7.2.1 Metallic membranes

Metal membranes are all dense type, following the solution-diffusion mechanism with the hydrogen molecules first dissolving in the metal frame-work at the high-pressure feed side, dissociating into two atoms, atomic hydrogen transporting through the membrane and recombining back to the molecular hydrogen at the low-pressure permeate side, as shown in Fig 7.1. The hydrogen flux, F, across the membrane with a thickness L can be described by

[7.7]

where P is the permeability, and p_feed and p_perm are the hydrogen partial pressure at the feed and permeate side, respectively. If n is equal to 0.5, Equation [7.7] becomes the well-known Siveret law. A deviation of n from 0.5 indicates presence of mass transfer resistances other than the bulk metal diffusion itself. Except for defects, metal membranes can produce very high purity hydrogen in the permeate side due to their ideal high selectivity. This contrasts greatly with the conventional thinking that membrane processes are considered primarily for bulk separation for enriching product rather than purification for high-purity product.

Palladium and its alloys are the most common metal membranes for hydrogen purification applications. Operating temperatures of the Pd membranes are in the range of 300–600°C. At low temperatures, Pd segregates into two phases and becomes brittle during hydrogen permeation (Shu et al., 1991). Binary alloys such as Pd-Ag (McCool et al, 1999; Tosti et al., 2003; Bhandari and Ma, 2009; Peters et al., 2009; Okazaki et al, 2011), Pd-Cu (Roa et al., 2002; Howard et al., 2004; Pomerantz et al., 2010) and Pd-Au (Gade et al, 2009; Chen and Ma, 2010) have been used to overcome this problem without sacrifice of hydrogen flux. Ternary alloy composite membranes have also been considered for the same purpose (Wang et al, 2007; Basile et al., 2008; Ryi et al., 2008; Coulter et al., 2010). Alloys have the advantage of reducing the amount of expensive Pd in the membrane. Further, by changing the surface morphology and the electronic structure of metal Pd, alloys exhibit better chemical stability than pure Pd, in terms of the resistance to poisoning by gaseous impurities such as H₂S, CO, H₂O (Gao et al, 2004). It is well documented that Pd-Cu alloy shows improved resistance to sulfur (Morreale et al, 2004; Kamakoti et al, 2005; Yang et al, 2008).

In addition to Pd, refractory metals in group IV and V elements such as V, Nb, Ta, Zr and Ti are all good candidate materials for hydrogen separation membranes. In fact their hydrogen permeabilities are higher than Pd (Buxbaum and Kinney, 1996). The major issue with these metals is that they can easily form an oxide layer on the surface in contact with air, rendering them incapable of dissolving or dissociating hydrogen molecules. Current practice uses a thin layer of Pd or Pd alloy coated on the surface of the refractory metal to catalyze the dissociation and reassociation of H₂ (Buxbaum and Marker, 1993; Moss et al., 1998; Mundschau et al., 2006). These self-supported membranes are strong enough to sustain high-pressure differentials and are able to overcome the hydrogen-induced embrittlement problem commonly associated with the Group IV and V metals (Mundschau et al., 2005a, 2005b; Xie et al., 2006). Development of non-palladium-based metal alloy materials will continue to play a significant role in reducing the cost, increasing the permeability, and improving the durability of H₂ separation membranes (Ozaki et al., 2003; Hashi et al, 2005; Phair and Donelson, 2006; Ryi et al, 2006; Dolan, 2010; Song et al, 2010).

In actual practice of metallic membranes, intermetallic diffusion at high temperatures is one concern that needs to be addressed. Due to the high cost of Pd metal, it is very desirable to fabricate an ultrathin membrane, which is then supported by a porous substrate. If a metal such as stainless steel is chosen as the support material, Pd and Fe or Cr intermetallic diffusion becomes difficult to avoid. One alternative approach is to use ceramic materials for support. However, ceramics have the drawbacks of difficult fabrication, lower pressure rating and poor sealing resulting in delamination between the metal and the support. A good compromise is to insert a thin layer of ceramic barrier between the metal membrane and the stainless steel support (Nam and Lee, 2001; Ma et al, 2004; Bosko et al, 2009; Zhang et al, 2009). Membranes produced by this approach have been shown to be stable after over 6000 h of continuous testing in the temperature range of 350–450°C (Ma, 2008). For palladium-coated vanadium membranes, hydrogen flux decay was also observed due to intermetallic diffusion, and inserting a layer of porous aluminum oxide has improved the membrane stability (Edlund and McCarthy, 1995).

Among all high temperature inorganic membranes for hydrogen separation, Pd membranes are in the most advanced stage of development. In fact, the Pd membrane system was successfully scaled up to 25 tonnes per day H. capacity in the early 1960s (McBride and McKinley, 1965). Smallscale palladium membranes are commercially available for hydrogen purification in the semiconductor industry. Membrane reactors incorporating Pd have also been considered for H₂ production integrated with CO₂ capture in power generation cycles, although this has only been tested experimentally on a laboratory scale (Tong et al, 2006; Barbieri et al, 2008; Tosti et al, 2008). Cost and stability are still the major barriers for commercialization of metallic membranes on a large scale.

7.2.2 Polymeric membranes

The only hydrogen membrane technology that has been widely used on a commercial scale is based on polymeric materials. In the early 1980s, Monsanto commercialized the first hydrogen membrane process – Prism®(MacLean et al., 1986). Since then, polymeric membranes have been used in hydrogen recovery from purge streams in ammonia plants and refineries. In syngas plants, they have also been used for adjustment of the hydrogen/carbon monoxide ratio. The major suppliers are Air Products, Air Liquide, Praxair, UOP, UBE (Japan).

Dense polymer membranes are typically made of polysulfone, polystyrene, cellulose acetate, polyimide or polyaramade among others (Koros and Fleming, 1993). Separation of hydrogen is mainly due to the fast-diffusion coefficients of smaller hydrogen molecules being transported through the bulk of the membrane. Other gas molecules can still permeate through the membrane, depending on the relative solubility and diffusivity in the polymer material. Therefore, polymeric membranes are rarely used for producing high-purity hydrogen. In general, improving the performance of H₂-selective membrane relies on increasing diffusivity selectivity of H₂ and decreasing the solubility selectivity of CO₂. In addition to designing new molecules for H₂-selective polymers, other techniques include blending, doping and crosslinking (Shao et al, 2009a). However, there is always a trade-off between the selectivity and the permeability and an 'upper bound', as first introduced by Robeson (1991), is difficult to cross, as illustrated in Fig. 7.2. Figure 7.3 shows the gas permeabilities for several different gas pairs at two different selectivities, 5 and 50. The figure is calculated based on the correlation of the Robeson's upper bound curves (Robeson, 2008). H₂/CO₂ is difficult to separate because of the similar kinetic diameters of the two molecules and the preferential sorption of CO₂. Table 7.1 lists the molecular diameters and critical temperatures for several gases. The higher the critical temperature is, the more easily the gas can be condensed and hence the higher the solubility of the gas in the polymers. Note that the difference of the molecular sizes between H2 and CO₂ is relatively small. Further, CO₂ has a much higher critical temperature than H₂ and therefore higher solubility.

Polymeric membranes are very susceptible to swelling effect and are easily plasticized by highly soluble gases such as heavy hydrocarbons or CO2. Pretreatment of the feed gas before the membrane can be complicated and costly. Pretreatment is also used to prevent condensation of hydrocarbon vapor on the membrane surfaces. Because hydrocarbons and other larger molecules are enriched on the feed side of the membrane after hydrogen permeation, the dew point of the residue stream can increase.

The possibility of condensation is further increased as the membrane temperature drops due to Joule-Thomson effect when hydrogen permeates from the high-pressure feed side to the low-pressure permeate side. Other problems include poor resistance to certain chemicals such as hydrochloric acid (HCl) and sulfur oxides (SO_x) (Adhikari and Fernando, 2006). The pretreatment issue and the low temperature capability make the polymeric membrane less attractive for applications in the power sector. The maximum operating temperature can reach about 110°C. The maximum pressure differential across the membrane, depending on the temperature, can be as high as 100 bars at 40°C (Air Products, 2011). The low H₂/CO₂ selectivity (< 10) is another disadvantage for power plant application, as the feed gas tends to contain a large amount of CO₂, especially after the water-gas shift reaction. Nevertheless, polymeric membranes have the advantages of low cost, easy fabrication and extensive field experience. Research on hightemperature (to 300°C) polymeric membranes has been reported (Costello et al, 1994; Rezac et al, 1995; Pesiri et al, 2003), but they are only limited to laboratory testing.

7.2.3 Mixed ionic-electronic membranes

Dense ceramic membranes are mainly of perovskite type, which has the following formula:

[7.8]

where A´is selected from the group consisting of Ba, Sr, Ca, Mg, and

A' is selected from the lanthinide series such as Ce, Pr, Nd, Gd, Yb;

B and B' are selected from any transition metal such as Ce, Y, Co, Ti, V, Cr;

O is oxygen;

x and y are numbers between 0 and 1;

z is a number sufficient to neutralize the charge in the mixed metal oxide.

