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7/30/2019 Stagewise Intro Lecture 1
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Equilibrium SeparationOperations
Lecture 1: IntroductionReading Assignment:
1. Foust, 1980 pp. 1-27
2. Geankoplis pp 653-6603. Geankoplis pp.696-705
SHORT QUIZ (30 min) 7/17/2007
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Separations
Crucial in Chemical Engineering
Most equipment - purifying products
Chemical Plants
50 - 90 % capital investment
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Common Separation Methods
Distillation
flash
continuous column
batch
Absorption/Stripping
Extraction
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Similarities of These Methods
Two phases contacted
Designed and analyzed as equilibrium stageprocesses
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Distillation
Separation depends on distribution of
components between gas and liquid phase
All components distribute at equilibrium
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Distillation
Gas phase - application of heat
Liquid phase - removal of heat
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Absorption/Stripping
Gas mixture contacted with liquid
Absorption - dissolving components of gasinto liquid
Stripping - mass transfer goes from liquid togas
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Liquid Extraction
Liquid solution contacted with another
insoluble liquid.
Constituents distribute differently between the
2 liquid phases
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Key terms for understanding
equilibrium staged processes
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Unit operation
Basic design principles for a given separation
method are always the same
Specific design depends on chemicals being
separated
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Stage
Device or combination of a device
2 insoluble phases are brought into intimatecontact
mass transfer occurs between the phases tending
to bring them to equilibrium
phases are mechanically separated
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Tray tower
Vertical assembly of trays on which vapor
and liquid are contacted
Liquid flows down tower due to gravity
Vapor flows upward as a result of a slightpressure drop from tray to tray
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Equilibrium stage
Equilibrium, ideal, or theoretical stage
Contacting device - a vessel - 2 or more phases incontact sufficiently to achieve equilibrium
Streams leaving a stage are in equilibrium
Building block of multistage processes
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Stage Efficiency
Fractional approach to equilibrium
Equilibrium stages coupled with stageefficiency -actual stages
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Cascade
A group of stages interconnected
Purpose - to increase the extent of masstransfer over and above that which is
possible with a single stage.
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3 Principles:Distribution of substances between 2
insoluble phases
Fixed temperature and pressure, there
exists a set of equilibrium relationships
No net diffusion of the components
between phases in equilibrium.
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3 Principles:Distribution of substances between 2
insoluble phases
If the system is not in equilibrium, diffusion of
the components between the phases will
occur so as to bring the system to a condition
of equilibrium.
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Not at equilibrium
Liquid and vapor can be:
at different pressure
at different temperature
present in different mole fractions
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At equilibrium
Temperature ceases to change
Pressure ceases to change
Fractions of the 2 phases cease to change
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Thermal Equilibrium
Heat transfer stops
Tliquid = Tvapor
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Mechanical Equilibrium
Forces between vapor and liquid balance
Staged separation processes:
Pliquid = Pvapor
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Phase Equilibrium Rate at which each species is
vaporizing is just equal to the rate at
which it is condensing
No change in composition (mole fraction).
Compositions of liquid and vapor are not
equal.(chemical potential i)liquid = (chemical potential i)vapor
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