Research

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17 pages, 6298 KiB

Open AccessArticle

Membrane-Assisted Crystallization: A Molecular View of NaCl Nucleation and Growth

by Jheng-Han Tsai, Maria Luisa Perrotta, Annarosa Gugliuzza, Francesca Macedonio, Lidietta Giorno, Enrico Drioli, Kuo-Lun Tung and Elena Tocci

Appl. Sci. 2018, 8(11), 2145; https://doi.org/10.3390/app8112145 - 02 Nov 2018

Cited by 12 | Viewed by 4190

Abstract

Membrane-assisted crystallization, aiming to induce supersaturation in a solution, has been successfully tested in the crystallization of ionic salts, low molecular organic acids, and proteins. Membrane crystallization is an emerging membrane process with the capability to simultaneously extract fresh water and valuable components [...] Read more.

Membrane-assisted crystallization, aiming to induce supersaturation in a solution, has been successfully tested in the crystallization of ionic salts, low molecular organic acids, and proteins. Membrane crystallization is an emerging membrane process with the capability to simultaneously extract fresh water and valuable components from various streams. Successful application of crystallization for produced water treatment, seawater desalination, and salt recovery has been demonstrated. Recently, membrane crystallization has been developed to recover valuable minerals from highly concentrated solutions, since the recovery of high-quality minerals is expected to impact agriculture, pharmaceuticals, and household activities. In this work, molecular dynamics simulations were used to study the crystal nucleation and growth of sodium chloride in bulk and with hydrophobic polymer surfaces of polyvinylidene fluoride (PVDF) and polypropylene (PP) at a supersaturated concentration of salt. In parallel, membrane crystallization experiments were performed utilizing the same polymeric membranes in order to compare the experimental results with the computational ones. Moreover, the comparison in terms of nucleation time between the crystallization of sodium chloride (NaCl) using the traditional evaporation process and the membrane-assisted crystallization process was performed. Here, with an integrated experimental–computational approach, we demonstrate that the PVDF and PP membranes assist the crystal growth for NaCl, speeding up crystal nucleation in comparison to the bulk solution and leading to smaller and regularly structured face-centered cubic lattice NaCl crystals. This results in a mutual validation between theoretical data and experimental findings and provides the stimuli to investigate other mono and bivalent crystals with a new class of materials in advanced membrane separations. Full article

(This article belongs to the Special Issue Modeling and Simulations for Membrane Processes of Industrial Interest)

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15 pages, 3677 KiB

Open AccessArticle

Modeling of Structure-Property Relationships of Polymerizable Surfactants with Antimicrobial Activity

by Giorgio De Luca, Roberta Amuso, Alberto Figoli, Raffaella Mancuso, Lucio Lucadamo and Bartolo Gabriele

Appl. Sci. 2018, 8(10), 1972; https://doi.org/10.3390/app8101972 - 18 Oct 2018

Cited by 6 | Viewed by 2351

Abstract

Polymerizable quaternary ammonium salts (PQASs) were synthesized in a previous work and some of them were used as surfactants in the antimicrobial coating of commercial membranes. Herein, the electrostatic charges, maximum length, and aspect ratio of these antibacterial surfactants were calculated with the [...] Read more.

Polymerizable quaternary ammonium salts (PQASs) were synthesized in a previous work and some of them were used as surfactants in the antimicrobial coating of commercial membranes. Herein, the electrostatic charges, maximum length, and aspect ratio of these antibacterial surfactants were calculated with the aim of investigating the relationship between the properties, recognized to control the biocidal activity of these molecules, and the molecular structures. The effect of the water molecules was considered through a quantum and molecular mechanics approach. The correlation between the number of carbons in the main aliphatic chain of PQAS and the above properties was investigated, by finding that the net charge on the ammonium group does not increase as the number of carbons in the aliphatic chain increase. Thus, although this number influences the antibacterial activity of the surfactants, this influence is not correlated with an increase of the ammonium positive charge. Unlike the partial charges, a different trend was obtained for the surfactants’ maximum length and aspect ratio in agreement with the experimental behavior. As this modeling does not use empirical or adjustable parameters, it can assist the synthetic plan of new structures for surface functionalization, in order to improve the biofouling resistance of the membranes. Full article

