So I just did my first titration and I am using new oil for practice. I added 10ml of methanol to a beaker, 1ml of oil, 5 drops of phenolphthalein and swirled this around for a minute to try to get the "yellowish" color that I should, but it didn't make it to "yellowish" instead it was a light milky white. Then I added my lye solution (3ml lye to 3 liters of distilled water) drop by drop and saw the reaction go from a light white to a light pink that lasted for at least 30 seconds. But as I kept adding lye solution it just keeps turning a more brilliant shade of pink/purple!! How do I know when to stop? Should I quit adding the lye solution as soon as I get a pink that lasts for 30 seconds? Or should I be shooting for a darker color? Should I get ph test strips to test for the correct acidity of 8.5? Since this oil is new, I figured I should be looking for results of about 2g to 3.5g of lye per liter. The moment I had a mixture that turned pink for 30 seconds I was barely at 1g of lye per liter. That is far off the mark that everybody says new oil should titrate at. On the biodiesel tutorial they say that new oil will need 3- 5 grams of lye per liter of oil. Did I understand that correctly? What am I doing wrong?
Your first error is to confuse the amount of NaOH needed as catalyst with the amount needed to neutralize the free fatty acids (FFA) in the oil.
The amount needed as catalyst depends on the degree of conversion you wish to attain. If you want to achieve ASTM level you need 5g NaOH to just scrape in. If you just want good biodeisel to use in your motor 3.5g will do. However if you are going to wash it you may find that 5g is better as it may wash more easily.
The amount needed to deal with the FFA is determined by titration. With new oil there should be very little.
Your second error is to assume that phenolphthalein is yellow in acid. It is colourless. Turmeric and phenol red are yellow in acid. Don't use phenol red, it does not go off at the right pH. Turmeric is near enough.
Re the degree of colour change, the industrial process says add enough NaOH to get a pink colour that lasts for 30 seconds. This is a more tricky area than many people realize. First you have to swirl or stir the mixture vigorously to ensure it is fully mixed, then stir or swirl gently while watching the colour. As we use smaller amounts of material than is standard in industry I think 20 seconds of colour is enough with phenolphthalein. Very vigorous stirring during this stage can remove the colour faster by incoporating CO2 from the air, especially if your are breathing over a wide topped container.
This is a little late in replying, but you have to make sure that you are careful when titrating. The tricky part is that when the solution is at a buffer point, the pH will not change much per drop until you reach the end point where an extra drop of NaOH can possibly change your pH from 8.5 all the way to 14 or higher. In order to prevent flawing your data, and to ensure accurate stoichiometric results take your time... don't rush it.
For 'good oil' (such as 1-4 ml on the titration) it hardly matters at all. The differences between phenol red and phenolpthaleine get more noticable as you begin to measure 'bad oil' (like 5, 8, 10 ml titrations).
Mark
Location: Pittsboro, North Carolina | Registered: 07 March 2001
For Girl Mark, I just started my set-up and tried a test with a new bottle of VO used to make home fries with Phenol Red and it appeared to work. So can I try using Phenol Red on WVO from a restaurant and see if the color changes to red under 4 ml of tritration added fluid? If it does, then is it safe to say it works? If the color doesn't change passed 4 ml then go with Turmeric or Phenolphalein?
