AustralianPyromaniac Posted July 12 Posted July 12 I have recently been investigating pH control of amature chlorate cells, and have a question for the electrochemist. When dosing HCl, a few reactions can take place, 1) The KOH / OH- ions (formed from the escape of chlorine gas from the cell) can react with the HCl, forming KCl and H2O, returning the pH to neutral 2) The KClO3 and intermediates (chlorites and hypochlorites) can react with HCl to form chlorine gas, KCl, and water 3) The HCl can be electrolysis and broken into chlorine gas at the anode and hydrogen gas at the cathode, which leaves the cell --- If a large dose of concentrated HCl is added, it is clear reaction 2 takes place, and clouds of chlorine are produced, if a small amount of dilute HCl is added, pH control is achieved, where reaction 1 takes place. In industry, 1% HCl solutions are used for adjusting pH with active pH monitoring and control, but for the amateur, a constant drip system is much more feasible without active control. If the pH becomes too low, the cell chemistry is unfavorable, and electricity is constantly being used to reduce chloride to chlorine and raise the pH. When a passive drip system like this is used, with - lets say 10% HCl dripped in constantly - how can the pH ever actually fall below, for example - pH 6? Reactions 1-3 all act to raise the pH and destroy all excess HCl in the cell. If the reactions that destroy it are so favorable, why does it matter what concentration the drip solution really is? So long as it is enough to keep the KOH production under control? --- If we imagine a cell that - lets say - ideally requires 40ml per day of 10% HCl to achieve perfect pH control and an ideal current efficiency of 85%. If we dose this cell instead with 40ml per day of 15% HCl, how much does current efficiency really suffer? My intuition tells me that the acid dose will first react with all OH- ions, and then all excess HCl will quickly be destroyed by either alternative reaction, and the pH will stabilise near 7. Why is this not the case? And what effect is there really if too much HCl is used? Note that this theoretical cell would have strong stirring and the acid would be added dropwise evenly across the whole day. 1
kingkama Posted July 12 Posted July 12 Diluted HCl Is Better in my opinion, you add water and also reduce the OH groups, have you tried the CaCl control sistem?
mx5kevin Posted July 13 Posted July 13 (edited) There are two very important things to pay attention to if mainly chlorine dioxide collects on top, mixed with hydrogen it will cause a very strong explosion that will blow the cell to pieces. It must be filled to the top with solution so that gases cannot accumulate. A lamp or sunlight and initiates the reaction. A plastic dunce bottle is also beneficial for this reason. Run the cell outdoor, and work with the solution outdoor. Cover it with a bigger bucket is enough for it, keep the adapter it only indoor. It can be easily extended with a 40 Ampere cable available in an electronics store. It hard to be ventilated indoors and is extremely oxidative. Use a M3 protetive mask what protecting from chlorine, rubber gloves your skin should not come into contact with chlorine substances and salts HCl, closed airtight glasses (not all closed safety glases are airtight) swimming goggles are that, the point is not to inhale chlorine even in small amounts. For a larger cell, there is an infusion set for plants 5ml/Hour are the smallest dosing. Even with a larger 3-liter cell, you cannot add more than 20 ml of liquid per day, you can't dose continuously. In one day, you can extend the pH regulation for a longer period of time. This is the most precise. This helps to avoid overdose. But you will get a 20 ml syringe and a long straw for less. If hydrochloric acid is suddenly added, the cell must be ventilated for at least 10 minutes before it is closed. The point is that it should be slowly distributed to the bottom. Or use 1500ml, 3000ml, 5000ml plastic bottles put in the solution so that it is half full add to it some HCl and shake it. With the latter solutions, you will overdose every time. If it's not a problem that it might be more acidic no pH needs to be measured. If a yellowish discoloration appears in the color of the solution, it is insoluble chlorine. In this point your cell pH are under 6. If chlorine accumulates on top of the cell, it will cause an powerful explosion. The empty space what must keep in minimal in the cell cannot be filled with yellow gas! Such gases are released when the acid is administered, if the hydrochloric acid is administered inside the cell, it must be administered in small drops minimum for more than two hour longer. You cannot prevent chlorine gas from escaping into the air. It is not only formed at the anode, but also actively escapes from the cathode. As the cell runs, it becomes constantly alkaline. It's impossible all the time keep it pH 6-7. If you control it once a day, it will fall out of this range after an hour. The gases coming out of the cell must be led away in a long plastic flexible pipe several meters away. You can feel this from meters away, you have to lead away it to a place where it won't cause problems for humans, animals, plants, and other tools. It is problematic to bubble this through a alkali solution because the pressure exerts resistance and the cell may leak as a result. Edited July 13 by mx5kevin 1
