DE2747408A1 - PERMSELECTIVE MEMBRANE AS WELL AS SOLUTION AND METHOD FOR MANUFACTURING THE SAME - Google Patents

Description

Dr.-Ing. Walter Abitz

Dr. Dieter F. Morf ~ j "

Dipl.-Phys.M.Gritschneder

8 Munich 86, Pienzenauerstr. 28

October 21, 1977 AD 4868

EGG. DU PONT DE NEMOURS AND COMPANY 10th and Market Streets, Wilmington, Delaware 19 898, V.St.A.

Permselective membrane and solution and method for making the same

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The invention relates to improved membranes for the selective separation of the components of aqueous compositions through reverse osmosis or ultrafiltration and a method for making the membranes.

Permeability-selective (permselective) membranes (on the concept of permselectivity see "Physik in our Time", Volume 6 (1975), No. 6, page 172), which preferentially let certain components of liquid mixtures through and others Withhold constituents, as well as the principle of reverse osmosis, in which a hydrostatic pressure that the osmotic If the equilibrium pressure of a liquid mixture is exceeded, the mixture is brought into action to make it easier constituents of the mixture that diffuse through, usually water, preferably before the less easily diffusing constituents, usually a salt to drift through the membrane opposite to the normal direction of osmotic flow, have long been known. More recent research in this area is primarily directed towards development of membranes for desalination of brackish water and sea water on a practical scale by reverse osmosis.

A complete separation of the more easily diffusing from the less easily diffusing components of liquid It is known that mixing is never achieved with permselective membranes in practical use. All components of a mixture diffuse to some extent through each membrane, which is a practically useful rate of passage for the more easily diffusing constituents.

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A main goal is to manufacture such membranes economically usable optimal equilibria between high passage speeds of the more easily diffusing .. Components and high degrees of repellency for the less easily diffusing salt components of liquid Mix. In this regard, aromatic, nitrogen bound synthetic organic polymers such as those described in U.S. Patent 3,567,632 have been found to be of value, and Since then, constant efforts have been made to strike a balance between the speed of passage and the salt repellency to improve in such membranes. For example, salt repellency is used improved by having the membranes with hydrolyzable tannins, as in the US patent application Serial No. 562 246 of March 26, 1975 is described, with a water-containing heavy metal composition according to the US Pat. No. 3,853,755 or treated with a selected ether according to US Pat. No. 3,808,303. All of these attempts to solve the Problems are directed to increasing the salt repellency by treating the membrane after it is made has been.

In contrast, according to the invention, the salt repellency is not but the water penetration speed improves compared to that speed, the membranes have that have not been treated according to the invention. Furthermore, in the context of the invention, the water penetration speed not by treating the membrane, but by treating the solution that increases the amount used to make the membrane serves.

One object of the invention is therefore a solution for production of permselective membranes, which are a water-miscible organic polar aprotic solvent essentially linear, aromatic, synthetic, organic

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niche, nitrogen-bound condensation polymer, which is used in The solution is contained in amounts of about 12 to 40 wt. #, based on the total weight of the solution, at least one in the Solvent soluble salt in amounts of from about 10 to 100 percent by weight based on the weight of the polymer and a surfactant in amounts from 100 to 10,000 ppm based on the weight of the polymer. The surfactant has a molecular weight of about 200 to 7,000 and contains (a) at least one hydrophobic moiety having a molecular weight of about 100 to 400, namely a hydrocarbon group represented by halogen (F, Cl, Br or J), -NOp or -OH may be substituted, and (b) at least a hydrophilic residue. The surfactant can

i) a non-ionic surfactant or ii) an anionic surfactant or
iii) an ampholytic surfactant of the general formula

COO ⁹

Y-CH

\ _Q be, ^N N® (CH)

in which Y is a hydrocarbon radical with about 6 to 20 carbon atoms means substituted by halogen, -NO2 or -OH can be.

The method according to the invention for the production of permselective Diaphragms is that one

(a) gives the solution described above the shape desired for a permselective membrane and

(b) the organic polar aprotic solvent in one removed from the solution in such a manner and at such a rate that the membrane is in the form it is in Stage (a) has solidified.

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Another feature of the invention is a permselective membrane, which consists essentially of an essentially linear, aromatic, synthetic, organic, nitrogen-bound Condensation polymers and a surfactant as defined above which is uniform in the polymer in an amount of about 10 to 10,000 ppm by weight of the polymer.

Permselective membranes should have high penetration speeds for one or more components of the mixture to be broken down and have a high repellency to one or more other components. The improved according to the invention Membranes have higher penetration speeds than similar membranes that do not contain a surfactant in their manufacture solution used have been generated. Particularly beneficial results can be obtained if you look at the improvement the passage speed according to the invention with the methods for improvement described above as known the salt repellency combined.

The permselective membranes according to the invention can be used in come in various forms, such as thin coatings on porous supports, thin films supported by porous supports be, thin-walled hollow fibers, etc. The porous supports in turn can be in the form of tubes, which inner or outer Carry membranes, or be designed, for example, in the form of flat plates or corrugated surface structures. Typical Devices for using the membranes for reverse osmosis separation are particularly disclosed in U.S. Patent 3,567,632 in Figs. 1, 2, 5 and 9 described.

