Hydrodeoxygenation of fatty acid esters for biofuel production over sulfur-free catalysts
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School of Chemical Technology |
Doctoral thesis (article-based)
| Defence date: 2022-12-02
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Author
Date
2022
Major/Subject
Mcode
Degree programme
Language
en
Pages
62 + app. 58
Series
Aalto University publication series DOCTORAL THESES, 173/2022
Abstract
Liquid biofuels are playing an important role to reduce the carbon footprint in the road transportation and aviation sectors. Catalytic hydrodeoxygenation (HDO) is an attractive technology to upgrade various bio-based feedstock such as triglyceride-based oils and fats or lignocellulose-based bio-oils into drop-in hydrocarbon biofuels. The main objective of this thesis was to gain new mechanistic insights into the HDO reactions over sulfur-free catalysts using aliphatic methyl esters and fatty acids as model components. The main focus was on Rh/ZrO2 catalyst. Supported cobalt catalysts were also tested to explore the effect of support acid-base property for the deoxygenation pathway. In addition, we were aiming for developing a suitable kinetic model for supporting the design of the HDO process. HDO experiments of methyl heptanoate, methyl palmitate and their corresponding fatty acids were conducted in a batch reactor under different temperatures and pressures. Reaction pathways for the HDO of methyl ester over Rh/ZrO2 catalyst were proposed. The fatty acid was initially formed by the hydrogenolysis reaction, which was further converted into Cn-1 alkane by the sequential hydrogenation-decarbonylation reaction steps via forming aldehyde as a surface intermediate. The catalytic activity of ZrO2 support was studied, based on which the active sites of Rh/ZrO2 catalyst were discussed. Both Rh metal and ZrO2 were found to contribute to catalyzing the HDO reactions, indicating the multifunctional nature of Rh/ZrO2 catalyst for HDO application. The interface between rhodium nanoparticle and ZrO2 was advocated to be the most active zone. Experimental results with cobalt catalysts indicate that acidic support was favorable for the deoxygenation pathway to alkane products, whereas basic support favored the formation of alcohol and suppressed the deoxygenation pathway. Kinetic experiments for the HDO of methyl heptanoate and palmitate were studied over Rh/ZrO2 catalyst in a batch reactor at a wide range of temperatures (250-330 °C) and pressures (40-100 bar). Power-law type of kinetic model and a more detailed mechanistic model were both successfully applied to fit the kinetic data. A surface reaction mechanism was proposed, based on which the mechanistic model was developed. The model includes two types of catalytic active sites: one for oxygenated components and the other for hydrogen. During the estimation of kinetic parameters, vapor-liquid equilibrium and the thermodynamic non-ideality were taken into consideration in a batch reactor model for mass balance calculation. The modeling methodology and reaction mechanism insights are applicable for further studies of more complex HDO process of biomass-derived feeds.Description
Supervising professor
Oinas, Pekka, Prof., Aalto University, Department of Chemical and Metallurgical Engineering, FinlandThesis advisor
Lehtonen, Juha, Prof., VTT Technical Research Center of Finland, FinlandKanervo, Jaana, D.Sc. (Tech.), Neste Corporation, Finland
Viljava, Tuula-Riitta, D.Sc. (Tech.), Aalto University, Finland
Keywords
hydrodeoxygenation, HDO, biofuel, fatty acid ester, kinetic modelling, reaction mechanism, rhodium, zirconium dioxide, noble metal catalyst, cobalt catalyst
Other note
Parts
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[Publication 1]: Bie, Yuwei; Gutiérrez, Andrea; Viljava, Tuula-Riitta; Kanervo, Jaana; Lehtonen, Juha. 2013. Hydrodeoxygenation of methyl heptanoate over noble metal catalysts: catalyst screening and reaction network. Industrial & Engineering Chemistry Research. 52 (33), 11544-11551.
DOI: 10.1021/ie4012485 View at publisher
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[Publication 2]: Bie, Yuwei; Kanervo, Jaana; Lehtonen, Juha. 2015. Hydrodeoxygenation of Methyl Heptanoate over Rh/ZrO2 Catalyst as a Model Reaction for Biofuel Production: Kinetic Modeling Based On Reaction Mechanism. Industrial & Engineering Chemistry Research. 54, 11986–11996.
DOI: 10.1021/acs.iecr.5b03232 View at publisher
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[Publication 3]: Bie, Yuwei; Lehtonen, Juha; Kanervo, Jaana. 2016. Hydrodeoxygenation (HDO) of methyl palmitate over bifunctional Rh/ZrO2 catalyst: Insights into reaction mechanism via kinetic modelling. Applied Catalysis A: General. 526, 183-190.
DOI: 10.1016/j.apcata.2016.08.030 View at publisher
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[Publication 4]: Liu, Qiying; Bie, Yuwei; Qiu, Songbai; Zhang, Qi; Sainio, Jani; Wang, Tiejun; Ma, Longlong; Lehtonen, Juha. 2014. Hydrogenolysis of methyl heptanoate over Co based catalysts: Mediation of support property on activity and product distribution. Applied Catalysis B: Environmental. 147, 236-245.
DOI: 10.1016/j.apcatb.2013.08.045 View at publisher
