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The development of cyanoethyl CA membrane for reverse osmosis
Desalination, 56 (1985) 191--202
191
Elsevier S c i e n c e P u b l i s h e r s B . V . , A m s t e r d a m - - P r i n t e d in T h e N e t h e r l a n d s
THE DEVELOPMENT OF CYANOETHYL CA NDEMBRANE FOR REVERSE OSMOSIS
HE CHANGSHEN and ZU XUEMING The Development Center of Desalination and Water Treatment Technology P.O.
Box 75 Hangzhou (The People's Republic of China)
ABSTRACT The membrane material of the cellulose acetate was prepared from cellulose by the reactions of esterification and etherification,
and
modified chemically and structurally by introducing a low d.s. specific functional group. This paper is primarily concerned with the optimal composition of the casting solution for cyanoethyl CA membrane which has been chosen by the method of orthogonal design. The fabrication technology of the membrane and the factors influencing membrane performance were investigated.
The cyanoethyl
bacteria-resistance,
CA ~as not only better performance of
better toughness and larger flux, but also exce-
llent resistance to inorganic acids comparing with the CA membrane.
INTRODUCTION The membrane material of cyanoethyl CA is a new material in which the structure and properties of Cellulose Acetate (CA) was modified by introducing
low d.s. specific functional groups. The performanmes
of Reverse Osmosis (RO) membranes were dependent on the membrane materials. Various equipments and the materials of the Reverse Osmosis membranes
have emerged in succession with uninterrupted progress of
the RO separation technology(ref,
I-5).
At present,
widely used. Because they have responsive hydrolysis, and erosion by microorganisms, larger restriction.
Therefore,
the CA was compaction,
their applications are subjected to all kinds
of CA membrane materials
modified have been investigated by many scientists
(ref. 6-18).
This paper present~, on the basis of the work of M.A.EL-TARABOUI~I et al (re~. 15), information about modified membrane using domestic materials and suitable membrane preparation technology.
192
Reverse Osmosis membranes
were successfully
soluble cyanoethyl CA having !.$.0.39. performance
prepared from acetone-
The membranes have excellent
of the biodegradation-resistance
and the inorganic
acid-
resistance.
EXPERIMENT I. Materials
and reagents
Cyanoethyl CA Cellulose
Guangzhou Institute of C h e m i s t r y
acetate
Shanghai Qunli Plastics Plant
Acetone
(A.R)
Hangzhou ChloroPhYl Factory
Stainless Cell
Second Institute Hangzhou
DDS-LLa Type
Shanghai Second Analysis Instrument Plant
2. Preparation
of Oceanography,
of casting solution and technique
of membrane making
The eyanoethyl CA membranes were made by loeb-sourirajan cyanoethyl CA and a mixture of solvent and additive(ref.15) solution was cast at room temperature evaporation.
from etc. The
to control the rate of acetone
After a given evaporation
period,
the film was immersed
in a water bath for I hour at I-3°C, Then it was followed by a heat treatment at 70°C for a given time. 3. Evaluation of membrane performance The evaluation
equipment consisted
in several test cells and high
pressure pump etc. The membrane were fixed in several cells to determine salt rejection and flux, its evaluation
condition as follow:
Effective membrane
area (cm 2)
4O
Operation pressure
(kg/cm2)
30 Hangzhou
Raw water Feed temperature Feed velocity
tap Water
(°C)
5-25
(cm/s)
The water quality are determined
40-50 by DDS-11
type conductometer.
RESULTS AND DISCUSSION The composition
of the casting solution,
tion and the membrane performance
the casting membrane condi-
193
The effect of the composition of the casting solution and the membrane preparation condition on membrane performsnce Table I shows effects of various polymer concentration on membrane performance. It can be also seen from table I that salt rejection increase while flux decrease with increases of the polymer concentration. The membranes had larger flux ~nd lower salt rejection when the polymer concentration was less than 18%. Even though salt rejection did not much change, considerable variations of flux was obs@rved when concentration was more than 22%. The membrane performance and its toughness was better when polymer concentration was 18-22%. TABLE I Effect of the polymer concentration Concentration of the polymer (%)
Salt rejection(%)
Flux(ml/cm~,hr.)
15
50.9
18
85.7
20.I 9.2
2o
89.5
7.7
22
91.8
6.0
25
91.8
5.O
Effect of the additivs on the membrane perf0rmance In order to prepare the reverse osmosis membrane having certain salt rejection and flux,
the effective porosity of membrane was usua-
lly controlled by the evaporation time or the additives. rials,
e.g. the ester, alcohol, aldehyde,
9-10 mate-
acid amine and water, can
be chosen as the additives. It is found that better memtrane performance could be all obtained for these additives, given in Fig.1.
