katchum
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HCl + NH3
Is it possible to react HCl and NH3 in the gas phase? And if so, how big are those aerosols? Which concentrations of the gases should be used? What's
the percentage of reaction?
Also: When you have a mixture of HCl, NH3, SO2 and N2 gases. How would you separate these gases?
I would think of first separating the NH4Cl with elektrofilters or mechanical filters and then wet scrubbing the SO2 with alkaline solution. What
would you suggest? Is it possible to combust SO2 to H2SO4 in these conditions?
[Edited on 10-10-2006 by katchum]
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woelen
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HCL and NH3, when perfectly dry, apparently do not react, but I have never tried that. Even the tiniest amounts of water vapor make them react and
then you obtain solid NH4Cl. The latter experiment I have done several times. Take a tube, full with NH3 gas (possibly mixed with air) and another
tube, full with HCl (also possibly mixed with air). If you bring them near each other, then you obtain intensely thick white smoke.
Even keeping bottles of the two aqueous liquids (e.g. 30% HCl and 10% NH3) close to each other already results in dense smoke.
Separation of these 4 gases:
NH3 + HCl react, giving a solid. But HCl or NH3 may remain, if their amounts are not precisely balanced. NH4Cl can be filtered.
Next, bubble the remaining mix through H2SO4: Any excess NH3 will be absorbed, the rest is bubbling through. Of course, you separated the NH3, but not
as free gas anymore.
Next, bubble through a solution of NaOH. Both SO2 and HCl are captured. N2 is bubbling through.
Finally, add excess dilute H2SO4 to the solution with NaOH/SO2/HCl and heat to near boiling. All SO2 is driven off, while hardly any HCl is driven
off.
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katchum
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Thanks!
So first off you should add some water vapour to get the NH4Cl reaction to occur. Then a filtration: maybe dry elektroprecipitation, you want to have
pure NH4Cl, if you use too much water you have to warm it up again and that's inefficient.
Then H2SO4 looks like a good idea when NH3 is still there. If NH3 is gone you use NaOH and then again H2SO4. So the end product is water with ions
from: Cl-, SO42-, Na+
What can I do with this stream? Also, the SO2 that is repelled can be used to make H2SO4 with O2 combustion.
Now, what about using CaO or CaCO3 as wet scrubber? I've read somewhere CaO would react with 2 HCl to form CaCl2 and water. Also CaO and SO2 reacts to
CaSO3. I'm not sure at which temperature this occurs... Problem is, the slurry is a real mess and you can't recuperate any of it or am I wrong?
There's also this one: using Zeolite as molecular sieve you can get rid of SO2, HCl and water vapor. Again a solution of molecules that needs to be
taken care of.
And a bit weird: When you only have HCl and SO2 in N2 you could decrease the temperature to -20 to make liquid SO2. How about that? Then you could
recuperate HCl by bubbling it through water.
So all these alternatives, which one is really the best...
PS: Now you use H2SO4 to get rid of NH3. Maybe it is better to turn SO2 into H2SO4 with combustion with O2. So you don't need to buy H2SO4 all the
time. The problem is: would HCl react at this high temperature? An alternative is using a selective solvent to capture HCl and then desorbing it to
have pure HCl. The SO2 would then be pure and you can make H2SO4 from it to reflux it back to NH3. But I don't know if there is a solvent that selects
HCl more than SO2...
[Edited on 10-10-2006 by katchum]
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12AX7
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If you want to oxidize, then you might lead all the stuff through a catalyst with oxygen. You may or may not get chlorine, that probably depends on
the catalyst. The rest would burn, 2NH3 + 5O = 2NO + 3H2O and SO2 + O = SO3. At lower temperature, NO + O = NO2 and NO2 dissolves in water to give
HNO3 and NOx (which can be reoxidized) and SO3 + H2O = H2SO4 of course. If chlorine is formed, you might get something like NO2 + H2O + Cl = HCl +
HNO3, which would help a bit.
