• Membrane and Water Treatment
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• v.2 no.3
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• pp.159-173
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• 2011

The air gap membrane distillation (AGMD) process was applied for water desalination. The main objective of the present work was to study the heat and mass transfer mechanism of the process. The experiments were performed on a flat sheet module using aqueous NaCl solutions as a feed. The membrane employed was hydrophobic PTFE of pore size 0.22 ${\mu}m$. A mathematical model is proposed to evaluate the membrane mass transfer coefficient, thermal boundary layers' heat transfer coefficients, membrane / liquid interface temperatures and the temperature polarization coefficients. The mass transfer model was validated by the experimentally and fitted well with the combined Knudsen and molecular diffusion mechanism. The mass transfer coefficient increased with an increase in feed bulk temperature. The experimental parameters such as, feed temperature, 313 to 333 K, feed velocity, 0.8 to 1.8 m/s (turbulent flow region) were analyzed. The permeation fluxes increased with feed temperature and velocity. The effect of feed bulk temperature on the boundary layers' heat transfer coefficients was shown and fairly discussed. The temperature polarization coefficient increased with feed velocity and decreased with temperature. The values obtained were 0.56 to 0.82, indicating the effective heat transfer of the system. The fouling was observed during the 90 h experimental run in the application of natural ground water and seawater. The time dependent fouling resistance can be added in the total transport resistance.

• Membrane Journal
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• v.13 no.4
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• pp.229-238
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• 2003

Pervaporation is mainly used to separate liquid mixtures because it exhibits a high selectivity compared with traditional distillation processes and it is known to be an energy saying separation process. Zeolite membranes show better thermal. mechanical, chemical stability than polymer membranes and especially silicalite-1 membrane can effectively separate organic compounds from water because of its high hydrophobicity. In this study, volatile organic compounds of ketone are separated by pervaporation using silicalite-1 membrane. As a feed concentration of acetone and MEK increases, a permeation flux of acetone and MEK increases while a selectivity decreases.

• Korean Chemical Engineering Research
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• v.49 no.5
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• pp.560-564
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• 2011

The objective of this study is to propose a mathematical model for a pervaporation process for concentrating hydrogen peroxide. The process was developed by NASA, which consists of a shell and membrane tubes, where a liquid hydrogen peroxide solution flows in the shell, and a sweep gas flows in the tubes countercurrent to each other. The liquid retentate is concentrated as more water molecules permeate and evaporate through the membrane than hydrogen peroxide. For this process, a mathematical model has been developed in the form of a system of nonlinear partial differential algebraic equations based on a sorption-diffusion mechanism for permeation, an Arrhenius relationship for the temperature dependency of the permeate flux, and mass and momentum balances for the liquid concentrations and flows in the membrane module. The dynamic behavior of the concentration of hydrogen peroxide in the retentate side has been simulated by solving a simplified version of the proposed model, and the result is compared with the experimental data reported in the NASA patent.

• Proceedings of the Membrane Society of Korea Conference
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• 2005.11a
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• pp.231-233
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• 2005

• Proceedings of the Membrane Society of Korea Conference
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• 2002.05a
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• pp.81-85
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• 2002

Small angle light scattering and field emission scanning electron microscope have been used to quantify the kinetics of liquid-liquid separation behavior during water vapor(RH52%[$\pm$3%] at 27$^{\circ}C$) quenching (non-solvent induced phase separation, NIPS) of polysulfone/NMP/Alcohol and CPVC/THF/Alcohol, respectively. Time dependence of the position of the light scattering maximum was observed at polysufone dope solutions, confirming spinodal secomposition (SD). while CPVC dope solutions showed a decreased scattered light intensity with a increased q-valuel, indicating nucleation & growth (NG). For the each system, domain growth rate in the intermediate and late stage of phase separation decreased with increasing the number of carbon of alcohol used as additive (non-solvent). Also, in the early stage for SD, the scattering intensity with time was in accordance with Cahns linear theory of spinodal decomposition,[1-3] regardless of types of non-solvent additive.

• Proceedings of the Membrane Society of Korea Conference
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• 1993.10a
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• pp.58-58
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• 1993

Pervaporation has become important as a method to separate liquid mixtures, sepecially azeotropic and close boiling-point mixtures. Especially, water-alcohol separations have been carried out a lot because of the practical interests in the industries. However, outstanding membranes with high selectivity and high permeability have not been available in common use yet. In order to separate selectively out the water mixed with alcohols with an aim of the purification of the alcohols, a membrane has tO have excellent affinity to water. Among the hydrophilic polymers, polyacrylic acid and poly(vinyl alcohol) are used widely. In recent years, ionomers and polyion complexes, better hydrophitic materials, start to be used. The polyion complex membranes, consisting of polyacrylic acid (PAA) and polycation, showed excellent permeation rates and selectivities. It was known that among the polycations, ioneries, which have quaternary ammonium groups in the backbone chain, were more effective in giving membranes of higher permselectivities. On this base, syntheses and characterizations of the polycations, with different chemical structures from the published ones, for the polyion complex membrane formation were studied in this paper.