The term "permselective" refers to the ability to preferentially allow one or more components of a liquid mixture to pass through, while at the same time the

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Obstructed passage of one or more other components will. The permeation rates through the permselective membranes become useful as the amount of a component expressed in a starting mixture, which in a given time under a certain pressure through a membrane of a given size passes through.

The efficiency of rejection of the solute by membranes in reverse osmosis for the passage of water (the repellency) are expediently expressed as a percentage of the salt in the aqueous starting mixture, which by the membrane passes through. The salt concentrations in the starting mixture and in the one that diffuses through the membrane Liquid can be determined by conductivity measurements and chemical analysis.

The permselective membranes are preferably used according to Invention used when the solute that is preferred to be rejected is a dissociated salt, such as sodium chloride, Sodium sulfate, or calcium chloride, and the salt is preferably rejected from an aqueous solution should, while water is under the influence of a pressure higher than the osmotic pressure of the solution opposite to that normal direction of osmotic flow passes through the membrane.

(1) The polymers

The polymers used in the present invention are essentially linear aromatic synthetic organic nitrogen-bound condensation polymers of the general formula

in the

(i) each -L group along the polymer chain independently of

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everyone else is a bonding group,

(ii) each -R- group along the polymer chain independently of each is an organic residue to others,

(iii) the degree of polymerization indicated by η is an integer corresponding to a film-forming molecular weight is. The terminal groups depend on the L and R groups.

The term "independent" means that each -L- or -R- group is the same or different from any other -L- or -R- group can be along the same polymer backbone chain.

"Condensation polymers" contain a backbone chain of alternating -L and -R groups, which are formed by a polycondensation reaction (as opposed to a polymerization reaction under the influence of free radicals). Usable are polymers with such high molecular weights that they are film- or fiber-forming, and which at room temperature in have a tack-free surface when dry. Polymers with an inherent viscosity greater than about 0.6 are for suitable for the purposes of the invention, and polymers having an inherent viscosity of about 0.8 to 3.0 are preferred.

"Nitrogen ^{-bonded 11} polymers contain nitrogen atoms in the polymer chain as links to at least about 50 % of the -L groups. The polymers can also contain other nitrogen atoms either as part of the -R groups or attached to the -R groups other functional groups that form during condensation reactions, such as ether and ester groups.

"Synthetic organic" polymers are man-made Polymers and consist essentially of carbon, hydrogen, oxygen, nitrogen and sulfur. This poly-

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mers can also contain smaller amounts of other atoms.

"Aromatic" polymers are those in which at least about 50% of the -R groups with a 5- or 6-membered ring system Contain resonance bonding, and which may contain heteroatoms such as oxygen and nitrogen.

"Substantially linear" polymers are essentially straight chain Polymers that have the general solubility and general characteristic melt properties of linear Polymers, in contrast to highly crosslinked polymers, have, however, smaller amounts of crosslinked and chain-branched structures.

The permselective membranes suitable for the purposes of the invention can consist of polymers which _{contain recurring 4L-R> n} units of a single type or of polymers which contain recurring units of several different types. Repeating units of different types can result from the presence of different -L groups, from the presence of different -R groups, or from the presence of different groups of both types. If the polymers contain different -L groups and different -R groups, these can be in ordered or random order. The membranes can also consist of compatible physical blends of polymers of the types described above.

(a) The binding group L:

The -L groups in the general formula fL-R ^ _n are preferably selected independently of one another such that at least 50 % of the -L groups in each polymer backbone chain are at least one of each of the structures

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X Z

η ι

-C- and -N-

contained in any order such that never a "* Structure of one of these two types is adjacent to more than one structure of the same type. It should be noted that the Structures of the linking groups mentioned here are given without regard to the direction in which the structures are read will; this means that these linking groups are in a single polymer chain both in the order listed as can also occur in the reverse structure.

In a class of for the membranes according to the invention Suitable polymers can include any "X" in the structure

Il

-C-

independently of any other oxygen or sulfur, preferably oxygen, and each ⁿ Z ⁿ in the structures

-N-

can independently of any other hydrogen, a Cj- to C ^ -alkyl radical or the phenyl radical, and preferably at least 1/4 of all radicals ¹¹ Z "are hydrogen atoms. Typical examples of -L groups of this class of polymers are

(a) O H

Il I

-C-N- (the amide group) '

(b) 0 O H

η η t

-C-C-N-

(the oxamide group) '

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(c) OHH

Il I I

-C-N-N- (the acylhydrazide group)

(d) OHHO

Il I I Il

-C-N-N-C- (the diacylhydrazide group)

(e) HOHH

I Il I I

-N-C-N-N- (the semicarbazide group)

L can also be the structure

in which the fourth valences of the carbonyl carbon atoms vizinally bound to an aromatic ring in the polymer chain structure, making the complete unit an imide structure of the type

forms.

In the preferred polymers of this type, two such units are one structure of the type

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O

η η

-Ν. ΕΓ N-

η η

O

, wherein E is a tetravalent aromatic radical tet signified that be a monocarbocyclischer, a monoheterocyclic, a fused carbocyclic or a fused hete rocyclischer radical or the general formula

can have, in which ρ has the value 0 or 1 and Y is a divalent radical, such as -CO-, -0-, -S-, -SO ₂ -, -NH-, or a lower alkylene radical.

