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The novel fixed-site-carrier (FSC) membranes were prepared by coating carbon nanotubes reinforced polyvinylamine/polyvinyl alcohol selective layer on top of ultrafiltration polysulfone support. Small pilot-scale modules with membrane area of 110-330 cm2 were tested with high pressure permeation rig. The prepared hybrid FSC membranes show high CO2 permeance of 0.084-0.218 m3 (STP)/(m2 h bar) with CO2/CH4 selectivity of 17.9-34.7 at different feed pressures up to 40 bar for a 10% CO2 feed gas. Operating parameters of feed pressure, flow rate, and CO2 concentration were found to significantly influence membrane performance. HYSYS simulation integrated with ChemBrane and cost estimation was conducted to evaluate techno-economic feasibility of a membrane process for natural gas (NG) sweetening. Simulation results indicated that the developed FSC membranes could be a promising candidate for CO2 removal from low CO2 concentration (10%) NGs with a low NG sweetening cost of 5.73E−3 $/Nm3 sweet NG produced. © 2014 American Institute of Chemical Engineers AIChE J 60: 4174-4184, 2014 [ABSTRACT FROM AUTHOR]

Highlights: [•] A blended PVAm/PVA membrane reinforced with carbon nanotubes was successfully prepared. [•] A selectivity of CO2/CH4 up to 45 was documented in the low pressure range (2–5bar). [•] A CO2 permeance of up to 0.35m3 (STP)/m2 hbar was documented in this range. [•] The addition of CNTs (1.0wt.%), provided good durability against compaction at elevated pressures. [Copyright &y& Elsevier]

Abstract: A new kind of self-supported dual layer mixed matrix membrane was developed in this work using ZIF-8 as inorganic filler in PEBAX-2533 polymer matrix. The developed dual layer flat sheet mixed matrix membrane was characterized to investigate the morphology of organic-based and inorganic-based layer. The gas separation properties of the mixed matrix membranes were tested using single gases CO2, CH4, N2, and O2 and a mixture of CO2 and N2 in dry and humidified conditions. The permeability of all examined gases increased as the inorganic filler content increased in the matrix membranes, and specifically it increased dramatically for CO2 in all cases, single feed gas and dry and humidified mixed gas. The CO2/N2 selectivity decreased slightly from 33.8 for the pure PEBAX membrane to 32.3 for the mixed matrix membrane with 35% ZIF-8 loading, while more significant drop in CO2/N2 selectivity was observed in experiments using mixed gases. [Copyright &y& Elsevier]

Abstract: This paper summarizes the results obtained in Nanoglowa EU project using polymeric polyvinylamine fixed site carrier membranes developed at NTNU Norway for CO2 removal from flue gas. The pilot scale testing using real flue gas was performed at Sines power plant of EDP in Portugal. The aim of the project was CO2 separation from flue gas of coal fired power plants using membrane technology and involved several aspects: membrane up-scaling, material durability and pilot testing in a power plant. Gas permeation experiments and material analyses confirmed that the membrane material and separation performances were not affected negatively by exposure to synthetic and real flue gas contaminants. A pilot scale module having installed a 1.5 m2 of NTNU membrane was tested continuously for 6,5 months. The membranes showed constant separation performances with a maximum content of 75% CO2 in permeate and a permeate flow of 525 l/day. The performances were kept constant despite several challenges related to power plant operation such as high levels of NOx (600mg/Nm3) and 200mg/Nm3 SO2, and frequent power plant outages. [Copyright &y& Elsevier]

Abstract: A high performance membrane based on polyvinylamine composite material has been reported with Fixed-Site- Carriers (FSC) for CO2 transport. This polyvinylamine based FSC membrane has a promising performance of high permeance as well as high selectivity and gives high potential to be applied for the post combustion CO2 capture where the driving force has been generally considered to be too low for membrane application. The membrane has been tested in both lab & pilot scale facilities and investigated further for evaluation by modelling and simulation, and its robustness against the toxic contaminants (SO2, CO and NOx) was reported in the previous GHGT-10. The chemical form of polyvinylamine changes with pH of the cast solution. The ratio of free amine group and the corresponding ammonium salt depends on pH of the cast solution. Furthermore the overall solubility of CO2 in the membrane increases as the pH increases. The membranes prepared from cast solutions of different pH have been characterized and tested for CO2 capture from post combustion gas. Permeation tests of membranes of different pH cast solutions have shown that the performance of the polyvinylamine composite membrane could be much affected and even enhanced remarkably by pH control. The performance increase was clearly pronounced when the post combustion gas contained more water molecules at higher level of humidity. According to the proposed mechanism of reaction for CO2 facilitated transport, water promotes the transport of CO2 by participating in the reaction as well as increasing the mobility of the transportation. The enhanced performance of the membrane at higher pH can be explained with regard to the increased number of free amino groups available on the polymer backbone chain for facilitated transport of CO2 or the degree of ionization of the functional groups. The increased CO2 solubility in the membrane at higher pH condition also assumed to contribute to the enhanced performance. At lower pH, the decreased number of free amines and the increased viscosity of casting solution have resulted in the decrease in membrane performance. [Copyright &y& Elsevier]

