Nitrogen

I don't think much.

I don't have the technical answer, but one time I had the brilliant idea of using liquid nitrogen to strip old lead based paint that was layered on the wood of an historical building. I just went and got some, and had the guy pour it into a stainless steel thermos...which I capped. It didn't explode.

why are you asking? any liquid with similar properties will change to a vapor once it is no longer held under pressure or its temperature rises to a point where it will boil off. do you have a real world application or just a theory?

Thanks - It is a question of maintaining constant volume on raising the temperature from below -200C to -say - 25C. at 200C the pressure is such that it gently boils off (open dewar flasks etc). But what if you cap as the T rises so will the P but to what? Real problem.

Well here is the phase diagram for Nitrogen from Wolfram.

What do you think will happen?

Honestly, all the information you need is here. Well this and the universal gas law of PV=nRT. You just need to think a little about what this diagram is saying.

Grateful to you. Yes I am familiar with the Wolfram graph but I confess I don't quite understand what happens after it ceases to be a liquid. I need someone to convert PV=nRT to 25C for nitrogen which at -200c was a pourable liquid. I realise it is the 'perfect gas' equation but not really quite what, in practical terms, it means. But I think it means that liquid nitrogen (so at high pressure or very low temperature) will be at about 4,000 psi at 25C or so. The Wolfram chart shows 10(3) or 1,000 psi at about -50C and then it goes off chart. The other thing is to know quite what is the practical distinction between a supercritical fluid and a liquid. I wish to know so I may know if the pressure generated by a supercritical fluid is a constant until it ceases to be supercritical or other than gaseous. Any help gratefully received.

A formula without explanation of the used parts is not very useful. The gas law (Boyle- Gay Lussac) is

p.V = constant T where p is pressure, V = volume and T = the gas constant for m as a constant also.

For n kmol of a ideal gas

p.V= nRT (where R = molaire or universal gas constant approx: 8314.41 J /(K.kmol)

units are SI.

This gas law is for Ideal gasses only.

JMCB-

To simplify your questions, hopefully not too simplified, and answer your question:

Take the transportation of cryogenic N₂ in a tractor trailer, an MC338 trailer (cryogenic liquid trailer, the one with the dog house on the back). When the trailer is loaded two hoses are connected, one in the top where the vapor is and one at the bottom where the liquid is. Both are opened and the nitrogen is pumped into the cryogenic tank of the trailer. As the liquid is pumped in, the vapor at the same pressure as the liquid is allowed to exhaust from the top where it is returned to the bulk storage tank. Now the nitrogen, liquid and vapor, are in the trailer and at the same pressure. The equalization of the liquids and vapors permits small transfer pumps to be used instead of high pressure pumps to transfer from one vessel at a lower pressure than it is in the receiving vessel.

As the trailer travels the nitrogen, both liquid and vapor, begins to warm up from the sun, ambient heat, etc. To counter the heat this small amounts of nitrogen are released to keep the nitrogen cool. This cooling is provided by the latent heat of evaporation. If this was not released the temperature would continue to rise. As it raises the pressure increases due to the ideal gas law as others have explained. Since the liquid and vapor are in the same container the pressure of both is equal, ideal gas law again.

Eventually you would reach a point within the temperature increasing where the pressure would exceed the pressure rating of vessel. Sorry, but I don't recall what range this would be in. As the temperature rose, more liquid turns to vapor but the same pressure increase slows down the rate of evaporation within the vessel to make this a slow process. To avoid this most containers with liquid/gases under pressure have safety releases. Most are made from low temperature melting metals so that they will either release from pressure or melt from excessive heat such as a flame. Some, as in the trailer, are pressure and/or temperature safety valves. Exceed one and it opens up. This is what makes those YouTube videos so dramatic for flammable materials tankers that catch on fire. First it looks like a large torch flame and all of a sudden it explodes into a ball of fire. The torch flame is the safety releasing gases that catch fire. The explosion is when the pressure within exceeds the rating of the vessel and it explodes. The large ball of fire is called a BLEVE, Boiling Liquid Expanding Vapor Explosion.

When the nitrogen trailer arrives at the customer location it is transferred to a cryogenic storage tank in the same manner as the trailer was loaded, a vapor hose, a liquid hose and a pump. The only difference is in the pumping the liquid, it is pumped out of the trailer and into the storage tank. In order to equalize the pressures in both tanks prior to pumping the vapor hose valves are opened and the higher pressure equalized with the lower pressure to a common single pressure.

