Method for producing highly permeable composite reverse osmosis membrane

Disclosed is a method for producing a composite reverse osmosis membrane comprising the steps of coating a porous support with (A) a solution containing a compound having at least two reactive amino groups per molecule and bringing (B) a solution containing a polyfunctional acid halide into contact with the solution (A) to induce crosslinking to form a crosslinked polyamide skin layer, in which the crosslinking is carried out in the presence of a substance having a solubility parameter of 8 to 14 (cal/cm.sup.3).sup.1/2. The resulting composite reverse osmosis membrane exhibits high salt rejection and high water permeability.

FIELD OF THE INVENTION 
This invention relates to a method for producing a composite reverse 
osmosis membrane for selectively separating a component of a liquid 
mixture. More particularly, it relates to a method for producing a 
composite reverse osmosis membrane which is composed of a porous support 
having a thin film consisting mainly of a polyamide and which exhibits 
both high salt rejection and high permeability. 
The composite reverse osmosis membrane is suitable for production of 
ultra-pure water or desalting of seawater or brackish water. It makes a 
contribution to water reclamation in a closed system, in which waste water 
which would cause environmental pollution, such as waste water from dyeing 
or waste water from electrodeposition coating, is treated to remove 
contaminants or to recover effective substances. It is also useful for 
concentration of an effective ingredient in food industry. 
BACKGROUND OF THE INVENTION 
A composite reverse osmosis membrane composed of a porous support having 
formed thereon a thin film capable of selective separation is known as a 
reverse osmosis membrane, which is structurally different from an 
asymmetric composite reverse osmosis membrane. 
At present, many composite reverse osmosis membranes each having formed on 
a support a thin film comprising a polyamide obtained by interfacial 
polymerization of a polyfunctional aromatic amine and a polyfunctional 
aromatic acid halide are known, e.g., in JP-A-55-147106 (corresponding to 
U.S. Pat. No. 4,277,344), JP-A-62-121603 (corresponding to U.S. Pat. No. 
4,761,234), and JP-A-63-218208 (the term "JP-A" as used herein means an 
"unexamined published Japanese patent application"). In addition, a 
support having thereon a polyamide thin film obtained by interfacial 
polymerization of a polyfunctional aromatic amine and a polyfunctional 
alicyclic acid halide has also been proposed as disclosed, e.g., in 
JP-A-61-42308 (corresponding to U.S. Pat. No. 5,254,261). 
The conventional composite reverse osmosis membranes have high desalting 
performance and water permeability, and yet it has been demanded to 
improve the water permeability while retaining the high desalting 
performance for attaining higher efficiency. While various additives have 
been proposed as described, e.g., in JP-A-2-187135 (corresponding to U.S. 
Pat. No. 4,872,984) in order to meet the demand, the conventional 
composite reverse osmosis membranes are insufficient, still leaving the 
demand for higher water permeability unfulfilled. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a method for producing a 
composite reverse osmosis membrane possessing both high salt rejection and 
high water permeability. 
The object of the present invention is accomplished by a method for 
producing a composite reverse osmosis membrane comprising the steps of 
coating a porous support with (A) a solution containing a compound having 
at least two reactive amino groups per molecule and bringing (B) a 
solution containing a polyfunctional acid halide into contact with the 
solution (A) to induce crosslinking to form a crosslinked polyamide skin 
layer, in which the crosslinking is carried out in the presence of a 
substance having a solubility parameter of 8 to 14 (cal/cm.sup.3).sup.1/2 
(hereinafter simply referred to as substance S). 
In a preferred embodiment of the above method, substance S is least one 
member selected from the group consisting of alcohols and ethers. 
In another preferred embodiment of the above method, substance S is present 
in at least one of solution (A) and solution (B). 
In a still another preferred embodiment of the above method, substance S is 
present in the porous support before the contact between solution (A) and 
solution (B). 
In a yet another preferred embodiment of the above method, the step of 
bringing solutions (A) and (B) into contact with each other to induce 
crosslinking reaction is conducted at a temperature of 30.degree. to 
90.degree. C. 
