modeling the adsorption of mixed-gases based on pure gas adsorption properties nir tzabar, harry j....
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Modeling the Adsorption of Mixed-Gases
Based on Pure Gas Adsorption Properties
Nir Tzabar, Harry J. Holland, Cris H. Vermeer, Marcel H.J. ter Brake
Energy, Materials and SystemsFaculty of Science and TechnologyUniversity of TwenteEnschede, Netherlands
CEC-ICMC, Tucson AZ, Nir Tzabar, July 2015
Outline
1. Motivation
2. Pure gas adsorption measurements
3. Sips isotherms
4. Mixed gas adsorption calculations
5. Summary
CEC-ICMC, Tucson AZ, Nir Tzabar, July 2015
1. Motivation
Joule-Thomson (JT) sorption cryocoolers have no moving parts;
therefore, are free of vibrations and have potentially a long lifetime.
Mixed-Regrigerants allows lower operating pressures for JT
cryocoolers (relative to pure gases) and higher COPs.
This study is a step in a research on mixed-refrigerant JT sorption
cryocooling
Developing an effective model to determine the adsorption of mixed gases out
of pure gas adsorption isotherms for the research on JT sorption cryocoolers
Developing an effective model to determine the adsorption of mixed gases out
of pure gas adsorption isotherms for the research on JT sorption cryocoolers
CEC-ICMC, Tucson AZ, Nir Tzabar, July 2015
2. Pure gas adsorption measurements
Experimental setupConnecting Tube
Gas SourceN2 / CH4 /
C2H6 / C3H8
Coriolis Flow Controller
PiP
VH
eate
r
V3 V2 V1
Vacuum Pump
Sorption Cell
T
Norit-RB2 Activated carbon, steam activated, extruded carbon.
CEC-ICMC, Tucson AZ, Nir Tzabar, July 2015
2. Pure gas adsorption measurements
Experimental results
300 K320 K
340 K360 K380 K
400 K
Nitrogen
Methane
Ethane
Propane
CEC-ICMC, Tucson AZ, Nir Tzabar, July 2015
3. Sips Isotherms
C0 – the saturated adsorption concentration
a – the adsorption affinity
n – adsorption heterogeneity parameter
C – adsorption concentration
p – pressure
CEC-ICMC, Tucson AZ, Nir Tzabar, July 2015
3. Sips Isotherms
Linearization:
CEC-ICMC, Tucson AZ, Nir Tzabar, July 2015
3. Sips Isotherms
T Nitrogen Methane Ethane Propane C0 a n C0 a n C0 a n C0 a n
[K] [mg/g] [1/bar] [mg/g] [1/bar] [mg/g] [1/bar] [mg/g] [1/bar] 300 84 0.0372 1.259 55 0.1323 1.372 109 1.2278 2.060 550 0.0041 6.333 320 83 0.0289 1.155 51 0.0919 1.303 100 0.6869 1.795 435 0.0403 4.713 340 78 0.0235 1.142 49 0.0625 1.273 97 0.3861 1.709 310 0.3406 3.080 360 78 0.0159 1.177 47 0.0442 1.286 99 0.2187 1.648 274 0.3846 2.422 380 75 0.0125 1.191 45 0.0316 1.262 99 0.1190 1.582 250 0.3497 2.065 400 75 0.0093 1.120 41 0.0272 1.173 99 0.0820 1.475 220 0.3774 1.623
CEC-ICMC, Tucson AZ, Nir Tzabar, July 2015
3. Sips Isotherms
340 K
380 K400 K
300 K320 K
360 K
Symbols – Experimental resultsSolid lines – Sips model
3. Sips Isotherms
Modified Sips model
CEC-ICMC, Tucson AZ, Nir Tzabar, July 2015
3. Sips Isotherms
Modified Sips model
