Upload
kamana
View
91
Download
3
Tags:
Embed Size (px)
DESCRIPTION
Separating Azeotropic Mixtures. CHEN 4460 – Process Synthesis, Simulation and Optimization Dr. Mario Richard Eden Department of Chemical Engineering Auburn University Lecture No. 6 – Review of Non-ideal Thermodynamics September 27, 2011 - PowerPoint PPT Presentation
Citation preview
Separating Azeotropic Mixtures
CHEN 4460 – Process Synthesis, Simulation and Optimization
Dr. Mario Richard EdenDepartment of Chemical Engineering
Auburn University
Lecture No. 6 – Review of Non-ideal Thermodynamics
September 27, 2011
Contains Material Developed by Dr. Daniel R. Lewin, Technion, Israel
Process Design/Retrofit Steps
Assess Primitive Problem
Development of Base-case
Plant-wide Controllability Assessment
Detailed Design, Equipment sizing,
Cap. Cost Estimation, Profitability Analysis,
Optimization
Detailed Process
Synthesis -Algorithmic
Methods
PART II
Algorithmic Methods
Lecture 6 – Introduction
• Separation sequences are complicated by the presence of azeotropes, often involving mixtures of oxygenated organic compounds:
Alcohols Ketones Ethers Acids Water
• In these cases, distillation boundaries limit the product compositions of a column to lie within a bounded region.
• This prevents the removal of certain species in high concentrations.
Lecture 6 – Objectives
Be able to sketch the residue curves on a ternary phase diagram
Be able to define the range of possible product compositions using distillation, given the feed composition and the ternary phase diagram
Basics: The Lever Rule
Basics: Ternary Phase Diagrams
0.15 H2O
0.65 DTBP
0.2 TBA
0.2 DTBP
Basics: Ternary Phase Diagrams
0.6 H2O
0.2 DTBP
0.2 TBA
Homogeneous Azeotropes 1:4
At equilibrium:
V L
j jff_ _
V L
j j j j jy P x f
s
1 1 1yP xP
s
2 2 2yP x P
s s s s
1 1 2 2 1 1 1 2P xP x P xP 1 x P( )
s s s
2 1 2 1P P P x( )
At fixed temperature
Homogeneous Azeotropes 2:4
Example – Phase diagrams for benzene-toluene mixture at 90 oC
Homogeneous Azeotropes 3:4
For non-ideal mixtures, the activity coefficients are different from unity:
S
1 1 1 1yP x P
S
2 2 2 2yP x P
s s
1 1 1 1 2 2P x P 1 x P( )
If the mixture has a minimumminimum-boiling azeotrope
i1
Example – Phase diagrams for Isopropyl ether-Isopropyl alcohol
Homogeneous Azeotropes 4:4
For non-ideal mixtures, the activity coefficients are different from unity:
S
1 1 1 1yP x P
S
2 2 2 2yP x P
s s
1 1 1 1 2 2P x P 1 x P( )
If the mixture has a maximummaximum-boiling azeotrope
i1
Example – Phase diagrams for Acetone-Chloroform
Heterogeneous Azeotropes
For a minimum-boiling azeotrope with large deviation from Raoult’s law ( ), phase splitting may occur and a minimum-boiling heterogeneous azeotrope forms, having a vapor phase in equilibrium with two liquid phases.
i1
Homogeneous Azeotrope Heterogeneous Azeotrope
Residue Curves 1:3
j j j j j jLx ydL Lx Ldx xdL dLdx j 1 C 1, , ,
Mass balance on species j:
j j j jLx L y L L x x j 1 C 1( ) ( )( ), , ,
As L 0:
Simple Distillation
j
j j j j
dxx y x 1 K T P x y
dL L( { , , , })
/
Rearranging:
j
j j
dxx y
dt
Residue Curves 2:3
Residue curves for Azeotropic
system
j
j j
dxx y
dt
Residue curves for zeotropic
system
• Residue Curves Liquid Compositions at Total Reflux
Residue Curves 3:3
• Residue Curves Liquid Compositions at Total Reflux
Species balance on top n-1 trays:
n
n n 1
dxx x
dh
n 1 n 1 n nDL x Dx Vy
Approximation for liquid phase:
Substituting:
n n
n n D
n 1 n 1
dx V Dx y x
dh L L
At total reflux, D = 0 and Vn = Ln-1
n
n n
dxx y
dh
Rectifying section of distillation
column
Sketching Residue Curves
j
j j
dxx y
dt
Plot pure components on vertices along with Tb
Plot all azeotropes on diagram along with their Tb
Plot residue curves connecting all azeotropes, azeotropes & vertices, and finally vertices & vertices with arrow heads pointing towards increasing boiling point temperatures
Plot additional residue curves that “arch” towards intermediate temperatures on the way to the end point
Product Compositions Regions
• For zeotropic systems– L: Lowest boiling component, I: Intermediate boiling
component, H: Highest boiling component, F: Feed composition
Pure L distillate
Pure H bottoms
Product Compositions Regions
• For azeotropic systems– Shaded regions: Feasible distillate and bottoms
product compositions
Two binary azeotropes Three binary azeotropes
and one ternary azeotrope
Summary – Non-ideal Thermo
Be able to sketch the residue curves on a ternary phase diagram
Be able to define the range of possible product compositions using distillation, given the feed composition and the ternary phase diagram
On completion of this part, you should:
Other Business
• Homework– SSLW: 8.14b-d, 8.15– Due Tuesday October 4
• Next Lecture (October 4)– Part 1: Sequencing Azeotropic Distillation Columns (SSLW
230-251)– Part 2: Review for Midterm Exam
• Midterm Exam– October 11 during lecture– Open book or closed book?
• Lab Session Tonight– I have to take our seminar speaker to dinner, so I am
unable to be there. Vivi and Charlotte will be there as usual though.