Extraction of Lignin from a Coproduct of the Cellulosic Ethanol Industry and Its Thermal Characterization

Abstract

Lignin was extracted from the solid coproduct of a lignocellulosic ethanol production by a solid-liquid extraction method using N,N-dimethyl formamide. This coproduct was the residue of a steam explosion pretreatment followed by enzymatic hydrolysis process. The coproduct was used as received and also after washing. Lignin content of the solid coproduct was reduced from 63% to 43% after lignin extraction. Fourier transform infrared spectroscopy (FTIR), molecular weight measurement (GPC), and elemental analysis provided information about the chemical structure and molecular weight of the fractions. The extracted lignin had lower molecular weight (~ 5000 Da.) and higher carbon content (63%) compared to the residue of extraction (Mw ≈ 8000 Da. and carbon % = 48%). Thermal stability measurements of the samples by thermogravimetry (TGA) showed that the extracted lignin had the highest carbon residue. Effects of different heating cycles on the glass transition temperature (Tg) were measured. The Tg of the soluble fraction was lower than that of the coproduct. Results of the X-ray diffraction (XRD) showed the crystalline structure of cellulose in both the coproduct and the solid residue after extraction. This extraction and material characterization is helpful for liquid processes such as solution spinning or electrospinning. The thermal properties can be used for optimization of heat treatment processes such as carbonization.