Characterization of tobacco stalk lignin using nuclear magnetic resonance spectrometry and its pyrolysis behavior at different temperatures

Abstract

Utilization of tobacco stalk is one of the most challenging issues in tobacco agriculture. This work investigated the pyrolysis behaviors of tobacco stalks lignin using thermogravimetric (TG) analysis, and the resultant liquid products of fast pyrolysis at various temperatures were thoroughly analyzed using GC–MS for promoting tobacco stalk valorization. In addition, lignin structure was characterized using two-dimensional heteronuclear single-quantum coherent nuclear magnetic resonance (2D HSQC NMR) spectroscopy. The results revealed that tobacco stalk lignin had higher contents of resistant structure like guaiacyl-type units, resinols, and phenylcoumarans than other straw lignin. The differential thermogravimetric (DTG) analysis showed that the pyrolysis of tobacco stalk lignin can be described by a two-stage kinetic model, which had the apparent activation energy of 61.64 and 66.42 KJ/mol for the first and the second stage, respectively. The fast pyrolysis of tobacco lignin showed narrower product distribution at medium temperature (600 ℃) than at high (900 ℃) and low temperature (300 ℃), which majorly produced guaiacyl-type mono-phenols. Three high-value products, namely creosol, 2-methoxyphenol and trans-isoeugenol, were selectively produced by the pyrolysis of tobacco stalk lignin. The studies thus paved a new path for valorizing tobacco waste into value-added products through fast pyrolysis.