Synthetic Membranes: Volume II - American Chemical Society

17 Chemically Resistant Asymmetric Membranes Made from PVA for the Separation of Organic Solvents and Phenols from Aqueous Solutions

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on June 2, 2015 | http://pubs.acs.org Publication Date: May 27, 1981 | doi: 10.1021/bk-1981-0154.ch017

S. P E T E R and R . S T E F A N Lehrstuhl für Technische Chemie, Universität Erlangen-Nürnberg, Egerlandstrasse 3, D-8520 Erlangen, West Germany

The i n c r e a s i n g q u a n t i t i e s o f industrial wastes r e q u i r i n g treatment are becoming an important problem. R e l a t i v e l y h i g h demands on t h e quality must be fulfilled, if the water has t o be discharged o r r e c y c l e d . The effluents r e q u i r i n g purification f r e q u e n t l y c o n t a i n a wide variety o f compounds w i t h differing p r o p e r t i e s . G e n e r a l l y t h e c o n c e n t r a t i o n s o f these organic and i n o r g a n i c p o l l u t a n t s may range between 0 , 5 and 5% by weight, o f t e n making an expensive treatment o f industrial wastes necessary. Reverse osmosis could p o s s i b l y become an attractive a l t e r n a t i v e t o the classical s e p a r a t i o n processes such as distillation, e x t r a c t i o n , evaporation e t c . , which are c u r r e n t l y in use. Reverse osmosis may be used t o increase t h e concentration of t h e compounds present in the wastes so t h a t t h e i r r e e x t r a c t i o n w i t h the aid o f classical s e p a r a t i o n methods becomes economical. A l s o it can be used as a step in the treatment o f wastes before d r a i n off. The differing p r o p e r t i e s o f t h e compounds present in industrial e f f l u e n t s r e q u i r e membranes that are s t a b l e a g a i n s t the s o l v e n t s in q u e s t i o n . Futhermore, the membranes have t o be sufficiently permeable. Thermal stability and durability over a wide pH range (1-14) are a l s o r e q u i r e d a s well as a sufficiently high selectivity w i t h regard t o the compounds t o be separated. The demand o f general stability against solvents is met by c r o s s - l i n k e d membranes. M a t e r i a l used For t h e i n v e s t i g a t i o n s reported here p o l y v i n y l a l c o h o l (PVA) and i t s d e r i v a t i v e s such as p o l y v i n y l a c e t a t e , p o l y v i n y l ether e t c . were used a s the b a s i c polymeric m a t e r i a l s . These compounds can e a s i l y be converted i n t o polymeric analogues [ l ] . I t was shown i n an e a r l i e r work [ 2 ] t h a t PVA-membranes w i t h an asymmetrical s t r u c t u r e can be obtained by phase-inverted p r e c i p i t a t i o n s i m i l a r t o the method o.f Loeb and S o u r i r a j a n [ 3 ] . These membranes can a l s o be rendered i n s o l u b l e i n water by 0097-6156/81/0154-0281$05.00/ 0 © 1981 American Chemical Society

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

282

SYNTHETIC

MEMBRANES:

HF

AND

UF

USES

c r o s s - l i n k i n g [4]*. The f o l l o w i n g substances were mainly used: PVA w i t h a h y d r o l y s i s grade o f 98% and a m o l e c u l a r weight o f 9.0 000, P o l y v i n y l a c e t a t e w i t h a molecular weight o f 110 000, p o l y v i n y l b u t y r a t e w i t h a molecular o f 7000 and 12-16% o f f r e e OH-groups.