The results a r e
Fig I shows that the membrane performance varies with the variation of the casting solution concentration.
So by varying of the
polymer concentration and selecting suitable formula,
the expectable
performance of the membrane can be acquired. Composition of castin ~ solution There are many factors, affecting membrane performance. nt of various compositions sting membrane condition.
The conte-
is a main factor in addition to the caTo optimize the formula of the casting so-
lution. The method of Lg ( ~
orthogonal design have been put forward.
Its results show in table 2.
[94
6o 50
4.0
S
,v~
i
i
i
i
95 9o 85 80
Q£ 75
J
/ 15
20
Z5
3o
3
4
5
6
9
12
15
IB
(Wt%)
Fig.1 Effects
of additives on m e m b r a n e p e r f o r m a n c e
Fig.2 shows the r e l a t i o n b e t w e e n various factors with the re~ection and flux of synthetic balance. A B C D were chosen as the basic formula of casting m e m b r a n e c o n d i t i o n and m e m b r a n e characte[ stic test.
195
TABLE 2 Lg (3 @) orthogonal design table Test polymer additives No. I
A I
B 1
C I
D I
89.5
2
"1
2
2
2
85.7
9.2
3 4 5 6 7 8 9
I 2 2 2 3 3 3
3 1 2 3
3 2 3 1 3 I 2
3 3 I 2 2 3 I
75.9 91.7 87.h 90.A 90.7 91 .I 91.2
13.5 4.4 7.7 6.6 ~.8 6.0 6.8
1
2 3
251 .I 269.5 273.0 83.7 89.8 91.0 7.3 30.8 18.7 19.6 10.3 6.2 6.5 4.1
271.9 264.2 257.5 90.6 88.1 85.4 4.8 19.3 22.9 26.9 6.4 7.6 9.0 2.6
271.0 268.6 254.0 90.3 89.5 84.7 5.6 20.7 20.4 28.0 6.9 6.8 9.3 2.5
8.1
268.1 266.8 258.7 89.4 88.9 86.2 3.2 22.6 22.6 23.9 7.5 7.5 8.3 0.5
The effect of the evaporatipn time The evaporation time is one of the important factor that influences the membrane performance. Table 3 shows small varying in the membrane performance when evaporation time was 90 second& The remarkable increase of osmosis of water and sE~It were observed with the increase of evaporation time when the evaporation time was more than 90 second. The better evaporation time was 30-60 second. TABLE 3 The effect of the evapor@tion time on membrane performance Evaporation ~ime (sec) I 0 15 30 60 90 120 130 Performance l flux of memb. I (ml/cm~hr.) 8.7 6.9 7.8 7.7 9.0 15.2 15.3 I
IRejection
87.1
90.5
90.3
91.4
84.5
49.5
45.~
196
80 ~
~ j
"~
1
80
an
*
/8
2o
22
i
20
Fig.2 Lg(3 4) orthogonal
l~
30
I
4
#.~
5.o
6
7
8
analysis
Effect of heat treatment temperature and time CA membranes for sea water should generally undergo the heat treatment of high temperature
but CA membrane
for ultrafiltration
membranes should not require heat treatment, and membrane for brackish water require only suitableitreatment at low or middle temperature. After treatment at a certain temperature,
the membrane skin
became denser, thus contributed to the salt rejection. The results showed in Fig.3 As illustrated in Fig.3, with the increases of the treatment temperature, the salt rejection increase while the flux decrease no matter how long time was took. The membrane when treatment
got worse performance
temperature was ibelow 65°C. the salt rejection
increased ripidly when treatment temperature was higher than 65"C. The salt rejection tended to balance but evident decrease in flux when the temperature
was higher than 70"C. The suitable temperature
19~
of heat t r e a t m e n t
was
65-70~C
7o' I/' ///
and the time was 10-20 minutes.
a.,-
- \'.
°c
Fig.
3 The effect
of the heat
treatment
time
on the m e m b r a n e
performance
C H A R A C T E R I S T I C S OF C Y A N E T H Y L CA M E M B R A N E Biochemical characteristics Chemical stability the resistance to chemicals for CA membrane was poorer than non-cellulose ester membrane. nce maintained fairly short time to NaO~,
The membrane performa-
ethyl acetate,
cyclohexa-
none and IONno~ when cyanoethyl CA and CA membranes were immersed in those chemical reagents in table 4. Two membranes were dissolved when they were immersed in ethyl acetate cyclohexanone for a month. Only the cyanoethyl CA membrane has better oerformance of the resistance to acid than CA membrane.
