Fabrication of TFC nanofiltration membranes via co-solvent assisted interfacial polymerization for lactose recovery

Fatemeh Esfandian; Majid Peyravi; Ali Asghar Ghoreyshi; Mohsen Jahanshahi; Ali Shokuhi Rad

doi:10.1016/j.arabjc.2017.01.004

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Original article

12 (

); 5325-5338

doi:

10.1016/j.arabjc.2017.01.004

Fabrication of TFC nanofiltration membranes via co-solvent assisted interfacial polymerization for lactose recovery

Fatemeh Esfandian^{^a}, Majid Peyravi^{^a,⁎}, Ali Asghar Ghoreyshi^{^b}, Mohsen Jahanshahi^{^a}, Ali Shokuhi Rad^{^c}

a Membrane Research Group, Nanotechnology Institute, Babol Noshirvani University of Technology, Shariati Ave., Babol 47148-71167, Iran

b Department of Chemical Engineering, Babol Noshirvani University of Technology, Shariati Ave., Babol 47148-71167, Iran

c Department of Chemical Engineering, Qaemshahr Branch, Islamic Azad University, Qaemshahr, Iran

⁎Corresponding author at: Head of Nano-Environmental Research Group, Research Director of Nanotechnology Institute, Iran. Fax: +98 1132 320342. http://www.nano.nit.ac.ir (Majid Peyravi) majid.peyravi@gmail.com (Majid Peyravi)

Received: 2016-9-5, Accepted: 2017-1-6, Published: 2017-12-01

Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.

Peer review under responsibility of King Saud University.

Abstract

This work has focused on the development of thin film composite (TFC) nanofiltration membranes via co-solvent assisted interfacial polymerization (CAIP) procedure by a new co-solvent to increase the membrane permeability. The nano-porous polyamide layer was made on the sulfonated polyethersulfone (SPES) support as a result of polymerization reaction between 1,3-Phenylendiamine and trimesoyl chloride. The effect of two types of ketone co-solvent (propanone and butanone) on the physiochemical characteristics of polyamide layer was studied by FTIR spectra, SEM and AFM analysis. The performance of membranes was evaluated using NaCl solution and pre-treated whey by ultrafiltration (UF) for lactose recovery. According to the AFM and SEM images, the membranes prepared using CAIP method demonstrated to have thin film layer with larger average pore size and lower roughness. The flux of these membranes was higher compared to the membrane prepared without the contribution of ketone co-solvent. In spite of flux increment, the rejection of lactose and NaCl did not exhibit any remarkable loss. Among propanone and butanone co-solvent, adding propanone to the organic phase led to form thinner and smoother polyamide layer, which was as a result of the difference in solubility parameter.

Keywords

Thin film composite membrane

Nanofiltration

Ketone co-solvent

Interfacial polymerization

Lactose separation

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1 Introduction

Thin film composite (TFC) nanofiltration membranes have attracted significant attentions in desalting of brine, water treatment and recovering effective materials from a contaminated liquid (Lau et al., 2012; Yamaguchi and Ikeda, 1992; Ghosh and Hoek, 2009; Turan, 2004 ). These membranes have gained much interest as compared to typical asymmetric nanofiltration membranes because of the selectivity and efficiency enhancement in various membrane separation processes. The main feature of TFC membrane is that this membrane comprised of a very thin active layer on the top of the microporous substrate (Misdan et al., 2014; Maruf et al., 2012; Xu et al., 2013; Chen et al., 2002; Xia et al., 2015 ). It must be mentioned that the separation performance of TFC membranes (i.e. selectivity and permeability) is mainly determined by the thin film structure and its chemical properties (Misdan et al., 2014; Mi et al., 2006). Therefore, the efforts have been assigned more to the development of top active layer.

In general, the composite membranes are prepared via interfacial polymerization (IP) method and the thin selective layer formed is polyamide type (Verissimo et al., 2005). In this method, the polymerization reaction takes place at the surface of porous support between two reactive monomers, a polyfunctional amine and a polyfunctional acyl chloride, dissolved in water and hydrocarbon solvent, respectively while these two phases are immiscible (Xu et al., 2013; Rahimpour et al., 2010; Verissimo et al., 2006; Ghosh et al., 2008 ). Mostly, m-phenylene diamine (MPD) and trimesoyl chloride (TMC) are two main reactive monomers in two aqueous and organic phases for the polyamide layer formation. The low water permeability of TFC membrane prepared with polymerization process is always the main challenge of this type of membrane (Jegal et al., 2002). Therefore, one of the objectives of the current work was the synthesis of a thin active layer with low mass transfer resistance to obtain high permeability without lowering the rejection.

Generally, a major problem in the formation of polyamide thin layer is the immiscibility of two organic and aqueous phases. If the immiscibility of two phases decreased, the formed layer density will be decreased. When IP process is used for formation of TFC membrane, by changing in immiscibility of aqueous and organic phases, the permeability can be increased. The immiscibility and solubility difference between two phases through IP reaction decrease by adding solvents such as alcohols, ethers, ketones and sulfur containing components in organic solution, which facilitate the transfer of amine molecules to the organic phase during the formation of thin active layer (Kim et al., 2005; Hirose et al., 1997). There is a novel concept of polymerization procedure for the synthesis of TFC membranes with controllable polyamide dense layer structure through the addition of co-solvent into the organic phase the so-called co-solvent assisted interfacial polymerization (CAIP) Kong et al., 2010. Many studies have demonstrated that TFC membranes with high water flux, permeability, and significant salt rejection are formed in the presence of these components. For example, Kong et al. (2010) added co-solvent (acetone) into organic phase for the preparation of TFC membranes. The results revealed that appropriate addition of co-solvent led to the production of TFC membrane with high flux and no remarkable rejection change as compared with the membrane synthesized by convectional IP technique. Moreover, Kim et al. (2005) synthesized TFC membranes via interfacial polymerization of MPD in aqueous phase and the addition of TMC in the organic phase (n-hexane). Dimethyl sulfoxide was added into the water solution in different concentrations. DMSO also plays a prominent role in increasing the water flux without any considerable loss in rejection.

In this research, a high permeable TFC membrane was synthesized by adding butanone co-solvent to the organic phase upon the SPES ultrafiltration support during co-solvent assisted interfacial polymerization (CAIP) process. In order to evaluate the effect of ketones on the performance and structural properties of the co-solvent assisted TFC membrane, two ketones (acetone and butanone) with different solubility parameters were applied and compared with conventional TFC membrane. Also, SPES was applied as a functional backing polymeric support instead of common support layer made by sulfone polymer family and the characteristics of the formed polyamide thin layer on the top of SPES substrate was studied during IP and CAIP process. Further, a conceptual model was presented to show how butanone can decrease the mass transfer resistance of the thin layer. In addition to salt solution flux and rejection, the recovery of lactose from whey, as a case study, was evaluated using the developed TFC membranes.

