Semipermeable composite membranes

Semipermeable composite membranes composed of a porous substrate and at least two layers of film-forming polymers coated thereon are provided, which comprise a first layer of monomeric or polymeric diazonium salts, which have been reacted with themselves and with an at least difunctional compound, and a second layer, which is chemically bonded to the first one, of a cross-linked, ionically charged hydrophilic polymer. The membranes show good mechanical, physical and chemical stabilities and are useful in reverse osmosis and ultrafiltration processes, particularly for desalting solutions of low molecular weight organic compounds.

The present invention relates to the field of semipermeable composite 
membranes composed of at least two layers, the first of which is made from 
a diazonium salt of a monomer or polymer, formed and coated onto a more 
porous semipermeable membrane substrate and then stabilised by 
cross-linking. The second layer comprises a cross-linked, ionically 
charged hydrophilic polymer. 
It is already known from the state of the art (U.S. Pat. No. 4,620,204) to 
prepare membranes which comprise a thin cross-linked hydrophilic film 
chemically bonded to a thicker more porous membrane. These membranes 
require reactive groups on the membrane to chemically bond the thin film 
to the said membrane and cross-link the membrane (e.g. with a reactive 
dyestuff). Without this chemical bonding the coated polymers cross-linked 
with a reactive dye for example have insufficient life time, especially at 
extreme pH-values and temperature, and are soluble in various organic 
solvents, such as N-methylpyrrolidone (NMP), dimethylformamide (DMF) or 
dimethyl-sulfoxide (DMSO). 
One approach of coating a porous substrate (UF-membrane) with hydrophilic 
polymers for improving rejection is described in U.S. Pat. No. 4,125,462. 
The coating polymers are water soluble amines that are physically adsorbed 
and there is no attempt to cross-link or bind the coated layers. 
These membranes with the coating alone decline in rejection with time; 
further they suffer from insufficient physical stability in that the 
coating is slowly washed away. 
It has now been found that these difficulties and drawbacks adhered to the 
known composite membranes can be overcome by the composite membranes 
according to the present invention which comprise two layers of 
film-forming polymers coated onto a porous substrate: the first layer 
being applied to the substrate by coating it with a monomeric or polymeric 
diazonium salt solution, which diazonium salts react with themselves and 
are then cross-linked, and the second layer which is coated--as a rule--on 
the first one comprises a cross-linked, ionically charged hydrophilic 
polymer. 
Therefore, it is one object of the present invention to provide new 
semipermeable composite membranes composed of a porous substrate and at 
least two layers of film-forming polymers coated thereon, which comprises 
a first layer of monomeric or polymeric diazonium salts, which have been 
reacted with themselves and with an at least difunctional compound, and a 
second layer, which is chemically bonded to the first one, of a 
cross-linked, ionically charged hydrophilic polymer. 
Other objects of the present invention are processes for the manufacture of 
the inventive membranes (membrane films of cross-linked polymers on and 
inside the pores of porous substrates), as well as the use of these 
membranes in ultrafiltration and reverse osmosis processes, viz. in fields 
involving concentration and purification of liquids, e.g. separating salts 
from organic compounds or purifying (waste) water. 
These and other objects of the present invention will be apparent from the 
following detailed description. 
A process for the preparation of the inventive semipermeable composite 
membranes--which is a further object of the present invention as indicated 
hereinbefore--comprises modifying a porous substrate through a sequence of 
chemical treatments consisting essentially of steps (a) to (e), wherein 
step (a) is treating the substrate with a monomeric or polymeric diazonium 
salt, 
step (b) is treating the product of step (a) with alkali, 
step (c) is treating the product of step (b) with an at least difunctional 
compound, 
step (d) is coating the product of step (c) with a hydrophilic polymer, and 
step (e) is cross-linking the product of step (d) with an ionic, at least 
difunctional compound, wherein at least one of the polymers of step (d) or 
the at least difunctional compound of step (e) contains ionic groups. 
More particularly, the inventive membranes are formed by first coating the 
substrate with a monomeric or polymeric diazonium salt which is made to 
condense with itself (in the presence of alkali) with the loss of the 
diazonium moiety forming covalent cross-links. Followed by a cross-linker 
containing at least two reactive groups and then the additional coating of 
a hydrophilic (or polyelectrolyte) polymer which may react with the 
cross-linkers on the first coating. The top portion of the second coating 
is finally also cross-linked preferably with an ionic, at least 
difunctional cross-linker. Thus the modification process which has several 
variations, is primarily based on the following sequence that physically 
or electrostatically adsorbs a diazonium polymer or monomer layer to the 
substrate. The said polymer condenses with itself and is further 
cross-linked and functionalised leaving reactive groups from the 
cross-linker for an additional chemical binding of a second polymer. This 
second polymer layer is then charged ionically and cross-linked. 
Therefore, treating in step (c) means, on the one hand, the cross-linking 
of the product of step (b), and, on the other hand, the functionalising of 
the cross-linked product to provide (additional) reactive sites for a 
chemical reaction with the polymer coating of step (d). 
The porous substrates (membrane substrates or basic membranes) used 
inventively comprise for example the vast number of ordinary 
reverse-osmosis (RO), microfiltration (MF) or preferably ultrafiltration 
(UF) membranes with average pore sizes varying from 1 to 500 nm. The 
preferred range, however, is 1 to 100 nm and most preferred 2 to 20 nm for 
the achievement of optimum rejection with flux. In addition, a minimum 
porosity of 10% is preferred for sufficiently high flux. 
Any of the known membrane forming materials may be used for preparing the 
porous substrate, as for example, organic polymeric membranes produced 
from polyacrylonitriles and copolymers on the basis of acrylonitrile, 
polyamides, polyvinyl chlorides and copolymers on the basis of vinyl 
chloride, cellulosics, epoxy resins, polyaryleneoxides, polycarbonates, 
polyetherketones, polyheterocyclics, copolymers containing in part 
heterocyclic rings, polyvinylidene fluorides, polytetrafluoroethylenes, 
polyesters, polyimides, aromatic polysulfones, sulfonated derivatives of 
aromatic polysulfones (preferably less than 1.5 or most preferably below 
1.0 eq sulfone groups per kilogramm of polymer), polyelectrolyte 
complexes, and polyolefines, they all may be used as both homo- and 
copolymer combinations. In addition UF-ceramic substrates may be used. 
