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

3

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

4

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….