This new discovery has aroused our
interest. Resistance to PH
As is stated above,
the cyanoethyl CA membrane
has better resistance to acid property than CA membrane. In order to verifz the ability of this membrane's resistance to acid, effect of feed solution PH on cyanoethyl CA membrane performance were investigated. The results are shown in Fig.4 The experiment was carried out for 2 hours and PH=2,
respectively,
in feed of PH=7, PH=3
and then continually run for 3 hours in feed
which was adjusted up to PH=IO by adding NaoH solutiom.
The results
showed the highest salt rejection of the membrane emerged in neutral ~olution. The salt rejection decreased obviously with PH reduction of the feed. The CA membrane had more decrease than cyanoethyl CA membrane for example,
the decrease of salt rejection for cyanoethyl
198
CA membrane was 15% whereas CA membrane decrease of salt rejectionfor
was 40.26% ;When PH=3,
cyanoethyl
CA membrane
was only 17.8%
whereas CA membrane was 54.45 when PH=2. Therefore resistance
to
acids of cyanoethyl CA membrane was superior to CA membrane.
In orde
to examine ability of resistance
they
were immersed table 5.
to acid for both membranes,
in HCI solution of PH=2 or more. The results
show
in
TABLE 4 Chemical stability of cyanoethyl CA and CA membranes Reagent
Immersing time(day)
3.5%
NaCI
85
0.3%
HCI
85
0.3% NaOH
85
0.5% K 2 C q O T
85
0.5% lqMnO~
30
30% alcohol
85
30% ethylene glycol methyl ether
85
cyanoethyl CA memb. suitable use
CA memb. suitable use
"
not
not
not
suitable use
suitable use
not
not
suitable
use
suitable
';
30% etLyl acetate
30
not
not
30% cyclohexa~one
30
not
not
TABLE 5 Resistance Immersing time (day)
0
to acid performance
of cyanoethyl CA membrane
cyanoethyl CA membrane Flux 2 Salt rejection (ml/cm -hr) ( % ) 7.0
CA membrane Flux 2 Salt (ml/cm .hr) rejection
86.8
4.7
81.2
I0.4
39.2
36
6.5
88.2
85
6.8
85.0
15o
8.7
86.9
18o
9.9
79. I
Table 5 shows that there were considerable variations membrane performance whereas brane performance
use
;;
this variations
in CA
in cyanoethyl CA me-
haven't been observed when they were immersed in
HC1 solution for one month. But evident increases
in flux were obse-
rved after they were immersed for five months. Therefore
the conclu-
199
sion can be reached that ~@llulose acetate modified chemically by introducing O-cyanoethyl group enabled the cyanoethyl membrane having far better resistance to acid performance
than CA mem~:rane.
Thus , adjusting acidity of the feed may obtaine~ high water productivity in module. Resistance ~olymers,
to bacteria
The cellulose acetate belongs to ester
and is easily eroded and hydrolyzed by microorganisms.
Its
membrane performance would be subjected to deterioration. Thus, the membrane can't be stored for long term, and its applications were confined in a smaller extent. When cyanoethyl CA and CA membrane were limmersed in the solution containing acetate bacteria, gliotoxin bacteria and in black sewage,
it is found that effect of black sewage
on membrane performance were greater than the others two solution. The results are presented in table 6. TABLE 6 Resistance to bacteria performance of the cyanoethyl CA membrane Immersing time(day)
bacteria species
Cyanoethyl CA memb. Flux 2 Salt reje(ml/cm .hr) ction (%)
Flux ^ salt (ml/cmZ.hr) rejection
(%)
0
0
7.0
86.8
4.7
81.2
10
black sewage
7.4
87.6
10.5
43.3
20
black sewage
6.9
76.1
44.4
0.4
black sewage
10.1
78.8
30 30
acetate bacteria
6.9
87.0
4.7
82.0
30
gliotoxin bacteria
7.1
86.8
6.5
54.8
Table 6 shows that the property of resistance t o ~acteria of cyanoethyl
CA membrane were greatly superior to CA membrane, which
agreed with the argument of M.A EL-T&BABOOLSI et al. Therefore,
the
problem of long-term storage and use for membrane have been solved.
Resistance to heat property The cellulose ester was not only affected by the microorganisms,
200
PH and pressure but also by temperature. flux and selectivity
Table 7 shows that the
increased with the temperature
rising of the
feed. Cyanoethyl CA membrane have larger flux than CA membrane at 40°C, but both membrane performance Therefore, obtained
rising temperature
were constant a~ more than 40°C.
of the feed up to 40°C or more may
better membrane performance.
