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Control of gas permeability for cellulose acetate membrane by microwave irradiation
DESALINATION Desalination 145 (2002) 375-377
ELSEVIER
www.elsevier.com/locate/desal
Control of gas permeability for cellulose acetate membrane by microwave irradiation Yusuke Nakai, Yoshiharu Tsujita, Hiroaki Yoshimizu* Department
qfMaterials Science and Engineering, Polymeric Materials Course, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan Tel. & Fax: +8/ (52) 735-5272; e-mail: [email protected] Received 29 January 2002; accepted 12 February 2002
Abstract It can be expected that a microwave acts as an accelerator of the mobility of polar functional groups such as hydroxyl groups in polymeric membranes, and then gas permeability improves because of the increasing free volume and/or temperature of the membranes. The permeability coeffkients of CO, for a cellulose acetate (CA) membrane were measured at 25°C using a hand-made apparatus which can irradiate a microwave (2,450 MHz) to the membrane. Both the permeability and diffusion coefficients of CO, for CA membranes are increased by irradiation of the microwave, and degree of enhancement increased with power of the microwave. Keywords: Gas permeability;
Microwave; Cellulose acetate; Polymeric membrane;
Diffusion coefficient;
Hydroxyl
group
1. Introduction been widely used for heating and drying materials such as rubber, food, and prints. In particular, it has been industrially applied for vulcanization in rubber, foam processing, polymerization-solidification, adhesions, etc. [l]. Also nonthermal effects of microwaves have been reported [2]. In general, Microwaves
*Corresponding
have
author.
Presented at the International July 7-12, 2002.
Congress on Membranes
the chemical compounds having the hydroxyl group, most typical compound is water, adsorb a microwave of 2,450 MHz very well. Therefore, we focused on the effect of microwaves on gas permeation properties of polymeric membranes with hydroxyl groups. To the polymeric membranes, it can be expected that the microwave acts as an accelerator of the mobility of polar functional groups such as hydroxyl groups in the membranes, and then, gas permeability improves because of increasing the free volume and Membrane
Processes
00 11-9 I64/02/$- See front matter 0 2002 Elsevier Science B.V. All rights reserved PII: so0 I I-9 164(02)00439-3
(ICOM), Toulouse, France,
Y. Nakai
376
et al. /Desalination
and/or temperature of the membranes. In this study, the ability of the control for gas permeation using a microwave was investigated. 2. Experimental 2.1. Samples
Cellulose acetate (CA: Mn = 30,000, DC = 2.4) as a hydroxyl group having polymer and polystyrene (PS: Mw = 280,000) as a reference sample were used in this study. The membrane samples of CA and PS were prepared by the casting method. A tetrahydrofuran solution ofCA (I .8 wt%) and a chloroform solution of PS (1.3 wt%) were respectively cast on a petri dish at room temperature and thoroughly dried at 30°C for 24 h or more and then annealed at 190°C (CA) and 110°C (PS) in vacuum for 6 h. The thickness of the CA and PS membrane was about 45 pm. Carbon dioxide (CO,) was used as a penetrant gas. 2.2. Methods The permeability coefficients of carbon dioxide for CA and PS membranes were measured at 25°C using a hand-made gas permeation apparatus, which have a permeation cell joined with a microwave generator via a waveguide. By using the apparatus, a microwave (2,450 MHz) can be irradiated to the membrane, and a conventional permeation measurement can be performed at the same time. The details of permeation measurements were described elsewhere [3]. The diffusion coefficients were determined by the time-lag method [4]. The time-lag was measured under microwave irradiation after microwave irradiation to the membrane for 1000 s. 3. Results
and discussion
The permeation curves of CO, for the CA membrane under microwave irradiation showed that the enhancement of CO, permeability by
145 (2002)
375-377
