Sciencemadness Discussion Board

300+ PSI Autoclave

Takron - 11-11-2011 at 15:13

I have been looking into the synthesis of Para-Nitrobenzoic Acid and in order to synthesize it, a reaction vessel capable of 300+ PSI is required during the reaction, as per I've seen in the Patent searches ' Here '.

However, my question is, all of the affordable autoclaves that are small and not giant wall mount behemoths, only handle pressure up to about 23 PSI and I was wondering if anyone has any information or insight into smaller more affordable autoclave units that can handle over 300 PSI?

Magpie - 11-11-2011 at 17:21

Quote: Originally posted by Takron  


... I was wondering if anyone has any information or insight into smaller more affordable autoclave units that can handle over 300 PSI?


Affordable is a very subjective term. What do you call affordable, in this case.

Takron - 11-11-2011 at 18:53

Quote: Originally posted by Magpie  
Quote: Originally posted by Takron  


... I was wondering if anyone has any information or insight into smaller more affordable autoclave units that can handle over 300 PSI?


Affordable is a very subjective term. What do you call affordable, in this case.


I was hoping for less than 300 dollars for an autoclave that can handle high pressure.

obo1234 - 12-11-2011 at 03:15

I bought an empty helium cylinder to use for high pressure work. Normal fill-pressure is 200 bar (2900 psi :o). But I haven't removed the top from it yet. It will screw-out with enough momentum, so I have bought a long iron rod to do the job, and I intend to park a car on-top of the cylinder (wrapped in rubber-sheet, and against a pavement) to keep it stationary ;)

The cylinder cost only £20. I intend to heat it directly with a camping stove, and attach a pressure-gauge on-top to assess the vapour-pressure - and hence the internal-temperature. The thread appears to be wrapped with teflon tape to keep it helium-tight, so when it is removed and cleaned I will do the same to keep chemicals inside.

One may also purchase teflon bags. I was considering putting one of these inside the cylinder, if any chemical I will be using may react with the steel.

[Edited on 13-11-2011 by obo1234]

Magpie - 12-11-2011 at 03:56

Check ebay for Parr bomb calorimeters. Some have Buna-N O-rings but I would think you could substitute Viton to allow higher temperatures.

unionised - 12-11-2011 at 08:34

anything that survives 300 PSI, nitric acid, and high temperatures isn't ever going to be cheap.

smuv - 12-11-2011 at 13:26

Why not try a transition metal oxidation of the nitrotoluene?

FWIW: I am sure you can find a stainless steel threaded tube and end caps rated for 300psi at McMaster; you might be able to get away with aluminum, but I don't know if 30% nitric acid is strong enough to passivate it.

WGTR - 14-12-2013 at 17:23

I'm synthesizing TiO2 nanocrystals from standard grade powders, as seen in this thread:

https://www.sciencemadness.org/talk/viewthread.php?tid=27624...

Several papers that I have read list procedures that involve the use of a high pressure/temperature
autoclave. While I could probably borrow one of the expensive ones from somebody, I'd rather use something
that's a bit more attainable for a wider variety of people.

The exact application involves clean water at about 400 psi and 230C. The pressure would come from the
vapor pressure of the water. It's my intention to contain the aqueous solution of powders inside of a
smaller glass or PTFE container that is contained within the pipe itself.

My first thought is using a threaded 316 stainless pipe nipple, with two caps on either end. I checked several
sources for pipe pressure ratings, this was just one that I picked to link to:

http://www.engineeringtoolbox.com/stainless-steel-pipes-pres...

It looks like 1" schedule 40 316 stainless pipe should handle about 2000 psi at 230C.

Schedule 40 nipple:
http://www.grainger.com/product/Nipple-1XAE9?functionCode=P2...

2800 psi caps:
http://www.grainger.com/product/SHARON-PIPING-Cap-2TY79?func...

While they seem expensive, I can get them for maybe half price, and they are available locally. PTFE pipe
tape might actually work in this application, but I'd have to verify that experimentally. I could also
try other pipe thread sealants (they would have to be removable, though).

The main question is a safety issue, am I about to try something really stupid? It's not my intention to make a
pipe bomb. I would be heating this thing up in the small kiln seen here:

https://www.sciencemadness.org/talk/viewthread.php?tid=26899...

This post is basically a sanity check of sorts. I think that the idea will work, but if someone disagrees, I'd
appreciate hearing about it.

[Edited on 15-12-2013 by WGTR]

confused - 14-12-2013 at 17:51

few things you might want to take note, the flash point of p-nitrobenzoic acid is 237 °C (according to sigma) so it depends on what temperature you're going to be heating the reaction vessel to.

also, i recommend some sort of a pressure relief valve to reduce the pressure should any undesirable pressure buildup occur. Ideally it should be vented somewhere far away from your heat source to prevent possible ignition. you definitely don't want anything like a pipe bomb of flammable products and mixed acids going off :D

http://en.wikipedia.org/wiki/Boiling_liquid_expanding_vapor_...

Magpie - 14-12-2013 at 18:16

WGTR: That should be plenty safe, ie, it will have a good factor of safety of 2000/400 = 5. Getting those threads to seal might be a problem, but should be solvable. Stainless steel threads tend to gall so that might become a problem, depending on how many times you reuse your vessel. One end could be welded shut, I suppose.

WGTR - 14-12-2013 at 22:00

Confused, I actually dropped in on Takron's old p-nitrobenzoic acid thread like a bird on a red tomato;
sorry for the confusion. I'm just planning on heating water in my setup, not anything flammable.

http://en.wikipedia.org/wiki/Boiling_liquid_expanding_vapor_...

This link provided a specific name to a vague concern that was going around in the back of my head.
There will be a certain amount of water in both the outer metal tube, and the inner PTFE one. I think between
my own thoughts on this, and Magpie's, the vessel should be safe enough to handle the pressure
without a pressure relief valve...if the pressure vessel is buried in something with thermal mass. My
original idea with just putting it in the kiln as is was probably not the safest way of doing this, because
the temperature in the kiln can rise rapidly if something goes wrong with the temperature control.

I'm going to give some more thought into different ways of heating this vessel, perhaps with a sand
bath, or one of the other ways mentioned in this thread:

http://www.sciencemadness.org/talk/viewthread.php?tid=17426

Thanks for the advice both of you.