PVA/TiO2nanocomposite membranes developed were investigated for chemical, mechanical, and gas separation properties. PVA/TiO2dispersion offers good optical property and less aggregation, as shown by UV-vis photospectroscopy. FT-IR spectra suggest strong interaction between PVA and TiO2. Mechanical properties of the composite membranes were enhanced by the addition of TiO2. Permeation results show that the addition of TiO2up to 20 wt.% increased the selectivity of gas pairs O2/N2,H2/N2,H2/CO2, and CO2/N2by 60%, 55%, 23%, and 26% respectively, with a corresponding decrease in the permeability. At higher loading of TiO2,a reverse trend was observed. [ABSTRACT FROM PUBLISHER]

Abstract: A CO2-facilitated transport composite membrane made of PVAm/PVA blend was exposed to a humid synthetic natural gas mixture with monoethylene glycol (MEG) and triethylene glycol (TEG). The effects of different parameters such as relative humidity, types of impurities, exposure temperature were analyzed to understand the real mechanism of interaction and their effects on the CO2/CH4 separation performance. Both the CO2 and CH4 permeances were increased after the exposure of hygroscopic MEG and TEG, except in one case. The CO2/CH4 selectivity was slightly reduced by the exposure to MEG since MEG plasticized the membrane a little bit, whereas the selectivity was slightly increased by the exposure to TEG. Water plays a significant role in the overall performance. For this facilitated transport PVAm/PVA blend membrane, the high relative humidity helps the facilitated transport of CO2 through the PVAm/PVA blend composite membrane to maintain its permeation properties to a value very close to that of a fresh membrane. This study reports the effect of MEG and TEG on the CO2/CH4 separation of a PVAm/PVA blend composite membrane, and documents a positive step forward for using this membrane in a rigorous environment of natural gas sweetening where entrained glycol is considered as a potential threat to the membrane. [Copyright &y& Elsevier]

Abstract: The PVAm/PVA blend composite membrane was exposed to synthetic natural gas mixtures containing aggressive gases like hydrogen sulfide (H2S) at a concentration of 1mol% and H2S in combination with the condensable hydrocarbons n-hexane and propane. The effect on the performance of the membrane was studied under different relative humidity conditions and the possible interactions between the membrane and impurities were analyzed. The performance of the membrane was found to be reduced at low humidity conditions due to H2S induced conditioning and sorption of n-hexane both in the polysulfone support and PVAm/PVA selective layer, while at high relative humidity the CO2 facilitated transport helps the membrane to retain its performance to a value very close to that of a fresh membrane. The CO2 facilitated transport is closely related to the membrane swelling. The combined effects of H2S and hydrocarbons are comparable to the effects of H2S alone. Under high humidified conditions, the maximum CO2 permeance loss is 18% and the maximum CO2/CH4 selectivity loss is 16% after two weeks exposure at this harsh and humidified conditions. Our conclusion based on the current investigations, is that the aggressive environment does not introduce permanent damage to the material and the PVAm/PVA blend membrane is keeping its separation performance quite well after the exposure to H2S and hydrocarbons, and may have a potential for being used in natural gas sweetening. [Copyright &y& Elsevier]

