See below
Thomas Kelly wrote:
Joe,
You wrote:
"Have you ever tried dosing the batch again with a little methoxide?
After you remove the glycerin it doesn't take much to get the last bit
of the reaction to go and settle out the remaining glycerin."
I've been concerned about the excess methanol and the catalytic
caustic that will leave with the glycerin I remove.
It is in the glycerin anyways, but the glycerin is stopping the reaction
so removing it shifts the equilibrium point in favour of completion.
You seem to be suggesting re-processing the BD using info from the QT.
Yep. There will be 1-2% v/v methanol in the esters anyways and the
remaining excess is disolved in the glycerin.
Instead of adding 10% (vol/vol) methanol, use an amount that
correlates to the volume of unreacted oil (from QT).
Ex QT suggests 8% unreacted oil in a 100L batch = 8 L of
unreacted oil in the batch. Add 1.6L of methanol (20% vol/vol of the
unreacted oil) and re-process. (Much better than the 10L normally
required for re-processing).
Have I got it right?
Yes
Do you still have to add 3.5g of lye (or KOH equivalent)/L ?
If so, is it 3.5g lye per liter of unreacted oil (calculated from
QT) or per L of batch?
Yes 28 g or 40 etc.
Don't you have to heat up the whole batch again? (Time and energy)
This is all done right after draining the glycerin. I leave the heater
on during this period. Do the rough QT right away before wash test.
BTW I still do the 'real' QT after all washing and drying are done.
If so, I suggest my way. Towards the end of the reaction,
interrupt the process and test the BD*. If it fails the QT add more
methanol** and let the reaction continue for a while.
Well basically yes that's what I'm doing but have drained the glycerin
and doing the test with methanol shows you exactly what percentage
unreacted stuff you've got so add methanol and 'X'OH for that amount of
oil. You can add the remains to the reaction or next batch of course.
* When I drain the sample to be tested, I allow some to flow before
taking the sample. In case there was oil in my drain plug I won't get
a false negative on the QT.
** I have simply added a liter or two based loosely on the QT. I will
now quantify based on the QT and be more accurate (Thanks).
>Kenji and many others do straight base catalysis as a two stage deal.
Two Stage Base/Base Method?
I know of someone who uses it; no titration ---> consistently good BD.
I wouldn't skip the titration but rather do the base step in two stages
and remove glycerin in between.
It seems to be a bit more time-consuming and uses more energy and
caustic than my simple (some would say "primitive") single stage base
method.
Yes a little more time since two settling periods but it's hard to get
it just perfect with one stage anyways so then some repro is called for
and....time.
Big Lunch,
Tom
LOL U funny!
Cheers
Joe
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