AustralianPyromaniac Posted July 13 Author Posted July 13 (edited) 10 hours ago, kingkama said: Diluted HCl Is Better in my opinion, you add water and also reduce the OH groups, have you tried the CaCl control sistem? Yes, I think the more dilute the better, mainly because it prevents a large localized dose of HCl which leads to chlorine production. But if the system is to dose constantly, there is a limit to how dilute the solution can be. If very dilute acid is used, more acid will be needed in ml than water is consumed (by evaporation and electrolysis consumption). Say a cell loses 50ml per day of water, at most 50ml per day of acid solution can be added. At 1% HCl, more than 50ml of acid would be needed, and so the cell would overflow if the inflow was continued in this way. This is why I am wondering where the limit for acid addition lies - if more concentrated acid can be used than the cell requires. The following is a quote from Swede, which indicates that there is no issue with adding concentrated HCl, but the question is where does the limit lie, and what happens if the cell is OVERDOSED. With "T-Cell Jr" (KCl, 19L, 50 amps) I had the dosing timer set up to turn on 6 times per day for one minute, and each cycle of the dosing pump delivered 12-15 ml, so somewhere around 100 ml per day of 21% acid worked. I could probably have added more, the pH was more often than not around 7.5 rather than 6.8, but I was very pleased at the stability. Once it was "forced" down to near neutral, there was no tendency to rapidly climb; periodic acid dosing as a concept works, and I believe it is a good alternative to full pH control with an immersed probe, with its associated probe poisoning problems. [This works out at approx. 0.146ml 12% HCl per amp per hour. An MMO Anode was used.] --- I am aware of the CaCl2 and MgCl2 methods for pH control, but I do not think they are appropriate when making KClO3 - they will remain in the product as contamination. Also, the hydroxides coat the cathode and destroy it over time, which is no issue if the cathode has a very high surface area and is cheap, like a stainless bucket - the coating is slow to build up and easy to deal with. But if an equally sized cathode and anode are used, and a titanium cathode, it will be destroyed over time and be expensive to replace. Edited July 13 by AustralianPyromaniac 1
AustralianPyromaniac Posted July 13 Author Posted July 13 Thanks for your input Kevin, I am a bit confused by some of your info. 41 minutes ago, mx5kevin said: Even with a larger 3-liter cell, you cannot add more than 20 ml of liquid per day, you can't dose continuously What do you mean by this? 20ml of what liquid? HCl solution - what concentration? Are you saying no more than 20ml can be used because it will overflow? And what do you mean you cannot dose continuously? Why does continuous dosing not work? 43 minutes ago, mx5kevin said: Or use 1500ml, 3000ml, 5000ml plastic bottles put in the solution so that it is half full add to it some HCl and shake it. With the latter solutions, you will overdose every time. I did not understand this at all. 44 minutes ago, mx5kevin said: It's impossible all the time keep it pH 6-7. What do you mean not possible? With active control it is possible? I am talking about continuous dosing. Thanks!
mx5kevin Posted July 13 Posted July 13 Quote Diluted HCl Is Better in my opinion, you add water and also reduce the OH groups, have you tried the CaCl control sistem? Actually, it is ideal to regulate slowly with a diluted HCl solution, but the cell has a capacity for how much liquid it can take in per day. 5ml/Hour with a plant infusion set are the slowest dosing with that setup. CaCl it does not work well covers the cathode and inhibits production. I did not notice that it would stabilize the pH. In industrial production, it is emphasized that the calcium level should be kept as low as possible (not added but present in the salt and water). Adding CaCl are a unprofessional method. Stabilizing pH the best way use Na or K persulfate at the beginning, use precise controlled lab power supply, start the electrolysis at 3V at the beginning. For perchlorate, this may be increased to a maximum of 7 volts. If the cell is too slow, this can be increased gradually, the point is that it is not advisable to use more than 3 volts, especially at the beginning when there is pure chloride in the cell. I was able to stabilize the pH value well with this only method to slow down the chlorine escape in a pH controlled cell.
mx5kevin Posted July 13 Posted July 13 (edited) 5 hours ago, AustralianPyromaniac said: Thanks for your input Kevin, I am a bit confused by some of your info. What do you mean by this? 20ml of what liquid? HCl solution - what concentration? Are you saying no more than 20ml can be used because it will overflow? And what do you mean you cannot dose continuously? Why does continuous dosing not work? I did not understand this at all. What do you mean not possible? With active control it is possible? I am talking about continuous dosing. Thanks! In small 400ml cell, i put the cell solution in a 1500ml plastic bottle. Added cc to this 2-4ml 30% HCl solutoin/day and shaked. If more chlorine came out of the solution, the bottle was under pressure. In this case the pH was under 5. Used another method I bought a 20 milliliter syringe at the pharmacy and I grabbed a long straw. In a 5000ml cell added 10ml 30%HCl/day. If the solution started to turn slightly yellow, I did not add more. After 10 minutes I let it air out, and another 5 minutes runned the cell before closed. The latter is important because here the hydrochloric acid was added fast way so that chlorine could not accumulate on top. And chlorine dioxide is a very powerful explosive mixture with hydrogen. In my case, it blew up a 5-liter cell so that it looked like an open flower. Half an hour after the pH controlling, I lifted the bucket, than the whole thing exploded with a sharp sound when contacted the sunlight. Nobody tries to open it after pH control! If it was closed after a fast pH control, chlorine would accumulate on top and cause an explosion after starting the cell. For this to happen, the condition is that hydrochloric acid must be added