Formation and characterization of amine-loaded hollow fiber sorbents will be described. These functional sorbents were created by infusing poly(ethyleneimine) (PEI) into the porous walls of cellulose acetate/mesoporous silica hybrid hollow fibers. The PEI infusion approach occurs during the final post-spinning solvent exchange steps after dry-jet, wet-quench, non-solvent induced phase separation spinning of the hollow fibers containing embedded mesoporous silica. The sorbents can be used for CO2 capture from dilute feed streams such as flue gases, and the resultant fibers have an equilibrium CO2 uptake of 1.2 mmol/g-fiber. The fiber sorbents were tested using a simulated flue gas at 100% relative humidity and 1 atm at 35 °C) in a shell-and-tube module. The modules show good capability to capture CO2 under realistic conditions and represent an important step towards realizing new, scalable process configurations for supported amine sorbents useful to treat large flue gas feeds.

A rise in atmospheric concentration of CO2 triggers the global warming and climate change. A number of investigations have been made to develop effective CO2 capturing technologies, and membrane separation would be one of the promising solutions. In this research group, CO2 separation with poly(amidoamine) (PAMAM) dendrimers has been investigated. Sirkar et al. reported promising potential of the dendritic molecules in preferential CO2 separation. CO2 sorption was facilitated by the specific interaction between CO2 and the primary amines of the branching end of the dendrimers. However, PAMAM dendrimers with lower generations flow at ambient condition, and thus the liquid dendrimer should be stably immobilized in a matrix especially under pressure.
We have exploited stable immobilization of PAMAM dendrimer, which is photo-crosslinking of poly(ethylene glycol) dimethacrylate (PEGDMA) in the presence of the dendrimer. The crosslinking reaction takes place very rapidly under mild conditions, and the polymeric membrane is obtained in a couple of minutes. Thus unfavorable side reactions, such as Michael addition reaction between C=C bond of methacrylate and primary amine, would be suppressed. The obtained polymeric membrane demonstrates a quite high CO2 selectivity over H2. CO2 permeates through the membrane with ca. 500 mu;m in thickness containing PAMAM dendrimer (0th generation) by 500 times faster than H2 at 5 kPa of CO2 partial pressure and 313 K under 80% relative humidity. The CO2 separation properties of the dendrimer containing membrane are associated with generation and weight fraction of the dendrimer, PEG length, and operation conditions. Especially, the CO2 separation performance is elevated under higher humidified conditions. The preferential permeation of CO2 has been also elucidated. Under humidified conditions, a part of CO2 turns to bicarbonate ion, which would be major species to penetrate membrane. On the other hand, the rest of CO2 forms carbamate with 2 primary amines of PAMAM dendrimers, which inhibits permeation of H2. The CO2-selective molecular gate effect enhances the CO2 permeation. The obtained results can be valuable in designing and developing CO2 separation materials. In this presentation, for practical use, further extension of the CO2 separation properties will be discussed to elevate CO2 permeability.

The development of advanced membrane technologies for gas separations has recently gained significant attention due to the energy and environmental efficiency of membrane processes. The separation properties of membranes depend upon membrane material, membrane structure and thickness, membrane configuration, and module and system design. Membranes can be made from polymeric, inorganic, or organic-inorganic hybrid materials, and can be formatted in a variety of modules including spiral wound, tube, plate, or hollow fiber.
The key for gas and vapor separation applications of membranes in challenging and harsh environments is the development of new tough, high performance membrane materials. The modular nature of membrane operations is intrinsically fit for process intensification, and this versatility might be a decisive factor to impose membrane processes in most gas separation fields, particularly for offshore natural gas applications such as floating liquefied natural gas (FLNG) and floating production storage and offloading vessel (FPSO) applications.
This talk highlights recent advances in gas separation membranes by considering the materials, membrane fabrication, the industrial applications, and finally the opportunities for the integration of membrane gas separation units in hybrid systems for the intensification of processes. Membrane processes for gas separations such as CO2 removal from natural gas and flue gas, H2 purification, and olefin/paraffin separations are of great interest to UOP. UOP Separextrade; spiral wound polymeric membrane systems have been extensively used for CO2 removal from natural gas and currently holds the membrane market leadership for this application. Advanced membrane materials and fabrication capabilities enable breakthrough development of new SeparexTM membranes for gas separations.

Both polyaniline (PANI) and polypyrrole (PPy) possess a complex of properties that are required for membrane material, which include good chemical stability under drastic chemical conditions, high thermal stability, and ability to form thin homogeneous layers on the surfaces of polymer supports. Both polymers deposited on porous polyethylene (PE) support were modified via photografting of a mixture of reactive and hydrophilic monomers followed by activation of the surface using reaction with diamines to provide the membranes with desired properties such as hydrophilicity, basicity, and affinity to CO2. The modified polymer membranes were characterized by scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. Incorporation of non-volatile solvents such as poly(ethylene glycol) and ionic liquids into the surface of the generic and modified PANI-PE and PPy-PE membranes significantly increased the transport of CO2 across the composite membrane. As a result, the membranes exhibit unprecedented high permselectivity for CO2.

Worldwide energy demands continue to increase to support development of modern economies. Much of this energy demand is met through combustion of fossil fuels, which generate carbon dioxide emissions that are believed to contribute to global climate change. A substantial research effort is focused on finding low cost ways to capture CO2 from power generation processes and prevent its emission to the atmosphere. Membranes are among a suite of emerging carbon capture technologies under development.
This presentation will describe the application of membranes to pre- and post-combustion carbon capture. In each capture scenario, understanding how a membrane unit would be integrated into the power process is critical to determining the desired membrane properties. The current state-of-the-art membrane materials will be reviewed and future performance targets will be described. Experience from ongoing membrane carbon capture slipstream testing will be discussed.

Gas separation by a membrane is one promising approach, since this process has the advantages of low cost, less CO2 emission, and small footprint of a system compared to other system. There have been many researches to develop CO2 membranes with high CO2 flux and selectivity. However, selectivity and permeability are conflicting each other, high flux membrane generally has low selectivity and vice versa. This is an intrinsic problem in membrane separations. In the design of a separation membrane, materials and thickness of a membrane are the most important points. Membrane thickness plays an important role on gas permeability, however, conventional membrane thickness still remains in a few micron scales, further thinning, especially to sub-100nm regions, has not been reached, even though the good performance of a gas separation is expected. Recently, we have developed a free-standing anda nanometer-thick membrane (nanomembrane) with a centimeter scale lateral size. By combining molecular imprinting technology in this nanomembrane, we succeeded to filtrate small organic molecules precisely by a nanomembrane. A Free-standing and nanometer-thick membrane with large lateral size would have a good potential for creating new gas separation membrane with high gas flux and high selectivity. In this presentation, we report the fabrication of a free-standing nanomembrane based on a spincoating process and the gas selectivity performance in CO2 separations.

A national need for enhanced energy security combined with rising energy costs and a growing awareness of the harmful effects of greenhouse gases has increased interest in cleaner energy, fuels, and chemicals production from hydrocarbon sources including coal, biomass, and natural gas. However, large scale production processes from these sources requires development of novel energy efficient technologies and process schemes for efficient hydrogen separation and carbon capture from hydrocarbon fuel derived synthesis gas. To that end, our team has been developing materials and membrane platforms based on those materials to execute those separations at industrially relevant conditions. Here we will discuss our work with polymer chemistries for this application, specifically those based on polybenzimidazole (PBI). The primary objectives of this effort have been to develop and demonstrate PBI-based membrane chemistries, structures, deployment platforms, and sealing technologies that achieve the critical combination of selectivity, permeability, chemical stability, and mechanical stability at elevated temperatures(>150 °C) and are amenable to incorporation into scalable, high area density membrane systems. We have developed PBI-based membranes with demonstrated hydrogen / carbon dioxide separation performance in realistic process environments greater than any other polymeric system reported to-date. We will describe our efforts to further improve membrane performance and utility through implementation of polymer design strategies that enable manipulation and control of membrane free volume architecture and morphology and realization of those polymer design strategies in the commercially viable hollow fiber membrane module format.

Our research has focused on the use of imidazoles as a tunable platform for developing novel liquid solvents and polymeric membranes for CO₂ capture. This presentation will provide an overview of our studies in this area, with an emphasis on structure-property relationships driving CO₂ absorption/reaction, solvent vapor pressure, pK_a, interactions with water, polymer membrane performances and molecular modeling. Furthermore, we will discuss the unique behaviors of imidazoles with sulfur dioxide (SO₂) which is often present alongside CO₂ in flue gas streams.

CO2 emissions from burning fossil fuels are thought to be one reason for the global warming. In the long term the best way to reduce these emissions is to find alternative energy sources which do not emit CO2 but it looks at least for number of years this is not possible for the technology to adopt these change. One solution is to capture the emitted CO2 before it reaches to the atmosphere. Several materials and methods have been proposed for the CO2 capture. Among these amine solvents are the most widely used and studied but they have a big disadvantage, which is the high cost for the regeneration of the solvent after capturing CO2 and this cost sometimes equal to the 40% of the energy output of power plants. Solid sorbents are a good alternative because of their relatively low regeneration cost. Basically, by pressure/temperature swing adsorption processes captured CO2 can be easily released from these sorbents. Here we report the first amidoxime porous polymers (APPs) where aromatic polyamides (aramids) having amidoxime pendant groups were synthesized through low temperature condensation of 4,49-oxydianiline (ODA) and p-phenylene diamine (p-PDA) with a new type of nitrile-bearing aromatic diacid chloride. The nitrile pendant groups of the polyamides were converted to an amidoxime functionality by a rapid hydroxylamine addition (APP-1 and APP-2). The CO2 adsorption capacities of these polyamides were measured at low pressure (1 bar) and two different temperatures (273 and 298 K) and high pressure (up to 225 bar - the highest measuring pressure to date) at 318 K. The low pressure CO2 uptake of APP-1 was found to be 0.32 mmol g21 compared with APP-2 (0.07 mmol g21) at 273 K, whereas at high pressure they showed a substantial increase in CO2 adsorption capacity exhibiting 24.69 and 11.67 mmol g21 for APP-1 and APP-2 respectively. Both aramids were found to be solution processable, enabling membrane applications.