In another class of for the membranes according to the invention Suitable polymers can have any structure

X η

-C-

a group in the -L group

N-η

-C-

be where the third valence of the nitrogen atom is attached to one aromatic ring is attached to that of the group

N-n -C-

in the polymer chain also through a structure

-N-

is separated, which is attached to the aromatic ring vizinal to the structure

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N-n

-C-

is bound so that the entire unit is a benzimidazole structure of type

.N,

forms. In the preferred polymers of this type, two such units in one structure are of the type

-e

I I

Z Z

linked together, where Z and E have the above meanings.

Preferably L has the meaning

OH
-CN- (amide).

(b) The organic group R:

The organic -R groups in the general formula ^ L-Rf _n are preferably selected independently of one another so that at least about 50% of the groups in each polymer backbone chain are aromatic radicals, the monocarbocyclic, monoheterocyclic, condensed carbocyclic or condensed heterocyclic radicals or radicals the general formula

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in which ρ has the value O or 1 and Y is a bivalent Group of the above definition means. These aromatic radicals can be unsubstituted or have substituents, which do not change the basic properties of the polymer. The particularly preferred substituents are the sulfonic acid group and the carboxyl group.

All other -R groups can be saturated aliphatic, carbocycloaliphatic or heterocycloaliphatic radicals with non-vicinal attachment points or alkylene radicals with fewer than about 6 carbon atoms between bond points.

The membranes according to the invention preferably consist of polymers which contain two or more different phenylene groups -R-. A particularly preferred class of polymers are those in which the -R groups consist of about 50 to 90 % m-phenylene groups and about 10 to 50% p-phenylene groups.

(c) "n" in the general formula fL-R ^ _n denotes the degree of polymerization and is an integer so large that the polymer has a film-forming molecular weight.

The polymers suitable for the purposes of the invention can be prepared according to US Pat. No. 3,567,632.

(d) Preferred polymer classes:

The preferred aromatic polyamides which are suitable for the membranes according to the invention include those with repeating structural groups of the general formula

H HO 0 ι ι η η

-N-Ar ₁ -NC-Ar ₂ -C-,

wherein Ar ₁ and Ar ₂ substituted or unsubstituted divalent

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term aromatic residues mean in which the chain-lengthening Bonds are in the m- or p-position to one another and any substituents on the aromatic nucleus are not condensed with the reactants during the polymerization will.

In a particularly preferred class of polymers, essentially all of the -L groups are amide groups and the -R groups are phenylene groups.

Among those preferred for the membranes according to the invention Polyimides include those that are formed by the action of heat and possibly chemicals on polyamic acids, as described in U.S. Patent 3,022,200 and in other patents and patent applications published in U.S. Patent No. 3,022,200 U.S. Patent 3,575,936 are mentioned. Suitable polyamic acids are those of the AB type, which are formed by self-condensation of a aromatic aminodicarboxylic anhydride or an acid salt thereof, as well as those of the AA-BB type which by reacting an aromatic tricarboxylic acid anhydride or an acid halide of the same or an aromatic tetracarboxylic acid dianhydride with an organic diamine form. The preferred polyamic acids have the structure

ι-HOOC. COOH-I

NC CNR ¹ -

in ni

HO OH

in ^ isomerism, R means a tetravalent organic

A radical containing at least 2 carbon atoms, with not more than 2 carbonyl groups of each polyamic acid unit being bonded to one carbon atom of the tetravalent radical, while R ^{1 is} a divalent radical which

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has at least 2 carbon atoms, each of the amide groups of adjacent polyamic acid units being bonded to a separate carbon atom of the divalent radical. The radical R of the tetracarboxylic acid dianhydride or the radical R ^{1 of} the organic diamine can be an aromatic radical, an aliphatic radical or a combination of an aromatic and an aliphatic radical connected to it by a bridge, the bridge consisting of carbon, oxygen, nitrogen, sulfur, silicon or phosphorus, or a substituted radical of this type, provided that at least about 50 % of these radicals are 5- and 6-membered ring systems with resonance binding included.

Aromatic polyhydrazides which are used for the membranes according to Invention preferred include hydrazine-derived aromatic condensation polymers of high (film and fiber-forming) Molecular weight. They are preferably characterized by the repeating structural unit

0 0
-Ar-C-NH-NH-C-

in the polymer chain, in which Ar is a divalent aromatic radical with at least 3 core carbon atoms between the binding sites means, wherein the aromatic radicals in the polyhydrazide to at least 35 mol% of other radicals than are p-phenylene radicals. The polymers of this structure include Condensation products of hydrazine and aromatic dihydrazides, e.g. a mixture of equal parts by weight of isophthalic acid dihydrazide and ethylene-bis-4-benzoyl hydrazide and one Mixture of aromatic dicarboxylic acid chlorides, e.g. a mixture of isophthalic acid chloride and terephthalic acid chloride.

The poly (amide hydrazides) which are preferred for the membranes according to the invention include polymers which are both amide and also contain hydrazide linking groups. Preferred Poly-

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mers of this structure are e.g. those produced by condensation one or more dicarboxylic acid chlorides, e.g. a mixture of 50 to 90% by weight isophthalic acid chloride and 50 bis-, 10% by weight of terephthalic acid chloride, with a mixture of m-phenylenediamine and at least one dihydrazide, e.g. ethylene 1- (3-oxybenzoic acid) -2- (4-oxybenzoic acid) dihydrazide, can be obtained. One especially for the membranes according to the invention the preferred polymer is that which is formed from a mixture of 80 mol% 3-aminobenzhydrazide and 20 mol% 56 4-aminobenzhydrazide and a mixture of 70 mol- # isophthalic acid chloride and 30 mol- # terephthalic acid chloride is synthesized. The production such polymers are described by Culbertson and Murphy in "Polymer Letters", Volume 5, pages 807-812 (1967).

