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Noble reverse osmosis composite membrane
Desalination, 96 (1994) 113-118 Elwvier Science B.V. Amsterdam -
113 Printed in The Netherlands
Noble reverse osmosis composite membrane Kenichi Ikeda’ and John Tomaschke? ‘NittoDenko Corporation, l-l-2, Shimohommi, lbaraki, Osaka (Japan) 2Hydranautics Inc., 8444 Miralani Drive, San Diego, CA (USA)
SUMMARY
New composite reverse osmosis (RO) membranes based on an m-phenylene diamine/l,2,3,4cyclopentane tetracarboxylic acid polyamide have been developed. These membranes exhibited the rejection of more than 99% and high flux. The durability of the membranes was influenced by the stereo structure of 1,2,3&cyclopentane tetracarbonyl chloride, and the membrane based on cis,trans,cis,trans-CPTC isomer indicated superior stability.
INTRODUCTION
Many kinds of RO membranes have been developed. Recently especially the performance improvement of thin film composite membranes as prepared by interfacial polycondensation are remarkable. Cadotte [l] originally had demonstrated the utility of interfacial polycondensation of trimesoyl chloride and m-phenylene diamine in preparing composite membranes with good properties. Sundet et al. [2] extended the original aromatic-aromatic polyamide chemistry of Cadotte and Peterson to aromatic-cycloaliphatic structures including the product of interfacial polyamidation. Specifically they replaced the trifunctional aromatic acyl halide with cyclohexane-1,3,5tricarbonyl chloride. OOll-9X4/94/$07.00 0 1994 Elsevier Science B.V. All rights reserved. SSDIOOll-9164(94)00027-L
114
US Patent 4,749,488 issued to Arthur et al. [3] discloses membranes of polyphenylene tetrahydrofuran-2,3,4,5tetracarboxyamide which may also include isophthalamide or terephthalamide units. Interestingly, examples of this patent describe a membrane prepared by reacting cyclopentane-1,2,3,4tetracarbonyl tetrachloride (CPTC) with m-phenylene diamine (MPD) which showed totally unacceptable salt rejection results compared to the membranes claimed in the patent. In this work we showed it is possible to prepare a membrane which showed acceptable salt rejection results by reacting CPTC with MPD; then we discovered the chlorine resistance of the membrane depends on the stereo structure of CPTC.
EXPERIMENTAL
Materials Monomers employed were obtained commercially except for the cyclopentane tetracarboxylic acid chloride. cis,trans,cis,cis-1,2,3,4cyclopentane tetracarboxylic acid (ctccCPTA) and cis,trans,cis,trans1,2,3,4_cyclopentane tetracarboxylic acid (ctctCPTA) were prepared from cis,cis,cis,cis-1,2,3,4_cyclopentane tetracarboxylic acid (ccccCPTA) by literature methods [4] (Fig. 1).
cc0
PC151 Heptane 65 ‘C
b
,,\\ co c I
4..
0 clco \\“
“/I COCI
ccccCPTC
PC151 Heptane 65 lc ctccCPTC
PC15 I Heptane 6s lc ctctCPTC
Fig. 1. CPTC synthetic pathway.
115
tetracarboxylic acid chloride cis,cis,cis,cis-1,2,3,4cyclopentane (ccccCPTC) was prepared by adding ccccCPTA to n-heptane containing phosphorous pentachloride in a round bottom flask fitted with a ,thermometer, heating mantle, reflux condenser, and stirrer. The temperature of reaction was increased gradually from 20°C to 65°C over a 3 h period. The temperature was maintained at 65°C for an additional 2rA h at which point no HCl gas evolution was detected. The obtained yellow solution was suction filtered through a coarse paper and then roto-evaporated to an oil several times using additional portions of heptane solvent. The amber colored oil was given high vacuum for an additional half hour and then extracted with several portions of anhydrous heptane to yield a 1% stock solution which may be diluted with further solvent to provide the desired concentration of reaction solution. The synthesis of cis,trans,cis,cis-1,2,3,4_cyclopentane tetracarboxylic acid chloride (ctccCPTC) and cis,trans,cis,trans-1,2,3,4_cyclopentane tetracarboxylic acid chloride (ctctCPTC) was carried out in substantially the same manner. Method of making and characterizing membranes Membranes were prepared by a method similar to the usual manner [ 11. A polysulfone substrate was impregnated with the amine solution containing MPD, triethylamine camphorsulfonic acid salt (TEACSA) and sodium dodecyl benzene sulfonate (SDBS) surfactant which was adjusted to a pH of 7.0 with HCl, and the surface was stripped of droplets. The loaded substrate was exposed to a solution of acid chloride in Isopar solvent (an isoparaffin mixture from Exxon Corp.) for a 5-10 s reaction period and dried in an air over for 5-30 min at 100°C. Membranes were characterized in cross-flow cells. The performance of the resulting water permeable membrane was measured by passing in aqueous solution containing 1500 ppm of NaCl (pH 6.5) through each membrane at 15 kg/cm2.