The increasing in earth&’s average temperature is one of the major problems that caused by the emission of greenhouse gas including carbon dioxide (CO2). The capture of CO2 technologies have been used through various techniques such as cryogenic distillation, membrane separation, absorption by liquids, and adsorption on solid sorbents; in order to reduce the release of carbon dioxide concentrations into the atmosphere. In this work, a green porous hybrid composite has been investigated as a CO2 solid adsorbent. This composite was prepared from non-toxic materials including polyvinyl alcohol (PVA) as a matrix, incorporated with calcium carbonate (CaCO3) and boric acid as a cross-linking agent by using the freeze-drying method. The amounts of PVA, CaCO3, and boric acid, were varied in order to obtain a good CO2 adsorbent capacity with synergistic properties. Moreover, the densities of the composites were characterized by using Helium pycnometer, BET and SEM was used for the morphology study. The CO2 capacity was measured by using the dynamic adsorption unit and evaluated by using a Gas-chromatography.
References:
1. Songolzadeh, M., Ravanchi, M.T. and Soleimani, M. (2012). Carbon Dioxide Capture and Storage: A General Review on Adsorbents. Proceedings of World Academy of Science, Engineering and Technology, World Academy of Science, Engineering and Technology.
2. Nie, L., Chen, D., Suo, J., Zou, P., Feng, S., Yang, Q., Yang, S. and Ye, S. (2012). Physicochemical characterization and biocompatibility in vitro of biphasic calcium phosphate/polyvinyl alcohol scaffolds prepared by freeze-drying method for bone tissue engineering applications. Colloids and Surfaces B: Biointerfaces 100, 169-176.
3. Bai, X., Ye, Z.-f., Li, Y.-f., Zhou, L.-c. and Yang, L.-q. (2010). Preparation of crosslinked macroporous PVA foam carrier for immobilization of microorganisms. Process Biochemistry 45(1), 60-66.

Conjugated microporous polymers (CMPs) are an intriguing class of π-conjugated extended polymeric systems (pore size <2 nm) with permanent porosity and high specific surface area. CMPs with strong covalent linkages and hydrothermal stability are potential for post-combustion CO2 capture applications with excellent lifetimes and recyclability. We report the design, synthesis, adsorption and photophysical properties of a novel tetraphenylethene (TPE) multifunctional CMP extended by diethynylbiphenyl linker. 3D polymeric network exhibits high thermal, chemical stability and shows microporous nature with high specific surface area of 854 m2/g. This high surface area material further showed good H2 (1.5 wt %) and CO2 (32.4 wt %) capture properties at 77K and 195K respectively. Quantum chemical gas-phase calculations of possible fragments (ethyne, biphenyl, diethynylbiphenyl and TPE core) of polymer interacting with CO2 are carried out. π-π interaction energy between CO2 and aromatic core of TPE is found to be -19.24 kJ/mol which is the more prominent binding site. TPE-CMP emits strong turn-on greenish yellow fluorescence due to polymer network induced restrictions of the phenyl rotor conformations. Strong solid-state luminescence of TPE-CMP is further exploited for efficient Förster resonance energy transfer (FRET) applications by encapsulation of rhodamine-B dye molecules.

Metal-organic frameworks (MOFs) have recently emerged as promising materials for carbon capture and methane storage. Amongst the many possible MOFs, metal-substituted compounds based on M-DOBDC and M-HKUST-1 have demonstrated amongst the highest capacities for CO₂ and CH₄ at moderate pressures and temperatures. Here we explore the possibility for additional performance tuning by computationally screening several metal-substituted variants of these compounds (M = Be, Mg, Ca, Sr, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, W, Sn, and Pb) with respect to their CO₂ adsorption enthalpies and CH₄ capacities. In the case of CO₂, our screening identifies 13 compounds having adsorption enthalpies within the targeted thermodynamic window -40 to -75 kJ/mol: 8 are based on M-DODBC (M = Mg, Ca, Sr, Sc, Ti, V, Mo, and W), and 5 on M-HKUST-1 (M = Be, Mg, Ca, Sr and Sc). Variations in the electronic structure and the geometry of the structural building unit are examined and used to rationalize trends in CO₂ affinity. In particular, the partial charge on the coordinatively unsaturated metal sites is found to correlate with the adsorption enthalpy, suggesting that this property may be used as a simple performance descriptor for carbon capture efficiency. For methane storage, calculated adsorption enthalpies are found to be 10-20 kJ/mol less exothermic than for CO₂, consistent with a weaker, dispersion-based CH₄—MOF interaction. In parallel with these thermodynamic analyses, methane adsorption isotherms were predicted using Grand Canonical Monte Carlo (GCMC) simulations across the remainder of the M-DOBDC series, with additional comparisons to prominent MOFs such as MOF-5, PCN-11, PCN-14, and HKUST-1. Beyond predicting total capacities, the amount of usable stored methane was examined for two operating scenarios: isothermal pressure swing (PS) and a combined temperature/pressure swing. Under these conditions, PCN-11 & Be-DOBDC yield the best combination of usable gravimetric and volumetric methane densities at pressures below ~50 bar, while MOF-5 is best at higher pressures. Due to their tendency to retain significant quantities of adsorbed methane at low pressures, we observe that enhanced binding sites, such as coordinatively unsaturated metal sites, can be detrimental for PS operation at higher pressures.

MOFs are currently being explored for many applications, including carbon capture and there is a need to characterize and evaluate a MOF structure for its potential use for this application. State-of-the-art surface and pore structure analysis using Ar (87 K) adsorption coupled with non-local density functional theory (NLDFT) was combined with CO₂ (273 K) adsorption in both high resolution low pressure and high pressure experiments (up to the saturation pressure of CO₂) to achieve a clear picture of MOF structure and pore volume. Although CO₂ cannot be used for pore size analysis due to its strong quadrupole moment, which leads to specific interactions with polar surface sites, it has the advantage that it can fill narrower micropores than can be accessed by N₂ or Ar. The pore volume from CO₂ (which includes the volume of these narrow micropores) is an important property in determining a material&’s usefulness for carbon capture. NLDFT methods, rather than classical methods, are now the standard tool for accurate pore size analysis over the complete micro- and mesopore size range and have been shown to be accurate for MOF pore size characterization. In this work, we have focused on the characterization of MOFs containing mesoporosity such as MIL-100 (Fe) and MIL-101 (Cr) and MOFs containing narrow micropores such as CuBTC and UiO-66.

Here we report a system that uses low grade waste-heat from surfaces to provide energy for chemical reactions. In particular, low grade waste-heat on surfaces is used to drive the regeneration of a CO2 capture solution. To access the waste-heat, we fabricated a microvascular stripping system composed of circular microchannels, up to meters in length, conformed directly onto heated ceramic and metal surfaces in complex three-dimensional configurations. Our stripping system can be adapted to pre-fabricated surfaces, as demonstrated by a coffee mug containing a 1.2 m long, 300 µm diameter micro-channel. In our microvascular system, we found that increased CO2 release resulted from; (1) decreasing the diameter of the microchannel, (2) increasing the surface temperature, and (3) increasing the solution residence time. Using high-speed photography, we observed a two-phase flow phenomenon in the form of bubbly, slug, and annular flow. We report a stripping rate of 1.9 mg/min for MEA in a 300 µm diameter microchannel conformed onto a surface heated to 125C.

