Natural Mg silicates with different structures and morphologies: Reaction with K to produce K₂MgSiO₄ catalyst for biodiesel production

Abstract

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.

Keywords

silicate / serpentinite / lizardite / antigorite / talc / chrysotile / biodiesel

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