Degree Type

Dissertation

Date of Award

2015

Degree Name

Doctor of Philosophy

Department

Mechanical Engineering

First Advisor

Robert C. Brown

Abstract

The objective of this study was to valorize two prominent products from the fast pyrolysis of lignocellulosic biomass. Biochar was converted to activated carbon and pyrolytic sugar was purified to improve their fermentability. After investigating the technical feasibility of producing ethanol from pyrolytic sugars a techno-economic analysis was performed to understand the economic impacts of the newly proposed pathway in a commercial scale thermochemical biorefinery.

Typical fast pyrolysis biochar has a very low porosity (<0.05 cc/g) and surface area (<10 m2/g). However, with one-step physical activation (steam or carbon dioxide), the surface area can be dramatically improved. Specific operating conditions resulted in red oak activated biochars with more than 800 m2/g and corn stover activated biochar with more than 500 m2/g. Various studies have shown that activated carbon and biochar can effectively adsorb numerous inorganic and organic compounds, potentially making them an integral component of a biorefinery.

In the second part of this study, various biochar and activated biochars were made and used to detoxify the water-soluble fraction of bio-oil to produce ethanol. It was shown that biochars, activated biochars, and commercially activated carbon were effective in removing fermentation inhibitors. Removing these inhibitors can lead to increased bacterial growth and ethanol production during the fermentation of pyrolytic sugar. All three materials showed that pyrolytic sugars can be detoxified and fermented to produce ethanol. Microplate studies showed that BET surface area, quantity of micropores, and external surface area were positively correlated with bacterial growth, but had weak or no correlation with ethanol production. The DFT pore mode and pH of the adsorbent material correlated with ethanol production.

A techno-economic analysis was performed to demonstrate the economic benefits of producing activated carbon. Activated carbon can be utilized within the biorefinery or sold externally as an alternative revenue stream. The newly proposed thermochemical biorefinery with ethanol fermentation of pyrolytic sugars, activated carbon manufacturing, and the use of lower-cost, sustainably harvested biomass presented fairly high internal rate of returns but with significantly higher capital costs compared to previous models. This model resulted in an internal rate of return of up to 16% with the commercialization of 31 million gallons of transportation fuels and various co-products. The gross revenue on an annual base was $154 million from a total project investment of $414 million. As demonstrated in our model, it is profitable to build a biorefinery under these conditions, particularly in the Midwest with an abundant corn stover supply.

Copyright Owner

Bernardo Gusman del Campo

Language

en

File Format

application/pdf

File Size

116 pages

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