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Author: search.filters.author.Numwong, NatthidaSubject: search.filters.subject.Oxidative stability

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    Effect of Pd particle size on activity and cis-trans selectivity in partial hydrogenation of soybean oil-derived FAMEs over Pd/SiO2 catalysts
    (2020-06-15)
    Numwong, Natthida
    ;
    Prabnasak, Panisa
    ;
    Prayoonpunratn, Patsakol
    ;
    Triphatthanaphong, Pholawat
    ;
    Thunyaratchatanon, Chachchaya
    Partial hydrogenation of soybean oil-derived fatty acid methyl esters (FAMEs) was performed to improve oxidative stability of biodiesel. The reaction was tested in a semi-batch reactor at 100 °C, 0.4 MPa. The effect of Pd particle size on activity and cis-trans selectivity was investigated over SiO<inf>2</inf>- and MCM-41-supported Pd catalysts, with different Pd loadings (0.5 and 1 wt.%). For Pd/SiO<inf>2</inf> catalysts with relatively large Pd particle sizes (6.1–7.8 nm), the adsorption of polyunsaturated C18:2 and C18:3 FAMEs was promoted on the flat metal surface, providing 2- to 3-fold higher turnover frequency (TOF) compared with Pd/MCM-41 catalysts. In contrast, the Pd/MCM-41 catalysts with relatively small Pd particle sizes (2.7–4.0 nm), showed higher selectivity towards the desired monounsaturated C18:1 FAMEs due to lower affinity of isolated double bond (presented in C18:1) on the Pd surface. In addition, selectivity towards the desired cis-C18:1 FAMEs was found to be highly sensitive to Pd particle size. The 0.5Pd/MCM-41 catalyst with small Pd particle size (2.7 nm), provided high cis-C18:1 selectivity, resulting in a biodiesel with better cold flow property compared with the trans-isomers. With partial hydrogenation over the prepared Pd catalysts, biodiesel with significantly improved oxidative stability (>10 h) could be obtained.
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    Influence of Mg modifier on cis-trans selectivity in partial hydrogenation of biodiesel using different metal types
    (2016-06-25)
    Thunyaratchatanon, Chachchaya
    ;
    Jitjamnong, Jakkapong
    ;
    Luengnaruemitchai, Apanee
    ;
    Numwong, Natthida
    ;
    Chollacoop, Nuwong
    The catalytic performance of Pd, Pt, and Ni supported on catalysts was investigated for partial hydrogenation of soybean methyl esters, in terms of FAME composition and biodiesel properties, especially oxidative stability and cold flow properties. The effect of Mg modifier over SiO-supported catalysts on cis-trans selectivity of polyunsaturated FAMEs was also examined. The catalytic testing was performed under reaction conditions of 4 bar hydrogen pressure and 80-120 °C. Hydrogenation activity was presented by turnover frequency (TOF) of diunsaturated fatty acid (C18:2) within 4 h of the reaction time. The highest TOF was obtained over Pd catalysts, while the lowest TOF was obtained from Ni catalysts. At high reaction temperature conditions showed a large amount of cis-monounsaturated fatty acid (cis-C18:1); however, it exhibited a large amount of trans-monounsaturated fatty acid (trans-C18:1) which has a negative impact on biodiesel properties. The XPS revealed that the introduction of Mg leads to a strong metal-support interaction caused by electron transfer from the support to the metal, which decreased trans-C18:1 formation and presented the higher oxidative stability than the catalysts without Mg modifier.