Membrane separation systems require no or very little chemicals compared to standard unit operations. They are also easy to scale up, energy efficient, and already widely used in various gas and liquid separation processes. Different types of membranes such as common polymers, microporous organic polymers, fixed-site-carrier membranes, mixed matrix membranes, carbon membranes as well as inorganic membranes have been investigated for CO2 capture/removal and other energy processes in the last two decades. The aim of this work is to review the membrane systems applied in different energy processes, such as post-combustion, pre-combustion, oxyfuel combustion, natural gas sweetening, biogas upgrading, hydrogen production, volatile organic compounds (VOC) recovery and pressure retarded osmosis for power generation. Although different membranes could probably be used in a specific separation process, choosing a suitable membrane material will mainly depend on the membrane permeance and selectivity, process conditions (e.g., operating pressure, temperature) and the impurities in a gas stream (such as SO2, NOx, H2S, etc.). Moreover, process design and the challenges relevant to a membrane system are also being discussed to illustrate the membrane process feasibility for a specific application based on process simulation and economic cost estimation. [ABSTRACT FROM AUTHOR]

The effects on sugar yields of acid concentration, temperature, and time in the first (decrystallization) stage of a two-stage concentrated sulfuric acid hydrolysis of softwood (Scots pine) and hardwood (aspen) were investigated. The study focused on the multi-variable effects of the decrystallization stage and applied a statistical modeling with Central Composite Face (CCF) design of experiment to systematically study and simulate the effect of decrystallization reaction conditions on hydrolysis products and degradation products. The models were statistically significant and showed that for both aspen and pine, the reaction temperature and acid concentration were the most influential variables on monosaccharides and total sugar yields compared to the reaction time. The interaction between temperature and acid concentration was the most important for both species. The sugar degradation products were much influenced by the decrystallization temperature on both aspen and pine. The models were validated by a test-set and showed a good agreement between the experimental and predicted values. The optimum predicted total sugar yields were 56 g / 100 g d.w for aspen (74% theoretical) and 64 g / 100 g d.w for pine (91% theoretical). [ABSTRACT FROM AUTHOR]

Abstract: Hollow fiber carbon membranes were prepared from the cellulosic precursors by controlling the carbonization protocol of CO2 using 823–4K/min for 2h. The prepared carbon membranes presented a symmetric structure and a much smaller wall thickness of 25μm compared to the precursor (40μm) from the SEM images. Single gas (i.e. O2, N2, CO2) permeation tests indicated that the molecular sieve mechanism was the dominating transportation mechanism for the gas species through the carbon membranes. The influences of operating parameters on the carbon membrane separation performance include pressure, temperature, retentate flow rate and feed CO2 composition. These parameters were systematically investigated by factorial design method. The experimental and process simulation results indicated that the CO2 purity can only achieve ca. 75% with one stage membrane configuration. Therefore, a simple two stage cascade configuration without sweep was designed for the process optimization based on the capital cost estimation of the major equipments. A CO2-purity of 90% was then achieved with 60% CO2 capture. Although the specific capital cost for carbon membrane technology is still high compared to the traditional chemical absorption method, simulation results also proved that the costs can be significantly decreased by reducing the carbon membrane wall thickness from 25 to 10μm—this is considered to be a realistic option. Therefore, the prepared hollow fiber carbon membranes needs to be further optimized in order to be a potential candidate for CO2 capture. [Copyright &y& Elsevier]

Abstract: The use of membranes for CO2 separation has been considered as a very good alternative to amine absorption thanks to potentially lower cost & process simplicity, energy saving and environmental friendliness. In this work CO2 separation performance of facilitated transport polymer composite membranes developed by MEMFO (membrane research group at NTNU, Norway) is presented together with the effect of contaminants which would be present in real process streams; basically for high pressure natural gas. These facilitated transport membranes where carriers are fixed on polymer show robust CO2 separation performance towards contaminants. There are also many challenges to overcome to develop a membrane successfully for a scaled-up module because many parameters developed for a small lab scale may not apply directly for a larger scale. In this work and presentation, some of the difficulties during scaling-up of the FSC (fixed-site-carrier) membranes are introduced. [Copyright &y& Elsevier]

Abstract: Carbon dioxide accounts for about 80% of all greenhouse gases (GHG) and thus becomes the major source responsible for global warming which is considered as the greatest environmental challenge the world is facing. The efforts to control the GHG emissions include the recovery of CO2 from flue gas. In this work, a feasibility analysis has been carried out with an in-house membrane program interfaced within process simulation program (AspenHysys) to investigate the influence of process parameters on the energy demand and flue gas processing cost. A novel CO2-selective membrane with the facilitated transport mechanism has been employed to capture CO2 from the flue gas mixtures. The results show that a membrane process using the facilitated transport membrane is feasible, even for low CO2 concentration (10%) in flue gas, compared to amine absorption in terms of energy requirement and it is possible to achieve more than 90% CO2 recovery and with a purity in the permeate above 90% CO2. Different process configurations are presented showing the effect of process conditions on the energy demand and gas processing cost to obtain 90% recovery and 90% purity. [Copyright &y& Elsevier]

