This Is AuburnElectronic Theses and Dissertations

Gasification and Pyrolysis of Eucalyptus, Prickly Pear, Gumweed, and lignin for Biofuel and Chemical Intermediates




Cross, Phillip

Type of Degree

PhD Dissertation


Biosystems Engineering


This focus of this dissertation is to advance our understanding of how the chemical makeup of feedstocks alters the performance of thermochemical conversion and alters the production of biofuel and chemical intermediates. In doing so we also develop strategies for obtaining a chemical makeup more suitable for producing the desired product slate. The large-scale use of non-food biomass as a source of renewable carbon for fuels and specialty chemicals will require the development of dedicated feedstocks with cell wall characteristics optimized for growth and efficient conversion (high carbon and hydrogen retention, low catalyst deactivation). Additionally, intensification of biomass production and reduction in water and nutrient consumption is crucial. Therefore, this dissertation is focused on understanding the thermochemical conversion of advanced feedstocks which will include woody biomass grown using state of the art agricultural practices, drought tolerant biomass species, and chemically isolated lignin’s. Harvesting age and presence/absence of bark have been selected as parameters to improve the agricultural practices and chemical makeup of short rotation Eucalyptus benthamii (E. benthamii). Additionally, Opuntia ficus-indica (prickly pear) and Grindelia squarrosa (gumweed), exceptionally drought tolerant plants, are converted to biofuels using thermochemical processes for the first time. Finally, chemically isolated lignin’s from hardwood and softwood species are a promising feedstock for the production of phenolic compounds as specialty chemicals for polymers and resins. Thermochemical gasification and pyrolysis of E. benthamii showed that by selecting the age at which E. benthamii was harvested and altering the presence/absence of bark, tar profiles of gasification can be altered. Older trees without bark produced more naphthalene and indene while younger trees produced more benzene and toluene. Additionally, syngas profiles from gasification are affected by these parameters. Older 7 year E. benthamii without bark (7EWoB) generated higher levels of CH4 leading to a higher heating value of the syngas compared to both younger samples harvested at 2 years with and without bark (2EWoB and 2EWB). The presence of bark was found to increase the H2 yield which leads to a higher H2: CO gas ratio with the 2EWB sample. By selecting the appropriate growth cycle and altering the presence/absence of bark, the product slate and kinetics of fast pyrolysis can be altered. Older samples had a higher CrI of the cellulose leading to the production of d-Allose while this compound was not observed in measurable quantities from younger samples. Additionally, the phenolic-monomers produced through fast pyrolysis were different for these samples. To further asses the formation of gasification tar as one of the main hurdles to the industrialization of the gasification technology, model lignin dimers were used to evaluate how different linkages of lignin and S, G, and H type lignin alter the reaction network and tar compounds. Pyrolysis at 850°C showed that S type dimers produce more indene and 2-ring aromatics through radical condensations. G type lignin was found to generate more furans and 3-ring tars while H type lignin produces more phenolics and 1-ring aromatics. Opuntia ficus-indica (prickly pear) and Grindelia squarrosa (gumweed) are two types of biomass that possess unique cell wall architectures tailored for prolific growth in arid and semi-arid climates. Fast pyrolysis of these feedstocks has potential as the unique carbohydrates and resins have been found to be efficiently converted to hydrocarbons and generate their own slate of oxygenates not yet observed in the catalytic fast pyrolysis of biomass. Vapor phase upgrading of these drought-tolerant feedstocks using zeolite catalyst was shown to be an effective method of reducing the oxygen content of the pyrolysis vapors and generating hydrocarbons and valuable chemicals. Pyrolysis vapors from prickly pear were effectively converted to aromatics and olefins with slightly lower yields than that of pine. The higher H/Ceff values lead to lower yields of aromatics even for the in-situ configuration and therefore ex-situ catalyst used to produce larger C3+ olefins are recommended. The ex-situ deactivation and coke formation were observed to be less severe for prickly pear than other feedstocks and is attributed to the higher H/Ceff values and elevated CO2 yields of non-catalytic pyrolysis vapors. Gumweed produced high levels of aromatics, moistly naphthalene’s and toluene with in-situ catalyst placement. Ex-situ catalyst can be used to produce high levels of olefins and potentially valuable oxygenates such as 3,3,5,6-tetramethyl-1-indanone. Ex-situ deactivation showed that these oxygenates can be produced even at a catalyst to biomass ratio of 1:2 while yields of light olefins and aromatics decreased. High-value chemicals are the leading area of research to make biofuels more economical. Phenolic compounds are produced from the lignin fraction of biomass and can be used in resins and specialty chemicals. Ethanol organosolv and ionosolv are two strategies to remove lignin from biomass and do so by different reactions. By evaluating the different structures of the resulting lignin using 2D-HSQC NMR and 31P NMR it is possible to correlate the interunit linkages to the pyrolysis products and determine which structures are more suitable for thermochemical conversion and production of higher value chemicals. Ionic liquid lignin was found to generate higher yields of phenolic monomers and also produced a much simpler product slate than whole biomass or EOL lignin