Robeson Plot Research Articles

Deep eutectic solvent engineered GO/ZrO2 nanofiller for mixed matrix membranes: An efficient hydrogen gas separation

AbstractThis study explores fabrication and characterization of mixed matrix membranes (MMMs) for gas separation, employing a cost‐effective solution casting method. Polycarbonate (PC) and polystyrene (PS) blends are combined with graphene oxide (GO) and zirconium dioxide (ZrO2) nanofillers, with and without a deep eutectic solvent (DES) obtained through hydrogen bond exchange. Various MMMs compositions (2–20 wt%) are systematically examined using diverse characterization techniques, including differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared spectroscopy, scanning electron microscopy, porosity determination, and water contact angle analysis. The MMMs exhibit enhanced gas permeability and selectivity, surpassing conventional membrane materials. Notably, H2 gas permeability reaches outstanding levels, with the composition PC/PS‐DES‐GO/ZrO2 at 20 wt% (PBC20‐IV) demonstrating the highest value of 86.32 Barrer. This superior performance is attributed to the unique properties of ZrO2, increased sorption capacity of GO, and enhanced thermal stability due to DES. Permeability data for CO2, N2, O2, and CH4 also show significant values, aligning with the observed trends in H2 permeability. Robeson's plot for the H2/CO2 gas pair surpasses the 2008 upper bound, placing the MMMs in a novel category for gas separation membranes. The incorporation of DES‐modified nanofiller blend composites presents a promising strategy for the potential production of pure hydrogen.

CFD simulation for CO2 separation using diamond-structured thermally rearranged (TR) polymer membrane: Effect of CO2 feed concentration, feed pressure and temperature

Abstract CO2 separation in natural gas purification is important in improving the properties of natural gas such as energy content, volume and corrosivity. Membrane separation using TR-450 polymer membrane is a potential approach to remove CO2 from natural gas efficiently. The study of CO2/CH4 binary gas mixture separation was simulated using a thermally-rearranged (TR) HAB- 6FDA membrane at 450 °C with a partial part of Schwarz Diamond structure because it exhibits advanced mechanical properties with low stiffness for relatively high strength. TR-450 membrane exhibits excellent separation performance that has the potential to exceed the Robeson plot 1991. Computational fluid dynamics (CFD) was used to simulate the fluid behavior within the geometry created using CAD software. The effect of feed pressure, temperature and CO2 feed concentration on the separation performance of TR-450 membrane was also studied. The results indicated that an increase in feed pressure leads to a decrease in CO2 recovery, hence the lower separation performance. It was also found that increasing the feed temperature leads to an increase in CO2 recovery. Concerning the concentration of CO2 in the feed, elevated levels impact the performance of membrane separation. The enhanced membrane separation performance demonstrated by the TR-450 membrane under various conditions underscores the necessity for additional investigation to unveil its potential in industrial gas separation applications.

Advancements in Gas Separation for Energy Applications: Exploring the Potential of Polymer Membranes with Intrinsic Microporosity (PIM).

Membrane-based Polymers of Intrinsic Microporosity (PIMs) are promising candidates for energy-efficient industrial gas separations, especially for the separation of carbon dioxide over methane (CO2/CH4) and carbon dioxide over nitrogen (CO2/N2) for natural gas/biogas upgrading and carbon capture from flue gases, respectively. Compared to other separation techniques, membrane separations offer potential energy and cost savings. Ultra-permeable PIM-based polymers are currently leading the trade-off between permeability and selectivity for gas separations, particularly in CO2/CH4 and CO2/N2. These membranes show a significant improvement in performance and fall within a linear correlation on benchmark Robeson plots, which are parallel to, but significantly above, the CO2/CH4 and CO2/N2 Robeson upper bounds. This improvement is expected to enhance the credibility of polymer membranes for CO2 separations and stimulate further research in polymer science and applied engineering to develop membrane systems for these CO2 separations, which are critical to energy and environmental sustainability. This review aims to highlight the state-of-the-art strategies employed to enhance gas separation performances in PIM-based membranes while also mitigating aging effects. These strategies include chemical post-modification, crosslinking, UV and thermal treatment of PIM, as well as the incorporation of nanofillers in the polymeric matrix.

