Commercial Hollow Fiber Membrane Research Articles

The Influence of Air Gap Length on the Characteristics and Performance of Hybrid Polyethersulfone/Cellulose Nanocrystal/Multiwalled Carbon Nanotubes Hollow Fiber Membrane for Humic Acid Removal

ABSTRACTReady‐made or commercial hollow fiber (HF) membranes have limited performance for removing humic acid (HA) from water streams unless they undergo surface modification. Alternatively, a membrane can be tailor‐made specifically for HA removal by developing a new formulation and adjusting its fabrication parameters. In this study, to enhance the performance and antifouling properties of HF membranes, a hybrid membrane was developed by blending polyethersulfone (PES) with cellulose nanocrystals (CNC) and multiwalled carbon nanotubes (MWCNT). The effect of air gap length during the dry–wet spinning process was investigated, ranging from 3 cm to 12 cm, to regulate the properties of the hybrid membrane. The membranes were evaluated in terms of morphology (FESEM and AFM), porosity, and hydrophilicity (contact angle). Water flux, HA rejection, and flux recovery ratio (FRR) were also measured. The air gap length significantly influenced the fiber structure, with the finger‐like structure expanding from the outer surface to the center of the fiber as the air gap extended up to 9 cm. This increase in air gap length resulted in a significant reduction in porosity, decreasing from 75.59% to 43.45%, while simultaneously enhancing the contact angle from 78° to 89.60°. The membrane produced at a 9 cm air gap length exhibited the best performance, with a pure water flux of 15.83 LMH, HA rejection over 95%, and a high FRR of 98.78%. The synergistic effect of combining CNC with MWCNT and simply adjusting the air gap distance proves to be an effective approach for preparing custom‐made HF membranes for HA removal.

Mitigation of Physical Aging of Polymeric Membrane Materials for Gas Separation: A Review

The first commercial hollow fiber and flat sheet gas separation membranes were produced in the late 1970s from the glassy polymers polysulfone and poly(vinyltrimethyl silane), respectively, and the first industrial application was hydrogen recovery from ammonia purge gas in the ammonia synthesis loop. Membranes based on glassy polymers (polysulfone, cellulose acetate, polyimides, substituted polycarbonate, and poly(phenylene oxide)) are currently used in various industrial processes, such as hydrogen purification, nitrogen production, and natural gas treatment. However, the glassy polymers are in a non-equilibrium state; therefore, these polymers undergo a process of physical aging, which is accompanied by the spontaneous reduction of free volume and gas permeability over time. The high free volume glassy polymers, such as poly(1-trimethylgermyl-1-propyne), polymers of intrinsic microporosity PIMs, and fluoropolymers Teflon® AF and Hyflon® AD, undergo significant physical aging. Herein, we outline the latest progress in the field of increasing durability and mitigating the physical aging of glassy polymer membrane materials and thin-film composite membranes for gas separation. Special attention is paid to such approaches as the addition of porous nanoparticles (via mixed matrix membranes), polymer crosslinking, and a combination of crosslinking and addition of nanoparticles.

A Membrane Contactor Enabling Energy-Efficient CO2 Capture from Point Sources with Deep Eutectic Solvents

We demonstrate a scalable and energy-efficient hollow fiber membrane contactor (HFMC)-based process using a green solvent for CO2 capture. This process uses a deep eutectic solvent (DES) in an HFMC to provide close interfacial interactions and contact between the DES and CO2. This approach overcomes disadvantages associated with direct absorption in DES and could potentially be applied to a variety of solvent-based CO2 capture methods. Commercial low-cost polymer hollow fiber membranes (e.g., microporous polypropylene) were evaluated for CO2 capture with reline, a prototypical DES. Single-gas measurements showed that the DES-based polypropylene HFMC can capture and separate CO2 while rejecting N2. From a mixed gas containing 50 mol % N2 and 50 mol % CO2, the DES-based HFMC separated CO2 with a purity of 96.9 mol %. The effect of several process parameters including solvent flow rate, pressure, and temperature on the CO2 separation performance was studied. The flux of the recovered CO2 was 67.43 mmole/m2/h at a feed pressure of 4 bar. In situ Fourier transform infrared (FTIR) measurements combined with density functional theory (DFT)-based molecular dynamics simulations revealed that reline absorbs CO2 by physical absorption without forming a new chemical compound, and CO2 separation by reline occurs via the pressure swing mechanism. This research provides fundamental insights about physical solvent-based separation processes and a pathway toward practical deployment.

