Effect Of Membrane Characteristics Research Articles

Effects of membrane characteristics on the evaporative cooling performance for hollow fiber membrane modules

The hollow fiber membrane-integrated evaporative cooler (MEC) is considered as a promising strategy for space air conditioning applications. For a counter-flow MEC, the appropriate fiber specification and flow configuration need to be identified to improve its comprehensive performance. A numerical model was developed to capture the coupled heat and mass transfer process, and its feasibility was verified by measured data. The influence of fiber specifications and flow configuration on its cooling, space-saving, energy and water conservation performance were investigated. The results revealed that a reasonable fiber specification required a packing fraction of about 0.1 and a length slightly longer than the air channel's entrance length, while the inner diameter and membrane thickness should be determined based on the priority index. The flow configuration of air flowing via shell-side and water going through tube-side was more suitable for counter-flow MEC, which was more energy efficient while maintaining cooling ability. In addition, the contribution of each component's resistance to the total heat and mass transfer resistance would fluctuate as the influencing factors changed. In general, the total heat transfer resistance was dominated by the air-side convective resistance, while the main contributor to the total mass transfer resistance was the membrane resistance.

Modeling of pre-combustion carbon capture with CO2-selective polymer membranes

CO2-selective polymer membranes were recently applied to pilot-scale and bench-scale pre-combustion capture and the obtained CO2 capture ratios were reported to be less than 90%, which limits their application in industrial processes such as IGCC plants. This work is aimed to explore the possibility of achieving a CO2 capture ratio >95% and CO2 purity >95% in a gas-separation unit equipped with currently-available CO2-selective polymer membranes. A mathematical model for single-stage membrane gas separation was developed, and the effect of membrane characteristics (permeance and selectivity), as well as the operating parameters such as feed and permeate pressure, and feed flow rate on the performance of CO2 capture was investigated. The simulation results reveal the optimal conditions that are necessary for a high-performance CO2 capture process using the real industrial syngas and highlight the potential of facilitated transport membranes for CO2 removal in both the oxygen-blown and air-blown IGCC processes.

Natural organic matter and sulphate elimination from rainwater with nanofiltration technology and process optimisation using response surface methodology.

In the current study, the effect of operating conditions including membrane characteristics and applied pressure on natural organic matter and sulphate removal of nanofiltration (NF) membranes for drinking water production was investigated. Water stress has been increasing all over the world due to population growth, climate change, and pollution; rainwater management stands out as one of the key solutions to this problem. Nanofiltration to treat rainwater stored in a cistern was studied. The objectives were sufficient treatment performance to overcome the taste problem and lower energy consumption. In this regard, three commercial nanofiltration membranes (NP010, NP030, and NF90) were used for the experiments carried out at 6-12 bar operating pressure regarding the response surface methodology. The correlation among the results of experiments and the model parameters were also calculated for all steps. According to the results, the effect of membrane characteristics was more abundant than the effect of the operating pressure. Finally, over 99% of natural organic matter and sulphate were eliminated in the optimum conditions. The results showed that it is possible to obtain treated rainwater with desired qualities, in a non-continuous NF plant operated at the pressure of 6 bar to reuse the rainwater and achieve water sustainability.

Reverse osmosis brine treatment using direct contact membrane distillation (DCMD): effect of membrane characteristics on desalination performance and the wetting phenomenon

PVDF membranes with different pore sizes were used to investigate effect of membrane properties on membrane flux and pore wetting in RO brine treatment by DCMD.

Recovery of Methyl Green from Aqueous Solution using NF Membrane

Recovery of a cationic synthetic dye, methyl green by nanofiltration (NF 270–400) membrane from commercial source (Filmtec, USA) was used for this study. The effect of membrane characteristics, applied pressure gradient ( ΔP ) and aqueous phase concentration of dye on the rejection, membrane fouling and water flux was studied over a range of pressure and concentration of 2 to 5 bar and 0.01 mmole L–1 to 0.05 mmole L–1 respectively. The solution flux increases with pressure in the pressure range studied indicate the effect of concentration polarization is not significant in this range. The cation shield effects of the dye on the negatively charged polyamide membrane perhaps result in decrease of permeate flux with concentration. The permeation phenomenon has been analyzed on the basis of pore flow transport model and the data analysis revealed that adsorption of dye on the membrane surface and intrinsic membrane resistance control the permeate flux.