Method o f producing the membranes F i l m s were c a s t from the polymer s o l u t i o n and a f t e r t h a t immersed i n a p r e c i p i t a t i o n bath. The asymmetric membranes obtained are s o l u b l e i n water and have t o be made i n s o l u b l e by c r o s s ^ - l i n k i n g . During the c r o s s - l i n k i n g r e a c t i o n s the asymmetric s t r u c t u r e produced by the phase-inverted p r e c i p i t a t i o n must remain unchanged. T h i s can be performed by t r e a t i n g the asymmetric membrane i n a f i x i n g bath o f an a c i d i c s a l t s o l u t i o n . A f t e r t h i s treatment, c r o s s - l i n k i n g i s p o s s i b l e by organic and i n o r g a n i c reagents without r e d u c t i o n o f the asymmetry. C r o s s - l i n k i n g renders the membranes i n s o l u b l e i n water; a d d i t i o n a l l y , the r e t e n t i o n of the organic compounds i s improved. The best r e s u l t s were obtained f o r the c r o s s - l i n k i n g e i t h e r by using both organic and i n o r g a n i c reagents together i n one step or by a p p l y i n g them one a f t e r another. C r o s s - l i n k i n g by means of metal s a l t s can e q u a l l y w e l l precede o r f o l l o w the t r e a t ment w i t h an organic reagent. P r o p e r t i e s o f the membranes The i n f l u e n c e o f d i f f e r e n t c r o s s - l i n k i n g reagents on the p r o p e r t i e s o f the membranes was i n v e s t i g a t e d by reverse osmosis experiments. A procedure f o r preparing the membranes was devised t h a t y i e l d e d membranes o f medium r e t e n t i o n o f phenol a g a i n s t an aqueous phenol s o l u t i o n o f 2 g / l i t r e a t pH 13. The membranes were always prepared i n e x a c t l y the same way. Thus the i n f l u e n c e o f the d i f f e r e n t c r o s s - l i n k i n g agents could be compared b e t t e r than under optimum c o n d i t i o n s o f p r e p a r a t i o n . A f t e r c r o s s - l i n k i n g by means o f organic compounds, some o f the membranes were a d d i t i o n a l l y t r e a t e d w i t h a s o l u t i o n c o n t a i n i n g Cr(III)-salts [5]. The osmotic p r o p e r t i e s of the membranes were t e s t e d a t room temperature and a pressure d i f f e r e n c e o f 50 bar. Phenol r e t e n t i o n and product f l u x were measured. The s t a b i l i t y o f the membranes obtained a g a i n s t v a r i o u s s o l v e n t s was i n v e s t i g a t e d by immersing the membranes i n the s o l v e n t concerned a t 40°C f o r about three weeks. A f t e r t h a t t h e i r mechanical and osmotic p r o p e r t i e s were t e s t e d again and compared w i t h t h e i r p r o p e r t i e s before t h e treatment. The r e s u l t s of the experiments are shown i n t a b l e I . The s t a b i l i t y o f the membranes subjected t o c r o s s - l i n k i n g by an organic reagent i s very s a t i s f a c t o r y . A d d i t i o n a l treatment w i t h C r ( I I I ) s o l u t i o n s


17.

PETER AND STEFAN

Chemically Resistant Asymmetric Membranes

283

Table I : Chemical s t a b i l i t y o f PVA-membranes i n o r g a n i c and i n o r g a n i c solutions- a t 40°C Membrane;

lompo-

Membrane

type

jsition-f

type

s o l v e n t mixtures I CH OH-C H OH-H 0 25:25 :50 DMSO- C H OH-H O 60:30 :10 50:50 DMSO- C H O H DMSO- DMF 75:25 60:30:10 DMSO-C H OH-FA 60:30:10 DMSO-CH OH-FA


3

2

5

2

5

2

5

2

2

isopropyl alcohol-H o 2

dioxane- E^O

DMSO - H 0 2

H0 2

50:50 25:75 75:25 100:1 S0:b6 25:75 75:25 100:1

98-100

HCOOH l

CH COOH 3

20 4

50

NH OH

25

H S0 2

4

HNO

3

benzene toluene

12 100 100 100

xylene

3,5

c r e s o l (o,m,p)