Membrane system for management and utilization of indoor CO2

Human exposure to elevated CO2 can have adverse health effects. As the proportion of indoor living expands, increases in atmospheric and indoor CO2 concentrations could pose potential health impacts. A strategy to decrease indoor CO2 levels depends heavily on ventilation, which brings outdoor air indoors, requiring alternative CO2 removal technology. However, indoor CO2 removal has been limited to sorption processes that require an additional step for desorption, which is challenging to adopt in urban buildings. This work applies membrane-based gas separation to remove CO2 in the atmosphere, mainly designed for indoor air conditions. The requirements for an effective and practical membrane process are discussed through theoretical calculations and experiments using a commercial hollow fiber membrane module. The membrane system allows the application of CO2-lean retentate gas to indoor air management for a healthy indoor environment (<1000 ppm). Besides, the CO2-rich permeate gas is successfully utilized to promote indoor plant growth, suggesting it for future farming. These results demonstrate that the membrane system has the potential to provide the optimized CO2 concentration for various applications in indoor spaces, which will guide the future development of membrane systems.

Unveiling the Impacts of Sodium Hypochlorite on the Characteristics and Fouling Behaviors of Different Commercial Polyvinylidene Fluoride Hollow Fiber Membranes.

Sodium hypochlorite (NaOCl) is a commonly used cleaning agent for recovering membrane performance in membrane technologies. A thorough understanding of the impacts of NaOCl exposure on membrane properties and fouling behavior is important for optimizing chemical cleaning process and extending membrane lifespan. In this study, three commercial polyvinylidene fluoride (PVDF) hollow fiber ultrafiltration membranes (SMM-1010, MEMCOR® CS II and ZeeWeed 500) were used to systematically explore the effects of NaOCl dose and solution pH (8 and 10) on membrane properties. The results showed that membrane pores increased with exposure time prolonging, and more pores were observed at pH 8 aging condition. The amide group in the Fourier transformation infrared spectra was disappeared, while the carboxylic acid and succinimide groups were formed at pH 10 and pH 8 conditions, respectively. The hydrophilicity and pure water permeability (PWP) of SMM-1010 and MEMCOR® CS II membranes had insignificant changes during NaOCl aging process, whereas the hydrophilicity of ZeeWeed 500 membrane slightly decreased and its PWP increased by 1.4-fold. The antifouling properties of NaOCl-aged SMM-1010 and MEMCOR® CS II membranes were slightly improved, whereas the NaOCl-aged ZeeWeed 500 membrane showed severer flux decline with humic acid filtration. Our findings could provide guidance for practical chemical cleaning process optimization.

Characterization of the cylindrical electrospun nanofibrous polysulfone membrane for hemodialysis with modelling approach.

Electrospun nanofibrous membrane (ENM) is a membrane fabricated using electrospinning technique which has considerable characteristics such as high porosity, nanometer pore size, and simple process. Although ENMs are being evaluated in various medical applications, the effectiveness for hemodialysis (HD) has not been evaluated carefully. Thus, in this study, the cylindrical electrospun nanofibrous polysulfone (CENP) membrane was fabricated and its performance in the dialysis adequacy in HD patients was evaluated.The CENP membrane was fabricated in a tabular shape. The physical characteristics of the membrane are examined using scanning electron microscope (SEM) images and the permporometry technique. Then, its efficiency in urea and creatinine removal from the blood serum of 21 HD patients was evaluated at a low blood flow rate (BFR) of 200 ml min-1 and dialysate fluid rate (DFR) of 300 ml min-1. Afterwards, the results were modeled and optimized using artificial neural network (ANN) and genetic algorithm (GA), respectively. Finally, sensitive analysis was performed via Spearman's rank correlation coefficient. The highest dialysis adequacy was observed in membranes with an inner diameter of 3 mm. The CENP membrane belongs to the super high-flux membrane and it could be replaced with existing commercial hollow fiber membranes.

