MOF-Workshop, Leipzig, March 2010 Possibilities and Limits for the Determination of Adsorption Data Pure Gases and Gas Mixtures Reiner Staudt Instutut für Nichtklassische Chemie e.v. Permoserstraße 15, D-04318 Leipzig, Germany Staudt@inc.uni-leipzig.de http://www.uni-leipzig.de/inc
Content Introduction Experimental methods pure isotherms Experimental methods mixed isotherms Examples Acurracy of different methods Technical Adsorption Process Conclusion
Adsorption on Adsorption on surfaces / separation Technical usable effects Thermodynamic effect (differences between the sorption capacities) Knowledge of Isotherms Kinetic effect (differences between the sorption velocities) Knowledge of transport coefficients Steric effect (molecular sieve effect) Knowledge geometrical parameters
Basics of sorption technique / processes amount adsorbed 30 25 20 15 10 5 0 A to B: pressure swing / purge with intert gas A to D: temperature swing A to C: mix of both B C 0 200 400 600 800 1000 1200 1400 1600 pressure A D T1 T2 > T1 Temperature swing process (TSA) Desorption by increase of T (A to D) Hot inert gas Water vapor Electrical heating Pressure swing process (PSA/VPSA) Desorption by decrease of p (A to B) PSA adsorption at higher pressures (>3 bar); regeneration at atmospheric pressure VPSA adsorption at higher pressures (>1,2 bar); regeneration under vacuum Combined TSA-PSAk Desorption by increase of T and decrease of p (A to C) (1) D. Bathen, M.Breitbach, Adsorptionstechnik, Springerverlag, 2001
Industrial application of adsorption Gas separation (Air to Oxygen and Nitrogen, Isoalkanes and n-alkanes) Gas purification (drying of natural gas, hydrogen etc.) Recovery of organic compounds (toluene, hydrocarbons etc.) Environmental (organic solvents from waste air etc.)
Industrial application of adsorption choice of best adsorbent optimal gas fluxes cycle time product quality energy costs adsorber to clean natural gas
Pressure Swing Adsorption (PSA) production Adsorber A regeneration Adsorber B Knowledge of: Isotherms Heat of adsorption kinetics coadsorption Prediction of Breakthrought Curves
Pressure Swing Adsorption (PSA) Knowledge of: Isotherms Heat of adsorption kinetics coadsorption Prediction of Breakthrought Curves production Adsorber B regeneration Adsorber A
Adsorption Isotherms of Ar, Kr, O 2 and Xe
Influence of a Surface barrier 1 relative Uptake Ψ(t) 0,8 0,6 0,4 0,2 0 0 500 1000 1500 2000 2500 3000 time [s] relative Uptakes for a untreated and a modified zeolite material for propane at 100 C: fitted with Nonisothermal model and fitted surface controlled model Transport diffusivities: 4*10-13 m 2 /s, 3*10-14 m 2 /s
Kinetics of Adsorption of Pure Ar, Kr, O 2 and Xe
Experimental Methods Pure Isotherm Gravimetry Volumetry Break through curves Mixed Isotherm Volume-Gravimetry Volumetry with Gaschromatography (GC) Modified van Ness Method Sum-Isotherm-Method
Experiment - Gravimetry Calibration of instrument: sampe holder... Measurement: p, T, m MB Calculation: as f Ω= m V ρ
Helium on Activated Carbon Microbalance [mg] 0-40 -80-120 -160-200 0 10 20 30 40 50 298 K 313 K 328 K 343 K Pressure [MPa]
Helium on Activated Carbon reduced mass [mg/g] 0-15 -30 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 298 K 313 K 328 K 343 K 298 K V = 0.461607 cm3/g 313 K V = 0.468982 cm3/g 328 K V = 0.473355 cm3/g 343 K V = 0.477686 cm3/g -45 He - Density [g/cm³]
CO 2 on AC Norit R1 Excess amount adsorbed [mg/g] 500 400 300 200 100 m exp, T = 343 K m LF,T, T = 343 K m exp, T = 328 K m LF,T, T = 328 K m exp, T = 313 K m LF,T, T = 313 K mc = 641.8 mg/g α = 1.05 b C = 1.06 1/MPa E = 13.41 kj/kmol V pore = 0.56 cm 3 /g 0 0 10 20 30 40 50 Pressure [MPa]
