Phase behavior and decomposition of lignin in hot-compressed water
Lignin (20%), cellulose (50%) and hemicellulose (25%) are three major constituents of typical lignocellulosic biomass like wood and grass. Among them, lignin is a phenolic biopolymer, which is the most thermal-stable and the most difficult to be degraded by normal biological or thermal methods. Additionallly, it is the industrial waste of cellulosic ethanol and paper making, which makes its recycle very significant. Adschiri group in TohokuUniversityfound that 99% of lignin degraded into phenolic oil in high temperature water-phenol (400 oC). The phenolic oil would not repolymerize to solid even after 2 h reaction. However, we did not know if these reactions were homogeneous reactions, as well as the actual reaction pathways. Professor Zhen Fang in biomass group of XTBG (Xishuangbanna Tropical Botanical Garden), CAS (http://brg.groups.xtbg.ac.cn/) collaborated withTohokuUniversity andSaskatchewanUniversity. They found that lignin was totally dissolved in hot-compressed water-phenol mixture, which greatly promoted the hydrolysis of lignin into phenolic oil. The addition of phenol prevented the repolymerization of formed phenolic oil. Afterwards, the author elucidated the homogeneous/heterogeneous pathway and mechanism of lignin degrading in hot-compressed water. According to the proposed pathway, lignin can totally be degraded into phenolic oil, which can be further processed into bioplastic, chemicals and biofuel. The related paper was published in the international journal “Bioresource Technology”.
Zhen Fang*, T. Sato, R. L. Smith Jr., H. Inomata, K. Arai, J. A. Kozinski, Reaction chemistry and phase behavior of lignin in high-temperature and supercritical water, Bioresource Technology, 99(9), 3424-3430 (2008).
(http://dx.doi.org/10.1016/j.biortech.2007.08.008)