Rehydrated Hydrotalcite In The Catalytic Properties Of The Transesterification Prepared Biodiesel Reaction

Biodiesel, an environmentally friendly and regenerable fuel, has become a global research hotspot. Conventional synthesis techniques rely on homogeneous acid and basic catalysts; however, removal of these catalysts is technically difficult and brings extra cost to the final product. Heterogeneous catalysts could improve the synthesis methods by eliminating the additional processing costs associated with homogeneous catalysts. Unfortunately, the application of heterogeneous catalyst has been restricted because of its low activity. So, the design of heterogeneous catalyst with high catalytic activity has recently gained much attention.In this paper, Mg-Al hydrotalcite was prepared using a co-precipitation method. The Mg-Al hydrotalcite as prepared were calcined at500℃to generate Mg(Al)O. Mg(Al)O was contacted with water to produce rehydrated hydrotalcite. The obtained catalyst was characterized using techniques of nitrogen physisorption, Scanning electron microscopy, and X-ray diffraction.Rehydrated hydrotalcite was tested for transesterification of vegetable oil with methanol to biodiesel. Its catalytic activity was compared with that of hydrotalcite as prepared, and Mg(Al)O. The results showed that hydrotalcite as prepared and Mg(Al)O had no catalytic activity, while rehydrated hydrotalcite had high catalytic activity.Influence of rehydration conditions, including the amount of water, rehydration time, and rehydration temperature, was studied. It was found that water amount and rehydration time affected the structure and catalytic performance of rehydrated hydrotalcite. In contrast, redydration temperature showed no effect. Rehydrated hydrotalcite showed the best catalytic performance under rehydration conditions of rehydration time (6h), amount of water (50mL)."Liquid-phase rehydration" method was also compared with'"Gas-phase rehydration" method. Compared with gas-phase rehydration, catalysts by "Liquid-phase rehydration" method showed higher catalytic performance.The reaction parameters that influence transesterification reaction, including mole ratio of methanol to oil and amount of catalyst, were investigated. Under optimum rehydration conditions, a methanol to oil molar ratio of48:1, an addition of5wt.%catalysts, at65℃reaction temperatures, biodiesel yield exceeded95%at a reaction time of3h.