Degree Type

Dissertation

Date of Award

2013

Degree Name

Doctor of Philosophy

Department

Mechanical Engineering

First Advisor

Robert C. Brown

Abstract

Fast pyrolysis is a promising method for producing advanced biofuels and chemicals from lignocellulosic biomass. The process will however require further optimization to produce fuels and chemicals at a price competitive to conventional fossil fuel-derived products. Research in this dissertation focuses on both pre- and post-processes for optimizing fast pyrolysis to produce increased yields of valuable anhydrosugars and phenolic monomers.

The concept of alkali and alkaline earth metal (AAEM) passivation using sulfuric acid had only previously been demonstrated in batch micropyrolyzer trials. A bench-scale, continuous-flow auger pyrolyzer was used in this work to demonstrate AAEM passivation on both woody and herbaceous feedstocks. Alkali and alkaline earth metal passivation of red oak and switchgrass increased total sugars by more than 105% and 260%, respectively. Light oxygenates simultaneously decreased by nearly 50% from each feedstock. The synchronous increase in sugars and decrease in light oxygenates provides evidence of the hypothesis that AAEM passivation prevents pyranose ring fragmentation and promotes glycosidic bond cleavage in holocellulose. An undesirable consequence of AAEM passivation was an increase in biochar from both lignin and carbohydrates. Demonstration of the enhanced production of sugars from AAEM passivated feedstocks in a continuous auger pyrolyzer at the kilogram scale is an important step in determining the feasibility of using fast pyrolysis to produce sugars from lignocellulosic biomass.

Lignin-derived biochar increased from AAEM passivated feedstocks which led to suspicions that thermally active AAEMs catalyze lignin pyrolysis. Effect of thermally active AAEMs on lignin pyrolysis was therefore investigated in more detail. Experimental results indicated that sodium was the most active AAEM on lignin pyrolysis in which it increased overall volatile aromatic monomers by over 16% compared to the control. Alkali metals as a group both increased char and decreased alkenyl side chains amongst volatile aromatics. Alkenyl side chains are known to result from the cleavage of certain bonds within the lignin structure. Therefore AAEMs are predicted to catalyze the cleavage of linkages within the lignin structure during pyrolysis.

The rate at which pyrolysis vapors are cooled in bio-oil collection equipment has been noted to have an influence on bio-oil composition, however prior to this research has never been quantified. A novel cold-gas quench system was developed that utilizes liquid nitrogen to quickly quench pyrolysis products, which produced a more than seven fold increase in cooling rate compared to a conventional shell and tube condenser. The increased cooling rate and elimination of radial temperature gradients in the quench system increased levoglucosan yield from cellulose by 23% compared to the conventional system.

Copyright Owner

Dustin Lee Dalluge

Language

en

File Format

application/pdf

File Size

190 pages

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