Enhancement of CO2 capture by polyethylene glycol-based polyurethane membranes

Application of poly(L-lactic acid)-based films for equilibrium modified atmosphere packaging of "Kyoho" grapes and its favorable protection for anthocyanins

Grapes were packaged by different Poly (L-lactic acid)-based packaging films (PLTL-PLEL) and stored at 5 °C for 35 days to investigate the effects of equilibrium modified atmosphere packaging on the quality of "Kyoho" grapes during storage. Changes in physiochemical quality, antioxidant content and senescence of grapes were studied. Furthermore, UPLC-Q-TOF-MS/MS was used to observe and identify key factors influencing the variation of grape anthocyanins under different atmosphere conditions. Alterations in gas components and enzyme activities significantly impacted anthocyanin levels, highlighting oxygen concentration as the primary influence on total anthocyanin levels. The PLTL-PLEL50 packaging resulted in an approximate 5.7% lower weight loss and increased soluble solids by approximately 14.4%, vitamin C, total phenols and flavonoids reaching 60.2 mg/100 g, 8.4 mg/100 g and 7.2 mg/100 g, respectively. This packaging also preserved higher anthocyanin levels, with malvidin-3-glucoside and peonidin-3-glucoside at 0.55 μg/mL and 1.62 μg/mL, respectively, on the 35th day of storage.

Enhancing CO2 Transport Across the PEG/PPG-Based Crosslinked Rubbery Polymer Membranes with a Sterically Bulky Carbazole-Based ROMP Comonomer

A series of poly(ethylene glycol)-block-poly(propylene glycol) (PEG/PPG)- and 5,6-di(9H-carbazol-9-yl)isoindoline-1,3-dione (2CZPImide)-based crosslinked rubbery polymer membranes, denoted as PEG/PPG-2CZPImide (x:y), are prepared from the norbornene-functionalized PEG/PPG oligomer (NB-PEG/PPG-NB) and 2-(bicyclo[2.2.1]hept-5-en-2-ylmethyl)-5,6-di(9H-carbazol-9-yl)isoindoline-1,3-dione (2CZPImide-NB) via ring-opening metathesis polymerization (ROMP). The molar ratio (x:y) of the NB-PEG/PPG-NB (x) to 2CZPImide-NB (y) monomers is varied from 10:1 to 6:1. X-ray diffraction (XRD), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), and pure gas permeability studies reveal that the comonomer 2CZPImide-NB successfully increases the d-spacing among the crystalline PEG/PPG segments, hence enhancing the diffusivity of gases through the membranes. The synthesized membranes exhibit good CO2 separation performance, with CO2 permeabilities ranging from 311.1 to 418.1 Barrer and CO2/N2 and CO2/CH4 selectivities of 39.4-52.0 and 13.4-16.0, respectively, approaching the 2008 Robeson upper bound. Moreover, PEG/PPG-2CZPImide (6:1), displaying optimal CO2 permeability and CO2/N2 and CO2/CH4 selectivities, shows long-term stability against physical aging and plasticization resistance up to 20 days and 10 atm, respectively.

Micro and Nanoporous Membrane Platforms for Carbon Neutrality: Membrane Gas Separation Prospects

Recently, carbon neutrality has been promoted as a potentially practical solution to global CO2 emissions and increasing energy-consumption challenges. Many attempts have been made to remove CO2 from the environment to address climate change and rising sea levels owing to anthropogenic CO2 emissions. Herein, membrane technology is proposed as a suitable solution for carbon neutrality. This review aims to comprehensively evaluate the currently available scientific research on membranes for carbon capture, focusing on innovative microporous material membranes used for CO2 separation and considering their material, chemical, and physical characteristics and permeability factors. Membranes from such materials comprise metal-organic frameworks, zeolites, silica, porous organic frameworks, and microporous polymers. The critical obstacles related to membrane design, growth, and CO2 capture and usage processes are summarized to establish novel membranes and strategies and accelerate their scaleup.