Decontamination of uranium contained low-level radioactive wastewater from UO2 fuel element industry with vacuum membrane distillation

The rapid development of nuclear industry has generated large quantities of low-level radioactive wastewater (LLRW) to pose a potential threat globally. In this study, the feasibility of vacuum membrane distillation (VMD) process for the decontamination of uranium contained LLRW from UO2 fuel element production has been studied using commercial PTFE hollow fiber membrane. The effects of operation conditions, such as feed temperature/pH, vacuum pressure and feed flow velocity were investigated and optimized with artificial UO2(NO3)2 solution. The real process wastewater from the UO2 fuel element factory were then treated by VMD process under the optimized conditions for 1400 min with the concentration factor up to 9. No clear evidence of membrane fouling or wetting were noticed during the VMD operation nor the membrane autopsy studies. With an average permeate flux of 7.3 L m−2 h−1, it exhibited excellent retention towards all major contaminates such as uranium, COD, and NH4+-N to meet the Integrated Wastewater Discharge Standard of China (GB 8978-1996) for direct discharge.

Novel PTFE hollow fiber membrane fabricated by emulsion electrospinning and sintering for membrane distillation

Polytetrafluoroethylene (PTFE) is an attractive membrane material due to its superior chemical resistance, thermal stability and strong hydrophobicity. However, PTFE hollow fiber membranes are challenging to produce by conventional technique due to the high solvent resistance and high melt viscosity of PTFE. In this study, novel PTFE hollow fiber membranes composed of pure PTFE nanofibers were firstly fabricated via a scalable and environment-friendly method based on emulsion electrospinning with a non-rotating collector and followed by a high-temperature sintering process. The effects of PTFE/PEO mass ratio and sintering temperature on the morphologies and properties of the resulting membranes were investigated. The prepared PTFE hollow fiber membrane shows the excellent characteristics combining the advantages of both electrospun nanofibers membrane and hollow fiber membrane, such as high porosity (more than 82%), self-supporting and superhydrophobicity. The membrane sintered at 380 °C present the highest mechanical strength, which shows the tensile strength, Young's modulus, strain at break of 30.5 Mpa, 53 Mpa, and 315%, respectively. The permeate flux of the prepared PTFE hollow fiber membrane is about 4.6–8.8 times as that of the commercial PTFE hollow fiber membranes, as well as is approximately 3.2–11.6 times higher than the date of the reported PTFE hollow fiber membranes. Additionally, the prepared membrane shows high and stable flux in long-term and rising salinity experiments, indicating it is very promising for membrane distillation (MD) application and even for the treatment of hyper-saline wastewater.

Pressure effect at permeability and deformation of the hollow fiber membrane gas separation module

In this paper, the deformation effect in the gas separation process of the hollow fiber membrane module is considered. A technique of gas permeability measurement in a commercial gas separation hollow fiber membrane module is provided. It is determined that permeability and selectivity are nonlinearly dependent on the pressure of the feed stream, this is justified by competing factors. The results of this work will allow introducing the membrane modules into hybrid gas separation units, in particular, into the drying unit of compressed gas.

