solo
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Behavior of pressure and temp in a sealed vessel
I have recently been doing some pilot studies on the stability of a sealed vessel rated at 60psi with water . the temperature and pressure were
measured as time advanced with the same setting on the hot plate. as the temp reached 110c at 30psi it suddenly started a steep curve such that at
130C the pressure was 38 psi and at 140C the pressure was 46psi....continuous plotting showed me an extrapolation of the curve that the vessel would
not hold the pressure that would be built up at 160C as needed for the follow up experiment.
That being the observation my question is if the solution was something of a lower boiling point would the parameters be the same or does it change
with the properties of the solvent being heated.......I forgot how to figure that out.......some assistance needed to clear that up for me .......solo
Shot with FinePix2650 at 2007-07-28
Shot with FinePix2650 at 2007-07-28
It's better to die on your feet, than live on your knees....Emiliano Zapata.
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bio2
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The pressure is proportional to the vapor pressure of the solvent and the relative
volatility/boiling point.
CRC has a table of pressures versus temperatures to 5 atmospheres for common chemical.
So yes methanol develops more pressure than say isopropanol at the same temperature in a closed vessel. For a mixture the partial pressures are added.
PV=nRT is the equation IIRC. Boyles Law
P is the pressure (SI unit: pascal)
V is the volume (SI unit: cubic metre)
n is the number of moles of gas
R is the ideal gas constant (SI: 8.3145 J/(mol K))
T is the thermodynamic temperature (SI unit: kelvin).
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solo
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Thanks now to figure my partial mixture pressures of HI, and Phenylalanine......see if my container can do the 160C test and stay within the 60psi
range of the test vessel....................solo
It's better to die on your feet, than live on your knees....Emiliano Zapata.
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bio2
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.......now to figure my partial mixture pressures ...........
There is more than a little "voodoo" in trying to calculate accurately mixtures of
substances because how do you determine the number of moles of
each component in the vapor phase. There might be some fancy formulas that
give an approximation of this.
Testing it very carefully is probably the only simple way to find out. You can use the
5 atmosphere temperature of the most volatile component from CRC as a starting
point to determine if it is feasible at all.
Here is a link for Daltons Law for mixtures.
http://en.wikipedia.org/wiki/Dalton%27s_law
[Edited on by bio2]
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Ozone
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That is...if you are dealing with a non-compressed *ideal* gas. In this case, you may need to think about Z (compression), and phase transition at
(think about) critical temperature and pressure. These parameters are particular to the solvent your looking at, and generalizations (in the real
world) can be dangerous (see catastrophic). The mole fraction of gas is a factor of (ideally) vapor pressure at a particular T, and is easily
calculated.
I'll cough up some more specifics if needed.
Oh yes (a little cooler) supercritical water is bad ass!
Cheers,
O3
-Anyone who never made a mistake never tried anything new.
--Albert Einstein
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solo
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Note:Review and change of course with the material being used and the reaction .
Just as a reminder back in 1909 Gatterman documents his efforts to reduce carboxylic acid in a glass tube sealed with Hi and RP which he raised the
temp to 160C and allowed for this to remain for 6 hours. ( this experiment was brought to our attention by garage chemist). Now the
compound in question in this experiment has an amine group hanging out there and HI reacts very violent with amines, also HI reacts and destroys metal
hence the brass on my experimental model has brass gas pressure gauge contact and also the rubber plug which can also be attacked.......hence I will
opt to the reaction RB flask with the column refrigerant and a balloon on top so that the variables of Pressure and volume can fluctuate and reach
equilibrium and at the same time the gases generated are maintained in the solution. The premise of a closed system is met and the reaction has some
flexibility (no pun intended). Also the balloon being rubber can be at risk of being attack by HI so the refrigerant column must be kept very cold
.....
However I will get a Polypropylene material to serve as a piston to work the gas pressure gauge and explore the truth's about rubber stopper and HI
and see if if in fact is true;.....then run the experiment keeping a close eye on sudden pressure rises as seen in the water experiment.
The equivalent system sealed but with an adjustable volume to keep pressure under control..........
Shot with FinePix2650 at 2007-07-29
I just reviewed the facts and decided against this compounds, instead i will run oxalic acid , and paraformaldehyde with phenylalanine and do the
E.C. mono methylation that occurs at 100C for one hour and then 120C for 10 minutes. In this reaction the ingredients are in solid form but the bit of
moisture in oxalic acid and puts the rest in a liquid solution especially once paraformaldehyde melts.
An earlier version of a sealed test tube within the metal pipe.....
Shot with FinePix2650 at 2007-07-29
I'm hunted by the note made in the article by .....
Inorganic Syntheses, Volume 1: Hydriodic Acid
G. B. Heisig, O. C. Frykholm, E. R. Caley, M. G. Burford
ISBN: 9780470132326
Excerp
..... In no case should rubber stoppers. or. tubing be used where ... explosion may be initiated by the catalyst in the reaction tube. ...
----------------------------------------------------------------------------------------
I will have to hunt this chapter from this volume to read more about it.....solo
[Edited on 29-7-2007 by solo]
It's better to die on your feet, than live on your knees....Emiliano Zapata.
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Quibbler
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Yes the pressure does increase exponentially.
ln(P)= -/\H/RT + /\S/R
So for water /\(vap)H= 44010 J, /\(vap)S = 118.9J
and the pressure should come out in atm.
So a quick calc gives
373K P=16 psi (should of course be 14.4)
383K P=23 psi
393K P=33 psi
403K P=46 psi
and 160°C P=115 psi
These values will not be totally accurate as H and S are temperature dependent.
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solo
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Quibbler .....by looking at my results and the results the of the In(P) function means that the solvent and it's properties are quite
significant, as I doubt that Gatterman's experiment tube could have withstood 115psi or reached that interior pressure.,......so the calculation of
partial pressures have to be looked at before this experiment can be move forward.......... I hope the balloon is flexible enough to bring the
environment within the reaction vessel to some manageable equilibrium and not burst the balloon........ solo
It's better to die on your feet, than live on your knees....Emiliano Zapata.
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bio2
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Combustion tubes (glass) like the ones intended to be sealed with a flame have constricted necks and are very thick.
My quess is that they would easily take over 115PSI maybe over 200PSI
Problem with these is the size of the large ones is relatively small something
like 25mm X 200mm.
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