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pH of Glycerin ???
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tried searching but got to much non relevant info to sort through.

Anyone know what the pH of glycerin is as it comes out of a reactor that uses KOH? (no acid stage used).

Does is vary from batch to batch? and if so, how much would you guess?

Thanks,


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Registered: March 09, 2006Reply With QuoteReport This Post
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Pure glycerin in water is a weak acid, as is methanol. Potassium soap is basic. There are variables between batches. When I measured the pH of Lye derived glycerin layer it was greater than or equal to to 10. How accurate do you need this information?
 
Location: Texas | Registered: April 27, 2011Reply With QuoteReport This Post
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Accuracy? To the whole number I guess will be good enough.

Just need to know if it comes out between 8 and 9 or 9 and 10, or whatever. I was hoping it was going to come out above 12.


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Registered: March 09, 2006Reply With QuoteReport This Post
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quote:
Originally posted by Murphy:
tried searching but got to much non relevant info to sort through.

Anyone know what the pH of glycerin is as it comes out of a reactor that uses KOH? (no acid stage used).

Does is vary from batch to batch? and if so, how much would you guess?

Thanks,

It will be affected by the titration amount and also what sort of base amount you use.

Excess catalyst ends up in the glycerin layer along with the soaps, both will be basic and as such it will directly affect the pH of that layer.

The amount of methanol and water will also have a bearing on the pH.

It is going to be a pretty difficult number to predict due to so many variables but a few test batches with high and low catalyst amounts and high and low FFAs etc. should give you some high and low limits to know which ball park you are in.
 
Location: East Yorkshire | Registered: January 14, 2006Reply With QuoteReport This Post
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Regardless of the titration number the glycerin will always be 20-25% away from full soap unless it is with new oil where the percentage drops to around 15%. The reason for this is that the acid numbers have been dealt with in the titration values, regardless of how high or low those numbers are and what remains is the part that has not been turned into complete soap (20-25%).

Fully cured soap's PH is usually between 9.5-10.5 where done right, so that would mean that the fully demethed by-product would be slightly more acid rather than alkaline as it contains more saponifiable ingredients, and by definition that means closer to neutral (7) or slightly higher to around 8 and when it reaches completed soap that number moves toward the more alkaline numbers.

That said, you can intentionally MAKE it high alkaline, like what happens in "lye soap", by over catalysing it so that it is "hot" or caustic. Move your soap numbers to 30% caustic and that should do it. I do not recommend using it on your skin though as it could result in a chemical burn. Be a pretty harsh degreaser though.

What application do you plan on using it for?

HTH



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Location: :-) Great White North eh ? | Registered: December 10, 2004Reply With QuoteReport This Post
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quote:
Originally posted by Legal Eagle:
Fully cured soap's PH is usually between 9.5-10.5 where done right, so that would mean that the fully demethed by-product would be slightly more acid rather than alkaline as it contains more saponifiable ingredients, and by definition that means closer to neutral (7) or slightly higher to around 8 and when it reaches completed soap that number moves toward the more alkaline numbers.



I think you are confusing alkalinity with pH, they aren't quite the same thing.

Murphy
The pH of your glycerin is going to be in the 10+ range from the leftover KOH. The more water present in your oil the less KOH will remain (soap reactions) and the pH may be slightly lower meaning you will have a range of pH values. I wouldn't expect it to drop below 10.

edit:
To answer your question, using dry oil I would imagine you would get a pH of 12 yes.
 
Registered: February 25, 2010Reply With QuoteReport This Post



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Hi folks,
Thanks for all the info.

I'm attempting to produce humic and fulvic acid concentrate from leonardite (lignite) coal via the potassium hydroxide alkaline extraction process.

Humic acids are long chain carbon molecules. As I understand it, glycerin is also a long'ish chain carbon molecule.
Since glycerin is normally a waste product and it has the KOH and proper (high alkalinity) pH already, I figured it might be a nice marriage to use it as the solvent media for the extraction process. Just guessing here as chemistry has never been one of my strong points.


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Registered: March 09, 2006Reply With QuoteReport This Post
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The PH scale goes this way; 1-6 = acidic, 7 is neutral and 8-14 is alkaline. Caustics, such as NaOH and KOH are alkaline. Therefore if you are looking for a solution that has a high PH you are in essence looking for an alkaline solution.
You want a solution whose PH is through the roof? saturate water with NaOH, just don't stick any body parts in it or you will end up with an alkaline burn.



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Location: :-) Great White North eh ? | Registered: December 10, 2004Reply With QuoteReport This Post
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quote:
Originally posted by Legal Eagle:
The PH scale goes this way; 1-6 = acidic, 7 is neutral and 8-14 is alkaline. Caustics, such as NaOH and KOH are alkaline. Therefore if you are looking for a solution that has a high PH you are in essence looking for an alkaline solution.
You want a solution whose PH is through the roof? saturate water with NaOH, just don't stick any body parts in it or you will end up with an alkaline burn.


