Sciencemadness Discussion Board - V2O5 catalyst for H2SO4 production.

V2O5 catalyst for H2SO4 production.

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axehandle - 1-3-2004 at 09:05

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...

vulture - 1-3-2004 at 09:09

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.

axehandle - 1-3-2004 at 09:57

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]

Thermostat.

axehandle - 1-3-2004 at 11:57

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....

BromicAcid - 1-3-2004 at 12:24

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.

vulture - 1-3-2004 at 12:43

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.

axehandle - 1-3-2004 at 13:04

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 should, 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]

axehandle - 1-3-2004 at 13:14

What about a mixture of portland cement, aluminum oxide and bentonite clay? That should be extremely inert.

Geomancer - 1-3-2004 at 16:57

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.

material of construction

Magpie - 1-3-2004 at 20:13

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!

Tacho - 2-3-2004 at 06:34

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?

axehandle - 3-3-2004 at 04:39

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

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).

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.

axehandle - 3-3-2004 at 04:45

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.

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?

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]

type K themocouple wire

axehandle - 3-3-2004 at 04:56

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...

vanadiumpentoxide

Organikum - 3-3-2004 at 05:51

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.

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.

axehandle - 3-3-2004 at 06:01

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]

Organikum - 3-3-2004 at 06:06

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....

axehandle - 3-3-2004 at 06:21

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]

Organikum - 3-3-2004 at 07:32

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.

axehandle - 3-3-2004 at 07:36

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]

Organikum - 3-3-2004 at 08:45

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]

axehandle - 3-3-2004 at 09:01

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.

Aha! That explains alot, thanks.

Quote:

Theres more than one way to skin a cat....

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]

axehandle - 3-3-2004 at 09:08

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]

Organikum - 3-3-2004 at 09:50

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?

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.

axehandle - 3-3-2004 at 10:48

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]

And here it is (picture).

axehandle - 3-3-2004 at 13:09

Here is the result of the first step. The V2O5 is on the right, the NH4VO3 is on the left. Beautiful.

vulture - 3-3-2004 at 15:07

Axehandle, where did you get the V2O5 and how much did it set you back?

axehandle - 3-3-2004 at 15:48

One of the 3 major ceramics suppliers in Sweden, the one based in Stockholm.

0.1kg cost me 207SEK including freight and VAT. That's about 20 Euro, I think.

Took me forever to find someone having it. The guy at the other end of the phone said that the can was very old, and I was the first to order some for as long as he could remember.

I found 1 (one) supplier in the US, but the price was the same, the freight would have cost more, and they required registration (including my credit card number!).

I found 0 suppliers on the European continent.

It's an elusive chemical, and I should probably stock up, before it too gets banned.

I don't know if they ship overseas.

They have a web site... let's see, yes, here:
http://user.tninet.se/~svq845w/

[Edited on 2004-3-4 by axehandle]

Found phosphate bonded cement for plugs.

axehandle - 4-3-2004 at 01:23

The first dental lab I called today offered me some for free, and if I wanted more, they would sell it to me for what they paid for it. I'm happy now. I asked what it cost, the guy replied "next to nothing".

Edit: Btw, the excuse I used was "casting mold for aluminum".

Now I only need some rockwool, and some more ammonia as NH4VO3 solvent, then I'm all set, apart from the thermostat thing.

[Edited on 2004-3-4 by axehandle]

Tacho - 4-3-2004 at 03:27

Phosphate cement.

I´m glad you foud it. I hope it suits your needs.

I had such a hard time trying to make a good material for high temperatures before I found it! All sorts of messy mixtures with sodium silicate, metal oxides, carbonates....eechh!

I just could not find information on the chemistry of its hardening. I’m not really interested in the chemistry itself, but on whether it hardens by hydratation or not.

A plaster without molecules of water could be a nice insulator for jacobs ladders.

I posted this in “general chemistry” but nobody seems to know.

axehandle - 4-3-2004 at 06:35

Quote:

I posted this in “general chemistry” but nobody seems to know.

I'll find out. I just got 500g of phosphate bonded cement from a dental lab, for FREE!

The broschure says you have to "burn it out" to remove the water. The process won't expand nor constrict the material.

Edit: And if you mix it with water instead of a special fluid he also offered me, it has a heat expansion of 0.58% maximum.

The lab guys say they regularly cast gold using it. So I suppose it's good up to 1800-ish C.

[Edited on 2004-3-4 by axehandle]

[Edited on 2004-3-4 by axehandle]

NH4VO3

axehandle - 4-3-2004 at 07:15

I wasn't too happy with the colour of the salt, it was slightly yellowish. It could be due to impurities in the V2O5, but it could also be that I didn't use enough an excess of ammonia.

So now I'm repeating the process, using TWO litres of ammonia. Ouch, my damned sinuses, and alas, my nose, and hope hope hope the neighbours won't notice the odor.

And I'm going to have to sit in it until it's boiled in. Oh, the fun I have.

Well, I have rockwool now as well. Only thing lacking is Glaubersalz. I suspect it can only be bought as "foot bath salt". I have to find a way to refine it (i.e. destroy the perfumes and colour agents and other shit).

axehandle - 4-3-2004 at 07:22

 Oh Holy Shit this stinks so bad I want to jump out the window from the 7th floor 

I find it ironic right now that my beloved government has banned the sale of even dilute sulfuric acid, while I can cheerfully buy saturated ammonia (aq) by the tonnes with no questions asked. And acetone. And diethylether. And hydrocloric acid. And ammonium nitrate. And calcium nitrate. And potassium nitrate. And sodium nitrate. The list goes on....

[Edited on 2004-3-4 by axehandle]

rikkitikkitavi - 4-3-2004 at 08:52

in princip it would not be so hard to come by battery acid, if you knew someone who owns a gas station...

/rickard

axehandle - 4-3-2004 at 09:19

Well, I unfortunately don't. Besides, I want a limitless supply of 98% H2SO4. And it's more fun to make it.

Edit: Seems most of the NH3 is boiled off now. The air is becoming breathable. Aaaaah.