After running the oxidized gasses through a scrubber, the wash water would be dilute mixed acid, quite a corrosive combination at that. A good reason
to use alkaline wash water in the first place, which will absorb better besides. The stuff can be disposed (potassium chloride, sulfate and nitrate
would make a reasonable fertilizer) or fractionally crystallized to seperate the stuff.
Tim
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katchum
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That fractional crystallisation thing you said gave me an idea to do the same to the solution of: Na+, H+, SO42-, Cl-, H2O.
Can I just boil this solution at 340 °C to get H2SO4 and salt? Although I think this requires too much energy...
But apparently you don't approve of calcination scrubbing. I also think this would be a waste of useable product.
[Edited on 10-10-2006 by katchum]
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12AX7
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Gnaw, HCl distills off loooong before H2SO4. You would have to include, say, phosphate (a more stable acid, it doesn't boil) in order to distill
H2SO4 out.
Tim
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not_important
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| Quote: | Originally posted by katchum
...
Also: When you have a mixture of HCl, NH3, SO2 and N2 gases. How would you separate these gases?
....
[Edited on 10-10-2006 by katchum] |
Electrostatic/electronic precipitators to remove reacted NH3+HCl As already stated, if not equal amount then one or the other will be left over. If
ammonia is in excess and there is much water you will get some NH4SO3.
Cool the rest with LN2 to condense everything except N2. Then slowly warm up the condensate and fractionally distill the 2 compounds:
HCl -85 C or NH3 -33 C
SO2 -10 C
This assumes that you wish to recover the compounds in their original form.
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katchum
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Okay, some waste-professor said that it isn't that interesting to recuperate those gases. So he suggested a wet addition of first CaCO3 to remove the
strong acid HCL and then a wet scrubber with CaOH2 to remove the less strong acid SO2. These processes should be separated because CaOH2 is more
expensive than CaCO3. The temperature is like 200°C.
First the gases would solve into the water and react to form CaCl2 and then CaSO3 + O2 = CaSO4.
You can dump this slurry but you can also reflux this slurry so that you don't have to dump anything and you get a certificate for not dumping
things... except water vapor.
Of course first off I should still filter the NH4Cl and add H2SO4 + NH3...
PS: not_important: why would you condense everything and not just till -20 °C? Is this because you know that when one gas condenses, it would never
be pure? There is always some HCl in the condensed SO2. I'm not sure if these gases are immiscible or not but I think when you cool of to -20°C you
can get pure HCl out of it and impure SO2 + HCl in liquid form.But I'm not sure. I forgot everything...
[Edited on 11-10-2006 by katchum]
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not_important
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Just condensing is similar to a simple distillation, neither liquid nor gas will be pure if the boiling points are not very far apart. Taking
everything to a liquid and using a fractionation column will give better separation.
Uh " but you can also reflux this slurry so that you don't have to dump anything" ? You are going to build up CaCl2 and CaSO4, at some point they
will fill you system completely.
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katchum
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Some more information:
54 kg/h HCl
47 kg/h SO2
15 kg/h NH3
maximum 1000 m^3/h
So it's like 1-2 tonnes of HCl or SO2 a day. Is it worth the investment?
Yes you're right about the purity of SO2. You need a distillation column to do it. But who would want to make a column for 2 tonnes of SO2, HCl a
day... Those products aren't interesting.
So making CaCl2 and CaSO4 and then dumping it is best. And about that not having to dump anything I meant you don't have to dump the waste water. You
make the CaSO4 and CaCl2 as a solid material without having to dump the waste water. It's this waste water that you have to pay money for. If you
don't dump waste water you get a certificate...
So what I want to do is vaporize water into the air and dry the CaSo4 and then dump that solid material.
I wonder if there are extraction solvents with a selectivity for HCl over SO2.
