1,720,977 research outputs found
Low-temperature heat utilization with vapor pressure-driven osmosis: Impact of membrane properties on mass and heat transfer
No full textThe emerging vapor pressure-driven osmosis (VPDO) membrane technology enables direct conversion of abundant low-temperature ( < 100 degrees C) heat resources to useful work. In this study, a theoretical model is established to understand mass and heat transfer of VPDO, and two hydrophobic nanoporous membranes, polypropylene (PP) and polytetrafluoroethylene (PTFE), of different chemistry and structural properties were evaluated. Although the PP membrane has a less effective transport pathway, the considerably larger pore size yields a much higher Knudsen diffusivity that results in consistently higher vapor fluxes across different temperature-pressure conditions. This finding provides strong evidence that mass transfer in VPDO is dominated by Knudsen diffusion. Additionally, we find that operation at higher pressurizations caused vapor flux decline that is attributed to the membrane morphological deformation. However, the PP membrane is less sensitive to the effects of compaction, underlining the importance of membrane mechanical robustness for VPDO. Lastly, the study shows that evaporative heat transfer is significantly greater than conducive losses and the PP membrane, with higher water fluxes, has better evaporation thermal efficiencies. This study provides fundamental understanding on the impacts of membrane properties on mass and heat transfer in VPDO, and highlights the centrality of vapor permeability and mechanical robustness in developing high-performance membranes.
Performance and stability evaluation of thin-film composite nanofiltration membranes under extreme oxidation conditions: Implications for reclamation of semiconductor waste solutions
No full textThe semiconductor industry consumes large quantities of ultra-pure water and high-value chemicals that turn into hazardous waste streams. Proper treatment and recovery of these waste streams are imperative for cost savings and environmental protection. In this study, we evaluated the performance and stability of thin-film composite nanofiltration (NF) membranes under exposure to strong oxidizing chemicals to assess their applicability in treatment of semiconductor waste solutions. Water flux and divalent cation (Mg2+) rejection of commercial acid-resistant NF membranes with three different selective layer chemistries-XUS (fully-aromatic polyamide), Duracid (polysulfonamide), and Hydracore (sulfonated-polyethersulfone)-were evaluated for 3 weeks under exposure to high concentration sulfuric acid (10 wt%) and hydrogen peroxide (1 wt%) solutions, and a mixture of the two (piranha solution). We found that all three NF membranes exhibited reasonable resistance to H2SO4, but they experienced significant performance deterioration when subjected to attack by H2O2, especially in flow-through operation mode. The changes in physical and chemical properties of the NF membranes were extensively characterized to elucidate the oxidative degradation mechanisms. We also discussed the potential and the need for developing NF membranes that are resistant to a broad range of oxidizing chemicals commonly used in high-tech industries.
Performance, limitation, and opportunities of acid-resistant nanofiltration membranes for industrial wastewater treatment
No full textVarious industrial activities generate highly acidic wastewaters, posing a particular concern due to their large volume, environmental impact, and limited disposal options. Nanofiltration (NF) has the potential to provide energy-, cost-, and space-effective solutions for wastewater treatment at industrial sites. However, conventional thin-film composite NF membranes degrade under acid exposures, largely limiting their applications in industrial wastewater treatment. Development of chemically robust NF membranes that are stable during operation with highly acidic feed streams has been a subject of active research and industrial interest. In this critical review, we first provide a comprehensive survey for the broad spectrum of industrial processes that yield acidic wastewaters. We then conduct in-depth analyses for short-and long-term rejection performances and stabilities of commercial NF membranes, especially under low solution pH conditions. Several key mechanisms responsible for the degradation of semi-aromatic polyamide networks by acid-catalyzed hydrolysis are discussed to highlight the limitation of commercially available NF membranes. Finally, we describe a wide variety of technical strategies to fabricate acid-resistant NF membranes, focusing on the key mechanism to enhance acid stability. We conclude by providing useful insights to guide the future directions for academic studies as well as industrial applications of acid-resistant NF membranes.
