DD150066A5 - METHOD FOR PRODUCING AN ANISOTROPIC MEMBRANE - Google Patents

Abstract

The invention relates to processes for the preparation of anisotropic membranes and in particular of hollow fiber membranes. These membranes are made from a solution of a membrane-forming polymer in a liquid carrier. The polymer solution is provided in the form of a precursor and then coagulated in a liquid coagulant containing water to form the anisotropic membrane. The liquid carrier used contains an N-acylated heterocyclic solvent of the general formula in which X is -CH &sub2;, -N (R ') - or -O-, R is hydrogen, methyl or ethyl, and R' is hydrogen or methyl , In the preparation of the anisotropic hollow fiber membranes, the solution of a hollow fiber-forming polymer in the liquid carrier is extruded through a donut-spinneret to form a hollow fiber precursor which is coagulated in a liquid water-containing coagulant to form the hollow fiber membrane. The method is particularly suitable for d. Production of Polysulfone hollow fiber membranes having a homogeneously formed, selective skin on an open-cell carrier and having a high resistance to collapse. The membranes are particularly useful for the separation of gases.

Description

The present invention relates to processes for the preparation of anisotropic membranes, and more particularly to hollow fiber membranes. *** "" Particularly interesting articles of the present invention include processes for producing polysulfone hollow fiber membranes suitable for the separation of gases in which the material of the hollow fiber membrane causing separation by selective permeation, and anisotropic polysulfone hollow fiber membranes.

Characteristic of the known technical solutions The service life of the membranes used for the separation of liquids often depends on the cost of the apparatus and its operation compared to other separation methods, such as absorption, adsorption and liquefaction, including the energy consumption, the desired degree of selectivity Separation, the total pressure losses caused by the apparatus for carrying out the separation process, which can be tolerated, the useful life and the size of such an apparatus, and the ease with which such an apparatus can be operated. Therefore, membranes are required which ensure the desired Trennselektxvitäten, flows and strengths. In addition, in order to be commercially attractive on an economical basis, the membranes are preferably used in large quantities while achieving a reliable product.

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quality and can be installed easily and relatively cheaply in a permeator. Particularly advantageous membranes are uniform, anisotropic hollow fiber membranes comprising a relatively thin layer (often referred to as a release layer, barrier layer or active layer) integrated with a porous structure which is a support for the release layer and the passage of liquids if anything, offers little resistance. In order to produce these integrated anisotropic membranes, a uniform membrane structure must be formed which has exactly opposite structures. The release layer must be formed to be thin and, if any, have few pores or other defects. On the other hand, the conditions under which a uniform anisotropic membrane is made must also provide a support structure which is highly open so as to offer little resistance to liquid flow.

Membranes were made in film and hollow fiber form. With regard to the production of uniform, anisotropic membranes in film form, numerous proposals have already been made. In general, anisotropic film membranes are formed by casting a solution of the polymer in a solvent to form the membrane on a surface, e.g. a polished glass surface, manufactured. One can

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at least partially allowing the polymer to coagulate in air or in a gaseous or vaporous environment, and then it is usually immersed in a liquid coagulant. The production of anisotropic film membranes takes place with considerable flexibility. For example, since the polymer solution is placed on a support, the membrane precursor structure does not need to be self-supporting, at least until after coagulation is complete. Similarly, since a surface of the cast membrane is in contact with the support, each side of the membrane may be subjected to various coagulation conditions, thereby making it possible to achieve substantially diverse structures on each surface of the membrane. As a result, membranes having a relatively thin layer substantially free of pores may be obtained on one surface of the film membrane while the remainder of the membrane may be relatively porous. In addition, coagulation conditions, including coagulation times, can be varied over a wide range to achieve the desired film-membrane structure since the film-membrane precursor is supported.

In many cases, however, film membranes are not as attractive as other gas separation equipment due to the need to support the film membranes with it

they withstand the operating conditions and due to the great complexity of an apparatus containing film membranes. Membranes in the form of hollow fibers can overcome many disadvantages of the film membranes for many separation operations. The hollow fibers are generally self-supporting even under operating conditions, and can provide a larger membrane surface per volume unit of the separation apparatus than such apparatuses provided with film membranes. Therefore, separation apparatuses containing hollow fibers may be very interesting and suitable from the standpoint of convenience, size and reduced complexity of construction.

Compared to the production of a film membrane many different considerations are necessary in the production of a hollow fiber membrane. For example, in a method of spinning a hollow fiber membrane, no solid support or barrier may be provided. Moreover, the polymer solution in spinning processes for providing a self-supporting extrudate before and during coagulation must have a sufficient viscosity, and the coagulation must be carried out rapidly after the extrusion, so that the hollow fiber membrane is not adversely affected.

Processes for the formation of uniform, anisotropic membranes need not only meet the criteria for the formation of

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they must also be compatible with the spinning performance for hollow fibers. Thus, many constraints are imposed on the procedures available for the preparation of uniform, anisotropic hollow fiber membranes. Usually, in the hollow fiber membrane spinning process for producing the hollow fiber membrane, a solution of the polymer in a solvent is extruded through a spinnerette suitable for forming a hollow fiber structure and a gas or liquid is held within the hollow fiber core of the hollow fiber extrudate such that that the hollow fiber shape is maintained. The hollow fiber extrudate must be rapidly coagulated, e.g. by contacting with the non-solvent for the polymer so that the hollow fiber shape is maintained. The hollow fiber spinning process contains many variables which may affect the structure or morphology of the hollow fiber membrane, such as the state of the polymer solution when extruded from the spinneret, the nature of the liquid held in the hollow fiber core of the hollow fiber membrane extrudate , the environment to which the exterior of the hollow fiber extrudate is exposed, the speed of coagulation of the polymer in the hollow fiber extrudate, and the like. Since the hollow fiber production process is one of coagulation of a polymer from a polymer solution, the nature of the solvent

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For the polymer for the determination of the morphology of the hollow fiber membrane and their separation properties of the polymer to be highly influential.

The solvent must have many properties to be suitable for the preparation of anisotropic membranes (especially anisotropic hollow fiber membranes). For example, the solvent (or solvent containing a liquid carrier) must be capable of dissolving the polymer for making the hollow fiber membrane, but allowing the polymer to coagulate rapidly to form the anisotropic structure. Moreover, if hollow fiber membranes are desired, the solvent (or solvent containing a liquid carrier) should be capable of facilitating the preparation of a polymer solution having suitable viscosities for the formation of a hollow fiber membrane, and these viscosities may advantageously be used without the use of excessively high concentrations of polymer in the solution can be achieved. Since beneficial hollow fiber membranes are often obtained when the extrudate suffers a significant temperature drop on exit from the spinneret, the liquid carrier should be able to provide suitable viscosities for the formation of the hollow fiber at elevated temperatures, which elevated temperatures achieve the significant temperature drop

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facilitate.The solvent or any other

increased /

Components of the liquid carrier should not be degraded at such temperatures. The solvent should be miscible with the non-solvent used to aid in the coagulation of the polymer and have the ability to be removed from the coagulated structure, e.g. by washing, so that the membrane is not improperly plasticized and weakened by the solvent. Moreover, the solvent (or solvent containing a liquid carrier) should not have excessively high heat of dilution in the non-solvent used to aid coagulation of the polymer.

In order to make the process interesting for the production of technical quantities of membranes, it is also desirable that the process operate safely and economically. Therefore, the solvent should not be excessively toxic, and advantageously the solvent should have a very high potency

low vapor pressure to minimize the risk of inhalation and / or air pollution. In addition, a solvent with a very low vapor pressure can also reduce the risk of explosion and fire to a minimum. Furthermore, waste materials from the spinning process should

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th that they can be economically and safely eliminated or recycled in a circle.

Since the solvent is only a component used in the spinning process, other components, such as the liquid within the hollow fiber core of the hollow fiber extrudate, the non-solvent to aid in the performance of coagulation, the wash liquors should be removed to remove solvent from the hollow fiber membrane £ n, and the like, also be economical and secure. Heretofore, it has been proposed to use, for example, gasoline, kerosene or other hydrocarbonaceous materials in the spinning process, either as a coagulant or to aid in drying, as for example in U.S. Patent 4,127,625. Such materials clearly exhibit toxicity and pose a fire hazard problem. as well as their elimination. Moreover, the cost of these hydrocarbonaceous materials in the amounts needed to achieve the effect, for example, for coagulation, washing, etc., can be a determining factor in the economics of the spinning process. Accordingly, it is desirable to use highly safe, readily available materials, such as water, wherever possible in the spinning process.

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special as a non-solvent to help carry out the coagulation and during the wash to remove solvent from the hollow fiber membrane. The ability to use water will, of course, to a considerable extent depend on the properties of the solvent with respect to water, i. from the solubility in water, the heat of dilution in water, the stability in water, and the like.

Object of the invention

This invention provides processes for making anisotropic membranes that use certain beneficial solvents. The process of the present invention can provide anisotropic membranes which are characterized by having a very thin, relatively small pore release layer on an underlying region of open-celled structure which provides low resistance to liquid flow. These membranes may be of particular interest for gas separations. In addition, polymers that can be used to make membranes in accordance with the present invention include polysulfones that have desirable strength and chemical resistance as well as desired permeation properties in terms of their permeate flux and selectivity. Advantageously, the process of the present invention may include water as a non-solvent

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use means to assist in the coagulation of the polymer and to wash out the solvent from the membranes. In addition, the solvents have low vapor pressures, show no undue explosion or fire hazards and can be economically or safely removed or recirculated.

Explanation of the essence of the invention

According to the present invention, an anisotropic membrane is prepared from a solution of a membrane-forming polymer in a liquid carrier containing an N-acylated heterocyclic solvent represented by the following general formula

χ ν-c-R

in which X is -CH--, -N (R ¹ ) - or -O-, R is hydrogen, methyl or ethyl, and R ^{1 is} hydrogen or methyl. The polymer solution is provided in the form of a precursor and then coagulated in a liquid coagulant containing water to form the anisotropic membrane. The anisotropic membrane may be a film, or preferably a hollow fiber. Typical N-acylated heterocyclic solvents include 1-formylpiperidine, 1-acetylpiperidine, 1-formylmorpholine and 1-acetylmorpholine. A preferred N-acylated heterocyclic

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Solvent includes 1-formylpiperidine. Reilly Tar & Chemical Corporation, in their brochure titled "1-Formylpiperidines", reports that 1-formylpiperidine has a boiling point of about 222 ° C, a vapor pressure of 0.111 mm Hg at 25 ° C, a flash point of about 102 ° C, and a LD ₅₀ (oral, rats) of about 0.88 g / kg body weight.

In the method of the present invention for making hollow fiber membranes, the polymer solution is at a temperature high enough to maintain the fiber-forming polymer substantially in solution and the polymer solution to a fiber-forming viscosity prior to extrusion of the hollow fiber precursor. The polymer solution is extruded through an annular spinnerette to form a hollow fiber precursor. The injection fluid is preferably highly miscible with the liquid carrier and therefore often contains water. The hollow fiber precursor is then contacted with the liquid coagulant, which is a non-solvent for the polymer in the polymer solution. The liquid coagulant is preferably highly miscible with the liquid carrier and the injection liquid. Usually, the temperature of the liquid coagulant is sufficiently low that the polymer solution is extremely viscous at this temperature and may even be a gel. The contact of the hollow fiber precursor with

the liquid coagulant is made for a sufficient period of time to substantially completely coagulate the polymer in the hollow fiber precursor under the conditions of the liquid coagulant and thereby provide a hollow fiber. The hollow fiber is then washed, i. contacted with a water-containing non-solvent for the polymer which is miscible with the liquid carrier to reduce the content of the liquid carrier in the hollow fiber to less than about 5 weight percent, based on the weight of the polymer in the hollow fiber , The washed hollow fiber may then be dried at a temperature at which the selectivity or flow developed by the hollow fiber is not unduly adversely affected.

In one embodiment of the present invention, the hollow fiber membranes preferably have a relatively circular cross-section with a circular, concentric hollow fiber core. In many cases, the hollow fiber membrane may be circular and concentric within the machining tolerances required to produce suitable spinnerets. The outer diameter of the hollow fiber membrane can vary widely, e.g. from about 100 or to 1000 or more microns. Often the outside diameter of the hollow fiber membrane is about 200 or 300 to 800 microns.

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The ratio of the thickness of the wall to the outer diameter of the hollow fiber membrane may also vary widely depending on the required collapse pressure that must be present for a given separation process. Since the porous support is open, an increase in wall thickness can not result in excessive reduction of flow through the membrane wall. Typical thickness to outside diameter ratios are about 0.1 or 0.15 to about 0.45, very often about 0.15 to 0.4.

The pore volume of the hollow fiber membranes, i. the lying within the wall of the hollow fiber membrane areas which are free of the material of the hollow fiber membrane is essential. The pore volume may be determined by a density comparison with a volume of the block polymer (or other hollow fiber material) which would correspond to a hollow fiber of the same superficial, overall physical dimensions and configurations as the wall of the hollow fiber membrane. Because the porous support of the hollow fibers is open, relatively low pore volumes for anisotropic hollow fiber membranes can be achieved without a disproportionately low permeate flux occurring. Often the pore volume is at least about 30 to 35, e.g. at least about 40, greater than about 45 or 50. Percent by volume, and it can be up to 65 or 70 or more vol%. , '*'

If

The liquid carrier may consist essentially of the solvent, or the solvent may be mixed with one or more other components to form the liquid carrier. The other components may be solid or liquid at room temperature, but are dissolved in the liquid carrier. In many instances, especially when the precursor is exposed to the atmosphere prior to coagulation of the polymer, it is preferred that the liquid carrier (including any diluent) be relatively non-volatile, eg, the liquid carrier advantageously has no component (solvent or diluent) a vapor pressure of above about 0.8, namely above 0.6 atmospheres at the temperature of the polymer solution in the extrusion. However, when a more volatile component is employed in the liquid carrier and the precursor is exposed to an atmosphere prior to contacting the liquid coagulant, the atmosphere to which the precursor is exposed may advantageously contain substantial amounts of such a more volatile component to delay the loss of the component from the precursor. Gaseous components are usually avoided, but can be used, especially if the precursor is immediately contacted with the liquid coagulant. The components are preferably with the solvent and the liquid

as

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Coagulant compatible. Often, the other components in the N-acylated heterocyclic solvent are very soluble, e.g. For example, at least about 50, preferably at least about 100 parts by weight may be dissolved in 100 parts by weight of the N-acylated heterocyclic solvent at room temperature (about 25 ° C) and the other components are preferably combined with the N-acylated heterocyclic solvent and the liquid coagulant miscible in all proportions. Components other than the N-acylated heterocyclic solvents which may be useful in the liquid carrier include solvents such as dimethylacetamide, dimethylformamide, N-methylpyrrolidone, dimethylsulfoxide, etc .; Viscosity modifiers, such as isopropylamine; Surfactants (interfacial, active compounds); plasticizers; and the same. A particularly useful component for the liquid carrier is a diluent, which may be a solvent or a non-solvent for the polymer. Preferably, the N-acylated heterocyclic solvent comprises at least about 50, viz, at least about 60 percent by weight of the liquid carrier.

