perchlorate cell running acidic.

[willowchar]

what would cause a perchlorate cell to have a ph of 1.8.My research shows they typically run basic with a ph between 8 and 10?

Will this effect production?

Can the ph be raised without compromising anything?

 

System setup,

6volts 12 amps

lead dioxide anode

ss cathode

 

Thanks

[Mumbles]

They typically do run basic. The intermediates produced tend to create basic solutions, and left unchecked often run overly basic. An optimally efficient cell usually requires acid adjustment to keep the pH in the ideal range.

 

How are you measuring the pH? If you're using a meter, I'd make sure it's calibrated. If you're using pH paper, the first thing I'd check is making sure the paper isn't getting bleached by the cell. Usually you can pre-wet it with water and add a drop of cell solution and look for what color it immediately changes. They may get degraded and have the color change drastically over a short period of time by some of the things produced.

 

Is there anything else strange looking? Odd colors? Unusually high amount of precipitate?

[willowchar]

Thanks for the reply mumbles.

 

So I'm using a quality ph meter. I made sure it is calibrated 100% with a buffer of ph 4.

As soon as I took a reading of the sample electrolyte the ph dropped like a rock to 1.8

The color of the electrolyte seems fine (slightly yellowish) the color of ice cold Budweiser after a hard days work

The ss. cathode dose have a slight pale tannish brown oxidation coating on it. Nothing solid and thick. Just a slight dusting. I removed it and cleaned it up with some emery cloth and continued running.

Also the density seems to not increase very much, hovering around 1.26 gm/ml for the past 3 weeks?

 

Any ideas/advise would be appreciated.

Regards,

[Arthur]

Swede's blog and posts indicate that he had lots of problems with pH meters -well the electrodes anyway. very few electrodes survive the corrosive solution in either a chlorate cell or a perc cell. His estimate was that the life of a pH electrode was measured in seconds of immersion.

 

Do please try a liquid indicator or a indicator paper.

[markx]

Meters and also indicator papers are pretty much useless in the highly active oxydising brew of the chlorate/perchlorate electrosynthesis cell liqour. Standard pH probes give up their ghost in mere seconds, as Arthur stated and indicator strips are being bleached instantaneously. So either way the numbers that you get are worth bollocks and trying to act upon them is going to end in loss and failure. There exist special probes for such an application, but their price range is well outside of the amateur realm. Just sit back, let chemistry take over and stop trying to control every aspect of the setup....it is pretty much a selfregulating system that will come to terms with itself and do its thing

[WSM]

They typically do run basic. The intermediates produced tend to create basic solutions, and left unchecked often run overly basic. An optimally efficient cell usually requires acid adjustment to keep the pH in the ideal range.

How are you measuring the pH? If you're using a meter, I'd make sure it's calibrated. If you're using pH paper, the first thing I'd check is making sure the paper isn't getting bleached by the cell. Usually you can pre-wet it with water and add a drop of cell solution and look for what color it immediately changes. They may get degraded and have the color change drastically over a short period of time by some of the things produced.

Is there anything else strange looking? Odd colors? Unusually high amount of precipitate?

 

If I'm not mistaken, Mumbles is a working chemist and his lab tips are spot on and brilliant. I have only used pH paper because pH meter sensors are quickly destroyed by hot concentrated chlor-alkali solutions (our chlorate cell "end-of-run" electrolyte and the starting electrolyte for perchlorate cells).

 

I have simply dipped the end of a piece of pH paper into the sample of electrolyte (usually a small bit removed from the cell) and read the color at the leading edge of the wetness as it soaks in. The pH paper quickly bleaches after the leading edge. I never thought to pre-wet the pH paper with distilled or deionized water before adding a drop of the electrolyte, which makes a lot of sense when I think about it. I expect that will give a better view of the actual pH color before the bleaching effect of the electrolyte destroys the reagents in the paper (much better than soaking electrolyte into dry paper and trying to see the "very thin" leading edge color).

 

Read Swede's blog entries ("You'll put your eye out") regarding pH meters for a more detailed description of pH meters and chlor-alkali cell conditions.

 

WSM

Edited December 23, 2020 by WSM

[WSM]

Thanks for the reply mumbles.

So I'm using a quality ph meter. I made sure it is calibrated 100% with a buffer of ph 4.

As soon as I took a reading of the sample electrolyte the ph dropped like a rock to 1.8

The color of the electrolyte seems fine (slightly yellowish) the color of ice cold Budweiser after a hard days work

The ss. cathode dose have a slight pale tannish brown oxidation coating on it. Nothing solid and thick. Just a slight dusting. I removed it and cleaned it up with some emery cloth and continued running.

