Biodiesel production from degummed soybean oil and glycerol removal using ceramic membrane

In the present study, biodiesel was produced by ethylic transesterification of degummed soybean oil using sodium hydroxide as a catalyst. The influence of temperature and oil:alcohol molar ratio was evaluated using experiment factorial design and response surface methodology. According to the results, the maximum yields of esters were obtained when the temperature was lower than 40 °C and the oil:alcohol molar ratio was higher than 1:7. A membrane separation process was used to separate glycerol from biodiesel after transesterification. The reaction mixture was directly microfiltered after the addition of acidified water without previous settling. Microfiltration runs were performed in batch mode using a 0.2-μm ceramic membrane at 1.0, 2.0, and 3.0 bar transmembrane pressures. Membrane performance was evaluated based on the capacity of glycerol retention and on the permeate flux values. The results showed that the water concentration added to the mixture plays an important role in glycerol separation, as well as in the permeate flux, according to the proposed glycerol separation mechanism using ceramic membrane. The use of filtration with ceramic membrane was efficient to remove glycerol from biodiesel, and the permeates obtained for all conditions showed free glycerol values lower than 0.02%, which is the maximum specification limit.

► Degummed soybean oil can be used to obtain biodiesel by ethylic transesterification.
► Free glycerol can be removed from biodiesel using a membrane separation process.
► Acidified water has a great effect in removing glycerol from the biodiesel phase.
► This novel process does not require previous decantation to separate the glycerol.