About 95% of the H2 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% CO2 as a byproduct, and the energy and capital–intensive pressure swing adsorption (PSA) procedures for CO2 removal exhibit some unavoidable H2 loss. Membrane separations, especially those with reverse-selective membranes that selectively permeate CO2 from H2 streams, are a promising alternative to pressure swing adsorption. The purified H2 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 CO2 solubility, but crystallization of PEO chains leads to low CO2 permeability and minimal CO2/H2 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 CO2/H2 selectivity of 12 with a CO2 permeability of about 20 Barrers. Cross-linking of poly(PEGMEMA) films may slightly decrease CO2 permeability and CO2/H2 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 CO2/H2 selectivities ranging from 6.5 to 19.9, but a CO2 permeability of 5–15 Barrer. Efforts to increase permeability included embedding SiO2 nanoparticles into the cross–linked poly(PEGMEMA–1100–co–PEGMEMA–475–co–PEGDA–700) film to increase fractional free volume (FFV). Unfortunately, nanoparticles didn't enhance the CO2 permeability, perhaps because the non–rigid chains.During the course of membrane preparation, growth of poly(PEGMEMA–1100–co–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.
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