DVS Vacuum Dynamic Gravimetric Sorption - Centralnews seminar - DVS... · 2015-10-09 · DVS Vacuum...

DVS VacuumDynamic Gravimetric Sorption

Dr Vladimir Martis

Product specialist

6th October 2015

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 25oC

from 0.1 to 5%P/Po in 0.1% step).

Solely water vapor or organic vapour adsorption.1

Why Dynamic Gravimetric Sorption?

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

3

Downstream sealed

Mass flow controllers opened

Downstream opened

Upstream opened

(2) Filling with sorbate

(3) Steady-state

Upstream sealed

Air

Downstream pumping

Sample pan

Air(1) Chamber evacuation Scheme of DVS vacuum

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

Measurable Physisorption Properties

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 0.1% P/Po

Wide range of sample and vapor temperatures (20 to 400oC). Isothermal control of entire system; no condensation issues.

Real time sorption kinetics

Wide range of sorbate molecules (Benzene, Toluene, Xylene, Aldehydes, Alcohols, H2S, NH3, CO2)

Competitive adsorption of two probe molecules

(H2O-CO2, H2O- NH3, H2O-MeOH)

Multiple sorption/desorption/outgassing cycles in one experiment

Sorbate molecules residence time control

5

6

Incubator

Vacuum pumpsassembly

Data acquisitionstation

DVS vacuum system

7

Rotary pump

Turbo pump controllerManual (speedi) valve

Turbo pump

Cooling Fun

Butterflyvalve

Incubator door

Incubator temperaturecontroller

Incubator switch

Cooler

Pressure controller 972 Pressure controller

Pre-heater temperaturecontroller

Pre-heater switch

DVS vacuum system

8

Vapour

Gas

UltraBalance hat

Sample side

Vacuum gas manifold

10 Torr Baratron 1000 Torr Baratron

Reference side

DVS vacuum stand

High temperature pre-heater

Miniature radiator style pre-heater for outgassing samples up to 400oC

Sample pan

Pre-heater

Instrument specs

Dynamic (or static) operational mode

Upstream and downstream vapor/gas flow controls

Temperature controlled incubator operating in the range from 20 (15) to 70oC

In-situ sample pre-conditioning /activation up to 400oC (using pre-heater) 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 90 %P/P0 up to 70oC and up to 150oC up to 7%P/P0

Highly accurate baratrons for pressure measurements (0.005 to 10 Torr and 0.01 to 1000 Torr)

Cold cathode/ MicroPirani transducer from very low (10-8 Torr) to atmospheric pressure measurements

10

Low end P/Po control

Vacuum /temperature drying behavior of 5A zeolite

12

Vacuum and preheater drying of 5A zeoliteInitial mass: 33.1724mg

Drying kinetics of hydrates

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0 100 200 300 400 500 600 700Time (minutes)

Ch

an

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in

ma

ss

(%

)

20ºC

30ºC

40ºC

50ºC

60ºC

Pressure: 10-3 Torr

Drying Behaviour of Pharmaceutical Hydrates: Carbamazepine (CBZ) dihydrate

0

0.04

0.08

0.12

0.16

0 100 200 300 400 500Time (minutes)