Due to their large surface areas and gas selectivity properties, nanoporous materials for the physisorption of gases are viewed by many within the scientific community as one viable solution to two problems in the application of porous solids: the storage of H2 for mobile applications[1], and for low energy gas separation via selective adsorption[2] (for CO2 capture from air for example). However, nanoporous materials for the physisorption of gases are passive in nature, and thus, in order to maintain high levels of gas adsorption often require cryogenic temperatures (~77 K for H2 sorption) and high pressures (up to 70 MPa for H2 storage systems) due to the low interaction energies (of the order of <15 kJ mol-1).
However, the practical implementation of nanoporous materials for H2 storage is often limited by containment vessel cost, as high pressure H2 causes metal embrittlement, leading to the use of increasingly more expensive containment materials such as carbon fibre wound tanks with polymer liners[3].
Issues are also highlighted for the practical use of selective adsorption gas separation, as any selectively adsorbed gas will desorb back into the bulk blend when the bulk gas pressure is reduced, due to the continual pressure required for adsorption and the fast desorption kinetics.
One possible solution to both problems is to move from passive nanoporous materials to active, responsive and easily controllable nanoporous materials, which would allow adsorbed gas to be trapped within the nanopores despite the removal of the bulk external gas, for example. This could lead to the lowering of the pressure in the storage tank for mobile H2 storage applications, aiding in the reduction of expensive tank materials and lowering the containment vessel cost. Such materials would also allow for selectively adsorbed gas to be contained separately from the bulk gas blend for low energy selective adsorption gas separation.
Here we present investigations into the controlled gas trapping and release abilities of the nanoporous materials[4] MIL-101-NH2[Cr] and TE-7 activated carbon beads (from MAST Carbon International) via gravimetric gas sorption, using the incorporation of a range of cheap and easily accessible materials for the trapping of gas within the pores of the nanomaterials.
References
[1] Rosi, N.L., et al., Hydrogen storage in microporous metal-organic frameworks. Science, 2003, 300(5622): p1127-1129
[2] Yang, Q.Y., et al., Molecular simulation of carbon dioxide/methane/hydrogen mixture adsorption in metal-organic frameworks. J. Phys. Chem. B, 2006, 110(36): p17776-17783
[3] Hua, T.Q., et al., Technical assessment of compressed hydrogen storage tank systems for automotive applications. Int. J. Hydrog. Energy, 2011, 36(4): p3037-3049
[4] Jiang, D., et al., Synthesis and post synthetic modification of MIL-101(Cr)-NH2 via a tandem diazotisation process. Chemical communications, 2012, 48(99): p12053-12055

CO2 absorbents with high capacity and stability, which can be used over a temperature range of 300 to 500 oC for CO2 removal, are highly desired because the cooling/heating treatments of the syngas stream can be eliminated, and the thermal efficiency is expected to be improved. Also, CO2 removal at this temperature range can be used to facilitate equilibrium-restricted processes, e.g. the water-gas-shift reaction. When integrated with a gas cleanup step and water-gas-shift reaction, it is possible to directly produce high purity hydrogen from gasified coal. According to thermodynamic considerations, MgO is an attractive absorbent for the capture of CO2 at 300- 400 °C. However, the kinetic rate for direct conversion of MgO to MgCO3 on exposure to CO2 is quite slow.
In this talk, we will report our recent progress on the development of molten salt-promoted MgO based absorbents for CO2 removal in the temperature range 300-500 oC. The absorbents include MgO and MgO-based double salts. A simple method has been developed for reproducible and scalable synthesis of these absorbents. We have found that the presence of alkali salts such as NaNO3 (melting point 308 °C) can facilitate not only the conversion of MgO to MgCO3 but also the decomposition of MgCO3 at 300-400C. MgO-based absorbents achieved a high CO2 capacity of over 10mmol/g when the molten NaNO3 was present, and the capacity was confirmed to have good repeatability. These absorbents can be easily regenerated through pressure swing or temperature swing. The effects of MgO to double salt ratio; molten salts concentration; and operation condition on CO2 removal will be reported. By adjusting the absorbents composition, we have developed a series of absorbents which can be used for different applications. The mechanism of molten salts-promoted CO2 adsorption on MgO has been investigated. These results will also be discussed.

Nature forms sophisticated structures through mechanisms involving only a few chemical reactions. These structures enable, for example, the strength of bones and the ability to respirate at high attitudes. Many of these structures are formed via morphogenesis controlled by reaction-diffusion. Reaction-diffusion involves at least two components, diffusing spatially and reacting with each other to either enhance or inhibit activity. While being studied and modeled for the last decade, reaction-diffusion has not been used to morph alter the structure of a microfluidic device.
In this work we present a new method to change the structure of a PDMS-based microfluidic device using reaction-diffusion. We use a concurrent flow of a depolymerizing agent (TBAF) and a blocking agent. The interaction between the two chemicals is controlled by the diffusion of the second reagent through a PDMS membrane. Strategic alignment of the channels containing the inhibition agent enabled us to control the final structure through reaction-diffusion mechanisms. Using this method we altered the structure of three-dimensionally patterned micro-channels. We were able to predict and observe the evolvement of the structure with time. Using programmed gradients of blocking agents, we created asymmetric structures starting from symmetric structures. Using selective pressure of transfer and controlled diffusion, we were able to “morph” our structures to create higher mass transfer of CO2 in response to selective pressure.
This work is the first step in developing a mechanism for the controlled alteration and refinement of structural materials through bio-mimetic, morphogenetic methods. Natural systems have the power to change and improve themselves over time, materials rarely do. This work presents an initial stepping stone in mimicking nature&’s ability to evolve.

CuBTC, also known as HKUST-1, is a nanoporous metal-organic framework materials with exposed metal ions. These structural features make CuBTC and related materials of great interest for applications in capturing and filtering gases such as CO₂. Unfortunately, CuBTC readily adsorbs H₂O in humid air, lowering its efficiency in practice, and destabilizing it under excessive humidity. We have combined density functional theory (DFT) calculations and experimental diffraction refinements to study water absorption in CuBTC in unprecedented detail. At a concentration of one H₂O molecule per Cu site, experiments show the H₂O are bound to the Cu, in agreement with previous studies. DFT calculations at the DFT+U level accurately reproduce the experimental results. At a saturation concentration of 2.7 H₂O per Cu site, experiments clearly show two additional adsorption sites for water. In this case, DFT+U results deviate from experiment, due to overly strong hydrogen bonding between H₂O molecules. Hybrid DFT calculations, although expensive, lead to improved results.

Carbon dioxide (CO₂) is the principle ingredient of greenhouse gases and a good indicator of air pollution in the atmosphere. Hence, it is necessary to reduce the amount of CO₂ before it is exhausted into the atmosphere and there is an ever increasing need to develop materials for direct capture of CO₂ [1]. In certain oxide materials if the oxygen defects tend to get ordered in a special manner, it may promote absorption of small molecules such as CO₂ [2]. This property may find technical application in reducing the industrial CO₂ output using non-harmful perovskites as temporary storage materials. In this work, we observe for the first time, the spontaneous capture of CO₂ from ambient air by oxygen-deficient perovskite CaFeO_2.5 and demonstrate a clear enhancement in CO₂ capture ability in nanostructured Brownmillerite CaFeO_2.5. The interaction between CO₂ (from atmosphere) and Brownmillerite bulk- as well as nano-CaFeO_2.5 has been investigated. We observed that while the physical properties of bulk-CaFeO_2.5 remain unaltered; nano-CaFeO_2.5 showed appreciable changes and transformed into CaCO₃ exhibiting strong reactivity towards CO₂. The kinetics for CO₂ absorption increases at higher temperatures as observed from thermogravimetric analysis (TGA). Although the maximum weight gain of 10 wt% is observed at 660 ^oC, a rapid CO₂ absorption started taking place at 440 ^oC onwards unlike in the case of other perovskites [2]. With increased CO₂ absorption kinetics above room temperature, this material can find application as CO₂ absorbing material in industrial surroundings with hot exhaust gases (emanated at temperatures > 400 ^oC).
The most significant outcome of this study is that the CO₂ absorption takes place at room temperature and CaFeO_2.5 can be recovered completely by heating, confirming that the absorption of CO₂ is reversible. This regenerated nano-CaFeO_2.5 retains the nano-size and hence can be re-used for CO₂ absorption which has also been confirmed by TGA in CO₂ atmosphere. These oxides are thus expected to be promising materials for the direct capture of CO₂ in combustion gas of fuels and can be potential candidates for practical applications in controlling the air-quality surrounding us.
[1] Keith D.W., Why Capture CO₂ from the Atmosphere?, Science 325, 1654 (2009).
[2] Homonnay Z. et al., Simultaneous Probing of the Fe and Co Sites in the CO₂-Absorber Perovskite Sr_0.95Ca_0.05Co_0.5Fe_0.5O_3-δ, Chem. Mat. 14, 1127 (2002).

We successfully synthesize a composite membrane made of proton conductive ceramic and palladium metal that allows for facile transport of hydrogen from a mixture of hydrogen and carbon dioxide at elevated temperature. Material characterizations including scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermo-gravimetric analysis are performed. XRD diffraction patterns indicate pure phases of Pd and perovskites. SEM mapping confirms homogeneous mixture of Pd and perovskites. For the hydrogen permeation test, we conduct the measurements through the gas chromatography from 400 to 700 °C, and the hydrogen flux of the Pd-BCZGD cermet reaches a steady state at 3 cm3/min-cm2 in pure wet hydrogen atmosphere for 100 hours. In addition, the selectivity of hydrogen and carbon dioxide is estimated at 32.66 at 700 °C.

CO2 emission to the atmosphere becomes gradually increased; this greenhouse gas leads to the global warming and climate change. Therefore, it is more imperative to reduce CO2 discharge. The kaolinite is a common clay mineral with the layered structure. In this study, the specific surface area of kaolinites are promoted by H2SO4 treatment. After preparation, the kaolinites are modified with MEA and EDA (amine) to enhance the capacity of CO2 adsorption. Amine-modified kaolinites are then analyzed via XRD, FTIR, BET measurements. The CO2 adsorption/desorption and multiple reaction cycles of modified kaolinites are examined by the thermo-gravimetric analyzer. It shows that the best amine-modified parameter to capture carbon dioxide is kaolinites with the ratio of amine/sample=1/1, the ratio of solid/liquid=1/10 at room temperature. Moreover, its CO2 capacity is 149 mg/g, which has a good durability of CO2 adsorption/desorption with 10 cycles. From these findings, it suggests the amine-modified kaolinite is the potential adsorbent for CO2 capture.

