Making hypochlorous acid

[Jeremy Harris]

One problem that seems looming on the horizon (may already be here) is that some very useful disinfectants may be in short supply, driving up the price.  I have a (now diminishing) stock of isopropyl alcohol, for making surface disinfectant and hand sanitiser, but this is now getting to be really hard to buy, and when it is available the price is very high.

 

There's an alternative that is very safe to use, and which can be produced using just water, salt (sodium chloride) and low power electricity, hypochlorous acid.  This can be produced using electrolysis, but it needs electrodes that are pretty inert, and ideally also needs a way to separate out the three reaction products, chlorine (which we want to dissolve in water), hydrogen (which needs to be safely vented) and sodium hydroxide (which we don't really want in the end product).

 

There are some (fairly dubious) Chinese made "hypochlorous acid" generators available (for around £20) but they clearly don't make any attempt to remove the sodium hydroxide, and that creates two problems.  The first is that sodium hydroxide is caustic, and undesirable in any disinfectant, the second is that it's a strong alkali, so will encourage the premature breakdown of the hypochlorous acid (ideally, the pH needs to be around 4 to give it a reasonable shelf life).

 

The raw materials seems to be fairly easily available, like titanium electrodes.  What's needed is an easily made device that can separate out the three products from electrolysis and produce relatively pure hypochlorous acid in solution.  This doesn't need to be concentrated, as it's pretty powerful when very diluted.  It's been proven to have a strong effect against both bacteria and viruses, and it's safe to use on or around foodstuffs.

 

I've ordered some titanium for the electrodes, and plan to try and make a useful hypochlorous acid over the coming days, making sure that the output from the thing is properly tested, both so I know it's safe and to determine how effective it is.  I believe this can be done with easily available test kit, as it seems that hypochlorous acid is already used to disinfect some swimming pools, in preference to using hypochlorite dosing and pH balancing.

[joe90]

In these uncertain time’s this is very interesting. I for one would be very interested in producing my own “brew” so will be watching this thread closely. Thanks @Jeremy Harris fir sharing ?

[Onoff]

15 minutes ago, Jeremy Harris said:

One problem that seems looming on the horizon (may already be here) is that some very useful disinfectants may be in short supply, driving up the price.  I have a (now diminishing) stock of isopropyl alcohol, for making surface disinfectant and hand sanitiser, but this is now getting to be really hard to buy, and when it is available the price is very high.

 

There's an alternative that is very safe to use, and which can be produced using just water, salt (sodium chloride) and low power electricity, hypochlorous acid.  This can be produced using electrolysis, but it needs electrodes that are pretty inert, and ideally also needs a way to separate out the three reaction products, chlorine (which we want to dissolve in water), hydrogen (which needs to be safely vented) and sodium hydroxide (which we don't really want in the end product).

 

There are some (fairly dubious) Chinese made "hypochlorous acid" generators available (for around £20) but they clearly don't make any attempt to remove the sodium hydroxide, and that creates two problems.  The first is that sodium hydroxide is caustic, and undesirable in any disinfectant, the second is that it's a strong alkali, so will encourage the premature breakdown of the hypochlorous acid (ideally, the pH needs to be around 4 to give it a reasonable shelf life).

 

The raw materials seems to be fairly easily available, like titanium electrodes.  What's needed is an easily made device that can separate out the three products from electrolysis and produce relatively pure hypochlorous acid in solution.  This doesn't need to be concentrated, as it's pretty powerful when very diluted.  It's been proven to have a strong effect against both bacteria and viruses, and it's safe to use on or around foodstuffs.

 

I've ordered some titanium for the electrodes, and plan to try and make a useful hypochlorous acid over the coming days, making sure that the output from the thing is properly tested, both so I know it's safe and to determine how effective it is.  I believe this can be done with easily available test kit, as it seems that hypochlorous acid is already used to disinfect some swimming pools, in preference to using hypochlorite dosing and pH balancing.

 

They have a commercial machine to do this bought in at the static site I'm stood down from. 

 

Ref DIY electrolysis, do I recall a problem using stainless steel electrodes? Something about poisonous off gassing?

