| الملخص | Abstract
polyphenylsulfone (PPSU) hollow fiber membranes are prepared by using phase inversion method from two different (PPSU) concentrations and various extrusion pressures. Cross-section and outer structures were characterized by using scanning electron microscope (SEM) and atomic force microscopy (AFM) . Mean pore size, pore size distribution, and mean roughness of the (PPSU) hollow fibers surfaces evaluated by (AFM) . It was found that the morphology of the (PPSU) fibers have sponge-like and finger-like structures with different extrusion pressures and (PPSU) concentrations. The mean pore size and mean roughness for inner and outer surfaces decreased with increase of extrusion pressure at two different (PPSU) concentrations . Moreover , the lead ion rejection was significantly improved from (19 to 78) % with increase of the extrusion pressure from (2.5 to 3) bar at (25 wt. %) PPSU concentration.
Keywords : (PPSU) ; Hollow fiber membrane ; Nanofiltration ; Morphology, Heavy metals removal.
Introduction
Recently there are more than (124) type of the polymers used for the preparation of membrane , most of them were used extensively. But still some of polymers are not widely used , among them (PPSU) . Some of the researchers used (PPSU) for the preparation of membrane for different applications. For example , Hwang et al .[1] improved the filtration efficiency and permeability of polymer membranes simultaneously during water treatment by using different ratios of activated carbon (AC) and polyethylene glycol (PEG) added into (PPSU) / polyetherimide (PEI) polymers to prepare the novel composite polymer membranes . The results showed that the addition of (AC) significantly affected the membrane morphology , pore size distribution , porosity , and chemical properties Siavash et al [2] . prepared (PPSU) hollow fiber membranes (HFM) due to its potential use in solvent resistant nanofiltration (SRNF) membranes . The membranes were prepared via the dry wet spinning method with three different concentrations of (PPSU) (22.5% , 25% and 27.5%) W/W in N -methy l – 2 - pyrrolidone (NMP) as the dope solution.
Zhong et al. [3] fabricated novel positively charged nanofiltration (NF) membranes using sulfonated polyphenylenesulfone (sPPSU) support with hydrophilic properties and fully sponge-like morphology via UV - induced grafting . The resultant (NF) membranes with a mean effective pore diameter of (1.13 – 1.20) nm , molecular weight cut off (MWCO) of (1627–1674) Da and high pure water permeability were successfully developed by utilizing two different types of positively charged grafting monomers .
In this study , (PPSU) hollow fiber nanofiltration membranes were prepared using phase inversion method . Effect of two different (PPSU) concentrations under various extrusion pressures on the morphology and separation performance of (PPSU) hollow fibers were investigated . (SEM) and (AFM) techniques were used to characterize the hollow fiber membranes . A lead ion was used to test the performance of the (PPSU) membranes.
Experimental work
Materials :
(PPSU) supplied by Solvay (Belgium) was used as the polymer material . 1 – methyl - 2 - pyrrolidone (NMP, 99.5%) was used as the polymer solvent supplied by Sigma - Aldrich (Germany) . Pb (NO3)2 heavy metal was used to explore the membrane separation performance supplied by (BDH) (England) .
(PPSU) Membrane preparation .
Grains of (PPSU) with concentration of [(25) and (29)] wt . % were dissolved in [(75) and (71) ] wt . % of (NMP) solvent , respectively by using magnetic stirrer at room temperature for two days . The final homogeneous (PPSU) solution was transferred to a vertical column and left for (24 h) to remove the air bubble from the (PPSU) solution as shown in Figure 1. After that the Nitrogen gas was employed to compresse the (PPSU) solution to the spinneret (polymer feed side) at different extrusion pressures . The water as a bore fluid was pumped at a rate of (3 ml / min) by employing precision Gear pump (Information Technology Engineering Co ., Guro-Gu , South Korea) to the spinneret (water feed top side) as shown in Figure 1. The two fluids were brought in to contact at the exit point of the spinneret and enter the tap water coagulation bath (at 36 °C) after air gap distance of (3.5 cm). Then , the nascent hollow fiber was drawn with a suitable speed without any starching in the nascent hollow fiber . The produced hollow fiber was kept in the water vessel for (24 h) to remove the remaining NMP from the hollow fiber . Finally the hollow fiber was treated with glycerol solution for (48 h) to prevent the collapse of the structure of the hollow fiber .