This class of material exhibits a mixed protonic–electronic conductivity at high temperatures, 600–1000°C (Iwahara et al., 1981; Norby and Larring, 2000; Qi and Lin, 2000; White et al, 2001; Hamakawa et al, 2002; Norby, 2007). When a H⁻ - containing gas mixture is introduced on one side of the membrane, H₂ dissociates into proton (H⁺) and electron (e +) on the surface. The dissociated species are transported through the membrane to its opposite side where the species recombine to a H₂ molecule, as illustrated in Fig. 7.4. This type of membrane has a very high selectivity as only hydrogen can permeate through the membrane. However, the hydrogen flux currently demonstrated in the lab is very low (Doong et al., 2005). Its unique high-temperature operating range makes it possible to closely couple with the coal or biomass gasifier without further cooling down the syngas. On the other hand, the high-temperature operation makes the robust design of membrane support, module and housing more challenging. The tolerance to contaminants in the coal-derived syngas is another concern, especially the stability issue in the presence of CO₂. Certain perovskites can be converted to more stable carbonate compounds in contact with CO₂. Dense perovskite membranes are still in an early stage of development.

To increase the hydrogen flux of dense ceramic membranes, a hydrogenpermeable metallic material can be incorporated into the dense mixed conducting ceramic phase, as a cermet (Dorris et al., 2003; Mundschau (2005). The transport mechanism is illustrated in Fig. 7.5. The hydrogen transport is predominantly carried by the metallic phase, which offers a high flux. Therefore, typical ceramic materials without ion-conducting property such as Al₂O₃ and stabilized ZrO₂, can also be used for the ceramic phase (Balachandran et al., 2005). With metals dispersed in the ceramic framework, the shape integrity of the metal phase is no longer an issue. The ceramic/metal composite structure offers better mechanical, chemical and thermal stability than metal membranes and can afford a high temperature operation (~ 900°C). At such a high temperature, it has better tolerance to sulfur compounds in the feed gas (Balachandran et al., 2006)

7.2.4 Porous ceramic membranes

Porous ceramic membranes are usually amorphous, made of alumina, silica, zirconia or titania in a form of metal oxide. These materials possess good thermal and chemical stability in harsh operating conditions. Other advantages include easy fabrication and low cost of production. In order to efficiently separate hydrogen, pore diameters of the membrane must be less than 1 nm (Diniz da Costa et al, 2002; Lee and Oyama, 2002; Verweij et al, 2006). As in dense membranes, the active layer with small pore size needs to be supported by a thick layer with a pore size between 0.5 and 50 μm. An intermediate layer with a pore size between 0.005 and 0.5 μm is also used to bridge the support and the active layer (Judkins and Bischoff, 2005). Figure 7.6 shows a SEM micrograph of a mesoporous silica membrane (pore size 20 Å) deposited on a coarse pore alpha-alumina (200 nm) support. Hydrogen product purity in porous ceramic membrane is almost always less than 100% as microporous membranes with uniform pore size and defect-free properties are difficult to fabricate. The improvement of selectivity comes with a reduction of flux for microporous ceramic membranes. One possible remedial solution to the H₂ purity deficiency problem is to use a multi-stage approach, where the microporous membrane is used for bulk removal of CO₂ and other larger contaminants, followed by a highly selective but more expensive Pd or metallic membrane.

Two main problems of the amorphous microporous membranes are their tendency to densify at high temperatures and the hydrothermal stability of silica membranes in the presence of steam (Yoshino et al., 2005). Supported silica membranes can suffer delamination and structural instability of the intermediate layer. Improvement in stability has been reported by incorporating methyl groups in the silica microstructure (de Vos et al., 1999), using metal doping such as Ni (Tsuru, 2008), introducing Si-C bonds to form silica organic hybrid structure (Kanezashi et al., 2009), or addition of TiO₂ to SiO₂ structure (Gu and Oyama, 2009).

7.2.5 Zeolite membranes

Zeolites are porous crystalline aluminosilicates with their framework consisting of an assemblage of SiO₄ and AlO₄ tetrahedra. The unique feature of uniform pore size distribution distinguishes the zeolites from other amorphous microporous materials. Zeolite membranes typically are prepared by growing polycrystalline zeolite into a continuous film on the surface of a porous support. More than 14 zeolite structures have been investigated for H.-selective membranes (Ockwig and Nenoff, 2007). Gas permeation is based on the diffusion of the gas molecules through the interconnected channels or intracrystalline pores (Lin, 2001). Gas separation could be affected both by the molecular sizes of the gases and by their adsorption properties (Hong et al, 2005; Kanezashi et al, 2008). Therefore, for hydrogen separation, high-temperature operation is used to suppress the adsorption of CO₂ and improve the H₂/CO₂ separation factor. Current research on zeolite membranes focuses on tailoring the micropore size and fabricating defect-free membranes (Caro and Noack, 2008).

7.2.6 Carbon molecular sieve membranes

Carbon molecular sieve is another group of material, similar to zeolite, which possesses a pore size in the range of gas molecular dimensions and a very sharp pore size distribution. The slit-shaped pores are formed from packing imperfections among planar aromatic structures (Kiyono et al, 2010). It is produced by pyrolysis of organic precursors such as polymers, coke, coal or biomass. Polyimides are the most used precursors with good H₂/CO₂ separation performance surpassing the Robeson's upper bound, as recently reported by Hosseini and Chung (2009). Flat, tubular or hollow fiber carbon molecular sieve membranes of asymmetrical structure can be fabricated from the precursors of the same geometry (Jones and Koros, 1994; Ismail and David, 2001; Saufi and Ismail, 2004). However, these may have the disadvantage of brittleness and difficulty to handle for scale-up. Alternatively, the membranes can be produced by coating on a porous ceramic or stainless steel support. Carbon molecular sieve membranes supported on ceramic tubes have been tested in a refinery pilot plant using hydrocracker off-gas for about 100 h (Liu, 2005). Operating at 220°C, the membranes were stable in the presence of significant H₂S, NH₃ and higher hydrocarbons, presumably due to low adsorption of these contaminants on carbon at high temperatures. The hydrogen flux was quite comparable to the dense Pd membranes. Like any microporous membrane, the carbon molecular sieve membrane has the difficulty of producing ultrahigh purity hydrogen from a feed gas containing a significant amount of CO₂.

7.3.1 Polymeric membranes

To increase the solubility of CO₂ vs H₂, one approach is to incorporate polar groups such as ethylene oxide (EO), propylene oxide (PO) or ethylene glycol (EG) units to increase their interactions with quadrupolar CO₂ molecules. The affinity of the membrane material for CO₂ must not be so high as to inhibit its mobility. For example, the high molecular weight polyethylene oxide (PEO) has low CO₂ permeability due to its tendency to crystallize. The other issue is the negative effect of plasticization by CO₂, resulting in an increase of H₂ permeability and hence reduced CO₂ selectivity. To over-come this shortcoming, uses of cross-links, copolymers, or polymer blends have been suggested. Freeman's research group has developed a series of cross-linked and highly branched PEOs, containing different terminal functional groups and network copolymers (Lin et al, 2006; Kusuma et al, 2009; Reijerkerka et al., 2011). They showed the effect of free volume and glass transition temperature or polymer chain mobility on CO2 permeability. Plasticization actually increases both CO2 permeability and CO2/H2 selectivity. Poly (amide-b-ether) or Pebax is a well-known copolymer consisting of flexible polyether segments (PEO) and the rigid amide blocks. Reijerkerka et al. (2010) studied the tuning of mass transport properties of multi-block copolymers using PEO and/or PPO as a soft segment and a monodisperse di-amide as a hard segment. They demonstrated the influence of the length of the soft segment and the type of soft segment on CO₂ permeability. Other copolymer examples include poly (ether-urethane) and poly (ether-urea) block that contains glycol units (Simmons, 2005). Car et al. (2008) blended Pebax with low molecular weight PEG resulting in a two-fold increase of CO₂ permeability and 20% increase in CO₂/H₂ selectivity.

Very high free-volume polymers such as poly(1-trimethylsilyl-1-propyne) (PTMSP), poly(4-methyl-2-pentyne) (PMP) and polydimethylsiloxane (PDMS) are more permeable to the more condensable gases such as CO₂ and H₂S than H₂, at room temperature (Merkel et al, 2001; Shekhawat et al, 2003; Bernardo et al, 2009). Their high CO₂ permeability allows these polymers to be further modified to increase the selectivity by blending or crosslinking. Another option is to introduce inorganic particles to form hybrid membranes, which will be discussed in Section 7.3.3.

The design of CO₂-selective polymeric membrane faces two counter-effects of higher CO₂ solubility and higher H₂ diffusivity. Rubbery polymers exhibit high solubility selectivity for CO₂ over H₂, but lack the diffusivity difference. Glassy polymers offer good diffusivity selectivity for H2 over CO2, but fall short of the solubility difference. One alternative approach is to resort to chemical reaction as in a facilitated transport membrane.

7.3.2 Facilitated transport membranes

Facilitated transport membranes (FTMs) offer high selectivity and high flux by incorporating a carrier agent into a polymer matrix to react with CO2 reversibly. There are generally two types of FTMs: mobile carrier and fixed carrier. The mobile carrier can move freely across the membrane. This type of membrane is also called supported liquid membrane (SLM) or 'immobi-lized' liquid membrane (ILM). The carrier first reacts with CO₂ on the feed side and the reaction product moves across the membrane. On the permeate side, CO₂ is released while H₂ or other gas species is not affected by this facilitated transport. The fixed carrier is covalently bonded to the polymer backbone and its mobility is limited. The CO₂ molecule reacts with one carrier site and then hops to the next site until it reaches the permeate side. Figure 7.7 illustrates the two types of CO2 transport mechanism in FTMs.

