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Cold flow improvements to biodiesel through the use of heterogeneous catalytic skeletal isomerization Reaume, Stephen John


Biodiesel is a promising alternative to petroleum diesel with the potential to reduce overall net CO₂ emissions. However, the high cloud point of biodiesel must be reduced when used in cold climates. Cloud point is the temperature at which solid crystals first start to appear. Skeletal isomerization of biodiesel and/or its feedstocks was investigated to reduce the high cloud point. Catalytic isomerization and hydroisomerization reactions were carried out on pure unsaturated fatty acid (UFA) and saturated fatty acid (SFA) samples, respectively. The catalyst used for the experiments was a beta zeolite and 0.5 wt% Pt-doped beta zeolite for the isomerization and hydroisomerization reactions, respectively. Reaction conditions of temperature, pressure, co-catalyst and time were varied to find an optimal reduction in the cloud point of the products. It was concluded that isomerization was unsuccessful at reducing the cloud point; in contrast, hydroisomerization was successful at reducing cloud point. A 10 degree Celsius reduction was achieved at 285 degrees Celsius and 4.0 MPa H₂ pressure. The next stage of the research studied the combined effects of isomerization and hydroisomerization on a mixture of UFAs and SFAs, namely oleic and palmitic acids. It was shown that the combination of the reaction gave a cloud point reduction of 7.5 degrees Celsius on a 55/45 mass ratio of oleic to palmitic acids. These results led to the conclusion that SFAs and UFAs through skeletal isomerization can reduce the cloud point of a mixture of fatty acids. Thus, vegetable oil feedstocks can be improved for their biodiesel cloud point. A study of ten different oils was conducted with varying contents of fatty acids. Results have shown that high unsaturated fatty acid biodiesels increased in cloud point, due to the hydrogenation side reaction. In contrast, low unsaturated fatty acid biodiesels yielded cloud point reductions, and overall improvement in the flow properties. A maximum cloud point reduction of 16.5 degrees Celsius was observed with coconut oil as the starting material. These results led to the design of an optimal cloud point improvement process of for vegetable oil biodiesel of: hydrolysis (of vegetable oil → hydroisomerization (300 degrees Celsius, 4.0 MPa H₂ pressure → and esterification.

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