Selectivity in sorption and hydrogenation of methyl oleate and elaidate on MFI zeolites

Abstract

a b s t r a c tDifferent zeolites were tested for selective removal of methyl elaidate (trans isomer) from an equimolar mixture with methyl oleate (cis isomer). Sorption experiments of the geometric isomers show that only ZSM-5 samples with reduced Al content in the framework are able to discriminate among the bent cis and the linear trans fatty acid methyl esters. Hydrogenation experiments of equimolar methyl oleate and elaidate mixtures at low temperature (65°C) and high hydrogen pressure (6.0 MPa), using Pt catalysts, confirm this result. Only with a Pt/Na-ZSM-5 catalyst outspoken selectivity for the hydrogenation of the trans isomer is obtained. In order to prepare a selective Pt/ZSM-5 catalyst, the influence of Pt addition (impregnation, ion-exchange and competitive ion-exchange) and Pt activation (different calcination and reduction temperatures) on the Pt-distribution and Pt particle size was investigated using SEM, bright-field and HR TEM, EDX, electron tomography, CO-chemisorption, XPS, XRD, and UV-vis measurements. The best result in terms of hydrogenation activity and selectivity is obtained with a Pt/ZSM-5 catalyst, which is prepared via competitive ion-exchange, followed by slow calcination up to 350°C under high O 2 flow and a reduction up to 500°C under H 2 . This preparation method leads to a Pt/ZSM-5 catalyst with the best Pt distribution and the smallest Pt clusters occluded in the zeolite structure. Finally, the influence of zeolite crystal size, morphology, and elemental composition of ZSM-5 on hydrogenation activity and selectivity was investigated in detail.

Large Ferrierite Crystals as Models for Catalyst Deactivation during Skeletal Isomerisation of Oleic Acid: Evidence for Pore Mouth Catalysis

“…The higherr ate of skeletal isomerisation with EA compared to OA suggests that the trans form is favoured for entry into the channels, and this is also intuitively expected as it has as maller molecular cross-section;s uch shape-selectives orption has been recently demonstrated in the preferential hydrogenationo fm ethyl esters of EA over OA. [52] Under our reaction conditions, even weakly acidic sites on the external catalyst surfacea re able to catalyset he initial isomerisation of OA to EA. However,i ti sn ot possible to determine whether cis/trans isomerisation is a prerequisite for the branching reaction, as it occurst oasignificant level at the reaction temperature even in the absence of any catalyst (exp.…”

Hat die Hydrierung von Pflanzenölen noch eine Zukunft?

“…[29] So beschrieb eine Patentanwendung bereits 1998 die selektive Entfernung von transFettsäuren aus teilhydrierten Fetten durch Chemokatalyse. [30] In diesem Fall katalysierten Pt-beladene Zeolithe die selektive Hydrierung von trans-Fettsäureketten im Triglyceridmolekül.…”

Heterogeneous Bifunctional Metal/Acid Catalysts for Selective Chemical Processes

“…[150] During their studies on the hydrogenation of these oils by heterogeneous Pt catalysts, [151] the research groups of Jacobs and Sels found that zeolite-supported catalysts perform better than the corresponding alumina-supported promoters, in terms of both partial hydrogenation and regioselectivity. [150] During their studies on the hydrogenation of these oils by heterogeneous Pt catalysts, [151] the research groups of Jacobs and Sels found that zeolite-supported catalysts perform better than the corresponding alumina-supported promoters, in terms of both partial hydrogenation and regioselectivity.…”