Sciencemadness Discussion Board

Alternatives to using a "pipe bomb" for a reaction?

querjek - 11-11-2008 at 18:42

I've seen referenced in literature a few times to use a "pipe bomb"--that is, a small, stainless-steel threaded pipe with caps and teflon tape containing a reaction matrix. This is typically put into some sort of high-temperature device.


Maybe I don't understand the purpose of it completely, but--couldn't one use something like a flask submerged in a deep fryer or something of the sort and avoid the "pipe bomb" all together?

watson.fawkes - 11-11-2008 at 18:56

Devices such as this are appropriate when internal pressures generated are greater than glass can withstand, or when the reaction temperature is too high for glass.

Nicodem - 11-11-2008 at 23:45

Quote:
Originally posted by querjek
I've seen referenced in literature a few times to use a "pipe bomb"--that is, a small, stainless-steel threaded pipe with caps and teflon tape containing a reaction matrix. This is typically put into some sort of high-temperature device.

I have doubts you saw the phrase "pipe bomb" mentioned in the literature. Using that term to search scientific literature only yields forensic papers about pipe bombs of the exploding type. Can you show a paper where you have seen this phrase used?
The correct term for autogenous pressure resistant vessel is autoclave (in English as well). Alternatively, for pressures up to 20 bar glass closed cap vessels can be used (there are several commercially available types).

Sauron - 12-11-2008 at 04:40

The term "bomb" does get applied to certain laboratory pressure vessels, for example calorimeter bombs. I have seen the term used more generally for pressure reactors. For instance "reaction bomb".

This of course does not mean that the device is an explosive weapon, or anything of the sort. It is somewhat startling when you first encounter the term.

Plumbing pipe of steel or stainless steel is usually cast and not very pressure resistant. The design and fabrication of pressure vessels is a specialized engineering art and best left to the experts. References in the literature to reactions in sealed tubes be they glass or metal were generally low pressure of autogenous origin.

chief - 12-11-2008 at 13:38

In autoclaves usually the material is contained within an ampoule, close-sealed, possibly under high-vacuum. An glass-ampoule can withstand high pressures, eg. a close-fused test-tube is gonna go up to 100 bar, and maybe much higher; the lower the diameter, the higher the pressure ...

Glass with 1mm strenghth, but only maybe 3 mm inner diameter, will withstand several hundered of bar.

Only: Sometimes these ampoules do fail ... and thats _one_ reason to contain them within an autoclave; another is to reach higher pressures, by filling the autoclave partially with water, so within the autoclave will be some counter-pressure, relative to the inner of the ampoule ...

Definately such setups are regularly used in some sciences, to research hydrothermal crystallizations: Filling the ampoule with the reaction-stuff and water to a precalculated %age will yield upon heating (several hundered centigrade, maybe well above the critical point of water) a known pressure. Like that volcanic and geologic conditions are made in the lab ...

Also crystals may be grown that way, eg. quartz, but economically within large steel-tubes.

Anyhow: Such experimentation I would only touch with remote-controlling, in a distant bunker where it doesn't hurt, because who is gonna guarantee, that after cooling down the ampule doesn't contain any residual pressure by some unforeseen reaction ... ???

[Edited on 12-11-2008 by chief]

[Edited on 12-11-2008 by chief]

zed - 20-11-2008 at 04:57

querjek,

Glass is generally not a suitable material for "Bombs". The experimental device that you have proposed, quite possibly might kill you.

Let's do a little thought experiment.....You want to run a reaction. for the reaction to take place, high temperatures are required. So, (as an example) you fill a deep fryer (or a big pot) with two gallons of vegetable oil. Then, you place a 500ml glass flask in it, and you turn on the deep fryer. The flask contains ethanol, water, and some reagents.....And for a little while, all seems well.

Unfortunately, as the temperature rises to the boiling point of your solvents, internal pressure in evolved. The higher the temperature goes the higher the pressure goes

With a little luck, bad luck that is, that flask might actually withstand 10 atmospheres of internal pressure before it explodes. When it does explode, there is a good chance it will blow Most of that boiling-hot vegetable oil right in your face. Along with broken glass and whatever is left of your reaction mixture. Bad news.

If you must run a reaction that requires high temperature/pressure, and you do not have a suitable pressure vessel, a coil of small diameter stainless steel tubing can sometimes be used as a reaction vessel. Small diameter tubing ( 1/4 in or less) can withstand very high pressures without rupturing.
http://www.webcoindustries.com/tubing/stainless/laserline/co...

