Is Acetylene Compressible in Gaseous Form?

Search for "compressibility of gasses".

Er thanks - Google, good one.

Done that and can't find any standard.

Doesn't that say something, then? Why would a standard be needed for a Process operation in the first place? Wouldn't it be commercially-sensitive information?

Agreed.

But the standards that we have seen all relate to LIQUID acetylene not acetylene in a gaseous form.

This would be a Compressed Gas Association standard or something similar not proprietary process centric but industry standard related.

<...we...> How abstruse.

the Compressed Gas Association, then.

<unsubscribes>

What is needed here is a phase diagram for the acetylene/hydrogen mixture, showing the boundaries between gas and liquid across all percentages and a range of pressures. A search using an internet search engine might reveal one.

<...a mixture of hydrogen 70% and acetylene 30%, is it compressible to say 2,400 PSI...>

With no constraints on temperature? Of course it is.

Thanks PWSlack,

But is it acceptable in the industry to compress or is the risk of a spontaneous exothermic reaction still there in gaseous form given the 70% Hydrogen / 30% Acetylene mixture?

Apologies for my layman's terms here....

Thanks again,

The circular logic to that question is a thing of great wonder:

• If a facility is already compressing this mixture then clearly acceptability must have been determined by the organisation running the facility and its indemnity insurers.
• If no compression of the mixture is taking place and the desire is to actually do this for real, then it is up to the organisation expressing that desire and its indemnity insurers to determine the acceptability of the operation. It starts with Process Engineering.

There are no other answers to it!

<reunsubscribes before Digital Dementia takes hold>

Based on the information Wikipedia gives (without an actual phase diagram), it sounds like it is unlikely that it would be possible to compress acetylene to 2400psi and have it stay in gaseous form. The triple point is stated as -80.8^oC at 1.27 ATM. Compressing as high as 2400psi would probably force it into liquid state anyway, assuming you keep the temp from climbing dramatically. This link has some good info:

http://encyclopedia.airliquide.com/Encyclopedia.asp?GasID=1

Seems to me that this would have been tried sometime in the long, forgotten past, and the guy who looked down into the crater that was left behind decided it was not a good idea.

A minibus might be handy. No-one likes to travel solo.

<rereunsubscribes, whatever..>

try this link..

http://pubs.rsc.org/en/content/articlelanding/1956/df/df9562200157

remember, Acelylene LIKELY to self- ignite at pressures above 15PSI., or approx. 1 atm. above atmospheric pressure.

It is compressible but explosive, unless stored in what amounts to an acetone sponge.

Tornado,

Agreed and thanks for that but that applies to liquid acetylene.

What about gaseous acetylene?

That is exactly my point, the whole industry is focused on standards surrounding liquid and not gaseous acetylene.

What are the standards of compressibility for gaseous acetylene?

The point we are trying to get across is that is the only way to store or pressurized acetylene is as a liquid.

...as a solution in acetone.

<rerereunsubscribes>

From Generalair.com:

"...Never permit the delivery pressure of Acetylene to exceed 15 psig..."

"...Never attempt to transfer Acetylene into another cylinder or mix any gas with Acetylene in a cylinder..."

As you should know, Acetylene is unstable as a gas, and is stored in cylinders containing a porous media and a solvent, usually acetone; once in solution it is very stable.

It sounds like you're intentionally creating a really nasty situation with this experiment.

We are getting acetylene coming out of our gasification process.

It in our Syngas just trying to figure out what can be done with it.

Thanks,

_{Don't know if I should actually say this..}

Have you considered stripping it out with acetone, if you are producing enough to make it viable?

Yes you should! As that is my next questions.

We now need to find a way to take it out or transform it into something else.

How would stripping it out with Acetone work? Again it is in a gaseous state as opposed to liquid which I believe is usually the medium it is absorbed by acetone.

Thanks

First let me ask- what do you actually want to do with it??? Why are you trying to remove it?

Good question:.

1. Our gasification process using this particular feedstock yields a powerful gas that has 30% acetylene.

2. Although an industry standard seems difficult to come by the input from this forum and industry professionals is that it should not be compressed..

3. As a result we would like to transform it into ethylene using a hydrogenation catalyst which we are trialing..

4. If #3 doesn't work then we need to remove it..

To achieve #4 you suggested acetone and that is an interesting proposal.

