Membranes for flue gas treatment : transport behavior of water and gas in hydrophilic polymer membranes

Fossil fuel fired power plants produce electricity and in addition to that large volume flows of flue gas, which mainly contain N2, O2, and CO2, but also large quantities of water vapor. To prevent condensation of the water vapor present in this flue gas stream, water needs to be removed before emission to the atmosphere. Commercial dehydration processes such as the use of a condenser or a desiccant system have several disadvantages and membrane technology is an attractive, energy efficient alternative for dehydration of gas streams. The work presented in this thesis focuses on the characterization of the molecular gas and water vapor transport properties of two different types of polymeric membranes. The fundamental understanding of water vapor and gas transport phenomena through these materials is particularly interesting since both materials are different in their chemistry and physical state:\ud - PEBAX® is a block copolymer which shows molecular transport through the soft\ud polyethylene oxide based rubbery phase.\ud - S-PEEK (sulfonated poly ether ether ketone) shows molecular transport through an amorphous glassy phase with ionic groups present which will preferentially be\ud hydrated over the apolar matrix.\ud The two polymeric systems vary strongly in relation to polymer/vapor interactions, relaxation phenomena, and separation performance of the membranes

Sorption induced relaxations during water diffusion in S-PEEK

This paper presents an analysis of the sorption kinetics of water vapor and liquid water in the glassy polymer sulfonated poly(ether ether ketone) (S-PEEK). Sorption isotherms are determined experimentally using a gravimetric sorption balance, and the relative contributions of Fickian diffusion and relaxational phenomena are quantified as a function of the water concentration in the polymer using the model of Hopfenberg and Berens.Analysis of the sorption isotherms and determination of the sorption kinetics prove the occurrence of both Fickian sorption behavior and relaxational phenomena already at very low water concentrations in the polymer. With increasing water concentration, the relative importance of relaxation phenomena increases, whereas the relative contribution of Fickian diffusion decreases.Based on the water vapor sorption kinetics only, the Fickian diffusion coefficient increases over two orders of magnitude with increasing water vapor concentration. Taking also the diffusion kinetics from liquid water sorption experiments into account reveals a change of even three orders of magnitude of the Fickian diffusion coefficient when the water concentration in the polymer increases

Mixed water vapor/gas transport through the rubbery polymer PEBAX® 1074

This work investigates the transport behavior of a hydrophilic, highly permeable type of poly ethylene oxide (PEO)-based block copolymer (PEBAX® 1074) as membrane material for the removal of water vapor from light gases. Water vapor sorption isotherms in PEBAX® 1074 represent Flory–Huggins type of sorption and the highly hydrophilic nature of the block copolymer results in high amounts of absorbed water (up to 0.4 g of water per gram of dry polymer at 20 °C). When taking into account the swelling of the polymer due to water vapor sorption, the Fickian diffusion coefficient increases over the full activity range and changes over two orders of magnitude. As determined from measurements with binary gas mixtures, the water vapor permeability increases exponentially with increasing water vapor activity whereas the nitrogen permeability slightly decreases with increasing water vapor activity. Consequently, the water over nitrogen selectivity increases with increasing water vapor activity.\ud \ud The results not only show the high potential of hydrophilic PEO-based block copolymers for dehydration purposes (e.g. the dehydration of flue gases, natural gas dew pointing or the humidification of air). Because of the high interaction of CO2 with the polar ether linkages in PEO-based block copolymers, these polymers also offer attractive routes to the integration of dehydration and CO2 capture using membrane technology

Mixed water vapor/gas transport through the rubbery polymer PEBAX\u3csup\u3e®\u3c/sup\u3e 1074

\u3cp\u3eThis work investigates the transport behavior of a hydrophilic, highly permeable type of poly ethylene oxide (PEO)-based block copolymer (PEBAX\u3csup\u3e®\u3c/sup\u3e 1074) as membrane material for the removal of water vapor from light gases. Water vapor sorption isotherms in PEBAX\u3csup\u3e®\u3c/sup\u3e 1074 represent Flory-Huggins type of sorption and the highly hydrophilic nature of the block copolymer results in high amounts of absorbed water (up to 0.4 g of water per gram of dry polymer at 20 °C). When taking into account the swelling of the polymer due to water vapor sorption, the Fickian diffusion coefficient increases over the full activity range and changes over two orders of magnitude. As determined from measurements with binary gas mixtures, the water vapor permeability increases exponentially with increasing water vapor activity whereas the nitrogen permeability slightly decreases with increasing water vapor activity. Consequently, the water over nitrogen selectivity increases with increasing water vapor activity. The results not only show the high potential of hydrophilic PEO-based block copolymers for dehydration purposes (e.g. the dehydration of flue gases, natural gas dew pointing or the humidification of air). Because of the high interaction of CO\u3csub\u3e2\u3c/sub\u3e with the polar ether linkages in PEO-based block copolymers, these polymers also offer attractive routes to the integration of dehydration and CO\u3csub\u3e2\u3c/sub\u3e capture using membrane technology.\u3c/p\u3

