Development of a Novel Hollow Fiber Cation-Exchange Membrane

Ind. Eng. Chem. Res. 2010, 49, 3079–3087

3079

Development of a Novel Hollow Fiber Cation-Exchange Membrane from Bromomethylated Poly(2,6-dimethyl-1,4-phenylene oxide) for Removal of Heavy-Metal Ions Zhenfeng Cheng, Yonghui Wu, Na Wang, Weihua Yang, and Tongwen Xu* CAS Key Laboratory of Soft Matter Chemistry, Laboratory of Functional Membranes, School of Chemistry and Materials Science, UniVersity of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China

A novel hollow fiber cation-exchange membrane was prepared from a bromomethylated poly(2,6-dimethyl1,4-phenylene oxide) hollow fiber by amination and sulfonation. The membrane exhibited good performance for adsorption of Cu2+, and its maximum capacity can reach 69.12 mg/g. In particular, the adsorption capacity increased with an increase in adsorption time, initial Cu2+ concentration, and ion-exchange capacity of the membrane, and the adsorption isotherms were of Langmuir and Freundlich types. When these membranes were taken for desorption in solutions of hydrochloric acid, the regeneration ratio increased with an increase in regeneration time (before 20 min) and acid concentration. This study can provide new material for removal of heavy-metal ions in an energy-saving manner. 1. Introduction Heavy-metal ions, such as copper(II), lead(II), cadmium(II), and mercury(II), are often discharged into the environment in large quantities from nuclear, metallurgical, tannery, mining, and battery plants. These toxic metal ions can cause environmental pollution and many health problems. For example, copper can cause stomach and intestinal distress, liver and kidney damage, and anemia,1-3 while lead can damage the central nervous system and cause dysfunction of kidneys and the immune system.4-6 Admittedly, it is necessary to remove heavy metals before discharge. To date, several techniques have been developed for such purpose, such as filtration,7,8 flotation,9 cementation,10 solvent extraction,11-13 reverse osmosis,14 coprecipitation,15,16 and adsorption.17 Among them, adsorption is considered an effective method due to its high efficiency and convenience,18 and a number of polymeric materials have been developed as absorbents, such as chitosan,19-22 cellulose,23-25 polyethylene,26-28 polyvinylalcohol,29,30 and polysulfone.31 Poly(2,6-dimethyl-1,4phenylene oxide) (PPO), characterized by a high glass transition temperature (Tg ) 212 °C) and good thermal stability under nonoxidizing conditions, is one of the most widely used engineering plastics,32 and its distinctive but simple structure allows a variety of modifications in both aryl and benzyl positions:33 (1) electrophilic substitution on the benzene ring of PPO, (2) radical substitution of the hydrogen from the methyl groups of PPO, (3) nucleophilic substitution of the bromomethylated PPO (BPPO), (4) capping and coupling of the terminal hydroxyl groups in PPO chains, and (5) metalation of PPO with organometallic compounds. These modifications can tune PPO for preparation of proton conductive membranes (PCMs). In particular, its brominated form (BPPO) not only inherits the excellent properties of PPO but also acquires better membrane formation characteristics and can be further modified by introducing negatively and/or positively charged groups.34-36 In our laboratory, the BPPO-based plane membrane has been extensively studied, and our previous study showed the duration * To whom correspondence should be addressed. E-mail: [email protected].

of BPPO raw material can last more than 5 years, and the final cation-exchange membrane is strong in acid and nonpolar solvents, such as chloroform and chlorobenzene. To avoid the use of chloromethyl methyl ether, BPPO-based positively charged membranes were prepared by quarteramination, and these membranes can be used for diffusional dialysis,37 electrodialysis with bipolar membranes,38 and nanofiltration.39 In particular, to extend the applications of BPPO membranes, BPPO-based hollow fiber anion-exchange membranes have been prepared and these membranes have high specific surface areas, well-controlled porosity, and good mechanical properties.40 However, these membranes can only be applied to acid recovery using diffusion dialysis and fail to remove heavy-metal ions because these anion-exchange membranes have positive fixed charges and are thus repulsive to heavy-metal ions. To remove metal ions, it is required to introduce a high density of negatively charged groups to the membranes by surface modification but without sacrificing the physical and chemical stability of the original BPPO membranes. Surface modification can be carried out by many methods, such as plasma treatment, grafting polymerization, and surface chemical modification.41 Of them, grafting and surface chemical modification are more widely used.42 Extensive explorations indicate that the former (UV irradiation, low-temperature plasma, ozonization, gamma-ray or electron beam treatment) has some drawbacks. For example, UV irradiation might destroy membrane structure and reduce the mechanical strength. Ozonization or gamma-ray treatment needs expensive equipment.43 Accordingly, surface chemical modification was often chosen for preparation of BPPO-based ion-exchange membranes since there are bromomethylated precursors in the polymer matrix. In this research, BPPO hollow fiber cation-exchange membrane (HFCM) containing sulfonic groups are prepared by chemical modification. Effects of various conditions, such as reagent concentration, reaction time, and temperature, on the ion-exchange capacities of HFCMs are investigated. Furthermore, to evaluate the adsorption capacity of heavy-metal ions on the resultant BPPO HFCM, the common metal ion Cu2+ is chosen as a model metal ion. Effects of