Delaminated or multilayer Ti3C2TX-MXene-incorporated polydimethylsiloxane mixed-matrix membrane for enhancing CO2/N2 separation

Membrane-based gas separation is currently attracting tremendous attention as this unit operation has been considered as one of the available strategies that can contribute toward carbon neutrality. Nevertheless, polymeric membranes suffer from material-related limitation, namely the permeability/selectivity trade-off as exemplified through the Robeson plot due to the intrinsic properties of polymers. Recently, a new rising star in 2D nanomaterial, MXenes, shows a new route to produce high-performance gas separation membranes. This study investigates the potential utility of 2D MXenes as nanofillers to enhance the gas separation performance of polydimethylsiloxane (PDMS) membrane, which generally possesses high intrinsic permeability but low selectivity. Thus, we fabricated mixed-matrix membranes by incorporating multilayer MXene (ML-MXene) and single-layer MXene (D-MXene) under different loading (1–5 wt%) into PDMS matrices. The addition of MXene improved the separation capacity of the rubbery dense layers. Based on the optimization study performed in this work, D-MXene-loaded mixed-matrix membrane at 1 wt% loading demonstrated an increment in both CO2 permeability and CO2/N2 selectivity by 64.1% and 21.3%, respectively, with respect to pure PDMS membrane.

Helium recovery from natural gas over CC3 membranes

Although helium is a valuable inert gas available in abundance in the earth's atmosphere, the major source of helium is from natural gas reservoirs. Membrane based separation processes pose many advantages like being cost effective and non-energy intensive. In this current study, we have successfully demonstrated the synthesis of continuous Porous Organic Cage: CC3 membranes to separate equimolar helium methane mixture with permeance of 4.45 × 10−7 mol/ (m2s Pa) and separation selectivity (α) as high as 8. We also compared the diffusion coefficients of the gases through the membrane to evaluate the dominant mechanism for separation. Lastly, we compared the performance of our membranes to the state-of-the-art membranes with the help of a Robeson plot and found that our membranes outperformed the upper bound.

Factorial analysis on nanocomposite membranes for CO2, CH4 and N2

This study aims to develop, characterize, and optimize the nanocomposite membranes comprised of the coated polyether block amide (Pebax) filled with two different types of nanoadsorbent derived from agricultural wastes on the commercial polyvinylidene fluoride (PVDF) support membrane. To systematically investigate the influence of several membrane preparation conditions on gas separation performance, fractional factorial design (FFD) was applied. The considered conditions include Pebax concentration (3 and 6 wt%), type of nanoadsorbents which are oil palm frond (OPF) and pineapple peel (PP), nanoadsorbents concentration (0.5 and 5 wt%) and sonication time (15 and 60 min). Analysis of variance (ANOVA) technique was used to identify the main and interaction effects of the considered conditions on the gas permeability (CO2, CH4 and N2) and selectivity (CO2/CH4 and CO2/N2). The findings from the screening study suggested that the most influential factors that affect the permeability and selectivity are Pebax concentration and nanoadsorbent type. The incorporation of 5 wt% nano-pineapple peel activated carbon (PPAC) into 6 wt% of Pebax matrix had resulted in a high CO2 permeability, CO2/CH4 selectivity and CO2/N2 selectivity of 1682.76 Barrer, 33.17, and 37.03, respectively, which manage to perform beyond the Robeson plot.

Silica sol gel assisted defect patching of SSZ-13 zeolite membranes for CO2/CH4 separation

• Silica sol post-treatment effectively patched defects of SSZ-13 zeolite membrane. • Ethanol content of silica sol is a significant parameter in defect patching process. • More than 6-fold increase in selectivity is achieved for CO 2 /CH 4 mixed gas test. • The modified SSZ-13 membrane has superior performance in Robeson plot of CO 2 /CH 4. Intercrystalline defects are commonly present in zeolite membranes formed during membrane synthesis and calcination process. Therefore, the selection of a suitable post-treatment method is of particular importance. In this work, SSZ-13 membrane defects were significantly reduced by dipping in the different ethanol/TEOS molar ratios of the silica sol solutions. Characterizations including FTIR, FESEM, EDX, BET, and gas adsorption isotherms of CO 2 and CH 4 revealed that silanes groups were properly placed on the surface of the zeolite while the crystal structure and zeolitic pores remained intact. Permporometry analysis was also carried out to find the effectiveness of the applied patching method. Permeation of CO 2 and CH 4 and CO 2 /CH 4 ideal and mixture selectivity through the fresh and improved membranes was investigated. The results showed that ethanol/TEOS molar ratio of 95.5 increased the single gas selectivity from 33 to 176 at 30 °C and the pressure difference of 100 kPa, while the permeation of CO 2 declined by 15%. In the mixed gas conditions, the selectivity of CO 2 /CH 4 reached a really high value of 660, proving that this post-treatment modification is very effective in SSZ-13 zeolite membrane.

