Influence of oil quality on biodiesel purification by ultrafiltration

• Ultrafiltration membranes are used for the biodiesel purification.
• The influence of the oil quality on the glycerol separation is evaluated.
• The percentage of acid in the oil contributes to glycerol retention by the membrane.
• This purification process eliminates the step of separation by settling.
• Reduction of the amount of water used for washing is an advantage.

In the present study, biodiesel was produced by ethylic transesterification of soybean and canola oils using sodium hydroxide as a catalyst. It was evaluated the influence of oil quality on the biodiesel and glycerol separation by ultrafiltration. The experiments were carried out with tubular a-Al2O3/TiO2 membranes with average pore diameter of 0.05 µm and 20 kDa, varying the transmembrane pressure and the concentration of the feed mixture. The comparison among the use of degummed soybean oil, refined soybean oil, crude canola oil, and refined canola oil, demonstrated that free fatty acid presented in the oils influence the formation of droplets containing glycerol. The separation was efficient when reaction mixture was produced from degummed soybean oil and crude canola oil, both with a higher acidity value. The highest free fatty acid content in the crude canola oil, not only favored the formation of a dispersed phase containing glycerol, which was retained by the membrane, but also resulted in the lowest flux decline rates. The ultrafiltration was efficient in removing glycerol, since the highest glycerol content in the permeate was 0.013 wt%. This novel refining process of biodiesel showed the advantage of not requiring previous decantation to separate the two phases obtained after transesterification and the reduction in the amount of water used in the washing steps. The properties of the biodiesel produced, which were evaluated, meet the ANP biodiesel standards required for marketing.