Desenvolvimento de processo de deslignificação da palha de milho assistida por ultrassom

Abstract

In this work, the ultrasound (US) was investigated in acid hydrolysis process for corn straw delignification, in comparison with the conventional process proposed by National Renewable Energy Laboratory (NREL). This procedure consists in 300 mg of corn straw hydrolysis with 72% H2SO4 for 1 hour at 30 ºC, followed by a dilution at 4% acid, and autoclaving for 1 hour at 121 ºC. For the ultrasound-assisted acid hydrolysis process it was evaluated ultrasonic baths in several conditions of frequencies (25 to 130 kHz), nominal power (100 to 330 W), and amplitudes (50 to 100%). This procedure was performed in the same conditions of time, temperature, and acid concentration as the reference method (NREL). After the selection of the most efficient ultrasonic system, other parameters were evaluated, as sonication time, ultrasonic amplitude, and autoclaving time. The more suitable conditions for corn straw delignification were achieved in 10 minutes of sonication at 35 kHz and 50% of amplitude, 72% H2SO4 at 30 ºC followed by 60 minutes of autoclaving. To verify if the acid hydrolysis solubilized all the carbohydrates in the corn straw, the contents of glucose, xylose, and arabinose were determined by HPLC-RID. The total carbohydrate content of 86.68% was obtained for the reference method (NREL), while 91.67% was recovered when the proposed method with US was used. The results referring to lignin extraction and carbohydrate solubilization for both methods exhibit no significant difference, according to the t student statistical test (95% confidence level). Additionally, the characterization of the functional groups and morphological analysis of the lignin resulting from the acid hydrolysis process was carried out by infrared spectroscopy (IR) and scanning electron microscopy (SEM), respectively. The proposed ultrasound-assisted delignification process allowed the delignification of corn straw under mild temperature conditions and reduced extraction time when compared to the conventional method.