(This article belongs to the Special Issue Modeling and Simulations for Membrane Processes of Industrial Interest)

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14 pages, 5516 KiB

Open AccessFeature PaperArticle

Elucidating the Energetics and Effects of Solvents on Cellulose Hydrolysis Using a Polymeric Acid Catalyst

by Xiaoquan Sun and Xianghong Qian

Appl. Sci. 2018, 8(10), 1767; https://doi.org/10.3390/app8101767 - 30 Sep 2018

Cited by 1 | Viewed by 2672

Abstract

A novel polymeric acid catalyst immobilized on a membrane substrate was found to possess superior catalytic activity and selectivity for biomass hydrolysis. The catalyst consists of two polymer chains, a poly(styrene sulfonic acid) (PSSA) polymer chain for catalyzing carbohydrate substrate, and a neighboring [...] Read more.

A novel polymeric acid catalyst immobilized on a membrane substrate was found to possess superior catalytic activity and selectivity for biomass hydrolysis. The catalyst consists of two polymer chains, a poly(styrene sulfonic acid) (PSSA) polymer chain for catalyzing carbohydrate substrate, and a neighboring poly(vinyl imidazolium chloride) ionic liquid (PIL) polymer chain for promoting the solvation of the PSSA chain to enhance the catalytic activity. In order to elucidate the mechanism and determine the energetics of biomass catalytic processing using this unique catalyst, classical molecular dynamics (MD) coupled with metadynamics (MTD) simulations were conducted to determine the free energy surfaces (FES) of cellulose hydrolysis. The critical role that PIL plays in the catalytic conversion is elucidated. The solvation free energy and the interactions between PSSA, PIL, and cellulose chains are found to be significantly affected by the solvent. Full article

(This article belongs to the Special Issue Modeling and Simulations for Membrane Processes of Industrial Interest)

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9 pages, 20952 KiB

Open AccessFeature PaperArticle

Theoretical Study of Nanoporous Graphene Membranes for Natural Gas Purification

by Giovanni Tronci, Federico Raffone and Giancarlo Cicero

Appl. Sci. 2018, 8(9), 1547; https://doi.org/10.3390/app8091547 - 03 Sep 2018

Cited by 18 | Viewed by 4293

Abstract

Gas filtration by means of membranes is becoming increasingly important for industrial processes due to its low cost. In particular, membranes can be applied to separate methane in natural gas from pollutants such as hydrogen sulfide and carbon dioxide. The recent advent of [...] Read more.

Gas filtration by means of membranes is becoming increasingly important for industrial processes due to its low cost. In particular, membranes can be applied to separate methane in natural gas from pollutants such as hydrogen sulfide and carbon dioxide. The recent advent of nanoporous graphene as material for membranes helped to overcome the current problems of polymeric membranes, namely the permeability/selectivity tradeoff. However, the factors that determine gas filtration through nanoporous graphene are not completely clear yet. In this work, we show that pore size, shape and functionalization severely affect the selectivity of the membrane toward CO

_{2}

and H

_{2}

S with respect to CH

_{4}

. We identified that the critical diameter of circular pore for the separation of contaminants from methane with graphene membranes is 5.90 Å. An elliptical pore is discovered to select gas species having similar sizes on the basis of their shape. The more elongated CO

_{2}

is allowed to pass though the pore while the more spherical H

_{2}

S and CH

_{4}

are rejected. Finally, the gas-membrane interactions are found to decisively affect the filtration performances. Functionalization with hydroxyl groups led to a higher permeability of the gas species with polar bonds while keeping an excellent selectivity. Full article

(This article belongs to the Special Issue Modeling and Simulations for Membrane Processes of Industrial Interest)

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20 pages, 2806 KiB

Open AccessArticle

Modeling of Gas Permeation through Mixed-Matrix Membranes Using Novel Computer Application MOT

by Aurelia Rybak, Aleksandra Rybak and Petr Sysel

Appl. Sci. 2018, 8(7), 1166; https://doi.org/10.3390/app8071166 - 18 Jul 2018

Cited by 21 | Viewed by 3548

Abstract

The following article proposes a modern computer application MOT (Membrane Optimization Tool) for modeling of gas transport processes through mixed-matrix membranes (MMMs). The current version of the application is based on the Maxwell model, which can be successfully used to model gas transport [...] Read more.