[Edited on 20-11-2008 by zed]

Sauron - 20-11-2008 at 12:03

Commercial glass pressure reactors are rated for 40-60 psig, depending on capacity. Larger sizes = less pressure capability.

So we are talking 3-4 atmospheres only. See Parr's website for more information. Also Ace Glass, who make pressure reactors in glass. They really are constrained to low pressure reactions and relatively low temperatures (obviously strength is inversely proportional to temperature, this is also true of steel and other metals and alloys.)

kalacrow - 24-11-2008 at 11:05

One safer home brew alternative is to use a tank designed for holding gases at high pressure, aka a small O2, N2, He2 or other tank (NOT H2 or anything else. SCUBA tanks as well, but nothing that held gaseous reagents, H2 or hydrocarbons). The tanks are steel, so they might interfere with your reaction, and unless you know steel will not interfere you shouldn't use them as is. They generally are rated at 2000PSI or greater. That's usually high enough for any reaction, assuming you leave enough headroom in the tank. Also, acids could corrode the plug and cause it to pop during a reaction.

If you have a few extra dollars, you can have a machine shop cut the bottom off, and make a screw fitting that screws on the bottom of the entire tank which is rated at or above the pressure rating of the tank. That would be adequate for any pressure reaction that didn't require agitation.. you could just put a flask inside the tank, secure it so it doesn't tip or fall, and heat the entire thing. You wouldn't have a way to measure temp inside the tank, but the temp of the heating fluid would be a reasonably good approximation.

You can go farther and have the entire inside lined with glass. And have the shop add a pressure rated valve near the top of the apparatus so you can drain your reaction mixture without removing the valve at the top and/or vent the pressure from a valve that is not the gas introduction valve, thus lessening the need for worry about that seal.

At this point you have a tank that can even do hydrogenation, and if you know what you are doing you could use it in a roughly equivalent means as a Parr shaker. Not as convenient, but probably not as expensive either.

In all of these cases, you would want to seal the valve entirely with teflon before the reaction, and also have swapped out the brass or steel gas valve with stainless. Inspect the thing after and before every reaction to make sure it's not damaged, and inspect the threads in the apparatus as well.

This is all second hand from folks whom I know have done this and have talked about it. I haven't done this myself, so do the research!!!!! If you are at all worried about it, just save your money and get an autoclave and/or a parr shaker.

a pipe "bomb" is dangerous. The plumbing pipe found at hardware stores could be safely used for low pressure reactions, but anything that could run away, you are risking explosion. Unless you know the pressure rating of a particular apparatus, and the maximum pressure that could be developed by a reaction, its a gamble.

If you really want to do a reaction with a "bomb" type device, do the reaction surrounded by cinder blocks and have a shield between you and the blocks. But if the reaction involves anything more hazardous than solvents, I wouldn't try it. The danger is too great.

[Edited on 24-11-2008 by kalacrow]

MagicJigPipe - 27-11-2008 at 16:34

Quote:

The term "bomb" does get applied to certain laboratory pressure vessels, for example calorimeter bombs. I have seen the term used more generally for pressure reactors. For instance "reaction bomb".


My guess would be that the term came about because of a pressure reactor's potential to become an "explosive device". Do you think so?

And also, I have seen "bomb" in the literature before. Give me a little bit and I'll find exactly where.

[Edited on 11-27-2008 by MagicJigPipe]

Nicodem - 28-11-2008 at 00:10

The term "bomb" is a general term (not just in English but in many languages: http://www.etymonline.com/index.php?term=bomb ) and it is now widely applied also for pressurized gas vessels and as such it has certainly found its way in the scientific literature. Yet, I don't remember seeing the phrase "pipe bomb" ever being used instead of "autoclave" in the literature. It sounds as a really too dumb phrase to be used in scientific literature for something that already has a name.

497 - 29-11-2008 at 20:29

I've seen "bomb" in some older literature, like on OrgSyn. Never "pipe bomb" though..

Sauron - 30-11-2008 at 07:28

"Reaction bomb"

Sample bomb"

"calorimeter bomb"

All commonly used for pressure containment vessels and none having anything to do with explosive devices.

Substitute "vessel" or "cylinder" as appropriate if the term makes you uneasy.

Or just take a tranquilizer.