Carbon Membranes for High Temperature Gas Separations: Experiment and Theory

TY - JOUR

T1 - Carbon Membranes for High Temperature Gas Separations

T2 - Experiment and Theory

AU - Sznejer, Gabriel A.

AU - Efremenko, Irena

AU - Sheintuch, Moshe

PY - 2004/3

Y1 - 2004/3

N2 - The transport and separation of hydrogen and light alkanes are studied in a molecular-sieve carbon membrane hollow-fiber module at the temperature range of 25-400°C; nitrogen is used as a sweeping gas in the study of mixtures, and the fluxes of pure components are studied under a pressure gradient. The membrane selectivity, the ratio of hydrogen to hydrocarbon permeabilities, may reach 100 to 1,000 in propane, or in (normal or iso-) butane mixtures with hydrogen, making the membrane an excellent candidate for a membrane dehydrogenation reactor. The permeabilities measured in pure-component studies differ from those in mixtures. Specifically, counterdiffusion of nitrogen and C2 to C4 alkanes significantly inhibits the fluxes of both, whereas the hydrogen flux is only slightly diminished. To account for these results, molecular mechanics simulations are used to find the energetics of adsorption, diffusion, and desorption of individual gases in cylindrical nanopores modeled by carbon nanotubes. In pore sizes that are up to 2-3 times the dimension of the molecule, diffusion of the molecule inside the pore is nonactivated, whereas desorption is activated and typically is the rate limiting step; the molecular transport proceeds essentially by the single-file diffusion mechanism. A rate expression for a single-species transport in a molecular-sieve carbon membrane is derived by a mean-field approach. The pore-size distribution calculated by comparing experimental and computed fluxes favorably compares with the measured distribution.

AB - The transport and separation of hydrogen and light alkanes are studied in a molecular-sieve carbon membrane hollow-fiber module at the temperature range of 25-400°C; nitrogen is used as a sweeping gas in the study of mixtures, and the fluxes of pure components are studied under a pressure gradient. The membrane selectivity, the ratio of hydrogen to hydrocarbon permeabilities, may reach 100 to 1,000 in propane, or in (normal or iso-) butane mixtures with hydrogen, making the membrane an excellent candidate for a membrane dehydrogenation reactor. The permeabilities measured in pure-component studies differ from those in mixtures. Specifically, counterdiffusion of nitrogen and C2 to C4 alkanes significantly inhibits the fluxes of both, whereas the hydrogen flux is only slightly diminished. To account for these results, molecular mechanics simulations are used to find the energetics of adsorption, diffusion, and desorption of individual gases in cylindrical nanopores modeled by carbon nanotubes. In pore sizes that are up to 2-3 times the dimension of the molecule, diffusion of the molecule inside the pore is nonactivated, whereas desorption is activated and typically is the rate limiting step; the molecular transport proceeds essentially by the single-file diffusion mechanism. A rate expression for a single-species transport in a molecular-sieve carbon membrane is derived by a mean-field approach. The pore-size distribution calculated by comparing experimental and computed fluxes favorably compares with the measured distribution.

KW - Carbon membrane

KW - Carbon nanotube

KW - Molecular sieves

KW - Molecular transport and separation

UR - http://www.scopus.com/inward/record.url?scp=1642412612&partnerID=8YFLogxK

U2 - 10.1002/aic.10054

DO - 10.1002/aic.10054

M3 - 文章

AN - SCOPUS:1642412612

SN - 0001-1541

VL - 50

SP - 596

EP - 610

JO - AICHE Journal

JF - AICHE Journal

IS - 3

ER -