The most commonly used mobile carriers are amine and carbonate-bicar-bonate solutions. The primary drawback for SLMs is the loss of solvent due to evaporation or wash out under a high trans-membrane pressure. Ionic liquids, which are liquid salts at room temperature with negligible vapor pressure and are chemically and thermally stable, have recently been explored as carriers for SLMs (Hanioka et al., 2008; Myers et al., 2008; Scovazzo, 2009). They can be synthesized with specific functional groups to enhance CO₂ solubility. Furthermore, certain ionic liquids are polymerizable and can be blended with another polymeric membrane to form fixed carrier FTMs (Tang et al.. 2005; Bara et al.. 2007; Carlisle et al., 2010).

In general, fixed carrier membranes are considered more stable. Poly vinyl alcohol, poly(allylamine) or polyethyleneimine have been investigated for FTMs for CO₂ separation due to the presence of reactive functional groups of amines (Matsuyama et al, 1999; Zou and Ho, 2006; Huang et al, 2010). Hydroxy groups in poly (vinyl alcohol) or chitosan is another example (El-Azzami and Grulke, 2008, 2009). Ion-exchange membranes are intermediate between the mobile and the fixed carrier types (LeBlanc et al, 1980). They typically can be made by neutralizing an ionomer membrane with organic amine counter ions such as monoprotonated ethylenediamine (EDA) (Hagg and Quinn, 2006). Most data were reported for CO₂/N₂ separation, but the barrier to N₂ in ionic membrane can be extended to H₂ as well.

7.3.3 Inorganic membranes

A few zeolite membranes, instead of H₂ -selective as discussed in Section 7.2.5, actually show CO₂ selectivity over H₂. This is mainly due to stronger CO₂ adsorption. Figure 7.8 shows that zeolite membranes can be CO₂-selective due to competitive adsorption or H₂-selective due to molecular sieving effect. Lindmark and Hedlund (2010) reported a CO₂/H₂ separation factor of 6.2 for a BaZSM-5 membrane at room temperature. CO₂/H₂ selectivity greater than 100 was reported for a SAPO-34 membrane at 253 K and 1.7 MPa by Hong et al. (2008). As the temperature is increased, the CO₂/H₂ separation factor is always reduced because the adsorption of CO₂ is decreased. Other microporous membranes such as silica, alumina or carbon have also been considered for CO₂./N₂ separation (Shekhawat et al, 2003) due to their molecular sieving capabilities. For CO₂/H₂ separation, the materials need to be modified to increase CO₂ adsorption, as mentioned earlier.

A new class of carbonate–ceramic dual-phase membrane has been discovered recently by Yamaguchi et al. (2007), Anderson and Lin (2010) and Wade et al. (2011). These membranes are composed of porous solid oxide electrolyte filled with molten carbonate, operating at a temperature exceeding 600°C. Carbonate and oxide ions are transported through the liquid phase electrolyte and the solid phase substrate, respectively, in opposing currents, as shown in Fig. 7.9. The CO₂ permeability was quite high at about 1 × 10^− 10 mol m/(m² s Pa). If leak-tight, this type of membrane should have infinite CO₂/H₂ selectivity. Similar to the mobile carrier FTMs, this material has the issue of retaining the liquid electrolyte during prolonged operation.

7.3.4 Mixed-matrix membranes

Mixed-matrix membranes (MMMs) enhance the properties of polymeric membranes by combining the easy processability of polymers and the superior selectivity of inorganic materials. The difficult and costly fabrication of inorganic membranes can be avoided by using MMMs, which use polymers as the continuous phase and the inorganic particles as the dispersed phase. The presence of the solid particles modifies the polymer membranes through the following different effects: (a) increasing the sorption of CO.. (b) creating a barrier to reduce the permeability, especially for H₂, (c) disrupting the polymer structure, and hence its free volume and chain mobility and (d) improving the overall thermal and mechanical strength. Figure 7.10 is a simplified diagram showing how MMMs can improve the selectivity of CO₂/H₂.

The successful development of the MMMs depends on the judicious selection of polymer matrix and inorganic filler. The major challenge is to improve the poor contact or eliminate the interfacial defect between the two phases. This is still a very wide open area, as numerous pairs of polymers/ inorganic fillers have been investigated. MMMs can be H₂-selective (Zhang et al., 2008a, 2008b; Khan et al., 2010; Ordõnez et al., 2010; Zornoza et al, 2011) or CO.-selective (Jha and Way, 2008; Shao et al, 2009b; Ahn et al, 2010). Xing and Ho (2011) blended fumed silica with cross-linked polyviny-lalcohol-polysiloxane containing both fixed and mobile amine carriers. They reported a CO₂ permeability of 1296 barrers (1 Barrer = 3.35 × 10^− 16 mol m/ (m² s Pa)) and a very high CO₂/H₂ selectivity of 87. Fumed silica with PMP or PTMSP can potentially increase CO₂/H₂ selectivity and/or permeability as the presence of the particles can increase the diffusivity of CO₂ or the larger molecule more than H2, thus reducing the diffusivity selectivity for H₂, based on the results from Merkel et al. (2003a, 2003b, 2003c). A comprehensive review on MMMs was recently published by Chung et al. (2007), in which more details can be found.

Adhikari, S., Fernando, S. Hydrogen membrane separation techniques. Industrial & Engineering Chemistry Research. 2006; 45:875–881.

Ahn, J., Chung, W.J., Pinnau, I., Song, J., Du, N., Robertson, G.P., Guiver, M.D., Gas transport behavior of mixed-matrix membranes composed of silica nano-particles in a polymer of intrinsic microporosity (PIM-1). Journal of Membrane Science 2010; 346:280–287, doi: 10.1016/j.memsci.2009.09.047.

Air Products and Chemicals (2011), Available from www.airproducts.com/products/Gases/supply-options/prism-membrane-hydrogen-recovery-and-purification.aspx.

Anderson, M., Lin, Y.S., Carbonate-ceramic dual-phase membrane for carbon dioxide separation. Journal of Membrane Science 2010; 357:122–129, doi: 10.1016/j.memsci.2010.04.009.

Babarao, R., Jiang, J., Unprecedentedly high selective adsorption of gas mixtures in rho zeolite-like metal-organic framework: A molecular simulation study. Journal of the American Chemical Society 2009; 131:11417–11425, doi: 10.1021/ja901061j.

Baker, R.W. Membrane Technology and Applications. West Sussex: Wiley; 2004.

Balachandran, U., Lee, T.H., Chen, L., Song, S.J., Picciolo, J.J., Dorris, S.E., Hydrogen separation by dense cermet membranes. Fuel 2006; 85:150–155, doi: 10.1016/j,fuel.2005.05.027.

Balachandran, U., Lee, T.H., Chen, L., Song, S.J., Picciolo, J.J., Dorris, S.E. Current status of dense cermet membranes for hydrogen separation. 22nd Annual Pittsburgh Coal Conference, Pittsburgh, USA, 12–15, September 2005. 2005.

Baltus, R.E., Counce, R.M., Culbertson, B.H., Luo, H., DePaoli, D.W., Dai, S., Duckworth, D.C., Examination of the potential of ionic liquids for gas separations. Separation Science and Technology 2005; 40:525–541, doi: 10.1081/SS-200042513.

Banerjee, R., Furukawa, H., Britt, D., Knobler, C., O'Keeffe, M., Yaghi, O.M., Control of pore size and functionality in isoreticular zeolitic imidazolate frameworks and their carbon dioxide selective capture properties. Journal of the American Chemical Society 2009; 131:3875–3877, doi: 10.1021/ja809459e.

Bara, J.E., Lessmann, S., Gabriel, C.J., Hatakeyama, E.S., Noble, R.D., Gin, D.L., Synthesis and performance of polymerizable room-temperature ionic liquids as gas separation membranes. Industrial & Engineering Chemistry Research 2007; 46:5397–5404, doi: 10.1021/ie0704492.

Bara, J.E., Carlisle, T.K., Gabriel, C.J., Camper, D., Finotello, A., Gin, D.L., Noble, R.D., Guide to CO₂ separations in imidazolium-based room-temperature ionic liquids. Industrial & Engineering Chemistry Research 2009; 48:2739–2751, doi: 10.1021/ie8016237.

Barbieri, G., Brunetti, A., Tricoli, G., Drioli, E., An innovative configuration of a Pd-based membrane reactor for the production of pure hydrogen: Experimental analysis of water gas shift. Journal of Power Sources 2008; 182:160167, doi: 10.1016/j.jpowsour.2008.03.086.

Basile, A., Gallucci, F., Iulianelli, A., Tereschenko, G.F., Ermilova, M.M., Orekhova, N.V., Ti-Ni-Pd dense membranes - The effect of the gas mixtures on the hydrogen permeation. Journal of Membrane Science 2008; 310:44–50, doi: 10.1016/j. memsci.2007.10.028.

