DVS Vacuum Dynamic Gravimetric Sorption

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1 DVS Vacuum Dynamic Gravimetric Sorption Dr Vladimir Martis Product specialist 6 th October 215

2 Why Dynamic Gravimetric Sorption? All current vacuum sorption instruments operate in a static mode The sorbate enters the sample chamber, the chamber is sealed and the experiment occurs under static conditions, i.e. no gas flow. The system pressure can change for various reasons, but commonly due to vacuum leaks. Studying dynamic processes is not possible. Why is Vacuum desirable? Materials such as microporous solids, nanomaterials, chemical adsorbents and strong hydrates need extensive drying/outgassing, which is not possible with traditional methods such as dry gas flow and thermal convection heating. Guarantee of clean and dry environment for air or moisture sensitive samples. Gas and vapor adsorption at low relative pressures (e.g. water adsorption at 25 o C from.1 to 5%P/Po in.1% step). Solely water vapor or organic vapour adsorption. 1

3 Dynamic Gravimetric Sorption Sub-atmospheric vapor sorption technique that measures the uptake and loss of vapor/gas using micro-balance in dynamic mode. Controls both upstream rates of sorbate entry and the downstream rates of sorbate exit by dynamic butterfly valve on the exit side of the system. Permits control over the residence time of the sorbate in the chamber. Estimates amount of sites that are accessible to organic or water vapors at ambient temperatures which is not possible with traditional volumetric methods (nitrogen adsorption at 77K).

Principle of Dynamic Gravimetric sorption

4 Principle of Dynamic Gravimetric sorption Air Air (1) Chamber evacuation Scheme of DVS vacuum Downstream pumping Sample pan (2) Filling with sorbate Upstream sealed Downstream sealed (3) Steady-state Mass flow controllers opened Downstream opened Upstream opened 3

5 Measurable Physisorption Properties Adsorption and desorption Isotherms (T constant, P variable) Adsorption Isobars (T variable, P constant) BET (Brunauer, Emmett and Teller) Surface Area Micro/meso-pore size distributions Diffusion coefficients Heat of sorption 4

6 Benefits of DVS Vacuum The use of the same chamber for in-situ activation/outgassing immediately followed by sorption measurements Sorption measurements from very low up to atmospheric pressures using step size of.1% P/Po Wide range of sample and vapor temperatures (2 to 4 o C). Isothermal control of entire system; no condensation issues. Real time sorption kinetics Wide range of sorbate molecules (Benzene, Toluene, Xylene, Aldehydes, Alcohols, H 2 S, NH 3, CO 2 ) Competitive adsorption of two probe molecules (H 2 O-CO 2, H 2 O- NH 3, H 2 O-MeOH) Multiple sorption/desorption/outgassing cycles in one experiment Sorbate molecules residence time control 5

7 DVS vacuum system Vacuum pumps assembly Data acquisition station Incubator 6

DVS vacuum system Incubator temperature controller Cooler Butterfly valve Cooling Fun Incubator switch Incubator door Pre-heater temperature

8 DVS vacuum system Incubator temperature controller Cooler Butterfly valve Cooling Fun Incubator switch Incubator door Pre-heater temperature controller Pre-heater switch Turbo pump Rotary pump Pressure controller 972 Pressure controller Manual (speedi) valve Turbo pump controller 7

9 DVS vacuum stand 1 Torr Baratron 1 Torr Baratron UltraBalance hat Sample side Reference side Gas Vacuum gas manifold Vapour 8

10 High temperature pre-heater Miniature radiator style pre-heater for outgassing samples up to 4 o C Sample pan Pre-heater

11 Instrument specs Dynamic (or static) operational mode Upstream and downstream vapor/gas flow controls Temperature controlled incubator operating in the range from 2 (15) to 7 o C In-situ sample pre-conditioning /activation up to 4 o C (using preheater) and high vacuum Multi vapor and/or gas injection system for sorbates (2 gasses or 2 vapors or 1 gas and 1 vapor) Water vapor adsorption up to 9 %P/P up to 7 o C and up to 15 o C up to 7%P/P Highly accurate baratrons for pressure measurements (.5 to 1 Torr and.1 to 1 Torr) Cold cathode/ MicroPirani transducer from very low (1-8 Torr) to atmospheric pressure measurements 1

