Written by Rickdatech
This biodiesel titration test is used to determine the amount of soap in unwashed biodiesel. It is not part of ASTM D6751 biodiesel testing. It is used for determining the amount of Magnesol or synthetic magnesium silicate to use when washing without water. Other uses include process improvement and biodiesel analysis.
The test procedure is a variation the one found in the Biodiesel Analytical Methods by the NREL pg 41, and has been tuned specifically for unwashed biodiesel analyasis.
The test uses isopropyl alcohol as a solvent, 0.01N aqueous solution of hydrochloric acid as reagent, 0.04% bromophenol blue and 1% phenolphthalein as indicators. In this test we use a triple beam and determine the ratio of soap to biodiesel by weight.
Materials need for test:
0.1N Aqueous solution of HCL
0.04% Bromophenol Blue in water
1% Phenolphthalein in IPA
Triple Beam Balance
Requirements for Materials
You will need isopropyl alcohol for the test. It must be pH neutral. You can tell by testing it with pH strips. If it is not at 7.0 then add enough of your lye water solution that you use in your normal WVO titration to bring it to a pH of 7.0
You can buy 0.1N aqueous solution of HCL at most laboratory supply houses for about $16 per liter. Shipping will be another $20 to $30 after paying the hazmat fees. Muriatic Acid is used as a swimming pool treatment and is commonly available in hardware stores for about $4.00 a gallon.
See Preparing Stock Solutions for instructions on making a 0.01(N) solution of HCL using inexpensive hardware store Muriatic Acid. We will use our stock 0.1(N) aqueous solution of HCL, to make a small amount of 0.01(N) as needed for testing.
Making 0.01(N) HCL
The Test procedure calls for 0.01(N) aqueous HCL and we can get it by diluting our stock 0.1(N) HCL with water. For best accuracy it is best to purchase this solution already mixed.
Place beaker on scale and weigh.
Add 90g to weights and pour water in beaker until the scale balances
Add 10g of 0.1N aqueous HCL
Adjusting for Catalyst
Unwashed biodiesel will contain KOH or NaOH catalyst that can slightly throw off the results of the test. This will zero the titration to adjust for catalyst similar to the blanking we do when we titrate WVO.
Place a 250mL beaker on the scale and add 100mL of isopropyl alcohol.
Add 5 drops of phenolphthalein.
Weigh and move the weights for an additional 10grams.
Add oil until the scale balances.
If the liquids in the test beaker stay clear then there is no catalyst in the biodiesel
If the liquids in the test beaker go pink, remove the beaker from the scale and, while stirring add 0.01N aqueous HCL until the phenolphthalein changes from pink to clear.
Titrating for Soap
Now we will continue to add the 0.01N aqueous HCL to break apart all the soap.
Add 20 drops of Bromophenol blue to the solution; it should turn blue.
Weigh the sample and record the weight. (the starting weight)
Remove the beaker from the scale.
While stirring add 0.01 aqueous HCL until the Bromophenol blue changes to yellow.
Weigh again and record the weight (the ending weight)
The Math the hard way
["B" ml of additional 0.01N HCl added] x [1 liter/1000ml] x [0.1 moles of HCl/liter] x [1 mole of soap/mole of HCl] x [320.56 g/mole of soap] / ["W" grams of sample] = grams of soap (as potassium oleate) per gram of sample.
B = The ml of 0.01 aqueous HCL
W = grams of biodiesel in sample (should be 10g)
Use 304.4 instead of 320.56 if using NaOH or catalyst.
Multiply by one million to get grams of soap per million grams of sampleThe Math the easy way Subtract the starting weight from the ending weight for the net weight.
Multiply the net weight by 320 for the ppm of soap.
How Much Magnesol?
Use 1% by weight per 1000ppm of soap, according to the Dallas Group. If we take the specific gravity of biodiesel to be .860 then we add 8.6 grams of Magnesol per liter per 1000ppm of soap to give the formula:
["A" ppm of soap] x ["B" Liters of Biodiesel] x [8.6] /  = Grams of Magnesol
Monitoring Soap and Catalyst in Biodiesel Production Process - LSU Ag Center Biodiesel Program