Sciencemadness Discussion Board - Distilling HCl

Distilling HCl

dann2 - 29-10-2007 at 18:50

Hello,

Having used up all my lab grade HCl acid and finding it impossible to get reasonably pure, fairly concentrated Hydrochloric acid I have decided to distill some 'Loo Boss'
28% Hydochloric acid. The container states that the 'Loo Boss' also contains surfactants + unique inhibiter (bless them).
Will distilling get rid of the unwanted stuff and leave me with 28% Hydrochloric acid?
I distilled 220ml, discarded the first 50 ml and kept the next 120ml that came over. I am used a Claisen adapter filled with small pieced of glass tubes as a quick and dirty fractional columb. The acid I kept came accross at a steady 109C. (according to my thermometer). The distilled acid is clear, not yellow like the starting material.

Dann2

woelen - 29-10-2007 at 23:18

You will indeed get much purer acid, but what you have obtained has a lower concentration. HCl forms an azeotrope with water at appr. 20% concentration.

You start with 28% material. So, initially, the mix will be much richer in HCl, but finally, the concentration will converge to around 20%. You could make higher concentration acid of reasonable purity, by taking you 20% acid, and leading the gaseous products from heating the 28% stuff through this 20% solution. I see no reason why you should discard the first 50 ml, because that is the most concentrated part, while it does not contain surfactants and inhibiter.

kilowatt - 30-10-2007 at 09:20

Once you have obtained your 20% HCl from the distillation, plus whatever else you have collected by bubbling initial HCl gas into solution, you can concentrate it further using dehydration. Just drip the aqueous acid into concentrated H2SO4 (slowly, with plenty of stirring!) to liberate anhydrous HCl which you can then bubble into distilled water. You can get a stable concentration of HCl up to about 38% by bubbling the gas into solution. Once you're done, though, you will have a bunch of wet sulfuric acid to contend with, and you probably know how high of temperatures you need to distill it (upwards of 340°C). I have read where you can also use anhydrous CaCl2 as a dessicant to liberate the HCl gas, and this might be cheaper all things considered.

Antwain - 30-10-2007 at 09:47

Or you could just throw NaCl into concentrated battery acid. No water, pure HCl. Actually Better to drip H2SO4 onto NaCl, less dying that way.

Distillation

chloric1 - 30-10-2007 at 16:00

Dann2 - I don' t think I have the necessary distillation set up right now or I would try this myself. So, could you please, repeat the set up and tell us whether the first 50 ml came over at 109C or at a lower temperature. Even though many acids have specific azeotropes, sometimes more volatile fractions may emerge with high concentrations. I "thought" I read that 38% HCL boils at 40 or 50 Celsius. Don't quote me on that BTW. Thats why I ask.

kilowatt - 30-10-2007 at 16:10

Concentrated (anhydrous) H2SO4 doesn't do much when it comes in contact with dry NaCl, been there done that. Battery acid (33% H2SO4, very pure, and cheap) will work if you can that but will yield a lot of aqueous HCl. You can distill that product and then dehydrate it though, and it will be a heck of a lot cheaper than distilling a household product, which I imagine is fairly expensive. It will also be of very high purity, which I imagine even your distillate is not, unless you have a very tall reflux column.

dann2 - 30-10-2007 at 18:08

Hello,

Thanks for replys.

I should have read up a bit on HCl acid .

There is info on HCl here
http://www.epa.gov/tri/guide_docs/1999/hclguidance.pdf
and also wiki.

The apparatus I am using is an ordinary distillation set up.
I am heating boiling bulb with liquid paraffin in a kettle controlled by a variac. The liquid paraffin is a vetinary product.
The extra bit in the apparatus is a claisan adaptor in between the boiling bulb and the T conector. There is pieces of glass placed in it to make a short fractionating columb. There is probably no need for this, I put it in because I had it to hand.
Output flask is connected to condenser using a vacuum adapter. I have a tube on the vacuum connection leading to outside to get rid of fumes for HCl.

The HCl starts to come over at 105C and not 109C as I said above. The temp. then goes up to 109.

I will have to generate HCl gas to bring up the concentration of the 20% stuff (distillate) to 36% (approx.)

Should I put the 20% stuff in a high narrow container (like a measuring cylinder) and put the HCl emitting tube to the bottom of this container to get as much HCl to dissolve as possible or is it sufficient to just bubble the HCl into the 20% stuff a small distance under the surface?

