pH control for chlorate cells

[WSM]

Amen to that !!! I would love to follow on learning curve as well. It is fun to do this as a team effort, with combined knowledge. I think we can avoid some bumps in the road because of that .

 

Too true. If I reach any heights, it's because I stand on the shoulders of giants. My work is based on following those who did it before me, plus inspiration from my fellows and what insights I can muster. All together, a great combination (IF I get something done ).

 

WSM

[WSM]

Getting back to the subject of this thread, There are many methods of attempting pH "control". I use parenthasis because we are trying passive control instead of active control. Active control is difficult because the "state of the art" sensors are rapidly poisoned by the liquids in our cells (hypochlorite, hypochlorous acid, etc.) and sensors capable of withstanding those are prohibitively expensive.

 

Reasonably accurate passive pH control is possible because others have discovered that there is a decent correlation between current used (Ah or Amp/hours) and the HCl (or hydrochloric acid) required to acheive the desired pH range for optimal performance of our cells. Swede has shared this ratio:

 

0.057 ml of concentrated (32%) HCl per ampere, per hour, with the HCl delivery volume cut by 33% after the chlorate crystals begin to form.

This ratio works based approximately on full strength pool acid (~31.45% HCl, where I live) and to use dilute acid we adjust appropriately to maintain the concentration of acid being applied (according to the current consumed). For example, say we want to use acid diluted to 8% (one fourth the concentration of straight pool acid). To do so we add four times the dilute acid. This will also aid in replacing water used in the process.

 

To apply the acid, many methods have been tried; again, both active and passive. Active methods, usually involve one of various types of pumps, and there are several pros and cons to pumping the acid (refer to Swede's blogs and follow his learning curve). The passive methods usually involve gravity fed systems with minimal power consumption as a bonus.

 

The safest methods do not involve manually inserting acid into the open cell where chlorine gas can evolve and endanger the operator !!! The simple elegance of using a gravity fed system is attractive because it's economical and effective. So a small assembly of compatible valves and an accurate timer are required (or, at the very least, a simple IV drip system as Swede suggests).

 

It's advisable to do accurate metering of your system so you know (reasonably well) how much liquid your system delivers for a given amount of time, and adjust your timer to deliver the required amount to keep your pH as close to the ideal (6.8) as possible. Swede suggests that anything close to this level is better than no control, and gets us closer to the magical number of over 90% CE.

 

Again, our friend, Swede, has travelled this road and documented it well for us in his blogs. I advise anyone wanting to increase the yield and efficiency of their cells to make a thorough study of those blogs, and follow his example.

 

WSM

[Arthur]

Remember that pH control in chlorate cells will allow running at high current efficiency. HOWEVER attempting pH control in a perc cell means adding chloride ions which will cause the expensive electrodes to erode rapidly.

[WSM]

Remember that pH control in chlorate cells will allow running at high current efficiency. HOWEVER attempting pH control in a perc cell means adding chloride ions which will cause the expensive electrodes to erode rapidly.

 

If we aren't sure of this then a quick glance at the subject title of this thread should remind us.

 

Thanks for the caution about excess chlorides in perchlorate cells, Arthur (I don't think any of us wants to compromise their expensive perchlorate anodes!).

 

WSM

[Mumbles]

The initial obvious choice would be to use perchloric acid instead. It's a strong acid and will behave the same way as HCl. This comes with the downside of actually using perchloric acid, though most of the danger comes from concentrated acid. There is some 10% perchloric acid on ebay at the moment for not a terrible price.

 

http://www.ebay.com/itm/PERCHLORIC-ACID-10-W-W-500ML-ACS-REAGNET-/110891080424?pt=LH_DefaultDomain_0&hash=item19d19f9ae8

 

Ensure you're getting perchloric acid if you go through with it. The image of the bottle clearly says phosphoric acid.

 

I'm not sure what else would work well and not be decomposed by the cell environment.

[WSM]

The initial obvious choice would be to use perchloric acid instead. It's a strong acid and will behave the same way as HCl. This comes with the downside of actually using perchloric acid, though most of the danger comes from concentrated acid. There is some 10% perchloric acid on ebay at the moment for not a terrible price.

http://www.ebay.com/itm/PERCHLORIC-ACID-10-W-W-500ML-ACS-REAGNET-/110891080424?pt=LH_DefaultDomain_0&hash=item19d19f9ae8

Ensure you're getting perchloric acid if you go through with it. The image of the bottle clearly says phosphoric acid.

I'm not sure what else would work well and not be decomposed by the cell environment.

 

Hi Mumbles,

 

That's an excellent and insightful suggestion, except if perchloric acid is available, why bother with electrochemistry?

