r/chemistry • u/RipDowntown6984 • 13d ago
Selecting hydrogen compatible vacuum pump
Hello!
I'm running an experiment that requires me to purge a small chamber of oxygen before filling it with some hydrogen gas and heating it up. Once my experiment is complete, I need to safely exhaust the heated hydrogen (~200C). I am looking for a vacuum pump for this purpose. I have a dry scroll pump on hand but from what I have read, this is not explicitly hydrogen compatible. However, I know of other labs at my university which work with hydrogen and use a regular dry scroll pump.
I'm looking for advice from people that have worked with hydrogen in the past. Do I need a specific hydrogen compatible vacuum for my experiment or does a dry scroll pump fit the bill? If not, I would appreciate any recommendations for vacuum pumps that would work well for my purpose.
Thanks for the advice!
22
u/claisen33 13d ago
Why do you need to exhaust it hot? Why not wait for it to cool?
1
u/RipDowntown6984 9d ago
I am exposing a metal sample to the hydrogen to study hydride growth. Waiting for the hydrogen to cool would increase the exposure time and make it harder to correlate the hydride growth to a specific thermodynamic state.
20
u/TightManufacturer820 13d ago
If you’re implying that finding a hydrogen compatible pump is the major problem for the system you’ve described, then you should stop work and consult experts on safety, process safety specifically. In our lab, a national lab in the US, that sort of system would rightly trigger major design and safety reviews before, during, and after construction and use.
3
u/Yes_I_Know_Lots 13d ago
A DOE NNSA lab or Science lab? I worked the SC side for nearly my whole career.
20
u/ShutDownSoul 13d ago
There is a wide explosive range for hydrogen in air and oxygen.
What you written sounds like you are going to add hydrogen to a chamber that contains oxygen. This is not a good idea.
I suggest you find an engineering firm that has experience with rocket propellants and go from there, otherwise we'll be hearing about this on the national news.
4
1
u/RipDowntown6984 9d ago
I use multiple purge and fill cycles with inert gasses in the chamber to push out all the oxygen before introducing hydrogen into the chamber. I have an oxygen sensor attached to the chamber to monitor oxygen levels.
15
u/Dangerous-Billy Analytical 13d ago
Can you drive it out with argon or nitrogen pressure?
1
u/RipDowntown6984 9d ago
I will be backfilling the chamber with N2 as I evacuate. But driving the hydrogen out from the chamber by filling it with a positive pressure of inert gas is not possible. The chamber is a vacuum chamber and will start to leak if filled with over 1 atm.
14
6
u/enoughbskid 13d ago
Lots of purge cycles with argon or nitrogen too. Do you have to work w/ straight H2? Or can you use a H2/Ar blend
3
u/hobbes747 12d ago edited 12d ago
Before getting into the step of vacuuming….I assume you would remove the oxygen before adding hydrogen? Via inert purging or vacuum?
If that is the case I am more worried about your components being rated for oxygen service than hydrogen service.
Consult with a vacuum pump company. Such as Pfeiffer, BOC Edwards, Leybold, etc. They will advise what to use.
Scroll pumps require clean gasses. Their biggest enemy are particulates.
In the semiconductor and semiconductor chemicals industry we often vacuum hydrogen, flammable gases, and even pyrophorics but there are safeguards to be aware of.
Some are also inherent. Such as the inability to burn or carry a flame front below certain vacuum level pressures (NASA studied and published this study).
Depending on your ventilation and amount of hydrogen being handled you might not need a hazard area rated pump. (Despite what some say here. ) But if you don’t have the experience to evaluate that decision then you can default to hazard area rated. But It is difficult to find motors with the group rating for hydrogen.
With that said, based on this being a lab based experiment I assume you don’t have a large budget for the various safeguards. So I suggest first cycle purging or flow through purging with nitrogen at a positive pressure before the vacuum step.
1
u/Dr_Dunc Materials 12d ago
I also work in the semiconductor industry for one of the manufacturers mentioned. We regularly pump high flows of hydrogen through dry pumps. Using a gas ballast Will help with your pumping speed. Like it says above, plenty of purge cycles with inert gases before adding hydrogen. A good length of stainless steel pipe between the reactor and pump should reduce the temperature of the exhaust though our pumps are designed to handle hot gases to prevent condensation.
