In situ synthesis and characterization of Ca–Mg–Al hydrotalcite on ceramic membrane for biodiesel production

In situ surface synthesis of Ca–Mg–Al hydrotalcite (HT) on inorganic ceramic membrane (CM) was investigated with urea as precipitator. The effects of molar ratio of raw materials, crystallization time, and temperature on surface synthesis of HT were examined. The as-prepared HT/CM samples were characterized by XRD and SEM and an in situ growth mechanism of HT on CM was proposed. KF/HT/CM obtained by loading potassium fluoride (KF) on the HT layer by impregnation and calcination method was used as catalyst for transesterification between palm oil and methanol. The comparison of KF/HT/CM and pure KF/HT powder under identical reaction conditions shows that the production of fatty acid methyl ester is equivalent, which means that the use of inorganic catalytic membrane in the transesterification is a viable alternative.

Graphical abstractThe in situ surface synthesis of Ca–Mg–Al hydrotalcite on inorganic ceramic membrane was performed and investigated. A possible simple growth mechanism of hydrotalcite on ceramic membrane was given: the γ-Al2O3 introduced on the CM surface by dip-coating act as a second support as well as part of aluminum source, it was activated under the alkaline circumstances and built the layers with the cations in the solution. And then the crystals grew continuously under hydrothermal conditions in the synthesis gel. The aluminum atoms shared by the CM and HT layers act as a bridge connecting these two parts. The modified membrane was then used as a catalyst support for transesterification.Figure optionsDownload full-size imageDownload as PowerPoint slide