Mo

istu

re c

on

ten

t, X

A

0 Torr, 20ºC0 Torr, 30ºC0 Torr, 40ºC0 Torr, 50ºC50 Torr, 20ºC50Torr, 30ºC50 Torr, 40ºC50 Torr, 50ºC

Very strong kinetic dependence of drying rate with temperature and level

of vacuum for CBZ dihydrate

Benzene sorption of porous material at 25oC

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Ch

an

ge In

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ss

(%

) -

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% P/Po

DVS Isotherm Plot

Cycle 1 Sorp Cycle 1 Desorp

© Surface Measurement Systems Ltd UK 1996-2014DVS - The Sorption Solution

Temp: 25.0 °CMeth: MRef: 23.7754

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f

Time/mins

DVS Change In Mass (ref) Plot

dm - dry Target % P/Po



Pt-SiO2 toluene sorption at 55oC

15

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DVS Isotherm Plot




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DVS Isotherm Plot




P/Po increased in 0.2 %

Isotherm comparison for Pt-SiO2 toluene sorption at 25 and 55oC

16

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Sample % P/Po

DVS Isotherm Plot

PtSiO2 toulene 55c PtSiO2 toulene 55c 14-11-2014 17-11-24_DVS Cycle 1 Sorp

PtSiO2 toulene 55c PtSiO2 toulene 55c 14-11-2014 17-11-24_DVS Cycle 1 Desorp

Pt- SiO2 toulene 25c Pt- SiO2 toulene 25c 27-10-2014 18-19-29_DVS Cycle 1 Sorp

Pt- SiO2 toulene 25c Pt- SiO2 toulene 25c 27-10-2014 18-19-29_DVS Cycle 1 Desorp


Comparison of isotherms for Pt-SiO2 Toluene sorption at 25( adsorption in green and desorption in purple)and 55oC (adsorption in red and desorption in blue)

Cyclohexane and methanol adsorption

MOR FER

C1210872 C1414425

N2 512 285

Surface area (m2/g) Methanol 422 374

Cyclohexane 208 148

n-Octane 220

N2 0.18 0.09

Micropore volume (cm3/g) Methanol

Cyclohexane 0.14 0.09

0

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DVS Isotherm Plot




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Time/mins





Acetaldehyde and benzene sorption

Acetaldehyde sorption at 17oCBenzene sorption at 20oC

SampleSurface Area

[m²/g]:Monolayer Capacity

[Mol/g]:

MOF beads 1035 0.004

Beads 293 0.0011

SampleSurface Area

[m²/g]:Monolayer Capacity

[Mol/g]:

MOF beads 1756 0.006

Beads 654 0.002

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DVS Isotherm Plot

beads 18C acetaldehyde_2cycles Bs 21-11-2014 18-29-24_DVS Cycle 1 Sorp

beads 18C acetaldehyde_2cycles Bs 21-11-2014 18-29-24_DVS Cycle 1DesorpMOF beads 18C acetaldehyde_2 24-11-2014 15-40-00_DVS Cycle 1 Sorp


Water sorption isotherm of freeze-dried polymer at 40oC

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DVS Isotherm Plot




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-10

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f

Time/mins





Adsorption

desorption

Adsorption/desorption cycles showing water sorption kinetics 40oC (Po = 55.3Torr).

Ionic liquid water sorption at 25oC

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46

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750 800 850 900 950 1000

Pa

rtia

l P

res

su

re (

%)

Ma

ss

/mg

Time/mins


Sylosiv A10 water sorption at 40oC

21

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Time/mins




Date: 11 Dec 2011Time: 10:46 amFile: Sylosiv A10 water 40C_2cycles Sylosiv A10 water 40C_2cycles 05-12-2014 18-36-36_DVS.xlsbSample: Sample: Sylosiv A10 water 40C_2cycles


Sylosiv A10 water sorption at 40oC

22

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Ch

an

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In

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(%

) -

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f

Sample % P/Po

DVS Isotherm Plot

Cycle 1 Sorp Cycle 1 Desorp Cycle 2 Sorp Cycle 2 Desorp



Water adsorption isobars

SAPO-34 water adsorption isobars at 27oC

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% P

/Po

Ax

is T

itle

Time/mins

Mass/mg Temperature (degC) P/Po (%)



SAPO-34 water adsorption isobars at 27oC

-5

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40 60 80 100 120 140 160

Ch

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(%

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f

Temperature (°C)

DVS Isobar Plot

Cycle 1 Increasing T Cycle 1 Decreasing T





% P/Po: 48.28%Meth: MRef: 25.1724

Cycle 1: 8.01 TorrCycle 2: 13.35 TorrCycle 3: 21.36 TorrCycle 4: 25.37 Torr

Cyclohexane carbon sorption at 25oC

25

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P/P0 (%)



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/P0

(%)

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Time/mins


Cyclohexane carbon sorption at 25oC

26

SampleSurface Area

[m²/g]:

Monolayer Capacity[Mol/g]:

Sorption constant

R[%]

Carbon 675 0.003 -23.2 99.2

BET Surface area determination

BET plot

DMMP carbon sorption at 25oC

27

Partial Pressure Control up to 1Torr

28

0

0.2

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1

1.2

0 200 400 600 800 1000 1200 1400

Ac

tua

l P

res

su

re [

To

rr]

Time/mins

Dimethyl methylphosphonate


Dynamic adsorption of 2-hexanol onactivated carbon

0

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100 600 1100 1600 2100 2600 3100

Time/mins

Ch

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in

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/ %

18.93 Pa

6.59 Pa

2.41 Pa

0.89 Pa0.33 Pa0.23 Pa

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.

