Bromomethylated Poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO

Ind. Eng. Chem. Res. 2010, 49, 8741–8748

8741

Bromomethylated Poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO)-Based Amphoteric Hollow-Fiber Membranes: Preparation and Lysozyme Adsorption Zhenfeng Cheng,† Cuiming Wu,‡ Weihua Yang,† and Tongwen Xu*,† CAS Key Laboratory of Soft Matter Chemistry, Laboratory of Functional Membranes, UniVersity of Science and Technology of China, Hefei, Anhui 230026, P. R. China, and School of Chemical Engineering, Hefei UniVersity of Technology, Hefei, Anhui 230009, P. R. China

For the recovery and purification of proteins, an amphoteric hollow-fiber membrane (AHFM) was prepared from bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO) by ethylenediamination and carboxylation. The success in modifying BPPO was confirmed by FTIR spectra, amphoteric group density, anionexchange capacity (AEC), and cation-exchange capacity (CEC). For potential applications, the membranes were tested for the adsorption of lysozyme, and the results showed that the adsorption amount increased with increasing initial lysozyme concentration. The adsorption fits the Langmuir isotherm and the Freundlich equation well, and the maximum experimental amount of lysozyme adsorbed was found to be 4.00 mg/g, which was close to the calculated values (3.85 and 4.13 mg/g according to the Langmuir and Freundlich equations, respectively). 1. Introduction Currently, proteins are widely used in the fields of medicine, biology, and chemical engineering. For example, lysozyme1-3 can be used as a cell disrupting agent, an antibacterial agent, and a food additive, and lipases4,5 are often employed in the dairy, oil-processing, and pharmaceutical industries. In these applications, the purity of protein is the greatest concern. Accordingly, technologies for protein isolation and purification have attracted increasing attention during the past decade. To date, many separation techniques have been developed, such as ultrafiltration (UF),6 packed-bed chromatography,7 and membrane chromatography.8-11 UF is an efficient pressuredriven separation technique and has been extensively studied in recent years. The membrane used for filtration or concentration of proteins has a pore size ranging from 1 to 100 nm, and it is difficult to achieve high selectivity at high productivity. Packed-bed chromatography, as a typical chromatography technology, has dominated bioseparation operations for years.7 Nevertheless, it also has some major limitations, such as the large pressure drop across packed beds, a long recovery time, and a large recovery liquid volume; hence, this technique is restricted from large-scale application. To overcome these drawbacks, membrane chromatography was developed. It uses microporous or macroporous membranes as absorbents, and the flow of solution through the pores predominantly depends on convection. Consequently, the mass-transfer resistance is reduced significantly, and the process, including adsorption, washing, elution, and regeneration, requires less time. Meanwhile, this technique can be easily scaled up and is thus promising for large-scale recovery and purification of proteins. Based on the interaction modes between proteins and membranes, several adsorption mechanisms have been proposed, including affinity,12,13 ion exchange,14,15 hydrophobic interaction,16 and reverse-phase chromatography.17 Among these, ionexchange membrane chromatography18 demonstrates broad applicability, high resolution, and large adsorption capacity in * To whom correspondence should be addressed. E-mail: twxu@ ustc.edu.cn. † University of Science and Technology of China. ‡ Hefei University of Technology.

large-scale protein purification processes. For such processes, the structure and properties of the chromatographic membrane are of vital importance. Flat-sheet ion-exchange membranes have been widely used and extensively investigated.19 However, compared with flat-sheet membranes, hollow-fiber membranes, which have large specific surface areas and are self-supporting, can meet different application demands and have gained much attention recently. Bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO) hollow fibers with a high glass transition temperature and good thermal stability have been prepared successfully in our laboratory. Based on these BPPO fibers, anion-exchange and cation-exchange membranes have been developed through amination or sulfonation and employed for the recovery of acids or metal ions.20,21 In the present work, we focus on a further development of BPPO-based hollow fibers, preparing amphoteric membranes, rather than anion- or cation-exchange membranes, by chemical modification. Because amphoteric membranes have both acidic (negatively charged) and basic (positively charged) groups, they can carry different amounts of negative or positive charges as pH varies.22 Therefore, they have advantages over common cation- or anion-exchange membranes for the adsorption and separation of proteins. In this work, the structure and properties of the developed membranes are characterized by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), water uptake, amphoteric group density, anion-exchange capacity (AEC), and cation-exchange capacity (CEC). Further, lysozyme is used as a model protein for evaluation of the adsorption performance of the prepared membranes. The effects of various factors on the adsorption capacity are also studied, including adsorption time, pH, initial lysozyme concentration, and ionic strength of the lysozyme solution. 2. Experimental Section 2.1. Materials. BPPO with 90% benzyl substitution and 10% aryl substitution was kindly supplied by Shandong Tianwei Membrane Co., Ltd., Weifang, China. The porosity of the membrane was ∼70%, and the inside and outside diameters were ∼0.82 and ∼1.22 mm, respectively. Ethylenediamine (EDA),