Aromatic polybenzimidazoles, which are preferred for the membranes according to the invention, are characterized by recurring Structural units of type

H H

AT

in the -R ¹ - a divalent radical of the type described above and E a tetravalent aromatic radical, such as one of the types

and

means where ρ has the value 0 or 1 and Y means a divalent radical of the above definition. These aromatic Polybenzimidazoles can, for example, by condensation of one or more aromatic tetramines of the type

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NH ₂

with one or more Dicarbbnsäurechloriden the general formula

0 0

It Il

Cl-C-R-C-Cl

according to US Reissue PS 26 065 for US Patent 3,174,947 and according to Marvel et al in Journal of Polymer Science ", Volume 50, pages 511-529 (1961) and in" Journal of Polymer Science ", Part A, Volume 1, pages 1531-1541 (1963) will. Polymers of the same general type can also be derived from bis (3,4-diaminophenyl) compounds of the type

H ₂ N

as described by Foster and Marvel in "Journal of Polymer Science", Part A, Volume 3, pages 417-421 (1965) is. Other tetraamino compounds useful in making such polymers are described in U.S. Patent 2,895,948.

The polymers suitable for the membranes according to the invention are preferably so soluble in certain water-miscible dipolar aprotic solvents that the solutions can easily be brought into the membrane shape; See US Pat. No. 3,567,632. The polymers preferably have a solubility of at least about 10% by weight at 25 ° C. in a medium consisting essentially of 0 to 3% by weight of lithium chloride in dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, hexamethylphosphoric acid triamide or mixtures of these solvents.

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(2) solvents

The solvent in the one used to make the membranes Solution is a water-miscible polar aprotic * organic solvent. Any solvent that can be mixed in all proportions is called water-miscible mixes with water without phase separation. A polar aprotic solvent is one with a dielectric constant greater than about 15, which may contain hydrogen atoms but is incapable of producing suitable labile hydrogen atoms to donate with the formation of strong hydrogen bonds with an appropriate type of connections. Particularly preferred, water-miscible polar aprotic organic solvents are Ν, Ν-dimethylformamide, dimethyl sulfoxide, Tetramethylurea, N-methylpyrrolidone, dimethylacetamide, Tetramethylene sulfone and hexamethylphosphoric acid triamide.

The preferred solvents can be expressed by the general formula

^R 4 R <

N

_T_ [R ₃ J _b

represent in which FU, R ^ and Rc can be the same or different and denote alkyl or alkylene radicals with 1 to 4 carbon atoms, which are selected so that the total number of carbon atoms in all radicals R ,, R ^ and R ₅ no longer than 6, while a is 1 or 2, b is 0 or 1 and T is an acid residue such as

* C = 0 or -P- -N I

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and the sum a + b satisfies the valencies of the remainder T given above. R ,, R ^ and Rc can, as indicated, separate Be alkyl groups; however, two of these groups can also be present in combination in the form of an alkylene group, so that they form a heterocyclic ring which must contain a total of 5 or 6 nucleus atoms.

(3) The salt

The salt is soluble in the polymer and can be contained in the solution used to prepare the membrane in amounts of about 10 to 100% by weight, based on the weight of the polymer. 10 to 40% salt is used for the production of hollow fibers, because larger amounts impair the behavior of the solution during spinning.

The salts usually increase the water permeability of the finished product Membrane at least roughly speaking in the ratio of the percentage by volume of the salt, based on the volume of the polymer. The volumetric fraction of the salt can be determined from the weight of the salt and the weight of the polymer and calculate their densities. The densities of many suitable salts are given in the Handbook of Chemistry and Physics by Chemical Rubber Publishing Company. Although the densities of different polymers vary somewhat it has been found that a value of 1.31 g / cm is the density of each polymer suitable for the production of the membranes can be assumed without causing a significant error in the calculation of the volumetric fraction of the salts arises.

The type of salt influences the permeability and the separability of the membrane made from it. To the ones here Eligible soluble salts include the salts of metals in Groups IA and HA of the Periodic Table, the

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are preferably highly dissociated, and those in the existing The amount is soluble and chemically indifferent to the other substances used in the process. Suitable - .. Salts are lithium chloride, lithium bromide, lithium nitrate, calcium nitrate and calcium chloride. A suitable combination of properties can often be found through the cheapest selection on the type and amount of the polymer solubilizing salt in the solution.

Mixtures of several salts are preferred for the production of hollow fiber membranes. Particularly preferred are salts containing mixtures of lithium nitrate and lithium chloride between about 5 and 25% lithium nitrate and about 5 to 15 % lithium chloride, in which the total amount of lithium nitrate and lithium chloride is between about 10 and 40 % , all percentages being based on weight of the polymer.

(4) The surfactant

The surfactant is as defined above. In general, the form of surfactants, sometimes referred to as surface-active agents are, micelles and set the surface tension at relatively low concentrations in aqueous Solution.

The term "nonionic" means that the hydrophilic and hydrophobic residues of the surfactants are not positively or negatively charged.

The term "anionic" means that the surfactant is hydrophobic Contains remainder in a negatively charged group.