[Edited on 12-10-2006 by katchum]
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12AX7
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CaCl2 dissolves quite a bit in H2O but CaSO4 does not.
Don't know how much CaCl2 is worth.
Tim
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not_important
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| Quote: | Originally posted by katchum
Some more information:
54 kg/h HCl
47 kg/h SO2
15 kg/h NH3
maximum 1000 m^3/h
So it's like 1-2 tonnes of HCl or SO2 a day. Is it worth the investment?
Yes you're right about the purity of SO2. You need a distillation column to do it. But who would want to make a column for 2 tonnes of SO2, HCl a
day... Those products aren't interesting.
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True, fairly low value unless there was a local use. Howeverm continuing with the next portion...
| Quote: |
So making CaCl2 and CaSO4 and then dumping it is best. And about that not having to dump anything I meant you don't have to dump the waste water. You
make the CaSO4 and CaCl2 as a solid material without having to dump the waste water. |
The weight of anhydrous CaCl2 produced will be about 75 Kg/h, one and a half tonnes a day. CaSO3 + 2H2O is going to be ... um, even taking off my
shoes doesn't help but around 100 Kg/h, nearly two and a half tonnes a day; obviously if oxidised to the sulfate it will weight even more.
So you're talking roughly 4 tonnes of solid per day, of which roughly 40% is a very water soluble - hydroscopic even - chloride. I know some areas
don't take kindly to solid waste that will leach chlorides into the ground water, simply from the salinity issue.
| Quote: |
It's this waste water that you have to pay money for. If you don't dump waste water you get a certificate... So what I want to do is vaporize water
into the air and dry the CaSo4 and then dump that solid material.
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I must be too used to solid waste dumping charges
It's going to take energy to do that evaporation, you must have a fair amount of waste heat to take advantage of.
| Quote: |
I wonder if there are extraction solvents with a selectivity for HCl over SO2.
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A weak amine, off the top of my head something like a dialkyl-aniline, might work. HCl would be a strong enough acid to form a salt, SO2 wouldn't.
Done on the raw feed would likely result in NH4Cl mostly as a solid suspended in the wash amine, perhaps also the HCl salt of that amine, with the SO2
mostly left in the gas phase. You'd still have something a bit like a fractionating column - a multiplate absorption tower.
What would seem to be idea would be a solvent that would keep the HCl amine-salt in solution, allowing the NH4Cl to be removed by filtration, then be
able to strip the HCl from the solvent to recover it. Getting those three streams, if of acceptable purity, should allow recovery of some of the costs
of the clean-up, especially if there is any chemical industry in the region, metal processing might use the HCl to cleaning.
Another solution might exist in selective permability membranes. Differences in polarity and size might allow separation of the gas streams, after
removal of the NH4Cl.
I could be hired to do some research on this problem 8-)
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katchum
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What do they do with that CaSO4 actually? Just burn it? I know there is too much of CaSO4 nowadays so nobody needs it.
I'm gonna investigate those selective membranes.
An alternative:
Can I just put excess NH3 in the mixture of vapor + HCl + SO2 in order to make NH4Cl + filtration. Then I get SO2 and NH3 that react a little bit.
Then I put in H2SO4+H2O in to get rid of NH3 and then I can search the library for SO2 scrubbers.
So now you don't need that column for HCl amine absorption. And NH4Cl is a pretty interesting material in a pharmaceutical company. Well, I'm doing
this for Janssen Pharmaceutica.
Also, your absorber + stripper is in liquid form => energy costs! If you just put in NH3 gas and some vapor you also get NH4Cl. I don't have to be
afraid of the SO2 solving into the vapor because when heated enough, the vapor will vaporise again and SO2 released. The solid NH4Cl could be
filtrated pure.
Another question: I have ammonia in solid form at home, why isn't it a gas?
But, really, I think the scrubbing would be better just to scrub HCl + SO2 together. Because the CaCl2 when in solution, will make the CaCO3 solve 6
times better! But when it gets too expensive... you can better recuperate HCl of course.
