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NaA zeolite composite membrane
Accepted Manuscript Title: Dehydration of ethylene glycol by pervaporation using gamma alumina/NaA zeolite composite membrane Author: Mostafa Jafari Arash Bayat Toraj Mohammadi PII: DOI: Reference:
S0263-8762(13)00143-3 http://dx.doi.org/doi:10.1016/j.cherd.2013.04.016 CHERD 1225
To appear in: Received date: Revised date: Accepted date:
22-11-2012 10-4-2013 14-4-2013
Please cite this article as: Jafari, M., Bayat, A., Mohammadi, T., Dehydration of ethylene glycol by pervaporation using gamma alumina/NaA zeolite composite membrane, Chemical Engineering Research and Design (2013), http://dx.doi.org/10.1016/j.cherd.2013.04.016 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Dehydration of ethylene glycol by pervaporation using gamma alumina/NaA
Mostafa Jafari, Arash Bayat, Toraj Mohammadi*
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zeolite composite membrane
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Research Centre for Membrane Separation Processes, Faculty of Chemical Engineering, Iran University of Science and Technology (IUST), Narmak, Tehran, Iran
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Corresponding author: E-mail: [email protected]
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Tel: +98 21 789 6621; Fax: +98 21 789 6620 Abstract
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High-quality zeolite NaA membranes were synthesized on modified -alumina supports. The surface of macroporous -alumina supports was modified by deposition of an ultrafiltration layer
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of γ-alumina. The zeolitic top layers were synthesized via the secondary growth method. The
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required seeds for the membrane synthesis were prepared via the hydrothermal synthesis using
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organic template of tetra methyl ammonium hydroxide (TMAOH) to obtain nano-sized seeds. The synthesized seeds and membranes were characterized using Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). The separation performance of membranes was evaluated in pervaporation (PV) dehydration of ethylene glycol (EG). Effect of operational parameters including feed composition, feed flow rate, and feed temperature on separation performance of the synthesized NaA zeolite membranes were investigated. The membranes showed separation
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factor of 10996 and high total flux of 7.16 kg m−2 h−1 for feed temperature of 80 ℃, feed flow
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rate of 1.5 L/min, and feed concentration of 90 % wt. EG.
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Keywords: Zeolite; Membrane; γ-alumina layer; Composite support; Ethylene glycol 1. Introduction
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Ethylene glycol (EG) is the simplest and the most important dihyroxyl alcohol. EG is one of the major chemicals which is widely used as raw material in polyester industry (Guo et al., 2006).
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Since EG has low freezing point, it is widely used as antifreezer in cars and aircrafts. High boiling point of ethylene glycol (197 ◦C) and its good affinity towards water make it as an ideal
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absorbent for dehydration of natural gas (Du et al., 2008).
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The conventional synthesis route for preparation of EG includes hydrolysis of ethylene oxide in
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which excess water is used to enhance EG yield. It requires an extra dehydration stage to obtain pure product (Yu et al., 2012). Therefore, dehydration is an important process in manufacturing of EG.
As mentioned above, applications and also its production process involve separation of water from EG. It is often carried out by multi-stage evaporation followed by distillation. Although EG and water do not form an azeotropic mixture over the entire range of composition, separation of EG /water mixtures by evaporation or distillation is still energy intensive due to high boiling point of EG (Du et al., 2008; Guo et al., 2006; Rao et al., 2007; Yong Nam and Moo Lee, 1999). To overcome this problem, the pervaporation (PV) membrane technology has attracted much attention due to its high efficiency and low operational costs. Dehydration by PV is commonly 2 Page 2 of 34
utilized in many industries such as chemical, electronic, food, pharmaceutical, etc. (Dogan and Durmaz Hilmioglu, 2010; Iravaninia et al., 2012; Khosravi et al.).
membranes. The researches in this area are listed in Table 1. Table 1:
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Several studies have been carried out on pervaporative dehydration of EG aqueous solution using
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It is notable that in most cases, the polymeric membranes have been used for dehydration of EG.
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Few studies have been carried out on dehydration of EG using zeolite membranes.
Nik et al. studied separation properties of NaA zeolite membranes for dehydration of EG using
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pervaporation (PV). Their results showed total flux of 0.94 kg m−2 h−1 and separation factor of
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1177 at feed temperature of 70 ℃ and feed concentration of 30 wt.% water (Nik et al., 2006).
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Recently Congli Yu et al. synthesized zeolite NaA membranes on mullite substrates via secondary growth method. The membranes were applied in PV dehydration of EG. Total flux of 1.83 kg m−2 h−1 and separation factor of more than 4000 were achieved for a feed solution of 10
wt.% water in EG at 120 ℃ (Yu et al., 2012).
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The main disadvantage of EG dehydration using polymeric membranes is weak separation factor and total flux. The low separation factor is slightly improved using zeolite membranes, but total flux is still low for these membranes.
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Recently, some researches have been performed to improve zeolite membranes by applying nano seeds (Liu et al., 2011; Shao et al., 2011). Use of nano seeds can avoid formation of defects and
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non-zeolitic pores during membrane synthesis (Shao et al., 2011). On the other hand, if the nano
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seeds are not consistent with the support surface, intrusion of the nano seeds into the support pores may occur during the seeding and the membrane synthesis. This decreases total flux
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drastically. In other words, use of nano seeds for membrane synthesis needs supports with consistent pores (Liu et al., 2011).
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In this work, high-quality zeolite NaA membranes with high separation factor and total flux were
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synthesized on double-layered alumina substrates. The substrates are composed of a sub layer of
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α-alumina and a thin layer of γ-alumina as an intermediate layer. The membranes were synthesized via the secondary growth method with the aid of nano seeds. The nano seeds were
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prepared via hydrothermal method using an organic template. The membranes and seeds were characterized using sold characterization methods including XRD and SEM. The synthesized membranes were also used in PV dehydration of a water/EG mixture to evaluate their separation performance.
2. Experimental
2.1. Preparation of nano seeds Nano crystals of zeolite NaA were first synthesized as seeds for synthesis of zeolite membranes. The secondary growth method was applied for preparation of zeolite membranes. A hydrogel with formula of 1Al2O3: 6SiO2: 0.32Na2O: 7.28(TMA)2O: 350H2O was used for synthesis of
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nano seeds. For this purpose, aluminate and silicate precursors were mixed to form the synthesis hydrogel. Sodium hydroxide (0.312 g) was dissolved in 23.616 g distilled water and then 63.612 g TMAOH was added to the aqueous solution of sodium hydroxide. The solution was then
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divided into two equal volumes and kept in polypropylene beakers. Aluminate solution was prepared by adding 5.052 g aluminum isopropoxide to one part of the solution. It was mixed
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thoroughly. Silicate solution was prepared by adding 8.652 g colloidal silica to another part of
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the solution. Silicate solution was then poured into aluminate solution and mixed until a thick homogenized gel was formed. After crystallization, the sample was carefully washed with
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deionized water till pH < 9 by repeating consequence process of dispersion–ultrasonication–
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2013).
