Michigan State University
Reverse-selective gas-separation membranes prepared by atom transfer radical polymerization
Abstract
dc:descriptionAbout 95% of the H<sub>2</sub> synthesized in the United States is produced by steam reforming of hydrocarbons followed by the water gas shift reaction. However, this process gives ∼25 mol% CO<sub>2</sub> as a byproduct, and the energy and capital–intensive pressure swing adsorption (PSA) procedures for CO<sub>2</sub> removal exhibit some unavoidable H<sub>2</sub> loss. Membrane separations, especially those with reverse-selective membranes that selectively permeate CO<sub>2</sub> from H<sub>2</sub> streams, are a promising alternative to pressure swing adsorption. The purified H<sub>2</sub> on the high–pressure feed side of the membrane could directly go to storage and transportation without re–pressurizing. This research aims to develop reverse–selective membranes containing thin poly(ethylene oxide) (PEO)–based polymer films grown from porous substrates via surface–initiated atom transfer radical polymerization (ATRP). PEO has an excellent CO<sub>2</sub> solubility, but crystallization of PEO chains leads to low CO<sub>2</sub> permeability and minimal CO<sub>2</sub>/H<sub>2</sub> selectivity. To prevent crystallization, we copolymerized poly(ethylene glycol)methyl ether methacrylate (PEGMEMA) monomers containing PEO side chains with 23–24 (PEGMEMA–1100) and 8–9 (PEGMEMA–475) PEO unites. The shorter PEO chains prevent crystallization, and the copolymer membranes still exhibit a CO<sub>2</sub>/H<sub>2</sub> selectivity of 12 with a CO<sub>2</sub> permeability of about 20 Barrers. Cross-linking of poly(PEGMEMA) films may slightly decrease CO<sub>2</sub> permeability and CO<sub>2</sub>/H<sub>2</sub> selectivity, but it should also enhance the membrane's chemical and physical durability. Cross–linked copolymer films prepared by polymerization of PEGMEMA–1100, PEGMEMA–475 and poly(ethylene glycol)diacrylate (PEGDA–700) on RC membranes showed CO<sub>2</sub>/H<sub>2</sub> selectivities ranging from 6.5 to 19.9, but a CO<sub>2</sub> permeability of 5–15 Barrer. Efforts to increase permeability included embedding SiO<sub>2</sub> nanoparticles into the cross–linked poly(PEGMEMA–1100–<italic>co</italic>–PEGMEMA–475–<italic>co</italic>–PEGDA–700) film to increase fractional free volume (FFV). Unfortunately, nanoparticles didn't enhance the CO<sub>2</sub> permeability, perhaps because the non–rigid chains.During the course of membrane preparation, growth of poly(PEGMEMA–1100–<italic>co</italic>–PEGMEMA–475) films in water resulted in an exceptionally rapid polymerization (200 μm–thick films in just 30 min of polymerization). The remarkable thickness does not stem from precipitation, but seems to arise from a unique increase in catalyst activity in the presence of water and PEO side chains. Future work should include further examination of the kinetics of the very rapid polymerization as well as studies of nanoparticle–containing membranes made with glassy, reverse–selective polymers. The nanoparticles embedded in glassy polymer should give more FFV, and finally increase the permeability and selectivity of the membrane.
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
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- Dong, Xiaojie
- Contributors dc:contributor
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- BRUENING, Merlin L.
- BAKER, GREGORY L.
- BLANCHARD, GARY
- TARABARA, VOLODYMYR V.
Subjects
dc:subject × 4Rights
dc:rights- Statement dc:rights
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- In Copyright
- Language dc:language
- English
Identifiers
dc:identifier.*- Identifier
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etd:109
isbn:9781267586698
isbn:1267586699
oclc:931869071
umi:3524319
local:DONG_grad.msu_0128D_11385 - OAI identifier oai:identifier
- oai:d.lib.msu.edu:etd_109