Abstract: The biogas upgrading by membrane separation process using a highly efficient CO2-selective polyvinylamine/polyvinylalcohol (PVAm/PVA) blend membrane was investigated by experimental study and simulation with respect to process design, operation optimization and economic evaluation. This blend membrane takes advantages of the unique CO2 facilitated transport from PVAm and the robust mechanical properties from PVA, exhibits both high CO2/CH4 separation efficiency and very good stability. CO2 transports through the water swollen membrane matrix in the form of bicarbonate. CO2/CH4 selectivity up to 40 and CO2 permeance up to 0.55m3(STP)/m2 hbar at 2bar were documented in lab with synthesized biogas (35% CO2 and 65% CH4). Membrane performances at varying feed pressures were recorded and used as the simulation basis in this work. The process simulation of an on-farm scale biogas upgrading plant (1000Nm3/h) was conducted. Processes with four different membrane module configurations with or without recycle were evaluated technically and economically, and the 2-stage in cascade with recycle configuration was proven optimal among the four processes. The sensitivity of the process to various operation parameters was analyzed and the operation conditions were optimized. [Copyright &y& Elsevier]

Abstract: Hollow fibre carbon membranes (HFCMs) were fabricated from deacetylated cellulose acetate precursors based on a multi-dwell carbonization protocol. Membrane structure and morphology were characterized by scanning electronic microscope (SEM), and membrane separation performances for single gas and gas mixtures were tested by the in-house gas test setup. Simulations of CO2 capture by hollow fibre carbon membranes were conducted based on Aspen Hysys® integrated with ChemBrane. The characteristic diagrams and optimal configuration were obtained, and the process was optimized based on the necessary membrane area, energy demands for the compressor and cooler, recovery and purity of CO2, and capital cost. [Copyright &y& Elsevier]

Abstract: The recovery of hydrogen from gas mixtures with hydrocarbons may provide a commercial niche for carbon molecular sieve membranes. A potential application is the recovery of hydrogen transmitted with natural gas in a mixed network in a hydrogen economy scenario. Performance data measured on the bench-scale were applied to a techno-economic evaluation of hydrogen recovery and the results were compared to a commercial polyimide membrane''s performance. The carbon membranes produced higher purity hydrogen, consumed less energy in separation and achieved competitive specific separation costs under certain conditions. Recovery of 90% of the hydrogen from a feed stream containing 5mol% hydrogen was feasible in a single stage. [Copyright &y& Elsevier]

Abstract: Three different types of membranes were experimentally evaluated for CO2 recovery from blast furnace effluents: semi-commercial adsorption selective carbon membranes, in-house tailored carbon molecular sieving membranes, and fixed site carrier (FSC) membranes with amine groups in the polymer backbone for active transport of CO2. In the single gas experiments the FSC membranes showed superior selectivity for CO2 over the other relevant gases (CO, N2 and H2) and high CO2 permeance (productivity). In addition, it is easy to process and handle, relatively inexpensive to produce and the water in the feed gas is an advantage rather than a problem, since the membrane must be humidified during operation. Based on these experiments a simulation study of a full scale process was performed. The technology showed notable low energy cost, even when converted to the thermal equivalent. Total costs for the CO2 recovery unit (CO2 prepared for pipeline transport) were estimated to be in the range 15.0–17.5€/tonnes CO2. [Copyright &y& Elsevier]

The capture of CO2 is of high interest in our society representing an essential tool to mitigate man-made climate warming. Membrane technology applied for CO2 capture offers several advantages in terms of energy savings, simple operation, and easy scale-up. Glassy membranes are associated with low gas permeability that negatively affect on their industrial implementation. Oppositely, rubbery membranes offer high permeability, but their selectivity is low. Here we report rubbery organic frameworks (ROFs) combining the high permeability of soft matrices with the high sieving selectivity of molecular frameworks. The best performing membranes provide a CO2/N2 selectivity up to 104 with a CO2 permeability up to 1000 Barrer, representing relevant performances for industrial implementation. Water vapors have a positive effect on CO2 permeability, and the CO2/N2 selectivity is higher than in dry conditions, as most of CO2 gas emissions are present in fully humidified gas streams. The synergetic high permeability/selectivity performances are superior to that observed with current state-of-the-art polymeric membranes. [ABSTRACT FROM AUTHOR]