Some say H2SO4 + NaCl is good for HCl generation.
Some say you need above + HCl
What is the HCl for, (when mixed with NaCl?)
I know you can use H2SO4 + HCl too but I will not be doing it that way for now.
I have heard that the HCl + NaCl (as opposed to NaCl on it's own) gives a more gentle output of gas.

Dann2

[Edited on 31-10-2007 by dann2]

Xenoid - 30-10-2007 at 19:36

Quote:

Originally posted by kilowatt
Concentrated (anhydrous) H2SO4 doesn't do much when it comes in contact with dry NaCl, been there done that.

Hey what! According to my Mellors this was the first step of the old Leblanc process.

It's essentially the same reaction as making HNO3. Heat at a relatively low temperature to get NaHSO4 + HCl and then heat the NaHSO4 to red heat with further NaCl to get Na2SO4 + HCl.

@Dann2 Be carefull dissolving HCl you may get suck back, best to bubble through an inverted funnel, so there is a large surface area or use an intermediate container to retain any sucked back liquid.

Regards, Xenoid

dann2 - 30-10-2007 at 19:54

Hello,

Will take percautions for suckback.

Some more HCl stuff here.
http://www.resistoflex.com/hci_graphs.htm#2

The price of the 'Loo Boss' (28% HCl + unwanted additives) is more than ordinary brick cleaner (12%HCl + no additives) per
actual amount of HCl (gas) purchased.
I would be better distilling the cheap stuff, discarding distillate that comes over below 108C (below 20% Hydrochloric acid) and keeping
that which comes after (20% acid) leaving some in the boiling flask (impurities?/yellow colour).
Then generate HCl and bring the 20% stuff up to ~36%.

Then again I will lose alot of HCl when I get rid of the 'below 20% stuff' I will have in the receiver.

When I distill the 'loo boss' I am not 100% sure that additives are staying behind in boiling flask.

What additives may be in there. Are they volatile?

Dann2

kilowatt - 30-10-2007 at 20:37

Quote:

Concentrated (anhydrous) H2SO4 doesn't do much when it comes in contact with dry NaCl, been there done that.

Unless you heat it strongly, you'll get a little out but only due to residual water in the concentrated sulfuric allowing aqueous solution to form. When I tried it with stochiometric and fairly dry reagents (didn't know at that time it had to be heated), the vast majority of the NaCl never dissolved - ever, even after sitting around for weeks. Yes it will work when heated strongly, but it also works quite well if you use aqueous reagents. Either way is good just depending on what apparatus you've got handy. You're might be better off to heat the resultant NaHSO4 to recover half the sulfate as SO3, than to heat it with further NaCl to generate further HCl. That one is up to you as either way it requires red heat, if you even consider it worth the effort (which I doubt most people would). To my knowledge, the spent Na2SO4 is extremely difficult to recycle to anything useful, requiring heating with coke and silica and full implementation of the Contact Process.

Quote:

When I distill the 'loo boss' I am not 100% sure that additives are staying behind in boiling flask.

It's hard to say what ingredients might be found in a consumer product like 'Loo Boss' and I'm sure you wouldn't be asking if it said on the bottle. You might be able to find the info in an MSDS online if you're lucky.

Regardless, if you use a dehydrating method to get the HCl out as gas, especially after your first distillation, and pass that into solution, you should get very little impurities coming though.

You could just put a condenser between your HCl gas generator and the bubbler, so even fairly volatile contaminants with will not escape. If you want to get every last bit of HCl out of the distillate and into your final solution you might consider a bubbler containing H2SO4 between the gas generator and condenser that precedes the aqueous bubbler, which will remove water that would otherwise form an azeotrope and condense back into your generator. Again this all depends on how available concentrated sulfuric is to you or if you can make it in your still. It's hard to give good advice without knowing what you have available and how far you are willing to go to get good yield and purity.

You could even take the brick cleaner and add it directly to concentrated H2SO4 (or anhydrous CaCl2) to extract the gas. If that stuff is clean enough otherwise, all you've got to do is bubble the gas right into solution and you're all set.

