Simulation and Experimental Study on Methanol Recovery in Continuous Production of Biodiesel via Supercritical Transesterification

Recycling excessive methanol is simulated and experimentalized by adiabatic flash evaporation. The simulated results show that: methanol recovery and methanol purity in gas phase for one-stage flash process are almost same with two-stage flash process and one-stage flash process is more beneficial by thinking of equipment and operation cost. The experimental results show that flash pressure has a significant influence on methanol recovery and methanol purity in gas phase which can be effectively improved when flashing pressure is reduced. Meanwhile, reaction temperature and reaction pressure also have important effects on methanol recovery and methanol purity in gas phase. For continuous producing biodiesel in supercritical methanol, when the reaction temperature, the reaction pressure and the molar ratio of methanol/oil are kept at 300°C, 15 MPa and 25:1, respectively, methanol recovery and methanol purity in gas phase can reach 90% and 98.8% respectively if the flashing pressure is kept at 0.2MPa. Therefore, the flash evaporation device coupled with tubular reactor for high purity separation of methanol is very effective which can realize comprehensive utilization of heat energy and separation and recycle of methanol.