Gas Separation Experiments Research Articles

Heteroepitaxial growth of ZIF-67 nanoparticles on the ZIF-L(Zn) nanosheets for fabrication of Pebax mixed matrix membranes with highly efficient CO2 separation

ZIF-67 nanoparticles were grown on ZIF-L(Zn) nanosheets by in-situ heteroepitaxial method, resulting in ZIF-67@ZIF-L(Zn) as a charming two-dimensional (2D) nanocomposite for incorporation into the Pebax-1657 and improving its CO2/N2 separation performance. The fabricated nanofillers and membranes were analyzed by characterization tests (FTIR, XRD, FESEM, and EDAX-mapping) and gas separation experiments (effect of filler loading, filler type, feed pressure, and long-term stability). It was observed that the nanosheets were well dispersed in the matrix, and they had formed a proper interaction by creating hydrogen bonds at the interface; in addition, due to their crystalline nature, they increased the crystallinity of the MMMs. The results of the gas permeability test showed that these nanofillers, with their composite structure, had a synergistic effect on the gas solubility and screening and caused a significant improvement in the separation performance of MMMs. So that the best performance achieved with a CO2 permeability of 72.9 Barrer and a CO2/N2 selectivity of 102.9 at 10 bar for the MMM containing 2 wt% of ZIF-L(Zn)@ZIF-67, also exceeding Robeson's upper bound. Moreover, Mindex as a criterion for evaluation of the gas separation performance of MMMs in simultaneous improvement of the permeability and selectivity was proposed in this work. The Mindex values in the range of 0.5–1.5 were calculated for the MMM containing 2 wt% of ZIF-L(Zn)@ZIF-67 nanosheet which indicating a good quality for the gas separation performance. Furthermore, at equal filler loading (2 wt%), this membrane outperformed all MMMs containing other nanofillers (ZIF-67, ZIF-8, ZIF-L(Co), or ZIF-L(Zn)).

Preparation of OH/TiO2/PES composite membrane by a novel gas-phase hydrolysis method in gas-liquid membrane contactor to improve the separation efficiency of CO2 and CH4

Conventional gas separation methods are very limited for CO2 separation in terms of separation efficiency and cost. In this study, We obtained fluorinated TiO2/polyethersulfone (PES) composite membranes by gas-phase hydrolysis and compared the characterization results with the composite membranes prepared by the graft coating method. In the mixed gas separation experiment, we used diethanolamine (DEA) as the absorbent to test the separation performance of CO2/CH4 using the composite membranes prepared by gas phase hydrolysis in a gas-liquid membrane contactor (GLMC) system. DEA flow rate and concentration and feed gas flow were found to have a significant effect on separation performance. When the feed gas flow rate was kept constant at 30 ml/min and the DEA flow rate and concentration were 16 L/h and 1 mol/L, respectively, the collected CH4 concentration was 99.4 %. Meanwhile, the CO2 flux was 10.096 × 10−3 mol m−2 s−1, and the separation factor reached 110.444. Collectively, the application of TiO2/PES composite membranes in GLMC is an efficient method for CO2 capture and mixed gas separation.

Double-Layered Pebax® 3533/ZIF-8 Membranes with Single-Walled Carbon Nanotube Buckypapers as Support for Gas Separation.

Single-walled carbon nanotube buckypapers (SWCNT-bps) coated with a metal-organic framework ZIF-8 layer were used as supports for the preparation of Pebax® 3533 TFC membranes by both phase inversion and spin coating techniques. Upon proper characterization of the materials by X-ray diffraction, IR spectroscopy, thermogravimetry and electron microscopy, the obtained membranes were tested in gas separation experiments with a 15:85 CO2/N2 mixture. These experiments proved that the ZIF-8 layer prevented from the penetration of the polymer selective film into the SWCNT-bp support, giving rise to a highly permeable selective membrane. The optimum membrane was achieved by the spin-coating method, with better permeation results than that prepared by the phase inversion method, obtaining a CO2 permeance of 566 GPU together with a CO2/N2 selectivity of 20.9.