7

pyridine

6

50:50 25:75 75:25 100:1

formaldehyde

50:50 25:75 75:25 100:1

formamide - H 0

50:50 25:75 75:25 100:1

CH OH-H 0

50:50 25:75 75:25 100:1

2

100

phenole

50:50 25:75 75:25 100:1

2

NaOH

50:50 25:75 75:25 100:1

eyelohecanone - H 0 2

In

weight%

5

5

3

X

2

C H OH-H 0

DMF

II

2

3

2

I reactant

35

isobuty-methy1-ketone

100

1 = s t a b l e , no change i n membrane p r o p e r t i e s 2 = not s t a b l e 3 = d e s t r u c t i o n o f membrane Type o f membrane I = PVA, c r o s s - l i n k e d by o r g a n i c compounds Type o f membrane I I = PVA, c r o s s - l i n k e d by o r g a n i c compounds and t r e a t e d w i t h Cr(III) + Concentrations r e f e r t o aqueous s o l u t i o n s .


284

SYNTHETIC MEMBRANES:

HF

AND

USES

increases the s t a b i l i t y as w e l l as the phenol r e t e n t i o n as i s shown l a t e r . In F i g . 1 the phenol r e t e n t i o n of membranes c r o s s - l i n k e d i n s a t u r a t e d s o l u t i o n s of d i c a r b o x y l i c a c i d s i s represented as a f u n c t i o n of the number of carbon atoms of the d i c a r b o x y l i c acid. The s o l u b i l i t y of the d i c a r b o x y l i c a c i d s i n water i s a l s o represented. As can be seen the a l t e r n a t i n g behavior of homologous s e r i e s w i t h the number of carbon atoms i s r e f l e c t e d i n the phenol r e t e n t i o n of the c r o s s - l i n k e d membranes. The r e s u l t s of the i n v e s t i g a t i o n are s p e c i f i e d i n t a b l e I I . Besides the r e t e n t i o n of phenol, the r e t e n t i o n of Na S was, s i m i l a r l y measured. The t a b u l a t e d v a l u e s are mean v a l u e s f o r the membranes obtained from about 3 separate t r i a l s . The r e p r o d u c i b i l i t y of the^ measurements amounts to about 2% f o r the r e t e n t i o n and 0,003 m /(m d) f o r the product f l u x . The a d d i t i o n a l treatment of the membranes i n C r ( I I I ) s a l t s o l u t i o n s caused a notable improvement i n phenol r e t e n t i o n while the f l u x remained p r a c t i c a l l y unaltered. The behavior of membranes c r o s s ^ l i n k e d by v a r i o u s ketones was i n v e s t i g a t e d i n the same way. These membranes possess e x c e p t i o n a l l y good mechanical p r o p e r t i e s . Moderate values f o r f l u x and phenol r e t e n t i o n were found (see t a b l e I I I ) . Since the o b j e c t o n l y was to compare d i f f e r e n t c r o s s - l i n k i n g reagents, no f u r t h e r attempt was made t o improve the f l u x and the r e t e n tion. Table IV g i v e s the r e t e n t i o n and product f l u x f o r membranes c r o s s - l i n k e d by d i c a r b o n y l compounds i n presence of v a r i o u s aqueous s o l u t i o n s of phenol, sodium s u l f i d e , p y r i d i n e and ammonia. The strong c o n c e n t r a t i o n dependence of the r e t e n t i o n i n the presence of phenol and the dependence of the f l u x on the s o l u t e i s i n t e r e s t i n g . Membranes w i t h 95% r e t e n t i o n f o r phenol a t f l u x e s of about 0.100 m /(m d) can be e a s i l y obtained. In biotechnology, the products concerned are removed from aqueous s o l u t i o n by e x t r a c t i o n w i t h methylacetate, b u t y l a c e t a t e , i s o b u t y l methyl ketone e t c . The remaining aqueous substrate i s s a t u r a t e d w i t h the e x t r a c t i o n s o l v e n t s . Sometimes t h i s causes problems w i t h regard t o environmental r e g u l a t i o n s . Table V shows t h a t the s o l v e n t s can be remored almost e n t i r e l y by reverse osmosis. The concentrate c o n s i s t s of two phases, namely, the s o l v e n t saturated w i t h water and the water s a t u r a t e d w i t h s o l v e n t . These can be separated by means of a s e t t l e r . The water phase i s r e c i r c u l a t e d to the reverse osmosis. The s a t u r a t e d s o l u b i l i t y i n Water a t room temperature i s 19 000 m g / l i t r e f o r i s o b u t y l methyl ketone, 3300 m g / l i t r e f o r b u t y l acetate and 9 500 m g / l i t r e f o r methyl acetate. As the r e s u l t s i n t a b l e V show, the r e t e n t i o n f o r isobutyl-methyl ketone increases w i t h i n c r e a s i n g c o n c e n t r a t i o n . T h i s r e s u l t i s remarkable, as g e n e r a l l y a decrease i n r e t e n t i o n i s observed with increasing concentration. f

