Study On The Basic Physical Properties Of Fatty Acid Methyl Ester And The Vapor-liquid Phase Equilibrium

As a new type of environmentally friendly substituted energy, biodiesel attracts the world's attention for its excellent characters, like the renewable raw material, combustion safety, and reduced pollutant. The biodiesel production process with supercritical methanol has many special advantages, including fast reaction speed, no by-product, simply separation process. So it is one of the most promising green processes. However, the basic physical properties and the relevant vapor-liquid equilibrium data are rare, which hinders the development of the technology and the production process.In this paper, the experimental data of the basic physical properties, including melting point, boiling point, critical properties, acentric factor, and the vapor pressure for 20 fatty acid methyl esters was collected. All the data was analyzed and evaluated. Different estimation methods for each kind of the basic physical properties were tested and compared. The reliable method was used to calculate the property for fatty acid methyl esters. A reliable basic physical properties' database for fatty acid methyl esters has been built. In the database, 7 physical properties including melting point, boiling point, critical temperature, critical pressure, critical volume, acentric factor and saturated vapor pressure for fatty acid methyl esters were contained. The melting points are all evaluated experimental data. Some boiling points are evaluated experimental data, the others are estimated by the formula fitted from the experimental data. The critical temperatures and critical pressures were estimated by Gani group contribution method. The critical volumes were estimated by C-G group contribution method. The acentric factor can be estimated by Han-Peng or C-G method. Vapor pressures were estimated by the Riedel corresponding state equation modified by Vetere.A high pressure vapor-liquid phase equilibrium apparatus was built, and a flow-type method was adopted to measure the near critical vapor-liquid equilibrium data of one binary system(methanol + methyl palmitate) and three ternary systems(methanol + glycerol + methyl laurate, methanol + glycerol + methyl myristate, methanol + glycerol + methyl palmitate). The near critical vapor-liquid equilibrium data of binary systems related to biodiesel(methanol + glycerol, methanol + methyl laurate, methanol + methyl myristate, methanol + methyl palmitate) was correlated by RKS EOS and PR EOS with van der Waals one-fluid mixing rule using Aspen plus software. The binary interaction parameters independent and dependent on temperature were obtained. The correlated results of different equations with different interaction parameters are all satisfactory. The temperature function modified by Boston and Mathias was applied to RKS EOS(RKSBM model), and RKSBM model can correlate the binary systems well.The binary interaction parameters obtained from RKS EOS and RKSBM EOS were used to predict the near critical vapor-liquid equilibrium of ternary systems(methanol + glycerol + methyl laurate, methanol + glycerol + methyl myristate, methanol + glycerol + methyl palmitate), and the binary interaction parameter between glycerol and ester was set to 0. Both of the two methods can predict the ternary systems well, and the RKSBM EOS performances better.