Bubble Point Dan Dew Point 642r17

Penyajian Data Kesetimbangan (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 of K values defined as:

Ki = yi/xi correlated empirically or theoretically in 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

Ki yi / xi α ij = = K j yj / xj

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

Dalton’s law (Ideal gas):

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

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

K i / K j = Pi s / Pjs Antoine equation:

ln Pi s (T ) = Ai −

Bi T + Ci

L

T, P

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

Lecture 5

8

Lecture 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 ( the lever rule?) What about the multi-component system?

y*

xA

Thermodynamic calculations using K-values Bubble point T

V

L

1

- Model system: binary mixture A, B

x A + xB = 1 - Consider the process in the figure: we start with a mixture of composition 1 and temperature T1 and start increasing the temperature - 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 + yB = 1 - On the other hand:

K A (T ) x A + K B (T ) xB = 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 x

i i

i

d) if

∑K x

i i

>1

T is too high

i

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

K i xi yi = ∑ 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 + yB = 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 + xB = 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)

yi ∑i K i y d) if ∑ i > 1 i Ki c)

T is too low

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

yi / K i xi = ∑ 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