 

If I have access to perchloric acid, neutralizing it with a basic potassium compound will provide all the potassium perchlorate I can use.

 

But then again, if I have perchlorates and good sulfuric acid, I can make perchloric acid...

 

So what comes first, the chicken or the egg??!

 

WSM

[pdfbq]

We need a Perchlorate only thread.

 

I made NaClO4, KClO4, HClO4 and NH4ClO4

 

I tried making 70% HClO4 (not with H2SO4 but with HCl) and that one scared me a bit.

It started fuming when I was boiling it down. Did not know what the fumes were but I guess the 70% azeotrope.

Read those horror stories about fumes getting absorbed by wood (and my impro fumehood is woord)

Was an interesting experiment though. I was doing it to find a good path to NH4ClO4 (NaCl free) but abandoned this one quite fast .

Edited August 9, 2012 by pdfbq

[Swede]

Everything I've read says to ignore pH in a perchlorate cell, and that yes indeed, chloride ions in modest to high concentrations stresses the anode, Pt moreso than LD. The factories don't need to worry so much about Pt loss as they have Pt recovery systems (chemical) to retrieve lost Pt. We don't have that luxury, which is why when using Pt, I think it is best to isolate the chlorate in a two-step process, THEN convert chlorate to perchlorate. This is easy to do with potassium, very hard to do with sodium.

 

- Create bulk chlorate salts, wash in recovery and allow to dry

- Dissolve in clean H2O to create a perchlorate cell stock with minimal Cl-

 

The K-chlorate process via MMO makes crystals that are thick, large, and very easily washed. It is the nature of crystal formation for the xtal to be pure, to exclude foreign material from the interior of the xtal. Thus, when you separate the KClO3 from the liquor, give it a good wash. Don't be shy about it, and the wash will strip the vast majority of clinging chloride ion.

 

Of course, the wash runoff will be laden with chlorides, chlorates, other chlorine species, and it all goes back into the leftover cell liquor for recharging with additional chloride. That was the "make it or break it" fact that we determined yes, it works, and that is, used liquor, over a bed of potassium chloride salt (usually those big nuggets) will take up chloride ion again almost to the level of pure water over KCl. That is, right on back up to nearly 14% to 16% Cl- by weight.

 

If the liquor did not behave in this manner, we'd be hosed, as we'd all have huge volumes of nasty leftover electrolyte that is full of desirable precursor ions as well as being 100% saturated with chlorate itself. A 25 liter batch of used electrolyte has a large amount of chlorate dissolved in it, a couple of kilograms IIRC.

 

When the recharged liquor is used in another run, new chlorate xtals form almost immediately, due to the head start the cell receives, being already saturated with both the product and the bulk reaction precursors.

 

Back to perchlorate pH - I have not done enough runs with LD or Pt to even attempt any sort of experiments with pH, and as mentioned, everything I've read says "ignore it." Remember, the 6.8 pH thing relates to the ratios of two of the bulk reaction components, which exist relative to the cell pH. 6.8 creates a 2:1 ratio that is optimum for the bulk reaction. In a perc cell, nothing of the sort is taking place, so 6.8 is meaningless. However, there MIGHT be an optimum pH for the particular perc formation mechanism, which I believe to be purely anodic in nature. And it might vary between LD and Pt.

[WSM]

We need a Perchlorate only thread.

I made NaClO4, KClO4, HClO4 and NH4ClO4

I tried making 70% HClO4 (not with H2SO4 but with HCl) and that one scared me a bit.

It started fuming when I was boiling it down. Did not know what the fumes were but I guess the 70% azeotrope.

Read those horror stories about fumes getting absorbed by wood (and my impro fumehood is woord)

Was an interesting experiment though. I was doing it to find a good path to NH4ClO4 (NaCl free) but abandoned this one quite fast .

 

Hi pdfbq,

 

If you start it, I'll post on it !

There is a lot to discover there and some safety issues to be aware of...

 

WSM

[WSM]

Everything I've read says to ignore pH in a perchlorate cell, and that yes indeed, chloride ions in modest to high concentrations stresses the anode, Pt moreso than LD. The factories don't need to worry so much about Pt loss as they have Pt recovery systems (chemical) to retrieve lost Pt. We don't have that luxury, which is why when using Pt, I think it is best to isolate the chlorate in a two-step process, THEN convert chlorate to perchlorate. This is easy to do with potassium, very hard to do with sodium.

