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axehandle
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V2O5 catalyst for H2SO4 production.
I not sure if this is the right section for this topic, but here goes.
I'm constructing a sulfuric acid plant using V2O5 catalyst.
I'm slightly confused about several things though (and yes, I've done my homework and found nothing (well, not much at least)). Noone seems
to have tried this before, at home.
A) There are two realistic methods methods (with my equipment) of making the catalyst:
1) NH4VO3, ammonium metavanadate, is prepared by dissolving V2O5 in an excess of ammonia-in-water solution, pieces of pumice are tossed in, the
suspension is allowed to evaporate and then the pumice is heated strongly with e.g. a propane torch.
2) V2O5 and water are mixed together in a 1:1 to 1:2 ratio, the mixture is mechanically stirred together with pumice bits, which are then dried in
a vaccuum and heated to 120C.
My first question regards the preparation of ammonium metavanadate. I got the process from the 1911 encyclopedia. Is it valid, i.e. have I interpreted
the information therein correctly? Here is the entry, btw: http://2.1911encyclopedia.org/V/VA/VAN_BEERS.htm
My 2nd question is: Is the vacuum drying mentioned as the second method, is it really necessary? I don't have a vaccuum pump.
My 3rd question is: Which of these two methods would yield the best catalyst? (Me, I think the metavanadate route seems best.)
My 4th question is rather idiotic, but I can't find the pertinent information using google, so here goes nothing: Is the oxidation of SO2 -->
SO3 using V2O5 catalyst exothermic (i.e. do I have to somehow cool the catalyst once the process is running)?
My 5th and final question is on par with question 4 on the IQ scale: Is nichrothal wire corroded by burning sulfur in an air atmosphere (I intend to
use electrical ignition inside the burner and was planning on bare NiCr wire)?
-----------------------------------------------
I realize this is much, but if any industrial catalyst wizard out there would care to reply to some of the questions, I would be eternally grateful. I
have 3 projects going simultaneously, and would rather avoid the "error", skipping directly ahead to the "trial" so to speak...
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vulture
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SO2 --> SO3 oxidation is exothermic, the process provides it's own activation energy, cooling should not be required.
The metavanadate route is superior, because you'll have a much larger dispersion than any physical method could ever achieve.
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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axehandle
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Thank you. Good --- good...... *rubbing palms together laughing hysterically* (when thinking about how much oleum I'm going to make...) 
Btw, another idiotic question: How big should the pumice pieces be? I was thinking of arranging a date between a piece of pumice lying in front of me
and my hydraulic press, resulting in ~4..5 mm dia pieces.
[Edited on 2004-3-1 by axehandle]
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axehandle
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Thermostat.
I have (inside my head only) finished the catalyst chamber + heater. Basically, the catalyst resides between two rockwool "plugs" inside a
200mm long, 20mm ID borosilicate tube. A NiCr wire connected to a light dimmer or thermostat is wound along the tube, leaving 10mm of free spacing at
the ends for practical reasons.
The wound part of the tube is then covered in a 10mm thick layer of plaster of paris or concrete for thermal insulation.
Now, there are one big problem and one small one.
The big one is: What to make the stoppers with the glass pipes for inlet and outlet out of? The optimal temperature for V2O5 catalyst is between 400
and 500 centigrades, and I doubt any rubber could withstand these temperatures.
Suggestions? My intuition says "cast aluminum using the tube as a mold", but 1) Aluminum shrinks alot when cooling and 2) the glass would
probably shatter.
This is my GREAT dilemma.
The second design obstacle is: How to construct a thermostat? I can't find any bimetal thermostats in that range, and buying a type K
thermocouple is out for economical reasons. The only cheap way I can think of is to make a small "bowl" in the thermal layer, and keep a
piece of metal with a melting point of ~450C there. This would, however, require trimming using visual inspection and a light dimmer, and be sensitive
to the room temperature as well.
I'm eagerly willing to entertain suggestions....
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BromicAcid
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Maybe you could cast plugs out of magnesium oxide cement. That holds up to very high temperatures, but it's not terribly inert, although the
binder can help to a decent extent, exp. sodium silicate or ptich. For the temperature measurement, you could heat a spot on your tubing and deform
it in and use that to cradel a temperature probe, many probes out there now withstand tempearatures in excess of 500 C and are reasonably priced. You
could just construct your insulating layre around it.
