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Unit OperationsLecture 9
16 June 2010
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Overview• Last timeLast time…• Column Internals; sizing• Batch (Rayleigh) Distillation
E ti• Evaporation • Crystallization
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Residue Curve MapsMaps
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Complex Multicomponent Systems
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Pressure Swing DistillationDistillation
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Pressure Swing Distillation
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Complex or Enhanced Distillation• Extractive Distillation
o Higher boiling solvento Enters near top of columno Interacts with other components to affect volatility or activity coefficients
• Homogeneous Azeotropic Distillation• Homogeneous Azeotropic Distillationo Add entrainer that forms min/max boiling point AZ w/ 1 or more of feed compdso Added near top or bottom, depending upon if AZ is min or max BP
• Heterogeneous Azeotropic Distillationo Add entrainer to form min BP heterogeneous azeotrope (EtOH-H2O + benzene)
• Pressure – Swing Distillationo For pressure sensitive azeotropes and distillation boundaries
• Salt Distillation• Salt Distillationo Alter relative volatilities of feed compds by dissolving a soluble ionic salt into
the reflux• Steam Distillation
o Steam is added to reduce temperature of distilling organic mixture• Reactive Distillation
o add reactant &/or catalyst to cause a reversible/selective reaction with one of the feed components
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feed componentso Reaction and distillation occur in same vessel
Column Internals
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Column Internals
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Column Internals
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Column Internals
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Column Internals
Jaeger Product Bull. 400-09
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Column Internals
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Random and Structured Packing
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Packed Columns (Distillation)• Usually for small diameter y
columnso Usually more
economical for columns < 75 cm (2 5columns < ~75 cm (2.5 ft)
o Lower pressure drop than trayed columns
o Good for vacuum operations
• Wide choice of packing materials (random ormaterials (random or structured)
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Column Internals
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Packed Columns (Distillation)• Column diamter
o Dcol/Dpacking ~ 8 – 12 (rule of thumb)o If Dcol/Dpacking > ~40, watch for channelingo Sized based usually on approach to flooding or acceptable pressure drop
• Packing height• Packing height
stagesltheoreticanumberheightpacking
NH
HETPTH
packing
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Overview• Last timeLast time…• Column Internals; sizing• Batch (Rayleigh) Distillation
E ti• Evaporation • Crystallization
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Batch (Rayleigh) Distillation• Usually for small capacityUsually for small capacity
systems• 1 column handle multi-
”campaigns”• Produce sample new products• Batch upstream processes• Feed contains solids/foulants
Seader & Henley (2006) Material Balance:leads to Rayleigh Equation
x
xo oxy
dxWWln where:
][moleschargeinitialFWchargeinitialoffractionmolexx
o
Fo
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Batch (Rayleigh) Distillation
x dxWl
xo o
xyWln
a) P = constant; K = f(T) only
xKW
W ln1
1ln
oo xKW 1
b) Binary with = constant
oo xxW 1lnln1ln b) Binary with = constant
oxxW 1
lnln1
ln
c) y = K x ; but K = f(T,x) Solve graphically or numerically
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Multistage Batch DistillationModes of operation:p• Constant reflux rate or ratio
• xD varies with time• easily implemented (flow sensors)• Relatively simple and cost effective• Relatively simple and cost effective
• Constant distillate composition• R or D varies with time• Requires fast response composition sensors• Sensors might not be available or only
justified for larger batch systems• Optimal control mode
• x and R varied with timeSeader & Henley (2006)
• xD and R varied with time• Designed to:
Minimize operation time Maximize amount of distillate Maximize profit
• More complex control scheme
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Multistage Batch Distillation
Removing volatile impurities.
Flexible multi-purpose system
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Seader & Henley (2006)Flexible, multi purpose system
Questions?
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