Simulation Study of Distillation, Stripping, and Flash Technology for an Energy Efficient Methanol Recovery Unit in Biodiesel Production Processes

Abstract

Biodiesel is an important alternative renewable energy source currently produced by transesterification reaction of oil or fat with methanol. To improve the conversion, excess methanol is required, which must be recovered from the product stream and recycled back into the process for further biodiesel production. The intensive energy requirements for methanol recovery are an important issue that directly impacts the production costs of biodiesel. To reduce the cost of biodiesel production, an energy efficient methanol recovery unit (MRU) is crucial. This work focuses on energy requirement reduction by distillation, flash-based recovery, and newly-introduced stripping-based methanol recovery units. Four different continuous methanol recovery units were simulated using Aspen Plus. Energy requirements with respect to process parameters including percentage of methanol recovery, operating pressure, and methanol-to-oil ratio for all methanol recovery units were analyzed. Units were compared in terms of energy requirement and purity of recovered methanol product. The simulation results show that energy requirement for methanol recovery units increases with increase in % methanol recovery and reflux ratio (for distillation), but decreases with decrease in operating pressure and increase in methanol-to-oil ratio. The recovered methanol is pure for distillation and stripping-based MRUs. However, for flash-based MRUs, the purity of recovered methanol degrades at the high heat duty supplied. Consequently, the single- and double-flash-based MRUs have narrow ranges of operation. Moreover, double-flash-based MRUs have no significant advantages over single-flash-based MRUs in terms of heat duty. Comparison of heat duty among distillation, stripping, and single-flash reveals that the single-flash-based MRU is the most energy efficient followed by stripping and distillation-based MRUs.