Modeling pyrolytic behavior of pre-oxidized lignin using four representative β-ether-type lignin-like model polymers

Weikun Jiang, Jiangyong Chu, Shubin Wu, Lucian A. Lucia

Index: 10.1016/j.fuproc.2018.03.041

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Abstract

A better understanding of the pyrolytic characteristics of pre-oxidized lignin in which CαH–OH was oxidized to Cα O group was obtained through four selected β-ether-type lignin-like model polymers containing the H- and G-type subunits. These models were depolymerized in closed ampoule reactor system and interrogated using in-situ FTIR. The results show that their degradation products differ significantly in species and yield due to CαH–OH, Cα O, and aryl–OCH3. The yield of phenolic monomers from oxidized G-type polymer rose to 27.87 wt%, almost twice that of initial G-type polymer. Nevertheless, as for H-type polymer, oxidation of the CαH–OH to Cα O group lead to decreases in phenolic monomers yield by ~half. The in-situ FTIR indicates that oxidation of the CαH–OH to Cα O accelerates cleavage of interunit linkages and simplifies depolymerization pathways resulting in better selectivity of phenolic monomers, especially at low pyrolysis temperatures (<500 °C). Several important transformation pathways are proposed that clearly explain the pyrolytic behavior of pre-oxidized polymers.