Several methods, including absorption and gas separation membranes, have been proposed for capturing the CO2 emitted into the atmosphere by human activity. To date, mainly mono-ethanol-amine (MEA)-based absorption processes are currently amongst the more promising systems for post-combustion CO2 capture. Replicating in an industrial scale process what nature already does efficiently is highly attractive and offers the major advantage of potentially obviating the need for CO2 compression and sequestration. Carbonic anhydrase (CA) an enzyme that physiologically mediates carbon dioxide build up by accelerating dissolution has previously shown some promise for capturing and converting CO2 into protons and bicarbonate. This overcomes the low solvation rate of CO2 in the aqueous phase and thereby accelerates CO2 scrubbing from the flue gases. Although free CA enzyme may offer a greater specific activity compared to an immobilized enzyme, the technical difficulty in recovering the active enzyme for reuse and its instability in tertiary amines, are two major obstacles for industrial scale processes. Immobilization is often the key to optimize the performance and cost of enzymatic industrial processes, permitting their use for a longer time by enabling the reuse of the enzyme and enhancing the enzyme stability against thermal denaturation by preventing the unfolding of the protein. Using nanoscale materials as an enzyme support offers several performance advantages but rapid recovery of nanoparticles from large volumes of liquid is practically challenging. Here we have applied an ultrasonic-based assembly technique that transforms nanoparticulate powders into mechanically durable mesoporous microparticles towards the application of enzyme immobilisation for carbon dioxide capture. These mesoporous microparticles can be used to simultaneously immobilise CA and to facilitate the recovery by simple decantation process. Our approach was based on the synthesis of nanoparticles, their assembly followed by a layer-by-layer deposition process to additionally physically retain the enzyme. These mesoporous microparticles in addition to efficiently retaining the enzyme on its surface allows for an efficient supply and presentation of CO2 to the non-aqueous solvent and the enzyme catalytic center. Additionally the use of organic polymer had preserved the enzymatic activity against denaturation and provided a very stable environment for the biocatalyst in organic solvent. These hierarchically structured particles were 70% more active than the free enzyme in amine solvent at 50C. To the best of our knowledge, this is the first time that mesoporous microparticles was used to successfully immobilise CA with improved activity and stability; and to simplify separation and re-use in CO2 capture bioreactors.

To impact carbon emissions, new materials for carbon capture must be inexpensive, robust, and able to adsorb CO₂ specifically from a mixture of other gases. In particular, materials must be tolerant to water vapor, which will always be present at some level in gas streams produced by using fossil fuels to generate electricity. We show that a porous organic polymer has excellent CO₂ capacity and high CO₂ selectivity under pressures that are relevant for pre-combustion CCS. Unlike polar adsorbents, such as Zeolite 13x and certain metal-organic frameworks, such as HKUST-1, the CO₂ adsorption capacity for the hydrophobic polymer is hardly affected by the adsorption of water vapor. At elevated pressures, the polymer adsorbs CO₂ in a different way from rigid materials by swelling, like a sponge, by more than half of its volume at 60 bar. This gives rise to a higher working CO₂ capacity and much better CO₂ selectivity than for rigid, water-tolerant frameworks such as activated carbon and ZIF-8. The polymer has enhanced function as a selective gas adsorbent, even though its monomer is one of the cheapest feedstocks imaginable for materials preparation on the large industrial scales required for carbon capture.

Carbon dioxide is a major component of the greenhouse gases. It is expected that the atmospheric CO2 level will continue to increase over the current concentration of approximately 400 ppm in the near future, as fossil fuels remain the major source utilized to meet global energy demand. Carbon capture and storage is a technology developed to prevent release of large quantities of CO2 into the atmosphere from power generation by capturing CO2 and securely storing it away from the atmosphere. However, current state-of- the-art technology for CO2 capture is to use liquid phase amine scrubbing, which is corrosive and energy intensive due to the high heating capacity of water. On the other hand, solid sorbent with lower heat capacity than water exhibits fewer thermal effects, which requires less energy for regeneration. Therefore, porous carbon with high thermal conductivity is desirable for such application.
Mesoporous carbons are promising for CO2 capture due to chemical inertness, low cost, high surface area and tunable pore structures. Its porous structure and high surface area allow addition of chemical functionality by grafting or impregnation. Amine chemistry tells us that nitrogen functionalization plays an important role in surface chemistry to achieve high CO2 adsorption capacity. We report here an ordered mesoporous nitrogen-doped carbon made using co-assembly of modified-pyrrole and triblock copolymer through a soft-templating method, which is facile, economical and fast compared to the hard template approach. In the synthesis, pyrrole precursor provides both the carbon and nitrogen source; therefore, additional nitrogen precursors are not required. Carbonization of the resultant polymeric assembly generates graphitic carbon structure and porous network through the removal of block copolymer template. High surface area mesoporous carbon was achieved that are comparable to the silica counterpart. The resulting material shows promising CO2 capture performance, reaching equilibrium adsorption of 1.0 mmol CO2/g of materials at 0.1 bar CO2. Furthermore, the macroscopic structure of this mesoporous N-doped carbon can be fine tuned through the use of different synthetic conditions to achieve a hierarchical macro-meso-microporous structure that allows fast diffusion of CO2 gas into the adsorption sites and controlled pore condensation within the meso/microporous structure. Another potential benefit is that the thermal conductivity of mesoporous carbon is higher than its silica counterpart, resulting in a faster regeneration step with enhanced stability using temperature swing process. These overall properties of mesoporous carbon made from conducting polymer made it a desirable material for CO2 capture.

Control of carbon dioxide emissions without significant penalties requires effective CO₂ scrubbing from point sources, such as fossil fuel burning power plants, cement factories and steel making. Capturing process is the most costly; hence the research is directed to finding solutions to it. Solids with slight chemisorptive nature are identified as most likely candidates for a sustainable solution. Nanoporous (pore size < 100 nm) materials show considerable CO₂ uptakes and are likely to replace monoethanol amine (MEA) solutions for industrial CO₂ capture. We have developed nanoporous covalent organic polymers (COPs), which show significant capacities and selectivities for CO₂. To name a few, COP-1 shows 5.6 g/g CO₂ uptake at 200 bar and 45 °C, COP-2 shows a CO₂/H₂ selectivity of over 10k:1, COP-79 has a CO₂/N₂ selectivity of 308 at 50 °C, COP-83 has CO2 uptake capacity of 5 mmol/g at 298 K and 1 bar and COP-97 showed an uptake of 8 % (w/w) CO₂ in 2 minutes from a simulated flue gas mixture (CO2 15%, H₂O 3.8%, He 81.2%, 40 C, flow rate : 80 mL/min). Our results point to an ideal nanoporous structure to be made from a highly porous, inexpensive, physisorptive solid, which is chemically modified with chemisorptive functionalities such as amines.
References:
1. H. A. Patel, et al., Nature Commun., 4:1357, (2013)
2. H. A. Patel, et al., Adv. Funct. Mater., 23, 2270-2276 (2013).
3. H. A. Patel, et al., J. Mater. Chem., 22, 8431-8437 (2012).
4. Image adapted from The Economist, Mar 5, 2009.

Nanostructured architectures and unconventional separation media hold the key to future chemical separations in gas storage and purification, environmental remediation, and many clean-up activities. Replacing energy-intensive separation methods by energy-efficient processes, such as membrane separation or adsorption, is an essential step toward substantial future energy savings. This talk will be focused on our recent investigation on development of porous carbons, ionic liquids, and their combination for CO2 separation. Hierarchical synthesis methodologies for porous carbons and polymers based on self-assembly will be examined to generate controlled adsorption sites integrated within novel separation media. The methodology to control the multitude of interactions that determine separation efficacy within ionic liquids will be also discussed.

Porous polymers are getting increasingly more studied as candidate adsorbents, membranes and parts in membrane composites for CO2 capture from flue gas or natural gas mixtures. As adsorbents they are relevant as both physisorbents and chemisorbents for CO2. As physisorbents targeting CO2 capture from flue gas it is crucial that the polymers have a significant amount of (ultra)micropores, which enable a high working capacity for CO2 removal. The ultramicropores leads to a high mass transport restriction and micro-/mesoporous organic polymers (MMOPs) could offer a way to lessen those. Three armed monomers of 1,3,5-tris(4-aminophenyl)benzene and 1,3,5-benzenetricarboxaldehyde were used to synthesize MMOPs by Schiff base condensation reactions. The fraction of micro- and mesopores in the MMOPs depended strongly on the amine/aldehyde ratio used. A mechanism based on oligomeric self-templating is proposed that rationalize the dependency on the amine/aldehyde ratio on the mesopores formation. The MMOPs had specific surface areas and pore volumes up to 694 m2/g and 0.67 cm3/g. They exhibited a high CO2 uptake (21~38 cm3/g at 0.15 bar and 49~76 cm3/g at 1 bar; 273 K), and the CO2-over-N2 selectivity was 31~90. The mesopores appeared to be of an “ink-bottle” type as revealed by cavitation on N2 desorption. The ultramicropores appeared to form by templating by either DMSO or by an excess of the aldehyde. The MMOPs could potentially be relevant for applications in carbon capture and storage (CCS), where the mesopores would facilitate a rapid mass transport. We will conclude with comparing the MMOPs with zeolites, metal organic frameworks and alike.