Performance evaluation of trimethylamine–carbon dioxide thermolytic draw solution for engineered osmosis
No full textWe evaluated the performance of trimethylamine-carbon dioxide (TMA-CO2) as a potential thermolytic draw solution for engineered osmosis. Water flux and reverse solute flux with TMA-CO2 draw solution were measured in forward osmosis (FO) and pressure retarded osmosis (PRO) modes using thin-film composite (TFC) and cellulose triacetate (CTA) FO membranes. Water flux with the TMA-CO2 draw solution was comparable to that obtained with the more common ammonia-carbon dioxide (NH3-CO2) thermolytic draw solution at similar (1 M) concentration. Using a TFC-FO membrane, the water fluxes produced by 1 M TMA-CO2 and NH3-CO2 draw solutions with a DI water feed were, respectively, 33.4 and 35.6 L m(-2) h(-1) in PRO mode and 14.5 and 152 L m(-2) h(-1) in FO mode. Reverse draw permeation of TMA-CO2 was relatively low compared to NH3-CO2, ranging from 0.1 to 0.2 mol m(-2) h(-1) in all experiments, due to the larger molecular size of TMA. Thermal separation and recovery efficiency for TMA-CO2 was compared to NH3-CO2 by modeling low-temperature vacuum distillation utilizing low-grade heat sources. We also discuss possible challenges in the use TMA-CO2, including potential adverse impact on human health and environments. (C) 2014 Elsevier B.V. All rights reserved.
Novel Isothermal Membrane Distillation with Acidic Collector for Selective and Energy-Efficient Recovery of Ammonia from Urine
No full textThe high concentration of ammonia in source-separated urine offers propitious opportunities for N recovery. Membrane distillation (MD) can recover volatile ammonia from hydrolyzed urine, but conventional operation suffers from the simultaneous permeation of water vapor that results in poor selectivity for ammonia transport and high energy demand. Here, we present a novel operation of MD-isothermal membrane distillation with acidic collector (IMD-AC)-to overcome the limitations of conventional MD. The innovative isothermal operation, i.e., same feed and collector temperatures, effectively suppressed water vapor permeation while maintaining ammonia vapor flux and, thus, significantly improved selectivity for ammonia transport. The acidic collector further enhanced ammonia vapor flux by an average of 46.5% compared to using a deionized water collector. Against a total ammoniacal nitrogen concentration gradient, i.e., uphill transport, ammonia recovery of approximate to 60% was attained, highlighting the prospect of the technology for high-yield recovery. Critically, IMD-AC achieved approximately 95% savings in vaporization energy consumption relative to conventional MD by practically eliminating the evaporation of water. The resultant energy requirement of approximate to 2.2 kWh/kg-N is less than the Haber-Bosch process for N fixation and N removal by nitrification-denitrification (8.9-19.3 and 2.3-6.5 kWh/kg-N, respectively). This study shows the promising potential of IMD-AC for the selective and energy-efficient recovery of ammonia from source-separated urine.
High-Performance Nanofiltration Membrane with Dual Resistance to Gypsum Scaling and Biofouling for Enhanced Water Purification
No full textNanofiltration (NF) technology is pivotal for ensuring a sustainable and reliable supply of clean water. To address the critical need for advanced thin-film composite (TFC) polyamide (PA) membranes with exceptional permselectivity and fouling resistance for emerging contaminant purification, we introduce a novel high-performance NF membrane. This membrane features a selective polypiperazine (PIP) layer functionalized with amino-containing quaternary ammonium compounds (QACs) through an in situ interfacial polycondensation reaction. Our investigation demonstrated that precise QAC functionalization enabled the construction of the selective PA layer with increased surface area, enhanced microporosity, stronger electronegativity, and reduced thickness compared to the control PIP membrane. As a result, the QAC NF membrane exhibited an approximately 51% increase in water permeance compared to the control PIP membrane, while achieving superior retention capabilities for divalent salts (>99%) and emerging organic contaminants (>90%). Furthermore, the incorporation of QACs into the PIP selective layer was proved to be effective in mitigating mineral scaling by allowing selective passage of scale-forming cations, while simultaneously exhibiting strong antimicrobial properties to combat biofouling. The in situ QAC incorporation strategy presented in this study provides valuable guidelines for the fit-for-purpose design of the selective PA layer, which is crucial for the development of high-performance NF membranes for efficient water purification.