Interesting- the reason I asked was that I was going to suggest bubbling it into acetone solution and passing that through a platinum/ vanadium sponge at higher pressure, as you have already got the perfect mixture for hydrogenation. You could tweak your process parameters towards ethylene or fully hydrogenate to ethane depending on what your preference is.

Regardless, a hydrogenation plant is a serious undertaking. Other options would also include condensing (if -84 C is practical) and stripping with pressure swing desorption. Note for this that acetylene dissolves in a lot more than just acetone- even water can hold more than one gas volume under the right circumstances.

Apart from managing the heat why is hydrogenation such an undertaking?

Pressure, the fact that hydrogen at higher temperatures and pressure can accelerate embrittlement of metals as well as it's flammability and the permeation issues due to molecular size; also that the catalysts themselves are often a serious fire hazard if exposed to air uncontrolled.

These are issues I know about. I'm not qualified to actually engineer a hydrogenation plant.

JNB, Thanks for your intelligent comment.

We are working with a provider of hydrogenation catalysts and constructed a small unit with the catalyst, simple stainless steel piping with catalyst inside.

There were no restrictions regarding pressure only the ability to manage heat which we were told was the critical factor.

That said it didn't work and in the end the provider stated that he has never seen it not work so asked for the catalyst back for analysis, we await his feedback.

You have to apply basic chemistry- Le Chateliers principle.

Many hydrogenation catalysts also work for dehydrogenation. Because you are condensing a larger number of molecules into fewer, a higher pressure and lower temperature stresses the equilibrium to favour hydrogenation, and higher temperature/ lower pressure favours dehydrogenation.

If you tried it at atmospheric pressured I'm not surprised it didn't work. But when you say that, do you mean there was zero catalysis, only 0.5%, 5%, what?

Sounds like you need the services of a chemical engineer.

The 15 psig delivery pressure is not because of compression issues it is because the liquid acetylene cannot evaporate quickly enough resulting in possible expulsion of acetone or liquid acetylene, both being undesirable.

Both those items relate to liquid acetylene not specifically gaseous...

But thanks.

The 15 psig delivery pressure is not because of compression issues it is because the liquid acetylene cannot evaporate quickly enough resulting in possible expulsion of acetone or liquid acetylene, both being undesirable.

Wrong.

Acetylene is not liquid at 15 psig, other than at very low temperatures. In an acetylene tank, (to which the Generalair site refers) the acetylene is not liquid and does not evaporate. It precipitates out of solution, just as CO2 bubbles precipitate out of a Coke, when the pressure is reduced as you remove the bottle cap.

Given the dangers involved, perhaps you should hire an engineer.

Don't do it or you, and everyone within close range, will be blown into little tiny specs of bloody flesh.

If you have to ask, find a different line of work.

This is another example of questions/questioners that should NOT BE ALLOWED here.

<unsubscribe, again>

Please stay unsubscribed. Thanks.

With a triple C-C bond, acetylene is just dying to react with something - hydrogen is ideal! The reaction is very exothermic. Trying to compress a mixture of acetylene and hydrogen to 2,400 psi is foolhardy in the extreme. Even if it were possible in an ultra clean environment at low temperature, the slightest thing could set it off - UV light, shock or a surface irregularity in the vessel that might act as a catalyst.

Acetylene cylinders have been know to explode spontaneously years after they were regarded as "empty." Acetylene forms acetylides with various metals, such as copper and silver, Cu₂C₂ and Ag₂C₂, which are violently explosive. As JohnDG says, let us know when you are going to try this!

This thread seems to have a high number of unsubscribed yet active participants.

Guess how that seems to happen on CR4 is a whole other discussion for another thread.

There are some NDA issues I am working against hence the "Anonymousness"

I have many posts on this site and generally find two camps of responders, those interested in making a difference through intelligent comments and others who are neither worried about intelligent comments nor making a difference.

Please join the ranks of the blissfully unsubscribed!

Probably the most common (and logical) reason why you're having difficulty with this topic is that your predecessors realized/decided that it was too dangerous to pursue and/or no insurance company would underwrite the endeavor.

As with many byproduct gases in a refinery you may just have to flare it, that's what happens to methane when there's no convenient way to get it to a pipeline, the equivalent of 25% of the world's natural gas consumption gets flared every year.