The use of diluents can provide particularly interesting liquid carriers, such that certain solvent activities can occur with the individual polymer molecules.

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From

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are folded such that often the polymer can be coagulated or gelled from the polymer solution with a small energy change, if any. The behavior of polymeric molecules in solution is believed to be influenced not only by interaction between the polymer molecules, but also by the action of the solvent (and liquid carrier) on the polymer molecule.

In accordance with the theory described by Flory, Principles of Polymer Chemistry (1953), Chapter XIV, pages 595 to 639, incorporated herein by reference, the molecular dimension of the polymer in a given solvent-polymer system may be at a given temperature remain undisturbed by intramolecular interactions. As the temperature rises from this given temperature (theta temperature), the polymer swells in the solution. The greater the "swelling" of the polymer molecule at the reference temperature, the better the solvent for the polymer at the reference temperature. As the temperature decreases from the theta temperature, a polymer molecule of infinite molecular weight would gel or precipitate, i. the intramolecular forces of the polymer molecule are greater than the forces between the solvent and the polymer molecule.

A significant evaluation of a liquid carrier polymer system can be made by viscosity measurements of a very dilute solution of the polymer in the liquid carrier to determine the intrinsic viscosity (the ability of a polymer to increase the viscosity of a solution) (eg at approximately 25 ° C for consistency although other temperatures may be used as long as they are compatible) and the intrinsic viscosity of the polymer is performed at the intrinsic theta viscosity. The ratio of intrinsic viscosity to intrinsic theta viscosity (hereinafter referred to as "intrinsic viscosities ratio") indicates the effect of the solvent (liquid carrier) on the polymer molecules. The intrinsic viscosity for a given liquid carrier-polymer system is obtained by determining the viscosity of the polymer solution (η) at several different dilute polymer concentrations. The viscosity of the liquid carrier (η) is also determined at the same temperature. The ratio of η: η is the relative viscosity and a plot of the natural logarithm of the relative viscosity divided by the polymer concentration versus the polymer concentration when extrapolated to a polymer concentration of zero provides the intrinsic viscosity. Suitably, the dilute polymer solutions used are selected to be relative

To provide viscosities in the range of about 1.1 to 2.5. To determine the intrinsic viscosity of the polymer at the theta temperature, several procedures may be used, as described in the reference to Plory (supra) at pages 612-622. For example, the intrinsic viscosity of the polymer in a theta solvent at the theta temperature can be determined by viscosity measurements _f as described above. Theta solvents and theta temperatures can be found in the literature for many polymers, for example, in Brandrup et al., Polymer Handbook, Second Edition (1975), pages IV-157 to IV-173, incorporated herein by reference. If necessary, theta solvents and temperatures may be prepared by any of the methods described by Brandrup et al. on the pages IV-157 to IV-159. The temperature of the polymer solution during the viscosity determinations must be kept precisely as close as possible to the theta temperature, since the intrinsic viscosity of many polymer solutions changes rapidly at temperatures near the theta temperature. Alternatively, the intrinsic viscosity can be determined by using a light scattering method to determine the second virial coefficient of the polymer in a solvent at various temperatures. A suitable method was developed by Kaye in "Low Angle Laser

Λ9

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Light Scattering ", Analytical Chemistry, 45 (1973), pp. 221 to 225, and involves determining the amount of light scattering of a laser beam passing through the polymer solution at several temperatures, see, for example, Stacy, Light Scattering in Physical Chemistry (1956 For a description of the relationship between light scattering and the second virial coefficient, it is to be noted that any solids from the polymer solution which can affect the light scattering results, eg, by filtration, are removed on pages 117 et seq Each of these temperatures, at which the second virial coefficient is determined, is obtained and a plot of intrinsic viscosities and second virial coefficients can be prepared and extrapolated to the point where the second virial coefficient is zero, the intrinsic viscosity at that point is the intrinsic the ta viscosity. The method for determining intrinsic theta viscosity is an approximation method; however, such an approximation method may still provide for the provision of a suitable polymer-liquid carrier system

for use in accordance with the present invention for rendering / disposing a hollow fiber membrane from a polymer.

Usually, suitable polymers in the liquid carriers according to the present invention become dilute solutions

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which have an "intrinsic viscosities ratio" of about 1.05 to 1.7, namely about 1.05 to 1.5, and most often about 1.1 to 1.5.

The second virial coefficient of the liquid carrier / polymer system may similarly be useful in determining suitable liquid carrier / polymer systems. Often, the second virial coefficient shown by many liquid carrier / polymer systems is often below about 15, eg, below about 12, viz., Below about 10, mole / cm (times 10) (at 25 ° C.) The second virial coefficient for the liquid carriers / Polymer systems is often above about 0.5, above about 1, and sometimes above 3, for example, between about 3 and 8, mol.cm ³ / g ² (times ΙΟ ⁴ ) (at 25 ° C).

Another useful method for the determination of liquid vehicle / polymer systems, which may be advantageous for the creation of hollow fiber membranes according to the present invention, is that of Blanks et al., In "Solubility of Styrene-Acrylonitrile Copolymers", Structure Solubility Relationships in Polymers, edited by Harris et al., (1977), pages 111 to 122, which publication is incorporated herein by reference, described interaction parameters. The interaction parameter (A ₂ ) can be defined as follows

A4

- .. ** ~ 2 1 9 9

where V is the molar volume of the solvent in ml per mole, R is the gas constant (about 12 cal / ° K mol), T is the temperature in K ^0, δ, and δ, the (London) dispersion force compo-

^a 'r''s

P 0 5

of the solubility parameter, (cal / ml) ', of the polymer or solvent, δ_ and δ the polar bond

Ρ ' _η P » _fi .

P 0 5

solubility parameter, (cal / ml), of the polymer or solvent, and δ, and δ, the hydrogen

n, n,

P 0 5

Bonding member of the solubility parameter, (cal / ml) ', the polymer or the solvent mean. The total solubility parameter (δ) can be expressed by the following equation

⁶ d

be reproduced.

Solubility parameters are suitably used to characterize liquid carriers and solutes, and values for solubility parameters and components can often be found in the literature; see. See, for example, Shaw, "Studies of Polymer-Polymer Solubility Using a Two-Dimensional Solubility Parameter Approach", J. of Applied Polymer Science, IjJ, pp. 449-472 (1974), and Brandrup et al., The Polymer Handbook, Second Edition, Pages IV-337 to IV-359 (which also covers the experimental tech-

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nikel to determine the solubility parameters and components describes). The components of the solubility parameter used to calculate the interaction parameter for a liquid carrier containing more than one component can be determined on the average basis of a volume fraction. This determination is an approximate determination because in many cases the volume of the components of the liquid carrier is not additive. Frequently, the interaction parameter of the polymer and liquid carrier at 20 ° to 30 ° C is less than about 0.5, namely less than about 0.3. The interaction parameter

about / usually has at least a value of 0.01, preferably

at least about 0.02, e.g. at least about 0.05.

Also, the liquid carrier advantageously has a solubility parameter of approximately equal (ie, within 5 or 10%), or more than the value of the solubility parameter of the polymer. In many cases, the values of at least one, and sometimes both, of the following members, namely the polar bond member and the hydrogen bonding member of the solubility parameter, are greater (ie, not greater than) 0.5, greater than 0.3 (cal / ml) ^{0 '5,} below the corresponding element for the polymer. Advantageous membranes can be made from polymer solutions

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in which the addition of liquid coagulant, even in very small amounts, does not substantially improve the ability of the solvent to dissolve the polymer. Often, the values for the polar binding member and the hydrogen bonding member of the solubility parameter of the liquid carrier are each individually larger than the corresponding members of the solubility parameter of the polymer.

Often, the surface tension of the liquid carrier is within about 10, namely about 5 or 7, dyn / cm, of the surface tension of the polymer at room temperature (25 C). When the liquid carrier / polymer system, if in a dilute polymer solution, has a suitable intrinsic viscosities ratio, second virial coefficient and interaction parameter, the liquid carrier also has a surface tension approximated to the surface tension of the polymer. Often, particularly useful liquid carriers exhibit a surface tension at room temperature (25 ° C) of less than about 3 or 5 dynes / cm above the surface tension of the polymer. Surface tensions for polymers can be determined experimentally by any conventional method, and such a method is described by Tanny in J. of Applied Polymer Science, Vol. 18, pages 2153 to 2154 (1974).

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Often, liquid carriers used in the process of the present invention contain a diluent which is a non-solvent for the polymer. Non-solvents are usually characterized by having a low ability to dissolve the polymer, e.g. For example, the polymer solubility is less than about 10, less than 2, often less than about 0.5 g, per 100 ml of non-solvent. The non-solvent has little, if any, swelling effect on the polymer. The non-solvent, if added in an amount sufficient, is generally capable of providing phase separation of the polymer solution. Preferably, the non-solvent is not added in an amount such that the polymer solution becomes unduly unstable at the processing conditions prior to the formation of the precursor. Often, the amount of non-solvent in the liquid carrier is at least about 2, e.g. at least about 5 parts by weight per 100 parts by weight of liquid carrier.

Suitable non-solvents may include the liquid coagulant or one or more components of the liquid coagulant. Some desirable solvents may be the polymer in the presence of at least about 5%, namely at least about 10% by weight of liquid

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Coagulants, based on the weight of the solvent (e.g., at 25 ° C), in solution. Preferably, however, the addition of relatively small amounts of liquid coagulant to a solution of the polymer in the liquid carrier will result in phase separation or gelling of the polymer solution.

Typical diluents / include non-solvents include formamide, acetamide, ethylene glycol, water, trimethylamine, triethylamine, isopropylamine, isopropanol, methanol, nitromethane, 2-pyrrolidone, acetic acid, formic acid, aqueous ammonia, methyl ethyl ketone, acetone, glycerol, and the like. Inorganic salts of low molecular weight, such as lithium chloride, lithium bromide, zinc chloride, magnesium perchlorate, lithium nitrate, and the like, may also be useful in the liquid carrier.

In order to allow the precursor to be formed, a sufficient amount of polymer is included in the polymer solution. Therefore, when fabricating a hollow fiber membrane, the polymer concentration is sufficient for the polymer solution to be at a fiber-forming viscosity at the temperature of the polymer solution as it forms into a hollow fiber precursor (i.e., extruded). becomes. Impermissibly low

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Viscosities may result in breakage of the hollow fiber precursor and the inability to maintain the desired hollow fiber shape. High viscosities are desired, however, excessively high viscosities may be undesirable as a result of the pressures required to extrude the polymer solution. Often, the viscosity of the extruding polymer solution is at least about 5,000, often at least about 10,000 centipoise, and can be up to 500,000 or 1,000,000 centipoise at the extrusion temperature. Many interesting hollow fiber membranes are made using polymer solution viscosities at the extrusion temperature in the range of about 10,000 to 500,000 centipoise. In some instances, sufficient polymer may be included in the polymer solution such that at the temperature of the liquid coagulant the polymer solution becomes a substantially non-flowing structure, for example, becoming extremely viscous or undergoing a physical change, e.g. forms a gel (i.e., an elastic structure in which at least some of the polymer is insoluble in the liquid carrier and liquid carrier is entrapped in the interstices) or results in phase separation.

The polymer concentration of the polymer solution is suitably high enough to ensure that the membrane

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contains sufficient polymer to form the desired high strength of the membrane. If the polymer concentration of the polymer solution is too low, large pores, including large cells and macropores, may occur in the membrane wall, thereby resulting in low strength of the wall structure. At higher polymer concentrations, the resulting hollow fiber wall is usually denser and macropores are usually rarer, and therefore, the hollow fiber membrane can have greater strength. Macropores are large pores with a major dimension greater than about 3 microns. Preferably, a sufficiently high polymer concentration is used such that, under coagulation conditions, few, if any, macropores are formed. Since the present invention can advantageously provide an open-celled structure in the membrane wall, the increase in polymer density can be achieved with little, if any, reduction in flow through the bulk of the membrane wall. The maximum polymer concentrations that can be used in a polymer solution are usually determined in practice by the ability of a conventional apparatus to form membranes from high viscosity polymer solutions. The maximum preferred concentrations of the polymer in the polymer solution will also depend on the nature of the polymer and the liquid carrier. Beispiels-

si

that is, with lower molecular weight polymers, higher polymer concentrations may be more desirable than with higher molecular weight polymers. Often, the polymer concentration is at least about 25 percent by weight of the polymer solution. Polymer concentrations up to 45 or 50 percent by weight may be useful in many situations. Polymer levels of about 28 or 30 to 38 or 40 weight percent are particularly often desired. ,

Often, the viscosities of the polymer solutions used in accordance with the present invention have relatively high activation energies. An activation energy is a relationship between temperature and viscosity, and this ratio can be represented by the following equation:

.Π = Ae ^E / ^RT

in which n. the viscosity of the polymer solution, E is the activation energy, R is the gas constant (approximately 2 cal / ° K, mol) and T is the temperature ( ⁰ K). See Art et al., Fifth International Symposium on Fresh Water from the Sea, Vol. 4 (1976), which publication is incorporated herein by reference. The slope of a graph of the logarithm of viscosity (Poise) to the reciprocal absolute temperature (° K ~) is usually linear, and out of this

- 2

Diagram can be obtained approximately the activation energy (cal / mole). Often, the activation energy is at least about 8 kcal / mole, about 8.5 to 15, e.g. about 9 to 12, more often about 9.5 to 12 kcal / mole. Usually, the activation energy with desired liquid carriers containing a non-solvent diluent increases with increased concentration of non-solvent.

The polymer solution can be prepared in any suitable manner, for example, the liquid carrier can be added to the polymer, the polymer can be added to the liquid carrier, or the polymer and the liquid carrier can be simultaneously combined. Of course, if the liquid carrier contains more than one component, it can be mixed with the polymer on a component-by-component basis. For example, if the liquid carrier contains a solvent and a non-solvent, the polymer may be advantageously mixed with the solvent prior to adding the non-solvent. When the non-solvent is added subsequent to the dissolution of the polymer in the solvent, the non-solvent is usually added slowly such that the localized zones of the increased non-solvent concentrations are used.

