| Pages:
1
2 |
dann2
International Hazard
Posts: 1523
Registered: 31-1-2007
Member Is Offline
Mood: No Mood
|
|
Distilling HCl
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
Super Administrator
Posts: 8014
Registered: 20-8-2005
Location: Netherlands
Member Is Offline
Mood: interested
|
|
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
Hazard to Others
Posts: 322
Registered: 11-10-2007
Location: Montana
Member Is Offline
Mood: nitric
|
|
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.
The mind cannot decide the truth; it can only find the truth.
|
|
|
Antwain
Hazard to Others
Posts: 252
Registered: 21-7-2007
Location: Australia
Member Is Offline
Mood: Supersaturated
|
|
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.
|
|
|
chloric1
International Hazard
Posts: 1141
Registered: 8-10-2003
Location: GroupVII of the periodic table
Member Is Offline
Mood: Stoichiometrically Balanced
|
|
Distillation
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.
Fellow molecular manipulator
|
|
|
kilowatt
Hazard to Others
Posts: 322
Registered: 11-10-2007
Location: Montana
Member Is Offline
Mood: nitric
|
|
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.
The mind cannot decide the truth; it can only find the truth.
|
|
|
dann2
International Hazard
Posts: 1523
Registered: 31-1-2007
Member Is Offline
Mood: No Mood
|
|
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
National Hazard
Posts: 775
Registered: 14-6-2007
Location: Springs Junction, New Zealand
Member Is Offline
Mood: Comfortably Numb
|
|
| 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
International Hazard
Posts: 1523
Registered: 31-1-2007
Member Is Offline
Mood: No Mood
|
|
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
Hazard to Others
Posts: 322
Registered: 11-10-2007
Location: Montana
Member Is Offline
Mood: nitric
|
|
| 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.
The mind cannot decide the truth; it can only find the truth.
|
|
|
Antwain
Hazard to Others
Posts: 252
Registered: 21-7-2007
Location: Australia
Member Is Offline
Mood: Supersaturated
|
|
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
International Hazard
Posts: 1523
Registered: 31-1-2007
Member Is Offline
Mood: No Mood
|
|
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
Harmless
Posts: 28
Registered: 19-5-2004
Member Is Offline
Mood: No Mood
|
|
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
Hazard to Others
Posts: 447
Registered: 15-1-2005
Member Is Offline
Mood: No Mood
|
|
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
Hazard to Others
Posts: 252
Registered: 21-7-2007
Location: Australia
Member Is Offline
Mood: Supersaturated
|
|
@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
Super Administrator
Posts: 8014
Registered: 20-8-2005
Location: Netherlands
Member Is Offline
Mood: interested
|
|
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
International Hazard
Posts: 3873
Registered: 21-7-2006
Member Is Offline
Mood: No Mood
|
|
| 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.
|
|
|
dann2
International Hazard
Posts: 1523
Registered: 31-1-2007
Member Is Offline
Mood: No Mood
|
|
Distilling H2SO4
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
Hazard to Others
Posts: 252
Registered: 21-7-2007
Location: Australia
Member Is Offline
Mood: Supersaturated
|
|
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
International Hazard
Posts: 2961
Registered: 18-1-2007
Location: UTM
Member Is Offline
Mood: LaGrangian
|
|
@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
Hazard to Others
Posts: 322
Registered: 11-10-2007
Location: Montana
Member Is Offline
Mood: nitric
|
|
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.
The mind cannot decide the truth; it can only find the truth.
|
|
|
dann2
International Hazard
Posts: 1523
Registered: 31-1-2007
Member Is Offline
Mood: No Mood
|
|
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
Hazard to Others
Posts: 447
Registered: 15-1-2005
Member Is Offline
Mood: No Mood
|
|
.....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
International Hazard
Posts: 1523
Registered: 31-1-2007
Member Is Offline
Mood: No Mood
|
|
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
Hazard to Others
Posts: 246
Registered: 31-5-2006
Location: Deep South, USA
Member Is Offline
Mood: Inquisitive
|
|
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.
|
|
|
| Pages:
1
2 |
![[*]](images/xpblue/default_icon.gif){kind=icon}