Mixed water vapor/gas transport through the rubbery polymer PEBAX® 1074

This work investigates the transport behavior of a hydrophilic, highly permeable type of poly ethylene oxide (PEO)-based block copolymer (PEBAX® 1074) as membrane material for the removal of water vapor from light gases. Water vapor sorption isotherms in PEBAX® 1074 represent Flory–Huggins type of sorption and the highly hydrophilic nature of the block copolymer results in high amounts of absorbed water (up to 0.4 g of water per gram of dry polymer at 20 °C). When taking into account the swelling of the polymer due to water vapor sorption, the Fickian diffusion coefficient increases over the full activity range and changes over two orders of magnitude. As determined from measurements with binary gas mixtures, the water vapor permeability increases exponentially with increasing water vapor activity whereas the nitrogen permeability slightly decreases with increasing water vapor activity. Consequently, the water over nitrogen selectivity increases with increasing water vapor activity. The results not only show the high potential of hydrophilic PEO-based block copolymers for dehydration purposes (e.g. the dehydration of flue gases, natural gas dew pointing or the humidification of air). Because of the high interaction of CO2 with the polar ether linkages in PEO-based block copolymers, these polymers also offer attractive routes to the integration of dehydration and CO2 capture using membrane technology

Transport of water vapor and inert gas mixtures through highly selective and highly permeable polymer membranes

This paper studies in detail the measurement of the permeation properties of highly permeable and highly selective polymers for water vapor/nitrogen gas mixtures. The analysis of the mass transport of a highly permeable polymer is complicated by the presence of stagnant boundary layers at feed and permeate side. Such resistances are generally specific to the permeation cell used and can be extracted from the measurement of the overall resistance of polymeric films having different thickness. Water vapor permeabilities of ethyl cellulose and polysulfone films are determined and corrected for the resistance in the stagnant boundary layer and measured values correspond to those in literature. Permeability values of even higher permeable and more selective poly(ethylene oxide) poly(butylene terephthalate) multi-block copolymer (PEO-PBT) are presented to illustrate the contribution of the stagnant boundary layer at various process conditions. The mixed gas nitrogen permeability remains constant with an increase of water vapor activity on the feed side of the membrane, but increases significantly when the sweep gas is humidified. The water vapor permeability shows a strong dependence on the feed pressure. An increase of the feed pressure results in a larger resistance of the stagnant feed boundary layer, thereby lowering the total water vapor flux. The mixed gas nitrogen permeability decreases slightly with an increase of pressure most likely due to the compaction of the material

The role of ionic strength and odd-even effects on the properties of polyelectrolyte multilayer nanofiltration membranes

The modification of membranes by polyelectrolytes via the Layer-by-Layer technique is an attractive method to obtain nanofiltration membranes. We prepare such membranes by alternatively coating a polycation (poly(diallyldimethylammonium chloride) (PDADAMAC)) and a polyanion (poly(styrene sulfonate) (PSS)) on a porous support. Depending on the coating conditions, hollow fiber membranes with rejections of up to 71% NaCl and 96% Na2SO4 are obtained. Moreover, we demonstrate that the final membrane properties can be easily controlled by variation of the ionic strength of the coating solution, the number of layers and the choice of terminating polyelectrolyte layer. Coating at higher salt concentrations results in thicker multilayers that are more open to permeation. Furthermore, we show that by taking the effect of the terminating layer (the so called “odd–even” effect) into account, information on the structure of the multilayers on the membrane is obtained. Depending on the coating conditions and number of layers, two different regimes can be distinguished. Thinner layers show a pore-dominated regime, where the multilayer is coated on the inside of the pores. Thicker layers show a layer-dominated regime, in which case the multilayer is predominately coated on top of the pores. This conclusion is supported by our ion rejection measurements: for thin layers the rejections are primarily based on size exclusion, whereas for thick layers the ion rejections are based on Donnan exclusion