Cleaning Catalytic Converters with SodiumHydroxide

  • EricTheCarGuy
  • EricTheCarGuy's Avatar Topic Author
  • Offline
  • Administrator
  • Administrator
More
4 years 8 months ago #109859 by EricTheCarGuy
There were some concerns about the last catalytic converter cleaning video that I did. So this time I tried to be as through as I could. My efforts may not have been successful, but I still think it might be a viable option for some. What are your thoughts?


Stay dirty

Please Log in or Create an account to join the conversation.

Advertisement
  • Rereonehundred
  • Rereonehundred's Avatar
  • Offline
  • 4th Gear
  • 4th Gear
  • Honda motorcycles and cars
More
4 years 8 months ago #109870 by Rereonehundred
Replied by Rereonehundred on topic Cleaning Catalytic Converters with SodiumHydroxide
Got rid of tetraethyl lead octane improver since the lead poisoned the cat.

Same for MMT, another metallic octane improver. Methylcyclopentadienyl Manganese Tricarbonyl, poisoned the cat also.

Reduced the zinc, zinc dialkyldithiophosphate, in engine oils, as the zinc poisons cats with oil consumption.

What these have in common that poisons the cat is the metal. Lead, Manganese, and Zinc.

You've washed the cat with tap water. Are there any metallic minerals in your tap water that could be poisoning the cat?

Of course your cat sees water of combustion, but that's derived from the hydrocarbon fuel, which is mineral free, so that's mineral free water.

Funny stuff this science business.

Rereonehundred
Precession stability

Please Log in or Create an account to join the conversation.

More
4 years 8 months ago #109886 by MetaphysicalEngineer
Replied by MetaphysicalEngineer on topic Cleaning Catalytic Converters with SodiumHydroxide
Someone please correct me if I'm wrong, but the way I learned was that the heat of combustion breaks down the metal-containing molecules of octane improvers and oil additives and vaporizes the metal. The vaporized metal then condenses on the relatively cooler exhaust parts, including the surfaces of the catalytic converter.

While the exhaust pipe doesn't care about a few atoms thick layer of extra metal, the catalytic converter relies on direct contact with the exhaust gases. Once it gets coated with condensed metal vapors, the catalyst is sealed off from the exhaust gas and can't function anymore. Soot burns off at typical catalytic converter operating temperatures but since most metals have a pretty high boiling point, the exhaust system can't get hot enough to burn them off. If it did, the exhaust system and the ceramic in the converter would probably have issues as well.

Tap water doesn't contain that much metal (it would be deadly if it did), and for the most part minerals tend to stay dissolved. Over hundreds of thousands of gallons, some of the minerals can solidify and cause problems with old pipes and fittings, but that is very unlikely with the amount used for rinsing in the video.

Please Log in or Create an account to join the conversation.

More
4 years 8 months ago #109904 by apostolis
Heavy metals do poison the cat. Tap water does not contain such metals or if it does the concentration is very low. Moerover it is unlikely that metals contained in tap water to poison the cat because at room temp the active metals of the cat are non-reactive (thats why we call these metals like platinum noble, because they react with almost nothing at "normal temterature". Also the temperature related reactivity is the reason that a cold engine(and the cat respectively) emmits NOx and HC like any non catalytic car. However i would use deionized water for a final rinse just to be on the safe side.
Eric, if you get another chance for a similar case i would suggest to use a mixture of equal volumes of concentrated sodium hydroxide and isopropanol (rubbing alcohol) or just plain gasoline(whitch is very cheap, an exellent solvent and cleans very well) but in either case the cat should be submerged in the cleaning solution and left overnight to soak (when you want to clean something without the use of mechanical force time really counts). Finally i think it is safe to say that this particular cat is too far gone.

Please Log in or Create an account to join the conversation.

More
4 years 8 months ago #109905 by apostolis

MetaphysicalEngineer wrote: Someone please correct me if I'm wrong, but the way I learned was that the heat of combustion breaks down the metal-containing molecules of octane improvers and oil additives and vaporizes the metal. The vaporized metal then condenses on the relatively cooler exhaust parts, including the surfaces of the catalytic converter.

While the exhaust pipe doesn't care about a few atoms thick layer of extra metal, the catalytic converter relies on direct contact with the exhaust gases. Once it gets coated with condensed metal vapors, the catalyst is sealed off from the exhaust gas and can't function anymore. Soot burns off at typical catalytic converter operating temperatures but since most metals have a pretty high boiling point, the exhaust system can't get hot enough to burn them off. If it did, the exhaust system and the ceramic in the converter would probably have issues as well.

Tap water doesn't contain that much metal (it would be deadly if it did), and for the most part minerals tend to stay dissolved. Over hundreds of thousands of gallons, some of the minerals can solidify and cause problems with old pipes and fittings, but that is very unlikely with the amount used for rinsing in the video.


1. the heat of combustion does breaks down the metal-containing molecules of octane improvers and oil additives but does not vaporise the metal (vapor means it is at gaseous state) the metal becomes a very very fine powder,like soot
2. The metal forms a bond with the active metals (in a non reversible way, hense the term poisoning) of the cat due to the high temp of the cat.
3. The substances that the cat breaks down form a bond with the active metal of the cat, then the substance breaks down ( for example 2NO -> N2 + O2) and finally the bond breaks and the newly formed molecules are released.
4.in a poisoned cat the exhaust gasses do come in contact with the active metals but they cannot form a bond with them because there is already a bond between the active metal with the heavy metal that caused the poisoning.

