Extraction of Organosolv Lignin from Rice Husk under Reflux Conditions

The rice husk is a very abundant residue, being rich in cellulose and lignin, whose main destination in the southern Brazil is burning for power generation. This study aims at extracting the lignin from the rice husk, applying a methodology called Organosolv, in a modified process by the use of atmospheric pressure. As the extraction solution, a mixture of ethanol/water with ethanol concentrations of the 25 to 100% v/v were used. As the catalyst for extraction, concentrated sulfuric acid, in proportions of the 0.5 to 3.0% v/v under reflux and heating by 24 hours were used. The yields obtained were between 3 and 48% for the amount of Klason lignin analyzed. The tests, which applied smaller quantities of ethanol and catalyst (sulfuric acid), presented lower yields, while the highest yields was found in the extraction solutions with 75% v/v of ethanol and 3% of catalyst. The extracted lignin was characterized by spectroscopic, chromatographic and thermal analysis. The extracted samples showed great structural homogeneity, good thermal stability, low polydispersivity (< 2,0) and low presence of contaminants such as cellulose and hemicellulose. The studied procedure aims at the reuse of an abundant agro-industrial waste, in order to reduce the environmental impact of its burning and to obtain the lignin, a natural polymer with great potential for industrial application.