Basile, A., Iulianelli, A., Advanced membrane separation processes and technology for carbon dioxide (CO₂) capture in power plantsMercedes Maroto-Valer, M., eds. Developments and innovation in carbon dioxide (CO₂) capture and storage technology: Carbon dioxide capture, transport and industrial applications; Volume 1. Woodhead Publishing, Cambridge, UK, 2010:203. [Chapter 7].

Bates, E.D., Mayton, R.D., Ntai, I., Davis, J.H., Jr., CO₂ capture by a task- specific ionic liquid. Journal of the American Chemical Society, 2002;124(6):9, doi: 10.1021/ja017593d.

Belmabkhout, Y., Serna-Guerrero, R., Sayari, A., Adsorption of CO₂- containing gas mixtures over amine-bearing pore-expanded MCM-41 silica: Application for gas purification. Industrial & Engineering Chemistry Research 2010; 49:359–365, doi: 10.1021/ie900837t.

Bernardo, P., Drioli, E., Golemme, G., Membrane gas separation: A review/ state of the art. Industrial & Engineering Chemistry Research 2009; 48:4638–4663, doi: 10.1021/ie8019032.

Bhandari, R., Ma, Y.H., Pd-Ag membrane synthesis: The electroless and electro-plating conditions and their effect on the deposits morphology. Journal of Membrane Science 2009; 334:50–63, doi: 10.1016/j.memsci.2009.02.014.

Bose, A.C. Inorganic Membranes for Energy and Fuel Applications. New York: Springer; 2008.

Bosko, M.L., Ojeda, F., Lombardo, E.A., Cornaglia, L.M., NaA zeolite as an effective diffusion barrier in composite Pd/PSS membranes. Journal of Membrane Science 2009; 331:57–65, doi: 10.1016/j.memsci.2009.01.005.

Brennecke J F and Maginn E J (2003), 'Purification of gas with ionic liquids', US Patent 6579343

Burggraff, A.J., Cot, L. Fundamentals of Inorganic Membrane Science and Technology. Amsterdam: Elsevier; 1996.

Buxbaum, R.E., Kinney, A.B. Hydrogen transport through tubular membranes of palladium-coated tantalum and niobium. Industrial & Engineering Chemistry Research. 1996; 35:530–537.

Buxbaum, R.E., Marker, T.L. Hydrogen transport through non-porous membranes of palladium-coated niobium, tantalum and vanadium. Journal of Membrane Science. 1993; 85:29–38.

Camper, D., Bara, J.E., Gin, D.L., Noble, R.D., Room-temperature ionic liquid-amine solutions: Tunable solvents for efficient and reversible capture of CO₂. Industrial & Engineering Chemistry Research 2008; 47:8496–8498, doi: 10.1021/ ie801002m.

Car, A., Stropnik, C., Yave, W., Peinemann, K.V., PEG modified poly(amide- b-ethylene oxide) membranes for CO₂ separation. Journal of Membrane Science 2008; 307:88–95, doi: 10.1016/j.memsci.2007.09.023.

Carlisle, T.K., Bara, J.E., Lafrate, A.L., Gin, D.L., Noble, R.D., Main-chain imidazolium polymer membranes for CO. separations: An initial study of a new ionic liquid-inspired platform. Journal of Membrane Science 2010; 359:37–43, doi: 10.1016/j.memsci.2009.10.022.

Caro, J., Noack, M. Zeolite membranes - Recent developments and progress. Microporous and Mesoporous Materials. 2008; 115:215–233.

Chen, C.H., Ma, Y.H., The effect of H.S on the performance of Pd and Pd/Au composite membrane. Journal of Membrane Science 2010; 362:535–544, doi: 10.1016/j.memsci.2010.07.002.

Chung, T.-S., Jiang, L.Y., Li, Y., Kulprathipanja, S., Mixed matrix membranes (MMMs) comprising organic polymers with dispersed inorganic fillers for gas separation. Progress in Polymer Science 2007; 32:483–507, doi: 10.1016/j. progpolymsci.2007.01.008.

Costello, L.M., Walker, D.R.B., Koros, W.J. Analysis of a thermally stable polypyrolone for high temperature membrane-based gas separations. Journal of Membrane Science. 1994; 90:117–130.

Coulter, K.E., Way, J.D., Gade, S.K., Chaudhari, S., Sholl, D.S., Semidey-Flecha, L., Predicting, fabricating, and permeability testing of free-standing ternary palladium-copper-gold membranes for hydrogen separation. Journal of Physical Chemistry C 2010; 114:17173–17180, doi: 10.1021/jp1039628.

Cullinane, J.T., Rochelle, G.T., Kinetics of carbon dioxide absorption into aqueous potassium carbonate and piperazine. Industrial & Engineering Chemistry Research 2006; 45:2531–2545, doi: 10.1021/ie050230s.

Diniz da Costa, J.C., Lu, G.Q., Rudolph, V., Lin, Y.S. Novel molecular sieve silica (MSS) membranes: Characterization and permeation of single-step and two-step sol–gel membranes. Journal of Membrane Science. 2002; 198:9–21.

Dolan, M.D., Non-Pd BCC alloy membranes for industrial hydrogen separation. Journal of Membrane Science 2010; 362:12–28, doi: 10.1016/j. memsci.2010.06.068.

Doong, S.J., Ong, E., Lau, F. Direct extraction of hydrogen from coal using a membrane reactor integrated with a gasifier. 22nd Annual Pittsburgh Coal Conference, Pittsburgh, USA, 12–15, September 2005. 2005.

Dorris S E, Lee T H and Balachandran U (2003), 'Metal/ceramic composites with high hydrogen permeability', US Patent 6,569,226 B1.

Drage, T.C., Blackman, J.M., Pevida, C., Snape, C.E., Evaluation of activated carbon adsorbents for CO₂ capture in gasification. Energy & Fuels 2009; 23:2790–2796, doi: 10.1021/ef8010614.

Drioli, E., Membrane reactors. Chemical Engineering and Processing 2004; 43:1101–1102, doi: 10.1016/j.cep.2004.04.002.

Ducrot-Boisgontier, C., Parmentier, J., Faour, A., Patarin, J., Pirngruber, G.D., FAU-type zeolite nanocasted carbon replicas for CO. adsorption and hydrogen purification. Energy & Fuels 2010; 24:3595–3602, doi: 10.1021/ ef100011q.

Edlund, D., McCarthy, J. The relationship between intermetallic diffusion and flux decline in composite-metal membranes: implications for achieving long membrane lifetime. Journal of Membrane Science. 1995; 107:147–153.

El-Azzami, L.A., Grulke, E.A., Carbon dioxide separation from hydrogen and nitrogen by fixed facilitated transport in swollen chitosan membranes. Journal of Membrane Science 2008; 323:225–234, doi: 10.1016/j.memsci.2008.05.019.

El-Azzami, L.A., Grulke, E.A., Carbon dioxide separation from hydrogen and nitrogen facilitated transport in arginine salt-chitosan membranes. Journal of Membrane Science 2009; 328:15–22, doi: 10.1016/j.memsci.2008.08.038.

EPRI and NETL (2000), 'Evaluation of innovative fossil fuel power plants with CO2 removal', Technical Report, 1000316, EPRI, Palo Alto and NETL, Pittsburgh

Field J H (1975), 'Separation of CO₂ from gas mixtures', US Patent 3,907,969

Freeman, B., Yampolskii, Y., Pinnau, I. Materials Science of Membranes for Gas and Vapor Separation. West Sussex: Wiley; 2007.

Gade, S.K., Payzant, E.A., Park, H.J., Thoen, P.M., Way, J.D., The effects of fabrication and annealing on the structure and hydrogen permeation of Pd-Au binary alloy membranes. Journal of Membrane Science 2009; 340:227–233, doi: 10.1016/j. memsci.2009.05.034.

Gaffney T R, Golden T C, Mayorga S G, Brzozowski J R and Talyer F W (1999), 'Carbon dioxide pressure swing adsorption process using modified alumina adsorbents', US Patent 5917136

Gao, H., Lin, Y.S., Li, Y., Zhang, B., Chemical stability and its improvement of palladium-based metallic membranes. Industrial & Engineering Chemistry Research 2004; 43:6920–6930, doi: 10.1021/ie049722f.

Gielen D (2003), 'The future role of CO₂ capture and storage: Results of the IEA- ETP model', International Energy Agency Working Paper, EET/2003/04, Paris.

Goeppert, A., Meth, S., Prakash, G.K.S., Olah, G.A., Nanostructured silica as a support for regenerable high-capacity organoamine-based CO₂ sorbents. Energy & Environmental Science 2010; 3:1949–1960, doi: 10.1039/c0ee00136h0.

Gu, Y., Oyama, S.T., Permeation properties and hydrothermal stability of silica-titania membranes supported on porous alumina substrates. Journal of Membrane Science 2009; 345:267–275, doi: 10.1016/j.memsci.2009.09.009.

Hagg, M.-B., Quinn, R. Polymeric facilitated transport membranes for hydrogen purification. MRS Bulletin. 2006; 31:750.

Hamakawa, S., Lin, L., Li, A., Iglesia, E. Synthesis and hydrogen permeation properties of membranes based on SrCeYbO. thin films. Solid State Ionics. 2002; 48:71.