Numerical Simulation on Supercritical CO2 Fluid Dynamics in a Hollow Fiber Membrane Contactor

This research answers the following question: What is the fluid dynamic behavior of a supercritical fluid (SCF) inside a membrane module? At this time, there is very little or no reported information that can provide an answer to this question. The research studies related to the themes of supercritical CO2 (SC-CO2), hollow fiber membrane contactors (HFMCs), and numerical simulations have mainly reported on 2D simulations, but in this work, 3D profiles are presented. Simulations were performed based on the experimental results and other simulations, using the geometry of a commercial module. The results were mainly based on the different operating conditions and geometric dimensions. A mesh study was performed to ensure the mesh non-dependence of the results presented here. It was observed that the velocity profile developed at 10 mm from the wall of the supercritical CO2 entrance pipe. A profile equilibrium around the fiber close to the entrance of the module was achieved in the experimental hollow fiber membrane contactor when compared to the case of the commercial hollow fiber membrane contactor. The results of this research provided a visualization of the boundary layer, which did not cover the entire fiber length. Finally, the results of this paper are interesting for technical applications and contribute to our understanding of the hydrodynamics of SCFs.

PERFORMANCE OF THE CATALYTIC MEMBRANE REACTORS OF DIFFERENT PORE SIZE WITH PALLADIUM AS CATALYTIC PHASE IN HYDROGENATION AND OXIDATION REACTIONS

The catalytic membrane reactors (CMR) were prepared using commercial Hollow Fiber Membranes of corundum with 4 nm or 1400 nm pores and impregnated with palladium. The tests performed were phenol hydrogenation, hydrogen peroxide generation to oxidize phenol by advanced oxidation processes and chromium (VI) reduction. Reactions were performed in aqueous solution, at mild temperature and under atmospheric pressure. For all tests, the hydrogen passed through the membrane to be activated with palladium. The test with phenol showed that, in the absence of oxygen, the activated hydrogen reacts with the organic matter, leading to the formation of hydrogenated products; in the presence of oxygen, active hydrogen reacts with oxygen to form hydrogen peroxide and subsequently hydroxyl radicals that attack the organic matter until its mineralization. Furthermore, the CMR is capable of reducing chromium (VI) to chromium (III). The CMRs of smaller pore size presented better performance in all reactions.

Intensification of CO2 separation performance via cryogenic and membrane hybrid process — Comparison of polyimide and polysulfone hollow fiber membrane

Cryogenic-membrane hybrid CO2 capture process has been considered as a promising alternative for the standalone processes to mitigate the critical challenge of energy penalty. In this work, two different commercial hollow fiber membranes were tested at low temperature condition to find the possibility of consisting a novel cold-membrane-cryogenic hybrid process. The gas permeation properties of membranes were evaluated at different operating temperature, CO2 concentration and stage cut. The experimental results indicated that cryogenic condition could facilitate to improve the CO2/N2 selectivity with a minimum permeance reduction. Specifically, with the operating temperature dropped to −20 °C and feed pressure set at 0.7 MPa, the CO2 selectivity of polyimide membrane increased by 166% with the permeance declined by 31%. Meanwhile, the CO2 recovery and purity of polyimide membrane achieved 92% and 49% at the temperature of −20 °C and pressure 0.7 MPa, respectively. It can be observed that operating membrane at cold condition could be a promising approach to intensify the CO2 separation, and thus decrease the energy consumption of subsequent CO2 liquefaction or desublimation in the hybrid process.

Treatment of cake shop wastewater by pilot-scale Submerged Membrane Bioreactor (SMBR)

In this work, the treatment of cake shop wastewater using Submerged Membrane Bioreactor (SMBR) on pilot-scale has been studied. The commercial hollow fiber membrane was used with a total surface area of 0.609 m2. The experiment was set up with three different conditions as follows: model 1 - the SMBR system used suspended activated sludge; model 2 – the SMBR system was combined with the substrate inside; model 3 – the SMBR system was added with PAC (Poly Aluminium Chloride) excluding substrate. Effects of organic loading rates (OLR) were investigated to assess the performance of each model. The results showed that the optimal OLR of model 1 achieved at 11 kgCOD/m3.day and COD, TN, TP removal efficiencies were 97.93%, 71.04% and 79.04%, respectively. The optimal OLR of model 2 was 13.3 kgCOD/m3.day and the COD, TN, TP removal efficiencies were 98.04%, 82.35% and 84.59%, respectively. 11 kgCOD/m3.day was optimal OLR for model 3 with COD, TN, TP removal efficiencies 98.10%, 73.35% and 84.70%, respectively. Trans-membrane pressure (TMP) of the whole operation was in range of 20 to 55.5 CmHg and flux values were observed in the range of 35.86 to 333.24 L/m2.h. Depending on discharge requirements, an approximate processing model for cake shop wastewater treatment is chosen.

