469433 Lignin Depolymerization into Aromatic Monomers over Acidic Mesoporous Silicates

Wednesday, November 16, 2016: 9:10 AM
Franciscan B (Hilton San Francisco Union Square)
Kakasaheb Nandiwale1, Andrew Danby2, Anand Ramanathan2, Raghunath V. Chaudhari3 and Bala Subramaniam3, (1)Department of Chemical and Petroleum Engineering, Center for Environmentally Beneficial Catalysis, The University of Kansas, Lawrence, KS, (2)Center for Environmentally Beneficial Catalysis, The University of Kansas, Lawrence, KS, (3)Department of Chemical and Petroleum Engineering, Center for Environmentally Beneficial Catalysis, University of Kansas, Lawrence, KS

Lignin Depolymerization into Aromatic Monomers over Acidic Mesoporous Silicates

Kakasaheb Y. Nandiwalea,b, Andrew M. Danbya, Anand Ramanathana, Raghunath V.Chaudharia,b, and Bala Subramaniama, b

aCenter for Environmentally Beneficial Catalysis, The University of Kansas, Lawrence, KS 66047, USA.

bDepartment of Chemical and Petroleum Engineering, The University of Kansas, Lawrence, KS 66045, USA.

Keywords: Biomass, Lignin depolymerization, mesoporous silicates

     

We report on novel applications of Zr-incorporated mesoporous silicates for the one-pot conversion of lignin into value added aromatic monomers. Quantitative analysis of the depolymerized products along with mass balance based on the overall solid and liquid products are reported.

Cubic mesoporous silicates, KIT-6 and KIT-5, modified with different Zr loadings (1-6 wt%) display dominant Lewis acidity. These materials display superior lignin depolymerization activity compared to commercial zeolites that are typically Brønsted acids. Briefly, batch depolymerization of dealkaline lignin (TCI chemicals) was carried out in a 300 mL Parr reactor at 250°C, 100 psi N2, 1000 RPM for 30 min in a methanol + water solvent mixture.  The performances of 12 commercially available zeolite catalysts were evaluated. H-ZSM-5 (Si/Al = 11.5) was found to be the best catalyst among the commercial zeolites evaluated, providing 92% lignin conversion. Approximately 54 wt.% of the products are soluble in THF while the lignin substrate is insoluble in THF. The identified aromatic monomers in the THF-soluble fraction represent 4.4 wt. % of the initial lignin. These results with H-ZSM-5 are consistent with those reported in the literature. Commercial H-ZSM-5 catalyst was therefore selected for further comparative study with Zr-KIT-5 and Zr-KIT-6 catalysts. Zr-KIT-5(Si/Zr = 20) provided the best catalytic performance with 97% lignin conversion, yielding 65% of THF soluble products containing 5.5% identified monomers. Gel permeation chromatography (GPC) analysis of depolymerized product from both runs indicates a decrease in the molar mass when compared to the lignin substrate, clearly implying lignin deconstruction. Approximately 25 monomers were identified (by GC-FID, GC-MS) in the THF-soluble product mixture and 15 monomers were identified using external standards. Most of the identified products are typically expected from lignin depolymerization as reported in the literature.  These results, along with fundamental insights into the correlation between catalyst activity and total acidity of catalyst are presented.


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