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

Measuring and Modeling of Mixed Adsorption Isotherms for Supercritical Fluid Chromatography Overview Objectives Experimental Modeling Empirical Thermodynamic Conclusions Lazo, Giese, Lübbert

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 Lazo, Giese, Lübbert 6/21/00 2

Experiment Description I System Components Experimental Set-up Mobile Phase SCF CO 2 Modifier Isopropanol Feed Phytol Fixed Phase Silica Gel Phytol Molecule C 20 H 40 O 1 Gas Supply 7 Oven 2 High Pressure Pump 8 Mixing Loop 3 Pressure Control Unit 9 Analytical Column 4 Manometer 10 Detector CH 2 OH 5 Modifier 11 PC 6 Feed 12 Chromatograms Lazo, Giese, Lübbert 6/21/00 3

Experiment Description II Experimental Conditions Elution Experiments Characteristic Band Profile for a Sigmoidal Isotherm T = 313.15 K 4 Dimensionless Concentration Modifier 3.5 P [bar] [mL/min] 3 120 0.153 SHARP FRONT DIFFUSE REAR 150 0.153 2.5 210 0.153 Single 2 Isotherms 240 0.153 1.5 SHARP REAR 210 0.100 DIFFUSE FRONT 1 210 0.237 0.5 120 0.153 Binary 210 0.153 0 Isotherms 0 1 2 3 4 5 6 210 0.237 Dimensionless Time ! Isotherm with point of inflection Lazo, Giese, Lübbert 6/21/00 4

Perturbation Method ! The Perturbation Method is based on Equilibrium Theory 2 Perturbation Desorption 1.5         − − − − ε ε ε ε _ UV Signal   1 dq       = = = = + + + + i t ( C ) t 1         R , i o ε ε ε ε dC _         i C 1 Adsorption Analysis 0.5 t Trans t Cis 0 0 5 10 15 20 25 30 Dimensionless Time Lazo, Giese, Lübbert 6/21/00 5

Binary Quadratic Isotherm trans-phytol data c i s - phy t ol da t a quadratic mixture isotherm qua dr a t i c mi x t ur e i s ot her m 4.5 5.6 4.4 Time [min] 5.4 4.3 5.2 4.2 P IN = 210 bar P IN = 210 bar IPA FLOW =0.153 mL/min IPA FLOW = 0.153 mL/min 5.0 4.1 0 1 2 3 4 5 6 7 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Concentration [mg/mL] Concentration [mg/mL] + + + + 2 + + + + q b C b C C 2 b C Binary Quadratic Isotherms: Θ Θ Θ Θ = = = = 1 = = = = 1 1 3 1 2 4 1 1 + + + + + + + + + + + + + + + + 2 + + + + 2 q 1 b C b C b C C b C b C s 1 1 2 2 3 1 2 4 1 5 2 ! Five Parameters were fitted + + + + + + + + 2 b C b C C 2 b C q Θ Θ = = = = Θ Θ = = 2 = = 2 2 3 1 2 5 2 ! 21 Parameters in total 2 + + + + + + + + + + + + + + + + 2 + + + + 2 q 1 b C b C b C C b C b C s 1 1 2 2 3 1 2 4 1 5 2 Lazo, Giese, Lübbert 6/21/00 6

Thermodynamic Model Equation of State Literature, Experiments Critical Constants ! PVT Interaction Parameters ! VLE ! Solubility Gibbs Thermodynamic SCF Solute Modifier Isotherm Model Literature, Experiments ! Gravimetric Adsorption Data ! Volumetric ! Chromatographic Adsorbed Phase Model Lazo, Giese, Lübbert 6/21/00 7

Vapor Pressure of Phytol Temperature [K] 300 350 400 450 500 550 600 650 700 750 800 1E7 1000 Critical Point Tc=664.04 K Pressure [Pa] Pc=8.7685 bar 0.1 Acentric Factor w =2.24590 w w w 1E-5 Operating Pv PRSV EOS k k 1 =2.46767 k k Conditions 1E-9 Pv Experimental Points T=313.15 K Pv 1-Eicosanol P=8.5e-10 Pa 1E-13 Lazo, Giese, Lübbert 6/21/00 8

Phytol Solubility T = 313.15 K 0 10 Molar Fraction of Phytol x 2 [-] Decrease in solubility -5 10 ( ( ) ) ( ( ) )         P T V P 1 = = = = v m x exp         2 ∞ ∞ ∞ ∞ φ φ         φ φ P RT 2 -10 10 Phytol Sol. PRSV EOS x IPA = 0 Phytol Sol. PRSV EOS x IPA = 0.0314 Phytol Experimental Solubility Experimental range, upper limit -15 10 0 100 200 300 400 500 600 Pressure [bar] ! The experimental data are inside the theoretical solubility region Lazo, Giese, Lübbert 6/21/00 9

Single Adsorption Isotherms Loadings versus Fugacities Loadings versus Concentrations 45 120 350 350 150 40 210 300 300 cis-phytol loading [mg/mL] 240 35 210- 250 250 210+ 30 200 200 25 150 150 20 100 100 dq/dc [-] 15 50 50 10 0 0 0.0 0.2 0.4 0.6 0.8 0 2 4 6 8 10 C [mg/mL] Fugacity [nPa] Lazo, Giese, Lübbert 6/21/00 10

Single Adsorption Data Fitting 450 trans-phytol loading [mg/mL] 400 ! 10 parameters were fitted T = 313.15 K 350 300 ! Expansion till third virial 250 coefficient 200 ! Loadings of CO 2 and IPA 150 are assumed to be proportional to their 100 fugacities o Pseudo-experimental data 50 — Virial EOS model 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 trans-phytol fugacity [nPa]         ∑ ∑ ∑ ∑ ∑ ∑ ∑∑ ∑ ∑ ∑ ∑ ( ( ( ( ) ) ) ) f 2 3         i = = = = − − − − + + + + + + + + + + + + ! ln ln K A n B n n C         Virial Isotherm: i j ij j k ijk 2     n     A 2 A i j j k Lazo, Giese, Lübbert 6/21/00 11

12 Single Adsorption Isotherm at T = 313.15 K Lazo, Giese, Lübbert 6/21/00

Binary Adsortion Data Fitting trans-phytol mixture isotherm at T = 313.15 K 450 ! Single Parameters remain 400 o Data trans-phytol loading [mg/mL] — Correlation 350 ! 5 additional Parameters — Prediction — Single ads. 300 ! 25 Parameters in total 250 200 150 100 50 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 trans-phytol fugacity [nPa] Lazo, Giese, Lübbert 6/21/00 13

Linear Equilibrium Constants C IPA = 0.1 mL/min C IPA = 0.153 mL/min C IPA = 0.237 mL/min Experimental Points 120 120 110 110 Linear Equilibrium Constant K [-] 100 100 trans-phytol cis-phytol 90 90 80 80 70 70 C IPA increase C IPA increase 60 60 50 50 40 40 30 30 20 20 10 10 0 0 120 160 200 240 280 120 160 200 240 280 Pressure [bar] Pressure [bar] Lazo, Giese, Lübbert 6/21/00 14

Conclusions • Enhanced solubility of phytol at higher fluid density and IPA concentration. • There is competition for the adsorbent actives sites among CO 2 , 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 Lazo, Giese, Lübbert 6/21/00 15