Enhancement of Propadiene/Propylene Separation Performance of Metal-Organic Frameworks by an Amine-Functionalized Strategy.

Here, a hexanuclear Co6(μ3-OH)6 cluster-based metal-organic framework (MOF), [Co6(μ3-OH)6(BTB)2(bpy)3]n (JXNU-15) (bpy = 4,4'-bipyridine), with the 1,3,5-tri(4-carboxyphenyl)benzene (BTB3-) ligand was synthesized for the challenging propadiene/propylene separation. The combination of a large pore volume and a suitable pore environment boosts the significantly high propadiene (C3H4) uptake (311 cm3 g-1 at 298 K and 100 kPa) for JXNU-15. An amine-functionalized MOF of JXNU-15(NH2) was further obtained with the 1,3,5-tri(4-carboxyphenyl)benzene analogue of 3,3″-diamino-5'-(3-amino-4-carboxyphenyl)-[1,1':3',1″-terphenyl]-4,4″-dicarboxylic ligand. The comparative studies of propadiene/propylene(C3H4/C3H6) separation performance between isostructural JXNU-15 and JXNU-15(NH2) are provided. JXNU-15(NH2) exhibits an impressive C3H4 capacity at low pressures with 69.1 cm3 g-1 at 10 kPa, which is twice that of JXNU-15 under the same conditions. Moreover, the separation selectivity of JXNU-15(NH2) is 1.3-fold higher as compared to JXNU-15. JXNU-15(NH2) with enhanced C3H4/C3H6 separation performance was elegantly illustrated by gas separation experiments and theoretical simulations. This work presents an amine-functionalized strategy for the enhancement of the C3H4/C3H6 separation performance of MOF.

Efficient separation of methane, ethane and propane on mesoporous metal-organic frameworks

Adsorption and separation of light saturated hydrocarbons (methane, ethane and propane) as main components of natural gas on a series of isoreticular mesoporous metal–organic frameworks NIIC-20-G (G = ethyleneglycol, 1,2-propyleneglycol, 1,2-butyleneglycol, 1,2-pentylenglycol, glycerol) has been thoroughly investigated. An impact of the size and nature of the glycol moiety on fundamental parameters of the adsorption (gas uptakes, adsorption constants, enthalpy and entropy, adsorption selectivity factors) was revealed and rationalized. The highest gas uptakes at 1 bar and 298 K are 13.2 ml(STP)·g−1 for CH4, 55.0 ml(STP)·g−1 for C2H6 and 125.4 ml(STP)·g−1 for C3H8. The IAST adsorption selectivities at ambient conditions (298 K, 1:1 gas mixture) reach 24.2 for C2H6/CH4, 29.0 for C3H8/C2H6 and as high as 1110 for C3H8/CH4. A rare combination of high adsorption uptakes and superb adsorption selectivity values achieved for NIIC-20-G put those MOFs ahead of the most other materials for light saturated hydrocarbon adsorption and separation. Dynamic breakthrough gas separation experiments on NIIC-20-Pr fully confirm effective separation of lighter alkanes from the corresponding binary or ternary mixtures. The obtained methane productivities are 1182 ml(STP)·g−1 (52.8 mol·kg−1) for C2H6/CH4, and 4193 ml(STP)·g−1 (187.3 mol·kg−1) for C3H8/CH4 equimolar gas mixtures, which greatly surpass earlier published data. The ethane productivity for an equimolar C3H8/C2H6 gas mixture is 3009 ml(STP)·g−1 (134.4 mol·kg−1). The breakthrough separation experiments validate a remarkable performance of the studied MOFs in the practical separation of natural gas or other relevant mixtures of light alkanes to valuable individual components.