Hanioka, S., Maruyama, T., Sotani, T., Teramoto, M., Matsuyama, H., Nakashima, K., Hanaki, M., Kubota, F., Goto, M., CO₂ separation facilitated by task- specificionic liquids using a supported liquid membrane. Journal of Membrane Science 2008; 314:1–4, doi: 10.1016/j.memsci.2010.06.047.

Harlick, P.J.E., Sayari, A., Applications of pore-expanded mesoporous silica. 5. Triamine grafted material with exceptional CO₂ dynamic and equilibrium adsorption performance. Industrial & Engineering Chemistry Research 2007; 46:446–458, doi: 10.1021/ie060774+.

Harrison, D.P., 'Calcium enhanced hydrogen production with CO 2 capture. Energy Procedia 2009; 1:675–681, doi: 10.1016/j.egypro.2009.01.089.

Hashi, K., Ishikawa, K., Matsuda, T., Aoki, K., Hydrogen permeation characteristics of (V, Ta)-Ti-Ni alloys. Journal of Alloys and Compounds 2005; 404–406:273–278, doi: 10.1016/j.jallcom.2005.02.085.

Hassanzadeh, A., Abbasian, J. Regenerable MgO-based sorbents for high- temperature CO. removal from syngas: 1. Sorbent development, evaluation, and reaction modeling. Fuel. 2010; 89:1287–1297.

Hayashi, H., Taniuchi, J., Furuyashiki, N., Sugiyama, S., Hirano, S., Shigemoto, N., Nonaka, T. Efficient recovery of carbon dioxide from flue gases of coal-fired power plants by cyclic fixed-bed operations over K₂CO₃-on-carbon. Industrial & Engineering Chemistry Research. 1998; 37:185–191.

Heintz, Y.J., Sehabiague, L., Morsi, B.I., Jones, K.L., Pennline, H.W. Novel physical solvents for selective CO₂ capture from fuel gas streams at elevated pressures and temperatures. Energy & Fuels. 2008; 22:3824–3837.

Hicks, J.C., Drese, J.H., Fauth, D.J., Gray, M.L., Qi, G., Jones, C.W., Designing adsorbents for CO₂ capture from flue gas-hyperbranched aminosilicas capable of capturing CO. reversibly. Journal of the American Chemical Society 2008; 130:2902–2903, doi: 10.1021/ja077795v.

Hong, M., Li, S., Falconer, J.L., Noble, R.D., Hydrogen purification using a SAPO-34 membrane. Journal of Membrane Science 2008; 307:277–283, doi: 10.1016/j.memsci.2007.09.031.

Hong, M., Falconer, J.L., Noble, R.D. Modification of zeolite membrane for H₂ separation by catalytic cracking of methyldiethoxysilane. Industrial & Engineering Chemistry Research. 2005; 44:4035–4041.

Hosseini, S.S., Chung, T.S., Carbon membranes from blends of PBI and polyimides for N₂/CH₄ and CO₂/CH₄ separation and hydrogen purification. Journal of membrane Science 2009; 328:174–185, doi: 10.1016/j.memsci.2008.12.005.

Howard, B.H., Killmeyer, R.P., Rothenberger, K.S., Cugini, A.V., Morreale, B.D., Enick, R.M., Bustamante, F., Hydrogen permeance of palladium-copper alloy membranes over a wide range of temperatures and pressures. Journal of Membrane Science 2004; 241:207–218, doi: 10.1016/j.memsci.2004.04.031.

Hsieh, H.P. Inorganic Membranes for Separation and Reaction. Amsterdam: Elsevier; 1996.

Huang, H.Y., Yang, R.T., Chinn, D., Munson, C.L., Amine-grafted MCM-48 and silica xerogel as superior sorbents for acidic gas removal from natural gas. Industrial & Engineering Chemistry Research 2003; 42:2427, doi: 10.1021/ie020440u.

Huang, J., Zou, J., Ho, W.S.W. CO₂-selective membranes for hydrogen fuel processing'. In: Liu K., Song C., Subramani V., eds. Hydrogen and Syngas Production and Purification Technologies. Hoboken, New Jersey: Wiley and AIChE; 2010:385. [Chapter 9].

Hufton, J.R., Mayorga, S., Sircar, S. Sorption-enhanced reaction process for hydrogen production. AIChE Journal. 1999; 45(2):248.

Hutson, N.D., Speakman, S.A., Payzant, E.A., Hutson, N.D., Speakman, S.A., Payzant, E.A. Structural effects on the high temperature adsorption of CO. on a synthetic hydrotalcite. Chemistry and Materials Science. 2004; 16:4135–4143. [0.1021/cm040060u].

Ida, J.-I., Lin, Y.S., Mechanism of high-temperature CO₂ sorption on lithium zirconate. Environmental Science & Technology 2003; 37:1999–2004, doi: 10.1021/ es0259032.

Ismail, A.F., David, L.I.B. A review on the latest development of carbon membranes for gas separation. Journal of Membrane Science. 2001; 193:1–18.

Iwahara, H., Esaka, T., Uchida, H., Maeda, N. Proton conduction in sintered oxides and its application to steam electrolysis for hydrogen production. Solid State Ionics. 1981; 3/4:359.

Jha, P., Way, J.D., Carbon dioxide selective mixed-matrix membranes formulation and characterization using rubbery substituted poly- phosphazene. Journal of Membrane Science 2008; 324:151–161, doi: 10.1016/j. memsci.2008.07.005.

Jiang, J., Charged soc metal-organic framework for high-efficacy H₂ adsorption and syngas purification: Atomistic simulation study September. AIChE Journal, 2009;55(9):2422–2432, doi: 10.1002/aic.11865.

Jones, C.W., Koros, W.J. Carbon molecular sieve gas separation membranes-I. Preparation and characterization based on polyimide precursors. Carbon. 1994; 32:1419–1425.

Judkins, R., Bischoff, B., Scale-up of microporous inorganic hydrogen- separation membrane. 22nd Annual Pittsburgh Coal Conference, Pittsburgh, USA, 2005.

Kamakoti, P., Morreale, B., Ciocco, M., Howard, B., Killmeyer, P., Cugini, A., Sholl, D. Prediction of hydrogen flux through sulfur-tolerant binary alloy membranes. Science. 2005; 37:569–573.

Kanellopoulos, N.K. Recent Advances in Gas Separation by Microporous Ceramic Membranes. Amsterdam: Elsevier; 2000.

Kanezashi, M., O'Brien-Abraham, J., Lin, Y.S., Suzuki, K., Gas permeation through DDR-type zeolite membranes at high temperatures. AIChE Journal, 2008;54(6):1478–1486, doi: 10.1002/aic.11457.

Kanezashi, M., Yada, K., Yoshioka, T., Tsuru, T., Design of silica networks for development of highly permeable hydrogen separation membranes with hydrothermal stability. Journal of the American Chemical Society 2009; 131:414415, doi: 10.1021/ja806762q.

Khan, A.L., Cano-Odena, A., Gutiérrez, B., Minguillón, C., Vankelecom, I.F.J., Hydrogen separation and purification using polysulfone acrylate-zeolite mixed matrix membranes. Journal of Membrane Science 2010; 350:340–346, doi: 10.1016/j.memsci.2010.01.009.

Kiyono, M., Williams, P.J., Koros, W.J., Effect of pyrolysis atmosphere on separation performance of carbon molecular sieve membranes. Journal of Membrane Science 2010; 359:2–10, doi: 10.1016/j.memsci.2009.10.019.

Knowles, G.P., Graham, J.V., Delaney, S.W., Chaffee, A.L., Aminopropyl- functionalized mesoporous silicas as CO₂ adsorbents. Fuel Processing Technology 2005; 86:1435–1448, doi: 10.1016/j.fuproc.2005.01.014.

Knowles, G.P., Delaney, S.W., Chaffee, A.L., Knowles, G.P., Delaney, S.W., Chaffee, A.L., Diethylenetriamine[propyl(silyl)]- functionalized (DT) mesoporous silicas as CO₂ adsorbents. Industrial & Engineering Chemistry Research 2006; 45:2626–2633, doi: 10.1021/ie050589g.

Korens N, Simbeck D R, Wilhelm D J, Longanbach J R and Stiegel G J (2002), 'Process screening analysis of alternative gas treating and sulfur removal for gasification', Revised final report. SFA Pacific, Inc., Mountain View, CA; U.S. Department of Energy, National Energy Technology Laboratory, Pittsburgh, PA, Task Order 739656–00100.

Koros, W.J., Fleming, G.K. Membrane-based gas separation. Journal of Membrane Science. 1993; 83:1–80.

Kusuma, V.A., Matteuccia, S., Freeman, B.D., Danquahb, M.K., Kalika, D.S., Influence of phenoxy-terminated short-chain pendant groups on gas transport properties of cross-linked poly(ethylene oxide) copolymers. Journal of Membrane Science 2009; 341:84–95, doi: 10.1016/j.memsci.2009.05.043.

LeBlanc, O.H., Jr., Ward, W.J., Matson, S.L., Kimura, S.G. Facilitated transport in ion-exchange membranes. Journal of Membrane Science. 1980; 6:339–343.