Ethylacetate on Activated Carbon at 303 K 4.50 Amount adsorbed [mmol/g] 4.00 3.50 3.00 2.50 2.00 1.50 1.00 0.50 0.00 0.00 20.00 40.00 60.00 80.00 100.00 120.00 Pressure [mbar]
Experiment - Volumetry p* T* p T V* V VP GS Calibration of instrument: Volume of vessel... Measurement: p, T m S Ω = m - V as ρ(p,t) = V* ρ(p*,t*) - (V*+V) ρ(p,t) Calculation: as f Ω= m V ρ
Pure Gases on Norit R1 at 298 K Excess amount adsorbed [mmol/g] 12.5 10.0 7.5 5.0 2.5 CO 2 CH 4 N 2 0.0 0 1 2 3 4 5 6 7 Pressure [MPa]
Experiment Gravimetry dynamic Calibration of instrument: sampe holder... Measurement: p, T, m MB, concentration c(t), Calculation: as f Ω= m V ρ
Butene ant Water in Nitrogen on Catalyst 4 3 Mass change [mg] 2 1 0-1 -2-3 -4 0 50 100 150 200 250 300 Heating to 280 C in N2 flow 30' at 280 C in air 30' at 160 C in N2/Butene flow 65' in N2/Butene flow + H 2 O -5-6 Cooling to 160 C Time [min]
Experiment - Break through curves 7 5 Concentration 1 2 3 4 Time Temp. C Temp. C Temp. C Temp. C 8 6 4 2 CO 1 Calibration of instrument: bulk density... Measurement: concentration c(t), massflow m flow time t Pressure bar Temp. C 1 Gas supply 2 Flowmeter 3 Pressure/temp. gauge 4 Adsorber 3 5 Thermocouples 6 Capacitor 7 Impedance analyser 8 Concentration detector (TCD) 2 1 He Calculation: as f Ω= m V ρ as f Ω= ρ m flow V = m *t V * ρ col f
CO2 in Air on Zolithe at 295 K Concentration CO2 [ppm] 600.0 500.0 400.0 300.0 200.0 100.0 Dry air 28 l/h, 30 g zeolithe 0.0 0.0 500.0 1000.0 1500.0 2000.0 2500.0 3000.0 Time [min]
CO2 in N2 on Zeolithe 13X at 295 K 66.5 1.0 66.0 IA 0.8 Elec. capacity [pf] 65.5 65.0 64.5 TCD 0.6 0.4 Concentration 64.0 63.5 0.0 0 200 400 600 800 1000 1200 Time [s] T = 295 K p = 0.107 MPa 0.2 N2: 30 l/h, CO2: 10 l/h, zeolithe 100 g
N 2 / CO 2 / CH 4 (10% / 40% / 50%) on AC Norit NR1 Extra 1 Durchbruchskurve Konzentration C/Co 0.75 0.5 0.25 N2 CH4 CO2 0 200 400 600 800 1000 1200 1400 1600 Zeit in Sekunden Mass AC = 75,9 g, p = 1,2 bar
N 2 / CO 2 / CH 4 (10% / 40% / 50%) on AC Norit NR1 Extra 40 Temperaturverlauf Temp. der Thermoelemente in C 35 30 25 31 20 0 200 400 600 800 1000 1200 1400 1600 Zeit in Sekunden Mass AC = 75,9 g, p = 1,2 bar
Experiment accuracy Pressure Temperature Mass Volume of sample holder p = 0.002 MPa T = 0.01 K m = 0.01 mg V = 0.0002 cm 3 Volume of vessel Concentration Gas Flow Time V = 0.02 cm 3 c = 0.1 % V t =0.1 ml/min t =0.01 s Gravimetry Volumetry Breakthrough Gravimetry dyn. m/m = 0.1 % m/m = 0.5 % m/m = 0.5 % m/m = 0.25 %
Experiment Gravimetry Direct measurement of m, p, T Mass change during sample preparation Uptake curve Adsorption isotherm, (Kinetics) Volumetry Direct measurement of p, T Simple apparatus Adsorption isotherm Breakthrough curve Direct measurement of c, p, T Simple apparatus Concentration dependency in carrier gas Close to technical separation
Volume-Gravimetry & Volumetry with GC 94,22547 g magnetic coupling microbalance T p Calibration: Volume of vessel & sample holder, GC... Volume-Gravimetry: storage vessel 1 gas supply Measurement: p, T, m Calculation: sample IS 2 IS 1 injection systems gas circulation pump m fl 1, m fl 2, m 1, m 2 storage vessel 2 T Volumetry with GC: Measurement: p, T, c T gas chromatograph vacuum pump Calculation: m fl 1, m fl 2, m 1, m 2
CO/H2 Mixture on 5A Zeolite Excess amount adsorbed [mmol/g] 4 3 2 1 0 IAST: n = n CO + n H2 IAST: n CO IAST: n H2 Experiment: n = n CO + n H2 Experiment: n CO Experiment: n H2 0 1 2 3 4 5 6 7 Pressure p [MPa] T = 303 K, y(co)=0.3
Volume-Gravimetry accuracy Pressure Temperature Mass Volume of sample holder p = 0.002 MPa T = 0.01 K m = 0.01 mg V = 0.0002 cm 3 Volume of vessel Concentration Gas Flow Time V = 0.02 cm 3 0.1 % V t =0.1 ml/min t =0.01 s For CO/H2 on Zeolite: Concentration of fluid phase Concentration of adsorbed phase Total amount adsorbed c/c = 1.25 % m/m = 1.5 % c/c = 3.5 %