10.1021/ie100348e  2010 American Chemical Society Published on Web 08/11/2010

8742

Ind. Eng. Chem. Res., Vol. 49, No. 18, 2010

Figure 1. Preparation of the CEBPPO membrane.

succinic anhydride (SA), hydrochloric acid (HCl), lysozyme (LZ), and acetone were all purchased from Sinopharm Chemical Reagent Co., Ltd., Shanghai, China, and used without further purification. Lysozyme was dissolved in a 0.02 M tris(hydroxymethyl)aminomethane hydrochloride (tris-HCl; Hefei Bomei Biotechnology Co., Ltd., Hefei, China) buffer solution before use. Other chemicals were of analytical grade. 2.2. Preparation of Amphoteric Hollow-Fiber Membrane (AHFM) from BPPO. The BPPO-based hollow fibers were prepared by dissolution, filtration, spinning, coagulation, and take-up, as detailed in our previous work.20 An amphoteric hollow-fiber membrane containing amino and carboxylic groups was prepared from the BPPO-based hollow fibers by following two steps, as shown in Figure 1. (1) In step 1, ethylenediamination, BPPO-based hollow fibers were immersed in an EDA aqueous solution at different temperatures (30, 50, and 70 °C), and the volume ratio of EDA ranged from 30% to 100%. After the reaction, the hollow fibers were removed and rinsed repeatedly with deionized water to remove residual EDA. The obtained fibers are denoted as EBPPO. (2) In step 2, carboxylation, the EBPPO hollow fibers from step 1 were dipped into a succinic anhydride (SA)/acetone solution at different temperatures (20, 30, and 40 °C) to convert the amino groups into carboxylic acid groups. After a given time, the fibers, denoted as CEBPPO, were removed, washed thoroughly with an aqueous acetone solution and deionized water, and then dried at 60 °C until constant weight. 2.3. Characterizations. 2.3.1. Fourier Transform Infrared (FTIR) Spectroscopy. FTIR spectra of BPPO, EBPPO, and CEBPPO were collected to study their chemical compositions and verify the modifications at different steps. The spectra were recorded on a Bruker Vector 22 FTIR spectrometer, with a wavenumber range of 4000-400 cm-1 and a resolution of 4 cm-1. Dry samples were prepared by mixing the samples with KBr and pressing each mixture into a clear semitransparent pellet. 2.3.2. Scanning Electron Microscopy (SEM). The morphological changes of the hollow fibers were imaged with a field-emission scanning electron microscope (XL30-ESEM, Philips) with an accelerating voltage of 5 kV. The freeze-fracture

technique was used, and both the cross section and the outer surface were observed. 2.3.3. AEC, CEC, and Amphoteric Group Density of the CEBPPO Membrane. The AEC and CEC of the CEBPPO membrane were measured as follows: About 0.20 g of dry CEBPPO hollow-fiber membrane was cut into small pieces (∼0.5 cm long) and immersed in 30 mL of a HCl (0.04 M) or NaOH solution (0.03 M) for 24 h, after which 25 mL of the solution was removed and neutralized by NaOH or HCl. The AEC and CEC values were then calculated as AEC (mmol/g) )

30 (30CHCl - VCNaOH)/W 25

(1)

CEC (mmol/g) )

30 (30CNaOH - VCHCl)/W 25

(2)

where CHCl and CNaOH are the concentrations of HCl and NaOH solutions, respectively; V is the volume of titrated solution; and W is the weight of the membrane. Amphoteric group density is defined as the total density of positively and negatively charged groups23 and was determined from the CEC and AEC values as amphoteric group density (mmol/g) ) CEC + AEC

