Removal of Boron Using Nylon-Based Chelating Fibers - Industrial

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Removal of Boron Using Nylon-Based Chelating Fibers Kohsuke Ikeda,† Daisuke Umeno,† Kyoichi Saito,*,† Fujio Koide,‡ Eiji Miyata,‡ and Takanobu Sugo§ †

Department of Applied Chemistry and Biotechnology, Chiba University, Inage-ku, Chiba 263-8522, Japan Nippon Rensui Co., Minami-Otsuka, Toshima-ku, Tokyo 170-0005, Japan § Environment Purification Research Institute Co., Shinden-machi, Takasaki, Gunma 370-0833, Japan ‡

ABSTRACT: By using electron-beam-induced graft polymerization, an epoxy-group-containing monomer, glycidyl methacrylate (GMA), was appended onto a 6-nylon fiber; subsequently, N-methylglucamine as a chelate-forming moiety was added to the epoxy group. The chelating group density of the resultant chelating fiber was 2.0 mmol/g, which was 74% of that of a commercially available chelating bead containing the same functionality. A 150 mg-B/L boron solution was forced to flow through the chelatingfiber-packed bed at the space velocity range from 10 to 100 h-1, defined by dividing flow rate by bed volume (0.3 mL). At a space velocity of 20 h-1, the dynamic binding capacity of the chelating-fiber-packed bed was 2.5-fold higher than that of the chelatingbead-packed bed.

’ INTRODUCTION Poisonous ions represented by the lead ion Pb2þ are removable with polymeric adsorbents. Polymeric adsorbents include ionexchange and chelate-forming resins. Chelating resins are specific or highly selective for target ions compared with ion-exchange resins. Chelating beads, i.e., chelating resins in bead form, packed into a bed have been used in various industrial fields such as chlorine and alkali production1 and water purification.2 To improve the mass-transfer characteristics of the chelating-bead-packed bed, chelating fibers, i.e., chelating resins in fiber form, were suggested by Toray Co.,3 Nitivy Co.,4 and Chelest Co.5 By applying electron-beam-induced graft polymerization, we have thus far prepared chelating resins in various forms: fibers,6 films,7 nonwoven fabrics,8 hollow fibers,9 and porous sheets.10 Chelating groups were introduced into polymeric matrices by reacting a cyano group of a grafted poly acrylonitrile chain with hydroxylamine6 or an epoxy group of a grafted poly glycidylmethacrylate chain with iminodiacetic acid,11 ethylenediamine,12 iminodiethanol,13 N-methylglucamine,14 and nucleic acid bases.15 Previous studies of chelating resins prepared by electron-beaminduced graft polymerization are summarized in Table 1. One of the merits of electron-beam-induced graft polymerization is that a variety of shapes and qualities of trunk polymers are selectable, thereby enabling the preparation of chelating resins with novel shapes and qualities16 different from commercially available chelating resins. 6-Nylon is a feasible polymeric material owing to its sufficiently strong mechanical strength. Miyazawa et al.17 prepared novel ion-exchange membranes by the graft polymerization of ion-exchange-group-containing monomers onto an electronbeam-irradiated 6-nylon film and demonstrated almost the same performance in electrodialysis of 0.5 M NaCl as that observed in currently used ion-exchange membranes. Fibrous 6-nylon is suitable for packing into a bed. However, 6-nylon-based chelating fibers have not yet been reported. The objective of this study was 3-fold: (1) to prepare chelating fibers based on 6-nylon fiber by electron-beam-induced graft r 2011 American Chemical Society

polymerization, (2) to demonstrate the adsorption and elution performance of the chelating-fiber-packed bed for poisonous ions in a flow-through mode, and (3) to compare the adsorption and elution performance of the chelating-fiber-packed bed with that of a commercially available chelating-bead-packed bed. Thus far, polyethylene-coated polypropylene fiber,18 polyethylene hollow fibers and nonwoven fabrics,14,19 and cellulose beads20 have been used for the immobilization of N-methylglucamine by electron-beam-induced grafting, and applied to the capturing of boron ionic species, as summarized in Table 2. In this study, N-methylglucamine as the chelate-forming functionality was immobilized onto 6-nylon fiber.

