Sciencemadness Discussion Board - Homemade Autoclave

Homemade Autoclave

Magpie - 12-10-2010 at 17:33

Homemade Autoclave

by Magpie 10/12/10

Introduction
The reason I constructed an autoclave is twofold. Firstly I wanted it to make N,N-dimethylaniline which requires a pressure of 30atm. Secondly, I wanted to see if I could with only the help of a skilled welder.

Design Basis
The SM library book Autoclaves and High Pressure Work, by Goodwin outlined the various options for autoclave construction. I opted for the simplest design to minimize the resources needed. It would be expensive enough without machined surfaces, an agitator, or special alloys. Therefore, I chose to fabricate a flanged head vessel made of carbon steel. I chose the smallest diameter pipe, 2.5”, for a body that would still accommodate a thermowell and a pressure/fill tap penetration. The capacity is 350mL.

The pressure holding capability was first estimated using the well known Barlow’s Formula and an assumed operating temperature of 400F (204C). At this temperature Perry’s Chemical Engineers’ Handbook, 4th ed. pp. 24-41 gives a yield stress for pipe steel (A106 Gr B carbon steel) as 17,250 psi. This gave a burst pressure of 2866 psi. Then I performed a 2nd calculation using a more conservative formula found in a paper by Fred Gasche, founder and president of Autoclave Engineers, ie, “Design of Reactors and Closures,” Industrial and Engineering Chemistry, vol 48, No 5, p.838, May 1956. This calculation yielded a burst pressure of 2730 psi. Lastly, the internet delivered the ANSI/ASME B31.1 table A106 Grade B Carbon Steel Pipes – Pressure and Temperature Ratings. The maximum allowable pressure from this table for 2.5” pipe was interpolated between that for 2” and 3” pipe at 400F to be 2485 psi.

Therefore I felt there was adequate factor of safety for a test of methanol at 215C which would give a vapor pressure of ~ 760 psia.

Construction
I procured all the parts through local and internet suppliers. I spent some time searching for a qualified welder. At first I found one whose bid was way too low. Another welder really wanted the work but his shop was at least an hour away. The third welder seemed perfect: a semi-retired business owner who at one time had a staff of 20 welders and machinists. He had done almost any kind of metal work that I could imagine. I didn’t even ask him for a bid. I just gave him the job.

He also constructed a carbon steel tripod stand to support the autoclave when in use.

Cold Hydrostatic Testing
Way before putting the autoclave into service I conducted a series of tests. Initially the testing was hydrostatic using a discarded brake master cylinder and brake fluid. This testing indicated numerous leaks at the threaded fittings. After trying a couple different sealants I asked my welder to seal the connections with silver solder. I left only two threaded connections: a ¼” female port for the pressure gauge, and a ¼” female opening for the fill port. Once the leaks had been stopped the pressure was brought up 1500psi with brake fluid where it held steady.

Heaters
A silicone oil bath was used to heat the lower portion of the autoclave below the flanges. Temperature was controlled via thermocouple and PID controller. The flange head was heated with a 1000w calrod element formed into the shape of a sine wave and held in place with a radiator hose clamp. Power to this heater was controlled manually with a variac. A thermometer inserted in the thermowell was used to indicate autoclave internal temperature. The flange head was heavily insulated using kaowool overlayed with cheap firberglass insulation.

Hot Testing
This was done first with silicone oil in the autoclave and water in the bath. Then a test was done with silicone oil in the bath and water in the autoclave. For this second test the water was brought up to 215C. The final test was done with methanol, also bringing the temperature in the thermowell up to 215C.

Gasket & Thread Sealant
For all testing the gasket was a Garlock Bluegard 3000, 1/8”, ring gasket. This is composed of nitrile filled with Aramid fiber. In any use the gasket material must be compatible with the chemical compostion at the conditions of the process. Each gasket has a bolt torque requirement. In this testing phase 100 or 120 ft-lbs was used. Bolts must be torqued in 4 or 5 steps in a certain sequence.