Pressure effect at permeability and deformation of the hollow fiber membrane gas separation module

In this paper, the deformation effect in the gas separation process of the hollow fiber membrane module is considered. A technique of gas permeability measurement in a commercial gas separation hollow fiber membrane module is provided. It is determined that permeability and selectivity are nonlinearly dependent on the pressure of the feed stream, this is justified by competing factors. The results of this work will allow introducing the membrane modules into hybrid gas separation units, in particular, into the drying unit of compressed gas.

Modelling of water-to-gas hollow fiber membrane humidifier

A microscopic mathematical model is developed for membrane based water-to-gas humidification by rigorously accounting for phase equilibrium between the membrane and water phases as well as membrane and gas phases in addition to the coupled heat and mass transfer occurring across the membrane. The model is then integrated along the length of a hollow fiber membrane humidifier in order to predict humidifier performance as a function of design variables, operating variables and operational strategies. For realistic values of membrane thickness and flow parameters, the model suggests that while membrane-gas interfacial resistance alone is crucial for heat transfer, the vapor transfer is governed by the combined resistances of diffusion within the membrane and membrane-gas interface. The model is validated against experimental data obtained using a commercial hollow fiber membrane module.

A new commercial biomimetic hollow fiber membrane for forward osmosis

Hollow fiber membranes have shown great promise as a platform for osmotic processes such as forward osmosis (FO) and pressure retarded osmosis (PRO). Numerous hollow fiber FO membranes have been designed by academic researchers around the world. However, few of these designs have made it to full scale production. In this study, we report on the newly launched Aquaporin Inside™ hollow fiber FO membrane from Aquaporin A/S, Denmark. These membranes were tested in miniature modules under various osmotic testing conditions. With incorporating biomimetic aquaporin proteins as “water channel” in the selective layer, these membranes exhibited excellent FO performance with water flux of 21 LMH, reverse salt flux of 3.6 gMH and specific reverse salt flux of 0.18 g/L in PRO mode with 1 M NaCl and deionized water as draw and feed solutions, respectively. The structure parameter was determined to be 210.5 ± 55.5 μm, which is one of the lowest S values reported for thin film composite hollow fiber membranes.

Evaluation of membrane microfiltration fouling in landfill leachate treatment

The membrane separation capacity allows the retention of the remaining organic matter that could not be removed by the biological process, increasing the treatment efficiency. The aim of this study was to evaluate the microfiltration (MF) process in a tertiary treatment system for landfill leachate from the Rincao das Flo-res, Caxias do Sul/RS/Brazil. The microfiltration system of commercial hollow fiber membrane poly(ether-imide) was tested in oder to promote leachate treatment. The tests carried out were leachate permeation, con-centration factor, determination of fouling and obtention of the values of the resitance to the flux. The re-sistance due to fouling and flux decline were evaluated to determine the best operating conditions. The poten-tial for fouling was 53% and was evaluated by comparing the pure water permeability before and after the leachate filtration. It was observed that the resistance due to fouling express 32% of the total resistance. The results showed that the MF process allows the elimination of up to 43% of the organic matter measured as chemical oxygen demand (COD) and 63% of that measured as biological oxygen demand (BOD5). Keywords: leachate; microfiltration; fouling; membrane resistance.

