Year of Publication

2006

Document Type

Dissertation

College

Engineering

Department

Chemical Engineering

First Advisor

Eric A. Grulke

Abstract

We have developed CO2-selective membranes to purified hydrogen and nitrogenfor fuel cell processes. Hydrogen purification impacts other industries such as ammoniaproduction and flue gas purification at reduced costs.Dense chitosan membranes were used for the first time to separate CO2 from amixture of 10% CO2, 10% H2, and 80% N2 at temperatures of 20 – 150oC and feedpressures of 1.5 atm – 5 atm. At 1.5 atm and 20 – 150oC, dry chitosan membranesachieved CO2 permeabilities, CO2/N2 and CO2/H2 separation factors of 0.383 – 24.3barrers, 10.7 – 3.40, and 4.54 – 1.50, respectively. The dry chitosan acted as an ordinarysolution-diffusion membrane: permeability increased with temperature but selectivitydecreased. The CO2/H2 and CO2/N2 separation factors at all temperatures enhanced CO2removal, making this membrane a candidate for fuel cell processes. The dual modetransport model fitted the transport data well.To achieve higher CO2 transport properties, chitosan was swollen with water.Water mediated the reaction of chitosan's amino groups with CO2. Humidifing the feedand sweep gases increased the membrane's performance. At 1.5 atm and 20 – 110 –150oC, CO2 permeabilities, CO2/N2 and CO2/H2 separation factors were 213 – 483 – 399barrers, 69.4 – 250 – 194, and 18.9 – 43.4 – 29, respectively. The presence of free waterand bound water facilitated the transport of CO2. Increasing feed pressure removed themaxima in permeability and selectivities at 110oC, but led to reduced CO2 permeabilities,CO2/N2 separation factors, and CO2/H2 separation factors to 156 – 286 barrers, 44.2 –131, and 12.0 – 16.7, respectively.To acquire higher CO2 transport properties, arginine-sodium salts wereincorporated in chitosan membranes as additional sites for facilitated transport. The salt'spercolation threshold was 40 wt %. At 1.5 atm and 20 – 110 – 150oC, CO2 permeabilities,CO2/N2 and CO2/H2 separation factors were 403 – 1498 – 1284 barrers, 122 – 852 – 516,and 31.9 – 144 – 75.5, respectively. Increasing feed pressure to 5 atm resulted indeclining CO2 permeabilities, CO2/N2 and CO2/H2 separation factors to 118 – 1078barrers, 21.6 – 352, and 5.67 – 47.9, respectively.Chitosan was characterized in terms of morphology, solution properties, thermalproperties, crystallinity, and degree of deacetylation.

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