Thread sealant for the fill port and the pressure gauge is Ace TFE.

Drawings & Pictures
The attached drawings were used to communicate my design to the welder. All parts are shown on sheet 2, “Bill of Materials,” except the ¼” pipe and fittings. These were obtained locally at a hydraulic fittings supplier.

Pictures are also attached. There are quite a few, so will post separately.

Conclusions
The autoclave did perform as intended and N,N-dimethylaniline was prepared from aniline and methanol in a 75% yield. Boiling point of the product was a steady 192C per procedure.

As noted on sheet 3 of the drawings the autoclave weighs 33lbs. It is difficult to move back and forth from its “drydock” to my hood. Also, the bolt torquing is a challenge and a two-man job.

If one could locate the pressure/fill port tree and thermowell in a smaller area, use of a smaller pipe, say 2” or even 1.5”, would be possible. The autoclave could then be made smaller and with a longer body. The autoclave book referenced above recommends a length to diameter ratio of 2 to 3. My ratio is a little less than 2.

Heating of the flanges is another possible area of improvement. With a smaller autoclave one could consider total oil immersion, thus guaranteeing a more even heating and a more trustworthy temperature indicated at the thermowell.

I would use welded fittings right from the start, minimizing use of any threaded connections.

Building and commissioning an autoclave is not quick or cheap, even with my cost saving measures. But it can take you into an area of chemistry not ordinarily accessible to the home chemist.

Errata:
Obviously the checker didn't catch the error on the number of nuts required in the "Bill of Materials." It should be 16.

autoclave dwg sht 1.JPG - 37kB

[Edited on 13-10-2010 by Magpie]

[Edited on 2-11-2010 by Magpie]

psychokinetic - 12-10-2010 at 17:45

Looking good there Magpie.
Superbly fitting with your signature

Magpie - 12-10-2010 at 18:08

Thanks psycho. Here's the pictures:

autoclave on side.JPG - 127kB

autoclave final pressure test.JPG - 127kB

gsd - 12-10-2010 at 18:44

Very nice Magpie! well done.

But I am wondering for such a small autoclave, why start with a pipe, a cap and pair of flanges with lot of high-skill welding?

Why not do it with a bar-stock and one flange and lot of skilled machining? - especially if you are using MS and not SS.

gsd

Magpie - 12-10-2010 at 19:21

Quote: Originally posted by gsd

Very nice Magpie! well done.

But I am wondering for such a small autoclave, why start with a pipe, a cap and pair of flanges with lot of high-skill welding?

Why not do it with a bar-stock and one flange and lot of skilled machining? - especially if you are using MS and not SS.
gsd

Thanks gsd.

I don't see where that would be much easier or cheaper. Also I have no experience with something like that.

I know that modern small autoclaves like those of Parr and Autoclave Engineers do use special machined heads, possibly then requiring special gaskets. But this is a totally different closure system than what I used.

I tried to stay as close to ancient technology as possible, keeping with SM traditions and all.

psychokinetic - 12-10-2010 at 21:11

I think I just got jealous.

aonomus - 12-10-2010 at 21:30

Very well done Magpie. That autoclave is pretty comparable to commercial ones in terms of pressure range and build quality. Commercial autoclaves tend to have more engineering put into the closure mechanism to allow for fast(er) opening and closing without compromising strength. They do involve gaskets made of special (read: expensive!) inert materials. They have the ability to make vessels out of materials other than 316 SS (titanium and hastelloy C)

A few questions for future development:
- Have you considered modifying a beaker (ie: cutting off the 'lip' and flame polishing) to act as a glass insert for the autoclave?
- What about mechanical stirring? I know a bit about the Parr magnetic stirring system used on their hydrogenators, and if you do decide to investigate further, send me a message and I'd be happy to help.
- Have you thought about additional ports on the lid of the autoclave? Parr and Buchi pressure vessels have ports for dip tubes, internal cooling loops, vent lines, addition funnels, etc. It all depends on your chemistry though.

watson.fawkes - 13-10-2010 at 06:11

Your welder did really good work. The pipe-cap joint is barely detectable from the photo. It's pretty clear that he ground bevels before welding. Did he put it on a lathe with a tool-post grinder to clean up?