2 Experimental

2.1

2.1 Materials

Polyethersulfone (PES ultrason with M_w = 58,000 g/mol) as a polymer material for fabrication of substrate and N,N-dimethylformamide (DMF, Merck) as a solvent were used for the preparation of casting solution. Active monomers were used for synthesizing the top thin layer included 1,3-Phenylendiamine (MPD, Merck), and trimesoyl chloride (TMC, Merck). n-Hexane (>95%, Merck), propanone and butanone (Merck) were used as the solvent of organic solution and co-solvent of organic solution, respectively. For performance tests of TFC membranes, sodium chloride (NaCl > 99.5%, Merck) was dissolved in DI water and cheese whey was supplied from Kalleh factory dairy products (Amol-Iran). The characteristics of fresh cheese whey are presented in Table 1.

Table 1 The whey characteristic of Kalleh factory.

Parameters	Value
PH	5–6
Proteins (g/l)	4–6
Lactose (g/l)	60 ± 0.5
Conductivity (mS/cm)	6.05 ± 0.08
Total dissolved solids (mg/l)	2940 ± 15

2.2

2.2 Sulfonation method of PES

Sulfonation of PES was performed by sulfuric acid (98%) as the sulfonating agent and solvent. A 100 ml glass reactor, equipped with a magnetic stirrer and a nitrogen inlet/outlet was charged with PES pellet, and sulfuric acid (98%). The temperature for polymer dissolution was 25 °C. The reaction was allowed to proceed for 3 h and then sulfonated PES (SPES) was gradually precipitated into ice-cold deionized water under stirring. The resulting precipitate was recovered by filtration and washed multiple times with de-ionized water until pH became approximately 5–6. In this study, the sulfonated PES was insoluble in water and was totally recovered by precipitation separated by filtration. Finally, the SPES was dried under vacuum at 40 °C overnight (Rahimpour et al., 2010).

2.3

2.3 Preparation of SPES support layer

SPES (16 wt.%) was stirred in the DMF for at least 8 h until the solution became homogeneous. The solution was sprinkled and cast on the polyester non-woven fabric using a homemade casting knife with 100 μm thickness. The whole composite was immediately immersed in the precipitation bath including DI water at room temperature to initiate the phase inversion. The prepared membranes were washed and stored at 25 °C distilled water for 1 day to completely leach out the residual solvents. As the final stage, the membranes were dried by placing between two sheets of filter paper for 24 h at room temperature.

2.4

2.4 Fabrication of TFC membranes by the CAIP and conventional IP procedure

The SPES ultrafiltration membranes were used as support layers for active layer formation. For fabricating TFC membrane via conventional IP procedure, the SPES substrate was immersed in the aqueous solution of MPD (2 wt.%) for 2 min. After 2 min, the remaining MPD solution on the surface of the substrate was removed using rubber roller. MPD saturated membrane was then immersed in 0.1 wt.% TMC in n-hexane for 45 s to complete the interfacial polymerization. After that, for curing, membranes were held at 80 °C in an oven for 5 min. TFC membrane via CAIP procedure was prepared similar to TFC membrane fabricated via conventional IP procedure with difference in organic solution. The co-solvent (propanone and butanone) was added to TMC solution (organic solution) in concentration (1.5 wt.%). In CAIP procedure, the interfacial polymerization reaction was done between the resultant solution as an organic solution and an aqueous solution (2 wt.% MPD in water).

2.5

2.5 Structural characterization

In order to study the morphological properties of TFC membrane, cross section and top surface imaging were accomplished using a SEM (TESCAN) operating at 15 kV. For the cross-sectional scanning, the membranes were fractured in the liquid nitrogen. Then, all samples were coated with a gold thin layer for observation by a sputter coater (BAL-TEC, SCDOOS). Atomic force microscopy was used to determine the surface morphology and roughness of the TFC membranes. The model of AFM device was a Nanosurf scanning probe-optical microscope (EasyScan II). Small squares of the prepared membranes (approximately 1 cm²) were cut and glued on a glass substrate. The membrane surfaces were imaged in a scan size of 5 μm × 5 μm.

The chemical structure of the synthesized TFC membrane was evaluated by the attenuated total reflection (ATR) technique using infrared spectrometer (WQF-510A). The wavenumber range was measured between 4000 and 400 cm⁻¹.

To study the wetting property of SPES membrane sublayer and TFC membranes, water contact angle was measured for evaluation of the membrane hydrophilicity using a contact angle measuring instrument [G10, KRUSS, and Germany]. Deionized water was used as the probe liquid in all measurements. To minimize the experimental error, the contact angle was measured at five random locations for sample and the average value was reported.

The pore radius (r_p) and effective thickness to porosity (Δx/A_k) of NF membranes were calculated by Donnan Steric Pore Model (DSPM) based on the direct measurement method (Jahanshahi et al., 2010; Mohammad et al., 2003). This approach is known as an extended Nernst-Planck equation. It is assumed that the transport of solutes is done through discrete pores of membranes regarding all of the three significant aspects in transport mechanisms such as diffusion, electromigration and convection:

(1)

j_{i} = - D_{i, p} \frac{{dc}_{i}}{dx} - \frac{z_{i} c_{i} D_{i, p}}{RT} F \frac{d ψ}{dx} j_{i} + K_{i, c} c_{i} v

For uncharged solutes, only two terms of diffusive and convective affect the transport of solute inside the membrane. Thereby the electromigration term of Eq. (1) can be removed and rearranged as follows:

(2)

j_{i} = - D_{i, p} \frac{{dc}_{i}}{dx} + K_{i, c} c_{i} v

where

D_{i, p}

is the diffusivity of solute, and

K_{i, c}

and

K_{i, d}

are the hindrance factors for diffusivity and convection which are defined as below:

(3)

D_{i, p} = K_{i, d} D_{i, \infty}

(4)

K_{i, c} = (2 - Φ) (1.0 + 0.054 λ - 0.988 λ^{2} + 0.441 λ^{3})

(5)

K_{i, d} = 1.0 - 2.3 λ + 1.154 λ^{2} + 0.224 λ^{3}

Ф is the steric partition coefficient attributed to the finite size of the solute and pore size.

λ

is the dimensionless ratio of solute radius to pore radius. Ф and λ can be measured as follows:

(6)

Φ = {(1 - λ)}^{2}

(7)

λ = \frac{r_{s}}{r_{p}}

r_{s}

and

r_{p}

are the pore and the solute radius respectively. The integration and final form of Eq. (2) across the membrane can be expressed in terms of real solute rejection by the membrane as follows:

(8)

R_{real} = 1 - \frac{K_{i, c} Φ}{1 - \exp (- {Pe}_{m}) [1 - Φ K_{i, c}]}

(9)

{Pe}_{m} = \frac{K_{i, c}}{K_{i, d}} \frac{J_{v}}{D_{i, \infty}} \frac{Δ x}{A_{k}}

The water flux is related to the applied pressure as well as $r_{p}$ and $Δ x / A_{k}$ in the Hagen–Poiseuille equation.

