Transport Of Pure Water Research Articles

Exploring capillary adsorption of corrosive medium in epoxy resin-modified calcium-silicate-hydrate channels

In coastal environment development and island construction, cement-based materials are crucial, but they are exposed to high temperatures, humidity, salt, and weathering in marine environments, leading to the deterioration of offshore concrete structures' durability. To mitigate these effects, epoxy resin, a polymer material with excellent adhesion with cement-based materials and chemical corrosion resistance, can slow down harmful ion erosion and improve concrete structure durability. This paper proposes a molecular dynamics simulation model to investigate the transport of pure water and NaCl solution in calcium-silicate-hydrate (C-S-H) gel pore channels with and without epoxy coating. The study demonstrates that epoxy resin can effectively slow down water molecule and ion transport in the C-S-H channels. When the solution passes through the C-S-H gel pore channel, the water molecules occupy the adsorption sites of the epoxy molecules, resulting in partial exfoliation of the epoxy resin. The exfoliated epoxy resin forms an enhanced hydrogen bonding network with the water molecules and forms ion pairs with the ions, which induces the ions and water molecules to gather around the epoxy molecules and form a larger cluster structure, thus slowing down the migration of ions and water molecules in the C-S-H pore channel.

Cellulose acetate polymer matrix loaded Olea europaea nanosolids as low fouling membrane composite

A considerable hindrance in application of ultrafiltration membranes for aqueous application is an occurring fouling which promotes deterioration of the membrane separation processes. Natural Olea europaea leaves extract nanosolids embed in cellulose acetate polymer matrix to enhance anti-biofouling properties of ultrafiltration membrane. Olea europaea phenolic compounds extracted by using Microwave-assisted Extraction (MAE) method and evaporated to obtain nanosolid particles. The cellulose acetate/Olea europaea nanosolids (CA/OEN) membrane composite prepared using phase inversion method. The membrane properties evaluated in term of mechanical, mass transport and anti-biofouling properties. The membranes show a good mechanical property with the membrane tensile ranged within 3.3 N/mm2 and 6.8 N/mm2, and can acts as ultrafiltration composite membranes based on the pure water transport across the membrane, with the pure water flux ranged from 0.3 L/m2.h.bar to 0.9 L/m2.h.bar. In term of anti-biofouling properties, the membrane shows a good anti-biofouling property against Escherichia coli, Bacillus subtilis, and Staphylococcus aureus, with the percentage of area covered by bacteria are ranged between 0.39 % and 1.41 %. Yet, penetration of phenolic substance into bacterial cells could effectively occurred in a Gram-negative bacterium such as Escherichia coli due to low affinity, thin cell wall, and few peptidoglycans structure.

Untangling the physics of water transport in boron nitride nanotubes.

Carbon nanotubes (CNTs) have long been heralded as the material of choice for next-generation membranes. Some studies have suggested that boron nitride nanotubes (BNNTs) may offer higher transport of pure water than CNTs, while others conclude otherwise. In this work, we use a combination of simulations and experimental data to uncover the causes of this discrepancy and investigate the flow resistance through BNNT membranes in detail. By dividing the resistance of the nanotube membranes into their contributing components, we study the effects of pore end configuration, membrane length, and BNNT atom partial charges. Most molecular simulation studies of BNNT membranes use short membranes connected to high and low pressure reservoirs. Here we find that flow resistances in these short membranes are dominated by the resistance at the pore ends, which can obscure the understanding of water transport performance through the nanotubes and comparison between different nanotube materials. In contrast, it is the flow resistance inside the nanotubes that dominates microscale-thick laboratory membranes, and end resistances tend to be negligible. Judged by the nanotube flow resistance alone, we therefore find that CNTs are likely to consistently outperform BNNTs. Furthermore, we find a large role played by the choice of partial charges on the BN atoms in the flow resistance measurements in our molecular simulations. This paper highlights a way forward for comparing molecular simulations and experimental results.