Oh, and you didn't take in account that NH4Cl is filtrated, so the scrubber with CaCO3 isn't 4 tonnes of solid. But something like 2 tonnes or
something.
[Edited on 17-10-2006 by katchum]
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12AX7
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| Quote: | Originally posted by katchum
Another question: I have ammonia in solid form at home, why isn't it a gas?
|
Must be ammonium carbonate (or bicarbonate). It decomposes easily ((NH4)2CO3 <--> 2NH3 + H2O + CO2) and being an alkali carbonate, tends to be
somewhat basic; ammonia tends to get released in basic conditions.
Tim
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not_important
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| Quote: | Originally posted by katchum
What do they do with that CaSO4 actually? Just burn it? I know there is too much of CaSO4 nowadays so nobody needs it. |
Make some into wallboard, some gets used as a soil additive. Don't know if any recovery of sulfur from it is done. The rest must end up in landfills.
| Quote: |
I'm gonna investigate those selective membranes.
An alternative:
Can I just put excess NH3 in the mixture of vapor + HCl + SO2 in order to make NH4Cl + filtration. Then I get SO2 and NH3 that react a little bit.
Then I put in H2SO4+H2O in to get rid of NH3 and then I can search the library for SO2 scrubbers.
So now you don't need that column for HCl amine absorption. And NH4Cl is a pretty interesting material in a pharmaceutical company. Well, I'm doing
this for Janssen Pharmaceutica.
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You could, but I expect a little of the SO2 to end up in the NH4Cl, going to need some secondary processing.
It might be possible that adding some water and O2/air could get the SO2 to end up as aqueous or damp (NH4)HSO4 or (NH4)2SO4. The bisulfites and
sulfites seem to oxidise fairly quickly when wet. | Quote: |
Also, your absorber + stripper is in liquid form => energy costs! If you just put in NH3 gas and some vapor you also get NH4Cl. I don't have to be
afraid of the SO2 solving into the vapor because when heated enough, the vapor will vaporise again and SO2 released. The solid NH4Cl could be
filtrated pure.
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Solvent absorption and stripping is fairly common, it typically takes a lot less energy than evaporating water.
I don't understand exactly what you are saying here. If you have any water in the mix you will get a bit of NH4HSO3 along with the NH4Cl. While it is
a less stable compound, oxygen converts it to the sulfates which are roughly as stable as the chloride. I don't know how easy it would be to avoid
any SO2 remaing in the NH4Cl. Certainly heating the chloride is fairly energy expensive.
| Quote: |
Another question: I have ammonia in solid form at home, why isn't it a gas? |
I'm seconding an ammonium carbonate, or ammonium chloride or sulfate mixed with sodium carbonate or even calcium hydroxide. Ammonium carbonates just
need warmth to emit ammonia, the Cl/SO4 salt plus base needs a little moisture too
| Quote: |
But, really, I think the scrubbing would be better just to scrub HCl + SO2 together. Because the CaCl2 when in solution, will make the CaCO3 solve 6
times better! But when it gets too expensive... you can better recuperate HCl of course.
Oh, and you didn't take in account that NH4Cl is filtrated, so the scrubber with CaCO3 isn't 4 tonnes of solid. But something like 2 tonnes or
something.
[Edited on 17-10-2006 by katchum] |
Uh, if the HCl ends up as CaCl2, how are you getting the HCl back? CaCl2 is a waste problem, and expensive to get from solution to solid form.
Yeah, I was ignoring the amount pulled out as ammonium chloride
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katchum
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Those aerosols formed are something of 0,5 micron or less which is good, but the resistivity of NH4Cl in water is really low, like 0,2 Ohm.cm. So
elektroprecipitation with water vapor could be a problem because they require resistivity of 10000 Ohm.cm.