Antwain - 31-10-2007 at 08:39

I would go for half efficiency on this one ie. 1:1 H2SO4:NaCl. In order to make sure the reaction between H2O4 and NaCl is smooth heat it, preferably to ~150-200. At this temperature the NaHSO4 is either molten or VERY soluble in H2SO4. Then very slowly run the sulfuric acid in, while applying continuous heat. I did it in a test tube with 1-2g of NaCl when I was in college and nearly gassed myself (well not really, but it stunk). You do want anhydrous (or >90%) and you will need to heat it. Also, grinding the NaCl to a fine powder beforehand will significantly aid in its dissolution. Also.... You will probably need an excess of H2SO4 to get the reaction to go to completion (that is to form a melt) and you don't want to open that flask until it has all melted and stopped bubbling or you willstink your room out.

Lastly, be careful of suckback. As you can imagine a gas with a bp. of -85*C which can dissolve up to 40% at room temp and has a constant boiling mixture at 109*C of ~20% is VERY VERY highly and rapidly soluble in water. If you are going to bubble this through a solution you will need to take precautions. Alternatively you could have it blowing down gently just above a solution which is being stirred like mad. In the latter case its strong affinity for water is your friend.

dann2 - 31-10-2007 at 14:24

Hello,

I am inclined to think (guess) that the HCl's affinity for water (or Hyrochloric acid solution to be very exact) will get less and less as I approach the 37% mark. Is is sufficient just to 'show' (using a upsidedown funnel or stirring as you said) the HCl gas to the Hydrochloric acid solution (34, 35, 36%) and it will go on dissolving easily?

I will be using a three necked round bottomed flask + separation funnel (as a dropping funnel) to generate gas. Glass tube from 3 necked flask to HCl solution via upturned funnel (as Xenoid suggested).

Dann2

Centimeter - 31-10-2007 at 15:23

This distillation problem is perplexing to me. I thought that once the azeotrope was broken, it does not hinder the distillation anymore. For example, ethanol's 96% azeotrope is broken under diminished pressure to form ~97% ethanol. The ethanol is then distilled at normal pressure where the azeotrope would be 96%. However since the concentration is already above 96% it experiences no azeotropic character.

Why is the same not the case for 28% HCl? The azeotrope of 20% at atmospheric pressure has already been broken and subsequently it seems to me that you would be able to distill the HCl no problem at even much higher concentrations than 28%. I assume that my understanding of pressure-swing distillation is flawed...

Dann2, you should titrate your distillate to see what concentration is coming over.

bio2 - 31-10-2007 at 19:34

As the 28% acid is heated the low boiling HCl outgasses from the solution until the azeotropic concentration is reached, then it distills.

At concentrations higher than the azeotropic concentration, the vapor is enriched in HCl relative to the liquid.

........."When a dilute solution of hydrochloric acid boils, more water than hydrochloric acid is volatilized so that the concentration of the remaining acid increases. and the boiling point of the
solution rises. This process continues until the acid concentration reaches 20.222 weight % HCl, when
an azeotrope (a mixture of two liquids that boils at constant composition; i.e., the composition of the
vapor is the same as that of the liquid) is formed and the concentration of hydrochloric acid in the vapor
is the same as that of the solution. Above the azeotropic concentration, the partial pressure of
hydrochloric acid increases rapidly with concentration and hydrochloric acid aerosol production will be substantial"..........

[Edited on by bio2]

[Edited on by bio2]

Antwain - 31-10-2007 at 22:11

@dann2 - please be careful of suckback

. It wouldn't be so bad though, as you will not have conc.H2SO4 in the distillation flask, only mostly salt.

Or, as I nearly suggested earlier, if you distill your plumbing acid in batches, but into the same bottle then you should be able to obatin something of at least 28% concentration. Only the first batch will vent HCl, after that there will be solution for it to dissolve in. And as you said, the solubility will not be bad enough (violent enough) for suckback when the acid is already at least 22%. In this case I would use an upturned funnel, and stirring in the solution below.

And have some way to let air into the system, because it will likely suckback a little, so you can vent air in... and subsequently the air will probably bubble out at the funnel followed by more gentle suckback. This has been my experience.

woelen - 1-11-2007 at 02:15

A suckback IS bad in your case. The melt is hot and contains a lot of H2SO4. If you get the water in this hot melt, then you'll severely regret what you have done! BE CAREFUL!

