(535a) Dual Functional Zr-KIT-5 Shows Remarkable Activity for Depolymerization of Corn Stover Lignin into Stable Phenolic Monomers
Kakasaheb Y. Nandiwale1,2, Andrew M. Danby1, Anand Ramanathan1, Raghunath V. Chaudhari1,2, and Bala Subramaniam1,2
1Center for Environmentally Beneficial Catalysis, University of Kansas, Lawrence, Lawrence, Kansas 66047, United States
2Department of Chemical and Petroleum Engineering, University of Kansas, Lawrence, Kansas 66045, United States.
Keywords: lignin depolymerization, Zr-KIT-5, Lewis acid, acetic acid
We previously showed that Zr-KIT-5 exhibits superior performance than H-ZSM-5 for depolymerization of dealkaline lignin yielding up to 77wt% of THF-soluble products (monomers and dimers). Structural degradation and loss of acidity occur in spent Zr-KIT-5 catalyst primarily due to a lack of hydrothermal stability in aqueous methanol solvent.1
These insights motivated us to screen various non-aqueous solvents such as 1,4-dioxane, acetic acid, and Î³-valerolactone (GVL) for their ability to solubilize lignin and to avoid the hydrothermal degradation of Zr-KIT-5 catalyst. As expected, the organosolv (corn stover-derived) lignin was completely soluble in acetic acid, the solvent used for separating the lignin from cellulose fraction. Significantly, the solvent exhibited thermal stability at typical depolymerization temperatures. Furthermore, Zr-KIT-5 catalyst showed much better physical stability in acetic acid solvent compared to aqueous (water + methanol) solvent. About 12 different phenolic monomers (including a few that are acetylated) were identified in the depolymerized product mixture by GC-MS/FID. The Lewis-acid sites of Zr-KIT-5 catalyst appear to facilitate not only depolymerization of lignin, but also acetylation of the monomers, thus preventing monomeric condensation/repolymerization. High yield of identified monomers (28 wt%), comparable to those reported to date, and ethyl acetate soluble aromatic species (43 wt%) were obtained with thermo-solvolytic treatment of lignin followed by catalytic depolymerization over Zr-KIT-5 catalyst. The Zr-KIT-5 was found to be a promising solid Lewis acid catalyst displaying stable activity for up to five catalytic lignin depolymerization cycles.
(1) K.Y. Nandiwale, A.M. Danby, A. Ramanathan, R.V. Chaudhari, B. Subramaniam, ACS Sustainable Chem. Eng. 2017, 5, 7155.