Insights in the hydrotreatment of fast pyrolysis oil using a ruthenium on carbon catalyst† Jelle Wildschut, a Muhammad Iqbal, a Farchad H. Mahfud, a Ignacio Meli an Cabrera, a Robbie H. Venderbosch b and Hero J. Heeres * a Received 4th November 2009, Accepted 7th April 2010 First published as an Advance Article on the web 8th June 2010 DOI: 10.1039/b923170f The use of Ru/C (5%-wt.) as a catalyst for the hydrogenation of fast pyrolysis oil was explored at 350  C and 200 bar pressure in a batch reactor set-up with the main objective to determine the effect of the reaction time on the oil yield and elemental compositions of the product phases. Highest oil yields (65%-wt.) were obtained after 4 h using a 5%-wt. intake of catalyst on fast pyrolysis oil. Longer reaction times lead to a reduction of the oil yield due to the formation of gas phase components (methane, ethane, propane, CO/CO 2 ). A solvent–solvent extraction procedure was applied to gain insights into the molecular transformations during the catalytic hydrotreatment experiments. It appears that specifically the carbohydrate fraction is very reactive. The observations are rationalized by a set of reaction pathways for the various product phases. 1. Introduction Environmental concerns and possible future shortages have boosted research on alternatives for fossil derived liquid trans- portation fuels. Biomass is considered a promising alternative due to its high abundance and renewability. Various products from different sources of biomass have been proposed. A potentially interesting second generation transportation fuel is fast pyrolysis oil and bio-liquids derived thereof. Fast pyrolysis oils can be obtained from biomass in yields up to 70%-wt. 1 As of now, crude fast pyrolysis oil is not suitable for application in internal combustion engines and some upgrading is required. A suitable upgrading technology is hydrogenation of the pyrolysis oil with a catalyst, leading to a reduction in the amount of bound oxygen in the form of water. Typically, harsh operating condi- tions (300–400  C and 100–350 bar) are required to obtain reasonable deoxygenation levels. 2–5 The majority of the catalytic and reactor engineering know- how on pyrolysis oil hydrodeoxygenation (HDO) is derived from the hydrodesulfurization of fossil feeds (HDS). Typical hydro- treatment catalyst such as NiMoS and CoMoS on g-Al 2 O 3 are applied and the process is typically performed in packed bed reactor configurations. 2–5 A two stage approach appears neces- sary for hydrodeoxygenation to avoid severe coking. In the first stage (140–275  C) the oil is stabilized, while the second stage (350–450  C at pressures up to 300 bar) is applied to treat the ‘stabilized’ oil and obtain deep oxygen removal. Continuous operation in a downflow mode gave an oil in a yield of 30 to 55% with a deoxygenation level of 99%. 6,7 A limited number of studies in batch mode have been published. 5,8,9 As well as the conventional desulfurization catalysts, noble metal catalysts have also been reported for the hydrotreatment of a Department of Chemical Engineering, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands. E-mail: H.J. Heeres@rug.nl; Tel: +31-503634174 b BTG Biomass Technology Group B.V., Josink Esweg 34, 7545 PN Enschede, The Netherlands † This article was submitted as part of a Themed Issue on fuels of the future. Other papers on this topic can be found in issue 3 of vol. 3 (2010). This issue can be found from the Energy & Environmental Science homepage (http://www.rsc.org/ee). Broader context Pyrolysis oil is considered a very promising second generation energy carrier. However, upgrading is required before the oils can be used as a substitute for conventional liquid transportation fuels. A variety of upgrading technologies have been proposed in the last decades, of which catalytic hydrotreatment is currently receiving a great deal of attention. Ru on carbon catalysts have shown to be good candidates for this process. In this paper, the use of Ru/C (5%-wt.) as a catalyst for the hydrogenation of fast pyrolysis oil was explored at 350  C and 200 bar pressure in a batch reactor set-up with the main objective to gain insights in the effect of the reaction time on the oil yield and (elemental) compositions of the product phases. Highest oil yields (65%-wt.) were obtained after 4 h using a 5%-wt. intake of catalyst on fast pyrolysis oil. Longer reaction times lead to a reduction of the oil yield due to the formation of gas phase components (methane, ethane, propane, CO/CO 2 ). Thus, the catalytic hydrotreatment is, despite the high pressure and temperature, a relatively slow process and takes place on a timescale of hours. This observation will have major impact on the design of suitable reactor configurations for the catalytic hydrotreatment. A combination of solvent extraction and analytical techniques has provided valuable insights in the reactivity of component classes in the fast-pyrolysis oil and revealed that particularly the carbohydrate fraction is converted during the hydrotreatment process. 962 | Energy Environ. Sci., 2010, 3, 962–970 This journal is ª The Royal Society of Chemistry 2010 PAPER www.rsc.org/ees | Energy & Environmental Science Published on 08 June 2010. Downloaded by University of Groningen on 30/04/2014 02:04:20. View Article Online / Journal Homepage / Table of Contents for this issue