H2/CO2 separation enhancement via chemical modification of polybenzimidazole nanostructure

Carbon Dioxide Capture by Emerging Innovative Polymers: Status and Perspectives

A significant amount of research has been conducted in carbon dioxide (CO2) capture, particularly over the past decade, and continues to evolve. This review presents the most recent advancements in synthetic methodologies and CO2 capture capabilities of diverse polymer-based substances, which includes the amine-based polymers, porous organic polymers, and polymeric membranes, covering publications in the last 5 years (2019-2024). It aims to assist researchers with new insights and approaches to develop innovative polymer-based materials with improved capturing CO2 capacity, efficiency, sustainability, and cost-effective, thereby addressing the current obstacles in carbon capture and storage to sooner meeting the net-zero CO2 emission target.

Improving the Separation Properties of Polybenzimidazole Membranes by Adding Acetonitrile for Organic Solvent Nanofiltration

In research on membranes, the addition of co-solvents to the polymer dope solution is a common method for tuning the morphology and separation performance. For organic solvent nanofiltration (OSN) applications, we synthesized polybenzimidazole (PBI) membranes with high separation properties and stability by adding acetonitrile (MeCN) to the dope solution, followed by crosslinking with dibromo-p-xylene. Accordingly, changes in the membrane structure and separation properties were investigated when MeCN was added. PBI/MeCN membranes with a dense and thick active layer and narrow finger-like macrovoids exhibited superior rejection properties in the ethanol solution compared with the pristine PBI membrane. After crosslinking, they displayed superior rejection properties (96.56% rejection of 366-g/mol polypropylene glycol). In addition, the membranes demonstrated stable permeances for various organic solvents, including acetone, methanol, ethanol, toluene, and isopropyl alcohol. Furthermore, to evaluate the feasibility of the modified PBI OSN membranes, ecamsule, a chemical product in the fine chemical industry, was recovered. Correspondingly, the efficient recovery of ecamsule from a toluene/methanol solution using the OSN process with PBI/MeCN membranes demonstrated their applicability in many fine chemical industries.

Tailoring sub-3.3 Å ultramicropores in advanced carbon molecular sieve membranes for blue hydrogen production

Carbon molecular sieve (CMS) membranes prepared by carbonization of polymers containing strongly size-sieving ultramicropores are attractive for high-temperature gas separations. However, polymers need to be carbonized at extremely high temperatures (900° to 1200°C) to achieve sub-3.3 Å ultramicroporous channels for H₂/CO₂ separation, which makes them brittle and impractical for industrial applications. Here, we demonstrate that polymers can be first doped with thermolabile cross-linkers before low-temperature carbonization to retain the polymer processability and achieve superior H₂/CO₂ separation properties. Specifically, polybenzimidazole (PBI) is cross-linked with pyrophosphoric acid (PPA) via H bonding and proton transfer before carbonization at ≤600°C. The synergistic PPA doping and subsequent carbonization of PBI increase H₂ permeability from 27 to 140 Barrer and H₂/CO₂ selectivity from 15 to 58 at 150°C, superior to state-of-the-art polymeric materials and surpassing Robeson's upper bound. This study provides a facile and effective way to tailor subnanopore size and porosity in CMS membranes with desirable molecular sieving ability.

Development of Thin-Film Composite Membranes for Nanofiltration at Extreme pH

Water recycling is one of the most sustainable solutions to growing water scarcity challenges. However, wastewaters usually contain organic pollutants and often are at extreme pH, which complicates the treatment of these streams with conventional membranes. In this work, we report the synthesis of a robust membrane material that can withstand prolonged exposure to extreme pH (of 1 or 13 for 2 months). Polyamine thin film composite (TFC) membranes are prepared in situ by interfacial polymerization between 1,3,5-tris(bromomethyl)benzene (tBrMeB) and p-phenylenediamine (PPD). Contrary to conventional polyamide TFC membranes, enhanced pH stability is achieved by eliminating the carbonyl groups from the polymer network. The membranes showed pure water permeance and molecular weight cutoff (MWCO) of 0.28 ± 0.09 L m^-2 h^-2 bar^-1 and 820 ± 132 g mol^-1, respectively. The membrane performance is further enhanced by manipulating the monomer structures and replacing p-phenylenediamine with m-phenylenediamine, resulting in a higher permeance of 1.3 ± 0.3 L m^-2 h^-1 bar^-1 and a lower MWCO of 566 ± 43 g mol^-1. Given the ease of fabrication and excellent stability, this chemistry represents a step forward in the fabrication of robust membranes for industrial wastewater recycling.

Facilely Cross-Linking Polybenzimidazole with Polycarboxylic Acids to Improve H2/CO2 Separation Performance

Polybenzimidazole (PBI) with a strong size-sieving ability exhibits attractive H₂/CO₂ separation properties for blue H₂ production and CO₂ capture. Herein, we report that PBI can be facilely cross-linked with polycarboxylic acids, oxalic acid (OA), and trans-aconitic acid (TaA) to improve its separation performance. The acids react with the amines on the PBI chains, decreasing free volume and increasing size-sieving ability. The acid doping increases H₂/CO₂ selectivity from 12 to as high as 45 at 35 °C. The acid-doped samples demonstrate stable H₂/CO₂ separation performance when challenged with simulated syngas containing water vapor at 150 °C, which surpasses state-of-the-art polymers and Robeson's upper bound for H₂/CO₂ separation.

Green Preparation of Thin Films of Polybenzimidazole on Flat and Hollow Fiber Supports: Application to Hydrogen Separation

This work shows the preparation of thin films, with thickness from 70 nm to 1 μm, of meta-polybenzimidazole (m-PBI) on polyimide P84 supports. Ethanolic solutions of m-PBI were used to coat flat and hollow fiber supports of asymmetric P84 with m-PBI in a process where the coating and drying was performed at room temperature. A solution of NaOH in EtOH allowed the dissolution of the m-PBI powder, providing the perfect coating solution to build thin films of m-PBI without damaging the polymeric support. It also meant a green alternative, avoiding the use of toxic solvents, such as dimethylacetamide. The resulting membranes have been tested for the separation of H₂ mixtures at high temperature at different setups to allow checking their reproducibility. With 100 nm thickness the membranes showed their best gas separation performance. For flat membranes at 180 °C and 3 bar feed pressure a H₂ permeance of 48.5 GPU was obtained, with respective H₂ /CO₂ and H₂ /N₂ selectivities of 33.3 and 55.8. Besides, the hollow fibers under a feed pressure of 6 bar and tested at the same temperature showed near 90 GPU of H₂ with a H₂ /CO₂ selectivity of 13.5 in the one-fiber module and over 39 GPU of H₂ with a H₂ /CO₂ selectivity of 20.2 in the five-fiber module. Finally, the stability of the membranes was proved for 22 days at 180 °C.

Unprecedented toughening high-performance polyhexahydrotriazines constructed by incorporating point-face cation-π interactions in covalently crosslinked networks and the visual detection of tensile strength

We described a new concept for the design of high-performance supramolecular thermosets by incorporating point-face cation-π interactions in covalently crosslinked networks. Our findings showed an unprecedented increase in tensile strength and extensibility at once, a previously unknown behavior for stiff high performance polymers.