’ EXPERIMENTAL SECTION Materials. 6-Nylon fiber 25 μm in diameter, purchased from Toray Co., was used as the trunk polymer for grafting. Glycidyl methacrylate (GMA, CH2dCCH3COOCH2CHOCH2) was purchased from Nakalai Tesque Co. and used without further purification. N-Methylglucamine (NMG) was acquired from Sigma-Aldrich Co. The other chemicals were of analytical grade or higher. Boric acid was dissolved in a buffer whose pH was adjusted at 7.0. For comparison, a commercially available chelating bead containing an NMG moiety (DIAION CRB05) supplied by Mitsubishi Chemical Co. was also used. Immobilization of N-Methylglucamine onto Nylon Fiber. The immobilization scheme of N-methylglucamine to nylon fiber or 6-nylon fiber consisted of three steps, as shown in Figure 1. (1) Electron-beam irradiation: the nylon fiber was irradiated with an electron beam in nitrogen atmosphere at ambient temperature. The dose was 200 kGy. (2) GMA grafting: The irradiated nylon fiber was immersed in 10 (v/v)% GMA/methanol for a prescribed Received: September 25, 2010 Accepted: February 18, 2011 Revised: February 5, 2011 Published: March 21, 2011 5727

dx.doi.org/10.1021/ie101968h | Ind. Eng. Chem. Res. 2011, 50, 5727–5732

Industrial & Engineering Chemistry Research

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Table 1. Chelating Resins Prepared by Electron-Beam-Induced Graft Polymerization and Subsequent Chemical Modificationsa trunk polymer shape

a

chelating group

quality

target ion or molecule

year

reference

fiber

TFE-E

amidoxime

uranium (UO2þ)

1985

Omichi et al.6

porous hollow-fiber membrane

PE

iminodiacetate

cobalt

1991

Yamagishi et al.11


PE

ethylenediamine

palladium

1995

Li et al.12


PE

iminodiethanol NMG

germanium (GeO2)

2000

Ozawa et al.13

nonwoven fabrics, porous hollow-fiber membrane

PE

NMG

boron

2004

Saito et al.14


PE

nucleic-acid base

palladium

2008

Yoshikawa et al.15

fiber

6-nylon

NMG

boron

This study

Abbreviations: tetrafluoroethylene-ethylene copolymer (TFE-E), polyethylene (PE), N-methylglucamine (NMG).

Table 2. Equilibrium Binding Capacities of NMG-Group-Immobilized Adsorbents Prepared by Electron-Beam-Induced Graft Polymerization density of NMG

feed concn.

equilibrium binding

dynamic binding capacity in a

immobilized [mmol/g]

[mg-B/L]

capacity [mg-B/g]

flow-through mode [mg-B/mL-bed]

2.1

108

-

3.4 (SV 10 h-1)

Saito et al. Hoshina et al.19

2.4 2.4

150 10

21 -

2.4 (SV 10 h-1)

Zhao et al.20

-

20

-

2.8 (SV 10 h-1)

this study

2.0

150

12

2.5 (SV 10 h-1)

reference Jyo et al.18 14

Figure 1. Scheme of immobilization of N-methylglucamine to 6-nylon fiber.

reaction time at 313 K. The degree of GMA grafting was evaluated from the mass gain of the fiber using degree of GMA grafting ð%Þ ¼ 100ðW 1 - W 0 Þ=W 0

Figure 2. Experimental apparatus for studying flow of boron solution through bed charged with chelating fibers and beads.

evaluated using molar conversion ð%Þ ¼ 100½ðW 2 - W 1 Þ=195

ð1Þ

where W0 and W1 are the masses of the trunk and GMA-grafted fibers, respectively. The resulting GMA-grafted fiber was referred to as the GMA(dg) fiber. Here, dg is the degree of GMA grafting. To prevent the aggregation of the fibers, dg was set at 200%. (3) Addition of N-methylglucamine to the epoxy group of the GMA(200) fiber: The GMA(200) fiber was immersed in 0.20 M NMG aqueous solution at 353 K. The solvent used was a mixture of dioxane and water in a volume ratio range from 8:2 to 0:10. The reaction time ranged from 20 to 180 min. The molar conversion of the epoxy group of the GMA(200) fiber into the NMG moiety and the density of NMG immobilized were

