Environmentally friendly catalysts for the conversion of renewable limonene feedstocks
The Madeira archipelago is situated 310 miles from the North West coast of Africa. Madeira is the larger of the two inhabited islands – the other being Porto Santo.
Paula Castilho and Cesar Fernandes from the Chemistry Department at the University of Madeira identified and collected a useful, high surface area clay from Serra de Dentro which had a high structural iron content. This clay formed the basis of a joint collaboration between the University of Madeira and Chris Breen at MERI.
The project focused on developing the Serra de Dentro (SD) clay for use as a catalyst to convert limonene, a high volume, low value chemical from pine trees into p-cymene, a high value added product used as a solvent in the ink and varnish industry, for the production of p-cresol and carvacrol, as an intermediate in the synthesis of anti-oxidants (eg BHT), in the production of synthetic resins, in perfumery and as a thermal fluid in heat exchanging systems.
The study involved comparing the catalytic activity and selectivity of ion-exchanged SD clay with that for acid-leached SD clays. The materials produced were analysed using XRD, XRF, DRIFTS, nitrogen surface area analysis (at the university of Evora) TG-MS and the catalytic conversion of limonene to p-cymene.
XRD and XRF analysis confirmed that the ion exchange processes had been successful and that the acid-leaching process had produced a coherent series of surface restructured clays. The surface area analysis figures confirmed an increase in surface area.
The results from the catalytic reaction show that the activity increased as the extent of acid leaching increased up to the most active system which was SD-3M-95-30. After this the activity decreased. The decrease was attributed to a reduction in surface area combined with a reduction in acid sites. Note that production of p-cymene was controlled by the thermodynamics of the process and did not increase above 15 weight per cent (wt%) in the mixture. The production of high molecular weight compounds dominated the reaction when using acid-leached SD.
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