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Soap Calculation question
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Hi,

Ive seen some of the soap testing vids that are about and they suggest using the formula:

304*mL of 0.01HCL = soap ppm.
(for using 10mL of sample and NaOH soaps)

Firstly, if there is any residule catalyst in your biodiesel will this not throw off the calc?
This would be due to neutralizing the catalyst first, before the soaps start getting neutralized.

Would this formula work on testing the amount of soaps in your glycerin or waste water which are rich in catalyst and soaps?

To get better accuracy could we titrate with 0.001N HCL? (just use a whole bunch more).

To test for soap in wash water or glycerin do we have to use the phenolphthalein red first method?
 
Registered: March 02, 2009Reply With QuoteReport This Post
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Reece,

Actually you are correct and your idea is on track with the true AOCS methodology for determining the exact amount of soap.

However for most intents and purposes the amount of residual catalyst SHOULDN'T be that significant so the need to first bring the solution to a pH of 7 isn't really all that important (this is because any catalyst in the presence of oil or biodiesel will form soap, they are not inert).

Having said this I explain it more clearly in my soap test instructions so the user actually learns what is going on during the soap test.

When explaining to my 6 year old son once - I asked him if he actually understood what I just told him. He answered immediately saying, "sure Dad, its like two really tiny armies fighting, ones blue and the others yellow. First the yellow acid army has to over come the front line troops and then after that they have to defeat all the other soliders before they can give the yellow (flag) signal."

What other soap test instructions and videos leave out is the simple fact that soap isn't really basic (its relatively neutral) since the Free Fatty Acid is bound to a metal ion like Sodium or Potassium.

What HCL does in the soap test really, is break the Sodium bond and thus free's up the two ions and when all the soap is broke down the solution is completely into the ACIDIC portion of the pH band: around 3-3.5 pH.

Interestingly Bromophenol blue is the strongest dichromatic chemical which exhibits this two color nature based on concentration and pH. Its very useful in this case because it specifically doesn't turn yellow until well below a pH of 4.6 - this is what allows it to be fairly accurate in measuring the soap content because if it changed as soon as the catalyst was neutralized and the solution was at a pH of 6-7, then the complete soap molecule would still be floating around in the solution.

Additionally, Free Fatty Acids are a relatively weak acid so these acids by themselves don't drive the solution's pH to the necessary 3.5 to 3 (for a color change) since if they did, then a portion of the soap could still be in the solution undissociated and once again you won't have an accurate measurement of the soap content.

By using an indicator which forces the solution to go well beyond a pH of 5, we ensure an acid concentration sufficient to completely dissociate the soap molecules and also have a close approximation of that very same soap, based on the amount of acid necessary to achieve this splitting.

A little long - that's why I don't usually go into it, but you asked. Wink

GCG

This message has been edited. Last edited by: GCG,
 
Location: Michigan | Registered: May 08, 2007Reply With QuoteReport This Post
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Yes you can use lower concentrations to determine more accurately the low soap concentrations as well as using less or a smaller sample volume (e.g. from 10ml of the biodiesel to 1 ml of the biodiesel).

Keep in mind though that chemist tend to shy away from small samples do to measurement error (random error) unless the tool being used is design to take samples of very small quantities.

Also you can do a soap test on glycerin similarly but yes you should first take the solution to a pH of 7 and then start counting the amount of acid used to turn the solution from blue to yellow.
NOTE: You should choose another indicator like Bromothymol Blue or perhaps Phenol Red since Phenolphthalein changes to high at a pH of 8.3 and is difficult to see with a glycerin sample...

Keep in mind that glycerin may require slightly more alcohol to fully dissolve the sample quantity - typically the 100 ml of Isopropanol or Isopropyl alcohol recommended in the soap test method and the 10 ml sample conforms to the 10 to 1 rule. Often we cheat this in order to save on isopropyl alcohol. You may need a slightly higher ratio for a 10 ml glycerin sample.

Hope that helps...

GCG
 
Location: Michigan | Registered: May 08, 2007Reply With QuoteReport This Post
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By the time your son is 12 he will be a biodiesel expert!