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vulture
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That holds up to very high temperatures, but it's not terribly inert
Magnesium oxide that has been fused above 1500C for some times is HIGHLY inert.
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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axehandle
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Sounds good. Where would one find magnesium oxide cement? (What's it used for, what does it contain, etc?)
Another solution that strikes me is that thye plugs could be constructed from many layers of aluminum foil. It <b>should</b>, with a bit
of work, be possible to get an airtight seal.
Aluminum shouldn't be affected by SO3 and small amounts (from air humidity + SO3) H2SO4, if I'm not mistaken...
Edit: I'm an idiot. I have a furnace that can melt glass. I'll simply pre-heat the borosilicate "mold" (i.e. catalyst pipe), put
the inlet/outlet pipes in place and pour some glass in there. That should keep the little SO3 buggers in!
Edit2: But this sounds kind of iffy when I think about it.... mixing different glass types with different thermal expansion coefficients etc... GAK.
[Edited on 2004-3-1 by axehandle]
[Edited on 2004-3-1 by axehandle]
[Edited on 2004-3-1 by axehandle]
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axehandle
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What about a mixture of portland cement, aluminum oxide and bentonite clay? That should be extremely inert.
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Geomancer
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Interesting. You seem to have come to somewhat different conclusions regarding how to run a tiny contact plant than I have.
Why did you decide on vanadate rather than platinum catalyst? Platinum has the signifigant advantage of a much lower "ignition"
temperature. Also, to me, it is more readily available.
You seem to want to control the temperature by careful heating. I had been thinking the other way around: controlled cooling.
You work with glass. I have yet to find any good info as to what SO3 likes, but I had been thinking some sort of metal, preferably copper (easy to
obtain, easy working and facilitates temperature control).
Frankly, I had come to the conclusion that this process is rather difficult--not becuase of the actual catalytic conversion, but because of the
ancillary processes of feedstock generation, product absorbtion, and dilution of the resulting oleum (or is it feasible to absorb directly to water
when working on a small scale)? Any one of these might be fairly straightforward, the hard part would be to integrate them into a smooth running
process.
For the SO2 generation, I had been thinking about echewing a bulk sulfer burner and instead burning a column of sulfur coated sorbent.
Unfortunately, while this solves many problems, it is very much a small batch process. The product could, perhaps, be stored for later use. Dithionite
salts are relatively easy to handle. As for absorbtion, a glass or stainless steel bubble column, followed by a wash bottle, seems the only way to go.
Materials are the sticking point here.
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Magpie
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material of construction
Geomancer: I checked my copy of Shreve's 'The Chemical Process Industries", 2nd ed, (1956) on the contact process. Quoting:
"Although unlined bubble-cap towers have been used to absorb sulfur trioxide, the most common type is the packed steel towers lined with
acidproof masonry. Unlined towers are now being employed where cast iron is used for the 98 to 99.5 per cent acid and steel for the oleums."
I do remember that cast iron is good for sulfuric acid down to a certain %. I recommend checking the chemical compatibility tables
in the back of Perry's handbook.
It is great to see you guys grappling with typical chemical engineering problems like materials of construction, integrating feed streams, and process
control!
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Tacho
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axehandle
I can think of a thermostat for high temperatures using a coiled wire inside the furnace. The wire is part of a bridge that gets unbalanced with
temperature change. When the temperature reaches X degrees, an op-amp triggers off the heating. Measuring the unbalancing gives you the temperature.
It is probably a simple circuit, but I’m not skilled enough to think of it without a simetric power source (+9v – 0 - -9V). Would it be a problem?
If you don´t have one, I will be glad to try to make one with a simple power source.
In fact, this is a project I have been planning to do for a while! Interested?
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axehandle
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| Quote: | Interesting. You seem to have come to somewhat different conclusions regarding how to run a tiny contact plant than I have.
Why did you decide on vanadate rather than platinum catalyst? Platinum has the
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Simple. V2O5 was cheaper, besides there must be a reason it's more used than Pt in industrial production of H2SO4. Also, if there are impurities
like arsenic in the sulfur, the Pt catalyst would slowly be destroyed. V2O5 is much more robust.
| Quote: |
signifigant advantage of a much lower "ignition" temperature. Also, to me, it is more readily available.