It looks like there's a quarter-round sub flange on the unit as constructed that's not in the drawing. Am I seeing that right? It seems like too much material to be weld metal.

It there a reason you didn't weld the bottom nuts on? It's quick and makes it much easier to tighten. If the nuts need to be replaceable, welding/brazing on bits of square rod stock on two sides of a nut provides a built-in second wrench. Another option, not very applicable at the point, would be to have used automobile wheel studs and use a built-in bolt with a free nut.

As for being a two-person process, a simple plywood jig with a single central circle, holes for nut/bolt around the perimeter, and a quarter-wedge of the whole cut out to provide a space to tighten a bolt. You'd have to lift it up and rotate for each bolt.

Another small modification that would make manipulation easier is to weld on handles, either to the top or bottom or both.

I would be interested in seeing final costs by line item, to go with your bill of materials.

Magpie - 13-10-2010 at 07:59

Quote: Originally posted by aonomus

A few questions for future development:
- Have you considered modifying a beaker (ie: cutting off the 'lip' and flame polishing) to act as a glass insert for the autoclave?
- What about mechanical stirring? I know a bit about the Parr magnetic stirring system used on their hydrogenators, and if you do decide to investigate further, send me a message and I'd be happy to help.
- Have you thought about additional ports on the lid of the autoclave? Parr and Buchi pressure vessels have ports for dip tubes, internal cooling loops, vent lines, addition funnels, etc. It all depends on your chemistry though.

Thank you anonomus.
- I really like that idea about a glass beaker insert. Having a glass-lined autoclave would be the cat's meow.
- Mechanical shaft stirring would mean a packed gland or a mechanical seal and there is no room for one. A magnetic stirrer, however, would be great! Thanks for the offer of help on that.
- There's just room now for the pressure/fill port tap and the thermowell, so couldn't add anything more.

Magpie - 13-10-2010 at 08:22

Quote: Originally posted by watson.fawkes

Your welder did really good work. The pipe-cap joint is barely detectable from the photo. It's pretty clear that he ground bevels before welding. Did he put it on a lathe with a tool-post grinder to clean up?

No, I don't believe he did. He does have a complete machine shop, however.

Quote: Originally posted by watson.fawkes

It looks like there's a quarter-round sub flange on the unit as constructed that's not in the drawing. Am I seeing that right? It seems like too much material to be weld metal.

No, he just welded the slip-on flange as is.

Quote: Originally posted by watson.fawkes

It there a reason you didn't weld the bottom nuts on? It's quick and makes it much easier to tighten. If the nuts need to be replaceable, welding/brazing on bits of square rod stock on two sides of a nut provides a built-in second wrench. Another option, not very applicable at the point, would be to have used automobile wheel studs and use a built-in bolt with a free nut.

The welder suggested those tack welds on the bottom nuts too. But I like being able to take everything apart for inspection and cleaning.

Quote: Originally posted by watson.fawkes

As for being a two-person process, a simple plywood jig with a single central circle, holes for nut/bolt around the perimeter, and a quarter-wedge of the whole cut out to provide a space to tighten a bolt. You'd have to lift it up and rotate for each bolt.

I thought about that also. But at 90-120 ft-lbs it's a 2 man job anyway. Unless your jig was bolted to the floor and some strong vertical force applied the autoclave would just pop out.

Quote: Originally posted by watson.fawkes

Another small modification that would make manipulation easier is to weld on handles, either to the top or bottom or both.

Those would help.

Quote: Originally posted by watson.fawkes

I would be interested in seeing final costs by line item, to go with your bill of materials.

I'll pull something together.

For the real cost I would include tools (1/2" drive torque wrench), silicone oil and can for same, insulation, aux heater, tripod stand, small diameter thermometer, gaskets, 1/4" piping and fittings, and most of all: welding costs. I'm afraid to add that all up.