10.1021/ie901408c  2010 American Chemical Society Published on Web 02/23/2010

3080

Ind. Eng. Chem. Res., Vol. 49, No. 7, 2010

Figure 1. Preparation of BPPO hollow fiber cation-exchange membrane.

adsorption time, initial Cu2+ concentration, and the ion-exchange capacity of membrane on the adsorption capacity are also studied. 2. Experimental Section 2.1. Materials. A porous BPPO fiber with 90% benzyl substitution and 10% aryl substitution, which was kindly supplied by Tianwei Membrane Corp. Ltd. of Shandong (China), was used as a starting polymer for chemical modification. The porosity of the hollow fiber is about 70%, and the inner and outer diameters were about 0.82 and 1.22 mm, respectively. AR-grade monoethanolamine (MEA) and chlorosulfonic acid (CSA) were purchased from Sinopharm Chemical Reagent Co., Ltd. and used without further purification. 2.2. Preparation of Hollow Fiber Cation-Exchange Membrane (HFCM) from BPPO. The preparation of the base hollow fibers is detailed in our previous work.40 Briefly, PPO was dissolved in chlorobenzene and brominated by chorobenzene-diluted bromine, and then the solution was precipitated with methanol, washed, and dried at 353.15 K for at least 20 h to obtain the brominated polymers. Finally, the BPPO base hollow fiber was prepared by the following procedures: dissolution, filtration, spinning, coagulation, and take up. The HFCM was prepared by the following two steps, as shown in Figure 1. (1) Amination of the BPPO hollow fiber was conducted by immersing the fiber into a monoethanolamine (MEA) aqueous solution at different temperatures (293.15, 313.15, and 333.15 K). The volume ratio of MEA ranged from 30% to 100%. After the reaction, the fiber was taken out and washed with deionized water to remove the residual MEA. Similar to the degree of grafting,26 the degree of reaction was calculated from the reduced weight in eq 1 degree of reaction (100%) ) 100

W0 - W1 W0

(1)

where W0 and W1 are the weights of BPPO and MBPPO (amination of BPPO) hollow fibers, respectively. (2) Sulfonation of the MBPPO hollow fiber was performed by dipping the fiber into chlorosulfonic acid (CSA)/1,2dichloroethane solution at different temperatures (293.15,

303.15, and 313.15 K). The volume ratio of CSA ranged from 1% to 5%. After a given interval, the resultant hollow fiber membrane was taken out and washed repeatedly with deionized water and then dried at 333.15 K for some time until the weight remained constant. 2.3. Characterization of Membranes. 2.3.1. Scanning Electron Microscope. Surface morphologies of the fibers and final membranes were examined by a field emission scanning electron microscope (XL30-ESEM, Philips) with an accelerating voltage of 5.0 kV. The fibers and final membranes were fractured using liquid nitrogen, and then a thin layer of Pd/Au was sputtered onto the samples. The cross-section and outer surface were analyzed. 2.3.2. Scanning Electron Microscope (SEM)/EnergyDispersive Using X-ray (EDX). To investigate the depth of modification, a scanning electron microscope (XT30 ESEMTMP, PHILIP) with an accelerating voltage of 20.0 kV was used, and the sulfur distribution on the SMBPPO hollow fiber membrane cross-section was measured. 2.3.3. Fourier Transform Infrared Spectra. To verify the sulfonation of BPPO hollow fibers by chlorosulphonic acid, a Bruker Vector 22 Fourier transform infrared spectrophotometer was used and spectra were measured in a wavenumber range of 4000-500 cm-1. The dry sample (about 0.01 g) was mixed with KBr (about 0.10 g) and pressed into a tablet. 2.3.4. Ion-Exchange Capacity (IEC). The degree of sulfonation of the MBPPO hollow fiber was estimated by the following titration method. Dry SMBPPO (sulphonated MBPPO) hollow fiber membranes were immersed in 30.00 mL of a 0.03 M solution of NaOH for 24 h, and then 25.00 mL of the solution was neutralized with 0.04 M HCl. The ion-exchange capacity was determined in eq 2 IEC(mmol/g) ) (30/25)(30CNaOH - VCHCl)/W

(2)

where CHCl and CNaOH are the concentrations of HCl and NaOH solutions, respectively, V is the volume of the titrated HCl solution, and W is the weight of the SMBPPO hollow fiber membrane. 2.3.5. Water and Methanol Uptakes. The water and methanol uptakes of the SMBPPO hollow fiber membrane were measured as follows. The membranes with a known weight were first immersed into deionized water and methanol at room


3081

temperature for 24 h, respectively, and then the membranes were taken out and weighed again after the liquid adhering to the surface was quickly wiped away by filter paper. The water and methanol uptakes were determined in eq 3 uptake(%) ) 100

W w - Wd Wd

(3)

where Ww and Wd are the weights of the membranes in wet and dry states, respectively. 2.3.6. Adsorption and Desorption of Cu2+. Adsorption experiments were conducted at room temperature in a 250 mL beaker. About 0.20 g of a SMBPPO membrane sample was placed in 30.00 mL of an aqueous solution of CuCl2 for a given time and then taken out of the solution. The Cu2+ uptake can be calculated from the change of Cu2+ concentration in eq 4 Q)