Enhanced ethylene transport of mixed-matrix membranes by incorporating anion-pillared hybrid ultramicroporous materials via in situ growth

The separation of ethylene/ethane based on mixed-matrix membranes (MMMs) is a promising yet challenging task. In this work, high-performing GeFSIX-3-Ni/6FDA-DAM MMMs consisting of anion-pillared hybrid material GeFSIX-3-Ni (also termed ZU-36-Ni, GeFSIX = hexafluorogermanate, 3 = pyrazine) and 6FDA-DAM were synthesized via a simple in situ method, which surpasses 2013 upper bound for C2H4/C2H6 separation. Further investigations revealed that the interfacial compatibility between GeFSIX-3-Ni and 6FDA-DAM was improved with the enhancement of hydrogen bonds and the regulated small particle size (<50 nm). Both single- and mixed gas separation experiments confirmed that the separation performance of 10 wt% GEF-PI-S MMMs (GEF = GeFSIX-3-Ni, PI = 6FDA-DAM, S = in situ method) surpassed the C2H4/C2H6 upper bound in terms of C2H4 permeability (131.4 Barrer) and C2H4/C2H6 selectivity (3.80) for equimolar C2H4/C2H6 mixed gas. This work provides insights into more efficient way of obtaining defect-free MMMs with high performances for diversified separations.

Uncoordinated Hexafluorosilicates in a Microporous Metal-Organic Framework Enabled C2H2/CO2 Separation.

Metal-organic frameworks (MOFs) represent a kind of low-energy physisorbent with modifiable pores and framework structures; however, a deep understanding of how these structural features influence properties is a prerequisite for the rational design and development of tailor-made materials for advanced applications. In this report, a MOF, [Ni2(TCPP-Ni)1/4(TPIM)2(COOH)F][(Me2NH2)SiF6]·xS (SDU-CP-1; S = solvent molecules, SDU = Shandong University, and CP = coordination polymer), assembled by tetrakis(4-carboxyphenyl)porphyrin (TCPP-Ni) and 2,4,5-tris(4-pyridyl)imidazole (TPIM) ligands as well as Ni2+ cations is reported. Interestingly, inorganic SiF62- anions do not serve as the pillars like precedents in the framework but are just counterions, which endows SDU-CP-1 with high uptake for C2H2 and adsorption selectivity (2.5-4.2) for C2H2/CO2 at room temperature, as certified by gas adsorption and separation experiments and grand canonical Monte Carlo calculation.

MOF Membranes for CO2 Capture: Past, Present and Future

As the society is projected to continue relying on fossil fuels for energy needs in the next decades, the increasing level of CO2 emissions due to fossil fuel use can pose bigger threats to humans and environment, considering the associated amplified greenhouse effects. Membrane technology is a promising energy-efficient pathway to tackle the growing conundrum of CO2 emissions. Among various classes of porous materials, metal-organic frameworks (MOFs) deserve much interest regarding membrane applications due to their highly versatile structures that can be tailored for different gas separation needs. Computational modeling of MOFs for membrane-based separations can provide molecular-level information that may not be accessible via experiments and help establish the theoretical foundation for the performance trends observed in gas separation experiments. This perspective focuses on the investigation of pure MOF membranes and MOF-based composite membranes for CO2 capture applications such as post-combustion (CO2/N2) and pre-combustion CO2 separation (CO2/H2), and natural gas purification (CO2/CH4), with particular emphasis given to computational studies. We highlight the key advances and future directions in the development, modeling, and testing of early MOF membranes, ionic liquid/MOF membranes, ultrathin MOF membranes, MOF-COF (covalent organic framework) membranes, MOF glass membranes, and MOF-based mixed-matrix membranes (MMMs). Finally, an outlook on the potential opportunities and challenges associated with the computational modeling of MOF-based membranes and their use for carbon capture is provided.