(3) 2.3.4. Water Uptake. Water uptake is an important property of ion-exchange membrane and is also an effective indicator of membrane hydrophobicity. The water uptakes of EBPPO fibers and CEBPPO membrane were measured as follows: The sample of EBPPO fibers or CEBPPO membrane was dried in an oven at 60 °C for 1 h and then dipped into deionized water at room temperature for 24 h. Subsequently, the sample of fibers or membrane was removed and weighed after the liquid on the surface had been quickly wiped off with filter paper. The water uptake was calculated as24 water uptake (%) ) 100

Ww - Wd Wd

(4)

where Ww and Wd are the weights of the fibers or the membrane in the wet and dry states, respectively.


Figure 2. Effects of reaction temperature and reaction time on the anionexchange capacity of the EBPPO hollow fibers.

8743

Figure 3. Effects of EDA concentration and reaction time on the AEC of the EBPPO hollow fibers at 50 °C.

2.3.5. Adsorption of Lysozyme on the CEBPPO Membrane. The adsorption of lysozyme on the CEBPPO membrane was measured according to a method reported previously.25 The CEBPPO membrane was dried at 60 °C for 2 h and weighed. Then, the membrane was submerged in 10 mL of a lysozyme solution and shaken at a rate of 100 rpm at room temperature for a given time. The amount of lysozyme adsorbed was determined from the initial and final concentrations of the lysozyme solution as26 Q)

(C1 - C2)V W

(5)

where Q is the amount of lysozyme adsorbed; W is the weight of the CEBPPO membrane; V is the volume of solution; and C1 and C2 are the concentrations of lysozyme before and after adsorption, respectively. The concentration of lysozyme was analyzed at 280 nm with a spectrophotometer (UV-757CRT, Shanghai Youke Co., Ltd., Shanghai, China) at room temperature. 2.3.6. Breakthrough Curve. The experimental apparatus for measuring breakthrough curves was the same as reported in our previous work.21 A wet CEBPPO amphoteric hollow-fiber membrane was positioned in a U-shaped membrane module. One end of the module was connected with a peristaltic pump, and the other end was sealed. A 10 mg/L (C3) lysozyme solution was forced to permeate from the inside to the outside of the hollow-fiber membrane, and the effluent solution (C4) was collected in 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. General Investigations of Preparation Conditions. As shown in Figure 1, the amphoteric hollow-fiber membrane was prepared from BPPO-based fibers by ethylenediamination (step 1) and carboxylation (step 2). To verify the reactions at different steps, the CEC, AEC, and amphoteric group density of the membrane were measured. In addition, various preparation conditions, such as reagent concentration, reaction time, and temperature, were investigated. Figure 2 illustrates the effects of reaction temperature and reaction time on the AEC of the CEBPPO membrane. Although the reactions were controlled at different temperatures, similar trends were found. The AEC increased with reaction time at first and then leveled off after the first 5 h. In addition, the AEC increased with reaction temperature. This conforms to common sense that a higher reaction temperature and a longer reaction time will lead to a higher reaction degree.

Figure 4. Effects of EDA concentration and reaction time on the CEC of the CEBPPO membrane. AEC ) 4.00 mmol/g.

For investigation of the effect of the ethylenediamine (EDA) concentration on the AEC, medium temperature (50 °C) was applied, and the results are shown in Figure 3. Similar trends were found for the three EDC concentrations (30%, 60%, and 100%). As the immersion time increased, AEC first increased abruptly and then became nearly constant. Consequently, the AEC was found to depend strongly on reaction temperature and EDA concentration. Figure 4 shows the effects of reaction temperature and reaction time on the CEC of the CEBPPO membrane with fixed AEC value (4.00 mmol/g). In every case (20, 30, and 40 °C), the CEC increased rapidly with increasing reaction time before 1 h and then increased at a lower rate. The CECs of the membranes after 10 h were 3.04, 3.62, and 3.75 mmol/g at 20, 30, and 40 °C, respectively; these values are close to or higher than those of other reported cation-exchange membranes.27,28 3.2. Characteristics of the Prepared Membranes. 3.2.1. Membrane Chemical Structure (FTIR Spectroscopy). Figure 5 shows FTIR spectra of (a) the base BPPO hollow fibers, (b) the EBPPO hollow fibers, and (c) the CEBPPO membrane. In the cases of curves a and b, adsorption peaks of the symmetrical and asymmetrical stretching vibrations of C-O at 1191 and 1302 cm-1 and those of phenyl groups at 1463 and 1601 cm-1 can be observed. In addition, the BPPO hollow fibers have a characteristic peak at 589 cm-1, which can be attributed to the stretching vibration of C-Br groups. However, no such peak can be observed in the spectra of the EBPPO or CEBPPO hollow fibers (curves b and c). This indicates that a reaction between the BPPO hollow fibers and ethylenediamine occurred and that most of the C-Br groups reacted during step 1. Comparison of curve c with curve a or b reveals a new peak at 1718 cm-1, which should be assigned to the CdO stretching vibration of carboxylic acid groups. At the same time, the