A safe way of preventing suckback is the use of a small inverted funnel, which you immerse just a mm into the liquid, which must be in a fairly tall beaker (total surface of liquid must not be much larger than surface liquid, covered by the inverted funnel opening). If HCl gas reaches the surface of the liquid, and liquid is sucked into the inverted funnel, then the level of the liquid will go down, and the funnel is no longer immersed in the liquid. Some tweaking may be needed to get the level of immersion adjusted well, but this method definitely works and is safe. At any cost should suckback be prevented with your hot NaCl/H2SO4 melt.

not_important - 1-11-2007 at 03:14

Quote:

Originally posted by Centimeter
This distillation problem is perplexing to me. I thought that once the azeotrope was broken, it does not hinder the distillation anymore. For example, ethanol's 96% azeotrope is broken under diminished pressure to form ~97% ethanol. The ethanol is then distilled at normal pressure where the azeotrope would be 96%. However since the concentration is already above 96% it experiences no azeotropic character.

The azeotrope isn't broken, you're just distilling the excess component until azeotropic proportions are reached again. With EtOH-water qnd low enough pressure you can truly break the azeotrope, reaching a pressure at which no mixture of ethanol and water forms an azeotrope. But above that pressure you can distill water from the more dilute or ethanol from the more concentrated solutions.

At 1 atmosphere you can distill pure ethanol from an ethanol-water mixture, provided the ethanol concentration is above the azeotropic concentration. Thus starting with 98% ethanol, EtOH will distill until the ~95.6% composition is reached, after which the azeotrope distills.

bio2 has already addressed what happens with HCl-water mixes. No different than EtOH-water, just different concentrations and one component is a gas.

Distilling H2SO4

dann2 - 1-11-2007 at 12:55

Hello,

I do not intend to distill my H2SO4 but simply heat in an ovenware bowl in the open untill dense white fumes appear.
~98% H2SO4 left in bowl.
Distilling at 300C+ would not be too easy for me. I would hate to put a bunsen to my round bottomed flasks.

Dann2

Antwain - 1-11-2007 at 13:24

Yeah, that works fine. It helps if there is a fan on low blowing across it too. It means that you can pump several times as much heat into it without boiling it and making it explode everywhere.

chemrox - 1-11-2007 at 17:33

@kilowatt- been there done that? That is the process I use to make HCl. It come off a little slower than if the salt is made into a paste with aq. HCl but it's dry. I don't know what happened when you tried but I'd suggest trying again. I would like to know the best way to convert muriatic to 37%. I have to fill out forms for the 37% if its shipped from CA or NY. Locally it costs too much!

kilowatt - 2-11-2007 at 00:16

Yes, like I said, my attempt was not heated. Also, it was rock salt which is in large crystals. I will have to try it again with the proper provisions.

I wouldn't bother to concentrate muriatic acid directly since it's not very pure anyway. Hydrochloric acid is not supposed to be green/yellow and that stuff always is. My guess (just a guess) is that it's made in an iron HCl furnace which imparts the green color due to ferrous chloride. Just dehydrate the entire works and bubble it into distilled water.

dann2 - 5-11-2007 at 15:28

Hello,

The density of my distilled HCl is 1.1g/cc (measured with a car battery hydrometer). This was the fraction that came over at 108/109C. 12%HCl was being distilled. Some (30cc or so) left behind is boiling flask. This 30CC retains yellow colour.

Is PVC tubing and polypropylene resistant to HCl gas?

Dann2

bio2 - 6-11-2007 at 15:49

.....Is PVC tubing and polypropylene resistant to HCl gas?....

PVC tubing will harden due to the plasticizers being leached.
Rigid PVC is resistant best to use the blue transparent unmodified type.

PP is resistant and is a much better choice.

dann2 - 15-11-2007 at 19:08

Hello,

Got around to increasing the concentration of my (approx.)20%, density 1.1g/cm2. Added 500ml 92% Sulphuric to 700 grams NaCl in a three necked flask.

Fed HCl gas into 500ml beaker containing 450ml 20%HCl acid. Used a plastic funnel slightly smaller than diameter of beaker to allow gas to make contact
with acid and to prevent suckback. PVC tubing to connect the two together. This tubing had been previously used to transmit HCl to outside when distilling and had all the plasticizers leached out. It had turned from transparent to white. Would have been better to start with unplastisized stuff at this stuff was inclined to collapse at bends.
I stirred the beaker with a magnetic stirrer.
Heated three necked flask after a while, I heated more and more as time went on. I had one episode where I heated too much and had the contents
of 3 necked flask come out into heating liquid. Bit of a mess. When HCl stoped coming accross I stopped. The 3 necked flask was heated to about 100c.

