DIY HCL, upper limits of % by volume

[jungle_Dave]

Hi Everyone, This is my first real question (yea!!)

Im setting up my lab in a country that acids are hard to come by.

What otc acids I can get,

Dilute HCL 8%
Sulpheric acid ( dilute and concentrated 98% )
Dilute nitric acid 43% (insane price better to make at home but ok)

My biggest problem is with hydrochloric acid that is only available in 8% (dirty) solution.

This could work with a 1:1 8% HCL to 3% Hydrogen peroxide for an AP process to remove foils but If I want to do any refining, I need a higher concentration hcl.

This means I have to synth my own. No problem and has been covered well but I have 1 small problem. HCL will max out at 20% (azeotrope) with every process "I know" to force hydrogen chloride gas through distilled water.

AR solution or Hot HCL (crock pot method) both require "concentrated" HCl at 30-34%

Nitric and sulfuric acid can both be concentrated much higher, as I remember nitric acid can go to 60% + with distillation / temperature controlled evaporation .

The questions,,,,,

Worst case, dilute solution= slower AR reaction or lack of reactive efficiency ?

Would hot 20% HCL be enough for foil separation or base metal stripping run on Au plated/filled material?

Can I dry HCL further then 20% or is my math off, in other words is 20% really 20% :shock: ?

 

[Geo]

You should be able to concentrate the HCl to 32% by evaporation through slow and gentle heating. At 32%, it will start to decompose in normal atmospheric pressure. When you have it concentrated, cap it in a suitable container.

 

[FrugalRefiner]

Actually, jungle_Dave is correct, the azeotrope of HCl is just over 20%. The ~32% acid many of us use is stronger than what can be obtained by simply evaporating a weak solution. If you start with 32% acid and heat it, it will become less concentrated.

The 20% should work for most of what we do. It will be slower, and you'll have to deal with a greater volume of solution, but it will work.

Dave

 

[Irons]

You can make Con. HCL with H2SO4 and Salt. It's not the cheapest way to do it, but probably the easiest.

 

[jungle_Dave]

You should be able to concentrate the HCl to 32% by evaporation through slow and gentle heating. At 32%, it will start to decompose in normal atmospheric pressure. When you have it concentrated, cap it in a suitable container.

Hi Geo, I was originally thinking the same thing as Hydrochloric acid has a boiling point 8.6 C higher then H20 at 20% concentration. That said, the azeotrope remains at 20%.The problem I am seeing is that the boiling point goes down as the concentration gets higher.

Hydrochloric acid
20% concentration has a boiling point of 108.6 C, 8.6 degrees higher then water
34% concentration has a boiling point of 71 C, 29 degrees lower then water..........

Actually, jungle_Dave is correct, the azeotrope of HCl is just over 20%. The ~32% acid many of us use is stronger than what can be obtained by simply evaporating a weak solution. If you start with 32% acid and heat it, it will become less concentrated.

The 20% should work for most of what we do. It will be slower, and you'll have to deal with a greater volume of solution, but it will work.

Dave

Thanks Dave!

I was just worried that the weaker solutions would result in a lower efficiency, slower I can live with.

It still leaves me with the theoretical question, How do they do it?
Vacuum distillation?

Irons,
Please correct me if I am wrong. Doesn't reacting H2SO4 + NACL result in producing hydrogen chlorine gas to be captured in water. How can this change the azeotrope?

 

[Geo]

This is a video. I trust Nurdrage that the chemistry is correct.

https://www.youtube.com/watch?v=YGjd7xxTuZw

 

[Irons]

Irons,
Please correct me if I am wrong. Doesn't reacting H2SO4 + NACL result in producing hydrogen chlorine gas to be captured in water. How can this change the azeotrope?

jungle_Dave
Member

Posts: 4
Joined: Fri Oct 31, 2014 12:58 pm
Location: Brazilian Amazon

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The max HCl concentration in H2O at 20*C is something less than 40%, so use the amount of Water needed to make a saturated solution of HCl.

http://www.qvf.com/qvf-process-systems/mineral-acids/absorption-of-hydrogen-chloride/adiabatic-absorption.html

 

[jungle_Dave]

This is a video. I trust Nurdrage that the chemistry is correct.

https://www.youtube.com/watch?v=YGjd7xxTuZw

Great video, I did see this one before as I did most of yours too. Im a big fan of your set up Geo!

They do mention getting higher concentrations in less water but don't say how much. I believe them, just trying to work out why this works. I need a few more flasks to try this myself, when I do I'll post the results.

Irons,
Please correct me if I am wrong. Doesn't reacting H2SO4 + NACL result in producing hydrogen chlorine gas to be captured in water. How can this change the azeotrope?

jungle_Dave
Member

Posts: 4
Joined: Fri Oct 31, 2014 12:58 pm
Location: Brazilian Amazon

Top

The max HCl concentration in H2O at 20*C is something less than 40%, so use the amount of Water needed to make a saturated solution of HCl.

http://www.qvf.com/qvf-process-systems/mineral-acids/absorption-of-hydrogen-chloride/adiabatic-absorption.html

Thanks for the link,
The process of concentrating hydrogen chloride looks allot like distilling vodka. The more plates involved the purer the end product, he he, thats where 2 hobbies meet ... My wife will love this! (not)
quoting qvf.com

" hydrochloric acid of 30wt% may only be produced if the concentration for hydrogen chloride is greater than 82wt% with reference to inert-free gas state at the column inlet."

What this is all showing me is that the key is in the concentration of gas and the temperature of the water which explains the ice.