Amphiphilic triblock copolymer as the gas chromatographic stationary phase with high-resolution performance towards a wide range of isomers and the components of lemon essential oil

This work presents the investigation of using the amphiphilic triblock copolymer composed of poly(ethylene oxide)(PEO)-poly(propylene oxide) (PPO)-poly(ethylene oxide) (PEO) (denoted as EPE) as the stationary phase for gas chromatographic (GC) analyses. The EPE capillary column exhibited moderate polarity and column efficiency of 4348 plates/m determined by naphthalene at 120 °C (k = 11.52). Different from the PEG and polysiloxane homopolymers, it showed high-resolution performance towards a wide range of aliphatic and aromatic isomers in terms of polarity and acid-base properties. Particularly, the EPE column displayed distinct advantages for separating the critical isomers of alkanes, anilines and phenols and the components of the lemon essential oil over the commercial PEG and polysiloxane columns. In addition, the EPE column exhibited excellent separation repeatability and reproducibility with the relative standard deviation (RSD) values in the range of 0.03% - 0.08% for run-to-run, 0.14% - 0.61% for day-to-day and 3.1% - 4.0% for column-to-column, respectively. Moreover, the EPE column was investigated in terms of thermal stability, the minimum allowable operating temperature (MiAOT) and sample loadability. Its application to GC-MS analysis of the essential oil demonstrated its feasibility for practical analyses. This work demonstrates the promising future of triblock copolymers as a new class of selective stationary phases for GC analyses, which is barely reported up to date. The findings of this work is of important value for fundamental researches and practical applications.

The prospect of synthesis of PES/PEG blend membranes using blend NMP/DMF for CO2/N2 separation

Carbon dioxide (CO2) emissions have been the root cause for anthropogenic climate change. Decarbonisation strategies, particularly carbon capture and storage (CCS) are crucial for mitigating the risk of global warming. Among all current CO2 separation technologies, membrane separation has the biggest potential for CCS as it is inexpensive, highly efficient, and simple to operate. Polymeric membranes are the preferred choice for the gas separation industry due to simpler methods of fabrication and lower costs compared to inorganic or mixed matrix membranes (MMMs). However, plasticisation and upper-bound trade-off between selectivity and permeability has limited the gas separation performance of polymeric membranes. Recently, researchers have found that the blending of glassy and rubbery polymers can effectively minimise trade-off between selectivity and permeability. Glassy poly(ethersulfone) (PES) and rubbery poly(ethylene) glycol (PEG) are polymers that are known to have a high affinity towards CO2. In this paper, PEG and PES are reviewed as potential polymer blend that can yield a final membrane with high CO2 permeance and CO2/nitrogen (N2) selectivity. Gas separation properties can be enhanced by using different solvents in the phase-inversion process. N-Methyl-2-Pyrrolidone (NMP) and Dimethylformamide (DMF) are common industrial solvents used for membrane fabrication. Both NMP and DMF are reviewed as prospective solvent blend that can improve the morphology and separation properties of PES/PEG blend membranes due to their effects on the membrane structure which increases permeation as well as selectivity. Thus, a PES/PEG blend polymeric membrane fabricated using NMP and DMF solvents is believed to be a major prospect for CO2/N2 gas separation.

Influence of microstructural variations on morphology and separation properties of polybutadiene-based polyurethanes

Polybutadiene-based polyurethanes with different cis/trans/1,2-vinyl microstructure contents are synthesized. The phase morphology and physical properties of the polymers are investigated using spectroscopic analysis (FTIR and Raman), differential scanning calorimetry (DSC), X-ray scattering (WAXD and SAXS) and atomic force microscopy (AFM). In addition, their gas transport properties are determined for different gases at 4 bar and 25 °C. Thermodynamic incompatibility and steric hindrance of pendant groups are the dominant factors affecting the morphology and properties of the PUs. FTIR spectra, DSC, and SAXS analysis reveal a higher extent of phase mixing in high vinyl-content PUs. Moreover, the SAXS analysis and AFM phase images indicate smaller microdomains by increasing the vinyl content. Smaller permeable soft domains as well as the lower phase separation of the PUs with higher vinyl content create more tortuous pathways for gas molecules and deteriorate the gas permeability of the membranes.

Integration of Stable Ionic Liquid-Based Nanofluids into Polymer Membranes. Part I: Membrane Synthesis and Characterization

In this work, polymeric membranes functionalized with ionic liquids (ILs) and exfoliated graphene nanoplatelets (xGnP) were developed and characterized. These membranes based on graphene ionanofluids (IoNFs) are promising materials for gas separation. The stability of the selected IoNFs in the polymer membranes was determined by thermogravimetric analysis (TGA). The morphology of membranes was characterized using scanning electron microscope (SEM) and interferometric optical profilometry (WLOP). SEM results evidence that upon the small addition of xGnP into the IL-dominated environment, the interaction between IL and xGnP facilitates the migration of xGnP to the surface, while suppressing the interaction between IL and Pebax^®1657. Fourier transform infrared spectroscopy (FTIR) was also used to determine the polymer-IoNF interactions and the distribution of the IL in the polymer matrix. Finally, the thermodynamic properties and phase transitions (polymer-IoNF) of these functionalized membranes were studied using differential scanning calorimetry (DSC). This analysis showed a gradual decrease in the melting point of the polyamide (PA6) blocks with a decrease in the corresponding melting enthalpy and a complete disappearance of the crystallinity of the polyether (PEO) phase with increasing IL content. This evidences the high compatibility and good mixing of the polymer and the IoNF.