• Membrane Journal
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• v.26 no.4
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• pp.291-300
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• 2016

Techniques for selectively separating molecules of gas and liquid states using various separation membranes have been widely used in variety of applications such as chemical, biological, pharmaceutical, and petrochemical industries. As the nanochannel diameter, inter-channel distance and length of the nanochannel of the anodic aluminum oxide (AAO) membranes can be precisely controlled, various studies to effectively separate mixture of various molecules using AAO membrane have been widely carried out. In this study, we fabricated AAO membranes of cylindrical nanochannels of various diameter sizes and of through-hole structure, that is, nanochannels of which both ends of each nanochannel are open. Using those AAO membranes of through-hole nanochannel structure, we studied the selective permeation polymer chains dissolved in a solvent based on hydraulic volume of the polymer chains. We found a precise, quantitative relationship between the radius of gyration of polymer chains that permeated through nanochannels inside AAO membrane and the diameter of nanochannels. In addition, we demonstrate that the behavior of the polymer solution flowing through nanochannel of the AAO membrane can be successfully described with the Hagen-Poiseuille relationship. It is, therefore, possible to theoretically interpret the nanoflow of the solution flowing inside the cylindrical nanochannel.

• Membrane and Water Treatment
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• v.10 no.4
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• pp.287-298
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• 2019

Lotus leaf has a special dual micro and nano surface structure which gives its highly hydrophobic surface characteristics and so-called self cleaning effect. In order to endow PVDF hollow fiber membrane with this special structure and improve the hydrophobicity of membrane surface, PVDF hollow fiber composite membranes was obtained through the immersion coating of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) dilute solution on the outside surface of PVDF support membrane. The prepared PVDF composite membranes were used in the vacuum membrane distillation (VMD) for the desalination. The effects of PVDF-HFP dilute solution concentration in the dope solution and coating time on VMD separation performance was studied. Membranes were characterized by SEM, WCA measurement, porosity, and liquid entry pressure of water. VMD test was carried out using $35g{\cdot}L^{-1}$ NaCl aqueous solution as the feed solution at feed temperature of $30^{\circ}C$ and the permeate pressure of 31.3 kPa. The vapour flux reached a maximum when PVDF-HFP concentration in the dilute solution was 5 wt% and the coating time was kept in the range of 10-60 s. This was attributed to the well configuration of micro-nano rods which was similar with the dual micro-nano structure on the lotus leaf. Compared with the original PVDF membrane, the salt rejection can be well maintained which was greater than 99.99 % meanwhile permeation water conductivity was kept at a low value of $7-9{\mu}S{\cdot}cm^{-1}$ during the continuous testing for 360 h.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.11 no.3
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• pp.193-198
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• 2013

In general, boron recovery of 40-90% could be achieved by Reverse Osmosis (RO) membranes in neutral pH condition. As an emerging technology, Forward Osmosis (FO) membrane has attracted growing interest in wastewater treatment and desalination. The objective of this study is to evaluate the possibility of the boron removal in radioactive liquid waste by FO. In this study, the performance of FO was investigated to remove boron in the simulated liquid waste as the factors such as pH, osmotic pressure, ionic strength of solution, etc. The pH of feed solution is a major operating parameter which strongly influences to the permeation of boron and more than 80% of boron content can be separated when conducted at pH values less than 7. The water flux is not influenced but the boron flux and permeation rate tends to decrease in the low salt concentration of 1,000 mg/L. The boron flux increases linearly, but the permeation ratio of reducing boron is nearly constant even with changes in the draw solution concentration.

• Membrane Journal
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• v.27 no.1
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• pp.43-52
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• 2017

The air injection nozzle tube was inserted inside of the tubular membrane module to reduce membrane fouling and improve the permeate flux. The average pore size of membrane was $0.1\;{\mu}m$ and the yeast was used as a foulant. All of permeate experiments were started without air injection for the module equipped with the nozzle tube, then carried out continuously with air injection. Finally, the nozzle tube was removed from the module and the permeate was measured without air injection. The measured permeate fluxes were compared to examine the effect of air injection. The fluxes for air injection were consistently maintained or increased. The fluxes of no-air injection with the nozzle tube were greater than those of the empty tubular module. As operating pressure decreased to 0.4 bar, the flux enhancement of air injection based on no-nozzle case increased to 21%. Flux enhancements of air injection were above 30% as the gas/liquid two-phase flow was changed from the stratified-smooth to the intermittent pattern due to increase of gas flowrate.