(C1 - C2)V W

(4)

where Q is the Cu2+ uptake, W is the weight of the SMBPPO membrane, V is the volume of the solution, and C1 and C2 are the concentrations of Cu2+ before and after adsorption, respectively, and measured by iodometric method. Desorption of Cu2+ ions was studied in hydrochloric acid solutions of different concentrations (0.02, 0.20, and 2.00 M) at room temperature. The SMBPPO membranes used for adsorption were put into the desorption medium to allow the adsorbed Cu2+ to release, and the regeneration ratio (R) of the SMBPPO membrane was calculated in eq 5 R(%) ) 100

C·V m

(5)

where m is the amount of Cu2+ ions adsorbed on the membrane and C and V are the final concentration of Cu2+ ions in the desorption medium and the volume of the desorption medium, respectively. 2.3.7. Evaluation of Adsorption Isotherms. The Langmuir and Freundlich isotherms,44-46 which are the earliest and simplest adsorption isotherms, were used to describe the adsorption of Cu2+ on the SMBPPO hollow fiber cationexchange membrane. The Langmuir isotherm is based on the assumption that the maximum adsorption occurs when a saturated monolayer of solute molecules is present on the adsorbent surface, the energy of adsorption is constant, and there is no migration of absorbed molecules on the surface. The linearized form of the equation is given in eq 6 Ce Ce 1 ) + Q Qmax Qmax · b

(6)

where Ce is the equilibrium concentration (mg/L), b is the adsorption equilibrium constant of the system, and Qe and Qmax are the amount of material adsorbed on the adsorbent at equilibrium and the maximum adsorption capacity, respectively. The experimental data can be linearized in the above equation by plotting Ce/Qe against Ce, and the parameter b and the maximum adsorption capacity can be obtained in the linear regression equation. The Freundlich isotherm assumes that the adsorption energy of a metal binding to a site on an adsorbent depends on whether the adjacent sites are occupied, and the empirical equation can be expressed in eq 7 log Qe )

( n1 )log C + log k e

(7)

Figure 2. Effects of amination temperature and amination time on the degree of reaction.

where k and n are the Freundlich constants which indicate adsorption capacity and adsorption intensity, respectively. If the plot of ln Ce vs ln Qe yields a straight line, it implies that the adsorption process conforms with the Freundlich isotherm, then the parameters k and n can be obtained from the intercept and slope, respectively. 2.3.8. Breakthrough Curve. The experimental apparatus for measuring the breakthrough curve is similar to that reported in other papers,47 and the measurement method is as follows. A wet SEBPPO hollow fiber membrane with an ion-exchange capacity of 2.01 mmol/g was set in a U-shaped membrane module, and 10 mg/L copper solution was forced to permeate from the inside to the outside of the hollow fiber membrane with a peristaltic pump. The permeate solution was collected by measuring cylinders. After the experiment, the length of the hollow fiber membrane (∼6 cm) was measured in the dry state with a vernier caliper. 3. Results and Discussion 3.1. Optimization of Membrane Preparation Conditions. As stated in the Experimental Section, the membranes were prepared from BPPO hollow fiber by amination and sulfonation, so the conditions affecting the two processes were investigated, and these conditions include reagent concentration, reaction time, and reaction temperature. Figure 2 illustrates the effects of amination temperature and amination time on the degree of reaction in monoethanolamine (MEA). As shown in the figure, although the reactions were controlled at different temperatures, there are similar changing trends and the degree of reaction increases with an increase in amination time initially but levels off after 1 h. The effect of MEA concentration on the degree of reaction at 313.15 K is shown in Figure 3. As can be seen from the figure, curves of similar shape are obtained for three MEA concentrations. As the immersion time of membrane increases, the degree of reaction increases abruptly and then approaches to a constant. In general, the degree of reaction significantly depends on amination temperature and MEA concentration. Figure 4 illustrates the effects of sulfonation temperature and sulfonation time on the ion-exchange capacity of membrane. The MBPPO hollow fiber with the maximum reaction degree (11.5%) at 313.15 K was used for sulfonation in a 5% chlorosulfonic acid (CSA)/1,2-dichloroethane solution. In every case, the ion-exchange capacity increases rapidly as reaction time elapses before 1 h; when the curve levels off, the ionexchange capacity of the SMBPPO membrane reaches 3.70 mmol/g at 293.15 K, 3.50 mmol/g at 308.15 K, and 3.40 mmol/g

3082


Figure 3. Effects of ethanolamine concentration and amination time on the degree of reaction at 313.15 K.

Figure 4. Effects of sulfonation temperature and sulfonation time on the ion-exchange capacity of SMBPPO hollow fiber membrane. The degree of reaction ) 11.5%.

Figure 5. Effects of chlorosulfonic acid concentration and sulfonation time on the ion-exchange capacity of SMBPPO hollow fiber membrane at 308.15 K. The degree of reaction ) 11.5%.

at 323.15 K. This indicates that the ion-exchange capacity of the SMBPPO membrane is similar to or higher than that of other reported membranes. For example, Kim et al.48 prepared a polyethylene cation-exchange hollow fiber membrane, and the density of sulfonic acid groups was in the range of 0.2-4.0 mmol/g. Figure 5 is a plot of the ion-exchange capacity vs sulfonation time at different chlorosulfonic acid concentrations and with 11.5% of the reaction degree. In the initial stage, the ionexchange capacity increases rapidly with an increase in sulfonation time; however, after 1 h reaction, the cation-exchange capacities of the SMBPPO membranes rise to about 2.00, 2.80, and 3.50 mmol/g for different concentrations, respectively. These results suggest that the content of ion-exchange groups in the SMBPPO membrane can be controlled by adjusting sulfonation time, sulfonation temperature, and reagent concentration.