Thanks for the awesome response, was exactly the answers I was looking for. I like to know a little bit of the science behind it rather than just accepting formula and applying it blindly. The answer makes good sense. Glad I now have that one cleared up Smile
 
Registered: March 02, 2009Reply With QuoteReport This Post
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That was a great explanation!!!!
I loved it!
-Graydon




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Location: Utah | Registered: October 08, 2004Reply With QuoteReport This Post
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Yep, thanks for taking the time to post that explanation.

But now I feel dumber than a 6 year old Confused
 
Location: Somewhere in the swamp... | Registered: April 03, 2008Reply With QuoteReport This Post



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Superb explaination on this sometimes confusingly described test!


--------------------------
www.doctordiesel.co.uk


"As for testing, know now that----
only mechanisms built by bunglers require testing.---
Properly-built machines work properly." 'Doc' Smith.
 
Location: Swansea, U.K. | Registered: March 09, 2002Reply With QuoteReport This Post
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With the soap testing method on the UBS site they multiply the ml of HCL used to bring the test soln to yellow by 304. Is this number used for both NaOH and KOH as catalyst?

Thanks


Dana Knight "dckfly"
Boulder, CO

Chevy Silverado Duramax
3 VW TDI (wife and friends)
 
Location: Boulder, CO | Registered: May 13, 2007Reply With QuoteReport This Post
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304 for NaOH and 320 for KOH
 
Registered: March 02, 2009Reply With QuoteReport This Post
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Thanks, it's not a big difference but the more accurate the better.


Dana Knight "dckfly"
Boulder, CO

Chevy Silverado Duramax
3 VW TDI (wife and friends)
 
Location: Boulder, CO | Registered: May 13, 2007Reply With QuoteReport This Post
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quote:
NOTE: You should choose another indicator like Bromothymol Blue or perhaps Phenol Red since Phenolphthalein changes to high at a pH of 8.3


GCG
Do you mean to say phenol red from a pool kit is an adequate indicator?

How can I make 0.01HCL from stock HCL? - 1L distilled water/1ml HCL?

I coulda been soap testing this whole time.

Brian


1996 K2500 4x4 6.5TD
 
Location: Southern Indiana USA | Registered: June 20, 2008Reply With QuoteReport This Post
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Brian,

I think you need bromophenol blue for soap testing. To make the .01HCL solution, look at the tutorial by girlmark http://www.biodieselcommunity.org/testingforsoap/. I made the stock solution as it reduces the potential for measurement errors. You then use a little stock solution to make the .01HCL solution. You don't need the full soap kit, but it would make things a little easier.
 
Location: Chambodia | Registered: December 31, 2007Reply With QuoteReport This Post



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quote:
Originally posted by Weldshop:
quote:
NOTE: You should choose another indicator like Bromothymol Blue or perhaps Phenol Red since Phenolphthalein changes to high at a pH of 8.3


GCG
Do you mean to say phenol red from a pool kit is an adequate indicator?

How can I make 0.01HCL from stock HCL? - 1L distilled water/1ml HCL?

I coulda been soap testing this whole time.

Brian


The easiest way I have found is this:
A .01N solution contains .01 (1/100th) moles of your solute. In this case the solute is HCl. The molar mass of HCl is 36.5g
36.5/100= .365 moles
Muriatic acid comes in different %, with the % indicating how much HCl is in it.

.365/b = c

b = % indicated on the bottle, ie 36% is written in as .36
c = number of grams of muriatic to use per liter of water.
Always add acid to water not water to acid. So you'll be adding half a liter or so of water to the container first, then the muriatic, then finish filling to the 1L mark with more water.

For example,
My muriatic acid says 31.45% on the bottle
.365/.3145= 1.16g so I use 1.16g muriatic acid to create a .01N solution.
 
Location: central virginia | Registered: March 13, 2008Reply With QuoteReport This Post
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ok, thanks
but it doesn't help me.
I know someone with a tote of HCL.
It doesn't say what %age it is. Only 20* Balm Inhibitor.

I'd guess it's pretty potent. The tote fumes off when open.

But what about the phenol red GCG mentioned? This stuff is everywhere for $2.88 a bottle.

Maybe I'll just bite the bullet and get the kit. I'm doing waterless settling right now.

