Membranes For CO2 Separation Research Articles

Multi-Functional Polymer Membranes Enable Integrated CO2 Capture and Conversion in a Single, Continuous-Flow Membrane Reactor under Mild Conditions.

Herein, we present a membrane-based system designed to capture CO2 from dilute mixtures and convert the captured CO2 into value-added products in a single integrated process operated continuously under mild conditions. Specifically, we demonstrate that quaternized poly(4-vinylpyridine) (P4VP) membranes are selective CO2 separation membranes that are also catalytically active for cyclic carbonate synthesis from the cycloaddition of CO2 to epichlorohydrin. We further demonstrate that quaternized P4VP membranes can integrate CO2 capture, including from dilute mixtures down to 0.1 kPa of CO2, with CO2 conversion to cyclic carbonates at 57 °C and atmospheric pressure. The catalytic membrane acts as both the CO2 capture and conversion medium, providing an energy-efficient alternative to sorbent-based capture, compression, transport, and storage. The membrane is also potentially tunable for the conversion of CO2 to a variety of products, including chemicals and fuels not limited to cyclic carbonates, which would be a transformative shift in carbon capture and utilization technology.

Constructing polymer/metal-organic framework nanohybrids to design compatible polymer-filler-polymer membranes for CO2 separation

Membrane technology is energy-saving and environmentally friendly for gas separation. Mixed matrix membranes containing filler-polymer two components and adjusted transport pathways are promising for carbon capture. However, weak filler-polymer interfacial interaction and filler agglomeration usually cause defect formation and performance deterioration. In this study, we report a concept of polymer-filler-polymer membranes for efficient CO2 separation, highlighted by polymer of intrinsic microporosity (PIM)-metal-organic framework (MOF)-PIM combination. Key point is that the membrane systems consist of polymer matrices, MOFs as fillers for membranes and as hosts for inserted polymers, and polymer guests in MOFs. With partial functionalization of PIM to generate linker-analogous segments and retain unmodified sections, the PIM derivative chains can be uniformly coordinated in MOF nanohybrids and service as interfacial binders to enhance filler-polymer compatibility and filler dispersibility. Meanwhile, the PIM incorporation can regulate the morphologies and inner channels of MOF nanohybrids. For CO2/N2 separation, the polymer-filler-polymer membranes exhibit substantially improved permeability of 9532 Barrer, selectivity of 63.2, and antiaging property. We envisage that this concept reported here provides an alternative route to design compatible and high-performance membranes and other composites for separations and other applications.

Pilot-scale fabrication, separation performance and field test of tubular SSZ-13 membranes for efficient CO2 separation

Large-area SSZ-13 membranes were reproducibly prepared on 50-cm-long commercial and alumina tubes by secondary growth. Separation performance of the long membranes were higher than that of most small-area membranes. The effects of operation parameters such as pressure, temperature, feed flow rate and CO2 concentration on the separation performance of membranes were investigated. A mathematic model for concentration polarization index was established to evaluate the extent of concentration polarization in the single-tube and the muti-module test. A separation system with four single-tube modules connected in series was applied to field test of real biogas. The biogas could be purified to pipeline-grade natural gas (>98 mol%) by this small system at feed flow rate of 12 standard liter per minute at 1.4 MPa pressure drop. The membrane displayed long-term stability in the wet and dry biogas. This work has made an important progress toward the industrialization of zeolite membranes for gas separation.

High CO2 adsorption of ultra-small Zr-MOF nanocrystals synthesized by modulation method boosts the CO2/CH4 separation performance of mixed-matrix membranes

The separation performance of mixed matrix membranes (MMMs) is greatly impacted by both the inherent structure of porous fillers and the interfacial compatibility between the filler and matrix. Here, ultra-small Zr-MOFs (UiO-66-mod and NH2-UiO-66-mod) with more defect sites were synthesized through a simple sodium formate modulation strategy. Then, these modulated Zr-MOFs were used as porous fillers in combination with polyetherimide (PEI) to construct a high-quality mixed matrix membrane for efficient CO2 separation. The modulated Zr-MOF not only exposed more defect sites, which significantly enhanced the CO2 adsorption capacity but also exhibited high dispersion in the PEI matrix due to strong interfacial forces, avoiding non-selective voids. The 10-UiO-66-mod-PEI and 10-NH2-UiO-66-mod-PEI membranes developed here showed admirable CO2/CH4 separation performance (CO2 permeability of around 400 and 440 Barrer, CO2/CH4 selectivity of ∼33 and ∼47, respectively) much higher than that of non-modulated UiO-66-PEI membranes, surpassing the 2008 upper bound of MMMs. This work demonstrated that the proposed UiO-66-mod-PEI and NH2-UiO-66-mod-PEI MMMs could be potential candidates for an efficient CO2 capture process.