CO2/CH4, CO2/N2 and CO2/H2 selectivity performance of PES membranes under high pressure and temperature for biogas upgrading systems

Abstract Currently, thermal treatments are used extensively to convert millions of tons of biomass and municipal solid waste into energy products. Although biogas represents ∼ 50% of these energy products, usually disposed due to the difficulty to extract CH4 and H2 (main flammable compounds) from their complex composition contaminated by CO2, N2, etc. Recently, Polyethersulfone (PES) membranes have been employed for that purpose as an effective and cheap technology, however, their permeation properties under higher pressure and temperature are still undefined. Within this context, this research aims to study the influence of high temperatures and pressure on CO2/N2, CO2/H2 and CO2/CH4 selectivity performance of PES membranes and their potential applications in biogas upgrading systems. The experiments were started with preparation of the PES membranes using phase inversion methods, then observing their morphology, physical, chemical, thermal, and mechanical behaviors using SEM, XRD, FTIR, TGA, and universal testing machine. Consecutively, the initial gas separation experiments using CO2 gas were conducted to determine the maximum pressure and temperatures that the synthesized PES membranes can withstand without being damaged or thermally degraded. Based on the results of initial experiments, CO2/CH4, CO2/N2, and CO2/CH4 selectivity of the PES membranes was measured up to 60 °C and 6 bar (absolute pressure) using a set-up built especially for that purpose. Also, the effect of separation temperature and pressure on the separation mechanism were studied. The results revealed that the lowest pressure (1 bar) and the highest temperature (60 °C) can help to achieve the maximum selectivity performance for CO2/N2 (0.91), CO2/H2 (1.25), and CO2/CH4 (3.07), with improvement of 9, 20, and 17%, respectively. In addition, permeability of CO2 > N2 > H2 > CH4 increased by 13.2% (CO2), 15.1% (N2), 11% (H2), and 4.6% (CH4) at the same temperature. Based on that, pressure and temperature are considered as key factors that can be used to enhance the gas permeation and to control their pore shape. Also, PES membranes can be classified as a promising emerging technology for biogas upgrading with high selectivity, especially at high separation temperatures and low pressure.

The assessment of honeycomb structure UiO-66 and amino functionalized UiO-66 metal-organic frameworks to modify the morphology and performance of Pebax®1657-based gas separation membranes for CO2 capture applications.

A new type of honeycomb structured UiO-66 metal-organic frameworks (MOF) was synthesized and amino functionalized followed by employing them to prepare mixed matrix membranes (MMM). The influences of dimethylformamide (DMF) and H2O/ethanol (70/30wt.%) blend were firstly investigated on morphology, structure, and CO2/CH4 separation efficiency of Pebax®1657 membranes. Based on the transmission electron microscopy (TEM) analysis, the synthesized MOF has 15nm in diameter. DMF led to the formation of a more crystalline (based on X-ray diffraction (XRD) analysis) and more porous structure. Higher CO2 permeability and CO2/CH4 selectivity were observed as DMF was employed to fabricate neat membranes. Scanning electron microscopy (SEM) exhibited MOF agglomeration as the UiO-66 was used while the nanoparticle dispersion was enhanced when UiO-66-NH2 was exploited. Fourier transform infrared spectroscopy (FTIR) confirmed the successful MOF incorporation into the MMMs. Ultimately, the gas separation experiments showed that CO2 permeability was enhanced compared to the neat membrane by 44.7% and 49.4% as 10wt.% UiO-66 and UiO-66-NH2 were used, respectively. Moreover, the Pebax®1657-UiO-66-NH2 MMMs exhibited 71.7% and 34.5% improvement in selectivity of CO2/N2 and CO2/CH4, respectively, owing to enhancing CO2-OH interactions while the CO2/O2 was declined by 8.8%.

Effect of Humidity on CO2/N2 and CO2/CH4 Separation Using Novel Robust Mixed Matrix Composite Hollow Fiber Membranes: Experimental and Model Evaluation.

