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FuriousGeorge
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Feasibility of turning 85% H3PO4/H20 into X% H3PO4/Alcohol
I have no background in chemistry, so forgive me if this sounds ignorant.
Phosphoric Acid is typically found in an 85% Aqueous Solution (by weight, I believe).
One obvious solution would be to distill it and just add methanol, but I think i remember reading that bringing the H3PO4 out of solution will cause
the formation of polyphosphates. Is this true?
If so, someone suggested that a molecular sieve might work. Is there a sieve that would work to separate the H20 from a solution of CH3OH / H20 /
H3PO4 and get me at least a 10% Phosphoric Acid / Methanol Solution.
How feasible is this solution where cost per liter is an important consideration?
[Edited on 1-9-2009 by FuriousGeorge]
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DJF90
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100% orthophosphoric acid can be purchased (if you're lucky) or prepared by yourself (if you're not - See Brauer for details). This is a crystalline
solid which could then be dissolved in methanol to a 10% solution. Can I ask what this is for? I'm curious. Also, 3A molecular sieves should work fine
for dehydrating 85% H3PO4/MeOH.
[Edited on 1-9-2009 by DJF90]
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FuriousGeorge
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It's for a waste vegetable oil recycling application. I need it for the acid phase of an acid/base process. The base part uses KOH, so I'm trying to
determine if its worth using H3PO4 to get K3PO4 as a byproduct.
My understanding is that most people use Sulfuric Acid as the acid catalyst and end up with (I think) S2PO4 which is less valuable, but Sulfuric Acid
is cheaper by a factor of 3 or 4.
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DJF90
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You're way out with regards to the chemistry involved here. Using sulfuric acid will get you K2SO4, or KHSO4, depending on stoichiometry. Water is
produced as a byproduct in the reaction, so this suggests using anhydrous H3PO4/methanol is pointless - just use the required volume of 85% H3PO4 in
methanol. I doubt that K3PO4 will be the byproduct - you are more likely to get a mixture of phosphate/hydrogenphospate/dihydrogenphosphate.
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FuriousGeorge
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Sorry, I should have just said "Potassium Sulfate" rather than trying to remember the molecule offhand. In my defense I meant to say "S2KO4" which
would have just been a simple inversion error which i would have seen and corrected 
I was told that the reaction may not complete unless the Phosphoric Acid was anhydrous because water slows the reaction, and the extra 15% in addition
to the water byproduct would potentially cross some threshold where it would stop the reaction.
As far as the byproduct, why would K3PO4 not be the majority? I thought that:
3 KOH + H3PO4 -> 3 H2O + K3OH4
... and I read ...
| Quote: |
1. First Potassium di hydrogen phosphate will be produced
2. Further neutralization will take place then to form Di Potassium Hydrogen Phosphate
3. Then, finally Potassium Phosphate Tri Basic will be formed. |
What factors will result in more of #1 and #2 and less of #3?
[Edited on 1-9-2009 by FuriousGeorge]
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kclo4
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The others would form if you added to much acid, to little base, etc. If you added the correct amount, you'd end up with K3PO4, assuming you've given
it all enough time to react.
You can probably just heat up the 85% phosphoric acid to produce a higher concentration, you'll need a resistant container to heat it up in,
obviously. Don't do it in anything that will break or react.
Why not just use sulfuric acid? I highly doubt you will be able to cheaply purify any salt for what its market value is and actually make a profit
from such a byproduct.
Especially since it sounds like you are making biodesiel and it would be obnoxious to separate any crystals or liquid from the methyl esters and the
glycerin. This would require heating ($$) cooling ($$) and time ($$) to completely separate them and get a decent purity.
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FuriousGeorge
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Thanks for the response. i thought I'd read that distilling and 85% Phosphoric Acid solution would lead to the formation of other phosphates. Am I
wrong there?
| Quote: |
The others would form if you added to much acid, to little base, etc. |
Would it be more correct to say they would form if I added too little acid? If I added too much wouldn't I just have left over Phosphoric Acid, or is
it not that simple?
| Quote: |
Why not just use sulfuric acid? I highly doubt you will be able to cheaply purify any salt for what its market value is and actually make a profit
from such a byproduct. |
You're probably right. I was just trying to do the math because I'd read in a few places that this was sometimes done depending on the scale. I
don't know if this is accurate or not.
| Quote: |
Especially since it sounds like you are making biodesiel and it would be obnoxious to separate any crystals or liquid from the methyl esters and the
glycerin. This would require heating ($$) cooling ($$) and time ($$) to completely separate them and get a decent purity. |
To separate the glycerin byproduct you just need to add enough Phosphoric Acid to neutralize the lye from the second stage (which in turn neutralizes
the Phosphoric Acid in the first stage). It's like the opposite of making soap. The byproduct is more Potassium Phosphate.