2


UF

2

3

2


STEFAN


285


PETER AND

Figure 1. Concentration of carboxylic acid and retention of the PVA membrane: ( ) concentration of acid in the cross-linking solution; ( ) retention on 0.2 wt %, phenol, pH =13.



Malonic A c i d

Succinic Acid

Glutaric Acid

Adipic Acid

Pimelic Acid

Suberic

Azelaic Acid

Sebacic A c i d

3

4

5

6

7

8

9

10

Ap = 50 bar T

Acid

Oxalic Acid

2

A c i d

25°C

207,25

188,22

174,19

160,17

146,14

132,11

118,OO

104.06

90.04

MW

+

-

+

-

+

-

+

-

+

-

+

-

+

-

+

-

+

58 65 25 38 66 74 45 69 58 65 58 66 63 69 40 46 64 70

2000 [5H]

Cr (III) phenole

Retention phenole

IO

25

20

10

0.070 0.066 0.120 0.250 0.078 0.060 0.105 0.075 0.090 0.080 0.105 0.080 0.100 0.075 0.130 0.105 0.080 0.075

r 3

1

0. 300

0. 220

0. 200

0. 119

2400

m .m d_ ammonia

Product F l u x

2400 [5H; 2000

ammonia

[%]

PVA-Membranes C r o s s - l i n k e d by D i c a r b o x y l i c Acids and C r ( I I I ) s o l u t i o n

Number o f C-atoms i n molecule

Table I I :


to

in W

oo ON


9 9

acetophenone

propiophenone

benzylmethylketone

6 8 4

iso-butylmethylketone

eyelohexanone

dimethylcyclohexanone

diacetyl

10

benzoylacetone

Ap = 50 bar T = 25°C

5

acetylacetone

14

6

ethylmethylketone

benzil

3 4

acetone

10

8

K E T O N E

butyrophenone

C-atoms in molecule

162.18

100.11

210.22

86.09

126.20

98.14

lOO.16

72.10

58.08

148.20

134.17

134.17

120.14

MW

0.102

0.166

0.079

0.193

0.132

0.169

0.166

0.230

0.286

0.112

0.124

0.124

0.138

mole f r a c t i o n o f ketone i n the cross-linking solution

Table I I I : PVA membranes c r o s s - l i n k e d by ketones

R

L

56

61

63

69

66

59

63

68

60

73

46

69

59

J

L

2j m d

268

62

32

74

420

96

80

26

100

100

185

100

m

PR

1 pH 13

[%]

20CO

phenole content o f feec



u

2

aldehyde

2

H

3

3

5

3

2

3

2

3

2

CH OH,H 0

2° DMSO,H 0

2

DMSO,H 0

99

Ap = 50 bar T = 25°C

PVA

CH OH,H 0 99 PVB C H OH,DMI PVAC CH OH, CH COCH

dialdehyde

adipic-

PVA

2

H0

2

57

cone, [^-j

80

65

63

99 55 33

97

95

63

50

38

81

93

96

78

f

62

3

CH OH H 0

400

96

66

30000

70

66

2000

2

Na S

[%]

