Separation Processes Laboratory - Prof. Mazzotti - Rate Controlled Separations

Adsorption

Chromatography

Separation Processes Laboratory - Prof. Mazzotti - Rate Controlled Separations

Feed Eluent

Time

Principle of chromatography

Time

Chromatogram

• Chromatography is a technique used for the separation of two or more compounds in a mixture

• With the help of an eluent (mobile phase), the mixture is fed into and travels through the column

• Since the different species of the fed mixture have different affinities with the adsorbent (porous or non-porous, called stationary phase), they travel the column at different speeds and are collected separately at the end of the column

Separation Processes Laboratory - Prof. Mazzotti - Rate Controlled Separations

Geometry of a packed bed column

Flow Molecules can be:• in the interstitial phase F (fluid)• in the pores P (fluid)• on the solid surface A (adsorbed)

Separation Processes Laboratory - Prof. Mazzotti - Rate Controlled Separations

Chromatography: examples

Example: bio-separation Stationary phases - adsorbents

Monobeads(APhBiotech)

Silica gel 60(Merck)

Separation Processes Laboratory - Prof. Mazzotti - Rate Controlled Separations

Types of chromatography: high pressure liquid chromatography (HPLC)

Separation Processes Laboratory - Prof. Mazzotti - Rate Controlled Separations

Types of chromatography: column chromatography

High pressure

Medium pressure

Separation Processes Laboratory - Prof. Mazzotti - Rate Controlled Separations

Types of chromatography: multicolumn chromatography

Separation Processes Laboratory - Prof. Mazzotti - Rate Controlled Separations

UOP Sorbex (~100’000 t/y), since 1960

IFP Eluxyl (>400’000 t/y), since 1998 (only p-xylene on zeolite, 5 units)

• p-xylene from C8aromatics on Y-zeolite (53 units)

• n-/iso-parafins on 5A-zeolite (33 units)

• others on zeolites (~15 units)

Types of chromatography: simulated moving bed

Separation Processes Laboratory - Prof. Mazzotti - Rate Controlled Separations

Chromatography operation modes and solute propagationElution chromatography• The sample is injected at the

beginning of the column (solutes A + B) and a mobile phase is continuously fed (elute C)

• The retention time of each specific compound can be obtained

ABC C C

time

intensity

B

A + B

time

intensity

timeB

A

intensity

C

Frontal analysis• Pure sample (A+B) continuously

fed to the column

• Provides a general measure of how compounds are retained in the column

Displacement chromatography• Sample (A+B) injected at the

beginning of the column and is displaced by a more highly retained solute (C)

• Higher product concentration and increased throughput may be obtained

Separation Processes Laboratory - Prof. Mazzotti - Rate Controlled Separations

Phase equilibrium: linear adsorption isotherm

Linear adsorption isotherm:• All species decoupled• Valid in dilute systems

Selectivity

3D fluid phase: T, P, V, ci (moles i/fluid phase volume)

2D adsorbed phase: T, π, A, ni (moles i/particle volume)

3D fluid phase: T, P, V, ci (moles i/fluid phase volume)

2D adsorbed phase: T, π, A, ni (moles i/particle volume)

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Separation Processes Laboratory - Prof. Mazzotti - Rate Controlled Separations

Retention time

Zero velocity in the pores

v:interstitial fluid velocity time fraction spent in fluid phase

time fraction spent in adsorbed phase

average velocity of species i

retention time

linear adsorption isotherm

Separation Processes Laboratory - Prof. Mazzotti - Rate Controlled Separations

Retention time

Separation Processes Laboratory - Prof. Mazzotti - Rate Controlled Separations

Propagation of a linear pulse

• Peak area remains constant

• Peak shape changes: band broadening

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Separation Processes Laboratory - Prof. Mazzotti - Rate Controlled Separations

Propagation of a linear pulse

ideal non-ideal

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Separation Processes Laboratory - Prof. Mazzotti - Rate Controlled Separations

Selectivity S

A+B AB

Chromatogram: ideal system

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Separation Processes Laboratory - Prof. Mazzotti - Rate Controlled Separations

Resolution R

non-ideal

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Separation Processes Laboratory - Prof. Mazzotti - Rate Controlled Separations

Comparison of performance

Low selectivity

High selectivity

same in both cases

Separation Processes Laboratory - Prof. Mazzotti - Rate Controlled Separations

Preparative chromatography

Inject pulses of mixture with components i = 1, 2 for a pulse duration tp (ideal behavior – each pulse at equal velocity) to a column initially filled with solvent

Plug flow

Baseline separation: intersection within the column

No baseline separation: intersection outside the column • tp too long

• L too short • v too large

Separation Processes Laboratory - Prof. Mazzotti - Rate Controlled Separations

Preparative chromatography (2)

Condition for separation: intersection within the column

Intersection:

Separation of 3-component mixture

Critical and designcondition

Both conditions must be satisfied

Plug flow

Separation Processes Laboratory - Prof. Mazzotti - Rate Controlled Separations

Summary

• Geometry of a packed bed column

• Principle of chromatography

• Types of chromatography

• Chromatographic modes:- Elution chromatography- Frontal analysis- Displacement development

• Linear adsorption isotherm

• Retention time

• Selectivity and resolution

• Preparative chromatography