Magpie - 13-10-2010 at 10:05

Quote: Originally posted by watson.fawkes

It looks like there's a quarter-round sub flange on the unit as constructed that's not in the drawing. Am I seeing that right? It seems like too much material to be weld metal.

I see what you are saying here now. The drawing is just representational in that area.

Magpie - 13-10-2010 at 10:11

Quote: Originally posted by aonomus

- Have you considered modifying a beaker (ie: cutting off the 'lip' and flame polishing) to act as a glass insert for the autoclave?

The outside dimensions for a Berzelius tall form beaker are 57mm x 104mm. That would be nearly perfect as the inside dimensions for the autoclave straight side body portion are 61.5mm x 101.6mm.

What's the best way to cut that lip off? Will a diamond wheel on a Dremel tool do the job?

Magpie - 13-10-2010 at 11:59

Quote: Originally posted by watson.fawkes

I would be interested in seeing final costs by line item, to go with your bill of materials.

Autoclave Material Costs

4” of pipe…………………….6.50
Pipe cap………………………6.83
Slip-on flange……………12.35
Blind flange………………18.94
8 stud bolts………………11.62
16 nuts………………………18.70
16 washers.................4.15
Thermowell................34.50
Pressure gauge.........37.08

TOTAL.....................$150.67

aonomus - 13-10-2010 at 16:52

There is a catch to the magnetic stirring used on Parr hydrogenators which means the bearings and seals don't need to withstand the pressure differential between inside and 1atm, just a tiny bit of pressure until it equalizes, and then keep the reaction mixture out of the stirrer mechanism.

Magpie - 13-10-2010 at 18:25

Kimax makes a Berzelius beaker without a lip, otherwise same dimensions.

I really don't want to even think about seals and bearings for an agitator shaft.

aonomus - 13-10-2010 at 19:12

Probably the best way to cut the lip off is to score the circumference and use heat-shock to break the seam.

See: http://www.youtube.com/watch?v=sFXngPx3w3M

Because borosilicate glass has a lower thermal expansion coefficient, you might have trouble using heat-shock to make a nice crack propagate around the circumference.

You should come up with a plan to fill the bottom semi-circular portion of the vessel with some sort of heat transfer medium (metal BB's come to mind) so that all sides of the glass insert are evenly heated.

Again, cool work for super-cheap autoclaving goodness. Look forward to seeing the actual writeups from using it for chemistry.

Magpie - 13-10-2010 at 20:00

Quote: Originally posted by aonomus

You should come up with a plan to fill the bottom semi-circular portion of the vessel with some sort of heat transfer medium (metal BB's come to mind) so that all sides of the glass insert are evenly heated.

Yes, the heat transfer to the glass beaker would be terrible because of the air gap, not just on the bottom, but also on the side of the beaker. What is needed is a heat transfer fluid that is inert to reaction conditions and gases.

Quote: Originally posted by aonomus

Look forward to seeing the actual writeups from using it for chemistry.

I might do that for N,N-dimethylaniline.

watson.fawkes - 13-10-2010 at 20:44

Quote: Originally posted by Magpie

I really don't want to even think about seals and bearings for an agitator shaft.

The yellow pages under "hydraulic equipment and supplies" should yield adequate seals. You'd likely need a stack of V-seals, just like those used to seal hydraulic actuator cylinders. They do come in Viton; not sure about PTFE.

The bearings aren't any special problem, since you can use a pair of them outside the pressure zone. The sequence on the shaft look like stirrer > seal stack > bearing > bearing. A taper bearing is adequate for one of those, I don't see a need to add a thrust bearing. Remember, the outward force on, say, a 3/8" shaft at 200 psi is about 221 lbs, which a decent taper bearing will handle.