You seem to want to control the temperature by careful heating. I had been thinking the other way around: controlled cooling.
You work with glass. I have yet to find any good info as to what SO3 likes, but I had been thinking some sort of metal, preferably copper (easy to
obtain, easy working and facilitates temperature control).
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Well, in all fairness I only plan on using glass for the catalyst chamber and the SO3 piping. The SO2 pipe could very well be made of e.g. copper.
Much easier to work with. But consider this: Some of the SOx generated when burning sulfur will be SO3. Admittedly a very low percentage. When it
combines with humidity in the air, it will form H2SO4. I don't don't what will happen to copper piping then, and to avoid it I'm going
to use a lead pipe or (preferably) a glass pipe.
Also (now I'm giving my entire design away before it's done =) the combustion chamber will probably be made of concrete or lead. I plan to
use a "cradle" made out of ceramics hanging in the middle of the chamber, heated by internal NiCr wire. Sulfur will be fed in
"pellet" form (I have a hydraulic press) through an airlock in the top (double, airtight doors, lower one spring-loaded). The heating in the
cradle will be hot enough to initiate combustion of the sulfur as long as there is oxygen.
Air will be fed into the combustion chamber using the space age technology called "aquarium pump" 
There is still the matter of temperature controlling the catalyst to solve.
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axehandle
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| Quote: |
axehandle
I can think of a thermostat for high temperatures using a coiled wire inside the furnace. The wire is part of a bridge that gets unbalanced with
temperature change. When the temperature reaches X degrees, an op-amp triggers off the heating. Measuring the unbalancing gives you the temperature.
It is probably a simple circuit, but I’m not skilled enough to think of it without a simetric power source (+9v – 0 - -9V). Would it be a problem?
If you don´t have one, I will be glad to try to make one with a simple power source.
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No problem at all. We're only talking center tap secondary here, right?
| Quote: |
In fact, this is a project I have been planning to do for a while! Interested?
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Very much so. Btw, I have basic electronics skills, although I'm a little unskilled with the soldering iron. I've built a few circuits, one
of them interfaced to the parallell port of a Linux PC.
Speaking of which, part of my plan is to integrate a process control computer in the plant, with statistics output in HTML format etc. Nice idea, I
think.
Edit: YES! My V2O5 has arrived. To the post office I go!
[Edited on 2004-3-3 by axehandle]
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axehandle
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type K themocouple wire
How does it work? Does the resistance change with the temperature, and if so, does it do so linearly or in another way? I'm asking because the
wire is cheap, the probes are not...
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Organikum
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vanadiumpentoxide
This was posted by a friend of mine at the HIVE some time ago, it might be helpful.
| Quote: |
Several times vanadiumpentoxide was mentioned over the the times as catalyst useful for oxidations mostly in the gasphase. One example is the
oxidation of toluene to benzaldehyde. Also always was mentioned that vanadiumpentoxide is easy available at pottery supply houses. Thus maybe true but
true is also that a successful reaction with this compound bought from a pottery supply is not very probable. It is the same as with manganesedioxide
(MnO2) - the catalyst has to be fresh prepared for maximal activity - also bought catalyst from chemsupplyhouses equals not the properties of a
freshly prepared one. (exemptions exist, TiO2 catalyst from DEGUSSA is told to beat everything else to buy or to prepare by oneself...) Vanadium
oxidation catalyst on silicagel: Chemicals: Silicagel ((SiO2)n), uncolored, granulated Potassiumsulfate (K2SO4) Ammoniummetavanadate (NH4VO3)
all of those should be available without hassle not at least as only small amounts are needed. Preparation: Prepare a hot saturated solution
of 5gram ammoniummetavanadate and 1gram potassiumsulfate with about 50ml H2O. Mix with 50gram silicagel, evapourate under stirring and heating, dry
until completeness in the oven at 130°C. The catalyst has to be activated by heating in a stream of dry oxygen (air) at 450°C. This forms the
actual catalyst divanadiumpentaoxide (V2O5) from ammoniummetavanadate. 2 NH4VO3 -> V2O5 + 2 NH3 + H2O Potassiumsulfate stays unchanged and
functions as a promotor of the oxidation in the following catalysis. The catalyst described is useful for SO2 -> SO3 and many other reactions.