Microfiltration of oil in water (O/W) emulsions: Effect of membrane microstructure and surface properties

In this work, oil in water (O/W) emulsions prepared with a natural emulsifier and different oil phase concentrations were processed by using Anodisc, cellulose acetate (CA), polyester/nylon, silicon nitride microsieves and polycarbonate track etched (PCTE) membranes of different pore sizes (0.22–0.8μm). The effect of membrane characteristics on properties of the emulsions was assessed by droplet size distribution, ζ-potential and pH. Results suggest that membrane hydrophilicity is critical to avoid breaking during microfiltration of O/W emulsions. Partial or total retention of oil droplets from concentrated emulsions (10–30% oil) occurred with all 0.22μm membranes, except with the 0.26μm microsieves. PCTE membrane (uniform straight pores) performance was function of the d¯droplet/dpore ratio, i.e. (a) if d¯droplet/dpore<1, emulsions fully filtered, (b) if 1.0<d¯droplet/dpore≤1.5, partial breaking of larger droplets occurs and (c) if d¯droplet/dpore≥2, retention and probably coalescence of larger drops led to fouling and total pore blockage. Performance of CA membranes (interconnected pores) was rather related to the oil concentration and the number of droplets found in the emulsion. Breaking into the pores and coalescence onto the 0.22μm CA membrane surface started when processing a 5% oil emulsion with estimated concentration of ≥2.42×1012 oil droplets/mL.

Polymer Electrolyte Membranes for Water Photo-Electrolysis.

Water-fed photo-electrolysis cells equipped with perfluorosulfonic acid (Nafion® 115) and quaternary ammonium-based (Fumatech® FAA3) ion exchange membranes as separator for hydrogen and oxygen evolution reactions were investigated. Protonic or anionic ionomer dispersions were deposited on the electrodes to extend the interface with the electrolyte. The photo-anode consisted of a large band-gap Ti-oxide semiconductor. The effect of membrane characteristics on the photo-electrochemical conversion of solar energy was investigated for photo-voltage-driven electrolysis cells. Photo-electrolysis cells were also studied for operation under electrical bias-assisted mode. The pH of the membrane/ionomer had a paramount effect on the photo-electrolytic conversion. The anionic membrane showed enhanced performance compared to the Nafion®-based cell when just TiO2 anatase was used as photo-anode. This was associated with better oxygen evolution kinetics in alkaline conditions compared to acidic environment. However, oxygen evolution kinetics in acidic conditions were significantly enhanced by using a Ti sub-oxide as surface promoter in order to facilitate the adsorption of OH species as precursors of oxygen evolution. However, the same surface promoter appeared to inhibit oxygen evolution in an alkaline environment probably as a consequence of the strong adsorption of OH species on the surface under such conditions. These results show that a proper combination of photo-anode and polymer electrolyte membrane is essential to maximize photo-electrolytic conversion.

Removal of cobalt ions from aqueous solution by forward osmosis

Abstract The performance of Co(II) removal from aqueous solution by forward osmosis (FO) was investigated. NaCl solutions were used as the draw solutions (DS). The effects of membrane characteristics, feed solutions properties, DS concentration, cross-flow rates on FO performance (water flux, Co(II) flux and retention, and reverse NaCl flux) were determined. The separation mechanisms under the various operational conditions were discussed. Changes of the FO membrane after Co(II) separation were characterized. The results show that CTA-ES featured the highest water fluxes of 15.5 ± 0.5 L m−2 h−1 at AL-FS and 23.4 ± 2.5 L m−2 h−1 at AL-DS among the three membranes. The active layer charge of the FO membrane was a main factor affecting Co(II) retention by FO. The texture of the support layer played a great role in the water permeability and reverse NaCl flux. The optimal operational conditions for Co(II) retention was NaCl concentration of 1.0 M in DS, the cross-flow rates of 11 and 5 cm s−1 at the feed and DS sides respectively. After used, the active layer of the CTA-ES membrane became more rough and hydrophobic. Co might attach to the membrane and became the membrane foulants. FO process could be an alternative technology for radioactive wastewater.

