Natural Mg silicates with different structures and morphologies: Reaction with K to produce K2MgSiO4 catalyst for biodiesel production
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In this work, different magnesium silicate mineral samples based on antigorite, lizardite, chrysotile (which have the same general formula Mg3Si2O5(OH)4), and talc (Mg3Si4O10(OH)2) were reacted with KOH to prepare catalysts for biodiesel production. Simple impregnation with 20wt% K and treatment at 700-900°C led to a solid-state reaction to mainly form the K2MgSi04 phase in all samples. These results indicate that the K ion can diffuse into the different Mg silicate structures and textures, likely through intercalation in the interlayer space of the different mineral samples followed by dehydroxylation and K2MgSi04 formation. All the materials showed catalytic activity for the transesterification of soybean oil (1:6 of oil: methanol molar ratio, 5wt% of catalyst, 60°C). However, the best results were obtained for the antigorite and chrysotile precursors, which are discussed in terms of mineral structure and the more efficient formation of the active phase K2MgSi04.
Keywordssilicate serpentinite lizardite antigorite talc chrysotile biodiesel
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The authors acknowledge Pedras Congonhas LTDA for the samples, the UFMG microscopy center for the images and the support of CNPQ, INCT Midas, CAPES and FAPEMIG.
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