(SEM) measurement:
One of the powerful techniques for characterizing of the membrane structure is scanning electron microscope (SEM) . The structure of the membranes prepared in this work was obtained using (SEM) [ Model : Quanta (FENG 200) , (FEI) Company] at the University of Technology , Baghdad , Iraq .
(AFM) measurement (Atomic Force Microscope)
In order to measure the pore size and pore size distribution of the membrane , samples of (PPSU) hollow fiber membrane were subjected to spacious surface analysis by using atomic force microscope (AFM) via contact mode with a suitable silicon tip [Angstrom Advanced Inc . (USA) , model (AA3000)] .
Preparation of heavy metal solution and (PPSU) membrane performance
Salts solution was synthesized in single - salt solution for (Pb (NO3)2 with concentration of (160 mg) of Pb (NO3)2 with (1000 ml) of pure water (100 ppm of lead) in order to study the effect of heavy metal ions concentration on the performance of the (PPSU) membrane .
Before (NF) experiments of the heavy metal aqueous solution , the pure water permeability experiment of the PPSU membranes was carried out at a temperature of (25±3 °C) and pressure of (1.5 bar) for (1 h) by using the (NF) system shown in Figure ( 2).
Pure water permeability (PWP) (kg/(m2•hr.bar) was estimated by using the following equation :
(1)
t : collection time of permeate (hr)
P : Trans membrane pressure (bar)
A : surface area of fiber (m2)
M : mass of permeate in (kg)
The (NF) experiments of heavy metal solution were performed in batch circulation mode , both permeate and retentate being returned to feed tank in order to maintain a constant concentration in feed tank .
The solute separation factor , F, was calculated by the following equation :
(2)
Concentration of feed
=Concentration of permeate
Results and discussion
(SEM) measurement :
Outer surface of (PPSU) hollow fibers :
To investigate the effects of two different (PPSU) concentrations and extrusion pressures and to study the performance of the (PPSU) hollow fiber membranes , the outer surface and cross-section of the (PPSU) hollow fibers were accurately studied with (SEM) . The (SEM) images of the (PPSU) hollow fiber outer surface . It can be seen that the (PPSU) hollow fiber membrane prepared from (PPSU) with (25 wt .%) , and extrusion pressure of (3.0 bar) , at (3 ml / min) bore fluid flow rate have a rough and dense surface . While the (PPSU) hollow fiber prepared with [25 wt . % (PPSU)] and extrusion pressure of (2.5 bar) present a less rough and dense surface compare with the former (PPSU) . This is due to the formation of the aggregates during the fast speed of the hollow fiber within the air gap of (3.5 cm) throughout the formation of the hollow fibers . similar behavior was observed for two (PPSU) hollow fiber membranes prepared from (29 wt .%) and two different extrusion pressures such as (2.5) and (1.5 bar) .
Cross - section of (PPSU) hollow fibers :
The effect of (PPSU) concentration and extrusion pressure on the cross sectional structure of the (PPSU) hollow fiber membranes . It can be observed that the (PPSU) hollow fiber membrane prepared from (PPSU) with (25 wt . %) , and extrusion pressure of (3.0 bar) , at (3 ml/min) bore fluid flow rate have sponge -like structure appear near inner edge of the hollow fiber and there is a large finger - like layer near the edge of the outer surface of the hollow fiber membrane . Whereas , the (PPSU) hollow fiber prepared with [25 wt . % (PPSU)] and extrusion pressure of
(2.5 bar) have sponge - like structure appear at whole the hollow fiber and there is a small ellipsoidal voids near the edge of the inner surface of the hollow fiber membrane.
It can be seen that as the extrusion pressure decreased from [(2.5) to (1.5)] bar at [(29) wt . % (PPSU)] concentration , two layers of the finger - like structure start to appear near the inner and outer edge of the hollow fiber membrane. This is perhaps due to the increase of contact time between the polymer solution and coagulation water which results to increase the water diffusion or penetration inside the structure of the nascent hollow fiber .
