Graphene oxide membranes for gas separation

Recently, the carbon based materials1 attracted attention of the scientific community for applications in membrane gas separation. Tremendous number of carbon based materials such as carbon nanotubes, chemically modified graphene, graphene oxide (GO) or graphite (nano)particles in mixed matrix membrane (MMM) composites was tested within past decade2. It was found that even small loading of graphene and (GO) additives, i.e. 0.05 to 1 wt.%3, led to considerable changes of composite materials properties (elastic modulus, tensile strength, electrical conductivity, and thermal stability) compared to neat polymers. Please click Additional Files below to see the full abstract

Aging of polymers of intrinsic microporosity studied by sorption and permeation

Polymers of intrinsic microporosity (PIMs)1 seem to be effective materials for gas and vapor separations.2 However, gas separation efficiency of PIMs can be strongly influenced by the material aging process connected with the changes of PIMs inner structure.3 With respect to potential industrial applications, the investigation of such changes and their effect on gas and vapor transport is necessary. In this work, we present a detailed study of i) CO2 sorption in PIM-1 via momentary measurements during four years and ii) methanol permeation in PIM-11 and EA-TB-PIM2 via continuous and momentary experiments. Sorption experiments were performed gravimetrically using a self-developed apparatus equipped with McBain’s spiral balances. In this case, PIM-1 membranes were pre-treated (soaking in ethanol with consequent drying at different temperatures) in order to study the influence of temperature on PIM-1 aging. Methanol permeation experiments were performed using a differential flow permeameter with H2 and He as carrier gases. Permeation experiment were performed with PIM-1 and PIM-EA-TB methanol treated membranes. CO2 sorption measurements revealed that, assuming the validity of the solution-diffusion model, the decrease of permeability during aging can be attributed directly to the decrease of diffusivity, whereas solubility is time independent in the studied period of four years. Although higher preparation temperature led to the initial drop of diffusivity, this process stabilized separation performance of PIMs over time (Figure 1). MeOH permeation experiments confirmed previous findings from CO2 tests, that the permeability decrease during the aging is a diffusivity controlled process. Moreover, it was found that the momentary permeation data can be mathematically transferred to continuous data, which are more relevant for applications but more difficult to measure. The nature of aging process was studied by infrared spectroscopy. We have found that aging of PIMs does not influence their chemical structure and; therefore, they undergo only the so called physical-aging. Please click Additional Files below to see the full abstract

A Novel Time Lag Method for the Analysis of Mixed Gas Diffusion in Polymeric Membranes by On-Line Mass Spectrometry: Pressure Dependence of Transport Parameters

This paper presents a novel method for transient and steady state mixed gas permeation measurements, using a quadrupole residual gas analyser for the on-line determination of the permeate composition. The on-line analysis provides sufficiently quick response times to follow even fast transient phenomena, enabling the unique determination of the diffusion coefficient of the individual gases in a gas mixture. Following earlier work, the method is further optimised for higher gas pressures, using a thin film composite and a thick dense styrene-butadiene-styrene (SBS) block copolymer membrane. Finally, the method is used to calculate the CO2/CH4 mixed gas diffusion coefficients of the spirobisfluorene-based polymer of intrinsic microporosity, PIM-SBF-1. It is shown that the modest pressure dependence of the PIM-SBF-1 permeability can be ascribed to a much stronger pressure dependence of the diffusion coefficient, which partially compensates the decreasing solubility of CO2 with increasing pressure, typical for the strong sorption behaviour in PIMs. The characteristics of the instrument are discussed and suggestions are given for even more versatile measurements under stepwise increasing pressure conditions. This is the first report on mixed gas diffusion coefficients at different pressures in a polymer of intrinsic microporosity