TABLE 7 Relationship
of feed temperature
and membrane
performance
Feed temperature
(°C)
20
40
50
60
Cyanoethyl CA
Flux (ml/cm2-hr)
6.9
10.2
11.1
11.1
membl.ane
Salt rejection(%)
89.5
92.0
92.5
93.5
CA membrane
Flux (ml/cm2-hr)
4.7
6.3
6.6
6.6
Salt rejection(%)
77.9
83.7
83.4
87.0
Physical
characteristic
The ~ u x
run time at a given pressure.
decreased with increases
For low pressure membrane,
nal flux is low, and its flux can approach period.
Generally,
of
the origi-
constant in a shorter
it can reach the constant value in 60 minutes.
But it required 27 hours to reach constant rejection for cyanoethyl CA membrane while 27-39 hours for CA membrane (see table 8). It shows that cyanoethyl CA membrane structure were more compact and stable than CA membrane. TABLE 8 Pressure-resistance Run time (hours)
performance of membrane
Pressure (kg/cm 2 )
CA memb.
Cyanoethyl CA memb. Flux(ml/cm2.hr)
rejection(%)
Flux 2 (ml/cm .hr)
rejection(%)
3
30
6.9
85.1
6.2
75.0
7
30
7.1
88.5
6.4
77.0
15
30
7.0
91.5
6.3
81.4
27
30
6.7
93 .I
6.3
81.9
39
30
6.4
93.9
6.0
82.6
52
30
6.8
93.1
6.2
83.4
100 hours run experiment Cells.
_
The membranes
were fixed in two test
Test was car~i?d out by method of accumulating
rrupted run at 30 kg/cm 2 pressure.
time and inte-
The, results show in Fig. 5.
201 9.o
[ I
~.~//
.--o....-.
"- ...
E
5.0
2
.~
4-
5
6
7
~,
9
1o
pH Fig.4
Relation
between
the
feed
PH a n d
the
membrane
performance
It can be seen from Fig.5 the flux was more stability when test was conducted interruptedly for 11 days (accumulative time 100 hours) Runnung for first 40 hours the salt rejection increased contiunally with time. The membrane performance tend to constant. The time required for the constant was shorter for the cyanoethyl CA membrane (27 hours)
than for CA membrane
(39 hours).
CA membrane have better structure
Therefore,
and resistance
cyanoethyl
to pressure
property.
1o.0
9,o
6.0 To
c~-~
8~
E
6.0
80 ~
"
CA T5
~0 i
I0
i
i
i
i
50
i
i
i
i
i
100
i
Io
Fig. 5 The running test result for 100 hours
~
i
50
i
i
i
i
i
~o (Ar~
202
CONCLUSION I. The reverse osmosis membranes having salt rejection about 90% and flux 7 ml/em2, hr were successfully prepared from acetonesoluble cyano~thyl CA contaning d.s. 0.39 cyanoethyl groups by 2.
Loeb-Sourirajan technology. Cyanoethyl CA membrane has excellent property of resistance to bacteria and resistance to acid. Their properties kept basically constant when they were stored and run in the liquid bred microorganisms or solution of PH=2 for five months. The membrane still maintained fairly stable performance (satl rejection was 86.9%, flux was 8.7 ml/cm 2. hr).
REFERENCE I. S. Sourirajan, "Reverse Osmosis", Logos Press London, Second Impression 1971. 2. Lonsdale, H.K. et al, "Reverse Osmosis ~embrane Research" Plenum Press, N.Y.~ London pp503 1972. 3. 4. 5.
27, Cantor, P.A, et al, O.S.W, No, 340, 1976. Kaup, R.E.C, Chem. Eng.~SD, 46-75, 1973.
6. 7o
0.S.W. NO, 386. 5th Inter. Syrup. On Fresh Water from the Sea, Vol.4. 267-291,
1976. 8. O.S.W. No, 968. 9. O.S.W. No, 577. 10. Cannon. C.R., U.S.P., 3497072, 1970 11. King, W.M., et al., O.S.W. No. 682,1971. 12. Saltonstall, C.W., et al., O.S.W. No. 700~J971. 13. C.A. 72, 24464s,1970. 14. M.A.EL-Taraboulsi. et al., Carbonhydra±e Research 13. 1970. I 5. S. Loeb and S. Sourirajan, University of California, Department of Engineering, Progress Report, No. 60-6, 1960 17. C.A. 77, 63595h 18. C.A. 77. 118062q
1972 1972
191
Elsevier S c i e n c e P u b l i s h e r s B . V . , A m s t e r d a m - - P r i n t e d in T h e N e t h e r l a n d s
THE DEVELOPMENT OF CYANOETHYL CA NDEMBRANE FOR REVERSE OSMOSIS
HE CHANGSHEN and ZU XUEMING The Development Center of Desalination and Water Treatment Technology P.O.