[Jeremy Harris]

15 minutes ago, Onoff said:

 

They have a commercial machine to do this bought in at the static site I'm stood down from. 

 

Ref DIY electrolysis, do I recall a problem using stainless steel electrodes? Something about poisonous off gassing?

 

 

From what I've found out so far, the two materials that seem to be best able to survive without corroding and producing unwanted compounds are graphite and titanium.  The latter seems to be slightly better, but I may try both.

 

What I'd like to do is come up with something that's fairly easy to make, safe to use and can produce a fairly pure product. The key thing seems to be getting rid of the unwanted hydrogen and sodium hydroxide.

[ProDave]

Watching with interest.

 

My little brain is struggling with how you get three products from 2 electrodes.

[Jeremy Harris]

19 minutes ago, ProDave said:

Watching with interest.

 

My little brain is struggling with how you get three products from 2 electrodes.

 

 

It's down to the chemistry, rather than the physical stuff.  You start with water (H₂O) and salt (NaCl), and when you chuck some energy into this solution, via the electrodes, then you get diatomic hydrogen (H₂) liberated from the cathode, diatomic chlorine (Cl₂) liberated from the anode and sodium hydroxide (NaOH) in the remaining solution.  To make hypochlorous acid, the chlorine needs to be dissolved in pure water.  To make it stable, the pH of the water needs to be reduced to about 4.  I think that just using acetic acid (vinegar) should do this OK.

 

The mechanical stuff will just be devising an easy way to collect and disperse the hydrogen from the cathode, collect and dissolve the chlorine from the anode into the acidified water solution and coming up with an easy to use, charge and clean reaction vessel, without resorting to lab glassware.

[SteamyTea]

1 hour ago, Jeremy Harris said:

From what I've found out so far, the two materials that seem to be best able to survive without corroding and producing unwanted compounds are graphite and titanium.  The latter seems to be slightly better, but I may try both.

 

Would platinum be the best, can get that from underneath cars.

[Jeremy Harris]

Just now, SteamyTea said:

Would platinum be the best, can get that from underneath cars.

 

 

Yes, but the area of the electrodes needs to be fairly large, which means using quite a bit more platinum per unit than there is in a catalytic converter.  Titanium looks affordable, just over a fiver for enough to make two fairly large electrodes.  I'm working on something that may be able to produce about 100ml to 300ml in maybe ten minutes, with a shelf life of maybe two or three weeks.  It'll need between 3g and 9g of pure (no anti-caking agents added) salt, and so far it looks like salt is still readily available.

[tommyt]

Titanium electrode with iirc 12v socket built in

made for water softener chlorine generation. 
 

https://www.termoidraulicarv.com/en/parkin-softener-s-parts/352-titanium-electrode-for-chlo-active-with-tee-38--0793597724069.html

[dpmiller]

So, ignoring the TV-shopping aspect... Is that what this is?

https://h2o-e3.thanedirect.co.uk/

[Jeremy Harris]

2 minutes ago, dpmiller said:

So, ignoring the TV-shopping aspect... Is that what this is?

https://h2o-e3.thanedirect.co.uk/

 

 

Yes and no.  The problem with these pretty cheap units is that they make no attempt to get rid of the sodium hydroxide.  That remains in solution with the hydrochlorous acid.  The main issue with that is that hydrochlorous acid is pretty unstable if in a strong alkaline solution, it probably has a half-life of just few days under those conditions.  Similar gadgets are available from Chinese sellers on eBay (for a higher price than they were selling for a few weeks ago: https://www.ebay.co.uk/itm/UK-Disinfection-Sterilizing-Hypochlorous-Acid-Water-Making-Machine-Spray-Bottle/153879920799?hash=item23d3f5409f:g:dvcAAOSwJiRef0iH ).

 

What I'd like to do is separate out the reaction vessel from the hypochlorous acid collection vessel if possible, just so what's produced is relatively pure and fairly stable, leaving the sodium hydroxide and any residue from the electrodes behind. 

