-- The Home Page of the Finishing Industry
  HOMEFAQsBOOKSHelpWantedAdvertiseContactFORUM Letter 27815

The Hotline: Serious Education ... plus the most fun you can have in metal finishing. Ted Mooney, Webmaster

Distilling hydrochloric acid


Anyone know how to increase the strength of muriatic acid, HCl? Have 33% from a hardware store and want to concentrate it to approx. 70%. Distilling seems obvious but how? Any ideas.

Bonnie Hanlon
student - Sydney, NSW, Australia


The only idea that comes to mind is this: hydrogen chloride fumes are NASTY. Could you please tell us: do you really need concentrated HCl? What is the application?

Steve Bizub
- St Louis, Missouri


Why don't you purchase some Conc. HCl from a chemical supply house and then dilute to the strength required. This is what most chemists would do.

Ronald Zeeman
Coil Coating - Brampton, Ontario, Canada


Dear sir, it is not advisable to distill HCl, because hydrogen chloride gas is dissolved in water to give the acid. If you distill the acid then acid vapours (HCl) will escape and will further reduce the concentration. Vapours from this acid will just inflame your nostrils and wreak havoc.


- Chennai, Tamilnadu, india


Agree with Steve. A hydrochloric acid solution of 70 wt% HCl is only stable under very high pressure (about 5.15 MPa or 50.8 atm) HCl vapor at 30 C) and is extremely dangerous. Before doing anything else, please read the safety info "Medical Management Guidelines (MMGs) for Hydrogen Chloride (HCl)" at

Two options for preparation of 70 wt% HCl solution: distillation (under some very specialized conditions) or addition of pressurized HCl gas. The US EPA's "Guidance for Reporting Hydrochloric Acid (acid aerosols including mists, vapors, gas, fog, and other airborne forms of any particle size)" contains most of the physical data necessary for distillation.

Additional HCl solution data is at The freezing point curve indicates that partial freezing can only concentrate a 33% HCl solution to 40%; a composition corresponding to an HCl.3H2O complex.

The largest problem in distillation is the very high vapor pressure of the distillate. This, plus the health hazard and corrosiveness, requires the use of Teflon®-lined metal equipment rather than laboratory glassware. The change in composition of the still liquid is another consideration. The initial vapor will be ~90% HCl by weight, but by continuing the distillation until the remaining liquid reaches the azeotropic composition (~22.2 wt% HCl) and a total vaporization of ~22.6 wt%, the average distillate should be the desired 70 wt% HCl. To maintain a flow of vapor from the "boiler" to the condensing vessel, it may be necessary to solidify the condensate by keeping the latter at very low temperature with a dry ice/acetone or liquid nitrogen bath, while gradually raising the temperature of the still liquid. Use Pyrex glass boiling beads and avoid rapid heating to prevent "burping" of liquid. The condensing vessel should obviously be valved and detachable, and of suita! ble construction to withstand pressure, low temperature and corrosiveness. Perhaps, a 1 L Teflon®-coated, austenitic stainless steel pressure vessel, with appropriate valving, etc.

It is easier to add HCl gas under pressure to the 33% solution in order to reach the desired 70%. Again, use a 1 L Teflon®-coated SS vessel (e.g., a bomb calorimeter). Order a high-pressure cylinder of anhydrous HCl, an appropriate regulator, valving and tubing. Set the vessel on a weighing scale, fill ~90% full with the 33% HCl liquid, then add the desired weight of HCl gas. Close valving and give it some time to cool before using.

Ken Vlach
- Goleta, California honored Ken for his countless helpful
& well researched responses. He 'disappeared' in
2008, never answering our several inquiries about
his situation. But we believe that this is his obit
and would greatly appreciate hearing from anyone
who knew him. Thank you Ken, and rest in peace.


You can always add kitchen salt* to sulfuric acid* to get hydrochloric acid?

*must be 100% NaCl

*get it from hardware stores or uncharged car batteries (if you get it from the batteries, which is unadvised, filter out the chunks of lead).

Kit Callahan
- Folsom, California, U.S.A


Thanks for helping out, Kit, but I don't think that's true. Can you quote a source?

Ted Mooney,
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey


"Jabir or Geber, is also credited with the invention and development of several chemical instruments that are still used today, such as the alembic, which made distillation easy, safe, and efficient. By distilling various salts together with sulfuric acid, Jabir discovered hydrochloric acid (from salt) and nitric acid (from saltpeter). By combining the two, he invented aqua regia, one of the few substances that can dissolve gold. Besides its obvious applications to gold extraction and purification, this discovery would fuel the dreams and despair of alchemists for the next thousand years. He is also credited with the discovery of citric acid (the sour component of lemons and other unripe fruits), acetic acid (from vinegar), and tartaric acid (from wine-making residues)."


