Role of catalysis in oleochemistry

Branched fatty acids, usually referred to as isostearic acid, are a very valuable oleochemical product. This is owed to their interesting physicochemical properties. Their saturated character, combined with the presence of one or more methyl or ethyl branches on the carbon chain, makes them stable against oxidation while resembling the physicochemical properties of unsaturated fatty acids. Their current industrial production as a side product of the acid clay catalyzed dimerization of unsaturated fatty acids is inefficient and energy-consuming. Efforts have thus been made in the past to look for more efficient and sustainable catalytic systems. Zeolites have shown great potential here, producing branched fatty acids very selectively, while being regenerable multiple times. Unfortunately, mechanistic insights in the catalytic system are limited up to date, as are those in the product composition. Nevertheless, this knowledge would make it possible to develop application specific, industrial, additive-free and robust zeolite systems yielding high amounts of branched fatty acids under moderate reaction conditions. A first part of this dissertation focused on the development of a superior protocol for the analysis of the obtained reaction product. Both the monomeric and oligomeric fractions were analyzed and quantified, while the different compounds of the monomeric fraction were identified in more detail. Special attention was paid to the isomers of the branched fatty acids themselves, several of which were identified individually for the first time. In a second part of this dissertation, the developed analysis protocol was used to closely look at the catalytic mechanisms that take place during reaction. Nine different, commercially available zeolites were screened under the same reaction conditions for their activity and selectivity in reaction. Zeolites with a one dimensional 10 membered ring pore system have shown superior behavior, both with regard to activity and selectivity towards the desired branched fatty acids. This can be explained by the confined environment of the catalytically active Brønsted acid sites and less severe deactivation of the catalyst compared to zeolites with a more open pore structure. This deactivation already occurs strongly very early in reaction. Performing additional reactions on a liquid phase continuous fixed bed reactor made it possible to investigate the deactivation and thus stability of a selection of zeolites in more detail. Additionally, the regenerability of the zeolite catalysts was demonstrated, if performed under the right conditions. In a third part of this dissertation, a selection of superior zeolites and one economically more interesting zeolite were post-synthetic treated with a combination of acids and/or bases to introduce additional mesoporosity in the zeolite framework. The aim here was to increase the activity of the zeolites, while retaining their selectivity towards the desired branched fatty acids. Not only was this successful in certain cases, also the selectivity towards the branched fatty acids was maintained. By characterizing these post-synthetically treated zeolites thoroughly, more mechanistic insights were obtained in the catalytic system. As such, there was found strong evidence for the first time showing that pore mouth catalysis takes place during reaction. With this dissertation, the reader gains a deepened insight in the reaction product and the catalysis that takes place during reaction. This is a big step forward towards a more efficient and sustainable production of branched fatty acids.

Jaar van publicatie:2022

Toegankelijkheid:Closed