Figure 6. FTIR spectra of (a) BPPO hollow fiber, (b) MBPPO hollow fiber, and (c) SMBPPO hollow fiber membrane.

3.2. Characterization. 3.2.1. FT-IR. The chemical structures of the BPPO hollow fibers were studied by FT-IR. As shown in Figure 6a, the BPPO hollow fiber has a characteristic peak at 589 cm-1, which can be attributed to the stretching vibration of C-Br groups. However, there is no adsorption at 589 cm-1 in the spectrum of the MBPPO hollow fiber (Figure 6b). This indicates that the reaction between the BPPO hollow fiber and monoethanolamine has happened. As for the SMBPPO membrane (Figure 6c), it has absorptions at 1394, 747, 673, 624, and 576 cm-1, which are not observed in the spectrum of the MBPPO hollow fiber. The bands at 1394, 624, and 576 cm-1 are assigned to the asymmetric vibration, the in-plane deformation, and the out-plane deformation of OdSdO groups, respectively. At the same time, the symmetric stretching vibration of OdSdO groups and the vibration of SdO groups make the adsorption peaks at 1189 and 1029 cm-1 shift to 1206 and 1037 cm-1; moreover, the adsorption peaks become broader. In addition, the adsorption peaks at 747 and 673 cm-1 are related to the out-plane deformation of C-H groups in the substituted benzene ring. These results confirm that the sulfonic group has been successfully introduced into the BPPO hollow fiber. 3.2.2. SEM. Micrographs of the BPPO, MBPPO fibers, and SMBPPO hollow fiber membranes are presented in Figure 7. As compared with the unmodified membrane (Figure 7A1), the MBPPO fiber (Figure 7B1) has a smoother outer surface but the SMBPPO membrane (Figure 7C1) has a rougher one. This is attributed to the surface reaction of BPPO hollow fiber with monoethanolamine and chlorosulfonic acid. SEM micrographs of the cross sections of BPPO hollow fiber, MBPPO hollow fiber, and SMBPPO hollow fiber membrane are shown in Figure 7A2, 7B2, and 7C2, respectively, and all the membranes consist of a dense middle layer and porous outer and inner layers. Figure 7A3, 7B3, and 7C3 shows the magnified SEM micrographs of the cross sections of BPPO hollow fiber, MBPPO hollow fiber, and SMBPPO hollow fiber membrane. There is no significant difference in the cross-section morphology between the original BPPO hollow fiber and the prepared BPPO cation-exchange membranes, suggesting that surface modification does not damage the pore structure of the membrane. 3.2.3. SEM/EDX. The sulfur distribution on the SMBPPO hollow fiber membrane cross-section is shown in Figure 8. As seen from the figure, the sulfur contents of the outer layer and the inner layer are bigger than that of the middle layer, which indicates that the surface of the membrane can react with chlorosulfonic acid easily. That is because the middle layer is denser than the surface layer (Figure 7), which leads to the difficult diffusion of reaction regent into the middle layer of the membrane.


3083

Figure 7. SEM images of the outer surface and cross-section morphologies for (A) original BPPO hollow fiber, (B) MBPPO hollow fiber, and (C) SMBPPO hollow fiber membrane. The number 1 denotes the outer surface of membranes, and 2 or 3 denotes the cross-section of membranes.

Figure 8. Sulfur distribution on the cross-section of the SMBPPO hollow fiber membrane.

3.2.4. Water and Methanol Uptakes. Water uptake is a convenient parameter to characterize the hydrophilicity of a membrane surface. As shown in Figure 9, when the ionexchange capacity of a SMBPPO hollow fiber membrane varies from 2.0 to 4.0 mmol/g, the water uptake increases from 21% to 74%. This is caused by the introduction of hydrophilic sulfonic groups into the BPPO hollow fiber. For comparison, the methanol uptake is also presented, and the results indicate that the methanol uptake decreases markedly from 110% to 60% with an increase in the ion-exchange capacity. When the ionexchange capacity rises to about 3.8 mmol/g, the methanol uptake is nearly equal to the water uptake. This indicates that the SMBPPO hollow fiber membrane can contain more methanol than water when the ion-exchange capacity is smaller than 3.8 mmol/g. A supporting fact is that the -NHCH2CH2OH groups have strong affinity to methanol while -SO3H groups have strong affinity to water. In general, the water and methanol

Figure 9. Effect of the ion-exchange capacity of SMBPPO hollow fiber membrane on water and methanol uptake. The degree of reaction ) 11.5%.

uptakes further confirm the occurrence of amination and sulfonation reactions.

3084


Figure 10. Effect of adsorption time on the adsorption amount of Cu2+ on SMBPPO hollow fiber membrane. IEC, 3.01 mmol/g; the initial concentration of Cu2+, 1.54 g/L; pH, 4.75.

Figure 11. Effect of the initial concentration of Cu2+ on the adsorption capacity of Cu2+ onto SMBPPO hollow fiber membrane. IEC, 2.79 mmol/ g; adsorption time, 3 h; pH, 4.75.