In a further preferred embodiment of the above method, the crosslinking 
reaction is carried out by bringing solution (A) and solution (B) into 
contact with each other in a gas phase of substance S. 
DETAILED DESCRIPTION OF THE INVENTION 
The term "solubility parameter" as used herein denotes a value 
(.increment.H/V).sup.1/2 (cal/cm.sup.3).sup.1/2, wherein .increment.H is 
a molar heat of evaporation (cal/mol) of a liquid, and V is a molar volume 
(cm.sup.3 /mol). The solubility parameter can be obtained, for example, 
according to the method described in the item "Solubility Parameter 
Values" of "Polymer Handbook", third edition, edited by J. Brandrup and E. 
H. Immergut and published by John Willey & Sons, Inc. in 1989, and the 
solubility parameters of various solvents are shown on pages VII-526 to 
VII-532 of the document. 
According to the constitution of the present invention, in a method for 
producing a composite reverse osmosis membrane comprising the steps of 
coating a porous support with (A) a solution containing a compound having 
at least two reactive amino groups per molecule and bringing (B) a 
solution containing a polyfunctional acid halide into contact with the 
solution (A) to induce crosslinking to form a crosslinked polyamide skin 
layer, the presence of substance S in the site of the crosslinking 
reaction realizes production of a composite reverse osmosis membrane 
having both high salt rejection and high water permeability. 
It is preferable for assuring a particularly high salt rejection and 
particularly high water permeability that substance S be at least one 
member selected from the group consisting of an alcohol and an ether. 
It is preferable for obtaining an increased permeation flux to add 
substance S to at least one of solution B and solution A. Where substance 
S is added to solution A, it is preferably added in an amount of 10 to 50% 
by weight. If the amount is less than 10% by weight, the effect of 
increasing the permeation flux is liable to be insufficient. If it exceeds 
50% by weight, the rejection tends to be reduced. If added to solution B, 
substance S is added in an amount of 0.001 to 10% by weight. If the amount 
is less than 0.001% by weight, the effect of increasing the permeation 
flux is be liable to be insufficient. If it exceeds 10% by weight, the 
rejection tends to be reduced. 
It is preferable for obtaining a particularly high salt rejection and 
particularly high water permeability to previously impregnate a porous 
support with substance S before the step of bringing solution A and 
solution B into contact with each other. Impregnation of a porous support 
with substance S is carried out by, for example, dipping, coating, 
spraying, and the like. Impregnation may be conducted in an arbitrary 
stage before or during crosslinking. 
It is preferable for achieving an increased permeation flux to carry out 
the step of bringing solution A and solution B into contact with each 
other to induce crosslinking at a temperature of 30.degree. to 90.degree. 
C., especially 30.degree. to 60.degree. C. 
It is preferable for attaining a particularly high salt rejection and a 
particularly high permeation flux to bring solution A and solution B into 
contact with each other to induce crosslinking in a gas phase of substance 
S. 
The method of the present invention is characterized in that the 
interfacial polycondensation reaction between a polyfunctional acid halide 
and a compound having at least two reactive amino groups per molecule is 
performed in the presence of substance S, i.e., a substance having a 
solubility parameter of 8 to 14 (cal/cm.sup.3).sup.1/2, preferably 8 to 14 
(cal/cm.sup.3).sup.1/2. Presence of a substance having a solubility 
parameter of less than 8 (cal/cm.sup.3).sup.1/2 produces no substantial 
effect of improving water permeability. A substance having solubility 
parameter of more than 14 (cal/cm.sup.3).sup.1/2 is difficult to mix with 
solution B. 
Where substance B is added to solution B, the amount to be added is from 
0.001 to 10% by weight, preferably 0.05 to 5% by weight. If the amount is 
less than 0.001% by weight, there is a possibility that the effect of 
increasing the permeation flux is insubstantial. If it exceeds 10% by 
weight, there is a possibility that an interfacial membrane is not formed 
satisfactorily. 
Substance S which can be used in the present invention is not particularly 
limited as far as its solubility parameter falls within the range of from 
8 to 14 (cal/cm.sup.3).sup.1/2 and includes alcohols, ethers, ketones, 
esters, halogenated hydrocarbons, and sulfur-containing compounds. 