Mixed matrix membrane with amorphous metal-based complexes displays high CO2 separation performance

Design and exploration of advanced nanofillers that can be highly compatible with the existing polymeric membrane materials remain a subject of future study for mixed matrix membranes for gas separation. In this study, we propose the use of the newly synthesized metal-based complex (Zn-SiF6-py) as a promising filler to prepare high-performance PIM-1 based mixed matrix membranes for efficient CO2 separation. Results demonstrated that the as-synthesized Zn-SiF6-py features an amorphous mesoporous structure, and the inclusion of Zn-SiF6-py in the PIM-1 matrix can concurrently elevate the CO2 permeability and CO2/N2 selectivity. The significant improvements in membrane separation performance can be ascribed to the combined effects of additional gas transport channels and abundant active sites to CO2 molecules provided by Zn-SiF6-py fillers as well as a rigidified polymer region at the filler/matrix interface. Consequently, the optimized mixed matrix membrane at only 5 wt% filler loading achieves a CO2 permeability of 6268 Barrer and a CO2/N2 selectivity of 26.3, surpassing the 2008 Robeson upper bound.

Constructing double-faced CO2-capture domains by sandwich-like fillers in membranes for efficient CO2 separation

The sandwich-like composites were used as fillers, and prepared MMMs for effective CO2 separation by incorporating them into Pebax matrix. Zeolite imidazolate framework-8 (ZIF-8) was grown on two faces of a 2D amino-functionalized Al-metal organic framework (NH2-MIL-53(Al)) to fabricate the sandwich-like ZIF-8/NH2-MIL-53(Al) (ZM). Wherein, ZIF-8 in ZM was long-range ordered because ZIF-8 was evenly distributed throughout the double faces of NH2-MIL-53(Al). And the long-range ordered ZIF-8 constructed double-faced CO2-capture domains to quickly enrich CO2, contributing to improving CO2/CH4 selectivity of MMMs. The introduced NH2-MIL-53(Al) can endow MMMs with the increased CO2 permeability of MMMs. Therefore, the excellent CO2 separation performance was shown by using Pebax/ZM MMMs. The best CO2 separation performance was exhibited in Pebax/ZM MMM with the loading of 6 wt% ZIF-8/NH2-MIL-53(Al), which had a CO2 permeability of 488 ± 9 Barrer and a CO2/CH4 selectivity of 37.5 ± 0.6. It suggests that an efficient method for CO2 separation is the introduction of fillers that resemble sandwiches.

Defect-free PEO membrane fabrication by hydrogen bonding coupling thermal annealing for carbon capture

Reduction of CO2 emission is an urgent global demand to deal with the current extreme climate and ecosystem destruction. Polyethylene oxide (PEO) is an ideal material for CO2 separation membranes, because of its moderate affinity for CO2. However, due to its high tendency of crystallization, the mass transfer of CO2 is significantly hampered, resulting in poor separation performance. This study proposed of employment of trehalose as the filler to PEO membrane with subsequent thermal annealing, that is hydrogen-bond suppression crystallization coupling thermal annealing healing defects strategy, to simultaneously enhance the gas transport and selectivity. The trehalose plays the role of suppressing PEO crystallization while thermal annealing charges for healing defects. Consequently, the optimized trehalose-loaded PEO membrane exhibits a CO2 permeability of 117 Barrer and an ideal CO2/N2 selectivity of 51, which is superior to the pure PEO membrane. Moreover, the membrane offers merits of anti-plasticization feature and long-term running stability.