Both tanks, in the vapor sections and the liquid sections of each tank are at the same pressure. The liquid stays liquid because the vapor pressure stays constant and prevents the liquid from expanding.

Remember also that as pressure is increased the boiling point also increases and as the pressure is decreased the boiling point also decreases.

Good Luck, Old Salt

Thank you so much my dear Gurus, DVMDSC and Old Salt. Yes I understand what you are telling me and to have it made plain has been hugely helpful. I understand the equation and I understand that in normal circumstances cold liquid Nitrogen (with its vapour header space is vented) to keep it cool and the vapour and liquid P is equal so any php can be used to pass it from one tanker to bulk storage - cold and so under no great pressure or - as graphically shown, canisters fail. But what I need to know is really three things. 1. What is the formula to give me the thickness of what grade steel or titanium to contain what quantity of nitrogen which filled the container cold and as a liquid with low VP, and which will continue to contain the nitrogen as the temperature rises to ambient without venting; and 2. At what pressure would the VP be in such circumstances of containment at ambient T; and 3. If one were to begin to occasionally vent the nitrogen at the pressure 2 would the pressure it vents at stay steady (as does CO2 when vented from liquid state (815psi or so at ambient) - until just gas was left to vent? Many thanks for you kind help to a layman.

This liquid nitrogen tank has an operational maximum pressure of 3 bar:

http://www.wessingtoncryogenics.com/products/cryogenic-vessels/phv-series-tanks.html

Note that venting does not cool the contents of the tank; it cools the objects surrounding the vented gas on the outside, the tank being protected by the reduction in pressure.

Amending my previous post #7, the DOT 338 cryogenic tanker is dewar type with a vacuum insulation between the inner liquid/vapor contacting vessel and the outer shell (outside you see). They made with various maximum working pressures depending upon the material they will be hauling. The trailers with the highest maximum working pressure are those which are rated at 500psi. Since safety pop-off valves are usually rated anywhere from 105% to 115% of the working pressure and pallet type safety exhaust devices are usually rated 5% to 10% above that pressure.

Based on the above and current DOT and Safety Standards the pressure you are looking for would be less than 500psi or slightly above that but no more than 550psi. Yes this is not an extreme scientific way to find the answer but it is a way to approximate (which is more common than many think) the pressure through the work of others done before this question came up.

There is no reason to reinvent the wheel if someone has invented the piston and sliced a piece off of the end of it.

Good Luck, Old Salt

*!*

Unfortunately this is not what the OP asked for. You end up with describing existing safety systems or the effect of it.

OP has a hypothetical question. thus without all the hidden build in protections. I fear that your answer give a bad wrongmisrepresentation. What do you think about, say up to 3-10 times your indicated 500 psi pressure without safety systems? If the tank holds out.

N2 in cylinders may have 130 bar or higher. (13 MPa or 1,885.5 psi)

It depends on local safety regulations and test when the safety valve operates.

Not as reply to you but in general:

P is NOT the symbol for pressure but for Power in all science branches.

pressure = p, or p.

Hope this helps the topic. D.

dvmdsc-

Thank you for bringing the discrepancy to my attention. It has been a long time since I solved hypothetical's just to solve them. Labs change a lot when the transition from academia to industry takes place. It is one thing to learn for the sake of learning but different when your goal is to keep the products continuing to go out the shipping door. As one philosopher wisely stated "It is hard to remember that your goal is to drain the swamp when you're up to your a __ __ hole in alligators!"

With over 1/3 of the 28 comments coming from the originator or the question it is extremely difficult to determine what the OP was/is. I am well aware of the pressures of vaporous N₂ in cylinders but that too is difficult to keep clear under the conditions that have been handed out then reexamined, changed, clarified, etc. It is also confusing to be projecting this in a hypothetical manner where the conditions stated would be extremely difficult, if not impossible, to replicate in real world conditions.

From a practical standpoint vaporous nitrogen at room temp can be compressed to extremely high pressures. Liquid cannot when it is in a closed vessel with vapors. The hypothetical vs. the practical. Having had my life immersed in the practical end of engineering until my retirement, I tend to lean towards what works instead of what cannot be produced except in the minds of the seekers. Since retirement I have tried to forget as much about it and the pressures included. Now I can spend a greater part of my time doing what I enjoy and not what has to be done to earn the dinero.

Good Luck. Old Salt

The pressure in your enclosed tank will go up, right until a safety device will open.