Preferred polymers are cellulosics, polyacrylonitriles, aromatic 
polysulfones, polyamides, polyvinylidene fluorides or 
polytetrafluoroethylenes, polyetherketones, UF-ceramic substrates and the 
sulfonated derivatives of polyether ketones and polysulfones. 
Membrane casting may be performed by any number of casting procedures cited 
in the literature (for example U.S. Pat. No. 4,029,582, GB-A-2,000,720, 
U.S. Pat. No. 3,556,305, U.S. Pat. No. 3,615,024, U.S. Pat. No. 
3,567,810). Thus, the polymer or its derivatives, may be dissolved in a 
suitable solvent or mixture of solvents (for example NMP, DMF, DMSO, 
hexamethylphosphortriamide, N,N-dimethylacetamide, dioxane), which may or 
may not contain co-solvents, partical solvents, non-solvents, salts, 
surfactants or electrolytes, for altering or modifying the membrane 
morphology and its flux and rejection properties (i.e. acetone, ethanol, 
methanol, formamide, water, methylethylketone, triethyl phosphate, 
sulfuric acid, hydrochloric acid, partial esters of fatty acids and sugar 
alcohols or their ethylene oxide adducts, sodium dodecyl sulfate (SDS), 
sodium dodecylbenzene sulfonate, sodium hydroxide, potassium chloride, 
zinc chloride, calcium chloride, lithium nitrate, lithium chloride, 
magnesium perchlorate, etc.). 
The casting solution may be filtered by any of the known processes (i.e. 
pressure filtration through microporous filters or by centrifugation), and 
cast on a support such as e.g. glass, metal, paper or plastic from which 
it may then be removed. It is preferred, however, to cast on a porous 
support material from which the membrane is not removed. Such porous 
supports may be non-woven or woven clothes such as of cellulosics, 
polyethylenes, polypropylenes, polyamides (nylon), polyvinyl chlorides and 
its copolymers, polystyrenes, polyethylene terephthalates (polyesters), 
polyvinylidene fluorides, polytetrafluoro ethylenes, polyether ketones, 
polyether-ether-ketones, glass fibers, porous carbon, graphite, inorganic 
membranes based on alumina and/or silica, optionally coated with zirkonium 
oxide or other oxides, or ceramics. The membrane may alternatively be 
formed as flat sheet or as a hollow fiber or tubulet, not requiring a 
support for practical use. 
The concentration of polymer in the casting solution may vary as a function 
of its molecular weight and of the further additives between 5 to 80%, but 
preferably between 10 and 50% and most preferred between 15 to 30%. The 
temperature of casting may vary from -20.degree. to 100.degree. C., but 
the preferred range is between 0.degree. and 60.degree. C., varying as a 
function of the polymer, its molecular weight, and the cosolvents and 
additives, in the casting solution. 
The polymer casting solution may be applied to the above mentioned supports 
by any of the well known techniques, known to those practised in the art. 
The wet film thickness may vary between 5 to 2000 micron. The preferred 
range being 50 to 800 micron and the most preferred 100 to 500 micron. The 
wet film and support may then be immersed immediately, or after a partial 
evaporation step (from 5 seconds to 48 hours) at ambient condition or 
elevated temperature, or vacuum or any combination thereof into a gelling 
bath of a non-solvent. Such baths are usually water, or water with a small 
percentage of a solvent (for example DMF or NMP) and/or a surfactant (for 
example sodium dodecyl sulfate, SDS) at a temperature of 0.degree. to 
70.degree. C. An example of a commonly used gelling bath is water with 
0.5% SDS at 40.degree. C. In another mode of forming membranes, a polymer 
solution containing a component that may be leached out in water or 
another solvent, is cast and dried before immersion. After immersion, 
leachable material is removed resulting in a porous membrane. In a third 
variation, a polymer solution without any leachable materials is cast and 
taken to dryness, resulting in a porous membrane by virtue of the 
physico-chemical properties of polymeric material-solvent combination or 
by a subsequent chemical reaction that creates pores. All the above 
methods may be used to form membranes (substrates) for further 
modification as described hereinafter. 
The inventively used diazonium salts can be obtained by diazotization of 
primary amino group-containing monomeric or polymeric, aromatic or 
preferably aliphatic compounds. 
Low molecular weight polyamines used to form diazonium salts may be 
aromatic, heterocyclic or preferably aliphatic. The aromatic compounds 
should contain one or more primary amino functions on a single aromatic, 
fused aromatics of two, three or four aromatic rings or non fused aromatic 
rings. Examples are aniline, phenylene diamines such as m-phenylene 
diamine or p-phenylene diamine, aminonaphthalenes such as diamino 
naphthalene or 1-amino-8-hydroxy-3,6-disulfonic naphthalene. 
An example of a heterocyclic amine is 2,6-diamino-pyridine. The low 
molecular weight aliphatic polyamines may be acyclic or cyclic and they 
may contain further heteroatoms, such as oxygene, for example as hydroxyl 
groups or in form of an -O-ether-bridge. Examples are alkylene diamines of 
the formula H.sub.2 N(CH.sub.2).sub.1-10 NH.sub.2, ether amines of the 
formula H.sub.2 N(CH.sub.2).sub.2-4 O(CH.sub.2).sub.2-4 NH.sub.2 and 
aliphatic hydroxyl groups containing amines (alkanolamines) of the formula 
HOCH.sub.2 CH(OH)CH.sub.2 NH(CH.sub.2 CH.sub.2 NH).sub.1-3 H (cf. EP-A-8 
945). 
Primary amino groups containing polymers are converted into polymeric 
diazonium salts and are used to coat the porous (semipermeable) membrane 
substrate. Preferred are polyfunctional oligomers or polymers which 
contain active hydrogen atoms bound to nitrogen. The nitrogen atoms may be 
present as aliphatic (acyclic or cyclic), aromatic or heterocyclic amino 
groups, which can be primary, secondary or tertiary. A certain amount of 
primary amino groups has to be present. 
