I had a chance to visit the Springboard Biodiesel factory a couple weeks ago to film the new T76 dry wash tower.

While I was there, I had Daniel, the chemist there, let me video him doing a soap test and explaining how it works.

Here's the link to the video:
http://www.youtube.com/watch?v=tzIXwL9GKuQ

This is the method he followed:

The Method:
==========
1- Add 10 mL Biodiesel to 100 mL Isopropyl Alcohol
2- Add 15-20 drops Bromophenol Blue
3- Add measured amounts of Hydrochloric Acid until it turns yellow
4- Record the number of milliliters (mL) used

Calculating Soap Content:
=====================
mL of Acid Used x conversion factor = ppm's of soap

Conversion Factor:
=====================
NaOH reacted Biodiesel - 304
KOH reacted Biodiesel - 320

ASTM Acceptable Soap Levels:
=============================
NaOH Reacted Bio - No more than 41 PPM
KOH Reacted Bio - No more than 66 PPM

Thanks to Producer and Arbor Biofuels for all the great information on soap testing. I utilized their methodology & information to put the video together.

Here's the link to the soap testing kit supplies he used to do the soap test in the video:
http://utahbiodieselsupply.com/soaptestkit.php

Enjoy!
-Graydon

Here's the thread where producer discusses the ASTM limit equivalents.
http://biodiesel.infopop.cc/ev...21001332/m/987106011

-Graydon

So then...To pass with KoH, I should not need to add more than 0.2mL of acid??? (320x0.2)=64ppm.

Need a smaller pipet than a 10mL if that is the case.

Yep. That's how it works...
-Graydon

If 0.2mL is the maximum allowable acid to pass KOH soap content, then a pipette with an accuracy of less than 0.2mL would be needed...say 0.1 or 0.05mL accuracy. I've not been able to find an affordable pipette with that accuracy. I guess one could calculate the weight of 0.2mL and then see how many drops it takes to get to 0.2. If not done accurately this could lead to a large error in soap content.

Graydon, how do you measure less than 0.2mL? Am I making this more difficult than it needs to be? The process looks easy enough and the videos that you put together are great, but being able to measure 3000+ ppm on the video using a 10mL pipette is one thing, but being able to measure down to less than 0.2mL is tough without being able to measure miniscule amounts. Can a different acid concentration be used?

Sorry if i'm making too much of this....

While the pipette is a 10 mL pipette, it's got graduations all the way up it that are a lot more accurate than your average syringe.

Kind of like these:


That said, yep, you want a pretty accurate pipette.
-Graydon

The pipette he was using in the video was accurate to 0.1 accuracy.

I'll have some up on my site pretty soon.
I do have the soap test kit that has pipettes in it that are that accurate as well, but I'll be getting a pipette pump & pipettes up soon that can be purchased separately that'll work great for the test.

Here's the link to the soap test kit that I do have up so far.
http://www.utahbiodieselsupply.com/soaptestkit.php

They're accurate to 1/10th of a mL.

Graydon,

Great video as always, thanks for sharing with us.

Two things, it was noisy in here so I might have missed it but did he mention how pure the alcohol needs to be and it looked green to me not yellow. I was expecting a much more yellow result.

Arbor recommends using as pure of alcohol as possible.
If you can get 99% pure, all the better.

He said in the video 91% or better though. But the purer you can get it the better it will be.

The light in the room kind of threw off my video camera so it came through looking more greenish than yellow. But, it was really yellow.

I'm doing another video with some more footage from that day where he did the test on some finished fuel and it came through looking really yellow (I think we turned off the flourescent lights above us and that did the trick).

-Graydon

Arbor recommends using as pure of alcohol as possible.
If you can get 99% pure, all the better.

We did a little digging and found some to offer that's labelled 100% pure.
http://www.utahbiodieselsupply...micals.php#isopropyl

I didn't think they made it that pure, but, apparently so...

He said in the video 91% or better though. But the purer you can get it the better it will be.

The light in the room kind of threw off my video camera so it came through looking more greenish than yellow. But, it was really yellow.

I'm doing another video with some more footage from that day where he did the test on some finished fuel and it came through looking really yellow (I think we turned off the fluorescent lights above us and that did the trick).

-Graydon

I got some 99%+ pure isopropyl special order from a pharmacy. It can now be found in some grocery stores' pharmacy section.

I finally got the pipettes up...

http://www.utahbiodieselsupply.com/pipettes.php

-Graydon

Do i need a magnetic stirrer to do this test or does using it make it easier?

It's not absolutely necessary to use a magnetic stirrer, but it sure makes it easier to do the test.

Hello Graydon, For us poor boys who can't throw for a an accurate pump how would htis work?
Making a stock solution 500 ml alcohol and 1ml of acid. With each soap test you could pull off 100 ml of stock solution to run your test. Almost the same way we do the 1% titrate for raw oil solution.

I'm not sure. I'll defer that one to GCG or others here that are more experienced with it.

I know that everyone I've talked to recommends getting the 0.01 N Acid Solution because the numbers we're working with are so small & you want to be extremely accurate (41 ppm just isn't that much).

Wal,

I'm not sure I really know your question.

To be clear:

The 100% pure Isopropyl Alcohol or Isoproponal is used to dissolve the oil/biodiesel sample (It has to dissolve it COMPLETELY, that is why the ratio of alcohol to biodiesel is approximately 10 to 1. This way you can be sure there is enough alcohol present to break apart the biodiesel and get a good mixture)

We also use the 10 ml of biodiesel because it means we use approx. 10 grams of biodiesel and in chemistry every thing is done by weight so by using 10 grams of biodiesel we ensure easier math much like using the metric system.

Lastly we use 10 ml of biodiesel so that the test requires less chemicals (in this case acid) to completely neutralize the soaps present in the mixture - a larger sample of biodiesel would require more acid and this makes the whole test take longer and cost more. (note on the flip side if you use to little of a sample of biodiesel you run the risk of an inaccurate test so its a bit of a balancing act)

As to the Acid, you mention using 1 ml of acid and 500 ml of alcohol as a stock solution;
many labs have stock solutions which match there particular test closely so they have less work to do however in this particular case I would need to know what the Molarity or Normality is of the 1 ml of HCl and then perform a calculation to determine the stock solutions strength and then develope a different equation specific to this and the number of milliters used.

For example if I assume your using 0.01 N HCL like the videos then the stock solution would be in a sense pre-titrated to .2 ml of 0.01 N HCL per every 100 ml of alcohol used so in effect if your biodiesel sample was yellow even after adding 15 drops of bromophenol blue - then you would know that the soap concentration was less than 50 ppm.

This might be a fine GO-NO-GO test...

GCG

Let me just confirm, in the case of HCL 0.1 Normality is the same as having 0.1 Molar solution right?

As you have 1 mole of H+ ions....