 

[FrugalRefiner]

It still leaves me with the theoretical question, How do they do it?
Vacuum distillation?

Irons,
Please correct me if I am wrong. Doesn't reacting H2SO4 + NACL result in producing hydrogen chlorine gas to be captured in water. How can this change the azeotrope?

There are several ways to create concentrated HCl. Take a look at Concentration of Hydrochloric Acid above the azeotropic point.

The method Irons described doesn't change the azeotrope. The azeotrope is the balanced concentration of two fractions achieved at a "constant boiling" point. As I said above, if you were to take concentrated HCl, either purchased or produced as Irons described, and boil it, the concentration would decrease until it reached the azeotrope of 20.2% at STP.

Dave

 

[Irons]

Exothermic process. Needs serious cooling.

 

[jungle_Dave]

Thanks again for this link and everyone responses.
Its great to understand this process better as I have to make my own. Will definitely help in understanding reclaiming and regenerating spent acid as well.

2 systems were presented for concentrating hydrochloric acid. Dual pressure, and extractive rectification.
The dual pressure system I could wrap my head around.
it works on the principal that the location of the azeotrope point is contingent to pressure. Low pressure reaction creates the azeotrope, high pressure condenses the solution much like an alcohol still with concentrated HCL from the head and lower % solution at the bottom which gets recycled again. Cool 8)

If i understand this concept right,
Bubbled HCL gas through H2O at 30,000 ft, you would get close to 30% concentration with no special equipment.
Would that explain why you get a higher concentration in ice cold water too?

 

[jason_recliner]

Would that explain why you get a higher concentration in ice cold water too?

Cold water is far more able to absorb gases. Or keep them in solution.

We all know the difference between opening a bottle of room temperature soda versus one out of the fridge: The warm one is far more likely to overfizz out the top; it just can't wait to expel all that extra CO₂.

 

[jungle_Dave]

That makes sense :lol: ,

 

[jungle_Dave]

Just a quick update,

I had to take some time off due to a back surgery but I have tried both approaches to synthesizing hydrochloric acid.
SMB approach works, its a bit tricky (with my really basic setup) and I had to concentrate the acid by way of controlled evaporation. The method I used was similar to the nerd rage video, only change I made was 1 extra flask with 2 hoses to compensate for the vacuum. Anyone who has distilled alcohol knows the concept of a thumper. This worked great and with some tweaking I should be able to get near 20% on the first go.

H2SO4 and NaCl worked very well and I got a higher concentration on the first go. The downside was(as Irons pointed out) that it did get really hot but this was pretty easy to mitigate.

Both processes rendered close to 20% and was fine for what we are doing here as Dave correctly stated,thanks Dave .
I was able to make both AP and AR solutions albeit dilute.
One thing I should point out, I did manage to get a small amount of concentrated HCL and Nitric to use as a control.
My diluted AR produced much more gas when dissolving gold alloy then the control solution. Hoke was a little lax on the subject of ventilation and fume management, I can't blame her as it was the 40's.
New members like myself should take this into consideration and have a way of dealing with it by way of adequate ventilation + attention to volume (not overloading your AR vessel )
My conclusion is that both methods have there benefits for the home refiner. Cost of production is much less then if you were to purchase ready made Hydrochloric acid. SMB due to its wide use world wide in a multitude of applications wins the price per liter game.

 

[FrugalRefiner]

Hoke was a little lax on the subject of ventilation and fume management, I can't blame her as it was the 40's.

As you said, in 1940 no one recognized some of the dangers in using these processes. I highlighted some of the worst in the introduction I added to my versions of her book. If you haven't already, take a look at one of the copies in my signature line.

I will do another update one day, and this time I will be including a strong warning about refing the platinum group metals. Lou has convinced me of the dangers when creating salts of these metals. We've had forum members who have developed serious PGM allergies that have forced them to stop refining them.

Dave

 

[jungle_Dave]

Hoke was a little lax on the subject of ventilation and fume management, I can't blame her as it was the 40's.

As you said, in 1940 no one recognized some of the dangers in using these processes. I highlighted some of the worst in the introduction I added to my versions of her book. If you haven't already, take a look at one of the copies in my signature line.

I will do another update one day, and this time I will be including a strong warning about refing the platinum group metals. Lou has convinced me of the dangers when creating salts of these metals. We've had forum members who have developed serious PGM allergies that have forced them to stop refining them.

Dave

I did indeed and my compliments Dave! Like most noobs I started understanding this process by way of youtube (dangerous!)
then digging in to my badly neglected inorganic chemistry books, not finding the answers I wanted and finally finding GRF then getting your screen readable version of Hokes bible .

It's sad news to hear a forum member got so ill! I would like very much to know more about the risks involved with platinum group metal salts(I'm suspecting vapors too) as I used to work with palladium and tantalum in industrial applications.

Just to point out how far back safety was in Hokes time she states that by tasting solutions you could determine the respective state :shock:

The forum states read Hokes book front to back ( I agree) before posting, should be stated read the entire safety section before even doing "acquaintance experiments "

 

[FrugalRefiner]

It's sad news to hear a forum member got so ill! I would like very much to know more about the risks involved with platinum group metal salts(I'm suspecting vapors too) as I used to work with palladium and tantalum in industrial applications.

More than one member.

I'm trying to learn more about them myself. Hoke and others have taken a very casual approach to the PGMs, and that has led many to try their hands at them. I would say that any contact with vapors, solutions, and/or the dried powders is hazardous.

If we're lucky, maybe Lou will join in here. He is very involved in the subject.

Dave