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Partial oxidation of pyrolysis oil by model compounds

University of British Columbia

The challenges of upgrading pyrolysis oil to transportation fuel limit the economic viability of biomass pyrolysis. Therefore, this dissertation investigated partial oxidation of pyrolysis oil to produce value-added chemicals. Two model compounds, acetic acid (AcOH) and acetaldehyde (AcH) were selected for gas phase oxidation trials. Thermal oxidation of AcOH emphasized AcOH’s refractory nature as the maximum conversion of AcOH was less than 6% at 350 ⁰C at 1 atm with GHSV of 2000 h-¹. AcH was more reactive; conversion of AcH was approximately 40% under identical conditions. Thermal oxidation of both compounds produced only carbon dioxide (CO₂). Although the true reaction mechanism of AcH thermal oxidation could not be determined, the activation energy was calculated to be between 47.1±0.55 kJ/mol and 55.2±0.6 kJ/mol. Catalytic partial oxidation (CPO) of AcOH and AcH was examined using vanadium pentoxide supported by titanium oxide (V₂O₅/TiO₂). Conversion of CPO of AcOH was slightly higher than thermal oxidation but produced only CO₂. CPO of AcH generated AcOH, a desirable product, as well as formic acid (FA), carbon monoxide (CO) and CO₂, suggesting that multiple reactions occurred. However, the selectivity to AcOH was relatively low (43% at 175 ⁰C, GHSV=20000 h-¹, 2.4V/TiO₂). The selectivity of AcH to AcOH was improved by adjusting temperature, adopting higher vanadium (V) loading catalysts, and increasing oxygen (O₂) concentration. At 200 ⁰C, GHSV=20000 h-¹, and using 6.9V/TiO₂, the selectivity to AcOH increased to 70%. Constant selectivity of all products with respect to residence time indicates the reactions are likely parallel. The rate constant for AcH CPO was calculated assuming an overall 1st order reaction. The linearized Arrhenius law yielded an activation energy of 43.9 kJ/mol for the overall AcH CPO reaction. Simultaneous CPO of AcH and AcOH was also examined. The conversion of AcH in the mixture was similar to the conversion of CPO of AcH alone. This study demonstrated the feasibility of producing AcOH via CPO of AcH. The viability of partial oxidation of pyrolysis oil must be confirmed using model compounds with more complex functional groups and pyrolysis oil.

Text

2017-01-21

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/60188

Chemical and Biological Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/