Surface tuning of silica by deep eutectic solvent to synthesize biomass derived based membranes for gas separation to enhance the circular bioeconomy

Membrane technology and deep eutectic solvents (DESs) have demonstrated their efficient and alterable functionality against environmental pollutants in a cost-effective way. This research focuses on the surface tunning and interface engineering of DES using cetyltrimethylammonium bromide (CTAB) and acetic acid to immobilize on mesoporous silica MCM-41 to mitigate the environmental pollutants. Surface tuned MCM-41 was blended with dope solution of tetrahydrofuran (THF) and polysulfone (Psf) to fabricate uniform composition of mixed matrix membranes (MMMs) for carbon dioxide (CO2) separation as CO2 is a barrier in environment as well as in the industrial applications. The characterization of DES has confirmed the presence of CTAB and acetic acid composition that was physically pasted on silica surface. SEM images disclosed that increasing amount of MCM-DES loading up to 20%, improved its dispersion ability on membrane surface. FTIR analysis revealed that there was no reaction took place among the constituents of MMMs. UTM analysis described the strength reduction in membranes with respect to the increase in percentage of filler loading. MCM provided the porous structure, better pore size distribution and large surface area whereas DES supplied amino and carboxyl functional groups for the attraction of CO2. Blending of MCM-DES filler with Psf led to enhanced selectivity (63–67%) and permeability (70–71%) of CO2 gas than pristine Psf and it was also proved better than pure MCM-41 containing membranes and verified by Robeson plot. Hence, these MMMs are very much suitable to reduce environmental pollutants like CO2 from gaseous biomass like natural gas to improve the circular bioeconomy.

Hydrogen separation using polybenzimidazole membrane with palladium nanoparticles stabilized by polyvinylpyrrolidone

An innovation in hydrogen (H2) selective membrane holds the substantial key of H2 economy. Polymers are the most practical and economical material for membrane fabrication, but their application in H2 separation is always constrained within the selectivity-permeability “trade-off” boundary. The expensive palladium (Pd) thin films offer higher selectivity by facilitating the dissociation, diffusion and re-association of H2 gas. This work reports on the incorporation of Pd nanoparticles into polybenzimidazole (PBI) membranes to surpass the mentioned limitations. Pd nanoparticles were synthesized and stabilized in the inversed microemulsion of polyvinylpyrrolidone (PVP) prior to blending. The X-ray diffraction and energy dispersive X-ray results proved the presence of Pd nanoparticles blended into PBI membrane with dense structure. The agglomerated and the stabilized Pd nanoparticles PBI matrix behaved very differently in H2 adsorption at the rising temperature as shown in temperature-programmed reduction results. The ideal H2/CO2 selectivity of PBI membrane with 1 wt% of Pd nanoparticles was improved by 49% compared to the PBI membrane at 150°C. This membrane surpassed the upper bound Robeson plot at 300°C (ideal H2/CO2 selectivity of 83.57; H2 permeability of 151.73 Barrer) and the H2 permeation could be correlated with Van't Hoff-Arrhenius equation.

Carbon Molecular Sieve Membranes Comprising Graphene Oxides and Porous Carbon for CO2/N2 Separation.

To improve the CO2/N2 separation performance, mixed-matrix carbon molecular sieve membranes (mixed-matrix CMSMs) were fabricated and tested. Two carbon-based fillers, graphene oxide (GO) and activated carbon (YP-50F), were separately incorporated into two polymer precursors (Matrimid® 5218 and ODPA-TMPDA), and the resulting CMSMs demonstrated improved CO2 permeability. The improvement afforded by YP-50F was more substantial due to its higher accessible surface area. Based on the gas permeation data and the Robeson plot for CO2/N2 separation, the performances of the CMSMs containing 15 wt % YP-50F and 15 wt % GO in the mixed polymer matrix surpassed the 2008 Robeson upper bound of polymeric membranes. Hence, this study demonstrates the feasibility of such membranes in improving the CO2/N2 separation performance through the appropriate choice of carbon-based filler materials in polymer matrices.