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d
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centrifugation (15000 rpm, 25 min). The product was finally dried at 80 ℃ for 12 h (Jafari et al.,
2.2. Preparation of γ- alumina intermediate layer Homemade porous -alumina disks with thickness of 1.8 mm and diameter of 21 mm were used as macroporous supports. γ-alumina layer was synthesized as an intermediate layer on the macroporous support surface to improve the quality of zeolite membranes. The γ-alumina layers were prepared by dip-coating of α-alumina supports in boehmite sols. Stable boehmite sols of 1 M aluminum concentration were prepared from hydrolysis and condensation of aluminium trisec-butoxide (ALTSB). Then the alkoxide precursor was slowly hydrolyzed in water at 80-85 °C, and after 1 h of stirring, the resulting slurry with AlOOH precipitates was peptized with nitric acid at a HNO3/AlOOH molar ratio of 0.07 using reflux for more than 12 h at 90-100 °C. The 5 Page 5 of 34
remaining alcohol was evaporated by refluxing the sols open to air for 2 h at 90 °C to obtain stable boehmite sols. The following procedure was adopted for synthesis of the γ-alumina layer: 20 ml of 1 M
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boehmite sol was mixed with 13 ml of 3 wt. % PVA (polyvinyl alcohol) solution. The α-alumina supports were dipcoated on the polished side in the boehmite/PVA mixture for 5 sec. The
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supports were removed from the dipping sol and the excess sol was dried. The samples were
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dried at 40 ºC for 2 days and then calcined at 550 ºC for 3 h at 1 ºC /min heating rate. 2.3. Seeding of support
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To synthesize the zeolite layer on the surface of γ-alumina layer, the hydrothermal method was applied. For this purpose, the porous γ-alumina intermediate layer was seeded using the
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synthesized nano seeds. The rubbing-dip coating method was used for seeding the supports.
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First, the zeolite seeds were rubbed on the surface of the supports and then for uniform
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dispersion, they were immersed in a colloidal zeolite suspension for 30 sec. The supports were
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then dried at 60 ℃ overnight. The colloidal suspension was prepared by dispersing the nano
seeds of NaA zeolite (1 g) in 100 ml deionized water with ultrasonic treatment. 2.4. Synthesis of zeolite membranes A-type zeolite membranes were synthesized hydrothermally for 3 h at 100
on the seeded
composite supports. Composition of the hydrogel for synthesis of A-type zeolite is represented by the following molar ratio: 1Al2O3: 2SiO2: 3.4Na2O: 155H2O (Jafari et al.). The synthesis solution was prepared by mixing aluminate and silicate solutions. Sodium hydroxide (1.977 g) 6 Page 6 of 34
was dissolved in 41.583 ml of deionized water. The solution was divided into two equal volumes and kept in polypropylene bottles. Aluminate solution was prepared by adding 3.238 g sodium aluminate to one part of the NaOH solution. It was mixed until cleared. Silicate solution was
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prepared by adding 7.557 g sodium silicate to another part of the NaOH solution. Silicate solution was then poured into aluminate solution and mixed until a thick homogenized gel was
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formed.
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After synthesis, the membrane was washed with deionized water as many times as required to reduce the filtrate pH to less than 10 and dried at room temperature. To prevent probable heat
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shocks, the rate at which temperature was increased/ decreased to/ from 100 °C was less than 0.5 °C min–1.
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3. Characterizations
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The crystal structures of the synthesized zeolite seeds and also the as-synthesized zeolite
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membranes were characterized by solid characterizations including X-ray diffraction (XRD) and scanning electron microscopy (SEM). The average pore size of γ-alumina intermediate layer was
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determined by Brunauer, Emmett and Teller (BET) analysis. XRD measurements were conducted by a Siemens diffractometer using Cu K radiation working at 30 mA and 40 kV. The morphology and thickness of the as-synthesized zeolite membranes and the γ-alumina supports were measured using SEM images. The size and morphology of the synthesized A-type zeolite nano seeds were also determined using SEM. The SEM images were obtained using a Vega Tescan scanning electron microscope. The ultrafiltration intermediate γ-alumina layer was also characterized by milk concentration.
4. Pervaporation tests
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The separation performance of the synthesized A-type membranes for dehydration of ethylene glycol (EG) was evaluated using pervaporation (PV) experiments. The experimental set up used for the PV experiments is schematically depicted in Figure 1. As shown, the permeate side was
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evacuated and permeate vapor was condensed using a cold trap immersed in liquid nitrogen. The PV performance of the membranes was determined using separation factor (α) and permeation
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flux (J). Separation factor for component i over component j and total permeation flux (J) were
(1)
xi x j
w A.t
(2)
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J
yi y j
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i j
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respectively defined as:
where xi and xj are weight fractions of component i and component j in feed mixture; yi and yj are
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corresponding weight fractions in permeate; w is the total weight of permeate, kg; Δt is the
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experiment time, h; and A is the effective membrane area.
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Figure 1:
5. Results and discussion 5.1. Nano seeds
The synthesized nano seeds were characterized using X-ray diffraction (XRD) analysis to assure formation of LTA phase. The XRD patterns of the synthesized nano seeds are presented in Figure 2. The main peaks associated with zeolite NaA can be observed in the XRD patterns. The obtained results confirm that all the samples are pure A-type zeolite. The low background also shows that the amorphous phase is negligible and high crystalline zeolite seeds are obtained which are quite appropriate for the membrane synthesis.
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To further evaluate the morphology and size of the synthesized zeolite nano seeds, SEM images were obtained. Figure 3 shows the SEM micrographs of the synthesized nano seeds. As seen from the SEM images, the synthesized nano seeds are smaller than 100 nm and spherical.
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Figure 2: Figure 3:
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5.2. γ-alumina intermediate layer
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The -alumina support layer as a macroporous layer was first coated by a less porous
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intermediate γ-alumina layer and a zeolite NaA active layer was then synthesized over this layer.
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Figure 4A shows SEM images of the macroporous support surface. The macroporous support layer (-alumina) is not suitable for seeding and hydrothermal synthesis of zeolite layer because
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a significant amount of the zeolite gel can penetrate to be crystallized inside the support pores and this makes the zeolite layer very thick. Thus, an intermediate layer is required for smooth and thin crystallization of the zeolite layer (membrane) on the support. The intermediate layer has smaller pores and this prevents pore penetration and thus makes the zeolite layer thinner. Figure 4B and C shows SEM images of the support with the intermediate layer. As observed, the thin intermediate γ-alumina layer is uniformly coated on the α-alumina sub layer. The images confirm the successful coating of the support by the γ-alumina layer. It is also observed that the coated intermediate layer has good adhesiveness and uniformity to the sub layer and this is
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because the both layers are made of alumina (see Figure 4B). As observed, thickness of the intermediate γ-alumina layer is approximately 4 m (see Figure 4C). BET characterization of the intermediate layer at adsorption temperature of 77 K and vapor
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pressure of 88.7 KPa showed that the average pore size of the γ-alumina layer is about 20.2 nm. Separation performance of the synthesized γ-alumina intermediate layer was evaluated in milk
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concentration. The latter test is typically used for characterization of ultrafiltration membranes.
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The experiments were carried out at a temperature of 25 °C and a pressure of 3 bar using an ultrafiltration set up. The permeation tests showed permeation flux of 242.3 and 155.7 kg m−2 h−1
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for water and milk respectively. Turbidity was reduced from 136.68 (feed) to 19.07 NTU (permeate).
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Figure 4:
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5.3.1. Seeding
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5.3. NaA zeolite membranes
A thin and uniform layer of NaA zeolite must be deposited on the composite support surface to
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synthesize a high-quality NaA zeolite membrane. To do this, the seeds should be dispersed homogeneously on the surface of the intermediate layer and the amount of seeds should be optimal. Otherwise, the as-synthesized NaA zeolite membrane becomes too thick or has defects (Li et al., 2012).
Figure 5 shows a schematic of the membrane formation on a macroporous support surface (Figure 5A) by the secondary growth method. The gray phase refers to the support phase and the black phase is the zeolite nano seeds and the zeolite film. Based on these results, it is concluded that the ratio of the support pore diameter to the seed diameter plays a crucial role in synthesis of zeolite membranes.
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Modification of the support surface with the γ-alumina intermediate layer can avoid penetration of the nano seeds and the synthesis zeolite gel into the support pores. This causes the formation
Figure 5:
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of an ultrathin layer of zeolite which provides a high quality zeolite membrane (Figure 5B).