You need to build that in your tank. Pressure cylinders, used for welding and other application have that device build in the valve- (manifold). These release the pressure to a permissible level.

For that reason temperature of the cylinder should be kept under 52 degrees Celsius (125 degrees Fahrenheit)

When no safety device, the pressure will go up and up until your cylinder explodes or the valve shoots out.(whatever comes first)

The "if released slowly" question has been answered by Old Salt. The pressure you might obtain out of Redfred's link. (wolfram)

Forgot this:

But at what pressure would the nitrogen 'explode' at 25C? on the assumption that a vessel would fail at that P. Or put another way. If a vessel was made to contain nitrogen in liquid form at 25C at what pressure would the container be? I am seeking answers to the 3 questions but it seems no-one has contemplated Nitrogen in any state but for cryogenic use (except for all sorts of things at atm). It is its qualities as liquid at ambient temperature so high pressure that interest me - in particular what is the pressure curve as T rises but containment remains 100% - no safety valves no venting before 25C.

Sigh, the Nitrogen does not explode the container explodes at the maximum structural pressure that it can contain.

Let's go back to the ideal gas law and discuss the factors.

PV=nRT

P→ Pressure. This is the value you wish to know. This is what you wish The unit of pressure will depend on the other unit values chosen.

V→ Volume. This has not been specified but can be assumed to be a constant value for this discussion. This is then an unknown constant.

n→ Quantity. This is the number of molecules of your ideal gas. Presuming that no leak happens this will be another unknown constant.

R→ Gas constant. This is a known constant that was long ago found to be the combination of two other constants; Avogadro's and Boltzmann's constants. The unit selection will determine the magnitude of this number.

T→ Temperature. This value must be in one of the absolute temperature scales. So instead of 25°C this should be 298 K.

So why have I labored so hard to explain all of this? Well I am occasionally a glutton for punishment but my point here is that there are two unknown constants as this problem has been stated. There is also the unstated initial pressure and temperature values of the liquid nitrogen. Referring back to the Wolfram phase diagram you should notice that the triple point for Nitrogen tells you that liquid nitrogen must be under some pressure in order to exist.

In short, insufficient data provided.

DEAR REDFRED, THANK YOU> CAN I TRY AND TAKE IT FURTHER. Sigh, the Nitrogen does not explode the container explodes at the maximum structural pressure that it can contain. YES I UNDERSTAND THAT AND THE SIGH - ! ONE THING I NEED TO KNOW IS THE FORMULA ONE APPLIES TO DETERMINE CONTAINER WALL THICKNESSES ONCE ONE HAS ESTABLISHED WHAT P THE CONTAINER HAS TO WITHSTAND. ALLOWING FOR A BURST POINT AT 200% OF THE P AT 298K Let's go back to the ideal gas law and discuss the factors. PV=nRT - RIGHT. Pressure. This is the value you wish to know. This is what you wish The unit of pressure will depend on the other unit values chosen. YES (AND DOES IT STAY CONSTANT AS DOES LIQUID CO2 ON VENTING IT OUT UNTIL ALL THE LIQUID HAS BECOME GAS?). Volume. This has not been specified but can be assumed to be a constant value for this discussion. This is then an unknown constant. LET THIS BE 20ML/CC Quantity. This is the number of molecules of your ideal gas. Presuming that no leak happens this will be another unknown constant. THIS FOR NITROGEN. Gas constant. This is a known constant that was long ago found to be the combination of two other constants; Avogadro's and Boltzmann's constants. The unit selection will determine the magnitude of this number. WHICH IS? Temperature. This value must be in one of the absolute temperature scales. So instead of 25°C this should be 298 K. VERY WELL, BUT WOLFRAM DOES ALLOW ALTERNATIVES. BUT I UNDERSTAND KELVIN (BUT NOT AS INTUITIVELY AS C. So why have I laboured so hard to explain all of this? BECAUSE YOU ARE A GOOD HEARTED GURU! (I TOO HAVE BEEN KNOWN TO HELP THE ODD SOUL TOO) AS Well I am occasionally a glutton for punishment but my point here is that there are two unknown constants as this problem has been stated. There is also the unstated initial pressure and temperature values of the liquid nitrogen. Referring back to the Wolfram phase diagram you should notice that the triple point for Nitrogen tells you that liquid nitrogen must be under some pressure in order to exist. I THINK ONE COULD TAKE THE INITIAL T TO BE THE T AT WHICH ONE COULD POUR 15CC INTO A CONTAINER WITHOUT MAKING IT BOIL I SUPPOSE BY ROBOTICS IN A CLOSED ENVIRONMENT [BUT I LIKE TO THINK OF DOING IT IN THE KITCHEN AND EXTRAPOLATE FROM THERE INTO MORE RARIFIED CONDITION, AND SO - IN THE KITCHEN P, AS I UNDERSTAND IT, WOULD BE AT ATM (14.8 PSI). In short, insufficient data provided. DOES THIS ALLOW YOU TO TAKE IT FURTHER? I AM GRATEFUL TO YOU