12 Low end P/Po control

13 Vacuum /temperature drying behavior of 5A zeolite Vacuum and preheater drying of 5A zeolite Initial mass: mg 12

14 Drying kinetics of hydrates Drying Behaviour of Pharmaceutical Hydrates: Carbamazepine (CBZ) dihydrate Pressure: 1-3 Torr Change in mass (%) ºC 3ºC 4ºC 5ºC 6ºC Moisture content, X A Torr, 2ºC Torr, 3ºC Torr, 4ºC Torr, 5ºC 5 Torr, 2ºC 5Torr, 3ºC 5 Torr, 4ºC 5 Torr, 5ºC Time (minutes) Time (minutes) Very strong kinetic dependence of drying rate with temperature and level of vacuum for CBZ dihydrate

15 Benzene sorption of porous material at 25 o C 45 DVS Isotherm Plot Cycle 1 Sorp Cycle 1 Desorp Temp: 25. C Meth: MRef: Change In Mass (%) - Ref Change In Mass (%) - Ref DVS Change In Mass (ref) Plot dm - dry Target % P/Po Temp: 25. C Meth: MRef: Target % P/Po Time/mins % P/Po Surface Measurement Systems Ltd UK Surface Measurement Systems Ltd UK

16 Pt-SiO 2 toluene sorption at 55 o C 9 2 DVS Isotherm Plot Cycle 1 Sorp Cycle 1 Desorp Temp: 25. C DVS Isotherm Plot Meth: MRef: Temp: 54.8 C Meth: MRef: Cycle 1 Sorp Cycle 1 Desorp Change In Mass (%) - Ref P/Po increased in.2 % % P/Po Surface Measurement Systems Ltd UK Change In Mass (%) - Ref Sample % P/Po Surface Measurement Systems Ltd UK

17 Isotherm comparison for Pt-SiO 2 toluene sorption at 25 and 55 o C 9 DVS Isotherm Plot 8 7 PtSiO2 toulene 55c PtSiO2 toulene 55c _DVS Cycle 1 Sorp PtSiO2 toulene 55c PtSiO2 toulene 55c _DVS Cycle 1 Desorp Pt- SiO2 toulene 25c Pt- SiO2 toulene 25c _DVS Cycle 1 Sorp Pt- SiO2 toulene 25c Pt- SiO2 toulene 25c _DVS Cycle 1 Desorp Change In Mass (%) - Ref Sample % P/Po Surface Measurement Systems Ltd UK Comparison of isotherms for Pt-SiO 2 Toluene sorption at 25( adsorption in green and desorption in purple) and 55 o C (adsorption in red and desorption in blue) 16

18 Cyclohexane and methanol adsorption 18 Cycle 1 Sorp Cycle 1 Desorp DVS Isotherm Plot Temp: 25. C Meth: MRef: DVS Change In Mass (ref) Plot Temp: 25. C Meth: MRef: dm - dry Target % P/Po 1 Change In Mass (%) - Ref Change In Mass (%) - Ref Target % P/Po Sample % P/Po Surface Measurement Systems Ltd UK Time/mins Surface Measurement Systems Ltd UK MOR C FER C N Surface area (m 2 /g) Methanol Cyclohexane n-octane 22 N Micropore volume (cm 3 /g) Methanol Cyclohexane.14.9

19 Acetaldehyde and benzene sorption Benzene sorption at 2 o C Acetaldehyde sorption at 17 o C 8 7 DVS Isotherm Plot beads 18C acetaldehyde_2cycles Bs _DVS Cycle 1 Sorp beads 18C acetaldehyde_2cycles Bs _DVS Cycle 1 Desorp MOF beads 18C acetaldehyde_ _DVS Cycle 1 Sorp 6 Change In Mass (%) - Ref % P/Po Surface Measurement Systems Ltd UK Sample Surface Area Monolayer Capacity [m²/g]: [Mol/g]: MOF beads Beads Sample Surface Area Monolayer Capacity [m²/g]: [Mol/g]: MOF beads Beads 654.2