The glycerin byproduct then separates into a salt layer, a glycerin/alcohol/water layer, and a top layer of Fatty Acids. This purifies the glycerin
to about 90% and hopefully makes it salable to refiners. The fatty acids can be added to future batches and esterified or burned in a waste oil
heater, so separation is desirable and worth the while in its own right.
The salts still need to be washed, but since potassium phosphate and potassium sulfate are completely insoluble in alcohol while phosphoric acid,
glycerin, fatty acids, and water are not, this doesn't sound too complicated.
So, regardless of whether you use phosphoric acid or sulfuric acid the process is basically identical. I imagine if done in a bi-annual batch the
expense of labor and energy could be kept to a minimum.
It still might not be worth the added expense of phosphoric acid, but I have no way of knowing that without knowing the relative values and purities
of the respective salt layers when all is said and done.
Perhaps someone could guesstimate the purity based on the process I described (that would be interesting, actually), but I don't think anyone would
know the value of the substances at those purities.
[Edited on 2-9-2009 by FuriousGeorge]
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kclo4
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| Quote: | Would it be more correct to say they would form if I added too little acid? If I added too much wouldn't I just have left over Phosphoric Acid, or is
it not that simple? | Quote: |
Not that simple, since phosphoric, and sulfuric are polyprotic acids you can from potassium hydrogen phosphate, potassium dihydrogen phosphate,
potassium hydrogen sulfate, etc.
Here are the equations that I think will help better explain it:
H3PO4 + KOH = KH2PO4 + H2O
KH2PO4 + KOH = K2HPO4 + H2O
K2HPO4 + KOH = K3PO4 + H2O
Or:
H2SO4 + KOH = KHSO4 + H2O
KHSO4 + KOH = K2SO4 + H2O
Phosphoric acid also neutralizes more potassium hydroxide then does sulfuric acid, so consider that in the prices, as three moles of phosphoric acid
is equal to two moles of sulfuric acid.
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not_important
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OK, I think what you are trying to do is
1) Use H3PO4 as the acid catalyst to esterfy the free fatty acids in the waste oils.
2) add KOH to that and do the standard transesterfication of the fats.
3) Use H3PO4 to neutralise the KOH/KOMe from stage #2.
If so, yes water reduces the amount of ester formation and slows down the formation of whatever amount of ester does get formed:
(fatty acid) RCO2H + MeOH <=> H2O + RCO2Me
adding more of one compound on one side of the equilibrium pushes the reaction in the other direction. Adding a lot of methanol will overcome the
presence of some water. Removing a compound from one side of the reaction will drive the reaction in that direction; removing water will result in
more ester being formed. In this case the polyphosphoric acids formed by heating H3PO4 will help, as they slowly react with water to reform
H3PO4.
As already said adding an excess of KOH, as needed for the transesterfication stage #2, will result in K3PO4. In stage #3 just enough H3PO4 (85% is
OK) is added to react with the KOH to form K3PO4; this will be alkaline as a 1% solution og K3PO4 has a pH in the range of 12.
The problems with this include
* there is likely some NaCl in the waste fats, enough decreases the value of the phosphates even as fertilisers.
* fertiliser grade phosphates are much less expensive than phosphoric acid, you're using an expensive reagent to make a cheap product - buy high, sell
low.
* There's enough crap in waste fats that I doubt the ~90% glycerol would have much if any value. Enough salts dissolve in the gycerol rich layer to be
troublesome, and generally coloured and odoriferous compounds from the fats end up in the glycerol as well.
The basic problem is that backyard biodiesel is wasteful and inefficient. To get reasonable amounts of transesterfication you need a large excess of
methanol, typically I seen people using 2X the theoretical. Unless you distill it out of the water/alcohol layer it's just becoming a load on the
sewage system. Bigger biodiesel plants can justify the equipment to recover the excess, small time operations usually can't.
And you're still using consumables, the base and acid are an expense and likely a waste of very low value by-product.
YTou migh look into sold acids for the first step esterfication, that's what the big players are moving towards along with a large amount of MeOH.
