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How to track the KOH?
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Hello! I was wondering if anyone had any ideas on how to track the KOH catalyst as it goes through the biodiesel making process. I know it supposedly sticks to the glycerin and falls to the bottom, but is there a way to test that? And, similarly, test how much catalyst (if any) is in the biodiesel itself? Also, what exactly happens with the catalyst as it separates the fatty acids from the glycerin. Where does it go, does it break apart, how does it separate?

I would love to use the GC on this, but unfortunately, ours can't handle anything with a boiling point above 200C Frown

Any ideas would be appreciated, Thanks!!
 
Registered: April 11, 2012Reply With QuoteReport This Post
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catalyst- a substance that causes or accelerates a chemical reaction without itself being affected.

reagent- a substance participating in a chemical reaction, especially one used to ...produce another substance.



 
Location: coldest N.America | Registered: May 03, 2005Reply With QuoteReport This Post
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DearMr Galt,
I am confused by your reply. Are you attempting to answer some or or all of Alison's Questions or are you just posting random tidbits of useful information?
If it is the former can you be more specific as to which of Alison's questions you were attempting to answer and how you feel your post answer it/them.
If it is the latter it would be better to start a new thread.
quote:
Originally posted by john galt:
catalyst- a substance that causes or accelerates a chemical reaction without itself being affected.

reagent- a substance participating in a chemical reaction, especially one used to ...produce another substance.
 
Registered: October 26, 2010Reply With QuoteReport This Post
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You ask tough questions. Part of the KOH quickly makes soap with the free fatty acids and is removed from the reaction so the soap doesn't act as catalyst. So all the KOH doesn't act as catalyst.
 
Location: Texas | Registered: April 27, 2011Reply With QuoteReport This Post
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As wesley pointed out, some of the KOH turns into soap. If you look up "soap titration" and perform this test on the glycerin you can get an idea of how much potassium is in the glycerin, the calculations for the soap test assume all of this potassium is soap, though some could be un-reacted KOH.

I believe it is possible to do a titration to find out how much of this is KOH. You can set up a titration like you would with your oil before the biodiesel reaction, only add the glycerin instead of the oil. The solution will turn pink/purple(if you are using phenolphthalein). Instead of titrating 1g/L KOH and water, titrate with 0.1N HCl (this is part of the soap titration process). When the solution turns clear, you have supposedly reacted all of the KOH, but not the soap. If you do this in conjunction with a normal soap titration, you can subtract the KOH portion of from the normal soap titration. This way you know how much KOH and soap there is.

I have not done this, but this is the way I understand the theory.
 
Registered: September 16, 2006Reply With QuoteReport This Post
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All right then it has been several hours and there is not much responses. Alison you are asking a similar question to the one I asked 5 years ago or so. I asked where does the sodium go? I asked a Dr of chemistry and he didn't know right off hand. The KOH (a base) reacts relatively quickly with free fatty acids ( an acid) to make potassium soap (a salt) plus water. The old rule an acid plus a base makes a salt plus water. But, In saponification a triglycerol fatty acid(vegetable oil, lard, grease) plus KOH plus water plus a little heat also makes a potassium soap plus glycerol. So in our type of reaction soap is formed by two different path ways. Generally, the drier the better. KOH plus dry, anhydrous, with out water, methanol (alcohol) makes methoxide plus water. Water decomposes methoxide. There's an equilibrium established. The potassium in a way is in solution with methanol/methoxide/water solution. About 2/3 of the unreacted methanol ends up in the glycerine layer. About 1/3 of the unreacted methanol ends up in the crude biodiesel layer in a successful reaction. I expect that other than the potassium that has formed soap, the remainder is equally distributed in the methanol. But methanol is infinitely soluble in glycerine and methanol is miscible in biodiesel so glycerine follows methanol a little into biodiesel. But the methanol carries some potassium with it into the biodiesel. I remove potassium from my biodiesel by boiling off excess alcohol, then using magnesium silicate to adsorb the more polar compounds from my biodiesel product. But I only make batches less than a liter. I wouldn't put biodiesel into a GC unless I was sure it was pure. It might foul an expensive column. Oh yes, when a methoxide ion reacts with the triglyceride it makes biodiesel a diglyceride and regenerates the methoxide ion from a nearby methanol molecule.
 
Location: Texas | Registered: April 27, 2011Reply With QuoteReport This Post



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quote:
How to track the KOH?

WesleyB, you helped me in clearing my doubts..You gave an excellent explanation..
 
Location: 560 Mill Race Rd, Superior, NE 68978 | Registered: April 25, 2012Reply With QuoteReport This Post
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quote:
Originally posted by john galt:
catalyst- a substance that causes or accelerates a chemical reaction without itself being affected.

reagent- a substance participating in a chemical reaction, especially one used to ...produce another substance.


Correction:
A catalyst can be used in a reaction but must be returned to its original chemical composition, so a catalyst can be affected mid reaction.

KOH is a catalyst in transesterification, not a reagent. OH does deprotonate methanol to make methoxide. Methoxide attacks the ester carbocation and the complex collapses to boot out glycerol. The glycerol is missing a proton and since it is existing in a mostly aprotic environment, it easily deprotonates the previously produced water, thus regenerating the catalyst.
 
Location: Dunnville, ON | Registered: May 01, 2012Reply With QuoteReport This Post
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Are you sure the glycerol missing a proton doesn't deprotonate an adjacent methanol molecule to regenerate methoxide? Since there is so little water present relative to the concentration of methanol. Thanks
 
Location: Texas | Registered: April 27, 2011Reply With QuoteReport This Post
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It could very well, but methanol has such a strong conjugate base that it would need to be used for transesterification right away. Eventually hydroxide is going to be regenerated, either by glycerol or free methoxide.
 
Location: Dunnville, ON | Registered: May 01, 2012Reply With QuoteReport This Post
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