20 Water sorption isotherm of freeze-dried polymer at 4 o C DVS Change In Mass (ref) Plot dm - dry Target % P/Po DVS Isotherm Temp: Plot 4. C Cycle 1 Sorp Meth: MRef: Cycle 1 Desorp Temp: 4. C Meth: MRef: Change In Mass (%) - Ref Change In Mass (%) - Ref Time/mins Surface Measurement Systems Ltd UK Target % P/Po Adsorption 2 1 desorption Sample % P/Po Surface Measurement Systems Ltd UK Adsorption/desorption cycles showing water sorption kinetics 4 o C (P o = 55.3Torr).

21 Ionic liquid water sorption at 25 o C 1 5 Cycle 1 Sorp Cycle 1 Desorp 1 Change In Mass (%) - Ref Mass/mg Time/mins Surface Measurement Systems Ltd UK Partial Pressure (%) Sample % P/Po Surface Measurement Systems Ltd UK

22 Sylosiv A1 water sorption at 4 o C 35 DVS Change In Mass (ref) Plot Date: 11 Dec 211 Time: 1:46 am File: Sylosiv A1 water 4C_2cycles Sylosiv A1 water 4C_2cycles _DVS.xlsb Sample: Sample: Sylosiv A1 water 4C_2cycles dm - dry Target % P/Po Temp: 4. C Meth: MRef: Change In Mass (%) - Ref Target % P/Po Time/mins Surface Measurement Systems Ltd UK

23 Sylosiv A1 water sorption at 4 o C 35 DVS Isotherm Plot Cycle 1 Sorp Cycle 1 Desorp Cycle 2 Sorp Cycle 2 Desorp Temp: 4. C Meth: MRef: Change In Mass (%) - Ref Sample % P/Po Surface Measurement Systems Ltd UK

24 Water adsorption isobars SAPO-34 water adsorption isobars at 27 o C 16 Mass/mg Temperature (degc) P/Po (%) Temp: 27. C Meth: MRef: Axis Title 8 6 % P/Po Time/mins Surface Measurement Systems Ltd UK

25 SAPO-34 water adsorption isobars at 27 o C Change In Mass (%) - Ref Cycle 1 Increasing T Cycle 2 Increasing T Cycle 3 Increasing T Cycle 4 Increasing T DVS Isobar Plot Cycle 1 Decreasing T Cycle 2 Decreasing T Cycle 3 Decreasing T Cycle 4 Decreasing T Cycle 1: 8.1 Torr Cycle 2: Torr Cycle 3: Torr Cycle 4: Torr % P/Po: 48.28% Meth: MRef: Temperature ( C) Surface Measurement Systems Ltd UK

26 Cyclohexane carbon sorption at 25 o C Cycle 1 Sorp Cycle 1 Desorp Change In Mass (%) - Ref Change In Mass (%) - Ref Time/mins Target P/P (%) Surface Measurement Systems Ltd UK P/P (%) Surface Measurement Systems Ltd UK

27 Cyclohexane carbon sorption at 25 o C BET Surface area determination BET plot Sorption constant R [%] Sample Monolayer Surface Area Capacity [m²/g]: [Mol/g]: Carbon

28 DMMP carbon sorption at 25 o C 27

29 Partial Pressure Control up to 1Torr 1.2 Dimethyl methylphosphonate 1 Actual Pressure [Torr] Time/mins Surface Measurement Systems Ltd UK

30 Dynamic adsorption of 2-hexanol on activated carbon 6 Change in mass / % Pa 1.7x1-3 Torr 4.9x1-2 Torr 1.8x1-2 Torr 6.59 Pa 6.7x1-3 Torr 2.5x1-3 Torr 2.41 Pa.89 Pa.33 Pa 1.4x1-1 Torr Pa Time/mins Normal static vacuum methods suffer from the effect of system leak rates for sorption at low pressures, resulting in the system pressure not equalling the vapour pressure. Dynamic vacuum overcomes this problem by continuously bleeding the vapour into the system and continuously taking vapour out using the down stream butterfly controlled vacuum.

