NF/RO faujasite zeolite membrane-ammonia absorption solvent hybrid system for potential post-combustion CO2 capture application

Polyelectrolyte nanofiltration membranes for base separation and recovery

Nanofiltration (NF) membranes have the potential to significantly advance resource recovery efforts where monovalent/divalent ion separation is critical, but their utilization is limited by inadequate stability under extreme conditions. "Base separation"-i.e., separating hydroxide from other ions-has emerged as an essential approach in resource recovery, enabling the extraction of multivalent anions (e.g., carbonates and phosphates) from hydroxide-rich streams. There is a particularly high demand for membranes capable of separating carbonates from hydroxide-rich CO2 capture solvents and phosphates from hydroxide-rich adsorbent regeneration solvents. However, conventional polyamide NF membranes degrade during long-term exposure to alkaline conditions, limiting their application in extreme conditions. In this study, alkaline-resistant polyelectrolyte membranes are fabricated by depositing alternating layers of polycation, poly(diallyl dimethylammonium chloride) (PDADMAC), and polyanion, poly(sodium 4-styrenesulfonate) (PSS) to a polyethersulfone substrate. The membranes are tested for hydroxide/carbonate and hydroxide/phosphate separation performance, as well as performance stability during prolonged exposure to highly alkaline conditions. Results indicate that higher feed solution pH improves carbonate and phosphate rejection by promoting ion deprotonation and strengthening electrostatic repulsion from the negatively charged membrane. In contrast, increasing carbonate and phosphate concentrations in the feed solution reduces the rejection due to charge screening. The six-bilayer PDADMAC/PSS membrane removes more than 99 % of carbonates and phosphates while allowing extensive passage of hydroxide at pH 13. Stability tests confirm that PDADMAC/PSS membranes maintain excellent ion selectivity over four weeks of exposure to pH 13 KOH, whereas commercial polyamide NF membranes degrade within one week. These findings highlight the potential for PDADMAC/PSS membranes to advance critical resource recovery efforts, providing a durable and effective solution for applications under extreme conditions.

Covalent organic frameworks (COFs): a promising CO2 capture candidate material

Covalent organic frameworks (COFs) are an emerging kind of porous crystal material.

Advances in the Use of Nanocomposite Membranes for Carbon Capture Operations

The adoption of nanodoped membranes in the areas of gas stream separation, water, and wastewater treatments due to the physical and operational advantages of such membranes has significantly increased. The literature has shown that the surface structure and physicochemical properties of nanodoped membranes contribute significantly to the interaction and rejection characteristics when compared to bare membranes. This study reviews the recent developments on nanodoped membranes, and their hybrids for carbon capture and gas separation operations. Features such as the nanoparticles/materials and hybrids used for membrane doping and the effect of physicochemical properties and water vapour in nanodoped membrane performance for carbon capture are discussed. The highlights of this review show that nanodoped membrane is a facile modification technique which improves the membrane performance in most cases and holds a great potential for carbon capture. Membrane module design and material, thickness, structure, and configuration were identified as key factors that contribute directly, to nanodoped membrane performance. This study also affirms that the three core parameters satisfied before turning a microporous material into a membrane are as follows: high permeability and selectivity, ease of fabrication, and robust structure. From the findings, it is also observed that the application of smart models and knowledge-based systems have not been extensively studied in nanoparticle-/material-doped membranes. More studies are encouraged because technical improvements are needed in order to achieve high performance of carbon capture using nanodoped membranes, as well as improving their durability, permeability, and selectivity of the membrane.

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.

Enhanced water transport and salt rejection through hydrophobic zeolite pores

The potential of improvements to reverse osmosis (RO) desalination by incorporating porous nanostructured materials such as zeolites into the selective layer in the membrane has spurred substantial research efforts over the past decade. However, because of the lack of methods to probe transport across these materials, it is still unclear which pore size or internal surface chemistry is optimal for maximizing permeability and salt rejection. We developed a platform to measure the transport of water and salt across a single layer of zeolite crystals, elucidating the effects of internal wettability on water and salt transport through the ≈5.5 Å pores of MFI zeolites. MFI zeolites with a more hydrophobic (i.e., less attractive) internal surface chemistry facilitated an approximately order of magnitude increase in water permeability compared to more hydrophilic MFI zeolites, while simultaneously fully rejecting both potassium and chlorine ions. However, our results also demonstrated approximately two orders of magnitude lower permeability compared to molecular simulations. This decreased performance suggests that additional transport resistances (such as surface barriers, pore collapse or blockages due to contamination) may be limiting the performance of experimental nanostructured membranes. Nevertheless, the inclusion of hydrophobic sub-nanometer pores into the active layer of RO membranes should improve both the water permeability and salt rejection of future RO membranes (Fasano et al 2016 Nat. Commun. 7 12762).