Date of Award

2016

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy in Chemical Engineering (PhD)

Administrative Home Department

Department of Chemical Engineering

Advisor 1

David Shonnard

Committee Member 1

Ezra Bar Ziv

Committee Member 2

Michael Mullins

Committee Member 3

Julio Sacramento Rivero

Abstract

Biofuels are an important advancement in alternative energy that can provide substantial environmental benefits compared to their conventional fossil fuel counterparts Said benefits are usually measured using life cycle assessments. However, it is not well understood yet how different methodological choices such as system boundaries, biomass feedstocks, conversion pathways, geographical data, etc. affect the conclusions drawn from biofuels LCA. This research shows large variability in life cycle assessment results and limits comparison across different biofuel pathways due to methodological choices set forth by policy and certification schemes. Advanced biofuels have not reached large scale production due to a limited understanding of thermochemical conversion of various feedstocks and the cost of these feedstocks.

To address the issues of feedstock cost, municipal solid waste (MS) was evaluated as a feedstock for the production of bio-oil via fast pyrolysis. MSW (paper waste, grass clippings, fiberboard, waferboard, microllam, plywood) produced similar yields as that of its traditional feedstocks (switchgrass, corn stover and hybrid poplar). Bio-oil yields ranged from 58% to 77% for the MSW feedstocks. The woody waste had the highest yields and the largest production of lignin derived compounds while the paper waste had higher levels of carbohydrate derived compounds and lower yields.

To understand how controlled variations in feedstock affected bio-oil speciation, 8 genetically different hybrid poplar samples with increasing lignin content from 17%-22% were pyrolyzed at 500°C, 550°C and 600°C. The purpose of this work was to evaluate how the effect of increasing lignin content with respect to increasing temperature affects product distribution and bio-oil speciation. With increasing lignin content at 500°C the char yield increased from 17.5% to 27.2% and the bio-oil yield decreased from 73% to 65%. With increasing temperature the increase in lignin, allowed for a higher percentage of lignin derived compounds within the bio-oil.

To gain a better understanding into biomass degradation, kinetic data was obtained using a micropyrolysis GC/MS experimental set-up. This data was quantified and the mass of bio-oil species produced with respect to time was calculated. The kinetic data showed that hemicellulose derived bio-oil compounds such as acetic acid was produced in large quantities initially, whereas lignin derived compounds such as methyl syringol had a delay in production and took a longer time to reach maximum production. Application of a first order exponential decay model and a six-step degradation model were applied to the data. The first order exponential decay model was insufficient for capturing the initial production of the bio-oil compounds. The six stage degradation model fit the data very well and was able to give insight into biomass degradation with respect to the stoichiometric parameters. These parameters showed that hemicellulose degrades first and then cellulose and lignin degrade at later times agreeing with previous literature. These data along with the application of the six stage degradation model gives a better understanding of biomass degradation with the use of a semi-empirical model. Overall this work shows that MSW and hybrid poplar bio-oil produced via fast pyrolysis are a viable option for the production of biofuels and contributes to the overall knowledge needed for the implementation and advancement within the biofuel industry

Available for download on Monday, July 31, 2017

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