Box 75 Hangzhou (The People's Republic of China)
ABSTRACT The membrane material of the cellulose acetate was prepared from cellulose by the reactions of esterification and etherification,
and
modified chemically and structurally by introducing a low d.s. specific functional group. This paper is primarily concerned with the optimal composition of the casting solution for cyanoethyl CA membrane which has been chosen by the method of orthogonal design. The fabrication technology of the membrane and the factors influencing membrane performance were investigated.
The cyanoethyl
bacteria-resistance,
CA ~as not only better performance of
better toughness and larger flux, but also exce-
llent resistance to inorganic acids comparing with the CA membrane.
INTRODUCTION The membrane material of cyanoethyl CA is a new material in which the structure and properties of Cellulose Acetate (CA) was modified by introducing
low d.s. specific functional groups. The performanmes
of Reverse Osmosis (RO) membranes were dependent on the membrane materials. Various equipments and the materials of the Reverse Osmosis membranes
have emerged in succession with uninterrupted progress of
the RO separation technology(ref,
I-5).
At present,
widely used. Because they have responsive hydrolysis, and erosion by microorganisms, larger restriction.
Therefore,
the CA was compaction,
their applications are subjected to all kinds
of CA membrane materials
modified have been investigated by many scientists
(ref. 6-18).
This paper present~, on the basis of the work of M.A.EL-TARABOUI~I et al (re~. 15), information about modified membrane using domestic materials and suitable membrane preparation technology.
192
Reverse Osmosis membranes
were successfully
soluble cyanoethyl CA having !.$.0.39. performance
prepared from acetone-
The membranes have excellent
of the biodegradation-resistance
and the inorganic
acid-
resistance.
EXPERIMENT I. Materials
and reagents
Cyanoethyl CA Cellulose
Guangzhou Institute of C h e m i s t r y
acetate
Shanghai Qunli Plastics Plant
Acetone
(A.R)
Hangzhou ChloroPhYl Factory
Stainless Cell
Second Institute Hangzhou
DDS-LLa Type
Shanghai Second Analysis Instrument Plant
2. Preparation
of Oceanography,
of casting solution and technique
of membrane making
The eyanoethyl CA membranes were made by loeb-sourirajan cyanoethyl CA and a mixture of solvent and additive(ref.15) solution was cast at room temperature evaporation.
from etc. The
to control the rate of acetone
After a given evaporation
period,
the film was immersed
in a water bath for I hour at I-3°C, Then it was followed by a heat treatment at 70°C for a given time. 3. Evaluation of membrane performance The evaluation
equipment consisted
in several test cells and high
pressure pump etc. The membrane were fixed in several cells to determine salt rejection and flux, its evaluation
condition as follow:
Effective membrane
area (cm 2)
4O
Operation pressure
(kg/cm2)
30 Hangzhou
Raw water Feed temperature Feed velocity
tap Water
(°C)
5-25
(cm/s)
The water quality are determined
40-50 by DDS-11
type conductometer.
RESULTS AND DISCUSSION The composition
of the casting solution,
tion and the membrane performance
the casting membrane condi-
193
The effect of the composition of the casting solution and the membrane preparation condition on membrane performsnce Table I shows effects of various polymer concentration on membrane performance. It can be also seen from table I that salt rejection increase while flux decrease with increases of the polymer concentration. The membranes had larger flux ~nd lower salt rejection when the polymer concentration was less than 18%. Even though salt rejection did not much change, considerable variations of flux was obs@rved when concentration was more than 22%. The membrane performance and its toughness was better when polymer concentration was 18-22%. TABLE I Effect of the polymer concentration Concentration of the polymer (%)
Salt rejection(%)
Flux(ml/cm~,hr.)
15
50.9
18
85.7
20.I 9.2
2o
89.5
7.7
22
91.8
6.0
25
91.8
5.O
Effect of the additivs on the membrane perf0rmance In order to prepare the reverse osmosis membrane having certain salt rejection and flux,
the effective porosity of membrane was usua-
lly controlled by the evaporation time or the additives. rials,
e.g. the ester, alcohol, aldehyde,
9-10 mate-
acid amine and water, can
be chosen as the additives. It is found that better memtrane performance could be all obtained for these additives, given in Fig.1.