This is a fairly common misconception. pH of 8+ is BASIC or CAUSTIC not alkaline. Alkaline has a different meaning

http://en.wikipedia.org/wiki/Alkalinity

It is generally reported in equivalent amounts of carbonate...

Another way to think of it is that the pH is the strength of the acid/base and the alkalinity is the concentration of all bases... much like how acid # or titration gives us the amount of all acids in oil. Although that's a little over simplified.

The confusion here seems to be that since there are unsoponifiables present they will change the pH... this isn't quite true. The pH of the glycerin will depend on the 'strongest' base present. Since there is KOH present that will be the pH controlling factor. However the more soaps present the higher the alkalinity will be correct. The pH will change very little with KOH concentration in our glycerin so long as it is present. If there is enough water to make soap and completely use up remaining KOH then the next strongest base will control the pH number. This would be soaps I would imagine with pH values in the 10 range.

Murphy I know almost nothing about coal chemistry but glycerin has the same carbon length as propane if that helps at all.
 
Registered: February 25, 2010Reply With QuoteReport This Post
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I read humic acid is insoluble in mineral acids AND alcohols. So extracting humic acid with glycerin a poly alcohol might be a problem. I've just looked it up this minute. I'll think about it.
 
Location: Texas | Registered: April 27, 2011Reply With QuoteReport This Post
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Murphy,

I have tested a ton of different BDG from different sources. The pH seems to be between 10 and 10.5 in most cases. I have had a few samples where the pH was near 12, and they have been from bio-pros and had undergone the acid stage. BTW... This is with BDG that has had the methanol removed.

I have found that the pH of the BDG will keep falling to 10.5 as you add a caustic/water solution until which time everything saponifable left in the BDG has been turned to soap. At that point the pH will climb quickly. Which falls in line with what BWilder is saying about the "Strongest base".

quote:
Originally posted by BWilder:
The confusion here seems to be that since there are unsoponifiables present they will change the pH... this isn't quite true. The pH of the glycerin will depend on the 'strongest' base present. Since there is KOH present that will be the pH controlling factor. However the more soaps present the higher the alkalinity will be correct. The pH will change very little with KOH concentration in our glycerin so long as it is present. If there is enough water to make soap and completely use up remaining KOH then the next strongest base will control the pH number. This would be soaps I would imagine with pH values in the 10 range.


The rage for saponifiable ingredients I have found is somewhere between 11% and 35% although I have seen higher and lower.

In the case where the pH of the BDG is higher than 10.5 there seems to be nothing left to be saponified. This falls in line with what BWilder said about the water, as I have only seen the pH being higher than 10.5 with BDG that has undergone the acid stage during biodiesel production.

<-- Because of the water created during the acid stage?? BWilder??

This is why a SAP test is important when using BDG to make soap, once all saponifable ingredients have been turned to soap the pH will climb quickly making the soap caustic hot and dangerous. Undersaponified and the soap can leave a greasy feeling when used and could possibly go rancid over time -- especially if other whole oils are being added. The maximum the soap should be allowed to be under-saponified is around 6% -- Traditional soapers do this and call it super-fatting or lye discounting. They do this to keep their cold processed soaps safe and also to keep some of the raw whole oils in the soap. Whole oils such as Shea Butter are said to have other benefits as whole oils.


-Rick

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Location: S.E. Michigan | Registered: April 15, 2007Reply With QuoteReport This Post
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Hi Rick
The main point I was trying to make is that KOH and saponifiable material can be in glycerin at the same time. If this happens the pH will be controlled by the KOH present. Although your description of what happens as you add KOH/water when making soap essentially corresponds to this.

You do bring up a good point I didn't address though. Murphy asked about glycerin 'from the reactor' I assumed this was before demething and hadn't had water prewash or anything of that sort added. Both you and Legal are answering from a soap making perspective which is understandable.

Straight from the reactor is what I meant when I said a pH of 10 would be the minimum I would expect with very wet oil. The drier the oil to begin with the higher the pH I would expect with pH values of 12 or more with dry oil. Also during de-mething the pH will drop as the heat and any water present will cause the residual catalyst to be used up in soap making reactions and cause the pH to drop to that of the soap.

I do not know anything about the biopro to be honest but a higher demethed glycerin AFTER an acid stage is a bit surprising. Although if there are no saponifiable materials present too that would explain it as during demething the KOH would not be as readily reacted. Does the biopro dry oil between acid and base stages?
 
Registered: February 25, 2010Reply With QuoteReport This Post



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