Brian


1996 K2500 4x4 6.5TD
 
Location: Southern Indiana USA | Registered: June 20, 2008Reply With QuoteReport This Post
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weldshop,

He was referring to when you need the solution to be close to ph7 before doing a soap titration. If the solution is above ph 7 there is catalyst in your biodiesel and therefore if u do a soap calculation using the normal ml acid* 304 or 320 it will be incorrect, due to neutrolizing the catalyst not the soaps.

So therefore u use an indicator like phenol red or something that changes colour near ph 7. Washed biodiesel assumes no catalyst so we just do soap titration straight away.

If you want to find the ppm soap in your wash water or glycerine you need to start at ph 7. Initially both these will be high due to all the catalyst so u need to bring down to 7 to ensure catlayst is neutrolized. Then u can do ur bromophenol blue soap titration..if indicators get confusing just buy a pH meter.. im going to get one soon to save always using up indicators and get more accuracy..

using phenol red instead of phenolphthaline for wvo titrations also gives slightly lower titrations due to the color changing point of phenol red being of lower ph than phenolphtaline
 
Registered: March 02, 2009Reply With QuoteReport This Post
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Reese123,
That explains alot. I misinterpreted what I was reading.
In fact, I just had to read what you posted more than twice.

I understand more about the soap titration now.
It also enlightened me more on the WVO titration.

Very well written, Sir.

I was hoping to build the test console from store bought chemicals, but for now, I should get the right stuff and learn how it works. It's only like $30.

I also think having a ph meter is an asset to more control.

I'm staying tuned...

Brian


1996 K2500 4x4 6.5TD
 
Location: Southern Indiana USA | Registered: June 20, 2008Reply With QuoteReport This Post
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You don't need the Kit - Just go to you local chemical store and get some concentrated HCL to make your soln, Bromophenol blue, and a 5 ml syringe or 5 ml pipet with pipet pump. I would go with the pipet since you will end up going throught a number of syringes. You can get the hardware on the internet but buy the chemicals local since they charge you an arm and a leg to ship chemicals. That's what I did and it is all fairly basic. The hardest part is making the .01 M HCL soln - just follow girlmarks instructions poster earlier. Oh, a stiring rod helps too or a mag stirer if you want to get fancy.

Have fun!


Dana Knight "dckfly"
Boulder, CO

Chevy Silverado Duramax
3 VW TDI (wife and friends)
 
Location: Boulder, CO | Registered: May 13, 2007Reply With QuoteReport This Post
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Weldshop it took me a little to catch on, hence why i posted the thread for some clarity..got it cleared up now after reading GCG post a few times and letting it digest over night.

I also noticed in the AOCS methodology they use 0.1 molar instead of 0.01 molar HCL. Im guessing they did this because if u were calculating the ppm soaps in glycerine or wash water, you would be titrating all day (10 times as much) with the 0.01molar compared to 0.1M.

dckfly I scored a really old magnetic stirrer for free and theyre fantastic for more instantaneous colour changes.
 
Registered: March 02, 2009Reply With QuoteReport This Post



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Added to fav's, thanks reese123.


1996 K2500 4x4 6.5TD
 
Location: Southern Indiana USA | Registered: June 20, 2008Reply With QuoteReport This Post
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quote:
Originally posted by Double D:

The easiest way I have found is this:
A .01N solution contains .01 (1/100th) moles of your solute. In this case the solute is HCl. The molar mass of HCl is 36.5g
36.5/100= .365 moles
Muriatic acid comes in different %, with the % indicating how much HCl is in it.

.365/b = c

b = % indicated on the bottle, ie 36% is written in as .36
c = number of grams of muriatic to use per liter of water.
Always add acid to water not water to acid. So you'll be adding half a liter or so of water to the container first, then the muriatic, then finish filling to the 1L mark with more water.

For example,
My muriatic acid says 31.45% on the bottle
.365/.3145= 1.16g so I use 1.16g muriatic acid to create a .01N solution.


Thanks for that clear and flexible explanation/method.


mathematical elegance -- desired result achieved with minimal complication
 
Location: Manchester UK | Registered: June 03, 2003Reply With QuoteReport This Post
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