Right I've found some info posted by GL, obviously it was for neutralizing catalyst before demething the whole batch, but it should neutralise soap and instead of demething you guys will then just drain glyc and water wash instead, or maybe even experiment and try water wash with all the glyc in, obviously no good if you need it for glycwashing though
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Hi GM
As Nick mentioned, the viscosity rises dramatically as methanol concentration in the glycerol drops, so the venturi fails to operate if using glycerol alone..
So here's an interesting twist, which works well, I have had no issues with back reaction as far as I can tell, and no problems with foaming....
After reaction, keep the pump running and do NOT drain the glycerol, and do NOT do 5% prewash,.
Instead, add a 1/2 teaspoon of phenolphthalein powder per 100 litres batch and allow to mix thoroughly. You'll need a sight tube to view the mixture. A narrow clear branched tube, off the outlet of the pump is safest - you want to be able to instantly see the colour change, so the tube must carry some of the pump outlet flow thru it.
Very slowly (I mean VERY SLOWLY) dose 34% conc. HCl into the inlet of the pump and note the colour change. When you get to about 0.1% dosed volume, you'll see the deep red will lighten up a bit.
STOP adding HCL at this point.
The colour will darken again in a few minutes, DON'T add any more HCl or you will start to make FFA from the soap. The lye will preferentially neutralise first with the HCL, then the soap.
The NaOH or KOH should mostly be neutralised now, making it an ineffective catalyst for what follows...
Add heat to the whole batch and start distilling off the methanol, you'll need to go up to 90C or more.
When this becomes a trickle, stop.
The glycerol will drop out within a matter of seconds when you stop the pump, drain it before it cools and solidifies.
Then drain off the remaining biodiesel into a settling tank to allow soap to drop out, or you can wash it gently as is - it should wash fairly easily if you treat it gently for the first one.
Key things
1. Use a pump which can deal with the viscosity.
2. Don't OD on HCL.
3. Don't dose HCL too fast, or you'll make FFAs
For a 100 litre batch, you'll use around 100ml HCL, depending on titration, amount of lye, water in oil etc.
My pump is roughly 1/2 batch volume per minute.
Dose the HCL at a rate which will take around 30 minutes to complete, at the inlet of your pump so it mixes well.
This is info to the best of my knowledge to date - there is a lot still to learn and much can be done to improve the process, but it is showing good promise as a simple, fast efficient way to recover methanol from the whole batch and aid washing or eliminate the use of water.