No. The only reason one will design a whole container to withstand a certain pressure is when that container is intended to be the container of a bomb. I will not assist in that endeavor. A properly designed cryogenic dewar includes at least one burst seal away from the vent in case the vent gets closed. The most common accidental closing of a vent happens from an ice dam forming. This discussion started with a simple explanation of liquid to gas phase state expansion into the fundamentals of bomb making.

STOP!

Nothing to do with anything like that. It is a question of using Nitrogen not as a cryogenic fluid but at ambient T when its pressure can be used for a variety of purposes where currently other low VP fluids or CO2 are used. It remains a simple question of what container would one need to specify to safely contain a given quantity of nitrogen as liquid, introduced at low pressure so low temperature, when the temperature is allowed to rise to ambient. If you know enough to be able to help fine, if not thanks for the assist so far.

Ok, let my try two different tactics here to get through to you.

In my first reply, the reason that "Wolfram" is in blue letters is that it is hyperlinked directly to the phase state diagram for Nitrogen. Please click on that word. The letters STP indicate the point on the graph known as Standard Temperature and Pressure. Nowhere on the vertical line that intersects this point (a constant temperature line of 25°C and different pressures) does liquid Nitrogen exist. Your premise is fatally flawed. Nitrogen is a gas at room temperature not a liquid.

For my next tactic, let me ask you a question. How much mass is 6.023 * 10^23 molecules of Nitrogen?

If I knew the answer to your numbers I'd not be asking the questions I am. But you say that at no stage can nitrogen be a liquid. If correct what is the runny stuff in a dewar that can be poured and is used in cooking. What I am trying to establish is the relationship between T and P to keep nitrogen in that state as T rises. But thank you for your help which has taken me part of the way in a subject which is not, in any way, what I am familiar with, but need to understand in this instance.

What is this hard clear thing in my glass with my whiskey? My whiskey and the glass were at about 25° C, so these clear blocks must also be at 25° C. I wonder why they keep getting smaller?

I'm sorry. My answer may have been clouded to the point of obfuscation for you.

The liquid nitrogen used in cryogenic cooking in a 25° room at a nominal 1 atmosphere of pressure is itself no warmer than about -196° C. This is why liquid nitrogen can be used to make ice cream on the spot without any other refrigeration.

No amount of pressure can make Nitrogen liquid at 25° C. Now enough pressure can solidify Nitrogen at 25° C. This requires pressures that are almost astronomical in magnitude. This is after it goes to a super critical fluid.

My glass is now empty. I think I'll get some more.

But PV=nRT should still be capable of telling us what that 'astronomical' pressure maybe - No? And your premise seems to be what you have denied - the possibility that P and T are both variable to produce liquid N2. Or have I misunderstood this? P of1 atm/-196C odd so P of ? atm/25C (forgive me I forget the K) Thank you for sticking with this. I appreciate it. It is not an idle question and to do with carbon footprint so is worth while ?

PV=nRT is the ideal gas law. It is only valid for the compressible phase state of a gas. It does not work for the non-compressible phase states of solid and liquid nor the chaotic state of supercritical fluid. Technically when any gas approaches any phase change there is a boundary region where the ideal gas law is no longer accurate. In any phase state diagram the area of this boundary region is less than 0.1% of the area of gas state.

Converting from Celsius to Kelvin is painfully easy and critical for any gas analysis. Add 273.16 to the Celsius number to obtain the temperature in Kelvin. So an ideal gas at 1 atmosphere of pressure and about 77 K temperature when heated to about 300 K in a fixed volume will be at a pressure of (300 K/70 K)*1 atmosphere, about 4.25 atmospheres if what fixes that volume can handle this pressure increase. This does not include any phase state change like liquid to gas. This quick calculation is only valid for a gas.

