Making Bio diesel using Ethanol

Making bio diesel using ethanol is a process that is comparatively more difficult than using methanol. The main reasons for this are :-

• Water sensitivity of the reaction
• Getting highly pure Ethanol that has less that .5 % water is difficult.
• This process is done better with KOH which too is not easily sourced
• The oil needs to be heated to 120 degree or more(Celsius)
• The amount of ethanol required is more
• Glycerin separation is a matter of luck (There are some ways to driving it to separate though)

Materials and Quality:-

Raw oil 100 L

Anhydrous Ethanol 27.4 L 199(99.5 % pure)

Potassium Hydroxide 1.30 Kg (85% or higher)

Ethanol in liters = 0.2738 x Amount of oil in liters

Amount of KOH in Kg = 0.013 x Amount of oil in liters

Process:-

Using a 100 liter batch of oil as an example, the KOH used reacts with 1.07kg of ethanol to produce 1.95kg of potassium ethoxide. This mixture now contains (27.4x0.789)-1.07 = 20.55kg of free ethanol and 1.07kg of ethanol as potassium ethoxide catalyst. Any water added to the entire system reverses the above reaction and quenches a proportional amount of the potassium ethoxide catalyst. One part of water can quench up to 84.15/18.02 = 4.67 parts of catalyst.The ethanol-KOH mixture is then poured into the oil(maintained at 60 degree Celsius) and the transesterification process occurs.

100 liters (91kg) of oil reacts with 13.1kg of ethanol. The 21.62kg (or27.4L) of ethanol used in the batch represents 21.62/13.1x100 = 165% of that required for complete transesterification of 100 liters of oil. (A 65% excess over the theoretical requirement). This values change according to the oil used and thus mastering of the process can take time.

Steps:-

1. Oil is measured.
2. The required amount of ethanol is placed into a small covered container.
3. The required amount of potassium hydroxide is quickly weighed.With minimum atmospheric exposure
4. The solid potassium hydroxide is added to all of the ethanol which is then vigorously stirred in the covered container until completely dissolved. At this point the dissolved KOH is presumed to have been converted to potassium ethoxide catalyst.
5. The ethanol-catalyst mixture is poured into the oil in the main reactor and stirred rapidly. Mixing is continued for 6 hours at 50+ temperature. The reaction mixture usually changes to a turbid orange-brown color within the first few minutes; then it changes to a clear transparent brown color; finally, as the reaction is completed, the mixture again becomes somewhat turbid and orange-brown colored due to the emulsified free glycerol which has been formed.
6. In the completed reaction, the glycerol begins to separate immediately upon cessation of stirring, and the settling mostly complete in one hour. After initial settling, the entire contents of the reaction vessel are again mixed together and stirred vigorously for 40 minutes. After the first 20 minutes of re stirring, water is added at 15% of the initial volume of oil used in the reaction. Stirring should continue an additional 20 minutes after the water is added for a total of 40 minutes of re stirring. This mixture is then allowed to settle. A longer separation time facilitates the washing process. Remixing the glycerol layer with the ester layer while adding water has the effect of collecting and removing impurities and products of incomplete reaction from the ester. The washing phase can then proceed at a more rapid pace than if the remixing stage were left out.
7. Wash the given mixture as usual

An entry on producing ethanol at home will be posted soon
links and news items on Bio Diesel on the right side