Towards the global efforts to reduce carbon emission, carbon dioxide capture and reuse is currently being investigated as a potential strategy towards this goal. Materials that can offer solutions to these outsdanding technological challenges are of considerable interest. It is argued that carbon dioxide reuse process is as vital and challenging as CO2 capture process. Our focus herin is directed towards developing materials capable to affect CO2 reuse, as catalytic platforms in CO2-insertion processes.
Novel porous organic polymers (POPs) and Covalent-Organic Frameworks (COFs) are synthetically accessible through utilization of specific, pre-programmed molecules (building blocks) under carefully chosen reaction conditions. Research in this area benefits from the large body of accumulating knowledge in both synthetic chemistry and catalysis, aiming to merge the two realms to effect fabrication of novel functional materials as platforms in CO2-insertion catalytic transformations. Key characteristics of such platforms are structural stability under working conditions, enhanced catalytic-site accessibility due to permanent porosity, recyclability, and ease of separation/recovery.
We have successfully synthesized, using functionalized molecular building blocks, a family of porous solids containing catalytically-active metallocomplexes as integral part of the porous polymers backbone. This permitted utilization of such materials as solid-state catalysts in CO2-epoxide insertion reactions. Investigation of CO2 insertion catalytic activity showed a drastic enhancement of catalyst recyclability, and hence lifetime, as well as ease of catalyst separation as compared to homogenous systems.

Large specific surface areas of the microporous molecular networks do not necessarily guarantee high performance of the adsorbent under practical conditions. Optimization of the network structure to enhance the adsorption efficiency of pore surface, such as formation of transport channels through the networks, is needed, whereas post-modification of molecular networks is usually forbidden due to their inherent insolubility and infusibility. Here we demonstrate that reticulated nanoporous morphology can be generated by exploiting reversible chemistry of the urea bonded organic molecular networks. The nanoscopic channels through the rearranged microporous urea networks provided exceptional adsorption selectivity to carbon dioxide with a high capacity even at low partial pressure.

High permeability whilst keeping a reasonable selectivity is the most important challenge in developing membrane systems for gas separation. Valuable performances are usually obtained with polymeric membranes for which the gas transport is controlled by the gas-diffusivity in glassy polymers and by gas-solubility in rubbery polymers. During the last decade, important advances in this field are related to the molecular control of the gas separation properties. The combination/replacement of classical glassy polymers with metal-organic crystalline frameworks (MOFs, ZIFs, zeoliteshellip;) providing reasonable permeability through porous free volume network and high selectivity due to so-called “selectivity centers” specifically interacting with the gas molecules. Despite the impressive progress, important difficulties are observed to get dense mechanically stable thin layer MOFs on various supports. Taking advantage of high permeabilities observed with the rubbery polymers and to their flexible casting properties, there should be very interesting to build rubbery organic frameworks-ROFs, as alternative for gas membrane separation systems. Here we use low macromolecular constituents and dialdehyde core connectors in order to constitutionally generate rubbery organic. Differently to rubbery polymeric membranes the ROFs performances depend univocally of diffusional behaviors of gas molecules through the network. For all gases, a precise molecular composition of linear and star-type macromonomers generates an optimal free volume for a maximal diffusion through the matrix. These results should initiate new interdisciplinary discussions about highly competitive systems for gas separation, constitutionally controlled at the molecular scale.
1. M. Barboiu, , Encyclopedia of Membrane science and Technology, Review, 2013, Wiley.
2. G. Nasr, A. Gilles, T. Macron, C. Charmette, J. Sanchez, M. Barboiu, Israel J. Chem. 2013, 53, 97-101.
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4. G. Nasr,T. Macron, A. Gilles , Z. Mouline, M. Barboiu, Chem. Commun.,2012, 48, 6827-6829.
5. G. Nasr, T. Macron, A. Gilles, E. Petit, M. Barboiu, Chem. Commun., 2012, 48, 7398-7400.

Work into synthesizing microvascular materials has recently taken a step forward in the form of a new synthetic process VaSC (Vaporization of a Sacrificial Component) that enables the formation of 3D microstructures that are meters in length. We report on our recent advances in using VaSC to create three-dimensional gas exchange units modeled on the design of avian lungs and vascular systems for heat distribution. We are focused on mass transfer applications for the capture and release of CO2. In particular, we will report on recent research into creating ultra-high surface area micro-structures and the use of two phase flow systems to release gas from capture solutions using radiant waste heat. We will discuss at length the design, execution and testing of a compact, portable system for the capture of CO2 from point sources and the use of a second system for the use of heat radiating from emission producing devices.

Owing to their high surface areas, tunable pore dimensions, and adjustable surface functionality, metal-organic frameworks (MOFs) can offer advantages for a variety of gas storage and gas separation applications. In an effort to help curb greenhouse gas emissions from power plants, we are developing new MOFs for use as solid adsorbents in post- and pre-combustion CO2 capture, and for the separation of O2 from air, as required for oxy-fuel combustion. In particular, MOFs with open metal cation sites or alkylamine-functionalized surfaces are demonstrated to provide high selectivities and working capacities for the adsorption of CO2 over N2 under dry flue gas conditions. Breakthrough measurements further show compounds of the latter type to be effective in the presence of water, while calorimetry data reveal a low regeneration energy compared to aqueous amine solutions. MOFs with open metal cation sites, such as Mg2(dobdc) (dobdc4- = 2,5-dioxido-1,4-benzenedicarboxylate), are highly effective in the removal of CO2 under conditions relevant to H2 production, including in the presence of CH4 impurities. Redox-active Fe2+ sites in the isostructural compound Fe2(dobdc) allow the selective adsorption of O2 over N2 via an electron transfer mechanism. The same material is demonstrated to be effective at 45 °C for the fractionation of mixtures of C1 and C2 hydrocarbons, and for the high-purity separation of ethylene/ethane and propylene/propane mixtures. Finally, it will be shown that certain structural features possible within MOFs, but not in zeolites, can enable the fractionation of hexane isomers according to the degree of branching or octane number.

Many Metal-Organic Frameworks (MOFs) are synthesized by chemists without a particular application in mind. Here we lay out a series of screening steps to determine the likely potential that the material can be used as a membrane or an adsorbent for carbon capture applications. Each step includes a ranking based on calculated properties such as surface area, porosity, heat of adsorption, maximum pore size, critical window size, adsorption capacity and transport diffusivity. Computational time and property prioritization measures are utilized to optimize the decision process. The most promising candidates are reported to date.

Displacing established and inexpensive sorbents such as zeolites, activated carbon, and alumina is a daunting task. Performance of coordination polymers in many applications is extremely promising but ultimately pricing remains above what can be tolerated for commercial scale deployment. These barriers and potential approaches to circumvent them will be discussed in the context of recent studies. Aspects of synthesis and materials activation will be presented.

Because of their high surface areas, crystallinity, and tunable properties, metal-organic frameworks (MOFs) have attracted intense interest as next generation materials for gas capture and storage. An often-cited benefit of MOFs is their large number of possible structures and compositions. Nevertheless, this design flexibility also has drawbacks, as pinpointing optimal compounds from thousands of candidates can be time consuming and costly using conventional experimental approaches. As a consequence, computational approaches are garnering increasing importance as a means to accelerate the discovery of high-performing MOFs. Here we demonstrate a range of computational techniques that have been applied to predict the performance of MOFs for CO2 capture and the storage of methane and hydrogen. The techniques include: (i) high-throughput screening based on data-mining and empirical correlations [1]; (ii) semi-empirical Monte Carlo simulations of usable capacities [2]; and (iii) first-principles calculations of thermodynamics and electronic structure [3,4]. For CO2 capture and CH4 storage, these techniques are illustrated on metal-substituted MOFs based on M-DOBDC and M-HKUST-1, which have demonstrated amongst the highest capture/storage capacities at moderate pressures and temperatures. In the case of H2, we identify trends and promising adsorbents from amongst 4,000 known metal-organic compounds mined from the Cambridge Structure Database.
[1] Goldsmith et al., Chem. Mater. 25, 3373 (2013).
[2] Rana et al., submitted to J. Phys. Chem. C
[3] Koh et al., Phys. Chem. Chem. Phys. 15, 4573 (2013)
[4] Rana et al., J. Phys. Chem. C 116, 16957 (2012)

Metal-organic frameworks are promising adsorbents for gas separations due to their high surface areas and chemical tunability. For low pressure CO2 separations, most relevant in carbon capture applications, adsorbents with strong binding sites specific for CO2 can realize working capacities significantly better than those of aqueous amine adsorbents. Efforts to synthesize and characterize metal-organic frameworks appended with basic amine functional groups for CO2 adsorption from gas mixtures will be presented. Namely, the post-synthetic incorporation of aliphatic diamine molecules onto coordinatively unsaturated metal-sites within the M2(dobpdc) series of metal-organic frameworks has been shown to be an effective method for drastically enhancing the capacity of metal-organic frameworks for CO2 at very low partial pressures. Differences between framework metal cation as well as primary, secondary, and tertiary functionalized pores will be presented along with a proposed adsorption mechanism. Recent results including studies on the stability of the adsorbent in the presence of H2O, SO2, and high temperatures will also be presented, as well as a regeneration energy analysis indicating substantial regeneration improvements over amine solutions.

Metal organic frameworks (MOFs) represent a viable approach for post combustion CO2 capture. The approach of using a solid sorbent offers significant prospects for energy savings when incorporated in an appropriately engineered capture system. Robust frameworks with high CO2 working capacities and selectivities are needed. This presentation will concern our recent efforts to make such robust and water stable frameworks and also gauge their suitability for incorporation into engineered systems.