Modeling of the fouling of inside-out hollow fiber UF membranes

Membrane processes often experience a decline in the permeate flux or an increase in the operating pressure from membrane fouling. A mathematical model that describes the fouling of inside-out hollow fiber ultrafiltration (UF) membranes was derived from hydrodynamic equations coupled with the theory of depth filtration. The correlation predictions obtained in this study are simpler, as the effect of membrane characteristics, water recovery, and membrane washing processes on UF membrane fouling were expressed using a single parameter: the membrane blocking coefficient. Membrane filtration tests were conducted using diluted paper industry wastewater in a constant-pressure and constant-current operational mode. The effects of different operating conditions, such as water recovery and cleaning methods, and membrane characteristics, on the membrane blocking coefficient were evaluated. The predictive capability of the proposed model was excellent, according to a comparison of the experimental results and model simulations.

The effect of membrane characteristics on nanofiltration membrane performance during processing of practically saturated salt solutions

Information on the effect of membrane characteristics on the performance of nanofiltration membranes during processing of concentrated sodium chloride solutions is scarce. This hampers membrane selection for these applications. In this study nanofiltration membranes, ranging from very tight to very open, have been evaluated for processing of sodium chloride solutions obtained from solution mining. Sulfate retention of these membranes is inversely related to their pore radius obtained from membrane characterization. The chloride retention during nanofiltration of practically saturated salt solutions is a function of the sulfate concentration difference between concentrate and permeate. The observed relation is explained by the small sodium chloride chemical potential difference between concentrate and permeate, indicating low membrane resistance for sodium chloride transport. This is concluded from the sodium chloride concentration product ratios of permeate over concentrate, which were found to be between 0.9 and 1 for all membranes evaluated. This ratio is proportionally related to the membrane pore radius obtained from characterization. Based on the results the sulfate and chloride retention of nanofiltration membranes for processing of saturated sodium chloride solutions can now be obtained from a simple characterization experiment.

Effects of membrane characteristics on performances of pressure retarded osmosis power system

Effects of the characteristics of membrane such as water permeability-coefficient, solute permeability-coefficient, and membrane resistivity on the performances of the spiral wound module in the PRO system have been studied numerically. Fluxes of water and solute through membrane, and concentrations and flow rates in the channels were obtained. The water flux through membrane increases almost linearly with the water permeability-coefficient, but it is insensitive to the solute permeability-coefficient. Decreasing the membrane resistivity makes the water flux through membrane and the power density increase. Effects of the membrane resistivity on the water flux through membrane and flow rates in the channels are small when the difference between the inlet-pressures of draw- and feed-channel is large and vice versa. The power density increases and then decreases as the channel-inlet pressure difference increases. The maximum power density is 16 W/m2 at 14 atm of the channel-inlet pressure difference in our system.

Treatment of high salinity brines by direct contact membrane distillation: Effect of membrane characteristics and salinity

Direct contact membrane distillation (DCMD) is one of the attractive technologies for high salinity brine treatment. In this study, four polytetrafluoroethylene (PTFE) membranes were examined in treating highly concentrated salt solutions. Results showed that non-supported membranes generally have a higher overall mass transfer coefficient but porosity seems to be the most important parameter controlling membrane flux and thermal efficiency. Supported membranes with large thickness had relatively higher thermal efficiency than small thickness. This can be attributed to their reduced heat loss through heat condition. In addition, KCl, NaCl and MgCl2 solutions showed distinct trends over flux decline at high salt concentrations (⩾2.0M). The difference in flux was largely due to the discrepancy in water activities of these solutions (KCl>NaCl>MgCl2). However, the effect of viscosity on permeate flux could not be neglected for MgCl2 at high salt concentrations as the suddenly increased viscosity could lead to serious temperature polarization. This study indicates that membrane distillation is a promising technology for high salinity brine treatment.

Optimization study of small-scale solar membrane distillation desalination systems (s-SMDDS).