The following article proposes a modern computer application MOT (Membrane Optimization Tool) for modeling of gas transport processes through mixed-matrix membranes (MMMs). The current version of the application is based on the Maxwell model, which can be successfully used to model gas transport through the simplest types of hybrid membranes without any defects. The application has been verified on the example of four types of hybrid membranes, consisting of various types of polymer matrix, such as: poly (vinyl acetate), 2, 2′-BAPB + BPADA, Ultem, hyperbranched polyimide (ODPA-MTA) and zeolite 4A. The average absolute relative error (AARE) and root-mean-square error (RMSE) were calculated in order to compare the theoretical MOT-predicted results with the experimental results. It was found that the AARE ranges from 29% to 36%, while the RMSE is in the range of 10% to 29%. The article presents also the comparison of MOT-predicted data obtained with Maxwell and Bruggeman models. To obtain more accurate reproduction of experimental results, further versions of the proposed application will be extended with next-generation permeation models (Lewis–Nielsen, Pal, modified Maxwell or Felske models), allowing for the description of transport in more complex systems with the possibility of taking into account possible defects. Full article

(This article belongs to the Special Issue Modeling and Simulations for Membrane Processes of Industrial Interest)

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17 pages, 3806 KiB

Open AccessArticle

Modelling Shear Induced Diffusion Based Particle Segregation: A Basis for Novel Separation Technology

by Ivon Drijer and Karin Schroën

Appl. Sci. 2018, 8(6), 1008; https://doi.org/10.3390/app8061008 - 20 Jun 2018

Cited by 5 | Viewed by 4217

Abstract

Shear induced diffusion (SID) based flow segregation is a technique that can be used for concentration and fractionation purposes, and it has the potential to become an economical and sustainable alternative for e.g., membrane separation. When compared to conventional microfiltration, problems related to [...] Read more.

Shear induced diffusion (SID) based flow segregation is a technique that can be used for concentration and fractionation purposes, and it has the potential to become an economical and sustainable alternative for e.g., membrane separation. When compared to conventional microfiltration, problems related to fouling and cleaning are expected to be minimal. To make the best use of the opportunities that this technique holds, detailed insights in flow and particle behavior are needed. Modelling this process allows for us to chart particle segregation in flow, as well as the effect of suspension removal through a pore and the restoration of the flow profile after the pore. As a starting point, we take the computation fluid dynamics (CFD) model that is presented in a previous study. A difference in channel height to particle diameter ratio influences the entrance length of the SID profile as well as its fully developed profile. When extracting liquid through one pore, particles are systematically transmitted at a lower concentration (59–78%) than is present in the bulk. The recovery lengths of the SID profile after the pore were short, and thus pores can be placed at realistic distances, which forms a good foundation for further design of this novel separation technology that will ultimately be applied for fractionation of particles taking relatively small differences in diffusive behavior as a starting point. Full article

(This article belongs to the Special Issue Modeling and Simulations for Membrane Processes of Industrial Interest)

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17 pages, 40466 KiB

Open AccessFeature PaperArticle

A Novel Connectivity Factor for Morphological Characterization of Membranes and Porous Media: A Simulation Study on Structures of Mono-Sized Spherical Particles

by Stefano Bellini, Giulia Azzato, Monia Grandinetti, Virgilio Stellato, Giuseppe De Marco, Yu Sun and Alessio Caravella

Appl. Sci. 2018, 8(4), 573; https://doi.org/10.3390/app8040573 - 06 Apr 2018

Cited by 13 | Viewed by 4670

Abstract

In this study, we propose to define a connectivity factor as the inverse of the diffusional tortuosity to measure quantitatively the connectivity of whatever type of structure. The concept of connectivity used here is related to the diffusional accessibility of the structure voids. [...] Read more.