Figure 6 illustrates surface of the modified support seeded by the nano powder of NaA zeolite. It
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is observed that the support surface is uniformly covered by the seeds.
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Figure 6: 5.3.2. As-synthesized NaA zeolite membranes
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Figure 7 presents SEM images of the NaA zeolite membrane synthesized via hydrothermal method on surface of the composite support. As observed, a uniform zeolite layer is deposited on
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surface of the γ-alumina intermediate layer. Thickness of zeolite layer is estimated to be less than
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te
d
8 μm.
Due to consistency between the support and the seeds used for the membrane synthesis, a distinguishable interface between the support and the zeolite layer can be observed. Growth of the zeolite layer inside the support pores is prevented by the intermediate layer and this can improve separation properties of the zeolite membranes in separation of liquid mixtures. Figure 7: 5.4. Pervaporation studies 5.4.1. Effect of operating temperature
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Figure 8 shows effect of feed temperature on permeation flux of water through the synthesized zeolite membrane. As seen, increasing temperature increases total permeation flux through the zeolite membrane. The observed behavior can be justified by two reasons; first, saturated
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pressure of mixture increases with increasing temperature and this results in enhancement of driving force for transport of feed through the membrane (Nik et al., 2006).
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Figure 8:
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Second, viscosity of the feed is one of the major resistances for the feed transport in the membrane module. Dynamic viscosity of EG has great effect on Reynolds number and can
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impact total permeation flux higher than 50 %.
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Viscosity values of water/EG mixture at different temperatures are listed in Table 2. As seen,
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te
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with 15 ℃ increasing feed temperature, 35 % viscosity decline is obtained. Therefore, increasing
temperature increases Reynolds number significantly and this enhances permeation. Table 2:
Figure 8 also shows that increasing feed temperature increases separation factor. This can be justified by increasing water permeation more significantly with temperature. With increasing temperature, water permeation increases, but EG permeation does not increases significantly and increasing water permeation results in increasing separation factor (Nik et al., 2006; Zhang and Liu, 2011) 5.4.2. Effect of feed concentration
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Effects of feed concentration on separation factor and permeation flux are illustrated in Figure 9. It is observed that with increasing EG concentration in the feed, total permeation flux decreases. With increasing EG concentration in the feed, more active sites on the membrane surface are
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occupied by EG and this reduces water permeation through the membrane and in turn total permeation.
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The reduction of permeation flux can be also attributed to the reduction of driving force for water
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transport. At high concentration of EG, water activity in the feed decreases and thus chemical potential gradient between the two sides of the membrane for water decreases and this result in
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reduction of permeation flux. As observed in Figure 9, with decreasing EG concentration in the feed, separation factor decreases. According to Eq. 1, a small change in water concentration
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causes a significant change in the denominator of Eq. 1. This means that separation factors is
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higher at lower water concentrations (Zhang and Liu, 2011).
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Figure 9:
5.4.3. Effect of feed flow rate
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Figure 10 shows the effects of feed flow rate on separation factor and permeation flux. As observed, permeation flux and separation factor increase with increasing feed flow rate. This behavior can be attributed to the enhancement of Reynolds number and turbulency (Kunnakorn et al., 2011).
Figure 10:
One of the most important factors that increase permeation flux across a membrane is turbulency on the membrane surface. With increasing turbulency on the membrane surface, the sites which are occupied by EG molecules and thus deactivated, are replaced with water molecules and become activated. To show the effect of increasing turbulency in the membrane module on
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permeation flux, a CFD study was carried. Geometry of the membrane module is drawn in Figure 11 a. The CFD study shows effect of feed flow rate on the flow field on the membrane surface. The numerical solution for solving the conservation equations was carried out using a
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CFD package. The results are presented in terms of contours for kinetic energy of the feed in the module. Figure 11 b shows contours of kinetic energy for different flow rates of 1, 1.5, and 2
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L/min. As observed, increasing feed flow rate enhances feed kinetic energy which in turn
permeation flux across the membrane.
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Figure 11:
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increases the extent of feed turbulency on the membrane surface. This, as a result, increases
6. Conclusions
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Zeolite NaA membranes on double-layered supports were synthesized using the secondary
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growth method. The used supports consisted of two layers composing a macroporous -alumina
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sub layer and a deposited by γ-alumina intermediate layer to modify the support for the membrane formation. The NaA zeolite membranes were synthesized by the secondary growth
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method on the modified supports. The NaA nano seeds for the membrane preparation were synthesized via the hydrothermal method with an organic template of TMAOH. The seeds and the membranes were characterized using Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) to assure formation of the zeolite structure. The synthesized zeolite membranes were utilized in pervaporation (PV) dehydration of ethylene glycol (EG). Feed composition, feed flow rate, and feed temperature were varied to find the optimum conditions. A
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high separation factor of 10996 and a total permeation flux of 7.16 kg/m2.h for feed temperature
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an
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cr
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of 80 ℃, flow rate of 1.5 L/min, and feed concentration of 90 % wt. EG were obtained.
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References
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Chen, F.R., Chen, H.F., 1996. Pervaporation separation of ethylene glycol-water mixtures using crosslinked PVA-PES composite membranes. Part I. Effects of membrane preparation conditions on pervaporation performances. Journal of Membrane Science 109, 247-256. Dogan, H., Durmaz Hilmioglu, N., 2010. Chitosan coated zeolite filled regenerated cellulose membrane for dehydration of ethylene glycol/water mixtures by pervaporation. Desalination 258, 120-127. Du, J.R., Chakma, A., Feng, X., 2008. Dehydration of ethylene glycol by pervaporation using poly(N,Ndimethylaminoethyl methacrylate)/polysulfone composite membranes. Separation and Purification Technology 64, 63-70. Feng, X., Huang, R.Y.M., 1996. Pervaporation with chitosan membranes. I. Separation of water from ethylene glycol by a chitosan/polysulfone composite membrane. Journal of Membrane Science 116, 6776. Guo, R., Hu, C., Li, B., Jiang, Z., 2007a. Pervaporation separation of ethylene glycol/water mixtures through surface crosslinked PVA membranes: Coupling effect and separation performance analysis. Journal of Membrane Science 289, 191-198. Guo, R., Hu, C., Pan, F., Wu, H., Jiang, Z., 2006. PVA–GPTMS/TEOS hybrid pervaporation membrane for dehydration of ethylene glycol aqueous solution. Journal of Membrane Science 281, 454-462. Guo, R., Ma, X., Hu, C., Jiang, Z., 2007b. Novel PVA–silica nanocomposite membrane for pervaporative dehydration of ethylene glycol aqueous solution. Polymer 48, 2939-2945. Hu, C., Guo, R., Li, B., Ma, X., Wu, H., Jiang, Z., 2007a. Development of novel mordenite-filled chitosan– poly(acrylic acid) polyelectrolyte complex membranes for pervaporation dehydration of ethylene glycol aqueous solution. Journal of Membrane Science 293, 142-150. Hu, C., Li, B., Guo, R., Wu, H., Jiang, Z., 2007b. Pervaporation performance of chitosan–poly(acrylic acid) polyelectrolyte complex membranes for dehydration of ethylene glycol aqueous solution. Separation and Purification Technology 55, 327-334. Huang, R.Y.M., Shao, P., Feng, X., Anderson, W.A., 2002. Separation of Ethylene Glycol−Water Mixtures Using Sulfonated Poly(ether ether ketone) Pervaporation Membranes: Membrane Relaxation and Separation Performance Analysis. Industrial & Engineering Chemistry Research 41, 2957-2965. Hyder, M.N., Chen, P., 2009. Pervaporation dehydration of ethylene glycol with chitosan–poly(vinyl alcohol) blend membranes: Effect of CS–PVA blending ratios. Journal of Membrane Science 340, 171180. Iravaninia, M., Mirfendereski, M., Mohammadi, T., 2012. Pervaporation separation of toluene/nheptane mixtures using a MSE-modified membrane: Effects of operating conditions. Chemical Engineering Research and Design 90, 397-408. Jafari, M., Nouri, A., Kazemimoghadam, M., Mohammadi, T., 2013. Investigations on hydrothermal synthesis parameters in preparation of nanoparticles of LTA zeolite with the aid of TMAOH. Powder Technology 237, 442-449. Jafari, M., Nouri, A., Mousavi, S.F., Mohammadi, T., Kazemimoghadam, M., Optimization of synthesis conditions for preparation of ceramic (A-type zeolite) membranes in dehydration of ethylene glycol. Ceramics International. Khosravi, T., Mosleh, S., Bakhtiari, O., Mohammadi, T., Mixed matrix membranes of Matrimid 5218 loaded with zeolite 4A for pervaporation separation of water–isopropanol mixtures. Chemical Engineering Research and Design. Kunnakorn, D., Rirksomboon, T., Aungkavattana, P., Kuanchertchoo, N., Atong, D., Kulprathipanja, S., Wongkasemjit, S., 2011. Performance of sodium A zeolite membranes synthesized via microwave and autoclave techniques for water–ethanol separation: Recycle-continuous pervaporation process. Desalination 269, 78-83.