Examples of alcohols suitable as substance S are ethanol, propanol, 
1-butanol, 2-butanol, 1-pentanol, 2-pentanol, t-amyl alcohol, isoamyl 
alcohol, isobutyl alcohol, isopropyl alcohol, undecanol, 2-ethylbutanol, 
2-ethylhexanol, octanol, cyclohexanol, tetrahydrofurfuryl alcohol, 
neopentyl glycol, t-butanol, benzyl alcohol, 4-methyl-2-pentanol, 
3-methyl-2-butanol, pentyl alcohol, allyl alcohol, ethylene glycol, 
diethylene glycol, triethylene glycol, and tetraethylene glycol. 
Examples of suitable ethers are anisole, ethyl isoamyl ether, ethyl t-butyl 
ether, ethyl benzyl ether, crown ether, cresyl methyl ether, diisoamyl 
ether, diisopropyl ether, diethyl ether, dioxane, diglycidyl ether, 
cineole, diphenyl ether, dibutyl ether, dipropyl ether, dibenzyl ether, 
dimethyl ether, tetrahydropyran, tetrahydrofuran, trioxane, dichloroethyl 
ether, butyl phenyl ether, furan, methyl t-butyl ether, 
monodichlorodiethyl ether, ethylene glycol dimethyl ether, ethylene glycol 
diethyl ether, ethylene glycol dibutyl ether, ethylene glycol monomethyl 
ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, 
diethylene glycol dimethyl ether, diethylene glycol diethyl ether, 
diethylene glycol dibutyl ether, diethylene glycol monomethyl ether, 
diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, and 
diethylene chlorohydrine. 
Examples of suitable ketones are ethyl butyl ketone, diacetone alcohol, 
diisobutyl ketone, cyclohexanone, 2-heptanone, methyl isobutyl ketone, 
methyl ethyl ketone, and methylcyclohexane. 
Examples of suitable esters are methyl formate, ethyl formate, propyl 
formate, butyl formate, isobutyl formate, isoamyl formate, methyl acetate, 
ethyl acetate, propyl acetate, butyl acetate, isobutyl acetate, and amyl 
acetate. 
Examples of suitable halogenated hydrocarbons are allyl chloride, amyl 
chloride, dichloromethane, and dichloroethane. 
Examples of suitable sulfur-containing compounds are dimethyl sulfoxide, 
sulfolane, and thiolane. 
Of these compounds, alcohols and ethers are preferred. These compounds may 
be used either individually or in combination of two or more thereof. 
The amine component contained in solution A is not particularly limited as 
long as it is a polyfunctional compound having two or more reactive amino 
groups per molecule, and includes aromatic, aliphatic or alicyclic 
polyfunctional amines. Examples of the aromatic polyfunctional amines are 
m-phenylenediamine, p-phenylenediamine, 1,3,5-triaminobenzene, 
1,2,4-triaminobenzene, 3,5-diaminobenzoic acid, 2,4-diaminotoluene, 
2,4-diaminoanisole, amidol, and xylylenediamine. Examples of the aliphatic 
polyfunctional amines are ethylenediamine, propylene diamine, and 
tris(2-aminoethyl)amine. Examples of the alicyclic polyfunctional amines 
are 1,3-diaminocyclohexane, 1,2-diaminocyclohexane, 
1,4-diaminocyclohexane, piperazine, 2,5-dimethylpiperazine, and 
4-aminomethylpiperazine. These amines may be used either individually or 
as a mixture thereof. 
The polyfunctional acid halide which is contained in solution B is not 
particularly limited and includes aromatic, aliphatic or alicyclic 
polyfunctional acid halides. Examples of the aromatic polyfunctional acid 
halides are trimesic acid chloride, terephthalic acid chloride, 
isophthalic acid chloride, biphenyldicarboxylic acid chloride, 
naphthalenedicarboxylic acid dichloride, benzenetrisulfonic acid chloride, 
benzenedisulfonic acid chloride, and chlorosulfonylbenzenedicarboxylic 
acid chloride. 
