macckone
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Separation of ammonium sulfate and urea
Ammonium Sulfate/Urea fertilizer is readily available.
It is supposedly fairly pure with just the two components.
I am looking at a method to separate the two components without converting the ammonia to gas.
At high temperature Urea is much more soluble 7330g/L vs 1030g/L.
For the separation I am looking at adding sufficient water to completely dissolve the solid at room temperature and filter any insolubles then
evaporate at 100C until substantial crystallization occurs, which should be a fairly pure ammonium sulfate with most of the urea remaining in
solution.
One method of removing remaining urea in the ammonium sulfate would be heating to high temp (150-250C) where urea would convert to ammonia and related
compounds which decompose. Where ammonium sulfate is stable to 250C where it decomposes to ammonium bisulfate.
Does anyone have a less labor intensive method?
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Melgar
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Sure. Urea is quite soluble in methanol, but ammonium sulfate is not. So that might get you started.
You also might want to take a look at the granules. If there are two distinct different types of granules, it might be possible to separate them
mechanically, with a sieve or something.
The first step in the process of learning something is admitting that you don't know it already.
I'm givin' the spam shields max power at full warp, but they just dinna have the power! We're gonna have to evacuate to new forum software!
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macckone
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Knowing how this is produced, sulphuric acid, ammonia, and urea are combined.
The urea winds up primarily as a coating as it remains in solution longest.
In some processes the urea is actually broken down by the sulfuric acid to form the ammonium sulfate so no ammonia is utilized as an input.
Methanol might be the answer if I can rinse the product with methanol I can probably remove most of the urea.
Adding enough acid to fully break down the urea is another solution I have considered.
Urea hydrolyzes quite well at 90C apparently but I will need to neutralize the formed ammonia.
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RogueRose
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Quote: Originally posted by macckone  | Knowing how this is produced, sulphuric acid, ammonia, and urea are combined.
The urea winds up primarily as a coating as it remains in solution longest.
In some processes the urea is actually broken down by the sulfuric acid to form the ammonium sulfate so no ammonia is utilized as an input.
Methanol might be the answer if I can rinse the product with methanol I can probably remove most of the urea.
Adding enough acid to fully break down the urea is another solution I have considered.
Urea hydrolyzes quite well at 90C apparently but I will need to neutralize the formed ammonia. |
Have you already purchased the mix of the two salts? I have both in large amounts and they are quite pure (for fertilizers). If you want I could
send you some of each.
From what I have read, ammonium sulfate fertilizer is usually a byproduct of steel production, where the H2SO4 is used to remove mill scale from the
steel and then it is neutralized with ammonia. IDK what happens to the iron content in the sulfate, but it doesn't seem to make it into the
fertilizer but FeSO4 is about the same price as (NH4)2SO4 (dirt cheap for 50lbs - $12-16) so I suspect that it is also a byproduct of steel
production.
Urea on the other hand is specifically made as an additional step of ammonia production, a method to make it transportable in a solid form. I've
never seen the two mixed together as I can't understand the point of it.
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macckone
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I have a couple of bags of the stuff, they were end of summer clearance.
I am going to be trying several versions of the purification.
The process to make the urea/ammonium sulfate mix actually starts with sulfuric acid and urea (because it is transportable as you noted). Adding the
sulfuric acid causes the urea to break down and form ammonium sulfate and carbon dioxide. The heat of the reaction dries the end product and produces
a urea coated ammonium sulfate. This has some added benefits as a fertilizer. If less urea is added then they are left with an ammonium sulfate with
minimal urea. In the steel industry they are using urea not raw ammonia, again see easily transportable.
Which gives me another idea of adding sulfuric acid to the mix to break down the urea and then crystallizing. There may be some residual urea which I
need to figure out how to measure.
As for the iron sulfate, my guess is that it crystallizes out as the heptahydrate is much less soluble in water. So there is little iron
contamination in the ammonium sulfate product.
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RogueRose
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"Ammonium sulfate is made by treating ammonia, often as a by-product from coke ovens, with sulfuric acid"
This is where I remembered the connection to the steel industry. The sulfuric acid is first used to remove mill scale, as I had said, and then
neutralized with the ammonia gas from making coke. At least that is how some of it is made, probably fertilizer grade. I suspect there is more than
one way to skin a cat in this case.
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macckone
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I finally got around to working with this stuff 5 years later, most of it has been used as fertilizer. It is far from pure. It even contains rock.
But the urea appears to be mostly on the outside of the prills. Once I finish the 99% isopropyl soaks, I am going to dissolve the remains in water,
filter and then crystalize. It may take more than one crystalization.
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fx-991ex
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Can't heat urea to recrystallize it will decompose to ammonia.
Have to do it slowly with desiccator or a fan.
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macckone
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I finally got around to working with this stuff 5 years later, most of it has been used as fertilizer. It is far from pure. It even contains rock.
But the urea appears to be mostly on the outside of the prills. Once I finish the 99% isopropyl soaks, I dissolved the remains in water, filtered and
then crystalized. I stopped after about half was crystals. It bumped a lot. I then rinsed the crystals with isopropyl alcohol and dried on coffee
filters in a baking pan on the hot plate. I got a nice white product. The soaking steps are tedious. I am going to do another larger batch and use
isopropyl to extract the urea after a first recrystalization. The urea crystalizes last so it crystalizes pretty cleanly.
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macckone
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Update, it uses less isopropyl to dissolve it, crystallize part then rinse. Nice white crystals.
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