Re-processing failed batches.

[julianf]

A while back i had one of those batches where the glycerol just would not split out.  I tried dosing more, overdosing, mixing in other stuff, etc. all with no joy, and canned it for a later day.

Yesterday, i loaded up the reactor with a ratio of about 2/3 good oil to 1/3 of this 'stuff'.

I then glyc washed it with good glycerol, hoping this to pull the old glycerol out of suspension, and get out far more glycerol than i put in.

This was not the case - quantity out was about the same as normal.  (in truth i was just glad the glycerol came out at all, and did not just get locked up also!)


I then dosed with my usual method but at 2/3 the amount (ie for the oil, ignoring the failed batch).

Dropped the glycerol - no more than expected from the 2/3 oil.

90/10 showed 33% converted.

Dosed for the remaining 1/3.

Dropped a bit more glycerol, and 90/10 showed zero drop out.


Total glycerol from the entire batch was a little over 20%.  Normally i actually get more than this, but then it reduces down again when the remaining bio settles out - so, whilst the figure, on paper, is about right, i would have expected this much from the 2/3 good oil alone.

So, im thinking im a bit low on glycerol, and wondering if this is in any way related to it not splitting out the first time?



Also, another, related, question -

When ive had failed batches in the past, ive always, cautiously, added in the mix to subsequent batches.  Im guessing this is what other people do too?

If so, what sort of ratios do you use?  I felt like i was chancing it with 33%, but, as it all went smoothly, im wondering if i couldnt have gone 50/50.

[Julian]

My last two batches were reluctant to drop glycerol, no idea why, and I overdosed both catalyst and methanol to cure the problem.

I didn't measure anything, but I ave to say the level in the settling barrel after a heavy demeth, seemed a bit higher than normal, possibly indicating a slightly higher yield.

[julianf]

Can you recall / clarify the quantity you use to 'overdose' with?

I tried overdosing a sample with more naoh, and got a hard lump...
Ive had splitting issues before that im sure were due to overdosing with both caustic and meth, and then (i think) the meth keeping the glyc in suspension.

So, now im cautious about adding much more meth, hence just going with caustic, hence a solid lump on the test...

...and me giving up until yesterday - when it all went surprisingly well???

[Julian]

I've been using NaOH for the main batch, but for additional processing I use ASM.

You can add it to a bio sample and give it a stir.  It goes thick and soapy, but if you're quick you can get it in the processor before it get too bad ... I stick my additional ingredients down the sight tube. 

Really don't know quantities as they are not measured and added in increments, but at a guess, for the last batch, possibly 30% of the batch quantity ... may well be overkill.