In this work, the performance of new robust mixed matrix composite hollow fiber (MMCHF) membranes with a different selective layer composition is evaluated in the absence and presence of water vapor in CO2/N2 and CO2/CH4 separation. The selective layer of these membranes is made of highly permeable hydrophobic poly(trimethyl-1-silylpropine) (PTMSP) and hydrophilic chitosan-ionic liquid (IL-CS) hybrid matrices, respectively, filled with hydrophilic zeolite 4A particles in the first case and HKUST-1 nanoparticles in the second, coated over compatible supports. The effect of water vapor in the feed or using a commercial hydrophobic PDMSXA-10 HF membrane has also been studied for comparison. Mixed gas separation experiments were performed at values of 0 and 50% relative humidity (RH) in the feed and varying CO2 concentration in N2 and CH4, respectively. The performance has been validated by a simple mathematical model considering the effect of temperature and relative humidity on membrane permeability.

Modified Porous SiO₂-Supported Cu₃(BTC)₂ Membrane with High Performance of Gas Separation.

The structures and applications of metal-organic framework materials (MOFs) have been attracting great interest due to the wide variety of possible applications, for example, chemical sensing, separation, and catalysis. N-[3-(Trimethoxysilyl)propyl]ethylenediamine is grafted on a porous SiO2 disk to obtain a modified porous SiO2 disk. A large-scale, continuous, and compact Cu3(BTC)2 membrane is prepared based on a modified porous SiO2 disk. The chemical structure, surface morphology, thermal stability, mechanical stability, and gas separation performance of the obtained Cu3(BTC)2 membrane is analyzed and characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and a gas separation experiment. The results show that the prepared Cu3(BTC)2 membrane has an intact morphology with its crystal. It is continuous, compact, and intact, and has good thermal stability and mechanical stability. The result of the gas separation experiment shows that the Cu3(BTC)2 membrane has a good selectivity of hydrogen and can be used to recover and purify hydrogen.

Synthesis of graphene oxide membranes on polyester substrate by spray coating for gas separation

Graphene oxide (GO) membranes have shown promising gas separation characteristics specially for hydrogen showing potential for industrial applications. However, GO membranes made by filtration, the most common synthesis method, contain wrinkles affecting their gas separation characteristics and the method itself is difficult to scale up. In this work, high quality GO membranes are made from GO suspension by easily scalable spray coating technique (and also by filtration method for comparison) on hydrophilic polyester track etch substrates. GO sheet suspensions of large sheet average size (33 µm) and dilute concentrations are used to minimize GO sheet edge-to-edge interactions and minimize extrinsic wrinkle formation. Single gas permeation and separation experiments of equimolar H2/CO2 binary mixture were conducted to evaluate the permeation and separation characteristics of prepared membranes. GO membranes prepared by spray coating offer gas characteristics similar to those made by filtration, however using dilute GO suspension in spray coating reduces the formation of extrinsic wrinkles causing reduction in the porosity of the inter-sheet pathway where the transport of large gas molecules dominates. This study demonstrates an efficient, scalable and cost-effective approach for synthesizing large area GO membranes with enhanced hydrogen separation.

Carbon membranes for oxygen enriched air – Part I: Synthesis, performance and preventive regeneration

Abstract Chemisorption of oxygen on the active sites of carbon layers limits the use of carbon membranes in air separation application. A novel online electrical regeneration method was applied to prevent the active sites on carbon surface to be reacting with O2 while the membrane was in operation. This method reduced the aging effect and the membrane showed relative stable performance with only 20% loss in O2 permeability and 28% increase in O2/N2 selectivity, over the period of 135 days using various feeds containing H2S, n-Hexane and CO2-CH4 gas. The carbon membranes reported here were produced at the pilot-scale facility by the carbonization of regenerated cellulose under optimized conditions to achieve good air separation properties. The permeation properties of the membranes were tested by single gas separation experiments at 5 bar feed pressure (50 mbar permeate) and temperature range 20–68 °C. It was observed that O2 permeability is increasing exponentially with increase in operating temperature without significant loss in the O2/N2 selectivity. The O2 permeability of 10 Barrer (1 Barrer = 2.736E − 09 m3(STP)m/m2 bar h) with O2/N2 selectivity of 19 was achieved at 68 °C. Thermal (80 °C), chemical (propylene) and online-electrical (10 V DC) regeneration approaches were studied to lessen the aging effect on carbon membranes.

