Double bonds hydrogenation with particular reference to partial hydrogenation of vegetable oils
Summary of the work made
Hydrogenation of oils, in particolar vegetable oils is largely practiced in industry to produce margarine or to increase the oil stability. Together with the hydrogenation reaction many side isomerization reactions occur such as cis-trans isomerization or double bond shifting reaction. Moreover, some catalyst leaching often occurs. We have studied the use of supported palladium for promoting the hydrogenation. Palladium is more expensive than Nickel but much more active and selective in limiting the hydrogenation to only trienes and dienes.
Partial hydrogenation of fatty oils is important in industry for the production of frying oils, shortenings, margarines, soap stocks, industrial oils and greases. Hydrogenation reduces colour and odour and raises the melting point by giving solid or semisolid products at room temperature. Some vegetable oils, such as soybean, linseed or rapeseed oils, contain trienic and dienic fatty acids in admisture with monoenic and saturated ones. The main purpose of partial hydrogenation is to obtain monounsaturated fatty acids from polyunsaturated ones. As a consequence, chemical stability of the oil for both the use as edible and industrial application. The hydrogenation of triglyceride oils has a complex reaction mechanism because the occurrence of side reactions such as cis-trans geometrical isomerization and positional double bond isomerization. Moreover, fatty oils hydrogenation is normally performed in gas-liquid-solid reactors and reaction rates and selectivities
are strongly affected by mass transfer limitation. Nickel based catalysts are universally employed in industry but these catalysts have many drawbacks as low activity and selectivity and unnegligible metal leaching. Palladium based catalysts seems promising as possible substitute, because, much more active in mild operative conditions (temperature, pressure). Much less metal is necessary to obtain activities comparable with nickel based catalyst , the performances are better and no leaching effect has been observed. In particular, palladium hydrogenates selectively polyunsaturated fatty acids. A detailed kinetic approach has been developed by us considering also all the mass transfer steps occurring in this reaction . In a successive work , different palladium based catalysts have been examined to evaluate the metal dispersion with afast and original method of analysis. A kinetics and mass transfer in the hydrogenation of polyunsaturated organic compounds, in the presence of
supported Pd catalysts, is described in [3,4,5], while, examples of different hydrogenation processes in semibatch and continuous slurry reactors are reported in . This work has been made in collaboration with Novamont SpA.
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