The solid catalyst is just filtered out of the solution of fats in methanol, washed with MeOH, and reused. Similar solid catalysts for the
transesterfication are being developed, or just solid acid catalyst with enough excess of MeOH to give fast and near complete conversion.
But even that is likely to be put out of business by reactive distillation, which can handle high amounts of FFA, has no consumption of base/acid, and
yields high grade glycerol.
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FuriousGeorge
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| Quote: | OK, I think what you are trying to do is
1) Use H3PO4 as the acid catalyst to esterfy the free fatty acids in the waste oils.
2) add KOH to that and do the standard transesterfication of the fats.
3) Use H3PO4 to neutralise the KOH/KOMe from stage #2.
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Yes that's it.
| Quote: |
If so, yes water reduces the amount of ester formation and slows down the formation of whatever amount of ester does get formed:
(fatty acid) RCO2H + MeOH <=> H2O + RCO2Me
adding more of one compound on one side of the equilibrium pushes the reaction in the other direction. Adding a lot of methanol will overcome the
presence of some water. Removing a compound from one side of the reaction will drive the reaction in that direction; removing water will result in
more ester being formed. In this case the polyphosphoric acids formed by heating H3PO4 will help, as they slowly react with water to reform
H3PO4.
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Are you saying that trying to distill the 85% aq. H3PO4 solution would form polyphosphoric acids, but that it wouldn't be a bad thing?
| Quote: |
As already said adding an excess of KOH, as needed for the transesterfication stage #2, will result in K3PO4. In stage #3 just enough H3PO4 (85% is
OK) is added to react with the KOH to form K3PO4; this will be alkaline as a 1% solution og K3PO4 has a pH in the range of 12.
The problems with this include
* there is likely some NaCl in the waste fats, enough decreases the value of the phosphates even as fertilisers.
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I had considered that, but NaCL is soluble to some extent in methanol (13 g per liter), and, assuming it would be less than 10% of the salt layer (~1g
per liter of byproduct), it could be washed out with most of the other contaminants....
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* fertiliser grade phosphates are much less expensive than phosphoric acid, you're using an expensive reagent to make a cheap product - buy high, sell
low.
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How much less? How does one find out the average price of a chemical by grade? I haven't figured it out yet. Perhaps it would have saved me some
research time. Anyway, sounds like you don't think it's worth it.
| Quote: |
* There's enough crap in waste fats that I doubt the ~90% glycerol would have much if any value. Enough salts dissolve in the gycerol rich layer to be
troublesome, and generally coloured and odoriferous compounds from the fats end up in the glycerol as well.
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I read somewhere that separating the glycerol is basically the difference between it being a liability and breaking even when disposing of it. In
other words, it has minimal (but some) value.
| Quote: |
The basic problem is that backyard biodiesel is wasteful and inefficient. To get reasonable amounts of transesterfication you need a large excess of
methanol, typically I seen people using 2X the theoretical. Unless you distill it out of the water/alcohol layer it's just becoming a load on the
sewage system.
Bigger biodiesel plants can justify the equipment to recover the excess, small time operations usually can't.
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You should check out the newer Open Source Reactor designs. They include condensers.
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And you're still using consumables, the base and acid are an expense and likely a waste of very low value by-product.
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Yes, but for under 1,000,000 liter per year they are a necessary evil, are they not?
| Quote: |
You migh look into sold acids for the first step esterfication, that's what the big players are moving towards along with a large amount of MeOH. The
solid catalyst is just filtered out of the solution of fats in methanol, washed with MeOH, and reused. Similar solid catalysts for the
transesterfication are being developed, or just solid acid catalyst with enough excess of MeOH to give fast and near complete conversion.
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I've heard about solid catalysts but I haven't really researched the availability / feasibility of using them. I'll look into it.
UPDATE: The Catilin T300 looks promising.
| Quote: |
But even that is likely to be put out of business by reactive distillation, which can handle high amounts of FFA, has no consumption of base/acid, and
yields high grade glycerol.
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If I need to ask then I can't afford it Anyway, it sounds like you think it best
to just go with Sulfuric Acid.
Thanks for the detailed response.
[Edited on 2-9-2009 by FuriousGeorge]
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not_important
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| Quote: | Are you saying that trying to distill the 85% aq. H3PO4 solution would form polyphosphoric acids, but that it wouldn't be a bad thing?
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They shouldn't be, so long as you are willing to take time.