Abstract: Composite hollow fibers membranes were prepared by coating poly(phenylene oxide) (PPO) and polysulfone (PSf) hollow fibers with high molecular polyvinylamine (PVAm). Two procedures of coating hollow fibers outside and respective inside were investigated with respect to intrinsic PVAm solution properties and hollow fibers geometry and material. The influence of operating mode (sweep or vacuum) on the performances of membranes was investigated. Vacuum operating mode gave better results than using sweep because part of the sweep gas permeated into feed and induced an extra resistance to the most permeable gas the CO2. The composite PVAm/PSf HF membranes having a 0.7–1.5μm PVAm selective layer, showed CO2/N2 selectivity between 100 and 230. The selectivity was attributed to the CO2 facilitated transport imposed by PVAm selective layer. The CO2 permeance changed from 0.006 to 0.022m3(STP)/(m2 barh) in direct correlation with CO2 permeance and separation mechanism of the individual porous supports used for membrane fabrication. The multilayer PVAm/PPO membrane using as support PPO hollow fibers with a 40nm PPO dense skin layer, surprisingly presented an increase in selectivity with the increase in CO2 partial pressure. This trend was opposite to the facilitated transport characteristic behaviour of PVAm/porous PSf. This indicated that PVAm/PPO membrane represents a new membrane, with new properties and a hybrid mechanism, extremely stable at high pressure ratios. The CO2/N2 selectivity ranged between 20 and 500 and the CO2 permeance from 0.11 to 2.3m3(STP)/(m2 barh) depending on the operating conditions. For both PVAm/PSf and PVAm/PPO membranes, the CO2 permeance was similar with the CO2 permeance of uncoated hollow fiber supports, confirming that the CO2 diffusion rate limiting step resides in the properties of the relatively thick support, not at the level of 1.2μm thin and water swollen PVAm selective layer. A dynamic transfer of the CO2 diffusion rate limiting step between PVAm top layer and PPO support was observed by changing the feed relative humidity (RH%). The CO2 diffusion rate was controlled by the PPO support when using humid feed. At low feed humidity the 1.2μm PVAm top layer becomes the CO2 diffusion rate limiting step. [Copyright &y& Elsevier]

Abstract: A defect-free ultra thin PVAm/PVA blend facilitated transport membrane cast on a porous polysulfone (PSf) support was developed and evaluated in this study. The target membrane was prepared from commercial polyvinyl amine (PVAm) and polyvinyl alcohol (PVA). Effects of experimental conditions were investigated for a CO2–N2 mixed gas. A CO2/N2 separation factor of up to 174 and a CO2 permeance up to 0.58m3(STP)/(m2 hbar) were documented. Experimental results suggest that CO2 is being transported according to the facilitated transport mechanism through this membrane. The fixed amino groups in the PVAm matrix function as CO2 carriers to facilitate the transport whereas the PVA adds mechanical strength to the blend by entanglement of the polymeric chains hence creating a supporting network. The good mechanical properties obtained from the blend of PVA with PVAm, enabled an ultra thin selective layer (down to 0.3μm) to be formed on PSf support (with MWCO of 50,000), resulted in both high selectivity and permeance. The PVAm/PVA blend membrane also exhibited a good stability during a 400h test. [Copyright &y& Elsevier]