Examples of such polymers are polyethyleneimine (M.W. 150 to 1,000,000), 
which can be partially alkylated or otherwise modified, polyvinylamines 
(M.W. 1000 to 2,000,000), vinylamine/vinylsulfonate copolymers, 
polyvinylaniline, polybenzylamines, polyvinylimidazoline, amino modified 
polyepihalohydrin (described in GB-A-1,558,807), polydiallylamine 
derivatives, polymers containing piperidine radicals (described in 
GB-A-2,027,614), amino (aminalkyl) substituted polysulfones, amino 
(aminoalkyl) substituted polyarylene oxides (e.g. amino methylated 
polyphenylene oxide), polyamide-polyamine-epichlorohydrin condensation 
products, or polymers of 2-aminomethylmethacrylate. The above polymers may 
be in part a copolymer or a polymer containing other monomeric units, 
block polymers or graft polymers. If they are copolymers the other 
monomeric units may or may not contain ionic groups such as --SO.sub.3 
.sup..crclbar., --COO.sup..crclbar. or --NR.sub.3.sup..sym.). 
One preferred polymer comprises poly-aliphatic (acyclic or cyclic) amines. 
Polyethyleneimine is an example of this group. The range of molecular 
weights may be between 150 to 2,000,000, but preferably between 1000 and 
200,000 and most preferred between 10,000 and 70,000. Low molecular weight 
polymers or oligomers (150 to 1000) may be used, but the increase in 
solute rejection of the final membrane is not as great when higher 
molecular weight polymers are used. 
In another preferred case, one can use water soluble amphoteric or block 
mosaic polymers containing both cationic and anionic group, together with 
reactive amino (primary) amino functions. 
The above monomers or polymers are converted to the diazonium salts by 
dissolving the polymer in a solution of e.g. sodium nitrite and adjusting 
the pH of the solutions with hydrochloric or sulfuric acid to less than a 
pH of 2 and preferably to a pH between 1.5 and 0.5. Though this is the 
preferred method any other method of producing diazonium salts may be 
used. Water is the preferred solvent for this diazonium salt formation, 
though other solvents, such as low molecular weight alcohols or ketones 
may be used alone or in combination with water. The range of monomer or 
polymer concentration may be from 0.1 to 30%, but preferably between 0.5 
and 15%, and most preferred between 0.5 and 5%. 
After immersion of the membrane substrate in the polydiazonium salt 
solution the coated membrane is removed, drained and immersed in a more 
basic pH solution. pH-values above 7 and most preferred above pH 10 
(pH-range of 7 to 12) give the best results. The time of immersion in the 
basic solution may vary from one 30 seconds to 48 hours, but most 
preferably from 1.0 minutes to 4 hours. 
The diazonium salts--as indicated hereinbefore--can react with themselves, 
e.g. by the loss of the diazo (--N.dbd.N--) group under the influence of 
water and alkali (e.g. alkali metal or alkaline metal hydroxides such as 
lithium, sodium, potassium or calcium hydroxide) and form covalent bonds 
which may be intermolecular or intramolecular ones. The present invention 
is not limited to this mechanism. 
The monomeric and polymeric diazonium salts are thus made to undergo a 
certain self-condensation. These particular (polymeric) self-condensation 
products form--after they have been cross-linked and functionalised by an 
at least difunctional compound--the unique first layer in the inventive 
composite membranes which highly contributes to the superior effects of 
said membranes. 
The so-called self-condensation of the diazonium salts can be carried out 
separately and the condensation products are then applied (coated) to 
(onto) the substrate, or and this is the preferred embodiment, the 
self-condensation is carried out in-situ, that is in the presence of the 
membrane substrate. 
After the immersion of the membrane (coated with the first layer) in the 
alkaline bath, it is rinsed at pH 4 to 7 to rinse off unreacted material 
and to adjust the pH back to neutral conditions. 
To the above coated layer at least difunctional compounds, which may be 
ionic or preferably non-ionic ones are applied. They possess cross-linking 
properties and can enter into chemical bonding with the condensed polymer 
(obtained from the diazonium salts) and optionally substrate. Further they 
can functionalise the condensed polymer to provide reactive sites for 
chemically binding the two polymer layers together. 
These compounds, which have at least two functional groups, possess their 
reactivity by virtue of reactive multiple bonds, or epoxide, aziridine, 
aldehyde, imidate, isocyanate, isothiocyanate, hydroxyl, (carboxylic acid) 
anhydride, or N-methylol groups (these bonds or groups may be further 
substituted); or said compounds contain substituents detachable as 
tertiary amines or preferably as anions. Combinations of these are also 
possible. 
The compounds may contain, for example, the groupings 
##STR1## 
as a multiple bond to which further substituents can be added on. The 
isocyanate or isothiocyanate group can also be considered as a group of 
this type. They can contain quaternary ammonium groups, which are split 
off as tertiary amines, for example, a trimethylammonium or pyridinium 
group. However, they preferably contain substituents with groups that 
split off as an anion, and preferably contain a reactive halogen atom, as 
the reactive group. These leaving groups possess their reactivity by 
virtue of, for example, the influence of electrophilic groups, such as the 
--CO-- or --SO.sub.2 -- group in saturated aliphatic radicals (acyl 
halides). They also possess their reactivity by virtue of the influence of 
a quaternary nitrogen atom, such as in the group 
##STR2## 
or in aromatic radicals by virtue of the influence of electrophilic groups 
in the o- and p-position, for example, nitro, hydrocarbonsulfonyl, or 
hydrocarbon carbonyl groups, or of the bond to a ring carbon atom, which 
is adjacent to a tertiary ring nitrogen atom, as in halogenotriazine or 
halogenopyrimidine radicals. 
The at least difunctional compounds may be selected from the following 
groups: 
A. s-Triazines, containing at least two identical or different halogen 
atoms bonded to carbon atoms, for example, cyanuric chloride, cyanuric 
fluoride, cyanuric bromide and also their primary condensation products 
with, for example, water, ammonia, amines, alkanols, alkylmercaptans, 
phenols or thiophenols. 