Enhanced hemocompatibility of flat and hollow fiber membranes via a heparin free surface crosslinking strategy

Insufficient hemocompatibility is challenging for current dialysis membranes. The current modification methods have some limitations in effectiveness, practicality and cost. Herein, we develop a heparin-free crosslinking approach to enhance the hemocompatibility of both the flat (polylactide) and hollow fiber (polysulfone) membranes with heparin-mimicking surface. Poly (triethoxyvinylsilane-N-vinyl-2-pyrrolidone) (P (VTES-VP)) is first introduced to the membrane surface to improve the hydrophilicity, which is facilitated to the adsorption and further crosslinking of poly (triethoxyvinylsilane-Acrylic acid-Sodium 4-vinylbenzenssulfonate) (P(VTES-AA-SSNa)). The mixture of N, N-dimethylacetamide (DMAc) and water was modulated for good solubility, swelling and adsorption of precopolymer. The chemical structure of the heparin-mimicking membrane was confirmed by attenuated total reflectance Fourier transform infrared spectra (FTIR-ATR), X-ray photoelectron spectroscopy (XPS), weight measurement and scanning electron microscopy (SEM). The hydrophilicity was improved by the heparin-mimicking surface. Moreover, the heparin-mimicking membranes presents higher platelet resistance, prolonged coagulation time (APTT for ~180.1s), decreased Plasma fibrinogen (FIB for ~122mg/dL), and suppressed complement activation. More importantly, the heparin-free crosslinking approach can be utilized to significantly enhance the hemocompatibility of commercial PSF hollow fiber membranes, indicating its potential application in heparin free dialyzers.

Designing and optimization of continuous direct contact membrane distillation process

Membrane distillation (MD) is a relatively less-explored membrane operation with the potential to achieve high recovery factor by using low grade heat. The current study proposes the design of a continuous direct contact MD process to achieve high recovery factors by using a commercial hollow fiber membrane. The design consists of multiple MD stages connected in series to achieve a predefined final solution concentration. Depending upon the outlet temperatures of feed and permeate, the design considers the option of heat recovery from permeate. Under a given set of operating conditions, there exists a module length (named as optimum module length) where the net thermal energy consumption and overall permeate productivity are optimum. The optimum module length has been analyzed as function of feed to permeate flow rate (F/P) ratio, feed temperature and concentration. It has been observed that for given feed temperature and concentration, the optimum module length can be tuned by changing F/P ratio. The minimum value of the optimum length is observed at the highest F/P ratio considered. Mathematical analysis was extended to evaluate the appropriate length and the corresponding thickness for each stage. The results reveal a strong nexus among membrane thickness, solution concentration and optimum length.

Enhancement of operating flux in a membrane bio-reactor coupled with a mechanical sieve unit

Filtration flux is one of the key factors in regulating the performance of membrane bio-reactors (MBRs) for wastewater treatment. In this study, we explore the effectiveness of a mechanical sieve unit for effective flux enhancement through retardation of the fouling effect in a modified MBR system (SiMBR). In brief, the coarse sieve unit having 100 μm and 50 μm permits small size microorganism flocs to adjust the biomass concentration from the suspended basin to the membrane basin. As a result, the reduced biofouling effect due to the lowered biomass concentration from 7800 mg/L to 2400 mg/L, enables higher flux through the membrane. Biomass rejection rate of the sieve is identified to be the crucial design parameter for the flux enhancement through the incorporation of numerical simulations and operating critical-flux measurement in a batch reactor. Then, the sieve unit is prepared for 10 L lab-scale continuous SiMBR based on the correlation between sieve pore size and biomass rejection characteristics. During continuous operation of lab-scale SiMBR, biomass concentration is maintained with a higher biomass concentration in the aerobic basin (7400 mg/L) than that in the membrane basin (2400 mg/L). In addition, the SiMBR operations are conducted using three different commercial hollow fiber membranes to compare the permeability to that of conventional MBR operations. For all cases, the modified MBR having a sieve unit clearly results in enhanced permeability. These results successfully validate that SiMBR can effectively improve flux through direct reduction of biomass concentration.