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