[Jeremy Harris]

Some progress, although I'm still waiting for stuff to arrive.  Rather bizarrely, the only thing ordered from China, a supposed "hypochlorous acid generator" has been the first thing to arrive.  This is what it looks like:

 

 

First thing I did was take it apart to see what's inside and how it works.  It is really simple, just a timer circuit that switches a controlled current through a couple of titanium electrodes that spiral around the base, and which are covered with a plastic grille.  The timer runs for 8 minutes when the button is pressed.  All the instructions are in Chinese and are indecipherable (I've spent an hour trying to just get the basics, to no avail).

 

I went back to basic chemistry and decided that the starter solution probably needed to be about 1.2g of sodium chloride to 300ml of water electrolysed for 8 minutes at about 1 A, in order to give a solution with about 500 to 800ppm of hypochlorous acid (that's a pretty strong disinfectant, 50ppm would probably just about be OK).  This thing cannot just produce hypochlorous acid, and produces a fair bit of sodium hydroxide in the end solution.  Not enough to cause any significant harm, and it may well mean the solution is a bit better at cleaning surfaces.

 

The main issue is that the pH increases way above the point where the hypochlorous can remain stable for long.  I ended up with a final pH of around 8, and ideally this needs to be below 5, perhaps down around 3 to give a few weeks of shelf life.  I've tried to assess the free chlorine, as a crude measure of hypochlorous acid concentration, but failed, as my test kit can't work up at this range, which bodes well for it actually having worked (as does the slight smell of chlorine).  I have some stuff on order, including a high range chlorine test kit, that should allow a better assessment of the effectiveness of this thing.  I also have some acetic acid on order, as I want to try lowering the pH to see how that impacts the shelf life.  I'd like to try using very cold water as a starter, too, as that may increase the solubility of the chlorine gas liberated from the anode in the water.  The hydrogen liberated from the cathode when the thing is running is just vented to the air.

 

Also on order are some larger titanium electrodes, as I want to have a go at making a proper hypochlorous acid generator, one that separates out the hypochlorous acid from the sodium hydroxide, and allows better control of the pH.  This will need an ion exchange membrane to separate the anode and cathode, but I'm hoping I can knock something up using standard waste pipe fittings.

 

More to follow once I get more stuff delivered.

[Jeremy Harris]

Just finished doing some more experimentation with the Chinese unit bought from eBay.  I managed to decipher the Chinese characters for "salt", "gram" etc in the instructions and found that they seemed way off, 15g of salt for 300ml of water, with a probable electrical energy into the water of about 0.7 Wh.  I tried this, but there was a massive excess of salt left in the solution.  However, reducing the salt to 1.2g, seems to work, although at best it seems that the concentration of free chlorine is only a bit over 100ppm.  I stabilised the pH with acetic acid (white vinegar) so that the starting pH (before electrolysis) was about 4.  I used just a couple of drops of 70% concentrated acetic acid, but if using weaker white vinegar about 2ml might be needed to get the pH about right.  This seems to work OK, and at this pH the solution should be pretty stable.

 

From what I've read, anything over about 50ppm hypochlorous acid concentration is very effective as a disinfectant, so the ~100ppm solution that one of these units produces should be fine.  It needs to be stored in a cool, dark, place, though, as heat and light will tend to cause it to breakdown more rapidly.  In theory it should breakdown back to sodium chloride, so just plugging it in and giving it another burst of power should bring it back up to full strength again.

 

The next stage is to try and get the bigger, home made version working.  The plan is to get this to produce pure hypochlorous acid if I can, without the residual sodium hydroxide.

[Ferdinand]

..

Edited April 16, 2020 by Ferdinand

[SteamyTea]

5 hours ago, Jeremy Harris said:

The next stage is to try and get the bigger, home made version working

 

[Jeremy Harris]

Funny old thing, but I delivered another 5 litres of alcohol based home made sanitiser to our local volunteer coordinator this afternoon.  Still no official supplies, but we have now received some grant funding from the council to pay for PPE.

[SteamyTea]

On tonight's COVID briefing (may have been on PM just before it) there was a comment about how well the public are accepting of the lockdown.  Better than most countries apparently.

 

Is this because most of us hate our jobs?

Edited April 16, 2020 by SteamyTea

[vivienz]

1 hour ago, SteamyTea said:

On tonight's COVID briefing (may have been on PM just before it) there was a comment about how well the public are accepting of the lockdown.  Better than most countries apparently.