A Review on Ionic Liquid Gas Separation Membranes

Ionic liquids have attracted the attention of the industry and research community as versatile solvents with unique properties, such as ionic conductivity, low volatility, high solubility of gases and vapors, thermal stability, and the possibility to combine anions and cations to yield an almost endless list of different structures. These features open perspectives for numerous applications, such as the reaction medium for chemical synthesis, electrolytes for batteries, solvent for gas sorption processes, and also membranes for gas separation. In the search for better-performing membrane materials and membranes for gas and vapor separation, ionic liquids have been investigated extensively in the last decade and a half. This review gives a complete overview of the main developments in the field of ionic liquid membranes since their first introduction. It covers all different materials, membrane types, their preparation, pure and mixed gas transport properties, and examples of potential gas separation applications. Special systems will also be discussed, including facilitated transport membranes and mixed matrix membranes. The main strengths and weaknesses of the different membrane types will be discussed, subdividing them into supported ionic liquid membranes (SILMs), poly(ionic liquids) or polymerized ionic liquids (PILs), polymer/ionic liquid blends (physically or chemically cross-linked ‘ion-gels’), and PIL/IL blends. Since membrane processes are advancing as an energy-efficient alternative to traditional separation processes, having shown promising results for complex new separation challenges like carbon capture as well, they may be the key to developing a more sustainable future society. In this light, this review presents the state-of-the-art of ionic liquid membranes, to analyze their potential in the gas separation processes of the future

Improved CO2/CH4 Separation Properties of Cellulose Triacetate Mixed–Matrix Membranes with CeO2@GO Hybrid Fillers

The study of the effects associated with the compatibility of the components of the hybrid filler with polymer matrix, which ultimately decide on achieving mixed matrix membranes (MMMs) with better gas separation properties, is essential. Herein, a facile solution casting process of simple incorporating CeO2@GO hybrid inorganic filler material is implemented. Significant improvements in material and physico-chemical properties of the synthesized membranes were observed by SEM, XRD, TGA, and stress-strain measurements. Usage of graphene oxide (GO) with polar groups on the surface enabled forming bonds with ceria (CeO2) nanoparticles and CTA polymer and provided the homogeneous dispersion of the nanofillers in the hybrid MMMs. Moreover, increasing GO loading concentration enhanced both gas permeation in MMMs and CO2 gas uptakes. The best performance was achieved by the membrane containing 7 wt.% of GO with CO2 permeability of 10.14 Barrer and CO2/CH4 selectivity 50.7. This increase in selectivity is almost fifteen folds higher than the CTA-CeO2 membrane sample, suggesting the detrimental effect of GO for enhancing the selectivity property of the MMMs. Hence, a favorable synergistic effect of CeO2@GO hybrid fillers on gas separation performance is observed, propounding the efficient and feasible strategy of using hybrid fillers in the membrane for the potential biogas upgrading process

CO2/CH4 and H2/CH4 Gas Separation Performance of CTA-TNT@CNT Hybrid Mixed Matrix Membranes

This study explored the underlying synergy between titanium dioxide nanotube (TNT) and carbon nanotube (CNT) hybrid fillers in cellulose triacetate (CTA)-based mixed matrix membranes (MMMs) for natural gas purification. The CNT@TNT hybrid nanofillers were blended with CTA polymer and cast as a thin film by a facile casting technique, after which they were used for single gas separation. The hybrid filler-based membrane depicted a higher CO2 uptake affinity than the single filler (CNT/TNT)-based membrane. The gas separation results indicate that the hybrid fillers (TNT@CNT) are strongly selective for CO2 over CH4 and H2 over CH4. The increment in the CO2/CH4 and H2/CH4 selectivities compared to the pristine CTA membrane was 42.98 from 25.08 and 48.43 from 36.58, respectively. Similarly, the CO2 and H2 permeability of the CTA-TNT@CNT membrane increased by six- and five-fold, respectively, compared to the pristine CTA membrane. Such significant improvements in CO2/CH4 and H2/CH4 separation performance and thermal and mechanical properties suggest a feasible and practical approach for potential biogas upgrading and natural gas purification

Mass transfer through graphene-based membranes

The problems related to the transport of gases through nanoporous graphene (NG) and graphene oxide (GO) membranes are considered. The influence of surface processes on the transport of gas molecules through the aforementioned membranes is studied theoretically. The obtained regularities allow finding the dependence of the flux of the gas molecules passing through the membrane on the kinetic parameters which describe the interaction of the gas molecules with the graphene sheets. This allows to take into account the influence of external fields (e.g., resonance radiation), affecting the aforementioned kinetic parameters, on the transport of gas molecules through the membranes. The proposed approach makes it possible to explain some experimental results related to mass transfer in the GO membranes. The possibility of the management of mass transfer through the NG and GO membranes using resonance radiation is discussed.Web of Science102art. no. 45

Stanoveni transportnich parametru par organickych latek a jejich smesi v polymernich mebranach.

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