[Edited on 2004-3-4 by axehandle]

axehandle - 4-3-2004 at 10:19

Now. Finally. But the damned thing began to spatter as it thickened, and covered both me and my stove as well as some of my cookware with toxic NH4VO3

I estimate a 1/3 loss, but what remained should be more than enough for at least 3 catalyst tubes.

But I hate getting poison spilled all over me.

axehandle - 4-3-2004 at 10:25

Fucking stove. Next thing I build will be a proper heating mantle, provided I can find glass fibre tubing.

Damned, NH4VO3 on the skin itches like hell. Don't try it at home, kids...

And YES, Mr. Marvin, I rinsed and cleaned the exposed skin immediately, and I'm in no fucking way encouraging people to repeat the fucking accident.

[Edited on 2004-3-4 by axehandle]

Log with pictures.

axehandle - 5-3-2004 at 11:16

I have a construction log with some very uninteresting pictures up now, for those interested:
http://species8472.dyndns.org/so3/so3.html

Edit: Oh, this is my 0x100th post! This calls for a celebration!

[Edited on 2004-3-5 by axehandle]

Is this right?

axehandle - 5-3-2004 at 15:13

Could THIS really be the colour of the finished catalyst??? I thought it was supposed to be yellow, not reddish-brown????

[Edited on 2004-3-5 by axehandle]

Edit: Apparently it's normal for a catalyst to change color both during preparation and in use. I'll use it.

[Edited on 2004-3-8 by axehandle]

processed.jpg - 8kB

axehandle - 8-3-2004 at 13:59

A very interesting concept just struck me. Why heat the catalyst tube? The process of burning the sulfur should give very hot SO2 as a result, which would then heat up the catalyst automagically. But I'm probably missing something really obvious here....

Geomancer - 8-3-2004 at 15:06

The problem, as usual, is control. You don't want the temperature at the catalyst to rise too high, because the yeild decreases with temperature. I still think that, even on a small scale, the catalyst bed should be able to keep itself more than warm enough if properly designed. Moreover, it is advantagous to decouple the parts of the process as much as posible, so you don't need to optimize everything at once.You may want to warm your feed a bit to achieve ignition, though an electric heater has more versatility. If I ever get around to this, I think I'd cool the feed and not use a heater.

axehandle - 8-3-2004 at 22:45

Yes! Geomancer, that's exactly how also I think! There are 3, possibly 4 variables involved in the control of the SO2 burner exhaust temperature:
1) Air inlet pump speed.
2) Microwave power.
3) Insulation around the catalyst tube.
4) Air inlet air pre-heating (spin a dimmer
controlled heating wire coil around the pipe) or pre-cooling (wrap a wet towel around the pipe).

If all these are kept so that the catalyst temperature is keeps itself at 400-500C _most_ of the time, there should be no need for spinning a complex heating wire around the catalyst tube.

With a bit of luck (now I'm being optimistic) it should work.

Edit: Btw, my burner is almost done. An old coffee machine glass pot now has a new task in life....

Edit2: Fucking hell. Cracked the pot. Ah well, I'll buy a real E-flask prerably with NS-coupling today, then cast a plug with integral air in/out pipes using phosphate bonded cement.

Just as good the damned thing cracked, in retrospect I doubt it would have coped with (what can it be? 500C?) temperature shock of microwave heated, burning sulfur.

[Edited on 2004-3-9 by axehandle]

[Edited on 2004-3-9 by axehandle]

[Edited on 2004-3-9 by axehandle]

Might be of interest,

axehandle - 9-3-2004 at 04:22

especially for you, Rickard. It seems Melitta brand coffee pots are made out of borosilicate glass.

I just put the remains of my cracked (by a screwdriver impact accident) pot inside the top of my propane furnace and turned it on to full blast. That's from 26C (my room temperature) to about 900C in a couple of seconds. I let the burner run for about a minute, then I turned it off. The glass pot remained unscathed.

My conclusion is that a Melitta brand coffee pot can be used as a sulfur burner, given this design (ASCII art):

/
/
| |
| |
-------

Edit: My drawing got fucked by the board code, but you'll all probably get the idea anyway.

As you can see, the converging/diverging top lends itself easily to a gypsum/cement/whatever cast unremoveable plug, with pipes going in and out, and some sort of re-sealable fuel addition hole.

And they only cost about 50 SEK each, much less than an NS-topped E-flask of borosilicate glass...

Tacho - 9-3-2004 at 08:27

I was planning to post a precise description of a practical thermostat when I had all the details figured out, but there has being a lot of talk about temperature control here.

I have spent some time trying to figure out a way to make a cheap, easy to make, thermostat to keep the tube furnace at 450º.

I studied three options. I believe the first is the most attractive, although I have never seen it implemented anywhere.

MOLTEN SALT THERMOSTAT.
I am still doing experiments on this. I intent to post a detailed practical project soon.
The idea is that a salt is much more conductive molten than solid. So, a capsule filled with salt has two electrodes, when the temperature of fusion is achieved, the increase in current triggers off the power. A few observations must be made:
1) Very low current should pass through the salt, to prevent electrolysis that would corrode the electrodes and produce gas. Therefore, an electronic trigger circuit should be used.
2) The eutectic mixture should melt at a lower temperature, I estimate 440ºC, to compensate for thermal inertia and heat of fusion of the salt.
3) Salt hydrates should be made anhydrous before they are put in the capsule.
4) Since the salts mixtures used to obtain a 440ºC are hygroscopic (if not deliquescent), the capsule should be closed to the atmosphere. On the other hand, the heating produces increase in pressure due to inevitable (to the amateur) residual water and electrolysis produces a bit of gas, no matter how low the current. How to solve this? The best I could come with is to connect the system to a rubber bladder like a balloon, or better yet, a condom. Kind of a joke, but I am still working on it.
5) To find the appropriate eutectic mix:
http://ras.material.tohoku.ac.jp/~molten/molten_eut_query1.p...
I have just begun to test mixes of NaCl, KCl, ZnCl2 and MgCl2.

