Structures and pyrolytic characteristics of organosolv lignins from typical softwood, hardwood and herbaceous biomass

Three typical lignins from pine (softwood), poplar (hardwood), and bamboo (herbaceous biomass) were isolated using organosolv dioxane. Their chemical structures were identified and the pyrolytic characteristics were investigated comprehensively. The results indicated that pine lignin possessed the highest content of guaiacyl (G) units, the least beta-O-4' aryl ether linkages and best thermal-stability. A high selectivity of 77.26 % for guaiacoltype products from pine lignin was obtained at 400 degrees C. Bamboo lignin had the most uniform molecular distribution and 40.31 % p-coumarate (pCA) units. The dominant pyrolytic product of bamboo lignin was 4-vinyl phenol with a high content up to 32.64 % at 500 degrees C. 48.17 % p-hydroxybenzoates (PB) and abundant syringyl (S) units existed in poplar lignin, and phenol was the predominant pyrolytic product with the maximum content of 23.19 % at 600 degrees C.

Automated summary

Pine lignin has the highest G unit content and best thermal stability; bamboo lignin has uniform molecular distribution and a high pCA unit content; poplar lignin contains abundant PB and S units, with phenol as the main pyrolytic product.