Production of Biodiesel from Waste Cooking Oil using A Zinc-Based Metal-Organic Framework (Zn-MOF) As Catalyst

Due to fossil fuel diminishing reserves, global warming, and high petroleum prices, there is a need to generate alternative, sustainable, renewable, and biodegradable biodiesel. In this paper, a zinc-based Metal-Organic Framework (Zn-MOF) was solvothermally synthesized, characterized and then used as a catalyst in place of the traditionally used toxic acids and bases as catalysts in biodiesel production. The Zn-MOF was synthesized using zinc nitrate hexahydrate, (ZnNO3)2.6H2O as the source of metal ion (a Lewis acid), while benzene-1,4-dicarboxylic acid (BDCA) served as a ligand (a Lewis base). A mixture of dimethylacetamide (DMA) and H2O (1:1 ratio) functioned as solvent. In a clean and dry beaker, 0.297 g (0.999 mmol) of Zn(NO3)2.6H2O was completely dissolved in 2 ml of distilled water. In another clean and dry beaker, 0.166 g (0.999 mmol) of BDCA was dissolved in 2 mL of DMA. Then, both solutions were mixed together and then transferred into a Teflon-lined autoclave. The Teflon-lined autoclave containing the mixture was put in an oven and heated at 150 °C for 24 h. After this period, the Zn-MOF was formed as colourless plate crystalline solids. The Zn-MOF remain unmelted even beyond 360 °C. Furthermore, the Zn-MOF was characterized by FTIR and powder X-ray diffraction. The FTIR shows the incorporation of the ligand into the Zn-MOF. The melting point and the powder X-ray diffraction results agree with the properties of MOFs in the literature. After that, the Zn-MOF was used as a catalyst in the transesterification of treated Waste Cooking Oil (WCO) for biodiesel production. The biodiesel was obtained by transesterification process at a temperature of 60 °C using a 1:5 molar ratio of oil to methanol. The biodiesel yield was 96%. The biodiesel diesel produced was physicochemically characterized. The analysis results revealed that the experimentally obtained values for viscosity, density, flashpoint, cloud point and pour point were 4.1 cSt, 821 kg/m³, 170 °C, below 0 °C and 2 °C, respectively. These values, when compared with standards (ASTM), were in agreement. The Zn-MOF recovered and recycled five times without degradation. Hence, it can be said that Zn-MOF is a good catalyst in the transesterification process of biodiesel production and can, therefore, replace the traditionally used toxic acids and bases.