(10)

J_{w} = \frac{r_{p}^{2} Δ P}{8 η (\frac{Δ x}{A_{k}})}

In order to estimate the membrane structure parameter by using the mathematical software, Vitamin B12 is used as an uncharged solute with certain characteristics ( $D_{i, \infty} = 0.33 \times 10^{- 9} m^{2} / s$ and $r_{s} = 0.74 nm$ ) to measure the flux and solute rejection. This software has been developed based on the solute transport mechanisms across the porous membrane (Peyravi et al., 2014).

2.6

2.6 Filtration assay

The performance of TFC membranes was evaluated as follows.

The fluxes of pure water and NaCl solution with a concentration of 2000 ppm as well as the rejection of NaCl solution were measured in the dead-end unit at an applied pressure of 6.5 bar and constant temperature of 25 °C. The effective membrane area in the filtration cell was 19.64 cm². All membranes were first wetted with the pure water at the applied pressure of 6.5 bar until the permeate flux became steady. The flux (J) through the composite membranes was determined by the following equation:

(11)

J = \frac{m}{A \times Δ t}

where m is a mass of permeate, A is the membrane area and

Δ t

is the permeation time. NaCl rejection (R) was calculated using conductivity measurement of feed and permeate:

(12)

R = (1 - \frac{C_{p}}{C_{f}}) \times 100

where

C_{f}

and

C_{p}

are the NaCl concentrations in the feed and permeate, respectively. In another set of experiment, the flux and lactose rejection of pre-treated whey were measured. In order to pre-treat the whey, the fresh whey was filtered using ultrafiltration (UF) membrane prior to TFC membrane to remove the proteins and fat to reduce the fouling of TFC membrane and enhance the lactose recovery (Cuartas-Uribe et al., 2009). The UF membrane that was used to separate the macromolecules of whey (proteins and fat) was SPES membrane. Permeate of UF membrane was collected and passed through the TFC membrane in the dead-end system at the operation pressure of 6.5 bar and a constant temperature of 25 °C. The schematic representation of experimental methodology is shown in Fig. 1. To determine the rejection of lactose in pre-treated whey, the lactose concentration in feed and permeate (

C_{f}

and

C_{p}

) was obtained by following method (Das et al., 2015):

Representation of the experimental methodology of whey filtration.

1 ml of sample is taken into a test tube and 1 ml of solution of 5% phenol in water is added. Then 5 ml of concentrated sulfuric acid is added rapidly directed against the liquid surface rather than the wall of the test tube in order to obtain a good mixing. After 10 min, the tubes are shaken and placed in a water bath at about 25–30 °C for 10–20 min. The absorbance of the cooled sample was taken at a wavelength of 490 nm with the help of UV–Vis Spectrophotometer.

3 Result and discussion

3.1

3.1 Characteristics of SPES substrate layer

In order to ensure about the sulfonation reaction, the degree of sulfonation (DS) was determined using ion exchange capacity and titration process (Rahimpour et al., 2010; Guan et al., 2006). The value of DS was 0.467.

Fourier transform infrared spectra of SPES substrate membrane confirmed the presence of sulfonic acid groups (—SO₃H) on this membrane. As shown in Fig. 2, the peak ∼1011 cm⁻¹ is attributed to (—SO₃H) and indicated the effective presence of SPES in the membrane structure (Sahebi et al., 2015). It can be clearly seen that the polar hydroxyl groups (OH) are formed onto the fully SPES membrane which can be confirmed by the absorption band at 3400 cm⁻¹. Furthermore, the absorption peaks of PES polymer are observable in the FTIR spectra of the substrate. Peaks at 1245 and 1322 cm⁻¹ indicate the asymmetric stretching vibration of C—SO₂—C and C—O bonds, respectively. The absorption peak at 1570 cm⁻¹ is ascribed to the C₆H₆ ring of PES polymer. So, the appearance of PES absorption peaks in the FTIR spectra of SPES sublayer demonstrated that sulfonation has not changed the chain nature of PES polymer.

FTIR spectra of synthesized SPES-100 membrane.

The (—SO₃H) functional group in SPES polymer affects the interfacial polymerization process between MPD and TMC during TFC membrane preparation over the SPES porous membrane. Indeed, the presence of (—SO₃H) group would certainly influence the diffusion rate of MPD from membrane surface to inside the pores. The presence of hydrophilic sulfonic group increases the tendency of MPD molecules to diffuse within the pores of SPES support due to the formation of hydrogen bonding between MPD and SPES polymer. This leads to diffuse MPD molecules with more penetration depth because of the capillary force when the SPES support was dipped in the aqueous phase at the defined dip coating time. On the other hand, the interfacial polymerization occurs more toward the organic phase when the impregnated SPES support is placed at the expose to the organic phase because TMC is less soluble in water than MPD in the organic phase. The authors believe that the polymerization occurs within the pores near the membrane surface because the amine monomer well diffused. It seems that a section of the thin layer forms within the support pore and another part forms upon the support surface.

It has been pointed to this issue in some literatures. For instance, Ghosh et al. prepared TFC membrane using interfacial polymerization of MPD with TMC on the PSF support layer which contained PEG as a hydrophilic polymer. They reported that the diffusion rate of MPD within the support pores could be certainly affected by the presence of PEG in the sublayer. This caused to diffuse out MPD from inside pore to the membrane interface to react with TMC. As they have been stated, polyamide thin layer formed deep within the pores- creating a thicker film (Ghosh and Hoek, 2009). Zhang et al. synthesized TFC membrane on the disulfonated poly (arylene ether sulfone) hydrophilic-hydrophobic multi-block copolymer/PSF support by interfacial polymerization of MPD and TMC. A hydrophilic substrate is likely to hold MPD in the pores which is influenced on the MPD diffusion and is decreased interfacial reaction rate (Zhang et al., 2016).

So, it is expected that the higher salt rejection is for polyamide composites formed on the sublayer membranes modified with functional groups which interact with MPD molecules (Han et al., 2012).

Cross section and surface SEM image of SPES ultrafiltration membrane are shown in Fig. 3. Fig. 3a exhibits an asymmetric structure, which consists of thin and dense skin layer and a porous bulk with finger-like and macrovoid structure at the bottom. As shown in Fig. 3b, the surface of SPES membrane was quite uniform without any defects and the pores distributed uniformly through the surface. The presence of SPES polymer in the structure of SPES substrate membrane can cause to increase its hydrophilicity. The contact angle of SPES membrane was 73.2°. The surface wettability of SPES sublayer was influenced by hydrophilic SO₃H functional group in SPES polymer chains.

(a) Cross-sectional SEM image and (b) surface SEM image of SPES-100 membrane.

