4. Concluding remarks
To produce hydrocarbons from plant oil as renewable diesel
fuel, the conventional hydrotreating and catalytic cracking processes
are not really specific for the products selectivity due to
unsaturated double bonds. In this study, therefore, the process
composed of hydrolysis/hydrogenation and subsequent decarboxylation
was proposed. In the first treatment, triglycerides in
rapeseed oil were converted into saturated fatty acids through
hydrolysis in hot-compressed water and simultaneous
hydrogenolysis under the presence of Pd/C catalyst and H2 gas. In
the second treatment, the obtained saturated fatty acids were
decarboxylated into the corresponding hydrocarbons under the
presence of Pd/C. In this process, unsaturated double bonds in fatty
acid moieties, which lead to various side reactions, were
hydrogenated into saturated ones prior to the second treatment.
Therefore, the selective conversion was achieved by this two-step
treatment without any side reaction. As a result, the composition
of the obtained hydrocarbons corresponded to the fatty acid composition
of rapeseed oil.
However, the obtained renewable diesel fuel should be
improved in cold-flow properties because saturated linear hydrocarbons
have relatively high melting points, whereas other properties
such as flash point, kinematic viscosity and density satisfied
the requirements of the fossil diesel. To satisfy the requirements,
a blend of renewable diesel with fossil diesel was found out to
weaken the inferior fuel properties of pour point and cold filter
plugging point. Consequently, 20 vol% blend of the renewable diesel
was found out to satisfy the requirements for the Japanese
specification standard of the fossil fuel.