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How much less? How does one find out the average price of a chemical by grade? |
Hydroponic grade:
Mono-Potassium Phosphate (MKP) (0-52-34) 50lbs $84.95
Dipotassium Phosphate (DKP) 50lbs $125.95
Phosphoric Acid (75% Tech. Grade) 5 Gal. (66lbs) $146.95
| Quote: | | I read somewhere that separating the glycerol is basically the difference between it being a liability and breaking even when disposing of it. In
other words, it has minimal (but some) value. |
Interesting, because I've read ads for free biodiesel glycerol, in amounts from 20 to 250 liters.
| Quote: | can't.
You should check out the newer Open Source Reactor designs. They include condensers. |
Interesting, and a decent design although I'd have both methoxide and pre-wash tanks with extra valving rather than dismounting; although it would be
nice to work out the mass flows and all that for it. One thing to note is that he does not nutralise the methoxide, which cuts down on corrosion
problems but leaves the glycerol/soap layer quite alkaline; some methanol goes with that layer, too. And while have the oil as dry as possible does
cut down on soap production, the free fatty acid content also contributes and that can be quite high in used cooking oils and fats.
| Quote: | | Quote: | | And you're still using consumables, the base and acid are an expense and likely a waste of very low value by-product. |
Yes, but for under 1,000,000 liter per year they are a necessary evil, are they not?
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And a necessary additional cost, lower profits, more pollution. As I've said, as rising petroleum prices increase the pressure to use biodiesel, the
big boys with lower production costs are going to be able to tie up most of the waste oil sources, being able to pay a little bit more for it. That
will mostly leave the "doing it to be green" crowd as the small timers, and often they are less "green" than the big time players, or those that are
die hard DIY types who are willing to rate their time as zero cost.
I'm under NDA, but there's stuff in development that will let larger plants utilize more of the waste streams they consume, cutting back on or
eliminating most of their other consumables. If integrated with other waste processing facilities, they'll beable to live off waste process heat and
so eliminate most of their heating costs. Going to be real tough to compete with such in a few years.
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FuriousGeorge
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Quote: Originally posted by not_important  |
Hydroponic grade:
Mono-Potassium Phosphate (MKP) (0-52-34) 50lbs $84.95
Dipotassium Phosphate (DKP) 50lbs $125.95
Phosphoric Acid (75% Tech. Grade) 5 Gal. (66lbs) $146.95
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TKP isn't listed there, though. The cheapest I can find that for "reagent grade" (as low as 97%) is:
| Quote: |
Potassium Phosphate Tribasic, Anhydrous, Reagent - K3PO4 - 12 KG $1,195.92 |
Does 97% sound unreasonable from a methanol wash, followed by dissolving in water, followed by distillation?
If not, what's reasonable (95%? 90%? 85%?)
Based on that I can determine if the Acid + Base - Byproduct cost is worth the cost of phosphoric acid over sulfuric, but it doesn't matter.
OK, I'm convinced solid catalysts are the way to go.
Any thoughts that wouldn't violate any NDAs on the Catilin T300 solid catalyst I mentioned earlier?
It's apparently available right now and is usable in continuous flow (vs. batch) processing.
[Edited on 2-9-2009 by FuriousGeorge]
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not_important
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TKP, like it's sodium sib TSP, is rather alkaline and unlikely to be used as a fertilizer, so it's not going to be very common as a tech grade
compound. It is used in the food processing industry, where there are tight limits on heavy metals. An example is the following, to be at least 94%
TSP with DKP likely the main minor component:
| Quote: | grade purum p.a.
assay ≥94% (T)
loss ≤13% loss on ignition, 800 °C
anion traces chloride (Cl-): ≤50 mg/kg
sulfate (SO42-): ≤200 mg/kg
cation traces Ca: ≤50 mg/kg
Cd: ≤50 mg/kg
Co: ≤50 mg/kg
Cu: ≤50 mg/kg
Fe: ≤50 mg/kg
Na: ≤1000 mg/kg
Ni: ≤50 mg/kg
Pb: ≤50 mg/kg
Zn: ≤50 mg/kg |
It can be had in small quantities for less than that reagent grade you reference, a bit cheaper at $69.00 / each (USD) per kg
http://www.coleparmer.com/catalog/product_view.asp?sku=88256...