B. Pyrimidines, containing at least two reactive, identical or different 
halogen atoms, such as 2,4,6-trichloro-, 2,4,6-trifluoro- or 
2,4,6-tribromo-pyrimidine, which can be further substituted in the 
5-position, for example by an alkyl, alkenyl, phenyl, carboxyl, cyano, 
nitro, chloromethyl, chlorovinyl, carbalkoxy, carboxy-methyl, 
alkylsulfonyl, carboxamide or sulfonamide group, but preferably by 
halogen, for example, chlorine, bromine or fluorine. Particularly suitable 
halogenopyrimidines are 2,4,6-trichloro- and 
2,4,5,6-tetrachloropyrimidines; further derivatives of pyrimidine similar 
to those of (A) above. 
C. Halogenopyrimidinecarboxylic acid halides, for example, 
dichloropyrimidine-5- or -6-carboxylic acid chloride. 
D. 2,3-Dihalogeno-quinoxaline-, -quinazoline- or -phthalazine-carboxylic 
acid halides or -sulfonic acid halides, such as 
2,3-di-chloroquinoxaline-6-carboxylic acid chloride or acid bromide. 
E. 2-Halogeno-benzthiazole- or -benzoxazole-carboxylic acid halides or 
-sulfonic acid halides, such as 2-chloro-benzthiazole- or -benzoxazole-5- 
or -6-carboxylic acid chloride or -5- or -6-sulfonic acid chloride, and 
F. Halogeno-6-pyridazonyl-1-alkanoyl halides or 1-benzoyl halides, 
4,5-dichloro-6-pyridazonyl-1-propionyl chloride or -1-benzoyl chloride. 
Further compounds which contain at least two reactive substituents which 
can be employed are, for example: 
G. Anhydrides or halides of aliphatic, .alpha.,.beta.-unsaturated mono- or 
dicarboxylic acids having preferably 3 to 5 carbon atoms, such as maleic 
anhydride, acryloyl chloride, methacryloyl chloride and propionyl 
chloride. 
H. Carboxylic acid anhydrides or halides of aliphatic mono- or dicarboxylic 
acids having preferably 3 to 10 carbon atoms, or of aromatic carboxylic 
acids, containing reactive halogen atoms, for example, chloroacetyl 
chloride, .beta.-chloropropionyl chloride, 
.alpha.,.beta.-dibromopropionylchloride, .alpha.-chloro- or 
.beta.-chloro-acryloyl chloride, chloromaleic anhydride and 
.beta.-chloro-crotonyl chloride, and fluoronitro- or chloro-nitro-benzoic 
acid halides or -sulfonic acid halides in which the fluorine atom or the 
chlorine atom is in the o-position and/or p-position relative to the nitro 
group. 
I. Carboxylic acid N-methylolamides or reactive functional derivatives of 
these methylol compounds. Carboxylic acid N-methylol-amides are in 
particular N-methylol-chloroacetamide, N-methylol-bromoacetamide, 
N-methylol-.alpha.,.beta.-dichloro- or -dibromo-propionamide, 
N-methylolacrylamide and N-methylol-.alpha.-chloro- or 
-.alpha.-bromo-acrylamide. Reactive derivatives of the carboxylic acid 
N-methylolamides, are for example, the corresponding N-chloro-methyl- or 
N-bromo-methyl-amides. 
J. Free or etherified N-methylolureas or N-methylolmelamines, for example, 
N,N-dimethylolurea, N,N-dimethylolurea dimethyl ether, 
N,N'-dimethylolethylene- or -propylene-urea, 
4,5-dihydroxy-N,N'-dimethylolethyleneurea or 
4,5-dihydroxy-N,N'-dimethylol-ethyleneurea dimethyl ether and di- to 
-hexamethylolmelamine, trimethylolmelamine dimethyl ether, 
pentamethylolmetlamine pentamethyl or hexamethyl ether. 
K. Condensation products of dialkylalkanes containing at least one phenolic 
hydroxyl group and halogenohydrines, for example, the diepoxide obtained 
from 2,2-bis(4'-hydroxyphenyl)-propane and epichlorohydrin, as well as 
glycerol triglycidyl ethers and also corresponding diaziridines. 
L. Di-aldehydes, for example, glutaraldehyde or adipaldehyde. 
M. Diisocyanoates or diisothiocyanates, such as alkylene (C.sub.2 
-C.sub.4)-diisocyanate, e.g. ethylene diisocyanate, phenylene- or 
alkyl(C.sub.1 -C.sub.4)-substituted phenylenediisocyanates, e.g. 
phenylene-1,4-diisocyanate or toluene-2,4-diisocyanate, or 
phenylene-diisothiocyanates, for example, phenylene-1,4-diisothiocyanate, 
or 
N. Further reactive compounds, such as trisacryloyl-hexahydro-s-triazine, 
epoxides or aziridines. 
Non-ionic at least difunctional compounds which are preferred and have 
proved particularly advantageous are halogeno-diazines or -triazines 
containing at least two reactive substituents, as well as compounds 
containing isocyanate or isothiocyanate groups. Tri- and 
tetrachloropyrimidine and in particular cyanuric chloride have proved 
particularly advantageous. 
The cross-linking of the polymeric species of the first layer of the 
inventive composite membranes can be carried out--although less 
preferred--with ionic, at least difunctional compound, too. These may 
contain the same reactive moieties or groups as the non-ionic 
cross-linking agents. 
Therefore, the ionic, at least difunctional compounds contain as functional 
moieties multiple bonds or epoxide, aziridine, aldehyde, imidate, 
isocyanate, isothiocyanate, anhydride, hydroxyl, or N-methylol groups, or 
said at least difunctional bompound contains substituents detachable as 
anions or tertiary amines, and as ionic groups sulfonic acid, sulfato, 
carboxylic acid, ammonium, sulfonium or phosphonium groups. 
Among the at least difunctional compounds that contain substituents 
detachable as anions, di- and triazines containing at least two halogen 
(chlorine, fluorine) atoms, sulfonic acid halides and di- and halides 
(chlorides) of di- and tricarboxylic acis, respectively, may be mentioned. 
While many of the above reagents can be applied in aqueous solutions within 
a narrow range of pH and temperature, the acyl halides must be dissolved 
in aprotic solvents. 
