Liquefaction and hydrodeoxygenation of polymeric lignin using a hierarchical Ni microreactor catalyst

Zhicheng Luo, Jiechen Kong, Bing Ma, Zichun Wang, Jun Huang, Chen Zhao*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

22 Citations (Scopus)

Abstract

The depolymerization of lignin into liquid products in high yields is particularly challenging because of the poor solid-solid contact during heterogeneous catalysis and the formation of benzylic carbocations (Ph-CαH-OH) and unstable intermediates bearing aldehyde groups, leading to repolymerization. Herein, we report a hierarchical Ni/ASA microreactor catalyst for the hydrodeoxygenation of lignin comprising ca. 17 aromatic monomers into light cyclic hydrocarbons in a nearly theoretical yield at a high reactant/catalyst ratio. The matched sizes in the macropores of Ni/ASA (3-6 μm) and the particle size of polymeric lignin (4.4 μm) resulted in fast lignin particle entrapment and an increased adsorption rate for larger amounts of lignin into the Ni/ASA, with better solid-solid contact compared to nonhierarchical Ni/ASA, as evidenced by UV-vis spectra. The lignin aromatics trapped in the macropores are quickly and fully hydrogenated to poly-cyclitols (stable intermediates), which are then transferred to the mesopores for further depolymerization and hydrodeoxygenation to the final cyclic hydrocarbons, as monitored and tracked by two-dimensional heteronuclear single quantum correlation NMR, in situ Fourier transform infrared, gel permeation chromatography, and time-of-flight mass spectrometry. The designed microreactor with suitable hierarchical pores facilitated the entrapment, adsorption, and catalyst-lignin macromolecule contact. The fast elimination of unstable intermediates of aromatics and aldehydes by efficient hydrogenation suppresses repolymerization and increases yields. We suggest that this can be a useful strategy for the efficient direct liquefaction of a diverse set of lignin or lignite polymeric materials and for the hydrogenation of polyaromatics in coal tar.

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Original languageEnglish
Pages (from-to)2158-2166
Number of pages9
JournalACS Sustainable Chemistry and Engineering
Volume8
Issue number5
DOIs
Publication statusPublished - 10 Feb 2020
Externally publishedYes

Keywords

  • hierarchical Ni catalyst
  • hydrogenation
  • fast stabilization
  • C-O bond hydrogenolysis
  • alkanes
  • in situ FTIR

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