inside the cell fast way. There was a similar case with a 400 ml cell, where the top was torn to pieces. This is a cheap solution, but the precise solution is a plant infusion set around a 3 liter cell. Continuous dosing not work because even when using concentrated 30% hydrochloric acid 5ml x 24 hour 120ml/day. And you can't set the pH to just drip and be uniform. If it acidifies even a little bit faster, the chlorine appears in the color of the solution, and then no further dosing should be done. It will disappear after days or hours. If the acid is even diluted, there is even more extra fluid on a daily basis than the cell can handle. And this must be kept in line with how much liquid evaporates from the cell every day. If you use hydrochloric acid, it doesn't matter how much dilute it, chlorine will always produced there. And although it is produced at the anode, but it largely escapes at the cathode. As you dose the acid, from the other side the gas escapes into the air even if slowly dosed. This problem could be solved with chloric acid HClO3 instead of hydrochloric acid. Chlorine production is so intense because hydrochloric acid reduces the solution. After the addition, what is produced during the electrolysis in the acid solution still produces gas, not only during the addition. If no reductive reaction occurs when the acid is added, significantly less chlorine enters the air in the electrolysis. The chemical and other properties of the solution change during electrolysis. If I have a pH 10 solution it can be one more time, or a quarter of the amount of hydrochloric acid. Can not measured for the previous occasion what you need next time in the same pH to get a pH 6-7 from 10. It is not possible to calculate exactly how much acid is needed evenly. Because here not work a uniform dosage, here need adjusted with a measuring device. In all cases, it is not necessary to measure this with expensive devices, if the electrodes tolerate it, it can be set without a measuring device. Edited July 13 by mx5kevin
mx5kevin Posted July 13 Posted July 13 (edited) For 400-2000ml cells (maximum) using a mininum 50-200micron thick pure platinum on a 3mmx70mm silver base what are fully closed mode surrounds the platinum with no exposed silver surface. It is not necessary to measure the pH precisely here. With perchlorates, if you go down to a negative pH, it won't hurt anything to this anode. A cheap 6V 4A car battery charger enough for this. This electrode are using 2A from the 4A supply. In terms of money, it costs a fraction of a lab or more complicated power supply. The problem is that if more amperes pass through the power supply than it can withstand during a long run time, it can be very dangerous, there is no problem here with this small electrode. these electrolyte solutions bleaches the pH papers immediately. You can dilute it, you can boil it, it doesn't help it when you test it. It can be tested with a digital pH meter, but it is expensive (must be calibrated regularly with buffer solutions). Even if it is washed with baking soda after use, chlorine destroys the electrode within two years what are not cheap. The advantage of this is that it does not require a pH meter, the other advantage is that you have to buy the electrode once and it lasts a lifetime (for chlorates and perchlorates too using chloride to perchlorate direct conversions). I have had the electrode for 15 years. Has produced more than 20 kilos of chlorate and perchlorate so far. This must be manufactured individually by a company specialized in this. The 5 micron platinum titanium based electrodes are unusable, the ones that work with them break down very quickly, and the price is not much more expensive. Even the professional factory lead dioxide electrodes for perchlorates have a service life of half a year in domestic conditions and there need precise pH controlling. Cheap MMO is of course very good for chlorates, but not suitable for perchlorates. Edited July 13 by mx5kevin
Arthur Posted July 13 Posted July 13 Look at Iwaki Bellows Pumps (inc ebay!) find a small one and set it with a timer and adjust the cam so that you can get sensible rate per hour of liquid flow, Then look at using dilute HCl for the liquid, maybe even dilute HCl in some brine. There was a good reason why the Pepcon factory was in the Nevada desert! Likely any mist from the running cells will strip paint from cars in the car park
mx5kevin Posted July 13 Posted July 13 In homemade conditions, from the beginning to the end of the process, I am sure that it is not possible to keep the pH between 6-7. This would require an expensive, precise instrument that continuously measures the pH and dispenses slowly drops the HCl. The pH meter should handle the continuous chlorine solution. If I dose the hydrochloric acid with a dropper in doses of 5 ml/h for a 5-liter 5000ml cell, after 2-3 hours of dosing, it must be completely stopped to adding it that day. The 30% hydrochloric acid cannot be particularly diluted here, much more liquid would enter it than can fit into the cell. If it is dosed in small drops deep at the bottom of the solution, it is absorbed in the solution. Under 3000ml, 5ml/h would be a dangerously fast dosage. The ideal acid would be chloric HClO3 acid. But that would be too complicated. The solution will not be full of chlorine there. Hydrochloric acid is a reductive acid that produces chlorine and its oxides. And if even though the solution has later a higher oxidation state, this does not bring the chlorine generated from freshly added hydrochloric acid to a higher oxidation stage so that it doesn't want to run away so easily. It is not worth using a more expensive solution for an infusion set for a amateur setup. Even with the cheapest device, one pH control per day is more than enough for a amateur setup.
