Argox's HI production method - discussion

[borolithium]

Argox's high volume hydriodic acid production method is an efficient, easy, and cost effective way of producing large amounts of acid. However, even with my many dreams and thorough understanding of the procedure, there is still some weaknesses that I have yet to overcome.

For those not familiar with the method, please read:

Post 271993

(Argox: "Hydriodic Acid--Step by Step Write-Up", Stimulants)
The reaction works pretty much as he describes, with a small amount of a milky substance identified as hydrogen sulphide distilling off before the aqueous HI starts flowing. The hydrogen sulphide needs to be carefully removed and neutralized with a weak lye solution, and this all must be performed in the confines of a fume hood.

 I did not dream of the violent bumping that Argox described, and instead have found the reaction to proceed quite fine without the need for stirring.

 The water trap suck back that he describes is constant and anoying. A simple plastic tee fitting with two teflon or polypropylene check valves solves this nuisance, with one valve allowing air to be sucked in from the open air during a suck back, while the other valve allowing HI gas to be pushed into the water trap, but preventing the suck back of the water trap into the receiving flask.

 It is very important to use as much heat as possible during the reaction, as MOST of the HI produced is at a very very high temperature. The initial acid that comes over in distillation is quite weak, but the longer and hotter the reaction goes, the stronger and stronger the acid becomes. We continually dream acid with specific gravity of 1.82 - 1.9, which is considerably more than the azeotrope of 1.72. Rather than diluting, when used as is, we have found exceptionally improved yields in the RP/HI reaction. 75% w/w is not at all uncommon and is expected with super strength acid. However, this acid fumes like nothing you have ever seen, and should be kept in a sealed container and in a freezer before use.

 75% Phosphoric acid should be used with the reaction, in equal weight to the Potassium Iodide, if the super strength acid is desired. The water trap will have weak acid, but it can be reused in subsequent batches or used to dilute the super strength acid in the receiving flask down to something you are more comfortable with.

 I have also found that the concrete residue that is left over can be removed easier if it is refluxed with some phosphoric acid, after the reaction is over and cooled of course.

 Here is the problem I am yet to overcome: No matter what we do, the boiling flask always develops cracks, most likely due to the extreme temperatures required for this reaction. No matter how slowly the reaction is allowed to cool, with only slight reductions in temperature over several hours, the vessels still crack. We have also found that using a lower power setting on the varistat results in a poorer yield, but cracking still occurs.

 Has anyone had any success with using materials other than glass? The glassware guy that made this said that this is the best glass for the job. Teflon is not an option because the reaction temperature is too high. Quartz has been suggested but I have no experience with this.

 I am wondering if some type of ceramic vessel can be constructed, but is ceramic compatible with strong acids?

[Osmium]

> No matter how slowly the reaction is allowed to cool, with only slight
> reductions in temperature over several hours, the vessels still crack.

When using big flasks temperature differences will develop in the flask walls. Maybe you can surround the flask with a thick layer of glass wool insulation. Do not switch off the heating at the end, but reduce it slowly, over the course of several hours.
Another option is using two heating mantles. One of them must have a big opening on its bottom, so it can be placed upside down over the flask. Use both heating mantles to heat up the flask. It hopefully will act as insulation and reduce the thermal stress.

[ragnaroekk]

If you would use 100% H3PO4 instead of 75% you would need much lower temperatures for the reaction and you could produce even fuming HI with approx. 70%. H3PO4 is easily dehydrated by boiling the water away at 150°C+ - anhydrous H3PO4 is crystalline at roomtemperature and melts at about 55°C.
If you really have hydrogen sulfide you should ask yourself where the sulfur comes from and get cleaner reagents. But H2S is a gas with a very specific odor and no liquid.

Anhydrous H3PO4 + KI is the way to go. Catch the gas in a wellcooled vessel with water for getting HI (aqueous) in any wanted concentration up to "fuming HI" with density about 1,9 and about 70% concentration.

Your vessels crack because the residues cemented onto the flasks walls and the glass have an different expansion coefficient - so whilst cooling this "double layer structure" will make the glass crack. The only way to circumvent this would be to hold the vessel at high temperatures and fill in - slowly - preheated phosphoric acid to unbound the residue from the flask before it cools down.
But as told: Using anhydrous H3PO4 will allow much lower temperatures to be used and will avoid most of the residueformation.
If you want to stick to the (suboptimal) method using aqueous H3PO4 you may try clay retorts instead of glassware. Every pottery will make you those for cheap.


hope this helps
RAGnARoEkK

PS: If you are sure this is H2S you talked about you might consider to add some iodine in water (better: in diluted HI) to the receiving flask. The H2S will convert the iodine to HI and sulfur will shit out.