³⁰ 0 1 Qq 7

message coagulation or precipitation of the polymer in such localized zones are kept as small as possible. To facilitate mixing of the polymer of the liquid carrier, elevated temperatures may be employed. However, the temperature should not be so high as to deleteriously affect any of the components of the solution thus prepared. The time required to conduct blending to prepare a polymer solution may vary widely depending on the dissolution rate of the components, the temperature, the efficiency of the blender, the viscosity of the prepared polymer solution, and the like. Desirably, the mixing of the polymer solution should continue until a substantially uniform composition is present throughout the polymer solution. For the purposes of the present invention, any suitable mixing device may be used to prepare the polymer solution. Preferably, the mixing device does not introduce improper air pockets into the polymer solution to facilitate any subsequent degassing of the polymer solution. Often, components of the polymer solution have appreciable volatility under the blending conditions. These volatile components can pose an unacceptable risk of damage to health and fire, and the loss of

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Volatile components change the composition of the polymer solution. As a result, in most cases, the mixing of the polymer and the liquid carrier is carried out in a substantially sealed container. In such sealed containers an inert atmosphere may be provided. It is possible that components intended for the polymer solution will be adversely affected when exposed to atmospheric conditions (e.g., ambient air). The total pressure of the atmosphere in the mixing vessel is preferably relatively low so as to minimize any dissolution or entrapment of the inert atmosphere in the polymer solution during the preparation of the polymer solution. In most cases, pressures below about 2 or 3 atmospheres are absolutely applied.

Often, the polymer solution contains trapped or dissolved gases used to form anomalies, e.g. of macropores, in which membranes can lead. As a result, it is generally desirable to degas the polymer solution. Preferably, the polymer solution is substantially free of entrapped or dissolved gases prior to extruding the hollow fiber precursor. To effect the desired degassing, any suitable degassing apparatus and any suitable degassing conditions may be used

his. For example, sufficient degasification can be achieved by maintaining the polymer solution in a closed vessel for a sufficient period of time to allow the trapped or dissolved gases to escape from the polymer solution. Conventional degassing devices, such as ⁿ "J" tubes, centrifugal degassing devices, ultrasonic degassing devices, and the like, can be used to degas the polymer solution. "Since many of the polymer solutions useful in accordance with the present invention have a relatively high viscosity, the polymer solution can be used in the degasser The increased temperatures to which the polymer solution may be subjected and the periods during which the polymer solution is maintained at such elevated temperatures should not be maintained at an elevated temperature to lower its viscosity and facilitate the release of trapped or dissolved gases be so high or so long that they lead to a detrimental effect on the polymer solution or its components.The degassing can be carried out at relatively low absolute pressures (eg in vacuum), or at such higher pressures n, that, for example, unauthorized volatilization or evaporation of any of the components of the polymer solution is prevented. However, the pressure should not be so high as to make it inadmissible.

tion dissolution or redissolution of gases from the atmosphere contained in the degassing leads. In general, degassing is preferably carried out at an absolute pressure of below about 2 atmospheres, and more often at a subatmospheric pressure. The degassing can be carried out in a sealed container. During degassing, an inert atmosphere can be used.

The degassed polymer solution can then be used for the preparation of the membrane precursor. When transporting the polymer solution, it is preferred that the conduits and pumps are constructed so that no gas (e.g., air) enters the polymer solution via leaks in the transport system. The polymer solution may contain solid impurities, e.g. Dust, polymeric oligomers, and the like, which may adversely affect the membrane. The polymer solution is therefore usually filtered before entering the spinneret. Preferably, the filtering operation is sufficient to remove by filtration substantially all solid particles larger than about 50 microns in the main direction, and often substantially all particles larger than about 0.5 micron in the largest dimension. To facilitate transport and filtration of the polymer solution can

- / 3S-

- * · - 219976

elevated temperatures are applied. However, such elevated temperatures should not be so high as to damage the polymer solution or its components in any way.

Frequently, water will make up a majority of the liquid coagulant sufficient to provide a suitable non-solvent content to effect coagulation of the polymer. For example, the liquid coagulant may contain at least about 50, viz. At least about 75, and most often at least about 85, weight percent water. Advantageously, the liquid coagulant does not cause appreciable swelling of the polymer. Since water often constitutes a major amount of the liquid coagulant, the polymer preferably exhibits little, if any, swelling in water. Desirably, the composition of the liquid coagulant is such that the heat of dilution of the liquid carrier in the liquid coagulant is greater than about -3.5, greater than about -3, eg greater than about -2.5, and often greater than about -2 kcal / mole. The absolute value of the heat of dilution of the liquid carrier in the liquid coagulant is often less than about 3 kcal / mole. In many cases, the heat of dilution is within the range of about -0.5 to -2 kcal / mole. The

2 1.9 9 76

Dilution heat can be determined using any conventional method, usually at about 25 ° C.

The liquid coagulant will, especially in the production of hollow fiber membranes on a continuous basis, contain liquid carrier which will be removed from the precursor. The liquid carrier may extract a content of liquid coagulant from the non-solvent. The liquid coagulant is therefore desirably replaced by fresh or circulated liquid coagulant which contains little, if any, liquid carrier. Often, the concentration of the liquid carrier in the liquid coagulant is less than about 10, preferably less than about 5, namely, less than about 2 weight percent.

The liquid coagulant may contain additional components, such as surfactants, materials which increase or decrease the non-solvent content of the liquid coagulant with respect to the polymer, materials which increase the solubility of the components of the liquid carrier in the liquid coagulant, Materials which lower the heat of dilution of the liquid carrier in the liquid coagulant.

-ml- 2 1997

, freezing point depressants, and the like. Useful additional components for the liquid coagulant which may find application in the manufacture of the membranes include low molecular weight alcohols such as methanol, isopropanol, etc., salts such as sodium chloride, sodium nitrate, lithium chloride, etc., organic acids such as for example, formic acid, acetic acid, etc., and the like.

The liquid coagulant is desirably maintained at a temperature at which the polymer solution is substantially non-flowing. While suitable temperatures are usually low, some polymer solutions may be substantially non-flowing at room temperature or above. Therefore, temperatures of up to about 90 ° C or above can be used for the liquid coagulant. Often, however, the temperature of the liquid coagulant is below about 35 ° C, and highly desirable membranes are often made below about 20 ⁰ C, namely below about 1O ° C using temperatures for the liquid coagulant from. Very often, the temperature of the liquid coagulant for the sake of convenience, above about 0 ⁰ C, for example at about 0 ° to 10 ° C. However, with a

3?

-ge

temperatures of -15 ° C and below are achieved in the liquid coagulant in the presence of freezing point depressants.

The residence time of the precursor in the liquid coagulant should be sufficient so that the amount of coagulation at the temperature of the liquid coagulant provides adequate strength of the membrane for further processing. It is often desired that coagulation of the polymer in the precursor occur within a few seconds, so that the size of the equipment for the coagulation stage is not unduly large. Since the outside of e.g. the hollow fiber precursor directly contacts the liquid coagulant, it is usually coagulated almost instantaneously. In some cases, substantially complete coagulation of the polymer in the precursor under the conditions of the liquid coagulant may occur almost instantaneously. More often, the precursor in the liquid coagulant exhibits an observable transition from a clear or translucent structure to an opaque structure. This transition can be gradual, and sometimes the progression of the transition can be observed. The time for this transition under the conditions of the liquid coagulant can vary widely, but in many cases is

at least about 0.001, for example about 0.01 to 1, namely about 0.02 to 0.5 seconds.

Usually, even after coagulation of the precursor, the membrane still contains substantial amounts of liquid carrier, which may adversely affect its strength properties, and which may even enable coagulated polymer to be redissolved. The membrane is therefore particularly suitably subjected to at least one washing step for further removal of liquid carrier. Often, the washing of the membrane is begun under substantially the same conditions (eg, temperature) that prevailed during coagulation. The temperatures used in the wash are often based on the strength of the membrane containing the liquid carrier, the appropriate range of temperatures to which the wash liquid can be subjected, and the ease of obtaining a wash liquid at such temperatures. In general, temperatures should be avoided during washing, which could lead to undesired tempering of the membrane surface. Very often, the temperature of the laundry in the range of about 0 ° to 50 ⁰ C, preferably in the range of about 0 ° to 35 ° C. In particular, when the liquid carrier and the liquid coagulant are miscible with water, suitably

eer used as a washing liquid. The washing liquid may contain additives, for example those which enhance removal of the liquid carrier. For example, if the washing liquid is water, then a water-miscible organic material (e.g., methanol, isopropanol, etc.) may aid in facilitating the removal of the liquid carrier.

Often, the level of liquid carrier in the membrane can be reduced with ease, namely to less than about 20 weight percent of the liquid carrier (e.g., by passing the hollow fiber through a wash liquid for a period of 2 to 5 minutes). However, reducing the level of liquid carrier in the membrane to desirably low levels, e.g. less than about 5, and sometimes less than about 2 weight percent liquid carrier, relatively long periods of additional laundry. This additional wash is often for at least about 3 hours, and may be up to 20 or more days. The additional washing may be carried out by passing washing liquid over the membrane with, if at all, little liquid carrier (rinsing), or by soaking, or by storing in washing liquid. Usually, a combination of rinsing and storage is used to remove the liquid carrier from the membrane.

Wundt. If the membranes are stored in washing liquid, periodic replacement of the washing liquid may be advantageous if the concentration of the liquid carrier in the washing liquid becomes undesirably high. Although the membranes can be stored in the wash liquor for periods longer than 20 days, usually only small additional amounts of liquid carrier are removed from the membranes after such long storage periods. Most often, washing of the membranes is continued until the level of liquid carrier in the membrane is less than about 4 or 5 percent by weight of the membrane.

The membranes are dried after washing to remove the washing liquid. The presence of liquid in the anisotropic membranes can reduce the flow of substances, e.g. Gases which penetrate the membrane significantly decrease, and therefore the presence of liquid in the membrane is usually not desired. Suitable drying can be carried out by exposing the membranes to a gaseous atmosphere. Air is usually a suitable gaseous atmosphere. Useful drying conditions can vary widely. For example, suitable drying conditions may be temperatures in the range of -15 ° C or below to 90 ° C or above, and relative humidities in the range of about 0 to 95, namely, about 5 to 60%.

2 19976

lock in. Frequently the temperature is in the range of about 0 ° to 80 ° C, with absolute humidity values of less than about 20 or 30, namely about 5 to 15 g / m. In many cases, drying of the membranes under standard laboratory conditions, e.g. at about 20 to 25 C and 40 to 60% relative humidity.

Useful materials for the production of anisotropic membranes may include organic polymers, or organic polymers coated with inorganic materials, e.g. Fillers, reinforcing agents, and the like. Accordingly, the process of the present invention may find advantageous use in the preparation of hollow fiber metal membranes according to US Pat. No. 4,175,153, which is incorporated herein by reference. Suitable polymers are soluble according to the process of the present invention in the N-acylated heterocyclic solvents used. Desirably, at least about 50, preferably at least about 100 parts by weight of the polymer can be dissolved in 100 parts by weight of the N-acylated heterocyclic solvent (at 25 C), and most often the N-acylated heterocyclic solvent and the polymer are miscible in all proportions. But although the N-acylated heterocyclic solvent is a good solvent for the polymer and with the liquid

If the coagulant is miscible, the polymer may not be acceptable for the preparation of membranes if the solvent is unable to be readily separated from the membrane after coagulation. If the polymer retains the solvent, the polymeric structure of the membrane may be weakened to result in undue densification of the anisotropic structure, thereby causing undesirable lowering of the permeability of the membrane to permeants, e.g. Gases, is obtained. Moreover, if excessive amounts of the solvent remain even after drying, the resulting membrane will not have sufficient structural strength to withstand the separation conditions.

Often, the intrinsic viscosities ratio for suitable dilute solution polymers in the N-acylated heterocyclic solvent is at least about 1.05, preferably at least about 1.3. Often the "intrinsic viscosities ratio" is up to about 2, namely about 1.3 to 1.75, or even 1.5 to 1.75.

Frequently, the second coefficient of viscosity for polymer solutions containing a suitable polymer in the N-acylated heterocyclic solvent is below about 20, namely, below about 15 mol.cm ³ / g ² (times 10 ⁴ )

25 ° C). In many cases, the second virial coefficient is at least about 0.5, viz. At least about 1, eg, at least about 3 mol.cm ³ / g ² (^ a 10 ⁴ ) (at 25 ° C). Often, the interaction parameter for suitable polymers with the N-acylated heterocyclic solvent at about 20 ° to 30 ° C is less than about 0.5, viz less than about 0.3, and most often at least about 0.005, viz. At least about 0, 01, and sometimes at least about 0.02.

Usually it is preferred that the polymer is substantially non-crystalline, e.g. is less than about 25 weight percent, and often less than about 1 or 2 weight percent crystalline, because crystalline polymers usually have low permeability coefficients. However, sometimes polymers that have considerable crystallinity may be desirable. Often, the polymer is also nonionic to facilitate the preparation of anisotropic membranes.

The polymeric material is preferably selected based on its release capabilities, i. its ability to provide the desired separation selectivity with suitable permeate flow resistance and chemical resistance, particularly with respect to the components of the

-J * - -21997

Liquid streams to be treated using the membrane. The polymer should have a molecular weight which is sufficient to form e.g. a hollow fiber is sufficient. In general, for a given type of polymer, the longer the polymeric chain, the greater the tensile strength of the polymer and the higher the glass or glass transition temperature of the polymer. This increase in increasing molecular weight physical properties can often be achieved with little, if any, change in the release capabilities of the polymer. Accordingly, by using high molecular weight polymers, the anisotropic membrane can be made more solid and more compatible with the components of the feedstream which can deleteriously affect the polymer. However, polymers with increased molecular weights usually result in an increase in the viscosity of the polymer solutions for preparing the precursor. Therefore, it is often desirable to use a polymer having a narrow molecular weight distribution such that the polymer has high strength properties without an undue increase in its viscosity. For example, the broad molecular weight distribution polymer may contain a significant portion of low molecular weight polymeric molecules, but due to the presence of polymeric molecules having significant molecular weight.