The density of my HCl acid is now 1.16 at 20C (32% approx).

Can I get more HCl gas from the Sulphuric acid + salt by heating with a flame?

The amount of HCl gas available (in theory) from the amount of Sulphuric/salt that I used is about three times what I thought I would need to bring
450ml of 20% HCl acid to 37% acid. There is either alot of HCl (gas) still in there or I have wasted lots of it with my set up.

Dann2

Phosphor-ing - 16-11-2007 at 04:50

If you go to any hardware store, look for a ice maker repair line for a refridgerator/freezer. these small hoses are made from polyethylene and will stand up to much more abuse than polyvinylchloride. The only disadvantage is the hose is a frosty white instead of the clear pvc.

dann2 - 28-11-2007 at 19:53

Hello,

Reading an 'H2SO4' thread Chloric1 said:

The cheap black stuff I bought is 90%. If diluted with water the black separates. It is charcoal. I get crystal clear dilute acid but why trouble with the boiling scenario. Would like to try rooto or that stuff labeled "liquid fire". Any case any of these would be satisfactory for drying chlorine or other gasses that don't dissolve/react,dissolving ammonium chloride to make anhydrous hydrochloric acid,catalyst in ester or ether prep etc. If you decide to concentrate the dilute acid by heat make sure it boils at 338 degrees C!

Can 37% HCl acid be make using H2SO4 (Conc.) + Ammonium Chloride.?? (Sorry for doubting you Chloric1

)
Sounds like the way to go if you need conc. HCl, much handier than messing around making HCl gas and bubbling into water or more dilute HCl acid.
Then again adding dilute HCl to conc. Sulphuric is fairly easy but you still need a distilling outfit.

Dann2

cnidocyte - 25-1-2011 at 01:08

Sorry if this has been asked a million times but what temperature does hydrochloric acid distill at? Does it distill over at the same temperature as the water?

cnidocyte - 31-1-2011 at 13:07

I almost had a serious accident just there. I was distilling HCl and I checked on it and noticed it was bumping heavily because I forgot to turn the stirrer on. I turned the stirrer on. Big mistake. The still head went flying and acid shot out of the flask. To make matters far worse, I was using an oil bath so the acid solution got into the hot oil. Its a good thing I wasn't standing too near to the setup or I would probably be in the back of an ambulance right now. Luckily I didn't get any acid or oil on me. I learned a lesson I'll never forget. Never turn on the stirrer when the solution is already boiling. I knew that its dangerous to add boiling chips to an already boiling solution but I didn't know the same thing went for turning on the stirrer. Lesson learned.

Cynic - 1-2-2011 at 12:37

>I almost had a serious accident just there. I was distilling HCl and I checked on it and noticed it was bumping heavily because I forgot to turn the stirrer on.

Been lurking here for some time and am learning a great deal - thanks. Still not too up-to-speed on the practical side of things. Could some one please explain to a chemistry newbie how this operation should be performed. So I don't kill myself when I try it.

I looked up "bumping" so I now know what that means. I have never seen anything other than water boil - do other mixtures have a different boiling pattern (more violent etc)? After thinking a bit I can see how this might be the case due to poor heat transmission in the liquid, different viscosities etc. How should the distillation have been done? Should the hot plate temperature have been kept lower to just barely boil the HCL? Should anti-bumping chips have been added as a matter of course. Do you always add them? Are there safe ways of doing it without them? What solutions do the bumping chips react with and so you cannot add them to it. I know none of this and I would welcome all advice.

I was thinking of buying a bit of distillation glassware on ebay and having a go myself. If I wanted to practice this sort of separation by distillation does anybody have a suggestion regarding two common household liquids could I mix together and then separate due to the different boiling temperatures? Ideally it would be two liquids where the only danger is the heat rather than hot and caustic and explosive.

Edit: a bit more thought on the above suggested cheap vodka might not be a bad thing to try distillation on. Any opinions and advice on that?

[Edited on 1-2-2011 by Cynic]

bbartlog - 1-2-2011 at 13:24

Quote:

Should anti-bumping chips have been added as a matter of course.