8744


Figure 5. FTIR spectra of (a) BPPO-based hollow fibers, (b) EBPPO hollow fibers, and (c) CEBPPO membrane.

introduction of carboxylic acid groups induces a shift of the adsorption peak from 1601 to 1644 cm-1; moreover, the adsorption peak becomes broader. Hence, the reaction of the fibers with succinic anhydride can be considered successful. These results confirm that carboxylic acid groups were successfully introduced into the BPPO hollow fibers, which supports the results for the AEC, CEC, and amphoteric group density (section 3.1). 3.2.2. SEM. Figure 6 shows images of the outer surface and cross sections of BPPO hollow fibers, EBPPO hollow fibers, and the CEBPPO membrane. As compared with the unmodified membrane (Figure 6A1) and the CEBPPO membrane (Figure 6C1), the EBPPO hollow fibers (Figure 6B1) have a smoother outer surface. This is attributed to the surface reaction of BPPO hollow fibers with ethylenediamine and succinic anhydride. The images of the cross sections indicate that all of the fibers consist of a dense middle layer and porous outer and inner layers. As compared with the original BPPO hollow fibers, no significant changes in EBPPO and CEBPPO are found on the cross-section morphologies. Therefore, the microporous structure of the fibers remains intact after the chemical modifications. 3.2.3. Water Uptake. The effect of the AEC on the water uptake of the EBPPO membrane was examined, and the results are shown in Figure 7. The water uptake decreased gradually with increasing AEC. When the AEC rose from 0.64 to 2.15 mmlo/g, the water uptake decreased slightly from 21.6% to 16.4%. This is mainly due to the cross-linking of branched chains on the BPPO hollow fibers during ethylenediamination. Figure 8 shows the effect of the CEC on the water uptake of the CEBPPO membrane. The changing trend in this figure is similar to that in Figure 7. When the CEC varied from 1.32 to 2.65 mmol/g, the water uptake decreased from 43.3% to 24.2%. This behavior can be attributed to the attraction between amine groups and carboxyl groups. As the attraction strengthened, the polymeric chains in the membrane matrix were compressed, and the water uptake decreased correspondingly. 3.3. Lysozyme Adsorption on the CEBPPO Amphoteric Hollow-Fiber Membrane. 3.3.1. Effect of Adsorption Time on the Amount of Lysozyme Adsorbed. The relationship between the amount of lysozyme adsorbed and the adsorption time is illustrated in Figure 9. As expected, an increase in the adsorption time led to an increase in the amount of lysozyme adsorbed from 0.58 to 1.47 mg/g, and the increase leveled off after 25 h. A further increase in the adsorption time