1.7x10-3Torr2.5x10-3Torr

6.7x10-3Torr

1.8x10-2Torr

4.9x10-2Torr

1.4x10-1Torr

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

30

CO2 Gas Sorption on Hydroxide at 25oC

31

26,4

26,5

26,6

26,7

26,8

26,9

27

27,1

27,2

0 180 360 540 720 900 1080 1260

0.00 Torr

0.05 Torr

2.00 Torr

4.00 Torr

6.00 Torr

8.00 Torr

10.00 Torr

Hydroxides can be potentially used for CO2 capture for environment protection.

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 CO2 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

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

NaY water sorption at 25 and 65oC

34

Development of adsorption based thermal batteries (MIT)

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0,0 20,0 40,0 60,0 80,0 100,0

Am

ou

nt

adso

rbe

d (

wt.

%)

Relative pressure x100

normal

normal_desor

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Am

ou

nt

adso

rbe

d (

wt.

%)

relative pressure X100

65C_adsor

65C_desor

25C_adsor

25C_desor

Very good reproducibility Sample regenerated for 8h at 370oC

13x Zeolite outgassing at high temperature and vacuum

35

24.5

25

25.5

26

26.5

27

27.5

0 50 100 150 200 250

Ma

ss

/mg

Time/mins

DVS Drying Curve

Drying Mass


Date: 11 Dec 2011Time: 10:46 amFile: 13x water 25c 13x water 25c 15-07-2014 18-07-56_DVS.xlsbSample: Sample: 13x water 25c


Outgassing : 250min at 370oC using the pre-heater and high vacuum

13x Zeolite water sorption at 25oC

36

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f

Time/mins





Adsorption/desorption cycles showing water sorption kinetics 25oC (Po = 23.8Torr).

13x Zeolite water sorption isotherm at 25oC

37

0

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Sample % P/Po

DVS Isotherm Plot

Cycle 1 Sorp Cycle 1 Desorp Cycle 2 Sorp Cycle 2 Desorp



38

13x Zeolite water sorption BET calculation at 25oC

0

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20

0 0.05 0.1 0.15 0.2 0.25

p/[

n(p

0-p

)] [

g/M

ol]

p/p0

BET Linear Plot

linear fit

experiment

Surface Area: 698m²/g, Monolayer Capacity: 0.011 [Mol/g], Sorption Constant: -162, R: 0.999

Surface area is derived from water sorption isotherm.

SO2 gas sorption on three different Zeolites at 25oC

39

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.

BET surface area measurement of 13x using SO2 gas at 25oC

40

BET surface area of a 13x Zeolite measured by DVS Vacuum using SO2 gas. The result correlates well with the established value of 750m2/g, measured using N2 at –196°C.

41

Water/Ethanol Zeolite Sorption Isotherms at 130oC

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DVS Isotherm Plot for water sorption at 130oC



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DVS Isotherm Plot for ethanol sorption at 130oC


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DVS Isotherm Plot for 95% ethanol and 5% water at 130oC



Molecular sizes:Water: 0.28nmEthanol: 0.44nm

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54

55

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Ma

ss

/mg

Time/mins

DVS Drying Curve



Outgassing: 7 hours at 300oC using the pre-heater and high vacuum

Drying of 4A zeolite at 70oC

4A Zeolite water sorption at 70oC

43

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Adsorption/desorption cycles showing water sorption kinetics at 70oC (Po = 233.7Torr).