The results a r e
Fig I shows that the membrane performance varies with the variation of the casting solution concentration.
So by varying of the
polymer concentration and selecting suitable formula,
the expectable
performance of the membrane can be acquired. Composition of castin ~ solution There are many factors, affecting membrane performance. nt of various compositions sting membrane condition.
The conte-
is a main factor in addition to the caTo optimize the formula of the casting so-
lution. The method of Lg ( ~
orthogonal design have been put forward.
Its results show in table 2.
[94
6o 50
4.0
S
,v~
i
i
i
i
95 9o 85 80
Q£ 75
J
/ 15
20
Z5
3o
3
4
5
6
9
12
15
IB
(Wt%)
Fig.1 Effects
of additives on m e m b r a n e p e r f o r m a n c e
Fig.2 shows the r e l a t i o n b e t w e e n various factors with the re~ection and flux of synthetic balance. A B C D were chosen as the basic formula of casting m e m b r a n e c o n d i t i o n and m e m b r a n e characte[ stic test.
195
TABLE 2 Lg (3 @) orthogonal design table Test polymer additives No. I
A I
B 1
C I
D I
89.5
2
"1
2
2
2
85.7
9.2
3 4 5 6 7 8 9
I 2 2 2 3 3 3
3 1 2 3
3 2 3 1 3 I 2
3 3 I 2 2 3 I
75.9 91.7 87.h 90.A 90.7 91 .I 91.2
13.5 4.4 7.7 6.6 ~.8 6.0 6.8
1
2 3
251 .I 269.5 273.0 83.7 89.8 91.0 7.3 30.8 18.7 19.6 10.3 6.2 6.5 4.1
271.9 264.2 257.5 90.6 88.1 85.4 4.8 19.3 22.9 26.9 6.4 7.6 9.0 2.6
271.0 268.6 254.0 90.3 89.5 84.7 5.6 20.7 20.4 28.0 6.9 6.8 9.3 2.5
8.1
268.1 266.8 258.7 89.4 88.9 86.2 3.2 22.6 22.6 23.9 7.5 7.5 8.3 0.5
The effect of the evaporatipn time The evaporation time is one of the important factor that influences the membrane performance. Table 3 shows small varying in the membrane performance when evaporation time was 90 second& The remarkable increase of osmosis of water and sE~It were observed with the increase of evaporation time when the evaporation time was more than 90 second. The better evaporation time was 30-60 second. TABLE 3 The effect of the evapor@tion time on membrane performance Evaporation ~ime (sec) I 0 15 30 60 90 120 130 Performance l flux of memb. I (ml/cm~hr.) 8.7 6.9 7.8 7.7 9.0 15.2 15.3 I
IRejection
87.1
90.5
90.3
91.4
84.5
49.5
45.~
196
80 ~
~ j
"~
1
80
an
*
/8
2o
22
i
20
Fig.2 Lg(3 4) orthogonal
l~
30
I
4
#.~
5.o
6
7
8
analysis
Effect of heat treatment temperature and time CA membranes for sea water should generally undergo the heat treatment of high temperature
but CA membrane
for ultrafiltration
membranes should not require heat treatment, and membrane for brackish water require only suitableitreatment at low or middle temperature. After treatment at a certain temperature,
the membrane skin
became denser, thus contributed to the salt rejection. The results showed in Fig.3 As illustrated in Fig.3, with the increases of the treatment temperature, the salt rejection increase while the flux decrease no matter how long time was took. The membrane when treatment
got worse performance
temperature was ibelow 65°C. the salt rejection
increased ripidly when treatment temperature was higher than 65"C. The salt rejection tended to balance but evident decrease in flux when the temperature
was higher than 70"C. The suitable temperature
19~
of heat t r e a t m e n t
was
65-70~C
7o' I/' ///
and the time was 10-20 minutes.
a.,-
- \'.
°c
Fig.
3 The effect
of the heat
treatment
time
on the m e m b r a n e
performance
C H A R A C T E R I S T I C S OF C Y A N E T H Y L CA M E M B R A N E Biochemical characteristics Chemical stability the resistance to chemicals for CA membrane was poorer than non-cellulose ester membrane. nce maintained fairly short time to NaO~,
The membrane performa-
ethyl acetate,
cyclohexa-
none and IONno~ when cyanoethyl CA and CA membranes were immersed in those chemical reagents in table 4. Two membranes were dissolved when they were immersed in ethyl acetate cyclohexanone for a month. Only the cyanoethyl CA membrane has better oerformance of the resistance to acid than CA membrane.
