Submitted to: Fuel Processing Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/31/2014
Publication Date: 2/21/2014
Citation: Elkasabi, Y.M., Mullen, C.A., Pighinelli, A.L., Boateng, A.A. 2014. Hydrodeoxygenation of fast-pyrolysis bio-oils from various feedstocks using carbon-supported catalysts. Fuel Processing Technology. 123:11-18.
Interpretive Summary: Fast-pyrolysis is a technology that has shown much promise for producing crude oil from renewable agricultural products (termed “bio-oil”). Recent work shows that fast-pyrolysis can easily produce bio-oil on a large scale. This makes it applicable to various global economies which vary in their agricultural resources. Agricultural wastes work just as well, thus quelling the food vs. fuel debate. Before bio-oils can be used as gasoline, they need to be chemically refined in order to improve their shelf life. This upgrading can be done by catalytically removing oxygen and adding hydrogen, which makes it a better fuel and removes harmful contaminants. Very few studies have investigated bio-oils from varying agricultural resources, with regard to their ability for refinement. This kind of assessment will be necessary for expanding bio-oil production. In this study, bio-oils were produced from three abundant sources: switchgrass, eucalyptus, and horse manure. Different processing conditions were also employed in their production, and the effects of these variables were investigated. The chemistry, acidity, moisture, and efficiency of oxygen removal were linked back to the feedstock characteristics. It was found that, of the catalysts used in the study, switchgrass bio-oil catalyzed with platinum produced the best quality product and consumed the least amount of hydrogen. It was also found that switchgrass was the most efficient at retaining carbon. Eucalyptus bio-oil consumed more than twice the normal amount of hydrogen for the same or lesser product quality, which would significantly increase process costs if used on a larger scale. Manure bio-oil showed better oxygen loss with ruthenium catalysts, although less product was obtained overall.
Technical Abstract: While much work has been accomplished in developing hydrodeoxygenation technologies for bio-oil upgrading, very little translation has occurred to other biomass feedstocks and feedstock processing technologies. In this paper, we sought to elucidate the relationships between the feedstock type and the suitability of their fast-pyrolysis bio-oils for hydrodeoxygenation (HDO) upgrading. Switchgrass, Eucalyptus benthamii, and equine manure feedstocks were pyrolyzed into bio-oil using a continuous fast-pyrolysis system. We also synthesized variations of switchgrass bio-oil using catalytic pyrolysis methods (HZSM-5 catalyst or tail-gas recycle method). Bio-oil samples underwent batch HDO reactions at 320 oC under ~2100 psi H2 atmosphere for 4 hours, using Pt, Ru, or Pd on carbon supports. Hydrogen consumption was measured and correlated with compositional trends. The resulting organic, aqueous, and gas phases were analyzed for their chemical compositions. Moisture content and total acid numbers (TAN) of the upgraded organic phases were also measured. Switchgrass bio-oil over Pt/C performed the best in terms of hydrogen consumption efficiency, deoxygenation efficiency, and types of bio-oil compounds. Eucalyptus feedstocks consistently consumed more than twice the normal amount of hydrogen gas per run, primarily due to the elevated syringol content. Catalytically pyrolyzed bio-oils deoxygenated poorly over Pt/C but hydrogenated more extensively than other oils. Although the relative deoxygenation (%DOrel) varied based on feedstock and catalyst, the absolute deoxygenation (%DOabs) depended only on the overall yield. The total extent of upgrading (hydrogenation + deoxygenation) remained independent of feedstock and catalyst.