Examples of the aliphatic polyfunctional acid halides include 
propanetricarboxylic acid chloride, butanetricarboxylic acid chloride, 
pentanetricarboxylic acid chloride, a glutaryl halide, and an adipoyl 
halide. 
Examples of the alicyclic polyfunctional acid halides are 
cyclopropanetricarboxylic acid chloride, cyclobutanetetracarboxylic acid 
chloride, cyclopentanetricarboxylic acid chloride, 
cyclopentanetetracarboxylic acid chloride, cyclohexanetricarboxylic acid 
chloride, tetrahydrofurantetracarboxylic acid chloride, 
cyclopentanedicarboxylic acid chloride, cyclobutanedicarboxylic acid 
chloride, cyclohexanedicarboxylic acid chloride, and 
tetrahydrofurandicarboxylic acid chloride. 
The above-mentioned amine component and acid halide component are subjected 
to interfacial polymerization to form a thin film consisting mainly of a 
crosslinked polyamide on a porous support thereby providing a composite 
reverse osmosis membrane. 
The porous support which can be used in the present invention is not 
particularly limited as far as it can support the thin film. For example, 
polysulfone, polyaryl ether sulfone such as polyether sulfone, polyimide, 
and polyvinylidene fluoride may be mentioned. In particular, a porous 
support comprised of polysulfone or polyaryl ether sulfone is preferred 
for their chemical, mechanical and thermal stability. While not limiting, 
the porous support usually has a thickness of about 25 to 125 .mu.m, 
preferably about 40 to 75 .mu.m. 
In carrying out the interfacial polymerization, solution A containing the 
amine component is applied to the porous support to form a first layer, 
and a layer consisting of solution B containing the acid halide component 
is then formed on the first layer to conduct interfacial polycondensation 
to form a thin film composed of a crosslinked polyamide on the porous 
support. 
In order to facilitate film formation or to improve the performance of the 
resulting composite reverse osmosis membrane, solution A containing the 
polyfunctional amine may contain a small amount of a polymer, such as 
polyvinyl alcohol, polyvinylpyrrolidone or polyacrylic acid, or a 
polyhydric alcohol, such as sorbitol or glycerol. 
The amine salts described in JP-A-2-187135 (corresponding to U.S. Pat. No. 
4,872,984), such as salts of tetraalkylammonium halides or trialkylamines 
with organic acids, may also be added to solution A for the purpose of 
facilitating film formation, improving penetrability of the amine solution 
into the support, and accelerating the condensation reaction. 
Surface active agents, such as sodium dodecylbenzenesulfonate, sodium 
dodecylsulfate, and sodium lauryl sulfate, may also be incorporated into 
solution A. These surface active agents are effective to improve 
wettability of solution A to a porous support. 
In order to accelerate the polycondensation in the interface, it is 
beneficial to use sodium hydroxide or sodium tertiary phosphate, which is 
capable of removing a hydrogen halide generated from the interfacial 
reaction, or an acylation catalyst. As stated above, solution A may 
contain substance S in order to improve the permeation flux. 
The concentrations of the acid halide or polyfunctional amine in solutions 
B or A are not particularly limited. In general, the concentration of the 
acid halide in solution B is 0.01 to 5% by weight, preferably 0.05 to 1% 
by weight, and that of the polyfunctional amine in solution A is 0.1 to 
10% by weight, preferably 0.5 to 5% by weight. 
After solution A is applied to the porous support and solution B is applied 
thereon, excess of the solvent is removed from both solutions, and the 
coating layers are heat dried generally in the range of about 20.degree. 
to 150.degree. C., preferably about 70.degree. to 130.degree. C., for 
about 1 to 10 minutes, preferably about 2 to 8 minutes, to form a 
water-permeable thin film consisting of a crosslinked polyamide. The thin 
film usually has a thickness of about 0.05 to 2 .mu.m, preferably about 
0.1 to 1 .mu.m. 
