Catalytic Depolymerization of Lignin over Mesoporous Solid Lewis Acid Catalysts

Catalytic Depolymerization of Lignin over Mesoporous Solid Lewis Acid Catalysts

Kakasaheb Y. Nandiwale^1,2, Andrew M. Danby¹, Anand Ramanathan¹, Raghunath V. Chaudhari^1,2, and Bala Subramaniam^1,2

¹Center for Environmentally Beneficial Catalysis, The University of Kansas, Lawrence, Lawrence, Kansas 66047, United States

²Department of Chemical and Petroleum Engineering, The University of Kansas, Lawrence, Kansas 66045, United States.

Keywords: Biomass, Lignin depolymerization, Lewis acid

In this work, we report the performances of predominantly Lewis acidic, Zr-incorporated mesoporous silicates (Zr-KIT-5 and Zr-KIT-6)^1-2 for deconstruction of lignin into value added aromatic monomers. This work is motivated by several factors. First, homogeneous Lewis acidic catalysts metal triflates³ have been shown to be effective in selective cleavage of ether linkages in lignin. Further, Brønsted acid sites are known to promote undesired condensation of the depolymerized products that may form during lignin deconstruction.⁴ We therefore hypothesized that the use of a predominantly Lewis-acidic solid catalyst should increase the yield of the monomeric products compared to a predominantly Brønsted acidic catalyst such as H-ZSM-5. Indeed, high yields of monomeric and dimeric oxoaromatic compounds (up to 75 wt%) were observed during depolymenrization of dealkaline lignin on Zr-KIT-5 catalysts at 250°C. At similar operating conditions, the Zr-KIT-5 catalyst outperforms reported yields on H-ZSM-5 catalyst⁵ with much lower formation of heavier residues. The effects of various solvents (1, 4-dioxane, acetic acid, methanol + water) and operating conditions on the depolymerization of various lignins [including corn stover lignin, PC 1369 hardwood lignin (MeadWestvaco), Indulin 80 and dealkaline lignin, (TCI chemicals)] along with the product selectivity and catalyst stability will be presented.

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