Membrane distillation (MD), which can utilize low-grade thermal energy, has been extensively studied for desalination. By incorporating solar thermal energy, the solar membrane distillation desalination system (SMDDS) is a potential technology for resolving energy and water resource problems. Small-scale SMDDS (s-SMDDS) is an attractive and viable option for the production of fresh water for small communities in remote arid areas. The minimum cost design and operation of s-SMDDS are determined by a systematic method, which involves a pseudo-steady-state approach for equipment sizing and dynamic optimization using overall system mathematical models. Two s-SMDDS employing an air gap membrane distillation module with membrane areas of 11.5 m2 and 23 m2 are analyzed. The lowest water production costs are $5.92/m3 and $5.16/m3 for water production rates of 500 kg/day and 1000 kg/day, respectively. For these two optimal cases, the performance ratios are 0.85 and 0.91; the recovery ratios are 4.07% and 4.57%. The effect of membrane characteristics on the production cost is investigated. For the commercial membrane employed in this study, the increase of the membrane mass transfer coefficient up to two times is beneficial for cost reduction.

Removal of hardness by electrodialysis using homogeneous and heterogeneous ion exchange membranes

The effect of membrane characteristics on removal of hardness ions from its dilute solutions using electrodialysis (ED) system by applying batch recirculation mode has been investigated. Two types of membrane pairs were used. Type I: Ionac MC3470 and MA3475 (Sybron Chem. Co.); Type II: Neosepta CMX and Neosepta AMX (Astom Corp.). These membranes have different ionic permselectivity, electrical resistance and thickness. In the first part of the study, the effects of the feed concentration, dilute flow rate and dilute pH on the hardness removal were investigated using Type I membranes. The optimum values for feed concentration, flow rate and pH were determined as 0.01 M, 2.6 mL/s and 6.8, respectively. In the second part, the experiments were conducted at different voltage values using Type II membranes under the optimum conditions of these variables obtained. The 95% removal of Mg2+ with the energy consumption of 2.07 kWh/mol and 93% removal of Ca2+ with the energy consumption of 2.12 kWh/mol were obtained in 200 min, applying 20 V potential using Type I membranes. On the other hand, the 100% removal of Mg2+ was achieved by the energy consumption of 1.69 kWh/mol in only 60 min. and the removal of Ca2+ was 98.3% with the energy consumption of 3.39 kWh/mol in 170 min. applying 20 V and using Type II membranes. The results obtained from this study showed that the membrane characteristics affect the efficiency of the ED significantly.

Effect of membrane characteristics on the performance of membrane bioreactors for oily wastewater treatment

Influence of membrane material and pore size on the performance of a submerged membrane bioreactor (sMBR) for oily wastewater treatment was investigated. The sMBR had a working volume of about 19 L with flat sheet modules at the same hydrodynamic conditions. Five types of micro- and ultra-polymeric membranes containing cellulose acetate (CA), cellulose nitrate (CN), polyamide (PA), polyvinylidene difluoride (PVDF) and polyethersulfone (PES) were used and their filtration performance in terms of permeability, permeate quality and fouling intensity were evaluated. Characterization of the membranes was done by performing some analysis such as pore size distribution; contact angle and scanning electronic microscopy (SEM) microphotograph on all membranes. The quality of permeates from each membrane was identified by measuring chemical oxygen demand (COD). The results showed more irreversible fouling intensity for membranes with larger pore size which can be due to more permeation of bioparticles and colloids inside the pores. Membrane characteristics have a major role in the preliminary time of the filtration before cake layer formation so that the PA with the highest hydrophilicity had the lowest permeability decline by fouling in this period. Also, the PVDF and PES membranes had better performance according to better permeate quality in the preliminary time of the filtration related to smaller pore size and also their better fouling resistance and chemical stability properties. However, all membranes resulted in the same permeability and permeate quality after cake layer formation. An overall efficiency of about 95% in COD removal was obtained for oily wastewater treatment by the membranes used in this study.

A modeling study on the effects of membrane characteristics and operating parameters on physical absorption of CO 2 by hollow fiber membrane contactor

The mathematical model has been developed to investigate the physical absorption of CO 2 using the hollow fiber membrane contactor. The model takes into account the effect of membrane pore size distribution. The simulation is thoroughly performed for various membrane properties and operating conditions. The pressure drop of the liquid flow in the lumen side of the fiber leading to the different wetting ratio ( x*) along the fiber length is presented. The wetting behaviors and degree of membrane wetting of the membrane with different characteristics such as pore size, pore size distribution, hydrophobicity, porosity, thickness, fiber diameter, and fiber length are reported. The membranes with large pore radius, high standard deviation and high porosity show higher CO 2 absorption flux in completely dry mode operation. However, these membranes are sensitive to the membrane wetting if the liquid feed pressure ( P L0 ) is increased, resulting in absorption flux deterioration. In addition, the effect of important operating parameters including gas/liquid flow rates, gas composition and liquid temperature on absorption performance are also investigated.