44

0

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% P

art

ial P

res

su

re

Time/mins

DVS Partial Pressure Plot


Temp: 70.0 °C

Target P/Po

Actual P/Po

Partial pressure control of water vapor at 70oC

4A Zeolite water sorption isotherm at 70oC

45

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Sample % P/Po

DVS Isotherm PlotCycle 1 Sorp Cycle 1 Desorp



4A water sorption isotherms at 25 and 70oC

46

Water sorption cycling /outgasssing of 4A Zeolite at 25 and 140oC

47

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Time/mins





25oC 140oC

Prior to determination of isotherms at 25oC ( Po=23.7 Torr) and 140oC the sample was outgassed at 300oC for 5 hours and high vacuum. In 2nd cycle sample was kept at 140oC using the pre-heater, while the incubator temperature was maintained at 70oC throughout experiment. (Po (water at 70oC)= 233.7Torr). The P/ Po

of 7.6 % at 90 % was reached.

Adsorption/desorption cycles showing water sorption kinetics at 25and 140oC

4A Zeolite water sorption isotherms at 25, 70 and 140oC

48

0

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0 10 20 30 40 50 60 70 80 90 100

Am

ou

nt

ad

so

rbed

(%

)

P/Po (%)

Isotherm plot

adsorption 25degC

Desorption 25degC

Desorption 70degC

Adsorption 70degC

Adsorption 140degC

Desorption 140degC


49

CO2 Adsorption/Desorption Isotherms for 4 samples

BET calculation

50

Experimental Parameters

Molecular weight: 44.0088 g/mol

Effective molecular area: 20.34 A²

Adsorbate: Carbon Dioxide

Temperature entered by user

Calculation Options

P/Po fraction lower limit range: 0.05

P/Po fraction higher limit range: 0.30

% P/Po type: Target

Half cycle: Sorption

Isotherm cycle 1

Analysis Results

Vm: 36.75 cm³/g

c: 9.988

Specific surface area: 20009 m²/g

R-squared of line fit: 99.846 %

0

0.002

0.004

0.006

0.008

0.01

0.012

0 5 10 15 20 25 30 35

% P

/Po

/ [(

1 -

% P

/Po

) *

M]

% P/Po

DVS BET Plot

BET Data Line Fit


Experimental Parameters

Molecular weight: 18.02 g/mol

Effective molecular area: 20.34 A²

Adsorbate: Carbon Dioxide

Temperature entered by user

Calculation Options

P/Po fraction lower limit range: 0.05

P/Po fraction higher limit range: 0.30

% P/Po type: Target

Half cycle: Sorption

Isotherm cycle 1

Analysis Results

Vm: 76.43 cm³/g

c: 11.52

Specific surface area: 4178 m²/g

R-squared of line fit: 99.878 %

0

0.0005

0.001

0.0015

0.002

0.0025

0.003

0.0035

0.004

0.0045

0.005

0 5 10 15 20 25 30 35

% P

/Po

/ [(

1 -

% P

/Po

) *

M]

% P/Po

DVS BET Plot

BET Data Line Fit


Sample B BET Surface AreaSample C BET Surface Area

CO2 Diffusion Calculation

51

Sample B Diffusion Calculations

61.92 micron particle diameter used

Previous Target Diffusion

% P/Po % P/Po Coeff. (cm²/s) R-sq. (%)

0.5 1.0 2.08E-08 94.86 *

1.0 2.0 2.00E-08 95.51 *

2.0 4.0 1.93E-08 96.83 *

4.0 8.0 5.30E-09 99.22

8.0 10.0 2.15E-08 95.77 *

10.0 20.0 5.42E-09 99.01

20.0 30.0 6.45E-09 99.09

30.0 40.0 5.53E-09 99.03

40.0 50.0 4.73E-09 99.00

50.0 60.0 5.02E-09 99.03

60.0 70.0 4.74E-09 99.01

70.0 80.0 4.10E-09 99.10

80.0 90.0 3.73E-09 99.14

90.0 95.0 5.84E-09 99.07

* Minimum R-squared not met with three or more points

Sample C Diffusion Calculations

10.69 micron particle diameter used

Previous Target Diffusion

% P/Po % P/Po Coeff. (cm²/s) R-sq. (%)