DMS0,H Q

glutar-

97

485

phenole a pH 13

R E T E N T I O N

PVA

2

o ft

H0

w

o

i—i

CD >

o m

glyoxal

Dicarbonyl compound i n the crossl i n k i n g solution

35

32

36

50

56

53

24

30

26

10

30

30

28

14

8

17

3

P y r i - NH dine 13000 2400

Table IV: membranes c r o s s - l i n k e d by d i c a r b o n y l

485

90

60

80

55

60 70 140 300

85

70 150

80

60

70

2000

82

75

30000

phenole a t pH 13

P R O D U C T

compounds


65

70

80

97

82

80

95

90

400

2

Na S

3

125

140

100

90

65

70

100

120

85

320

110

90

80

90

140

40

P y r i - NH dine 130CO 2400

F L U X [-y-]

to oo 00

17.

PETER

AND


Table V


STEFAN

289

Separating performance bf PVA c r o s s - l i n k e d membranes for certain solvents

ISOBUTYL METHYL KETONE

N-BUTYL- METHYLACETATE ACETATE

19 OOO SSL

9 OOO SSL

3 300 53. 9 500 *5. 6 4oo

R PR

R PR

R PR

R PR

R PR

R PR

35 120

75 80

35 IOO

45 105

60 200

70

90

DMSO

sa 40 OOO ^ \

•

..J Ap = 50 bar

t = 25°C

R [%]

PR [ — ^ — 1 md

Table VI g i v e s the r e t e n t i o n and product f l u x of a PVA crossl i n k e d membrane f o r the organic and i n o r g a n i c compounds i n e f f l u e n t from a coking p l a n t . Several membranes w i t h good v a l u e s f o r the r e t e n t i o n o f organic and i n o r g a n i c compounds were i n v e s t i g a t e d by reverse osmosis experiments w i t h the e f f l u e n t s from the manufacture of organic intermediate products. The composition o f the e f f l u e n t s were complex w i t h a n a l y s i s a s f o l l o w s : Type B

pH = 9

i o n concentration Type C pH = 8

ion

concentration

TOC COR BOD^ D

TOC COR BOD,,

14 40 1 51 14 40 6 67

OOO 800 900 000 600 400 OOO 725

[mg/1]

The t e s t s were c a r r i e d out under the f o l l o w i n g c o n d i t i o n s : a) a t room temperature and 50 bar and 85 bar r e s p e c t i v e l y b) a t 42°C and 50 bar. Each t e s t l a s t e d a week. I n a l l cases no change i n the r e t e n t i o n or f l u x was observed during the experiment. The f o l l o w i n g r e t e n t i o n values were obtained a t a product f l u x o f about 20 l i t r e / ( m d ) and were found t o be independent o f the pH value o f waste: 2

phenolic TOC SO " 2

compounds

60-90% 60-70% 76-82%



57

18

IV

V

10

17

14

14

12000 [SSL]

sulphide

62

56

62

54

5000

15

26

21

24

ammonia i n ammonia salts 65000 [SSL]

w a t er

[SSL]

ammonia free

[%]

w a s t e

Ap = 50 bar T = 25°C

+ p h e n o l i c OH-groups i n phenol e q u i v a l e n t s

66

58

II

III

67

I

isooo

membrane

+

[SSL]

phenolic OH-groups

Type o f

i

c o k e r y

RET E N T I 0N

F e e d

0.961

0.080

0.450

0.043

0.048

[ ™ ]

FLUX 3

PRODUCT

m

m

35

59

69

72

77

4500 [3&]

6.262

0.432

0.860

0.415

0.292

+

PR [ 2 ] md

p h e n o l i c OH-groups

R

of c r o s s - l i n k e d PVA-membranes i n waste water from a coke p l a n t

Table V I : Retention and product f l u x w i t h regard t o organic and i n o r g a n i c compounds


to

O

17.