3.3. Adsorption Performance of HFCM. To explore applications for the prepared HFCM, copper ion was chosen as model heavy-metal ion to be adsorbed onto HFCMs, and the factors such as adsorption time, feed concentration, ion-exchange capacity, and pH were investigated. Figure 10 shows the effect of adsorption time on the adsorption amount of Cu2+. As expected, an increase in adsorption time leads to an increase in the adsorption amount of Cu2+, i.e., from 36.45 to 57.28 mg/g. However, after about 2 h, the adsorption equilibrium is almost achieved and the curve levels off. Therefore, a further increase in the adsorption time does not result in any significant change in the adsorption amount. This phenomenon can be also found in the adsorption of Cu2+ on other materials reported.49-51 Figure 11 is a plot of the adsorption capacity of the SMBPPO membrane for Cu2+ vs the initial concentration of Cu2+. The adsorption capacity increases rapidly when the initial concentration of Cu2+ is no more than 3.0 mg/mL and then reaches a maximum at about 5.0 mg/mL of Cu2+ concentration. The trend conforms to the conventional adsorption theory: the higher the feed concentration, the longer time will be needed for the adsorption saturation. It should be noted that the competition between H+ released from the membranes and Cu2+ will also affect such adsorption equilibrium for every initial concentration. Figure 12 demonstrates the relationship between the adsorption capacity and ion-exchange capacity. As the ion-exchange capacity increases, the adsorption capacity of Cu2+ increases sharply. The maximum adsorption capacity, 46.18 mg/g, is achieved at the ion-exchange capacity ranging from 0.65 to 3.16 mmol/g. This phenomenon can be ascribed to the charge-charge interaction between Cu2+ and the membrane. The adsorption capacity of a SMBPPO membrane for Cu2+ was also measured from pH 1 to pH 6.0, and the results are given in Figure 13. The adsorption is strongly pH dependent. At pH 1.8, the adsorption capacity is about 28.80 mg/g; after

Figure 12. Effect of the ion-exchange capacity on the adsorption amount of Cu2+ onto SMBPPO hollow fiber membrane. Adsorption time, 3 h; the initial concentration of Cu2+, 1.09 g/L; pH, 4.75.

Figure 13. Effect of pH on the adsorption capacity of Cu2+ onto SMBPPO hollow fiber membrane. IEC, 2.47 mmol/g; adsorption time, 3 h; the initial concentration of Cu2+, 1.19 g/L.

Figure 14. Langmuir isotherm for the adsorption of Cu2+ onto SMBPPO hollow fiber membrane.

pH increases, the maximum adsorption capacity leaps to 37.44 mg/g at pH 2.5. However, as pH increases further, the adsorption capacity initially holds almost constant and then reduces quickly to 32.64 mg/g at pH 4.8. The change in the adsorption capacity with pH can be explained by the fact that H+ can prevent the adsorption of Cu2+ in an acid medium and OH- can reduce the concentration of Cu2+ in an alkaline medium. 3.4. Adsorption Mechanism. To clarify the adsorption mechanism of cupric ions on HFCM, the data points for Cu2+ adsorption were first fitted by the Langmuir equation. As shown in Figure 14, the correlation coefficient is calculated to be 0.99900, suggesting a satisfactory fitting. According to the Langmuir isotherm, the maximum adsorption amount of Cu2+ is calculated to be 69.78 mg/g, which is close to the experimental result (69.12 mg/g). Figure 15 illustrates the fitting results using the Freundlich equation. Using the slope and intercept, the parameters k and n are calculated to be 0.90 and 1.85, respectively. However, the correlation coefficient is only 0.95167, much smaller than that


Figure 15. Freundlich isotherm for the adsorption of Cu2+ onto SMBPPO hollow fiber membrane.

3085

Figure 17. Breakthrough curve of copper ions. The initial concentration of Cu2+, 10 mg/L; pH, 4.75.

3.6. Breakthrough Curve. The breakthrough curve of copper ion is shown in Figure 17. As expected, when the ratio of permeate volume to membrane surface area is smaller than 5.2 cm, the copper concentration of permeate solution is almost zero and then becomes larger, and the ratio of breakthrough is 23.41 cm. From the breakthrough curves, the equilibrium adsorption capacity can be calculated to be 19.68 mg/g. 4. Conclusions

Figure 16. Effect of hydrochloric acid concentration on the regeneration ratio of SMBPPO hollow fiber membrane.

