Evolution Process of Pseudo-lignin Derived from Lignocellulose.

Pseudo-lignin formation severely limits lignocellulose utilization, yet its study is hindered by mixing with unconverted lignocellulosic components. Here, corncob-derived pseudo-lignin was successfully separated for the first time through tetrahydrofuran (THF)/petroleum ether (PE) extraction, providing a basis for the elucidation of the pseudo-lignin formation mechanism. The key intermediate trans-p-coumaric acid (TPCA) from lignin degradation was captured, which plays a crucial role in the formation of pseudo-lignin. In combination with comprehensive characterizations, the reaction network and the structural models of pseudo-lignin were established. Furthermore, through sodium chlorite/acetic acid (SCA) pretreatment to selectively remove lignin, the structural difference between pseudo-lignin formed in the presence of lignin and holocellulose-derived humins formed in the absence of lignin was clearly revealed, verifying that it is the lignin component that introduces the benzene ring structure into pseudo-lignin via its degradation product, while in situ SEM energy-dispersive spectroscopy (EDS) showed pseudo-lignin has a much higher C/O ratio than lignin.