Experimental and theoretical studies of single gas component are well established for CO2 adsorption into metal organic frameworks (MOFs). However, understanding co-adsorption of muticomponent mixtures CO2/(H2O, N2, CH4, N2) is critical and required to evaluate gas separation and purification methods. For example, the presence of water was shown to be detrimental to CO2 capture (i.e. lowering CO2 loading), especially for the MOFs with unsaturated open metal sites such as MOF-74, which has the highest reported CO2 uptake at 296 K and 1 Bar among all MOFs. Combining infrared absorption spectroscopy and ab initio density functional theory (DFT) calculations, we have derived a detailed picture of the co-adsorption adsorption process of mixtures of CO2 with H2O, N2, CH4, or O2 in MOF-74 with different metal centers (Ni, Co, Mg). While each molecule has been shown to preferentially adsorb at the metal site, as evidenced for instance by single component neutron/X-ray diffraction studies, we find a competition between mixture components for the metal adsorption site. In the case of CO2/H2O, where CO2 is initially preadsorbed, water molecules are found to diffuse into the MOF-74 unit cells, gradually displacing preadsorbed CO2. Spectroscopic data confirm that CO2 is initially in the metal sites and then moves out in adjacent sites (possibly the center of the channel) when water binds to the metal site, eventually diffusing out of the MOF crystal all together at room temperature (i.e. their binding energy is much lower if they are not at the metal sites). Our temperature dependent experiments suggest that the exchange process is activated (i.e. characterized by a kinetic barrier), as confirmed by our DFT modeling. Furthermore, our NEB DFT calculations find the explicit pathway for H2O displacing CO2 molecules. For the other gases such as O2, CH4, N2, there is no competitive adsorption as CO2 remains at the metal site. The joint investigation combining vibrational spectroscopy and DFT calculation provides a microscopic understanding for the co-adsorption mechanism in this class of materials.

The "platform" metal-organic framework material, NU-1000, offers 30 angstrom diameter channels that can be systematically tailored with both metal ions and organic functional groups. This paper will describe some new work based on this material and aimed at enhancing uptake of carbon dioxide under simulated flue gas conditions, while excluding competitive sorption of water.

The global climate change induced by greenhouse gases has stimulated active research for developing efficient strategies to mitigate CO2 emission. In the present study, we prepared a series of polyamine/metal-organic frameworks (MOF) composites as highly selective CO2 adsorbents from CO2/N2 mixture, which is relevant to CO2 capture in the flue gas. We show that loading polyethyleneimine (PEI) into MIL-101(Cr) frameworks can significantly enhance the selective CO2 adsorption capacity at low pressure and ambient temperature. Further, the comparative study reveals that both the particle size of MOF and molecular-weight of PEI play an important role in the CO2 capture ability. Regarding the particle size, smaller MIL-101(Cr) particles can facilitate the loading of PEI into the inner pores and result in lower surface area/pore volume. Thus, the resulting PEI/MIL-101(Cr) composites possess relatively lower CO2 adsorption capacity, but are compensated by higher selectivity of CO2 over N2. On the other hand, lower molecular-weight linear PEI could readily diffuse into the inner pores and effectively block the N2 adsorption. As a result, the as-prepared A-PEI-300 sample in this work exhibits an excellent CO2 uptakes of 3.6 mmol g-1 and ultrahigh CO2/N2 selectivity at 0.15 bar and 25 oC. In contrast, the higher molecular-weight branched PEI is advantageous at elevated temperature, since the composites can retain high CO2 adsorption capacity owing to the large amount of primary amine groups. Overall, polyamine/MOF composites are shown to be good candidate adsorbents for CO2 capture from flue gas. To achieve the optimal CO2 capture ability, a comprehensive optimization of the polyamine and MOF structures should be performed.

Metal-Organic Materials (MOMs) assembled from metal-based or organic molecular building blocks (MBBs) and organic linkers (spacers) have attracted increasing scientific interest during the past decade. Their structure (especially their modularity) and properties (especially extra-large surface area) have made them an attractive class of porous materials for applications including gas purification and storage, catalysis, small molecule separations and chemical sensing. In comparison to their purely inorganic analogues (e.g. zeolites), their high surface areas and amenability to fine tuning of composition, i.e. crystal engineering, [1] affords an exceptional level of control over pore size, pore chemistry and, ultimately, physicochemical properties.
Two classes of fine-tunable families or “platforms” of MOMs will be addressed in this presentation:
1. Pillared grids afford control over both pore size and binding energy.[2] New results that highlight highly selective carbon capture in narrow pore MOMs with pcu or mmo topology will be presented. We attribute the exceptional performance of some variants to a combination of strong electrostatics from inorganic linker anions and pore size modulation through organic linkers.
2. Multinodal nets offer exceptional opportunities for fine-tuning but they are rare because of the synthetic challenges associated with self-assembly of multiple nodes. We recently reported a 2-step crystal engineering strategy[3] and will present new work that details the design, synthesis and properties of several new classes of multinodal nets that are fine-tunable using inexpensive MBBs.
References:
[1]. B. Moulton, M.J. Zaworotko, Chemical Reviews, 2001, 101, 1629-1658.
[2]. (a). P. Nugent, Y. Belmabkhout, S.D. Burd, A.J. Cairns, R. Luebke, K. Forrest, T. Pham, S. Ma, B. Space, L. Wojtas, M. Eddaoudi, M.J. Zaworotko, Nature, 2013, 495, 80-84. (b) M. Mohamed, S. Elsaidi, L. Wojtas, T. Pham, K.A. Forrest, B. Tudor, B. Space, M.J. Zaworotko, J. Amer. Chem. Soc. 2012, 134, 19556-19559.
[3]. Schoedel, A.; Wojtas, L.; Kelley, S.P.; Rogers, R.D.; Eddaoudi, M.; Zaworotko, M.J. Angewandte Chemie International Edition 2011, 50, 11421-11424.

Oxygen-enriched (oxy-fuel) combustion offers a viable low-cost route to CO2 capture. This consists of burning the fossil fuel in an oxygen rich atmosphere that would generate a final flue gas composed mainly of CO2 and water, with little or no SOX and NOX emissions. The captured CO2 could be then inputted back into the system, or could be transported for further utilization or geological storage. The limiting step of this technology is the efficiency of the air separation units which are currently separating oxygen and nitrogen using cryogenic distillation, a costly and energy intensive process. New highly selective materials are needed to increase the efficiency of this separation process. Metal-organic frameworks (MOFs) have shown great potential in challenging separations of molecules with very similar kinetic diameters. This work investigates fundamental studies aimed at understanding the structure-property relationship of selective O2 over N2 adsorption in metal-organic frameworks (MOFs). Emphasis is placed on identifying key structural features for highly selective oxygen adsorption, leading to efficiency improvements through oxy-fuel combustion.
Here we implement a synergistic approach involving predictive molecular modeling, experimental synthesis and guest-host crystallographic determination of known and novel MOF materials. Density functional theory (DFT) calculations were used to measure the binding energy for oxygen and nitrogen on coordinatively unsaturated metal sites in MOFs. Several different transition metal analogs of prototypical MOFs with these built-in features were evaluated. The effect of the metal on preferential guest binding was examined in detail. Guided by the modeling results, experiments were directed at both the synthesis of analogs of known materials and of novel frameworks. A post-synthetic metal substitution approach was considered for known insostructural series; this has been especially useful in the context of considering metals that are not traditionally used in MOFs synthesis. Results indicate increased sensitivies in the oxygen vs. nitrogen adsorption upon these modifications for single gas sorption measurements conducted at or in the room temperature range. Importantly, high oxygen selectivity over nitrogen is shown on a novel MOF material. Ongoing studies are evaluating the selectivities of the studied materials under industrially relevant mixed gas sorption studies. The focus is also placed on the modeling-directed design of novel MOFs with anticipated high performances.
* Sandia National Laboratories is a multi-program lab managed and operated by Sandia Corp., a wholly owned subsidiary of Lockheed Martin Corporation, for the US DOE&’s NNSA under contract DE-AC04-94AL85000.

Caused by widespread use of fossil fuels, the dramatically increasing concentration of CO2 in atmosphere is considered as the primary reason for Global warming, which is viewed as the main reason for many other environmental problems. To capture CO2 from anthropogenic emission sources such as power plants and automobiles, numerous materials have been designed. But systematic methods to evaluate these materials are not yet sufficiently developed. Here we explored a variety of MOFs, PPNs, and zeolite. By analyzing the experimental data obtained in our laboratory, we established a simple but useful model to predict the CO2 adsorption behavior of these porous materials, and developed a method to evaluate these candidates for carbon capture by using energy efficiency as a standard.

Motivated by recent experimental reports on zirconium porous frameworks, which have demonstrated good stability and CO2 adsorption capacity, we investigate the influence of flue gas impurities, functional groups and post-synthetic metal exchange on the performance of zirconium frameworks in selective CO2 capture. Using a combination of grand canonical Monte Carlo (GCMC) simulations and first principles calculations, we find that O2 and SO2 impurities in flue gas have a negligible influence on CO2 selectivity in all zirconium frameworks. However, due to a strong chemical interaction between H2O molecules and the framework, CO2 selectivity decreases in functionalized zirconium frameworks in the presence of water impurities in the flue gas. However, no significant change in selectivity is observed in the presence of H2O in zirconium frameworks without any functional groups. Our studies suggest that functionalization enhances CO2 adsorption and selectivity, however the flue gas impurities such as H2O has a negative impact on selectivity.

