Tutorial 3 - Water Washing Purification Procedure

Tutorial 3 - Water Washing Purification

Motivation

Unwanted contaminates in crude biodiesel left over from transesterification can cause fuel filter clogs and engine decay.  Purify crude biodiesel of material such as excess reagent, excess catalyst, and glycerin by-products by continually washing sample(s) with distilled water.  Unwanted charged particles will be drawn out by water.  

Materials

• crude biodiesel
• distilled water
• separatory flask
• 100 mL beaker
• 100 mL graduated cylinder 
• scientific weighing scale

Procedure 

OPTIONAL:  Conduct a pre-wash to avoid emulsions.  Using warm distilled water or hard water (http://make-biodiesel.org/Water-Washing/washing-techniques.html) during the washing procedure can also reduce emulsification.  

1. Pour 50 mL of crude biodiesel into a separatory funnel.
2. Add 50 mL of distilled water (or in a 1:1 mL ratio) into the same funnel (see NOTE for below technique).
3. Let mixture sit for 20 to 30 minuets.  Gently stir the mixture during this time by rotating the funnel on an angle.  Ideally the mixture should not be subjected to a lot of rapid motion.  
4. Record the mass of your beaker.  
5. After substances have separated, drain water from funnel into the beaker.  Stop draining when you see the first drop of "oil" come out from the funnel.  The water should appear soapy and opaque (Figure 1).  If too much biodiesel has been drained out of the funnel, pour all drained material back in and repeat steps 3-5.  
6. Record the mass of your beaker with waste water.  Perform calculations [1] to determine how much material was drained out.  Record the mass and settling time (time you let mixture settle in step three. 
7. Repeat procedure until drained water from funnel is absolutely clear.  CLEAN BEAKER THOROUGHLY between washes and record the mass of the empty, clean beaker each time.  
8. Once clean, measure amount of purified biodiesel and put into a storage container.  It should appear cloudy and turbid.  This is normal. 

NOTE:  Water can be added to the crude biodiesel in many different ways.  In order to avoid emulsions, various methods can be used to gently pour the water onto the biodiesel.  It is recommended to mist wash the samples, where misting distilled water is sprayed on top of samples.  Other methods can be read about here (http://make-biodiesel.org/Water-Washing/).  

Calculations

[1]    (mass of beaker with waste water)  -  (mass of beaker)  -  (mass of distilled water added)  =  (material drained out)

Figure 1 - Washed waste material