Sciencemadness Discussion Board

Most effective solvent for coked carbon deposits.

foxtrotuniform - 26-6-2013 at 08:53

Mechanical engineering student here. I've got a carbon chemistry question that y'all might have some insight into.

The problem:
I'm working up a few design prototypes for thermal mosquito foggers similar to this.

They work by forcing a dilute pesticide mixture into a heated copper or aluminum tube. The heat vaporizes the pesticide and solvent (usually mineral oil or kerosene) which then blows out the end in a spectacular cloud of fog.

I'm currently playing with propane-powered units as well as electric "fog machine" type heating elements. A related design which has some promise injects the mix into the hot exhaust gasses of an internal combustion engine, kind of like the smoke system on an acrobatic aircraft.

Ideally, the vaporized mix should be expelled before any combustion happens, but 'ideal' ain't the world we live in. During testing, i've frequently clogged tubes with experimental chemical mixes, high temperatures, low flow rates and general incompetence. The exhaust gas prototype avoids the tube problems, but has the nasty habit of clogging injector nozzles, which I've mitigated, but not eliminated, with nozzle geometry changes.

Solutions?
So for the sake of testing efficiency (and my sanity) I'm in need of a "solvent of last resort" that I can use to revive a carbon-choked tube before it clogs completely, (requiring tear down and rebuild.)

DJ fog machine companies recommend a 50/50 mix of vinegar and water to restore output to clogged machines, but I think that's only effective with the water and glycol based solutions they typically use, because I saw little effect with my mix.

Manufacturers of commercial mosquito foggers recommend running a nonpolar solvent like mineral spirits or napatha through the unit during cool down, but I've found that's that's only effective as a preventative measure.

Based on past experience, I've also tried xylene, but I've found it only works acceptably when combined with scrubbing, which isn't possible inside the coil.

My most promising prospects:
--Lye solutions, commonly used in oven cleaners,

--Chlorinated brake cleaners, which mechanics swear by as the "nuclear option" for freeing coked piston rings and other engine components.

--Combining the above with an ultrasonic parts cleaner. (This is less desirable, since it still requires disassembly.)

I'm getting ready to test those, but after that, I'm at a dead end. Has anyone got any ideas for a solvent to reduce various charred compounds into a liquid or slurry that could be blown out by compressed air?

Exotic stuff is on the table, as long as it's something an individual could buy at a chemical supply house without too much hassle. (i.e. no hydrazine, watch-listed chemicals, etc.)

Thanks for any ideas. I've read this forum a lot over the years, but I've never had anything to contribute. Let me just say that y'all are my kind of people...

AndersHoveland - 26-6-2013 at 09:45

Many of these intermolecular hydrocarbons are not soluble in any solvent.

For getting rid of it, I would suggest base piranha.
It can be a bit corrosive to metals, but it should be able to remove the carbon deposits before excessive attack on the metal.

Another option may be to use NaOH instead of the ammonia in the base piranha. I suspect this would be less corrosive to metal (ironically, even though it is a stronger base).

[Edited on 26-6-2013 by AndersHoveland]

papaya - 26-6-2013 at 12:13

Oxygen gas + heating?

ElectroWin - 26-6-2013 at 13:03

you might try chlorosulphonic acid.

this acid is known to spontaneously dissolve carbon nanotubes; not sure whether it might loosen the deposits?

note: i have never worked with this, myself.

violet sin - 26-6-2013 at 17:26

Not 100% on this but I think strong hydrogen peroxide (30%) might work with the aluminum tubing. The oxide pasivation layer from combustion should protect it from what I have read in the past for ozone production. But the type of insecticide might interfere with that, I don't really know. Also you can buy it by the gallon from a good gardening shop for ~30$/gal, or at least I was able to. Some one should easily be able to speak up if I'm mistaken.

I used 3% recently to clarify a potassium carbonate solution derived from banana peel ashes. It came out honey colored from incomplete combustion residues. With a 10-20ml once or twice and a little heat (<100'C) became clear and had a fine grey sediment that was easily filtered. Maybe the stronger stuff would wreck shop on the build up for ya.

12AX7 - 26-6-2013 at 19:50

I don't know offhand if molten sodium chlorate reacts with bulk aluminum or copper metal. It's stable around stainless steel though.

The reaction of molten sodium chlorate (a strong oxidizer, and it melts at 600F or so) with whatever gunk has blocked the tube will assuredly result in the rapid removal of the blockage. :) Example:
http://youtu.be/txkRCIPSsjM

Tim

Jekyll - 28-6-2013 at 02:35

For cleaning "organic matter" from Pyrex fritted glassware, Corning recommends hot concentrated cleaning solution or hot concentrated sulfuric acid plus a few drops of sodium or potassium nitrite. Many lab manuals recommend warm sulfuric acid for organic deposits.

Note that concentrated sulfuric acid, particularly when warm or hot, is very dangerous stuff and appropriate safety precautions must be utilized.

Good advice in general on the care and handling of glassware:
http://catalog2.corning.com/Lifesciences/media/pdf/glass_car...

