Continuous Process Of Two-step Biodiesel Production

The world energy crisis, environmental pollution and global warming caused by fossil fuels are impelling human to search for alternative sources of clean and renewable energy. Biodiesel is clean and renewable alternative energy to petroleum-based diesel.The continuous process of biodiesel production was studied based on the non-catalyst two-step reaction which was proposed by our preceding work. Taking methyl oleate and isopropyl palmitate production as the experimental object, the kinetics and thermodynamics of the synthesis of straight-chain and branched-chain ester were studied. Then the continuous process of biodiesel production based on continuous stirred tank reactors (CSTRs) in series was studied.Methyl oleate and isopropyl palmitate were synthesized by acyl chlorination and alcoholysis reaction. The kinetic studies showed that two steps of methyl oleate or isopropyl palmitate synthesis is a second order reaction both and the reactions follow tetrahedral mechanism. The activation energies are121.6kJ·mol-1,46kJ·mol-1and frequency factors are2.76×1019,4.63×105for the acyl chlorination reaction step of methyl oleate and isopropyl palmitate synthesis, respectively. For the alcoholysis reaction step of methyl oleate and isopropyl palmitate synthesis the activation energies are115.2kJ·mol-1,54.15kJ·mol-1and frequency factors are4.03×1018,9.08×106respectively.The thermodynamic analysis of methyl oleate and isopropyl palmitate synthesis results show that acyl chlorination reactions are endothermic and increasing temperatures are in favor of the acyl chlorination reactions. Alcoholysis reactions are exothermic and decreasing reaction temperatures favor the alcoholysis reactions.The optimum conditions of the continuous process of methyl oleate synthesis are as follows:reactant molar ratio n(oleic acid):n(thionyl chloride):n(methanol)=1:1.2:1.2, reaction temperature30℃, residence time120min,6CSTRs in series for the whole processes. The esterification rate of oleic acid can get to99%. The optimum conditions of the continuous process of isopropyl palmitate synthesis are asfollows: reactant molar ratio n(palmitic acid): n(thionyl chloride): n(isopropyl alcohol)=1:1.4:1.4, reaction temperature72℃, residence time100min,6CSTRs in series forthe whole process,3CSTRs for acyl chlorination reaction,3CSTRs for alcoholysisreaction. The esterification rate of palmitic acid can get to96.27%.The methyl oleate and isopropyl palmitate product’s quality was examined andthe results show that methyl oleate and isopropyl palmitate synthesis by the two stepsprocess meet the national quality standards very well.