×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Vapor Pressure, Decomposition , and Temperature

Vapor Pressure, Decomposition , and Temperature

Vapor Pressure, Decomposition , and Temperature

(OP)
Does anyone know of any liquid that when heated increses its vapor pressure, but while being heated decomposes to another chemical, and then starts reducing its vapor pressure?

i.e. Vapor pressure would increase and suddenly or gradually decrease with temperature due to heat decomposition?

 

RE: Vapor Pressure, Decomposition , and Temperature

heat of decompositions is exothermic, how could you get lower pressure as the temperature rises?  And at decomposition, you get more molecules subject to pv=nRt

RE: Vapor Pressure, Decomposition , and Temperature

Sort of, you could have a monomer that as it heats the vp goes up until it reaches the point it polymerizes then it would turn into a polymer with much less vp.  Such as VCM.  

RE: Vapor Pressure, Decomposition , and Temperature

polymerize is not decomposition.

RE: Vapor Pressure, Decomposition , and Temperature

(OP)
ash9144 and dcasto, I'm not a chemical engineer, so bear with me. Maybe decomposition is not the right term, but I am looking for something that behaves like what ash9144 indicated. Is there a monomer that polymerizes and reduces its vp? I'm looking for this special case.

RE: Vapor Pressure, Decomposition , and Temperature

Styrene, ethylene, propylene, vinyl chloride, formaldehyde, and numerous others have significant vapor pressure and will polymerize. Polymerization is exothermic so temperature control can be a problem.

RE: Vapor Pressure, Decomposition , and Temperature

Decomposition reaction is generic term for reaction leading to more molecules.  It will be exo or endo thermic depending on physical properties.

Polymerization reaction takes many molecules and makes one really big molecule

So something like vinyl chloride monomer or styrene would have increasing vapor pressure with increasing temperature.  Then would rapidly polymerize giving off large amounts of heat.  Then you would a blob of polymer with a significantly lower vp than the monomer you started with.

RE: Vapor Pressure, Decomposition , and Temperature

(OP)
For styrene (or ethylene, propylene, vinyl chloride, formaldehyde):
1) What temperature does it polymerize to ploystyrene?
2) What is the vapor pressure of styrene prior to polymerization?
3) What is the vapor pressure of polystyrene just after polymerization?

If someone has a plot or reference, that would be great. Or point me to a place where I can find this info. I'm having a hard time finding information for these materials outside of NTP/STP
 

RE: Vapor Pressure, Decomposition , and Temperature


Vapor pressure, in Pa, of styrene, following Perry's Chem. Eng. Handbook, 8th Ed., McGraw-Hill:

ln P = C1 + C2/T + C3.lnT +C4.TC5

C1 = 105.93
C2 = -8685.9
C3 = -12.42
C4 = 7.5583 E-06
C5 = 2

between Tmin = 242.54 K (melting point) and Tmax = 636 K.

P at Tmin = 10.6
P at Tmax = 3.823 E+06

Perry also gives a table of vapor pressures in mm Hg between 1mm and 760 mm Hg.

Left alone at room temperature, styrene will eventually polymerize with itself to a clear glassy solid. Technical grade styrene is 99% minimum purity. It is shipped with a polymerization inhibitor in it, in standard tank cars or trucks.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources