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Unit Operations: Introduction^ What is chemical engineering?
Chemical Engineering is a group of
industrial processes in which row materials are changed or separatedinto useful products Historical development:
As the
Industrial Revolution
steamed along
certain basic chemicals quickly became necessary to sustain growth
- Example
: Sulfuric acid
was first among these "industrial chemicals".
Chemistry: - to create a new substance- to study its properties- to investigate
all
possible
pathways from one substance toanother
Chemical Engineering: - to design the most optimal technology
for production of a specified substancefrom row materials
- to develop and discover new
technological applications for materials
Comparison of two processes
Units: - Heaters/heat exchangers- Pumps- Distillation units- Reactors- …
Actions: - Heat exchange- Material transport- Separation- Mixing- …
Unit Operations:
- Unit Operations is a method of analysis and design of chemical
engineering processes in terms of individual tasks/operations
- It is a way of organizing chemical engineering knowledge into
groups of individual tasks/operations
- A unit operation: basic step in a chemical engineering process
Chemical separation processes:required background
V B
D
- How do we know that at pressure P
and temperature T, vapour and liquidphase are present in the system?
- What is the composition of the phases?
Chemical engineering thermodynamics
L
a
,x
a
V
a
,y
a
V
b
,y
b
L
b
,x
b
- How do we know the amount of mass
exchanged by two phases?
- What is the new composition of the
phases?^ Mass transfer methods
Chemical separation processes
- play a central role in chemical engineering
Use
Technology maturity
Distillation
Gas Absorption
Crystallization Adsortion
Membranes
Chromatography
Distillation process design
Step 1: Thermodynamics data and methods to predict equilibrium
phase compositions
- Separation utilizes the difference in volatility of
components
Thermodynamic considerations and phaseequilibria: Binary fluids
T
xA
Tb(B)
Tb(A)
V
L
y*
x*
T, P
V L
Thermodynamic considerations and phaseequilibria
T
xA
Tb(B)
Tb(A)
V
L y*
x*
P=const
Thermodynamic considerations and phaseequilibria
T
xA
Tb(B)
Tb(A)
V
L y*
x*
K
A
= y
A
/x
A
K
B
= y
B
/x
B
=(1-y
A
)/(1-x
A
Distribution of a componentamong the two phases canbe characterized with a
K-value B
B
A
A
A B
AB
x
y
x
y
K K
Relative volatility
Thermodynamic considerations and phaseequilibria: Binary fluids
T
xA
Tb(B)
Tb(A)
P4 P3 P2 P
P1<P2<P3<P
Thermodynamic data for mixtures
- graphs (T-y-x, P-y-x, y-x), tables (usually limited to binary mixtures)- K-values, relative volatilities
DePriester charts
- Analytical methods (part of most chemical process design software)
ASPEN Tech See a brief ‘Thermodynamics of multicomponentphase equilibria file’Promax
Ideal gas/Ideal solution
Light hydrocarbon mixtures: DePriester charts(1953)
Light hydrocarbon mixtures: DePriester charts(1953)