Integrating two-dimensional MXene fillers into nanocellulose for the fabrication of CO2 separation membranes

To achieve high capability mixed matrix membranes for CO2 separation, it is vital to construct the suitable transport channels to enhance the diffusivity-enabled selectivity as well as an excellent affinity toward target gas molecules to increase the solubility-based selectivity. Herein, composite membranes were constructed by integrating two-dimensional MXene nanosheets into a carboxylated nanocellulose matrix. The carboxyl-rich cellulose interacts with the surface groups of MXene, which contributes to a superior interface compatibility and repairs the non-selective voids. In particular, one-dimensional nanocellulose can intercalate into MXene laminates to regulate the interlayer spacing and suppress the re-stacking of MXenes. The resulting MC-3 membrane (with a MXene loading of 15.4 wt%) possesses the optimal separation performance, bearing a CO2 permeability of 156.7 Barrer with ideal selectivities of 47.8 for CO2/CH4 and 42.6 for CO2/N2. For the mixed gas separation, the MC-3 membrane exhibits separation factors of 48.5 and 55.3 for CO2/N2 and CO2/CH4, respectively. This excellent separation performance is resulted from the enhanced interfacial property, suitable MXene channel size and good CO2-solubility of nanocellulose.

Environmental Impact Improvement of Chitosan‐Based Mixed‐Matrix Membranes Manufacture for CO2 Gas Separation by Life Cycle Assessment

AbstractThe environmental impacts of the manufacture of chitosan (CS) and polymeric poly(1‐trimethylsilyl‐1‐propyne) (PTMSP) mixed‐matrix membranes (MMMs) for CO2 separation by life cycle assessment (LCA) are compared. An ionic liquid of non‐reported toxicity is used in CS membranes to enhance the mechanical strength, and different fillers are used to increase mechanical and functional properties: ETS‐10, ZIF‐8, HKUST‐1, and Zeolite A. Results with the same CO2 permeation flux indicate that ETS‐10/IL‐CS is the membrane manufacture with highest impacts due to its lower permeability. When comparing impacts with same permeation areas, the polymeric one is the membrane with highest impacts. Biopolymer and polymer manufacture are the components with highest contribution to the total environmental impacts of each membrane. To decrease all their impacts below fossil polymer membrane for the same CO2 permeation flux, CS membranes permeabilities should be improved by a numerical factor of 1000, 100, and 2 for the ETS‐10, ZIF‐8, and HKUST‐1/IL‐CS MMMs, respectively.

Imperfect perfection: Selective induction of CO2 during diffusion in mixed matrix membranes

Metal-organic frameworks (MOFs) are one of the optimal choice to be endowed for designing high-performance CO2 separation membranes as the fillers, ascribing their unprecedented tunability and chemical functionalities. However, while pursuing more types of MOFs, researchers have slightly explored their inherent properties. Thus, we incorporated missing-linker defects into Zirconium Metal−Organic Framework for tailoring the superior CO2 transport channel through tune their microporosity. And a series of defect-engineered UiO-66 (UiO-AcOH) fillers were synthesized and mingled into PIM-based matrix with large free volume. Resistance model simulations and gas permeation tests confirmed that the defective UiO-66 can greatly improved the competitive adsorption of the dispersed phase in Mixed Matrix Membranes (MMMs), offering more degree of freedom for the transportation of CO2. At the optimal ratio, the CO2 permeability of the UiO-AcOH-1.4/PIM-15 wt% MMMs increased nearly 3.5 times (CO2 =11261 Barrer, and the CO2/N2 selectivity is 26, almost increasing 23% contrasted pure film. Moreover, MMMs possess excellent long-term working stability and anti-aging properties, showing excellent gas separation performance.

Studies on application of Petcoke-based graphene membranes for CO2 separation

ABSTRACT Graphene-based separation membranes exhibit high separation potential to separate ions and molecules by the interlayer spacing with high surface area, porosity and tunable nanosized channels. The large-scale manufacturing of graphene-based membranes for gas separation is limited and challenging. Deposition of uniform, and selective ultrathin films as membrane is a big challenge for scalable separation with existing methods. In present study, solvent-ink-jet printing technique is applied for dispersing and uniform coating of graphene layers onto the membrane support. Preparation of graphene-based ink is the core objective of the operation for evaluating stability, coating and followed by separation studies. As prepared, graphene ink is filled in the cartridge of HP Desk-Jet-1110 series, which is available and slightly modified for the printing on the RO-membrane as support. The prepared membranes are characterized and analyzed for gas separation performance study. The decrease in gas composition of CO2 in permeate is observed and around 93% ± 0.5 of CO2 is separated from the gaseous mixtures.

