Synthesis of modified layered double hydroxide of MgAl catalyst with Ba and Li for the biodiesel production

In this study, the layered double hydroxide of MgAl was synthesized and utilized as a catalyst for transesterification. The catalyst structure was modified by adding Ba and Li to improve biodiesel production yield and decrease the reaction temperature and time, methanol-to-oil ratio, and concentration catalyst. To this end, five hydrotalcite catalysts, including MgAl, MgAlBa, MgAl/Li20%, MgAl/Li40%, and MgAlBa/Li20%, were prepared and analyzed by XRD, FE-SEM, and EDX in terms of Hydrotalcite pattern, morphological structure, and distribution of the elements in the catalysts. Biodiesel samples were produced using sunflower oil, and hydrotalcite catalysts concerning the effects of temperature, reaction time, amount and the types of the catalysts, methanol-to-oil molar ratio, and Li, Ba loading ratio. The Taguchi method was used for experimental design and results analyzed with ANOVA method. The results demonstrated that the Li or/and Ba ratio, reaction time, temperature, and methanol-to-oil molar ratio had a significant effect on the yield. Furthermore, the produced biodiesel by MgAl/Li40 catalyst reaches to more than 90% yield in 8 h that was same as 10% MgAl catalyst but with lower reaction temperature (from 75 to 55 °C), catalyst amount (from 10 to 7%), and methanol-to-oil ratio (from 30:1 to 12:1). The ratio of divalent cations to trivalent cations in the hydrotalcite structure of MgAl and MgAlBa, the type of cations and their ratio were essential parameters in yield calculation of transesterification reaction. The ratio of divalent cations to trivalent cations in this work was 0.33. The reusability of the catalysts was tested by analyzing the viscosity of biodiesel production. The results showed that the viscosity of products with MgAl and MgAl/Li catalysts increased to 8 mm²/s and 23 mm²/s after two uses.