Hydrogenolysis of lignins: influence of the pretreatment using microwave and ultrasound irradiations.
Hydrolytic eucalyptus lignin was converted to oils by hydrogenolysis. The lignin was obtained by acid hydrolysis of eucalyptus chips from two semi-industrial sources in Brazil: FTI and Coalbra. Hydrogenolysis was performed in an 1-L reactor using lignin/water ratio 1/4 (w/v), pH 9 (adjusted with NaOH), 0.1 g sodium formate/g lignin, 20 MPa (argon pressure) at 280 degrees C for 15 min. After reaction, the products were filtered and the solids extracted with chloroform/ethanol 3/1 (v/v). The solvent was evaporated from the organic phase and a dark oil was obtained. The solid remaining after extraction was weighed to calculate the conversion. Without pretreatment conversions were 41.3 and 47.9% for Coalbra and FTI, respectively. The oil yields were 22.7-27.6% for Coalbra and FTI, respectively. Using microwave pretreatment (30 min of irradiation at 490 W) the conversions were 41.6-50.5% and the oil yields increased slightly to 25.2-31.4%. The polymeric chains in the lignin breakdown due to the action of water near the boiling point under microwave irraditation. On the other hand, by using ultrasound (30 min at 50 degrees C in a ultrasound bath of 25 kHz and 0.8 W/cm2) the conversions were 35.2-46.9% and oil yields were 22.0-27.1%. Ultrasound favors the formation of radicals that probably caused the reticulation of lignins, decreasing the conversion and yield. Oils analyzed by infrared spectroscopy showed an increase in C=O bond intensities, compared with the original lignins.
Gonçalves
Adilson R
AR
Department of Biotechnology--FAENQUIL, Lorena, SP, Brazil. adilson@debiq.faenquil.br
Schuchardt
Ulf
U
D002241:Carbohydrates / Q000032:analysis*; D005052:Eucalyptus / Q000737:chemistry*; D006868:Hydrolysis; D007202:Indicators and Reagents; D007700:Kinetics; D008031:Lignin / Q000737:chemistry*; D008872:Microwaves; D010938:Plant Oils / Q000737:chemistry; D013050:Spectrometry, Fluorescence; D013696:Temperature; D013816:Thermodynamics; D014934:Wood
D002241:Carbohydrates; D007202:Indicators and Reagents; D010938:Plant Oils; D008031:Lignin