- ** - 2 1997

Higher molecular weight provide a high solution viscosity. A suitable way of characterizing the molecular weight distribution of a polymer is by the ratio of the average molecular weight (weight average) of the polymer to the number average molecular weight of the polymer. The higher ratios indicate that the molecular weight distribution is broader. Often, this ratio is less than about 3,

The strength of the polymer should be sufficient to prevent damage to the release layer during foreseen handling and transport during manufacture of the membrane, production of a permeator containing the membrane, and installation and use of the permeator. Likewise, the polymer must have sufficient strength such that the membrane resists the gas separation operating conditions. The strength of the polymer can be given, for example, as tensile strength, Young's modulus, etc. While any of these mechanical properties can affect the overall strength of the membrane, often an indication of whether the polymer has adequate strength can be obtained by considering the tensile strength of the polymer. Usually, polymers suitable for membranes have a tensile strength of at least about 350, namely at least about

400, preferably at least about 500, namely at least

about 600 kg / cm. The tensile strength can be as high as achievable, but few polymers that are advantageous as membrane materials have tensile strengths of

over about 2000 kg / cm. The strength of a polymer may be adversely affected by materials which, for example, dissolve, soften, or swell the polymer. Often many polymers suitable for membrane separations are dissolved, softened, swollen, or otherwise adversely affected by one or more materials. In some cases, industrial streams to be treated using membranes for separations, e.g. Gas streams, one or more components, which may adversely affect the membrane material. By using a membrane material which has high strength, a reduction in the strength of the membrane due to the presence of such harmful components in the feed mixtures can be tolerated because the weaker membrane still endures the conditions of the separation process.

The selective permeation of many liquids, including gases, in many polymers has already been described. In these described permeations, the mechanism of separation apparently involves an interaction

ί9976

with the material of the membrane. Therefore, by using various polymers in a wide range, differing releasing ability can be obtained. For example, polyacrylonitrile allows nitrogen to permeate more than 10 times as fast as methane, whereas in a polysulfone membrane, methane is enforced slightly faster than nitrogen. Numerous information regarding the permeation properties of polymers can be found in the literature. For example, see Hwang et al., Gas Transfer Coefficients in Membranes, Separation Science, Vol. 9, pp. 461-478 (1974); and Brandrup et al., Polymer Handbook, Second Edition, Section III (1975). The suitability of a polymer for, for example, gas separation can readily be determined using, for example, conventional techniques for determining permeability constants, permeabilities, and separation factors, as described by Hwang et al., Techniques of Chemistry, Vol. VII, Membranes in Separations (1975) in Chapter 12, pages 296 to 322.

Typical polymers suitable for preparing uniform, anisotropic membranes include substituted and unsubstituted polymers selected from polysulfones; Poly (styrenes), including styrene-containing copolymers, such as acrylonitrile-styrene copolymers and styrene-vinyl

benzyl halide copolymers; Polycarbonates, cellulosic based polymers such as cellulose acetate butyrate, cellulose propionate, ethyl cellulose, methyl cellulose, nitrocellulose, etc .; Polyamides and polyimides, including aryl polyamides and aryl polyimides; polyether; polyacetal; Poly (arylene oxides) such as poly (phenylene oxide) and poly (xylylene oxide); Poly (esteramide diisocyanate); polyurethanes; Polyesters (including polyarylates) such as poly (ethylene terephthalate), poly (alkyl methacrylates), poly (alkyl acrylates), poly (phenylene terephthalate), etc .; polysulfides; polymers other than those mentioned above having α-olefinic unsaturation of monomers having α-olefinic unsaturation, such as polyvinyls, e.g. Poly (vinyl chloride), poly (vinyl fluoride), poly (vinylidene chloride), poly (vinylidene fluoride), poly (vinyl alcohol), poly (vinyl esters) such as poly (vinyl acetate) and poly (vinyl propionate), poly (vinyl pyridines), poly (viny! pyrrolidones), poly (vinyl ethers), poly (vinyl ketones), poly (vinyl aldehydes), such as poly (vinyl formal) and poly (vinyl butyral), poly (vinyl amines), poly (vinyl phosphates) and poly (vinyl sulfates); PoIyallyle; Poly (benzobenzimidazol); polyhydrazides; polyoxadiazoles; polytriazoles; Poly (benzimidazole); polycarbodiimides; polyphosphazines; etc., and copolymers including block copolymers containing repeating units of the above polymers such as terpolymers of acrylonitrile-vinyl bromide-sodium salt of p-sulfophenylmethallyl ethers; and

Graft polymers and blends containing any of the polymers listed above. Typical substituents which provide substituted polymers include halogens such as fluoro, chloro and bromo; hydroxyl groups; lower alkyl groups; lower alkoxy groups; monocyclic aryl; lower acyl groups, and the like.

One class of polymers that may be of interest for many gas separations are copolymers of styrene and acrylonitrile, or terpolymers containing styrene and acrylonitrile. Often, the styrene content is up to about 60 or 70, about 10 to 50 mole percent of the total monomers in the polymer. Advantageously, the acrylonitrile monomer makes at least about 20, e.g. about 20 to 90, often about 30 to 80 mole percent of the polymer. Other monomers which may be used with styrene and acrylonitrile, e.g. To provide terpolymers include olefinic monomers such as butene, butadiene, methyl acrylate, methyl methacrylate, maleic anhydride, and the like. Other monomers that may be used include vinyl chloride. The copolymers or terpolymers of styrene and acrylonitrile often have a weight average molecular weight of at least about 25,000 or 50,000, or about 75,000 to 500,000, or higher.

50 - "5 * -

One of the preferred polymers for anisotropic membranes is polysulfone due to its strength, chemical resistance and relatively good gas separation capabilities. Typical polysulfones are characterized by having a polymeric backbone which is the repeating structural unit of the following formula

1 l -2

-R ¹ -S-R-

ii

1 2

wherein R and R may be the same or different and are aliphatic or aromatic hydrocarbyl-containing radicals having from 1 to about 40 carbon atoms, and wherein the sulfur in the sulfonyl group is attached to an aliphatic or aromatic carbon atom, and the polysulfone is for the Film or fiber production has a suitable average molecular weight of often at least about 8,000 or 10,000. When the polysulfone is not crosslinked, the molecular weight of the polysulfone is usually less than about 500,000, and often less than about 100,000. The recurring units can be joined, ie, R ¹ and R can be linked by carbon-to-carbon bonds, or various connecting groups, such as

- __C-, -C-N-,

1 997

be connected. Particularly advantageous polysulfones are

1 2 before, in which at least one of the radicals R and R is a

contains aromatic hydrocarbyl-containing radical, and the sulfonyl group is bonded to at least one aromatic carbon atom. Common aromatic hydrocarbyl containing radicals include phenylene and substituted phenylene radicals, bisphenyl and substituted bisphenyl radicals, bisphenylmethane and substituted bisphenylmethane radicals of the following general formula

12

substituted and unsubstituted bisphenyl ethers of the general formula

-X-

in which X is oxygen or sulfur; and the same. In the above Bisphenylmethan- and

si

3 12

Bisphenyl ether radicals represent R to R substituents which may be the same or different and have the following general formula.

X ¹

1 2

in which X and X are identical or different and are hydrogen or halogen (eg fluorine, chlorine and bromine), ρ is zero or an integer, eg from 1 to about 6, and Z is hydrogen, halogen (eg fluoro, Chlorine and bromine), -fY -) - R ¹³ (where g is zero or 1, Y is -O-, -S-, -SS-,

13 11 13

-OC- or -C- and R is hydrogen, substituted

or unsubstituted alkyl, namely having from 1 to about 8 carbon atoms, or substituted or unsubstituted aryl, namely monocyclic or bicyclic aryl having from about 6 to 15 carbon atoms), a heterocyclic radical, wherein the heteroatom is at least one of nitrogen, oxygen and sulfur and is monocyclic or bicyclic having about 5 to 15 ring atoms, sulfato and sulfono, especially lower alkyl-containing or monocyclic or bicyclic aryl-containing sulfato or sulfono, phosphorus-containing groups such as phosphino and phosphates and phosphono / especially lower alkyl

219976

containing or monocyclic or bicyclic aryl-containing phosphato or phosphono, amine, including primary, secondary, tertiary and quaternary amines, often containing lower alkyl or monocyclic or bicyclic aryl groups, isothioureyl, thioureyl, guanidyl, trialkylsilyl, trialkylstannyl, trialkylplumbyl, dialkylstibinyl _f etc., means. Frequently, the phenylene groups of the bisphenylmethane and bisphenyl ether residues are the substituents

provided so that at least one of the radicals R to R, and R to R is hydrogen. The polysulfones having aromatic hydrocarbyl-containing groups generally have good thermal stability, are resistant to chemical attack, and have an excellent combination of toughness and flexibility.

Useful polysulfones are marketed under the trade names such as "P-1700" and "P-35OO" by Union Carbide. The two commercial products are bisphenolmethane-derived polysulfones (especially derivatives of bisphenol A) and have a linear chain of the general formula

^5ί - 2 19976

wherein the index η, which represents the degree of polymerization, has a value of about 50 to 80. These commercially available polysulfones derived from bisphenol A sometimes contain a crystallized fraction which is believed to. she is an oligomer. With solvents for polysulfone, such as dimethylformamide and dimethylacetamide, this crystallized fraction remains unresolved and can even be increased in crystal size and fraction. This crystallized fraction can increase the difficulty of obtaining desired anisotropic hollow fiber membranes. The N-acylated heterocyclic solvents employed in the process of the present invention appear to provide solutions containing these polysulfone polymers which, if any, have only a very small fraction of these crystals. In addition, the polymer solutions show good stability against inadmissible crystal formation; therefore, the polymer solution can be stored even before use. This stability ensures adequate storage time for the polymer solution to perform adequate degassing.

With respect to the polysulfone polymer, e.g. from "P-35OO", Table A below gives a list of solvents and diluents which are of interest for the preparation of membranes, in particular hollow fiber membranes, according to the methods of the present invention.

- £ - 21

Table A

Common Liquid Carrier Preferred Liquid Carrier Preparations. (Parts by weight) (weight parts)

thinner

1-formyl-dilute 1-formyl-diluent

Piperidine Pesticide Nutrient

None 100 0 100 0 formamide 85-98 2-15 87-95 5-13 ethylene glycol 65-98 2-35 75-95 5-25 water 90-98 2-10 95-98 2-5

The methods of the present invention are particularly advantageous for producing hollow fiber membranes. With respect to this embodiment of the present invention, the polymer solution is extruded through a spinneret to form a hollow fiber precursor. Although any suitable hollow fiber spinneret may be used to make the hollow fibers of this invention, it is preferred that the spinnerette be of the tube-in-die type. Pipe-in-nozzle type spinnerets are characterized by having a continuous annular ring surrounding an inner injection tube. It is particularly desirable that the injection tube is concentrically disposed within the nozzle such that substantially the same amount of polymer solution is present at all points of the annular ring

is extruded and the resulting hollow fiber precursor has a substantially uniform wall thickness. In most tube-in-nozzle type spinnerets, the polymer solution enters a cavity behind the annular ring to help distribute the polymer solution around the annular ring. Sometimes at least about 4, preferably at least about 5 polymer solution inlet ports are provided and desirably may be spaced equidistant.

When spinning some polymer solutions, it may be desirable to maintain the polymer solution at an elevated temperature to ensure desired spinning conditions. In such cases, it is desirable to provide a heater for holding the spinnerette at the desired extrusion temperature. Suitable heaters include electric heaters or liquid heated sheaths, embedded electrical heating coils, and the like. Often, since the residence time of the polymer solution in the spinneret is relatively short, the polymer solution is often heated to the desired or near the desired temperature prior to entry into the spinneret. Often the temperature of the polymer solution in the spinneret is at least about 20 ° C, but preferably it is not at such high temperatures

.U- 2 199 76

during the residence time of the polymer solution at such temperatures, the polymer solution is unduly adversely affected. Often the polymer solution in the spinneret is at a temperature in the range of about 20 to 90 ° C, namely about 25 ° to 80 ° C. ,

The size of the spinneret will vary with the desired inner and outer diameters of the desired hollow fiber membrane. One class of spinnerets may have nozzle diameters (outer diameter) of about 3QO to 1000 microns and an inner nozzle diameter (often the injection tube outer diameter) of about 100 to 500 microns with an injection capillary within the injection tube. The diameter of the injection capillary can vary within the limits set by the injection tube. The thrust of the injection tube is usually in the plane of the spinneret nozzle. Spinnerets are most frequently described in terms of their location of entry into the annular ring and the ratio of length to width of the annular annular portion of the spinneret. The entry assembly into the annular ring portion of the spinneret may be steep, e.g. at an angle greater than about 80 ° to the flow direction of the polymer solution in the annular ring portion of the spinneret, or it may be disposed inclined in the annular portion of the spinneret, e.g. at an angle below

- »· - 2 19976

from about 80 °, namely about 75 ° to 30 °, from the direction of polymer solution flow through the annular spinneret. The ratio of the length to which the annular ring member expands from the front of the spinneret to the width of the annular ring at the front of the spinneret may vary within a wide range; however, the length of the annular ring portion of the spinneret should not be so excessive that an improper pressure drop occurs as the polymer solution passes through the spinneret. Frequently these ratios vary between about 0.7 to 2.5, namely between about 1 to 2.

The dimensions of the hollow fiber precursor are determined, for example, by the dimensions of the spinneret, the flow rate of the polymer solution through the spinneret, the beam elongation at the hollow fiber precursor, and the rate and pressure of the liquid. which will be injected into the hollow fiber core of the hollow fiber precursor. The flow rate of the polymer solution through the spinneret may vary widely depending on the winding speed. However, the flow rate should not be so great as to cause breakage of the hollow fiber precursor. Often the size of the hollow fiber can vary within a wide range, e.g. from about 100 or 150 microns to 1000 or more microns in outside diameter, and the length of the per unit time

55 - βθ -

2 1 997.6

hollow fiber (spinning speed or take-up speed) can also vary within a wide range, e.g. from about 5 to 100 meters per minute (although higher spinning speeds can be used, provided that the fiber is not unduly stretched and sufficient residence time is provided in the subsequent processing stages), the spinning process is often described by the term jet elongation. Spinnability (Ray Elongation) is here expressed as the ratio of (I) milliliter polymer solution extruded through the spinneret per minute divided by the cross-sectional area of the annular extrusion zone in square centimeters to (II) the length in centimeters of the per-minute extruded hollow fiber precursor ( ie the winding speed). The spin elongation is often about 0.6 to 2, namely about 0.7 to 1.8, preferably about 0.75 to 1.5.

