Environmentally benign chemical
processes (EBChemP)
Technologies at elevated pressureErika Vági, Edit Székely
BME, Department of Chemical and Environmental Process Engineering
Scope
• Distillation at elevated pressures
• Pressure swing distillation
• Pasteurization with pressure
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Column distillation at elevated pressures
Separation of volatile components (with close boiling points)
• With P change the phase diagram shifts
• Applied in oil and gas refining
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Separation of light hydrocarbons (C1-C4)
Components
methane ~0.7
Ethane 0.4 - 0.55
Propane 0.35 - 0.50
Pc
PPr
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Purification of monomers
pressure (bar) Condensation temperature
(°C)
ethylene 4-6 -68
20 -29
propylene 4-6 -12
16 10
Distillation of monomers at elevated P
Distillation of propylene and propane at 2 MPa
J.D Seader, E. J. Henley, D. K. Roper, Separation Process Principles, Wiley, 2010.
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Column distillation at elevated pressures
Volatile components
Separation of azeotropes:
• If the binary azeotrope:
• disappears at some P or;
• changes composition by 5 mol% or more over a moderate pressure range.
Bubble point – dew point curve and the equilibrium curve
mixture of isopropyl-ether–isopropanol at atmospheric pressure
Minimum-boiling-point azeotrope
isopropyl-ether–isopropanol system
More common;For example: • EtOH:water• EtOH: hexane• Acetone:
formamide• i-prop-ether:i-
propanol
Bubble point – dew point curve and the equilibrium curve
mixture of acetone-chloroform at atmospheric pressure
Maximum-boiling-point azeotrope
Acetone - chloroform system
Minimum-boiling-point heteroazeotrope
Bubble point-dew point curve and equilibrium curve of mixture of ethyl-acetate – water at atmospheric pressure
Minimum-boiling-point two liquid phases azeotrope
Water – n- butanol system
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Modifying the azeotropic composition
The azeotropic composition frequently changes with pressure of even it might disappear
acetone - methanol:
0,26 bar ‹ azeotropic composition‹ 21 bar
Addition of a third component can be avoided
Effect of pressure on azeotropes
J.D Seader, E. J. Henley, D. K. Roper, Separation Process Principles, Wiley, 2010.
Effect of pressure on azeotrope conditions a) temperature of azeotrope; b) composition of azeotrope
Pressure swing distillation
J.D Seader, E. J. Henley, D. K. Roper, Separation Process Principles, Wiley, 2010.
a) T-y-x curves at pressures P1 and P2 for minimum-boiling azeotropes; b) distillation sequence for minimum-boiling azeotrope; c) distillation sequence for maximum-boiling azeotrope.
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Pressure swing distillation (THF-water)
P1 = 1 atm, P2 = 7.8 atm
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tetrahydrofuran (THF) - water
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THF – water separation (with distillation and membrane separation)
Feed
Water
Azeotrope
Permeate
Water
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Industrial examples
THF – water
Acetonitrile – water
methanol – methyl-ethyl ketone (MEK)
acetone – methanol
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Further possibilities
ethanol – ethyl-acetate
benzene – n-propanol
benzene – iso-propanol
ethanol – 1,4-dioxane
methanol – methyl-acetate
MEK – cyclohexane
methanol - dichloromethane
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The effect of elevated pressure
If P increases:Tbp → increases
reboiler → disadvantage
condenser → beneficial
Increase of R and / or N is needed
Plate efficiency (ηplate )→ increases• ηplate (1 bar) ~ 60-75 %
• ηplate (1 bar‹P) ~ 90-100%
Wall thickness → increases → weight of column increases → capital cost increases.
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Pasteurization of food
• Most widely used: heat
• Other possibilities• X-ray
• UV
• gases
• High pressure
Fundamental of pasteurization
B. Caballero, P. Finglas, Encyclopedia of Food Sciences and Nutrition, 2003.
Time-temperature conditions for destruction of Mycobacterium tuberculosis in milk
• Widely used and accepted term to destruct vegetative pathogens in food products with at least possible damage to the sensory qualities of products.
• Prolonged shelf-life.
• Bacterial-spores and heat-resistance enzymes can survive.
Caballero B., Trugo L. C., Finglas P. M., Encyclopedia of Food Science and Nutrition, 2003.
• Continuous operation
• High surface: volume ratio (500:1)
• Turbulent flow on rippled plates
• Residence time: ~10 min
• Pasteurization T: 72-73°C
Heat exchanger panels, 1) Cold product in, 2) Cool water out, 3) Hot water in, 4) Hot water out
Continuous milk pasteurization process
Dairy processing handbook, by Tetra Pak, 2015.
Pasteurization at high P
• HPP – High pressure processing:
– Shelf-life extension process
– Without the application of heat or chemicals
– Applies ultra high pressure (103422 – 620000 kPa)
– For few minutes
– Spores and common food enzymes tolerate high P
Effect of HPP on milk processing
Mussa D. M., Ramaswamy H. S., Ultrahigh pressure pasteurization of milk, LWT, 1997.
Application of HPP
• Higher quality
• But higher equipment cost and limited scale
• Specialty products (Bioactive milk protein hydrolysates, lactoferrin-enriched jelly, probiotic drinks, etc.)
Avure HPP (20-35 million liter / year)
Huppertz T., High pressure processing of milk, Woodhead Publ, 2010.
• For seafood, fruit and vegetables, juices and meat products….