I have a batch of oil in my plant which according to the 27/3 test has not separated sufficiently. It has cooled down and I have not yet extracted the triglycerides. My question is:-

Should I drain off the glyc and retreat the oil or is it out of the question to reheat the batch, mix it up and add more methanol and caustic?

Also:-

Has anyone tried, for want of a better word, an "air stick" connected to a compressor hose for agitation of the converter contents?
I am presently using a home made "paddle" with an electric drill and I would prefer something much simpler.

I apologise for my ignorance and will look forward to some responses, even if they bruise my ego.
Thanks.

Yes you can re-process your bio, but I suggest trying to find out why the conversion wasn't complete.

how does the air stick work? Does it put bubbles into the oil, or does the air move the "stick?"

Justin

Drover,
Yes, you can reprocess the poorly converted batch.
Providing the batch has not been left open and has lost most of the methanol, you can reprocess with minimal methanol added. If you have lost methanol, determine the current batch volume compared to the initial batch volume (the difference will be the methanol volume lost) this amount of methanol will need to be added back to the batch for reprocessing.

I believe that it is not necessary to separate off the byproduct to reprocess, but you should take precautions to minimise methanol loss (this will need to be added back if the reprocess is to result in good conversion).
Take well remixed 1 litre samples of the biodiesel and byproduct and add some caustic in methanol to re-process.

Here is my suggestion:
Use 100mL of methanol and dissolve 10g of caustic in it (I think that this is not too much to fully dissolve). This makes a concentrated solution, of which 10mL will contain 1g of caustic.

To 3, one litre samples at 50°C, add 1, 1.5 and 2 mL respectively of this concentrate and agitate for 20 - 60 minues. (if methanol loss is significant, you will need to add back the lost methanol volume)
When the separation is complete, perform a 3/27 test on the biodiesel from each and determine the lowest amount of added caustic which results in good conversion.

Multiply this up for the batch oil volume (minus the test litres), dissolve in the smallest amount of methanol possible, add any lost methanol and reprocess the batch. This allows the methanol which is still in the procesoser (in the byproduct layer) to be used in the reprocessing of the batch.

Please report back to the forum on the success or otherwise of this suggested process, as others could benefit if you have success with it.

The alternative, after removing the byproduct will require much more methanol to be added.

Hi Tony,
Thank you once again for your help.
I will try and overcome my problem in the manner you suggest and, yes, I will report back on the results.
Apart from being a newbie, I am also a wrinkly with limited computing and practical skills of the type required for making bio diesel and so I am going to need all the help I can get.
I am presently out of methanol and it will be midweek before I can get some more.
I will succeed.
Now would some kind soul tell me how to print out Tony's post. When I attempt to print only the first page of the thread will print out and I have not encountered this problem before.
Thanks.
Drover.

Just a quick addition

It is best to drain the glycerine layer before reprocessing.
The "Standard" reprocess for unwashed biodiesel is 1g NaOH mixed into 25- 35ml methanol per litre of biodiesel in the reactor.
You do not need to re-heat as long as everything is liquid, just run the reactor twice as long for every 10deg C the temp has dropped

Thanks Tilly,
A query though, if I remove the glycerin, aren't I removing a significant amount of methanol with it?

Hello Drover

The Glycerine acts like a Sponge to methanol.
If the reaction has stopped you have reached equalibrum with your chemicals, some is in the biodiesel and some is in the glycerine and no amount of mixing will significantly improve the reaction.
The methanol would much rather be with the glycerine than with the biodiesel because they are both alcohols.

If you leave the glycerine layer and add more methoxide, about 2/3 of the added methanol will be "Sponged" up in the glycerine layer and effectivly removed from the reaction leaving about 1/3 for the reaction.
If you remove the glycerine layer then all of the added methanol will initially be available for the reaction.
That is why in a 2 stage base/base method you can use substantially less methanol overall.

I apologise if my suggestion is chemically flawed.
I realised that the byproduct held the unused methanol so was trying to see if it could be used to assist the reprocessing.

Still, it would be worth a try, if only for the methanol saving.

Tilly, have you tried this method or is this an opinion, like my suggestion?

Regards

Tony

Hello Tony

This is neutrals explanation of why you need to remove the glycerine before doing a second stage

Hi all
This is a very timely thread!
I made a batch a week ago. All seemed fine, as it was from the same stock as previous, titrated the same (though it did produce only about half the usual amout of glycerine for some reason).
After washing, I aggressively bubble / fan dried it. I do this on a timer for about 6 hours a day during these cold months (Sydney hills district), for a couple of days. Problem was (?) I forgot to turn off the fan/ bubbler and went away for work. Came back 4 days later, and yes the level was lower in the drum.(loss of methanol?) What was more surprising was when a sample was left overnight (about 4 degC) it seperated into a combination of what looked like bio, with a layer of 'cous cous' on the bottom (flakey) and even what looked like mould on the glass jar sides.Obviously not mould, but similar speck appearance. I assumed it was just the cold, as when it is heated in the sun / left at room temperature it all goes back to normal. My older samples dont change when cold, so there is another problem.
I am guessing from the previous posts I dried the methanol out of it? My guess is the loss was in the order of 8 litres, though it is difficult to know as i had added some older unwashed bio before washing / drying, so didnt have an accurate amount at the start of drying.
Ideas.....reprocess as above posts (Tilly 1g/35ml per litre?).....anything else? I appreciate the help.
Notwithstanding any of the above, Is it fair to say settling is far better than drying, and what do most people think is enough drying without methanol loss?
Carl