If desired, the resulting composite reverse osmosis membrane may be 
subjected to a chlorine treatment with hypochlorous acid, etc. for further 
improving the salt rejection performance as described in JP-B-63-36803 
(the term "JP-B" as used herein means an "examined published Japanese 
patent application").

The present invention will now be illustrated in greater detail with 
reference to Examples, but it should be understood that the present 
invention is not construed as being limited thereto. Unless otherwise 
indicated, all the percents are by weight. 
EXAMPLE 1 
Aqueous solution A containing 2.0% m-phenylenediamine, 0.15% sodium lauryl 
sulfate, 2.0% triethylamine, and 4.0% camphorsulfonic acid was applied to 
a porous polysulfone supporting membrane, and excess of solution A was 
removed to form a layer of solution A on the supporting membrane. 
Hexane solution B containing 0.20% trimesic acid chloride and 0.5% 
t-butanol was then applied onto the layer of solution A, and the coated 
supporting membrane was maintained in a hot air drier at 120.degree. C. 
for 3 minutes to form a polymer thin film on the supporting membrane. 
The performance of the resulting composite reverse osmosis membrane was 
evaluated by testing against an aqueous solution containing 1500 ppm of 
sodium chloride (pH 6.5) under a pressure of 15 kgf/cm.sup.2. As a result, 
the salt rejection was 99.4% as measured from the conductivity of the 
permeated liquid, and the permeation flux was 1.1 m.sup.3 /m.sup.2 
.multidot.day. These results are shown in Table 1 below. 
COMATIVE EXAMPLES 1 AND 2 
Composite reverse osmosis membranes were obtained in the same manner as in 
Example 1, except for changing the t-butanol concentration to 0% (no 
additive) or 20%. The test results are shown in Table 1. 
EXAMPLES 2 TO 5 
Composite reverse osmosis membranes were obtained in the same manner as in 
Example 1, except for adding 20% isopropyl alcohol to solution A and 
replacing the t-butanol of solution B with 0 to 0.3% isopropyl alcohol. 
The test results are shown in Table 1. 
EXAMPLES 6 TO 12 AND COMATIVE EXAMPLE 3 
Composite reverse osmosis membranes were obtained in the same manner as in 
Example 1, except for changing the concentration of the trimesic acid 
chloride in solution A to 0.15% and replacing the t-butanol of solution B 
with 0.1% of various ethers shown in Table 1. The test results are shown 
in Table 1. 
TABLE 1 
__________________________________________________________________________ 
Solution B 
Trimesic 
Additive in Acid Salt Permeation 
Example 
Solution A Chloride 
Rejection 
Flux 
No. (Concn.; wt %) 
Additive (Concn.; wt %) 
(wt %) 
(%) (m.sup.3 /m.sup.2 .multidot. day) 
__________________________________________________________________________ 
Example 1 
none t-butyl alcohol (0.5) 
0.2 99.4 1.1 
Compara. 
none none (t-butyl alcohol: 0) 
0.2 99.7 0.7 
Example 1 
Compara. 
none t-butyl alcohol (20) 
0.2 16 17 
Example 2 
Example 2 
isopropyl 
none (isopropyl 
0.2 99.7 1.5 
alcohol 
alcohol: 0) 
(20) 
Example 3 
isopropyl 
isopropyl alcohol (0.1) 
0.2 99.5 1.9 
alcohol 
(20) 
Example 4 
isopropyl 
isopropyl alcohol (0.2) 
0.2 99.5 1.9 
alcohol 
(20) 
Example 5 
isopropyl 
isopropyl alcohol (0.3) 
0.2 99.5 1.6 
alcohol 
(20) 
Example 6 
none ethylene glycol monomethyl 
0.15 99.7 1.5 
ether (0.1) 
Example 7 
none ethylene glycol monoethyl 
0.15 99.3 1.8 
ether (0.1) 
Example 8 
none ethylene glycol monomethyl 
0.15 99.7 1.3 
ether acetate (0.1) 
Example 9 
none ethylene glycol monobutyl 
0.15 99.7 1.3 
ether acetate (0.1) 
Example 10 
none diethylene glycol dimethyl 
0.15 99.7 1.4 
ether (0.1) 
Example 11 
none diethylene giycol diethyl 
0.15 99.7 1.4 
ether (0.1) 
Example 12 
none diethylene glycol dibutyl 
0.15 99.7 1.2 
ether (0.1) 
Compara. 