3.2

3.2 Physiochemical properties of synthesized TFC membranes

3.2.1

3.2.1 Chemical properties of surface of TFC membrane

Fig. 4 shows a comparison between the FTIR spectra for different polyamide TFC membranes (TFC-0, TFC-P and TFC-B). The characteristic peaks of polyamide groups represent that in the interfacial polymerization process, the formation of polyamide layer has been done on top of the sub-layer as well. The peaks of the asymmetric stretching vibration at around 1670–1680 cm⁻¹ appear for carbonyl (C⚌O, amide I) and the appearance of band at 1400 cm⁻¹ is attributed to (C—N stretch) in the polyamide group. The peak of N—H bending vibration of polyamide ring appeared in the range of 1570–1580 cm⁻¹ (Peyravi et al., 2014; Wang et al., 2012). In addition, the absorption band at around 3000–3100 cm⁻¹ in the FTIR spectra can be assigned to the (—OH) group which is presented on the carboxylic acid side of polyamide aromatic ring. The absorption peaks of C⚌N group were observed in the FTIR of TFC-P and TFC-B membranes in addition to the previous peaks. The peaks with rather weak intensity at 1620 cm⁻¹ appeared in the TFC-P and TFC-B membranes which were attributed to the C⚌N bond of imine which may be formed in the reaction of MPD and ketone co-solvent (Rothschild and Marrero, 1982).

FTIR spectra of TFC-0, TFC-P and TFC-B membranes.

The interfacial polymerization immediately occurs between MPD and TMC after immersion of sublayer into the organic solution of TMC. In the CAIP system, it is possible that the side reaction is also done between MPD and ketone co-solvent in addition to the polymerization reaction of MPD and TMC. The mechanism of reaction between MPD and ketone co-solvent is depicted in Fig. 5. According to this figure, the attack reaction of amine (NH₂) group of MPD to ketone is carried out in several steps, (i) attack of the N nucleophile of MPD to the electrophilic C of the C⚌O group of ketone, (ii) proton transfer, protonation at O of the C⚌O group and removal of the proton on the N and forms the carbinolamine intermediate, and (iii) to form the imine we need to dehydrate. However, before —OH leaves, it needs to be protonated, so a simple acid/base reaction is done, (iv) use the electrons of the N to help push out a neutral water molecule and to form an iminium ion, and (v) an acid/base reaction. Deprotonation of the iminium N reveals the imine product (Zaikov et al., 2006; Vollhardt and Schore, 2011). As shown in the FTIR spectra of TFC-P and TFC-B membranes, the appearance of C⚌N peaks justifies the formation of imine in the CAIP system. The weak peaks of C⚌N observed in FTIR diagram can be attributed to the weak chemical reaction between MPD and ketone.

Schematic illustration of mechanism of reaction between MPD and co-solvent in the CAIP system.

3.2.2

3.2.2 Cross section and surface morphology of TFC membranes

The morphological structure of synthesized TFC membranes via conventional IP and CAIP procedure was investigated by FESEM, SEM and AFM analysis to confirm the formation of composite thin layer on the top of SPES support. The cross-sectional FESEM and surface SEM images of membranes are presented in Fig. 6. According to the cross-sectional FESEM images, the support layer of these membranes had high porosity along with finger like pores. The required sub-structure should ideally provide an appropriate porosity for the skin layer and should not give any additional transport resistance. The finger-type structure of SPES with interconnecting pores has been shown to give a good support to the separating skin and gives very little resistance to transportation (Brown et al., 2002). The cross-sectional FESEM image shows that the composite membrane consists of distinctive polyamide active layer on top of the porous sublayer with finger like pores. This confirms that polyamide nano-porous layer was successfully made over the SPES substrate. The average thickness of the polyamide active layer is in the range of 300–400 nm. As visually seen in FESEM cross-sectional images of the membranes, the thickness of the dense active layer is slightly decreased when propanone and butanone were used in the organic solution.

Cross‐sectional FESEM images of (a) TFC-0, (b) TFC-P, (c) TFC-B and surface SEM images of (d) TFC-0, (e) TFC-P and (f) TFC-B.

Fig. 6 illustrates the SEM micrographs of the top surface of TFC membranes. Commonly, the surface of synthesized TFC membranes has shown a “ridge and valley” morphology (Emadzadeh et al., 2014; Tang et al., 2007). The surface image of TFC-0 shows a rougher surface morphology for composite polyamide membrane prepared via conventional IP procedure in comparison with the other two membranes prepared via CAIP procedure (TFC-P and TFC-B).

It seems that the smoother surface of TFC-P and TFC-B is due to the effect of co-solvent on the reaction zone during the polymerization reaction. The appearance of reaction zone at the initial stage of interfacial polymerization was theoretically predicted by Freger (2005). During polymerization process, the polymer begins to form in a zone named as reaction zone, as a result of reaction between two monomers (MPD and TMC). In the CAIP system, the narrow miscibility zone is formed due to the decrease in the interfacial tension and solubility differences of aqueous and organic phase by addition of co-solvent to organic phase. Hence, the polymerization reaction is carried out beyond the initial reaction zone. Schematic picture of conventional interfacial polymerization (IP) and polymerization in the presence of co-solvent (CAIP) for polyamide layer formation is depicted in Fig. 7.

Schematic picture for polyamide layer formation on the sublayer by IP and CAIP process.

This conceptual model represents the creation of narrow miscibility zone in the CAIP system. It may cause to decrease the collision between two monomers (MPD and TMC) and limit the polymerization reaction and cross-linking of polyamide on top of the substrate. So the addition of co-solvent in the organic phase leads to form a composite membrane with loose and thin polyamide layer and smoother surface (Kong et al., 2010).

As can be seen in SEM images of membranes surface, the morphology of nodular which is a common morphology for commercial TFC was observed for TFC-0. By applying propanone in CAIP process, the surface morphology of TFC-P changed from popular nodular shape while after using butanone instead of propanone in CAIP process, the surface morphology was rougher. On the other words, the surface SEM image of TPC-B shows morphology between the familiar morphology of neat TFC and morphology of TFC-P. The difference in the structure of active polyamide layer of TFC membranes prepared via CAIP process (TFC-P and TFC-B) could be due to the fact that two co-solvents (propanone and butanone) have different solubility parameters. The solubility parameter of the component is defined as follows:

(13)

solubility parameter = {[\frac{Δ H - RT}{v_{m}}]}^{1 / 2}

where

Δ H

is the molar evaporation heat of a liquid (Cal/mol),

v_{m}

is the molar volume (cm³/mol) and R is gas constant (Cal/mol·K). The solubility parameter of propanone and butanone is 9.9 and 9.3 (Cal/cm³)^1/2, respectively (Burke, 1984). Propanone (acetone) as a ketone is completely soluble in water and organic solvent while the butanone is completely soluble in organic solvent and partially soluble in water. This may be due to the length of hydrocarbon chain in chemical structure of butanone which is longer than acetone. Since there is difference in solubility parameter between organic and aqueous solution for two applied ketones, it is expected that the miscibility zone formed after adding butanone is thinner. So the polymerization between two monomers slightly decreases and active thin layer is difficult to form while the difference in solubility parameter is minor, the active layer is formed with smoother structure (Hirose and Ikeda, 1996).