Lee, C.S., Chae, H.J., Lee, S.J., Choi, B.Y., Yi, C.K., Lee, J.B., Ryu, C.K., Kim, J.C., Development of regenerable MgO-based sorbent promoted with K₂CO₃ for CO₂ capture at low temperatures. Environmental Science and Technology 2008; 42:2736–2741, doi: 10.1021/es702693c.

Lee, D., Oyama, S.T. Gas permeation characteristics of a hydrogen selective supported silica membrane. Journal of Membrane Science. 2002; 210:291–306.

Lee, K.B., Verdooren, A., Caram, H.S., Sircar, S., Chemisorption of carbon dioxide on potassium-carbonate-promoted hydrotalcite. Journal of Colloid and Interface Science 2007; 308:30–39, doi: 10.1016/j.jcis.2006.11.011.

Lee, K.B., Beaver, M.G., Caram, H.S., Sircar, S., Novel thermal-swing sorption-enhanced reaction process concept for hydrogen production by low- temperature steam-methane reforming. Industrial & Engineering Chemistry Research 2007; 46:5003–5014, doi: 10.1021/ie0701064.

Lee, K.B., Beaver, M.G., Caram, H.S., Sircar, S., Chemisorption of carbon dioxide on sodium oxide promoted alumina. AIChE Journal 2007; 53:2824, doi: 10.1002/aic.11312.

Lee, K.B., Sircar, S., Removal and recovery of compressed CO₂ from flue gas by a novel thermal swing chemisorption process. AIChE Journal 2008; 54:2293, doi: 10.1002/aic.11531.

Lee, K.B., Beaver, M.G., Caram, H.S., Sircar, S., Reversible chemisorbents for carbon dioxide and their potential applications. Industrial & Engineering Chemistry Research 2008; 47:8048–8062, doi: 10.1021/ie800795y.

Liang, Y., Harrison, D.P., Gupta, R.P., Green, D.A., McMichael, W.J., Carbon dioxide capture using dry sodium-based sorbents. Energy & Fuels 2004; 18:569–575, doi: 10.1021/ef030158f.

Lin, H., van Wagner, E., Freeman, B.D., Toy, L.G., Gupta, R.P., Plasticization- enhanced hydrogen purification using polymeric membranes. Science 2006; 311:639–642, doi: 10.1126/science.1118079.

Lin, Y.S. Microporous and dense inorganic membranes: Current status and prospective. Separation and Purification Technology. 2001; 25:39–55.

Lindmark, J., Hedlund, J., Carbon dioxide removal from synthesis gas using MFI membranes. Journal of Membrane Science 2010; 360:284–291, doi: 10.1016/j. memsci.2010.05.025.

Liu, K., Song, C., Subramani, V. Hydrogen and Syngas Production and Purification Technologies. Hoboken, New Jersey: Wiley and AIChE; 2010.

Liu, P. Hydrogen production via a commercially ready inorganic membrane reactor. US DOE Annual Hydrogen Program Review Meeting, Washington, DC, 23–26. (May 2005):2005.

Liu, Y., Kravtsov, V.C., Larsen, R., Eddaoudi, M., Molecular building blocks approach to the assembly of zeolite-like metal-organic frameworks (ZMOFs) with extra-large cavities. Chemical Communications 2006; 14:1488–1490, doi: 10.1039/b600188m.

Liu, Y., Xu, J., Jin, L., Fang, Y., Hu, H., Synthesis and modification of zeolite NaA adsorbents for separation of hydrogen and methane. Asia-Pacific Journal of Chemical Engineering 2009; 4:666–671, doi: 10.1002/apj.315.

Lopes, F.V.S., Grande, C.A., Ribeiro, A.M., Oliveira, E.L.G., Loureiro, J.M., Rodrigues, A.E., Enhancing capacity of activated carbons for hydrogen purification. Industrial & Engineering Chemistry Research 2009; 48:3978–3990, doi: 10.1021/ ie801132t.

Ma, Y.H., Composite Pd and Pd/alloy membranesBose A., ed. Inorganic Membranes for Energy and Fuel Applications. Springer: New York, 2008:241–254, doi: 10.1007/978-0-387-34526-0_13. [chapter 13].

Ma, Y.H., Akis, B.C., Ayturk, M.E., Guazzone, F., Engwall, E.E., Mardilovich, I.P. Characterization of intermetallic diffusion barrier and alloy formation for Pd/Cu and Pd/Ag porous stainless steel composite membranes. Industrial & Engineering Chemistry Research. 2004; 43:2936–2945.

MacLean, D.L., Bollinger, W.A., King, D.E., Narayan, R.S., 'Gas separation design with membranesLi, N.N., Calo, J.M., eds. Recent Development in Separation Science; Vol. IX. CRC Press, Boca Raton, FL, USA, 1986:227–244. [Chapter 12].

Mahajan, R., Koros, W.J., Factors controlling successful formation of mixed- matrix gas separation materials. Industrial & Engineering Chemistry Research 2000; 39:2692–2696, doi: 10.1021/ie990799r.

Mallada, R., Menendez, M. Inorganic Membranes: Synthesis, Characterization and Applications. Amsterdam: Elsevier; 2008.

Mani, F., Peruzzini, M., Stoppioni, P., Combined process of CO₂ capture by potassium carbonate and production of basic zinc(II) carbonates: CO₂ release from bicarbonate solutions at room temperature and pressure. Energy & Fuels 2008; 22:1714–1719, doi: 10.1021/ef7006936.

Maroto-Valer, M.M. Developments and Innovation in Carbon Dioxide (CO₂) Capture and Storage Technology: Carbon Dioxide Capture, Transport and Industrial Application; Volume 1. Woodhead Publishing, Cambridge, UK, 2010.

Marcano, J.G.S., Tsotsis, T.T. Catalytic Membrane and Membrane Reactors. Weinheim: Wiley-VCH; 2002.

Matsuyama, H., Terada, A., Nakagawara, T., Kitamura, Y., Teramoto, M. Facilitated transport of CO₂ through polyethylenimine/poly(vinyl alcohol) blend membrane. Journal of Membrane Science. 1999; 163:221–227.

Mayorga S G, Weigel S J, Gaffney T R and Brzozowski J R (2001), 'Carbon dioxide adsorbents containing magnesium oxide suitable for use at high temperatures', US Patent 6,280, 503

McBride, R.B., McKinley, D.L. A new hydrogen recovery route. Chemical Engineering Progress. 1965; 61:81–85.

McCool, B., Xomeritakis, G., Lin, Y.S. Composition control and hydrogen permeation characteristics of sputter deposited palladium-silver membranes. Journal of Membrane Science. 1999; 161:67–76.

Merkel, T.C., Gupta, R.P., Turk, B.S., Freeman, B.D. Mixed-gas permeation of syngas components in poly(dimethylsiloxane) and poly(1-trimethylsi- lyl-1-propyne) at elevated temperatures. Journal of Membrane Science. 2001; 191:85–94.

Merkel, T.C., He, Z., Pinnau, I., Freeman, B.D., Meakin, P., Hill, A.J., Effect of nanoparticles on gas sorption and transport in poly(1-trimethylsilyl-1-pro- pyne). Macromolecules 2003; 36:6844–6855, doi: 10.1021/ma0341566.

Merkel, T.C., He, Z., Pinnau, I., Freeman, B.D., Meakin, P., Hill, A.J., Sorption and transport in poly (2,2-bis(trifluoromethyl)-4,5-difluoro-1,3-dioxole-co- tetrafluoro-ethylene) containing nanoscale fumed silica. Macromolecules 2003; 36:8406–8414, doi: 10.1021/cm020672j.

Merkel, T.C., Freeman, B.D., Spontak, R.J., He, Z., Pinnau, I., Meakin, P., Hill, A.J., Sorption, transport, and structural evidence for enhanced free volume in poly(4-methyl-2-pentyne)/fumed silica nanocomposite membranes. Chemistry of Materials 2003; 15:109–123, doi: 10.1021/cm020672j.

Millward, A.R., Yaghi, O.M., Metal-organic frameworks with exceptionally high capacity for storage of carbon dioxide at room temperature. Journal of the American Chemical Society 2005; 127:17998–17999, doi: 10.1021/ja0570032.

Morreale, B.D., Ciocco, M.V., Howard, B.H., Killmeyer, R.P., Cugini, A.V., Enick, R.M., Effect of hydrogen-sulfide on the hydrogen permeance of palladium- copper alloys at elevated temperatures. Journal of Membrane Science 2004; 241:219–224, doi: 10.1016/j.memsci.2004.04.033.

Moss, T.S., Peachey, N.M., Snow, R.C., Dye, R.C. Multilayer metal membranes for hydrogen separation. International Journal of Hydrogen Energy. 1998; 23:99–106.

Mulder, M. Basic Principles of Membrane Technology. Dordrecht: Kluwer; 1997.

Mundschau M V (2005), 'Hydrogen transport membranes', US Patent 6,899,744 B2.

Mundschau, M.V., Xie, X., Evenson, C.R., IV., Sammells, A.F., Dense inorganic membranes for production of hydrogen from methane and coal with carbon dioxide sequestration. Catalysis Today 2006; 118:12–23, doi: 10.1016/j. cattod.2006.01.042.

Mundschau, M.V., Xie, X., Evenson, C.R., IV., Sammells, A.F. Membranes for the purification of hydrogen produced from coal-derived water-gas shift mixtures. 22nd Annual Pittsburgh Coal Conference. Pittsburgh, USA, 12–15, September 2005. 2005.

