Efficient Method of Lignin Isolation Using Microwave-Assisted Acidolysis and Characterization of the Residual Lignin

• Published in: ACS sustainable chemistry & engineering Vol. 5; no. 5; pp. 3768 - 3774
• Main Authors: Zhou, Long, Budarin, Vitaliy, Fan, Jiajun, Sloan, Raymond, Macquarrie, Duncan
• Format: Journal Article
• Language: English
• Published: American Chemical Society 01.05.2017
• Subjects: acidolysis; aromatic compounds; biomass; carbon; cellulose; Fourier transform infrared spectroscopy; gas chromatography-mass spectrometry; hemicellulose; lignin; liquefaction; microwave treatment; nuclear magnetic resonance spectroscopy; softwood; stable isotopes; sulfuric acid; temperature; thermal stability; Microwave; Lignin; Acidolysis; Lignocellulosic biomass
• DOI: 10.1021/acssuschemeng.6b02545
• ISSN: 2168-0485

Microwave heating is characterized by high efficiency and selectivity in biomass treatment. Due to the high thermal stability and low polarity of lignin, isolation of lignin by high-temperature microwave treatment is a promising subject for investigation. In this paper, microwave treatment is applied to polysaccharide liquefaction and lignin isolation from softwood at 160–210 °C for 10 min with dilute sulfuric acid. Mass balance/element analysis/FTIR/TG/solid-state 13C NMR/Py-GC/MS are applied to investigate the processed residues (residual lignin). At 190 °C processing temperature, the residual lignin is a material rich in aromatics. High lignin purity (93 wt %) and yield (82 wt %) could be achieved by a simple protocol, which usually takes days or even weeks using conventional milled wood lignin protocols. The Py-GC/MS is applied to check the structure of lignin by a newly developed approach. The liquid phase after isolation is analyzed by GC-MS and liquid carbon NMR. Most chemicals in processed liquid are from cellulose and hemicellulose, suggesting that lignin is preserved well in the residue. By comparison, we found that microwave isolation causes less lignin degradation than conventional acidolysis under equivalent conditions. It is concluded that microwave treatment is potentially a promising tool for isolation of polysaccharide-free lignin with high efficiency.