So maybe a normal filtration would be better than ESP. I hope that the NH3HSO4 doesn't form when perfectly dry. We can then just react in a dry
environment to NH4Cl. Filtration of 0,5 micron can be done with normal filters. Adding a little, really a little water can speed up the reaction.
Does NH3HSO4 remain as solid when water is vaporised? I don't know how much it will contaminate NH4Cl but I'll look into that reaction rate.
Question: You say HCl is absorbed into dialkylaniline. Is that a gas solved in dialkylaniline? I assume NH3 is also absorbed into dialkylaniline and
then forms the salt. How can you strip the remaining HCl out of dialkylaniline? So SO2 doesn't solve into dialkylaniline?
[Edited on 18-10-2006 by katchum]
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not_important
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The HCl forms a salt - subsituted ammonium chloride, PhMe2NHCl for example. If there is ammonia around then at least some would dissolve. The NH3 and
aromatic amine are going to compete for the HCl, as the NH3 is a stronger base it will combine first when the amount of HCl is limited compared to the
amount of bases.
But you would want to remove NH3 first as the chloride, then separate the remaining HCl from the SO2.
The SO2 will dissolve some in the amine, but the aromatic amines are weak enough bases than the salt is not very stable and can be broken up with mild
heat and/or reduced pressure. With proper choice of amine and solvent I suspect that SO2 absorption would not be a problem.
You're getting into chem engineering territory, need actual data tables and calculations. I believe the HCl salt, with proper choice of amine and
solvent again, could be stripped with steam, which would then be condensed to form aqueous HCl, but don't ask me for actual "how-to" conditions. Ion
exchange resin might work for HCl recovery, need to research that.
I don't think you can get the gases dry enough to completely suppress the NH3 + HCl reaction; in the old experiments they would dry it for days over
P2O5. You don't need enough water to make a solution, 0,1% as much water as resulting NH4Cl is considerably more than enough so the NH4Cl can be in
the solid phase. You want to keep it rather dry until the HCl has been removed, to reduce corrosion problems.
The reaction of SO2 and NH3 is more two way, weak acid and weak base. With actual excess of water, enough to allow formation of water films, and
addition of O2/air you can get a liquid phase oxidation of bisulfite to bisulfate. Even without that you will get some traces of the bisulfite in the
NH4Cl, and unless there is no oxygen at all, you will get some small amount of bisulfate or sulfate as well. How much is going to depend on the exact
conditions.
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katchum
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I've read an article on the net:
http://pubs.nrc-cnrc.gc.ca/cgi-bin/rp/rp2_abst_e?cjc_v75-375...
They say without water and with excess SO2 only NH3•SO2 appears at −150 °C. The 1:1 complex disappears at about −20 °C.
And apparently our streams do have excess SO2 because of the reaction of NH4Cl. So if I just don't insert water in the gas stream and use high
temperatures maybe nothing of those bisulphites will form. Actually I read somewhere that ammonium bisulphites are used to make pharmaceutical
compounds... If I could separate this one and NH4Cl...
Of course when I do use water, those bisulfites will definately form... They are stable at room temperature.
There is only this problem: I couldn't read the entire article so maybe I'm wrong at some points.
PS: Tim, you wouldn't accidentally be Tim C. Keener, no? Like in:
http://www.osti.gov/bridge/servlets/purl/10139178-huEg20/nat...
[Edited on 18-10-2006 by katchum]
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12AX7
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That link doesn't open.
Nah, I'm nobody... buried among the hundreds of Tim Williamses on the internet (hint, I'm not a country musician... gack!). Check out my website.
Tim
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katchum
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The calcination technology wasn't a good idea because it required too much space.
I'm looking for a compact scrubber which can scrub both alkaline and acid together without having two columns placed after each other. The best
solution would be neutralisation with common fluids instead of solids.
Do such things exist, anybody?
[Edited on 5-11-2006 by katchum]
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