CO2/N2 an AK Norit R1, T = 298 K 14 12 10 8 6 Excess amount adsorbed [mmol/g] 4 2 0 0.8 0.6 0.4 Conc. yco2 0.2 0.0 0 1 2 3 4 5 6 7 Pressure [MPa]
CH4/CO2/N2 an AK Norit R1, T = 298 K nch4, nch4 + nco2, ntot [mmol/g] 12 10 8 6 4 2 0 y CH4 = 0,72 / y CO2 = 0,12 / y N2 = 0,16 0 1 2 3 4 5 6 7 Pressure [MPa]
Volumetry with GC Pressure Temperature Mass Volume of sample holder p = 0.002 MPa T = 0.01 K m = 0.01 mg V = 0.0002 cm 3 Volume of vessel Concentration Gas Flow Time V = 0.02 cm 3 0.1 % V t =0.1 ml/min t =0.01 s Concentration of fluid phase Concentration of adsorbed phase Total amount adsorbed c/c = 1.0 % c/c = 2-5 % m/m = 1.5 %
Experiment Volume- Gravimetry Direct measurement of m, p, T Mass change during sample preparation Adsorption isotherm Partial load Kinetics Needs: Equation of State for mixed gas M 1 M 2 Volumetry with GC Direct measurement of p, T Simple apparatus Adsorption isotherm Partial load Needs: Gaschromatograph Equation of State for mixed gas Van Ness Method Direct measurement of m, p, T Simple measurement Adsorption isotherm Partial load (Calculated) Application to non ideal gases difficult
Typical 4 Bed-Adsorber for H2 Purification via PSA n e g o r d y H s a g D - t e g r u P A 0 3 A c u d o r P d e e
Adsorption Process PSA and TSA Amounr adsorbed [Nl/kg] 30 25 20 15 10 5 0 A nach B: Pressure Swing Adsorption A nach D: Temperature Swing Adsorption A nach C: Combination PSA and TSA B C 0 200 400 600 800 1000 1200 1400 1600 Partial pressure [mbar] A D T1 T2 > T1
PSA for Hydrogen Purification Open questions: How many Adsorber (3, 4 or 5 beds) Cycle Time Adsorption Isotherm (p,t) Kinetik of Adsorption Adsorption and Desorption Pressure Adsorption and Desorption Temperatur Purity of Product
Amount Adsorbed / NL.kg -1 60 50 40 30 20 10 CO2 CH4 CO N2 H2 Design 0 0 500 1000 1500 Partial Pressure / mbar 1.0 relative concentration 0.8 0.6 0.4 0.2 0.0 0 200 400 600 800 1000 time / s * Mahler AGS GmbH, 2008.
Hydrogen production and purification The most common and economical route: Steam Reforming of Natural Gas combined with a water-gas shift reaction Steam-Methane-Reformer-Off-Gas (SMROG): H 2 -rich stream (70 80%) Impurities: H 2 S (traces) H 2 O vapor (<1%) N 2 (<1%) CH 4 (3 6%) CO (1 3%) CO 2 (15 25%) Pressure Swing Adsorption (PSA) (85% - H 2 producers) H 2 : 98 99.99+ mol% *Sircar S. and Golden T.C., Sep. Sci. Tech., 35, 5, 667-687, 2000. * Mahler AGS GmbH Internal Note, 2008.
Adsorption Equilibria of H 2, CO 2, CO, CH 4, N 2 60...on Activated Carbon 60...on Zeolite CO2 Amount Adsorbed [Nl/kg] 50 40 30 20 CH4 CO N2 H2 Amount Adsorbed [Nl/kg] 50 40 30 20 CO CH4 N2 H2 10 10 0 0 500 1000 1500 0 0 500 1000 1500 Partial Pressure [mbar] Partial Pressure [mbar]
Hydrogen - PSA Process Steps Product H 2 H 2 N 2 CO CH 4 CO 2 Tailgas Process gas Pressure equilisation Pressure equilisation Purge Pressurisation H 2 /N 2 /CO/ CH 4 /CO 2 Process gas Desorption Tailgas
Real measurable Quantity Total mass in system: a fl mtot = m + m Mass adsorbed: m =Ω+ V * ρ a as fl Mass in fluid phase: ( )* ρ (, ) m fl = V V as fl pt m =Ω+ V ρ tot * fl
Conclusion 1. Only measurable properties of adsorption equilibria are the surface excess quantities. 2. Different experimental methods for specific application. 3. Full determination of mixed gas adsorption equilibria leads to minimum error in experimental data. 4. Characterization Volumetry Pure isotherm Gravimetry Mixed gas Volumetry with GC Binary mixture Volume-Gravimetry Separation Breakthrough curve