MgAl mixed oxide derived alkali-free hydrotalcite for transesterification of waste cooking oil to biodiesel

Abstract

The heterogeneous catalyst, MgAl hydrotalcite (MgAl HT) was synthesised via alkali-free method spanning from 4:1 to 2:1 ratio of Mg and Al respectively and underwent subsequent calcination process at 450°C for 3 h. The diffraction patterns of MgAl HT indicated the high crystalline structure was obtained. The increasing of the reflection intensity and the sharpness of diffraction lines were seen with the increasing of Mg:Al ratio. Calcination has removed the carbonates and hydroxyl layers, thus left only the mixed oxide of MgO and Al2O3 as proven by XRD, SEM, EDX and FTIR. This catalyst was used in the transesterification reaction with Waste Cooking Oil (WCO) as feedstock for the production of biodiesel. WCO underwent a pretreatment process to remove the impurities and moisture content. Acid-base titration was performed to determine the acid value and percentage of Free Fatty Acid (%FFA). The FFA content was 0.073% (less than 1%), hence transesterification reaction has been proceeded without before esterification process using methanol to oil ratio 30:1 for 24 h. Results show high percentage yield of biodiesel in 5 wt% 3:1 MgAl (87.23%) compared to 84.01% yield in 5 wt% 4:1 catalyst and only 79.23% yield with 5 wt% 2:1 catalyst.