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[lynxpilot]

Rex,

In answer to your question, yes you are checking pH by definition of the process. And as was answered before, it is to determine the amount of lye to completely react the oil in the biodiesel reaction (There are a bizzillion different titrations done for chemical checks and processes in many industries).

I am very suspicious of the accuracy of titrations on an oil. I am also very suspicious of the value and benefits of such pain. I have never titrated my oil, despite the fact that I used to be a nuclear reactor plant chemist and am very famililiar with the titration process, and every single batch has turned out fine. I think if you take the whole thing into perspective, understand what you are doing, and let history and other peoples' mistakes guide you, you can avoid such things. Unused oil needs about 3.5g/l and used oil that isn't black muck needs 6.5-7.5g/l. Mucky oil is a different story, but 8.5g/l would be a good starting point. Using a little bit of excess methanol also helps (about 20%). Doing little test batches measured accurately is a lot better than titration. There are too many variables when you are dealing with a substance that could have stratified into layers which will produce different results when you are only drawing a few cc's for a sample. You'd be a lot better off investing in a half decent gram scale that measures tenths or better and doing a 1 liter test batch (or more) to determine the quantity of lye to use.

Lastly, whatever you may have missed by not doing titration is taken care of by washing. Excess lye is removed by the wash process and too little lye just means you have some unreacted oil in your biodiesel, which is no problem at all, especially if you have a little bit of excess methanol in the mix to keep the viscosity low.

I'd recommend not even worrying about titration.