Removal of volatile organic compounds from aqueous solutions applying thermally driven membrane processes. 2. Air gap membrane distillation

Air gap membrane distillation technique (AGMD) was applied for removal of ethanol, butanol and acetone–butanol–ethanol mixture from water. The influence of various parameters (feed temperature, cooling wall temperature) on pure water transport in AGMD was determined and the efficiency of organic solvents removal from water through two porous membranes (PTFE and PP) was investigated in the detail.Selectivity of organic components recovery did not change significantly with an increase of feed temperature from 41°C to 63°C in case of AGMD applied for ethanol and butanol recovery, however significantly higher fluxes were obtained at higher feed temperature. Slightly higher fluxes were obtained during experiments performed with PTFE membrane comparing with PP one.It was found that both PTFE and PP membranes are wetted during AGMD process of water–butanol feed mixture if organic concentration exceeds 2.5wt% (PTFE) and 1wt% (PP) at 63°C feed temperature. This fact limits the possibility of wider AGMD application in organic solvent recovery.The comparison of the efficiency of AGMD with the efficiency of thermopervaporation (TPV) was also performed. In case of 1wt% ethanol feed mixture it was found that AGMD seems to be more suitable due to higher process separation index value (PSI in the range of 6kgm−2h−1) than in the case of TPV (PSI in the range of 3kgm−2h−1). On the contrary, in the case of water–butanol or water–ABE systems TPV is much more efficient method for organics recovery from aqueous mixtures than AGMD. In contact with 3wt% ABE mixture PSI is equal to 28 and 9kgm−2h−1 for TPV and AGMD processes, respectively.

Highly hydrophobic ceramic membranes applied to the removal of volatile organic compounds in pervaporation

Abstract Highly hydrophobic titania, alumina and zirconia porous ceramic membranes were prepared by grafting of C 6 F 13 C 2 H 4 Si(OEt) 3 (C6) and C 12 F 25 C 2 H 4 Si(OEt) 3 (C12) molecules and subsequently applied in pervaporation (PV) process for removal of volatile organic compounds (methyl tert-butyl-ether/MTBE and ethyl acetate/EtAc) from binary aqueous solutions. Transport of pure water through pristine and hydrophobized membranes were compared. The transport and separation properties in PV process of investigated hydrophobic membranes were discussed. The influence of the membrane materials, pore size of the membranes as well as conditions of the grafting procedure (time and type of molecules) on the pervaporative properties was presented. All investigated membranes were selective toward organic compounds. The highest efficiency was found for the TiO 2 membranes, independently of the utilized system and applied grafting molecules. Better transport and selective properties were observed for membrane modified by C6 molecules than by C12 ones. TiO 2 and ZrO 2 membranes modified by C6 were characterized by high β separation factors 84 (TiO 2 ) and 56 (ZrO 2 ). The least effective membrane was alumina one. Additionally, the influence of contact of different solvents (water, EtAc and MTBE) with the hydrophobic layer was discussed. It was found that in the presence of organic compounds in the aqueous solution, the conformation of hydrophobic chains is changing from tangled to straight one.

Nonequilibrium molecular dynamics simulation of water transport through carbon nanotube membranes at low pressure

Nonequilibrium molecular dynamics (NEMD) simulations are used to investigate pressure-driven water flow passing through carbon nanotube (CNT) membranes at low pressures (5.0 MPa) typical of real nanofiltration (NF) systems. The CNT membrane is modeled as a simplified NF membrane with smooth surfaces, and uniform straight pores of typical NF pore sizes. A NEMD simulation system is constructed to study the effects of the membrane structure (pores size and membrane thickness) on the pure water transport properties. All simulations are run under operating conditions (temperature and pressure difference) similar to a real NF processes. Simulation results are analyzed to obtain water flux, density, and velocity distributions along both the flow and radial directions. Results show that water flow through a CNT membrane under a pressure difference has the unique transport properties of very fast flow and a non-parabolic radial distribution of velocities which cannot be represented by the Hagen-Poiseuille or Navier-Stokes equations. Density distributions along radial and flow directions show that water molecules in the CNT form layers with an oscillatory density profile, and have a lower average density than in the bulk flow. The NEMD simulations provide direct access to dynamic aspects of water flow through a CNT membrane and give a view of the pressure-driven transport phenomena on a molecular scale.