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Li, J., Shao, J., Ge, Q., Wang, G., Wang, Z., Yan, Y., 2012. Influences of the zeolite loading and particle size in composite hollow fiber supports on properties of zeolite NaA membranes. Microporous and Mesoporous Materials 160, 10-17. Liu, W., Zhang, J., Canfield, N., Saraf, L., 2011. Preparation of Robust, Thin Zeolite Membrane Sheet for Molecular Separation. Industrial & Engineering Chemistry Research 50, 11677-11689. Nik, O.G., Moheb, A., Mohammadi, T., 2006. Separation of Ethylene Glycol/Water Mixtures using NaA Zeolite Membranes. Chemical Engineering & Technology 29, 1340-1346. Pandey, L.K., Saxena, C., Dubey, V., 2005. Studies on pervaporative characteristics of bacterial cellulose membrane. Separation and Purification Technology 42, 213-218. Rao, P.S., Sridhar, S., Wey, M.Y., Krishnaiah, A., 2007. Pervaporative Separation of Ethylene Glycol/Water Mixtures by Using Cross-linked Chitosan Membranes. Industrial & Engineering Chemistry Research 46, 2155-2163. Sekulić, J., ten Elshof, J.E., Blank, D.H.A., 2004. Selective Pervaporation of Water through a Nonselective Microporous Titania Membrane by a Dynamically Induced Molecular Sieving Mechanism. Langmuir 21, 508-510. Shao, J., Ge, Q., Shan, L., Wang, Z., Yan, Y., 2011. Influences of Seeds on the Properties of Zeolite NaA Membranes on Alumina Hollow Fibers. Industrial & Engineering Chemistry Research 50, 9718-9726. Yong Nam, S., Moo Lee, Y., 1999. Pervaporation of ethylene glycol–water mixtures: I. Pervaporation performance of surface crosslinked chitosan membranes. Journal of Membrane Science 153, 155-162. Yu, C., Zhong, C., Liu, Y., Gu, X., Yang, G., Xing, W., Xu, N., 2012. Pervaporation dehydration of ethylene glycol by NaA zeolite membranes. Chemical Engineering Research and Design 90, 1372-1380. Zhang, J., Liu, W., 2011. Thin porous metal sheet-supported NaA zeolite membrane for water/ethanol separation. Journal of Membrane Science 371, 197-210.
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Table captions
Table 1: Studies on water–EG membrane separations. Table 2: Effect of temperature on viscosity of water/EG mixture.
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Figure captions Figure 1: A schematic view of pervaporation set up used in the experiments. F: flow meter, T:
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thermometer, PI: pressure indicator.
Figure 3: SEM images of the synthesized A-type zeolite seeds.
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Figure 2: XRD patterns of the A-type nano zeolite seeds.
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Figure. 4: SEM images of the composite support (A) -alumina surface, (B) γ-alumina surface,
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and (C) cross section.
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Figure 5: A schematic representation of zeolite membrane synthesis on porous supports;
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A: macroporous α-alumina support, B: nanoporous γ-alumina support.
Figure 6: Surface SEM image of the seeded support using nano seeds of NaA zeolite. Figure 7: SEM images of the zeolite layer synthesized on the composite support. Figure 8: Effects of feed temperature on permeation flux and separation factor (Feed flow rate = 1.5 L/min, water content in the feed = 10 wt. %). Figure 9: Effect of feed concentration on separation factor and permeation flux
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ip t
(feed temperature = 65 ℃, feed flow rate = 1.5 L/min).
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Figure 10: Effect of feed flow rate on separation factor and permeation flux
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an
(feed temperature = 65 ℃, feed concentration = 10 wt. % water).
Figure 11: (a) Geometry of the membrane module used in the experiments and (b) Countors of
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kinetic energy of the feed on the membrane surface at different flow rates.
Table 1: Studies on water–EG membrane separations. No.
1
Membrane
Chitosan/poly vinyl
Water in
Feed
Separation
Permeation
feed
Temp.
factor
flux
(wt. %)
(K)
10
343
(kg m−2 h−1) 986
0.460
alcohol 2
Chitosan/poly acrylic
Ref.
(Hyder and Chen, 2009)
20
343
105
0.216
(Hu et al., 2007b)
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acid 3
Chitosan coated
5
323
76
0.406
(Dogan and
zeolite filled cellulose
Durmaz
7
PVA/PAN(GFT1001)
Surface cross linked
17.5
353
10
20
acid
343
PVA-GPTMS/TEOS
10 11
12
d 343
(Feng and Huang,
0.338
993
0.224
1996)
(Chen and Chen, 1996) (Yong Nam and Moo Lee, 1999)
0.211
(Guo et al., 2007a)
105
0.216
(Hu et al., 2007a)
20
343
714
0.060
(Guo et al., 2006)
PDMAEMA/PSF
6
303
600
0.222
(Du et al., 2008)
Bacterial cellulose
40
307
66
0.270
(Pandey et al.,
Ac ce p
9
20
0.300
1116
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Chitosan/poly acrylic
231
348
PVA 8
104
cr
308
us
6
PVA/PES
10
an
5
Chitosan/Polysulfone
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4
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Hilmioglu, 2010)
2005)
NaA Zeolite
30
343
1117
0.944
(Nik et al., 2006)
13
NaA Zeolite
10
393
4000
1.830
(Yu et al., 2012)
14
Sulfonated Poly(ether
30
323
800
0.390
(Huang et al.,
ether ketone) 15
Cross-linked chitosan
2002) 12
303
148
0.225
(Rao et al., 2007)
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16
PVA/MPTMS/Silica
20
343
311
0.067
(Guo et al., 2007b)
Microporous titania
11
353
27
0.648
(Sekulić et al.,
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d
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an
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cr
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2004)
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Table 2: Effect of temperature on viscosity of water/EG mixture.