This new discovery has aroused our
interest. Resistance to PH
As is stated above,
the cyanoethyl CA membrane
has better resistance to acid property than CA membrane. In order to verifz the ability of this membrane's resistance to acid, effect of feed solution PH on cyanoethyl CA membrane performance were investigated. The results are shown in Fig.4 The experiment was carried out for 2 hours and PH=2,
respectively,
in feed of PH=7, PH=3
and then continually run for 3 hours in feed
which was adjusted up to PH=IO by adding NaoH solutiom.
The results
showed the highest salt rejection of the membrane emerged in neutral ~olution. The salt rejection decreased obviously with PH reduction of the feed. The CA membrane had more decrease than cyanoethyl CA membrane for example,
the decrease of salt rejection for cyanoethyl
198
CA membrane was 15% whereas CA membrane decrease of salt rejectionfor
was 40.26% ;When PH=3,
cyanoethyl
CA membrane
was only 17.8%
whereas CA membrane was 54.45 when PH=2. Therefore resistance
to
acids of cyanoethyl CA membrane was superior to CA membrane.
In orde
to examine ability of resistance
they
were immersed table 5.
to acid for both membranes,
in HCI solution of PH=2 or more. The results
show
in
TABLE 4 Chemical stability of cyanoethyl CA and CA membranes Reagent
Immersing time(day)
3.5%
NaCI
85
0.3%
HCI
85
0.3% NaOH
85
0.5% K 2 C q O T
85
0.5% lqMnO~
30
30% alcohol
85
30% ethylene glycol methyl ether
85
cyanoethyl CA memb. suitable use
CA memb. suitable use
"
not
not
not
suitable use
suitable use
not
not
suitable
use
suitable
';
30% etLyl acetate
30
not
not
30% cyclohexa~one
30
not
not
TABLE 5 Resistance Immersing time (day)
0
to acid performance
of cyanoethyl CA membrane
cyanoethyl CA membrane Flux 2 Salt rejection (ml/cm -hr) ( % ) 7.0
CA membrane Flux 2 Salt (ml/cm .hr) rejection
86.8
4.7
81.2
I0.4
39.2
36
6.5
88.2
85
6.8
85.0
15o
8.7
86.9
18o
9.9
79. I
Table 5 shows that there were considerable variations membrane performance whereas brane performance
use
;;
this variations
in CA
in cyanoethyl CA me-
haven't been observed when they were immersed in
HC1 solution for one month. But evident increases
in flux were obse-
rved after they were immersed for five months. Therefore
the conclu-
199
sion can be reached that ~@llulose acetate modified chemically by introducing O-cyanoethyl group enabled the cyanoethyl membrane having far better resistance to acid performance
than CA mem~:rane.
Thus , adjusting acidity of the feed may obtaine~ high water productivity in module. Resistance ~olymers,
to bacteria
The cellulose acetate belongs to ester
and is easily eroded and hydrolyzed by microorganisms.
Its
membrane performance would be subjected to deterioration. Thus, the membrane can't be stored for long term, and its applications were confined in a smaller extent. When cyanoethyl CA and CA membrane were limmersed in the solution containing acetate bacteria, gliotoxin bacteria and in black sewage,
it is found that effect of black sewage
on membrane performance were greater than the others two solution. The results are presented in table 6. TABLE 6 Resistance to bacteria performance of the cyanoethyl CA membrane Immersing time(day)
bacteria species
Cyanoethyl CA memb. Flux 2 Salt reje(ml/cm .hr) ction (%)
Flux ^ salt (ml/cmZ.hr) rejection
(%)
0
0
7.0
86.8
4.7
81.2
10
black sewage
7.4
87.6
10.5
43.3
20
black sewage
6.9
76.1
44.4
0.4
black sewage
10.1
78.8
30 30
acetate bacteria
6.9
87.0
4.7
82.0
30
gliotoxin bacteria
7.1
86.8
6.5
54.8
Table 6 shows that the property of resistance t o ~acteria of cyanoethyl
CA membrane were greatly superior to CA membrane, which
agreed with the argument of M.A EL-T&BABOOLSI et al. Therefore,
the
problem of long-term storage and use for membrane have been solved.
Resistance to heat property The cellulose ester was not only affected by the microorganisms,
200
PH and pressure but also by temperature. flux and selectivity
Table 7 shows that the
increased with the temperature
rising of the
feed. Cyanoethyl CA membrane have larger flux than CA membrane at 40°C, but both membrane performance Therefore, obtained
rising temperature
were constant a~ more than 40°C.
of the feed up to 40°C or more may
better membrane performance.
