Simulation Of Methanol Recovery Section Of Typical Biodiesel Production Process Via Supercritical Method

In this paper, a simulation of typical biodiesel production process usingsupercritical methanol was carried out. This paper studied on the factors, suchas reaction temperature, pressure and mole ratios of alcohol to plant oil, whichaffecting recovery percentage of methanol and the concentration of methanolrecovered, and a preliminary estimate was carried out on the energyconsumption of the process.For the experimental flash system, simulating effects of the adiabaticflash model and the PSRK equation were acceptable for methanol flashprocess，simulation and experimental results were in good agreement. Thispaper predicted the pseudo-molecular formulas of soybean oil and biodiesel,and estimated the critical parameters, the normal boiling points by C-Gmethod, and the acentric factors of them by Chen equation, and heat capacitywere fitted of these two substances, the results could be used on mass balanceand heat balance in the process of biodiesel production while a appropriatesoftware was applied. NRTL thermodynamic model was selected as K-valuemodel for most units in the simulation. The binary interaction parameters ofthe newly defined materials and other components could be got by regressionwith CHEMCAD, when the UNIFAC LLE model was selected.Then, a process simulation of biodiesel production process usingsupercritical methanol was carried out on the methanol recovery unit whilethree representative methods were selected. Some factors, such as reactionpressure, flashing temperature and mole ratios of alcohol to plant oil, whichaffecting the concentration of methanol recovered and recovery percentage ofmethanol of flash devices were investigated, and some other factors, such asreaction pressure, reaction temperature and mole ratios of alcohol to plant oil,which affecting the energy consumption of distillation column were alsostudied. Simulated results indicated that: increasing flash temperature and outlet pressure was not conducive to improving the purity of methanolrecovered, but it contributed to improve the recovery percentage of methanolfor flash devices; the energy consumption required for methanol distillationwould reduce while increasing reaction pressure and reaction temperature;increasing alcohol oil ratio was not favorable for the purity of methanolrecovered and methanol recovery percentage of flash devices, and could helpto increase the energy consumption of the whole process.Based on the simulation results, the appropriate flash temperature was260℃~270℃, in that condition, when mole ratios of alcohol to plant oil was30:1, compared with the process without flash device, the process includingflash column could reduce about62.9%of heat consumption, the flashprocess after product cooling could reduce about39.9%of heat consumption;when mole ratios of alcohol to plant oil was40:1, compared with the processwithout flash device, the process including flash column could reduce about61.0%of heat consumption, the flash process after product cooling couldreduce about38.2%of heat consumption. At this point, the purity (massfraction) of methanol recovered by flash device was close to99%.