RESULTS AND DISCUSSION
The salt rejection and flux rates for the membranes are given in Table I. In spite of the sort of isomers, all the membranes exhibited more than 99% rejection and high flux.
116
TABLE I Membrane performance Ex.
Isomer
No. 1 2
9 10
CPTC
MPD
W
(96)
vol%)
TEACSA Surfactant (%I
pH
Rejection Flux
Flux
(%)
(m3/ m2/d)
(gfd)
(4%)
CCCCCPTC 0.1 0.1
2.0 2.0
1.0 1.0
0.3 0.3
7.3 7.3
99.1 99.2
0.9 0.9
23.0 23.0
ctcccPTc
0.1 0.1 0.1 0.1 0.1 0.1
2.0 2.0 2.0 2.0 2.0 2.0
1.0 1.0 1.0 1.0 3.0 3.0
0.3 0.3 0.3 0.3 0.3 0.3
7.3 7.3 7.3 7.3 7.3 7.3
99.2 99.4 99.3 99.1 99.5 99.6
0.9 0.8 1.1 1.1 1.5 1.4
21.8 19.8 26.8 26.8 37.0 34.5
ctctCPTC
0.1 0.1
2.0 2.0
6.6 6.6
0.3 0.3
7.3 7.3
99.4 99.5
1.2 1.1
31.0 27.8
Measuring condition: 25”C, 15 kg/cm2 (214 psig).
To evaluate the stability of the membrane, the chlorine exposure test is most typical because the polyamide membrane is susceptible to attack by chlorine. Fig. 2 shows the stability of three kinds of membranes which have different stereo structures. The ctctCPTC membrane was very stable, but the ccccCPTC membrane was not. The stability of the ctccCPTC membrane was intermediate. This phenomenon shows that the stereochemistry of the polycondensation polyamide membrane is important. Fig. 3 shows the geometric isomers of CPTC. The steric hindrance caused by the acid chloride groups of CPTC has an important effect on the reaction rate of the interfacial polycondensation. As a result, the crosslinking density of each polycondensation polyamide polymer may be different. The ctctCPTC has the lowest degree of steric hindrance, and the ccccCPTC has the highest one among the CPTC isomers. The steric hindrance of the ctccCPTC is intermediate. In spite of the different stereo structures of CPTC, the rejection of the CPTC membrane was more than 99%, so the degree of crosslinking density of the polyamide is not so low. However, the accelerated stability test using chlorine showed clearly that the difference of the stability depends on the stereo structures of the membrane.
117
100
*
0
‘:; \
(
ctctCPTC
+
ctcccPTc
L
CCCCCPTC
0
LOO
200
300
soo
400
600
700
800
900
LOO0
Exposure Time [h] Fig. 2. EC rejection vs. time of exposure to 1 ppm chlorine.
camIf,,. cc0
0
\\‘
*,,,\CICO "'klC0
CC0
ccccCPTC
\T CICO \\“
Q
"'klco
“‘~CICO
Cc0
CC0
**,,\ClCO CICO
CICO
If,,,
CICO \\‘c1:
ccctCPTC
a
cxo 4,.
cl!cCPTC
ctccCPTC CICO
Cc0 h;,.
,,,,\CICO
ClCO4,.
ccUCPTC
cc0 ctctCPTC
Fig. 3. Geometric isomers of CPTC.
CONCLUSIONS
The cyclopentane tetracarboxylic polyamide composite membrane provides high rejection and high flux at low pressure. The chlorine resistant test supports the conclusion that the stereochemistry of the CPTC is important for the design of long-range membrane stability.
118
REFERENCES 1 2 3 4
J.E. Cadotte, R.J. Peterson, R.E. Larson and E.E. Erickson, Desalination, 32 (1980) 25. S.A. Sundet, S.D. Arthur, D. Campos, T.J. E&man and R.G. Brown, Desalination, 64 (1987) 259. US Patent No. 4,749,488, 1988. German Patent No. 2105010, 1971.
