The Research Of Biodiesel From Transesterification By Lewis Acid AlCl₃ Catalysis In Ethanol And Carbon Dioxide As Cosolvent

With the increasing depletion of fossil resources, deterioration of environmental portion and the increase of the trend of vehicles with diesel, biodisel which is perfect for substituting petrochemical diesel has received more and more attention. According to incomplete statistics, China produces about five million tons of waste oil every year. The biodiesel industry adapts to the national conditions, and generally uses the waste oil as the raw material for biodiesal production. Therefore, this paper tried to find a more efficient method for the transesterification of triglycerides to biodiesel fuel (BD), with trilaurin as the model compound,.In this study, transesterification of trilaurin was carried out in a solution containing 4 wt% of the Lewis acid AICl3 dissolved in a cosolvent of ethanol and 5.1 MPa CO2. A conversion rate of over 90%was achieved within 1 h at the low temperature of 180℃. Even at a lower temperature of 80℃, the yield of ethyl ester was as high as 52% in 1 h. The amount of catalyst, the mass ratio of trilaurin to ethanol, the pressure of CO2 and any other reaction conditions were discussed.The process indicates a co-catalytic effect of the Lewis acid and CO2. We postulate several key steps for the mechanism. First, the CO2-ethanol mixture enhances the hydrogen bonding, increasing the concentration of C2H5O ·. Second, AlCl3 attacks the oxygen of C-O-C to weaken the bonds to form carbonyl carbon OR1, which is then easily attacked by C2H5O · to give the transesterified product (C2H4COOR1). Third, AlCl3 is finally replaced by H to form glycerin (GL) and intermediates, such as unethyl esterified compounds (uEE).Based on the experimental data, the kinetic analysis of transesterification was carried out. The activation energy is 55 ± 4.7 kJ/mol, the reaction order n is 3.05 and the frequency factor (1nA) is 14.71 ± 1.31. A kinetic model of unethyl esterified compounds (uEE) was developed and is summarized byAlCl3 was used as a flocculant and catalyst for converting waste cooking oil (WCO) to BD. The process achieved 97% free fatty acid (FFA) conversion at 120℃ in 90 min, making it one of the most efficient systems available for WCO recovery. AICl3 was also successfully applied to microalgae, signaling the potential for a process that combines harvesting, lipid extraction, and transterification, leading to fully integrated, microalgae-based BD production.