The term "ampholytic" means that the surfactant in the hydrophilic residue contains both an acidic and a basic function.

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The greatest increase in the speed of water penetration is observed with ampholytic and non-ionic surfactants. Of these two groups, the non-ionic ten- side preferred. In the case of the membrane produced with it, the salt repellency can decrease; but this decrease can be caused by it eliminates the need for the membrane after its production according to the known ones mentioned at the beginning of this description Procedures dealt with.

The nonionic surfactants are preferably reaction products of ethylene oxide and optionally propylene oxide with others Compounds that make the resulting surfactant hydrophobic Give properties such as alcohols, acids and alkylphenols. The particularly preferred nonionic surfactants correspond to the general formula

(1) R [0 (A) _n H] _X ,

in which (A) _{n is} the group f C ^ ¹ * 4 ⁰ ^ n or a mixture of the groups fC ₂ H ₄ O ^ and fC, H ^ O ^ _b , where η is an integer from 4 to in all cases 150 and preferably from 6 to 18, b is an integer from 0 to 30 and a is an integer of at least 2, the sum a + b = η, χ has the value 1, 2 or 3 and R is a saturated or unsaturated, straight-chain or branched-chain aliphatic hydrocarbon group, a cyclic hydrocarbon group or a combination of such groups and generally contains 8 to 24, preferably 8 to 18, carbon atoms. Examples of groups R are stearyl, lauryl, decyl and groups derived from aliphatic glycols and triols;

(2) R · -C ₆ H ₄ O (B) _n H,

where B is the group fC-jH ^ O} or a mixture of the groups fC ₂ H ₄ O ^ ₀ and fC ₅ H ^ O ^ _d , where m in all cases is an integer from 4 to 150 and preferably from 8 to 20, d an integer from 0 to 30, c-an integer from min-

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at least 2, the sum c + d = m and R ^{1 is} a usually saturated, monovalent aliphatic radical having 4 to 20, preferably 8 to 12, carbon atoms;

R ²

(3) R ³ -CON [(CH ₂ CH ₂ O) _p H] ₂

where ρ is an integer from 2 to 150, ζ the value 1 or 2, R is an alkyl group having 1 to 8 carbon atoms

2
and R for ζ = 2 a chemical bond to a group fCH, CHoO) H and for ζ = 1 an alkyl group with 1 to 8 carbon

P 2 3

material atoms means, with the proviso that R + R at least Contain 5 carbon atoms;

(4) the polyalkylene oxide block copolymers of the general formula

H0 (C ₂ H ₄ O) _e (C ₃ H ₆ O) _f (C ₂ H ₄ O) _g H,

in which f is an integer from 15 to 65 and e and g denote integers that are large enough that the sum e + g represents 20 to 90 % of the total weight of the polymer. Other special surfactants are

(5) CH ₃ (CH ₂ ) ₆ CH ₂ (OCH ₂ CH ₂ ) ₃ OH;

(6) CH ₃ (CH ₂ ) ₁₀ CH ₂ (OCH ₂ CH ₂ ) _χ2 (OCH (CH ₃ ) CH ₂ ) ₅ 0H?

(7) CH ₃ (CH J ₈ CH ₂ (OCH ₂ CH ₂ ) _{1 ()} OH;

(8) CH ₃ (CH ₂₎ J _{1 is} CH ₂ (OCH ₂ CH _{2) S} OH; and

(9) CH ₃ C (CH ₃ ) ₂ CH ₂ C (CH ₃ ) ₂ - ^ \ - (OCH ₂ CH ₂ ) _1Q 0H.

The non-ionic surfactant is particularly preferably one of the general formula

R [O (A) _n H],

in which R is an acyl radical (R ¹ CO-) with 8 to 20 carbon atoms, (A) has the meaning fCH ₂ CH ₂ 0}, η is a cardinal number between 8 and 18 and R ^{1 is} an alkyl, aryl, aralkyl

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or alkaryl radical. ^{R 1} is preferably an alkyl radical.

The anionic surfactant is preferably one of the general formula AM, in which M is a cation such as Na ⁺ , H ⁺ or NH ^, while A is an anion which is a hydrophobic hydrocarbon group with 8 to 20 carbon atoms

contains. A preferably has the general formula R ¹¹ A ¹ , in which R ^{n is} an alkyl group with 8 to 20 carbon atoms and A »has the meaning -COO ⁹ , -SO ₃ ⁹ or -OSO ₃ ⁹ .

The ampholytic surfactant is a betaine of the general formula

Y-CH

* (CH ₃ ) ₃

in which Y is preferably an alkyl radical having 8 to 15 carbon atoms means.

Representative special surfactants are

CH ₃ C (CH ₃ ) ₂ CH ₂ C (CH ₃ ) 2 - ^ "^ - (OCH ₂ CH ₂ ) ₁₀ 0H,

n-decyl polyethylene glycol, polyethylene glycol monolaurate, polyethylene glycol monostearate with a molecular weight of the glycol part of 400, 600, 800, 1000 or 6000,

CH ₃ (OCH ₂ CH ₂ ) X ₂ -O-CC ₁₇ H ₃₅ (n)

COO®
C ₁₄ H ₂₉ -CH ^

Ν · (CH ₃ ) ₃

CH ₃ (CH ₂ ) 3 ^ ₁ -O-SO ₃ Na and the like.