- Create bulk chlorate salts, wash in recovery and allow to dry

- Dissolve in clean H2O to create a perchlorate cell stock with minimal Cl-

The K-chlorate process via MMO makes crystals that are thick, large, and very easily washed. It is the nature of crystal formation for the xtal to be pure, to exclude foreign material from the interior of the xtal. Thus, when you separate the KClO3 from the liquor, give it a good wash. Don't be shy about it, and the wash will strip the vast majority of clinging chloride ion.

Of course, the wash runoff will be laden with chlorides, chlorates, other chlorine species, and it all goes back into the leftover cell liquor for recharging with additional chloride. That was the "make it or break it" fact that we determined yes, it works, and that is, used liquor, over a bed of potassium chloride salt (usually those big nuggets) will take up chloride ion again almost to the level of pure water over KCl. That is, right on back up to nearly 14% to 16% Cl- by weight.

If the liquor did not behave in this manner, we'd be hosed, as we'd all have huge volumes of nasty leftover electrolyte that is full of desirable precursor ions as well as being 100% saturated with chlorate itself. A 25 liter batch of used electrolyte has a large amount of chlorate dissolved in it, a couple of kilograms IIRC.

When the recharged liquor is used in another run, new chlorate xtals form almost immediately, due to the head start the cell receives, being already saturated with both the product and the bulk reaction precursors.

Back to perchlorate pH - I have not done enough runs with LD or Pt to even attempt any sort of experiments with pH, and as mentioned, everything I've read says "ignore it." Remember, the 6.8 pH thing relates to the ratios of two of the bulk reaction components, which exist relative to the cell pH. 6.8 creates a 2:1 ratio that is optimum for the bulk reaction. In a perc cell, nothing of the sort is taking place, so 6.8 is meaningless. However, there MIGHT be an optimum pH for the particular perc formation mechanism, which I believe to be purely anodic in nature. And it might vary between LD and Pt.

 

Hi Swede,

 

I completely agree.

 

As to pH in the perchlorate process, there is some indication a higher pH is the norm but I will not try to control it in my first experiments. I think my main focus will be keeping the chlorate levels up and not running the current too high, all to avoid stressing the anode. The final separation of chlorate from perchlorate will depend on whether I use sodium or potassium salts (and where).

 

Thanks for the lengthy overview; it seems fairly comprehensive.

 

WSM

[Swede]

IIRC, all of my perc cells went alkaline, and I did nothing to attempt to control it.

 

Maybe we'll get to the point where we can be making many kilos of perc, and efficiency will become important, but right now efficiency takes a back seat to anode longevity. It's pointless to dump $15 worth of Pt into a pound of perchlorate. We reach a point where we may as well buy the stuff.

 

I remember doing some math about the cost of our MMO chlorate relative to commercial, and our costs were insanely cheap, something like pennies on the dollar. But more important in my mind is the notion of self-sufficiency. The day will come when oxidizers are almost impossible to buy, due to "think of the children" legislation, and of all of the pyrotechnic oxidizers, at this point only chlorate and perchlorate make sense. Who is going to make KNO3? Not me. But the (per)chlorates can be tweaked to do almost anything we'd desire in pyrotechnics, everything from lift, burst, fuse, stars, etc.

[pyrojig]

IIRC, all of my perc cells went alkaline, and I did nothing to attempt to control it.

 

Maybe we'll get to the point where we can be making many kilos of perc, and efficiency will become important, but right now efficiency takes a back seat to anode longevity. It's pointless to dump $15 worth of Pt into a pound of perchlorate. We reach a point where we may as well buy the stuff.

 

I remember doing some math about the cost of our MMO chlorate relative to commercial, and our costs were insanely cheap, something like pennies on the dollar. But more important in my mind is the notion of self-sufficiency. The day will come when oxidizers are almost impossible to buy, due to "think of the children" legislation, and of all of the pyrotechnic oxidizers, at this point only chlorate and perchlorate make sense. Who is going to make KNO3? Not me. But the (per)chlorates can be tweaked to do almost anything we'd desire in pyrotechnics, everything from lift, burst, fuse, stars, etc.

 

What , Swede afraid to get a little horse dung on the hands for some kno3 ..... I have to agree completely on the "self sufficiency " . It is cheaper to make kclo3, and perch, so yes it is adaptable to most all pyro needs . I doubt they will get rid of kno3, but with all these cheesy laws who knows!

 

Could coating the electrode (where it was having probs dropping the LD coating nuggets off ) with MMO fix this prob? If one where able to obtain some expensive irridium salts or ruthenium , it would be a matter of re-coating the exposed surfaces to get a better "base material" to lock the LD onto. OR, as WSM suggested , spot welding a thin ribbon of MMO to the perimeter of the electrode mesh , covering the exposed surface, and locking the LD on .

