Soap testing kit question

[thewormman]

Hi all I have put this on the open forum rather than just contacting Nigel by PM so if anyone else wondered the same either previously or in the future they can read it.

I use one of NigelB's soap testing kits and wondered about my results.

As per instructions I prepare the IPA, it says
 

Using the 10ml syringe add 12ml of biodiesel into the blanked IPA. If soaps are present the solution will now have a green/blue tinge. If the solution takes on a yellow appearance this indicates that the bio has very low soap levels and you may need to add in some more indicator to give the solution a greenish colour.

When I add my bio it just goes straight yellow



If I now try and add more indicator to get it greenish I have to add about 5 or 10 times as much before it changes at all then it is slight.

So...

Does this mean that as my bio is already very low PPM I can dispense with adding acid to the sample to check it?
Even when I do do this it comes out usually as between 10 and 15 PPM, but adding so much indicator makes it difficult to judge.

Is there a way of doing the test so it is more accurate for very low PPM? I know it isn't necessary but I want to make it the best I can, not obsessive at all 

[Julian]

I find Nige's kit great, the only thing I find difficult is judging the colour change when soap levels are low.  I've never experienced what you are seeing though.

[Manfred]

Hi everyone. I'm new to all this Bio stuff and still reading n learning but
I'm getting the same when I try a acid test. If I do a 50/50 it shows soap though. When I passed through dry media I get the same result but a 50/50 pass.
 When I did one for a mate I got a 80ppm.
Must say I'm a bit confused

[thewormman]

I find Nige's kit great, the only thing I find difficult is judging the colour change when soap levels are low.  I've never experienced what you are seeing though.

Yes it is good. Do you mean yours does not go straight to yellow?

[Julian]

I find Nige's kit great, the only thing I find difficult is judging the colour change when soap levels are low.  I've never experienced what you are seeing though.

Yes it is good. Do you mean yours does not go straight to yellow?

I've never seen yellow.  It starts a light blue and turns a sort of turquoise green, hence the difficulty in detecting the change.

Perhaps you have a different indicator solution ... only Nige will know!

[Head Womble]

I've had it go straight to yellow a few times, at this point I just accept that it's good enough.

What I have found is this test is completely useless if you do acid titration water washing,
this, I think, is due to neutralising the PH of the raw bio,
so the soap test results are missleading until the acid has been washed away,
by this time you've removed all but small traces of soap anyway.

[nigelb]

All kits have the same indicator...bromophenol blue.

If the solution is yellow after you've added the bio then the bio is very low in soap levels.

As womble has intimated....if you acid wash this can give misleading results until the bio has been allowed to settle or the wash cycles have washed away the traces of whichever acid choice you used.

[thewormman]

Thanks for the replies 

Yes I am acid washing, this is the result I get after the fourth wash with 20 litres each time, in a 180 Litre batch with acid only in the first wash. PH of drained wash water is same as tap water after wash 2.

So will it be ok to read it as virtually free of soap and safe to use if it goes yellow straight away do you think?

What sort of PPM level do you guess that would be?

[nigelb]

In my oppinion, if it's yellow, it is virtually soap free and safe to filter and use.

I would guess at a soap ppm of between 10 and 40

As an aside I used a little bit of acid in wash 1 yesterday and it only took two more washes to clear the bio of soap. I didn't titrate it just chucked a bit in. I might do that again.

[thewormman]

Thanks Nigel 

What I am doing at the moment is demething then sending it into my washing/settling tank still at about 85C, adding usually about 1.8 litres of white vinegar and 20 litres of water, after an hour pumping with a 'static mixer', so no air is introduced, and a central heating pump (I don't do subtle  ) this comes out, I think it pretty much takes out nearly all the soap glyc and any remaining catalyst.



It looks like a frothy latte. There is NO emulsion, all this is water, acid and impurities.
The static mixer I made is the key I think in conjunction with the acid and the temp.

2nd wash 20 litres pumped again gets the last traces of acid out, after that its another couple of washes to clear the brown sedimentary stuff that I found was bypassing my 1 micron filters and settling in my storage cubies

[Julian]

That's very similar to what I do except I wash in the processor and titrate using conc sulfuric ... usually about 20ml for 80 ltrs of bio.  I don't get the yellowish waswater, mine tends to be a light brown colour on the first wash and pretty clear thereafter on on or two further washes.

I get the brown sediment which I believe is sodium sulfate, in my case, not sure what you'd get with vinegar ... sodium vinegarate perhaps.

Nige, should the bromophenol blue turn yellow or turquoise?

[thewormman]

Here is my 2nd and 3rd washes, wash four is clear and I don't get any sediment settling in the storage cubies. It was collecting in the j cloth and 2 x 1 micron sock filters but still getting through before I washed like this. I think it is fine particles from the feedstock but could be wrong 

It looks yellow but it is more brown really. the colour where the writing is is more accurate as the paper behind it near the bottom changes it in the photos.

[nigelb]

Nige, should the bromophenol blue turn yellow or turquoise?

At which stage of the soap test does your question relate Julian?

[Julian]

The point where you stop adding acid.

[nigelb]

Yellow.