Carbon dioxide produced by burning fossil fuels is believed to be a main contributor to climate change. To stabilize CO2 emissions at 1990 levels, it is necessary to couple new CO2 scrubbing systems to power plants and automobiles. One of the most important drawbacks in the currently industrial usage of monoethanolamine (MEA) is the high heat capacity of aqueous MEA solutions, since the energy input required for solvent regeneration can consume up to 70% of the total operating cost in a CO2 capture plant. To overcome the high energy consumption for solvent regeneration, solid adsorbents such as zeolites, activated carbons and metal-organic frameworks (MOFs) have been extensively exploited. Nevertheless, the CO2 uptake capacity of most of these materials drops in the presence of water, one of the main components of the flue gas.
Here we demonstrate that amyloids, self-assembling protein fibers, and amino-functionalized MOFs are effective for selective CO2 capture in the presence of moisture. We found that VQIVYK fibers are sufficiently open to allow the diffusion of small gaseous molecules, based on N2 adsorption measurements at 77 K. The amount of CO2 sorbed in the fibers was found to be one molecule per peptide. In addition, cross-polarization magic-angle-spinning (CP/MAS) 13C-NMR allowed us to conclude about the formation of carbamate during the uptake process and to demonstrate the reversibility of the reaction at 100 °C. Breakthrough experiments showed a capacity of kinetic CO2 adsorption of 0.48 mmol/g that was maintained even after introducing 3 wt% of water into the gas feed stream. These results inspired the design and preparation of a series of functionalized IRMOF-74-III structures with aromatic, primary and secondary amines covalently attached to the organic linkers. The CO2 sorption behavior and the energy required to regenerate these systems demonstrate the importance of an available the strategy to introduce customized functional groups in the architectured pore environments.

The improvement of data comparison methods for high pressure sorption isotherms is necessary for the development of gas separation materials. In order to improve the confidence of these comparisons, the results of a pilot-scale inter-laboratory study of light gas adsorption in common porous materials are compared in an effort to highlight the current need for quantifying measurement uncertainty. The labs participating in this study are located at the National Institute of Standards and Technology, U.S.A., and the University of Sydney, Australia. Initial experiments involved capturing excess CO2 and N2 sorption isotherms in zeolite 5A (Z5A) and ZIF-8 (ZIF8) at temperatures between 20 °C (293 K) and 50 °C (323 K) using manometric and gravimetric methods up to 25 bar. Based on the obtained results, several data comparison indicators are proposed and data discrepancies and sources of uncertainty are discussed. Preliminary results indicate that particle size distribution and gas uptake affect the variability of the data. Our investigations provide the basis for planning the development of reference materials and data for high-pressure gas adsorption.

Graphene as a building material for gas separation possesses one unique advantage: its one-atom-thin thickness. Membrane separations are advantageous because they are pressure-based and hence more energy-efficient than the heat-based cryogenic distillation process. Using graphene a membrane will fully utilize graphene&’s one-atom-thin thickness, as a membrane&’s permeance is inversely proportional to its thickness. In this talk we will fully explore the many opportunities in gas separations as offered by porous graphene membrane from classical molecular dynamics simulations, including CO2/N2, CO2/CH4, and H2/CH4 separations.

Although graphene shows impermeable nature to molecules or ions, if pores could be properly engineered in graphene, its atomic thickness, two-dimensional flatness, flexibility, and mechanical strength offers the opportunity for preparing the ideal and thinnest membrane materials. However, the scalable fabrication of graphene-based membranes with subnanometre pores and high porosity are a great challenge yet. Here we report that gas molecules can diffuse through defective pores and slit-like interlayers in large-area, few-layered graphene or ultrathin graphene oxide (GO) membranes with nanometric thickness, and that gas diffusion through these membranes can be tuned by randomly stacking, engineering channels, and creating pores. For few-layered GO membranes with 3 to 10 nanometric thickness, tunable gas transport behavior was strongly dependent on the degree of interlocking within the GO stacking structure. These GO membranes showed unusual CO2 transport properties depending on their stacking structure due to the strong affinity between CO2 and GO and are therefore excellent candidate materials for CO2 separations. Particularly, high CO2/N2 selectivity was achieved by well-interlocked GO membranes even under high relative humidity, which is most suitable for post-combustion CO2 capture process, including a humidified feed stream.

As carbon dioxide (CO₂) emissions resulting from the use of fossil fuels have been considered as the major contribution to abnormal climate change, substantial interest has been generated for the technologies of CO₂ capture to reduce atmospheric CO₂ concentration. Among various CO₂ capture technologies, adsorption has advantages of easy regeneration and low energy consumption without producing unfavorable by-products or any polluted sorbent.
In addition to the commercial adsorbents such as activated carbon and zeolite, carbon-based nanomaterials including carbon nanotube, carbon nanofiber, and graphene have been recently studied as promising CO₂ adsorbents due to their high surface area with superior physical and chemical properties.
In this study, polyvinylidene fluoride (PVDF) is used to synthesize carbon nanofiber (CNF). To the best of our knowledge, it is the first time to present PVDF-based CNF for CO₂ adsorption. The newly synthesized carbon nanofiber has advantage of possessing high surface area and pore volume without conventional KOH activation.
PVDF-based nanofibrous mat was prepared through electrospinning and carbonization was carried out at high temperature. SEM images showed PVDF-based CNF (PVDF-CNF) kept their nano-scale fibre morphologies after carbonization without structural degradation. PVDF-CNF exhibited high surface area more than 1000 m²/g, and the significant increase of surface area was due to the development of micropores during carbonization. CO₂ storage ability of PVDF-CNF was measured by CO₂ adsorption isotherm at different temperatures. The maximum CO₂ adsorption capacities at the temperature of 0 and 30°C were 5.11 and 3.07 mol/g, respectively under atmospheric pressure. Furthermore, PVDF-CNF was easily and totally regenerated over repetitive adsorption/desorption cycles without any loss of its adsorption ability, providing potential possibility in continuous CO₂ capture process. The characteristics of PVDF-CNF were further analyzed by transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Raman spectroscopy, and element analysis. This work is expected to pave the way for the efficient use of PVDF-CNF in capturing CO₂ based on its high adsorption performance and excellent cyclic stability.

Carbon materials are one of the most widely used substances for gas adsorption. While most of the recent work focuses on enhancing the adsorption capacity, there is still a lack of understanding the fundamentals involved in gas adsorption processes on carbon surfaces as well as in voids of porous carbons. CNTs represent ideal model systems, offering a well-defined morphology as well as interior and surface characteristics e.g. tuneable tube diameters and surface defect sites.
In our contribution we will present experimental and theoretical findings on adsorption studies of N2, CO2 and SO2 on vertically aligned 3D CNT array structures. These structures represent free standing films, are catalyst free and retain their highly aligned structure during gas absorption. These CNT array structures can even be modified chemically as well as structurally while still retaining their aligned morphology. High pressure gas adsorption studies were carried out on chemically and structurally modified 3D CNT arrays to understand the influence, both experimentally and theoretically, of the different parameters which are responsible for gas adsorption in these important carbon materials

The use of porous materials in industrially important gas separation and purification applications, e.g. CO2 separation from flue gas and purification of biogas require that the porous material is assembled into mechanically strong and hierarchically porous macroscopic structures. Hierarchically porous structured monoliths[1-2] and laminates[3] have been reported with high performance for CO2 separation from N2. Such structured monoliths and laminates with tailored porosity at various length scales combined high volumetric efficiency, good mass and heat transfer, rapid adsorption/desorption kinetics and structural integrity[1-3]. Here, we demonstrate a binder-less approach[4,5] to consolidate 8-ring window zeolite and aluminophosphate (AlPO4&’s) powders into mechanically strong monoliths with a high CO2 uptake capacity and CO2-over-N2 selectivity, and a rapid adsorption and release kinetics. Adsorption isotherms of CO2 and N2 were used to predict the co-adsorption of CO2 and N2 using ideal adsorbed solution theory (IAST). The IAST predictions showed that monolithic zeolite adsorbents of partially K exchanged NaA could reach an extraordinarily high CO2-over-N2 selectivity in a binary mixture with a composition similar to flue gas[1]. Furthermore, zeolite monoliths showed high tensile strength of 2.2 MPa. AlPO-17 and AlPO-53 monoliths were consolidated by the binder-less process with a tensile strength over 1 MPa. AlPO-17 monoliths showed high CO2 adsorption capacity while AlPO-53 exhibited high CO2-over-N2 selectivity. Cyclic CO2 adsorption tests showed that AlPO4 monoliths required less energy for regeneration compared to zeolite and could be regenerated to their full capacity at low pressures.
References:
1- Akhtar, F., Liu, Q., Hedin, N., Bergström, L. Energy and Environmental Science 5 (2012) 7664.
2- Akhtar, F., Andersson, L., Keshavarzi, N., Bergström, L.Applied Energy 97 (2012) 289.
3- Ojuva, A., Akhtar, F., Tomsia, A. P., Bergström, L. ACS Applied Materials and Interfaces 5 (2013) 2669
4- Akhtar, F., Ojuva, A., Kompiang, W., Hedlund, J., Bergström, L.Journal of Materials Chemistry 21 (2011) 8822.
5- Vasiliev, P., Akhtar, F., Grin, J., Mouzon, J., Andersson, C., Hedlund, J., Bergström, L., ACS Applied Materials and Interfaces 2 (2010) 732.