Omniphobic Membrane for Robust Membrane Distillation
Full text linkIn this work, we fabricate an omniphobic microporous membrane for membrane distillation (MD) by modifying a hydrophilic glass fiber membrane with silica nanoparticles followed by surface fluorination and polymer coating. The modified glass fiber membrane exhibits an anti-wetting property not only against water but also against low surface tension organic solvents that easily wet a hydrophobic polytetrafluoroethylene (PTFE) membrane that is commonly used in MD applications. By comparing the performance of the PTFE and omniphobic membranes in direct contact MD experiments in the presence of a surfactant (sodium dodecyl sulfate, SDS), we show that SDS wets the hydrophobic PTFE membrane but not the omniphobic membrane. Our results suggest that omniphobic membranes are critical for MD applications with feed waters containing surface active species, such as oil and gas produced water, to prevent membrane pore wetting.
Inorganic Scaling in Membrane Desalination: Models, Mechanisms, and Characterization Methods
No full textInorganic scaling caused by precipitation of sparingly soluble salts at supersaturation is a common but critical issue, limiting the efficiency of membrane-based desalination and brine management technologies as well as other engineered systems. A wide range of minerals including calcium carbonate, calcium sulfate, and silica precipitate during membrane-based desalination, limiting water recovery and reducing process efficiency. The economic impact of scaling on desalination processes requires understanding of its sources, causes, effects, and control methods. In this Critical Review, we first describe nucleation mechanisms and crystal growth theories, which are fundamental to understanding inorganic scale formation during membrane desalination. We, then, discuss the key mechanisms and factors that govern membrane scaling, including membrane properties, such as surface roughness, charge, and functionality, as well as feedwater characteristics, such as pH, temperature, and ionic strength. We follow with a critical review of current characterization techniques for both homogeneous and heterogeneous nucleation, focusing on the strengths and limitations of each technique to elucidate scale-inducing mechanisms, observe actual crystal growth, and analyze the outcome of scaling behaviors of desalination membranes. We conclude with an outlook on research needs and future research directions to provide guidelines for scale mitigation in water treatment and desalination.
Development of Omniphobic Desalination Membranes Using a Charged Electrospun Nanofiber Scaffold
No full textIn this study, we present a facile and scalable approach to fabricate omniphobic nanofiber membranes by constructing multilevel re-entrant structures with low surface energy. We first prepared positively charged nanofiber mats by electrospinning a blend polymer surfactant solution of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and cationic surfactant (benzyltriethylammonium). Negatively charged silica nanoparticles (SiNPs) were grafted on the positively charged electrospun nanofibers via dip-coating to achieve multilevel re-entrant structures. Grafted SiNPs were then coated with fluoroalkylsilane to lower the surface energy of the membrane. The fabricated membrane showed excellent omniphobicity, as demonstrated by its wetting resistance to various low surface tension liquids, including ethanol with a surface tension of 22.1 mN/m. As a promising application, the prepared omniphobic membrane was tested in direct contact membrane distillation to extract water from highly saline feed solutions containing low surface tension substances, mimicking emerging industrial wastewaters (e.g., from shale gas production). While a control hydrophobic PVDF-HFP nanofiber membrane failed in the desalination/separation process due to low wetting resistance, our fabricated omniphobic membrane exhibited a stable desalination performance for 8 h of operation, successfully demonstrating clean water production from the low surface tension feedwater.
