Catalytic Demonstration

This demo shows the oxidation of acetone in the presence of copper catalyst.

A catalyst is a chemical that takes part in a chemical reaction but is itself left unchanged after the reaction is complete. Many metals like to be catalysts. Platinum and palladium are two well known catalysts used in catalytic converters in cars. Nickel is used to speed up many chemical reactions. Boiled linseed oil is a mixture of linseed oil and metallic salts which help speed the oxidation of the liquid oil into a solid. Japan dryer is a mixture of metallic salts you can add to certain paints to speed up their hardening time. This demonstration is a little more dramatic. We will burn acetone without a flame.

CAUTION! DANGER!

Work with just a few milliliters at a time (less than an ounce, two teaspoons). Keep the acetone container closed and far away from the experiment. The point of this experiment is to burn the acetone without fire, but it doesn't always go this way. I've had the reaction flare up a few times. CAUTION! This demonstration will occasionally ignite into flame. When it does I cover it with large metal bowl to snuff out the flames. The greater danger is that the reaction jar may shatter from the heat stress. Work with a few teaspoons of fuel at a time. Again, keep your container of fuel closed and far away from the experiment while in operation. Keep a fire extinguisher handy. Work in an area away from other flammable materials. Don't do this experiment if you don't expect it to fail by flaring up, because it will do this from time to time. Your experimental setup should be such that this won't surprise you and you will be ready to deal with it. Do this in a place where when an accident happens you can just step back and let the flames burn themselves out.

Parts List

This demo can work with different types of hydrocarbons. Acetone is one of the easiest. The reaction will also work isopropyl alcohol, but it can be harder to get a self sustained reaction going.

You will need a source of high temperature to preheat the catalyst to get the reaction started. A propane torch works well. A butane powered micro-torch or jet lighter is also good. You can even get the reaction started with a common pocket lighter, but these lighters tend to coat the metal in soot which can cause two problems. The soot is a barrier that may prevent the metal catalyst from taking part in the reaction. Soot maybe itself also acts as a catalyst and can create hot spots which cause the acetone to burn erratically and flare up.

Clean the Reaction Chamber

A baby food jar makes a nice reaction chamber. Apple sauce tastes good, but I also like the little chicken sticks. Consume the baby food; remove the label; clean off the label glue. Coincidentally, acetone works well for cleaning off the glue.

Make a Hanger Rod

Start with a 2.5 inch (70 mm) length of straight wire. Bend it so that it sits comfortably in the middle of the jar opening. Bow it down slightly so that the catalyst hanger will center itself more or less in the middle when it hangs.

Make a Catalyst Coil

The purpose of the coil is to maximize surface area. The metal catalyst only takes part in the reaction where it comes into contact with oxygen and hydrocarbon vapors. So we need as much metal surface as possible. It is also better to have as much surface in as small a volume as possible as this will concentrate the reaction heat to keep the reaction going.

It is helpful to use round-nose pliers to wind the coil. Needle-nose pliers will work, too, but the results wont be as pretty. As you wind the coil wrap the wire below the loops you have already wound. The finished loops then wind off the tip of the pliers away from you. This may or may not seem obvious, but if it's been a long while since I've wound these coils I find that my intuition is to wind the wire above the loops and push down the finished loops. After a few loops I realize it can never work this way and I curse my stupidity and have to start over. This simple skill comes in handy when making air-core inductors for radios.

Make a Catalyst Hanger

Start with a 5 inch straight piece of wire and the catalyst coil. You might notice we are making the hanger out of the same material as the catalyst.

The catalyst coil rolls freely on the hanger. The coil and hanger could be made from a single piece, but assembling them from separate pieces makes construction easier and it improves performance because the hanger cannot as quickly sink heat away from the coil as it would if it were made from a single piece of wire.

Unanswered Questions

This reaction will work with other fuels and catalysts. Copper and acetone is one of the easier combinations to get to work. I have also tested silver, steel, and nickel as catalysts. Some were successful, but none were as easy as ordinary copper. For fuels I have also tested isopropyl alcohol and propane. Isopropyl worked sometimes, but it was difficult to get the reaction to self-sustain. Propane gas may have worked, but it was hard to control to be sure what was going on. Usually the a red hot copper wire would ignite a flame. If the gas rate was too high it would cool down the wire so that the reaction would not self-sustain.

In theory, an efficient catalyst that completely surrounds the fuel source would actually extinguish a flame. The setup I designed with a small catalysts coil hanging in an open reaction chamber allows a flame to bypass the catalyst, so the chamber sometimes flames up. It would be interesting to design a more efficient setup that would actually extinguish flames. Perhaps covering the entire open mouth of the reaction chamber with a grid mesh would work. I'm also not sure what triggers these occasional flareups. It would be interesting to figure out why this happens. I suspect that the catalyst simply gets so hot that it heats the acetone to a vapor so fast that that rises above the chamber unturned to mix with oxygen and burn outside of the reaction chamber. The catalyst coil itself gets hot enough to ignite the fuel/air mixture above the chamber.

Extra Science

You may notice that the copper wire is stiff and springy when it comes fresh of the roll. After it has been heated to red hot for a while in the reaction chamber and then cooled you should notice that the wire feels soft and pliable, almost limp. This is because the copper has been "annealed". Annealing is a physical process that takes place in metals and glass that makes them softer and more ductile. If you take a piece of annealed wire and straighten it and them tap the entire length with a hammer it should become stiff and springy again. This is called "work hardening". These effects are important to understand especially when working with copper. Having trouble bending some copper? Try heating it up. After it cools it will be much easier to bend.

Catalysts

Catalysts are everywhere. Our life on this planet would be difficult without them. Half of the protein that makes up your body can be traced directly back to an industrial chemical plant that fixes nitrogen using a process invented by Fritz Haber. This allows us to make cheap fertilizer. Here are is a list of some catalysts:

butane powered portable soldering irons
propane catalytic heaters
self-cleaning and continuous cleaning ovens
automotive catalytic converters
Oil driers in paints. Lead is a good catalyst for polymerizing linseed oil (AKA flax), which is why oil paints used to contain lead. Nowadays cobalt and zirconium are more commonly used. "Japan drier" is a common hardware store name for a cocktail of metal catalysts used to make oil-based coatings dry faster.
Döbereiner's lamp (hydrogen and platinum)
self-cleaning glass (photocatalysis, not the lotus effect (superhydrophobicity))
pocket hand warmers (powered by lighter fluid and glass wool coated in platinum).