113 Printed in The Netherlands
Noble reverse osmosis composite membrane Kenichi Ikeda’ and John Tomaschke? ‘NittoDenko Corporation, l-l-2, Shimohommi, lbaraki, Osaka (Japan) 2Hydranautics Inc., 8444 Miralani Drive, San Diego, CA (USA)
SUMMARY
New composite reverse osmosis (RO) membranes based on an m-phenylene diamine/l,2,3,4cyclopentane tetracarboxylic acid polyamide have been developed. These membranes exhibited the rejection of more than 99% and high flux. The durability of the membranes was influenced by the stereo structure of 1,2,3&cyclopentane tetracarbonyl chloride, and the membrane based on cis,trans,cis,trans-CPTC isomer indicated superior stability.
INTRODUCTION
Many kinds of RO membranes have been developed. Recently especially the performance improvement of thin film composite membranes as prepared by interfacial polycondensation are remarkable. Cadotte [l] originally had demonstrated the utility of interfacial polycondensation of trimesoyl chloride and m-phenylene diamine in preparing composite membranes with good properties. Sundet et al. [2] extended the original aromatic-aromatic polyamide chemistry of Cadotte and Peterson to aromatic-cycloaliphatic structures including the product of interfacial polyamidation. Specifically they replaced the trifunctional aromatic acyl halide with cyclohexane-1,3,5tricarbonyl chloride. OOll-9X4/94/$07.00 0 1994 Elsevier Science B.V. All rights reserved. SSDIOOll-9164(94)00027-L
114
US Patent 4,749,488 issued to Arthur et al. [3] discloses membranes of polyphenylene tetrahydrofuran-2,3,4,5tetracarboxyamide which may also include isophthalamide or terephthalamide units. Interestingly, examples of this patent describe a membrane prepared by reacting cyclopentane-1,2,3,4tetracarbonyl tetrachloride (CPTC) with m-phenylene diamine (MPD) which showed totally unacceptable salt rejection results compared to the membranes claimed in the patent. In this work we showed it is possible to prepare a membrane which showed acceptable salt rejection results by reacting CPTC with MPD; then we discovered the chlorine resistance of the membrane depends on the stereo structure of CPTC.
EXPERIMENTAL
Materials Monomers employed were obtained commercially except for the cyclopentane tetracarboxylic acid chloride. cis,trans,cis,cis-1,2,3,4cyclopentane tetracarboxylic acid (ctccCPTA) and cis,trans,cis,trans1,2,3,4_cyclopentane tetracarboxylic acid (ctctCPTA) were prepared from cis,cis,cis,cis-1,2,3,4_cyclopentane tetracarboxylic acid (ccccCPTA) by literature methods [4] (Fig. 1).
cc0
PC151 Heptane 65 ‘C
b
,,\\ co c I
4..
0 clco \\“
“/I COCI
ccccCPTC
PC151 Heptane 65 lc ctccCPTC
PC15 I Heptane 6s lc ctctCPTC
Fig. 1. CPTC synthetic pathway.
115
tetracarboxylic acid chloride cis,cis,cis,cis-1,2,3,4cyclopentane (ccccCPTC) was prepared by adding ccccCPTA to n-heptane containing phosphorous pentachloride in a round bottom flask fitted with a ,thermometer, heating mantle, reflux condenser, and stirrer. The temperature of reaction was increased gradually from 20°C to 65°C over a 3 h period. The temperature was maintained at 65°C for an additional 2rA h at which point no HCl gas evolution was detected. The obtained yellow solution was suction filtered through a coarse paper and then roto-evaporated to an oil several times using additional portions of heptane solvent. The amber colored oil was given high vacuum for an additional half hour and then extracted with several portions of anhydrous heptane to yield a 1% stock solution which may be diluted with further solvent to provide the desired concentration of reaction solution. The synthesis of cis,trans,cis,cis-1,2,3,4_cyclopentane tetracarboxylic acid chloride (ctccCPTC) and cis,trans,cis,trans-1,2,3,4_cyclopentane tetracarboxylic acid chloride (ctctCPTC) was carried out in substantially the same manner. Method of making and characterizing membranes Membranes were prepared by a method similar to the usual manner [ 11. A polysulfone substrate was impregnated with the amine solution containing MPD, triethylamine camphorsulfonic acid salt (TEACSA) and sodium dodecyl benzene sulfonate (SDBS) surfactant which was adjusted to a pH of 7.0 with HCl, and the surface was stripped of droplets. The loaded substrate was exposed to a solution of acid chloride in Isopar solvent (an isoparaffin mixture from Exxon Corp.) for a 5-10 s reaction period and dried in an air over for 5-30 min at 100°C. Membranes were characterized in cross-flow cells. The performance of the resulting water permeable membrane was measured by passing in aqueous solution containing 1500 ppm of NaCl (pH 6.5) through each membrane at 15 kg/cm2.