AustralianPyromaniac Posted July 13 Author Posted July 13 1 hour ago, mx5kevin said: In homemade conditions, from the beginning to the end of the process, I am sure that it is not possible to keep the pH between 6-7. This would require an expensive, precise instrument that continuously measures the pH and dispenses slowly drops the HCl. The pH meter should handle the continuous chlorine solution. If I dose the hydrochloric acid with a dropper in doses of 5 ml/h for a 5-liter 5000ml cell, after 2-3 hours of dosing, it must be completely stopped to adding it that day. The 30% hydrochloric acid cannot be particularly diluted here, much more liquid would enter it than can fit into the cell. If it is dosed in small drops deep at the bottom of the solution, it is absorbed in the solution. Under 3000ml, 5ml/h would be a dangerously fast dosage. The ideal acid would be chloric HClO3 acid. But that would be too complicated. The solution will not be full of chlorine there. Hydrochloric acid is a reductive acid that produces chlorine and its oxides. And if even though the solution has later a higher oxidation state, this does not bring the chlorine generated from freshly added hydrochloric acid to a higher oxidation stage so that it doesn't want to run away so easily. It is not worth using a more expensive solution for an infusion set for a amateur setup. Even with the cheapest device, one pH control per day is more than enough for a amateur setup. I appreciate all this advice, and the other things you have said, all very useful information, but I think there may be some misunderstanding about what question I am asking. In the cell I use, an overhead pressure equalizing system is used to maintain the water level of the cell 5mm from the top of the vessel. Above the cell is a supply reservoir under vacuum, which air is trying to enter. This is linked to a glass tube in the cell and a PTFE gas "valve". The details are not important, but the point is that the water level is constantly being kept at exactly the correct level by the inflow of liquid from the addition funnel above. This system is maintenance-free once the addition funnel is filled, the cell automatically maintains the water level. The inflow into the cell from this system is about 250ml per week, which cannot be adjusted - the cell conditions dictate the inflow based on evaporation + consumption rate. If pH control is not needed, the reservoir is filled with distilled water, but if pH control is needed, a solution of HCl is used instead. The concentration of this HCl solution must 10%-15% to get PERFECT pH control, but the exact concentration is not known for any individual run. Each second the cell conditions change, and so the ideal HCl concentration to maintain pH 6-7 changes. So, when setting up the system, if pH control is needed, then the addition funnel is loaded with - let's say - 15% HCl. This will be TOO CONCENTRATED - which is known based on experimental data - more HCl will be added each second than KOH produced. Too much HCl is being added, and if no mechanism existed to remove it, the pH would quickly fall to <1. But in reality, it does not do this! Because the cell conditions/ reactions are acting as a buffer. As HCl is added, all excess is quickly destroyed and the solution never falls below pH 5/6. So the question is, what is the actual effect of overdosing HCl into a chlorate cell on current efficiency? Has anyone who has experienced pH controlling a chlorate/ perchlorate cell seen the effects on the cell when too much acid is dosed over the course of a run. And what is the primary mechanism for the destruction of HCl when it is added in excess? We know that if the pH is too HIGH then the cell reaction changes to favor the 9-electron process over the 6-electron process, which is due to the disproportion of the hypochlorous acid species. This is the fundamental reason for the change in efficiency. But in the opposite case, when pH is too low, the literature says "current efficiency sufferers as electrons are used to reduce chloride to chlorine which is lost to the atmosphere" etc. etc. Which makes sense, but this alone should represent only a fraction of efficiency loss. If we consider a cell, where the pH is 7. Let's say this cell has just started running. The operator then introduces 100ml of 30% (10M) HCl, which is a very large dose. This is 1M of HCl, which is 1M of H+ ions and Cl- ions. In a 3L cell, the pH will now be around 0.5. Once the cell is started, the most favorable reaction will take place, which is the reduction of Cl- to Cl gas, and H+ to H2 gas. Assuming 100% efficiency and a cell running at 10A, this will take around 2.7 hours, which is a fraction of the run time the cell will require, and will hardly make a dint in the overall efficiency, assuming all is done normally from this point forward. So, if over the course of a 2-3 week chlorate electrolysis, 100 ml of excess HCl is added, hardly any efficiency loss or gain should be observed unless the operator is an industrial producer with extremely tight control of the cell. The same logic as above stands. This means that if the operator is to constantly dose HCl solution, he should much rather favor a solution of HCl that is too concentrated than one that is too weak. In the former case, almost nothing is lost, in the latter case, the whole point of pH control is lost. I am wanting to know if this is sound logic, and what the actual efficiency loss would be in this sort of scenario, specifically where HCl is overdosed into a pH-controlled cell.