EG concentration
Viscosity (cP)
(wt. %)
50
65
80
90
6.06
3.83
2.59
75
4.86
3.18
2.21
60
3.78
2.57
1.84
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Highlights Modification of macroporous -alumina support by deposition of ultrafiltration γ-alumina layer Synthesis of nanosize zeolite NaA with narrow particle size distribution
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Development of hydrothermal method for synthesis of high quality NaA zeolite membranes Effects of operational parameters on water/EG separation performance were investigated
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High flux and separation factor for dehydration of ethylene glycol were achieved
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S0263-8762(13)00143-3 http://dx.doi.org/doi:10.1016/j.cherd.2013.04.016 CHERD 1225
To appear in: Received date: Revised date: Accepted date:
22-11-2012 10-4-2013 14-4-2013
Please cite this article as: Jafari, M., Bayat, A., Mohammadi, T., Dehydration of ethylene glycol by pervaporation using gamma alumina/NaA zeolite composite membrane, Chemical Engineering Research and Design (2013), http://dx.doi.org/10.1016/j.cherd.2013.04.016 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Dehydration of ethylene glycol by pervaporation using gamma alumina/NaA
Mostafa Jafari, Arash Bayat, Toraj Mohammadi*
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zeolite composite membrane
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Research Centre for Membrane Separation Processes, Faculty of Chemical Engineering, Iran University of Science and Technology (IUST), Narmak, Tehran, Iran
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Corresponding author: E-mail: [email protected]
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Tel: +98 21 789 6621; Fax: +98 21 789 6620 Abstract
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High-quality zeolite NaA membranes were synthesized on modified -alumina supports. The surface of macroporous -alumina supports was modified by deposition of an ultrafiltration layer
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of γ-alumina. The zeolitic top layers were synthesized via the secondary growth method. The
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required seeds for the membrane synthesis were prepared via the hydrothermal synthesis using
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organic template of tetra methyl ammonium hydroxide (TMAOH) to obtain nano-sized seeds. The synthesized seeds and membranes were characterized using Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). The separation performance of membranes was evaluated in pervaporation (PV) dehydration of ethylene glycol (EG). Effect of operational parameters including feed composition, feed flow rate, and feed temperature on separation performance of the synthesized NaA zeolite membranes were investigated. The membranes showed separation
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factor of 10996 and high total flux of 7.16 kg m−2 h−1 for feed temperature of 80 ℃, feed flow
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rate of 1.5 L/min, and feed concentration of 90 % wt. EG.
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Keywords: Zeolite; Membrane; γ-alumina layer; Composite support; Ethylene glycol 1. Introduction
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Ethylene glycol (EG) is the simplest and the most important dihyroxyl alcohol. EG is one of the major chemicals which is widely used as raw material in polyester industry (Guo et al., 2006).
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Since EG has low freezing point, it is widely used as antifreezer in cars and aircrafts. High boiling point of ethylene glycol (197 ◦C) and its good affinity towards water make it as an ideal
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absorbent for dehydration of natural gas (Du et al., 2008).
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The conventional synthesis route for preparation of EG includes hydrolysis of ethylene oxide in
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which excess water is used to enhance EG yield. It requires an extra dehydration stage to obtain pure product (Yu et al., 2012). Therefore, dehydration is an important process in manufacturing of EG.
As mentioned above, applications and also its production process involve separation of water from EG. It is often carried out by multi-stage evaporation followed by distillation. Although EG and water do not form an azeotropic mixture over the entire range of composition, separation of EG /water mixtures by evaporation or distillation is still energy intensive due to high boiling point of EG (Du et al., 2008; Guo et al., 2006; Rao et al., 2007; Yong Nam and Moo Lee, 1999). To overcome this problem, the pervaporation (PV) membrane technology has attracted much attention due to its high efficiency and low operational costs. Dehydration by PV is commonly 2 Page 2 of 34
utilized in many industries such as chemical, electronic, food, pharmaceutical, etc. (Dogan and Durmaz Hilmioglu, 2010; Iravaninia et al., 2012; Khosravi et al.).
membranes. The researches in this area are listed in Table 1. Table 1:
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Several studies have been carried out on pervaporative dehydration of EG aqueous solution using
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It is notable that in most cases, the polymeric membranes have been used for dehydration of EG.
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Few studies have been carried out on dehydration of EG using zeolite membranes.
Nik et al. studied separation properties of NaA zeolite membranes for dehydration of EG using
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pervaporation (PV). Their results showed total flux of 0.94 kg m−2 h−1 and separation factor of
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1177 at feed temperature of 70 ℃ and feed concentration of 30 wt.% water (Nik et al., 2006).
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Recently Congli Yu et al. synthesized zeolite NaA membranes on mullite substrates via secondary growth method. The membranes were applied in PV dehydration of EG. Total flux of 1.83 kg m−2 h−1 and separation factor of more than 4000 were achieved for a feed solution of 10
wt.% water in EG at 120 ℃ (Yu et al., 2012).
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The main disadvantage of EG dehydration using polymeric membranes is weak separation factor and total flux. The low separation factor is slightly improved using zeolite membranes, but total flux is still low for these membranes.
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Recently, some researches have been performed to improve zeolite membranes by applying nano seeds (Liu et al., 2011; Shao et al., 2011). Use of nano seeds can avoid formation of defects and
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non-zeolitic pores during membrane synthesis (Shao et al., 2011). On the other hand, if the nano
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seeds are not consistent with the support surface, intrusion of the nano seeds into the support pores may occur during the seeding and the membrane synthesis. This decreases total flux
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drastically. In other words, use of nano seeds for membrane synthesis needs supports with consistent pores (Liu et al., 2011).
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In this work, high-quality zeolite NaA membranes with high separation factor and total flux were
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synthesized on double-layered alumina substrates. The substrates are composed of a sub layer of
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α-alumina and a thin layer of γ-alumina as an intermediate layer. The membranes were synthesized via the secondary growth method with the aid of nano seeds. The nano seeds were
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prepared via hydrothermal method using an organic template. The membranes and seeds were characterized using sold characterization methods including XRD and SEM. The synthesized membranes were also used in PV dehydration of a water/EG mixture to evaluate their separation performance.
2. Experimental
2.1. Preparation of nano seeds Nano crystals of zeolite NaA were first synthesized as seeds for synthesis of zeolite membranes. The secondary growth method was applied for preparation of zeolite membranes. A hydrogel with formula of 1Al2O3: 6SiO2: 0.32Na2O: 7.28(TMA)2O: 350H2O was used for synthesis of
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nano seeds. For this purpose, aluminate and silicate precursors were mixed to form the synthesis hydrogel. Sodium hydroxide (0.312 g) was dissolved in 23.616 g distilled water and then 63.612 g TMAOH was added to the aqueous solution of sodium hydroxide. The solution was then
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divided into two equal volumes and kept in polypropylene beakers. Aluminate solution was prepared by adding 5.052 g aluminum isopropoxide to one part of the solution. It was mixed
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thoroughly. Silicate solution was prepared by adding 8.652 g colloidal silica to another part of
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the solution. Silicate solution was then poured into aluminate solution and mixed until a thick homogenized gel was formed. After crystallization, the sample was carefully washed with
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deionized water till pH < 9 by repeating consequence process of dispersion–ultrasonication–
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2013).