Novel Thermal Desalination Membranes for Sustainable Treatment of Hypersaline Industrial Wastewaters
No full textAn increasing demand exists for the treatment of hypersaline industrial wastewaters such as those from the shale gas industry, seawater desalination plants, and thermoelectric power-generating facilities. Membrane distillation (MD) is an emerging thermal-based desalination process, which can potentially treat hypersaline industrial wastewaters by exploiting low-grade or waste heat. High performance MD membranes are the key to the advancement and further commercialization of this emerging desalination technology. This research aims at (i) developing novel MD membranes with special surface wettability using advanced materials and surface engineering techniques and (ii) gaining fundamental understanding of the scaling and fouling mechanisms of the newly developed MD membranes. Engineering the wettability of materials and interfaces can effectively be leveraged to membrane fabrication. Omniphobic membranes that resist wetting from both water and oil can extend MD applications for desalination of emerging high-salinity wastewaters containing diverse low surface tension contaminants. Fundamental understanding of interfacial phenomena and relating such knowledge to membrane surface wettability are crucial to improving omniphobic MD membrane design and performance. This work elucidates the factors that determine surface omniphobicity of microporous membranes and evaluates the potential application of these membranes in desalination of low surface tension wastewaters by membrane distillation. Specifically, the effects of surface morphology and surface energy on membrane surface omniphobicity were systematically investigated by modifying a prototype glass fiber substrate with silica nanoparticles and fluoroalkylsilane. A re-entrant structure, defined as a nanoscale architecture with increased air to solid ratio, developed by the spherical silica nanoparticles was found to play a critical role in rendering the membrane surface omniphobic, Electrospinning is a promising and versatile technique to fabricate omniphobic membranes, because electrospun nanofibers with cylindrical shape feature a re-entrant structure and could be further engineered for additional levels of re-entrant structures. This work presents a facile approach to fabricate a robust omniphobic membrane by exploiting the versatility of electrospinning, which allows the preparation of a nanofiber scaffold with targeted physical and chemical properties. The fabricated electrospun omniphobic MD membranes were evaluated in terms of wetting resistance to various low surface tension liquids and desalination performance with feed solutions of varying surface tensions. Microporous polyvinylidene fluoride (PVDF) membranes have been widely used for MD applications because of their hydrophobic nature, excellent chemical compatibility, and facile processability. However, application of conventional hydrophobic PVDF membranes in MD is limited due to their susceptibility to wetting and fouling by low surface tension contaminants. This study presents scalable surface engineering of a conventional hydrophobic PVDF microporous substrate to produce an omniphobic membrane. Desalination performance of the fabricated omniphobic membrane was evaluated in direct contact membrane distillation with synthetic wastewaters containing low surface tension contaminants, including surfactants and mineral oil. The performance of the fabricated omniphobic membrane with produced water from the shale gas industry was further examined to highlight its potential application in desalinating complex, high salinity industrial wastewaters. The performance of MD systems is hampered by fouling and inorganic scaling, particularly when a system treats hypersaline industrial wastewaters with high levels of total dissolved solids and organic matter. This dissertation research investigated fouling and scaling mechanisms of omniphobic membranes, focusing on the impact of surface chemistry. The omniphobic membranes were fouled by hydrophobic, low surface tension contaminants via attractive interactions, but further adsorption into the pores was prevented by a thermodynamic barrier created by a re-entrant structure, which sustains a metastable non-wetting condition. Also, the non-adhesive and slippery surface nature of the omniphobic membrane was shown to delay both homogeneous and heterogeneous nucleation, demonstrating its potential for a high recovery MD system to treat hypersaline industrial wastewaters. This work presents pioneering advances in the development of novel MD membranes with special wettability for extended MD applications. The fundamental understanding of the interfacial phenomena, advanced materials, and surface engineering techniques as well as fouling and scaling mechanisms will shed light on the design parameters for high membrane performance and efficient process operation. These important insights can inform the realization of emerging membrane-based technologies for sustainable treatment of challenging industrial wastewaters. The implications of the results in this dissertation are potentially far-reaching; we anticipate that they will shape the discussion of next generation desalination technologies
- …