31 Co-adsorption of Water and Octane on Activated Carbon Coated with Chitosan 3

CO 2 Gas Sorption on Hydroxide at 25 o C 27,2 27,1 6. Torr 8. Torr 1. Torr 27 2. Torr 4. Torr 26,9.

32 CO 2 Gas Sorption on Hydroxide at 25 o C 27,2 27,1 6. Torr 8. Torr 1. Torr Torr 4. Torr 26,9.5 Torr 26,8 26,7 26,6. Torr 26,5 26, Hydroxides can be potentially used for CO 2 capture for environment protection. 31

33 Adsorption Heat Pumps Adsorption heat pumps (AHPs) are alternative to conventional vapor compression based heating, ventilation and air conditioning systems. Benefits of AHPs Energy efficient and environmentally friendly Minimal electricity consumption Small CO 2 footprint Use sustainable energy sources such as solar or geothermal energies or waste heat from industrial processes The AHP rely on the reversible physisorption of the adsorptive (a refrigerant vapor) on porous material (the adsorbent). The adsorption cycle is driven by temperature swings applied to the adsorbent. 32

34 Adsorption Heat Pumps Requirements for the adsorbent in AHPs high water uptake capacities to maximize heating and cooling efficiencies Rapid adsorption desorption kinetics Zeolites are promising adsorbent materials because of their high surface area, tuneable hydrophilicity/hydrophobicity, uniform pore size, high adsorption capacity and shape/size selectivity. The aim of the work is to measure adsorption isotherms which are required to understand physisorption properties of the adsorbents. 33

35 NaY water sorption at 25 and 65 o C Development of adsorption based thermal batteries (MIT) Amount adsorbed (wt.%) normal normal_ desor, 2, 4, 6, 8, 1, Relative pressure x1 Amount adsorbed (wt.%) , 2, 4, 6, 8, 1, relative pressure X1 65C_adsor 65C_desor 25C_adsor 25C_desor Very good reproducibility Sample regenerated for 8h at 37 o C 34

36 13x Zeolite outgassing at high temperature and vacuum Date: 11 Dec 211 Time: 1:46 am File: 13x water 25c 13x water 25c _DVS.xlsb Sample: Sample: 13x water 25c DVS Drying Curve Drying Mass Temp: 25. C Meth: MRef: Mass/mg Time/mins Surface Measurement Systems Ltd UK Outgassing : 25min at 37 o C using the pre-heater and high vacuum 35

37 13x Zeolite water sorption at 25 o C DVS Change In Mass (ref) Plot dm - dry Target % P/Po Temp: 25. C Meth: MRef: Change In Mass (%) - Ref Target % P/Po -5 Time/mins Surface Measurement Systems Ltd UK Adsorption/desorption cycles showing water sorption kinetics 25 o C (P o = 23.8Torr). 36

38 13x Zeolite water sorption isotherm at 25 o C DVS Isotherm Plot Cycle 1 Sorp Cycle 1 Desorp Cycle 2 Sorp Cycle 2 Desorp Temp: 25. C Meth: MRef: Change In Mass (%) - Ref Sample % P/Po Surface Measurement Systems Ltd UK

39 13x Zeolite water sorption BET calculation at 25 o C p/[n(p-p)] [g/mol] BET Linear Plot linear fit experiment p/p Surface area is derived from water sorption isotherm. Surface Area: 698m²/g, Monolayer Capacity:.11 [Mol/g], Sorption Constant: -162, R:

40 SO 2 gas sorption on three different Zeolites at 25 o C Result shows typical Type I isotherms. Sorption was found to be irreversible at 25 C, i.e. desorption could not be achieved by vacuum alone. 39

