Hidrólise ácida de biomassa assistida por ultrassom para obtenção de furfural

Abstract

In this work, the applicability of ultrasound (US) for synthesis of furfural from biomass was investigated. Several US systems (baths, probes and a cup horn system) with different frequencies and power were evaluated (from 20 to 130 kHz and from 100 to 750 W, respectively). Acid hydrolysis assisted by ultrasound (UAAH) was performed and the following acids were evaluated: H2SO4, HNO3, HCl e C2O2H4. For the comparison of results, acid hydrolysis was also tried by using mechanical stirring (100 rpm) at the same conditions of time, temperature and acid concentration. Better results were obtained by using the cup horn system and a diluted solution of HNO3. After choosing the more suitable system, the following process parameters were evaluated in order to obtain better efficiency of conversion: temperature of reaction, acid concentration, sonication time, US amplitude and sample mass. The more suitable conditions were: 60 min of US (cup horn, 20 kHz, 750 W, amplitude of 50%) at 30 ºC for the treatment of 100 mg of biomass and 20 mL of 4 mol L-1 HNO3. Several biomass matrices (rice husk, cane straw, yerba-mate after infusion, grass and wood residue) were submitted to the UAAH process. The biomass conversion to furfural was from 36.4 to 223 mg g-1of biomass. It is important to emphasize that using the same experimental conditions but without ultrasound (mechanical stirring) the conversion of biomass to furfural was not observed. Functional groups and morphology of residues of UAAH process were evaluated by infrared spectroscopy and scanning electron microscopy. Chromatographic parameters for the determination of furfural by gas chromatography with flame ionization detector (GC-FID) were also optimized. The proposed process allowed the furfural synthesis using mild temperature conditions, diluted acids and with minimization of organic solvents.