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Author: Subject: Generating HOCl disinfectant solution at home
steveha
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Generating HOCl disinfectant solution at home

Recently I have been researching disinfectants. I discovered that there is a disinfectant that is easy to make with simple equipment, that simultaneously is effective while being safe.

That disinfectant is hypochlorous acid solution, sometimes called "electrolyzed water" or EW for short. I'll call it EW since that's less to type than "hypochlorous acid solution".

Before I post my actual question, here's a review of why I believe generating EW is a good idea:

I first became interested in EW when I read a review article posted on the NIH web site. This article strongly makes the case that EW is both safe and effective. In particular it claims that 200 parts-per-million (PPM) EW can disinfect the virus that causes COVID-19 with only one minute of dwell time, yet 200 PPM EW is mild enough that it has been used as a hand sanitizer and even as a wound wash with no bad effects observed. To test whether EW is safe to use as a disinfecting mouthwash, a study gave a group of lab mice only EW to drink for 8 weeks and then dissected the mice; no bad effects were detected. (I'd like to know the PPM strength of the EW fed to the lab mice but I haven't found that information.)

EW at 200 PPM strength is approved by the USDA for disinfecting food preparation surfaces with no rinse required. It is approved as a food wash at 60 PPM strength.

I have reviewed various Safety Data Sheets for prepared EW solutions, and for home equipment for producing EW by electrolysis of salt water.

For comparison, here is a Safety Data Sheet for Clorox bleach, and one for a disinfectant based on quaternary ammonium compounds ("quats").

Clorox: "causes severe skin burns and eye damage"

Quats: wear protective gear, contact requires medical attention

I know that many people use chlorine bleach or quats for disinfecting, every day, without any problem. But if there is something safer, that's what I would prefer to use in my home.

Checking online retailers, there are two home electrolysis gadgets for sale that have safety data sheets available. Much less scary.

Force of Nature
Ecolox Eco One

The one demerit of EW is that it's unstable and will decompose back into salt water after some period of time. However, based on my reading, I believe it will last for at least a week; and I can make a batch for a few pennies of ingredients and electricity, so I'm comfortable making it fresh when I need a disinfectant.

I found a patent for how to produce EW that will be stable for extended periods of time. The patented procedure appears to simply be to start with very pure water and store the EW in an opaque plastic container. The original review article article I found lists 14 days as the minimum expected useful lifetime of EW if it's not exposed to sunlight.

Also, the stores near me are currently nearly sold out on disinfectants and toilet paper. I would like to have the ability to make as much disinfectant as I want, when I need it.

So, at last, here is my question:

What do I need to know to safely make EW at home? I don't know very much about chemistry so I want to get advice from people who know more than I do.

Here's what I think I have figured out, followed by the references I used to figure it out.

If you apply electrolysis to a salt water solution, the NaCl will split and there will be some kind of chlorine in the result. According to a graph, the form of the chlorine will depend on the pH of the solution. Above a neutral pH (7) the OCl- ion will predominate; in effect you will be making something similar to a chlorine bleach solution. Below a pH of 2, free chlorine gas will be produced, so that should be avoided. But at a pH somewhere between 5 and 6, hypochlorous acid will be almost exclusively produced.

The graph is visible here and there's a citation for the source of the graph. I haven't looked up the original source for myself.

https://www.hypochlorousacid.com/hocl-chemistry

Common practice is to make a solution with water, kosher salt, and vinegar. The Force of Nature product provides pre-measured plastic capsules containing a mixture of vinegar and salt. The Ecolox Eco One simply provides a recipe for measuring vinegar and salt. It seems clear that the goal of this is to have the solution pH between 5 and 6 before electrolysis.

I accidentally bought a gadget that is sold as a sodium hypochlorite generator (I intended to buy an EW generator), and the instructions that came with it don't tell how to make EW with it. But I believe that it should work. (This isn't magic, it's science; and electrolysis is electrolysis.) The instructions simply say to make a solution of pure salt and water, and apply electrolysis; based on the graph, I would expect this to produce OCl- ions.

The Ecolox Eco One recipe is 1 litre of water, 2 grams of salt, and 1 teaspoon of 5% distilled white vinegar.