irradiating a microwave was clearly confirmed, and degree of the enhancement increased with the power of the microwave. Permeability of CO, for the CA membrane increased as soon as a microwave was irradiated, and returned quickly to the value before irradiation when the irradiation had stopped. It is suggested that a microwave of 2,450 MHz accelerates the mobility of dipoles in the CA membrane such as hydroxyl groups. The permeability and diffusion coefficients of CO, for CA membrane under irradiation of the microwave of various powers are listed in Tables 1 and 2, respectively. Both the permeability and diffusion coefficients are increased by irradiation by microwave. The ratio of coefficient under irradiation to that under non-irradiation (increasing ratio) increases with the power of the microwave, and this finding for the diffusion Table 1 Effect of microwave irradiation on mean permeability coeffkients for CO, in the CA membrane at 76 cmHg and 25°C Microwave power, W
100 300 500
Permeability coefficient, cm3 (STP) cm/cm2 s cmHg Before irradiation
With irradiation
5.3x1o-‘O 5.4x lo-‘O 5.4x lo-‘O
5.5x1o-‘O 6.1~10-‘~ 6.9x10-”
Increasing ratio
1.04 1.13 1.28
Table 2 Effect of microwave irradiation on mean difkion coeffkients for CO, in CA membranes at 1 atm and 25°C Microwave power, W
Diffusion coefficient, cm2/s
Increasing ratio
0 100 300 500
3.5x 1o-9 3.9x 1o-9 4.3x 10-9 4.8~ 1O-9
1 1.11 1.23 1.37
Y. Nakai et al. /Desalination
coefficient is slightly more remarkable than that for the permeability coefficient. Thus, it is concluded that the enhancement of gas permeability for the CA membrane by irradiation of microwaves was mainly caused by increasing the diffusion properties. According to the solution-diffusion model, the solubility of CO, for the CA membrane is slightly decreased by irradiation ofthe microwave. This means that the temperature of the CA membrane increases to some extent under irradiation of he microwave. On the other hand, the obvious enhancement of CO, permeability by irradiating the microwave was not confirmed for the PS membrane. This means that the effect of the microwave of 2,450 MHz occurs only for the hydroxyl group having a polymer. From these results, the microwave irradiation is one of the powerful techniques for improve-
145 (2002) 375-377
377
ment and control of gas permeation properties for polymeric membranes.
References
PI R.C. Metaxas and R.J. Meredith,
Industrial Microwave Heating, Peter Peregrinus, London, 1983. PI C. Gibson, 1. Matthews and A. Samuel, Microwave enhanced diffusion in polymeric materials, J. Microwave Power and Electromagnic Energy, 23( 1) (I 988) 17-28. [31 Y. Tsujita, K. Yoshimura, H. Yoshimizu, A. Takizawa, T. Kinoshita, M. Furukawa, Y. Yamada and K. Wada, Structureandgaspermeability ofsiloxaneimide block copolymer membranes: 1. Effect of siloxane content. Polymer, 34 (1993) 2597. [41 J.S. Chiou and D.R. Paul, Gas permeation in a dry Nation membrane, Ind. Eng. Chem. Res., 27 (1988) 2161.
ELSEVIER
www.elsevier.com/locate/desal
Control of gas permeability for cellulose acetate membrane by microwave irradiation Yusuke Nakai, Yoshiharu Tsujita, Hiroaki Yoshimizu* Department
qfMaterials Science and Engineering, Polymeric Materials Course, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan Tel. & Fax: +8/ (52) 735-5272; e-mail: [email protected] Received 29 January 2002; accepted 12 February 2002
Abstract It can be expected that a microwave acts as an accelerator of the mobility of polar functional groups such as hydroxyl groups in polymeric membranes, and then gas permeability improves because of the increasing free volume and/or temperature of the membranes. The permeability coeffkients of CO, for a cellulose acetate (CA) membrane were measured at 25°C using a hand-made apparatus which can irradiate a microwave (2,450 MHz) to the membrane. Both the permeability and diffusion coefficients of CO, for CA membranes are increased by irradiation of the microwave, and degree of enhancement increased with power of the microwave. Keywords: Gas permeability;
Microwave; Cellulose acetate; Polymeric membrane;
Diffusion coefficient;
Hydroxyl
group
1. Introduction been widely used for heating and drying materials such as rubber, food, and prints. In particular, it has been industrially applied for vulcanization in rubber, foam processing, polymerization-solidification, adhesions, etc. [l]. Also nonthermal effects of microwaves have been reported [2]. In general, Microwaves
*Corresponding
have
author.
Presented at the International July 7-12, 2002.