Into the hollow fiber core of a hollow fiber precursor, an injection fluid is introduced in an amount sufficient to keep the hollow fiber core of the hollow fiber precursor open. The injection liquid may be gaseous, or preferably liquid, under the conditions of spinning the hollow fiber. The injection fluid should be miscible with the liquid coagulant and with the liquid carrier (and is preferably miscible in all proportions).

foo

Often, the injection fluid is essentially a non-solvent for the polymer. In many cases, the injection fluid need not be a strong non-solvent for the polymer. The injection fluid may contain one or more components and often contains at least one component of the liquid coagulant to increase the miscibility of the injection fluid with the liquid coagulant. As a result, the injection fluid often contains water. Often, the injection fluid also contains a solvent or weak solvent for the polymer. The temperature of the injection liquid usually approaches the temperature of the polymer solution being extruded and the temperature of the spinneret because there is heat transfer through the wall of the injection capillary disposed within the spinneret. However, with proper isolation, or by other means for reducing heat transfer with the injection fluid to the spinneret to a minimum or using an injection fluid that has been cooled prior to introduction into the spinneret, the injection fluid may be significantly cooler than the temperature of the extruded polymer solution his. The rate and pressure of the injection fluid introduced into the hollow fiber core of the hollow fiber precursor should not be sufficient to prevent any deleterious effects of the release ability or structure of the hollow fiber.

- «· - 2 1 9976

to deliver this membrane. Often, the rate and pressure of the injection fluid is such that the ratio of the inner diameter of the hollow fiber to the inner diameter of the nozzle of the spinnerette is less than about 2.5 and preferably about 0.5 to 1.5 or 2.

The spinneret may be located below the level of the liquid coagulant (wet jet) or, preferably, above the liquid coagulant (dry jet). When the dry jet spinning technique is used, it is preferred that the components of the liquid carrier be substantially non-volatile. The distance above the liquid coagulant in which the spinneret is located (nip) can be significantly reduced without appreciable effect on the properties of the Hollow fiber membrane can be varied. Often, the spinneret is placed at a distance of within about 20 or 30 cm. Desirable hollow fibers can be made when the front surface of the spinnerette is within about 0.5 or less centimeters of the liquid coagulant. For convenience, the spinneret is often located within about 0.5 to 15 cm of the liquid coagulant. The dry-jet spinning technique is also preferred as a convenient process if the polymer solution must be extruded at elevated temperatures and the coagulation liquid

Bigkeit at a temperature substantially below, for example, at least 25 ° C, namely at least 30 ⁰ C, below the temperature of the polymer solution is kept in the extrusion.

The processes of the present invention are particularly advantageous for the preparation of anisotropic hollow fiber membranes from polysulfone, especially from polysulfones containing bisphenol methane (including substituted bis-phenylmethane) and bis-phenyl ether (including substituted bis-phenyl ether) groups. The polysulfone hollow fiber membranes of the present invention exhibit several significant structural properties which enable desirable strength properties in combination with advantageous liquid flow properties. The polysulfone membranes of the present invention may be of particular interest for the performance of gas separations.

A dry, uniform, anisotropic polysulfone hollow fiber membrane according to the present invention has a wall that has a thin outer skin on an open-celled support. The outer skin, if any, has few pores (i.e., continuous channels for fluid flow through the outer wall). The cells in the cellular support of the hollow fiber wall are preferably relatively small in all dimensions. Desirably, in the

- 2 19 9 7

cellular carriers have substantially no macropores having a maximum length to maximum width ratio of greater than about 10, preferably greater than about 5. The preferred polysulfone hollow fiber membranes of the present invention have substantially no macropores. "

A hollow fiber membrane for gas separations is often evaluated by indicating its gas separation properties, i. by their selectivity for the passage of a gas as compared to at least one other gas from the gaseous mixture, and by the passage of the selectively permeated gas through the membrane wall, and also by their strength. These properties depend on the chemical and physical nature of the material of the hollow fiber, as well as the structure of the hollow fiber. Since morphological structures that play important roles in determining the gas separation properties of the hollow fiber membrane are on the order of 10 angstroms or smaller in dimension, such structures can not be visually perceived even using the best available optical microscope technique. Such small structures are therefore referred to as "submicroscopic" structures. ,

O 1 Q O 7

The combination of microscopic techniques (particularly scanning electron microscopy and transmission electron microscopy) and observable modes of action in the coarse-based and submicroscopic-based characterizing hollow fiber membrane structures may be highly useful. A particularly useful microscopic technique for labeling hollow fiber membrane structures is scanning electron microscopy. To assist in understanding the use of scanning electron microscopy in describing the hollow fiber membranes of the present invention, reference is made to the attached figures. Figures 1 and 2 are scanning electron micrographs of hollow fiber membranes, in which Fig. La to Fig. Ic one of a. Polymer solution containing 32 percent by weight of polysulfone (P-3500), about 7 percent by weight of formamide and about 61 percent by weight of 1-formylpiperidine produced hollow fiber membrane. Fig. La shows the cross section of the hollow fiber at an enlargement of about 30Ofache. Fig. Ib shows a segment of the cross section of the hollow fiber at the outer edge of the hollow fiber at a magnification of about 20,000 times. Fig. Ic shows the structure of the cross section of the hollow fiber in an area approximately at the center of the wall of the fiber at about 20,000 times magnification.

- 2 19976

2 shows a cross-section of a hollow-fiber membrane produced from a polymer solution containing 36% by weight of polysulfone (P-3500) and 64% by weight of 1-formyl-piperidine at a magnification of approximately 30 times.

Samples of hollow fiber membranes (as depicted in the figures) for examination by scanning electron microscopy may conveniently by thorough drying of the hollow fiber, immersing the hollow fiber in hexane and immediate introduction of the hollow fiber in liquid nitrogen, so _f that the hollow fiber can be broken , getting produced. After obtaining a clean break of the hollow fiber, the sample can be assembled and then sputter coated with a gold and palladium mixture (using, for example, a Hummer II sputter coater). The coating process usually results in a layer of about 50 to 75 Angstroms applied to the hollow fiber sample. Therefore, the dimensions of very small external features can be blurred by the coating.

, As can be seen in particular from Fig. 1, the structure of the hollow fiber membranes is characterized in that they adjacent to the outer surface of a relatively dense structure with an underlying open-cell

- 2 1 997

Carrier has. An increase in the size of the cells in the hollow fiber wall can be seen, although the distance from the outer surface increases to a usually maximum size in a central region within the hollow fiber wall. The predominant structure of the cells in the central region of the cross section of the hollow fiber wall may be in the form of interconnected cells. (Cells with an open passage for a gas flow to adjacent cells), i. as an open-cell structure, be perceived. However, this interconnection between the cells can not be visually perceived when the cells are very small, e.g. less than 0.1 microns in the main dimension. This open-cell structure allows liquids to flow easily through the hollow fiber wall with minimal resistance. Advantageously, the outer skin (and, if present, the inner skin) provides the major part of the resistance to fluid flow through the membrane wall.

The dimensions of the cells, especially the larger cells that often occur in the central area of the hollow fiber wall, can often be determined using e.g. Scanning Electron Microscope Method, In estimating the approximate size and outer shape of the cells, the observable pathways between individual

(A

- 2 199

Cells are considered to be defects in the cell wall and therefore the dimensions of the cell do not continue through these communication paths. Another feature of the cells that may be important in evaluating the strength of the membrane is the thickness of the cell wall material that confines the larger cells of the hollow fiber membrane wall. These determinations can be made by visually observing photographs of the cell structure, or by using available computer scanning techniques, such as image analyzers for examining and analyzing the photographs. Suitable image analyzers include those useful for the analysis of conventional textile fibers, such as the Quantimet 720-2 image analyzer manufactured by Quantimet, Munsey, New York.

The shape of the cells, especially those of the larger cells, which often occur in the central region of the hollow fiber wall, can vary considerably. A suitable way of characterizing the shape of the cells is to divide the cross-sectional area of the cell by the square of the circumference of the cell at this cross-section to obtain a ratio characterizing the outer shape of the cell (hereinafter referred to as the aspect ratio). Consequently, the shape ratio of a fully compatible

- -es -

circle about 0.08, a square about 0.06 and a stick 0.01 or smaller. When the aspect ratio is in the range of 0.03 to 0.04, the cross section of the cells is very often almost polygonal in appearance. Such analyzes may be performed by visually viewing the photographs of the cell structure of the hollow fiber wall, or by using an image analyzer to examine the photographs. Suitably, the aspect ratio can be determined by analysis of any random segment of the cross-section of the hollow fiber wall which contains cells sufficiently large to be examined and which is free of macropores. The area of a segment that has been tested to be representative is usually at least about 25 square microns (e.g., a segment having a minimum dimension of at least about 5 microns). In many desirable hollow fiber membranes according to the present invention, the average aspect ratio is at least about 0.025, and in many cases, it is at least about 0.03 or even at least about 0.035. Preferably, segments of the cross-section of the hollow fibers containing the largest cells (excluding macropores) will have an average aspect ratio of at least about 0.03, e.g. at least about 0.035.

- / κ »- 219976

If cell sizes in a segment of a cross-section of the hollow fiber wall are greater than about 0.1, greater than 0.2 microns, analysis of the photographs of cell structures, such as those described in U.S. Pat. recorded by scanning electron microscopy, also useful for determining the ratio of average wall thickness to average cross-sectional area. In general, the greater the ratio of the thickness of the cell-supporting polymer to the cross-sectional area of the cell, the greater the hollow fiber will be. Often, this ratio, especially for the largest cells in the hollow fiber membrane cross-section, will be at least about 0.05, at least about 1, and sometimes in the range of about 2 to 20 reciprocal centimeters. When analyzing photographs of smaller cells and smaller wall thicknesses of scanning electron microscope images, the thickness of the reflective coating may become significant and should be taken into account. Very often, the greater part of the cells observable in such photographs will also have observable pathways connecting to adjacent cells.

Preferably, a major volume portion (as determined by the cross-sectional area) of the wall of the hollow fiber is made up of cells having a mean major dimension of small to medium size.

219976

ner than about 2 microns exist. Often there is at least about 75, namely at least about 90 volume percent of the wall of ropes having a major dimension of less than about 2 microns, preferably less than 1.5, viz less than 1 micron. In some advantageous hollow fiber membranes substantially no cells with major dimensions greater than 2 or 1.5 microns are present. As noted previously, the size range of the cell in the wall of the hollow fiber membranes usually varies substantially from a size too small to be resolved by scanning electron microscopy to cells with major dimensions of 2 microns or larger. In some hollow fibers according to the present invention, the major major dimensions of the larger cells in the hollow fiber membrane wall are less than about 0.75 microns, and in some cases substantially all of the cells in the zone of the largest rows in the hollow fiber membrane wall have major dimensions of about 0.1 to 0.7 microns. Often, this zone of the largest cells is at least about 30, namely at least about 40, e.g., up to about 50 or 75 volume percent of the wall of the hollow fiber. Very often desirable hollow fiber membranes have average major dimensions of the cells that are relatively uniform, carefree around the segment (namely, at least about 25 square microns in area, with a minimum dimension of at least about 5 microns) that is in at least one

- 219976

predominantly volume fraction (namely, at least about 75 volume percent) of the hollow fiber wall is observed.

In some cases, hollow fiber membranes may have adequate resistance to breakdown, although even macropores may be present. If macropores occur in the hollow fiber, they can vary in shape and location within the hollow fiber wall. Macropores that more closely approximate the shape of a circle can usually, to a greater extent, without undue diminution of the size. Resistance to collapse can be tolerated as long, finger-like macropores. When macropores occur, it is desirable that they occur substantially only in the area of the wall thickness of the hollow fiber membrane from the inner surface to about 0.5 or 0.75 of the distance of the outer wall. Preferably, substantially no macropores are present in the hollow fiber membrane having a maximum length to maximum width ratio of greater than about 10, namely, about 5. The major dimension of the macropores is preferably less than about 0.4 times, namely less than 0.3 times the thickness of the hollow fiber wall.

Scanning electron microscopy may sometimes be useful for checking the porosity of the inner skin (on the side of the hollow fiber core) of the hollow fiber membrane. In front-

lh

Preferably, the inner skin is highly porous to allow penetrating gases to penetrate under low resistance into the hollow core hollow core. A useful microscopic procedure for determining extremely small features, e.g. The porosity of the outer surface (and possibly the inner surface) of the Hohifaser membranes is the surface imprinting process. In this method, a metal layer, e.g. a platinum layer is applied to the surface and then the polymeric hollow fiber is removed from the metal coating. The metal layer is then removed using transmission electron microscopy, e.g. at 50,000 times magnifications or above, to determine the surface properties of the hollow fiber from which the metal layer imprinted. Usually, the particularly preferred hollow fiber membranes of the present invention provide smooth outer skin surface prints that have substantially no anomalies or imperfections (which could mean pores) greater than about 100, often greater than about 75 or even 50 angstroms.

A particularly valuable analytical tool for kinetic evaluations of hollow fiber membranes is the permeability of gases through the membrane. The permeability of a given gas through a membrane of a given thickness

- + * '- 2 1997

is the gas volume at normal temperature and normal pressure (STP) which passes through the membrane per unit area of the membrane per unit of time per unit of partial pressure differential. One method of indicating permeabilities is cubic centimeters (STP) per square centimeter of membrane area per second for a partial differential pressure of 1 centimeter of mercury across the membrane (cm / cm-sec-cmHg). Unless otherwise noted, all permeabilities herein refer to normal temperatures and pressures and have been measured using pure gases. The permeabilities are given in gas permeation units (GPU) _# which have the dimension cm (STP) / cm -sec-cmHg χ 10; consequently 1 GPU is equal to 1x10 cm (STP) / cm sec-cmHg. Several of the many procedures available for determining permeabilities and permeability constants (eg, gas volume (STP) passing through a given thickness of membrane material per unit area per unit time per unit pressure gauge across thickness) are described by Hwang et al., Techniques of Chemistry, Vol. VII, Membranes in Separations, John Wiley & Sons, 1975 (which publication is expressly incorporated herein by reference) in Chapter 12, pages 296-322. The permeability of a given gas reflects the permeation of the gas through the membrane, unconcerned by the mecha-

mechanism according to which the gas passes through the membrane.

A useful kinetic relationship, indicative of the absence of pores in the separating or barrier layer, and the size range of the pores in the barrier layer is obtained by determining the ability of the membrane to produce gases of different molecular weight, e.g. Gases of low molecular weight separate gases with significantly different molecular weights. Suitable gas pairs for this analysis often include such a pair of molecular hydrogen and helium, and a pair of molecular nitrogen, carbon monoxide or carbon dioxide. Preferably, the higher molecular weight gas of the selected gas pair will have a permeability constant (i.e., intrinsic permeability constant) of the polysulfone that is at least about 10 times smaller than the intrinsic permeability constant of the smaller molecular weight gas in the polysulfone. The analysis may suitably be carried out at ambient temperatures (e.g., room temperature of about 25 ° C) at a pressure of about 7.8 atmospheres absolute on the outside of the hollow fiber membrane, and about 1 atmosphere absolute in the hollow fiber core of the hollow fiber membrane. The polysulfone hollow fiber membranes of the present invention have a permeability ratio of (I) the permeability of the at least one pair of gases

- ** - 2 1

Lower molecular weight gas (P /)) _L divided by the permeability of the higher molecular weight gas (P /) _H ) to (II) the square root of the molecular weight of the lower molecular weight gas (v ^/ MW)), divided by the square root of the molecular weight of the higher molecular weight gas (/ MW) , of at least about 6 / often at least about 7.5. The theoretical maximum permeability ratio is the ratio of the intrinsic gas-pair separation factor to the quotient of the square root of the molecular weight of the lower molecular weight gas divided by the square root of the molecular weight of the higher molecular weight gas.