=½ðW 1 - W 0 Þ=142

ð2Þ

density of NMG immobilized ðmmol=gÞ ¼ 1000½ðW 2 - W 1 Þ=195=W 2

ð3Þ

where W2 is the mass of the NMG-immobilized fiber. The figures 195 and 142 are the molecular masses of NMG and GMA, respectively. The resulting NMG-immobilized fiber was referred to as the NMG(200, y) fiber. Here, y is the density of NMG immobilized. Boron Removal in a Flow-through Mode Using Chelating Fibers. The NMG(200, y) fiber in a wet state was packed into a cartridge with an inner diameter of 5.5 mm and a length of 50 mm 5728

dx.doi.org/10.1021/ie101968h |Ind. Eng. Chem. Res. 2011, 50, 5727–5732


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to fabricate a bed. The bed height was set at about 12-13 mm. A boron solution as the feed was forced to flow upward through the NMG-fiber-packed bed at a constant flow rate, as shown in Figure 2. The feed concentration of the boron solution ranged from 40 to 150 mg-B/L. The flow rate ranged from 3 to 30 mL/h, which was converted into the space velocity range from 10 to 100 h-1. Here, space velocity was defined as space velocity, SV ðh-1 Þ ¼ ðflow rateÞ=ðbed volumeÞ

ð4Þ

where C0, C, and V are the feed and effluent concentrations, and effluent volume, respectively. VE and VD are the effluent volumes at which C reaches C0 and 0.1 C0, respectively. For comparison, similar experiments using the nylon and GMA(200) fibers were performed. After the effluent concentration reached the feed concentration, adsorption operation was switched to elution operation with 0.5 M H2SO4. Elution percentage was defined as elution percentage ð%Þ ¼ 100ðamount elutedÞ=

The effluent flowing out of the exit of the bed was continuously sampled with fraction vials. The boron concentration of each fraction was determined by colorimetry. From the breakthrough curve, the equilibrium and dynamic binding capacities of the bed charged with the NMG fibers or NMG beads were evaluated using equilibrium binding capacity ðmg-B=g-fiber or beadÞ Z VE ðC0 - CÞdV=ðmass of fiber or beadÞ ¼

ðamount adsorbedÞ

ð7Þ

ð5Þ

0

dynamic binding capacity ðmg-B=mL-fiber or beadÞ Z VD ¼ ðC0 - CÞdV=ðvolume of fiber or beadÞ

ð6Þ

Figure 4. SEM images of the fibers: (a) nylon, (b) GMA(200), and (c) NMG(200, 2.0) fibers.

Figure 3. Molar conversion during addition of N-methylglucamine to epoxy group of poly-GMA chain grafted onto nylon fiber for various ratios of dioxane to water.

Figure 5. Breakthrough curves of NMG(200, 2.0) fiber and the NMG bead for boron at a space velocity of 20 h-1.

0

Figure 6. Adsorption equilibrium: (a) isotherm and (b) molar binding ratio of boron to NMG moiety. 5729



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A series of adsorption and elution cycles for the bed were performed at ambient temperature.

’ RESULTS AND DISCUSSION Density of NMG Immobilized. The molar conversion of the epoxy group of the GMA fiber into an N-methylglucamine (NMG) moiety is shown in Figure 3 for various ratios of dioxane to water. For each ratio, the molar conversion increased with increasing reaction time and leveled off at the final molar conversion. The higher the ratio of dioxane to water, the higher the final molar conversion of the epoxy group into the NMG moiety. After 3 h at a volume ratio of dioxane to water of 4.0, an immobilized NMG density of 2.0 mmol/g of the NMG(200, 2.0) fiber, which was 74% that of a commercially available chelating bead containing the NMG group (DIAION CRB05), was attained. Morphological changes in the fiber accompanied by graft polymerization and the subsequent introduction of the NMG functionality were observed by SEM (Figure 4). The diameter of the nylon fiber (25 μm) in the dry state increased to that of the NMG(200, 2.0) fiber (55 μm) in the dry state. Feed Concentration Dependence of Breakthrough Curves. Examples of the breakthrough curves of the NMG(200, 2.0) fiber and NMG bead are shown in Figure 5 at a constant flow rate of 6 mL/h, i.e., SV 20 h-1, of 40 mg-B/L boron solution. From the breakthrough curves for various feed concentrations, the equilibrium binding capacity for the feed concentration of boron was evaluated using eq 5 and adsorption isotherms are shown in Figure 6a. The parameters fitted by the Langmuir-type isotherm are listed in Table 3. The curves of the adsorption isotherm showed good agreement between the NMG(200, 2.0) fiber and the NMG bead. The molar binding ratio of boron to the NMG moiety is shown in Figure 6b as a function of the feed concentration. The molar binding ratios of the NMG(200, 2.0) fiber were higher than that of the NMG bead, which was close to the