calculated by the Langmuir equation. This indicates that the adsorption isotherm fits the Langmuir equation much better than the Freundlich equation. We also try to use some other models to correlate the data. When it comes to the “dual-mode sorption”, we employed the + KpCe) and the Freundilich-Henry equation (Q ) KiC1/n e Langmuir-Henry equation (Q ) (QmaxbCe)/(1 + bCe) + KpCe) correspondingly; the Frendilich-Henry equation cannot improve the accuracy of calculation (R ) 0.95167), and the fitting line does not change except for the changes of parameters. Similarly, the Langmuir-Henry equation52 cannot be used to fit the experimental results because of the minus value of the parameters (CH and b), which is not compatible with the physical meaning. Naturally, there is another equation often used for such data fitting, the BET equation, so we conducted the corresponding fitting. Though the experimental data are close to the fitting line, Qmax is calculated to be 0.013 mg/g and is much lower than the adsorption capacity at low CuCl2 concentrations. Therefore, it can be concluded that the single-layer adsorption is the main mechanism for the adsorption of Cu2+ on the SMBPPO hollow fiber cation-exchange membrane. 3.5. Desorption Performance. The desorption of adsorbed Cu2+ from the SMBPPO cation-exchange membranes was performed in an aqueous solution of hydrochloric acid. As shown in Figure 16, in 0.02 M HCl, the desorption equilibrium is achieved at about 60 min, which is longer than the others. In 2.00 M HCl, the regeneration ratio increases significantly with an increase in regeneration time (before 20 min) and the time needed to reach the equilibrium is the shortest. Figure 16 also shows that the higher the hydrochloric acid concentration, the higher the regeneration ratio. As hydrochloric acid concentration varies from 0.02 to 2.00 M, the regeneration ratio increases by about 200%. Therefore, it is important to control hydrochloric acid concentration and regeneration time for an effective and efficient regeneration of HFCM.

For removal of heavy-metal ions, a hollow fiber cationexchange membrane was prepared by amination and sulfonation of the BPPO hollow fiber. The ion-exchange capacity, which was controlled by adjusting reaction time, reaction temperature, and reagent concentration in both amination and sulfonation processes, could reach about 4.00 mmol/g. After such chemical modification, the membrane’s structure remained intact. The adsorption of the BPPO hollow fiber cation-exchange membrane for heavy-metal ions was examined for the first time using Cu2+ as a representative metal ion, and the maximum adsorption capacity was 69.12 mg/g. In addition, the adsorption isotherm fit the Langmuir equation well. As for the desorption, the regeneration ratio of the SMBPPO cation-exchange membrane depends on the concentration of hydrochloric acid and regeneration time. Nomenclature b ) the adsorption equilibrium constant of the system, L/mg C ) the final concentration of Cu2+ ions, g/L C1 ) the concentrations of Cu2+ before adsorption, mg/L C2 ) the concentrations of Cu2+ after adsorption, mg/L C3 ) the concentrations of Cu2+ before permeation, mg/L C4 ) the Cu2+ concentrations of permeate solution, mg/L Ce ) the equilibrium concentration, g/L CHCl ) the concentration of HCl solution, mol/L CNaOH ) the concentration of NaOH solution, mol/L k ) the Freundlich constant m ) the amount of Cu2+ ions adsorbed on the membrane, g n ) the Freundlich constant Q ) the Cu2+ uptake, mg/g Qe ) the amount of material adsorbed on the adsorbent at equilibrium, mg/g Qmax ) the maximum adsorption capacity, mg/g R ) the regeneration ratio, % V ) the volume of the solution, L W ) the weight of the membrane used, g W0 ) the weight of the BPPO hollow fiber, g W1 ) the weight of the MBPPO hollow fiber membrane, g Wd ) the weight of the membrane in dry state, g Ww ) the weight of the membrane in wet state, g

