Facile and solvent-free fabrication of PEG-based membranes with interpenetrating networks for CO2 separation

Tailoring the Structure-Property Relationship of Ring-Opened Metathesis Copolymers for CO2-Selective Membranes

In this work, we explore the use of ring-opening metathesis polymerization (ROMP) facilitated by a second-generation Grubbs catalyst (G2) for the development of advanced polymer membranes aimed at CO2 separation. By employing a novel copolymer blend incorporating 4,4'-oxidianiline (ODA), 1,6-hexanediamine (HDA), 1-adamantylamine (AA), and 3,6,9-trioxaundecylamine (TA), along with a CO2-selective poly(ethylene glycol)/poly(propylene glycol) copolymer (Jeffamine2003) and polydimethylsiloxane (PDMS) units, we have synthesized membranes under ambient conditions with exceptional CO2 separation capabilities. The strategic inclusion of PDMS, up to a 20% composition within the PEG/PPG matrix, has resulted in copolymer membranes that not only surpass the 2008 upper limit for CO2/N2 separation but also meet the commercial targets for CO2/H2 separation. Comprehensive analysis reveals that these membranes adhere to the mixing rule and exhibit percolation behavior across the entire range of compositions (0-100%), maintaining robust antiplasticization performance even under pressures up to 20 atm. Our findings underscore the potential of ROMP in creating precisely engineered membranes for efficient CO2 separation, paving the way for their application in large-scale environmental and industrial processes.

High-Loading Poly(ethylene glycol)-Blended Poly(acrylic acid) Membranes for CO2 Separation

Poly(ethylene glycol) (PEG) is an amorphous material of interest owing to its high CO₂ affinity and potential usage in CO₂ separation applications. However, amorphous PEG often has a low molecular weight, making it challenging to form into the membrane. The crystalline high average molar mass poly(ethylene oxide) (PEO) cannot exhibit CO₂ separation characteristics. Thus, it is crucial to employ low molecular weight PEG in high molecular weight polymers to increase the CO₂ affinity for CO₂ separation membranes. In this work, poly(acrylic acid) (PAA)/PEG blend membranes with a PEG-rich phase were simply fabricated by physical mixing with an ethanol solvent. The carbonyl group of the PAA and the hydroxyl group of the PEG formed a hydrogen bond. Furthermore, the thermal stability, glass transition temperature, and surface hydrophilicity of PAA/PEG blend membranes with various PEG concentrations were further characterized. The PAA/PEG(1:9) blend membrane exhibited an improved CO₂ permeability of 51 Barrer with high selectivities relative to the other gas species (H₂, N₂, and CH₄; CO₂/H₂ = 6, CO₂/N₂ = 63, CO₂/CH₄ = 21) at 35 °C and 150 psi owing to the enhanced CO₂ affinity with the amorphous PEG-rich phase. These PAA/PEG blend membrane permeation characteristics indicate a promising prospect for CO₂ capture applications.

CO2 Capture and Low-Temperature Release by Poly(aminoethyl methacrylate) and Derivatives

Poly(aminoethyl methacrylate) (PAEMA), poly(ethylene oxide)-block-(aminoethyl methacrylate) (PEO-PAEMA), and their guanidinylated derivates, poly(guanidine ethyl methacrylate) (PGEMA) and poly(ethylene oxide)-block-(guanidine ethyl methacrylate) (PEO-PGEMA), were prepared to study their capabilities for CO₂ adsorption and release. The polymers of different forms or degree of guanidinylation were thoroughly characterized, and their interaction with CO₂ was studied by NMR and calorimetry. The extent and kinetics of adsorption and desorption of N₂ and CO₂ were investigated by thermogravimetry under controlled gas atmospheres. The materials did not adsorb N₂, whereas CO₂ could be reversibly adsorbed at room temperature and released by an elevated temperature. The most promising polymer was PGEMA with a guanidinylation degree of 7% showing a CO₂ adsorption capacity of 2.4 mmol/g at room temperature and a desorption temperature of 72 °C. The study also revealed relations between the polymer chemical composition and CO₂ adsorption and release characteristics that are useful in future formulations for CO₂ adsorbent polymer materials.

An integrated materials approach to ultrapermeable and ultraselective CO2 polymer membranes

Advances in membrane technologies that combine greatly improved carbon dioxide (CO₂) separation efficacy with low costs, facile fabrication, feasible upscaling, and mechanical robustness are needed to help mitigate global climate change. We introduce a hybrid-integrated membrane strategy wherein a high-permeability thin film is chemically functionalized with a patchy CO₂-philic grafted chain surface layer. A high-solubility mechanism enriches the concentration of CO₂ in the surface layer hydrated by water vapor naturally present in target gas streams, followed by fast CO₂ transport through a highly permeable (but low-selectivity) polymer substrate. Analytical methods confirm the existence of an amine surface layer. Integrated multilayer membranes prepared in this way are not diffusion limited and retain much of their high CO₂ permeability, and their CO₂ selectivity is concurrently increased in some cases by more than ~150-fold.

Multicomponent Network Formation in Selective Layer of Composite Membrane for CO2 Separation

As a promising material for CO₂/N₂ separation, PolyActive^TM can be used as a separation layer in thin-film composite membranes (TFCM). Prior studies focused on the modification of PolyActive^TM using low-molecular-weight additives. In this study, the effect of chemical crosslinking of reactive end-groups containing additives, forming networks within selective layers of the TFCM, has been studied. In order to understand the influence of a network embedded into a polymer matrix on the properties of the resulting materials, various characterization methods, including Fourier transform infrared spectroscopy (FTIR), gas transport measurements, differential scanning calorimetry (DSC) and atomic force microscopy (AFM), were used. The characterization of the resulting membrane regarding individual gas permeances by an in-house built “pressure increase” facility revealed a twofold increase in CO₂ permeance, with insignificant losses in CO₂/N₂ selectivity.

PEG/PPG-PDMS-Based Cross-Linked Copolymer Membranes Prepared by ROMP and In Situ Membrane Casting for CO2 Separation: An Approach to Endow Rubbery Materials with Properties of Rigid Polymers

Rubbery polymer membranes prepared from CO₂-philic PEO and/or highly permeable PDMS are desired for efficient CO₂ separation from light gases (CH₄ and N₂). Poor mechanical properties and size-sieving ability, however, limit their application in gas separation applications. Cross-linked rubbery polymer-based gas separation membranes with a low T_g based on both PEG/PPG and PDMS units with various compositions between these two units are prepared for the first time in this work by ring-opening metathesis polymerization type cross-linking and in situ membrane casting. The developed membranes display excellent CO₂ separation performance with CO₂ permeability ranging from 301 to 561 Barrer with excellent CO₂/N₂ selectivity ranging from 50 to 59, overcoming the Robeson upper bound (2008). The key finding underlying the excellent performance of the newly developed cross-linked x(PEG/PPG:PDMS) membranes is the formation of a well-connected interlocked network structure, which endows the rubbery materials with the properties of rigid polymers, e.g., size-sieving ability and high thermomechanical stability. Moreover, the membrane shows long-term antiaging performance of up to eight months and antiplasticization behavior up to 25 atm pressure.