Of course exists a bunch of variations on amounts, cocatalysts and promotors, but te catalyst prepared afer this method will work for almost all
gasphase reactions calling for a vanadiumcatalyst. The principle of the preparation stays the same anyways. An interesting variation on
preparations of this group of (oxidation) catalysts is the so called "preparation by ignition". A search at espacenet will unveal the
related patents.
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The best way to measure high temperatures is a so called PTC (100/500/1000) whats a kind of platinum resistor with very high linearity, the second
best a thermocouple, type K is the common one used in those applications.
PTCs are quite cheap at EBAYs - I bought 4 of them for 12Euro so I remember it right, the usual price is about 4 to 5 Euro for one. For most exact
measurements you want one with 4 connectors for these eliminate the failure from the cables resistance but actually for your application it would be
overkill.
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axehandle
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Organikum: Very interesting. Do you know of an easy way to convert calcium sulfate (gypsum) to potassium sulfate (K2SO4)?
(I have 50kg of KCl and 1kg of KMnO4 to work with...).
Edit: And btw, does this mean my process using only V2O5, ammonia and water won't work without the K2SO4?
[Edited on 2004-3-3 by axehandle]
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Organikum
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Another good way to heat the sulfur would be by microwave irridation.
Advantages:
- selective heating of the sulfur IN the vessel (which must be made of glass then, is understood) . Sulfur is a very good microwave receptor - see
"sulfur lamp".
- easy control of the heating, as only the sulfur gets hot the burning stops almost immediately after the irridation stops, this should make refilling
a charm.
- household microwaves already come with a very stable "reaction chamber" made from metal what adds to safety.
just some thoughts....
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axehandle
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Hmmm, nice idea. Considering how cheap cheapo microwaves are right now, it might well turn out that it will be cheaper to boy one than to make my own
combustion chamber. Than there would only need to be two holes drilled in the oven. One for air in, one for SO2+air out...
About my desperate question concerning K2SO4 above...?
Edit: *cough* *cough* the microwave idea works. First, some of the sulfur sublimed (which means some sort of washing bottle must be employed), then it
burned. Thank you ever so much for the smell from Hell in my kitchen =)
Only kidding, I actually enjoy the smell of burning sulfur.
[Edited on 2004-3-3 by axehandle]
[Edited on 2004-3-3 by axehandle]
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Organikum
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Bad news:
I dont think there is a realistic way to convert gypsum into K2SO4.
Good news:
You can substitute the K2SO4 by Na2SO4 so available (Glaubersalz)....
Even better news:
K2SO4 is a mayor or even single ingredient of some common fertilizers, It should be easily available though.
If you have an mixture of salts in the fertilizer you can separate the K2SO4 by "salting it out", say you dissolve everything in almost
boiling hot water, what not dissolves after some time is to be discarded, then you saturate the solution slowly with KCl or ammoniumsulfate, voila
K2SO4 will fall out.
If you dont overdo it with the KCl you will have very pure K2SO4 then.
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axehandle
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Hmm, good good. But I'm wondering, is the K2SO4 really necessary? Your process in your quote involved SiO2 as the substrate, mine involves
pumice. Could the K2SO4 in your quote serve mostly as a binder, making it unnecessary when using a highly absorbant material, like pumice?
Btw, I don't care if the yield is 90 or 100%, as long as it's above 80 I'm happy. Sulfur is cheap.
Edit: The procedure I initially described seemed to come from a reputable source. Is it your opinion that it won't work?
[Edited on 2004-3-3 by axehandle]
[Edited on 2004-3-3 by axehandle]
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Organikum
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K2SO4 is a promotor - this says that it will work without also, but better with K2SO4. I dont know how much the process is improved by K2SO4, sorry.
Silicagel is at least as porous as pumice, but both should work fine.
More important IMHO is the activation process. I recommend to heat the tube not in one step to 450°C but to do so in steps, first to 250°C - holding
for at least half an hour, then 350°C and then up to 450°C for some hours. All under an airflow through the tube. To do this carefully is after my
experience much more important than any "promotor" or "cocatalyst" ever can be. The step by step heating/holding promotes the
formation of certain crystalline structures in the catalyst - this takes some time and stable temperatures. It doesnt matter if the temp. is 240°C or
260°C btw. what matters is that the temperature is as stable as any possible for the half hour needed for the crystal lattice to form.