theoretical value of 0.5. The equilibrium binding capacities of the nylon and GMA(200) fibers at a feed concentration of 150 mg-B/L were 0.25 and 0.23 mg-B/g, respectively, which amounted to approximately 2% of that of the NMG(200, 2.0) fiber. Boron ionic species adsorbed onto the NMG(200, 2.0) fiber were quantitatively eluted with 0.5 M H2SO4. After five cycles of adsorption and elution, the equilibrium binding capacity of the NMG(200, 2.0) fiber did not decrease, and no weight loss of the fiber was observed. Flow Rate Dependence of Breakthrough Curves. The breakthrough curves of the NMG(200, 2.0) fiber and NMG bead are shown in Figure 7a and b, respectively, as functions of the space velocity of the boron solution whose feed concentration was 150 mg-B/L. A higher flow rate of the boron solution led to lower dynamic binding capacities of both beds charged with the fibers and beads for boron ionic species or to a shorter breakthrough point where C/C0 reaches 0.1. The dynamic binding capacities of the beds charged with the NMG(200, 2.0) fibers and NMG beads are shown in Figure 8 for various flow rates or space velocities ranging from 10 to 100 h-1. In this range, the bed charged with the NMG(200, 2.0) fibers had a higher dynamic binding capacity than that charged with the NMG beads. This is because the diffusion path of boron ionic species to the NMG moiety of the NMG fiber is shorter than that of the NMG bead. The comparison

Table 3. Adsorption Isotherm Parameters for Chelating Fiber and Bead Langmuir equilibrium

maximum adsorption

constant [L/mg-B]

capacity [mg-B/g]

NMG(200, 2.0) fiber

0.11

12

NMG bead (DIAION CRB05)

0.088

12

Figure 8. Dynamic binding capacity as function of space velocity.

Figure 7. Breakthrough curves at various space velocities of boron solution: (a) NMG(200, 2.0)-fiber-packed bed and (b) NMG-bead-packed bed. 5730



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Table 4. Comparison of Boron Removal Performance between Chelating-Fiber- and Bead-Packed Beds NMG(200, 2.0) fiber (adsorbent mass)/(bed volume) [g/mL-bed]

NMG bead (DIAION CRB05)

0.38

0.43

size [μm]

55 (fiber diameter)

>400 (diameter)

density of NMG immobilized [mmol/g]

2.0

2.7

equilibrium binding capacity [mg-B/g]

12

12

binding ratio of boron to NMG moiety [-]

0.54

0.39

4.6 2.5

4.3 1.0

adsorbent

column mode (SV: 20 h-1, feed conc.: 150 mg-B/L) equilibrium binding capacity [mg-B/mL-bed] dynamic binding capacity [mg-B/mL-bed]

of properties and performance between the NMG(200, 2.0) fiber and the NMG bead is summarized in Table 4. The chelating fiber has the following advantages over the chelating beads: (1) the fiber with its smaller diameter minimizes the diffusion path of target ions and results in a higher specific surface area, (2) the fiber with its noncross-linked grafted polymer chain leads to a high molar binding ratio of target ions to the chelating group, compared with the beads with their crosslinked matrix, and (3) the fiber can be fabricated into woven and bound filters for high-throughput water treatment.

’ CONCLUSIONS 6-Nylon fiber is one of the polymeric materials suitable for appending various functionalities. We succeeded in modifying the 6-nylon fiber into a chelating fiber by the electron-beaminduced graft polymerization of glycidyl methyacrylate and the subsequent addition of N-methylglucamine to the epoxy group of the polymer chain grafted. A boron solution with a feed concentration range from 40 to 150 mg-B/L was forced to flow through a bed charged with the resulting chelating fibers with an immobilized NMG density of 2.0 mmol/g. The adsorption isotherm of the chelating fiber agreed well with that of a commercially available chelating bead with a density of 2.7 mmol/g. The dynamic binding capacity of the bed charged with the chelating fibers for boron at a space velocity of 20 h-1 was 2.5 mg-B/mL of the bed, which was 2.5-fold higher than that of the bed charged with the chelating beads. The boron adsorbed onto the chelating fiber was quantitatively eluted with 0.5 M sulfuric acid. Furthermore, the decrease in the binding capacity of the chelating fiber was not observed after five cycles of adsorption and elution. ’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected].

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Removal of Boron Using Nylon-Based Chelating Fibers - Industrial

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