Li Liu

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.

Furfural-derived humins were produced through acid-catalyzed hydrothermal synthesis, and a series of humin-based carbon materials with different pore structures were prepared via high-temperature carbonization and KOH activation. It was found that the carbon material activated at 800 °C with a KOH-to-humin ratio of 2/3 exhibited excellent CO₂ adsorption performance, whereby the activation temperature and KOH ratio synergistically modulated the porous structure. At 0 °C and 1 bar, its adsorption capacity reached 6.06 mmol/g, and the CO₂ uptake was highly linearly correlated with the volume of micropores smaller than 0.79 nm. Moreover, the 800 °C-2/3KOH material has exhibited an excellent CO₂/N₂ adsorption selectivity of 25.16, a moderate heat of adsorption (14–24 kJ/mol), and good recyclability. This study provides a novel approach to valorize humin-based porous carbons as efficient, sustainable, and economical CO₂ adsorbents.

Cellulose utilization has been seriously hindered by the formation of humins, while the humin structure remains challenging since unconverted cellulose and humins exist as a solid mixture. In this work, we developed a novel strategy to extract humins from unconverted cellulose and disclosed the structural evolution process of cellulose-derived humins for the first time. The key intermediate levoglucosan was successfully captured and identified, which significantly favors the formation of anhydro-sugars followed by polymerization due to its stability. By means of comprehensive HPLC-MS/MS, FT-IR, MALDI-TOF and SEM characterization studies, it was proposed that multiple elementary reactions were involved in the formation of cellulose-derived humins, including cellulose depolymerization, etherification, esterification, aldol condensation, dehydration and thermal oxidation. In the early stage, cellulose depolymerization results in glucose and levoglucosan (LG), which undergo etherification to form the early humins via a small molecule mechanism, accompanied by esterification and dehydration. In the later stage, glucooligosaccharides especially with the LG end from cellulose depolymerization undergo etherification via an oligomer mechanism. Meanwhile, etherification of HMF and aldol condensation with LA take place prominently, together with dehydration and oxidation, resulting in the enhancement of CC and CO conjugation.