Also the density seems to not increase very much, hovering around 1.26 gm/ml for the past 3 weeks?

Any ideas/advise would be appreciated.

Regards,

 

 

Please, please, please don't use a pH meter in a chlorate or perchlorate cell, especially an expensive one. The sensors are usually based on a silver chloride reference cell, and the electrolyte poisons them very quickly.

 

Also, stainless steel may work for the cathode but if possible or available, CP titanium works much better (due to being what's called a "valve metal") without adding unwanted ions (Fe⁺, Cr⁺, Ni⁺, et cetera) to the electrolyte as stainless steel may.

 

I don't recall if you are using potassium chlorate or sodium chlorate electrolyte in your perchlorate cell.

 

WSM

Edited December 25, 2020 by WSM

[Arthur]

Try a few checks after the reading that you mention.

Does the pH electrode read right in calibration buffer solutions now?

Check and check again that every connection is correct on the cell, control and power supply,

Check that the ingredients of the cell are what you expect.

 

If the pH you quote is correct than something else is wrong.

What is the cell made from?

[Mumbles]

I am a practicing chemist if it matters, and the water wetting trick is basically a dilution/extraction hack. It's a cheap quick way to test the pH of non-aqueous solutions or gases for example. It's a problem I run into fairly regularly. pH is regulated for waste disposal, even for non-water based waste. pH is actually very complex if you really dive into it. It varies with temperature, solvent, acid/base source, and several other things. At the simplest terms, it's still a concentration though and goes by orders of magnitude. pH 7 is 100x more acidic/less basic than pH 9.

 

I don't know if it'd work for this, but it'd be my first instinct to try. Electrolysis cells produce a lot of bleaching and oxidizing compounds which can mess up the color of pH strips. Dilution can slow this down, possibly enough to get good information before being degraded.

[Arthur]

https://www.sentek.co.uk/

 

Read it all, learn about pH electrodes and if necessary find a local supplier/distributor/manufacturer.

[willowchar]

Thanks for all the advise guys.

Greatly appreciated and helpful.

[eb666]

I have used a pH meter many many time to read the pH of Chlorate (and Perk.) cells. I always take a sample out of the cell. Dip the probe in for a few seconds and remove and wash immediately. Have had not problems with my probe. I do not think you can measure cell with power connected as the Voltage gradient may give you a crazy reading (I think). Taking a sample also cools the solution.

The probe is a Schott Blueline A030704 002

They cost about 300 bucks I believe.

 

You do not need very accure reading, to the first decimal point is good enough.

 

Add some Sodium Hydroxide if you want to take a perk cell up, some perk. acid is best of you want to lower pH. Not good to add HCl as you are then adding Chloride.

The CE is not effected in a perk cell if it is kept within a few points of neutral (from say 5 to 9). It may effect LD erosion etc.

 

Chlorate cell is a different matter.

 

EB

Edited January 22, 2021 by eb666

[WSM]

I have used a pH meter many many time to read the pH of Chlorate (and Perk.) cells. I always take a sample out of the cell. Dip the probe in for a few seconds and remove and wash immediately. Have had not problems with my probe. I do not think you can measure cell with power connected as the Voltage gradient may give you a crazy reading (I think). Taking a sample also cools the solution.

The probe is a Schott Blueline A030704 002

They cost about 300 bucks I believe.

You do not need very accure reading, to the first decimal point is good enough.

Add some Sodium Hydroxide if you want to take a perk cell up, some perk. acid is best of you want to lower pH. Not good to add HCl as you are then adding Chloride.

The CE is not effected in a perk cell if it is kept within a few points of neutral (from say 5 to 9). It may effect LD erosion etc.

Chlorate cell is a different matter.

EB

 

 

If I may make a suggestion:

 

When adding an acid or alkali to neutralize your electrolyte; the numbers will vary wildly if using concentrated acid/alkali to buffer the solution. Perhaps it would be wiser to use dilute acid or alkali (by at least 10 times, or even 100 times) so your pH corrections will be fine and not course adjustments. It's extremely difficult to be accurate with concentrated additions.

 

WSM

[SeaMonkey]

After reading this discussion I'm wondering whether a pH reading was taken

for the solution just prior to the electrolysis beginning?

 

Are we to assume that initially the pH of the solution in the cell was "normal" and

that after some period of electrolysis the solution had become acidic?