The expensive part is the machining, as you've no doubt learned. Speaking of which, how much was your outside labor cost? I was curious about the material vs. labor expense for the project.

aonomus - 13-10-2010 at 22:06

Regarding mechanical stirring: http://www.parrinst.com/default.cfm?Page_ID=164

The way Parr does it is by having a chamber above the vessel that is at pressure with the rest of the vessel, and the seal in the lid just has to be good enough to exclude any liquids from the compartment. Inside a shaft with embedded magnets transfers the rotation from the motor to the shaft inside. The seals are PTFE with cooling water running through the gland area to keep the temperature cool. It would appear that you might even be able to order one of those from Parr (at an arm and a legs cost!)

Edit: Another potential use comes to mind: supercritical fluid extraction of compounds from products using CO2. I'd suspect if you loaded the autoclave with the right amount of say, coffee beans and dry ice, sealed, then heated, you could get a stable SCF extraction going, then release the pressure to let your caffeine just appear at the bottom. This could be an interesting development

[Edited on 14-10-2010 by aonomus]

Magpie - 14-10-2010 at 07:57

Quote: Originally posted by watson.fawkes

Speaking of which, how much was your outside labor cost? I was curious about the material vs. labor expense for the project.

welding........................................240
blind flange drill & tap ................65
silver soldering............................60
silver solder.................................42

TOTAL......................................$407

Rosco Bodine - 14-10-2010 at 08:43

Here is another idea which might work okay. What about converting a tie rod hydraulic cylinder assembly, removing the operating rod and piston, leaving an empty chamber ? The way the cylinder sleeve fits into a bored socket in the end plates having an O-ring annular seal, there is not any real torque requirement on the tie rods, so nuts lightly tightened just sufficiently for mechanical takeup would do the trick of just holding the assembly together. The conversion could be done more simply than building something entirely from discrete parts.

[Edited on 14-10-2010 by Rosco Bodine]

Magpie - 14-10-2010 at 15:49

A further enhancement that might be possible for my autoclave is enameling. But I understand from Wiki that this is a tricky process and might not be an option for pipe steel due to high carbon content. I would also need access to a kiln as used in pottery making. If I couldn't do it myself I would think labor costs would be high.

aonomus - 14-10-2010 at 22:30

I wouldn't bother with enameling the surface, if you set it down too hard you risk chipping the surface and wasting your effort. Additionally it introduces additional material that may react with the reaction mixture in the headspace. If you're looking for corrosion resistance, maybe try bluing the steel?

Waffles SS - 31-5-2011 at 08:48

Excellent Magpie
Maximum how much pressure your auto clave can take?

Magpie - 31-5-2011 at 09:16

Thank you. In the ANSI/ASME B31.1 table A106 Grade B Carbon Steel Pipes – Pressure and Temperature Ratings - the maximum allowable pressure for 2.5” pipe was interpolated between that for 2” and 3” pipe at 400F to be 2485 psi.

I did not test the autoclave to destruction so we have to go with the calculated value. Using a safety factor of 2 an upper limit would be: 2485psi/2 = 1243 psi = 84.5atm at 400F (205C). If a higher temperature is used the maximum safe operating pressure would have to be de-rated accordingly.

Keep in mind that this is not my field of expertise.

The WiZard is In - 31-5-2011 at 13:39

Quote: Originally posted by Magpie

Thank you. In the ANSI/ASME B31.1 table A106 Grade B Carbon Steel Pipes – Pressure and Temperature Ratings - the maximum allowable pressure for 2.5” pipe was interpolated between that for 2” and 3” pipe at 400F to be 2485 psi.

I did not test the autoclave to destruction so we have to go with the calculated value. Using a safety factor of 2 an upper limit would be: 2485psi/2 = 1243 psi = 84.5atm at 400F (205C). If a higher temperature is used the maximum safe operating pressure would have to be de-rated accordingly.

Keep in mind that this is not my field of expertise.

I would think of replacing the bolts/nuts periodically. While the
internal pressure is trivial... depending on how high a toque
value you use when you tighten the bolts/nuts - the bolts will
stretch/weaken. When gas/diesel engines are taken down
the head bolts are never reused only replaced, and this is after
one use. Constantly removing/replacing your bolts put a lot
of strain on them. No doubt there is mechanical engineering
info on this out there somewhere.