EVALUATING THE SYSTEM PERFORMANCE OF A PRESSURE SWING ADSORPTION (PSA) UNIT BY REMOVING THE CARBON DIOXIDE FROM BIOGAS

Objectives: This study aims to assess the performance of a Pressure Swing Adsorption (PSA) unit in removing the carbon dioxide from biogas by evaluating the breakthrough and adsorption capacity of the adsorption process as well as determining the effects of cyclic regeneration of the adsorbent. Methods: The PSA system was developed in order to establish the behavior of different gas separation experiments. It can be operated up to 10 bars pressure at ambient temperatures and gas flow rate from 0 to 15 L min-1. It is composed only of one main vessel made up of 316 stainless steel components. Use of physical adsorbent (Zeolite 13X) in a Pressure Swing Adsorption (PSA) system will consume the gaseous impurities such as CO2 . Product gas was collected into 1 L Tedlar bags and analyzed using SRI gas chromatograph with TCD and HID detector to validate the CO2 and CH4 composition. Findings: The results of the Pressure Swing Adsorption (PSA) experiments showed an average increase of 160% in the net heating value over that of a certified gas standard. The amount of methane was also significantly higher although the amount of the other gasses (i.e. nitrogen) remained comparatively the same. The number of other gases was significantly lower and no trace of carbon dioxide was observed in the PSA product gas indicating that carbon dioxide had been completely absorbed by the system. Application: This study helps to reduce CO2 emitted to the atmosphere from the anaerobic co-digestion of biogas to produce high energy content bio-methane fuel. Keywords: Adsorption, Biogas, Carbon Dioxide, Methane Gas, Pressure Swing Adsorption, Zeolite 13X

Anti-Agglomerator of Tetra-n-Butyl Ammonium Bromide Hydrate and Its Effect on Hydrate-Based CO2 Capture

Tetra-n-butyl ammonium bromide (TBAB) was widely used in the research fields of cold storage and CO2 hydrate separation due to its high phase change latent heat and thermodynamic promotion for hydrate formation. Agglomeration always occurred in the process of TBAB hydrate generation, which led to the blockage in the pipeline and the separation apparatus. In this work, we screened out a kind of anti-agglomerant that can effectively solve the problem of TBAB hydrate agglomeration. The anti-agglomerant (AA) is composed of 90% cocamidopropyl dimethylamine and 10% glycerol, which can keep TBAB hydrate of 19.3–29.0 wt. % in a stable state of slurry over 72 h. The microscopic observation of the morphology of the TBAB hydrate particles showed that the addition of AA can greatly reduce the size of the TBAB hydrate particles. CO2 gas separation experiments found that the addition of AA led to great improvement on gas storage capacity, CO2 split fraction and separation factor, due to the increasing of contact area between gas phase and hydrate particles. The CO2 split fraction and separation factor with AA addition reached up to 70.3% and 42.8%, respectively.

Gas separation of flue gas by tetra-n-butylammonium bromide hydrates under moderate pressure conditions

Ionic clathrate hydrates are composed of water and ionic guest substance, which can selectively capture gas under moderate conditions. We performed gas separation experiments with tetra-n-butylammonium bromide (TBAB) widely-used for an ionic guest substance. The experiments in a closed system showed good CO2 gas selectivity of the TBAB hydrates even under the mild conditions: 1 MPa and 282 K. We also performed the gas separation with tetrahydrofuran (THF) which is a guest substance forming the structure II clathrate hydrate. Comparison with THF clearly revealed the better CO2 selectivity of TBAB than that of the structure II clathrate hydrate. We further compared our data with the literature, and found that the condition of low pressure and dense TBAB concentration provided superior CO2 selectivity. Gas separation with continuous gas flow was demonstrated. The hydrate formation behavior was similar to the cases without gas flow. The results showed that controlling the crystal growth temperature is important to capture gases by the TBAB hydrates.

