Submitted to: Energy and Fuels
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/13/2011
Publication Date: 10/20/2011
Citation: Mullen, C.A., Boateng, A.A., Mihalcik, D.J., Goldberg, N.M. 2011. Catalytic fast pyrolysis of white oak wood in-situ using a bubbling fluidized bed reactor. Energy and Fuels. 25:5444-5451. Interpretive Summary: In order to meet the renewable fuels standards set by the US government, 21 billion gallons of advanced bio-fuels will need to be produced by 2022. The largest source of feedstock to produce these advanced biofuels is lignocellulosic biomass, including woody materials, herbaceous grasses and crop residues (e.g. corn stover, straws). One promising process to convert biomass to a liquid is fast pyrolysis which produces a product called pyrolysis oil (bio-oil) which can be refined to “green” gasoline and diesel fuels that are indistinguishable from those produced from petroleum. However, pyrolysis oil is currently incompatible with petroleum for refining because it is corrosive and unstable, meaning its viscosity greatly increases during storage creating processing problems. Chemically, these unfavorable properties are due to the fact that pyrolysis oil, unlike petroleum, consists of reactive oxygenated molecules. One method to reduce the oxygen content of pyrolysis oil is to incorporate a catalyst material in the pyrolysis process. The catalyst acts to facilitate the removal of oxygen from the molecules that make up the pyrolysis oil resulting in hydrocarbons, the types of compounds found in petroleum. In this study we tested two catalysts in the pyrolysis process for oak. The major problem found was that catalysts are deactivated in the pyrolysis process, by being converted in carbon deposits from the oak. We developed a method where these deposits can be removed from the catalysts by combustion at periodic intervals. Using this method we were able to reduce the oxygen content in pyrolysis oil from about 40 wt% to about 17 wt%. This information will be useful to those considering using catalytic pyrolysis as a method to produce biofuels from biomass, and those who might refine pyrolysis oils into advanced biofuels.
Technical Abstract: Catalytic fast pyrolysis was performed on white oak wood using two zeolite-type catalysts as bed material in a bubbling fluidized bed reactor. The two catalysts chosen, based on a previous screening study, were Ca2+ exchanged Y54 (Ca-Y54) and a proprietary ß-zeolite type catalyst (catalyst M) both supplied by UOP. Each catalyst proved effective at partially deoxygenating the oak wood pyrolysis vapors during the initial pyrolysis process and adding aromatic hydrocarbons to the liquid product mixture. However, each incurred a penalty of reduced liquid yield and catalyst deactivation due to coke formation on the catalysts’ surfaces. The coking on the Ca-Y54 catalyst was relatively less severe because the deoxygenation process followed decarbonlylation and decarboxylation reaction pathways more severely compared to dehydration and dehydrogenation pathways for catalyst M although evidence that both catalysts were active for all the reaction mechanisms exist. The severe coking problem on catalyst M was mitigated by successfully regenerating the catalyst in situ resulting in effective production of partially deoxygenated pyrolysis oils over extended periods of time and concomitantly improving the C/O ratio of the upgraded pyrolysis oils from 1.8/1 to 5.9/1 at best. This demonstrates the potential of producing partially deoxygenated and stable fuel intermediates by in-situ catalytic fast pyrolysis for ready use as refinery fuel blendstock using the bubbling fluidized bed technology.