mx5kevin Posted July 13 Posted July 13 (edited) 2 hours ago, AustralianPyromaniac said: I appreciate all this advice, and the other things you have said, all very useful information, but I think there may be some misunderstanding about what question I am asking. In the cell I use, an overhead pressure equalizing system is used to maintain the water level of the cell 5mm from the top of the vessel. Above the cell is a supply reservoir under vacuum, which air is trying to enter. This is linked to a glass tube in the cell and a PTFE gas "valve". The details are not important, but the point is that the water level is constantly being kept at exactly the correct level by the inflow of liquid from the addition funnel above. This system is maintenance-free once the addition funnel is filled, the cell automatically maintains the water level. The inflow into the cell from this system is about 250ml per week, which cannot be adjusted - the cell conditions dictate the inflow based on evaporation + consumption rate. If pH control is not needed, the reservoir is filled with distilled water, but if pH control is needed, a solution of HCl is used instead. The concentration of this HCl solution must 10%-15% to get PERFECT pH control, but the exact concentration is not known for any individual run. Each second the cell conditions change, and so the ideal HCl concentration to maintain pH 6-7 changes. So, when setting up the system, if pH control is needed, then the addition funnel is loaded with - let's say - 15% HCl. This will be TOO CONCENTRATED - which is known based on experimental data - more HCl will be added each second than KOH produced. Too much HCl is being added, and if no mechanism existed to remove it, the pH would quickly fall to <1. But in reality, it does not do this! Because the cell conditions/ reactions are acting as a buffer. As HCl is added, all excess is quickly destroyed and the solution never falls below pH 5/6. So the question is, what is the actual effect of overdosing HCl into a chlorate cell on current efficiency? Has anyone who has experienced pH controlling a chlorate/ perchlorate cell seen the effects on the cell when too much acid is dosed over the course of a run. And what is the primary mechanism for the destruction of HCl when it is added in excess? We know that if the pH is too HIGH then the cell reaction changes to favor the 9-electron process over the 6-electron process, which is due to the disproportion of the hypochlorous acid species. This is the fundamental reason for the change in efficiency. But in the opposite case, when pH is too low, the literature says "current efficiency sufferers as electrons are used to reduce chloride to chlorine which is lost to the atmosphere" etc. etc. Which makes sense, but this alone should represent only a fraction of efficiency loss. If we consider a cell, where the pH is 7. Let's say this cell has just started running. The operator then introduces 100ml of 30% (10M) HCl, which is a very large dose. This is 1M of HCl, which is 1M of H+ ions and Cl- ions. In a 3L cell, the pH will now be around 0.5. Once the cell is started, the most favorable reaction will take place, which is the reduction of Cl- to Cl gas, and H+ to H2 gas. Assuming 100% efficiency and a cell running at 10A, this will take around 2.7 hours, which is a fraction of the run time the cell will require, and will hardly make a dint in the overall efficiency, assuming all is done normally from this point forward. So, if over the course of a 2-3 week chlorate electrolysis, 100 ml of excess HCl is added, hardly any efficiency loss or gain should be observed unless the operator is an industrial producer with extremely tight control of the cell. The same logic as above stands. This means that if the operator is to constantly dose HCl solution, he should much rather favor a solution of HCl that is too concentrated than one that is too weak. In the former case, almost nothing is lost, in the latter case, the whole point of pH control is lost. I am wanting to know if this is sound logic, and what the actual efficiency loss would be in this sort of scenario, specifically where HCl is overdosed into a pH-controlled cell. The harmful effect is that if the electrode is sensitive to pH, it will be faster destroyed, this is especially true for the lead dioxide used in perchlorates. This can be corrected by pH control, but it is unavoidable. In the case of MMO anode as the process progresses, the solution becomes more and more alkaline the fact that we want a pH of 6 but the pH will be 3 happens easily in household setups. This is not the same as putting it in concentrated acid and running it in it. If the cell is smaller, the slippage is greater. The addition of acid increases the speed of preparation of the product and the amount of extracted end product too at the end result. If you clean the cathode and as you dose the acid, you will see that in many cases the electrolysis speed is accelerated.The unpleasant effect is that a lot of chlorine gas is released into the environment. It is possible to calculate as if the whole material were purely transformed, this means. If you start it without pH controlling 150g KCl without pH control you will get less than 150g KClO3, with pH control this can be much more than 150g clean end product and more than 200g cristalls from the cell. In a NaClO4 cell from every 100g NaCl you will get 210g pure NaClO4. What you get as an uncleaned end product can be almost twice as heavy as the starting material. You produce much more than the starting material, but a lot is lost during cleaning. These must be recycled back into the process. The resulting alkali must be converted back into chloride here. I usually clean and recrystallize in very abundant solutions. washing the crystals and here a lot of material is lost from the original product, which is returned to the cell during the next production. When I wash it with water and recrystallize it, these solutions go back into the cell. I work with a 5 liter 5000ml cell. I recycle what can be recycled. Compared to perchlorates, potassium chlorate is a very simple product. I get back minimum the initial amount of material or much more at least for the finished purified product if the cell is pH controlled. But in this process, it is only a small detail in long-term efficient production. The first thing that is important is the power supply and the electrodes. Much more amperes should not pass through the electrodes what in a longer run can discharge the power supply. This must remain below the maximum power of the power supply at a level that can withstand a long operating time. The other important thing is not to overheat the solution. If it is a piece of equipment in which serious money is invested, larger electrodes, I recommend a precise laboratory power supply. Edited July 13 by mx5kevin