RTD (RESISTIVE TEMPERATURE DEVICE)
Thermistors could be used here, with the bridge circuit proposed, if you can find a cheap one rated 450ºC. IF YOU FIND IT, LET ME KNOW! The circuit is ready and it will save me a lot of time.
RTD are just long wires commonly made of platinum, copper or nickel. I add a link to a temperature sensing technologies text that I consider very good.: http://www.microchip.com/download/appnote/analog/adc/00679a....
There you find a table saying that a platinum wire increases its resistance by 38,5 ohms for every 100ºC of temperature change. An electronic circuit called a wheatstone bridge connected to an operational amplifier configured to act as a comparator triggers off your power when a certain resistance is achieved. This sounds complicated, but is a very simple circuit, just half a dozen components on a prototype printed circuit. I´ll post a picture ASAP.
The big problem here is that platinum is not an option and you need a lot of thin copper wire to get 100 ohms. You should use about that many ohms for the sake of accuracy and to prevent large currents on your circuit.
We are talking of 16,5 meters of 42 awg wire or 55,25 meters of 37 awg wire (those are the wires I have in stock). 42 is just too thin, I don´t think it will resist the harsh conditions of a furnace. 37 seem reasonable, but I can´t think of a practical way of putting 55 meters of wire on a sensor that goes in a furnace. Remember that the varnish will became a very strange thing at 450º, maybe conductive. You also have to protect the wire against the SO3.

CURIE TEMPERATURE SENSOR
Uh! I love this one, although I never tried it! The idea is that the magnetic properties of a nucleus made of ferromagnetic matter will change its inductance properties wildly at it´s curie temperature. The beauty is that only the nucleus goes in the furnace, the coil (or coils, if you are thinking about making a transformer) goes outside, cool and protected.
Shame the only practical materials are nickel (ct=358ºC) and iron (ct=770ºC)

Temperature control and its whereabouts.

axehandle - 10-3-2004 at 12:30

Tacho, I've decided that it's much smarter to heat the burner exhaust gas, instead of heating the catalyst. There are many reasons:

1) The burner gas consists only of dehydrated air and SO2, so it shouldn't be as corrosive to the heating element.
2) The heater's size can now be accomodated to fit the thermostat and heating element, instead of the otrher way around.
3) The catalyst is V2O5 on a pumice carrier. It's thermal capacity is therefore negligible. The catalyst temperature will probably be roughly the same as the temperature of the gas passing through it.

I've also decided against using a microwave oven as a burner initializer. The main reason is that I need that oven for food, and am too broke now to buy a new one...

So, we're left with one choice: A stand-alone sulfur burner, with a heating element for the combustion gas. From now on it gets easier:

I've identified 5 main physical components in the plant:
1: Air feed pump.
2: Air dessicator (CaCl2 filter).
3: Sulfur burner.
4: Exhaust heater and thermostat unit.
5: Catalyst tube (done, will attach a picture)
6: Absorber tank (simple water bubbler).
7) Absorber tank coolant system. (under
design)

We can now concentrate on (4), the most complex of all the parts. The fact that only dry SO2 and air will pass through it gives us plenty of material choices. It could be as simple as a concrete box (dehydrated) with a free-hanging NiCr coil, some sort of thermostat, and, say, copper tubing for the inlet and outlet. Dry SO2 shouldn't be corrosive to NiCr wire. At least, I don't think so. And if it is, it's probably best to design the heater so that the heating element is easily replaceable.

Brainstorming?

/A

cattube.jpg - 8kB

Tacho - 10-3-2004 at 15:38

Quote:

Originally posted by axehandle
Tacho, I've decided that it's much smarter to heat the burner exhaust gas, instead of heating the catalyst. There are many reasons:
(snip)
/A

Too late now.

I'll stick half a dozen thermostats down your thread.

Don't try to stop me.

Lets start with an abandoned Idea:This circuit is to be used with RTD (maybe with thermistors) devices. NOT with the molten salt idea because this will require a much simpler trigger circuit.
Although I believe the most practical idea for a thermostat will be the molten salt, I post this comparator just in case someone is interested. After all, I´ve already built it anyway.

comparator circuit.jpg - 48kB

axehandle - 10-3-2004 at 15:43

Even I could build that, on a testing board. Nice circuit.

But I like the molten salt idea. If encased in a glass "bubble" inside the exhaust heater, it should be completely impervious to corrosion.

Edit: Clarification: My new solution does not negate the need for a thermostat, it merely makes the job somewhat easier. (I.e. it doesn't have to be small).

[Edited on 2004-3-10 by axehandle]

[Edited on 2004-3-10 by axehandle]

THERMOSTATS! THERMOSTATS! THERMOSTATS!

Tacho - 11-3-2004 at 04:45

axehandle,

Don´t built the circuit on those solderless breadboards (protoboads)! The comparator depends on fractions of a ohm to work. The resistance of the contacts of those solderless boards plus oxidation on the wires is enough for erratic behavior. Use solder.

MOLTEN SALT THERMOSTAT
I used a mix of KCl and MgCl2 in 12cm Pyrex test tube. The electrodes are simple copper wires held together by plaster of paris. Results are good: resistance falls from off-scale to 30 ohms during melting. This test was repeated 4 times.

I added to the tube a bit of zinc I took from a common battery. The melting point of zinc is 420º and it seems to melt along with the salt mix, although it is not easy to tell when exactly each is molten. This proves that, at least, we are close to 440ºC.

Neither the zinc nor the copper electrode is (are?) attacked by the molten salt.

I repeated the test 24 hours latter and the results were the same (off-scale to 30ohms). This shows that water absorption is not a problem after all. You may use an open or loosely capped Pyrex test tube as capsule.

I added a trigger circuit that is very simple and I believe your thermostat is ready. I tested it many times and seems to work fine. THIS circuit can be built on a solderless breadboard, I did. As cheap and simple as possible. Probably needs some heating up to drive away the water after is left unused for long.

I will be doing some tests during the next days, if something changes I´ll let you know.

Notes:
1) MgCl2 has 6 molecules of water usually bonded to it, so it melts at a lower temperature (dissolves in it´s own water of hydratation), when heated for the first time. This is good, because it dissolves the KCl and makes a more homogeneous eutectic. Boil away the water and the solid that is left eventually melts close to 440ºC.