There is an interesting "rule of thumb" like table in the Wikipedia link on supercritical fluids. Specifically table #2. You should notice that the density ratio between a gas and a liquid is nominally 1000:1. Now this is a gross simplification that will change greatly depending on many factors of the chemistry of the substance going through a phase change. So a mL of liquid will become a L of gas with them both at the same pressure. Now a good deal of energy is needed to convert a liquid to a gas. This energy is known as the enthalpy of vaporization. Nothing is free.

OK - I understand that if one enclosed 1cc of vapour at 1 atm, at c77K, on heating it to c300K the pressure of the gas would rise to c4.25 atmospheres, or c63psi, but if one encloses 1cc of nitrogen as liquid, not vapour, at 77K - on heating it to c330K what would the pressure become (assuming the contained remained adequate). It is a real problem with which I am seeking something firmer than a 'suck it and see solution'. CO2 performs as expected but is far from being supercritical. Thank you so much for the continued thought on this.

I am so grateful to you. This takes me a long way along the road. Can you think of anyone who may be able to help further. t seems one has a supercritical fluid which as liquid at 1 atm and c77K will occupy the same space at 300K but i am still not quite there on at what pressure. But when that is to hand then I need to look to vessel spec in SS probably but which from past research will not need to be hugely thick walled if its column is say 15 cc. On point you mention that a 0C the gas column (if released) of the iml contained would be c650 cc. I am surprised it is not much higher given that liquid CO2 at that sort of temperature produces some 800 cc of gas, as I have understood it.

redfred-

Applause! Applause! Applause! After 13 posts by the OP, You have come up with an answer! Hurray, Hurray, Hurray!

For this flash of brilliance I genuflect to you all knowing redfred. No discrimination intended to any other contributors but of all the many highly intelligent people on this forum he got it!

Good Luck, Old Salt

Right. But to make the whisky saw water and alcohol heated until distilling could begin. Conversly to cause 'the vapour' (say 'gas') to become liquid in for glass then required cooling. Can that not be done with Nitrogen from atm reducing a gas to a liquid either by lowering the T to -290odd K OR by, at the same T compressing it? If not why not in what way is it different from - say - CO2?

You can buy nitrogen in cylinders that have passed the safety tests. Do you want to start a nitrogen production/distribution company?

Just buy it and use it for your purpose. If you need nitrogen gas and the cylinder volumes are too small or the use is not practical, consider a cryo tank outside, supplied by your supplier.

Or just use air and separate the other components. There is enough equipment to do that if you pay for it. Study the case good.

Thank you. Yes I am familiar with the nitrogen extraction from air kit. What I then need to be able to do is compress it to the PV =nRT liquid point without cooling. I think one is talking c4000 psi but this is what I am trying to get at.

I worked at a lab where we used nitrogen as both high pressure gas and a cryogenic liquid.

The high pressure N2 gas was stored in tanks not much different than high pressure oxygen or CO2. Those were typically at 3000 psi when full.

The cryogenic liquid nitrogen was stored in a stainless steel tank shaped more like a propane cylinder. It would vent periodically as the nitrogen evaporated and pressure built up in the tank. That tank had no pressure gauge only a level indicator for the liquid inside.

Lo Volt. I have replied to Retfred with; OK - I understand that if one enclosed 1cc of vapour at 1 atm, at c77K, on heating it to c300K the pressure of the gas would rise to c4.25 atmospheres, or c63psi, but if one encloses 1cc of nitrogen as liquid, not vapour, at 77K - on heating it to c330K what would the pressure become (assuming the contained remained adequate). It is a real problem with which I am seeking something firmer than a 'suck it and see solution'. CO2 performs as expected but is far from being supercritical. Thank you so much for the continued thought on this. Can I ask you - when you say "when full" what did it mean - "when the specified pressure had been reached or because no more could be compressed?

The 3000 psi was probably the safe working pressure for the tank.

I'm no thermodynamicist, so I haven't even got a feel for what your pressure would be with the increased temperature. I just wanted to highlight the difference in storage techniques between liquid and compressed gaseous nitrogen.

My guess is that the cryogenic liquid nitrogen is vented because it's too hard to predict what rising temperatures will do to the pressure in the vessel. I'll add that we kept an insulated thermos or dewar on site. We emptied the stainless tank into the dewar to keep the liquid nitrogen cold. Because it's insulated it stores longer in the dewar than it does in the uninsulated stainless tank.