Soap and glycerin removal from biodiesel using waterless processes.
Biodiesel is a proven alternative to petroleum diesel fuel. During production of biodiesel, the free fatty acids in the oil react with the sodium or potassium catalyst to form soaps. After the biodiesel and by-product glycerin are separated, trace amounts of glycerin remain in the biodiesel. These soap and glycerin impurities in the biodiesel can lead to engine operation and fuel storage problems. Traditionally, soap and glycerin are removed from the biodiesel by water washing. Water washing has several disadvantages, such as producing large amounts of waste water that requires treatment and causing plant operational problems such as emulsion formation. Recently, several alternative "waterless" purification procedures have been developed, such as ion exchange resins and solid adsorbents. The objective of this study was to investigate the use of ion exchange resins and characterize their performance so that biodiesel plant operators can use them more effectively. Four different mechanisms were identified for soap and glycerin removal. These mechanisms are filtration, physical adsorption, ion exchange, and soap removal by glycerin affinity. It was found that ion exchange resins can reduce soap levels from 1200 ppm to below 50 ppm for about 550 bed volumes (BV) of processed biodiesel. Glycerin levels can be reduced from 0.08% to below 0.02% for about 200 BV of processed biodiesel.