The following is from journeytoforever.org The REASON for titrations is to find out exactly how much LYE you need to correctly transesterify the glycerin from the oil. Too much and you get jelly. Not enough, and you will have an incomplete reaction.
[ QUOTE ]
Basic titration
An electronic pH meter is best, but you can also use pH test strips (or litmus paper), or phenolphthalein solution (from a chemicals supplier).
Dissolve 1 gram of lye in 1 liter of distilled or de-ionized water (0.1% lye solution).
In a smaller beaker, dissolve 1 ml of dewatered WVO oil in 10 ml of pure isopropyl alcohol. Warm the beaker gently by standing it in some hot water, stir until all the oil dissolves in the alcohol and the mixture turns clear. Add 2 drops of phenolphthalein solution.
Using a graduated syringe, add 0.1% lye solution drop by drop to the oil-alcohol-phenolphthalein solution, stirring all the time, until the solution stays pink (actually magenta) for 10 seconds.
Take the number of milliliters of 0.1% lye solution you used and add 3.5. This is the number of grams of lye you'll need per liter of oil.
With a pH meter or test strips, use the same procedure without adding the phenolphthalein. Add the 0.1% lye solution drop by drop as before until the pH reaches 8.5.
Better titration
Unless you have a very accurate scale, it's not easy to measure exactly 1 gram of sodium hydroxide. It's much easier to measure 5 gm than 1 gm, so mix 5 gm of sodium hydroxide with 500 milliliters of distilled or de-ionized water.
Before titration measure out 5 ml of the stock solution, add 45 ml of distilled or de-ionized water. This makes a 0.1% lye solution.
It's also not easy to measure exactly 1 milliliter of oil. Instead of the usual 1 ml of oil and 10 ml of isopropyl alcohol, mix 4 ml of oil in 40 ml of isopropyl alcohol in a glass beaker.
Warm the mixture gently by standing the beaker in hot water, stir until all the oil disperses and it becomes a clear mixture.
Then titrate as usual, measuring milliliters of stock solution used. When it reaches pH8.5 count up the number of milliliters used as normal and divide by 4. This will give a much more precise measurement.
To save on isopropyl alcohol, use 2 ml of oil in 20 ml of isopropyl and divide the results by two -- still twice as accurate.
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.
__________________
2003 BLACK F-250 6.0L Lariat CC LWB Fx4 Quadzilla Xzillaraider Standard (0/30/60/120)
Bear in mind it is grams of pure lye per liter of oil. Obviously the total reactant volume will be greater once you've added methanol into the picture at 15 to 25 percent, but the lye measurement pertains to the volume of oil only.
Don't be afraid to fudge on large volumes either. My system was about 114 gallons capacity and I usually measured for about 70-80 gallon batches. I used a clear PVC pipe on the outside of the tank as a gauge glass in order to note the volume in the reaction tank and measured in inches. I took the diameter of the drum and came up with the trig formula to get liters per inch to determine the amount of lye as well as a ballpark estimate of methanol required. I then dumped the lye in the standby tank along with the methanol and stirred it up until completely dissolved before transferring to the main tank.
If you look HERE , one of the pages is a demonstration of my test batch. It was complete fudge on volume of oil and methanol and only semi-accurate on the lye measurement and it still came out perfect.
In all honesty, I think I'd stay well on the short end of lye and not worry about unreacted too much unless the weather was cold. Then again (note signature), I forgot what cold weather was and don't have to worry about it here. Some folks are diluting their #2 dino-D with as much as 50% filtered WVO and I haven't heard any complaints yet. I'd guess that the TDI's might be more sensitive to such things than the PSD's due to the type of fuel pump, but only guessing.
__________________
2003 BLACK F-250 6.0L Lariat CC LWB Fx4 Quadzilla Xzillaraider Standard (0/30/60/120)
The AutoGuide.com network consists of the largest network of enthusiast-owned enthusiast-operated automotive communities.
AutoGuide.com provides the latest car reviews, auto show coverage, new car prices, and automotive news. The AutoGuide network operates more than 100 automotive forums where our users consult peers for shopping information and advice, and share opinions as a community.
Linear Mode