Fig. 8 represents the two and three-dimensional AFM images of the surface of composite membranes over a scan area of 5 μm × 5 μm. Moreover, the surface roughness parameters of synthesized TFC membranes calculated using AFM images are tabulated in Table 2. The surface seems to be smoother with polymerization of MPD and TMC at the presence of co-solvent in the organic solution. The roughness parameters of membranes also confirm the decrease in the roughness of TFC-P and TFC-B in comparison with TFC-0. The AFM images and roughness parameters of the TFC membranes surface are compatible with the SEM images of membrane surface. The results of the contact angle measurements are presented in Table 2. TFC-0 membrane showed higher contact angle than TFC-B and TFC-P membranes. It should be noted that there is a direct correlation between surface roughness and contact angle. The surface with higher roughness increases the contact angle (Jung and Bhushan, 2006). This can be interpenetrated by changing morphology of the TFC membrane induced by ketones. Existence of ketones in the polymerization solution leads to growing miscibility zone and limits the IP reaction during the formation of thin-film layer. By the possible decrease in reaction rate, the roughness of TFC membrane surface was decreased. This result has a good accordance with AFM data.

Two and three dimensional AFM images of TFC NF membranes (a) TFC-0, (b) TFC-P, and (c) TFC-B.

Table 2 Surface roughness parameters of synthesized TFC membranes.

Membrane	Roughness			Contact angle (°)
Membrane	S_a (nm)	S_q (nm)	S_z (nm)	Contact angle (°)
TFC-0	58.779	75.904	545.93	65.4
TFC-P	32.373	40.938	303.55	48.6
TFC-B	38.04	47.182	317.2	55

3.3

3.3 Effect of CAIP technique on the membrane performance

The performance of a membrane mainly depends on the structure of thin film (i.e. thickness, pore size, surface roughness and hydrophilicity) and its chemical properties (i.e. functional groups and cross-linking). Moreover, the properties of substrate affect the performance of TFC membrane (Lau et al., 2012). Results of the performance analysis of TFC membranes in terms of pure water, solution (2000 ppm NaCl concentration) and pre-treated whey fluxes are represented in Fig. 9. The pure water flux is increased from 4.85 (kg/m²·h) for TFC-0 to 7.7 and 9.97 (kg/m²·h) for TFC-P and TFC-B respectively. Comparison between the flux of modified and unmodified membranes indicated that the addition of co-solvent in the organic phase during the interfacial polymerization process caused to increase the fluxes. The authors believe that an increase in the flux of TFC-P and TFC-B is related to the surface pore size and polyamide layer structure. As it is observed in Table 3, the pore size of TFC-0 is smaller (0.47 nm) than TFC-P and TFC-B. The organic phase with aiding solvent in CAIP system creates a miscibility zone between two phases during the polymerization reaction and limits crosslinking degree which causes to the formation of TFC membrane with larger pore size. In the CAIP system, imine molecules along with MPD can be incorporated in the interfacial polymerization reaction with TMC because of the presence of imine molecules in the organic solution (Taggi et al., 2002). Therefore, it is expected that the reaction of polyamide formation is done in three possible routes as shown in Fig. 10. Route (i): the fully cross-linked polyamide is formed as a result of reaction between MPD with TMC. Routes (ii): MPD and imine attack the TMC where it interracially reacts with MPD and imine simultaneously. Route (iii): two imine molecules react with acyl chloride groups of TMC and finally polyamide layer is formed.

Water flux and NaCl solution flux and whey flux of TFC-0, TFC-P and TFC-B nanofiltration membranes.

Table 3 Structural characteristics of synthesized TFC membranes calculated from theoretical model.

Membrane	Experimental data^a		Calculated data
Membrane	Rej (%)	J_v (kg/m²·h)	$λ (r_{s} / r_{p})$	$r_{p}$ (nm)	$Δ x / A_{k}$
TFC-0	93 ± 0.5	2.975 ± 0.3	1.57	0.47	19.19
TFC-P	88 ± 0.4	6.87 ± 0.3	1.09	0.68	12.57
TFC-B	90 ± 0.5	8.65 ± 0.4	1.39	0.53	10.32

a Concentration of Vitamin B12 in distillated water was 500 ppm.

Three possible routes of polyamide formation.

The higher flux of TFC-P and TFC-B membranes may be because of the formation of polyamide with the structure shown in routes of (ii) and (iii) of Fig. 10 on top of the substrate in addition to polyamide with fully cross-linked structure (route (i)). Indeed, imine molecule in comparison with MPD molecule has lower reactivity toward acyl chloride groups of TMC. This also shows higher steric hindrance than MPD monomer. The authors believe that both parameters of lower reactivity and steric hindrance of imine act as the limiting factors on the growth of polyamide chains. It is possible that polyamide is formed with smaller chain and lower density in the routes of (ii) and (iii). Consequently, polyamide barrier layer formed on the surface of TFC-P and TFC-B would be thinner with a larger pore size which creates a lower barrier resistance against the water transport through membrane (Misdan et al., 2014). The calculated pore size data are in accordance with the respective ability for permeability. As it is shown in Fig. 9, the flux of TFC-B is higher than TFC-P. This can be explained by the increment in the pore size and the decrease in the surface roughness of TFC-B than TFC-P membrane, which results in the extension of available area of the membrane for water transport (Emadzadeh et al., 2014; Rana and Matsuura, 2010). Indeed, the effect of surface roughness on the flux was dominant over the thickness of polyamide thin layer and played a stronger role in facilitating high flux.

The NaCl and CaCl₂ rejection of solution containing 2000 ppm NaCl and lactose rejection of pre-treated whey related to the synthesized TFC membranes is compared in Fig. 11. The rejection of NaCl, CaCl₂ and lactose slightly decreased in the order of TFC-0 > TFC-B > TFC-P. Regarding Fig. 11, NaCl rejection of three membranes is higher than CaCl₂ rejection. The salt rejection can be affected by the surface charge of membranes and the surface charge of membranes changed with pH of feed solution. Under neutral pH of water solution, the surface of polyamide membrane (MPD-TMC) is negatively charged (Hoseinpour et al., 2016). The lower rejection of divalent salt (CaCl₂) compared to monovalent salt (NaCl) is due to the higher affinity between membrane surface and cations with higher valence (Liu et al., 2012; Zhou et al., 2014). The highest obtained value for lactose rejection was 98%. The obtained results of rejection were coincident with the properties of polyamide layer on top of SPES substrate. Fig. 12 also reveals that all three TFC membranes have higher lactose rejection than NaCl rejection, because of the larger size of lactose than Cl⁻ ion.

NaCl, CaCl2 and lactose rejection of TFC-0, TFC-P and TFC-B membranes.

Percentage of flux and rejection variations (%) of synthesized TFC membranes related to each other.

