Biodiesel purification using micro and ultrafiltration membranes

• Application of micro and ultrafiltration membranes for biodiesel purification.
• Comparison of permeate fluxes through micro and ultrafiltration membranes.
• Choice of a suitable membrane for free glycerol removal.
• Effect of soap removal on free glycerol removal.
• Effect of water addition to improve free glycerol removal.

Biodiesel is an environmental-friendly fuel that can replace petroleum diesel. However, after transesterification reaction of vegetable oils, the obtained crude biodiesel must be purified. The commonly applied purification step is water washing. This step is a concern in biodiesel production, since large quantities of clean water are used, generating a wastewater stream to be further treated. Here we propose the application of micro and ultrafiltration processes to purify crude biodiesel. Crude biodiesel was filtrated in a dead-end process at different transmembrane pressures and using membranes of different pore sizes. Flux results showed that greater transmembrane pressures, as well as greater pore sizes, enable greater fluxes. Density, viscosity and acid values of purified biodiesel (washed and filtrated) are in accordance to the international legislation for biodiesel quality. Both processes (water washing and membrane separation) were able to reduce the amount of soap detected in crude biodiesel. However, the proposed microfiltration membranes were not efficient as the washing method to reduce the free glycerol content. The ultrafiltration membrane of 30 kDa was also not able to produce a purified biodiesel according to the international legislation for free glycerol content. Between the analyzed membranes, the glycerol content limit (less than 0.02 wt%) was achieved only with the ultrafiltration membrane of 10 kDa. Water addition in the crude biodiesel improved the glycerol removal by membrane filtration. The obtained results showed that the membrane separation process is a suitable alternative for biodiesel purification.

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