Influence of acidified water addition on the biodiesel and glycerol separation through membrane technology

This study evaluated the application of micro- and ultrafiltration with ceramic membranes to separate biodiesel and glycerol produced by ethyl transesterification of degummed soybean oil. The experiments were carried out with tubular α-Al2O3/TiO2 membranes with average pore diameter of 0.2, 0.1 and 0.05 μm and 20 kDa. The experiments used the reaction mixture with mass concentrations of acidified water of 10%, 20% and 30%, transmembrane pressures of 1.0, 2.0 and 3.0 bar and temperature at 50 °C. By using the mass concentration of 20% acidified water the separation was efficient, but the fouling of the retained phase on the membrane surface led to a sharp reduction of flux over the filtration time. The mass concentration of 30% was excessive and in most experiments the aqueous phase containing glycerol has permeated through the membrane. The addition of 10% of acidified water, besides reducing the fouling on the membrane promoted the retention of aqueous phase containing glycerol, so that the permeate had free glycerol content below 0.02%, maximum value specified for commercialization. The glycerol separation through ultrafiltration is advantageous once it eliminates the settling step and reduces the amount of water used for washing. The properties of the produced biodiesel have met the standards required for commercialization.