Yes. IMO anytime you are boiling something you need boiling chips (water, too, will bump violently if it's distilled and the vessel is clean). I used to use some little rugose bits of quartz but have switched to carbon boiling chips. Graphite doesn't react with much... I guess if I were trying to distill piranha solution or something they might be attacked.
Keeping temperatures low doesn't help all that much. If you're pushing enough heat to boil something, it will be possible for it to superheat if there are not enough nucleation sites. Statistically I suppose there might be a little less bumping but then you'd also be boiling for longer, so it's not much of a solution.
One easy distillation if you just want practice is methanol and water; in the USA windshield washer fluid is 25-30% methanol and can easily be distilled to separate the methanol and water (along with colorants). Has the advantage over ethanol distillation that you have no azeotrope to deal with.

ScienceSquirrel - 1-2-2011 at 13:49

Boiling in lab glass does tend to result in bumping as the surfaces are so smooth.
Normal cooking pans have rough areas that let bubbles form and allow boiling.
So we either use stirrers, bumping granules or an air leak to provide nucleation sites where bubbles can form.

cnidocyte - 2-2-2011 at 12:11

Quote: Originally posted by Cynic

Been lurking here for some time and am learning a great deal - thanks. Still not too up-to-speed on the practical side of things. Could some one please explain to a chemistry newbie how this operation should be performed. So I don't kill myself when I try it.

I know exactly what I did wrong now. What I wasn't aware of was that when a solution is bumping (huge bubbles forming that cause the whole flask to shake as opposed to many little bubbles) it means that the solution is superheated and very unstable. Even a small shock (in my case turning on the stirrer) can cause the solution to "flash boil" meaning all the superheated liquid turns to vapour at once. If you understand this concept then you won't make the mistake I did. How I should have performed the operation is I should have had the stirrer on or put some boiling chips in the flask before I heated the solution which would have prevented superheating and allowed it to boil smoothly. Instead I forgot to turn the stirrer on so there was nothing to help the solution start boiling and as a result it became superheated. If a solution becomes superheated then remember that any small aggitation could cause the thing to explode (doesn't actually explode but I like to think of it like that) so just turn off the heat and let it cool down so you can put in some boiling chips or turn on the stirrer and start over. You'll know what bumping is when you see it, if the beaker or flask isn't clamped down then it'll shake every time one of those massive bubbles forms.

I've never seen water bump myself either but I don't see why it wouldn't. You need the hotplate temperature to be over the boiling point of what your distilling because there will always be heat losses. Yep if you don't have a magnetic stirrer or other means of facilitating boiling then you should always add boiling chips. Safe ways of boiling without them are stirring, bubbling inert gas into the solution and probably many more methods I'm not aware of. The boiling chips don't "react" with anything, they provide nucleation sites which are basically just air pockets where gas bubbles can form.

I highly recommend getting a distillation kit on ebay. You can find some insanely good deals there as sometimes people who just need to get rid of lab equipment put it up there. I recommend you start with a substance with a low boiling point such as dichloromethane from paint stripper or acetone from nail varnish remover or even methanol from paint stripper. A water bath will provide enough heat to distill each of those compounds and if those solvents superheat, I don't think the flash boiling would be as violent as higher BP solvents.

edgecase - 14-6-2012 at 05:09

Old topic but I thought I'd reply for completeness:

Boiling chips apparently don't work for vacuum distillation, since the air pockets are essentially missing. Also, the alumina variety I have "tamer tabs" says on the label it isn't compatible with conc. H2SO4.

This is the first I've heard of the air leak though.

I was searching for this topic since I have produced weak (pH 0) HCl solution by pyrolysis of polyvinylchloride. It works as an analytical technique, but let me tell you, you'd have to be *way* more desperate than the guy who started this thread to try to produce HCl this way.

metalresearcher - 21-10-2012 at 03:43

I have 10% hardware store grade hydrochloric acid which I want to concentrate to 36%.

I can distill it thereby concentrating the residu approaching the 20% azeotrope and then letting it cool down and adding CaCl2 to it and filtering the CaCl2, but many of the CaCl2 will dissolve in the water.

In found this site:

http://www.erowid.org/archive/rhodium/chemistry/equipment/ca...