TABLE 7 Relationship
of feed temperature
and membrane
performance
Feed temperature
(°C)
20
40
50
60
Cyanoethyl CA
Flux (ml/cm2-hr)
6.9
10.2
11.1
11.1
membl.ane
Salt rejection(%)
89.5
92.0
92.5
93.5
CA membrane
Flux (ml/cm2-hr)
4.7
6.3
6.6
6.6
Salt rejection(%)
77.9
83.7
83.4
87.0
Physical
characteristic
The ~ u x
run time at a given pressure.
decreased with increases
For low pressure membrane,
nal flux is low, and its flux can approach period.
Generally,
of
the origi-
constant in a shorter
it can reach the constant value in 60 minutes.
But it required 27 hours to reach constant rejection for cyanoethyl CA membrane while 27-39 hours for CA membrane (see table 8). It shows that cyanoethyl CA membrane structure were more compact and stable than CA membrane. TABLE 8 Pressure-resistance Run time (hours)
performance of membrane
Pressure (kg/cm 2 )
CA memb.
Cyanoethyl CA memb. Flux(ml/cm2.hr)
rejection(%)
Flux 2 (ml/cm .hr)
rejection(%)
3
30
6.9
85.1
6.2
75.0
7
30
7.1
88.5
6.4
77.0
15
30
7.0
91.5
6.3
81.4
27
30
6.7
93 .I
6.3
81.9
39
30
6.4
93.9
6.0
82.6
52
30
6.8
93.1
6.2
83.4
100 hours run experiment Cells.
_
The membranes
were fixed in two test
Test was car~i?d out by method of accumulating
rrupted run at 30 kg/cm 2 pressure.
time and inte-
The, results show in Fig. 5.
201 9.o
[ I
~.~//
.--o....-.
"- ...
E
5.0
2
.~
4-
5
6
7
~,
9
1o
pH Fig.4
Relation
between
the
feed
PH a n d
the
membrane
performance
It can be seen from Fig.5 the flux was more stability when test was conducted interruptedly for 11 days (accumulative time 100 hours) Runnung for first 40 hours the salt rejection increased contiunally with time. The membrane performance tend to constant. The time required for the constant was shorter for the cyanoethyl CA membrane (27 hours)
than for CA membrane
(39 hours).
CA membrane have better structure
Therefore,
and resistance
cyanoethyl
to pressure
property.
1o.0
9,o
6.0 To
c~-~
8~
E
6.0
80 ~
"
CA T5
~0 i
I0
i
i
i
i
50
i
i
i
i
i
100
i
Io
Fig. 5 The running test result for 100 hours
~
i
50
i
i
i
i
i
~o (Ar~
202
CONCLUSION I. The reverse osmosis membranes having salt rejection about 90% and flux 7 ml/em2, hr were successfully prepared from acetonesoluble cyano~thyl CA contaning d.s. 0.39 cyanoethyl groups by 2.
Loeb-Sourirajan technology. Cyanoethyl CA membrane has excellent property of resistance to bacteria and resistance to acid. Their properties kept basically constant when they were stored and run in the liquid bred microorganisms or solution of PH=2 for five months. The membrane still maintained fairly stable performance (satl rejection was 86.9%, flux was 8.7 ml/cm 2. hr).
REFERENCE I. S. Sourirajan, "Reverse Osmosis", Logos Press London, Second Impression 1971. 2. Lonsdale, H.K. et al, "Reverse Osmosis ~embrane Research" Plenum Press, N.Y.~ London pp503 1972. 3. 4. 5.
27, Cantor, P.A, et al, O.S.W, No, 340, 1976. Kaup, R.E.C, Chem. Eng.~SD, 46-75, 1973.
6. 7o
0.S.W. NO, 386. 5th Inter. Syrup. On Fresh Water from the Sea, Vol.4. 267-291,
1976. 8. O.S.W. No, 968. 9. O.S.W. No, 577. 10. Cannon. C.R., U.S.P., 3497072, 1970 11. King, W.M., et al., O.S.W. No. 682,1971. 12. Saltonstall, C.W., et al., O.S.W. No. 700~J971. 13. C.A. 72, 24464s,1970. 14. M.A.EL-Taraboulsi. et al., Carbonhydra±e Research 13. 1970. I 5. S. Loeb and S. Sourirajan, University of California, Department of Engineering, Progress Report, No. 60-6, 1960 17. C.A. 77, 63595h 18. C.A. 77. 118062q
1972 1972