Mundschau, M.V., Xie, X., Sammells, A.F., Hydrogen transport membrane technologies for simultaneous carbon dioxide capture and hydrogen separation in a membrane shift reactorThomas, D.C., Benson, S.M., eds. Carbon Dioxide Capture for Storage in Deep Geologic Formation; Vol 1. Elsevier, Amsterdam, 2005:291–306. [Chapter 16].

Myers, C., Pennline, H., Luebke, D., Ilconich, J., Dixon, J.K., Maginn, E.J., Brennecke, J.F., High temperature separation of carbon dioxide/hydrogen mixtures using facilitated supported ionic liquid membranes. Journal of Membrane Science 2008; 322:28–31, doi: 10.1016/j.memsci.2008.04.062.

Nair, B.N., Yamaguchi, T., Kawamura, H., Nakao, S.-I. Processing of lithium zirconate for applications in carbon dioxide separation: Structure and properties of the powders. Journal of the American Ceramic Society. 2004; 87(1):68–74.

Nam, S.-E., Lee, K.-H. Hydrogen separation by Pd alloy composite membranes: Introduction of diffusion barrier. Journal of Membrane Science. 2001; 192:177–185.

Norby, T. Ceramic proton and mixed proton-electron conductors in membranes for energy conversion applications. Journal of Chemical Engineering of Japan. 2007; 40:1166–1171.

Norby, T., Larring, Y. Mixed hydrogen ion-electronic conductors for hydrogen permeable membranes. Solid State Ionics. 2000; 136–137:139–148.

Ockwig, N.W., Nenoff, T.M., Membranes for hydrogen separation. Chemical Reviews 2007; 107:4078–4110, doi: 10.1021/cr0501792.

Okazaki, J., Ikeda, T., Tanaka, D.A.P., Sato, K., Suzuki, T.M., Mizukami, F., An investigation of thermal stability of thin palladium-silver alloy membranes for high temperature hydrogen separation. Journal of Membrane Science 2011; 366:212–219, doi: 10.1016/j.memsci.2010.10.011.

Ordõnez, M.J.C., Balkus, K.J., Jr., Ferraris, J.P., Musselman, I.H., Molecular sieving realized with ZIF-8/Matrimid® mixed-matrix membranes. Journal of Membrane Science 2010; 361:28–37, doi: 10.1016/j.memsci.2010.06.017.

Ozaki, T., Zhang, Y., Komaki, M., Nishimura, C. Hydrogen permeation characteristics of V-Ni-Al alloys. International Journal of Hydrogen Energy. 2003; 28:1229–1235.

Parsons. Evaluation of fossil fuel power plants with CO₂ recovery, 2002. [Final Report, DOE Contract No. DE-AM26-99FT40465].

Pesiri, D.R., Jorgensen, B., Dye, R.C., Thermal optimization of polyben- zimidazole meniscus membranes for the separation of hydrogen, methane, and carbon dioxide. Journal of Membrane Science 2003; 218:11–18, doi: 10.1016/ S0376-7388(03)00129-7.

Peters, T.A., Tucho, W.M., Ramachandran, A., Stange, M., Walmsley, J.C., Holmestad, R., Borg, A., Bredesen, R., Thin Pd-23%Ag/stainless steel composite membranes: Long-term stability, life-time estimation and post-process characterization. Journal of Membrane Science 2009; 326:572–581, doi: 10.1016/j. memsci.2008.10.053.

Perry, J.D., Nagai, K., Koros, W.J. Polymer membranes for hydrogen separations. MRS Bulletin. 2006; 31:745.

Phair, J.W., Donelson, R., Development and design of novel (non-palladium-based) metal membranes for hydrogen separation. Industrial & Engineering Chemistry Research 2006; 45:5657–5674, doi: 10.1021/ie051333d.

Pomerantz, N., Ma, E.Y.H., Payzant, A., Isothermal solid-state transformation kinetics applied to Pd/Cu alloy membrane fabrication. AIChE Journal, 2010;56(12):3062, doi: 10.1002/aic.12217.

Probstein, R.F., Hicks, R.E. Synthetic Fuels. New York: McGraw-Hill; 1982.

Qi, X., Lin, Y.S. Electrical conduction and hydrogen permeation through mixed proton-electron conducting strontium cerate membranes. Solid State Ionics. 2000; 130:149.

Reijerkerka, S.R., Arun, A., Gaymans, R.J., Nijmeijera, K., Wessling, M., Tuning of mass transport properties of multi-block copolymers for CO₂ capture applications. Journal of Membrane Science 2010; 359:54–63, doi: 10.1016/j. memsci.2009.09.045.

Reijerkerka, S.R., Nijmeijera, K., Ribeiro, C.B., Jr., Freeman, B.D., Wessling, M., On the effects of plasticization in CO₂/light gas separation using polymeric solubility selective membranes. Journal of Membrane Science 2011; 367:33–44, doi: 10.1016/j.memsci.2010.10.035.

Rezac, M.E., Koros, W.J., Miller, S.J., Chemical stability of polyimide membranes at temperature near Tg. Journal of Applied Polymer Science 1995; 58:165170, doi: 10.1002/app.1995.070580118.

Ritter, J.A., Ebner, A.D., State-of-the-art adsorption and membrane separation processes for hydrogen production in the chemical and petrochemical industries. Separation Science and Technology 2007; 42:1123–1193, doi: 10.1080/01496390701242194.

Robeson, L.M., The upper bound revisited. Journal of Membrane Science 2008; 320:390–400, doi: 10.1016/j.memsci.2008.04.030.

Robeson, L.M. Correlation of separation factor versus permeability for polymeric membranes. Journal of Membrane Science. 1991; 62:165.

Roa, F., Block, M.J., Way, J.D. The influence of alloy composition on the H₂ flux of composite Pd-Cu membranes. Desalination. 2002; 147:411–416.

Rowsell, J.L.C., Yaghi, O.M., Metal-organic frameworks: A new class of porous materials. Microporous and Mesoporous Materials 2004; 73:3–14, doi: 10.1016/j.micromeso.2004.03.034.

Ruthven, D.M. Principles of Adsorption & Adsorption Processes. New York: Wiley; 1984.

Ruthven, D.M., Farooq, S., Knaebel, K.S. Pressure Swing Adsorption. New York: Wiley; 1994.

Ryi, S.-K., Park, J.-S., Kim, S.-H., Cho, S.-H., Kim, D.-W., The effect of support resistance on the hydrogen permeation behavior in Pd-Cu-Ni ternary alloy membrane deposited on a porous nickel support. Journal of Membrane Science 2006; 280:883–888, doi: 10.1016/j.memsci.2006.03.007.

Ryi, S.K., Park, J.S., Kim, S.H., Kim, D.W., Cho, K.I., Formation of a defect-free Pd-Cu-Ni ternary alloy membrane on a polished porous nickel support (PNS). Journal of Membrane Science 2008; 318:346–354, doi: 10.1016/j. memsci.2008.02.055.

Saufi, S.M., Ismail, A.F., Fabrication of carbon membranes for gas separation - A review. Carbon 2004; 42:241–259, doi: 10.1016/j.carbon.2003.10.022.

Scovazzo, P., Determination of the upper limits, benchmarks, and critical properties for gas separations using stabilized room temperature ionic liquid membranes (SILMs) for the purpose of guiding future research. Journal of Membrane Science 2009; 343:199–211, doi: 10.1016/j.memsci.2009.07.028.

Serna-Guerrero, R., Da'na, E., Sayari, A., New insights into the interactions of CO, with amine-functionalized silica. Industrial & Engineering Chemistry Research 2008; 47:9406–9412, doi: 10.1021/ie801186g.

Shao, L., Samseth, J., Hagg, M.B., Crosslinking and stabilization of nan-oparticle filled poly(1-trimethylsilyl-1-propyne) nanocomposite membranes for gas separations. Journal of Applied Polymer Science 2009; 113:3078–3088, doi: 10.1016/j.memsci.2008.09.053.

Shao, L., Low, B.T., Chung, T.S., Greenberg, A.R., Polymeric membranes for the hydrogen economy: Contemporary approaches and prospects for the future. Journal of Membrane Science 2009; 327:18–31, doi: 10.1016/j.memsci.2008.11.019.

Shekhawat D, Luebke D R and Pennline H W (2003), 'A review of carbon dioxide selective membranes', A Topical Report, DOE/NETL-2003/1200.

Shu, J., Grandjean, B.P.A., van Neste, A., Kaliaguine, S. Catalytic palladium-based membrane reactors: A review. The Canadian Journal of Chemical Engineering. 1991; 69:1036–1060.

Simmons J W (2005), 'Block polyurethane-ether and polyurea-ether gas separation membranes', US Patent 6843829

Singh, R., Reddy, M.K.R., Wilson, S., Joshi, K., Diniz da Costa, J.C., Webley, P. High temperature materials for CO₂ capture. Energy Procedia. 2009; 1:623–630.

Sircar, S., Golden, T.C. Pressure swing adsorption technology for hydrogen production'. In: Liu K., Song C., Subramani V., eds. Hydrogen and Syngas Production and Purification Technologies. Hoboken, New Jersey: Wiley and AIChE; 2010:414. [Chapter 10].

