Yellow Grease, Animal Fats, & Waste Vegetable Oil (WVO) feedstocks consist of odors and impurities which need to be removed during the distillation process.
Canola (Rapeseed), Palm, and Jatropha which are treated oil feedstocks, have a peculiar odor that needs to be removed. This must be done during the distillation process.
Biodiesel can be made from various different feedstocks and will vary in color from oil to oil. In all cases, you can expect clear distillate depending on the type of impurities present in the oil. During the distillation process, the soluble solids and high boiling impurities will remain at the bottom and the color of the finished biodiesel may not always be crystal clear, depending on what feedstock was used. The decolorization is important as biodiesel tends to darken during storage due to oxidation. Antioxidants are added to increase shelf life during it’s time in storage.
With the new ASTM standards (ASTM 6751) recently revised, allowable levels of water, metals, and sediment has greatly reduced. This has been implemented to reduce particulate emissions, fouling, filter plugging and other potential engine problems.
How distillation works?
During the transesterification process sodium methylate is added which remains in traces along with unreacted oil, mono and diglycerides, metals, and other heavy contaminates which need to be removed.
After the transesterification process sodium hydroxide, water & soap are formed and remain in traces after physical separation or washing/polishing and must be removed to meet ASTM specifications. Any water that is present in the biodiesel tends to hydrolyse the long chain free fatty acids which cause the acid value to increase during storage. Water content cannot exceed 500ppm and biodiesel distillation will help with this process.