Has somebody ideas on this ?

triplepoint - 21-10-2012 at 09:04

I know this sounds obvious and self-evident, but if you do get something bumping and boiling after having forgotten boiling chips or stirring, TURN OFF the heat. Let it cool, then begin again.

weschem - 12-11-2012 at 22:28

There is a method. youll need 3 containers that are safe to hold HCl. 1 container must be able to fit the other 2. Fill one container with HCl and fill the other container with distilled water. Put both containers in a larger container and seal it air tight with parafilm or wax around the edges. what happens is the hcl fumes from the impure hcl will infuse the distilled water to virtually 100% pure acs reagent grade HCl. Downside it cuts the concentration to about half and takes about a week or 2. This is not too big of a deal because you end up diluting HCl to this concentration or lower.

Oromis - 13-11-2012 at 17:13

I don't know how it is else where but in Australia you can buy 37% HCl solution from pool shops for about $10-$15. So it may be worth checking out to your local pool shop for a more pure starting solution. (The solution is very clear and when the bottles open fumes pour out)

tetrahedron - 14-11-2012 at 03:34

Quote: Originally posted by weschem

There is a method. youll need 3 containers that are safe to hold HCl. 1 container must be able to fit the other 2. Fill one container with HCl and fill the other container with distilled water. Put both containers in a larger container and seal it air tight with parafilm or wax around the edges. what happens is the hcl fumes from the impure hcl will infuse the distilled water to virtually 100% pure acs reagent grade HCl. Downside it cuts the concentration to about half and takes about a week or 2. This is not too big of a deal because you end up diluting HCl to this concentration or lower.

nobody says you have to take the same volume of crude 37% hydrochloric acid and distilled water. if the former is about twice the latter then you'll end up with 2/3 the initial concentration (25%), if three times then 3/4 (28%) etc, so any concentration up to 37% can be reached.

weschem - 18-11-2012 at 20:43

[/rquote] nobody says you have to take the same volume of crude 37% hydrochloric acid and distilled water. if the former is about twice the latter then you'll end up with 2/3 the initial concentration (25%), if three times then 3/4 (28%) etc, so any concentration up to 37% can be reached.[/rquote]

That's not exactly how it works. You're assuming that all of the HCl in its entirety is infusing into the water. Doesn't matter if you put more or less water. The process of diffusion applies. Diffusion is where particles in an area of high concentration move to an area of low concentration till the two areas have the same concentration and are isotonic. So already you know it'll be half. Plus you must account for some of the concentration still in gaseous form so it'll be a little less than half. You can cut down on the gaseous concentration by cooling the system.

tetrahedron - 19-11-2012 at 05:32

Quote: Originally posted by weschem

till the two areas have the same concentration and are isotonic.

this is about the only smart thing you said. think about it: you put 1L conc HCl (12M) and 1mL H₂O in your device and you claim you obtain 1001mL 6M acid? how do you account for the loss of 5.994 moles of HCl?

ok this is an extreme case, but as i said the whole range of concentrations (0-12M) is attainable.

weschem - 19-11-2012 at 09:21

Wow really? There is no loss smart guy. The 1L of the impure muriatic acid still contains about half the concentration and the container containing the water contains the rest of the concentration and there is still some left over as fumes in the container. Doesnt matter if you put less distilled water it will still have the same concentration. Look why don't you try this experiment out yourself before you start running your mouth and see what kind of results you get. I have done this experiment and have done titrations to verify results.

Swede - 19-11-2012 at 11:24

Where I live, crude muriatic is cheap, and pure HCl unobtainium, so I tried the "1 week slow HCl gas diffusion" method.

I didn't get fancy... a PE shoe box storage container, and a 1 liter beaker. Into the beaker I added about 500 ml of distilled H2O. Into the floor of the box, I dumped a load of muriatic. The idea is to have large surface areas available.

After a week, I removed the beaker. Dumped the muriatic into my pool, which needed it anyhow, and the rig can be re-set with fresh muriatic. This can be repeated until the clean HCl in the beaker is close to the concentration of the original muriatic, which around here is 32%.

I have not tested yet the clean HCl thus produced, but it is quite strong, colorless, and free of those nasty impurities. The process is slow but super low-tech.

[Edited on 19-11-2012 by Swede]

Swede - 19-11-2012 at 12:10

I just checked the single gas diffusion run. From about 2/3 gallon of crude muriatic into 500 ml of distilled H2O, the 20 baume muriatic produced 16 baume clean HCl.