The amount of surfactant in the solution is between about 100 and 10,000 ppm, based on the polymer. Preferably lies

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the amount of surfactant between 300 and 1000 ppm, in particular between 400 and 880 ppm.

It can be assumed that the effect of the surfactant is to open the membrane structure when it solidifies. Sometimes will the surfactant is adsorbed onto the membrane, reducing the rate of passage. To the tendency to adsorb To counteract this, one can reduce the amount of surfactant used.

Since the surfactant is contained in the solution, it is evenly distributed in the membrane that forms from the solution. Extracting salts and solvents (as described below) releases some, if not all, of the surfactant from the Membrane removed. The amount of surfactant remaining in the membrane after extraction depends on the amount present at the beginning The amount and extent of extraction in the range of about 10 to 10,000 ppm.

To determine the surfactant content of the membrane, the Membrane extracted with a solvent for the surfactant and the extract analyzed. Polyethylene glycol monostearate is e.g. Extracted with methanol for 24 hours and the methanol extract analyzed by nuclear magnetic resonance spectroscopy. the Analysis of the membranes according to the invention by means of the attenuated total reflectance in ultrared spectroscopy shows no surfactant on the surface of the membrane.

(5) Production of the solution and production of a permselective membrane from the solution

The order of addition is for the preparation of the solution not decisive; however, the polymer is preferably added to the solvent which is the surfactant contains, and then one sets the salt or salts in sufficient

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lowing amounts in order to achieve the concentrations given above. Preferably, the polymer is present in amounts from 12 to 40 wt.%. The temperature and pressure of the addition are not decisive. Usually one works at temperatures between 20 and 80 C and atmospheric pressure. The mixed solution is used to make permselective membranes, and usually the solution is made by the action of heat and vacuum for the production of fibers to a polymer content of about 18 to 40% by weight and for the production of films to a polymer content of about 10% concentrated to 30 %, based on the total weight of the solution.

The membranes can be made by casting a film or spinning a hollow fiber can be produced from the concentrated solution.

In making films, the solution should preferably contain 15 to 18 percent polymer solids based on the total weight of the solution and 20 to 50 percent salts based on the weight of the polymer. The solution can be filtered through a fine filter and poured onto a support, carefully keeping dust and other foreign matter away. The film is spread with a doctor blade to a thickness of 0.05 to 1 mm and dried at a temperature between 75 and 150 ° C.

In the manufacture of hollow fibers, the dope preferably contains 28 to 30 percent by weight polymer solids and about 20 percent by weight up to 22% by weight of salt, the latter based on the weight of the polymer. The hollow fibers can be formed by spinning a heated solution of a suitable polymer through annular Spinnerets as described in US Pat. No. 3,397,427 at temperatures from 110 to 150 ° C, typically between 120 and 130 ° C. A usually pre-

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Partial drying of the spun threads can be done by heating them immediately after spinning Cell conducts through which a heated inert gas is passed at the same time.

After casting the film or spinning the hollow fiber, the product called the "protomembrane" contains Solvent and salt. The protomembrane contains about 25 to 80% by weight of polymer, based on the weight of the protomembrane, about 20 to 75% by weight organic polar aprotic solvent and about 10 to 100 weight percent salt based on the weight of the polymer. The "protomembrane" is a shaped structure (e.g. film or hollow fiber) that is dimensionally stable.

Solvent and salt are exchanged and extracted with a rinsing agent, which is a solvent for the salt, is miscible with the solvent, is practically chemically indifferent to the polymer and is practically a nonsolvent for the polymer. The detergent extracts most of the solvent and salt from the protomembrane, forming the actual membrane. Suitable rinsing agents are water, methanol, ethanol and the like. The Protomerabran should be treated with the detergent until at least 75 % of the salt or at least 75 % of the solvent has been extracted. Preferably, the salt and solvent are substantially completely removed. The temperature of the detergent should be between about 0 and 40 ° C.

The extraction of salts, any remaining solvent and other substances from protomembrane in the production of permselective membranes can be continuous or be carried out on a rudimentary basis. Immediately after the protomembrane is formed, the membranes are cooled and

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by flooding with water or with circulating Water containing the extract is partially extracted.

To increase the water speed through ~ * To observe hollow fiber membranes, it is advantageous to examine the fibers after the extraction of a solvent and salt Subject to heat treatment. The fibers can expediently for this purpose, be treated with water at 40 to 80 ° C for about 1/2 to 1 1/2 hours.

The following examples illustrate the invention. The ones specified therein Unless otherwise stated, parts of substances are based on weight. The percentages of the solution of polymers relate to the total weight of the solutions. The percentages of salts and of the polymer solutions other substances refer to the weight of the polymers in the solutions, unless otherwise stated. The inherent Unless otherwise stated, viscosities of the polymers are measured on polymer samples of 0.5 g in a solution determined the 4 g of lithium chloride in 100 ml of dimethylacetamide contains.

Comparative example A.

This comparative example illustrates the properties of fibers obtained using a cooling temperature of 13 C are spun from a solution that does not contain a surfactant.

A polyamide is prepared according to Example I of US Pat. No. 3,775,361 from a mixture of 67 % m-phenylenediamine and 33 % calcium salt of m-phenylenediamine-4-sulfonic acid and a mixture of 70 % isophthalic acid chloride and 30 % terephthalic acid chloride. The inherent viscosity of the polymer is between 1.2 and 1.3. It is neutralized with calcium hydroxide, washed three times by stirring with water and dried at 140.degree.