Preferred ionic, at least difunctional compounds useful as cross-linking 
agents are, however, ionic or charged compounds containing vinylsulfonyl, 
triazinyl, pyrimidinyl or 1,4-quinoxalinyl radicals. Reactive azo dyes 
(containing sulfonic acid groups, carboxyl groups or ammonium groups) 
belong to this class as do non-colored compounds with the aforementioned 
functions. An effective reagent may cross-link via chemical bonds, 
electrostatic interactions of ionic groups, and by chelation or 
coordination of polymeric functions with metal ions. The preferred mode of 
cross-linking is via a covalent bond, though the other two modes may also 
be used. In some cases all three modes of cross-linking may be operative 
via application of a single component (e.g. dye of formula (1), or may be 
reached by sequential or parallel application of 2 or 3 different 
compounds (dyestuff and metal salt). 
Multivalent metal salts that may find application in cross-linking said 
film via chelation or coordination bonds, are for example, CuSO.sub.4, 
CrCl.sub.3 and FeCl.sub.3. These salts may be applied alone, in 
combination with each other, or in combination with covalent (ionic) 
binding compounds. 
The ionic reactive dyes, which can belong to various categories, are for 
example, anthraquinone, formazan or preferably azo dyes, which are 
optionally metal complexe. Suitable reactive groups (which are part of the 
dyes) are the following: carboxylic acid halide groups, sulfonic acid 
halide groups, radicals of .alpha.,.beta.-unsaturated carboxylic acids or 
amides, for example, of acrylic acid, methacrylic acid, 
.alpha.-chloroacrylic acid, .alpha.-bromoacrylic acid, or acrylamide 
radicals of preferably low halogeno-alkylcarboxylic acids, for example, of 
chloroacetic acid, .alpha.,.beta.-dichloropropionic acid or 
.alpha.,.beta.-dibromopropionic acid; radicals of 
fluorocyclobutanecarboxylic acids, for example of tri- or 
tetra-fluorocyclobutane-carboxylic acid; radicals containing vinyl-acyl 
groups, for example, vinylsulfone groups or carboxyvinyl groups; radicals 
containing ethylsulfonyl (--SO.sub.2 CH.sub.2 CH.sub.2 OSO.sub.2 OH, 
--SO.sub.2 CH.sub.2 CH.sub.2 Cl) or ethylamino sulfonyl groups (--SO.sub.2 
NHCH.sub.2 CH.sub.2 OSO.sub.2 OH) and halogenated heterocyclic radicals 
such as dihaloquinoxalines, dihalopyridazonyl, dihalophthalizines, 
halobenzothiazoles and preferably halogenated pyrimidines or 
1,3,5-triazines, such as dihalotriazines, 2,4-dihalopyrimidines or 
2,4,6-trihalopyrimidines. Suitable halogen atoms are fluorine, bromine and 
especially chlorine atoms. 
Ionic groups are, for example, sulfato groups, sulfonic acid groups, 
carboxylic acid groups, ammonium groups formed from primary, secondary or 
tertiary amino groups and hydrogen, or quaternary ammonium groups and also 
phosphonium or sulfonium groups. Particularly advantageous results are 
achieved with substances containing sulfonic acid groups. 
The preferred reactive groups present in the ionic, at least difunctional 
compounds are dichlorotriazinyl, 2,4-dichloropyrimidinyl, 
2,3-dichloroquinoxaline-6-carbonyl, 4,5-dichloro-pyridazonylpropionyl, 
1,4-dichlorophthalazine-6-carbonyl, chlorobenzothiazole linked to the dye 
via --CONH--, --SO.sub.2 NH--, --NH--Ar--N.dbd.N-- (Ar=phenylene or 
naphthylene), 5-chloro-4-methyl-2-methylsulfonyl, pyrimidinyl, 
vinylsulfonyl, or precursors, which are convertible by alkaline treatment 
into vinylsulfonyl radicals, such as .beta.-sulfato ethylsulfonyl, 
.beta.-sulfatoethyl aminosulfonyl, .beta.-chloroethylsulfonyl or 
.beta.-sulfatopropionamido. 
Mostly preferred are reactive compounds (azo dyestuffs) containing sulfonic 
acid (--SO.sub.3 H) or carboxyl (--COOH) groups (either group may also be 
present in salt form, such as alkali metal salt (sodium salt)) and as 
functional moieties vinylsulfonyl (including the 
.beta.-sulfatoethylsulfonyl, .beta.-chloroethylsulfonyl or 
.beta.-sulfatoethylaminosulfonyl radical), halogenated triazinyl 
(dichlorotriazinyl), halogenated pyrimidinyl (2,4-dichloropyrimidinyl) or 
halogenated 1,4-quinoxalinyl radicals. 
The ionic or non-ionic at least difunctional compounds can be applied from 
0.1 to 20% aqueous solutions (suspensions) to the coated polymer. 
Preferably these solutions contain 0.5 to 10% or 0.5 to 5% by weight of 
the cross-linking agents. Their proportion to the coated membrane is about 
(0.5 to 10):1, preferably (0.5 to 5):1. 
By way of an example for the reaction of diazonium coating made from 
polyethyleneimine coating (containing hydroxyl and amino groups) when, 
e.g. cyanuric chloride is used, with an aqueous (aqueous-organic 
(acetone)) solution (suspension) of this reagent which (solution) can 
contain 0.5 to 5 parts of cyanuric chloride per part of membrane. The 
reaction temperature should be kept below 4.degree. C., for example, at 
0.degree. C., in order to prevent hydrolysis of the cyanuric chloride; the 
pH-value range is approximately between 8 and 11 and the reaction time can 
be from 1 minute to 5 hours. 
Non-ionic cross-linking agents can be used together with ionic ones. 
Unlike the state of the art practised in the manufacture of composite 
RO-membranes, the cross-linking for both the non-ionic and the ionic 
compounds preferably is carried out in an aqueous solution. Thus, water 
soluble or partially soluble at least difunctional reagents are found to 
give good results. 
After the application of the cross-linker a second polymer coating is 
applied. In this coating the hydrophilic polymers are used to further coat 
the semipermeable membrane substrate. The preferred polymers are aliphatic 
or aromatic polyfunctional oligomers or polymers which contain active 
hydrogen atoms bound to nitrogen, oxygen and/or sulfur atoms (amino, 
hydroxyl and/or thiol groups). The nitrogen atoms may be present as 
aliphatic (acyclic or cyclic), aromatic, or heterocyclic amino groups, 
which can be primary, secondary or tertiary. Or alternatively, but less 
preferred, they may be polymers of hydroxyl or thiofunctions. Examples of 
such polymers are polyethyleneimine (PEI) (M.W. 150 to 1,000,000), which 
can be partially alkylated or otherwise modified, polyvinylamines (M.W. 