In order to clarify the advantage of TFC-B (the membrane prepared with propanone) and TFC-P (the membrane prepared with butanone) rather than TFC-0 (common TFC) for lactose recovery of whey, the percentage of flux and rejection variations of modified TFC membrane related to neat TFC was estimated for pure water, salt solution, and whey which presented in Fig. 12. The obtained results showed that the flux increment of TFC-P and TFC-B related to TFC-0 for salt solution was 52.8% and 99%, respectively. These values after whey filtration were 17.6% and 35% for TFC-P and TFC-B, respectively. This shows that the flux values for modified TFC membranes were significantly increased when the co-solvents of propanone and butanone were used during the interfacial process. However, the flux enhancement of TFC-P and TFC-B was lower for whey filtration compared to pure water and salt solution filtrations. It can be related to the nature of whey and the fouling created by the particles of whey on the surface of synthesized membranes. In addition, the increased flux of TFC-B for whole media was higher than TFC-P. It should be noted that the reduction in lactose rejection by both TFC-P and TFC-B membranes that were applied for whey filtration, was negligible.

4 Conclusion

Three different TFC membranes with polyamide thin layer were prepared by conventional interfacial polymerization and co-solvent assisted interfacial polymerization (CAIP) process over porous sulfonated polyethersulfone (SPES) support layer. The impact of two types of ketone co-solvent (propanone and butanone) on the structural and chemical properties of nano-porous thin film and also performance of TFC membranes were investigated. FTIR spectra confirmed that the chemical properties of polyamide layer of membranes prepared using CAIP technique were altered depending on the used co-solvent. SEM and AFM images indicated that contribution of co-solvent, resulted in the formation of a polyamide active layer with smoother, larger pore size and less cross-linked structure, which was due to the decrease in solubility differences between two phases and collision of two monomers during the polymerization. These lead to flux enhancement for membranes fabricated via CAIP technique without considerable rejection loss. Thus, the presence of additives (i.e. co-solvent) in the organic solution of polymerization would affect the physiochemical properties of polyamide layer.

References

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Ghosh A.K., Jeong B.-H., Huang X., Hoek E.M., . Impacts of reaction and curing conditions on polyamide composite reverse osmosis membrane properties. J. Membr. Sci.. 2008;311:34-45.
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Guan R., Dai H., Li C., Liu J., Xu J., . Effect of casting solvent on the morphology and performance of sulfonated polyethersulfone membranes. J. Membr. Sci.. 2006;277:148-156.
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Han G., Chung T.-S., Toriida M., Tamai S., . Thin-film composite forward osmosis membranes with novel hydrophilic supports for desalination. J. Membr. Sci.. 2012;423:543-555.
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Hoseinpour H., Jahanshahi M., Peyravi M., Nozad A., . Feasibility study of a novel copolyamide thin film composite membrane assisted by melamine in terms of acid and thermal stability. J. Ind. Eng. Chem.. 2016;46:244-257.
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Jegal J., Min S.G., Lee K.H., . Factors affecting the interfacial polymerization of polyamide active layers for the formation of polyamide composite membranes. J. Appl. Polym. Sci.. 2002;86:2781-2787.
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Jung Y.C., Bhushan B., . Contact angle, adhesion and friction properties of micro-and nanopatterned polymers for superhydrophobicity. Nanotechnology. 2006;17:4970.
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Kim S.H., Kwak S.-Y., Suzuki T., . Positron annihilation spectroscopic evidence to demonstrate the flux-enhancement mechanism in morphology-controlled thin-film-composite (TFC) membrane. Environ. Sci. Technol.. 2005;39:1764-1770.
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Kong C., Kanezashi M., Yamomoto T., Shintani T., Tsuru T., . Controlled synthesis of high performance polyamide membrane with thin dense layer for water desalination. J. Membr. Sci.. 2010;362:76-80.
[Google Scholar]
Lau W.J., Ismail A.F., Misdan N., Kassim M.A., . A recent progress in thin film composite membrane: a review. Desalination. 2012;287:190-199.
[Google Scholar]
Liu M., Yao G., Cheng Q., Ma M., Yu S., Gao C., . Acid stable thin-film composite membrane for nanofiltration prepared from naphthalene-1,3,6-trisulfonylchloride (NTSC) and piperazine (PIP) J. Membr. Sci.. 2012;415:122-131.
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Mi B., Coronell O., Mariñas B.J., Watanabe F., Cahill D.G., Petrov I., . Physico-chemical characterization of NF/RO membrane active layers by Rutherford backscattering spectrometry. J. Membr. Sci.. 2006;282:71-81.
[Google Scholar]
Misdan N., Lau W.J., Ismail A.F., Matsuura T., Rana D., . Study on the thin film composite poly (piperazine-amide) nanofiltration membrane: impacts of physicochemical properties of substrate on interfacial polymerization formation. Desalination. 2014;344:198-205.
[Google Scholar]
Mohammad A.W., Hilal N., Seman M.N.A., . A study on producing composite nanofiltration membranes with optimized properties. Desalination. 2003;158:73-78.
[Google Scholar]
Peyravi M., Jahanshahi M., Rahimpour A., Javadi A., Hajavi S., . Novel thin film nanocomposite membranes incorporated with functionalized TiO₂ nanoparticles for organic solvent nanofiltration. Chem. Eng. J.. 2014;241:155-166.
[Google Scholar]
Rahimpour A., Jahanshahi M., Mortazavian N., Madaeni S.S., Mansourpanah Y., . Preparation and characterization of asymmetric polyethersulfone and thin-film composite polyamide nanofiltration membranes for water softening. Appl. Surf. Sci.. 2010;256:1657-1663.
[Google Scholar]
Rahimpour A., Madaeni S.S., Ghorbani S., Shockravi A., Mansourpanah Y., . The influence of sulfonated polyethersulfone (SPES) on surface nano-morphology and performance of polyethersulfone (PES) membrane. Appl. Surf. Sci.. 2010;256:1825-1831.
[Google Scholar]
Rana D., Matsuura T., . Surface modifications for antifouling membranes. Chem. Rev.. 2010;110:2448-2471.
[Google Scholar]
Rothschild K.J., Marrero H., . Infrared evidence that the Schiff base of bacteriorhodopsin is protonated: bR570 and K intermediates. Proc. Natl. Acad. Sci.. 1982;79:4045-4049.
[Google Scholar]
Sahebi S., Phuntsho S., Woo Y.C., Park M.J., Tijing L.D., Hong S., Shon H.K., . Effect of sulphonated polyethersulfone substrate for thin film composite forward osmosis membrane. Desalination 2015
[Google Scholar]
Taggi A.E., Hafez A.M., Wack H., Young B., Ferraris D., Lectka T., . The development of the first catalyzed reaction of ketenes and imines: catalytic, asymmetric synthesis of β-lactams. J. Am. Chem. Soc.. 2002;124:6626-6635.
[Google Scholar]
Tang C.Y., Fu Q.S., Criddle C.S., Leckie J.O., . Effect of flux (transmembrane pressure) and membrane properties on fouling and rejection of reverse osmosis and nanofiltration membranes treating perfluorooctane sulfonate containing wastewater. Environ. Sci. Technol.. 2007;41:2008-2014.
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Turan M., . Influence of filtration conditions on the performance of nanofiltration and reverse osmosis membranes in dairy wastewater treatment. Desalination. 2004;170:83-90.
[Google Scholar]
Verissimo S., Peinemann K.-V., Bordado J., . Thin-film composite hollow fiber membranes: an optimized manufacturing method. J. Membr. Sci.. 2005;264:48-55.
[Google Scholar]
Verissimo S., Peinemann K.-V., Bordado J., . Influence of the diamine structure on the nanofiltration performance, surface morphology and surface charge of the composite polyamide membranes. J. Membr. Sci.. 2006;279:266-275.
[Google Scholar]
Vollhardt K.P.C., Schore N.E., . Organic Chemistry: Structure and Function. WH Freeman; 2011.
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[Google Scholar]
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Xu G.-R., Wang J.-N., Li C.-J., . Strategies for improving the performance of the polyamide thin film composite (PA-TFC) reverse osmosis (RO) membranes: surface modifications and nanoparticles incorporations. Desalination. 2013;328:83-100.
[Google Scholar]
Yamaguchi, T., Ikeda, K., 1992. Composite reverse osmosis membrane and production thereof. Google Patents.
Zaikov G.E., Rakovsky S., Schiraldi D.A., . Diversity in Chemical Reactions: Pure and Applied Chemistry. Nova Publishers; 2006.
Zhang X., Tian J., Shi Wenxin, Zhang Z., Xu Y., Gao S., Cui F., . High performance thin-film composite (TFC) forward osmosis (FO) membrane fabricated on novel hydrophilic disulfonated poly (arylene ether sulfone) multiblock copolymer/polysulfone substrate. J. Membr. Sci.. 2016;520:529-539.
[Google Scholar]
Zhou C., Shi Y., Sun Ch., Yu S., Liu M., Gao C., . Thin-film composite membranes formed by interfacial polymerization with natural material sericin and trimesoyl chloride for nanofiltration. J. Membr. Sci.. 2014;471:381-391.
[Google Scholar]