2) Possible mixes(*):
NaCl 56 mol%(37g) + MgCl2 44 mol%(41,89g).................mp= 430ºC
NaCl 56,2 mol%(32,84g) + MgCl2 43,8 mol%(41,70g)......mp= 432ºC
KCl 66 mol% (49,20g) + MgCl2 34 mol% (32,37g)........... mp=430ºC
KCl 66,6 mol% (49,64g) + MgCl2 33,4 mol% (31,8g)....... mp=435ºC
KCl 66,7 mol% (49,72g) + MgCl2 34 mol% (31,7g) ..........mp=437ºC
KCl 65,2 mol% (48,6g) + MgCl2 34,8 mol% (33,13g)....... mp=433ºC
KCl 69 mol% (51,43g) + ZnCl2 31 mol% (42,25g) ............mp=433ºC
(*) I think is clear that the site I linked in the previous post means anhydrous salts, my calculations were based on it, so you have to add the molecules of water to the weight if using hydatated salt. To save you time: molecular weights: NaCl 58,44; ZnCl2 136,3; KCl 74,54; MgCl2 95,21.

2)My scale is not precise enough to make those different KCl-MgCl2 mixes, so I can only guess my exact melting point.

salt thermostat.jpg - 22kB

axehandle - 11-3-2004 at 04:50

Beautiful!!!!

And the best part is.......: I have both KCl, metallic zinc and HCl!

I'm concerned about the response time though. Probably best to use a metallic container. Aluminum has the best heat conductivity, and I can easily cast a probe-like thing.

Exhaust heater design, cross-section.

axehandle - 11-3-2004 at 05:05

--------------------------------------------------------------------------
Refractory mix
--------------------------------------------------------------------------
Concrete with heating coil + embedded thermostat
--------------------------------------------------------------------------

---> Exhaust flow, pipe length approx. 30cm

--------------------------------------------------------------------------
Concrete with heating coil + embedded thermostat
--------------------------------------------------------------------------
Refractory mix
--------------------------------------------------------------------------

Extremely ugly picture, but you get the idea. The (dehydrated) concrete will act as a heat buffer, so there will be little temperature variance over time even if the thermostat is slow.

[Edited on 2004-3-11 by axehandle]

Tacho - 11-3-2004 at 05:47

Sugestion:

...................Thermostat
------------------------|..|---------------------
Refractory mix......|..|
-------------------------|..|--------------------
C. w. heating coil..|..|
========================================= space for dilatation

---> Exhaust flow, pipe length approx. 30cm

========================================= space for dilatation
Concrete with heating coil
-----------------------------------------
Refractory mix
-----------------------------------------

lousy drawing, but the idea is to insert the thermostat tube vertically, somewhere along the tube.

I think you shold give your glass tube space to dilatate.

If you want to give your NiCr wire space to dilatate also , first give it a bath of molten paraffin, not very hot. This will create a layer of paraffin around your wire. Than embed it in phosphate cement. This will make a hellish stench the first time you heat it, but after the paraffin has disapeared (I don´t know if it evaporates, disintegrate or whatever, but I know it works, I´ve done it) Your wire will have space to diltate. I have made embedded heating elements without this procedure and they work OK, but I thought I should give you the idea, you will be investing a lot in it.

[Edited on 11-3-2004 by Tacho]

axehandle - 11-3-2004 at 07:08

Good idea. One modification though: I'll use stearin instead of paraffin, since I've got plenty of candles but no paraffin...

Edit: More progress has been made:
http://species8472.dyndns.org/so3/so3.html

[Edited on 2004-3-12 by axehandle]

axehandle - 12-3-2004 at 14:49

Oooooh! The first Macintosh browser to ever have accessed my webserver has accessed it. Interesting.

Tacho - 13-3-2004 at 11:32

I just tested the thermostat again and its is fine. Humidity is no problem at all.

Use thin electrodes. The heating of a thick wire takes long because it acts as a dissipator of heat. Causes slow response. Mine are 1,5mm2 and I noticed that effect.

Also, I just washed the test tubes I used for inicial tests and it seem the molten salt does not attack the glass at all.

How is the project?

Progress.

axehandle - 13-3-2004 at 16:26

It's progressing nicely. I'm basically just waiting for the concrete/bentonite mix in the burner bottom to fully harden, then I'm going to cast the top and construct the heater (again, you know what happened to the last one... fscking decimal signs.....).

I have bad experience dehydrating concrete/bentonite mix before it's fully hardened, hence the long waiting period.

I'm still not sure whether to have the NiCr coil exposed to SO2 vapors or to insulate it someway. I *think* that provided no water is introduced (eg. I'm going to use an air dessicator after the air pump), the NiCr wire won't get attacked. That would be the simplest way. Just a coil of 0.2mm dia NiCr wire inside a glass tube, controlled by a dimmer and using your salt thermostat idea as an indicator. But I could be wrong. And right now, I'm drunk as well. Perhaps it shows.

As previously said, I will construct this plant in an extremely modular way --- if one part fails, I'll just need to replace it.

But regardless, it's very exciting to downscale an industrial process by a factor of 1000. My goal is to make the entire plant fit on a 500x500 mm table. Then, when it's done, I'll cover the whole table with a fume hood and an air exhaust, just to be on the safe side.

scaledown

Magpie - 13-3-2004 at 19:36

Axehandle you are very right. You are doing the opposite of scaleup - a common task of chemical engineers. In fact there is a whole field devoted to this called dimensional similitude, like using models in wind tunnels, etc.

An anecdote: I once had a job to figure out how to get a 1 gallon lab corn starch converter to behave like a 3000 gallon plant production converter. The process consisted of "cooking" a water/starch slurry with an enzyme for about 2 hours. Of course I started using the same cooking time and same recipe. But the production size unit gave a higher conversion. I tried varying the recipe and agitator tip speed but never could duplicate the plant results. It probably could have been done I just gave up as it was taking too much time.