[borolithium]

I am not positive that the white, milky substance that first appears is in fact hydrogen sulphide, I only know two things for a fact: that a white milky substance does distill off first before the brown starts flowing, and that I am not about to smell it for the sake of confirmation! Argox stated that the hydrogen sulphide is likely due to a small amount of sulphur impurities that are present in the phosphoric acid. It is easy to remove and I don't think the additional cost of a high purity acid would be justifiable when the technical grade is so cheap and easy to obtain. It is certainly a minor inconvenience at best, provided one knows how to handle it.

 I agree with you both on the reasons for cracking. The temperature at the top of the vessel is often no more then 145 C and often the crack appears as a line at the exact spot where the top of the mantle and the glass meet. But often the crack appears on the bottom, leaking HI into the mantle and costing a small fortune. No amount of tin foil or baking soda will solve this problem.

 Using anhydrous phosphoric acid (phosphoric anhydride?) is an interesting idea but isn't that what we are mostly doing anyways? I mean, after the water boils off in the initial stages, isn't the reaction essentially what you described? A solid mass that emits mostly HI gas? The weak acid that is formed in the initial stages is distilled off quite quickly and the majority of the reaction is the generation of HI gas, which slowly dissolves itself into the liquid in the receiving flask and water trap, raising the volume and concentration of the distillate.

 I am not an expert, so please correct me if I am wrong, but it seems to me that you are suggesting I do step B, then A, and C, as opposed to A, B, and C, but I don't understand why it would be less residue at the end.

 One thing is for certain, if efficient, high yields are desired with Argox's reaction, a VERY high temperature is required.

 I just had another thought. If I put water in a large flask and I cool it, when the water freezes it expands at a much larger rate than the glass, in fact the glass reduces in size, but the ice does not cause it to crack. The water simply expands upward, correct? Wouldn't the same principle be true for this reaction? When the thick resin cools into a solid, shouldn't it behave the same?

[SHORTY]

The shit left after doing this distillation sticks to the glass and is almost impossible to remove without reheating or adding additional chemicals but ice doesn't actually stick to glass so that is probably why they don't have the same effect.

[biotechdude]

One thing is for certain, if efficient, high yields are desired with Argox's reaction, a VERY high temperature is required.

Rather than getting high yields and wrecking glassware, settle for lower yeilds and redistill at lower temps to obtain the >D1.7 fuming HI we all love.

As u understand, extreme heat is required when using lower %H3PO4 to drive the formation of HI(g); and raise the density from ~1.6 up to ~1.9 near the end of the reaction

However, if you stop the reaction before it gets to this extreme level; you will have collected a smaller volume of 'weak' HI.  Then you distill this until the boiling point of your desired %HI is obtained.  This is all done at much lower temps, and when combined with anhydrous H3PO4 initially; makes the reaction very tame.

The other suggestions were great, but as precursers are cheaper than equipment.  Calculate if its cheaper and safer in the long run to 'half do' two batches of KI and H3PO4 and redistill; or dangerously run one batch to completion (and destruction).

[borolithium]

Actually, the cost of KI has gone up considerably since Argox's post. If I could only get a 45% - 50% yield, it would be more economically feasible to simply buy it from a black market source.

That being said, you are giving me an interesting idea. Why don't I simply make slow water additions into the reaction after the intial amount of water has boiled off, maybe on a slow drip. These additions would prevent the temp from ever getting too high and I would know that there is no HI left when the brown stopped coming over.

 The first run would of course be weak acid, but the first run could be used in place of water in subsequent runs, thereby driving up the concentration. Then at some point, it could be distilled off to the azeotrope, if it hadn't been formed already. The weak distillate could then be used in subsequent batches.

The temp would never get above 127C, therefore no cracking. Also, when the acid starts getting too weak to be bothered, the mass that is left could be easily poured out, as it would have never been given the opportunity to harden.

I kinda like this idea. The HI would get generated alot slower, but so what? At least it would work! Maybe a significant excess of phosphoric acid will help things along too. It's REALLY cheap!