[Mumbles]

How much of the rarer metals are actually in an MMO electrode? I might be able to supply a little to a few people if it's not a whole lot, and they have the process down for plating.

[WSM]

How much of the rarer metals are actually in an MMO electrode? I might be able to supply a little to a few people if it's not a whole lot, and they have the process down for plating.

 

What a generous offer! If you can spare a gram or two of ruthenium chloride I could coat MMO on the bare titanium parts of cut anodes. Another use would be coating a prepared piece (several, actually) of CP titanium with MMO before plating with beta form LD for perchlorate research.

 

It's my understanding that RuO₂ is about 30% of a typical RuO₂/TiO₂ MMO, so a gram should go a long way if handled correctly. Thanks.

 

WSM

[Swede]

I've priced ruthenium salts, and they are crazy expensive, hundreds of $$ for a gram or three. Unless one was truly dedicated to the research, it simply isn't going to happen. I'm guessing platinum salts are going to be cheaper.

 

I don't know how much ruthenium is in an anode... probably not much, but unless one knows EXACTLY how to execute the coating process, it's going to be a very expensive risk.

 

I have a problem which is driving me nuts. It's a simple problem, and shouldn't be this tough. Maybe someone has some ideas.

 

I want to make a top-off / acid reservoir for drip. 2 liters to 4 liters would be ideal. The container must be able to handle strong HCl. It must have, near the bottom, a tap or a tubulation so I can run some flex tubing off of it. Placed above a cell, there's your acid drip system using whatever valves or mechanisms you'd like between reservoir and cell.

 

It'd be very easy if I simply used a siphon setup... simply drill a hole in the cap, run some tubing into the bottom, start the siphon. But I'd like something nice like a Nalgene HDPE container with a tubulation bottom, but these stupid things are $30 or more. So, how do we make an elegant, durable container do what I've described? I don't want to take a milk jug and make it work, hopefully something nicer. I'm thinking a 1/2" bulkhead PVC fitting in a hole cut into a decent container, and a little hose barb fitted into that, but again, even a 1/2" bulkhead fitting is ten bucks. What am I missing here?

[WSM]

I've priced ruthenium salts, and they are crazy expensive, hundreds of $$ for a gram or three. Unless one was truly dedicated to the research, it simply isn't going to happen. I'm guessing platinum salts are going to be cheaper.

I don't know how much ruthenium is in an anode... probably not much, but unless one knows EXACTLY how to execute the coating process, it's going to be a very expensive risk.

I have a problem which is driving me nuts. It's a simple problem, and shouldn't be this tough. Maybe someone has some ideas.

I want to make a top-off / acid reservoir for drip. 2 liters to 4 liters would be ideal. The container must be able to handle strong HCl. It must have, near the bottom, a tap or a tubulation so I can run some flex tubing off of it. Placed above a cell, there's your acid drip system using whatever valves or mechanisms you'd like between reservoir and cell.

It'd be very easy if I simply used a siphon setup... simply drill a hole in the cap, run some tubing into the bottom, start the siphon. But I'd like something nice like a Nalgene HDPE container with a tubulation bottom, but these stupid things are $30 or more. So, how do we make an elegant, durable container do what I've described? I don't want to take a milk jug and make it work, hopefully something nicer. I'm thinking a 1/2" bulkhead PVC fitting in a hole cut into a decent container, and a little hose barb fitted into that, but again, even a 1/2" bulkhead fitting is ten bucks. What am I missing here?

 

Check out eBay items:

390357602597

390357602609

390357602709

Pricey, but possible.

 

As for an acid dispenser, I was considering making one from a vertical piece of 6" diameter thinwall PVC pipe, solvent welded to 1/4" PVC plate with a 1/4" NPT PVC ball valve threaded to the bottom sidewall of the reservoir. A PVDF hose barb fitting (or compression fitting, depending on the acid feed tubing used) screwed into that would accept the tube to the valves of the pH control system. The removable lid of PVC plate could be fitted with a breather valve to prevent a vacuum in the reservoir, while at the same time preventing acid vapors from escaping.

 

The main question is, do you want to spend the time or the money for your acid reservoir?

 

WSM

Edited September 12, 2012 by WSM

[WSM]

For pH control, I've noticed US Plastics (http://www.usplastic.com/) has PVC needle valves in the $10-$20 range. They have MANY items useful for making custom electrochemical cells and they're ethical folks to deal with. Their prices are a bit high (full retail), but they have an outstanding selection of items including PVDF (Kynar) fittings (which I call "poor man's Teflon") which are completely compatible with the chlorate cell liquids. They ship by UPS and are fairly fast, plus if there are any problems with the order, they make it right. I can and do recommend them.

 

WSM