Geomancer - 13-3-2004 at 20:18

So I hacked together a sulfur burner today. Alas, the sulfur I got at the DIY warehouse ("Green Light" wettable dusting sulfur) is quite impure. It created huge masses of smoke and left large quantities of clinker in the device. The run was not succesfull. I'll make another go tomorrow, see if the impurities settle out of a melt.

Tacho - 14-3-2004 at 03:15

Geomancer,

Are you trying to make a small sulfuric acid plant like axehandle's or just experimenting with sulfur?

axehandle - 14-3-2004 at 03:18

I'm very sorry for your contaminated burner.

I get my sulfur in a store that sells mined sulfur from Sicily. It's quite pure. Another option would be sublimed sulfur ("flowers of sulfur"

available anywhere. But there will always be small contaminants.

I will insert a wash bottle after the burner to get rid of solid particles. Wouldn't want to poison my catalyst, I've invested far too much time in it....

Edit: I'd get a purer kind of sulfur, I've read that gardening sulfur contains up to 10% impurities.

[Edited on 2004-3-14 by axehandle]

Geomancer - 14-3-2004 at 12:41

I'm interested in the technical problems of the small scale contact process. It remains to be seen if I'll ever build a complete plant.
I think I will forgo any further experimentation with my current sulfur. Does anyone have good suggestions for sulfur sources (in the range of a few pounds) in the eastern US?

[Edit: I tried burning a nice yellowish chunk of sulfur that froze in the burner in open air. It ignited vigourously, burning with a blue flame, but quickly turned black and self-extinguished. When I scraped up the residue (sticky black stuff covered by a crunchy ash layer) and molded it into a ball, it once again burnt vigourously, charred, and went out. I was able to repeat the process several times.]

[Edited on 15-3-2004 by Geomancer]

axehandle - 15-3-2004 at 14:02

This is just idle speculation, but I'd think you'd be able to refine the sulfur by melting and sedimentation. Oop! Reminds me, time to turn off the oven. The sulfur burner bottom half should be done now. Tomorrow I'll cast the lid!

Edit: And I will take a lot of pictures. If the design works, it's probably the cheapest and most efficient burner I've ever seen. If it doesn't --- well, I've only made a fool of myself. I'm quite used to that by now...

[Edited on 2004-3-15 by axehandle]

Organikum - 15-3-2004 at 14:54

It should be possible to clean sulfur in the same way red phosphorus is cleaned: Washing with lots of water, dilute acids, water again, dilute NaOH solution and cupious amounts of distilled water at the end.

Geomancer - 15-3-2004 at 15:17

When I die, I'm going to sue both axehandle and Green Light

. I placed a sizeable amount of the dusting sulfur into a pan on a hot plate. At first, the heated sulfur became slightly more yellow. As it began to melt, there was a small amount of bubbling and the liquid in contact with the pan started to turn reddish. As the entire mass melted, the bubbling became vigorous, turning the mass into a watery foam, somewhere between the color of dog vomit at the top and brown sugar below.
I'm not sure what the evolved gas was. According to my mother, it doesn't smell like rotten eggs, so hopefully it's something less toxic than H2S. It definately smelled "sulfurous", but it didn't burn by eyes like I would expect SO2 to. Moreover, white smoke (perhaps condensation from the air, though it's not that humid here) also evolved at the hieght of the reaction. The only suitable vessel I could find was an aluminum pan. It may have been involved, but I think not. The mixture took a while to cool, and retained a low viscosity up to the point where it froze. Also, gas evolution continued at a diminished pace even after the upper layer had solidified.

What is it that makes this sulfur so evil?
What was the gas that was formed?
Will I survive?

Inquiring minds want to know.

axehandle - 15-3-2004 at 15:38

Oh dear. I didn't mean "on a hot plate"!!! My theory is that you got "hot spots" that lead to oxidation of some of the sulfur, yielding SO2. Don't worry, it's only lethal in 1000ppm++ amounts. There's no way you made H2S, at least not that I'm aware of.

What about using Organikum's method instead?

On a related note: You can't sue me. In my country we have laws that basically say that "whatever you've read or heard, you've only yourself to blame for taking the advise..."

I'm very sorry for not being more clear, though. Using hotplates together with combustible substances is suicidal. I'm sorry for not being more clear. Why not try melting the sulfur in a more controlled manner, like, say, in your kitchen oven?

Edit: Btw, SO2 in small amounts doesn't "burn your eyes" in my experience. It only leads to a bad cough. I know from a little accident I had that taught me some valuable lessons.

Edit2: I would blame the contaminants in the sulfur for the gas development after you stopped heating it. It could also be sublimed sulfur. When I tried to melt sulfur in a pan (!) in my oven, the damned thing got covered on the entire inside with sublimed sulfur. Took me 300C at 3 hours to burn it off.. use a somewhat closed vessel, like an E-flask. Then you can let it settle and pour the molten sulfur into cold water. Then wash with, say, acetic acid and then distilled water, just like Organikum said. But if I were you, I'd simply buy some purer sulfur...

[Edited on 2004-3-15 by axehandle]

[Edited on 2004-3-15 by axehandle]

Geomancer - 15-3-2004 at 15:54

I suspect that if I used the kitchen oven, my house would be full of the unknown gas. Ovens have poor temperature control, and the knobs are badly calibrated. Moreover, my oven is a gas oven, and so uses an open flame. I cannot discount the hot spot theory, but it seems unlikely that the temperature would be very much over that desired while there was still solid sulfur present. Moreover, very hot liquid sulfur becomes more viscous. My stuff remained watery the whole time. I also don't think that atmospheric oxygen was responsible. I just don't see that route causing foaming. While better temperature control would help settle things, I'm not going to try it without either a compelling reason or better information as to what's in this witches brew.

axehandle - 15-3-2004 at 16:05

For pete's sake mate, DON'T discount the hot spots! That's how I almost blew my face off melting rocket fuel on the stove!!!!!!

Believe me, hot-spots are BAD!!!!

Edit: That said, buy some purer sulfur. It should be called "flowers of sulfur", i.e. sublimed sulfur, quite pure.

