Doctor of Philosophy
Chemical and Biochemical Engineering
Dr. Chunbao (Charles) Xu
Concerns about declining non-renewable fossil resources, energy security, climate change and sustainability are increasing worldwide. This has resulted in an increased interest in the development of alternatives to fossil resources not only for energy, but particularly for chemical production on a global level. There are a number of promising alternatives to fossil resources, however, lignocellulosic biomass such as forestry residues and wood waste (limbs, bark, sawdust, etc.) seem to be the most promising. They are widely available, renewable and a non-food resource. Therefore woody biomass holds the promise of being a sustainable resources for both energy and chemical production.
The lignin component of woody biomass is of particular interest as it comprises the world's largest natural source of aromatic compounds and is produced in large quantities as a by-product of pulp and paper processing. The main challenge in lignin utilization for fuels and chemicals is that it is composed of very large molecules with lower heating values (due to high oxygen content) and decreased reactivity. Accordingly, the overall objective of this work is the production of chemicals and fuels by the catalytic hydrotreatment of lignin and lignin-derived bio-oils aiming to reduce its molecular weights and oxygen contents.
This work investigated the catalytic hydrotreatment of a number of different lignins and degraded lignins for the production of fuels and chemicals. Several supported metal hydrogenation catalysts were investigated for the depolymerization, deoxygenation and de-sulfurization of Kraft lignin (KL) and organosolv lignin (OL) under hydrogen atmospheres to produce degraded lignins in a 500 mL autoclave reactor. All of the catalysts tested were effective in depolymerizing the lignin feedstocks, however, the alumina-supported catalysts and the carbon-supported Ni catalyst did not perform as well as the carbon-supported Ru catalyst and FHUDS-2 (an industrial HDS catalyst). The molecular weights of the degraded lignins using these last two catalysts at 300 °C were markedly lower than the KL feed (~1,000 vs. 2,500 and 10,000 g/mol). In addition, the sulfur contents of the degraded Kraft lignins were drastically reduced.
Targeting the development of effective and inexpensive catalysts for hydrotreatment of lignin and lignin-derived bio-oils to produce chemicals and fuels, screening of catalysts was performed using guaiacol as model compound. The most effective catalyst under the conditions tested was found to be 1 wt.% Mo-doped 5 wt.% Ru supported on activated charcoal (Mo0.01Ru0.05/AC). The selected catalyst proved to be very effective for hydrotreatment of organosolv lignin (MW ≈ 2,600 g/mol) into a liquid product comprising >85% phenolic compounds with a MW of 460 g/mol at ~70% yield at 340°C. This catalyst was also employed in the hydrotreatment of hydrolysis lignin (HL) and depolymerized hydrolysis lignin (DHL).
Tymchyshyn, Matthew, "Hydrotreatment of Lignin into Green Fuels and Chemicals" (2015). Electronic Thesis and Dissertation Repository. 2979.