In this study, we propose to define a connectivity factor as the inverse of the diffusional tortuosity to measure quantitatively the connectivity of whatever type of structure. The concept of connectivity used here is related to the diffusional accessibility of the structure voids. This definition of connectivity factor arises from the consideration that, if we ideally imagine to decrease progressively the porosity of a regular structure, the porosity itself reaches a limit value below which the inner pores are not interconnected anymore. This leads to an evident situation of zero connectivity and infinite tortuosity, where there is no continuous diffusion path able to connect the structure voids. According to the proposed definition, the connectivity factor is comprised within [0, 1], with zero corresponding to a completely disconnected structure and unity to a completely connected one. To show the efficacy of the presented approach, a case study on the regular structure of mono-sized (mono-disperse) spherical particles (Simple Cubic (SC), Face-Centred Cubic (FCC), Body-Centred Cubic (BCC) and Tetragonal structures) is provided. In particular, the tortuosity of such structures is evaluated by Computational Fluid Dynamics simulations, calculating the connectivity factor consequently. The morphological modification with porosity is induced by changing the surface–surface interparticle distance, allowing us to take both positive (detached particles) and negative values (overlapping particles). For each structure, a comparison between the calculated trends and some correlations of literature is made, and a novel “hidden” morphological parameter has been identified, that is, the here-called Limit Porosity Value, below which the connectivity is zero. The presented approach represents a systematic methodology to quantify the connectivity of any structure and to compare the morphology of membranes, catalysts, and porous media in general. Full article

(This article belongs to the Special Issue Modeling and Simulations for Membrane Processes of Industrial Interest)

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16 pages, 4538 KiB

Open AccessFeature PaperArticle

Evaluation of the Toxin-to-Protein Binding Rates during Hemodialysis Using Sorbent-Loaded Mixed-Matrix Membranes

by Christos S. Stiapis, Eugene D. Skouras, Denys Pavlenko, Dimitrios Stamatialis and Vasilis N. Burganos

Appl. Sci. 2018, 8(4), 536; https://doi.org/10.3390/app8040536 - 31 Mar 2018

Cited by 5 | Viewed by 4458

Abstract

The transport and reaction phenomena that take place in multi-layered mixed-matrix membranes with activated carbon (AC) sorbents that are expected to improve extra-corporeal blood purification, are studied at the macroscopic scale. A model was developed that aims at the description of the removal [...] Read more.

The transport and reaction phenomena that take place in multi-layered mixed-matrix membranes with activated carbon (AC) sorbents that are expected to improve extra-corporeal blood purification, are studied at the macroscopic scale. A model was developed that aims at the description of the removal efficiency of harmful uremic toxins from the blood in the presence of carbon-adsorptive particles and produces results that are aligned with the experimental data. The importance of the generally unknown kinetic rate constants of the association of toxins to albumin is investigated through sensitivity analysis. Matching with further experimental data allowed the extraction of vital kinetic rate constants for key uremic toxins such as indoxyl sulfate (IS) and p-cresyl sulfate (PCS). Moreover, the effects of the plasma composition, as well as of the membrane loading with activated carbon, on the total removal of the protein-bound toxins are quantified and discussed. Full article

(This article belongs to the Special Issue Modeling and Simulations for Membrane Processes of Industrial Interest)

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11 pages, 301 KiB

Open AccessArticle

A Self-Consistent Physical Model of the Bubbles in a Gas Solid Two-Phase Flow

by Haiming Dong, Jingfeng He, Chenlong Duan and Yuemin Zhao

Appl. Sci. 2018, 8(3), 360; https://doi.org/10.3390/app8030360 - 02 Mar 2018

Viewed by 3342

Abstract

We develop a self-consistent physical model of bubbles in a gas solid two-phase flow. Using the Peng-Robonson state equation and a detailed specific heat ratio equation of bubbles, we obtain the kinetic equations of the bubbles on the basis of the Ergun equation, [...] Read more.