An intrinsic separation factor, as referred to herein, is the separation factor for a material that has no channels for gas flow through the material and is the highest achievable separation factor for the material. Such a material may be referred to as a continuous or non-porous material. The intrinsic separation factor of a material can be approximated by measuring the separation factor of a dense membrane of the material. However, several difficulties in determining a. intrinsic separation factor occur, the imperfections introduced in the production of dense membrane, such as

for example, by the presence of pores, the presence of fine particles in the dense membrane, undefined molecular order due to variations in membrane production, and the like. As a result, the particular intrinsic separation factor may be different from the intrinsic separation factor. Thus, a "particular intrinsic separation factor" as used herein refers to the separation factor of a dry, dense membrane of the material.

Another useful method for characterizing hollow-fiber membranes on a kinetic basis is by determining the permeabilities of a pair of low molecular weight gases having approximately the same molecular weights, but one of which has a permeability constant in the polysulfone that is at least about 5 times, preferably Typical gas pairs having approximately the same molecular weight, but differing substantially in their permeability constants for many polysulfones suitable for hollow fiber membranes, include ammonia and methane, carbon dioxide and propane, etc., at least about 10 times greater than the permeability constant of the other gas. , on. This relationship can be expressed as the quotient of the difference between the permeability of the more easily penetrating gas (P / i), and the per-

219976

mismatch of the less easily penetrated gas (PA) divided by (P / £) _c times the permeability constant of the less easily penetrated gas P _g divided by the permeability constant of the more easily passed gas P "

be specified. In many cases, this ratio has a value of at least about 0.001, namely at least about 50%, preferably at least about 0.02. This ratio is indicative of the material of the hollow fiber membrane which effects at least part of the separation.

Another useful kinetic analysis of a hollow fiber membrane is the ratio of the permeability of a gas to the permeability constant of the polysulfone for the gas:

(PA) P

The gas used to determine this ratio, 2.B. Hydrogen, helium, ammonia, or the like preferably passes easily through the membrane. Very often, this ratio has a value of at least about 5 × 10 , namely at least about 1 × 10, preferably at least about

2χΐΟ ⁵ , up to about 1 * 10 ⁶ , namely about lxlO ⁵ to 0.6x10 reciprocal centimeter. This ratio is indicative of low resistance to gas flow through the hollow fiber membrane structure and, therefore, to the high permeabilities of the desired penetrating gas that can be achieved.

The structure of the hollow fiber membranes of the present invention can also be determined by other kinetic calculations. For example, dried hollow fiber membranes exhibit very low permeability to liquid water due to the presence of, if any, few pores in the separating or barrier layer. The water permeability is often less than about 0.5 × 10 -4 or even less than about 0.2 × 10 -4, namely less than about

-6 -6 3

0 _f lxl0, and sometimes less than 0.01x10 cm (liquid) /

cm -sec-cmHg, even after soaking in water at room temperature (25 ° C) for a period of 4 days. The determination of the water permeability may suitably be carried out at room temperature with a pressure drop of 3.4 atmospheres from the feed side to the permeate side of the membrane at an absolute pressure of about 4.4 atmospheres on the feed side. Often, the maximum pore size is less than about 250 angstroms, and often less than about 150, e.g. less than about 100 angstroms.

- «* - 2 1997

A method for determining the size and opening of the cellular carrier is by subjecting the hollow fiber membrane to conventional Brunauer, Emmett and Teller (BET) adsorption analysis to determine surfaces. In a BET analysis, an attempt is essentially made to use a monomolecular gas layer of e.g. Adsorbing nitrogen to the available inner surface of the hollow fiber and then determining the amount of adsorbed gas that is believed to be proportional to the available surface area. In the BET analysis technique described herein, the analysis is performed essentially so that the inner surface cells that are not open will not make a significant contribution to determining the available surface area. Smaller cells provide a larger surface area per gram of polymer than larger cells. Consequently, a BET analysis can provide an indication of the opening of cells that are too small to be resolved, for example, by a scanning electron microscope method. Many hollow fiber membranes according to the present invention have certain surface areas, by the BET method, of at least about 18 or 20, preferably at least about 22 meters per gram. For very high BET surface areas, e.g. at over 50 or 70 m / g, it is often observed that the hollow fiber has a fibrillar structure instead of a cellular structure. Fibrillar structures

£ 0

can sometimes be relatively weak compared to cellular structures, usually the inner surface area of the hollow fiber membrane, as determined by BET analysis, is in the range of about 18 or 22 to 30 m / g. Hollow fibers, which have a predominantly closed-cell structure, often show one, according to the BET analysis

certain surface area of less than about 18 or 20 m / g.

Another useful method of numerically indicating BET surface areas is surface area per unit volume of the hollow fiber wall. Frequently, desired hollow fiber membranes according to the present invention show certain topical properties by BET analysis.

2 3

surfaces of about 10 to 30, namely about 10 to 20 m / cm

of hollow fiber wall volume.

The structures of the polysulfone hollow fiber membranes in the present invention allow the hollow fibers to withstand large pressure differentials from the outer wall to the hollow fiber core of the hollow fiber membrane, i. the hollow fiber membranes have high collapse pressure. Therefore, the hollow fiber membrane can have a relatively low thickness (wall) to outside diameter ratio, while maintaining a desired structural strength, thereby allowing a favorable large diameter hollow fiber core to withstand the pressure drop within the

9Λ

-β * - 2 1997

Hollow fiber to keep passing gases as small as possible. The collapse strength against the external pressure of a tube with a foamed wall structure depends on the strength of the material of the tube, the wall thickness of the tube, the nature of the foamed wall structure, the outside diameter of the tube, the density of the foam and the uniformity of the hollow fiber configuration (ie whether the outer and inner configurations are concentric and circular). In general, the pressure at collapse of the hollow fiber membranes according to the present invention has an approximate relationship to the strength of the material of the hollow fiber and the wall thickness divided by the outside diameter of the hollow fiber (t / D). This approximate relationship may be expressed in terms of the tensile strength of the material of the hollow fiber and the cube of the ratio of the wall thickness to the outer diameter. Similar relationships may be present with respect to the other strength properties of the material of the hollow fiber, such as the elastic modulus, and the like. Frequently, the hollow fiber membranes of the present invention have a collapse (kg / cm) pressure of large

than about

φ ³

where T _{g is} the tensile strength at the yield point (or

optionally at break) in kg / cm. Particularly advantageous

- 219 9

-like hollow fiber membranes according to the present invention also have a pressure upon collapse of greater than about 10 (φ) (T ₀₎ (^), wherein in the formula φ of Volumanteil of the material of the hollow fiber membrane in the wall of the hollow fiber Membrane is. The volume fraction of the material of the hollow fiber membrane (φ) is therefore 1 minus the amount of the pore volume (volume percent) / 100.

According to the present invention, anisotropic membranes can be made to keep the layer thickness of the release or barrier layer to a minimum value. Often, the tendency to form pores in the membranes increases as the barrier layer becomes smaller. According to the teachings of Henis et al., U.S. Patent Application Ser. No. 742,159, filed November 15, 1976, now withdrawn, and U.S. Patent Application Serial No. 4,342,159. No. 832,481, filed Sep. 13, 1977, which is incorporated herein by reference, a coating may be provided in occluding contact with a gas separation membrane containing pores to increase the separation selectivity exhibited by the gas separation membrane, wherein the coating material comprises the separation has no significant effect. Usually show suitable membranes for the coating according to the aforementioned US patent applications, a permeability ratio, as defined above, of at least about 6, _r 5, HAU

-M-

fig of at least about 7.5. In many cases, the uncoated membranes, which are particularly advantageously coated, will have a permeability ratio of less than about 40, e.g. less than about 20 or 25. The ratio of the permeability of a gas (preferably a gas which easily permeates the material of the membrane) to the permeability constant of the material of the membrane for the gas is at least about 10x, preferably

at least about 2x10, namely up to 1x10 reciprocal centi-. ' meter. For example, advantageous polysulfone (eg, P-35OO) hollow fiber membranes (and many other hollow fiber membranes) for coating have a hydrogen flow of about 100 to 1200 GPU or more and exhibit ratios of hydrogen permeability to methane permeability of about 1.5 or 2 to about 10, namely about 2 to 7.

In many cases, the separation selectivity for at least one gas pair after coating the membrane is at least about 40%, viz. At least about 50%, of the separation selectivity shown by a substantially non-porous membrane of the same material, ie a non-porous membrane Gases essentially only pass through interaction with the material of the membrane. The selectivity of the separation of the coated membrane may be at least about 35, e.g. at least about 50 or 100% larger

- / JW -

be as the Trennseiektivität for the gas pair, which could be supplied by the material of the coating, if it is in the form of a substantially non-porous membrane.

Moreover, after coating, the flow which can be obtained using the coated membrane is not unduly reduced, e.g. the ratio of the permeability of a gas to the permeability constant of the gas

Material of the membrane is preferably at least about

5x10, preferably at least about 1x10 reciprocal centime

Particularly advantageous coating materials for increasing the selectivity of separation of the membranes do not unduly reduce the permeation rate (flow) of the gas or gases desired to pass through the wall of the membrane. Often the materials for the coatings have relatively high permeability constants. The material of the coating should be capable of providing occluding contact with the outer surface of the membrane. For example, after application, it should be sufficiently wet and adhered to the hollow fiber to allow entry of an occlusive contact. The wetting properties of the material of the coating can be readily determined by placing the material of the coating, either alone or in solution.

SS

-Ae - 2 1

medium, with the material of the membrane in contact. Moreover, based on determinations of the average pore diameter in the separating thickness of the membrane, materials for the coating of suitable molecular size can be selected. If the molecular size of the material of the coating is too large to match the pores, the material may not be useful for providing an occluding contact. On the other hand, if the molecular size of the material for the coating is too small, it may be pulled through the pores of the membrane during coating and / or during the separation operations. If the pores are in a wide variety of sizes, it may be desirable to use a polymerizable material for the coating material that is polymerized after application to the membrane, or to use two or more coating materials of different molecular sizes, e.g. by applying the materials of the coating in order of their increasing molecular sizes.

The materials for the coating may be natural or synthetic substances and are often polymers, and advantageously have the appropriate properties to provide occluding contact with the membrane. Synthetic substances include both addition

and condensation polymers. Typical of these useful materials which can form the coating are polymers which may be substituted or unsubstituted and which are solid or liquid under gas separation conditions, and include the following: synthetic rubbers; natural rubbers; Relatively high molecular weight and / or high boiling point liquids; organic prepolymers; Poly (siloxanes) (silicone polymers); polysilazanes; polyurethanes; Poly (epichlorohydrin); polyamines; polyimines; polyamides; Acrylonitrile-containing copolymers such as poly (a-chloroacrylonitrile) copolymers; Polyesters (including polylactams and polyarylates), e.g. Poly (alkyl acrylates) and poly (alkyl methacrylates) which are believed to have the alkyl groups from 1 to about 8 carbon atoms, polysebacates, polysuccinates and alkyd resins; Terpenoidharze; Linseed oil; Cellulose-based polymers; Polysulfones, in particular polysulfones containing aliphatic radicals; Poly (alkylene glycols) such as poly (ethylene glycol), poly (propylene glycol), etc .; Poly (alkylene) -polysulfate; Polypyrrolidone; Polymers of monomers having ct-olefinic unsaturation, such as poly (olefins), e.g. Poly (ethylene), poly (propylene), poly (butadiene), poly (2,3-dichlorobutadiene), poly (isoprene), poly (chloroprene), poly (styrene), including poly (styrene) copolymers, e.g. Styrene-butadiene copolymer, polyvinyls such as poly (vinyl alcohols), poly (vinyl aldehydes) [e.g. Poly (vinyl-

formal) and poly (vinyl! butyral)], poly (vinyl ketones) [eg, poly (methyl vinyl ketone)], poly (vinyl esters) [eg poly (vinyl benzoate)], poly (vinyl halides) [eg poly (vinyl bromide)], poly (vinyl) vinyl halides), poly (vinylidene carbonate), poly (N-vinylmaleimide), etc., poly (1,5-cyclooctadiene), poly (methyl isopropenyl ketone), fluorinated ethylene copolymers; Poly (arylene oxides) '<, eg poly (xylylene oxide); polycarbonates; Polyphosphates, eg poly (ethylene methylphosphate); and the like, and any copolymers including block copolymers containing repeating units of the polymers listed above, and graft polymers and blends containing any of the compounds enumerated above. The polymers may or may not be polymerized after application to the membrane.

Particularly useful coating materials include poly (siloxanes). Typical poly (siloxanes) may contain aliphatic or aromatic radicals and often have repeating units of 1 to about 20 carbon atoms. The molecular weight of the poly (siloxanes) may vary widely, but is usually at least about 1000. Often, the poly (siloxanes) having a molecular weight of about 1,000 to 300,000 or more, when applied to the membrane, have conventional aliphatic ones and aromatic poly (siloxanes) include the poly (mono-

1997

substituted and disubstituted siloxanes), e.g. those in which the substituents are lower aliphatic radicals, for example lower alkyl, including cycloalkyl, in particular methyl, ethyl and propyl, lower alkoxy; Aryl, including mono- or bicyclic aryl, including bisphenylene, naphthalene, etc .; low mono- and bicyclic aryloxy; Acyl, including lower aliphatic and lower aromatic acyl; and the same. The aliphatic and aromatic substituents may be substituted, e.g. by halogens, e.g. Fluorine, chlorine and bromine, hydroxyl groups, lower alkyl groups, lower alkoxy groups, lower acyl groups, glycidyl groups, amino groups, vinyl groups, and the like. The poly (siloxane) may be crosslinked in the presence of a crosslinking agent to provide a silicone rubber, and the poly (siloxane) may be a copolymer with a crosslinkable comonomer such as α-methylstyrene to aid in crosslinking. Typical catalysts for promoting crosslinking include organic and inorganic peroxides. Crosslinking may occur prior to application of the poly (siloxane) to the membrane, but preferably the poly (siloxane) is crosslinked after application to the membrane. Often, the poly (siloxane) before crosslinking has a molecular weight of about 1,000 to 100,000 or above. Particularly advantageous poly (siloxanes) include

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Poly (dimethylsiloxane), poly (hydrogenmethylsiloxane), poly (phenylmethylsiloxane), poly (trifluoropropylmethylsiloxane), copolymers of α-methylstyrene and dimethylsiloxane, and postcured poly (dimethylsiloxane) containing silicone rubber having a molecular weight of about 1,000 to about 50,000 or above of networking. Some poly (siloxanes) do not wet the material of the hollow fiber sufficiently to provide such occluding contact as desired. However, dissolving or dispersing the poly (siloxane) in a solvent that does not significantly affect the material of the membrane can facilitate the achievement of an occluding contact. Suitable solvents normally include liquid alkanes, e.g. Pentane, isopentane, cyclohexane, etc., aliphatic alcohols, e.g. Methanol, some halogenated alkanes and dialkyl ethers, dialkyl ethers, and the like, and mixtures thereof.