Congress on Membranes
the chemical compounds having the hydroxyl group, most typical compound is water, adsorb a microwave of 2,450 MHz very well. Therefore, we focused on the effect of microwaves on gas permeation properties of polymeric membranes with hydroxyl groups. To the polymeric membranes, it can be expected that the microwave acts as an accelerator of the mobility of polar functional groups such as hydroxyl groups in the membranes, and then, gas permeability improves because of increasing the free volume and Membrane
Processes
00 11-9 I64/02/$- See front matter 0 2002 Elsevier Science B.V. All rights reserved PII: so0 I I-9 164(02)00439-3
(ICOM), Toulouse, France,
Y. Nakai
376
et al. /Desalination
and/or temperature of the membranes. In this study, the ability of the control for gas permeation using a microwave was investigated. 2. Experimental 2.1. Samples
Cellulose acetate (CA: Mn = 30,000, DC = 2.4) as a hydroxyl group having polymer and polystyrene (PS: Mw = 280,000) as a reference sample were used in this study. The membrane samples of CA and PS were prepared by the casting method. A tetrahydrofuran solution ofCA (I .8 wt%) and a chloroform solution of PS (1.3 wt%) were respectively cast on a petri dish at room temperature and thoroughly dried at 30°C for 24 h or more and then annealed at 190°C (CA) and 110°C (PS) in vacuum for 6 h. The thickness of the CA and PS membrane was about 45 pm. Carbon dioxide (CO,) was used as a penetrant gas. 2.2. Methods The permeability coefficients of carbon dioxide for CA and PS membranes were measured at 25°C using a hand-made gas permeation apparatus, which have a permeation cell joined with a microwave generator via a waveguide. By using the apparatus, a microwave (2,450 MHz) can be irradiated to the membrane, and a conventional permeation measurement can be performed at the same time. The details of permeation measurements were described elsewhere [3]. The diffusion coefficients were determined by the time-lag method [4]. The time-lag was measured under microwave irradiation after microwave irradiation to the membrane for 1000 s. 3. Results
and discussion
The permeation curves of CO, for the CA membrane under microwave irradiation showed that the enhancement of CO, permeability by
145 (2002)
375-377
irradiating a microwave was clearly confirmed, and degree of the enhancement increased with the power of the microwave. Permeability of CO, for the CA membrane increased as soon as a microwave was irradiated, and returned quickly to the value before irradiation when the irradiation had stopped. It is suggested that a microwave of 2,450 MHz accelerates the mobility of dipoles in the CA membrane such as hydroxyl groups. The permeability and diffusion coefficients of CO, for CA membrane under irradiation of the microwave of various powers are listed in Tables 1 and 2, respectively. Both the permeability and diffusion coefficients are increased by irradiation by microwave. The ratio of coefficient under irradiation to that under non-irradiation (increasing ratio) increases with the power of the microwave, and this finding for the diffusion Table 1 Effect of microwave irradiation on mean permeability coeffkients for CO, in the CA membrane at 76 cmHg and 25°C Microwave power, W
100 300 500
Permeability coefficient, cm3 (STP) cm/cm2 s cmHg Before irradiation
With irradiation
5.3x1o-‘O 5.4x lo-‘O 5.4x lo-‘O
5.5x1o-‘O 6.1~10-‘~ 6.9x10-”
Increasing ratio
1.04 1.13 1.28
Table 2 Effect of microwave irradiation on mean difkion coeffkients for CO, in CA membranes at 1 atm and 25°C Microwave power, W
Diffusion coefficient, cm2/s
Increasing ratio
0 100 300 500
3.5x 1o-9 3.9x 1o-9 4.3x 10-9 4.8~ 1O-9
1 1.11 1.23 1.37
Y. Nakai et al. /Desalination
coefficient is slightly more remarkable than that for the permeability coefficient. Thus, it is concluded that the enhancement of gas permeability for the CA membrane by irradiation of microwaves was mainly caused by increasing the diffusion properties. According to the solution-diffusion model, the solubility of CO, for the CA membrane is slightly decreased by irradiation ofthe microwave. This means that the temperature of the CA membrane increases to some extent under irradiation of he microwave. On the other hand, the obvious enhancement of CO, permeability by irradiating the microwave was not confirmed for the PS membrane. This means that the effect of the microwave of 2,450 MHz occurs only for the hydroxyl group having a polymer. From these results, the microwave irradiation is one of the powerful techniques for improve-
145 (2002) 375-377
377
ment and control of gas permeation properties for polymeric membranes.
References
PI R.C. Metaxas and R.J. Meredith,
Industrial Microwave Heating, Peter Peregrinus, London, 1983. PI C. Gibson, 1. Matthews and A. Samuel, Microwave enhanced diffusion in polymeric materials, J. Microwave Power and Electromagnic Energy, 23( 1) (I 988) 17-28. [31 Y. Tsujita, K. Yoshimura, H. Yoshimizu, A. Takizawa, T. Kinoshita, M. Furukawa, Y. Yamada and K. Wada, Structureandgaspermeability ofsiloxaneimide block copolymer membranes: 1. Effect of siloxane content. Polymer, 34 (1993) 2597. [41 J.S. Chiou and D.R. Paul, Gas permeation in a dry Nation membrane, Ind. Eng. Chem. Res., 27 (1988) 2161.