Science Buddies: "Ask an Expert"

Hello,

I am doing a project on the thermal depolymerization of HDPE (High-Density Polyethylene), and I'm having problems finding a heat source that can reach 740 Degrees Celsius and one that is also relatively inexpensive. First I tried hot plates, then I tried a propane burner, but when I measured they weren't hot enough.

Sincerely,

Promise

740 C is very hot, but a propane burner should reach ~1900 C. Have you tried adjusting the fuel-air mix while operating the burner?
Have you considered using different polymers that would break down at a lower temperature?
I would highly recommend a pair of welding gloves and a face shield if you are going to be working with melted plastics.

It really wasn't so much that the propane burner wasn't hot, but the pressure vessel, which is what I was actually measuring wasn't getting hot enough. So when I measured the wall of the pressure vessel it was only half of 740 degrees Celsius, I don't know if maybe it wasn't as effectively retaining heat because it was aluminum, and I need to switch metals. Or I need to sit it lower to the flame, and extend the time that I left it on the burner and then measure the temperature.

starkpr wrote:It really wasn't so much that the propane burner wasn't hot, but the pressure vessel, which is what I was actually measuring wasn't getting hot enough.

Your fundamental problem is that your pressure vessel was loosing heat to its ambient at too high a rate so the equilibrium temperature it reached was too low.

EXTREME SAFTETY ISSUE: Sealed pressure vessels reaching temperatures above 100 degrees C pose a VERY DANGEROUS EXPLOSION RISK.

You need to come up with a safer way to do this experiment or find another experiment. Consider using extremely small open containers and very small amounts of experimental material and experimenting under an appropriate chemistry lab vent hood with expert supervision. Heated plastics can give off some poisonous and/or caustic fumes.

I second the suggestion to experiment with polymers that break down at a lower temperature.

I second the warnings about high temperatures and pressure vessels. Also, at those temperatures they need to be made of steel and gaskets become a problem.