Carbon membrane (CM) separation process for producing oxygen-enriched air (OEA) at a concentration of 50–78 mol% O 2 in a single stage process with no recycle stream has been investigated. This paper (Part II of a two-part study) considers techno-economic analysis for O 2 -selective carbon membranes to yield the lowest production cost of “equivalent” pure oxygen (EPO 2 ) in a single stage separation process based on experimental and predictive membrane performance. Aspen Hysys® interfaced with ChemBrane (in-house developed model) was used to perform the simulations for air separation with CM. Three different approaches with respect to pressure were investigated; (1) feed compression, (2) vacuum on permeate side and (3) combination of (1) and (2). The simulation results and sensitivity analysis showed that with current performance (O 2 permeability: 10 Barrer ( 1 Barrer = 2.736E − 09 m 3 ( STP ) m /( m 2 bar h )) and O 2 /N 2 selectivity: 18), mechanical properties, and cost per m 2 of CM, it is economically most efficient to use the third approach “combination of feed compression and permeate vacuum” to produce EPO 2 . A stage cut of 10% was found to be as an average economical optimum when using vacuum pump (approach (2)) to produce OEA. However, the techno-economic analysis for the reported CM showed that a stage cut of 0.15–0.2 was the most cost-effective while using compression approach (1) or (3) to produce EPO 2 . [ABSTRACT FROM AUTHOR]

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 O 2 while the membrane was in operation. This method reduced the aging effect and the membrane showed relative stable performance with only 20% loss in O 2 permeability and 28% increase in O 2 /N 2 selectivity, over the period of 135 days using various feeds containing H 2 S, n -Hexane and CO 2 -CH 4 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 O 2 permeability is increasing exponentially with increase in operating temperature without significant loss in the O 2 /N 2 selectivity. The O 2 permeability of 10 Barrer (1 Barrer  =  2.736E − 09 m 3 (STP)m/m 2 bar h) with O 2 /N 2 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. [ABSTRACT FROM AUTHOR]

Carbon hollow fibers (CHF) were fabricated by carbonization of deacetylated cellulose acetate precursor. To enhance membrane permeation properties, pore structure was tailored by means of an oxidation and reduction process followed by chemical vapor deposition with propene. Permeation properties using shell-side feed configuration of 70 modules (0.2–2 m 2 ) for both CHF and modified carbon hollow fibers (MCHF) were investigated for single gases, N 2 and CO 2 at high pressure (2–70 bar feed vs 0.05–1 bar permeate pressure) and temperature from 25–120 °C. Maximum CO 2 permeance value for a MCHF module was recorded 50,000 times higher as compared to prior modification, and CO 2 /N 2 selectivity was improved 41 times in comparison with CHF for the same module. Results indicated that carbon membranes are hardly effected by high pressure, but significant drop in CO 2 permeability was observed at elevated temperature. Simulations of CO 2 /CH 4 separation by MCHF and polymeric membranes were conducted based on Aspen Hysys® integrated with ChemBrane, and the process was optimized for cost calculation based on membrane area and compression energy. Simulation results indicated that the required separation can be achieved by a single stage process for MCHF, while a two-stage process is needed for the polymeric membranes. [ABSTRACT FROM AUTHOR]

Abstract: TFC membranes with a cellulose triacetate (CTA) support layer were prepared using a modified interfacial polymerization (IP) method. In this method, a linking molecule covalently binds the polyamide (PA) active layer to the CTA support. The effects of three linking molecules (trimesoyl chloride (TMC), succinyl chloride and malonyl chloride) on membrane performance were investigated. The membrane prepared using TMC as the linking molecule displayed a strong decrease in salt rejection as a function of time in reverse osmosis (RO) and a strong increase in reverse salt flux as a function of draw solute concentration in forward osmosis (FO). The membranes made with bifunctional succinyl and malonyl chloride displayed a more stable performance. Confocal laser scanning microscopy (CLSM) images of the membranes indicate changes in CTA support morphologies upon exposure to high salt concentrations, especially for the TMC membrane. The different behavior of the trifunctional TMC membrane could be attributed to the higher number of charged groups on the support membrane, which causes anisotropic swelling/deswelling in the polymer. Our results suggest that bifunctional linkers can be used to ^fabricate membranes with performance characteristics less dependent upon salt concentration. The implications of the results for FO and pressure retarded osmosis are discussed. [Copyright &y& Elsevier]

Abstract: Polyvinyamine (PVAm) Fixed-Site-Carrier (FSC) composite membrane has been reported to have a good potential to be applied for large scale for CO2 capture applications with respect to high permeance and high selectivity. In this study, the membrane was investigated with respect to pH of the casting solution as a step for optimization of the membrane. It was found out that the pH of the PVAm casting solution could be easily controlled with a simple agent. The degree of protonation of the functional groups depends on the pH of the casting solution and influenced the reaction of carriers with CO2 and the solubility of CO2 in the FSC membrane swollen by water vapor in the feed flue gas. So it was expected that the pH could affect greatly the membrane’s CO2 capture performance. Membranes from casting solutions of different pH have been prepared, characterized and tested in a permeation set-up for CO2 separation from humidified flue gas. Permeation tests have shown that the performance of the PVAm FSC membrane for CO2 capture could be enhanced remarkably by pH control. This is explained by the increased number of free amine groups available for facilitated transport of CO2 with increasing pH. At low pH, it is assumed that the decreased number of free amines and the increased viscosity of casting solution have resulted in the decreased membrane performance. [Copyright &y& Elsevier]

