PS) blend ultrafiltration (UF) membranes

PS) blend ultrafiltration (UF) membranes

I DESALINATION ELSEVIER Desalination 101 (1995) 51-56 Polyacrylonitrilic/polysulfone (PAN/PS) blend ultrafiltration (UF) membranes Ling Ai-lian*, C...

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DESALINATION ELSEVIER

Desalination 101 (1995) 51-56

Polyacrylonitrilic/polysulfone (PAN/PS) blend ultrafiltration (UF) membranes Ling Ai-lian*, Chen Qing Beijing Polytechnic University, Beijing 100022, P.R. China Received 14 December 1993; accepted 11 November 1994

Abstract

Uitrafiltration (UF) membranes and a polymer blend of polyacrylonitril (PAN) and polysulfone (PS) were prepared. Their flux is higher than that of PAN UF membranes under the same conditions. The morphological structure of UF membranes was examined.

Keywords: Ultrafiltration membranes, PAN, PS

1. Introduction

2. Experimental

In order to make a systematic study of PAN material, used especially for separation membranes, a blend of PAN and PS was used. It was found that a PAN/PS blend is partly miscible, and the UF membrane prepared from it has good performance wtth an especially high flux. In this paper we shall d~seuss the main process for using the PAN/PS blend to prepare an asymmetric plate UF membrane.

2.1. Materials PAN produced by the Shanghai Petrochemical Complex and PS produced by the Shanghai Shuguang Chemical Factory were used. Bovine serum albumin (BSA) was used as a standard in the feed solution. Other chemicals were all All or CP grades.

2.2. Preparation of membranes and determination of performance *Corresponding author.

The casting solution with an additive of a desired amount containing PAN-PS blend and

0011-9164/95/$09.50 © 1995 ElsevierScience B.V. All rights reserved SSD! 00 ! !-9164(95)00008-9

A. la'ng, Q. Chen /Desalination 101 (1995) 51-56

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N,N-dimethylformamide (DMF) in the desired prol~rtion was prepared. The feeding order was: PAN-PS, additive, solvent. After agitation, solution, centrifugz, tion and static defoaming, the UF membranes were prepared according to the Loeb-Sourirajan method. The conditions were: PAN/PS: 10:1; evaporation time: 8 s ; thickness of wet membrane: 0.230.24 ram; gelating medium: 0.5% DMF aqueous solution (unless otherwise noted); room temperature: 20-25°C; RH, 65-75%. All membranes were pressurized at 0.35 MPa for 1 h prior to the UF experiment. The operating pressure was 0.2 MPa. The water flux (J) was obtained from deionized water, and the rejection (J9 was determined by 0.05% BSA solution.

2,3. Apparatus and measurements For details, see previous paper 11,21.

3.1.2. Lay aside time of casting solution The membrane performances are listed in Table 1. As the blend is partly miscible, laying aside may cause better diffusion, thus improving the performance. Table 1 Effect of lay-aside time of casting solution on membrane performance Additive Lay-aside Flux concentration time (ml/cm2 h) (%) (days)

Rejection (%)

1

94.7 95.7 66. ! 93.3 66.4 95.2 44.4 93.5

] 5 7

3 4 2 3 2 3 2 3

163.1 214.1 509.6 417.0 611.5 110.9 366.9 119.6

3. Results and discussion

3.1. Effects of compositions of casting solution 3.1.1. Solvent selection The solvent of the polymer was selected according to the solubility parameter (6) [31. Since the ~ of PAN is 15.4 and the 5 of PS is 12.6, finding an appropriate solvent is of prime importance for blend membrane manufacture. In our experiments eight different solvents with more than 20 different volume ratios were selected by changing the blend ratio, polymer molecular weight, additive types and concentration; the blend cannot be fully mixed. TEM photographs (Fig. 1) show that PAN-PS blend is partly miscible. The two-phase region exists, and the boundary is very clear; some PAN in PS, the size of macromolecular aggregate is even, and the pores are large. The rejection is slightly lower than 90%. but the flux is very high and the maximum is higher than 700 ml/cm 2 • h.

3.1.3. Content of blend polymer The variation of membrane performances with blend content laying between 10-15 % was investigated. The performances (see Table 2) had little difference, but they differed from those of the PAN/PVC UF membrane [I] (a fully miscible system). It may be explained that the distance between the macromoleculars of the blend is large, and the pore diameter has few changes within this range.

3.1.4. Type and content of addMves Various organic and inorganic additives were tested. The results of our studies are shown in Tables 3 and 4. The data in Table 3 show some effective additive for PAN and PS does not suit PAN/PS blend UF membranes. The performances are best when the 95% acetic acid and some amine and acetic ether

A. Ling, Q. (7hen /Desalination 101 (1995) 51-56

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Fig. !. TEM ofa PAN/PS UF membrane, a. Additive: Diethylamine x4800; b. Additive: TEP x37,000.

Fig. 2. SEM of a PAN/PS UF membrane, a. Surface x 1500; b. Back X 1500; c. Cross section × 1000.

were used as the additives. The data in Table 3 show that when TEP content varies from 1-7%, the flux exceeds 100 ml/cm2 h and is higher than that of the PAN UF membrane (see Table 4). The SEM of PAN/PS UF mem-

branes are shown in Fig. 2 where finger pores in the support layer were obse,'ved. The surface was very fine and close. At the bottom pores are largo,, numerous and even so that the flux and rejection were large.

