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I read the manufacturer’s manual on line and also the patent which is also available on line. Their proposed mechanism of the formation of NaCl deposits at the tank’s bottom doesn’t make sense.
Strange as it may sound, what seems like a more plausible mechanism serves their cause even better.
I wonder if any one (chem geek?) is interested in exchanging a few words about it.
If there’s an interest I’ll post a more detailed discussion with links.
I'd be interested (and we're in The China Shop). I thought the reasoning was similar to why the more concentrated chlorine levels stay on the bottom -- it's a "cline" and there is diffusion to mix the layers, but it is slow. The question that hasn't been answered is why the hypochlorous acid migrates across the layer more readily than salt.
Richard
The Liquidator’s US patent 4,879, 027 is presented here.
The manufacturer presents the details here.
In the patent in "claim 10" they say that "the sodium hypchlorite dissociates to deliver chlorine and leaves sodium chloride in the bottom."
A quote from the web site:
At the point in the tank where the two liquids meet, the molecules of pure chlorine are absorbed from the heavier liquid below into the lighter pool water above, then sent back to the pool through the suction line.
The heavier chemical salts remain in the bottom of the tank, while the chlorinated water is drawn into the pool for sanitation.
According to these quotes the inventor claims that the hypochlorite in the lower phase dissociates to chlorine (Cl2) and chloride (Cl-) . The Cl2 is supposedly transferred to the upper level which is comprised of pool water and thus it’s fed to the pool while the Cl- precipitates as NaCl in the tank.
I think that while everybody agrees that the invention is a cool way to add bleach continuously into the pool in a controlled way,
the proposed chemistry and mechanism are inherently wrong.
The lower level constitutes of water, undissociated hypochlorous acid, hypochlorite anion, sodium cations, a low concentration of hydronium cations and a higher concentration of hydroxyl anions.
Because the hypochlorous acid is a weak acid (pKa = 7.5) most of the chlorine is in the form of undissociated hypochlorous acid. There is no chloride (Cl-) in sodium hypochlorite solution, unless it is exposed to UV or suffers from thermal degradation. Chloride would form only when the hypochlorous acid is decomposed by UV to yield oxygen and HCL, the latter being the source for chloride.
When the lower, stationary phase is in contact with the moving upper phase, there’s an exchange of dissolved species between the two phases. The direction of this exchange, called diffusion, depends on the relative concentrations of the solutes in both phases.
Here’s an example of diffusion for those who aren’t familiar with the term:
If you put sugar in your coffee and you don’t stir it, first it settles on the bottom where it starts to dissolve, but if you wait long enough the entire cup of coffee will become sweet and you'll see no sugar in the bottom. The reason is that first the sugar dissolves at the bottom forming a concentrated solution of sugar, but slowly this dissolved sugar diffuses all over until its concentration is the same everywhere in the cup.
Since the concentration of hypochlorous acid is a lot higher in the lower phase, it diffuses into the upper phase and thus the pool water is constantly fed with “active chlorine” i.e. hypochlorous acid.
Just as hypochlorous acid diffuses from the lower phase to the upper phase, so do other species, including chloride ions, diffuse from the upper phase of the pool water into the lower phase.
The solid deposits are formed when the solubility limit in the lower phase has been reached, and most likely the solids comprise not only of sodium chloride. The inventor hasn’t produced any analysis of these deposits to substentiate his claim. The manufacturer recommends using acid to dissolve them. Sodium chloride doesn’t need acid to be dissolved. It simply washes out in water.
So, the bottom line, the liquidator doesn’t “keep out the salt” away from the pool water, nor does it do another silly claim, copied here from the web site : “With the chlorine under a bed of pool water, most of the odors associated with the cuse of these chemicals is eliminated” .
All it does is administering the hypochlorous acid into the pool water slowly in a controlled, metered way, and possibly removes calcium and chloride ions from the pool water.
Got the Liquidator and it's up and running. The papers refer to the deposits as "calcium deposits."
Despite the fact that the designer and maker don't know the underlying chemistry, the machine definitely does its job remarkably.