none none 0.15 99.7 1.0 
Example 3 
__________________________________________________________________________ 
EXAMPLE 13 
A porous polysulfone supporting membrane was dipped in a 20% aqueous 
solution of isopropyl alcohol for 10 minutes. Thereafter, aqueous solution 
A containing 2.0% m-phenylenediamine, 0.15% sodium lauryl sulfate, 2.0% 
triethylamine, and 4.0% camphorsulfonic acid was then applied onto the 
isopropyl alcohol-impregnated porous supporting membrane, and excess of 
solution A was removed to form a layer of solution A on the supporting 
membrane. 
Hexane solution B containing 0.20% trimesic acid chloride was brought into 
contact with the layer of solution A, and the coated supporting membrane 
was maintained in a hot air drier at 120.degree. C. for 3 minutes to form 
a polymer thin film on the supporting membrane. 
The performance of the resulting composite reverse osmosis membrane was 
evaluated in the same manner as in Example 1. As a result, the salt 
rejection was 99.6%, and the permeation flux was 1.4 m.sup.3 /m.sup.2 
.multidot.day. These results are shown in Table 2 below. 
COMATIVE EXAMPLE 4 
A composite reverse osmosis membrane was obtained in the same manner as in 
Example 13, except that the porous polysulfone supporting membrane was 
dipped in water which did not contain isopropyl alcohol. The test results 
are shown in Table 2. 
EXAMPLES 14 TO 15 
Composite reverse osmosis membranes were obtained in the same manner as in 
Example 13, except that dipping of the porous polysulfone supporting 
membrane in an isopropyl alcohol aqueous solution was replaced with 
coating or spraying with a 20% isopropyl alcohol aqueous solution. The 
test results are shown in Table 2. 
EXAMPLE 16 
A composite reverse osmosis membrane was obtained in the same manner as in 
Example 14, except that the isopropyl alcohol aqueous solution was 
replaced with a 10% ethylene glycol monoethyl ether aqueous solution. The 
test results are shown in Table 2. 
TABLE 2 
______________________________________ 
Treatment of 1500 ppm NaCl 
Porous Support Aqueous Solution 
Treating Aqueous Salt Permeation 
Example Solution Treating Rejection 
Flux 
No. (Concn.; wt %) 
Method (%) (m.sup.3 /m.sup.2 .multidot. day) 
______________________________________ 
Example 13 
isopropyl dipping 99.6 1.4 
alcohol (20) 
Compara. 
none dipping 99.7 0.7 
Example 4 
(water alone) 
Example 14 
isopropyl coating 99.6 1.3 
alcohol (20) 
Example 15 
isopropyl spraying 99.6 1.4 
alcohol (20) 
Example 16 
ethylene coating 99.5 1.2 
glycol monoethyl 
ether (10) 
______________________________________ 
EXAMPLE 17 
Aqueous solution A containing 2.0% m-phenylenediamine, 0.15% sodium lauryl 
sulfate, 2.0% triethylamine, 4.0% camphorsulfonic acid, and 20% isopropyl 
alcohol was applied to a porous polysulfone supporting membrane, and 
excess of solution A was removed to form a layer of solution A on the 
supporting membrane. 
A 0.15% solution of trimesic acid chloride in IP 1016 (isoparaffinic 
hydrocarbon oil produced by Idemitsu Petrochemical Co., Ltd.) was prepared 
as solution B. Solution B was heated to 40.degree. C. and brought into 
contact with the layer of solution A at that temperature, and the coated 
supporting membrane was maintained in a hot air drier at 120.degree. C. 
for 3 minutes to form a polymer thin film on the supporting membrane. 
The performance of the resulting composite reverse osmosis membrane was 
evaluated by testing against an aqueous solution containing 1500 ppm of 
sodium chloride (pH 6.5) under a pressure of 15 kgf/cm.sup.2. As a result, 
the salt rejection was 99.7% as measured from the conductivity of the 
permeated liquid, and the permeation flux was 1.7 m.sup.3 /m.sup.2 
.multidot.day. These results are shown in Table 3 below. 