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A. Ling, Q. Chen I Desalination 101 (1995)51-56

Table 2 Effect of additive type on membrane performance

Table 3 Effect of content on membrane performance

Additive

Rejection (%)

TEP content (%)

Flux (ml/cm2 h)

Rejection (%)

1 3 5 7 9 II 13 15 17

214.1 416.9 110.9 119.6 51.4 60.0 49.9 42.6 52.4

95.7 93.3 95.2 93.5 94.0 96.9 96. l 95.0 96.3

Flux (ml/cm 2 h)

Methanol Ethanol

56.6 30.6

93.9 95.7

n-Propyl alcohol s-Butanol t-Butanol Cyelohexanol Ethyl ether

66.9 35.3 35.2 44.6 49.5

97.1 93.3 98.3 96.9 86.7

Ethyl glycol Methyl ether Acetone Butanone

60.3 35.8 55.5

90.6 83.7 96.5

Cyclohexanone

61.6

97.5

Formic acid

15.3

95.8

Acetic acid (36%) Acetic acid (95 %) n-Propanoic acid Triethylamine Triethanolamine

10.6 326.1 51.2 159.0 173.5

94,5 94.5 91.3 93.5 80.4

Methyl formate Ethyl formate Methyl acetate Ethyl acetate

24.2 29.0 81.8 112.5

91.0 92.0 94.3 94.5

Ethyl lactate Triethyi phosphate Cyclohexane n-Heptane n-Hexane Benzene Dioxane Tetra_hydrofuran Polyvinyl pyrrolidone PEG-400

49. I 110.9 29.5 46.0 187.2 122.3 51.1 63.6 65.5 49.8

94.6 95.2 97.1 97.4 89.4 88.4 92.4 97.1 90.0 92.8

PEG-600 Diethylamine Aniline

34.3 110.4 85.3

94.5 94.7 92.5

Table 4 Comparison of PAN and PAN/PS membrane perfor mance

Polymer

Flux Rejection (ml/cm 2 h) (%)

PAN PAN PAN PAN

71.2 214.1 46.9 51.7

(AN-MA-MAS) (AN-MA-MAS)/PS (AN-MMA) (AN-MMA)/PS

96.5 95.7 97.9 97.4

Table 5 Effect of evaporation time Evaporation time (s) 8

15 30 45 60 90 120

Flux (ml/cm2 h) 146.8 53.7 49.1 74.9 98.0 61.2 136.8

Rejection

(%) 95.7 95.5 96.7 96.5 91.1 96.1 97.3

A. Ling, Q. Chen / Desalination 101 (1995)51-56 Table 6 Effect of casting solution temperature

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Table 9 Effect of the type of gelating medium

Temp., °C

Flux (ml/cm2 h)

Rejection (%)

Type of gelating medium (5% solutions)

2-4 23 50

35.3 48.0 60.5

98.1 96.7 95.7

Water Sodium chloride Ethanol TEP Triethanolamine Sodium dodecyl benzene sulfonate Tetrahydrofuran Pho~horic acid Diox,:.~ne Butanone i-Propylalcohol t-Butanol Methyl acetate Ethyl acetate

Table 7 Effect of content gelating medium Content of gelating medium (%)

Flux (ml/cm2 h)

Rejection

0.5 5 I0 15

53.7 71.8 137.6 120.0

94.8 93.8 94.2 97.9

(%)

Table 8 Effect of gelating medium temperature Temp. of gelating medium (°C)

Flux (ml/cm2 h)

Rejection (%)

0 23 53

20.2 114.0 102.2

98.0 97.9 93.8

Flux Rejection (ml/cm2 h) (%) 35.0 38.1 47.3 76.4 57.3 9.5

97.6 97.5 91.3 92.3 95.5 97.5

112.5 13.5 61.2 305.0 45.4 50.0 56.4 144.1

94.4 98.6 93.0 95.0 94.0 95.2 97.9 88.4

gelating medium, temperature of gelating medium, evaporation time), L s orthogonal tests were carried out. The result shows that the flux is 100-600 ml/cm 2 h (MWCO is 67,000) under appropriate technical conditions.

4. Conclusions

3.2. Effect o f technical condition The effect of evaporating time is shown in Table 5. Table 6 shows that tile flux increases with an increase in casting solution temperature. The effects of temperature, content and the type of gelating medium are listed in Tables 7-9. In order to take account of the corr'.prehensire effect of various factors (temperature of casting solution, type of additive, content of additive, content of polymer, lay-aside time,

1. A PAN/PS blend is partly miscible. The UF membranes prepared from it have good performances, and the flux is higher than U,at of PAN UF membranes. 2. The feeding order was polymer- additivesolvent, and after laying aside for the appropriate time, we got membranes of good performance. 3. From the scanning electron micrographs of PAN/PS UF membranes, finger pores in the support layer were observed. The surface is very fine and close, and at the bottom pores are very numerous and even.

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A. Ling, Q. Chen i Desalination 101 (1995) 51-56

References [I]

A. Ling, Y. Zheng, S. Bao and S. Fan, Desalination, 86 (1992) 291.

{2l A. Ling, S. Wang and Z. Wang, I. Beijing Polytechnic University, 1 (1990)62. [3] S. Ling, Y. Lu and Z. Lianh, Macromolecular Chemistry, Science Publishing, Beijing, 1982, pp. 120-160.