CO2 capture using membrane contactors: a systematic literature review

With fossil fuel being the major source of energy, CO2 emission levels need to be reduced to a minimal amount namely from anthropogenic sources. Energy consumption is expected to rise by 48% in the next 30 years, and global warming is becoming an alarming issue which needs to be addressed on a thorough technical basis. Nonetheless, exploring CO2 capture using membrane contactor technology has shown great potential to be applied and utilised by industry to deal with post- and pre-combustion of CO2. A systematic review of the literature has been conducted to analyse and assess CO2 removal using membrane contactors for capturing techniques in industrial processes. The review began with a total of 2650 papers, which were obtained from three major databases, and then were excluded down to a final number of 525 papers following a defined set of criteria. The results showed that the use of hollow fibre membranes have demonstrated popularity, as well as the use of amine solvents for CO2 removal. This current systematic review in CO2 removal and capture is an important milestone in the synthesis of up to date research with the potential to serve as a benchmark databank for further research in similar areas of work. This study provides the first systematic enquiry in the evidence to research further sustainable methods to capture and separate CO2.

PEG/PPG-PDMS-Adamantane-based Crosslinked Terpolymer Using the ROMP Technique to Prepare a Highly Permeable and CO2-Selective Polymer Membrane

In this study, precursor molecules based on PEG/PPG and polydimethylsiloxane (PDMS), both widely used rubbery polymers, were copolymerized with bulky adamantane into copolymer membranes. Ring-opening metathesis polymerization (ROMP) was employed during the polymerization process to create a structure with both ends crosslinked. The precursor molecules and corresponding polymer membranes were characterized using various analytical methods. The polymer membranes were fabricated using different compositions of PDMS and adamantane, to determine how the network structure affected their gas separation performance. PEG/PPG, in which CO2 is highly soluble, was copolymerized with PDMS, which has high permeability, and adamantane, which controlled the crosslinking density with a rigid and bulky structure. It was confirmed that the resulting crosslinked polymer membranes exhibited high solubility and diffusivity for CO2. Further, their crosslinked structure using ROMP technique made it possible to form good films. The membranes fabricated in the present study exhibited excellent performance, i.e., CO2 permeability of up to 514.5 Barrer and CO2/N2 selectivity of 50.9.

Pushing Rubbery Polymer Membranes To Be Economic for CO2 Separation: Embedment with Ti3C2Tx MXene Nanosheets

Sustainable and energy-efficient molecular separation requires membranes with high gas permeability and selectivity. This work reports excellent CO₂ separation performance of self-standing and thin-film mixed matrix membranes (MMMs) fabricated by embedding 2D Ti₃C₂T_x MXene nanosheets in Pebax-1657. The CO₂/N₂ and CO₂/H₂ separation performances of the free-standing membranes are above Robeson's upper bounds, and the performances of the thin-film composite (TFC) membranes are in the target area for cost-efficient CO₂ capture. Characterization and molecular dynamics simulation results suggest that the superior performances of the Pebax-Ti₃C₂T_x membranes are due to the formation of hydrogen bonds between Ti₃C₂T_x and Pebax chains, leading to the creation of the well-formed galleries of Ti₃C₂T_x nanosheets in the hard segments of the Pebax. The interfacial interactions and selective Ti₃C₂T_x nanochannels enable fast and selective CO₂ transport. Enhancement of the transport properties of Pebax-2533 and polyurethane when embedded with Ti₃C₂T_x further supports these findings. The ease of fabrication and high separation performance of the new TFC membranes point to their great potential for energy-efficient CO₂ separation with the low cost of $29/ton separated CO₂.

Maximizing Ether Oxygen Content in Polymers for Membrane CO2 Removal from Natural Gas

Membrane materials for CO₂ removal from natural gas are based on glassy polymers with a high CO₂/CH₄ diffusivity selectivity. However, these polymers suffer from competitive sorption by heavy hydrocarbons that decreases CO₂ permeability and physical aging that reduces gas permeability with time. We circumvent these issues by designing rubbery, solubility-selective polymers with a ratio of ether/ester oxygen to carbon as high as 0.8 through the use of 1,3-dioxolane and 1,3,5-trioxane. The ether/ester oxygen groups interact favorably with CO₂ but do not interact with CH₄, leading to a high CO₂/gas solubility selectivity that is unaffected by heavy hydrocarbons in the raw natural gas. These polar groups are incorporated in short branches to yield an amorphous and rubbery nature, leading to high gas permeability that is stable over time. A polymer with an O/C ratio of 0.71 (P71) shows a mixed-gas CO₂ permeability of 320 Barrers and a CO₂/CH₄ selectivity of 21 in the simulated natural gas at 50 °C, which is independent of the hexane content and above the upper bound for CO₂/CH₄ separation at 50 °C.