Polyaniline-grafted Cu-MOFs via coordination-driven strategy constructs facilitated transport hybrid membrane for CO2 separation

MOFs-based facilitated transport hybrid membranes (FTHMs) have shown their great potential in CO2-selective gas separation. However, rational membrane fabrication by distributing evenly and introducing functional groups in MOFs-based facilitated transport hybrid membrane is crucial but challenging. We herein report a facile coordination-driven approach to realize the integration of polyaniline (PANI) grafted Cu-MOFs onto a polymeric matrix through Cu(II)-N coordination interaction. The resulting facilitated membrane exhibited synergetic channels to process CO2-facilitated transport due to the CO2-philic nature of PANI and MOFs with low-density pore blockage observed. The even distribution of well-dispersed MOFs nanoparticles upon PANI is realized through coordination interaction between the metal center and amino and imine groups in PANI. Moreover, PANI is highly compatible with the polymeric matrix by forming hydrogen bonds, as verified by experimental characterization and molecular dynamics (MD) simulations. The resulting FTHMs exhibit a simultaneous enhancement of individual-gas permeance (676.6 GPU) and CO2/N2 ideal selectivity (28.3), as well as enhanced decomposition temperature up to 474 °C and lasting sustainability over 72 days (1728 h). The coordination-driven membrane fabrication paves a new and promising way for designing stable, uniform, and longevity FTHMs, thus offering a potential facile route to fabricate high-performance FTHMs for CO2/N2 separation.

Highly concentrated multivariate ZIF-8 mixed-matrix hollow fiber membranes for CO2 separation: Scalable fabrication and process analysis

Here, we report on the fabrication of mixed matrix hollow fiber membranes (MMHFMs) for CO2 separation using highly-concentrated 6FDA-DAM/triple-ligand, amine-modulated zeolitic imidazolate framework-8 (TAZIF-8) (60/40 w/w) via a dip coating process. The application of a γ-alumina interlayer serves a dual purpose of reducing the infiltration of the 6FDA-/TAZIF-8 coating solution into the porous α-alumina support, while also providing a smooth surface for the support. Importantly, the co-solvent comprising N-methyl-2-pyrrolidone and dichloromethane further inhibits the formation of defects by maintaining an appropriate balance of volatility and polarity. This balanced combination is crucial in promoting phase separation and facilitating the dispersion of nanofillers within the polymer matrix, enabling the formation of a thin defect-free selective layer. The subsequent 40 wt% TAZIF-8 MMHFM attains superior CO2 separation performance to most existing MMHFMs (CO2 permeance of 648 GPU and CO2/N2 and CO2/CH4 selectivity of 39.0 and 34.2, respectively). Furthermore, it maintains excellent CO2 separation performance over 120 d owing to good interfacial interaction between 6FDA-DAM and TAZIF-8s. Last, but not least, our process analysis reveals that the introduction of the TAZIF-8 MMHFM into the first stage of a dual-stage membrane process can improve the total energy demand for post-combustion CO2 capture due to its excellent CO2/N2 selectivity. Our current study provides significant progress toward the industrial application of post-combustion CO2 capture.

Selective CO2 permeation properties of a membrane composed of a three-component polymer blend and cesium carbonate

ABSTRACT A high-performance CO2 separation membrane was fabricated using a composite polymer composed of a crosslinked acrylic acid polymer sodium salt, sodium polyacrylate, polyvinyl alcohol, and cesium carbonate. Evaluation tests were conducted by varying the relative humidity (RH), temperature, total pressure (Ptotal), and CO2 partial pressure (PCO2) to determine optimal parameters for enhanced performance in selective CO2 permeation over He. The membrane shows a high separation performance and durability at 50% RH and 85°C, where the CO2/He selectivity exceeds 550 under conditions of Ptotal:0.1 MPa and PCO2:0.08 MPa. Furthermore, the operational stability of the membrane was evaluated at 85°C, 50% RH, Ptotal:0.7 MPa, and PCO2:0.56 MPa. The as-fabricated membrane was stable for 300 h of continuous operation in the separation performance evaluation test. The findings of this study suggest that the developed membranes can be applied for CO2 separation from gas mixtures such as CO2/H2 with high efficiency and stability.