The coating may take the form of a substantially continuous membrane, i. a substantially non-porous membrane in contact with the anisotropic membrane, or the coating may be discontinuous or discontinuous. Preferably, the coating is not so thick as to adversely affect the performance of the membrane, e.g. by causing an impermissible decrease in flow, or

by effecting such resistance to gas flow that the separation factor of the coated membrane is substantially that of the coating. Often, the coating may have an average thickness of up to about 50 microns. Of course, if the coating is interrupted, there may be areas where no coating material is present. The coating can often have an average thickness in the range of about 0.0001 to 50 microns. In some cases, the average thickness of the coating is less than about 1 micron, and may even be less than about 5,000 angstroms. The coating may comprise a layer or at least two separate layers, which may consist of the same materials or not of the same materials. The coating may be in any suitable manner, e.g. by a coating method such as spraying, brushing, immersion in a substantially liquid substance containing the material of the coating, or the like. The material of the coating is preferably contained when applied in a substantially liquid substance and may be in a solution using a solvent for the material of the coating, which is essentially a non-solvent for the material of the membrane. suitably

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For example, the coating may be applied after the arrangement of the membranes has been made for later incorporation into a permeator, or even after incorporation into the permeator, to minimize handling of the coated membrane.

It is often possible to use the outer surface of a membrane with a sealing means to seal the outer surface of the membrane, e.g. a plasticizer, a swelling agent, a non-solvent or a solvent (preferably a weak solvent) for the anisotropic membrane material. The selection of a suitable sealing agent will depend on the polymer of the membrane. Sealing agents that may be employed include liquids and gases such as ammonia, hydrogen sulfide, acetone, methyl ethyl ketone, methanol, isopentane, cyclohexane, hexane, isopropanol, dilute mixtures of solvents for the polymer (eg, toluene, benzene, methylene chloride in non-solvents for the polymer, etc. The treatment may be carried out before or after the membrane has been dried, and it may be passed through a wide temperature range. Temperatures of about 0 ° to 50 ° C, namely about 10 ° to 35 ° C v / earth usually used. The treatment of the membrane with a sealing agent before the

Coating to increase selectivity may be advantageous in some cases.

The membranes of the present invention are widely applicable to gas separation operations, particularly in the separation of low molecular weight gases by interaction of the penetrating gas with the material of the membrane. Gaseous mixtures which can be used in gas separation operations consist of gaseous substances, or substances which are normally liquid or solid but evaporate at the temperatures at which the separation is carried out. Typical gas separation processes that may be desired include, for example, the following separations: oxygen of nitrogen; Hydrogen of at least one of carbon monoxide, carbon dioxide, helium, nitrogen, oxygen, argon, hydrogen sulfide, nitrous oxide, ammonia, and hydrocarbyl having from 1 to about 5 carbon atoms, especially methane, ethane and ethylene; Ammonia of at least one of the gases, namely hydrogen, nitrogen, argon and hydrocarbon of 1 to about 5 carbon atoms, e.g. Methane; Carbon dioxide of at least one of the gases, namely carbon monoxide and hydrocarbon of 1 to about 5 carbon atoms, e.g. Methane; Helium of hydrocarbon of 1 to about 5 carbon atoms, e.g. Methane; Hydrogen sulfide of hydrocarbon having 1 to about 5 carbon atoms

such as methane, ethane or ethylene? and carbon monoxide from at least one of the gases, namely, hydrogen, helium, nitrogen, and hydrocarbon having 1 to about 5 carbon atoms. It should be emphasized that membranes according to the present invention also find advantageous application in separation processes using other gas mixtures.

In summary, anisotropic membranes from a solution of a membrane-form ¹ according to the present invention - manufactured 'the polymers in a liquid carrier. The polymer solution is provided in the form of a precursor and then coagulated in a liquid coagulant containing water to form the anisotropic membrane. The liquid carrier used in the process of the present invention contains an N-acylated heterocyclic solvent of the following general formula

* N-CR

in which X is -CH ₂ -, -N (R ¹ ) - or -O-, R is hydrogen, methyl or ethyl, and R ^{1 is} hydrogen or methyl. The process according to the present invention is particularly useful for making anisotropic hollow fiber membranes. In the production of anisotropic hollow fiber membranes

For example, the solution of a hollow fiber-forming polymer in the liquid carrier is extruded through an annular spinneret to form a hollow fiber precursor, and the hollow fiber precursor is coagulated in a liquid coagulant containing water to form the hollow fiber membrane. The processes are of interest for the production of polysulfone hollow fiber membranes which have a homogeneously formed, thin, selective skin on an open cell support and have high resistance to collapse. The membranes are particularly useful for the separation of gases.

The following examples serve to better understand the present invention and are not intended to limit it in any way. All parts and percentages of gases are parts by volume, and all parts and percentages of liquids are parts by weight, unless expressly stated otherwise. All gas permeabilities were determined using substantially pure gases having a pressure of about 70 atmospheres absolute on the outside and a pressure of about 1 atmosphere on the inside of the hollow fiber membrane, unless expressly stated otherwise.

Embodiment · e example 1

32 parts by weight of polysulfone (P-35OO, available from Union Carbide Corporation) and 68 parts by weight of a liquid carrier consisting of 90 parts by weight of 1-formylpiperidine and 10 parts by weight of formamide (reagent grade) are charged to a heated spinning solution mixer with a dry nitrogen atmosphere. Prior to introduction into the spinning solution mixer, the polysulfone polymer was dried at about 125 ° C for 5 to 7 days under vacuum (e.g., at an absolute pressure of less than about 10 or 20 mm Hg). The 1-formylpiperidine has a moisture content of about 0.45 g per 100 ml and the formamide of about 0.15 g per 100 ml. Exposure of the formamide to air during filling of the heated mixer for the spinning solution is kept as low as possible to avoid degradation of the formamide. In the heated mixer for the spinning solution, the polymer solution is maintained at about 80 ° C to 100 ° C for a time sufficient to completely dissolve the polysulfone (generally, residence times of about 8 hours are generally used). The polymer solution is transferred to a degassing vessel having a dry nitrogen atmosphere heated to about 80 ° C. The degassing container includes a conically shaped manifold with a

- / sr -

9h 2 1997

Cup on the crest of the distributor. The polymer solution, when introduced into the dwell, is introduced into the cup below the level of the polymer solution in the cup and the polymer solution flows down the edge of the cup over the conical shaped distributor in the form of a thin film. The polymer solution runs from the lower edge of the conically shaped manifold onto a wire net which leads into the polymer solution in the degassing vessel. During degassing, the polymer solution is circulated in the degassing tank. The degassing vessel is maintained at an absolute pressure of about 250 to 350 mm Hg. Satisfactory degassing can also be achieved by using a substantially atmospheric pressure in the degas tank. Adequate degassing is usually achieved in less than about 7 hours residence time in the degas tank.

The degassed polymer solution was pumped by means of a Zenith H pump at a rate of 8.6 g per minute to a tube-in-nozzle type spinnerette having a nozzle diameter of 533 microns, an injection tube outer diameter of 203 microns, and a Injection capillary diameter of 127 microns had. The spinneret had five polymer polymer solution inlets spaced equally behind the annular extrusion zone and was passed through

kept an outside electric heating jacket at a temperature of approximately 50 ° to 58 ⁰ C; the polymer solution was at approximately the same temperature. Deionized water of about room temperature (20 to 25 ° C) was fed to the spinneret at a rate of about 1.2 ml per minute. While dwelling in the spinneret, the deionized water was heated by heat transfer. The spinneret was located about 10 _f 2 cm above the coagulation bath. The hollow fiber precursor was extruded at a rate of about 42.7 meters per minute.

The hollow fiber precursor was fed from the spinneret down a long coagulation bath. The coagulation bath contains substantially tap water and sufficient fresh tap water is added and coagulation bath liquid (liquid coagulant) withdrawn to keep the concentration of 1-formylpiperidine in the coagulation bath to less than about 1 weight percent. The liquid coagulant is maintained at a temperature of about 2 ° to 4 ° C. The hollow fiber precursor is fed vertically down into the liquid coagulant over a distance of about 7.8 cm, then passes around a roller on a slightly obliquely upward path through the liquid coagulant and then leaves the coagulation bath. The distance from immersion in the coagulation bath is about 1.4 m.

The hollow fiber from the coagulating bath is then washed with tap water in three successive godet baths. In the first Godet bath, the hollow fiber is immersed at a distance of about 7 _f 3 m. The first Godet bath is maintained at a temperature of about 2 ° to 4 ° C and the concentration of 1-formylpiperidine in the bath is adjusted to a concentration of below about 3% by weight by adding fresh water and stripping the wash medium. The second and third Godetbad at ambient temperature (eg, about 15 ° to 25 ⁰ C, depending on the temperature of the tap water and the room temperature of the laboratory), and it is continuously fed to the Godet baths of fresh water. The wet hollow fiber has an outer diameter of about 440 microns and an inner diameter of about 155 microns.

The water-moist hollow fiber is wound onto a bobbin using a Leesona wind-up device under tension as low as possible. The bobbin contains about 3600 m of hollow fiber and the thickness of the hollow fiber wound on the bobbin is less than about 2 cm. The bobbin is placed in a tap water containing vessel and tap water at tap water temperatures (10 ° to 20 ° C) at a rate of about 4 to 5 liters per hour per hour over a period of about 24 hours

£, _ -.2 19976

Bobine added and removed from the jar. The bobbin is then stored for 7 days in the tap water containing vessel at about ambient temperature (20 ° to 25 ° C). After storage, while still wet, the hollow fiber is wound on a rod making machine to form hollow fiber hanks about 3 meters in length. The winding of the hollow fiber on the strand machine is accomplished using the minimum tension required to effect the winding. The hollow fiber hanks are suspended vertically with the openings of the hollow fiber cores open at the bottom, and the hanks are allowed to dry for a period of at least about 3 days at ambient conditions of the laboratory (about 20 ° to 25 ° C and 50% relative humidity). The dried hollow fiber has an outer diameter of about 390 microns and an inner diameter of about 140 microns and appears to be similar to the hollow fiber depicted in FIG. 1 under the scanning electron microscope.

Test loops were made from ten hollow fibers, each about 15 cm long. At one end, the test loop is embedded in a tube plate through which the hollow fiber cores of the hollow fibers communicate with each other. The other end is stuffed. The hollow fiber cores of the hollow fibers in each test loop become

199 7

B " φ ff

subjected to a vacuum (about 50 to 100 mm Hg absolute pressure) for a period of about 10 minutes. Each of the test loops is dipped in a coating solution of about 2 weight percent post-curable polydimethylsiloxane (Sylgard 184, available from Dow Corning Corporation) in isopentane while maintaining the vacuum for a period of about 10 minutes and then removed from the coating solution. The vacuum is held for about 10 minutes after the test loop has been removed from the coating solution, and the test loops dried at ambient laboratory conditions (20-25 ° C, about 40-60% relative humidity). The permeabilities of the test cycles for hydrogen and methane are \ using

I of substantially pure gases at ambient temperature I

of the laboratory (about 20 ° to 25 ° C), the j

outer charging surface (shell side) of the hollow fibers f

j at a pressure of about 70 atmospheres absolute, and the I

Hollow fiber core side of the hollow fibers at a pressure of about 1 atmosphere was absolute. The particular permeabilities j usually vary somewhat from trial loop to trial loop, and some variations may be due to leaks j in the tube plate, damage to the hollow fiber during handling, or the like. The average hydrogen permeability is often in the range

__ 219976

Range from about 75 to 150 GPU (lxlO ⁶ χ cm ³ (STP) / cm ² -seccm Hg), and the average methane permeability is often in the range of about 1 to 2 GPU. The ratio of permeabilities (separation factor) for hydrogen over methane is often about 50 to 60. The pressure at the failure of the

Hollow fiber was reported to be over 110 kg / cm (1600 pounds per

square inch).