1000 to 2,000,000), vinylamine/vinylsulfonate copolymers, polyvinyl 
alcohols (M.W. of 2000 to 200,000) or partially esterified (acetylated) 
polyvinyl alcohols, cellulosics, polybenzylamines, polyvinylanilines, 
polyvinylmercaptans, polyvinylimidazolines, polypiperidines, 
polydiallylamine derivatives (GB-A-2,067,614), amino modified 
polyepihalohydrin (GB-A-1,558,807), amino polysulfones, aminoalkyl 
polysulfones, amino polyarylene oxides, aminoalkyl polyarylene oxides, 
e.g. amino methylated polyphenylene oxide, 
polyamide-polyamine-epichlorohydrin condensation products, the 
condensation products of dicyandiamide, amine salts (ammonium chloride) 
and formaldehyde, or polymers of 2-hydroxyethyl or 
2-aminoethyl-methacrylates. Also of interest are the polymers prepared by 
using hydrophilic amines (EP-A-8945). 
The above polymers may be in part a copolymer or a polymer containing other 
monomeric units, block polymers or graft polymers. If they are copolymers 
the other monomeric units may or may not contain ionic groups 
(--SO.sub.3.sup..crclbar., --COO.sup..crclbar., --NR.sub.3.sup..sym.). 
One preferred polymer comprises poly-aliphatic (acylic or cyclic) amines. 
Polyethyleneimine is an example of this group. The range of molecular 
weights may be between 150 to 2,000,000, but preferably between 1000 and 
200,000 and most preferred between 10,000 and 70,000. Low molecular weight 
polymers of oligomers (150 to 1000) may be used, but the increase in 
solute rejection of the final membrane is not as great when higher 
molecular weight polymers are used. 
In another preferred case, water soluble amphoteric or block mosaic 
polymers containing both cationic and anionic groups, together with a 
reactive function (for example, --NH.sub.2 or --OH groups) for reaction 
with the polyfunctional cross-linking agents are useful for forming a 
mixed charge second layer. This type of membrane is particularly useful 
for separating salt from relatively low molecular weight organic solutes. 
An example of such a coating polymer is poly(vinylamine-vinyl sulfonate) 
or partially quaternized derivatives. 
Water is the preferred solvent for the aforementioned molecules, though 
other solvents such as low molecular weight alcohols or ketones may be 
used alone or in combination with water. The range of polymer 
concentration may be from 0.1 to 80%, but preferably between 1 and 30%, 
and most preferred between 1.0 and 15%. Liquid polymers can be used 
without solvents. The concentration of polymer needed to achieve optimum 
rejection/flux characteristics is a function of the molecular weights of 
the polymer and of molecular dimensions, membrane porosity and pore size, 
temperature, time of immersion, pH and subsequent washing steps. These 
factors (together with a rinse step after immersion) control the thickness 
of the polymer layer deposited on the membrane. The temperature of the 
polymer solution during membrane immersion may vary from 0.degree. to 
90.degree. C. The optimum temperature is a function of adsorption rates. 
The time of immersion may vary between 1 minute to 48 hours as a function 
of the temperature, pH, concentration, and the molecular weight, the 
dimensions and solution properties of the coating polymer. For example, at 
a pH of 8.0 and room temperature 10% polyethyleneimine in water coats a 
polysulfone membrane in 1 to 5 minutes, adequately for the practice of the 
present invention. On the other hand, polyvinylaniline (poly-aminostyrene) 
should be used for 1 hour in immersion to achieve optimum flux-rejection 
characteristics. 
The pH-value of the polymer solution may be adjusted to control the 
solubility of the polymer, the rate of reaction of the polymer to 
substrate and the quantity of polymer adsorbed to the surface. Thus, for 
amines, a pH-value above 7.0 increases nucleophilic reaction rates, and 
for membrane modifications a pH range of 7.0 to 10.0 was found to be 
optimum in most cases, though higher or lower pH-values could also be 
used. If more acidic pH-values are used to improve solubility of the 
coating polymer, a given time is allowed for adsorption of the polymer to 
the membrane and then the pH-value is increased above 7.0 for binding. 
After immersion the membrane coated with the second layer is rinsed in 
water to remove excess polymer. This step is a function of the coating 
polymers solution adsorption properties and concentration in solution and 
membrane porosity. The time of rinsing may vary from one minute to 48 
hours, but most preferably from 30 minutes to 4 hours for a 10% PEI 
solution used for 5 minutes. Excessive washing or rinsing results in 
membranes with lower than maximum rejection, but still higher than the 
unmodified membrane. Shorter rinsing time leaves a relatively thick 
deposit of polymer and results in relatively low fluxes. The pH-value and 
temperature of the rinsing solution may vary between 1.0 and 12, and 
0.degree. to 100.degree. C., respectively. Shorter rinsing times are 
requires at the higher temperatures, and may also vary as function of the 
pH-value. 
After the second coating the membrane is again cross-linked with preferably 
ionic at least difunctional compounds. They possess cross-linking 
properties and can enter into chemical bonding with both polymer layers. 
These compounds, which hat at least two functional groups, are chosen from 
the previously described class of ionic cross-linkers. The method of 
application is also as previously described. 
The ionic at least difunctional cross-linking agents serve to introduce 
positive or negative charges (ionic groupings) into the membrane surface 
and/or the pores and to cross-link the membrane, and is effected in one or 
two stages. 
The one-stage process means that the compound carrying the charge and the 
so-called fixing agent (for example, alkali) is used in one bath. 
The two-stage process comprises first the step involving the adsorption of 
the compound carrying the charge and then, in a separate reaction 
solution, the fixing step (chemical reaction between the polyfunctional 
compound and the coating polymer). The two-stage process is preferred 
since, on the one hand, the concentration of the at least difunctional 
compound in the adsorption solution can be kept lower and a solution of 
this type can optionally be used several times, and on the other hand, the 
total reaction time is shorter than in the case of the one-stage process. 