Pre-anchoring matrix onto zeolitic imidazolate frameworks towards defect-free mixed matrix membranes for efficient CO2 separation

Combined with the specific advantages of continuous polymer phase and dispersed filler phase, mixed matrix membranes (MMMs) possess the potential to serve as the next generation membrane materials. However, the further development of MMMs is hindered by a variety of challenges, such as the structural stability of fillers during processing, the homogeneity during the dispersion, the non-ideal interfacial morphology between matrix and filler. In this work, a strategy for pre-anchoring polymeric matrices to fillers was proposed, the amino group was introduced to ZIF-8 framework (ZIF-8-NH2) by mixed ligand method based on the principles of reticular chemistry, and the ZPX fillers were fabricated by pre-anchored Pebax onto the ZIF-8-NH2, the unique ZIF-8/pre-anchored Pebax/Pebax interfacial structure was fabricated. The as-prepared Pebax/ZPX-5(10) MMMs exhibited a competitive performance in CO2 capture: high CO2 permeability for 146.4 Barrer, excellent CO2/N2 selectivity for 88.3, which improved by 269.1% and 187.1% respectively, compared with Peabx membrane, the index of filler enhancement (Findex) was 2.79, and the Robeson upper bound (2008) was successfully surpassed. Our pre-anchoring strategy provided an alternative answer for the facile fabrication of voids-free MMMs.

Construction of high-performance thin-film composite membrane for CO2 separation via interface engineering

High-efficiency CO2 capture has become increasingly vital for alleviating the ongoing global temperature which leads to severe impacts on virtually every aspect of human life. Thin-film composite membranes (TFCM) have attracted growing attention for conducting CO2 capture, owning to their energy-efficient and environment-friendly merits. However, the nonideal interface between the gutter layer and the separation layer hampers the fabrication of defect-free and thin separation layer, which renders low separation performance. In this work, we developed a strategy, i.e., coupling the oxygen-plasma modification with spin-coating, for engineering the interface between the gutter layer and separation layer of TFCM. Leveraging this idea, the TFC membrane, consisting polydimethylsiloxane (PDMS) served as the gutter layer and poly (ether-block-amide) (PEBA) as the thin separation layer, was manufactured by conveniently spin-coating PEBA solution on the oxygen-plasma-treated PDMS layer. The optimized PEBA-based TFCM membrane realized superior separation performance, e.g., a CO2 permeance of 2011 GPU, a CO2/N2 selectivity of 24, and 100-hour stably running, which outperformed most of the reported PEBA-based TFCM. Thus, the interface engineering strategy proposed in this study opens a new door for rational fabrication of high-performance TFCM.

Sodium dodecyl sulfate coated-polystyrene nanobeads for polymer composite membrane

In this study, sodium dodecyl sulfate coated-polystyrene nanobeads were used as a carrier for CO2 separation membrane. Polystyrene nanobeads were prepared via emulsion polymerization and the surface potential of the particles remained unchanged, and the average value was −28 mV during the eight repeated measurements, indicating that the electrostatic dispersion stability of the SDS-PS NBs is very high. When sodium dodecyl sulfate coated-polystyrene nanobeads are incorporated into the polymeric composite membrane for CO2/N2 separation, these membranes surprisingly showed a selectivity of 252. In comparison with the neat PVP membrane, the separation performance was largely improved due to the interaction between polar CO2 molecules and polystyrene nanobeads to have −28 mV surface potential. FT-IR spectra shows the polystyrene nanobeads could weaken the carbonyl bond and caused the free volume to be abundant for N2 gas permeation. As a result, highly selective PVP/PS colloid composite membrane is successfully prepared for CO2 molecules, and the thermal stability was confirmed by TGA analysis.