P E T E R AND

STEFAN


291

A f t e r the i n v e s t i g a t i o n i n t o the h a n d l i n g and the a c t i o n of the most important reagents has been completed, f u r t h e r r e s e a r c h can be done t o improve those methods t h a t are most promising. I n i t i a l t r i a l s have r e s u l t e d i n membranes g i v i n g a f l u x o f 1 m /(m d) and a phenol r e t e n t i o n o f 70% f o r a phenol c o n c e n t r a t i o n o f 2 g / l i t r e a t pH = 1 3 . Membranes c r o s s l i n k e d by d i c a r b o n y l compounds have been found t o possess h i g h thermal s t a b i l i t y ; r e t e n t i o n and product f l u x remained u n a l t e r e d a f t e r one week o f t e s t i n g i n an phenol s o l u t i o n o f 2 g / l i t r e a t 50°C. I t i s worth remarking w i t h regard t o the treatment of e f f l u e n t s discharged a t h i g h temperature, t h a t the thermal s t a b i l i t y o f these membranes makes heat r e c y c l i n g by means o f reverse osmosis a p o s s i b i l i t y . T h i s work was supported by the M i n i s t e r i u m f u e r Forschung und Technologie (BMFT) o f the German F e d e r a l Government.


3

-linking

Abstract: Asymmetrical membranes were initially produced from p o l y v i n y l a l c o h o l s o f suitable m o l e c u l a r weight u s i n g phase -inverted precipitation. They were then t r e a t e d w i t h a c i d s o l u t i o n s o f sodium formate and sodium a c e t a t e . The asymmetrical s t r u c t u r e was stabilised as a result o f the slight cross of the polymers produced. A cross-linked membrane so prepared can then be made i n s o l u b l e in water and permanent in the presence o f s o l v e n t s by f u r t h e r c r o s s - l i n k i n g . T h i s was e f f e c t e d by treatment w i t h v a r i o u s compounds c o n t a i n i n g one or two aldehyde groups o r w i t h one or more c a r b o x y l groups (saturated and unsaturated d i c a r b o x y l i c and tricarboxylic a c i d s ) ; in this wayiswas p o s s i b l e t o m a i n t a i n the primary asymmetry completely. The chemical activity, c h a i n l e n g t h and c h a i n s t r u c t u r e o f the individual compounds used r e s u l t e d in different degrees of c r o s s - l i n k i n g o f the polyvinyl a l c o h o l s in the membran. The c r o s s - l i n k e d membranes produced have good chemical, mechanical and thermal durability in an pH - range of 1 - 1 4 . The membranes have been t e s t e d in reverse-osmosis experiments in aqueons s o l u t i o n s o f phenols, methyl i s o b u t y l ketone, a c e t i c a c i d e s t e r s e t c . The r e t e n t i o n and p e r m e a b i l i l y p r o p e r t i e s in the presence o f the above-mentioned s o l v e n t s are r e p o r t e d . Literature Cited 1) F. K a i n e r , P o l y v i n y l a l k o h o l e , Ferdinand Enke V e r l a g Stuttgart

(1949)

2)

S.Peter, N. 1 6 1 - 1 6 7 ; S. Fresh Water 3) S. Loeb, S.

Hese, R. S t e f a n , D e s a l i n a t i o n , 1 9 (1976) P e t e r , R. S t e f a n , Proc. 6 th I n t . Symp. from the Sea, V o l . 3 (1978) 2 3 9 - 2 4 6 ; S o u r i r a j a n , Advanced Chem. S e r i e s 38 (1962) 1 1 7 .

4)

DOS 2441 311

5)

N. Hese, T h e s i s (1976)

RECEIVED

( 1 9 7 4 ) ; DOS 27 30 528

(1977)

Erlangen

December 4, 1980.


Synthetic Membranes: Volume II - American Chemical Society

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