did not lead to any significant change in the amount of lysozyme adsorbed. This phenomenon was reported in previous research on protein adsorption.29 3.3.2. Effect of Ionic Strength on the Amount of Lysozyme Adsorbed. NaCl was used to adjust the ionic strength of the lysozyme solution. The effect of NaCl concentration on the amount of lysozyme adsorbed is shown in Figure 10. As the NaCl concentration increased, the amount of lysozyme adsorbed decreased from 1.21 to 0.10 mg/g. This is as expected because the debye length decreases with increasing ionic strength, so there was a decrease in the electrostatic interaction between lysozyme and the CEBPPO membrane. 3.3.3. Effect of Initial Concentration on the Amount of Lysozyme Adsorbed. The effect of the initial lysozyme concentration on the amount adsorbed is shown in Figure 11. Clearly, an increase in the lysozyme concentration in the adsorption medium led to an increase in the amount of adsorbed lysozyme on the membrane. This is because the activity of lysozyme in the membrane is equal to that in the solution at equilibrium and the activities in the two phases increase synchronously, leading to an increase in the amount of lysozyme adsorbed in the membrane. In addition, when the initial lysozyme concentration was lower than 1.93 mg/mL, the adsorption amount increased rapidly and then did not change much with a further increase in lysozyme concentration. This is due to the saturation of cation-exchange groups in the membrane by the adsorbed lysozyme. Adsorption isotherms, such as the Freundlich equation,30 the Langmuir isotherm,31 and the Redlich-Peterson isotherm,32 are convenient ways to explain the changes in the amount of protein adsorbed with protein concentration at constant temperature. The Freundlich equation and Langmuir isotherm are the simplest adsorption isotherms and have been used widely by many researchers. Therefore, they were chosen to describe the adsorption of lysozyme on the CEBPPO membrane. The general form of the Langmuir isotherm is Ce Ce 1 ) + Qe Qmax Qmaxb

(6)

where Ce is the equilibrium concentration (mg/L); b is the adsorption equilibrium constant of the system; and Qe and Qm are the amount of material adsorbed on the adsorbent at equilibrium and the maximum amount adsorbed, respectively. The Freundlich equation assumes that the adsorption energy of a protein depends on whether the adjacent sites are occupied and is expressed by the empirical equation log Qe )

( n1 ) log C + log k e

(7)

where k and n are the Freundlich constants, which indicate adsorption capacity and adsorption intensity, respectively. If a plot of ln Ce vs ln Qe yields a straight line, then the adsorption process conforms to the Freundlich isotherm, and the parameters k and n can be obtained from the intercept and slope, respectively. The experimental data on the equilibrium adsorption of lysozyme on the CEBPPO membrane were analyzed in terms of the Langmuir isotherm using Origin7.0 software, and typical results are shown in Figure 12. The correlation coefficient was calculated to be 0.9941, so it can be concluded that the adsorption of lysozyme on the CEBPPO membrane obeys the Langmuir isotherm, that is, lysozyme is adsorbed on a random copolymer of ethylene and vinyl alcohol (EVAL).29 From the


8745

Figure 6. SEM images of the outer surfaces and cross sections of (A) BPPO-based hollow fibers, (B) EBPPO hollow fibers, and (C) CEBPPO membrane. In each row, 1 represents the outer surface, whereas 2 and 3 represent the cross-section side.

Figure 7. Effect of AEC on the water uptake of EBPPO hollow fibers. Figure 9. Effect of adsorption time on the amount of lysozyme adsorbed onto the CEBPPO membrane. Amphoteric group density ) 7.11 mmol/g, CEC ) 3.11 mmol/g, initial concentration ) 0.25 g/L, pH ) 7.4.

Figure 8. Effect of CEC on the water uptake of the CEBPPO membrane. AEC ) 4.00 mmol/g.

Langmuir isotherm, the maximum lysozyme adsorption capacity was calculated to be 3.85 mg/g, which is close to the experimental value (4.00 mg/g). Figure 13 illustrates the fitting results obtained using the Freundlich equation. From the slope and intercept, the param-

eters k and n were calculated to be 0.10 and 2.10, respectively. From the Freundlich equation, the maximum lysozyme adsorption capacity was calculated to be 4.13 mg/g, which is slightly larger than the experimental value (4.00 mg/g). Furthermore, the correlation coefficient was 0.9957, nearly the same as that calculated by the Langmuir isotherm. This indicates that the adsorption fits both the Langmuir isotherm and the Freundlich equation well. Some other models were also tested for data correlation. The Freundlich-Henry equation (Q ) KiCe1/n + KpCe) cannot improve the accuracy of the calculation (R ) 0.9957). Therefore, single-layer adsorption is considered to be the main mechanism for adsorption of lysozyme on the CEBPPO amphoteric hollowfiber membrane. 3.3.4. Effect of pH on the Amount of Lysozyme Adsorbed. The amphoteric hollow-fiber membrane and lysozyme both have acidic (-COOH) and basic (-NH2) functional groups, and they acquire positive (-NH3+) and negative charges (-COO-) by accepting or donating protons when dissolved in

8746


Figure 10. Effect of NaCl concentration on the amount of lysozyme adsorbed onto the CEBPPO membrane. Amphoteric group density ) 7.42 mmol/g, CEC ) 3.42 mmol/g, initial concentration ) 0.28 g/L, adsorption time ) 10 h, pH ) 7.4.

