Homogeneous Synthesis Of Biodiesel In An Oil/methanol/ether Ternary System

Because triglycerides and alcohols are not totally miscible, the transesterification can occur only in the interfacial region and it is a very slow process. By adding cosolvent to effect formation of the single phase, the transesterification is rapid and proceeds essentially to completion. In this work, by homogeneous transesterification the waste frying oil of daily life was transformed to the substitute fuel - biodiesel. A kinetic model of conversion process of waste frying oil was established based on the studying of the process, transforming mechanism and the reacting kinetics.Several ternary phase diagrams comprising vegetable oils, methanol and ethers are obtained at ordinary pressure. The shorter chain length of the composing FFA ,the higher content of FFA and higher temperature of the ternary system could reduce the quantity of cosolvent , which is needed to achieve single phase.The transesterification in homogeneous phase to form methyl esters and glycerin are much faster than the traditional transesterification. The effects of reaction condition to the biodiesel yields are also discussed. The main factors affecting transesterification are the molar ratio of oil to alcohol, catalyst, reaction temperature and reaction time. By single factor test, a response surface analysis is designed to determine the optimum parameter of the transesterification. It was determined as follows: reaction temperature 64℃, the addition level of catalyst H2SO4 3.95%, reaction time 3.3h. In the condition, the fatty acids methyl ester yield was 98.1%.When putting excessive methanol, the transesterification presented for pseudo-first-order reaction, the reaction equation was d[TG]/dt =-K1[TG], and the activation energy was 55.83 kJ/mol on the study of transforming mechanism and the reacting kinetics. In the same condition, the traditional transesterification equation was d[TG]/dt = -K1α/(1+ζ1 Rv)[TG]. The immiscible of triglycerides and alcohols is the most important reason for the slowness of the traditional transesterification.