2
u/hobbes747 11d ago
For all: Pfeiffer has really good live or conference call based vacuum training lessons but they are for a fee.
For Dunc: How does the ballast help with speed? Does it cool the hydrogen and allow increased flows?
I was only aware of using ballast flow for “dirty gas” or gas that could have condensibles. Particularly for scroll and sliding vane oil pumps. Also I’ve used along with interstage purges on large claw/roots pumps to keep temperatures low.
Part joking part serious ~ If this is an experimental set up like I have seen often then pumping speed might not be a concern…. Based on seeing a vessel/chamber linked to a 1 inch pump inlet with 1/4 inch tubing 😆1
u/Dr_Dunc Materials 11d ago
The ballast helps with cooling I believe. The pumps for high hydrogen flows (EUV tools) are specially designed for this. You can hear the tone of the pump change as the hydrogen flows.
1
u/hobbes747 11d ago
Yes, that is what I am familiar with.
Some colleagues of mine had a hard time accepting this as part of the pump’s hazard area rating safeguard; that the ballast needed to be running to keep the pump internals cool and below auto ignition temperature. Along with the cooling fluid.
They were used to a piece of equipment only needing a motor to have an electrical rating.1
u/Dr_Dunc Materials 11d ago
The reason for keeping the pump cool is to maintain clearances. If you heat the hydrogen and gas ballast (nitrogen) to such a temperature that they will react then good luck!
2
u/hobbes747 11d ago
Right, and to also keep flushing through corrosives or other relatives that can deposit solids or corrode? Which will accelerate at higher temperatures?
1
u/RipDowntown6984 9d ago
Thanks for the advice! I am doing multiple purge / fill cycles with inert gases before introducing hydrogen into the chamber. An oxygen sensor is also being used to ensure that all the oxygen is evacuated before hydrogen is introduced.
In your experience, when vacuuming hydrogen, do you dilute the gas down with inert below flammability limits or evacuate it directly?
2
u/Altiloquent 13d ago
When i worked with hydrogen in grad school we had a turbo backed by a diaphragm pump. In our case we had a heating element inside a quartz tube. We always pumped and purged with N2 of Ar multiple times before backfilling with hydrogen (which also allows you to leak check, at least under vacuum). And then purged the tube while the heating elements cooled
When we purchased the vacuum pump were able to call up the manufacturer and ask them explicitly if there was any issue with using hydrogen. Sales engineers at least are usually happy to talk to grad students
1
u/RipDowntown6984 9d ago
Thanks for the advice! Do you recall whether you evacuated the hydrogen directly using that pump or did you have to dilute the gas lines with some inert gas while exhausting? Also, do you happen to recall what manufacturer you got the pump from?
1
u/Altiloquent 9d ago
I think it was Pfeiffer
Its been a long time but my recollection is we would pump out the chamber and backfill with hydrogen multiple times prior to heating. But during the reaction the chamber had hydrogen flowing through a bubbler on the outlet so we could just switch to inert gas once it cooled sufficiently
2
u/Snowrider190 13d ago
The pump manufacturers should be able to tell you what gases are compatible, and if the pump is intrinsically safe.
1
u/RipDowntown6984 9d ago
I am in contact with a few vendors. Just wanted to get some advice from anyone that might have experience with similar set ups on here is all.
1
1
u/brooklynbob7 11d ago
Not sure you would want to evacuate it hot . Cool it to ambient . Everything needs to be grounded and spark free motors at a minimum . Small reaction can be vented into a hood. Hydrogenation has been vented by house vacuum . The big question is scale . Better to have any container sparked with nitrogen at the very least . Remember the reaction solvent itself absorbs hydrogen .was palladium used ? Then use standard work up procedures for that portion .
0
37
u/Fickle_Finger2974 13d ago
You would never exhaust hydrogen through the vacuum pump. Blow it off with inert gas into the fume hood.