We develop a self-consistent physical model of bubbles in a gas solid two-phase flow. Using the Peng-Robonson state equation and a detailed specific heat ratio equation of bubbles, we obtain the kinetic equations of the bubbles on the basis of the Ergun equation, thermodynamic equations, and kinetic equations. It is found that the specific heat ratio of bubbles in such systems strongly depends on bubble pressures and temperatures, which play an important role in the characteristics of the bubbles. The theoretical studies show that with increasing height in the systems, the gas flow rate shows a downward trend. Moreover, the larger particles in the gas solid flows are, the greater the gas velocity is. The bubble sizes increase with the increasing heights of the gas solid systems, and then decrease. The bubble velocity is affected by the gas velocity and the bubble size, which gradually increase and eventually quasi-stabilize. This shows that gas and solid phases in a gas solid two-phase flow interact with each other and a self-consistent system comes into being. The theoretical results have exhibited important value as a guide for understanding the properties and effects of bubbles in gas solid two-phase flows. Full article

(This article belongs to the Special Issue Modeling and Simulations for Membrane Processes of Industrial Interest)

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9 pages, 810 KiB

Open AccessArticle

Mathematical Modelling of Nitrate Removal from Water Using a Submerged Membrane Adsorption Hybrid System with Four Adsorbents

by Mahatheva Kalaruban, Paripurnanda Loganathan, Wang Geun Shim, Jaya Kandasamy and Saravanamuthu Vigneswaran

Appl. Sci. 2018, 8(2), 194; https://doi.org/10.3390/app8020194 - 29 Jan 2018

Cited by 8 | Viewed by 4040

Abstract

Excessive concentrations of nitrate in ground water are known to cause human health hazards. A submerged membrane adsorption hybrid system that includes a microfilter membrane and four different adsorbents (Dowex 21K XLT ion exchange resin (Dowex), Fe-coated Dowex, amine-grafted (AG) corn cob and [...] Read more.

Excessive concentrations of nitrate in ground water are known to cause human health hazards. A submerged membrane adsorption hybrid system that includes a microfilter membrane and four different adsorbents (Dowex 21K XLT ion exchange resin (Dowex), Fe-coated Dowex, amine-grafted (AG) corn cob and AG coconut copra) operated at four different fluxes was used to continuously remove nitrate. The experimental data obtained in this study was simulated mathematically with a homogeneous surface diffusion model that incorporated membrane packing density and membrane correlation coefficient, and applied the concept of continuous flow stirred tank reactor. The model fit with experimental data was good. The surface diffusion coefficient was constant for all adsorbents and for all fluxes. The mass transfer coefficient increased with flux for all adsorbents and generally increased with the adsorption capacity of the adsorbents. Full article

(This article belongs to the Special Issue Modeling and Simulations for Membrane Processes of Industrial Interest)

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Review

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42 pages, 14740 KiB

Open AccessReview

Polymer Nanocomposite Membranes

by Svetlana V. Kononova, Galina N. Gubanova, Eleonora N. Korytkova, Denis A. Sapegin, Katerina Setnickova, Roman Petrychkovych and Petr Uchytil

Appl. Sci. 2018, 8(7), 1181; https://doi.org/10.3390/app8071181 - 19 Jul 2018

Cited by 30 | Viewed by 6446

Abstract

Based on the results of research works reflected in the scientific literature, the main examples, methods and approaches to the development of polymer inorganic nanocomposite materials for target membranes are considered. The focus is on membranes for critical technologies with improved mechanical, thermal [...] Read more.

Based on the results of research works reflected in the scientific literature, the main examples, methods and approaches to the development of polymer inorganic nanocomposite materials for target membranes are considered. The focus is on membranes for critical technologies with improved mechanical, thermal properties that have the necessary capabilities to solve the problems of a selective pervaporation. For the purpose of directional changes in the parameters of membranes, effects on their properties of the type, amount and conditions of nanoparticle incorporation into the polymer matrix were analyzed. An influence of nanoparticles on the structural and morphological characteristics of the nanocomposite film is considered, as well as possibilities of forming transport channels for separated liquids are analyzed. Particular attention is paid to a correlation of nanocomposite structure-transport properties of membranes, whose separation characteristics are usually considered within the framework of the diffusion-sorption mechanism. Full article

(This article belongs to the Special Issue Modeling and Simulations for Membrane Processes of Industrial Interest)

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