[Edited on 2004-3-16 by axehandle]

axehandle - 16-3-2004 at 09:38

Now the bottom is dehydrated. Stupidly enougn I'll have to wet the bottom of the burner hole, since that's where I will place a heating coil embedded into phosphate bonded cement. I have spun a coil of 0.3mm dia NiCr wire, resistance adjusted to a 300W dimmer.

I've learnt that sulfur has a boiling point of 444C, and an auto-ignition temperature of 248-266C. Hence there shouldn't be any need of an ignition device, heating it to the auto-ignition temperature and then holding that temperature while providing oxygen should suffice.

Now, the tricky part will be the connectors. They'll be in contact with burning sulfur in a molten state. What material? I'll have to think. The logical choice of material would be gold-plated nickel. I'll check up the prices.

BromicAcid - 16-3-2004 at 10:03

Sulfur in the molten state is actually quite corrosive. I read about it extensively when I was reading about carbon disulfide production. The molten/vaporized sulfur would come into contact with the heavily heated carbon and react. And guess what they use to coat the vessel? ALUMINUM! That has the incredibly high resistance to sulfur that one would dream of, however for the carbon disulfide reaction it wasn't very useful because at the temperatures employed for the vaporized sulfur to get the highest yield the aluminum would be molten. The papers went on to descibe the properties of high aluminum alloys to use in place of straight aluiminum to run at higher temperatures.

Also, Geomancer, the color changes and changes in viscosity were normal except maybe that last one where it turned like dog vomit. It is because the sulfur rings S8 break apart at the higher temperatures and form polymer sulfur (which you can pour in cool water and get plastic sulfur from) then at higher temperatures it breaks apart and changes color and texture again. Finally at exceedingly high temperature it boils and makes S2 molecules, S2 is green I think, could be wrong. Also, did you know that the alkali metal vapors are brightly colored, I'm pretty sure gaseous potassium is green too.

[Edited on 3/16/2004 by BromicAcid]

axehandle - 16-3-2004 at 10:14

Great! I'll just cut up a piece of aluminum pipe lengthwise to obtain 2 Al strips then. The temperature I anticipate in the burner will never exceed 400C, far below the 622C melting point of aluminum. Thanks.

Edit: It also means that I don't have to make the lid detachable! All that's needed is one 20mm aluminum pipe for sulfur addition, another one for a future temperature probe, sealed during burning with 2 soft-lead plugs! Halleluja!

Edit2: Thanks to my rocket hobby I've got tons of aluminum pipe! Oh, yes, precious...

[Edited on 2004-3-16 by axehandle]

[Edited on 2004-3-16 by axehandle]

[Edited on 2004-3-16 by axehandle]

Geomancer - 16-3-2004 at 10:25

Bromic: There was no change in viscosity. It was very fluid at all times.

It rained today. The solidified mass has turned to slush. Apparently, whatever made the stuff wettable concentrated at crystal boundries, and dissolved. From what I remember, the melt did not seem to have multiple condensed phases, although the foaming that was going on made it hard to tell.

axehandle - 17-3-2004 at 16:06

Ooooh.... My burner's melting sulfur.... I love the smell of brimstone. Let's see if it catches flame when the heating coil embedded in phosphate bonded cement manages to heat it to the auto ignition point....

Then to the impurities point. How to clean the exhaust from solid particles before it enters the exhaust heater (before the SO2 enters the catalyst chamber)? Ideas, anyone? Myself, I'm thinking a bubbler. But the water would heat up quickly. I'd prefer a replaceable filter. Would rockwool do it?

de-entrainment equipment

Magpie - 17-3-2004 at 20:45

The usual industrial way to remove particles in a gas stream is with a filter, demister pad, and/or sheet metal chevrons, depending on the particulates and the degree of removal required.

An industrial evaporator I worked on cleaned high velocity steam with a chevron pad followed by a demister pad (like a brillo pad). This was all up flow so the particles became entrained in condensate which then just drained back into the evaporator.

New burner design.

axehandle - 19-3-2004 at 11:45

Thanks. I think a filter will be simplest, and the easiest to replace.

Right now I'm trying to tackle the sulfur burner problem. I'm not happy with the current design. In fact, I'm very uphappy about it. I'm gonna scrap the old design and use a completely new one I came up with today.

I'm attaching it, since BB code is disabled here.

Explanation:

The burner is made of cast aluminium (white), with a number of thick rods protruding from the bottom into the combustion/melting chamber to distribute the heat evenly. Aluminum has excellent heat conductivity.

A simple circuit using the embedded thermocouple (red), essentially a thermostat, controls the heating mantle (blue) so that the pure, elemental sulfur (yellow) is kept in a molten state close to its auto-ignition point.

Dry, pure oxygen is fed very slowly through one of the pipe-like entries at the top of the Al chamber. As SO2 is formed, it's forced out the other opening, where it will be passed through a thick rockwool filter. Then it is led into a SO2 heating pipe, and then passed through the catalyst where it will get converted to SO3, after which it's led to a bubbler with water, where it will form H2SO4(aq).

The heating mantle could be replaced with a hot air gun blowing at the aluminium vessel's side, if a cheaper, more noisy solution is called for.

Now, I know that aluminium is resistant to molten sulfur, as well as to SO2. It should also be resistant to dry O2. However, I'm not sure what happens when it's exposed to burning molten sulfur combined with O2 and SO2.

It could be that the combustion temperature is higher than the MP of Al, and then my design is seriously fucked.

Anyone please care to give me some feedback?

axehandle - 19-3-2004 at 11:47

Damned. Here is the attachment:

aluminium.bmp - 352kB

rikkitikkitavi - 19-3-2004 at 13:37

axehandle , are you going to use 100 % oxygen as a feed?

imagine sulfur burning in a 100 % oxygen atmoshpere? try it with red-glowing steel wool...

It will be an extremely short buring, when all the oxygen inside the burning chamber is consumed quickly, and the temperature of the SO2 will be very high ( +1000K). You can calculate the energy released by the heat of reaction and the amount of O2 inside the chamber (296 kJ/mol)

Howver the large aluminium can will probably absorb the heat (if you burn 2 moles/h it equals 150W of power)

Also the auto ignition point of sulfur is increased a lot if SO2 is present , according to Ullmann.