41 BET surface area measurement of 13x using SO 2 gas at 25 o C BET surface area of a 13x Zeolite measured by DVS Vacuum using SO 2 gas. The result correlates well with the established value of 75m 2 /g, measured using N 2 at 196 C. 4

42 Water/Ethanol Zeolite Sorption Isotherms at 13 o C 9 Cycle 1 Sorp Cycle 1 Desorp DVS Isotherm Plot for water sorption at 13 o C 1.4 DVS Isotherm Plot for ethanol sorption at 13 o C Change In Mass (%) - Ref Change In Mass (%) - Ref t % P/Po Surface Measurement Systems Ltd UK % P/Po Measurement Surface Systems Ltd UK DVS Isotherm Plot for 95% ethanol and 5% water at 13 o C Change In Mass (%) - Ref Cycle 1 Sorp Cycle 1 Desorp Molecular sizes: Water:.28nm Ethanol:.44nm % P/Po Surface Measurement Systems Ltd UK

43 Drying of 4A zeolite at 7 o C DVS Drying Curve Temp: 7. C Meth: MRef: Mass/mg Time/mins Surface Measurement Systems Ltd UK Outgassing: 7 hours at 3 o C using the pre-heater and high vacuum 42

44 4A Zeolite water sorption at 7 o C 3 25 dm - dry Target % P/Po Temp: 7. C Meth: MRef: Change In Mass (%) - Ref Target % P/Po Time/mins Surface Measurement Systems Ltd UK Adsorption/desorption cycles showing water sorption kinetics at 7 o C (P o = 233.7Torr). 43

45 Partial pressure control of water vapor at 7 o C 1 DVS Partial Pressure Plot Temp: 7. C 9 Target P/P o Actual P/P o 8 7 % Partial Pressure Time/mins Surface Measurement Systems Ltd UK

46 4A Zeolite water sorption isotherm at 7 o C 3 Cycle 1 Sorp Cycle 1 Desorp DVS Isotherm Plot Temp: 7. C Meth: MRef: Change In Mass (%) - Ref Sample % P/Po Surface Measurement Systems Ltd UK

47 4A water sorption isotherms at 25 and 7 o C 46

48 Water sorption cycling /outgasssing of 4A Zeolite at 25 and 14 o C Change In Mass (%) - Ref o C DVS Change In Mass (ref) Plot dm - dry Target % P/Po 14 o C Temp: 47.9 C Meth: MRef: Target % P/Po Time/mins Surface Measurement Systems Ltd UK Adsorption/desorption cycles showing water sorption kinetics at 25and 14 o C Prior to determination of isotherms at 25 o C ( P o =23.7 Torr) and 14 o C the sample was outgassed at 3 o C for 5 hours and high vacuum. In 2 nd cycle sample was kept at 14 o C using the pre-heater, while the incubator temperature was maintained at 7 o C throughout experiment. (P o (water at 7 o C)= 233.7Torr). The P/ P o of 7.6 % at 9 % was reached. 47

49 4A Zeolite water sorption isotherms at 25, 7 and 14 o C 35 Isotherm plot 3 Amount adsorbed (%) adsorption 25degC Desorption 25degC Desorption 7degC Adsorption 7degC Adsorption 14degC Desorption 14degC P/P o (%) Surface Measurement Systems Ltd UK

50 CO 2 Adsorption/Desorption Isotherms for 4 samples 49

51 BET calculation Sample B BET Surface Area Experimental Parameters Molecular weight: g/mol Effective molecular area: 2.34 A² Adsorbate: Carbon Dioxide Temperature entered by user Sample C BET Surface Area Experimental Parameters Molecular weight: 18.2 g/mol Effective molecular area: 2.34 A² Adsorbate: Carbon Dioxide Temperature entered by user Calculation Options P/Po fraction lower limit range.5 P/Po fraction higher limit range.3 % P/Po type: Target Half cycle: Sorption Isotherm cycle 1 Calculation Options P/Po fraction lower limit range.5 P/Po fraction higher limit range.3 % P/Po type: Target Half cycle: Sorption Isotherm cycle 1 Analysis Results V m : cm³/g c: Specific surface area: 29 m²/g R-squared of line fit: % DVS BET Plot Analysis Results V m : cm³/g c: Specific surface area: 4178 m²/g R-squared of line fit: % DVS BET Plot BET Data Line Fit BET Data Line Fit % P/Po / [( 1 - % P/Po ) * M] % P/Po / [( 1 - % P/Po ) * M] % P/Po Surface Measurement Systems Ltd UK % P/Po Surface Measurement Systems Ltd UK