In the two-stage process, the concentration of e.g. a reactive dye in 
aqueous solution can be about 0.5 to 3%; the adsorption is carried out, 
for example, at temperatures of 20.degree. to 35.degree. C. over a period 
of 2 to 60 minutes; the pH-value can be 4 to 8. Fixing can then be carried 
out in an aqueous solution, the pH of which has been adjusted from 9 to 
12, and the reaction time can be about 30 minutes. The pH is adjusted to 
the desired value using any desired inorganic (sodium carbonate) or 
organic bases. 
If there are already ionic groups present in the coating polymers (anionic 
groups or anionic and cationic groups such as in amphoteric polymers) that 
form the second layer, the introduction of further charges into the 
surface of the membrane is not necessary; a cross-linking step with 
non-ionic cross-linking agents is sufficient. The second (top) layer of 
the inventive membrane, however, should always contain ionic charges, as 
hereinbefore defined. 
The inventive membranes which contain at least at the membrane surface 
(so-called second layer) an oligomer or polymer modified by an azo dye 
containing sulfonic acid groups, are particularly valuable and versatile 
in use. The azo dye can also contain a metal, for example, copper, bonded 
as a complex. 
Depending on the intended application, the inventive membranes can be in 
various (flat or tubular) forms, for example, in the form of sheets, 
leaves or tubes, or in the form of pockets, bags, cones or of hollow 
fibres. When subjected to severe pressure, the membrane can, of course, be 
protected by non-woven supports, supports made of textile fibres or paper, 
wire screens or perforated plates and tubes (modules). Within the range 
indicated further above, the pore size can be varied by means of different 
temperatures and can likewise be suited to the particular application. 
Thus, for example, by subjecting the membrane to heat treatment 
(50.degree. to 150.degree. C.) before or after their chemical modification 
it is possible to change the pore size and thus the flux and the rejection 
of the membranes. 
Compared with known modified membranes, the inventive membranes show good 
mechanical, physical and chemical stabilities, such as pressure, 
compaction, temperature, solvent, pH and (biological) degradation 
resistance. 
They further show a significant improvement in membrane rejection with 
minimal flux decline. Combined with a greater rejection stability, that 
is, the decline in rejection with time is reduced to a minimum. This 
improved performance can be derived from the first layer of the inventive 
composite membrane comprising the self-condensed polymer species which are 
cross-linked and by which penetration of subsequent layers into the 
smallest pores of the support is prevented. 
The final inventive membrane is useful in RO and UF and especially for 
applications in the range of pressures (5 to 50 bar) and cut-offs (100 to 
2000 MW) associated with membranes between RO and UF, with average pore 
sizes of between 1 to 500 A, preferably 10 to 100 A. 
The use of the inventive semipermeable composite membranes--which is an 
other object of the present invention--comprises in general processes for 
separating (ultrafiltration or reverse osmosis processes) solutes from a 
solution which comprises disposing the solution having an osmotic pressure 
on one side of the inventive composite membrane, and filtering it through 
the membrane by applying a hydraulic pressure, being greater than the 
osmotic pressure of said solution, against said solution and said 
membrane. 
The following applications (which can be characterised as separating 
concentrating or purifying methods) in particular are advantageous for the 
membranes according to the invention: 
1. The separation of low molecular organic and metal organic ionic 
substances from by-products from a reaction mixture and other substance 
which are contained therein, for example from salts, such as sodium 
chloride, sodium sulfate or sodium acetate (cut-off level about 300). 
2. The purification of effluents which are obtained from the production and 
use of dyes and fluorescent brighteners. 
3. The separation of ionic molecules (salts) from aqueous solutions which 
contain metal complexes, surfactants, dyes or proteins, the results 
obtained in this case being better, with regard to the efficiency 
(permeability/flux per unit time) and the separating effect, than those 
obtained with known membranes. 
The separation effect (the rejection) of the membranes can be measured as 
follows: a circular membrane with a surface area of 13 cm.sup.2, resting 
on a sintered stainless steel disc, is used in a cylindrical cell made of 
stainless steel. 150 ml of the solution (to be tested), which contains the 
substance to be tested in the concentration C.sub.1 (g of substance per g 
of solution), are introduced onto the membrane in the steel cylinder and, 
using nitrogen, subjected to pressure of 14 bars. The solution is stirred 
magnetically. The liquid which collects on the outlet side of the membrane 
is examined to determine its content (concentration) C.sub.2 of the 
substance to be tested, 3 samples of 5 ml each being taken from the start 
of the experiment. In general, the amount which flows through the membrane 
and the composition of the 3 samples are constant. The rejection can be 
calculated from the values obtained, using the equation: 
##EQU1## 
The amount of the material passed through the membrane per surface and time 
unit is found to be: 
EQU F=V.multidot.S.sup.-1 .multidot.t.sup.-1 
V: volume 
S: membrane surface area 
t: time 
F is approximately expressed in m.sup.3 .multidot.m.sup.-2 
.multidot.d.sup.-1, i.e. the number of cubic meters per square meter 
surface area of the membrane and per day, or in l/m.sup.2 .multidot.h, 
i.e. litres per square meter surface area of the membrane per hour. 
In addition to the measurement on flat membranes, measurements on tubular 
membranes 60 cm long, and with an outer diameter of 1.4 cm are also 
carried out. For this purpose, these tubular membranes are placed in a 
perforated tube made of stainless steel. 
The whole is placed in a tube made of polycarbonate. The outflow from the 
membrane is between this outer polycarbonate tube and the steel tube. The 
liquid is added as a stream of the solution in turbulent or laminar flow, 
under pressure. The flow rate is kept constant at 10 to 15 liters per 
minute. The rejection (R) and the flux (F) are calculated in the same way 
as for the flat membranes. 
In the following examples, the compounds of formula (1) to (6) can be used 
as reactive agents for cross-linking and charging the second polymer 
layer, while the dyes of formula (7) and (8) can be used in test 
solutions. Parts and percentages are given by weight--if not otherwise 
indicated. The temperature is indicated in degrees Centigrade. 