mabuse00 Posted July 21 Posted July 21 (edited) Considering the HCl dosing: How about metering the current and find a proper ratio, like so-and-so-much seconds running the dosing pump for every so-and-so-much amp-hours going through the cell? One could also include the cell temperature into the equation, whatever influence this might have on the process... On 7/13/2024 at 8:46 AM, mx5kevin said: And chlorine dioxide is a very powerful explosive mixture with hydrogen. In my case, it blew up a 5-liter cell so that it looked like an open flower. Half an hour after the pH controlling, I lifted the bucket, than the whole thing exploded with a sharp sound when contacted the sunlight Have you thought about some kind of forced ventilation to keep the chlorine dioxide from building up? Like every time the HCl is added, the cell is given a flush of fresh air by a fan? (...that need to be corrosion proof... Problems, problems, problems...) I find the idea of keeping the brine level constant/the cell 100% filled unrealistic, isn't this doomed to fail a some point? Keeping such a cell explosion proof gives me a headache. For practical purposes this would have to run while I'm at work... I cannot have huge chlorine plumes and smell, even more so I cannot have explosions (just a few thoughts, my ClO3 project is on ice for several years now...) Edited July 21 by mabuse00
mx5kevin Posted July 21 Posted July 21 (edited) 1 hour ago, mabuse00 said: Considering the HCl dosing: How about metering the current and find a proper ratio, like so-and-so-much seconds running the dosing pump for every so-and-so-much amp-hours going through the cell? One could also include the cell temperature into the equation, whatever influence this might have on the process... Have you thought about some kind of forced ventilation to keep the chlorine dioxide from building up? Like every time the HCl is added, the cell is given a flush of fresh air by a fan? (...that need to be corrosion proof... Problems, problems, problems...) I find the idea of keeping the brine level constant/the cell 100% filled unrealistic, isn't this doomed to fail a some point? Keeping such a cell explosion proof gives me a headache. For practical purposes this would have to run while I'm at work... I cannot have huge chlorine plumes and smell, even more so I cannot have explosions (just a few thoughts, my ClO3 project is on ice for several years now...) 5ml/h concentrate with 30% HCl drip a 3 liter CHLORATE cell can be well regulated. When chlorine appears in the solution, the dosing must be stopped. As the electrolysis progresses, the process becomes increasingly alkaline. This way you can't accidentally fast way overdose. HCl must be dropped deep down the sulution. Chlorine and its oxides can thus be absorbed in the solution. A large amount of chlorine is not released into the air either, because if the chlorine is more noticeable in the air, the dripping is also stopped. There is no need to measure the pH and open the cell in chlorate cell. With trial measurements at the first runnings, the dosage can be established for a given cell in the long term. In PERCHLORATE cell, it is possible that the solution does not become alkaline, but that a strongly acidic negative -1, 3 pH appears. Lead dioxide does not like this, nor does it like too alkaline a solution. In order for the cell to explode, fast way added high dose of HCl is required. This will happen when a dense gas like fog accumulates in the cell. If HCl is dosed fast way, it will be strongly felt when it reaches the environment, and the cell will be overdosed. It can be adjusted without pH measurement in a chlorate cell, but when chlorine appears in the cell solution, must be stopped adding more HCl. Even if it is set to pH 6-7, it won't be there for long. It can also be administered quickly with a syringe with a straw, so that the concentrated acid is dosed very slowly to the bottom of the cell. However, you can really feel this in the environment. With M3 anti-chlorine mask with swimming goggles and rubber gloves! If the HCl is dosed fast, it may be yellow, you have to wait minimum 10 minute, it must not be closed, after this must start the open cell. And if it is running, the solution itself is not bubbling, then it can be closed. There are plant infusions, it is best to administer the HCl with it slowly. If the HCl acid is diluted, it also produces gas when it comes into contact with chlorate. HCl dosing can be switched on once a day for X time. In amateur circles, this is more than enough. In the chlorate cell, if the solution becomes slightly more acidic, the cell itself compensates for this. In these homemade cell settings, very large pH swings are natural. pH 6-7 here is such a narrow range that it cannot be maintained. Before adjusting the pH, I regularly clean the cathode with a rag and put it in hot water, in which I add a little hydrochloric acid. Which matter here that it is for a 5 liter cell 10-15ml 30% HCl i added about 1 minute or 3 hour slowly dosed, than after 2-3 hour dosing i stopping the cell dosing at that day. If you have a precise power supply, precise setting of volts and amperes helps a lot. pH control with dilute hydrochloric acid did not worked for me. Edited July 21 by mx5kevin
AustralianPyromaniac Posted July 22 Author Posted July 22 (edited) 7 hours ago, mabuse00 said: How about metering the current and find a proper ratio, like so-and-so-much seconds running the dosing pump for every so-and-so-much amp-hours going through the cell? One could also include the cell temperature into the equation, whatever influence this might have on the process... I have considered this but the evaporation rate is too variable to use this for water level control. For HCl dosing, acid consumption is not directly related to current consumption, because the side reaction is not inherently ordered. It is possible to calculate the amount of KClO3/ Ah, but not KOH/ Ah. 7 hours ago, mabuse00 said: I find the idea of keeping the brine level constant/the cell 100% filled unrealistic, isn't this doomed to fail a some point? It is not that unreasonable. The video below shows a simple system for regulating water level in a fishtank that works on the same principle. The chlorate cell condition pose additional issues, but the principal is the same. I can maintain the water level, the question is what concentration of acid should the reservoir be loaded with. Edited July 22 by AustralianPyromaniac 1
mx5kevin Posted July 22 Posted July 22 9 hours ago, AustralianPyromaniac said: I have considered this but the evaporation rate is too variable to use this for water level control. For HCl dosing, acid consumption is not directly related to current consumption, because the side reaction is not inherently ordered. It is possible to calculate the amount of KClO3/ Ah, but not KOH/ Ah. It is not that unreasonable. The video below shows a simple system for regulating water level in a fishtank that works on the same principle. The chlorate cell condition pose additional issues, but the principal is the same. I can maintain the water level, the question is what concentration of acid should the reservoir be loaded with. Try this, it slowly dispenses drop by drop the HCl 5ml/hour. The aquarium video that you linked that are high dose dosage. It should only be added to the bottom of the solution, not to the top in small slow drops.
