Measuring and Modeling of Mixed Adsorption Isotherms for - - PowerPoint PPT Presentation

Lazo, Giese, Lübbert

Measuring and Modeling of Mixed Adsorption Isotherms for Supercritical Fluid Chromatography

Overview Objectives Experimental Modeling Empirical Thermodynamic Conclusions

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Objectives

• Model adsorption data measured at supercritical

conditions in a systematic way

• Gain a better understanding of adsorption under

supercritical conditions

• Highlight particular characteristics and problems of

adsorption from supercritical fluids

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Mobile Phase SCF CO2 Modifier Isopropanol Feed Phytol Fixed Phase Silica Gel System Components Experimental Set-up

1 Gas Supply 7 Oven 2 High Pressure Pump 8 Mixing Loop 3 Pressure Control Unit 9 Analytical Column 4 Manometer 10 Detector 5 Modifier 11 PC 6 Feed 12 Chromatograms

Experiment Description I

Phytol Molecule

CH2OH C20H40O

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1 2 3 4 5 6 0.5 1 1.5 2 2.5 3 3.5 4 Dimensionless Time Dimensionless Concentration Characteristic Band Profile for a Sigmoidal Isotherm DIFFUSE REAR DIFFUSE FRONT SHARP FRONT SHARP REAR

Experiment Description II

Elution Experiments Experimental Conditions

P [bar] Modifier [mL/min] 120 0.153 150 0.153 210 0.153 240 0.153 210 0.100 Single Isotherms 210 0.237 120 0.153 210 0.153 Binary Isotherms 210 0.237

!Isotherm with point of inflection T = 313.15 K

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5 10 15 20 25 30 0.5 1 1.5 2

Dimensionless Time UV Signal

Adsorption Perturbation Desorption Analysis t Cis t Trans

Perturbation Method

                                ε ε ε ε ε ε ε ε − − − − + + + + = = = =

_

C i i

• _

i , R

dC dq 1 1 t ) C ( t

! The Perturbation Method is based on Equilibrium Theory

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Binary Quadratic Isotherm

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.1 4.2 4.3 4.4 4.5

IPA

FLOW = 0.153 mL/min

PIN = 210 bar

c i s

• phy

t

• l

da t a qua dr a t i c mi x t ur e i s

• t

her m

Time [min] Concentration [mg/mL]

PIN = 210 bar IPA

FLOW=0.153 mL/min

1 2 3 4 5 6 7 5.0 5.2 5.4 5.6

trans-phytol data quadratic mixture isotherm

Concentration [mg/mL]

Binary Quadratic Isotherms:

2 2 5 2 1 4 2 1 3 2 2 1 1 2 1 4 2 1 3 1 1 s 1 1

C b C b C C b C b C b 1 C b 2 C C b C b q q + + + + + + + + + + + + + + + + + + + + + + + + + + + + = = = = = = = = Θ Θ Θ Θ

! Five Parameters were fitted ! 21 Parameters in total

2 2 5 2 1 4 2 1 3 2 2 1 1 2 2 5 2 1 3 2 2 s 2 2

C b C b C C b C b C b 1 C b 2 C C b C b q q + + + + + + + + + + + + + + + + + + + + + + + + + + + + = = = = = = = = Θ Θ Θ Θ

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Thermodynamic Model

Thermodynamic Model Gibbs Isotherm Adsorbed Phase Model Adsorption Data Equation of State Critical Constants Interaction Parameters Literature, Experiments ! Gravimetric ! Volumetric ! Chromatographic Literature, Experiments ! PVT ! VLE ! Solubility SCF Solute Modifier

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Vapor Pressure of Phytol

1E-13 1E-9 1E-5 0.1 1000 1E7 300 350 400 450 500 550 600 650 700 750 800

Operating Conditions T=313.15 K P=8.5e-10 Pa

Temperature [K]

Acentric Factor w w w w=2.24590 Critical Point Tc=664.04 K Pc=8.7685 bar

Pv PRSV EOS k k k k 1=2.46767 Pv Experimental Points Pv 1-Eicosanol

Pressure [Pa]

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100 200 300 400 500 600 10

• 15

10

• 10

10

• 5

10

Pressure [bar] Molar Fraction of Phytol x2 [-]

Phytol Sol. PRSV EOS x

IPA = 0

Phytol Sol. PRSV EOS x

IPA = 0.0314

Phytol Experimental Solubility Experimental range, upper limit

Decrease in solubility

T = 313.15 K

Phytol Solubility

( ( ( ( ) ) ) )

                        φ φ φ φ = = = =

∞ ∞ ∞ ∞

RT P V exp 1 P T P x

m 2 v 2

! The experimental data are inside the theoretical solubility region

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Single Adsorption Isotherms

2 4 6 8 10 10 15 20 25 30 35 40 45

Loadings versus Concentrations

dq/dc [-]

C [mg/mL]

50 100 150 200 250 300 350 0.0 0.2 0.4 0.6 0.8 50 100 150 200 250 300 350

120 150 210 240 210- 210+

Loadings versus Fugacities

cis-phytol loading [mg/mL]

Fugacity [nPa]

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Single Adsorption Data Fitting

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 50 100 150 200 250 300 350 400 450

trans-phytol fugacity [nPa] trans-phytol loading [mg/mL]

• Pseudo-experimental data

— Virial EOS model

T = 313.15 K

( ( ( ( ) ) ) )

∑ ∑ ∑ ∑ ∑ ∑ ∑ ∑∑ ∑ ∑ ∑

+ + + + + + + + + + + + − − − − = = = =                                

j j k ijk k j 2 ij j i i i

C n n A 2 3 B n A 2 A K ln n f ln !

Virial Isotherm: ! 10 parameters were fitted ! Expansion till third virial coefficient ! Loadings of CO2 and IPA are assumed to be proportional to their fugacities

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Single Adsorption Isotherm at T = 313.15 K

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Binary Adsortion Data Fitting

0.1 0.2 0.3 0.4 0.5 0.6 0.7 50 100 150 200 250 300 350 400 450

trans-phytol mixture isotherm at T = 313.15 K trans-phytol fugacity [nPa] trans-phytol loading [mg/mL]

• Data

— Correlation — Prediction — Single ads. ! Single Parameters remain ! 5 additional Parameters ! 25 Parameters in total

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Linear Equilibrium Constants

120 160 200 240 280 10 20 30 40 50 60 70 80 90 100 110 120

cis-phytol CIPA increase

CIPA= 0.1 mL/min CIPA= 0.153 mL/min CIPA= 0.237 mL/min Experimental Points

Linear Equilibrium Constant K [-] Pressure [bar]

120 160 200 240 280 10 20 30 40 50 60 70 80 90 100 110 120

trans-phytol CIPA increase Pressure [bar]

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Conclusions

• Enhanced solubility of phytol at higher fluid density

and IPA concentration.

• There is competition for the adsorbent actives sites

among CO2, IPA, and phytol isomers.

• Decreased desorption tendency at very high

pressures: repulsive forces and adsorbent saturation.

• The model can correlate the data very well but has

poor predictive capabilities. The adsorbed phase description should be improved