Defect control for large-scale thin-film composite membrane and its bench-scale demonstration

Recent Progress in the Engineering of Polymeric Membranes for CO2 Capture from Flue Gas

CO2 capture from coal- or natural gas-derived flue gas has been widely considered as the next opportunity for the large-scale deployment of gas separation membranes. Despite the tremendous progress made in the synthesis of polymeric membranes with high CO2/N2 separation performance, only a few membrane technologies were advanced to the bench-scale study or above from a highly idealized laboratory setting. Therefore, the recent progress in polymeric membranes is reviewed in the perspectives of capture system energetics, process synthesis, membrane scale-up, modular fabrication, and field tests. These engineering considerations can provide a holistic approach to better guide membrane research and accelerate the commercialization of gas separation membranes for post-combustion carbon capture.

Ultrathin Thin-Film Composite Polyamide Membranes Constructed on Hydrophilic Poly(vinyl alcohol) Decorated Support Toward Enhanced Nanofiltration Performance

Traditional polyamide-based interfacial polymerized nanofiltration (NF) membranes exhibit upper bound features between water permeance and salt selectivity. Breaking the limits of the permeability and rejections of these composite NF membranes are highly desirable for water desalination. Herein, a high-performance NF membrane (TFC-P) was fabricated via interfacial polymerization on the poly(vinyl alcohol) (PVA) interlayered poly(ether sulfone) (PES) ultrafiltration support. Owing to the large surface area, great hydrophilicity, and high porosity of the PES-PVA support, a highly cross-linked polyamide separating layer was formed with a thickness of 9.6 nm, which was almost 90% thinner than that of the control membrane (TFC-C). In addition, the TFC-P possessed lower ζ-potential, smaller pore size, and greater surface area compared to that of the TFC-C, achieving an ultrahigh water permeance of 31.4 L m^-2 h^-1 bar^-1 and a 99.4% Na₂SO₄ rejection. Importantly, the PVA interlayer strategy was further applied to a pilot NF production line and the fabricated membranes presented stable water flux and salt rejections as comparable to the lab-scaled membranes. The outstanding properties of the PVA-interlayered NF membranes highlight the feasibility of the fabrication method for practical applications, which provides a new avenue to develop robust polyamide-based NF desalination membranes for environmental water treatment.

Effect of Humidity on CO2/N2 and CO2/CH4 Separation Using Novel Robust Mixed Matrix Composite Hollow Fiber Membranes: Experimental and Model Evaluation

In this work, the performance of new robust mixed matrix composite hollow fiber (MMCHF) membranes with a different selective layer composition is evaluated in the absence and presence of water vapor in CO2/N2 and CO2/CH4 separation. The selective layer of these membranes is made of highly permeable hydrophobic poly(trimethyl-1-silylpropine) (PTMSP) and hydrophilic chitosan-ionic liquid (IL-CS) hybrid matrices, respectively, filled with hydrophilic zeolite 4A particles in the first case and HKUST-1 nanoparticles in the second, coated over compatible supports. The effect of water vapor in the feed or using a commercial hydrophobic PDMSXA-10 HF membrane has also been studied for comparison. Mixed gas separation experiments were performed at values of 0 and 50% relative humidity (RH) in the feed and varying CO2 concentration in N2 and CH4, respectively. The performance has been validated by a simple mathematical model considering the effect of temperature and relative humidity on membrane permeability.

Manipulation of Fibril Surfaces in Nanocellulose-Based Facilitated Transport Membranes for Enhanced CO2 Capture

The transition toward sustainable processing entails the use of biobased alternatives as functional materials to reduce the overall carbon footprint. Nanocellulose, due to its natural availability, biodegradability, excellent mechanical properties, tunable surface, and high aspect ratio, is attracting more and more interest as a nanoscale additive in polymeric membranes. In this work, an effective way to modify nanocellulose fibril surfaces for performance enhancement in CO₂ separation membranes has been demonstrated. The functionalization promptly triggered intrinsic property responses in favor of nanofiber dispersion and CO₂ transport. Thin composite membranes containing the modified nanofibers in water-swelling poly(vinyl alcohol) (PVA) as well as in the blend of sterically hindered polyallylamine (SHPAA) and PVA were fabricated and tested using humid gas permeation tests. Defect-free ultrathin (300 nm) hybrid selective layers containing evenly distributed nanofibers were successfully coated. The addition of nanocellulose exhibited enhanced CO₂ permeance and CO₂/N₂ selectivity compared to those of the neat PVA membranes. CO₂ permeance up to 652 GPU and a CO₂/N₂ selectivity of 41.3 with SHPAA/PVA blend were documented. Functionalization plays a categorical role in the dispersion of nanocellulose fibrils in the SHPAA/PVA blend, increasing the steric stabilization and interface compatibility with the polymer matrix. The tuned interface with PEG groups act as sites for water clusters retention and increased CO₂ solubility, thus creating fast diffusion pathways for CO₂ transport.

Potential and limitation of fluorescence-based membrane integrity monitoring (FMIM) for reverse osmosis membranes

In wastewater recycle for potable purposes, virus removal is the most critical issue from the public health stand point. Therefore, the regulatory agency sets minimum virus removal efficiencies that must be met by combining multiple treatment processes. In most potable reuse processes, reverse osmosis (RO) plays a critical role by removing salts, viruses, dissolved organic matters, etc. It has been reported that RO removes viruses at over 6 log efficiencies, but it receives no more than 2 log credits from regulatory agencies due to the lack of sensitive integrity monitoring technologies better than conductivity-based technologies. In recent years, fluorescence-based membrane integrity monitoring (FMIM) has drawn special attention because of its simplicity, capability of continuous monitoring, and the high resolution. Lab and field studies have shown FMIM can provide around 4 log resolution for commercially available RO membranes. In this study, potential and limitation of current FMIM technology are reviewed. Further, ideas to improve the resolution beyond 4 log are suggested.