Water Cleaning of Biodiesel. Effect of Catalyst Concentration, Water Amount, and Washing Temperature on Biodiesel Obtained from Rapeseed Oil and Used Oil

The effect of changing the NaOH wt % (0.7-0.9%) in the transesterification, the amount of water (30-90 wt % of the biodiesel), and the temperature (40-60 degrees C) in the water cleaning step of biodiesel has been investigated, specifically the influence of these factors on some properties (acidity, viscosity and density) and contaminants (methanol, Na, glycerine, water, and glycerides) of the resulting biodiesel produced from two different oils (rapeseed and used frying oil) using a three factor-two level experimental design, and statistical analysis by ANOVA of the results. The biodiesels produced from both oils show very similar trends: methanol, sodium, and glycerine are almost completely removed from the biodiesel phase in one single step, whereas the glycerides content is not affected by the washing conditions. Viscosity and density are only very slightly affected by the washing step. The water content of the biodiesel is affected by both the water amount used and the temperature in an inverse way: the higher the temperature and the lower the water amount used in the cleaning step, the higher the water content in biodiesel. This washing step was also simulated in Aspen HYSYS V7.0 software. Using the NRTL thermodynamic package for properties calculation, the results obtained showed a reasonable agreement with experimental ones, although it should be improved for a better calculation of biodiesel final properties.