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CONTENTS
Volume 7, Number 2, March 2016
 

Abstract
A numerical simulation of membrane evaporation process was carried out in this work. The aim of simulation is to describe transport of water through porous membranes applicable to the concentration of aqueous solutions. A three-dimensional mathematical model was developed which considers transport phenomena including mass, heat, and momentum transfer in membrane evaporation process. The equations of model were then solved numerically using finite element method. The results of simulation in terms of evaporation flux were compared with experimental data, and confirmed the accuracy of model. Moreover, profile of pressure, concentration, and heat flux were obtained and analyzed. The results revealed that developed 3D model is capable of predicting performance of membrane evaporators in concentration of aqueous solutions.

Key Words
membrane; mass transfer; membrane contactor; simulation; modeling

Address
(1) Mehrnoush Mohammadi, Mehdi Asadollahzadeh, Alireza Hemmati:
Faculty of Engineering, Department of Chemical Engineering, South Tehran Branch, Islamic Azad University, P.O. Box 11365-4435, Tehran, Iran;

(2) Azam Marjani:
Department of Chemistry, Arak Branch, Islamic Azad University, Arak, Iran;

(3) Seyyed Masoud Kazemi:
Faculty of Chemistry, Department of Analytical Chemistry, North Tehran Branch, Islamic Azad University, Tehran, Iran.

Abstract
In this study, to improve the water flux of porous hydrophobic membranes, various water-soluble polymers including neutral, cationic and anionic polymers were adsorbed using 'salting-out' method. The adsorbed hydrophobic membrane surfaces were characterized mainly via the measurements of contact angles and scanning electron microscopy (SEM) images. To enhance the durability of the modified membranes, the water-soluble polymers such poly(vinyl alcohol) (PVA) were crosslinked with glutaraldehyde (GA) and found to be resistant for more than 2 months in vigorously stirred water. The water flux was much more increased when the ionic polymers used as the coating materials rather than the neutral polymer and in this case, about 70% of 0.31 L/m2·h (LMH) to 0.50 LMH was increased when 300 mg/L of polyacrylamide (PAAm) was used as the coating agents. Among the cationic coating polymers such as poly(styrene sulfonic acid-co-maleic acid) (PSSA_MA), poly(acrylic acid-comaleic acid) (PAM) and poly(acrylic acid) (PAA), PSSA_MA was found to be the best in terms of contact angle and water flux. In the case of PSSA_MA, the water flux was enhanced about 80%. The low concentration of the coating solution was better to hydrophilize while the high concentration inclined to block the pores on the membrane surfaces. The best coating condition was found: (1) coating concentration 150 to 300 mg/L, (2) ionic strength 0.15, (3) coating time 20 min.

Key Words
hydrophobic membrane; hydrophilization; water-soluble polymers; salting-out; poly(vinyl alcohol); poly(styrene sulfonic acid-co-maleic acid); poly(acrylic acid-co-maleic acid)

Address
Department of Advanced Materials and Chemical Engineering, Hannam University, 1646 Yuseongdae-ro, Yuseong-gu, Daejeon 34054 Korea.

Abstract
In this study, computational fluid dynamics (CFD) analysis was conducted to investigate the flow pattern and to find the occurrence of dead zones in an existing capacitive deionization (CDI) cell. Newly designed cells—specifically designed to avoid dead zones —were analyzed by CFD in accordance with the flow rates of 15, 25 and 35 ml/min. Next, the separation performances between the existing and newly designed cell were compared by conducting CDI experiments in terms of salt removal efficiency at the same flow rates. Then, the computational and experimental results were compared to each other. The salt removal efficiencies of the hexagon flow channel 1 (HFC1) and hexagon flow channel 2 (HFC2) were increased 88-124% at 15 ml/min and 49-50% at 25 ml/min, respectively. There was no difference between the existing cell and the foursquare flow cell (FFC) at 35 ml/min.

Key Words
capacitive deionization (CDI); dead zone; flow channel; computational fluid dynamics (CFD); cell design

Address
Department of Advanced Materials and Chemical Engineering, Hannam University, 1646 Yuseongdae-ro, Yuseong-gu, Daejeon 34054 Korea.