52 CO 2 Diffusion Calculation Sample B Diffusion Calculations micron particle diameter used Sample C Diffusion Calculations 1.69 micron particle diameter used Previous Target Diffusion % P/Po % P/Po Coeff. (cm²/s) R-sq. (%) E * E * E * E E * E E E E E E E E E * Minimum R-squared not met with three or more points Previous Target Diffusion % P/Po % P/Po Coeff. (cm²/s) R-sq. (%) E * E * E E E * E E E E E E E E E * * Minimum R-squared not met with three or more points 51

53 CH 4 Adsorption Isotherm 52

54 CO 2 and CH 4 Isotherms 53

55 Heat of Sorption for alumina 16 DVS Isotherm Plots For Alumina at 25C and 6C al25 Cycle 1 Sorp al6 Cycle 1 Sorp Change In Mass (%) - Dry Target RH (%) Surface Measurement Systems Ltd UK

56 Heat of Sorption for alumina Alumina 25C 6C DH sorp Moisture 41-45kJmol -1 DH vap = 41kJmol -1* Sample: alumina 25C alumina 6C Temp ( C): M(): Interpolated P/mm Hg Heat of Sorption (J/mol) dm (%) T1 T2 T2->T

Incubator (2~7 o C) Clausius-Clapeyron equation Microbalance Vacuum ample pan

57 Vapor pressure measurements Knudsen Effusion Method Gravimetric measurement of the weight loss by evaporation through a small orifice into vacuum. Incubator (2~7 o C) Clausius-Clapeyron equation Microbalance Vacuum ample pan Reference pan Knudsen cell Sample Temperature sensor Pre-heater (2~4 o C) Sample pan 56

58 Vapor pressure measurements Material held in a cell, with an orifice of known dimensions will effuse through the hole via sublimation, under vacuum which prevents back scattering by air molecules. Through measurement of the rate of mass loss, temperature, molecular weight and orifice dimensions, the Knudsen equation can be applied to provide vapour pressure data. Time Gradient = dm/dt P 2 RT M A dm dt log P b T a dm/dt is the rate of mass loss P is the vapour pressure of the solid R is the universal gas constant (8.314 m 3.Pa.K -1.mol -1 ) Gradient = b 1/T T is temperature in Kelvin A is the area of the orifice M is the molecular weight of the solid DH is heat of sublimation a and b are constants a 57

59 Vapor pressure of benzoic acid 58

60 Vapor pressure of benzoic acid Temperature [ C] DM/DT [mg/min] Vapour Pressure [Pa] Vapour Pressure * [Pa] Note: The cell orifice size was 167micron Experimental values are in very good agreement with literature data * Monte et.al J. Chem. Eng. Data 26, 51, , Kruif et.al. J. Chem. Thermodynamics 1982, 14, Colomina et.al. J. Chem. Thermodynatnic. 1982, 14, published by: 59

61 Vapor pressure of naphthalene Vapor pressure at 25 o C: Measured value: Pa Environmental Protection agency value: 11.6 Pa 6

62 Acknowledgments Daryl Williams, Imperial college London, UK Evelyn Wang and Xiansen Li, MIT, USA Patrick Ruch, IBM, Zurich, CH

The Vacuum Sorption Solution

The Total Sorption Solution The Vacuum Sorption Solution The Vacuum Sorption Solution www.thesorptionsolution.com About the Technique DVS Vacuum - the only gravimetric system that supports static and dynamic