ChE 427 NOVEL TOPICS in SEPARATION PROCESSES

1
ChE 427NOVEL TOPICS in SEPARATION PROCESSES
Instructor Prof. Dr. Hayrettin YücelAssistant
Ms. Hale Ay
2
A Chemical process

• an integrated series of reactions and associated
  operating steps whereby available materials are
  converted into a desired product

In a typical chemical process

• physical treatment is made

• for raw materials
• purification
• mixing
• grinding

• for products
• recovery
• separation
• purification

• unused reactants are separated and recycled back
  to the reaction step

3
Raw Materials
1. Naturally occurring raw materials 2. Plant or
animal matter 3. Chemical intermediates 4.
Chemicals of commerce 5. Waste products

4
Chemical Process
5
Separation processes play critical roles in
industry

• the removal of impurities from raw materials
• purification of products
• separation of recycles
• removal of contaminants from air/water effluents

Overall separation processes account for 40-70
of both capital and operating costs in industry
6
Procedures for separating the components of
mixtures

• 1. Mechanical separations
• Useful for separating solid particles or liquid
  drops
• based on physical differences between particles

• size
• shape
• density

Examples filtration, sieving, sedimentation,
decantation
7

• 2. Mass Transfer Operations
• involve phase changes or transfer from one phase
  to another

Examples distillation, absorption, extraction,
leaching, humidification/dehumidification,
crystallization
8
Separations include
1. Enrichment 2. Concentration 3. Purification 4.
Refining 5. Isolation
9
GENERAL SEPARATION TECHNIQUES
phase creation
phase addition
barrier
solid agent
force field
10
Separation by phase addition or creation
Feed A homogeneous, single phase solution (gas,
liquid or solid) Principle Before separation of
species a second phase must often be developed or
added.
The second phase may be created by
1) Energy-separating agent (ESA) 2) Mass
separating agent (MSA)
11
Phase Creation
Phase Addition
12
ESA may involve
1) heat transfer and/or 2) shaft work
to or from the mixture to be separated. 3)
pressure change
Example Vapor may be created from a liquid phase
1) adding heat 2) by pressure reduction
13
Examples for separation involving ESA
1) Partial condensation or vaporization 2)
Evaporation 3) Distillation 4) Crystallization 5)
Sublimation/desublimation
14
Examples for separation involving MSA
1) Absorption 2) Extraction
Examples for separation involving both ESA and
MSA
1) Extractive distillation 2) Azeotropic
distillation
15
Barrier
16
Separation by a barrier
microporous and nonporous membranes
Membrane materials
Membrane forms
Membrane operations
1. Osmosis 2. Reverse osmosis 3. Dialysis 4.
Microfiltration 5. Ultrafiltration 6.
Pervaporation 7. Gas permeation 8.Liquid membrane
1. Natural fibers 2. Synthetic polymers 3.
Ceramics 4. Metals
1. Flat sheets 2. Tubes 3. Hollow fibers 4.
Spiral-wound sheets
17
Solid Agent
Force field
18
Separation by a solid agent and and external
field
External field
Solid agent
1. Centrifugation 2. Thermal diffusion 3.
Electrolysis 4. Electrodialysis 5.
Electrophoresis 6. Field-flow fractionation
1. Adsorption 2. Chromatography 3. Ion exchange
19
FRACTIONAL RECOVERY SEPARATION FACTOR
W molar(mass) flow rate X, Y, Z mole(mass)
fraction
20
FRACTIONAL RECOVERY (Split fraction)
The ratio of the amount of a key component j
appearing in the product stream to that in the
feed stream
21
Split ratio , SRJ
The ratio of the amount of a key component j
appearing in the product stream to that in the
byproduct stream
22
Separation Factor , SFJK
The ratio of the split ratio of a key component
J to the split ratio of component K. Components
J and K are chosen such that the separation
favors J in the product stream and K in the
byproduct stream i.e. SRJ gt 1 SRKlt 1 so
that SFJK gt 1
23
Ffficiency
Capacity
24
STEPS COMMON TO DESIGNING ALL SEPARATION PROCESSES
1. Establish bases a) Composition of feed and
products b) Rate to be processed c) Operating
conditions (temperature, pressure) d) Special
conditions (presence of suspended solids or
excursions of pH, temperature or pressure)
2. Obtain basic data a) Phase equilibrium or flux
data (for membranes) b) Density, viscosity,
diffusion coefficients c) Efficiency or mass
transfer data (use plant data available)
25
3. Perform process selection a) Critically
influenced by bases and basic data b) Complete
performance and economic evaluations
4. Complete process design a) Verify economics b)
may need to change process selection
26
Ease of scale-up the Common Separation Operations
27
Technological and use maturities of separation
processes
28
Distillation
most common type of separation 90-95 of all
separations
Advantages 1. has a simple flow sheet 2. has
relatively low capital investment 3. is hard to
beat if

• components have a relative volatility of 1.2 or
  more
• components are thermally stable

29
Disadvantages 1. has a low energy efficiency 2.
requires thermal stability of compound at its
boiling point 3. may not be attractive when

• azeotropes are involved or
• it is necessary to separate high boiling
  components, present in small concentrations, from
  large forms of a diluent, such as water.

30
Factors favoring distillation

• Relative volatility is greater than 1.2
• Products are thermally stable
• Rate is 2500-4500 kg/day or more
• High corrosion rates/unwanted side reactions
  /explosive conditions do not exist

31
Conclusion
Though not energy efficient distillation is a
well established separation and is the
benchmark with which all newer processes must be
compared.