/rickard

BromicAcid - 19-3-2004 at 13:45

I don't think axehandle is going to be using a 100% oxygen feed, he is just going to be hooking a desiccant system to his air intake, look here http://www.sciencemadness.org/talk/viewthread.php?tid=1691 I believe he might have mentioned that he would be using this for this reaction, if not in this thread then in another relating to it.

axehandle - 19-3-2004 at 15:28

Actually, BromicAcid, I intend to use pure oxygen, but fed very slooooowly. My experiment involving heating sulfur to the auto-ignition point showed that the sulfur never catches fire in an air athmosphere, it only begins to boil from overheating.

The failure could have been due to temperature differences in the bottom where the heating element was located and the top, but I imagine pure oxygen will work.

I don't intend to "whooosh" lots of pure O2 into the system, as that would probably lead to an explosion. I intend to feed it very slowly, say 0.1-0.5 litres/minute.

Edit: I'm repeating the experiment now, but this time I use a very thin layer of sulfur in a cooking pot on the stove. I'd hate to have to buy an O2 tank.

Edit2: No. The layer of molten sulfur (about 5mm deep) started to boil and sublime in the air. I let this continue for a few minutes before I gave up. It never caught fire. THis is very strange. The boiling point is far higher than the auto ignition point, so why the &%¤# doesn't the sulfur catch fire?

Edit3: I never anticipated the fscking burner to be the greatest obstacle. It's starting to lean towards the microwave solution after all.

Edit4: Either that, or finding an ignition wire capable of being heated to a red hot constantly, in an atmosphere of molten sulfur, air, and SO2. Great. The only one coming to mind is Pt. That's out.

[Edited on 2004-3-19 by axehandle]

[Edited on 2004-3-20 by axehandle]

[Edited on 2004-3-20 by axehandle]

[Edited on 2004-3-20 by axehandle]

Tacho - 20-3-2004 at 02:16

I could not download your attachment.

Sulfur burns so easily in air! Why don't you put in the burner a tiny loop of thin NiCr wire heated white hot by a small transformer. Maybe even touching the sulfur.

If you don't have the transformer, put it in series with a 100w light bulb. Or your heating coil.

Can't you leave a burning sulfur candle inside the vessel?

Can't you leave a small hole with a plug, so that you can open it, light the sulfur with a match and then plug it again?

An oxygen tube seems too much trouble.

axehandle - 20-3-2004 at 03:09

NiCr wire would be destroyed, I think.

How's a sulfur candle constructed?

/A

Tacho - 20-3-2004 at 06:50

Quote:

Originally posted by axehandle
NiCr wire would be destroyed, I think.

How's a sulfur candle constructed?

/A

Is... eh.... a candle! Made of... well, sulfur.

Serious: I have never seen a sulfur candle. Google gave me 10 results, none of them with a picture. I believe if you melt some sulfur, wet a wick (piece of string) in it and put the wick in the fused sulfur, it will work as a candle. The sulfur will be the parafin/stearin and the wick will be the... wick.

other idea:
Break the glass of a light bulb, put the lamp, connected, inside the burner. When temperature is OK, light the bulb. Boom: sulfur on fire. Well, curtains on fire, walls on fire, axehandle on fire... nah! No good.

Saerynide - 20-3-2004 at 07:31

ROFL You're real nice *cough*

But wouldnt the tungsten just burn with a quick flash? Or... does that flash explode sulphur....

Tacho - 20-3-2004 at 07:36

Would this help?

axehandle - 20-3-2004 at 08:28

Eeeehhh. Hmm. I think I'll try to cast a sulfur candle with a thick cotton whick.

Tacho, you may just have saved me about 2 weeks of work and about 150 Euro. I feel more than a bit stupid for not coming up with this idea myself....

Edit: But the casting will have to wait until Monday. My stock of candle whick went empty last week....

Or I could perhaps melt a few ordinary candles, recover the wicks and boil them. That should get rid of most of the stearin.
Worth a try. May even do it today, if the weather is favorable...

/A

[Edited on 2004-3-20 by axehandle]

[Edited on 2004-3-20 by axehandle]

Saerynide - 20-3-2004 at 08:52

I cant see the pic

Tacho - 20-3-2004 at 10:04

Saerenyde, the flash would ignite the sulfur, but maybe the gases from hot sulfur inside the burner would explode.

The picture displays a ignition coil and a circuit to provide sparks.

This is the first time I post pictures linked to my new website, does anybody else have trouble seeing it?

Saerynide - 20-3-2004 at 10:50

Hmmm.. your site doesnt load :|

Tacho - 20-3-2004 at 14:06

axehandle,

Take a look at this picture, maybe you will be interested. Maybe this is the solution to your sulfur ignition problem, if the candle does not work.

Sorry about the site & pictures, I'll have to find out what is going on.

Image012.jpg - 11kB

axehandle - 20-3-2004 at 15:30

I think a sulfur candle should be not too hard to make. I *think* that since sulfur has about 3 times as high an MP as stearin, the whick will need to be thick. (This sounds very funny in Swedish since "whick" has two meanings, catch my drift...). Maybe it could be made from a string of rockwool, if it needs to be incombustible. I will find out on Monday, because then I'll go out and get some whick.

Oh dear, that word should really be substituted by "burn-sustaining substrate".....

About the picture: Thanks, but I already have one of those, made for a very different project (which failed). It involved a battery powered car ignition coil 40kV spark generator. I also have one of these (it's an 8kg heavy resin block 9kV 60mA NST):

New design (again).

axehandle - 20-3-2004 at 16:21

Since multiple attachments can't be made, and the BB Code and IMG-tag is off, I have to make this a new post. Please bear with me, moderators.

This is a revised design. In fact, the cast aluminum vessel in the new design doesn't have to be cast, One could simply take a piece of 50x2mm aluminum pipe and cast the bottom piece out of gypsum or phosphate cement. The connectors could be made from 15mm Al roundbar, and screw-in pieces could be made from that using only a drill press and some machine-screw-making tools. They could even be copper or glass pipe in cork plugs. The heat production will be low.

Edit: Now I feel I'm finally getting somewhere! Thanks for the idea, Tacho!