I have a supply of powdered citric acid, and I would like to make my own recipe that uses the citric acid instead of vinegar. My gadget has a 2 litre capacity; I don't expect to need so much disinfectant so I want to work out a recipe to make one litre.

I have read that it's best to avoid copper or iron electrodes for the electrolysis; my gadget claims to use titanium. (The exact claim: "...with latest Platinum coated Titanium (SPE) electrolysis Plates and the long lifetime Proton Membrane (PEM) made by DuPont in the USA.")

I have a digital scale that claims to be accurate to +/-0.01 gram, a set of pH test strips, a set of chlorine PPM test strips, and my electrolysis gadget.

My planned procedure is to start with a litre of water, and add carefully measured amounts of powdered citric acid until the pH test strip shows a color about halfway between pH 5 and pH 6. Then add about 2.0 grams of kosher salt.

For my first attempt I plan to run electrolysis for a few minutes (timed with a timer) then stop and check pH and check the chlorine PPM. As long as the pH stays between 5 and 6 it shouldn't produce free chlorine gas; if I see the pH going badly out of spec I will stop, but based on this video I think the solution becomes a bit more basic, not more acidic, during electrolysis. As long as it seems to be staying within spec on the pH, keep repeating a few minutes of electrolysis until the chlorine PPM test strip indicates about 200 PPM strength.

I plan to set up the gadget on my stove, with the range hood fan running; it vents outside. This isn't as good as a chemistry lab fume hood but it's better than nothing and I have it.

I hope to work out a simple, repeatable recipe: 1 litre of water, X grams of citric acid powder, 2 grams of salt, Y minutes of electrolysis. (My gadget has a built-in timer that will automatically run for 5, 15, or 30 minutes, so I'm hoping that the total necessary time will be close to one of those numbers.)

I'm just planning to use tap water. I'm lucky enough to live in an area where our tap water is very pure.

Also, to measure how fast the solution decomposes back into salt water, I think I should be able to use a chlorine PPM test strip every few days. I should observe the indicator color lightening over time. I hope that it will still be pretty strong after one week.

So my questions:

• Should citric acid work just as well as vinegar for this application?
• Is my proposed plan safe?
• Any other things I should know?

Pre-made EW products, sold in spray bottles, cost something like $11 per litre. (Specifically:$15 for two 680 ml bottles) My gadget cost me $96 from an online retailer. So if I can get my gadget to make EW, I can pay back the purchase cost of the gadget by making a litre of EW 9 times. The Ecolox Eco One is sold for$280, over \$180 more than I paid for my gadget. On this web page, Ecolox makes some claims that their gadget is better and safer than cheap Chinese-made gadgets. I'm trying to decide if this is scare-mongering to justify a much higher price, or whether they have a point and I should box up my gadget and return it without using it. I don't mind paying a bit more for quality, but I do mind paying 2.8 times as much if there's no need. If my gadget would work equally well but would take twice as long... I don't care about that.

P.S. The Ecolox Eco One also comes with instructions for making a cleaning solution by applying electrolysis to a solution of potassium carbonate in water: 1 litre of water, 2 grams of potassium carbonate, and apply electrolysis to produce potassium hydroxide. Is that a good idea?

I don't much care because I already have a safe and effective cleaner/degreaser that I'm very satisfied with, called Quick 'n Brite.

I found a Safety Data Sheet and after reading it, I'm not interested in trying out this recipe. I understand that this SDS is for 100%, not a 200 PPM solution in water; still, as I said I already have a cleaner/degreaser I like.

Safety Data Sheet for potassium hydroxide

[Edited on 3-12-2020 by steveha]
IrishJeremy
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Sounds like you have a pretty good grasp of the process. Some trial and error will probably be involved in finding the best mid of salt and acid, but you will definitely get the product you want. Since your gadget has a platinised electrode, you can use it with a saturated salt solution to make the chlorate of the salt used. Sodium, potassium, etc. You can then used a saturated solution of sodium chlorate to produce sodium perchlorate. If you have an interest in pyrotechnics and energetics, you have a great tool how much www your device? You really don't have to worry about the chlorine being released. I have a similar device will a mixed metal oxide electrode and I have a chlorate cell running in my bathroom. There is a faint odor of chlorine if you are right above it, but it's not dangerous.