Numerical analysis of H2/He gas separation experiments performed with a MFI-type tubular zeolite membrane

Zeolite membranes were identified to be used in the future fusion reactors to separate traces of tritiated species from large helium flows. Due to the lack of data in the literature, separation experiments with helium, hydrogen and water vapor have been performed in the Tritium Laboratory Karlsruhe (Germany). The obtained results shall be used to predict performances at reactor scale. Therefore, a simulation tool of a permeator has been developed to perform calculations ab-initio of its performance at several experimental conditions. In the present work, numerical results for the binary mixture hydrogen/helium at different concentrations are compared with the experimental results obtained with a zeolite MFI-ZSM5 tubular membrane, where separation factors below 2 were measured for different cuts. Very good agreement between experiments and simulations was observed. This agreement gives confidence to integrate this numerical tool into a membrane cascade simulator, in development in the TLK, toward the modeling of the zeolite membranes’ performances at reactor scale.

Permselectivity improvement in membranes for CO2/N2 separation

In this work, small-pore zeolites of different topology (CHA, LTA5, Rho), all with Si/Al ratio of 5, have been added to highly permeable poly(1-trimethylsilyl-1-propyne) (PTMSP) to increase its selectivity and thermal and mechanical stability. Membranes were characterized by TGA, XRD, SEM and CO2 and N2 single gas permeation measurements at different temperatures. TGA reveal that the thermal resistance of the mixed matrix membranes (MMM) is as good as that of pure PTMSP polymer membranes. XRD and SEM results reflect that there is good interaction between the fillers and the membrane matrix, at 5 and 10 wt.% zeolite loadings, while at 20 wt.% a dual layer structure is formed, when Rho zeolite is the filler, because the particle size of Rho is higher than those of LTA5 or CHA, and voids appear that limit the permselectivity performance. In single gas permeation of N2 and CO2, the influence of temperature, zeolite loading and type is analyzed. The selectivity of pure PTMSP is considerably enhanced with the addition of the zeolites and the increase of temperature, and the MMM loaded with 5 wt.% zeolite surpassed the Robeson’s upper bound for CO2/N2 separation, without decreasing the permeability too much. Upon increasing temperature from 298 to 333 K, the permselectivity is enhanced even further without loss of permeability. The 5 wt.% loaded membranes were tested in CO2/N2 mixed gas separation experiments at 333 K and 12.5 wt.% CO2 in the feed, and the permselectivity of LTA5- and Rho-PTMSP membranes was further enhanced, compared with the single gas permeation experiments.

Separation of greenhouse gases (SF6, CF4 and CO2) in an industrial flue gas using pilot-scale membrane

The separation of greenhouse gases, such as sulfur hexafluoride (SF6), tetrafluoromethane (CF4) and carbon dioxide (CO2), from the flue gas that originated from a display manufacturing plant was investigated using the membrane technology. Permeation experiments were performed on single gases (N2 and SF6) and flue gas to demonstrate the applicability of membrane technology for the mitigation of greenhouse gas emissions. The gas separation experiments were performed using a pilot-scale membrane apparatus composed of a commercial PSf hollow fiber membrane under various conditions of feed pressure and stage cut. The flue gas was composed mostly of N2 and O2 and included less than 1% greenhouse gases such as SF6 (800–1000ppm), CF4 (50–100ppm) and CO2 (600ppm above the atmospheric level). In the flue gas separation experiment, SF6 and CF4 were enriched in the retentate. By increasing the stage cut, the enrichment ratio was increased, and the recovery was decreased. An increase in the feed pressure can enhance the efficiency by increasing the capacity without a significant decrease in the enrichment ratio and recovery at the pilot scale. The recovery and enrichment of SF6 was lower than expected based on the ideal selectivity due to the mixture effect. The enrichment ratio of CF4 was lower than that of SF6 due the higher permeance of SF6. Because the selectivity is not high, this membrane is not appropriate for the purification of SF6. CO2 was included in the retentate below the level in the atmosphere due to its high permeability. The result provided realistic information about the performance of membrane technology for the mitigation of greenhouse gas emissions.