EXAMPLES 18 TO 20 
Composite reverse osmosis membranes were prepared in the same manner as in 
Example 17, except for changing the temperature of solution B as shown in 
Table 3. The test results are also shown in Table 3. 
COMATIVE EXAMPLES 5 TO 6 
Composite reverse osmosis membranes were prepared in the same manner as in 
Example 17, except that solution A contained no isopropyl alcohol, and the 
temperature of solution B was changed as shown in Table 3. The test 
results obtained are shown in Table 3. 
TABLE 3 
______________________________________ 
Temp. 1500 ppm NaCl Aq. Soln. 
Additive in of Solu- 
Salt Permea- 
Example Solution A tion B Rejection 
tion Flux 
No. (Concn.; wt %) 
(.degree.C.) 
(%) (m.sup.3 /m.sup.2 .multidot. day) 
______________________________________ 
Example 17 
isopropyl 40 99.7 1.7 
alcohol (20) 
Example 18 
isopropyl 20 99.7 1.4 
alcohol (20) 
Example 19 
isopropyl 50 99.5 1.6 
alcohol (20) 
Example 20 
isopropyl 60 99.5 1.6 
alcohol (20) 
Compara. 
none 20 99.6 0.9 
Example 5 
Compara. 
none 50 99.7 0.9 
Example 6 
______________________________________ 
EXAMPLE 21 
Aqueous solution A containing 2.0% m-phenylenediamine, 0.15% sodium lauryl 
sulfate, 2.0% triethylamine, and 4.0% camphorsulfonic acid was brought 
into contact with a porous polysulfone supporting membrane for several 
seconds, and excess of solution A was removed to form a layer of solution 
A on the supporting membrane. 
Isopropyl alcohol was heated to generate isopropyl alcohol vapor, and a 
0.20% hexane solution of trimesic acid chloride (solution B) was brought 
into contact with the layer of solution A in the isopropyl alcohol vapor 
atmosphere. The coated supporting membrane was maintained in a hot air 
drier at 120.degree. C. for 3 minutes to form a polymer thin film on the 
supporting membrane. 
The performance of the resulting composite reverse osmosis membrane was 
evaluated by testing against an aqueous solution containing 1500 ppm of 
sodium chloride (pH 6.5) under a pressure of 15 kgf/cm.sup.2. As a result, 
the salt rejection was 99.6% as measured from the conductivity of the 
permeated liquid, and the permeation flux was 1.0 m.sup.3 /m.sup.2 
.multidot.day. 
COMATIVE EXAMPLE 7 
A composite reverse osmosis membrane was prepared in the same manner as in 
Example 21, except that the contact of solution B was not in an isopropyl 
alcohol atmosphere. When evaluated in the same manner as in Example 21, 
the resulting membrane had a salt rejection of 99.7% and a permeation flux 
of 0.7 m.sup.3 /m.sup.2 .multidot.day. 
As has been described and demonstrated, the method of the present invention 
comprises the steps of coating a porous support with solution (A) 
containing a compound having two or more reactive amino groups per 
molecule and bringing solution (B) containing a polyfunctional acid halide 
into contact with solution (A) to induce crosslinking to form a 
crosslinked polyamide skin layer, in which the crosslinking is carried out 
in the presence of a substance having a solubility parameter of 8 to 14 
(cal/cm.sup.3).sup.1/2. 
The composite reverse osmosis membrane of the present invention exhibits 
both high salt rejection and high permeability and makes it possible to 
conduct practical desalting under a relatively low pressure. Accordingly, 
the membrane of the present invention is suited for desalting of brackish 
water or seawater to obtain fresh water and preparation of ultra-pure 
water necessary for semiconductor manufacturing. 
While the invention has been described in detail and with reference to 
specific embodiments thereof, it will be apparent to one skilled in the 
art that various changes and modifications can be made therein without 
departing from the spirit and scope thereof.