Industrial scale production of carbon membrane is very challenging due to expensive precursor materials and a multi-step process with several variables to deal with. The optimization of these variables is essential to gain a competent carbon membrane (CM) with high performance and good mechanical properties. In this paper, a pilot scale system is reported that was developed to produce CM from regenerated cellulose precursor with the annual production capacity 700 m² of CM. The process was optimized to achieve maximum yield (>95%) of high quality precursor fibers and carbonized fibers. A dope solution of cellulose acetate (CA)/Polyvinylpyrrolidone (PVP)/ N -methyl-2-pyrrolidone (NMP) and bore fluid of NMP/H₂O were used in 460 spinning-sessions of the fibers using a well-known dry/wet spinning process. Optimized deacetylation of spun-CA hollow fibers (CAHF) was achieved by using 90 vol% 0.075 M NaOH aqueous solution diluted with 10 vol% isopropanol for 2.5 h at ambient temperature. Cellulose hollow fibers (CHF) dried at room temperature and under RH (80% → ambient) overnight gave maximum yield for both dried CHF, as well as carbon fibers. The gas permeation properties of carbon fibers were also high (CO₂ permeability: 50⁻450 Barrer (1 Barrer = 2.736 × 10 -9 m³ (STP) m/m² bar h), and CO₂/CH₄ selectivity acceptable (50⁻500).

The simultaneous carbonization of thousands of fibers in a horizontal furnace may result in fused fibers if carbonization residuals (tars) are not removed fast enough. The optimized purge gas flow rate and a small degree angle in the furnace position may enhance the yield of high quality carbon fibers up to 97% by removing by-products. The production process for several thousand carbon fibers in a single batch is reported. The aim was developing a pilot-scale system to produce carbon membranes. Cellulose-acetate fibers were transformed into regenerated cellulose through a de-acetylation process and the fibers were carbonized in a horizontally oriented three-zone furnace. Quartz tubes and perforated stainless steel grids were used to carbonize up to 4000 (160 cm long) fibers in a single batch. The number of fused fibers could be significantly reduced by replacing the quartz tubes with perforated grids. It was further found that improved purge gas flow distribution in the furnace positioned at a 4-degree to 6-degree angle permitted residuals to flow downward into the tar collection chamber. In total, 390 spun-batches of fibers were carbonized. Each grid contained 2000⁻4000 individual fibers and these fibers comprised four to six spun-batches of vertically dried fibers. Gas permeation properties were investigated for the carbon fibers.

In this article, we studied two different types of polyhedral oligomeric silsesquioxanes (POSS ® ) functionalized nanoparticles as additives for nanocomposite membranes for CO₂ separation. One with amidine functionalization (Amidino POSS ® ) and the second with amine and lactamide groups functionalization (Lactamide POSS ® ). Composite membranes were produced by casting a polyvinyl alcohol (PVA) layer, containing either amidine or lactamide functionalized POSS ® nanoparticles, on a polysulfone (PSf) porous support. FTIR characterization shows a good compatibility between the nanoparticles and the polymer. Differential scanning calorimetry (DSC) and the dynamic mechanical analysis (DMA) show an increment of the crystalline regions. Both the degree of crystallinity (Xc) and the alpha star transition, associated with the slippage between crystallites, increase with the content of nanoparticles in the PVA selective layer. These crystalline regions were affected by the conformation of the polymer chains, decreasing the gas separation performance. Moreover, lactamide POSS ® shows a higher interaction with PVA, inducing lower values in the CO₂ flux. We have concluded that the interaction of the POSS ® nanoparticles increased the crystallinity of the composite membranes, thereby playing an important role in the gas separation performance. Moreover, these nanocomposite membranes did not show separation according to a facilitated transport mechanism as expected, based on their functionalized amino-groups, thus, solution-diffusion was the main mechanism responsible for the transport phenomena.