Oh and by da - have you considered a safety pressure relief valve?

Magpie - 31-5-2011 at 14:29

Quote: Originally posted by The WiZard is In

Thanks for the tip about the bolts. I've probably reused them about 5 times, mostly during shake-down. Originally I was torquing to 100 ft-lbs but ended up only using 80 ft-lbs.

I did plan to use a safety relief valve. It would replace the fill port plug. I had actually found a good one for under $100, but never bought it. The main reason being that the plug was sealing and I was concerned that a new male thread device might not seal. As indicated, I had a lot of trouble getting the threaded connections to seal.

bobm4360 - 31-5-2011 at 22:03

Regarding bolt life-
An easy check is, if on opening, one of the nuts is significantly easier to break loose, then it's time to replace all fasteners

Exceeding the yield strength of three-quarter inch studs is not easy.........

Regards,
Bob

The WiZard is In - 1-6-2011 at 10:41

Quote: Originally posted by bobm4360

Exceeding the yield strength of three-quarter inch studs is not easy.........
Regards,
Bob

My 60-ton hollow core hydraulic cylinder does it with a
snap. If not I also own a 100-ton one. Any who - bolts are
torqued to "50-60% of the fracture torque... The tension in a bolt
tightened using this procedure will be about 60 - 70 per cent of the
elastic limit (yield strength) of the bolt material."

Now this do be for the bolts first use ... after the 2 -3rd use....
the bolt has been stretched and has lost a lot of strength.
This is why in critical application the bolts are only used once.

Speaking upon bolts - was watching some TV pgm. they were
installing a really large diesel engine in a ship. The bolts
used to hold the engine to its mounts were first
cooled in LN2 so they would fit into the holes. Any vibration
by an engine that large would in short time rip the
engine free/sink the ship.

Trivia - During WWII when the American Army shipped
RR locomotives to Burma ... the cribbing used shipboard
was - lead blocks.

Magpie - 1-6-2011 at 20:13

Quote: Originally posted by The WiZard is In

I looked up some bolt strength data and according to this site a torque of 100 ft-lbs places a stress of 30,000 psi on a 3/4-10 B7 bolt:

http://www.lamonsgasket.com/html/bolt_torque_data.html

The minimum yield stress for this bolt, according to this site, is 105,000 psi:

http://www.americanfastener.com/technical
/grade_markings_steel.asp

And these folks claim the B7 will maintain its strength to 1000F:

http://www.lightningboltandsupply.com/reference.html

Therefore, I don't understand why I should be replacing these bolts. What am I missing?

[Edited on 2-6-2011 by Magpie]

----------------------------------------------
I just realized that I forgot to add the pressure load to the bolt stress. Therefore, for 1500psi internal vessel pressure:

Pipe ID = 2.323 inches.
Force developed at 1500 psi = [(3.14/4)*(2.323in)^2](1500 lb/in^2) = 6354 lbs

Bolt tensile diameter for 3/4-10 coarse thread bolt = 0.334 in^2.

Bolt stress due to the load at 1500 psi = (6345 lbs)/[(8)(0.334 in^2)] = 2378 psi

This is an insignificant addition to the 30,000 psi developed by torquing the bolts to provide sufficient gasket compression.

[Edited on 3-6-2011 by Magpie]

watson.fawkes - 3-6-2011 at 05:24

Quote: Originally posted by Magpie

I looked up some bolt strength data and according to this site a torque of 100 ft-lbs places a stress of 30,000 psi on a 3/4-10 B7 bolt [...] The minimum yield stress for this bolt, according to this site, is 105,000 psi

The issue is that the yield strength and tensile strength listed on specification are "short time" values and do not take into account "long time" effects, particularly creep. Simply put, you can keep a piece of metal within its elastic deformation zone for a short time and it will spring back. You keep it there long enough and it's no longer fully elastic; it doesn't spring back all the way. The closer you are to the yield point (the transition between elastic and non-elastic behavior), the quicker the long-term effects start appearing.

