Reductive depolymerization of lignin-containing stillage (LA lignin) from 2nd generation bioethanol industrial plants have been studied using two different families of catalysts: conventional porous Ru catalysts supported on ZrO2 or activated carbon, and 1-dimensional Ru catalysts supported on multi-walled carbon nanotubes (MWCNT). The lignin depolymerization degree using conventional porous catalysts resulted in values of 42 and 53 %, for Ru/ZrO2 and Ru/C, respectively. Strikingly, when using 1D-supported catalysts (Ru/MWCNT and Ru/ZrO2/MWCNT), the extent of lignin depolymerization measured by 1H-13C HSQC NMR, reached values of c.a. 80 % of b-O-4 bond disappearance and a reduction of the average molecular weight from 3600 Da to ~ 1900 Da. The higher accessibility of the lignin agglomerates to the 1-D catalyst nanoparticles substantially improves the lignin depolymerization degree. This indicated that increasing the accessibility of the catalyst is critical to improve the catalyst utilization and ultimately the efficiency of the process. The mass transport limitations of lignin depolymerization are highlighted in this report and we hope that these observations are considered in the next generation of heterogeneous catalysts for lignin valorization to monomeric phenols and aromatics.

Catalytic valorisation of industrial 2G biomass stillage into monomeric phenolics using Ru catalyst supported on 1D multiwall carbon nanotubes (Ru-MWCNT) with enhanced molecular accessibility

255th National Meeting (2018)

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