CEC-ICMC, Tucson AZ, Nir Tzabar, July 2015
Symbols – Experimental resultsDashed lines – Modified Sips model
3. Sips Isotherms
T Nitrogen Methane Ethane Propane (K) Sips Modified
Sips Sips Modified
Sips Sips Modified
Sips Sips Modified
Sips 300 0.0999 0.0353 0.0242 0.0086 0.0183 0.0693 0.0058 0.0172 320 0.0104 0.0255 0.0061 0.0501 0.0059 0.0069 0.0065 0.0280 340 0.0134 0.0209 0.0039 0.0697 0.0061 0.0180 0.0093 0.0353 360 0.0167 0.0311 0.0099 0.0663 0.0055 0.0186 0.0101 0.0371 380 0.0156 0.0363 0.0109 0.0634 0.0144 0.0258 0.0086 0.0103 400 0.0126 0.0260 0.0171 0.0405 0.0146 0.1125 0.0140 0.1067
CEC-ICMC, Tucson AZ, Nir Tzabar, July 2015
4. Mixed gas adsorption calculations
The composition of the adsorbed phase:
The adsorption selectivity:
CEC-ICMC, Tucson AZ, Nir Tzabar, July 2015
j
i
njjiij
niijjiji
pyayMC
pyayMCS
1
0
1
0,
CEC-ICMC, Tucson AZ, Nir Tzabar, July 2015
T Nitrogen Methane Ethane Propane C0 a n C0 a n C0 a n C0 a n
[K] [mg/g] [1/bar] [mg/g] [1/bar] [mg/g] [1/bar] [mg/g] [1/bar] 300 84 0.0372 1.259 55 0.1323 1.372 109 1.2278 2.060 550 0.0041 6.333 320 83 0.0289 1.155 51 0.0919 1.303 100 0.6869 1.795 435 0.0403 4.713 340 78 0.0235 1.142 49 0.0625 1.273 97 0.3861 1.709 310 0.3406 3.080 360 78 0.0159 1.177 47 0.0442 1.286 99 0.2187 1.648 274 0.3846 2.422 380 75 0.0125 1.191 45 0.0316 1.262 99 0.1190 1.582 250 0.3497 2.065 400 75 0.0093 1.120 41 0.0272 1.173 99 0.0820 1.475 220 0.3774 1.623
j
i
njjiij
niijjiji
pyayMC
pyayMCS
1
0
1
0,
4. Mixed gas adsorption calculationsNitrogen - Methane Nitrogen - Ethane Nitrogen - Propane
0 10 20 30 40 50
0
0.1
0.2
0.3
0.4
0.5
0.6
Pressure [bar]
x N2
yN2
= 0.2
yN2
= 0.4
yN2
= 0.6
yN2
= 0.8
0 10 20 30 40 500
0.1
0.2
0.3
0.4
Pressure [bar]
x N2
yN2
= 0.2
yN2
= 0.4
yN2
= 0.6
yN2
= 0.8
0 10 20 30 40 500
0.1
0.2
0.3
0.4
Pressure [bar]
x N2
yN2
= 0.2
yN2
= 0.4
yN2
= 0.6
yN2
= 0.8
300 K 300 K 300 K
x – molar fraction in the adsorbed phasey – molar fraction in the vapor phase
= 0.22 @ 10 bar
i j
CEC-ICMC, Tucson AZ, Nir Tzabar, July 2015
5. Summary
The adsorption of nitrogen, methane, ethane, and propane on Norit-RB2 activated carbon have been measured.
The Sips adsorption model is used to describe the adsorption isotherms, and a linearization method is used to determine the parameters out of the experimental results.
A modified Sips model that incorporates the temperature dependence is suggested.
The adsorption model is further developed for the adsorption of gas mixtures.
The adsorption selectivity is discussed and the results of nitrogen-methane, nitrogen-ethane, and nitrogen-propane are presented.
Future work:
I. Pure gas adsorption measurements on other adsorbents
II. Experimental verification of the mixed gases adsorption model
III. Using the modified Sips model in a sorption compressor analysis
CEC-ICMC, Tucson AZ, Nir Tzabar, July 2015
Thank you for your attention
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