Constructing mixed matrix membranes for CO2 separation based on light lanthanide fluoride nanosheets with mesoporous structure

The incorporation of porous nano-fillers into mixed matrix membranes (MMMs) has a great impact on CO2 separation. In this study, a series of F-Ln (Ln is the Light Lanthanide, Ln = La, Ce, Pr, Nd) nanosheets with mesoporous structure was fabricated as a filler in Pebax®1657 matrix to improve the performance of CO2 separation. F-Ln nanosheets are uniformly distributed in the membrane and the mesoporous structure can construct multiple channels for CO2 fast transport in Pebax/F-Ln MMMs. The pore diameter of nanosheet is in order: F-La > F-Ce > F-Pr > F-Nd, and the smaller pore diameter of nanosheets is beneficial to improve the CO2 separation performance. In humidified conditions, Pebax/F-Nd-6 MMMs show optimum separation performance among MMMs, and the CO2 permeability is up to 1265 Barrer and CO2/CH4 selectivity is 36.7, which are 2.3 times and 1.9 times higher than pure Pebax and approaches 2019 upper bound. Meanwhile, to demonstrate the potential universal applicability of F-Ln nanosheets in CO2 separation, XLPEO/F-Ce MMMs were fabricated to separate CO2/N2 and the performance exceeds the 2019 upper bound. The efficient CO2 separation performance of 2D F-Ln nanosheets with mesoporous structure in membranes reveals the potential application of these nanosheets in industrial CO2 separation.

The Influence of Polycation and Counter-Anion Nature on the Properties of Poly(ionic liquid)-Based Membranes for CO2 Separation.

The current investigation is focused on the development of composite membranes based on polymeric ionic liquids (PILs) containing imidazolium and pyridinium polycations with various counterions, including hexafluorophosphate, tetrafluoroborate, and bis(trifluoromethylsulfonyl)imide. A combination of spectroscopic methods was used to identify the synthesized PILs and characterize their interaction with carbon dioxide. The density and surface free energy of polymers were performed by wettability measurements, and the results are in good agreement with the permeability and selectivity obtained within the gas transport tests. It was shown that the membranes with a selective layer based on PILs exhibit relatively high permeability with CO2 and high ideal selectivity CO2/CH4 and CO2/N2. Additionally, it was found that the type of an anion significantly affects the performance of the obtained membranes, with the most pronounced effect from bis-triflimide-based polymers, showing the highest permeability coefficient. These results provide valuable insights into the design and optimization of PIL-based membranes for natural and flue gas treatment.

Covalent “Bridge-crosslinking” strategy constructs facilitated transport mixed matrix membranes for highly-efficient CO2 separation

Facilitated transport mixed matrix membranes (FTMMMs) separation technology has shown advantages in improving CO2 recycling efficiency and reducing the environmental impacts associated with carbon emission. The design of FTMMMs is highly dependent on the selection of a compatible combination of polymer and filler. Herein, a novel grafted nanoparticles (GNPs) filler UiO-66-NM@PEG with multiple groups prone to hydrogen bond was designed to alleviate the phase separation and performance degradation caused by filler/polymer poor compatibility. In the GNPs configuration, by employing the coexistence strategy of coupling reaction and covalent bonds, maleic anhydride (MAH) was coupled with the amino group on UiO-66-NH2 without clogging or cracking, and the generated carboxyl groups can be cross-linked with the hydroxyl groups on the poly (ethylene glycol) (PEG) by covalent bonds. The UiO-66-NM@PEG demonstrated excellent interface compatibility between the filler and matrix phase of UiO-66-NM@PEG/PVDF, which was further convinced by molecular modelling. The resultant UiO-66-NM@PEG/PVDF achieved a simultaneous enhancement of gas permeability (537.6 Barrer) and ideal CO2/N2 selectivity (47.8), which surpassed Robenson upper bound. Moreover, the UiO-66-NM@PEG/PVDF has a lasting sustainability over 960 h (40 days), and a valid anti-acid/alkali corrosion resistance in harsh environments. More importantly, UiO-66-NM@PEG can also be well mixed with other mixture matrices such as hydroxy-terminated polydimethylsiloxane (PDMS) and polyether-block-polyamide copolymer (PEBAX) to promote permeability/ideal selectivity up to (724.1 Barrer/21.1) and (307.4 Barrer/31.4). We thus concluded that this rational-design GNPs approach provides a general toolbox for controllable engineering in GNPs whereby enhanced favorable filler/matrix compatibility in FTMMMs with optimized CO2/N2 separation properties.