##STR3##

EXAMPLE 1 
A polysulfone membrane (UF-membrane) made from a polymer of repeating units 
of the formula 
##STR4## 
having a flux/rejection profile for various solutes as described in Table 
1, below, (untreated membrane) is modified by the following procedure: 
Immersion of the membrane in an aqueous solution of 5% of sodium nitrite 
and 0.5% polyethyleneimine (PEI) (MW average 30,000) having a pH of 0.5, 
adjusted by hydrochloric acid, for 30 minutes; removing the membrane from 
that solution and immersing it for 30 minutes in an aqueous alkaline bath 
(pH=12); then rinsing the membrane for 30 minutes in tap water and 
immersing it thereafter in a 2% aqueous suspension of 0.degree. to 
4.degree. C. of cyanuric chloride for 10 minutes. Then the membrane is 
washed for 10 minutes with ice water, immersed in a 10% aqueous solution 
of PEI (pH 8.5) for 5 minutes, washed for 2 hours, and then placed in an 
aqueous bath containing 1% of the reactive dye of formula (1) and 10% of 
sodium chloride for 15 minutes. Finally, the obtained membrane is drip 
dried for 10 seconds, immersed in a 2% solution of sodium carbonate for 30 
minutes at room temperature, and washed for 10 minutes with tap water. 
The performance of the so modified membrane is given in Table 1. 
TABLE 1 
______________________________________ 
Solute Untreated Modified 
concen- membrane membrane 
tration Rejection 
Flux Rejection 
Flux 
Solute % % 1/m.sup.2 .multidot. h 
% 1/m.sup.2 .multidot. h 
______________________________________ 
Dye of 1.5 42 220 99.9 82 
formula (8) 
Dye of 2.0 60 65 99 42 
formula (7) 
Congo Red 
1.0 30 200 99.6 94 
Toluene 1.0 12.0 95 17 130 
Sulfonic 
acid 
NaCl 1.0 0 235 5.0 116 
Dinitro- 
1.0 48 130 94 120 
stilbene 
disulfonic 
acid 
______________________________________ 
Testing conditions: pHvalue 6.5; 30.degree. C.; 25 bar; flat sheets. 
EXAMPLE 2 
A membrane similar to that of Example 1, but instead of a polysulfone, a 
substrate UF-membrane made from a polyether-ether ketone cast from a 15% 
solution of 95% sulfuric acid at room temperature and gelled in water, is 
used, with a rejection to the dye of formula (8) of 20%. This substrate is 
then modified as indicated in Example 1. The modified membrane shows a 
flux and rejection to dye of formula (8) (testing conditions: 5% dye 
solution, 20 bar, pH 7.0) of 99.9% and 65 l/m.sup.2 .cndot.h. 
A tubular membrane made of the same polymeric material and modified in the 
same way, shows a rejection to dye of formula (8) of 99.6%. The rejection 
to dinitrostilbene disulfonic acid increased from 5% to 94% for the 
untreated and modified membranes, respectively. 
EXAMPLE 3 
A tubular polysulfone membrane made from a polymer of repeating units of 
the formula 
##STR5## 
is modified according to the procedure of Example 1. The rejection and 
flux of the untreated and modified membranes to the dye of formula (8) 
(testing conditions: 5% dye solution, 20 bar) in a flat test cell is 68%, 
122 l/m.sup.2 .cndot.h and 98.6% and 156 l/m.sup.2 .cndot.h, respectively. 
EXAMPLE 4 
Example 1 is repeated using diazonium salt solutions made from different 
polymers and monomers other than PEI. These are: 
(4.1) Polyvinylamine.cndot.HCI (MW 50,000) 
(4.2) Poly(vinylamine/vinylsulfonate) (80/20) (MW 40,000) 
(4.3) m-Phenylene diamine 
(4.4) Polyvinylaniline. 
The results are given in Table 2. 
TABLE 2 
______________________________________ 
Rejection 
Flux 
Diazonium salt % 1/m.sup.2 .multidot. h 
______________________________________ 
(4.1) 99.1 123 
(4.2) 99.9 35 
(4.3) 99.8 196 
(4.4) 99.2 83 
______________________________________ 
Testing conditions: 25 bar; 5% solution of dye of formula (8); 30.degree. 
C. 
When Example 4 is repeated, but instead of using PEI as the second coating 
material a polymer of structures (4.1, 4.2 and 4.4) is used, then all 
membranes have above 98% rejection to the said test solute. 
EXAMPLE 5 
Example 4 is repeated with diazonium salt polymers (4.2) with the exception 
that the substrate UF-membrane is made of polyacrylonitrile instead of 
polysulfone. After modification the rejection increased to 98.6% from 45% 
for the untreated membrane. 
EXAMPLE 6 
Example 1 is repeated, with the exception that the step of the reaction 
with the charged multifunctional compound (dye of formula (1)) is replaced 
by a charged multifunctional compound of the formulae (2), (3), (4), (5) 
or (6). All the resulting membranes have rejections above 98% to dye of 
formula (8) at 25 bars and 30.degree. C. with fluxes above 50 l/m.sup.2 
.cndot.h. 
EXAMPLE 7 
The modification procedure of Example 1 is repeated using a sulfonated 
polyvinylidene fluoride of MW of 100,000 instead of polysulfone. 
The untreated membrane has a rejection to solute of formula (8) of 65%, and 
shows a rejection of 97% after modification. 
EXAMPLE 8 
Example 1 is repeated, using for the second coating polymer polyvinylamine, 
vinylamine/vinyl sulfonate copolymer, polypiperidine or polyethylenimine 
(MW 1000), instead of polyethyleneimine (MW 30,000). All new membranes 
show more than 98% rejections to dye of formula (8), less than 20% to NaCl 
and fluxes above 500 l/m.sup.2 .cndot.d. 
EXAMPLE 9 
Example 1 is repeated using polyaramide (an aromatic polyamide) instead of 
polysulfone to make the substrate. The untreated membrane has a rejection 
to the dye of formula (8) of 20%. After modification the rejection is 
99.5% with a flux of 900 l/m.sup.2 .cndot.d. 
EXAMPLE 10 
Example 1 is repeated using an aluminum oxide ceramic substrate having a 
rejection to the dye of formula (8) of 10%. After modification the 
rejection was 98% with a flux of 200 l/m.sup.2 .cndot.d.