Lignin is the second abundant renewable biomass in the world. Since its special bio-aromatic structures and high carbon content, lignin has been regarded as a potential source for producing aromatic hydrocarbons or transportation fuels by depolymerization and hydrodeoxygenation (HDO) processes. However, we found that most works in this field were based on lignin model compound rather than real lignin. In reality, the conversion of real lignin is of very low efficiency due to fast deactivation of catalyst, which makes the technology far from industrial application. Thus, the processes and mechanisms of the transformation of real lignin need to be deeply studied. In this work, the deactivation of catalyst in transforming real lignin into fuels was studied. Unlike model compounds, real lignin showed strong poisonous effect to catalyst, leading to fast deactivation at the beginning of reaction. The catalyst and lignin before and after reaction were characterized by XRD, H2 chemisorption, TPO, TGA, SEM, N2 physical adsorption, GPC, elemental analysis and 2D HSQC NMR. The results showed that heavy carbonaceous deposit (22.3% by TGA), which physically deposited and strongly adsorbed on the surface of catalyst, was attributed to the deactivation. And ester structures, which was always neglect in researches, were confirmed to be another key factor for deactivation due to polymerization reaction. Because of the serious deactivation, we considered that it may be unsuitable to convert lignin into fuels in one stage. Thus, we developed a three-steps method which includes depolymerization of lignin, extraction of monomers and HDO of monomers. As a result, the production for fuels were 9 to 24 time more efficient than the one-step batch reaction. Moreover, many techniques could be applied in the three-steps strategy to make it easier to operate and more potential to be used in commercial production. In addition, products that are potential to be industrially produced by depolymerization of real lignin in the near future will be simultaneously introduced. We hope that researchers could pay more attention on industrial production rather than just conversion and yield.

Study on deactivation of catalyst in transforming lignin to fuels and improvement for the conversion

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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