(AFM) measurement :
(AFM) images of the inner and outer surfaces of (PPSU) hollow fiber membrane prepared at different extrusion pressures and two different (PPSU) contents . It can be noticed that the roughness of the inner surfaces decrease with increasing of extrusion pressure from [(2.5) to (3.0)] bar at [25 wt.% (PPSU)] and decreased with increase of the extrusion pressure from [(1.5) to (2.5)] bar at [29 wt.% (PPSU)] [see Table 2] .
Regarding the pore size and pore size distribution of (PPSU) membranes , Table (2) also shows the effect of extrusion pressures at two different (PPSU) concentrations on mean pore size . It can be noticed that the pore size of the inner surfaces of (PPSU) hollow fiber membrane prepared from[ (2.5) and (3)] bar extrusion pressures at [25 wt . % (PPSU)] in dope solution decreases with increasing of extrusion pressure. Similar behavior was observed for the pore size of the membrane prepared from [29 wt . % ( PPSU)] .
(PPSU) hollow fiber performance :
Table (2) shows the effect of two different (PPSU) concentrations and various extrusion pressures on pure water permeation flux and heavy metal ion rejection of the (PPSU) hollow fiber membranes . The pure water permeation flux was
(5 L m-2 h-1 bar-1) for the (PPSU) hollow fiber membrane under (2.5 bar) , whereas at extrusion pressure of (3.0 bar) , results to increase of pure water permeation flux from (2 L m-2 h-1 bar-1) . For the (PPUS) hollow fiber membrane prepared from (29 wt . %) under (1.5 bar) , the pure water permeation flux was (10 L m-2 h-1 bar-1) and decreased to (8 L m-2 h-1 bar-1) for (PPSU) hollow fiber membrane prepared from [29wt . % (PPSU] in the dope solution at extrusion pressure of (2.5 bar) . This phenomenon is attributed to the change of the (PPSU) structures during the formation of hollow fiber because of the higher amount of the polymer solution flow out from the spinneret at (2.5 bar) which is affected by the amount of the solvent / non - solvent exchange rate with internal coagulant and in the external coagulation bath .
This is attributed to the lower extrusion pressures in case of [29 wt .% (PPSU)] hollow fiber compared with that prepared from [25 wt .% (PPSU)] at extrusion pressures of [(2.5) and (3)] bar , which results to decrease the thickness of the hollow fiber , and in turn lead to decrease the (Pb+) rejection.
Conclusions
Preparation of different (PPSU) hollow fiber (NF) membranes for heavy metal removal results to several conclusions summarized as follows :
1- (PPSU) hollow fiber prepared with [25 wt.% (PPSU) ] and extrusion pressure of (2.5 bar) presents a less rough and dense outer surface compared with that prepared from extrusion pressure of (3 bar).
2- Different cross sectional structure was observed for all (PPSU) hollow fiber membranes most of them like sponge structure.
3-The mean pore size and mean roughness for inner and outer surfaces were decreased with increase of extrusion pressure at two different (PPSU) concentrations.
4-The lead ion rejection was significantly improved from (19%) to (78 %) with increase of the extrusion pressure from [(2.5) to (3)] bar at [25 wt.% (PPSU)] concentration.
References
1- Li - Luen Hwang , Jyh - Cherng Chen , Ming - Yen Wey , The properties and filtration efficiency of activated carbon polymer composite membranes for the removal of humic acid , Desalination [313 (2013) 166–175] .
2- Siavash Darvishmanesha , Franco Tasselli , Johannes C . Jansen , Elena Tocci , Fabio Bazzarelli , Paola Bernardo , Patricia Luis , Jan Degrèvea , Enrico Driolib , Bart Van der Bruggen , Preparation of solvent stable polyphenylsulfone hollow fiber nanofiltration membranes , Journal of Membrane Science [384 (2011) 89– 96].
3- Pei Shan Zhong, Natalia Widjojo, Tai-Shung Chung, Martin Weber, Christian Maletzko, Positively charged nanofiltration (NF) membranes via (UV) grafting on sulfonated polyphenylenesulfone (sPPSU) for effective removal of textile | en_US |