Introduction

Experimental

Materials
Sulfonation method of PES
Preparation of SPES support layer
Fabrication of TFC membranes by the CAIP and conventional IP procedure
Structural characterization
Filtration assay

Result and discussion

Characteristics of SPES substrate layer
Physiochemical properties of synthesized TFC membranes
Effect of CAIP technique on the membrane performance

Conclusion

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[1] Brown P.J., Ying S., Yang J., . Morphological structure of polyetherketone membranes for gas separation prepared by phase inversion. AUTEX Res. J.. 2002;2:101-108.
[Google Scholar]

[2] Burke, J., 1984. Solubility parameters: theory and application.

[3] Chen S.H., Chang D.J., Liou R.M., Hsu C.S., Lin S.S., . Preparation and separation properties of polyamide nanofiltration membrane. J. Appl. Polym. Sci.. 2002;83:1112-1118.
[Google Scholar]

[4] Cuartas-Uribe B., Alcaina-Miranda M., Soriano-Costa E., Mendoza-Roca J., Iborra-Clar M., Lora-García J., . A study of the separation of lactose from whey ultrafiltration permeate using nanofiltration. Desalination. 2009;241:244-255.
[Google Scholar]

[5] Das B., Sarkar S., Sarkar A., Bhattacharjee S., Bhattacharjee C., . Recovery of whey proteins and lactose from dairy waste: a step towards green waste management. Process Saf. Environ. Prot. 2015
[Google Scholar]

[6] Emadzadeh D., Lau W.J., Matsuura T., Rahbari-Sisakht M., Ismail A.F., . A novel thin film composite forward osmosis membrane prepared from PSf–TiO₂ nanocomposite substrate for water desalination. Chem. Eng. J.. 2014;237:70-80.
[Google Scholar]

[7] Freger V., . Kinetics of film formation by interfacial polycondensation. Langmuir. 2005;21:1884-1894.
[Google Scholar]

[8] Ghosh A.K., Hoek E.M., . Impacts of support membrane structure and chemistry on polyamide–polysulfone interfacial composite membranes. J. Membr. Sci.. 2009;336:140-148.
[Google Scholar]

[9] Ghosh A.K., Jeong B.-H., Huang X., Hoek E.M., . Impacts of reaction and curing conditions on polyamide composite reverse osmosis membrane properties. J. Membr. Sci.. 2008;311:34-45.
[Google Scholar]

[10] Guan R., Dai H., Li C., Liu J., Xu J., . Effect of casting solvent on the morphology and performance of sulfonated polyethersulfone membranes. J. Membr. Sci.. 2006;277:148-156.
[Google Scholar]

[11] Han G., Chung T.-S., Toriida M., Tamai S., . Thin-film composite forward osmosis membranes with novel hydrophilic supports for desalination. J. Membr. Sci.. 2012;423:543-555.
[Google Scholar]

[12] Hirose, M., Ikeda, K., 1996. Method of producing high permeable composite reverse osmosis membrane. Google Patents.

[13] Hirose, M., Ito, H., Maeda, M., Tanaka, K., 1997. Highly permeable composite reverse osmosis membrane, method of producing the same, and method of using the same. Google Patents.

[14] Hoseinpour H., Jahanshahi M., Peyravi M., Nozad A., . Feasibility study of a novel copolyamide thin film composite membrane assisted by melamine in terms of acid and thermal stability. J. Ind. Eng. Chem.. 2016;46:244-257.
[Google Scholar]

[15] Jahanshahi M., Rahimpour A., Peyravi M., . Developing thin film composite poly (piperazine-amide) and poly (vinyl-alcohol) nanofiltration membranes. Desalination. 2010;257:129-136.
[Google Scholar]

[16] Jegal J., Min S.G., Lee K.H., . Factors affecting the interfacial polymerization of polyamide active layers for the formation of polyamide composite membranes. J. Appl. Polym. Sci.. 2002;86:2781-2787.
[Google Scholar]

[17] Jung Y.C., Bhushan B., . Contact angle, adhesion and friction properties of micro-and nanopatterned polymers for superhydrophobicity. Nanotechnology. 2006;17:4970.
[Google Scholar]

[18] Kim S.H., Kwak S.-Y., Suzuki T., . Positron annihilation spectroscopic evidence to demonstrate the flux-enhancement mechanism in morphology-controlled thin-film-composite (TFC) membrane. Environ. Sci. Technol.. 2005;39:1764-1770.
[Google Scholar]

[19] Kong C., Kanezashi M., Yamomoto T., Shintani T., Tsuru T., . Controlled synthesis of high performance polyamide membrane with thin dense layer for water desalination. J. Membr. Sci.. 2010;362:76-80.
[Google Scholar]

[20] Lau W.J., Ismail A.F., Misdan N., Kassim M.A., . A recent progress in thin film composite membrane: a review. Desalination. 2012;287:190-199.
[Google Scholar]

