Catalytic Deoxygenation of Fatty Acids and Triglycerides for Production of Fuels and Chemicals

Abstract

Fossil fuels (i.e. coal, gas, oil) currently cover over 80 % of the world’s energy demand. The use of alternative resources for the production of fuels and chemicals has been an important research area over the last decade. This was not only stimulated by the declining fossil feedstock resources and consequently increasing oil prices, but also the desire for energy independence and growing awareness of the effects of the increasing greenhouse gas concentrations stimulates the use of alternative renewable resources. Many renewable feedstocks show potential for replacing part of the fossil fuels. Solar energy, wind power, hydropower, geothermal energy and biomass could all contribute to the transition from fossil to renewable energy. This thesis focusses on fats and oils as potential renewable feedstocks for the production of fuels and chemicals. Especially the use of waste fats and oils and other non-edible sources are of interest as this will not interfere with food production. The deoxygenation of fats and oils is a promising route for the production of fuels and chemicals since this process yields aliphatic paraffins and olefins in the diesel-range. The work presented in this thesis shows that the presence of H2 appears essential to obtain high deoxygenation activities and selectivities for realistic fat/oil feeds and their (unsaturated) model compounds. Although saturated compounds are selectively converted to hydrocarbons under inert atmosphere, the presence of unsaturations in the feed or products was shown to inhibit the deoxygenation activity tremendously. The reversibility of the inhibition in H2 atmosphere indeed confirms the necessity of H2 to retain catalytic deoxygenation activity. This thesis presents two deoxygenation methods with potential in the deoxygenation of fat/oil feeds. The first method is the novel one-pot hydrothermal deoxygenation of triglycerides over Pd/C. The in-situ H2 generation via glycerol reforming avoids inhibition by the unsaturated feed and products. Moreover, the use of additional glycerol is presented as a sustainable H2 source to increase the deoxygenation activity and avoid catalyst deactivation. The second method describes and compares the novel Mo2C and W2C-based carbide catalysts. These group 6 metal carbides are shown to be promising catalysts for the deoxygenation of unsaturated fatty acids and represent a less expensive alternative for the group 10 noble metals. The different hydrogenation activities of the catalysts also changes the potential applicability; W2C/CNF being most suitable for the production of high-value olefinic products and Mo2C/CNF being the preferred catalyst when paraffins are desired. Although further development and optimization of the presented processes are required for industrial implementation, both deoxygenation processes show potential as renewable alternative for the production of fuels and chemicals. The awareness of industry and governments for the necessity of renewable alternatives will lead to further developments in this field and hopefully results in the further implementation of sustainable processes for the production of fuels and chemicals, not only based on fats and oils but also from other renewable alternatives.