Nanofiltration of glucose solution containing salts: Effects of membrane characteristics, organic component and salts on retention

The understanding on nanofiltration especially the rejection of uncharged solutes, charged solutes and mixture of solutes is crucial for its application in food industry. This is because process streams in food industry usually contain organic components without charge and salts. In this work, DK and CK membranes were utilized for the separation of multi-component feeds containing glucose, NaCl and multivalent salts (MgCl 2 or Na 2SO 4). Glucose rejection is slightly affected by salt concentration which may due to pore swelling of CK membranes at high concentration of NaCl. Meanwhile, rejection of NaCl is reduced by the increment of glucose and NaCl concentration which causes concentration polarization. The addition of multivalent salts even induces negative rejection of NaCl in DK membranes. However, both membranes show high rejection of multivalent salts with or without the presence of glucose. The rejection behavior follows the pattern expected from the structural and electrical properties of the membranes.

Numerical simulation of colloid dead-end filtration: Effect of membrane characteristics and operating conditions on matter accumulation

The aim of this work is to develop a simulation capability applicable to dead-end filtration of colloidal dispersions in order to investigate the effect of process conditions, such as membrane configuration and operating parameters, on filtration efficiency through the analysis of the appearance of a deposit on the membrane. To reach this goal, a model describing the transport behaviour of a concentrated colloidal dispersion is implemented in a commercial CFD code (ANSYS-CFX). The collective diffusion induced by inter-particle interactions is accounted for from knowledge of the variation of the osmotic pressure with the particle volume fraction. Coupled with a transient, two dimensional hydrodynamic solution, such a model allows description of the mass transport properties both in the dispersed (concentration polarisation) and the condensed (deposit) forms of accumulation. Two-dimensional concentration profiles along the membrane are obtained. Simulations are used to understand the role of operating parameters and membrane characteristics on the appearance of a deposit at the membrane surface. This formation is controlled by the hollow fibre configuration, where there are zones working in both cross-flow and dead-end mode due to the particular hydrodynamic conditions.

Mass Diffusion in a Hydrophobic Membrane Humidification/Dehumidification Process: the Effects of Membrane Characteristics

Humidification and dehumidification are common processes in air conditioning industry. In this study, a new technique‐the hydrophobic membrane based air humidification and dehumidification are investigated. The effects of membrane characteristics on moisture exchange effectiveness of the system are studied. A two‐dimensional transient model which takes into account the combined mechanisms of Knudsen flow and ordinary diffusion in membrane pores is proposed and validated. Four membranes, 2 hydrophobic treated Nylon and 2 PVDF, are used in the test to validate the model. Then the effects of variations of membrane properties on the system performance and membrane to total resistance ratio, are evaluated. A dimensionless Number of Transfer Units (NTU) can be summarized to govern the moisture exchange performance. Following, a correlation has been obtained to reflect the relations between the moisture exchange effectiveness and the Number of Transfer Units.

Effect of Membrane Characteristics on Phase Separation and Domain Formation in Cholesterol-Lipid Mixtures

We examine, using an analytical mean-field model, the distribution of cholesterol in a lipid bilayer. The model accounts for the perturbation of lipid packing induced by the embedded cholesterol, in a manner similar to that of transmembrane proteins. We find that the membrane-induced interactions between embedded cholesterol molecules vary as a function of the cholesterol content. Thus, the effective lipid-cholesterol interaction is concentration-dependent. Moreover, it transitions from repulsive to attractive to repulsive as the cholesterol content increases. As the concentration of cholesterol in the bilayer exceeds a critical value, phase separation occurs. The coexistence between cholesterol-rich and cholesterol-poor domains is universal for any bilayer parameters, although the composition of the cholesterol-rich phase varies as a function of the lipid properties. Although we do not assume specific cholesterol-lipid interactions or the formation of a lipid-cholesterol cluster, we find that the composition of the cholesterol-rich domains is constant, independent of the cholesterol content in the bilayer.