3086


Acknowledgment The authors gratefully acknowledge the financial support from the National Science Foundation of China (nos. 20774090 and 20636050), the Joint Research Project under the KOSEF-NSFC Cooperative Program (no. 20911140273), and the National Basic Research Program of China (973 program, no. 2009CB623403). Literature Cited (1) Borba, C. E.; Silva, E. A.; Fagundes-Klen, M. R.; Kroumov, A. D.; Guirardello, R. Prediction of the copper (II) ions dynamic removal from a medium by using mathematical models with analytical solution. J. Hazard. Mater. 2008, 152, 366–372. (2) Lee, C. I.; Yang, W. F.; Hsieh, C. I. Removal of copper (II) by manganese-coated sand in a liquid fluidized-bed reactor. J. Hazard. Mater. 2004, B114, 45–51. (3) Rao, M. M.; Ramesh, A.; Rao, G. P. C.; Seshaiah, K. Removal of copper and cadmium from the aqueous solutions by activated carbon derived from Ceiba pentandra hulls. J. Hazard. Mater. 2006, B129, 123–129. (4) Ju, X. J.; Zhang, S. B.; Zhou, M. Y.; Xie, R.; Yang, L. H.; Chu, L. Y. Novel heavy-metal adsorption material: ion-recognition P(NIPAMco-BCAm) hydrogels for removal of lead(II) ions. J. Hazard. Mater. 2009, 167 (1-3), 114-118. (5) Meena, A. K.; Mishra, G. K.; Rai, P. K.; Rajagopal, C.; Nagar, P. N. Removal of heavy metal ions from aqueous solutions using carbon aerogel as an adsorbent. J. Hazard. Mater. 2005, B122, 161–170. (6) Boivin, M. J.; Giordani, B. A risk-evaluation of the neuropsychological effects of childhood lead toxicity. DeV. Neuropsychol. 1995, 11, 157–180. (7) Blo¨cher, C.; Dorda, J.; Mavrov, V.; Chmiel, H.; Lazaridis, N. K.; Matis, K. A. Hybrid flotation-membrane filtration process for the removal of heavy metal ions from wastewater. Water Res. 2003, 37, 4018–4026. (8) Karatepe, A. U.; Soylak, M.; Elci, L. Separation/preconcentration of Cu(II), Fe(III), Pb(II), Co(II) and Cr(III) in aqueous samples on cellulose nitrate membrane filter and their determination by atomic absorption spectrometry. Anal. Lett. 2002, 35, 1561–1574. (9) Polat, H.; Erdogan, D. Heavy metal removal from waste waters by ion flotation. J. Hazard. Mater. 2007, 148, 267–273. (10) Zarraa, M. A. Effect of gas sparging on the removal of heavy metal ions from industrial waste water by a cementation technique. Hydrometallurgy 1992, 28, 423–433. (11) Veen, F. V. Recycling of complex heavy metal wastes by solvent extraction and ion exchange as a contribution to the solution of environmental problems. ConserV. Recycl. 1979, 3, 461–467. (12) Lajunen, L. H. J.; Kubin, A. Determination of trace amounts of molybdenum in plant tissue by solvent extraction-atomic-absorption and direct-current plasma emission spectrometry. Talanta 1998, 33, 265–270. (13) Esalah, O. J.; Weber, M. E.; Vera, J. H. Removalof lead, cadmium and zinc from aqueous solutions by precipitation with sodium di-(n-octyl) phosphinate. Can. J. Chem. Eng. 2000, 78, 948–954. (14) Kim, B. S.; Lim, S. T. Removal of heavy metal ions from water by cross-linked carboxymethyl corn starch. Carbohydr. Polym. 1999, 39, 217–223. (15) Kagaya, S.; Araki, Y.; Kakehashi, K.; Hirai, N.; Sakai, K.; Tohda, K. Use of yttrium phosphate as a coprecipitant for separation/concentration of Lanthanoids. Anal. Sci. 2008, 24, 1643–1646. (16) Saracoglu, S.; Soylak, M.; Elci, L. Enrichment and separation of traces of cadmium, chromium, lead and manganese ions in urine by using magnesium hydroxide coprecipitation method. Trace Elem. Electrolytes 2001, 18, 129–133. (17) Ki, S. C.; Gang, E. H.; Um, I. C.; Park, Y. H. Nanofibrous membrane of wool keratose/silk fibroin blend for heavy metal ion adsorption. J. Membr. Sci. 2007, 302, 20–26. (18) Bayramoglu, G.; Arica, M. Y.; Bektas, S. Removal of Cd(II), Hg(II), and Pb(II) ions from aqueous solution using p(HEMA/Chitosan) membranes. J. Appl. Polym. Sci. 2007, 106, 169–177. (19) Juang, R. S.; Wu, T. C.; Tseng, R. L. Adsorption removal of copper(II) using chitosan from simulated rinse solutions containing chelating agents. Water Res. 1999, 33, 2403–2409. (20) Kaminski, W.; Modrzejewska, Z. Application of chitosan membranes in separation of heavy metal ions. Sep. Sci. Technol. 1997, 32, 2659– 2668. (21) Bassi, R.; Prasher, S. O.; Simpson, B. K. Removal of selected metal ions from aqueous solutions using chitosan flakes. Sep. Sci. Technol. 2000, 35, 547–560.

