"Miracle Liquid" Chemistry

shutterstock_6969091.jpgA story in the Los Angeles Times on Monday described a couple of environmentally-friendly "miracle liquids": one is a cleaner and degreaser, the other a disinfectant. They're so mild that you can drink them, straight up. What, exactly, are these potions? According to the LAT:
Actually, it's chemistry. For more than two centuries, scientists have tinkered with electrolysis, the use of an electric current to bring about a chemical reaction (not the hair-removal technique of the same name that's popular in Beverly Hills). That's how we got metal electroplating and large-scale production of chlorine, used to bleach and sanitize. It turns out that zapping salt water with low-voltage electricity creates a couple of powerful yet nontoxic cleaning agents. Sodium ions are converted into sodium hydroxide, an alkaline liquid that cleans and degreases like detergent, but without the scrubbing bubbles. Chloride ions become hypochlorous acid, a potent disinfectant known as acid water.
So they're making a solution of sodium hydroxide for cleaning, along with a solution of hypochlorous acid for disinfecting. If I've got my electrochemistry right, the system actually generates Cl2 at the cathode. The Cl2 then reacts with water to make HOCl and HCl. Sodium hydroxide is, of course, lye. It's not a big stretch to label that a cleaner. Nontoxic, though? Hopefully it's a very dilute solution. A review paper by one of the sources in the story, Yen-Con Hung, a professor of food science and technology at the University of Georgia, Griffin, says the pH is around 10.0-11.5. And yes, HOCl is akin to beach, which is generally made from NaOCl. Pools are also disinfected with NaOCl. The fact that HOCl is a relatively human-friendly disinfectant doesn't strike me as surprising. According to Hung, final "electrolyzed water" solutions typically have about 30-40 ppm HOCl and a pH of about 2.5. The low pH accounts for why "acid water" is a better disinfectant than bleach, because HOCl is a stronger oxidant than OCl-. Clearly there are no real surprises here. The electrochemical systems make dilute solutions of well-known chemicals. But I guess if you're pitching a $10,000 electrochemical set-up to a hotel, or a $3,000 unit to a home, you've got to justify it somehow. Calling it environmentally friendly seems to work. I have to question, however, whether the electrochemical approach is actually greener than, say, simply buying lye and bleach and diluting them. Alert C&EN readers will know that my colleague Marc Reisch covered this topic earlier this month in a story on industrial production of bleach using electrolysis. There, the principal benefit is avoiding transportation of chlorine gas. Reisch notes, however, that electrolysis consumes a lot of energy. Consequently, the industrial systems are more popular in states with inexpensive power. Going back to the home or hotel level, I think we need a lot more information on the full product cycles--manufacturing and maintenance of the electrolysis system, plus costs of water, salt, and electricity, compared to manufacturing and distribution of lye and bleach--to evaluate whether "electrolyzed water" is actually more environmentally friendly than traditional cleaners. As for why the LAT reporter didn't include a chemist in a story explicitly involving chemistry, I'm afraid I don't know. I sent her a draft of this post yesterday inviting her to comment but I haven't heard back. I'll update if I do. Image: Shutterstock

Author: Jyllian Kemsley

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3 Comments

  1. Is it feasible to run the electrolysis by solar power? That might be a good solution to this silly marketing spin.

    An interesting research proposal might be to find a catalyst that could do this with minimal energy requirements, similar to Daniel Nocera’s work on water splitting with his Co catalyst.

  2. Electrolyzed Water in the Fight against Antibiotic-Resistant Bacteria

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  3. Thanks for this — it is helpful. I’m amused to note that nowhere do they mention the dread elemental chlorine in their explanation — it might remove the “chemical-free” nature of their sales pitch.