RESULTS AND DISCUSSION
The salt rejection and flux rates for the membranes are given in Table I. In spite of the sort of isomers, all the membranes exhibited more than 99% rejection and high flux.
116
TABLE I Membrane performance Ex.
Isomer
No. 1 2
9 10
CPTC
MPD
W
(96)
vol%)
TEACSA Surfactant (%I
pH
Rejection Flux
Flux
(%)
(m3/ m2/d)
(gfd)
(4%)
CCCCCPTC 0.1 0.1
2.0 2.0
1.0 1.0
0.3 0.3
7.3 7.3
99.1 99.2
0.9 0.9
23.0 23.0
ctcccPTc
0.1 0.1 0.1 0.1 0.1 0.1
2.0 2.0 2.0 2.0 2.0 2.0
1.0 1.0 1.0 1.0 3.0 3.0
0.3 0.3 0.3 0.3 0.3 0.3
7.3 7.3 7.3 7.3 7.3 7.3
99.2 99.4 99.3 99.1 99.5 99.6
0.9 0.8 1.1 1.1 1.5 1.4
21.8 19.8 26.8 26.8 37.0 34.5
ctctCPTC
0.1 0.1
2.0 2.0
6.6 6.6
0.3 0.3
7.3 7.3
99.4 99.5
1.2 1.1
31.0 27.8
Measuring condition: 25”C, 15 kg/cm2 (214 psig).
To evaluate the stability of the membrane, the chlorine exposure test is most typical because the polyamide membrane is susceptible to attack by chlorine. Fig. 2 shows the stability of three kinds of membranes which have different stereo structures. The ctctCPTC membrane was very stable, but the ccccCPTC membrane was not. The stability of the ctccCPTC membrane was intermediate. This phenomenon shows that the stereochemistry of the polycondensation polyamide membrane is important. Fig. 3 shows the geometric isomers of CPTC. The steric hindrance caused by the acid chloride groups of CPTC has an important effect on the reaction rate of the interfacial polycondensation. As a result, the crosslinking density of each polycondensation polyamide polymer may be different. The ctctCPTC has the lowest degree of steric hindrance, and the ccccCPTC has the highest one among the CPTC isomers. The steric hindrance of the ctccCPTC is intermediate. In spite of the different stereo structures of CPTC, the rejection of the CPTC membrane was more than 99%, so the degree of crosslinking density of the polyamide is not so low. However, the accelerated stability test using chlorine showed clearly that the difference of the stability depends on the stereo structures of the membrane.
117
100
*
0
‘:; \
(
ctctCPTC
+
ctcccPTc
L
CCCCCPTC
0
LOO
200
300
soo
400
600
700
800
900
LOO0
Exposure Time [h] Fig. 2. EC rejection vs. time of exposure to 1 ppm chlorine.
camIf,,. cc0
0
\\‘
*,,,\CICO "'klC0
CC0
ccccCPTC
\T CICO \\“
Q
"'klco
“‘~CICO
Cc0
CC0
**,,\ClCO CICO
CICO
If,,,
CICO \\‘c1:
ccctCPTC
a
cxo 4,.
cl!cCPTC
ctccCPTC CICO
Cc0 h;,.
,,,,\CICO
ClCO4,.
ccUCPTC
cc0 ctctCPTC
Fig. 3. Geometric isomers of CPTC.
CONCLUSIONS
The cyclopentane tetracarboxylic polyamide composite membrane provides high rejection and high flux at low pressure. The chlorine resistant test supports the conclusion that the stereochemistry of the CPTC is important for the design of long-range membrane stability.
118
REFERENCES 1 2 3 4
J.E. Cadotte, R.J. Peterson, R.E. Larson and E.E. Erickson, Desalination, 32 (1980) 25. S.A. Sundet, S.D. Arthur, D. Campos, T.J. E&man and R.G. Brown, Desalination, 64 (1987) 259. US Patent No. 4,749,488, 1988. German Patent No. 2105010, 1971.