Having used up my stock of Sulphuric Acid I decided to start on my stock on 85% Phosphoric acid.
I have had repeated successes with the titrated acid wash using Sulphuric acid and like to think I have the process pretty much under control.
However, at the start of the week I did a batch using Phosphoric. Perfect 27/3 using Sodium Methylate - absolutely no haze in the 10/90 test and instant clarity. All glycerol drained and then acid washed using 20 litres of water and one litre of 85% Phosphoric (which is what the titration gave me for a 300 litre batch).
That is when problems started - real problems in settling.
Eventually I got the water to settle out (which came out crystal clear) and went on to water washes. No matter what I did I could not get clear separation although the water which did drop out was crystal clear (and a little acidic).
It took about 250 litres of water, including two mist washes to get clean bio which I then dried to sparkling clear.
Although confused for a while, some googling showed that Sodium Phoshate (which is the salt produced when using Phosphoric acid) is a detergent that was, until quite recently, commonly used. It is also water soluble.
Having a load of water soluble detergent in a mixture of water and biodiesel is, in general, a really bad thing.
I have rescued about 280 litres of the batch but it took a lot of work (and water - thankfully I am not on a meter). I have passed my experience to Paul (Carrington) for him to have a look at when he has time in order to try to identify what has really gone on but, in the meantime, I would seriously advice against the use of Phosphoric acid.
