Biodiesel production by supercritical methanol transesterification: process simulation and potential environmental impact assessment

A simulation of a biodiesel production process by supercritical transesterification was carried out in Aspen Plus® 2006, based on lab scale experimental results obtained at a continuous reactor working at a 9:1 methanol to triglycerides molar ratio and 400 °C. Simulation results showed that for a specified biodiesel production plant capacity set at 10,000 tons/year the total energy consumption of this process (573 kW) was considerably lower than that of a previously reported supercritical process working at a 42:1 molar ratio and 300 °C (2407 kW), and the conventional base catalyzed process (2326 kW). Mass flow rates, stream compositions and energy consumption of each process were used to assess the potential environmental impact (PEI) output of each alternative, in order to select the most environmentally friendly one, through a process design tool developed by the Environmental Protection Agency (EPA), the generalized Waste Reduction (WAR) algorithm. The environmental assessment results indicated the supercritical process, even when working at a 42:1 molar ratio, has a lower output PEI per mass of product than the conventional base catalyzed process. The supercritical process working at a 9:1 molar ratio and 400 °C had the lowest PEI per mass of product. This can be attributed to reduced energy consumption and the possibility of producing more biofuel through glycerol decomposition reactions that form ethers, which have the potential to be used as part of the fuel.