That's 1.160 vs. 1.125 specific gravity, or 32% to about 25%. Not bad at all. Obviously, to get results like that, you have to overwhelm the distilled water volume with a LOT of crude muriatic.

Just for fun, I set it back up; put the 500 ml of clean 25% HCl back into the rig, and added another 2000ml or so 32% muriatic. My guess would be, after another week, the sweet HCl will probably be close to 28% or 29%.

watson.fawkes - 19-11-2012 at 15:04

Quote: Originally posted by tetrahedron

These assertions are in contradiction to Henry's law, which is that the concentration of gas that will dissolve in liquid is proportional to the partial pressure of the gas. Henry's law is valid at constant temperature, and there's no mention of anything like a temperature difference.

EDIT: I have misunderstood the language tetrahedron used. Retracted.

[Edited on 20-11-2012 by watson.fawkes]

tetrahedron - 19-11-2012 at 16:29

whoa i didn't expect so much criticism for an observation that seemed completely straightforward to me.

my only assumption was that various strengths of HCl solutions, when enclosed in the same container, would tend to become

Quote: Originally posted by weschem

isotonic.

accordingly, from a volume V₁ of HCl at molarity c₁ and a volume V₂ of H₂O you'll get a total volume V₁ + V₂ containing c₁ * V₁ moles of HCl, i.e. the concentration (in both solutions) is eventually reduced to V₁ / (V₁ + V₂) of the original. of course it will take time to reach arbitrarily close to the equilibrium.

swede's result is corroborating:

Quote: Originally posted by Swede

From about 2/3 gallon of crude muriatic into 500 ml of distilled H2O, the 20 baume muriatic produced 16 baume clean HCl.

That's 1.160 vs. 1.125 specific gravity, or 32% to about 25%.

the half-assed invocation of

Quote: Originally posted by watson.fawkes

Henry's law, which is that the concentration of gas that will dissolve in liquid is proportional to the partial pressure of the gas

(which holds only for asymptotically dilute solutions of gases that don't dissociate in the solvent) does not lead to a contradiction: both solutions keep exchanging HCl with the atmosphere. the partial pressure of HCl in the container is sustained by the stronger 'crude' solution, until the 'absorbing' solution has reached the same strength. at equilibrium, the partial pressure is constant, which means that the rate of exchange is the same (no matter the exact mathematical relationship that exists between partial pressure and concentration). the diffusion can be accelerated by placing the container in a warmer environment, then cooling it back down in order to reabsorb the extra HCl pressure, and this has no influence on the final equilibrium (a state function).

as a final remark, given the quantities mentioned, the actual amount of gaseous HCl present at any time in the container is negligible. the only reasonable complaint that i would have expected (about the small change in volumes due to the solute being a gas) didn't come up.

PirateDocBrown - 15-12-2017 at 22:37

I'm giving this a go in real time, inspired by Nux Vomica's YouTube.

https://www.youtube.com/watch?v=WQ5Vn0is9_Y

Differences between his and mine:
He used a Graham condenser, with the coils loaded with water, I only had a Leibig, and bubbled the output into the receiver, which started out with a small bit of water.
He used boiling stones, I had a mag stirbar.
Looks like his boiling flask is 500, mine is 1000. I monitored temp, and saw it hold at the azeotropic BP.
I treated the fume exhaust through a grad cylinder bubbler.

[Edited on 12/16/17 by PirateDocBrown]

PirateDocBrown - 15-12-2017 at 23:56

So, yeah, lots of HCl outgassing, the boiling flask bubbles away merrily, yet little condenses. The receiver started out with some distilled water, with a tube attached to the adapter, so as to allow it to bubble under the water level. The gas takeoff was set to bubble into NaHCO3 in the grad cylinder.

I ran out of ice, so more later.

Takeaway:
LOTS of HCl comes off, more than a small amount of water can absorb, even at 0 degrees.
There was nowhere near enough NaHCO3, it was rapidly neutralized, with HCl then coming off after.
Therefore, good ventilation is a must. PPE too.
Don't use NaOH as your neutralizer, the heat of neutralization is enough to boil the water, then melt the Tygon, and even char it.
Suckback is a major consideration here, plan ahead.

Output is limited by the azeotrope of HCl/H2O, about 20%, but if HCl gas is absorbed into that cold, it could be more.