Figure 13. Freundlich equation for the adsorption of lysozyme onto the CEBPPO membrane.

Figure 14. Effect of pH on the amount of lysozyme adsorbed onto the CEBPPO membrane. Amphoteric group density ) 6.30 mmol/g, CEC ) 2.30 mmol/g, initial concentration ) 0.23 g/L, adsorption time ) 15 h. Figure 11. Effect of initial lysozyme concentration on the amount of lysozyme adsorbed onto the CEBPPO membrane. Amphoteric group density ) 6.37 mmol/g, CEC ) 2.37 mmol/g, adsorption time ) 10 h, pH ) 7.4.

Figure 12. Langmuir isotherm for the adsorption of lysozyme onto the CEBPPO membrane.

solution. When the negative and positive charges are equal in quantity, the membrane and lysozyme carry no net charge; the pH in this case is the isoelectric point (IEP) and can be calculated from the pKa values. At pH values above and below the IEP, the dominant species are -COO- and -NH3+, respectively. In addition, the amount of charges changes as pH varies. Figure 14 shows the effect of pH on the amount of lysozyme adsorbed onto the CEBPPO membrane at pH 1-13. When the pH is low (12.9), there is almost no adsorption of lysozyme. This is due to the strong repulsive interaction between lysozyme and the membrane because they

are both positively charged at low pH or negatively charged at high pH. In the two intermediate pH ranges 1.8-8.4 and 8.4-12.9, the amount of lysozyme adsorbed increases first with increasing pH and then decreases rapidly, and maximum values are reached (1.56 mg/g at pH 2.4 and 2.24 mg/g at pH 10.8). This is due to the increase in the attraction between lysozyme and the membrane because the amphoteric hollow-fiber membrane carries negative charges and lysozyme carries positive charges at pH < 11 (IEPlys). At pH 10.8 and pH 2.4, the amphoteric hollow-fiber membrane and lysozyme carry a large number of charges, and the attraction between the membrane and lysozyme is strong, so the maximum values are reached. In conclusion, the adsorption is strongly pH-dependent because pH determines the charge density and charge type of both lysozyme and the CEBPPO membrane simultaneously. 3.4. Breakthrough Curve. The breakthrough curve of lysozyme is shown in Figure 15. As expected, when the effluent volume was smaller than 5 mL, the lysozyme concentration in effluent decreased to almost zero and then became larger. The volume of breakthrough was found to be 18 mL. From the breakthrough curve, the equilibrium adsorption amount can be calculated as 1.05 mg/g. 4. Conclusions A CEBPPO membrane containing amino and carboxylic acid groups was prepared by chemical modification of BPPO-based fibers. FTIR spectra, amphoteric group density, and CEC data demonstrated that amino and carboxylic acid groups were successfully introduced into the BPPO-based hollow fibers. SEM


8747

Literature Cited

Figure 15. Breakthrough curve of lysozyme. Amphoteric group density ) 6.37 mmol/g, CEC ) 2.37 mmol/g, pH ) 7.4.

