Bubble Point Dan Dew Point

Penya enyajian jian Data Data Keset Kesetimbang imbangan an (presenting (presenting equilibrium data)

Thermodynamic considerations and phase equilibria: multicomponent mixtures For multicomponent mixtures simple graphical representations of  vapour-liquid equilibria data do not exist Most often such data (including binary systems) is represented in terms of  K values defined as:

Ki = yi/xi correlated empirically or theoretically in terms of temperature pressure and composition The ratio of two K-values, or relative volatility, indicates the relative ease or difficulty of separating components i and j 

α 

ij

=

K i K  j

=

 yi /  xi  y j /  x j

Thermodynamic data for mixtures: Simplified models V

Raoult’s law (Ideal solution/ideal gas):

 pi =  xi Pi s

 pi  is the partial pressure of component i 

T, P

Dalton’s law (Ideal gas):

 pi =  yi P K-value for ideal gas/ideal solution system: s

K i = Pi / P Relative volatility for ideal gas/ideal solution system: s

s

K i / K  j = Pi / P j Antoine equation:

ln Pi s (T ) =  Ai −

L

 Bi T  + C i

Persamaan Antoine •

Persamaan Antoine memberikan hubungan tekanan uap murni (P atau VP) suatu senyawa/komponen dengan suhu. °

•

Persamaan Antoine dan koefisien dinyatakan dalam beberapa bentuk:

•

•

Data koefisien Antoine dapat dilihat di Chemical Engineering Vol 6

Bentuk lain:

De Priester Chart •

•

Ada 2 jenis grafik: •

Suhu tinggi

•

Suhu rendah

Grafik menunjukkan hubungan nilai K untuk suatu komponen dengan suhu dan tekanan

L

5

8

L

5

9

DePriester: Low T

10

DePriester Charts: High T

11

Tugas 1(29/09/2016) •

Campuran terdiri n-hexane, n-heptane, noctane dan n-nonane pada suhu 40C dan 500 kPa

•

Tentukan nilai K dengan:

•

A. Grafis (de Priester)

•

B. Persamaan Antoine

Penentuan Bubble point dan Dew point •

•

Bubble point is the condition that the first bubble formed during liquid mixture boiled Dew point is the condition that the first drop formed during vapor mixture cooled

Thermodynamic calculations using K-values P

Bubble point Dew point Two phase systems

T V Tb(B)

-Given P, T, V/(V+L), find x*, y* Tb(A) - Given P, T, x*, y* , find V/(V+L)

L

x* Easy for 2 component system, if T-x-y diagram is available (remember the lever rule?) What about the multi-component system?

y*

xA

Thermodynamic calculations using K-values Bubble point - Model system: binary mixture A, B

T

V

L

 x A + x B = 1 - Consider the process in the figure: we start with a mixture of composition 1 and temperature T1 and start increasing the temperature

1

- As we increase the temperature we are going to reach a point where the first bubble forms - The vapour in this bubble obeys:

 y A + y B = 1 - On the other hand:

K  A (T ) x A + K  B (T ) x B = 1 - Thus as we increase the temperature we put new K-values in the above equation until this condition is met

Thermodynamic calculations using K-values Bubble point Procedure: a) Select T b) Ki(T) c)

∑ K i xi i

d) if

∑ K i xi > 1

T is too high

i

e) Adjusting T g) Final composition can be corrected using

 yi =

K i xi

∑ K i xi i

Campuran pada tekanan 300 kPa terdiri dari: 50 kmol Heptane 30 kmol Octane 20 kmol Nonane Tentukan bubble point! Gunakan de Priester Chart.

Thermodynamic calculations using K-values Dew point

1

T

L

- Model system: binary mixture A, B

V

 y A + y B = 1 - Consider the process in the figure: we start with a mixture of composition 1 and temperature T1 and start decreasing the temperature - As we decrease the temperature we are going to reach a point where the first drop of liquid forms - The liquid in the droplet obeys:

 x A + x B = 1 - On the other hand:

 y A / K  A (T ) +  y B / K  B (T ) = 1 - Thus as we decrease the temperature we put new K-values the above equation until this condition is met

Thermodynamic calculations using K-values Dew point Procedure: a) Select T b) Ki(T) c)

 yi

∑ K  i

d) if

i

 yi

∑ K  i

>1

T is too low

i

e) Adjusting T g) Final composition can be corrected using

 xi =

 yi / K i

∑  yi / K i i

Tugas 2 (29/09/2016) •

•

•

Campuran terdiri n-hexane (0.15), n-heptane (0.20), n-octane (0.30) dan n-nonane (0.35) Tentukan bubble point dan dew point pada tekanan 1 atm