Method for purifying biodiesel fuel
Provided is a method for purifying a biodiesel fuel while completely preventing or greatly reducing generation of waste water. The present invention relates to a method for purifying a biodiesel fuel characterized by applying an electric field to or heating a crude biodiesel fuel and a method for purifying a biodiesel fuel characterized by adding water (preferably containing a demulsifier such as an inorganic calcium salt or a magnesium salt) to a crude biodiesel fuel to form W/O emulsion, and breaking the emulsion by application of an electric field or heating, etc.
1. A method for purifying a biodiesel fuel, comprising the steps of:
subjecting a raw oil and methanol to transesterification using an alkaline catalyst to obtain a crude biodiesel fuel comprising methanol, alkali metals and free glycerin,
applying an electric field to the crude biodiesel fuel obtained by transesterification using the alkaline catalyst, and
separating a fuel phase and a waste-liquid phase after the application of the electric field to obtain a purified biodiesel fuel.
2. The method according to claim 1 , wherein the electric field is applied at an electric-field intensity of 0.01 to 5 kV/cm.
3. The method according to claim 1 , wherein the electric field is applied at an electric-field intensity of 0.1 to 2.5 kV/cm.
4. The method according to claim 1 , wherein the crude biodiesel fuel comprises methanol in an amount of 100 to 3500 mg/L.
5. The method according to claim 1 , wherein the crude biodiesel fuel comprises alkali metals in an amount of 5 to 200 mg/L.
6. The method according to claim 1 , wherein the crude biodiesel fuel comprises free glycerin in an amount of 200 to 800 mg/L.
7. The method according to claim 1 , which comprises adding water to the crude biodiesel fuel to form W/O emulsion before the electric field is applied, followed by applying the electric field to break the emulsion.
8. The method according to claim 7 , wherein the electric field is applied at an electric-field intensity of 0.01 to 5 kV/cm.
9. The method according to claim 7 , wherein the electric field is applied at an electric-field intensity of 0.1 to 2.5 kV/cm.
10. The method according to claim 7 , wherein the crude biodiesel fuel comprises methanol in an amount of 100 to 3500 mg/L.
11. The method according to claim 7 , wherein the crude biodiesel fuel comprises alkali metals in an amount of 5 to 200 mg/L.
12. The method according to claim 7 , wherein the crude biodiesel fuel comprises free glycerin in an amount of 200 to 800 mg/L.