PS: I dont doubt that the procedure you posted could work well, its just always good to know a second way.
The procedure of catalyst preparation is as far as I know from a german unversities webpage and as it is exactly on the preparation of an vanadium
cvatalyst for SO2/SO3 I thought it might be of interest.
Theres more than one way to skin a cat....
[Edited on 3-3-2004 by Organikum]
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axehandle
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| Quote: |
K2SO4 is a promotor - this says that it will work without also, but better with K2SO4. I dont know how much the process is improved by K2SO4, sorry.
Silicagel is at least as porous as pumice, but both should work fine.
More important IMHO is the activation process. I recommend to heat the tube not in one step to 450°C but to do so in steps, first to 250°C - holding
for at least half an hour, then 350°C and then up to 450°C for some hours. All under an airflow through the tube. To do this carefully is after my
experience much more important than any "promotor" or "cocatalyst" ever can be. The step by step heating/holding promotes the
formation of certain crystalline structures in the catalyst - this takes some time and stable temperatures. It doesnt matter if the temp. is 240°C or
260°C btw. what matters is that the temperature is as stable as any possible for the half hour needed for the crystal lattice to form.
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Aha! That explains alot, thanks.
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Theres more than one way to skin a cat....
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Personal experience?......
Btw, imy only heat sources are my kitchen oven and my propane furnace.
The oven only goes up to 300C. Would overheating the catalyst to, say, 700C, do any damage?
[Edited on 2004-3-3 by axehandle]
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axehandle
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Btw, organikum, I do have a quantity of FeSO4. Would the anhydrous form in a water solution precipitate K2SO4 if I were to add KCl?
I *think* SO4 would like K much more than it would like Fe...., but I could be mis-remembering.
PS: Thanks for the microwave idea. It worked perfectly, albeit in a very smelly way. I was planning to replace my antique microwave anyway, so
I'll use that. Just need to drill some holes..... and point them away from me.... I like warm climates, but there's a limit..... hehe.
[Edited on 2004-3-3 by axehandle]
[Edited on 2004-3-3 by axehandle]
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Organikum
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| Quote: |
Btw, organikum, I do have a quantity of FeSO4. Would the anhydrous form in a water solution precipitate K2SO4 if I were to add KCl?
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No. By no way. The described salting out precipates the K2SO2 by an simple solubility effect, this is no reaction taking place.
But as told, it will work without K2SO4 and the activation process is MUCH more important than K2SO4 present or not.
Keep the holes in the microwave smaller than 6cm in diameter (half wavelength) and never ever create a "slit" somewhere to the outside as
this works as an antenna - very bad. Better a open hole than a hole with a metal cover which creates a slit.
Microwaves are non-intuitive! So using "common sense" is a straight way to desaster. I posted some stuff on microwaves already here on the
board together with links for information, have a look.
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axehandle
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Ok. Thanks. I just dissolved about 40g of V2O5 in 1 litre of 24.5% industrial grade ammonia. It really cleared the sinuses.
There was fizzling as the V2O5 got converted to NH4VO3. Seems like an exothermic reaction.
A milky white precipitate, exactly like the colour of NH4VO3 immediately filled the pyrex beaker. Right now I have it on a slow boil on the stove. The
kitchen door is closed. The smell is overwhelming, but brings a freshness to the flat. Nothing beats the fresh smell of gaseous NH4.....
The holes will be 10mm to acommodate the tubing. Even more on the safe side w.r.t. the wavelength.
Tomorrow, I'll buy some Glauber salt to substitute for the K2SO4. I want this catalyst to be as good as humanly possible using my limited
equipment.
Provided I survive the ammonia vapours...
Btw, don't worry about microwaves and common sense. I have no common sense; at all.
Edit: I just figured a (kind of) way to keep the temperature at approx. 450C: Keep the catalyst tube in a bath of molten zinc. Zinc has a melting
point of 419C, so one _should_ be able to trim a hotplate with the help of a dimmer so that it barely keeps the zinc in a molten state. There are
probably better ways, though...
[Edited on 2004-3-3 by axehandle]
[Edited on 2004-3-3 by axehandle]
[Edited on 2004-3-3 by axehandle]
My PGP key, Fingerprint 5D96 E09E 365D 1867 2DF5 C2FE 4269 9C19 E079 CD35
\"Verbing nouns weirds the language!\"
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