Crystallization behaviors and rheological properties of biodiesel derived from methanol and ethanol

Take palm oil and soybean oil biodiesels as example, crystallization behavior and rheological property of methyl and ethyl biodiesels were investigated. Differential scanning calorimeter (DSC) technique was used to analyze the crystallization behaviors of methyl and ethyl biodiesels, including the crystallization onset temperature and the variation of amount of crystal precipitation with temperature. Meanwhile, a thermodynamic model of regular solution was proposed and compared with the crystallization experiments. Comparisons suggested that the model can give a reasonable description of crystal precipitation of biodiesel. The rheological properties of methyl and ethyl biodiesels including the viscosity temperature curves as well as the variation of viscoelastic parameters with temperature during the cooling gelation process were measured by rheometer. Experimental results suggested that the crystallization onset temperature and the gelation temperature of ethyl biodiesels are decreased as compared with methyl biodiesels. When temperature is just below the crystallization onset temperature of methyl biodiesel, the crystal precipitation of ethyl biodiesel is much lower than methyl biodiesel, meanwhile, the same characteristic can be observed for the viscosity and storage modulus of methyl and ethyl biodiesels. As the temperature decreased, the crystal precipitation of ethyl biodiesel is gradually close to until equal to the methyl biodiesel. So as the temperature decreased, the differences between the viscosity, storage modulus of methyl and ethyl biodiesels are getting smaller, and then the viscosity and storage modulus of ethyl biodiesel are greater than those of methyl biodiesel.