I know its expensive, but I've read that many commercial plants use it for the acid stage because when KOH is used as the base catalyst the salt byproduct is a fertilizer.

Does anyone use this? Is it just a matter of adjusting the multiplier in the dkenny method, or is it not that simple?

FG
-poshporic acid is used to split the glycerin from the byproduct. the only acid I know that will esterfy the ffa's is sulfuric. Tom

Phosphoric acid would work just fine for AE if you could get it in concentrated form. Most of what I have seen has been diluted with water. Water can slow down and even stop the AE process.

Eurocab,
I'm guessing 85% is considered diluted, right?

I believe the 15% water would hinder the reaction. I wonder if you could use a molecular sieve to soak up the water? That would definitely make the waste product more usable.

quote:

Originally posted by Eurocab:
I believe the 15% water would hinder the reaction. I wonder if you could use a molecular sieve to soak up the water? That would definitely make the waste product more usable.

If you removed the water wouldn't the acid come out of solution, meaning that any liquid coming out of the other end would be no more than 85% in concentration, and inside the sieve would be water and H3PO4 crystals?

I guess even if it did come out in the sieve you could dry the sieve media and run methanol through it to put it back into solution.

I am not sure. I just threw the idea out there. It might be an interesting experiment, but I would want more information before trying it.

I am not aware of any commercial plants where Phosphoric acid is used for up front Esterification of high FFA feedstocks. Plants that I have worked with find it would just be far too expensive and as mentioned above the water content would be a problem to the reaction.

As Biotom says above, Phosphoric acid is used by some plants for the Glycerin/ FFA separation and even then it is quite a bit more costly than using Hydrochloric acid.

Further to what I have aready said,if you where to use phosphoric acid, how wold you prevent the phase separation of the salt,glycerin and ffa's When you add phosphoric acid to the byproduct and mix it up, the whole mixture curdles, then it is allowed to sit, and the three phases separate, white salt on the bottom, a layer of methanol and glycerin, and ffa's on top I don't see any way this could be used in the AE process. If you try, let us know how you make out. Tom

quote:

Originally posted by Fuzznag:
I am not aware of any commercial plants where Phosphoric acid is used for up front Esterification of high FFA feedstocks. Plants that I have worked with find it would just be far too expensive and as mentioned above the water content would be a problem to the reaction.

I could be wrong. I only remember reading this in one source which said:

quote:

Acid catalysts are more commonly used for the esterification of free fatty acids. The typical choices include sulfuric acid and phosphoric acid.

...and...

quote:

... if phosphoric acid is used, the resulting salt has value as a chemical fertilizer.

... but if you've never heard of this perhaps it is not accurate.

quote:

Originally posted by Biotom:
Further to what I have aready said,if you where to use phosphoric acid, how wold you prevent the phase separation of the salt,glycerin and ffa's When you add phosphoric acid to the byproduct and mix it up, the whole mixture curdles, then it is allowed to sit, and the three phases separate, white salt on the bottom, a layer of methanol and glycerin, and ffa's on top I don't see any way this could be used in the AE process. If you try, let us know how you make out. Tom

Forgive my ignorance if I'm wrong, but my understanding is that in the acid phase the only byproduct is water, and when you move on to the base phase you use enough catalyst to convert the Phosphoric Acid into Potassium Phosphate (the fertilizer) plus your base catalyst amount.

As such, the only way to separate the glycerin byproduct would be to neutralize the base lye and acidify the byproduct using any number of acids (not just phosphoric). If you do use Phosphoric acid, the byproduct is once again potassium phosphate, and the salt layer would be mostly that plus the undissolved excess Phosphoric Acid.

Again, this is my understanding based on research that does not include JTF

Here is a link to a discussion about 4 years ago.

http://biodiesel.infopop.cc/ev...=131108959#131108959

Neutral explains that the reason sulfuric acid is used is it is much cheaper and more concentrated than phosphoric acid. Now if you can make the phosphoric acid more concentrated maybe it would be worth a try.

