Mild hydrotreatment of the light fraction of fast-pyrolysis oil produced from straw over nickel-based catalysts

Significance Statement

In the last decade hydrotreatment of pyrolysis oils has attracted an increasing attention for the production of fuels and chemicals as alternative to crude oil. One big challenge of this process is to find a catalyst that is active and stable with pyrolysis oils. For this target, alternative catalysts based on nickel were tested in this study, exploring different supports, loadings and eventual promoters: Ni/Al2O3, NiCu/Al2O3, Ni/SiO2, Ni/ZrO2, NiW/AC and Ni/TiO2. A light phase of a pyrolysis oil, containing mainly water (56.7%), sugar derivatives and low molecular weight compounds was hydrotreated in mild condition (at 250 °C, 8.0 MPa hydrogen at room temperature) in a batch reactor.

Similar activity was recorded for all nickel catalysts, with a slightly higher hydrogen consumption of NiCu/Al2O3, promoted probably by spillover effect enhanced by the presence of copper. The main products consisted of an upgraded oil (7-15% yield, water content around 9% ) and an aqueous phase (75-83% yield, water content around 70%).   Ru/C was used as benchmark (wide tested in literature) and it showed higher hydrogen consumption compared to nickel resulting in an upgraded oil with similar oxygen content, but more hydrogenated.  For all experiments the oxygen content decrease from  40% of the feed to 20-26%  of the upgraded,  as a result of hydrodeoxygenation and partitioning of the components into two phases. The majority of the organic components   were recovered in the upgraded oil (carbon recovery around 50%), providing therefore an energy densification in this phase (31±1 MJ/kg). GC-MS and 1H-NMR were powerful methods to monitor the reactivity of specific molecules and of their functional groups. Generally at 250 °C production of ketones was observed mainly over nickel-based catalysts, while alcohols over Ru/C.

The valorisation of the light phase of the pyrolysis oil was demonstrated possible, obtaining an upgraded oil with lower oxygen content from a non-valuable fraction containing mainly sugar derivatives.  While mild conditions are usually tested to reduce partially the oxygen content in order to produce with a lower hydrogen consumption a substrate that can be compatible and used as co-feed in an existing refinery, further studies should be addressed to hydrodeoxygenation at higher temperature to obtain higher deoxygenation degree.

Mild hydrotreatment of the light fraction of fast-pyrolysis oil produced from straw over nickel-based catalysts. Renewable Energy Global Innovations

Journal Reference

Chiara Boscagli1, Klaus Raffelt1, Thomas A. Zevaco1, Wolfgang Olbrich1,Thomas N. Otto1, Jörg Sauer1, Jan-Dierk Grunwaldt1,2. Mild hydrotreatment of the light fraction of fast-pyrolysis oil produced from straw over nickel-based catalystsBiomass and Bioenergy, Volume 83, December 2015, Pages 525–538.

Show Affiliations
  1. Karlsruhe Institute of Technology, Institute of Catalysis Research and Technology, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
  2. Karlsruhe Institute of Technology, Institute for Chemical Technology and Polymer Chemistry, Engesserstr. 20, 76131 Karlsruhe, Germany

 

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