A review on the emerging applications of cellulose, cellulose derivatives and nanocellulose in carbon capture

Carbon capture can be implemented at a large scale only if the CO2 selective materials are abundantly available at low cost. Since the sustainable requirement also elevated, the low-cost and biodegradable cellulosic materials are developed into CO2 selective adsorbent and membranes recently. The applications of cellulose, cellulosic derivatives and nanocellulose as CO2 selective adsorbents and membranes are reviewed here. The fabrication and modification strategies are discussed besides comparing their CO2 separation performance. Cellulose nanofibrils (CNFs) and cellulose nanocrystals (CNCs) isolated from cellulose possess a big surface area for mechanical enhancement and a great number of hydroxyl groups for modification. Nanocellulose aerogels with the large surface area were chemically modified to improve their selectivity towards CO2. Even with the reduction of surface area, amino-functionalized nanocellulose aerogels exhibited the satisfactory chemisorption of CO2 with a capacity of more than 2 mmol/g was recorded. Inorganic fillers such as silica, zeolite and MOFs were further incorporated into nanocellulose aerogels to enhance the physisorption of CO2 by increasing the surface area. Although CO2 adsorbents developed from cellulose and cellulose derivatives were less reported, their applications as the building blocks of CO2 separation membranes had been long studied. Cellulose acetate membranes were commercialized for CO2 separation, but their separation performance could be further improved with silane or inorganic filler. CNCs and CNFs enhanced the CO2 selectivity and permeance through polyvinyl alcohol coating on membranes, but only CNF membranes incorporated with MOFs were explored so far. Although some of these membranes surpassed the upper-bound of Robeson plot, their stability should be further investigated.

Pebax 1657 Nanocomposite Membranes Incorporated with Nanoadsorbent Derived from Oil Palm Frond for CO<sub>2</sub>/CH<sub>4</sub> Separation

Membrane technology has attracted significant attention from the researchers, especially in gas separation process due to their simple process design and low capital cost compared to conventional techniques. In this work, oil palm frond (OPF) waste was used as nanoadsorbent embodied in polyether block amide (Pebax 1657) nanocomposite membrane to improve the CO2/CH4 separation. The effectiveness of the nanoadsorbent derived from OPF was evaluated by varying the nanoadsorbent concentration (2–8 wt %) and controlling the Pebax 1657 concentration (5 wt %), dipping time (5 s), and number of sequential coatings (3 layers). The pore characteristics of the nanoadsorbent was analyzed using Brunauer–Emmett–Teller (BET) analysis. The morphology and the existence of active groups in the newly synthesized nanoadsorbent and nanocomposite membranes were investigated using field emission scanning electron microscopy (FESEM) and Fourier transform infrared spectroscopy (FTIR), respectively. The single gas permeation process was carried out at constant pressure (2 bar) and room temperature (25 ± 5 °C). The optimum condition with 5 wt % nanoadsorbent made the nanocomposite membrane exceeded the trade-off limit of the Robeson plot with a CO2 permeability and CO2/CH4 selectivity of 1475.09 Barrer and 40.48, respectively.

Novel PVA/PEG nano-composite membranes tethered with surface engineered multi-walled carbon nanotubes for carbon dioxide separation

Abstract Cross-linked polyvinyl alcohol/polyethylene glycol membranes tethered with surface engineered multi-walled carbon nanotubes (SE-MWCNTs) were prepared and characterized by FT-IR, TGA, SEM, DMA and AFM analysis. The membranes were then analyzed for permeation testing with CO2, methane and nitrogen gases. 0.5 wt. % SE-MWCNT tethered membrane was proved to be the best performing membrane. Effect of feed gas pressure was also studied for the best performing membrane in order to check the effect of plasticization. It has been found that the gas permeation properties decrease slightly by increasing pressure up to 20 bar which is an indication that the membrane does not suffer from plasticization at high pressure. The long term stability of the best performing membrane was checked by giving it exposure to each gas at 20 bar for 96 h and taking the permeation readings after every 12 h. The best performing membrane was then tested at high pressure under mixed gas conditions (50:50) as well. Finally, the gas permeation results were plotted on 2008 Robeson plot and was found that 0.5 wt. % SE-MWCNT tethered membrane crossed the trade-off lines for both CO2/N2 and CO2/CH4 separation under pure as well as mixed gas conditions at high pressure.