[Edited on 2004-3-21 by axehandle]

candleburner.jpg - 11kB

Polverone - 20-3-2004 at 17:21

Something is wrong here.

The thing that is wrong is that HTML, Smilies, BB Code, and img code are all available, but they're not showing up as available.

[Edited on 3-21-2004 by Polverone]

Sulfur candle mold woes.

axehandle - 24-3-2004 at 09:56

OK. This may make me stand out like an idiot, but I can't figure out how to make the mold for a sulfur candle. I've got lots of whick now, and have been thinking a lot.

Paper is out, because it would stick to the sulfur (very fluent when molten).

Aluminum foil is out too (weight of sulfur would collapse the mold).

Anything else is out due to the high melting point of sulfur.

I need a material and a way to make identical, 200mm high, 20..30mm thick sulfur staffs with an integral whick (leading to the problem of sealing the bottom of the mold while holding the whick in place).

I'm brainfried. Please assist...

Tacho - 24-3-2004 at 11:25

First I would make a small prototype in a mold of aluminium foil, just to see if it works as we hope it does. You don't have to remove the foil to test. Just 1cm long.

Paper would be perfect. Can't you paint it with sodium silicate (waterglass)? Maybe a thick sugar (syrup) solution? It would render the paper "sulfurproof" after it's dry, but would easily dissolve in water, releasing the paper.

Another idea: use thick Al foil, the kind they use to make disposable dishes or reinforce it with paper. Cast the thing and put it in HCl or NaOH solution. -> bubbles, fizz->no more Al foil.

Cast it sideways, in an easily removable mold in the shape of a groove. One side of your candle will be flat. So what?!

Cast it in an empty eggshell (to empty: make 4mm holes on each end and blow). Toss in acid and you have a nice looking egg shaped sulfur candle ready to spoil christmas.

If latex resist molten sulfur, cast it in a condom and remove the latex in the usual way. (edit) Then think of an explanation about that yellow object in your room.

[Edited on 24-3-2004 by Tacho]

axehandle - 24-3-2004 at 11:53

*thinking about how I explained that clay sculpture I made to my parents* ("It's a self portrait! No way, it can't be that big. etc"

Good ideas. I especially like the syrup idea. It should render the paper mold impervious to sulfur, as well as make the cancle "washable" in plain H2O afterwards. It's a pity I don't have any syrup at home right now, but tomorrow.... it's syrup time! The syrup idea also makes it easy to make the bottom part of "candle" out of plaster of paris, thereby holding the bottom part of the whick in place. Thank you again, Tacho!

Edit: No way that a condom would hold molten sulfur! Besides, I don't have the opportunity to test, my GF is on the pills and I don't have any stockpile of condoms...

[Edited on 2004-3-24 by axehandle]

BromicAcid - 24-3-2004 at 11:54

How about aluminum can, or sand molds?

axehandle - 24-3-2004 at 11:56

Yes BromicAcid, I've thought of that, but how do I keep the bottom part of the whick, as well as its entirety, in place?

BromicAcid - 24-3-2004 at 12:24

Take an aluminum can, puch a tiny hole in the bottom and put the wick in, tie it in a knot so that it wont go back through, take a rod of some type and lay it across the top of the can and wrap the wick around it till it is taught, then pour in the sulfur and when it dries unwrap the wick from the rod and cut to desired size.

Cut the top and bottom off the can then cut down the side, roll it into itself till you get the diamater that you want then run a bunch of tape around it or use a hose clamp to hold it in that shape. Put a rod at the bottom and wrap the wick around it do the same with a bar at the top to hold it tightly. Press it into the dirt a few mm so that it forms a seal then pour in your sulfur. Viola, when it dries cut the tape and unroll the aluminum and you've got your candle of whatever diameter you want.

[Edited on 3/24/2004 by BromicAcid]

Too thick

axehandle - 24-3-2004 at 12:40

Too thick candle, it needs to be 20-30mm in diameter. Good idea though, if beer cans came in 30mm diameter, which unfortunately, they don't. I've actually dreamt about it. It would be the _perfect_ size, that was what my dream was about. The candle needs to fit in a 50x2mm aluminum pipe with room to spare for the air feed. That's 46mm ID, 50mm OD. So 40mm would be good too, but I can't find anything here 40mm in ID...

Tacho - 24-3-2004 at 14:23

Get a big potato.

Drill a 2cm hole in it and cut in half or cut in half and carve a groove (a "V" shape would be easy to make with a knife and result in a square candle) in each half.

Hold the two halfes(sp?) together with a rubber band, with the wick in place and cast sulfur candle. Let sulfur cool.

Separate the halfes, save the sulfur stick, put halfes in microwave, cook for 10
minutes. Put two big chunks of camembert cheese on top of potato. Put a leaf of parsley on each half, some black pepper, and plenty of salt. Serve before camembert melts. Tell your friends it's "Batata au enxofre" by Tacho.

Edit: Oh! No, this won't work!. The melting point of sulfur is above the boiling point of water: you will end up with sulfur all over your face!

Do the camembert thing, though.
[Edited on 24-3-2004 by Tacho]

[Edited on 24-3-2004 by Tacho]

axehandle - 24-3-2004 at 15:00

Your McGyverism is only surpassed by your sense of humour, Tacho

Tacho - 24-3-2004 at 15:51

Very honored axe, but I must apologize: I forgot to mention the best parting agent of all times: Soap goo!

This is serious: Go to your bathroom. If you are like most of us, you have a white soap bar (maybe light green or light pink). Lift the soap bar and you will see that goo that is soap dissolved in a bit of water. Paint the paper with this goo and let it dry. The paper should end with a waxy look and feel. Like... dry soap.

This is a strong parting agent. It's excellent for plaster of paris. It is the only efficient parting agent for epoxy resin. Well, there is vaselin, but vaselin makes the... oooh.... that's off topic.

Try this before you try syrup. It's more available, smells better, and it's not sticky.

By the way, why did you choose syrup instead of table sugar in water?

The soap goo is probably good for aluminum. I think you didn't read Bromic Acid post carefully, he had a good idea.

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