Síntese e caracterização de hidrogel para processo de fracionamento da lignina extraída do bagaço de cana-de-açúcar

Abstract

Brazil is currently considered the largest producer of sugarcane in the world, which results directly in tons of lignocellulosic biomass residues. The use and recycling of these process residues would reduce the environmental problems associated with improper storage in nature, add value to the constituents of lignocellulosic materials and reduce the use of fossil fuels. The objective of the present work is to separate lignin fractions extracted from sugarcane bagasse in preparative scale gel permeation chromatography (GPC), containing as a stationary phase the hydrogel (HEDTA) derived from cellulose acetate (AC) and ethylenediaminetetraacetic acid dianhydride (EDTAD). The acetosolv pulping was used for the extraction of the lignin present in sugarcane bagasse, using acetic acid as solvent, hydrochloric acid as catalyst and water at the boiling temperature of the mixture. For the synthesis of HEDTA, the AC and EDTAD were solubilized in dimethylformamide (DMF), and triethylamine was used as the reaction catalyst for esterification and crosslinking between free hydroxyl groups of CA and EDTAD. After the curing period, HEDTA was neutralized, milled and sieved to obtain 35 mesh size particles. HEDTA was swollen with tetrahydrofuran (THF) before being packed in the fractionation column and the previously prepared lignin solution was passed through the separation column to generate different fractions of lignin moieties. The HEDTA and extracted lignin samples were characterized by the following techniques: Fourier Transform Infrared Spectroscopy (FTIR), GPC, Thermogravimetric (TG) and Scanning Electron Microscopy (SEM). For HEDTA, density analysis was also performed by pycnometry. The lignin fractions were characterized by GPC and FTIR. In the FTIR spectrum of lignin, the 1594 cm-1 stretching, attributed to the stretching of the aromatic skeleton CC and C = O stretching, and the stretching at 1511 cm -1 relative to the vibrations of the aromatic rings, together prove that the structure lignin was preserved after the acetosolv pulping process. The FTIR spectrum of AC and HEDTA demonstrate the esterification reaction between EDTAD and the free hydroxyls present in AC. HEDTA had a density of 1.344 g/cm3. The MEV characterization of AC and HEDTA found that they are visually similar. The fractionation of the lignin acetosolv sample (LA), lignin acetosolv hydrolyzate (LH) and phenol (EF) occurred according to its hydrodynamic volume, as evidenced by the GPC technique. The first fractions showed no GPC curves and no FTIR bands characteristic of phenol, proving their selective fractionation. Concluding that the applicability of HEDTA as stationary phase in GPC on a preparative scale has been proven.