Cellulose-Based Carbon Molecular Sieve Membranes for Gas Separation: A Review

In the field of gas separation and purification, membrane technologies compete with conventional purification processes on the basis of technical, economic and environmental factors. In this context, there is a growing interest in the development of carbon molecular sieve membranes (CMSM) due to their higher permeability and selectivity and higher stability in corrosive and high temperature environments. However, the industrial use of CMSM has been thus far hindered mostly by their relative instability in the presence of water vapor, present in a large number of process streams, as well as by the high cost of polymeric precursors such as polyimide. In this context, cellulosic precursors appear as very promising alternatives, especially targeting the production of CMSM for the separation of O2/N2 and CO2/CH4. For these two gas separations, cellulose-based CMSM have demonstrated performances well above the Robeson upper bound and above the performance of CMSM based on other polymeric precursors. Furthermore, cellulose is an inexpensive bio-renewable feed-stock highly abundant on Earth. This article reviews the major fabrication aspects of cellulose-based CMSM. Additionally, this article suggests a new tool to characterize the membrane performance, the Robeson Index. The Robeson Index, θ, is the ratio between the actual selectivity at the Robeson plot and the corresponding selectivity—for the same permeability—of the Robeson upper bound; the Robeson Index measures how far the actual point is from the upper bound.

Upgrading biogas with novel composite carbon molecular sieve (CCMS) membranes: Experimental and techno-economic assessment

The use of biogas as feedstock for hydrogen production was widely proposed in the literature in the last years as a strategy to reduce anthropogenic carbon emissions. However, its lower heating value compared to natural gas hampers the revamping of existing reforming plants. The use of composite carbon molecular sieve membranes for biogas upgrading (CO2 removal from biogas) was investigated experimentally in this work. In particular, ideal perm-selectivities and permeabilities above the Robeson plot for CO2/CH4 mixtures have been obtained. These membranes show better performances compared to polymeric membranes, which are nowadays commercialized for CO2 separation in natural gas streams. Compared to polymeric membranes, carbon membranes do not show deactivation by plasticization when exposed to CO2, and thus can find industrial application. This work was extended with a techno-economic analysis where carbon membranes are installed in a steam methane reforming plant. Results have been first validated with data from literature and show that the use of biogas increases the costs of hydrogen production to a value of 0.25 €/Nm3 compared to the benchmark technology (0.21 €/Nm3). On the other hand, the use of biogas leads to a decrease in carbon emissions up to 95%, thus the use of biogas for hydrogen production is foreseen as a very interesting alternative to conventional technologies in view of the reduction in the carbon footprint in the novel technologies that are to be installed in the near future.

Silica supported SAPO-34 membranes for CO2/N2 separation

Abstract In this work, SAPO-34 membrane was successfully synthesized on silica support by an optimized secondary growth method which combines ageing and rubbing with the use of enhanced synthesis gel. The enhanced synthesis gel was prepared by the addition of SAPO-34 crystals into the synthesis gel. Results of XRD and IR-ATR analysis of SAPO-34 seeds confirmed the formation of SAPO-34 crystal. SEM analysis showed that the crystal has cubic form and the size was about 200–400 nm. The resultant crystals were then used for the preparation of SAPO-34 membrane on the inner surface of the tubular silica support. XRD and XRF analysis showed that SAPO-34 layer was successfully formed on the membrane support with Si/Al ratio of 0.48–0.49. SEM images showed that the optimized secondary growth method could produce continuous and defect-free SAPO-34 membrane (SAPO-34-M2). In contrast, membrane prepared by rubbing method with conventional synthesis gel (SAPO-34-M1) displayed discontinued and defects layer. In single-gas permeation test, SAPO-34-M2 membrane showed two regions of N2 flux indicating the drastic effect of concentration polarization on N2 permeation at higher pressure. The concentration polarization phenomenon resulted in a decrease of CO2/N2 selectivity with increasing transmembrane pressure. It was demonstrated by single-gas permeation test that the SAPO-34-M2 membrane could surpass the Robeson plot (2008) for CO2/N2 separation (permeance = 2.01 × 10−6 mol/m2 s Pa; the highest selectivity = 53). The results showed that the prepared SAPO-34 membrane could be an alternative for CO2/N2 separation.

Top-Down Polyelectrolytes for Membrane-Based Post-Combustion CO2 Capture.