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centrifugation (15000 rpm, 25 min). The product was finally dried at 80 ℃ for 12 h (Jafari et al.,
2.2. Preparation of γ- alumina intermediate layer Homemade porous -alumina disks with thickness of 1.8 mm and diameter of 21 mm were used as macroporous supports. γ-alumina layer was synthesized as an intermediate layer on the macroporous support surface to improve the quality of zeolite membranes. The γ-alumina layers were prepared by dip-coating of α-alumina supports in boehmite sols. Stable boehmite sols of 1 M aluminum concentration were prepared from hydrolysis and condensation of aluminium trisec-butoxide (ALTSB). Then the alkoxide precursor was slowly hydrolyzed in water at 80-85 °C, and after 1 h of stirring, the resulting slurry with AlOOH precipitates was peptized with nitric acid at a HNO3/AlOOH molar ratio of 0.07 using reflux for more than 12 h at 90-100 °C. The 5 Page 5 of 34
remaining alcohol was evaporated by refluxing the sols open to air for 2 h at 90 °C to obtain stable boehmite sols. The following procedure was adopted for synthesis of the γ-alumina layer: 20 ml of 1 M
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boehmite sol was mixed with 13 ml of 3 wt. % PVA (polyvinyl alcohol) solution. The α-alumina supports were dipcoated on the polished side in the boehmite/PVA mixture for 5 sec. The
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supports were removed from the dipping sol and the excess sol was dried. The samples were
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dried at 40 ºC for 2 days and then calcined at 550 ºC for 3 h at 1 ºC /min heating rate. 2.3. Seeding of support
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To synthesize the zeolite layer on the surface of γ-alumina layer, the hydrothermal method was applied. For this purpose, the porous γ-alumina intermediate layer was seeded using the
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synthesized nano seeds. The rubbing-dip coating method was used for seeding the supports.
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First, the zeolite seeds were rubbed on the surface of the supports and then for uniform
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dispersion, they were immersed in a colloidal zeolite suspension for 30 sec. The supports were
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then dried at 60 ℃ overnight. The colloidal suspension was prepared by dispersing the nano
seeds of NaA zeolite (1 g) in 100 ml deionized water with ultrasonic treatment. 2.4. Synthesis of zeolite membranes A-type zeolite membranes were synthesized hydrothermally for 3 h at 100
on the seeded
composite supports. Composition of the hydrogel for synthesis of A-type zeolite is represented by the following molar ratio: 1Al2O3: 2SiO2: 3.4Na2O: 155H2O (Jafari et al.). The synthesis solution was prepared by mixing aluminate and silicate solutions. Sodium hydroxide (1.977 g) 6 Page 6 of 34
was dissolved in 41.583 ml of deionized water. The solution was divided into two equal volumes and kept in polypropylene bottles. Aluminate solution was prepared by adding 3.238 g sodium aluminate to one part of the NaOH solution. It was mixed until cleared. Silicate solution was
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prepared by adding 7.557 g sodium silicate to another part of the NaOH solution. Silicate solution was then poured into aluminate solution and mixed until a thick homogenized gel was
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formed.
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After synthesis, the membrane was washed with deionized water as many times as required to reduce the filtrate pH to less than 10 and dried at room temperature. To prevent probable heat
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shocks, the rate at which temperature was increased/ decreased to/ from 100 °C was less than 0.5 °C min–1.
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3. Characterizations
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The crystal structures of the synthesized zeolite seeds and also the as-synthesized zeolite
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membranes were characterized by solid characterizations including X-ray diffraction (XRD) and scanning electron microscopy (SEM). The average pore size of γ-alumina intermediate layer was
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determined by Brunauer, Emmett and Teller (BET) analysis. XRD measurements were conducted by a Siemens diffractometer using Cu K radiation working at 30 mA and 40 kV. The morphology and thickness of the as-synthesized zeolite membranes and the γ-alumina supports were measured using SEM images. The size and morphology of the synthesized A-type zeolite nano seeds were also determined using SEM. The SEM images were obtained using a Vega Tescan scanning electron microscope. The ultrafiltration intermediate γ-alumina layer was also characterized by milk concentration.
4. Pervaporation tests
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The separation performance of the synthesized A-type membranes for dehydration of ethylene glycol (EG) was evaluated using pervaporation (PV) experiments. The experimental set up used for the PV experiments is schematically depicted in Figure 1. As shown, the permeate side was
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evacuated and permeate vapor was condensed using a cold trap immersed in liquid nitrogen. The PV performance of the membranes was determined using separation factor (α) and permeation
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flux (J). Separation factor for component i over component j and total permeation flux (J) were
(1)
xi x j
w A.t
(2)
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J
yi y j
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i j
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respectively defined as:
where xi and xj are weight fractions of component i and component j in feed mixture; yi and yj are
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corresponding weight fractions in permeate; w is the total weight of permeate, kg; Δt is the
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experiment time, h; and A is the effective membrane area.
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Figure 1:
5. Results and discussion 5.1. Nano seeds
The synthesized nano seeds were characterized using X-ray diffraction (XRD) analysis to assure formation of LTA phase. The XRD patterns of the synthesized nano seeds are presented in Figure 2. The main peaks associated with zeolite NaA can be observed in the XRD patterns. The obtained results confirm that all the samples are pure A-type zeolite. The low background also shows that the amorphous phase is negligible and high crystalline zeolite seeds are obtained which are quite appropriate for the membrane synthesis.
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To further evaluate the morphology and size of the synthesized zeolite nano seeds, SEM images were obtained. Figure 3 shows the SEM micrographs of the synthesized nano seeds. As seen from the SEM images, the synthesized nano seeds are smaller than 100 nm and spherical.
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Figure 2: Figure 3:
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5.2. γ-alumina intermediate layer
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The -alumina support layer as a macroporous layer was first coated by a less porous
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intermediate γ-alumina layer and a zeolite NaA active layer was then synthesized over this layer.
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Figure 4A shows SEM images of the macroporous support surface. The macroporous support layer (-alumina) is not suitable for seeding and hydrothermal synthesis of zeolite layer because
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a significant amount of the zeolite gel can penetrate to be crystallized inside the support pores and this makes the zeolite layer very thick. Thus, an intermediate layer is required for smooth and thin crystallization of the zeolite layer (membrane) on the support. The intermediate layer has smaller pores and this prevents pore penetration and thus makes the zeolite layer thinner. Figure 4B and C shows SEM images of the support with the intermediate layer. As observed, the thin intermediate γ-alumina layer is uniformly coated on the α-alumina sub layer. The images confirm the successful coating of the support by the γ-alumina layer. It is also observed that the coated intermediate layer has good adhesiveness and uniformity to the sub layer and this is
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because the both layers are made of alumina (see Figure 4B). As observed, thickness of the intermediate γ-alumina layer is approximately 4 m (see Figure 4C). BET characterization of the intermediate layer at adsorption temperature of 77 K and vapor
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pressure of 88.7 KPa showed that the average pore size of the γ-alumina layer is about 20.2 nm. Separation performance of the synthesized γ-alumina intermediate layer was evaluated in milk
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concentration. The latter test is typically used for characterization of ultrafiltration membranes.
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The experiments were carried out at a temperature of 25 °C and a pressure of 3 bar using an ultrafiltration set up. The permeation tests showed permeation flux of 242.3 and 155.7 kg m−2 h−1
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for water and milk respectively. Turbidity was reduced from 136.68 (feed) to 19.07 NTU (permeate).
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Figure 4:
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5.3.1. Seeding
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5.3. NaA zeolite membranes
A thin and uniform layer of NaA zeolite must be deposited on the composite support surface to
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synthesize a high-quality NaA zeolite membrane. To do this, the seeds should be dispersed homogeneously on the surface of the intermediate layer and the amount of seeds should be optimal. Otherwise, the as-synthesized NaA zeolite membrane becomes too thick or has defects (Li et al., 2012).
Figure 5 shows a schematic of the membrane formation on a macroporous support surface (Figure 5A) by the secondary growth method. The gray phase refers to the support phase and the black phase is the zeolite nano seeds and the zeolite film. Based on these results, it is concluded that the ratio of the support pore diameter to the seed diameter plays a crucial role in synthesis of zeolite membranes.
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Modification of the support surface with the γ-alumina intermediate layer can avoid penetration of the nano seeds and the synthesis zeolite gel into the support pores. This causes the formation
Figure 5:
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of an ultrathin layer of zeolite which provides a high quality zeolite membrane (Figure 5B).