Siriwardane R V (2008), 'Regenerable sorbents for CO₂ capture from moderate and high temperature gas streams', US Patent 7314847

Siriwardane, R.V., Stevens, R.W., Jr., Novel regenerable magnesium hydroxide sorbents for CO₂ capture at warm gas temperatures. Industrial & Engineering Chemistry Research 2009; 48:2135–2141, doi: 10.1021/ie8011598.

Siriwardane, R.V., Robinson, C., Shen, M., Simonyi, T. Novel regenerable sodium-based sorbents for CO₂ capture at warm gas temperatures. Energy Fuels. 2007; 21(4):2088–2097.

Song, G., Kellam, M.E., Liang, D., Dolan, M.D., Influence of processing conditions on the microstructure and permeability of BCC V-Ni membranes. Journal of Membrane Science 2010; 363:309–315, doi: 10.1016/j. memsci.2010.07.051.

Sun, P., Lim, C.J., Grace, J.R., Cyclic CO₂ capture by limestone-derived sorbent during prolonged calcination/carbonation cycling. AIChE Journal, 2008;54(6):1668, doi: 10.1002/aic.11491.

Symonds, R.T., Lu, D.Y., Macchi, A., Hughes, R.W., Anthony, E.J., CO₂ capture from syngas via cyclic carbonation/calcination for a naturally occurring limestone: Modelling and bench-scale testing. Chemical Engineering Science 2009; 64:3536–3543, doi: 10.1016/j.ces.2009.04.043.

Tang, J., Tang, H., Sun, W., Plancher, H., Radosz, M., Shen, Y., Poly(ionic liquid)s: A new material with enhanced and fast CO₂ absorption. Chemical Communications 2005; 26:3325, doi: 10.1039/b501940k.

Tong, J., Su, L., Kashima, Y., Shirai, R., Suda, H., Matsumura, Y. Simultaneously depositing Pd-Ag thin membrane on asymmetric porous stainless steel tube and application to produce hydrogen from steam reforming of methane. Industrial & Engineering Chemistry Research. 2006; 45:648–669.

Tosti, S., Adrover, A., Basile, A., Camilli, V., Chiappetta, G., Violante, V. Characterization of thin wall Pd-Ag rolled membranes. International Journal of Hydrogen Energy. 2003; 28:105–112.

Tosti, S., Basile, A., Bettinali, L., Borgognoni, F., Gallucci, F., Rizzello, C., Design and process study of Pd membrane reactors. International Journal of Hydrogen Energy 2008; 33:5098–5105, doi: 10.1016/j.ijhydene.2008.05.031.

Tsuru, T., Nano/subnano-tuning of porous ceramic membranes for molecular separation. Journal of Sol–gel Science and Technology 2008; 46:349–361, doi: 10.1007/s10971-008-1712-5.

US DOE. A National Vision of America's Transition to Hydrogen Economy-To 2030 and Beyond, 2002. [Washington D.C.].

US DOE and DOT. Hydrogen Posture Plan: An Integrated Research, Development and Demonstration Plan, 2006. [Washington D.C.].

US DOE. Hydrogen, Fuel Cells & Infrastructure Technologies Program: Multi-Year Research, Development and Demonstration Plan, 2007. [Washington D.C.].

US DOE. Hydrogen from Coal Program: Research, Development, and Demonstration Plan, 2010. [Washington D.C.].

Verweij, H., Lin, Y.S., Dong, J. Microporous silica and zeolite membranes for hydrogen purification. MRS Bulletin. 2006; 31:756.

de Vos, R.M., Maier, W.F., Verweij, H. Hydrophobic silica membranes for gas separation. Journal of Membrane Science. 1999; 158:277–288.

Wade, J.L., Lee, C., West, A.C., Lackner, K.S., Composite electrolyte membranes for high temperature CO, separation. Journal of Membrane Science 2011; 369:20–29, doi: 10.1016/j.memsci.2010.10.053.

Wang, L., Yoshiie, R., Uemiya, S., Fabrication of novel Pd-Ag-Ru/Al, O₃ ternary alloy composite membrane with remarkably enhanced H₂ permeability. Journal of Membrane Science 2007; 306:1–7, doi: 10.1016/j.memsci.2007.08.057.

Wang, B., Cote, A.P., Furukawa, H., O'Keeffe, M., Yaghi, O.M., Colossal cages in zeolitic imidazolate frameworks as selective carbon dioxide reservoirs. Nature, 2008;453(8):207–211, doi: 10.1038/nature06900.

White J H, Schwartz M and Sammells F (2001), 'Solid state proton and electron mediating membrane and use in catalytic membrane reactors', US Patent 6,281,403

Xie, X., Evenson, C.R., IV., Mundschau, M.V., Wright, H.A., Grimmer, P.J., High-pressure operation of dense hydrogen transport membranes for pure hydrogen production and simultaneous CO₂ capture. 23rd Annual Pittsburgh Coal Conference, Pittsburgh, USA, 2006.

Xing, R., Ho, W.S.W., Crosslinked polyvinylalcohol-polysiloxane/fumed silica mixed matrix membranes containing amines for CO₂/H₂ separation. Journal of Membrane Science 2011; 367:91–102, doi: 10.1016/j.memsci.2010.10.039.

Xiong, R., Ida, J., Lin, Y.S., Kinetics of carbon dioxide sorption on potassium-doped lithium zirconate. Chemical Engineering Science 2003; 58:4377–4385, doi: 10.1016/S0009-2509(03)00319-1.

Xu, X., Song, C., Miller, B.G., Scaroni, A.W., Adsorption separation of carbon dioxide from flue gas of natural gas fired boiler by a novel nanoporous "molecular basket" adsorbent. Fuel Processing Technology 2005; 86:1457–1472, doi: 10.1016/j.fuproc.2005.01.002.

Yamaguchi, T., Niitsuma, T., Nair, B.N., Nakagawa, K., Lithium silicate based membranes for high temperature CO₂ separation. Journal of Membrane Science 2007; 294:16–21, doi: 10.1016/j.memsci.2007.01.028.

Yang, J.Y., Nishimura, C., Komaki, M., Hydrogen permeation of Pd,₀Cu₄₀ alloy covered V-15Ni composite membrane in mixed gases containing H/S. Journal of Membrane Science 2008; 309:246–250, doi: 10.1016/j.memsci.2007.10.036.

Yang, R.T. Gas Separation by Adsorption Processes. London: Imperial College Press; 1997.

Yang, R.T. Adsorbents: Fundamentals and Applications. New York: Wiley; 2003.

Yang, W., Kim, Y., Liu, P.K.T., Sahimi, M., Tsotsis, T.T. A study by in situ techniques of the thermal evolution of the structure of a Mg-Al-CO₃ layered double hydroxide. Chemical Engineering Science. 2002; 57:2945–2953.

Yokozeki, A., Shiflett, M.B., Hydrogen purification using roomtemperature ionic liquids. Applied Energy 2007; 84:351–361, doi: 10.1016/j. apenergy.2006.06.002.

Yong, Z., Mata, V., Rodrigues, A.E. Adsorption of carbon dioxide at high temperature - A review. Separation and Purification Technology. 2002; 26:195–205.

Yong, Z., Mata, V., Rodrigues, A.E., Adsorption of carbon dioxide on basic alumina at high temperatures. Journal of Chemical & Engineering Data 2000; 45:1093–1095, doi: 10.1021/je000075i.

Yoshino, Y., Suzuki, T., Nair, B.N., Taguchi, H., Itoh, N., Development of tubular substrates, silica based membranes and membrane modules for hydrogen separation at high temperature. Journal of Membrane Science 2005; 267:8–17, doi: 10.1016/j.memsci.2005.05.020.

Zhang, K., Wei, X., Rui, Z., Li, Y., Lin, Y.S., Effect of metal-support interface on hydrogen permeation through palladium membranes. AIChE Journal, 2009;55(3):630, doi: 10.1002/aic.11760.

Zhang, Y., Musselman, I.H., Ferraris, J.P., Balkus, K.J., Jr., Gas permeability properties of Matrimid® membranes containing the metal-organic framework Cu-BPY-HFS. Journal of Membrane Science 2008; 313:170–181, doi: 10.1016/j. memsci.2008.01.005.

Zhang, Y., Balkus, K.J., Jr., Musselman, I.H., Ferraris, J.P., Mixed-matrix membranes composed of Matrimid® and mesoporous ZSM-5 nanoparticles. Journal of Membrane Science 2008; 325:28–39, doi: 10.1016/j.memsci.2008.04.063.

Zimmerman, C.M., Singh, A., Koros, W.J. Tailoring mixed matrix composite membranes for gas separations. Journal of Membrane Science. 1997; 137:145–154.

Zornoza, B., Téllez, C., Coronas, J., Mixed matrix membranes comprising glassy polymers and dispersed mesoporous silica spheres for gas separation. Journal of Membrane Science 2011; 368:100–109, doi: 10.1016/j.memsci.2010.11.027.

Zou, J., Ho, W.S.W., CO ₂-selective polymeric membranes containing amines in crosslinked poly(vinyl alcohol). Journal of Membrane Science 2006; 286:310–321, doi: 10.1021/ie070449.