Well I appreciate your comment apart from the grade school humor of the last part.

We have had some conflicting information from some industry "experts" and in the past once you weed through the BS posters CR4 is an excellent resource to identify new ideas and explore new possibilities.

Isn't that the spirit of this forum?

A very good reason for not attempting hydrogenation is the explosion and fire hazards. Have you ever seen a hydrogenation process go literally up?

Worked for a outfit that would take castor oil and hydrogenate it with hydrogen at elevated temps. About a year after I left they had an explosion. Friend got me in to see it. The hydrogen tube trailers next to the building were moved 30 ft and on their sides. The rear wall of the building was in the bay behind it. The front wall was in the warehouse across the road. Side walls were all over the place as was the roof. All of this building had blow-away panels for explosion pressure relief.

The high pressure reactor looked like a giant rose flower, all of it!

The end product for this process was the wax base for personal stick deodorants!

Don't try it. I have also heard many frightening war stories about hydrogenation.

Good Luck, Old Salt

Please don't try to compress it!!

Both gasses mentioned could ignite due to the heat developed during the compression process alone. (Just like diesel fuel ignition relies on temperature (developed from compression) alone for ignition.)

I would suggest that the investigation turn to "How do we utilise this byproduct in a meaningful manner?"

This investigation might then revert to "cogeneration" or similar where the energy potential of the material is realised and transferred into electrical or heat energy to be returned to the plant or sold.

Even if you did (safely and succesfully) compress such a mixture, you would then be faced with finding a sufficient customer base to utilise the product. You would not be allowed to use the standard acetylene connections (since your gas is a mix), you would not be allowed to use standard propane fittings and so on.

You were seeking a "standard". The absence of any standard being directly cited by the multiple learned individuals here means that until one is developed this should not be done. (Until suitable research and development of adequate standards has been completed.)

Diesel Fuel needs Oxygen (from the air intake...) to ignite and not only temperature!

Ask an acetylene factory. By hook or by crook, they manage somehow to put the stuff into bottles. Go thou and do likewise.

Tornado,

As stated we are not trying to bottle acetylene, we are asking for input on removing or transforming the 30% acetylene that is in our Syngas.

In that case, I give up. And so should you.

Please unsubscribe. Thanks

No. I wouldn't miss this fiasco for the world.

You mention a by product of your process is a "Powerful Gas" 30% of which is acetylene. This sounds like a usable fuel for an internal combustion engine since it is volatile and explosive under compression. Assuming there are no other corrosive or otherwise hazardous elements in this by product I can see an engine designed to burn this fuel and do some sort of work for you like pump fluids or make electricity. A low pressure fuel system running safely under the 15psi danger threshold could deliver this mixture to a simple piston engine. Perhaps a special valve arrangement might be in order to be sure that no dangerous overlap occurs causing an explosion in the delivery system. A low pressure injector might be possible. And at the very least perhaps try burning this mixture to heat water and run a steam engine. Maybe a low tech solution might be safest and doable with off the shelf components and already proven designs. But dear god be careful. I hurt myself badly as a young man playing with acetylene, hydrogen and oxygen trying to make a giant exploding weather balloon. Yes it DOES explode with an enormous amount of energy at what seems like unusually low pressures. Good Luck.

Good comment and we agree 1000%.

This is a very useful fuel and transport is just one possible usage.

Thanks very much for your comment and idea.

I think this is what all the SMART posters are trying to get across!!!

Google this - "acetylene bottle explosion"

And THIS!!!

Any questions?

Yes?

Contact a qualified chemical engineer that deals with the gasses you want to process!

Agreed 100% thanks. That is fully understood.

May I suggest a readily available and less costly method of getting rid of this mixture of gasses:

Follow the process that most all refineries do for the same problem, put in a flare tower and consume it in a safe manner. Some unwanted gasses, a flame and a lot of literature on the subject = no more unwanted gasses.

Good Luck, Old Salt

Ok,

We have been able to reduce the acetylene to 7% and the syngas was sent to a lab for testing for over pressurization and shock.

It passed the over pressurization and now we are waiting on the shock testing.

So far so good at 7% it's stable in our syngas and we expect it to be highly marketable.