0.5 1.0 1.62E-09 88.77 *

1.0 2.0 6.40E-10 97.27 *

2.0 4.0 3.51E-10 99.05

4.0 8.0 3.34E-10 99.11

8.0 10.0 5.92E-10 96.67 *

10.0 20.0 1.76E-10 99.01

20.0 30.0 1.73E-10 99.19

30.0 40.0 1.56E-10 99.21

40.0 50.0 1.70E-10 99.03

50.0 60.0 1.76E-10 99.02

60.0 70.0 1.67E-10 99.04

70.0 80.0 1.61E-10 99.02

80.0 90.0 1.28E-10 99.13

90.0 95.0 4.41E-10 96.31 *

* Minimum R-squared not met with three or more points

CH4 Adsorption Isotherm

52

CO2 and CH4 Isotherms

53

Heat of Sorption for alumina

54

DVS Isotherm Plots For Alumina at 25C and 60C

0

2

4

6

8

10

12

14

16

0 10 20 30 40 50 60 70 80 90 100

Target RH (%)

Ch

an

ge In

Mass (

%)

- D

ry

al25 Cycle 1 Sorp al60 Cycle 1 Sorp


Heat of Sorption for alumina

55

Sample: alumina 25C alumina 60C

Temp (°C): 24.30 59.23

M(0): 46.2162 54.3436

Interpolated P/mm Hg Heat of Sorption (J/mol)

dm (%) T1 T2 T2->T1

0.98 2.52 15.47 -42728.51

1.95 10.38 60.14 -41347.90

2.93 14.11 88.96 -43326.36

3.90 15.71 101.66 -43951.55

4.88 16.49 108.05 -44232.25

5.86 17.11 114.44 -44727.91

6.83 17.72 118.90 -44801.36

7.81 18.31 122.75 -44779.46

8.79 18.67 126.60 -45044.68

9.76 19.03 130.46 -45296.99

– Alumina

– 25C – 60C

– DH sorp Moisture

– 41-45kJmol-1

– DH vap = 41kJmol-1*

Vapor pressure measurements

56

Knudsen Effusion Method

Gravimetric measurement of the weight loss by evaporation througha small orifice into vacuum.

Microbalance

Reference panSample pan

Pre-heater (20~400oC)Temperature sensor

Incubator (20~70oC)

Vacuum

Sample

Knudsen cell

Sample pan

Clausius-Clapeyron equation

Vapor pressure measurements

57

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.

dt

dm

A

M

RT

P

2

a

T

bP log

• dm/dt is the rate of mass loss • P is the vapour pressure of the solid • R is the universal gas constant (8.314 m3 .Pa.K-1.mol-1)• 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

Time

Gradient = dm/dt

1/T

Gradient = b

a

58

Vapor pressure of benzoic acid

5959

Temperature

[°C]DM/DT [mg/min] Vapour Pressure [Pa] Vapour Pressure* [Pa]

30 0.0008 0.23 0.23

35 0.0013 0.36 0.36

40 0.0023 0.65 0.65

45 0.0040 1.11 1.11

50 0.0067 1.91 1.9

55 0.0111 3.17 3.25

60 0.0178 5.11 5.16

65 0.0278 8.05 8.22

Vapor pressure of benzoic acid

Note: The cell orifice size was 167micron

Experimental values are in very good agreement with literature data * published by:Monte et.al J. Chem. Eng. Data 2006, 51, 757-766, Kruif et.al. J. Chem. Thermodynamics 1982, 14, 201-206

Colomina et.al. J. Chem. Thermodynatnic. 1982, 14, 779-784.

Vapor pressure of naphthalene

60

Vapor pressure at 25oC:Measured value: 11. 08 PaEnvironmental Protection agency value: 11.60 Pa

Acknowledgments

Daryl Williams, Imperial college London, UK

Evelyn Wang and Xiansen Li, MIT, USA

Patrick Ruch, IBM, Zurich, CH

DVS Vacuum Dynamic Gravimetric Sorption - Centralnews seminar - DVS... · 2015-10-09 · DVS Vacuum...

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