(22) Juang, R. S.; Shao, H. J. A simplified equilibrium model for sorption of heavy metal ions from aqueous solutions on chitosan. Water Res. 2002, 36, 2999–3008. ¨ . G.; Gu¨ner, F. S.; Dizman, M.; Erciyes, A. T. Heavy Metal (23) Beker, U Removal by Ion Exchanger Based on Hydroxyethyl Cellulose. J. Appl. Polym. Sci. 1999, 74, 3501–3506. (24) Bora, U.; Kannan, K.; Nahar, P. A simple method for functionalization of cellulose membrane for covalent immobilization of biomolecules. J. Membr. Sci. 2005, 250, 215–222. (25) Ruckenstein, E.; Guo, W. Cellulose and Glass Fiber Affinity Membranes for the Chromatographic Separation of Biomolecules. Biotechnol. Prog. 2004, 20, 13–25. (26) Ozawa, I.; Saitoa, K.; Sugita, K.; Sato, K.; Akiba, M.; Sugo, T. Highspeed recovery of germanium in a convection-aided mode using functional porous hollow-fiber membranes. J. Chromatogr., A 2000, 888, 43–49. (27) Saito, K.; Ito, M.; Yamagishi, H.; Furusaki, S. Novel hollow fiber membrane for the removal of metal ion during permeation: preparation by radiation-induced cografting of a cross-linking agent with reactive monomer. Ind. Eng. Chem. Res. 1989, 28, 1808–1812. (28) Saito, K. Charged polymer brush grafted onto porous hollow-fiber membrane improves separation and reaction in biotechnology. Sep. Sci. Technol. 2002, 37, 535–554. (29) Denizli, A.; Say, R.; Arica, Y. Removal of heavy metal ions from aquatic solutions by membrane chromatography. Sep. Sci. Technol. 2000, 21, 181–190. (30) Bessbousse, H.; Rhlalou, T.; Verche`re, J. F.; Lebrun, L. Removal of heavy metal ions from aqueous solutions by filtration with a novel complexing membrane containing poly(ethyleneimine) in a poly(vinyl alcohol) matrix. J. Membr. Sci. 2008, 307, 249–259. (31) Wang, B.; Cui, Y.; Du, Q.; Pei, Y. Study on Preparation of heterogeneous polysulfone affinity filter membrane and its sorption properties for Hg2+. J. Appl. Polym. Sci. 2003, 87, 908–915. (32) Pan, Y.; Huang, Y. H.; Liao, B.; Cong, G. M. Synthesis and characterization of aminated poly (2, 6-dimethyl-1, 4-phenylene oxide). J. Appl. Polym. Sci. 1996, 61, 1111–1116. (33) Xu, T. W.; Wu, D.; Wu, L. Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO)-A versatile starting polymer for proton conductive membranes (PCMs). Prog. Polym. Sci. 2008, 33, 894–915. (34) Liska, J.; Borsig, E. The amination kinetics of bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide) with diethylamine. J. Macromol. Sci., Part A: Pure Appl. Chem. 1994, A31, 2019–2031. (35) Xu, T. W.; Yang, W. H. Fundamental studies of a new series of anion exchange membranes: membrane preparation and characterization. J. Membr. Sci. 2001, 190, 159–166. (36) Cheney, G. D.; Van Dyke, M. E; Clarson, S J. Organosiloxanecross-linked poly(2,6-dimethyl-1,4-phenylene oxide) network structures. J. Inorg. Organomet. Polym. 1998, 8, 119–126. (37) Xu, T. W.; Yang, W. H. Industrial recovery of mixed acid (HF +HNO3) from the titanium spent leaching solutions by diffusion dialysis with a new series of anion exchange membranes. J. Membr. Sci. 2003, 220, 89–95. (38) Xu, T. W.; Yang, W. H. Effect of cell configurations on the performance of citric acid production by a bipolar membrane electrodialysis. J. Membr. Sci. 2002, 203, 145–153. (39) Xu, T. W.; Yang, W. H. A novel positively charged composite membranes for nanofiltration prepared from PPO by in situ amines crosslinking. J. Membr. Sci. 2002, 215, 25–32. (40) Xu, T. W.; Liu, Z. M.; Huang, C. H.; Wu, Y. H.; Wu, L.; Yang, W. H. Preparation of a novel hollow fiber anion exchange membrane and its preliminary performance in diffusion dialysis. Ind. Eng. Chem. Res. 2008, 47, 6204–6210. (41) Yu, H. Y.; He, X. C.; Liu, L. Q.; Gu, J. S.; Wei, X. W. Surface modification of polypropylene microporous membrane to improve its antifouling characteristics in an SMBR: N2 plasma treatment. J. Membr. Sci. 2008, 311, 216–224. (42) Yu, H. Y.; He, J. M.; Liu, L. Q.; He, X. C.; Gu, J. S.; Wei, X. W. Photoinduced graft polymerization to improve antifouling characteristics of an SMBR. J. Membr. Sci. 2007, 302, 235–242. (43) Zhu, L. P.; Zhu, B. K.; Xu, L.; Feng, Y. X.; Liu, F.; Xu, Y. Y. Corona-induced graft polymerization for surface modification of porous polyethersulfone membranes. Appl. Surf. Sci. 2007, 253, 6052–6059. (44) Rengaraj, S.; Moon, S. H. Kinetics of adsorption of Co(II) removal from water and wastewater by ion exchange resins. Water Res. 2002, 36, 1783–1793. (45) Bayramoglu, G.; Arica, M. Y. Removal of heavy mercury(II), cadmium(II) and zinc(II) metal ions by live and heat inactivated Lentinus edodes pellets. Chem. Eng. J. 2008, 143, 133–140. ¨ nlu¨a, N.; Ersoz, M. Removal of heavy metal ions by using (46) U dithiocarbamated-sporopollenin. Sep. Purif. Technol. 2007, 52, 461–469.

Ind. Eng. Chem. Res., Vol. 49, No. 7, 2010 (47) Nishiyama, S.; Saito, K.; Saito, K.; Sugita, K.; Sato, K.; Akiba, M.; Saito, T.; Tsuneda, S.; Hirata, A.; Tamada, M.; Sugo, T. High-speed recovery of antimony using chelating porous hollow-fiber membrane. J. Membr. Sci. 2003, 214, 275–281. (48) Kim, M.; Saito, K. Radiation-induced graft polymerization and sulfonation of glycidyl methacrylate on to porous hollow-fiber membranes with different pore sizes. Radiat. Phys. Chem. 2000, 57, 167–172. (49) Zu, J. H.; Tong, L.; Liu, X. W.; Sun, G. S. HDPE chelate membranes prepared by preirradiation grafting for adsorption of heavy metal ions. J. Appl. Polym. Sci. 2008, 107, 1252–1256. (50) Chen, C. Y.; Chiang, C. L.; Chen, C. R. Removal of heavy metal ions by a chelating resin containing glycine as chelating groups. Sep. Purif. Technol. 2007, 54, 396–403.

3087

(51) Meena, A. K.; Mishra, G. K.; Rai, P. K.; Rajagopal, C.; Nagar, P. N. Removal of heavy metal ions from aqueous solutions using carbon aerogel as an adsorbent. J. Hazard. Mater. 2005, B122, 161–170. (52) Wang, J. S.; Kamiya, Y. A method of validation and parameter evaluation for dual-mode sorption model. J. Membr. Sci. 1999, 154, 25– 32.

ReceiVed for reView September 9, 2009 ReVised manuscript receiVed February 3, 2010 Accepted February 9, 2010 IE901408C

Development of a Novel Hollow Fiber Cation-Exchange Membrane

Recommend Documents