Calculating K Values (VLE Coefficients)

  • Thread starter _Greg_
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  • #1
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Main Question or Discussion Point

Right so basically, I'm doing a multicomponent distillation with some exotic chemicals.
My feed comes in at 13kPa and 60*C, so it's under vaccum. This will be a two phase mixture.
What I need is the vapour-liquid-equilibrium coefficients, 'K- values' at feed conditions.
I'm basing this on an ideal system to start with then I'll do it as non-ideal (fugacity coefficients etc)

So for now, I'm planning on using the Antoine Equation ln P = A - ( B /( T + C) ) (from coulson & richardson vol 6)
Now the K values can be calulated with Raoults law Ki = Pi(sat)/Pt
My question is, will the pressure value I get from the Antoine equation be the saturated vapour pressure of component i? (Pi(sat))

Sorry this probably sounds terrible, but it's been a while
 

Answers and Replies

  • #2
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From google:

Mathematically, Raoult’s law is expressed as

y(i)P = x(i)P(i)sat for all species (i= 1, 2,...,N)

where xi is the liquid phase mole fraction, yi is the vapor phase mole fraction, P(i)sat is the vapor pressure of pure component i, and P is the total pressure. In words, Raoult’s law says that the partial pressure of each species in the vapor phase is equal to its mole fraction in the liquid phase times its pure-component vapor pressure.

And P(i)sat you can calculate with the Antoine equation at a given temperature, so you're right
 
  • #3
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Thanks Vulgar
Just wasn't sure because theres different forms of the antoine equation, some say Psat, other just say P. Could have done this like 2 years ago, now in my final year I struggle with some of the basics lol.
Cheers for clearing that up ;)
 

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