Document Type

Dissertation - Open Access

Award Date

2017

Degree Name

Doctor of Philosophy (PhD)

Department / School

Chemistry and Biochemistry

First Advisor

Douglas E. Raynie

Keywords

catalyst, depolymerization, hydrotreatment, lignin, pyrolysis, torrefaction

Abstract

Lignocellulosic materials derived from plants have the ability to serve as feedstocks in place of depleting petroleum and coal for production of fuels and chemicals. Lignin forms about 30% of lignocellulosic material, and is the second most abundant non-fossil organic carbon source in the biosphere. However, it is often treated as waste or, in some instances, burned to supply energy. Developing an efficient and environmentally benign method to convert lignin to high value-added aromatic monomers (e.g., guaiacol, vanillin, acetovanillone, and eugenol) for synthesis of polymers is of interest. Mineral bases, such as NaOH and CsOH, or supported-metal catalysts (Pt, Ru, Pd, and Ni on C) have been used to form aromatic monomers, but associated drawbacks are corrosion, catalyst recovery, sintering of metals, and loss of activity. Lignin conversion into useful aromatic compounds is highly desired but often hindered by recondensation and accompanied undesired products. Zeolite-supported metal oxide catalysts (CoO, LaO, and MoO) with subcritical water at 200°C and 240°C were used to convert lignin to value-added aromatic monomers. Separation of the resulting organic and aqueous phases was done by liquidliquid extraction using ethyl acetate. Our results indicate the formation of guaiacol, homovanillic acid, isoeugenol, 3-methoxyacetophenone, acetovanillone, and vanillin as the main products. GC-MS analysis of the organic extract shows 2-4.8 wt% and 3-15 wt% formation of phenolic compounds at 200 °C and 240 °C, respectively, at 12 MPa and 15 minutes. MoO catalyst gave the highest yield of phenolic monomers at both temperatures. The presence of the aromatic products was confirmed by FTIR, GC-MS, and UHPLC analysis. Extracted lignin from torrefied prairie cordgrass at 250 °C (Tor250), 300 °C (Tor300), and 350 °C (Tor350) yielded 23.5±1.6 wt%, 5.4±6.8 wt%, and 4.1±7.3 wt% of lignin respectively with 92-93.1 wt% recovered lignin relative to the organosolvent method. Torrefaction at 350 °C provided higher lignin purity (93.1±3.2 wt%) than lignin extracted from PCG (89.2±2.5 wt%). Thermogravimetric analysis shows breakdown of β- O-4 linkages in the lignin by mass loss between 250 to 350°C. Pyrolytic bio-oil obtained ranged between 13 and 37 wt% of prairie cordgrass at temperatures of 250°C, 300 °C, 350 °C, 600 °C, and 900 °C. The bio-oil contains the useful aromatic compounds - phenol, guaiacol, m-cresol, xylenol, ethyl-phenol, ethyl-guaiacol, catechol, syringol, furan-2-one, vanillin, and 3-furancarboxaldehyde.

Library of Congress Subject Headings

Lignin.
Pyrolysis.
Catalysis.
Biomass energy.
Biomass conversion.

Description

Includes bibliographical references (pages 95-121)

Format

application/pdf

Number of Pages

137

Publisher

South Dakota State University

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Included in

Chemistry Commons

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Rights Statement

In Copyright