Pervaporation of binary water–alcohol and methanol–alcohol mixtures through microporous methylated silica membranes: Maxwell–Stefan modeling

The transport of pure water and methanol and the selective pervaporation of binary mixtures of water or methanol in alcohols (ethanol, isopropanol, butanol) are studied for two methylated microporous silica membranes as a function of feed composition (0–15 vol% water or methanol) at 60 °C. Flux data show interaction effects between the polar components in the feed. Alcohol molecules block water and methanol transport, whereas water and methanol block or enhance the alcohol transport. A simplified Maxwell–Stefan model is set up to predict fluxes from pure component pervaporation data and from literature adsorption coefficients. The Vignes equation is used to describe the concentration dependency of the mutual diffusion coefficient. The model allows a good quantitative prediction of the ethanol–water, isopropanol–water and ethanol–methanol mixtures, but needs improvement for the isopropanol–methanol and for the butanol mixtures either in water or in methanol.

Temperature Polarization Coefficients in Membrane Distillation

ABSTRACT Membrane distillation is a membrane process in which two liquid phases at different temperatures are separated by a microporous hydrophobic membrane. The membrane plays the role of a physical support for the vapor—liquid interface. The aim of this paper is to study pure water transport by membrane distillation through a PTFE flat membrane. The dependence of the phenomenon on average temperature and recirculation rate at the membrane sides is investigated. The influence of these operating conditions on water transport is discussed by taking into account mass and heat transfer within the membrane and the adjoining liquid phases. The concept of temperature polarization is introduced into the transport equations and shown to be important in the interpretation of our experimental results.

Temperature polarization in mass transport through hydrophobic porous membranes

AbstractMembrane distillation is a membrane process in which two liquid phases at different temperatures are separated by a microporous hydrophobic membrane. The membrane plays the role of physical support for the vapor‐liquid interface. Pure water transport through PTFE and PVDF flat membranes was studied, as well as the dependence of the phenomena on average temperature and recirculation rate at membrane sides. The influence of these operating conditions on mass transfer is also discussed, taking into account mass and heat transfer within the membrane and adjoining liquid phases. The concept of temperature polarization introduced into the transport equations shows its importance in experimental results.

Nonisothermal Water Transport through Hydrophobic Membranes in a Stirred Cell

This paper studies the transport of pure water through microporous hydrophobic membranes in a stirred cell when bathed by two phases at different temperatures. The dependence of the phenomena on the stirring rate and on the average temperature has been investigated. The influence of these operating conditions on the mass transfer rate is discussed while keeping in mind the theories of mass and heat transfer within the membrane and adjoining liquids. The concept of temperature polarization is introduced in the transport equations, and it is shown to be important in the interpretation of our experimental results.

Water distillation through poly(tetrafluoroethylene) hydrophobic membranes in a stirred cell

The aim of this paper is the study of the transport of pure water through microporous hydrophobic membranes in a stirred cell containing two phases at different temperatures. The dependence of the phenomena on stirring rate and on the average temperature has been investigated. The influence of these operating conditions on mass-transfer rate is discussed, taking into account mass and heat transfer within the membrane and adjoining liquids. The concept of temperature polarization is introduced into the transport equations and shown to be important in the interpretation of experimental results.

REVERSE OSMOSIS IN DECRYSTALLIZED NYLON 6 AND DECRYSTALLIZED ACRYLIC ACID GRAFTED NYLON 6 MEMBRANES

Nylon 6 film and acrylic acid grafted nylon 6 membranes prepared by γ-irradiation method were reacted with paraformaldehyde and lactic acid in the presence of acid catalysts. Decrystallized nylon 6 (DN) and decrystallized grafted nylon 6 (DGN) membranes were thus obtained. The reverse osmosis properties of the membranes were investigated. The hydraulic permeability coefficient, K1, of water increased with increasing the volume fraction of water in the swollen membranes. Although the salt rejection, Rs, decreased with increasing the volume fraction for DN and 50% grafted DGN membranes, this pattern was not observed for the DGN membranes with more than 100% grafting. For the latter membranes the salt rejection decreased only slightly even at higher Kl values. An equation to relate Rs to K1 is described. For the parallel transport of pure water and salt solution with the same concentration of the feed solution through different parts of the swollen membranes, the salt rejection, Rs, can be represented as where k is the rate ratio of the volume flows in pure water and in the salt solution. V1/V0 represents the fraction of the volume of the pure water phase in the total membrane volume. B and K0 are constants.