Is this because most of us hate our jobs?

 

It's the good weather.

[Miek]

Just now, vivienz said:

 

It's the good weather.

Exactly my thoughts.

[Nila]

On 16/04/2020 at 10:29, Jeremy Harris said:

Just finished doing some more experimentation with the Chinese unit bought from eBay.  I managed to decipher the Chinese characters for "salt", "gram" etc in the instructions and found that they seemed way off, 15g of salt for 300ml of water, with a probable electrical energy into the water of about 0.7 Wh.  I tried this, but there was a massive excess of salt left in the solution.  However, reducing the salt to 1.2g, seems to work, although at best it seems that the concentration of free chlorine is only a bit over 100ppm.  I stabilised the pH with acetic acid (white vinegar) so that the starting pH (before electrolysis) was about 4.  I used just a couple of drops of 70% concentrated acetic acid, but if using weaker white vinegar about 2ml might be needed to get the pH about right.  This seems to work OK, and at this pH the solution should be pretty stable.

 

From what I've read, anything over about 50ppm hypochlorous acid concentration is very effective as a disinfectant, so the ~100ppm solution that one of these units produces should be fine.  It needs to be stored in a cool, dark, place, though, as heat and light will tend to cause it to breakdown more rapidly.  In theory it should breakdown back to sodium chloride, so just plugging it in and giving it another burst of power should bring it back up to full strength again.

 

The next stage is to try and get the bigger, home made version working.  The plan is to get this to produce pure hypochlorous acid if I can, without the residual sodium hydroxide.

 

Hello Jeremy,
I found this forum and your post while I was doing research about the electrolyzed water. Someone suggested it as a safer way of disinfecting surfaces at work when we open after the lockdown. Your post was very helpful, however since I am not familiar with chemistry I have a few questions that I will appreciate if you help me with.

 

https://mangatabox.com/collections/best-seller/products/300ml-disinfection-sterilizing-hypochlorous-acid-water-making-machine-spray-bottle?variant=33571800842299

 

The model in the link above looks like the one you purchased from China. Most of the similar models advertise them as 'Hypochlorous Acid making machine' but in their description they says it is making 'Sodium hypochlorite' which is different and it's bleach, if am I right? Then they say it is completely safe, chemical free and non-toxic and can be used to disinfect anything even food! This is very confusing as nobody in their right mind would use bleach on their fruits or vegetables!! So I don't understand. Can you please shed some light on this??

Many thanks.

 

Edited July 7, 2020 by Nila

[Temp]

I've read that 1L of 5% bleach in 49L of water is good enough for cleaning surfaces.Tesco sell 2L bottles of 1% thin bleach for £0.38p. I reckon 3 of those in 45L of water will give similar results. Total cost under £1 for 50L.

 

PS: yes their thin bleach is Sodium Hypochlorite.

 

 

Edited July 7, 2020 by Temp

[Temp]

46 minutes ago, Nila said:

nobody in their right mind would use bleach on their fruits or vegetables!!

 

The Americans use it on chicken don't they or is that different?

 

Edit:

https://thepoultrysite.com/articles/chlorine-still-the-most-popular-sanitizer-in-the-poultry-industry

 

Chlorine in the form of sodium hypochlorite, calcium hypochlorite tablets or chlorine gas is by-far the most commonly used carcass and equipment disinfectant in the US poultry industry. 

 

Coming to a supermarket near you after Brexit.

Edited July 7, 2020 by Temp

[joe90]

However we forget about salad!

 

Chlorine-rinsed bagged salads are common in the UK and other countries in the EU. 

[SteamyTea]

The use of chlorine in food processing is common practice.  The EUs 'problem' with American chlorinated chicken is to do with animal welfare standards, not the post production after slaughter.

[joe90]

1 minute ago, SteamyTea said:

The use of chlorine in food processing is common practice.  The EUs 'problem' with American chlorinated chicken is to do with animal welfare standards, not the post production after slaughter.

this is why I think people have the “wrong end of the stick” on this matter. I wonder how many people know we use chlorine as mentioned above?