Avaliação do uso de Solventes Eutéticos Profundos (DESs) na extração de lignina do bagaço de cana-de-açúcar

Abstract

Lignin has a high interest for the industrial sector once it can be used in the production of a vast number of products in chemical industries such as new polymers and antioxidants. Deep Eutectic Solvents (DESs) can be efficient solvents in the extraction of lignin from renewable sources, such as lignocellulosic biomass, favoring a significant delignification as well as playing an important role in the concept of green chemistry when compared to those using conventional organic solvents, as hexane and/or concentrated inorganic acids and bases, for example, which have some disadvantages due their high vapor pressure and high flammability Thus, this study has the aim to investigate and optimize the use of DESs in lignin recovery from sugarcane bagasse. Three different DESs were evaluated, ChLa (choline chloride: acid lactic), ChGy (choline chloride: glycerol) and ChU (choline chloride: urea), selecting the last one due to its better performance presented in preliminary tests. The experimental design approach, with center point added, was carried out to investigate the effect of DESs volume, water addition and extraction time on the studied recovery. The following techniques were used to understand the recovered lignin structure: Fourier-transform Infrared Spectrometry (FTIR), Thermogravimetry (TG) and X-ray Diffraction (DRX). The hydrothermal treatment of sugarcane bagasse was also carried out to be compared it to DESs treatments. After the extraction procedures, it was noticed the high mitigation of the lignin content using ChU (- 55.05 %). Although ChLa has presented a similar extraction capacity (-57.57%), this DESs also removed a significant content of hemicellulose, what indicated its poor selectivity. The hydrothermal treatment improved the lignin content (25.25 %), what indicate its capacity to remove other constituents instead of the target. After carrying out the experimental design, it was observed that the highest lignin removal was obtained under the following conditions: 0.3g of biomass, 3 mL of DES, 6% of water addition and 2h of extraction, obtaining an extraction of about 58.38% of the target biopolymer. The recovered lignin FTIR spectrum showed that the polymeric structure was preserved after the treatment and the DRX result pointed an increase of crystallinity index, as result of the realized extraction process. The studies carried out in this research reinforce the efficiency of using DES for lignin extraction, enabling faster removal with a reduction in temperature and extraction time.