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AD 4868 3 &

The polymer flakes are dissolved in dimethylacetamide, whereupon lithium chloride and lithium nitrate are added. The pH value determined with the glass electrode is determined by adding an aqueous =. rigen slurry of lithium hydroxide adjusted to 6 to 7. The solution thus obtained contains 24 % polymer, 6 % lithium chloride and 15.5 % lithium nitrate. The solution is filtered and concentrated to 28.5% polymer under the action of heat and vacuum for spinning.

The concentrated solution, i.e. the spinning solution, is spun through an annular spinneret with 150 holes, as shown in U.S. Patent 3,397,427. The temperature of the solution is 125 ° C.

The spun fibers are passed through a cell held at 160 to 180 ° C, 5.8 m long and 22.9 cm wide and in cocurrent at 185 °
(Nitrogen) treated.

in cocurrent at 185 ° C with an inert gas drawn in

When leaving the cell, the partially dried fiber is cooled with a liquid at 13 ° C. Then she will deposited in a container at a speed of 116 m / min, the liquid being sprayed into the container at 13 ° C will. The liquid used for cooling and laying down is a 4.2 percent solution of dimethylacetamide in water, determined by the refractive index.

The laid fiber is then heat treated using a two stage countercurrent extraction system in which liquid from each stage is sprayed over the fiber through a spray nozzle and circulated. The temperature is 50 ° C. The duration of each stage is 8 hours. Pure water is fed to the last stage. The first stage liquid is used to keep the cooling liquid at a dimethylacetamide concentration of 4.2 % as determined by the refractive index.

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The extracted fibers are made by the construction of diffusion systems, containing these fibers, and testing of diffusion systems. The results become the following data calculated:

The outer diameter of the fiber is determined by measuring the volume of water displaced by a given length of fiber and the Number of fibers calculated according to the following equation:

1/2

OD

4 χ V

JT χ L χ Ν

χ 10

In this equation:

V = displaced water volume, cm,

L = fiber length, cm

N = number of threads,

OD = outer diameter of the fiber, pm.

The clear width of the fiber is calculated using the following equation:

ID

7.05 x 10 ¹⁰ x F χ (Lp + La / 2) Pd χ Ν

1/4

In this equation:

ID = clear width of the fiber, pm,

F = the rate of water flow through the device in units of 3.785 l / day,

Lp = pot length of the diffusion device in units of 0.3048 m,

La = active length of the fiber in the device in units from 0.3048 m,

Pd = overpressure at the dead end of the tube in units of

0.07 kg / cm,
N = number of threads in the diffusion device.

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This equation applies assuming that the pressure at the dead end of the tube is less than 2/3 of the supply pressure.

The percentage salt passage SP is given by the following equation calculated:

Salt concentration in the diffusion product SP * - χ 100

Salt concentration in the feed

The water permeability constant Kw for films is defined as

F - Kw χ Α χ Pe.
In this equation mean

F = diffusion rate in units of

3,785 l / day,
A s = area of the film through which the diffusion takes place,

in units of 929 cm,
Pe = effective pressure in units of 0.07 kg / cm = hydraulic pressure drop from one side of the film to the other minus the difference in osmotic pressure

from one side of the film to the other, Kw = water permeability constant in units of [3.785 1] per day per [0.07 kg / cm ² ].

The corresponding equation for a fiber using the same definition for the water permeability constant as for movies is the following:

1,031 x 10 ~ ⁵ χ ID ^ χ Kw χ OD χ N χ La χ Ps ID ^ + 7,236 χ 10 ⁵ χ Kw χ OD χ La χ (Lp + La / 3)

In this equation, Ps means supply pressure reduced the osmotic pressure difference between the solution outside the fiber and the diffusion product. The other big ones

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are as defined above. The constraint imposed on this equation is the same as the constraint on the clear one Width of the fiber. Converted to Kw, the equation ~ " the following form

_Kw . ID x F

OD χ La χ (1.031 x 10 " ⁵ χ Ps χ ID ⁴ χ Ν - 7.236

χ 10 ⁵ χ F χ (Lp χ La / 3)).

This equation is used to calculate the water permeability constant used.

Each diffusion device is made from a single strand of fibers (150 filaments) as a two-end diffusion device, but studied as a single-end diffusion device. A strand of 150 hollow fibers is folded over half its length, so that 300 parallel fibers are obtained, and these are inserted, when wet, into a rigid tube which has two side tubes at one end. The two ends of the 150 thread strand are inserted into the two side tubes and cemented with epoxy resin. The loose ends outside the side tubes are cut off so that the hollow fibers are opened for the flow of liquid. A manometer is connected to one of the side pipes in order to measure the pressure at the dead end of the pipe. In its part containing the threads, the diffusion device is 76.2 cm long and has a pot length of 10.16 cm. The diffusion devices are operated at 25 ° C with feed of the starting material from the shell side under an overpressure of 28 kg / cm with a degree of conversion (i.e. diffusion rate, divided by feed rate, χ 100) of 4 to 6 % using 5000 ppm sodium chloride in water checked.

The average fiber properties in this comparative example A (in which the solution to be spun contains no surfactant) the following:

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OD = 87.8 µm

ID a 40.1 pm

Kw = 497 ml / m ² / day per 0.07 kg / cm ²

SP * 4.5 %.