mabuse00 Posted July 22 Posted July 22 Thanks for sharing your insight. Sometime in the future i'll get my hands dirty with this... I wonder how practical it would be to just skip the level control and just focus on an approximate PH control that adds so slowly that gas buildup can be avoided. Hydrogen would still be a problem, but it would volatise rather quickly - will it? Forklift lead batteries on quickcharge bubble like hell, I've never heard about explosions...
AustralianPyromaniac Posted July 23 Author Posted July 23 5 hours ago, mabuse00 said: I wonder how practical it would be to just skip the level control and just focus on an approximate PH control that adds so slowly that gas buildup can be avoided. Hydrogen would still be a problem, but it would volatise rather quickly - will it? This is definitely another option. To have two inlets to the cell, one which doses acid at a continuous rate, and a second which regulates water level with distilled water. So long as the acid dose is below the water consumption rate, the rest of the loss can be made up by distilled water. But it would be nicer to have them combined, hence the question. 5 hours ago, mabuse00 said: Forklift lead batteries on quickcharge bubble like hell, I've never heard about explosions... The hydrogen coming off a chlorate cell definitely can explode, as can battery hydrogen. But the risk is mitigated if the tube is lead into a body of water that works as a flashback arrester. The atmosphere inside a chlorate cell should be mostly hydrogen and little oxygen, so its possible it would not even sustain combustion. He is talking about the gas chlorine dioxide produced by the reaction of HCl and hypo/-chlor-/ate/ite. The gas is strongly oxidising, and so can cause explosions, but I had never heard of this being an issue until he brought it up. If weak HCl is added, none of these gases are made at all. If strong acid is used, strong stirring quickly causes them to dissolve. If the cell has no stirring, the risk is much greater and pH control is also not effectively achieved. Effective gas washing destroys these gasses in any case.
AustralianPyromaniac Posted July 23 Author Posted July 23 @WSM do you have any input on this question? 🙂
AustralianPyromaniac Posted August 16 Author Posted August 16 On 7/14/2024 at 12:08 AM, mx5kevin said: If you start it without pH controlling 150g KCl without pH control you will get less than 150g KClO3, with pH control this can be much more than 150g clean end product and more than 200g cristalls from the cell. In a NaClO4 cell from every 100g NaCl you will get 210g pure NaClO4. What you get as an uncleaned end product can be almost twice as heavy as the starting material. Can you elaborate more on this idea? Why does the cell not run to completion without pH control? Does this happen with NaCl electrolysis or only with KCl?
Arthur Posted August 16 Posted August 16 Look for "Iwaki bellows pump" on your local ebay etc. As film photography meets digital, film processors are being parted out in a hurry. The bellows pumps move most dilute acids and need to have the pump stroke and the pump time adjusted to give controlled solution replenishment (just like an electrochemistry cell!).
AustralianPyromaniac Posted August 16 Author Posted August 16 2 hours ago, Arthur said: Look for "Iwaki bellows pump" on your local ebay etc. As film photography meets digital, film processors are being parted out in a hurry. The bellows pumps move most dilute acids and need to have the pump stroke and the pump time adjusted to give controlled solution replenishment (just like an electrochemistry cell!). Thanks Arthur. I understand how to achieve the pH-control but not exactly why it is able to overcome the "cliff" at around 50% This thread is more questions about cell chemistry than basic cell design. --- In a completely pH-uncontrolled cell, where nothing is added to the liquor except distilled water, the cell efficiency of KCl -> KClO3 suddenly drops like 10% at around 50% Cl– conversion, drastically decreasing production rate. The cause of this change is not documented, but likely related to the buildup of OH– – which continues to be produced in small amounts even after the cell has stabilised and the dissociation/ reduction of water to H2 becomes disfavored. Likely, as OH– concentration reaches some threshold (around 12 maybe?) in the cell, one or more chlorate production reactions become disfavoured, or possibly one or more back reduction reactions become favored. This threshold is not accompanied by any obvious change in cell voltage. By adding a large dose of HCl once the threshold is reached, the pH can be returned to neutral, and chlorate production resumes as normal. To prevent this issue entirely, a 10% (3M) solution of HCl is used in place of pure distilled water when refilling the cell. A single HCl addition per day is not frequent enough to achieve pH control but will prevent pH from drifting too high above 10. But why this sudden drop in current efficiency happens I cannot figure out. Kevin mentioned it in his post and hoping he may have some further info that would help prevent it from happening when non-HCl additives or pH-uncontrolled cells are used. (additives like dichromate and persulphate)