Oh, and it's also temperature-dependent, happening quicker at higher temperatures.

So you're using bolts at 1/3 their yield strength, which is plenty of safety margin ordinarily. You're operating at elevated temperature, but not really that elevated (it's not visibly glowing or anything). And they're torqued down only for individual runs, not torqued constantly for weeks on end. And you're not using it on a daily basis, either. On balance, I think you're likely fine.

Learning to recognize the signs of bolt failure, though, would be a good idea. You have the advantage that you built and understand the apparatus, as opposed to a naive user that's just following directions with no particular understanding of the engineering involved. I should note, however, that this issue may well be important commercially, as a number of the autoclave designs I've seen use some clever mechanics to avoid loading any screw threads with internal pressure.

Panache - 6-8-2011 at 16:41

Could you briefly and qualitatively describe the rundown of the testing procedure from the standpoint of how you were feeling about each successive test. I ask because i often get nervous when testing new bits of kit and stop things early.
Did you get out of the room initially before each test, when the threaded sections failed how did you observe this?
Were you shitting yourself during the first methanol run? On subsequent runs?

As an aside you need to parkerize that bastard to schmic it up even more and for corrosion protection, works great on mild steel. Nitric/phosphoric/MnO2 solutions do it but kits cost like $30 from gunshops or online, not worth fucking around making it yourself, solutions are reusable several times also.

Agitation can be provided by attaching anything with vibration, this would also resolve your bolt concerns, as in you would simply need to replace them every go without question, oscillation effects inside could be interpolated from the observed oscillations on the silicon oil surface, which would obviously need to be larger to encompass fitting of the device producing the vibrations, an oil filter clamp around the main body could serve as a means of attaching the vibrating source. This may serve as a means of agitation that is far far simplier (and therefore cheaper and safer) than one involving any modification of the actual vessel.

Magpie - 6-8-2011 at 18:54

Quote: Originally posted by Panache

Could you briefly and qualitatively describe the rundown of the testing procedure from the standpoint of how you were feeling about each successive test. I ask because i often get nervous when testing new bits of kit and stop things early.
Did you get out of the room initially before each test, when the threaded sections failed how did you observe this?
Were you shitting yourself during the first methanol run? On subsequent runs?

I was not concerned about rupture during the testing phases because I was performing a hydrostatic test. I used brake fluid since an automobile brake master cylinder was my source of pressure. You can read more about hydrostatic testing here:
http://en.wikipedia.org/wiki/Hydrostatic_test

The leaks paths were very small so leaking would just show up as a dripping of brake fluid near the leak source, in my case the threaded joints. There was no squirting or such.

Once the autoclave had passed the hydrostatic tests I felt comfortable bringing it up to pressure with the methanol gas. The pressure I achieved here, which was completely in line with the expected methanol vapor pressures, did not concern me as it was well below the pressure I achieved during hydrostatic testing. Also, I personally supervised all phases of material selection and autoclave construction so was comfortable with those aspects. But it was successful hydrostatic testing that was the ultimate assurance. At no time did I leave the pressurized autoclave. Nor did I experience any diarrhea.

Lambda-Eyde - 30-3-2012 at 10:26

Magpie, let me first say that I'm thoroughly impressed and extremely jealous. Some day or another I'll have to put one together too. I have a reasonably sized machine shop, so I could machine the body out of bar stock as suggested by gsd. But I lack a mill and I'm a horrible welder, so I'd have to outsource that to someone else.

Have you performed any other high-pressure syntheses with the autoclave, or do you have any plans? While reading about sandwich compounds (metallocenes etc.) I noticed some complexes with cyclooctatetraene (COT). COT is by no means cheap, my local supplier sells 1g at ~50$. The cheapest I can get is 250 mg for half the price. I was surprised to find out that COT can relatively easily be synthesized by heating acetylene with nickel cyanide and calcium carbide in THF at 15 atm/60 degrees C - well below the maximum operating conditions of your autoclave. And it gives 90 % yield!

