arabinose) and products of value Aggregate (furfural and hydroxymethylfurfural). The "in natura" bagasse had 14.3 % of cellulose, 18.7 % of hemicellulose, 27.5 % of lignin, 30.7 % of extractives and crystallinity index of 42.41 %. The study was performed based on a fractional factorial design 24-1, followed by a central composite design (CCD), optimization through surface response graph and simultaneous optimization via nonlinear programming method. Statistical software 7.0 was used for data analysis. The effects of temperature (100.0-180.0 °C), time (15.0-60.0 min.), Solid/liquid ratio (4.0-16.0 mgmL-1) and AcOH concentration (1.0-5.0 % v/v) on the mass loss. The DCC was run in the temperature range of 140.0 to 180.0 ° C and the AcOH concentration of 3.0 to 5.0 % v/v, with time and solid/liquid ratio being set at 37.5 min and 4.0 mg mL-1, respectively. A batch reactor under argon atmosphere at 20 bar was used in pretreatment. High Performance Liquid Chromatography (HPLC) analyzed the sugars and degradation products present in the liquid fractions obtained after pretreatment. The PFB “in natura”and pre-treated were characterized as moisture content, ashes, extractives, cellulose, hemicellulose, total lignin, elemental analysis, thermogravimetry, X-ray diffraction, crystallinity index, surface analysis and higher calorific value . A kinetic study of the hydrolysis reaction of the hemicellulosic fraction of PFBunder optimized conditions was performed. The pretreatment with AcOH was efficient in the mass reduction of PFB, with the largest loss of mass (68.9%) occurring at 190.0 °C and 4.4 % v/v AcOH. The optimized condition for total sugars (171.0 °C and 4.3 % v/v AcOH) presented 67.06 mg L-1 sugars (close to that predicted by the model) and low concentration of furfural and HMF. The simultaneous optimization condition (187 °C and 4.9 % v/v AcOH) showed 49.71 mg L-1 of total sugars, 27.90 mg L-1 of furfural and 1.85 mg L-1 of hydroxymethylfurfural, values close to the values predicted by the model. The experiment performed at 200 °C and 6.0 % v/v of AcOH, to verify the behavior of the concentration of furfural and hydroxymethylfurfural, presented concentrations of 42.40 and 2.44 mg L-1, respectively. Also close to the values Predicted. After the pretreatment, the biomass presented high increases in the cellulose and lignin contents, and a reduction of 90.0 % of the extractive fraction and 45.0% of the hemicellulosic structures, for the test performed at 200 °C and 6.0 % v/v AcOH. Pretreatment promoted a maximum increase of 29.39 % in the index of crystallinity of the material. An increase in surface area and pore volume was observed. SEM analyzes showed changes in the surface of the material in all assays. Four thermal degradation events were observed for the thermogravimetric curves (TGA) of the "in natura" and pretreated biomasses, and an increase in degradation temperature after pretreatment. For the removal of the hemicelluloses, the results obtained showed that the acid hydrolysis reaction, under the conditions studied, was dependent on temperature and time variables. The maximum extraction of xylose (160 mg L- 1) occurred at 160 °C after 150 min of reaction and the maximum for arabinose was obtained at 160 °C after 120 min. The kinetic analysis showed that the reaction rate constant, k, for the disappearance reaction of xylan and arabinane present in hemicellulose, increased with increasing temperature. The value obtained for the activation energy (Ea) of xylose formation was 102.1 kJ mol-1 and for arabinose was 66.4 kJ mol-1.