Figure 6 illustrates surface of the modified support seeded by the nano powder of NaA zeolite. It
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is observed that the support surface is uniformly covered by the seeds.
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Figure 6: 5.3.2. As-synthesized NaA zeolite membranes
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Figure 7 presents SEM images of the NaA zeolite membrane synthesized via hydrothermal method on surface of the composite support. As observed, a uniform zeolite layer is deposited on
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surface of the γ-alumina intermediate layer. Thickness of zeolite layer is estimated to be less than
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8 μm.
Due to consistency between the support and the seeds used for the membrane synthesis, a distinguishable interface between the support and the zeolite layer can be observed. Growth of the zeolite layer inside the support pores is prevented by the intermediate layer and this can improve separation properties of the zeolite membranes in separation of liquid mixtures. Figure 7: 5.4. Pervaporation studies 5.4.1. Effect of operating temperature
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Figure 8 shows effect of feed temperature on permeation flux of water through the synthesized zeolite membrane. As seen, increasing temperature increases total permeation flux through the zeolite membrane. The observed behavior can be justified by two reasons; first, saturated
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pressure of mixture increases with increasing temperature and this results in enhancement of driving force for transport of feed through the membrane (Nik et al., 2006).
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Figure 8:
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Second, viscosity of the feed is one of the major resistances for the feed transport in the membrane module. Dynamic viscosity of EG has great effect on Reynolds number and can
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impact total permeation flux higher than 50 %.
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Viscosity values of water/EG mixture at different temperatures are listed in Table 2. As seen,
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with 15 ℃ increasing feed temperature, 35 % viscosity decline is obtained. Therefore, increasing
temperature increases Reynolds number significantly and this enhances permeation. Table 2:
Figure 8 also shows that increasing feed temperature increases separation factor. This can be justified by increasing water permeation more significantly with temperature. With increasing temperature, water permeation increases, but EG permeation does not increases significantly and increasing water permeation results in increasing separation factor (Nik et al., 2006; Zhang and Liu, 2011) 5.4.2. Effect of feed concentration
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Effects of feed concentration on separation factor and permeation flux are illustrated in Figure 9. It is observed that with increasing EG concentration in the feed, total permeation flux decreases. With increasing EG concentration in the feed, more active sites on the membrane surface are
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occupied by EG and this reduces water permeation through the membrane and in turn total permeation.
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The reduction of permeation flux can be also attributed to the reduction of driving force for water
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transport. At high concentration of EG, water activity in the feed decreases and thus chemical potential gradient between the two sides of the membrane for water decreases and this result in
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reduction of permeation flux. As observed in Figure 9, with decreasing EG concentration in the feed, separation factor decreases. According to Eq. 1, a small change in water concentration
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causes a significant change in the denominator of Eq. 1. This means that separation factors is
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higher at lower water concentrations (Zhang and Liu, 2011).
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Figure 9:
5.4.3. Effect of feed flow rate
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Figure 10 shows the effects of feed flow rate on separation factor and permeation flux. As observed, permeation flux and separation factor increase with increasing feed flow rate. This behavior can be attributed to the enhancement of Reynolds number and turbulency (Kunnakorn et al., 2011).
Figure 10:
One of the most important factors that increase permeation flux across a membrane is turbulency on the membrane surface. With increasing turbulency on the membrane surface, the sites which are occupied by EG molecules and thus deactivated, are replaced with water molecules and become activated. To show the effect of increasing turbulency in the membrane module on
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permeation flux, a CFD study was carried. Geometry of the membrane module is drawn in Figure 11 a. The CFD study shows effect of feed flow rate on the flow field on the membrane surface. The numerical solution for solving the conservation equations was carried out using a
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CFD package. The results are presented in terms of contours for kinetic energy of the feed in the module. Figure 11 b shows contours of kinetic energy for different flow rates of 1, 1.5, and 2
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L/min. As observed, increasing feed flow rate enhances feed kinetic energy which in turn
permeation flux across the membrane.
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Figure 11:
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increases the extent of feed turbulency on the membrane surface. This, as a result, increases
6. Conclusions
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Zeolite NaA membranes on double-layered supports were synthesized using the secondary
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growth method. The used supports consisted of two layers composing a macroporous -alumina
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sub layer and a deposited by γ-alumina intermediate layer to modify the support for the membrane formation. The NaA zeolite membranes were synthesized by the secondary growth
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method on the modified supports. The NaA nano seeds for the membrane preparation were synthesized via the hydrothermal method with an organic template of TMAOH. The seeds and the membranes were characterized using Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) to assure formation of the zeolite structure. The synthesized zeolite membranes were utilized in pervaporation (PV) dehydration of ethylene glycol (EG). Feed composition, feed flow rate, and feed temperature were varied to find the optimum conditions. A
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high separation factor of 10996 and a total permeation flux of 7.16 kg/m2.h for feed temperature
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of 80 ℃, flow rate of 1.5 L/min, and feed concentration of 90 % wt. EG were obtained.
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Chen, F.R., Chen, H.F., 1996. Pervaporation separation of ethylene glycol-water mixtures using crosslinked PVA-PES composite membranes. Part I. Effects of membrane preparation conditions on pervaporation performances. Journal of Membrane Science 109, 247-256. Dogan, H., Durmaz Hilmioglu, N., 2010. Chitosan coated zeolite filled regenerated cellulose membrane for dehydration of ethylene glycol/water mixtures by pervaporation. Desalination 258, 120-127. Du, J.R., Chakma, A., Feng, X., 2008. Dehydration of ethylene glycol by pervaporation using poly(N,Ndimethylaminoethyl methacrylate)/polysulfone composite membranes. Separation and Purification Technology 64, 63-70. Feng, X., Huang, R.Y.M., 1996. Pervaporation with chitosan membranes. I. Separation of water from ethylene glycol by a chitosan/polysulfone composite membrane. Journal of Membrane Science 116, 6776. Guo, R., Hu, C., Li, B., Jiang, Z., 2007a. Pervaporation separation of ethylene glycol/water mixtures through surface crosslinked PVA membranes: Coupling effect and separation performance analysis. Journal of Membrane Science 289, 191-198. Guo, R., Hu, C., Pan, F., Wu, H., Jiang, Z., 2006. PVA–GPTMS/TEOS hybrid pervaporation membrane for dehydration of ethylene glycol aqueous solution. Journal of Membrane Science 281, 454-462. Guo, R., Ma, X., Hu, C., Jiang, Z., 2007b. Novel PVA–silica nanocomposite membrane for pervaporative dehydration of ethylene glycol aqueous solution. Polymer 48, 2939-2945. Hu, C., Guo, R., Li, B., Ma, X., Wu, H., Jiang, Z., 2007a. Development of novel mordenite-filled chitosan– poly(acrylic acid) polyelectrolyte complex membranes for pervaporation dehydration of ethylene glycol aqueous solution. Journal of Membrane Science 293, 142-150. Hu, C., Li, B., Guo, R., Wu, H., Jiang, Z., 2007b. Pervaporation performance of chitosan–poly(acrylic acid) polyelectrolyte complex membranes for dehydration of ethylene glycol aqueous solution. Separation and Purification Technology 55, 327-334. Huang, R.Y.M., Shao, P., Feng, X., Anderson, W.A., 2002. Separation of Ethylene Glycol−Water Mixtures Using Sulfonated Poly(ether ether ketone) Pervaporation Membranes: Membrane Relaxation and Separation Performance Analysis. Industrial & Engineering Chemistry Research 41, 2957-2965. Hyder, M.N., Chen, P., 2009. Pervaporation dehydration of ethylene glycol with chitosan–poly(vinyl alcohol) blend membranes: Effect of CS–PVA blending ratios. Journal of Membrane Science 340, 171180. Iravaninia, M., Mirfendereski, M., Mohammadi, T., 2012. Pervaporation separation of toluene/nheptane mixtures using a MSE-modified membrane: Effects of operating conditions. Chemical Engineering Research and Design 90, 397-408. Jafari, M., Nouri, A., Kazemimoghadam, M., Mohammadi, T., 2013. Investigations on hydrothermal synthesis parameters in preparation of nanoparticles of LTA zeolite with the aid of TMAOH. Powder Technology 237, 442-449. Jafari, M., Nouri, A., Mousavi, S.F., Mohammadi, T., Kazemimoghadam, M., Optimization of synthesis conditions for preparation of ceramic (A-type zeolite) membranes in dehydration of ethylene glycol. Ceramics International. Khosravi, T., Mosleh, S., Bakhtiari, O., Mohammadi, T., Mixed matrix membranes of Matrimid 5218 loaded with zeolite 4A for pervaporation separation of water–isopropanol mixtures. Chemical Engineering Research and Design. Kunnakorn, D., Rirksomboon, T., Aungkavattana, P., Kuanchertchoo, N., Atong, D., Kulprathipanja, S., Wongkasemjit, S., 2011. Performance of sodium A zeolite membranes synthesized via microwave and autoclave techniques for water–ethanol separation: Recycle-continuous pervaporation process. Desalination 269, 78-83.