[Edited on 10-3-2021 by IrishJeremy]
mysteriusbhoice
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idk your proposed plan to do an electrolysis of NaCl with an acid present sounds like it will generate TONS of Cl2 gas and throwing an IEM ontop of that means you are basically making a chloro alkali cell.
I have made HOCl in a chloro alkali cell as an intermediate in the anode chamber and that stuff is nasty at high concentrations!! I basically call it chlorine soda cuz when you pour out the nasty yellow liquid and Disturb it then it will fizz out like a soda pop but instead of CO2 you get Cl2 gas that comes off.
The concentration of 200ppm sounds safe enough but still with these types of devices if you push many amps into it then it will produce lots of chlorine gas since even at pH 5 and 6 the evolution of chlorine will happen and quite a lot of it.
You also cannot check the pH of chlorinated water due to it turning the pH paper white due to bleaching but overall if your membrane works well then the pH shouldnt drift at all until the cathode side becomes a concentrated solution of NaOH.
This proposed device still gives me a concern for safety since you dont mention operating voltage or current which is important to know becuase at low current the evolution of chlorine is less but at higher currents it will really gas your entire room!!.
Id say even at around 3 amps this device is extremely dangerous based on experience and chlorine is emitted at any pH below the pH of 11 and at pH 5 and 6 the emission of chlorine is quite dangerous and at lower pH especially with a membrane involve which will drop the pH further instead of increasing it.
The operating temperature for such a cell should be 0 to 10 degrees celsius for the production of HOCl.
Id also say just like for making chlorates MMO is the best electrode for this application and me building a similar setup can probably crank out several tens of liters of this stuff in a matter of minutes since I can run such cells for like 15 amps or more and making large proton exchange membranes for cheap is one thing I have done.
mysteriusbhoice
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suggestions is to run the cell outside.
use set pH as 5 to 6 as suggested for minimum chlorine emission.
cool the cell as low as possible while running.
IrishJeremy
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Mysteriousbhoice has some really valid concerns here, and is VERY well versed in electrochemical reactions. If you are using a low current commercial device there shouldn't be too much Cl or Cl2 released, buy the addition of and acid can certainly make it worse. If you follow the instructions on your generator if should be safe. If you decide to alter the process you should definitely do it outside. Sodium hypochlorite is a good disinfectant, so only having the goal of producing hypochlorous acid seems a bit odd. The device will produce the acid and sodium hydroxide which will react to form hypochlorite. When it is first being run, the hydroxide level won't be high enough to react with all of the hypochlorous acid and the solution will be acidic. As the reaction progresses it will basify. Timing of how long it's run will determine the product.
Mush
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Great little device for small scale chlorate production. Brilliant!

"KCLO3 Production Review"

 Code: https://www.youtube.com/watch?v=GLnJC2z4Jds

"eBay: Chlorate /“Hypochlorite disinfectant generator” results + burn test"

"54g from this eBay “Hypochlorite Disinfectant Generator” which uses a stainless steel cathode and what we think is an “Iridium/Ruthenium Dioxide MMO” Anode.
It was run in 250/300ml saturated solution of KCl for 5 days using an apple cellphone charging wall wort that provides 5.2v 2.4A"
 Code: https://www.youtube.com/watch?v=oRNuism7Ktw

“How to” Chlorates from an Ebay Hypochlorite disinfectant generator
 Code: https://www.youtube.com/watch?v=aKDCgqcXIbI

 Sciencemadness Discussion Board » Special topics » Technochemistry » Generating HOCl disinfectant solution at home Select A Forum Fundamentals   » Chemistry in General   » Organic Chemistry   » Reagents and Apparatus Acquisition   » Beginnings   » Responsible Practices   » Miscellaneous   » The Wiki Special topics   » Technochemistry   » Energetic Materials   » Biochemistry   » Radiochemistry   » Computational Models and Techniques   » Prepublication Non-chemistry   » Forum Matters   » Legal and Societal Issues