University of Groningen
Catalytic hydrotreatment of pyrolysis liquids and fractions Yin, Wang
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Publication date: 2017
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Yin, W. (2017). Catalytic hydrotreatment of pyrolysis liquids and fractions: Catalyst Development and Process Studies. University of Groningen.
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Summary
The depletion of fossil resources like oil and natural gas and green house gas emissions related to its use have resulted in extensive global activities to identify, develop and implement alternative resources for energy, transportation fuels and chemicals. In this respect, the use of lignocellulosic biomass like wood, agricultural waste and forestry residues is of particular interest as it is the only sustainable resource containing renewable organic carbon.
Fast pyrolysis is a promising technology to convert lignocellulosic biomass to a liquid energy carrier. The product, known as fast pyrolysis liquids (PLs), has a higher energy density than solid biomass and is more easily transported and stored. The applications of PLs are limited due to a high water and oxygen content and limited storage stability. As such upgrading technologies have been developed to broaden the application range of PLs.
Catalytic hydrotreatment is such an attractive upgrading technology for PLs and leads to improved product properties like, among others, a higher thermal stability and energy density, reduced oxygen and water content, etc. Catalytic hydrotreatment is typically carried out at elevated temperatures (250-400 oC) and hydrogen
pressures (100-200 bar) in the presence of heterogenous catalysts.
The research described in this thesis involves the catalytic hydrotreatment of PLs and fractions thereof as well as model component studies using heterogenous catalysts. The overall objectives were the development of improved hydrotreatment catalysts, both with respect to activity and stability, as well as a better understanding of the molecular transformations taking place during the process.
The research described in Chapter 2 involves studies on the catalytic hydrotreatment of PLs at temperatures between 80-410 oC using a Ni-Cu catalyst characterised by a
high Ni loading (46 wt% Ni) in both batch and continuous set-ups to get insights in i) relevant product properties of the upgraded oils (such as flash point, viscosity, acidity and coking tendency) as a function of the reaction temperature and ii) the molecular transformations taking place at the various temperatures to assess the reactivity of various component classes in the PLs. The study revealed that the sugar fraction is very reactive, while the lignin fraction is converted at temperatures higher than 300 oC.
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Exploratory catalyst screening studies on the catalytic hydrotreatment of PLs using Ni based catalysts promoted by Cu, Pd and Mo are reported in Chapter 3. It involves studies at 350 oC, 140 bar H2 for 4 h in a batch reactor. Organic carbon yields and
relevant product properties (H/C ratio and TG residue) of the oil phase for the Mo promoted catalysts were compared with Cu and Pd promoted catalysts as well as with a monometallic Ni and a benchmark Ru/C catalyst. Product oils from experiments with Mo promoted catalysts showed improved product properties, e.g. a high H/C ratio and low TG residue, however, organic carbon recovery was reduced due to the formtaion of considerable amounts of methane.
Sugar chemistry mainly occurs in the low temperature range (around 200 oC), see
Chapter 2 for details. Experimental studies on the sugar fraction of PLs are reported in Chapter 4 and 5. In Chapter 4, the catalytic hydrotreatment of specifically the sugar fraction of PLs over Ni based catalysts with various Ni catalysts promoted by Pd, Cu and Mo on different supports (SiO2, SiO2-ZrO2 and SiO2-Al2O3) is described to
identify highly active catalysts for this fraction of PLs. A monometallic Ni catalyst supported on SiO2-Al2O3 was used as a reference catalyst to gain insights in promotor
effects. All experiments were performed using isolated sugar fractions (pyrolytic sugars) as the starting material. Ni based catalysts promoted by Mo were shown to be more active catalysts for sugar fraction hydrotreatment at low temperature compared to Cu and Pd promoted catalysts.
The catalytic conversion of the pyrolytic sugar fraction from PLs using a Cu-PMO catalyst in sc-MeOH and EtOH was investigated and the results are given in Chapter 5. The products were analysed in detail and shown to have a higher thermal stability and lower molecular weight than the feed and are enriched in alcohols and esters. In Chapter 6, a model component study is reported involving levoglucosan, the most abundant sugar derivative in PLs. Reactions were performed in water using a bifunctional Ru catalyst on a mesoporous carbon support (CMK-3). This support is characterized by a large surface area and a highly oxygen-functionalized surface containing acid sites. For comparison, hydrogenation of levoglucosan using a commercial Ru/C catalyst was also carried out. In addition, the scope of the catalytic reaction was investigated by performing reactions with disaccharides like cellobiose and sucrose. Quantitive yields of C6 sugar alcohols were obtained from levoglucosan and the disaccharides. A mechanistic proposal was set-up and studied in detail by performing experiments with the proposed intermediates.