Polymer-based CO2 selective membranes offer an energy efficient method to separate CO2 from flue gas. ‘Top-down’ polyelectrolytes represent a particularly interesting class of polymer materials based on their vast synthetic flexibility, tuneable interaction with gas molecules, ease of processability into thin films, and commercial availability of precursors. Recent developments in their synthesis and processing are reviewed herein. The four main groups of post-synthetically modified polyelectrolytes discern ionised neutral polymers, cation and anion functionalised polymers, and methacrylate-derived polyelectrolytes. These polyelectrolytes differentiate according to the origin and chemical structure of the precursor polymer. Polyelectrolytes are mostly processed into thin-film composite (TFC) membranes using physical and chemical layer deposition techniques such as solvent-casting, Langmuir-Blodgett, Layer-by-Layer, and chemical grafting. While solvent-casting allows manufacturing commercially competitive TFC membranes, other methods should still mature to become cost-efficient for large-scale application. Many post-synthetically modified polyelectrolytes exhibit outstanding selectivity for CO2 and some overcome the Robeson plot for CO2/N2 separation. However, their CO2 permeance remain low with only grafted and solvent-casted films being able to approach the industrially relevant performance parameters. The development of polyelectrolyte-based membranes for CO2 separation should direct further efforts at promoting the CO2 transport rates while maintaining high selectivities with additional emphasis on environmentally sourced precursor polymers.

Transport Properties of Thermoplastic R-BAPB Polyimide: Molecular Dynamics Simulations and Experiment.

The present work evaluates the transport properties of thermoplastic R-BAPB polyimide based on 1,3-bis(3,3′,4,4′-dicarboxyphenoxy)benzene (dianhydride R) and 4,4′-bis(4-aminophenoxy)biphenyl (diamine BAPB). Both experimental studies and molecular dynamics simulations were applied to estimate the diffusion coefficients and solubilities of various gases, such as helium (He), oxygen (O2), nitrogen (N2), and methane (CH4). The validity of the results obtained was confirmed by studying the correlation of the experimental solubilities and diffusion coefficients of He, O2, and N2 in R-BAPB, with their critical temperatures and the effective sizes of the gas molecules, respectively. The solubilities obtained in the molecular dynamics simulations are in good quantitative agreement with the experimental data. A good qualitative relationship between the simulation results and the experimental data is also observed when comparing the diffusion coefficients of the gases. Analysis of the Robeson plots shows that R-BAPB has high selectivity for He, N2, and CO2 separation from CH4, which makes it a promising polymer for developing gas-separation membranes. From this point of view, the simulation models developed and validated in the present work may be put to effective use for further investigations into the transport properties of R-BAPB polyimide and nanocomposites based on it.

Evaluating graphene oxide and holey graphene oxide membrane performance for water purification

Graphene oxide (GO) membranes have demonstrated desirable performance for purifying water, matching or exceeding the ion rejection and water flux properties of reverse osmosis (RO) membranes. Though previous methods (e.g., surface decoration and d-space tuning) have been investigated to improve GO membranes, thermal treatment can induce the formation of holes in GO nanosheets in a controlled manner. The resulting holey-GO (hGO) membranes are hypothesized to have improved water permeability via decreasing the path-length that water molecules must travel through the membrane; specifically, through cross-sheet junctions, which is currently one of the main bottlenecks in other GO membranes. GO and hGO membranes with varying thicknesses were fabricated on polycarbonate supports and evaluated with ion transport tests in a diffusion cell via permeate conductivity. Permeability tests were conducted using a dead-end filtration cell (0.27 MPa–0.48 MPa). Produced hGO membranes demonstrated up to 3.8 times higher permeability relative to GO membranes, despite being up to 4 times thicker. Additionally, the empirical upper bound for a modified Robeson plot measuring permeability and selectivity was exceeded by both GO and hGO membranes demonstrated in this work.

Chilled membranes—Efficient gas permeation at sub-ambient temperatures

Thousands of polymers have been synthesized to produce membranes for gas permeation. Currently, their potential as a viable material is often bench-marked in the so-called Robeson plot. This plot gives a first impression of the transport properties at ideal low pressure conditions and ambient temperature. However, these data are of limited significance as they do not represent realistic process conditions.Here, we present a new methodology which allows a more comprehensive judgment of membrane transport properties based on their influence on overall processing costs. In particular, we apply this methodology to the question whether the materials discovered so far offer benefits when applied at sub-ambient temperatures. For a variety of applications, this rigorous approach proves that for certain materials the overall process costs can be minimized by applying sub-ambient process conditions. It also emphasizes that temperature-dependent permeation data is important to be reported for new materials.