Abstract
Electrodialysis (ED) is known to be a useful membrane process for desalination, concentration, separation, and purification in many fields. In this process, it is desirable to work at high current density in order to achieve fast desalination with the lowest possible effective membrane area. In practice, however, operating currents are restricted by the occurrence of concentration polarization phenomena. Many studies showed the occurrence of a limiting current density (LCD). The limiting current density in the electrodialysis process is an important parameter which determines the electrical resistance and the current utilization. Therefore, its reliable determination is required for designing an efficient electrodialysis plant. The purpose of this study is the development of a predictive model of the limiting current density in an electrodialysis process using response surface methodology (RSM). A two-factor central composite design (CCD) of RSM was used to analyze the effect of operation conditions (the initial salt concentration (C) and the linear flow velocity of solution to be treated (u)) on the limiting current density and to establish a regression model. All experiments were carried out on synthetic brackish water solutions using a laboratory scale electrodialysis cell. The limiting current density for each experiment was determined using the Cowan-Brown method. A suitable regression model for predicting LCD within the ranges of variables used was developed based on experimental results. The proposed mathematical quadratic model was simple. Its quality was evaluated by regression analysis and by the Analysis Of Variance, popularly known as the ANOVA.

Key Words
electrodialysis; concentration polarization; limiting current density; response surface methodology; central composite design

Address
(1) Mourad Ben Sik Ali:
Engineering Preparatory Institute of Nabeul, Merezka University Campus, Merazka, 8000 Nabeul, Republic of Tunisia;

(2) Mourad Ben Sik Ali, Béchir Hamrouni:
Desalination and Water Treatment Research Unit, Chemistry Department, Faculty of Sciences of Tunis, El Manar II, 2092, Republic of Tunisia.

Abstract
Acetic acid can be removed from wastewater by esterification in a membrane reactor. Pervaporation membrane reactor (PVMR) is an alternative process to conventional separation processes. It is an environmentally friendly process. The main advantages of the PVMR are simultaneous water removal and production of an ester economically. In this study, the synthetic wastewater has been used. Esterification reaction of acetic acid with isopropanol has been studied in the presence of tungstosilicic acid hydrate as a catalyst in a batch reactor and in a PVMR. The effects of important operating parameters such as reaction temperature, initial molar ratio of isopropanol to acetic acid and catalyst concentration has been examined. Removal of acetic acid (conversion of acetic acid) was obtained as 85% using a PVMR by removal of water from the reaction mixture.

Key Words
acetic acid; esterification; pervaporation membrane reactor; removal; wastewater

Address
Departments of Chemical Engineering, Engineering Faculty, Kocaeli University, 41380 Kocaeli, Turkey.

Abstract
The present work has been focused on the development of polysulfone (PSf) ultrafiltration membrane via blending by sulfonated polyethersulfone (SPES) in order to permeability enhancement for ultrafiltration of cheese whey. In this regards, sulfonation of polyethersulfone was carried out and the degree of sulfonation was estimated. The effect of blend ratio on morphology, porosity, permeation and fouling of PSf / SPES membranes was investigated. Filtration experiments of whey were conducted for separation of macromolecules and proteins from the lactose enrichment phase. The morphology and performance of membranes were evaluated using different techniques such SEM, AFM, and contact angle measurements. The contact angle measurement showed that the hydrophilicity of membrane was increased by adding SPES. According to AFM images, PSf / SPES membranes exhibited lower roughness compared to neat PSf membrane. The water and whey flux of these membranes were higher than neat membrane. However, flux was decreased when the PSf / SPES blend ratio was 0/100. It can be attributed to pore size and morphology changes. Further, fouling parameters of PSf membrane were improved after blending. The blend membranes show a great potential to be used practically in proteins separation from cheese whey.

Key Words
sulfonation; PSf / SPES membranes; blending; proteins separation; cheese whey

Address
Membrane Research Group, Nanobiotechnology Institute, Babol University of Technology, Babol, Iran.



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