mx5kevin Posted August 16 Posted August 16 6 hours ago, AustralianPyromaniac said: Can you elaborate more on this idea? Why does the cell not run to completion without pH control? Does this happen with NaCl electrolysis or only with KCl? In both cases this is true. The hydroxide must be converted back to chloride. I wouldn't buy expensive, complicated tools for pH controlling, the important thing is that you don't come into contact with chlorine gas. Almost all of the raw materials are transformed into chlorate or perchlorate. The oxygen in it appears as extra weight, this can be calculated accurately using a periodic table. Weighed on a scale and the resulting product are much more than the used chloride for the production. In the case of NaCl the theoretical profit is also in practice if it is dried the NaClO3 or NaClO4. In the case of KCl, the are the KCl solution+KClO3 crystals, many by-products are recycled back into the process. Converting NaCl to NaClO4 conversion are a very slow process, about 4X as long as converting KCl to KClO3. In a 400ml cell KClO3 about 1 week are ready, in the same cell NaClO4 is 3-4 week (the NaClO3 are cc 2 week). I rarely use KClO3, but I need a lot of KClO4. It is easy to work with 1000-2000ml cells. NaClO4+KClO3 with hot filtering are faster, cheaper way. All solutions are recovered in the cell. The NaCl requirement is reduced to a fraction, it can be reused indefinitely. A minimum of 10 kg of KCl must be purchased. Production must continue until something breaks down. Converting NaClO3 to NaClO4 are much more faster, and the cell does not contaminated with high level of chloride in perchlorate cell, or perchlorate in chlorate cell which would harm the anode. I using a 70mmx3mm silver rod with 0,2mm 200 micron thick pure platinum, and a 6V 4A car battery charger. It does not require an expensive special adapter, the electrode does not fail even after many years, and good for chlorates and perchlorates too, does not required precise pH controlling. The most economical, cheapest method that I know. Chlorates and perchlorates, which are needed in the long term, should be produced in the shortest possible time because the various tools for use age. I use simple, cheap tools for pH control. MMO anode is only perfect for chlorates. Platinized titanium anodes are wasting of money, their lifespans are ridiculously short. PbO2 anodes, it can withstand half a year of active continuous use. It won't last for years. It requires expensive adapters with precise Amp and pH control.
AustralianPyromaniac Posted August 16 Author Posted August 16 Do you have any idea why the hydroxide must be converted back? The pH quickly becomes strongly basic (pH 10) after 2-3 hours but production is still good until the threshold. In basic conditions, chlorate should still be able to form at the anode by the reaction below, but for some reason, it does not, it stops after that point. It still makes chlorate but very slowly. 3 ClO− + 1.5 H2O → ClO3− + 3H+ + 2 Cl− + 0.75 O2 + 3 e− --- This is the reaction overall in basic conditions all the way from Cl to ClO3 Cl− + 4.5 H2O + 9 e− → ClO3− + 4.5 H2 + 0.75 O2 (OVERALL REACTION)
mx5kevin Posted August 16 Posted August 16 (edited) 2 hours ago, AustralianPyromaniac said: Do you have any idea why the hydroxide must be converted back? The pH quickly becomes strongly basic (pH 10) after 2-3 hours but production is still good until the threshold. In basic conditions, chlorate should still be able to form at the anode by the reaction below, but for some reason, it does not, it stops after that point. It still makes chlorate but very slowly. 3 ClO− + 1.5 H2O → ClO3− + 3H+ + 2 Cl− + 0.75 O2 + 3 e− --- This is the reaction overall in basic conditions all the way from Cl to ClO3 Cl− + 4.5 H2O + 9 e− → ClO3− + 4.5 H2 + 0.75 O2 (OVERALL REACTION) Chlorine is constantly escaping. After some days the pH will be 14. If the pH is not regulated for a long time (days), a lot of acid is needed to get pH7.0. In the case of NaClO4 cell without pH controlling the process has slowed down for me in a 400ml cell after a month was still NaClO3 (with pH control about 3 week the NaClO4 was ready). If there is no pH control, NaOH or KOH will be produced as byproducts. In the case of chlorate, much less finished product can be obtained. The invested hydrochloric acid pays for itself in proportion to the price. For me, the actual number of amperes is measured on the running cell. If the raw materials are recycled and we cannot talk about discarded by-products, the pH control is even more spectacular. It must be dosed economically, excess HCl acid is released into the air. If the pH is regulated at most once a day, that is more than enough (in a cell where a KClO3 production time are 1 week and not lower). The gas production of the cathode reveals a lot, it bubbling very slowly in strongly alkaline conditions, especially if it has deposits. If there is a deposit on cathode, it must be removed regularly. Cathode deposition is slower in a pH-controlled cell too. Quote It still makes chlorate but very slowly. I usually clean the copper contacts of the electrode with hydrochloric acid, then wash them in baking soda and clean water. The cell must be maintained at certain intervals. At the connection points, the copper wire often oxidizes. As electrolysis progresses, half as many amperes actually pass through the cell towards the end. The cathode should be cleaned most regularly (cleaning with a kitchen towel and put in hot water what added with some minimal HCl), all deposits come off completely in minutes. Edited August 16 by mx5kevin
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