[21] Liu M., Yao G., Cheng Q., Ma M., Yu S., Gao C., . Acid stable thin-film composite membrane for nanofiltration prepared from naphthalene-1,3,6-trisulfonylchloride (NTSC) and piperazine (PIP) J. Membr. Sci.. 2012;415:122-131.
[Google Scholar]

[22] Maruf S.H., Ahn D.U., Pellegrino J., Killgore J.P., Greenberg A.R., Ding Y., . Correlation between barrier layer T g and a thin-film composite polyamide membrane's performance: effect of chlorine treatment. J. Membr. Sci.. 2012;405:167-175.
[Google Scholar]

[23] Mi B., Coronell O., Mariñas B.J., Watanabe F., Cahill D.G., Petrov I., . Physico-chemical characterization of NF/RO membrane active layers by Rutherford backscattering spectrometry. J. Membr. Sci.. 2006;282:71-81.
[Google Scholar]

[24] Misdan N., Lau W.J., Ismail A.F., Matsuura T., Rana D., . Study on the thin film composite poly (piperazine-amide) nanofiltration membrane: impacts of physicochemical properties of substrate on interfacial polymerization formation. Desalination. 2014;344:198-205.
[Google Scholar]

[25] Mohammad A.W., Hilal N., Seman M.N.A., . A study on producing composite nanofiltration membranes with optimized properties. Desalination. 2003;158:73-78.
[Google Scholar]

[26] Peyravi M., Jahanshahi M., Rahimpour A., Javadi A., Hajavi S., . Novel thin film nanocomposite membranes incorporated with functionalized TiO₂ nanoparticles for organic solvent nanofiltration. Chem. Eng. J.. 2014;241:155-166.
[Google Scholar]

[27] Rahimpour A., Jahanshahi M., Mortazavian N., Madaeni S.S., Mansourpanah Y., . Preparation and characterization of asymmetric polyethersulfone and thin-film composite polyamide nanofiltration membranes for water softening. Appl. Surf. Sci.. 2010;256:1657-1663.
[Google Scholar]

[28] Rahimpour A., Madaeni S.S., Ghorbani S., Shockravi A., Mansourpanah Y., . The influence of sulfonated polyethersulfone (SPES) on surface nano-morphology and performance of polyethersulfone (PES) membrane. Appl. Surf. Sci.. 2010;256:1825-1831.
[Google Scholar]

[29] Rana D., Matsuura T., . Surface modifications for antifouling membranes. Chem. Rev.. 2010;110:2448-2471.
[Google Scholar]

[30] Rothschild K.J., Marrero H., . Infrared evidence that the Schiff base of bacteriorhodopsin is protonated: bR570 and K intermediates. Proc. Natl. Acad. Sci.. 1982;79:4045-4049.
[Google Scholar]

[31] Sahebi S., Phuntsho S., Woo Y.C., Park M.J., Tijing L.D., Hong S., Shon H.K., . Effect of sulphonated polyethersulfone substrate for thin film composite forward osmosis membrane. Desalination 2015
[Google Scholar]

[32] Taggi A.E., Hafez A.M., Wack H., Young B., Ferraris D., Lectka T., . The development of the first catalyzed reaction of ketenes and imines: catalytic, asymmetric synthesis of β-lactams. J. Am. Chem. Soc.. 2002;124:6626-6635.
[Google Scholar]

[33] Tang C.Y., Fu Q.S., Criddle C.S., Leckie J.O., . Effect of flux (transmembrane pressure) and membrane properties on fouling and rejection of reverse osmosis and nanofiltration membranes treating perfluorooctane sulfonate containing wastewater. Environ. Sci. Technol.. 2007;41:2008-2014.
[Google Scholar]

[34] Turan M., . Influence of filtration conditions on the performance of nanofiltration and reverse osmosis membranes in dairy wastewater treatment. Desalination. 2004;170:83-90.
[Google Scholar]

[35] Verissimo S., Peinemann K.-V., Bordado J., . Thin-film composite hollow fiber membranes: an optimized manufacturing method. J. Membr. Sci.. 2005;264:48-55.
[Google Scholar]

[36] Verissimo S., Peinemann K.-V., Bordado J., . Influence of the diamine structure on the nanofiltration performance, surface morphology and surface charge of the composite polyamide membranes. J. Membr. Sci.. 2006;279:266-275.
[Google Scholar]

[37] Vollhardt K.P.C., Schore N.E., . Organic Chemistry: Structure and Function. WH Freeman; 2011.

[38] Wang K.Y., Chung T.S., Amy G., . Developing thin-film-composite forward osmosis membranes on the PES/SPSf substrate through interfacial polymerization. AIChE J.. 2012;58:770-781.
[Google Scholar]

[39] Xia S., Yao L., Zhao Y., Li N., Zheng Y., . Preparation of graphene oxide modified polyamide thin film composite membranes with improved hydrophilicity for natural organic matter removal. Chem. Eng. J.. 2015;280:720-727.
[Google Scholar]

[40] Xu G.-R., Wang J.-N., Li C.-J., . Strategies for improving the performance of the polyamide thin film composite (PA-TFC) reverse osmosis (RO) membranes: surface modifications and nanoparticles incorporations. Desalination. 2013;328:83-100.
[Google Scholar]

[41] Yamaguchi, T., Ikeda, K., 1992. Composite reverse osmosis membrane and production thereof. Google Patents.

[42] Zaikov G.E., Rakovsky S., Schiraldi D.A., . Diversity in Chemical Reactions: Pure and Applied Chemistry. Nova Publishers; 2006.

[43] Zhang X., Tian J., Shi Wenxin, Zhang Z., Xu Y., Gao S., Cui F., . High performance thin-film composite (TFC) forward osmosis (FO) membrane fabricated on novel hydrophilic disulfonated poly (arylene ether sulfone) multiblock copolymer/polysulfone substrate. J. Membr. Sci.. 2016;520:529-539.
[Google Scholar]

[44] Zhou C., Shi Y., Sun Ch., Yu S., Liu M., Gao C., . Thin-film composite membranes formed by interfacial polymerization with natural material sericin and trimesoyl chloride for nanofiltration. J. Membr. Sci.. 2014;471:381-391.
[Google Scholar]

Fabrication of TFC nanofiltration membranes via co-solvent assisted interfacial polymerization for lactose recovery

Abstract

Keywords

Thin film composite membrane

Nanofiltration

Ketone co-solvent

Interfacial polymerization

Lactose separation

1 Introduction

2 Experimental

2.1 Materials

2.2 Sulfonation method of PES

2.3 Preparation of SPES support layer

2.4 Fabrication of TFC membranes by the CAIP and conventional IP procedure

2.5 Structural characterization

2.6 Filtration assay

3 Result and discussion

3.1 Characteristics of SPES substrate layer

3.2 Physiochemical properties of synthesized TFC membranes

3.2.1 Chemical properties of surface of TFC membrane

3.2.2 Cross section and surface morphology of TFC membranes

3.3 Effect of CAIP technique on the membrane performance

4 Conclusion

References

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