Kit Callahan
- Folsom, California, USA


Concentrated (100%) HCl is a gas, you can't have 100% concentrated HCl in liquid form, the acid forms an azeotrope at about 30% concentration, so you cannot purify it further by distillation, you CAN have a slightly more concentrated HCl when you distill a mixture of 30% HCl with some concentrated (98%) sulfuric acid.

Marcial Cordova
- Hermosillo, Sonora, Mexico

March 9, 2008

You can distill lower concentrations of HCl (less than 20%) also to produce up to 100 % HCl. For this you will need an extractant like H2SO4 or Calcium Chloride.

I suggest you produce 70% - 100% HCl at the point of use, and not store it.

Setting up a plant to produce such HCl is the option

Vinayak Madhekar
- Pune, Maharashtra, India

April 20, 2008

Hydrochloric acid is near saturation in water at about 33% to 40%, I believe, and higher concentrations would not be a reasonable solution to your problem as they really would only exist under laboratory conditions. Should you wish to have an acid with stronger qualities perhaps a different acid or a mix would give the field strength desired.

As for the salt gives hydrochloric acid, believe it or not I looked in the encyclopedia and found a 1600th century alchemist, Johann Rudolf Glauber, who's life work was highlighted by the discovery that hydrogen chloride gas is produced by the addition of sulfuric acid to table salt. Of course, one must bubble the HCl into water to make hydrochloric acid which, as indicated above, saturates near 33% at room temperature.

Dave Crippen
- Seattle, Washington

July 11, 2010

Hydrogen Chloride (HCl) is a gas, which can be produced by reacting Sulfuric acid with sodium chloride. However, an aqueous solution of HCl is saturated (at standard temperature and pressure) at around 40% concentration (like carbon dioxide in soda). Any solution which has been saturated under higher pressure to a higher concentration than this will go "flat" if exposed to normal atmospheric conditions, and return to 40% as the hydrogen Chloride escapes. Bubble hydrogen chloride gas (produced as said above) through water, and the gas will slowly saturate the solution. I wouldn't recommend this though, as hydrogen chloride is nasty stuff.

Austin Feathers
- Overland Park, Kansas, US

August 21, 2010

The others are correct, hydrochloric above the 37% mark can only be produced under pressure, to force the escaping hydrogen chloride back into solution. Otherwise, at room temperature and pressure, the water saturates and no more hydrogen chloride will dissolve.

I do produce large amounts of hydrogen chloride at home using the salt / sulphuric method. Table salt works, anhydrous CaCl2 works better (more gas per unit mass of salt). The acid has to be near it's maximum distillable limit (98%).

I also have thousands upon thousands of pounds worth of laboratory equipment to handle it and tens of other chemists providing tips on every detail.

It's doable at home. Get it wrong, however, and it's going to get very nasty, very quickly.

You should see the state of the area I generate the gas in, anything it touches it corrodes. Supposedly chemical safe plastics fall apart in minutes. The stainless is corroding, badly.

I have often inhaled some of the gas, and even let others have a go to see what it's like. It is physically impossible not to have a minute long coughing seizure from one inhalation; I also smoke, so am used to ignoring the urge to cough.

There is another way to generate what is essentially pure 'hydrochloric', but that's harder and more dangerous again, so it doesn't really need discussing.

John Heritage
- Wallasey, Merseyside, United Kingdom

October 22, 2010

Since HCl is in nothing but water, can't you juste use Driereite to purify the HCl by removing the water in the mixtures, which is also why it's almost impossible to distill upon mixture; the percentages are at the same degree of 110 for a water distill

Brian Mag
- victoria, texas, usa

August 24, 2011

Extractive Distillation followed by high pressure HCl gas dissolution will give you an Ideal Solution to get high concentration HCl solution.How ever,since High Concentration HCl solution is unstable,it has to be generated only at the time of use.

Salting effect will work here.

Prashanth M
- Trivandrum, Kerala, India

March 6, 2012

Could you get a slightly higher concentration of hydrochloric acid by freezing out the water?

Brandon Halliday
- Minden, Louisiana, U.S.

July 11, 2012

Q. If I had a large quantity of 15% HCl how do you increase it to 35% solution?

Ed Stribling
- Houston, Texas USA

Disclaimer: It is not possible to diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous; some names may be fictitious and some recommendations may be deliberately harmful.

  If you need a product/service, please check these Directories:

JobshopsCapital Equip. & Install'nChemicals & Consumables Consult'g, Train'g, SoftwareEnvironmental ComplianceTesting Svcs. & DevicesUsed & Surplus

©1995-2015     -    Privacy    -    Search