I should really make notes so that when I post some thoughts about the process the information seems to flow more logically - but I don't! It just comes from the grey cells (or whatever is left of them) So I will try and make
this as simple as possible.
I water wash quite aggressively with a compressor line at the bottom of the wash tank. After a wash which is usually a max of 20 mins per go I drain the water after settling. The dreaded emulsified mono layer is sometimes hardly noticeable and at other times it is considerable.
To create biodiesel the oil (triglyceride) molecule has to have the three fatty acid chains stripped from the glycerine molecule, which happens in sequence. When one acid chain is left, this monoglyceride molecule will be left in the biodiesel unless it is also converted, leaving the glycerine molecule.
If there is any unreacted oil left in the mix there will be a higher proportion of di and monoglycerides left as well.
According to tests done some years ago by gas chromatograph the methanol phase in our 10/90 tests can hold up to 2% oil even though it is clear, so when we conduct a 10/90 test we don't know if the methanol is free of oil or if it contains the 2% (in which case there will be a higher % of di and monoglycerides present)
A batch of bio that was processed some weeks ago washed really well with hardly any mono's showing. The batch I completed a few days ago was an absolute swine to wash with a considerable emulsified layer showing.
I decided to try some higher concentration variations of the 10/90 test on these 2x batches. Firstly the batch that washed well (low mono's) I first did a 20/80 which was clear, then a 30/70, then a 40/60, all the tests were totally clear with an immediate clear methanol phase.
Now to the hard to wash batch (high mono's) I only had to do the 20/80 test which showed 3.2 mls of dropout. Yes 3.2 mls I could hardly believe it. Let me say at this point that both batches showed a clear 10/90
If the poor batch really had the 2% of oil left in the methanol phase of the 10/90 then increasing the bio amount in relation to methanol would have resulted in some oil coming out of solution and because of the high amount of biodiesel dissolved in the methanol some of this would rather mix with the oil than stay in the methanol. Hence the massive dropout.
So, it seems that after a clear 10/90 if we do a 20/80 it will tell us if some oil still remains in the bio and (more importantly) how well we can expect it to wash.
We cannot use the 20/80 test to calculate the catalyst amount for a re-process and if the 20/80 is a fail and the 10/90 was a pass then how much catalyst do we add. Logically I would say 0.5gms/litre if using potassium. 0.3gms/litre for sodium and 1.0mls/litre for ASM.
Before anyone says 'why should we bother with all that extra complication' I do appreciate having really well converted bio can be said to be over doing it if using older vehicles, also for those who don't water wash the above is not as significant. However, for water washers, passing the 20/80 test will certainly make the washing process easier.
Quick after thought, having 2x dropout tubes for the above tests makes things a whole lot easier
