Multi-stage distillation was used for methanol recovery as well as purification of both the FAME
and glycerine products. Although the boiling point of methanol (65 C at 1 atm) is much lower than that of
FAME (approximately 320 C at 1 atm) or glycerol (300 C at 1 atm), simulations suggested that the desired
purities of biodiesel and glycerol (greater than 90 wt.%) could not be achieved by a simple flash unit. The ASTM
standard for purity of biodiesel product (i.e., 99.65 wt.%) was applied to both the acid- and alkali-catalyzed
processes in the present study. However, the large difference in the boiling points of the components facilitates
distillation; only five or six theoretical stages in the columns are sufficient to yield high quality biodiesel and glycerine. In our simulations, we assumed a tray effi-ciency of 60–70%. Because FAME and glycerol are susceptible to thermal decomposition above 250 and 150C, respectively (Newman, 1968; Goodrum, 2002), vacuum operation for the FAME and glycerine purification was necessary to keep the temperature at suitably low levels. Liquid–liquid extraction was used to separate FAME from glycerol, methanol and catalyst (i.e., waterwashing column T-301). Detailed sizing calculations of
the process equipment were presented by Zhang (2002