However you can't go by the cost of something in the kg range, that's lab supply retail pricing; like comparing the cost of a bottle of cooking oil to
that of a drum or tank car of the same. And you're likely to find it difficult to sell on a fairly small scale, especially for TKP where the main use
is in foods and other ingestible products with the need for an analysis.
The Catilin T300 sounds interesting (you edited after I started my comment so I missed it) especially if you're handy with the sort of work it takes
to build the processing equipment. You'd want more specs on it, efficiency of conversion for stated conditions, life of the catalyst; this is a
company promo piece and we all know about sales literature :-) . But it does reduce the consumables and the problem of waste, the glycerol should be
effectively salt free which is a big plus.
Note that they show it being used in two stages, with catalyst and glycerol separation at each. Some water will go with the glycerol, so this removes
those two products of transesterfication and esterfication respectively and forces the reaction towards the methyl esters. A third stage might be
needed if the FFA content is high. This process could be done in batch or continuous mode as they show, an issue is the "specially designed filters" -
how complex and tricky are they? After that they're using the same sort of MeOH distillation to recover it from the glycerol and biodiesel streams as
that open source reference; power and cooling water consumption that you want to analyze but nothing too tricky.
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FuriousGeorge
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| Quote: | And you're likely to find it difficult to sell on a fairly small scale, especially for TKP where the main use is in foods and other ingestible
products with the need for an analysis.
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By my estimation a .5M Liter/year plant would produce almost 10MT/year of TKP, out of about 5MT of H3PO4 and 7.5MT of KOH, depending on the FFA in
the feedstock. Being unfamiliar with the chemicals market, I still don't know what kind of purity I could expect after a reasonable wash, and I have
no idea if that breaks the threshold of "small quantity".
| Quote: |
The Catilin T300 sounds interesting (you edited after I started my comment so I missed it) especially if you're handy with the sort of work it takes
to build the processing equipment. You'd want more specs on it, efficiency of conversion for stated conditions, life of the catalyst; this is a
company promo piece and we all know about sales literature :-) . But it does reduce the consumables and the problem of waste, the glycerol should be
effectively salt free which is a big plus.
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I sincerely appreciate the feedback. You clearly know your stuff.
[Edited on 2-9-2009 by FuriousGeorge]
[Edited on 2-9-2009 by FuriousGeorge]
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hissingnoise
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It sounds very Sauron, Sauron!
It's nice to know you're still here.
The FuriousGeorge disguise is really very good!
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hissingnoise
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I can't resist saying DJF90, I found your direction to Sauron, for that is who FuriousGeorge is, to 'See Brauer for details' to be a delicious irony.
. .
Of course, directing a (non-chemical background) newbie to Brauer without giving details is curious by itself.
Perhaps it was a knowing irony?
(I was almost tempted to add a 'lol' or several.)
[Edited on 15-9-2009 by hissingnoise]
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dann2
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Good to know you still here Mr Bodine too (you old ravishing dead sheep you) 
Dann2
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wpenrose
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Trying to concentrate phosphoric acid past 85% will result in polyphosphates. Trying to replace water with methanol may do the same thing, and maybe
generate methyl esters besides.
If you want to give it a try, you have to start with phosphorus pentoxide (P2O5). CAUTION: VERY DANGEROUS PROCEDURE.
After measuring P2O5, add just enough water to form the 100% phosphoric acid, then add methanol to dilute to 85%. If you add the methanol first, you
are certain to get methyl esters.
I don't know the details of a method like this. You just want to be sure to try it on a milligram scale first. There will be a lot of heat and steam
and splattering, and you may not get the product you expect.
Dangerous Bill
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hissingnoise
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Why bring Rosco into it dann2, he hasn't posted here---I checked!
Or is there some deeper subtlety I'm missing here?
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entropy51
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Welcome to Science Madness.
You'll fit right in here.
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hissingnoise
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You're talking to our late-lamented Sauron, entropy51; he needs no introduction. . .
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dann2
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I'm afraid I have only one thing to say, and thats hiiiiiissssssssssssssssssssss
Dann2 (subtle as an Iron Lung)
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entropy51
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hiss, I was just reassuring him that nothing had changed during his absence. Well, Ok, may be the kewls have gotten a little out of hand without the
glare of the Dark Lord.
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hissingnoise
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Yeah! Gotta love that good ole' Southern 'humour'. . .
[Edited on 17-9-2009 by hissingnoise]
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FuriousGeorge
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Sauron Sauron
I'm not who you think I am. Whatever beef you have with this sauron fellow has nothing to do with me.
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