The original reference by Reppe (in German) can be found here.

[Edited on 30-3-2012 by Lambda-Eyde]

Magpie - 30-3-2012 at 12:08

Quote: Originally posted by Lambda-Eyde

Have you performed any other high-pressure syntheses with the autoclave, or do you have any plans?

Sadly, no. It is sitting quietly in my storage locker awaiting its next assignment. It's a shame I can't loan it out to other members who could put it to good use.

Hexavalent - 9-4-2012 at 04:05

Very, very nice Magpie. You fully deserve your title!!

One day in the summer I could attempt this, but to a smaller vessel size . . .my organic work tends to be less than 100ml at all times. My grandfather is a hydroelectric power station technician and my uncle a gas man/plumber, so both have a good knowldedge of parts and welding techniques. The autoclave could also be handy for sterilzing some of the instruments I use after an enjoyable dissection . . .

Mekwarrior - 20-8-2013 at 21:48

I'm new but I have an extensive background in Hydraulic's and Hydrostatic's 25 year's and if you are in need of a pressure vessel you could call around or just stop and ask a Hydraulic Repair Facility about scrap Hydraulic Cylinder's.All the hard work is already done except modifying the rod gland for gauge and port's. I've tested some to over 20,000 psi and all the shop will get is a scrap price for there dumpster pickup. I'm an Electronic's tech too.I'm here to brush up on Basic Organic Chemistry to recycle my own Board's and connectors.

watson.fawkes - 21-8-2013 at 05:27

Quote: Originally posted by Mekwarrior

if you are in need of a pressure vessel you could call around or just stop and ask a Hydraulic Repair Facility about scrap Hydraulic Cylinder's.All the hard work is already done except modifying the rod gland for gauge and port's.

The biggest problem here is chemical compatibility. Many of the seal materials used won't withstand chemical attack at the high pressures and elevated temperatures used in reactors. A secondary problem is that you've got a hydraulic chamber, presumably with a movable rod, and inside you're generating a fair bit of pressure, so you'll have to prevent the rod from flying out.

Having said all this, there still might be some application for your idea, but it's not going to substitute for a purpose-built chemical autoclave.

Magpie - 14-6-2017 at 12:22

I have made a modification to my autoclave to provide stirring. This consists of a packing gland that accepts a 5/16" stirrer shaft. This gland was built to my specifications by a machinist.

I have the gland packed with 4 rings of 1/8" ptfe square packing. Most gland designs incorporate a lantern ring to allow the flow of process fluid as lubricant. This adds a complication to the fabrication so I decided to try using the gland without one. It can be added later if required.

In the picture below I ran the stirrer at 250 rpm using my small stepper motor drive.

This will allow syntheses under pressure with stirring. The first one I want to try is the Kolbe process to make salicylic acid using CO2 at 100psi. Substrate is sodium phenoxide.

Questions, comments, and suggestions are welcomed.

installing ptfe packing rings

gland with 4 rings and follower.jpg - 118kB

gland with 4 rings and gland follower

flange assembly

testing mode for the stirrer

[Edited on 14-6-2017 by Magpie]

Magpie - 5-7-2017 at 20:52

I tested the autoclave packing gland with CO2 (est. pressure 900 psig). The gland sealed well with the shaft turning. However, an unanticipated problem occurred: the internal gas pressure blew the shaft straight up and out hitting the ceiling of the hood. It then bounced off the floor of the hood then slapped me on the arm. This did not hurt much but left a 2" bruise.

I have a fix for this as shown in the picture below. The calculated force on a 5/16" diameter shaft is 76 lbs for a 1000 psig internal gas pressure. Using 16 bricks I constructed a restraint for the shaft/motor. I'll test again tomorrow.

autoclave shaft counter weight.jpg - 140kB

[Edited on 6-7-2017 by Magpie]

JJay - 6-7-2017 at 00:11

Wow, that sounds pretty scary. An autoclave like that is only a dream to most hobbyists.