Penetrated COF Channels: Amino Environment and Suitable Size for CO2 Preferential Adsorption and Transport in Mixed Matrix Membranes

Developing mixed matrix membranes (MMMs) is challenging because the interface between different matrices often forms undesirable structures. Herein, we demonstrate a method of creating suitable CO₂-selective channels based on interface regulation that greatly enhances membrane separation performance. The poly(vinylamine), which also acts as a polymer matrix, was immobilized onto covalent organic frameworks (COFs) to obtain polymer-COF hybrid materials (COF_p). The COF_p and polymer matrix are highly compatible because they have the same segment. The polymer matrix was induced to penetrate the oversized COF_p, resulting in an amino-environmental pore wall and appropriately sized CO₂-selective channels dispersed in MMMs. The MMMs exhibited satisfactory membrane performance for CO₂/N₂, CO₂/CH₄, and CO₂/H₂ separation. A CO₂ transport model for preferential adsorption and transport is clearly presented for the first time. The membrane separation mechanism is also discussed. This work demonstrates potential applications for material, interface, and membrane investigations.

Tuning the Gas Selectivity of Tröger's Base Polyimide Membranes by Using Carboxylic Acid and Tertiary Base Interactions

Polyimide-based materials provide attractive chemistries for the development of gas-separation membranes. Modification of inter- and intra-chain interactions is a route to improve the separation performance. In this work, copolyimides with Tröger's base (TB) monomers are designed and synthesized. In particular, a series of copolyimides is synthesized with different contents of carboxylic acid groups (0-50 wt %) to alter the inter- and intra-chain interactions and enhance the basicity of the TB-polyimides. A detailed thermal and structural analysis is provided for the new copolyimides. Gas permeation data reveal a tunable trend in separation performance with increasing carboxylic acid group content. Importantly, this is one of the few examples of copolyimide membranes materials that show enhanced plasticization resistance to high-pressure gas feeds through physical cross-linking.

Pentiptycene-Based Polyurethane with Enhanced Mechanical Properties and CO2-Plasticization Resistance for Thin Film Gas Separation Membranes

The development of thin film composite (TFC) membranes offers an opportunity to achieve the permeability/selectivity requirements for optimum CO₂ separation performance. However, the durability and performance of thin film gas separation membranes are mostly challenged by weak mechanical properties and high CO₂ plasticization. Here, we designed new polyurethane (PU) structures with bulky aromatic chain extenders that afford preferred mechanical properties for ultra-thin-film formation. An improvement of about 1500% in Young's modulus and 600% in hardness was observed for pentiptycene-based PUs compared to the typical PU membranes. Single (CO₂, H₂, CH₄, and N₂) and mixed (CO₂/N₂ and CO₂/CH₄) gas permeability tests were performed on the PU membranes. The resulting TFC membranes showed a high CO₂ permeance up to 1400 GPU (10^-6 cm³(STP) cm^-2 s^-1 cmHg^-1) and the CO₂/N₂ and CO₂/H₂ selectivities of about 22 and 2.1, respectively. The enhanced mechanical properties of pentiptycene-based PUs result in high-performance thin membranes with the similar selectivity of the bulk polymer. The thin film membranes prepared from pentiptycene-based PUs also showed a twofold enhanced plasticization resistance compared to non-pentiptycene-containing PU membranes.

A facile synthesis of contorted spirobisindane-diamine and its microporous polyimides for gas separation

Microporous polyimides (PIM-PIs, KAUST-PIs) and polymers containing Tröger's base (TB) derivatives with improved permeability and selectivity have great importance for separation of environmental gas pairs. Despite the tremendous progress in this field, facile synthesis of microporous polymers at the industrial scale via designing new monomers is still lacking. In this study, a new potential approach for large scale synthesis of spirobisindane diamine (DAS) (3) has been reported from commercially available 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobisindane (TTSBI) and 3,4-difluoronitrobenzene. A series of DAS diamine based microporous polyimides were also synthesized. The resulting polymer membranes showed high mechanical and thermal properties with tunable gas separation performance.