images of the membranes showed that there was no obvious difference in the cross-section morphology between the BPPObased hollow fibers and the CEBPPO membrane, indicating that modifications did not damage the pore structure. Adsorption of lysozyme onto the CEBPPO membrane was also examined. The performance was affected by adsorption time, ionic strength, initial concentration, and pH, with pH being the most significant factor because of the amphoteric properties of the membrane. The amount adsorbed could be varied in the range 0.70-4.00 mg/g, and the findings here can provide guidance for further exploration of this type of membrane in chromatography applications. Acknowledgment The authors gratefully acknowledge financial support from the National Natural Science Foundation of China (20774090 and 20636050). Special thanks are extended to Dr. Chuanhui Huang for proof-reading the English. Nomenclature b ) adsorption equilibrium constant of the system, L/mg CHCl ) concentration of HCl solution, mol/L Ce ) equilibrium concentration, mg/L C1 ) concentration of lysozyme before adsorption, mg/L C2 ) concentration of lysozyme after adsorption, mg/L C3 ) initial lysozyme concentration in the breakthrough experiment, mg/L C4 ) lysozyme concentration in the effluent, mg/L CNaOH ) concentration of NaOH, mol/L k ) Freundlich constant indicating adsorption capacity n ) Freundlich constant indicating adsorption intensity Qe ) amount of material adsorbed on the adsorbent at equilibrium, mg/g Qm ) maximum adsorption amount, mg/g V ) volume of solution, L W ) weight of the membrane used, g Wd ) weight of the membrane in the dry state, g Ww ) weight of the membrane in the wet state, g AEC ) anion-exchange capacity AHFM ) amphoteric hollow-fiber membrane BPPO ) bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide) (fiber) CEBPPO ) carboxylated EBPPO (membrane) CEC ) cation-exchange capacity EBPPO ) ethylenediaminated BPPO (fiber) EDA ) ethylenediamine

(1) Jiang, Y. J.; Yang, D.; Zhang, L.; Jiang, Y.; Zhang, Y.; Li, J.; Jiang, Z. Facile Synthesis and Novel Application of Zirconia Catalyzed and Templated by Lysozyme. Ind. Eng. Chem. Res. 2008, 47 (6), 1876–1882. (2) Ghosh, R. Purification of lysozyme by microporous PVDF membrane based chromatographic process. Biochem. Eng. J. 2003, 14, 109–116. (3) Sofer, G. Preparative chromatographic separations in pharmaceutical, diagnostic, and biotechnology industries: Current and future trends. J. Chromatogr. A 1995, 707 (1), 23–28. (4) Yadav, G. D.; Borkar, I. V. Kinetic modeling of immobilized lipase catalysis in synthesis of n-butyl levulinate. Ind. Eng. Chem. Res. 2008, 47, 3358–3363. (5) Ghiaci, M.; Aghaei, H.; Soleimanian, S.; Sedaghat, M. E. Enzyme immobilization: Part 1. Modified bentonite as a new and efficient support for immobilization of Candida rugosa lipase. Appl. Clay Sci. 2009, 43, 289–295. (6) Arunima, S.; Vinod, K. S. pH controlled selective transport of proteins through charged ultrafilter membranes under coupled driving forces: An efficient process for protein separation. J. Membr. Sci. 2007, 299, 211– 221. (7) Przybycien, T. M.; Pujar, N. S.; Steele, L. M. Alternative bioseparation operations: Life beyond packed-bed chromatography. Curr. Opin. Biotechnol. 2004, 15 (5), 469–478. (8) Noboru, K.; Minoru, K. S.; Kazuyuki, S. Protein Adsorption and Elution Performances of Porous Hollow-Fiber Membranes Containing Various Hydrophobic Ligands. Biotechnol. Prog. 1997, 13, 89–95. (9) Suguru, M.; Noboru, K.; Hidetaka, K.; Kyoichi, S.; Kazuyuki, S.; Kohei, W.; Takanobu, S. High-throughput hydrolysis of starch during permeation across a-amylase-immobilized porous hollow-fiber membranes. Radiat. Phys. Chem. 2002, 63, 143–149. (10) Noboru, K.; Minor, K.; Kyoichi, S.; Kazuyuki, S.; Kohei, W.; Takanobu, S. Repeated use of a hydrophobic ligand-containing porous membrane for protein recovery. J. Membr. Sci. 1997, 134, 67–73. (11) Wei, G.; Eli, R. Crosslinked glass fiber affinity membrane chromatography and its application to fibronectin separation. J. Chromatogr. B 2003, 795, 61–72. (12) Brandt, S.; Goffe, R. A.; Kesser, S. B.; O’Connor, J. L.; Zale, S. E. Membrane-based affinity technology for commercial scale purifications. Bio/ Technology 1988, 6, 779–782. (13) Langlotz, P.; Kroner, K. H. Surface modified membranes as a matrix for protein purification. J. Chromatogr. A 1992, 591, 107–113. (14) Tsuneda, S.; Shinano, H.; Saito, K.; Furusaki, S.; Sugo, T. Binding of lysozyme onto a cation-exchange microporous membrane containing tentacle-type grafted polymer branches. Biotechnol. Prog. 1994, 10, 76– 81. (15) Gerstner, J. A.; Hamilton, R.; Cramer, S. M. Membrane chromatographic systems for high-throughput protein separations. J. Chromatogr. A 1992, 596, 173–180. (16) Kubota, N.; Kounosu, M.; Saito, K.; Sugita, K.; Watanabe, K.; Sugo, T. Preparation of a hydrophobic porous membrane containing phenyl groups and its protein adsorption performance. J. Chromatogr. A 1995, 718, 27– 34. (17) Yan, L.; Cooper, J. W.; Lee, C. S. Miniaturized membrane-based reversed-phase chromatography and enzyme reactor for protein digestion, peptide separation, and protein identification using electrospray ionization mass spectrometry. J. Chromatogr. A 2002, 979, 241–247. (18) Shinano, H.; Tsuneda, S.; Saito, K.; Furusaki, S. Ion exchange of lysozyme during permeation across a microporous sulfopropyl-groupcontaining hollow fiber. Biotechnol. Prog. 1993, 9, 193–198. (19) Raja, G. Protein separation using membrane chromatography: Opportunities and challenges. J. Chromatogr. A 2002, 952, 13–27. (20) 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. (21) Cheng, Z. F.; Wu, Y. H.; Wang, N.; Yang, W. H.; Xu, T. W. Preparation of bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO) hollow fiber cation-exchange membrane for removing heavy metal ions. Ind. Eng. Chem. Res. 2010, 49, 3079–3087. (22) Matsumoto, H.; Koyama, Y.; Tanioka, A. Preparation and Characterization of Novel Weak Amphoteric Charged Membrane Containing Cysteine Residues. J. Colloid Interface Sci. 2001, 239, 467–474. (23) Matsumoto, H.; Koyama, Y.; Tanioka, A. Interaction of Organic Molecules with Weak Amphoteric Charged Membrane Surfaces: Effect of Interfacial Charge Structure. Langmuir 2002, 18, 3698–3703. (24) Lv, C.; Su, Y.; Wang, Y.; Ma, X.; Sun, Q.; Jiang, Z. Enhanced permeation performance of cellulose acetate ultrafiltration membrane by incorporation of Pluronic F127. J. Membr. Sci. 2007, 294, 68–74.

