Extraction of lignin from wheat straw by catalysts in 1,4-butanediol medium under atmospheric pressure

Extraction of lignin from lignocellulosic materials in an autoclave using 1,4-butanediol medium has been examined by researchers. However, there has been no research on the extraction of lignin in a 1,4-butanediol medium at atmospheric pressure and no extraction of HBS lignin from wheat straw has been investigated. In this paper, lignin was isolated from wheat straw in 1,4-butanediol media (from 50% to 100%, v/v) that was catalyzed by H₂SO₄ or NaOH while refluxing under atmospheric pressure. Reaction time, liquid-solid ratio, the volume percentage of 1,4-butanediol, as well as catalysts were optimized to improve the lignin yield. The optimum extraction conditions were: 12-to-1 liquor-to-straw ratio of 80% 1,4-butanediol, 1.67% of H₂SO₄ or 0.83% of NaOH, and 3 h reaction time. The optimum yield of lignin was found to be 60.64%. Analysis with Fourier transform infrared spectroscopy, gel permeation chromatography, and thermogravimetry showed that the lignin obtained using the NaOH catalyst had fewer unconjugated C=O groups, fewer =C-O-C bonds, lower molecular weight, and was more thermally unstable than lignin obtained using the H₂SO₄ catalyst.