Comparative Research about Wheat Straw Lignin from the Black Liquor after Soda-Oxygen and Soda-AQ Pulping: Structural Changes and Pyrolysis Behavior

Structural changes and pyrolysis behavior of lignins derived from black liquor of soda-anthraquinone (SAL) and soda-oxygen pulping (SOL) for wheat straw at similar delignification rates have been investigated. The lignin was first isolated through acid precipitation and then was characterized by various analytical techniques, including elemental analysis, gel permeation chromatography, Fourier transform infrared spectroscopy,C-13-H-1 heteronuclear single quantum correlation spectra analysis, and thermogravimetry mass spectrometry. At similar delignification rates, the pulping process for gaining quality pulp, SOL contained more (beta-O-4) structure and hydroxyl and carbonyl groups, which provided promising results for depolymerization and pyrolysis. SOL showed superior pyrolysis properties including higher combustibility gas formation and lower pyrolysis temperature. Small group organic products like acetic acid and furural could be released from SOL at 100 degrees C lower temperature, while more methane could be produced in a larger temperature range.