Please Log in or Create an account to join the conversation.

Advertisement
  • Rereonehundred
  • Rereonehundred's Avatar
  • Offline
  • 4th Gear
  • 4th Gear
  • Honda motorcycles and cars
More
4 years 8 months ago - 4 years 8 months ago #109909 by Rereonehundred
Replied by Rereonehundred on topic Cleaning Catalytic Converters with SodiumHydroxide

apostolis wrote: Heavy metals do poison the cat. Tap water does not contain such metals or if it does the concentration is very low. Moerover it is unlikely that metals contained in tap water to poison the cat because at room temp the active metals of the cat are non-reactive (thats why we call these metals like platinum noble, because they react with almost nothing at "normal temterature". Also the temperature related reactivity is the reason that a cold engine(and the cat respectively) emmits NOx and HC like any non catalytic car. However i would use deionized water for a final rinse just to be on the safe side.
Eric, if you get another chance for a similar case i would suggest to use a mixture of equal volumes of concentrated sodium hydroxide and isopropanol (rubbing alcohol) or just plain gasoline(whitch is very cheap, an exellent solvent and cleans very well) but in either case the cat should be submerged in the cleaning solution and left overnight to soak (when you want to clean something without the use of mechanical force time really counts). Finally i think it is safe to say that this particular cat is too far gone.


Lead solder for joining copper pipes is leached into tap water, I think especially if the water's pH is a bit acidic. Copper is a heavy metal too. Mercury is sometimes a problem too in drinking water.

But on balance the amounts are likely pretty small. Perhaps the point is that it is fun to play with your cat, but expect the unexpected.

Rereonehundred
Precession stability
Last edit: 4 years 8 months ago by Rereonehundred. Reason: typo

Please Log in or Create an account to join the conversation.

More
4 years 8 months ago #109912 by Hanneman

MetaphysicalEngineer wrote: Someone please correct me if I'm wrong, but the way I learned was that the heat of combustion breaks down the metal-containing molecules of octane improvers and oil additives and vaporizes the metal. The vaporized metal then condenses on the relatively cooler exhaust parts, including the surfaces of the catalytic converter.


I could be wrong, but there may be a contribution from the plasma generated by the spark inside the combustion chamber that would liberate a metal from the additives. The flame produced by ignition is a plasma, which contains a lot of free electrons that wreak havoc and break molecules apart. Those free electrons and their collisions with other particles also generated light. The plasma is short-lived, and some things recombine and the others decompose.

MetaphysicalEngineer wrote: While the exhaust pipe doesn't care about a few atoms thick layer of extra metal, the catalytic converter relies on direct contact with the exhaust gases. Once it gets coated with condensed metal vapors, the catalyst is sealed off from the exhaust gas and can't function anymore. Soot burns off at typical catalytic converter operating temperatures but since most metals have a pretty high boiling point, the exhaust system can't get hot enough to burn them off. If it did, the exhaust system and the ceramic in the converter would probably have issues as well.


A catalyst poison (like lead, sulfur, or zinc) can "stick" or bind to the active site, preventing the desired species (CO, NOx) from being reacting. From what I remember (and I'm no expert here), the binding of a poison to the active site on a catalytic surface can be a fairly complex chemical bond. So, the poison doesn't vaporize (physical change) from the heat alone. Instead, the poison has to somehow react using the available thermal energy (heat), and hopefully it's product leaves the active site. Poisons with high binding affinities and high activation energies are not likely to react and/or leave the active site on the catalyst.

Please Log in or Create an account to join the conversation.

  • EricTheCarGuy
  • EricTheCarGuy's Avatar Topic Author
  • Offline
  • Administrator
  • Administrator
More
4 years 8 months ago #110132 by EricTheCarGuy
Replied by EricTheCarGuy on topic Cleaning Catalytic Converters with SodiumHydroxide
I don't think the cat was poisoned. As for my water pipes, they're pex so lead solder really isn't much of an issue. That said, I believe that the catalyst degraded and flaked off over time causing this cat to fail. It is more than 20 years old after all. At this point I feel it's as clean as it's going to be and the only fix is to replace it.

As for removing it and cutting it in half, remember that I welded my A pipe in such a way that in order to replace the catalytic converter I would need to also replace the A pipe. I'm not inclined to do that at this time. Perhaps at some point, but not anytime soon. I need to take a break from this catalytic converter debate for a while.

Stay dirty

Please Log in or Create an account to join the conversation.

  • wysetech
  • wysetech's Avatar
  • Offline
  • 6th Gear
  • 6th Gear
  • Certified Technician Staying Dirty After 47 Years.
More
4 years 8 months ago #110162 by wysetech
Personally, I liked watching the car blow bubbles.

I'm a mechanic because a badass miracle worker is not an official job title.

Please Log in or Create an account to join the conversation.

  • EricTheCarGuy
  • EricTheCarGuy's Avatar Topic Author
  • Offline
  • Administrator
  • Administrator
More
4 years 8 months ago #110299 by EricTheCarGuy
Replied by EricTheCarGuy on topic Cleaning Catalytic Converters with SodiumHydroxide

wysetech wrote: Personally, I liked watching the car blow bubbles.


Yea, me too.

Stay dirty

Please Log in or Create an account to join the conversation.

Advertisement
Time to create page: 0.260 seconds