The influence of various anions in Mg-Al mixed oxides on presence of sodium ions in transesterification of oil

Abstract

The paper is focused on the influence of sodium ions in Mg-Al mixed oxides as heterogenous catalyst in the transesterification of non-edible Camelina sativa oil. The Mg-Al mixed oxides with a constant molar ratio Mg:Al (2:1) were synthesized from hydrotalcites by thermal treatment (450 °C, 3 h) and rehydrated. The novelty lays in the synthesis of the hydrotalcites with various types of anions (SO4-2, Cl-, CH3COO-, HCO3-, C2O4-2), which influence the sodium amount in materials and so its properties. The results of various characterisation methods such as ICP-OES, XRD, TPD, N-2-physisorption, FTIR were statistically evaluated, including transesterification results. The sodium was bonded predominantly in the form of sodium nitrates (nitrates were used for hydrotalcite synthesis) for all types of anions and the rehydration (i) rapidly decreased the sodium content and (ii) caused more similarity of mixed oxides with each other regardless of anion type. The sodium influenced especially acid-base properties and so the ester yield, because the sodium nitrates blocked the pores and also disturbed the TPD determination, which is also a novelty. The explanation of the influence of sodium ions enables to synthesize more stable catalyst, whose use will be environmentally beneficial.