Developing solid adsorbents is of great research interest for CO2 capture applications. Experiments exhibited the phenomenon of sorption hysteresis, whereby the path to adsorb CO2 molecules by the solid materials differs from that of desorption. Through first-principles quantum simulations, based on van der Waals density functional theory, we found that the types, charges and concentrations of cations doped in the solid adsorbents significantly affect the structural features, sorption hysteresis, and CO2 capture properties of the adsorbents. Our presentation will focus on manganese dioxide OMS-2 (Octahedral Molecular Sieve), which is a nanoporous solid structurally stabilized in the present of cations, e.g. K+, Na+ and Ba2+. The cations behave as a "gate keeper", disturbing CO2 adsorption and diffusion in OMS-2 and resulting in the CO2 sorption hysteresis. These effects are tunable by varying the types and charges of the cations and the cation/manganese ratios. In the presentation, we will also discuss CO2/CH4 gas separation by OMS-2. Our results can advance the development of porous solids for effective CO2 capture and gas separation applications.

The CO2 capture from power plant exhaust gases requires substances with a high absorption potential at a reasonable working temperature and working reliable also under “realistic” conditions. Finding the appropriate material is of course one of the main tasks. On the other side it is desirable to have a flexible instrument combination for the investigation of new materials under such special conditions which helps characterizing and optimizing of those materials.
With a thermo balance (TGA) the desorption or absorption of CO2 under “normal” gas conditions can easily be measured. To be sure only CO2 is absorbed/desorbed a coupled gas analysis method like mass spectrometry (MS) or Fourier Transform Infrared Spectroscopy (FTIR) is required. These methods help also at the quantifying of the evolved gases which is especially a problem when overlaying TG steps occur which can&’t be separated. For investigations under humid or water vapor atmospheres special furnaces and water vapor generators were necessary.
In this paper the CO2 desorption/absorption of calcium oxide as a model substance is measured under dry and humid atmospheres with a TG-DSC-MS instrument equipped with a water vapor furnace and a PulseTA instrument. The quantification of the CO2 can be done either by the mass loss steps or by the calibration of the mass spectrometer signal by the PulseTA method.

Meso-macroporous ceramic particles were prepared by emulsion-assisted surfactant and colloidal templating, in which non-aqueous emulsions have been used for dealing with reactive sol-gel precursors such as titanium tetraisoproxide (TTIP), aluminum tri-sec-butoxide (AsB), tetramethylorthosilicate (TMOS). Submicron-sized crosslinked polystyrene (PS) beads were used as template for macropore and oil-soluble surfactants were used as templates for mesopores. The toluene-in-formamide emulsions including PS beads, surfactant, sol-gel precursors were prepared using high-speed homogenizer. Then, by evaporation of toluene by heat treatment, composite structured particles were produced, in which meso-structured ceramic walls were formed around polystyrene beads. Finally, meso-macroporus ceramic particles were obtained by two-step heat treatment. During first heat treatment under oxygen-free atmosphere, polystyrene and surfactant were carbonized and carbon was burned out during second heat treatment under air, which developed macropores surrounding mesopores inside particles. Meso-macroporous particles were further functionalized with various amine compounds, in which CO2 adsorption and desorption capacities and rates were compared.

Carbon capture and storage into deep geological formations has emerged to an important option to mitigate the environmental concern regarding ever-growing anthropogenic CO₂ emissions. A group of metal silicate minerals, X₂SiO₄ where X = Mg and Fe, hold promise as potential media to sequester carbon due to its broad availability in basalt deposits and reactivity to form stable metal carbonates. The reactions of wet supercritical CO₂ (sc-CO₂) with fayalite (Fe₂SiO₄) and forsterite (Mg₂SiO₄) result in a complex change in chemical composition and surface morphology. A combination of atom probe tomography (APT) and transmission electron microscopy (TEM) is used to better understand the changes in the structure related to element distribution upon the reaction with sc-CO₂. Using the needle-shape specimen guarantees the reaction zone within the tip and also allows TEM to be performed before and after reaction. The unique 3-D atomic-scale compositional map with a part-per-million sensitivity allows tomographic mapping of low-level as well as low-weight element, such as Li. Details will be discussed leading to the understanding of reaction mechanism of sc-CO₂ reacted with metal silicates related to the impurity distribution.

In this presentation we describe how computational techniques can be used to screen materials for carbon capture and sequestration. Our starting point is the question how to define the optimal material. We have introduced the concept of parasitic energy as a metric to compare different materials; the best material is the material that minimizes the loss of efficiency of a power plant. To compute this parasitic energy one need information on the mixture isotherms of the various components of flue gasses. In this presentation we focus on the question how one can accurately compute these adsorption isotherms for materials for which experimental data is lacking.

Metal-organic frameworks have received significant attention for use as adsorbents in capturing CO2 from the post-combustion flue gas of coal-fired power plants. While these materials have demonstrated record high CO2 capacities and CO2/N2 selectivities, the performance of the most promising frameworks in gas mixtures containing all of the components of an actual flue gas, such as H2O, O2, SOx, and NOx, has yet to be evaluated in detail. Here, a custom-built high-throughput gas adsorption instrument was fully validated and used to measure multicomponent equilibrium adsorption isotherms for a wide range of metal-organic frameworks at conditions relevant to CO2 capture. By performing high-throughput adsorption experiments at temperatures, pressures, and compositions similar to those expected in an actual power plant, these equilibrium measurements allow the separation performance of different adsorbents to be directly evaluated, rather than simply predicted based on single-component adsorption isotherms. Significantly, many frameworks that had appeared to be promising for post-combustion CO2 capture are found to perform poorly in mixtures containing CO2, N2, and H2O, while several frameworks are identified that exhibit high equilibrium CO2 capacities and CO2/N2 selectivities in simulated flue gas mixtures.

Several approaches have been developed to enhance the CO2 capture performances in advanced porous materials including metal-organic frameworks (MOFs) and porous carbons. Some strategies have been illustrated to rational design functional MOFs for chemical fixation of CO2 with high efficiency under ambient conditions.

Hemoglobin is used to transport oxygen efficiently, capturing oxygen in the lungs where the partial pressure is high and releasing it in the tissues where the partial pressure is low. Key to hemoglobin's efficiency is its ability to bind oxygen cooperatively, such that binding at one site affects the binding affinity of all remaining sites. Inspired by hemoglobin, we set out to design a small molecule system that would also exhibit cooperative binding, but bind carbon dioxide rather than oxygen. The system relies on chelate cooperativity, in which the first binding event lowers the entropic cost of subsequent binding events. We present design principles for how to achieve such a system and ongoing efforts to synthesize a system capable of practical CO2 transport.

Demand for functional materials targeted for specific applications is ever-increasing. Metal-organic materials, specifically metal-organic frameworks (MOFs), have emerged as a unique class of materials amenable to design and manipulation for desired function and application. Several design strategies have been utilized and developed to target viable MOF platforms, from the single-metal-ion molecular building block (MBB) approach to the hierarchical supermolecular building block and supermolecular building layer approaches (SBB and SBL, respectively). This inherent built-in information allows access to highly stabile and made-to-order porous materials toward applications pertaining to energy and environmental sustainability. Specifically, materials for CO2 separation and capture will be highlighted, as well as insights into MOF membrane construction and respective gas separation properties.

Carbon capture and storage (CCS) applications offer a plausible solution to the urgent need for a carbon neutral energy source from stationary sources, including power plants and industrial processes. The most mature technology for post-combustion capture currently uses a liquid sorbent, amine scrubbing. However, with the existing technology, a large amount of heat is required for the regeneration of the liquid sorbent, which introduces a substantial energy penalty. Operation at higher temperatures could reduce this energy penalty by allowing the integration of waste heat back into the power cycle. New solid absorbents for use at intermediate to high temperatures, such as CaO, have shown promise in pilot plant studies, but are still far from ideal due to their poor capacity retention upon successive cycling.
This presentation will describe our studies aimed at rationally selecting and designing materials for carbon capture and storage applications. We use ab initio calculations of oxide materials from the Materials Project database in an effort to screen for novel materials with optimal thermodynamic and kinetic properties for CO2 looping applications. We have then constructed a screening routine for materials within the database based on simulating their carbonation equilibria and phase stability under differing atmospheric concentrations of CO2. A number of promising materials were identified from the screening, and we are currently investigating their properties experimentally, by using a combination of methods (including thermogravimetric analysis, in situ x-ray diffraction and microscopy).

Ionic liquids (ILs) are an extremely versatile and promising materials medium for separating CO₂ from other light gases because of the intrinsic solubility of CO₂ in ILs relative to other gases. However, because of the flowable, liquid nature of ILs, there are inherent form factor and configurational stability problems with using ILs in membranes (even as supported liquid membranes). In order to circumvent many of the problems associated with using ILs in a membrane format, polymerized ILs (e.g., poly(IL)s) have been designed and tested for CO₂/light gas separations. Although solid poly(IL)s have good processability and better mechanical properties than ILs while retaining the desired CO₂/light gas sorption selectivity, poly(IL)s have have much lower gas diffusivities because of their more dense, solid nature. In order to obtain new materials for CO₂/light gas separations that have the properties of both ILs and poly(IL)s, our research group recently pioneered the design and development of poly(IL)/IL composite materials, which have many of the mechanical properties of solid poly(IL)s as well as a large degree of the high diffusivity of liquid ILs. In this presentation, recent advances in the design of imidazolium-based poly(IL)/IL composite materials from our group will be presented, as well as the design of nanostructured poly(IL)s and IL-based liquid crystal composite materials. Some initial results on the CO₂/light gas separation performance of these new IL-based materials will also be presented to demonstrate the relative benefits of these systems.