8748


(25) Greene, G.; Radhakrishna, H.; Tannenbaum, R. Protein binding properties of surface-modified porous polyethylene membranes. Biomaterials 2005, 26, 5972–5982. (26) Chen, X.; Liu, J.; Feng, Z.; Shao, Z. Macroporous chitosan/ carboxymethylcellulose blend membranes and their application for lysozyme adsorption. J. Appl. Polym. Sci. 2005, 96, 1267–1274. (27) Kubota, N.; Miura, S.; Saito, K.; Sugita, K.; Watanabe, K.; Sugo, T. Comparison of protein adsorption by anion-exchange interactiononto porous hollow-fiber membrane and gel bead-packed bed. J. Membr. Sci. 1996, 117, 135–142. (28) Tsuneda, S.; Shinano, H.; Saito, K.; Furusaki, S. Binding of Lysozyme onto a Cation Exchange Microporous Membrane Containing Tentacle-Type Grafted Polymer Branches. Biotechnol. Prog. 1994, 70, 76– 81.

(29) Saiful, B. Z.; Wessling, M. Enzyme capturing and concentration with mixed matrix membrane adsorbers. J. Membr. Sci. 2006, 280, 406–417. (30) Freundlich, H. Uber die adsorption in Losungen. Z. Phys. Chem. 1906, 57, 385–471. (31) Langmuir, I. The constitution and fundamental properties of solid and liquids. Part I, Solids. J. Am. Chem. Soc. 1918, 40, 1361–1403. (32) Jossens, L.; Prausnitz, J. M.; Fritz, W.; Schlunder, E. U.; Myers, A. L. Thermodynamics of multi-solute adsorption from dilute aqueous solutions. Chem. Eng. Sci. 1998, 33, 1097–1106.

ReceiVed for reView February 15, 2010 ReVised manuscript receiVed July 7, 2010 Accepted August 2, 2010 IE100348E

Bromomethylated Poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO

Recommend Documents