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Li, J., Shao, J., Ge, Q., Wang, G., Wang, Z., Yan, Y., 2012. Influences of the zeolite loading and particle size in composite hollow fiber supports on properties of zeolite NaA membranes. Microporous and Mesoporous Materials 160, 10-17. Liu, W., Zhang, J., Canfield, N., Saraf, L., 2011. Preparation of Robust, Thin Zeolite Membrane Sheet for Molecular Separation. Industrial & Engineering Chemistry Research 50, 11677-11689. Nik, O.G., Moheb, A., Mohammadi, T., 2006. Separation of Ethylene Glycol/Water Mixtures using NaA Zeolite Membranes. Chemical Engineering & Technology 29, 1340-1346. Pandey, L.K., Saxena, C., Dubey, V., 2005. Studies on pervaporative characteristics of bacterial cellulose membrane. Separation and Purification Technology 42, 213-218. Rao, P.S., Sridhar, S., Wey, M.Y., Krishnaiah, A., 2007. Pervaporative Separation of Ethylene Glycol/Water Mixtures by Using Cross-linked Chitosan Membranes. Industrial & Engineering Chemistry Research 46, 2155-2163. Sekulić, J., ten Elshof, J.E., Blank, D.H.A., 2004. Selective Pervaporation of Water through a Nonselective Microporous Titania Membrane by a Dynamically Induced Molecular Sieving Mechanism. Langmuir 21, 508-510. Shao, J., Ge, Q., Shan, L., Wang, Z., Yan, Y., 2011. Influences of Seeds on the Properties of Zeolite NaA Membranes on Alumina Hollow Fibers. Industrial & Engineering Chemistry Research 50, 9718-9726. Yong Nam, S., Moo Lee, Y., 1999. Pervaporation of ethylene glycol–water mixtures: I. Pervaporation performance of surface crosslinked chitosan membranes. Journal of Membrane Science 153, 155-162. Yu, C., Zhong, C., Liu, Y., Gu, X., Yang, G., Xing, W., Xu, N., 2012. Pervaporation dehydration of ethylene glycol by NaA zeolite membranes. Chemical Engineering Research and Design 90, 1372-1380. Zhang, J., Liu, W., 2011. Thin porous metal sheet-supported NaA zeolite membrane for water/ethanol separation. Journal of Membrane Science 371, 197-210.
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Table 1: Studies on water–EG membrane separations. Table 2: Effect of temperature on viscosity of water/EG mixture.
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Figure captions Figure 1: A schematic view of pervaporation set up used in the experiments. F: flow meter, T:
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thermometer, PI: pressure indicator.
Figure 3: SEM images of the synthesized A-type zeolite seeds.
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Figure 2: XRD patterns of the A-type nano zeolite seeds.
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Figure. 4: SEM images of the composite support (A) -alumina surface, (B) γ-alumina surface,
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and (C) cross section.
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Figure 5: A schematic representation of zeolite membrane synthesis on porous supports;
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A: macroporous α-alumina support, B: nanoporous γ-alumina support.
Figure 6: Surface SEM image of the seeded support using nano seeds of NaA zeolite. Figure 7: SEM images of the zeolite layer synthesized on the composite support. Figure 8: Effects of feed temperature on permeation flux and separation factor (Feed flow rate = 1.5 L/min, water content in the feed = 10 wt. %). Figure 9: Effect of feed concentration on separation factor and permeation flux
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(feed temperature = 65 ℃, feed flow rate = 1.5 L/min).
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Figure 10: Effect of feed flow rate on separation factor and permeation flux
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(feed temperature = 65 ℃, feed concentration = 10 wt. % water).
Figure 11: (a) Geometry of the membrane module used in the experiments and (b) Countors of
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kinetic energy of the feed on the membrane surface at different flow rates.
Table 1: Studies on water–EG membrane separations. No.
1
Membrane
Chitosan/poly vinyl
Water in
Feed
Separation
Permeation
feed
Temp.
factor
flux
(wt. %)
(K)
10
343
(kg m−2 h−1) 986
0.460
alcohol 2
Chitosan/poly acrylic
Ref.
(Hyder and Chen, 2009)
20
343
105
0.216
(Hu et al., 2007b)
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acid 3
Chitosan coated
5
323
76
0.406
(Dogan and
zeolite filled cellulose
Durmaz
7
PVA/PAN(GFT1001)
Surface cross linked
17.5
353
10
20
acid
343
PVA-GPTMS/TEOS
10 11
12
d 343
(Feng and Huang,
0.338
993
0.224
1996)
(Chen and Chen, 1996) (Yong Nam and Moo Lee, 1999)
0.211
(Guo et al., 2007a)
105
0.216
(Hu et al., 2007a)
20
343
714
0.060
(Guo et al., 2006)
PDMAEMA/PSF
6
303
600
0.222
(Du et al., 2008)
Bacterial cellulose
40
307
66
0.270
(Pandey et al.,
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20
0.300
1116
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Chitosan/poly acrylic
231
348
PVA 8
104
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308
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6
PVA/PES
10
an
5
Chitosan/Polysulfone
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4
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Hilmioglu, 2010)
2005)
NaA Zeolite
30
343
1117
0.944
(Nik et al., 2006)
13
NaA Zeolite
10
393
4000
1.830
(Yu et al., 2012)
14
Sulfonated Poly(ether
30
323
800
0.390
(Huang et al.,
ether ketone) 15
Cross-linked chitosan
2002) 12
303
148
0.225
(Rao et al., 2007)
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16
PVA/MPTMS/Silica
20
343
311
0.067
(Guo et al., 2007b)
Microporous titania
11
353
27
0.648
(Sekulić et al.,
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2004)
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Table 2: Effect of temperature on viscosity of water/EG mixture.
EG concentration
Viscosity (cP)
(wt. %)
50
65
80
90
6.06
3.83
2.59
75
4.86
3.18
2.21
60
3.78
2.57
1.84
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Highlights Modification of macroporous -alumina support by deposition of ultrafiltration γ-alumina layer Synthesis of nanosize zeolite NaA with narrow particle size distribution
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Development of hydrothermal method for synthesis of high quality NaA zeolite membranes Effects of operational parameters on water/EG separation performance were investigated
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High flux and separation factor for dehydration of ethylene glycol were achieved
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