Comparative example B

This example illustrates the properties of a fiber which, at a cooling temperature ' sid has been spun.

at a cooling temperature of 10 C from a solution without ten-

Polymer flakes and fibers are produced according to Comparative Example A with the difference that the temperature of the Cooling containers and the liquid used when laying the thread is 10 ° C. The experimental data become the following Calculated fiber properties:

OD = 87.2 µm

ID = 40.6 µm

Kw m 456.3 ml / m ² / day 0.07 kg / cm ^{2 each}

SP% 4.0 %.

example 1

This example illustrates the properties of fibers spun from a dope which is 857 ppm Polyethylene glycol monostearate (as a surfactant), based on the polymer, contains. The molecular weight of the polyethylene glycol unit of the monostearate is 1000.

The surfactant is produced as a 10 percent solution in dimethylacetamide. This solution becomes 1/4 of that used to dissolve the polymer flakes Dimethylacetamide used according to Comparative Example A was added. The solution of the polymer flakes and the Fibers are produced according to Comparative Example A. The cooling and thread depositing temperature is 13 ° C. From the

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The following fiber properties are calculated for search results:

OD = 87.5 pm

ID = 40.3 pm

Kw = 668 ml / m ² / day per 0.07 kg / cm ²

SP = 5.2 %.

As you can see, Kw is much higher than in Comparative Examples A and B.

If you have 894 ppm polyethylene glycol monostearate with a molecular weight the polyethylene glycol unit of the monostearate of 600, based on the polymer, used, the calculated following fiber properties:

OD = 87.5 µm

ID β 41.8 µm

Kw = 668 ml / m ² / day per 0.07 kg / cm ²

SP = 4.7 %.

If you have 440 ppm polyethylene glycol monostearate with a molecular weight the polyethylene glycol unit of the monostearate of 600, based on the polymer, used, the calculated following fiber properties:

OD ss 87.2 µm

ID - 41.3 pm

Kw - 607 ml / m ² / day per 0.07 kg / cm ²

SP = 4.5%.

Example 2

This example illustrates fibers that have been spun from a spinning solution containing 801 ppm of C-cetyl betaine (as a surfactant), based on the polymer. The cooling temperature is

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The surfactant is obtained as a 100 percent active ingredient and diluted with dimethylacetamide to a 10 percent solution. This solution is 1/4 of that used to dissolve the polymer flakes. Dimethylacetamide used according to Comparative Example A was added. Polymer flake and solution are according to the comparative example A manufactured. The fiber is spun according to Comparative Example B. Medium fiber properties:

OD = 86 2 around ID = 41, 7th around

Kw = 586.7 ml / m ² / day per 0.07 kg / cm ² SP = 7.9 %.

Example 3

This example illustrates the properties of fibers spun from a solution containing 816 ppm sodium stearyl sulfate (as a surfactant), based on the polymer, with some other long chain impurities. the Cooling temperature is 10 C.

A 47 percent aqueous solution is used as the surfactant, which is diluted to 10% with dimethylacetamide. This solution is added to 1/4 of the dimethylacetamide used to dissolve the polymer flakes according to Comparative Example A. Polymer flake and solution are produced according to Comparative Example A. The fiber is spun according to Comparative Example B. Medium fiber properties:

OD = 86.2 µm

ID = 41.3 µm

Kw = 513 ml / m ² / day per 0.07 kg / cm ²

SP = 8.4 %.

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The fiber properties given in Examples 1 to 3 are made by making diffusion devices and Carrying out the tests as in Comparative Example A -. wrote, determined.

End of description.

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Claims (3)

27A7A08 AD 4868 claims 1. Permselective membrane based on a linear, aromatic, synthetic, organic, nitrogen-bound condensation polymers, characterized in that they are evenly distributed in the polymer in amounts of about 10 to 10,000 ppm, based on weight of the polymer, a surfactant having a molecular weight of about 200 to 7,000 which (a) at least one hydrophobic radical with a molecular weight of about 100 to 400, namely a hydrocarbon radical or a substituted by halogen (F, Cl, Br or I), -N0_ or -OH Hydrocarbon radical, and (b) contains at least one hydrophilic radical and from the group of i) non-ionic surfactants,
ii) anionic surfactants and
iii) ampholytic surfactants of the general formula COO ⁹ V - CH _x is selected in which Y is a hydrocarbon radical having about 6 to 20 carbon atoms, which can be substituted _{by halogen, -NO 2 or -OH.} 2. Solution for the production of permselective membranes according to Claim 1 containing (A) a water-miscible organic polar aprotic Solvent, (B) an essentially linear, aromatic, synthetic, organic, nitrogen-bound condensation - 1 809817/0922 AD 4868 -2. " polymer in amounts of about 12 to 40 wt.%, Based on the total weight of the solution, and (C) at least one salt soluble in the solvent in Quantities of about 10 to 100% by weight, based on the polymer, characterized in that it is also a surfactant according to Claim 1 in amounts of 100 to 10,000 ppm based on the weight of the polymer contains. 3. Process for the production of permselective membranes according to claim 1, characterized in that one (A) gives a solution according to claim 2 the shape desired for the permselective membrane and (b) the organic polar aprotic solvent in such a manner and at such a rate from the solution removes that the membrane solidifies in the shape it took in step (a). 809817/0922