Comprehensive understanding the chemical structure evolution and crucial intermediate radical in situ observation in enzymatic hydrolysis/mild acidolysis lignin pyrolysis

Abstract

The in-depth understanding of free radical involved in lignin pyrolysis, is the most important technical barrier for pyrolysis mechanism research. Herein, we report an in situ project by using EPR high temperature cavity for the observation of generated radical in lignin pyrolysis, along with the other state-of-the-art techniques such as two-dimensional heteronuclear single-quantum coherence nuclear magnetic resonance (2D HSQC-NMR) and Py-GCMS combined with high temperature oven. The result showed that the originate lignin structure had significant influence on the pyrolytic products and the radical process. Compared with hardwood and non-wood lignin, softwood lignin tented to produce more amount of radical, due to the higher content of guaiacyl type subunits and phenylcoumaran structure. Corresponding with the two mainly pyrolytic reaction stage according the activation energy, the radical reaction of lignin pyrolysis was divided into three stages: radical inducing stage, the main reacting stage and the quenching stage.