Understanding fast pyrolysis of biomass

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Zhang, Jing
Major Professor
Brent H. Shanks
Committee Member
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Chemical and Biological Engineering

The primary reactions and secondary effects resulting from cellulose fast pyrolysis were investigated. It was found that mass transfer limitations existed when the sample weight of powder cellulose was larger than 0.8 mg or when the cellulose particles were pyrolyzed at a larger characteristic length scale. Similar pyrolysis product distributions were obtained for celluloses of differing crystallinity, degree of polymerization, and feedstock type, implying that the primary products from cellulose were not influenced by these factors.

Interactions between cellulose-hemicellulose and cellulose-lignin during fast pyrolysis were examined by comparing the pyrolysis products from their native mixture, physical mixture and superposition of individual components. Negligible interaction was found for either binary physical mixture. For the native cellulose-hemicellulose mixture no significant interaction was identified either. In the case of the native cellulose-lignin mixture, herbaceous biomass exhibited an apparent interaction. However, such interaction was not found for woody biomass.

An acid-base bi-functional catalyst, which was synthesized by acid treating a natural mixed metal oxide, serpentine, was studied for catalytic deoxygenation of bio-oil model compounds. Catalyst characterization revealed stronger acid sites were introduced by the formation of bridged hydroxyl groups between a Si atom and a heteroatom during acid treatment. It was also suggested that the acidic and basic sites are closely jointed together in the bi-functional catalyst. The acid-base bi-functional catalyst could best promote aldol condensation reactions, comparing to single acid, single base, and physical mixture of acid and base. The best deoxygenation was also observed for the bi-functional catalyst during catalytic conversion of the single model compound.

Catalytic deoxygenation during cellulose fast pyrolysis was performed over acid, base, transitional metal compounds and acid-base bi-functional catalyst. The results showed the bi-functional catalyst achieved the best balance between deoxygenation and bio-oil yield among the tested materials. It appeared that during catalysis, the acidic sites primarily promoted dehydration while the basic sites mainly promoted fragmentation reactions. Compared to a physical mixture of acid and base materials, the bi-functional catalyst appeared to promote deoxygenation reactions more effectively presumably due to the presence of adjacent acid and base sites.

Wed Jan 01 00:00:00 UTC 2014