[Edited on 28-6-2013 by Jekyll]

sonogashira - 28-6-2013 at 03:30

Hot concentrated sulphuric acid will oxidize any carbon containing substance.

paw_20 - 28-6-2013 at 05:57

Conc. sulphuric will eat through just about anything organic, often without heating (although it will heat up as it chews, exothermic and all that jazz). There's a reason people prefer those sorts of drain cleaners over the lye solutions.

AndersHoveland - 28-6-2013 at 10:28

Quote: Originally posted by paw_20  
Conc. sulphuric will eat through just about anything organic, often without heating (although it will heat up as it chews, exothermic and all that jazz). There's a reason people prefer those sorts of drain cleaners over the lye solutions.

"Concentrated sulfuric acid" tends to have a different meaning in chemistry than it does in other situations. In chemistry, it usually refers to >98% concentration. In drain cleaner, it just refers to the fact that the acid is concentrated enough to cause serious burns, 20-30%.

The "concentrated" sulfuric acid in drain cleaner is not nearly concentrated enough to char anything organic. It is however, concentrated enough to cause hydrolysis of esters, and dissolve cellulose/protein containing substances.

Sulfuric acid does not act as an oxidizer by itself unless heated.

[Edited on 28-6-2013 by AndersHoveland]

Oscilllator - 29-6-2013 at 01:54

Quote: Originally posted by AndersHoveland  
Quote: Originally posted by paw_20  
Conc. sulphuric will eat through just about anything organic, often without heating (although it will heat up as it chews, exothermic and all that jazz). There's a reason people prefer those sorts of drain cleaners over the lye solutions.

"Concentrated sulfuric acid" tends to have a different meaning in chemistry than it does in other situations. In chemistry, it usually refers to >98% concentration. In drain cleaner, it just refers to the fact that the acid is concentrated enough to cause serious burns, 20-30%.

The "concentrated" sulfuric acid in drain cleaner is not nearly concentrated enough to char anything organic. It is however, concentrated enough to cause hydrolysis of esters, and dissolve cellulose/protein containing substances.

Sulfuric acid does not act as an oxidizer by itself unless heated.

[Edited on 28-6-2013 by AndersHoveland]


I have no idea where you got the idea drain cleaner sulfuric acid was 20-30%. its not. Almost all brands are >95%, and the one I buy is a clear liquid, and is labelled as 98%.
battery acid is around 30%, however.

unionised - 29-6-2013 at 02:42

Quote: Originally posted by 12AX7  
I don't know offhand if molten sodium chlorate reacts with bulk aluminum

Tim

I'd be willing to bet that it does, violently.

madscientist - 30-6-2013 at 17:39

Quote:
Many of these intermolecular hydrocarbons are not soluble in any solvent.


Intermolecular hydrocarbons? :D
Quote:
Another option may be to use NaOH instead of the ammonia in the base piranha. I suspect this would be less corrosive to metal (ironically, even though it is a stronger base).


Ever heard of the "Works Bomb"? Al + [OH-] --(aq.)--> base in your face.

[Edited on 1-7-2013 by madscientist]

ScienceSquirrel - 5-7-2013 at 16:43

Quote: Originally posted by unionised  
Quote: Originally posted by 12AX7  
I don't know offhand if molten sodium chlorate reacts with bulk aluminum

Tim

I'd be willing to bet that it does, violently.


It might take a while to get going but I think it would take off like a Gummi bear dropped in to potassium chlorate on speed when the molten salt chewed through the oxide layer and the reaction got underway.
Real runaway potential here with the possibility of extensive painful burns and even death if done on a large enough scale.

ScienceSquirrel - 5-7-2013 at 16:52

Quote: Originally posted by AndersHoveland  
Quote: Originally posted by paw_20  
Conc. sulphuric will eat through just about anything organic, often without heating (although it will heat up as it chews, exothermic and all that jazz). There's a reason people prefer those sorts of drain cleaners over the lye solutions.

"Concentrated sulfuric acid" tends to have a different meaning in chemistry than it does in other situations. In chemistry, it usually refers to >98% concentration. In drain cleaner, it just refers to the fact that the acid is concentrated enough to cause serious burns, 20-30%.

The "concentrated" sulfuric acid in drain cleaner is not nearly concentrated enough to char anything organic. It is however, concentrated enough to cause hydrolysis of esters, and dissolve cellulose/protein containing substances.

Sulfuric acid does not act as an oxidizer by itself unless heated.

[Edited on 28-6-2013 by AndersHoveland]


UK and French sulphuric acid based drain cleaner is ca 95 - 98% acid.
It behaves as a powerful dehydrating agent, even in the cold, blackening paper quite quickly, sugar is blackened in the cold, almost instantly on using the warm acid.
Copper is dissolved with the evolution of sulphur dioxide when the cold acid is added to the finely divided metal, the reaction is much quicker on warming.

zed - 12-7-2013 at 13:42

I don't know how large your tubing is, but mechanical methods like running twine through it might work.