I guess, you just have to try it, I have used phosphoric acid to separate the glycerine, so I now how that works, as for ae, the acid with the methanol turns the ffa's to biodiesel. the fact that there are ffa's in the wvo, would indicate that glycerides are also present and if so, you could expect the reaction as I stated above. Tom

quote:

Originally posted by Biotom:
the acid with the methanol turns the ffa's to biodiesel. the fact that there are ffa's in the wvo, would indicate that glycerides are also present and if so, you could expect the reaction as I stated above. Tom

I think, and I could be wrong, that this does not apply to an acid stage. The glycerin byproduct of the base phase contains the catalyst base, glycerin, and saponified ffa in solution. By acidifying it, it comes out of solution as you suggested. In high FFA oil however, there is no soap yet. Unlike the caustic stage the ffa does not turn into soap but into esters, as you point out, with a byproduct of water. The amount of glycerin in the byproduct stream, however, should be unaffected.

I mangled that explanation, but I hope you can derive what I mean.

I asked around and a size 3A Molecular Sieve could dessicate a solution of Water/MeOH/Phosphoric Acid to a solution of ~90% MeOH / ~10% Phosphoric Acid / Trace Water. One could then regenerate the sieve by drying it. The sieve will hold about 20% of its weight in water, so a 5kg sieve could hold a liter of water, and dessicate about 41 liter or MeOH/H3PO4/H20 to a 10% H3PO4 solution. At which point the sieve would have to be dried before it could be reused.

Of course, I have no idea what the difference in value is between Potassium Sulfate and Potassium Phosphate as byproducts, so I haven't really answered anything. Still the speculation has been fun

FG
-I plead no contest But if neutral says it can be done, then it can be done. I learn everything I know from him.tilly and mickey mouse way back when Tom

This message has been edited. Last edited by: Biotom,

Furious George
-OK, I'm going to do a test batch using posphoric acid tomorrow, result will be posted the following day. I have consentrated phosphoric acid, but not sure what the regent is. I will use twice as much p acid as I do S acid. Any other requests before I start this test? Tom

quote:

Originally posted by FuriousGeorge:

quote:

Originally posted by Fuzznag:
I am not aware of any commercial plants where Phosphoric acid is used for up front Esterification of high FFA feedstocks. Plants that I have worked with find it would just be far too expensive and as mentioned above the water content would be a problem to the reaction.

I could be wrong. I only remember reading this in one source which said:

quote:

Acid catalysts are more commonly used for the esterification of free fatty acids. The typical choices include sulfuric acid and phosphoric acid.

...and...

quote:

... if phosphoric acid is used, the resulting salt has value as a chemical fertilizer.

... but if you've never heard of this perhaps it is not accurate.

FuriousGeorge
I did not say I have never heard of it, I said the plants I have worked with don't use it mostly because of cost. But also because the water does cause some issues in the reaction, more so than using sulfuric. So sulfuric is cheaper and easier to use from what I have seen.

There was a discussion earlier about using aqueous NaOH or aqueous KOH.

The little water with the base was not hardly enough to affect the overall reaction.

I would assume the same would be true with an aqueous acid.

However, if you can purchase the acid in salt form... perhaps that would even be better.

keelec
-the flake koh I use is 91%, the other 9 % is moisture. in the acid stage, the sufuric acid is 93% with the remainder being water. We have to be carfull with the amount of water that is carried into the ae process, this reaction is much more sensative to water than the transesterfication process. The ae process will only esterfy 5% of the ffa's with a water content of 5% by weight (ISU report on easerfication) Tom

you dont use phosphoric acid because its a weak acid. Sulfuric acid is a very strong acid. Acid strength is determined by how easily it donates its H+ ion. For the AE a strong acid catalyst works extremely well. Weak acid will work, but not as well.
Its like using Ca(OH)2 instead of KOH or NaOH, yes its a base but it is weak compared to KOH or NaOH.