Sciencemadness Discussion Board

Is a fire extinguisher a reliable high pressure autoclave?

wireshark - 11-8-2014 at 19:59

I want to do a free radical reaction between an organic liquid and a hydrocarbon gas (acetylene) from a cylinder @ 300 psi (21 bar) and 200 C. It is supposed to go in an autoclave made for such reactions.

I'm wondering if I can use an empty fire extinguisher. I'd pressurize it with an appropriate fire extinguisher refill adapter, filling it with the hydrocarbon gas to 300 psi. There are some videos of people refilling fire extinguishers, and this part seems pretty straightforward. I was also thinking of wrapping it with nichrome wire hooked up to a power source and a light dimmer. (I actually don't know how to do the nichrome part, but I can figure it out.) A magnetic stirrer would be placed underneath.

My main concern is if a standard halon fire extinguisher can withstand this pressure and temperature. Would I be creating something that would explode and kill me?

[Edited on 12-8-2014 by wireshark]

Bert - 11-8-2014 at 20:47

1. Why do you think pressurizing acetylene gas to 300 psi is a good idea?! Acetylene gas is NEVER regulated to more than 15 psi in welding equipment, it has a tendency to decompose (explode) at higher pressures. Doesn't need any Oxyge to do this...

2. What is the fire extinguisher made of... Something that will show up well on X-rays? It would be considerate to the ER staff.

wireshark - 11-8-2014 at 21:00

Quote: Originally posted by Bert  
1. Why do you think pressurizing acetylene gas to 300 psi is a good idea?! Acetylene gas is NEVER regulated to more than 15 psi in welding equipment, it has a tendency to decompose (explode) at higher pressures. Doesn't need any Oxyge to do this...

2. What is the fire extinguisher made of... Something that will show up well on X-rays? It would be considerate to the ER staff.


Thank you. Would mixing nitrogen not mitigate this?

So is there no way to reproduce this procedure?
Quote:
Example I

A run was carried out in which toluene was contacted with acetylene in the presence of di-tert-butyl peroxide to form allylbenzene.

In a 1 liter Magne Dash stirred autoclave, 500 ml. (430 grams, 4.67 mole) of toluene and 100 ml. (78 grams, 0.53 mole) of di-t-butyl peroxide were heated-28 hours at 257 F. using a pressure of 100 p.s.i. of acetylene. Nitrogen was added to a total pressure of 250 p.s.i.g.


Attachment: US3209043.pdf (695kB)
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Praxichys - 12-8-2014 at 05:38

I have a few points:

I would advise against starting at a large scale unless you really know what you're doing.

Wrapping it with nichrome is going to be a problem unless you insulate the nichrome from the conductive body of the extinguisher. An oil bath with an immersion heater may be better; just be aware that an explosion could throw very hot oil. Plan accordingly.

Acetylene undergoes exothermic self-polymerization at moderate pressures and will cause an explosion. Dilution with nitrogen may increase the pressure at which this happens. I am not sure how you plan to pressurize this acetylene to 100psi. Some kind of pump?

Steel weakens significantly with temperature. That said, 200C should be fine. This weakening does not start until about 400C.

I would highly recommend a pressure gauge and a blow-off safety valve. However, do not rely on the safety valve to prevent rupture of the container. An exothermic reaction could easily overwhelm it. I would highly advise housing the container in a pit, with gas valves and such located in a safe place, with a lot of earth between the operator and the vessel.

The magnetic stirring field will be severely weakened by a ferromagnetic container. You may have to consider other stirring options. Look up a "shaker hydrogenator."

Dr.Bob - 12-8-2014 at 06:12

Did the patent mention anything of safety equipment, or that the autoclave was in a shielded area? I would not work with acetylene at those pressures, nor di-t-butyl peroxide heated to any temperature except behind a blast shield. That combination, at that scale could wipe out a good sized lab, and yes, it has happened before, about 20 years ago, just down the road from where I work, were someone did something like that (heating toluene with an oxidant), in a proper autoclave, behind a blast shield, and the blast destroyed most of the lab, fortunately not killing anyone.

Patents like this are often about industrial scale processes that are not designed to be done in small scale or without serious safety measures. Just the mixture of the peroxide and toluene could auto-ignite/detonate if the wrong steps are followed.

There are many MUCH safer ways to make allylbenzene, the simplest might be a simple Freidel Crafts of benzene with allyl bromide, both of which are more likely easier to find and safer than di-t-butyl peroxide.

subsecret - 13-8-2014 at 10:43

Perhaps you could use a section of steel pipe, capped on both ends, as the reaction vessel. As Praxichys said, you'd want to conduct the reaction in a pit. Also, remember to cover the pit with something heavy, like a piece of plywood with dirt on top.

The reason that acetylene doesn't explode in welding cylinders is that there's an acetone-soaked sponge in the bottom. The acetylene dissolves into the acetone, absorbing much of the volume and therefore decreasing the pressure.

unionised - 13-8-2014 at 11:37

Laboratories that work with high pressure autoclaves have special "bomb rooms" set aside for such work.
Nobody is permitted in the room while the system is under pressure and the reactions are controlled and monitored remotely.

There's a simple reason for that.
Even high pressure autoclaves are not reliablehigh pressure autoclaves. They fail from time to time and you have to be sure that when (not "if") they fail, nobody gets hurt.

Using a makeshift container for hot high pressure acetylene in the deliberate presence of another explosive- the peroxide- is a pretty sure route to a Darwin award.

subsecret - 13-8-2014 at 18:04

I'd be most afraid of opening the container after heating it. If the autoclave did happen to explode, even if it was in a covered pit, it would still make quite a loud bang, possibly prompting investigation from the neighbors or the police. It would be a difficult mess to get yourself out of, despite the fact that safety measures were in place to prevent injuries. I personally do not advise this experiment, but you are responsible for your laboratory and your safety.

[Edited on 14-8-2014 by Awesomeness]

forgottenpassword - 14-8-2014 at 02:25

I looked into pressure vessels myself, and ended up buying a helium cylinder. They withstand up to 200 bar. Or higher, in fact, that is their fill pressure, if I recall. I was always too scared to use it, although I only intended to heat methanol, not high pressure acetylene. Besides, I couldn't get the top off! :D


[Edited on 14-8-2014 by forgottenpassword]