Example 2

A degassed polymer solution containing 32 percent by weight polysulfone P-35OO and a liquid carrier consisting of 1-formylpiperidine and formamide was spun through a spinneret (jet) of the type described in Example 1 to give a hollow fiber membrane according to Table I below spun. The temperature of the polymer solution (spinning solution) for the experiments 885-1, 533-1-7 and 537-1 was not measured directly and can be 60 ° to 70 ° C. Deionized water was used as injection fluid and provided at a rate sufficient to maintain the inside diameter of the hollow fiber. The coagulation bath contains water and the concentration of 1-formylpiperidine is maintained in the coagulation bath by drawing off bath fluid at a level of less than about 1 percent by weight. The hollow fiber is immersed in the coagulation bath over a distance of about 1 m. The

T a b e 1 le

1-formylpiperidine conc. in liquid carrier (% by weight) • i Beam dimension AD (μ), ID (μ) Capillary (μ) Beam stretching Spinning solution rate (ml / min) Spinning speed (ifi / min) Spinning solution p at the nozzle ( ⁰ C) Distance from nozzle of coagulation bath (can) temperature l.Goth bath ⁰ C .3.Goddash 92.5 Fiber Diitensions * AD (μ) / ID (y) 457/127/76 0.96 6 36.6 About 60 ° 12.7 Coagulation bath 4 2.Godd bath RT Yes. : No. 92.5 416/134 457/127/76 0.96 6 38.1 About 60 ° 12.7 3 4th RT RT 85-1 92.5 410/136 457/127/76 0.96 6 38.1 About 60 ° 12.7 3 3 RT RT 33-1-7 92.5 416/136 533/203/127 1.15 7.1 42.7 53 ° 10.2 3 1-3 RT RT 37-1 90 425/150 533/203/102 0.98 8.3 42.7 53 ° 10.2 2 1 1.5-20 RT 93-4-6 90 456/150 533/203/102 0.98 8.3 42.7 55 ° 10.2 1 1 RT RT 95-1 87 448/148 533/203/102 0.98. 8.3 42.7 52 ° 10.2 1 3 RT RT 95-2 87 456/152 533/203/102 0.98 8.3 42.7 ' 54 ° 10.2 3 3 RT RT 94-1. 90 448/149 457/127/76 0.77 6 30.5 55 ° 5.1 3 1 RT 11 94-2 ' 90 479/217 457/127/76 0.77 6 30.5 65 ° 5.1 1 1 11 11 04-3 92.5 445/205 635/178/102 1.75 7.1 42.7 64 ° 10.2 1 3 11 RT 04-6 406/146 2 RT 93-2

* Before drying

Ί03

Residence time of the hollow fiber in each of the three wash baths (first, second and third Godet bath) is as follows:

Approximate spin speed Approximate dwell time in each wash (m / mln) · (see)

30.5 56.9

36.6 47.4 38.1 45.5

42.7 40.6

The hollow fiber is wound on a bobbin, keeping it in a wet state, and the bobbins are washed in cold running tap water for about 16 to 24 hours, and then stored in a water-filled tub for 7 days. The hollow fiber is then dried under ambient conditions of the laboratory (22 ° to 25 ° C and about 40% to 60% relative humidity), formed into test loops, coated and tested as described in Example 1, except that a weight percent Sylgard 184 solution was used and twenty hollow fibers were used in the test loop. The observed behavior of the hollow fiber is given in Table II below. '.

table

Permeability, (GPU ⁴ **) hydrogen methane

Separation factor Approximate pressure at collapse (kg / cm ^)

533-1-7

893-4-6

124 187 157 132

98 117

97 130

89 142 131

4.2

2.7

2.4

0.97

1.53

1.2

1.7

1.2

2.3

8.8

70 45 58 56 101 77 83 78 74 63 15 140 125 125 125 155 155 110 155

70-110 70-HO 125

Based on the fiber dimension before drying

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Example 3

The procedure of Example 2 is substantially repeated with the following exceptions. The degassed polymer solution consists essentially of 35 weight percent polysulfone P-35OO and 64 weight percent 1-formylpiperidine, the spinneret has an outside diameter of 533 microns, an inside diameter of 203 microns and an injection capillary diameter of 127 microns. The spinneret is located about 10 _f 2 cm above the liquid level in the coagulation bath, the polymer solution feed rate to the spinneret is about 11.8 cm per minute, and the spinning speed is about 42.7 m per minute. The temperature of the polymer solution extruded from the spinneret is about 54 ° C. The coagulation bath is at a temperature of about 1 to 2 ° Cj the first Godet bath has about 1 ° to 2 ° C, and the second and third Godet baths about 20 ° C. The residence time of the hollow fiber in each of the Godet baths is about 40.6 seconds. The hollow fiber has an outer diameter of 445 microns and an inner diameter of 166 microns before drying. A scanning electron microscope photograph of a dried hollow fiber according to this example is shown in FIG. The collapse pressure shown by the hollow fiber is about 170 kg / cm. The hollow fiber is formed into test loops, coated (except that a 2% by weight Sylgard 184 solution is used) and

examined as described in Example 1. The hydrogen and methane permeabilities of the uncoated hollow fiber are about 39 GPU and 2.1 GPU. A similarly prepared hollow fiber except that the temperature of the coagulation bath was about 5 ° C has an inside diameter (wet) of about 190 microns, and shows one

Pressure at collapse of about 100 to 150 kg / cm, and has coated and in experimental loops, a hydrogen permeability of about 100 GPU and a methane permeability of about 3.3 GPU.

Example 4

The procedure of Example 2 is essentially repeated, but with the following exceptions. A degassed polymer solution of 36 weight percent polysulfone P-35OO and 64 weight percent of a mixture of 87 weight parts of 1-formylpiperidine and 13 weight parts of formamide is passed through a spinneret having an outside diameter of 457 microns, an inside diameter of .127 microns, at a temperature of about 52 ° C and a 76 micron injection capillary diameter at a rate of 5 cm / minute. The spinneret is located 10.2 cm from the liquid level in the coagulation bath. The spinning speed is about 30.5 m / minute. The coagulation bath and the first Godet bath have a temperature of about 3 ° C _{? J} and that

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second and third godet baths are at about room temperature. The residence time in each of the three Godet baths is about 56.9 seconds. The hollow fiber is stored in water in a storage chest for periods of 1, 2 and 24 days, rather than 7 days, and samples of the hollow fibers for their hydrogen and methane permeabilities, their collapse pressures, and solvent content after each of the storage periods. examined. The hydrogen and methane permeabilities of a test loop containing the sample of uncoated hollow fiber are determined for the 1 day hollow fiber using a shell side pressure of about 7.8 atmospheres absolute and a hollow fiber core pressure of about 4.4 atmospheres absolute and for the coated hollow fibers that had been stored for 1 and 24 days using a shell side pressure of about 70 atmospheres absolute, and a hollow fiber soul pressure of about 1 atmosphere absolute. The hollow fiber, when dry, has an outer diameter of 456 microns and an inner diameter of 188 microns. The results are set forth in Table III below.

Table III

Days in Lagerbüttes 1 2 24

Uncoated, H ^ -permeabi-

quality (GPU) .... Τ ....... 457

  Uncoated, CH Permeablity (GPU) 167

Coated, H ^ -Permeabi-

quality (GPU) 93 102 114

Coated, CH. Permeability (GPU) .... 2.8 3.3 1.9

Pressure on collapse

(kg / cm ² ) 140 140 170

1-Formylpiperidine in fiber

(Weight percent) 2.25 1.46 0.95

At s ρ ie 1 5

The procedure of Example 4 is essentially repeated, except that the spinning speed is about -45.7 m / minute and the residence time in each of the Godet baths is about 38 seconds. In one experiment, a chimney was placed between the spinneret and the liquid level in the coagulation bath so that there was a saturated atmosphere inside the chimney. The spinneret was 10.2 cm away from the liquid level in the coagulation bath. Another attempt was conducted in substantially identical fashion, except that no

- -tie - '

Fireplace was used and the spinneret was located 5.1 cm above the liquid level in the coagulation bath. Hollow fiber samples were formed into experimental loops, coated and the hydrogen and methane permeabilities determined after 7 days storage in water. The results were the following:

fireplace

No fireplace

H ₂ Permeability (GPU) CH ₄ Permeability (GPU) Outside Diameter (Micron) Inside Diameter (Micron)

129 123 1.5 1.3 370 364 171 165

Example 6

The procedure of Example 2 was substantially repeated, but with the following exceptions. A degassed polymer solution consisting of 38 weight percent polysulfone P-35OO and 62 weight percent liquid carrier of 87 weight parts of 1-formylpiperidine and 13 weight parts of formamide is passed through a spinneret having an outside diameter of 635 microns, an inside diameter of 228 microns, and at about 70 ^° C Injection capillary diameter of 152 microns at

spun at a rate of 6 cm / minute. The spinneret is placed about 2.5 cm above the liquid level in the coagulation bath, and the spinning speed is about 30.5 m / minute. The coagulation bath and the first Godet bath have a temperature of about 3 ° C, and the second and third Godet baths a Temperature of about room temperature. The residence times of the hollow fiber in each of the three Godet baths are about 56.9 seconds. The coagulation bath contains 7.5% by weight of acetic acid. The dried hollow fibers have an outside diameter of 444 microns and an inside diameter of 171 microns. The hollow fiber shows a collapse pressure of about 180 kg / cm. Samples of the hollow fiber were processed into experimental loops and the hydrogen and methane permeabilities were determined both before and after coating (the uncoated permeabilities were determined absolutely at a shell pressure of about 7.8 atmospheres absolute and a pressure in the hollow fiber core of about 1 atmosphere absolute). , The results are as follows:

Uncoated Coated

^ Permeability (GPU) CH ₄ Permeability (GPU)

409 107

136 2.1

Example 7

, The procedure of Example 6 is essentially repeated except that the spinneret has a 483 micron OD, a 152 micron ID, and a 76 micron injection capillary diameter, and the hollow fibers in a vat under various conditions as described in US Pat the following Table IV are stored.

Example 8

The procedure of Example 2 is essentially repeated, but with the following exceptions. The polymer solution contains 32 weight percent polysulfone P-35oo and 68 weight percent of a liquid carrier with 85 parts by weight of 1-For ny! Piperidine and 15 parts by weight Äthyienglykol, and is at about 70 ° C through a spinneret with a Außendurchmeseer of 635 microns, an inside diameter of 229 Micron, and a 152 μm injection capillary diameter spun at a rate of 7.2 cm / minute. The spinning speed is about 42.7 m / minute. The spinneret is located about 10.2 cm from the liquid level in the coagulation bath. The coagulation bath and the first Godet bath have a temperature of about 3 ° C, and the second and third Godet baths have a temperature of about room temperature. The residence time of the hollow fiber in each of the

table

IV

Days of storage in Bütte

Stored in water

Stored in water: isopropanol 5: 5 (by weight)

jerk when collapsing, kg / cm ²

jerk at collapse, kg / cm ''

sw. -% 1-Formylpiperidine in fiber

2w "-% 1-Formyl piperidine in fiber

Outer diameter, micron diameter, micron

H ₂ • ^CH 4

CH .

175

28 175 759 0.85 Uncoated 7 2.45 262 0.35 2330 28 1.93 854 427 1060 .- 439 321 125 - T 131 Permeabilities, (GPU) - coated 243 7 9.27 7 108 28 24 28 Permeabilities, (GPU) Coated Uncoated 205 5.7 140 3.1

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three godet baths is about 40.6 seconds. The outside diameter of the hollow fiber is about 456 microns and the inside diameter is about 205 microns. The hydrogen permeability of the coated hollow fiber is about 64 GPU and the carbon monoxide permeability is about 0.65 GPU,

Example 9

The procedure of Example 2 is essentially repeated, but with the following exceptions. The polymer solution contains 32 weight percent polysulfone P-35OO and 68 weight percent liquid carrier with 90 weight parts of 1-formylpiperidine, 5 weight parts of ethylene glycol and 5 weight parts of water. The polymer solution is spun at 65 ° to 70 ° C through a spinneret having an outer diameter of 508 microns, an inner diameter of 152 microns and an injection capillary diameter of 102 microns. The spinning speed is 43.5 m / minute. The spinneret is located about 17 cm from the liquid level in the coagulation bath. The coagulation bath and the first Godet bath have a temperature of about 5 ° C, and the second and third Godet bath each have a temperature of about room temperature. The residence time of the hollow fiber in each of the three godet baths is about 38 seconds. The outside diameter of the hollow fiber is about 450 microns and the inside diameter about 236 microns. The hydrogen permeability

the coated hollow fiber is about 100 GPU, and the carbon monoxide permeability is about 2.3 GPU. The permeabilities were determined using a gas mixture of about 25 mole percent hydrogen and 75 mole percent carbon monoxide using a shell side pressure of about 150 centimeters of mercury absolute and laboratory vacuum in the hollow fiber core of the hollow fiber.

Example 10

The procedure of Example 2 is essentially repeated, but with the following exceptions. The polymer solution is prepared from 32 weight percent polysulfone P-35OO and 68 weight percent liquid carrier with 80 weight parts of 1-formylpiperidine, 10 weight parts of ethylene glycol and 10 weight parts of acetone. The concentration of acetone is not determined after degassing. The polymer solution is spun at about 80 ° C through a spinneret having an outside diameter of 635 microns, an inside diameter of 228 microns and an injection capillary diameter of 152 microns. The spinning speed is 26.2 m / minute. The spinneret is located about 20.3 cm from the liquid level in the coagulation bath. The coagulation bath and the first Godet bath have a temperature of about ⁰ ° C., and the second and third Godet baths each have a temperature of about 14 ° C. The residence time of the hollow fiber

, 21997η

in each of the three godet baths is about 66 seconds. The hollow fiber core of the hollow fiber is eccentric and the outer diameter of the hollow fiber (wet) is about 342 microns, and the inner diameter about 165 microns. The hydrogen permeability of the uncoated hollow fiber is about 225 GPU, and after coating about 82 GPU, and the methane permeability of the uncoated hollow fiber about 50 GPU, and after coating about 1.6 GPU.

Example 11

The procedure of Example 2 is essentially repeated, but with the following exceptions. The polymer solution contains 40 weight percent polysulfone P-1700 (a lower molecular weight polysulfone, but otherwise similar to polysulfone P-35OO available from Union Carbide Company) and 60 weight percent of a liquid carrier containing 87 weight parts of 1-formylpiperidine and 13 weight parts of formamide. The polymer solution is spun at about 70 ° C through a spinneret having an outside diameter of 635 microns, an inside diameter of 229 microns and an injection capillary diameter of 152 microns at 9 cm / minute. The spinnerette is located about 7.6 cm from the liquid level in the coagulation bath. The spinning speed is about 30.5 m / minute. The coagulation bath and the first Godet bath have a temperature of about

The residence time of the hollow fiber in each of the three Godet baths is about 56, s seconds. The outside diameter of the hollow fiber is about 4.39 microns

and the inner diameter about 154 microns. The hollow fiber

has a collapse pressure of about 175 kg / cm. Samples of the hollow fibers were stored in water for T, or 22 or 23 days, dried and placed in trial loops. The trial loops were treated in several ways. Some test loops were rinsed with isopentane before coating. In this process, the hollow fiber cores of the hollow fibers were subjected to vacuum for about 10 minutes, immersed in isopentane at room temperature (about 22 to 25 ° C) for a period of 10 minutes, maintaining the vacuum on the side of the hollow fiber core of the hollow fibers, and then removed from the isopentane and maintaining the vacuum for a further 10 minutes. The test loops (coated and uncoated) were also suspended in a closed container with gaseous ammonia at room temperature and a pressure of about 18 kg / cm. Both the coated and uncoated hollow fibers were subjected to this ammonia treatment. The permeabilities of the hollow fiber for hydrogen and methane were measured using various man-

11?

telseitiger prints determined. The pressure on the side of the hollow fiber core is about 1 atmosphere absolute. The results are set forth in Table V. below.

Example 12

The procedure of Example 2 was substantially repeated, but with the following exceptions. The polymer solution contains 34% by weight of polysulfone P-35OO and 66% by weight of a liquid carrier consisting of a mixture of 42.4 g of substantially anhydrous lithium chloride per 1000 ml of a solution of 1-formylpiperidine. The polymer solution is spun at about 70 ° to 80 ° C through a spinneret having an outer diameter of 635 microns, an inner diameter of 228 microns, and an injection capillary diameter of 152 microns. The spinneret is located 3.5 cm above the liquid level in the coagulation bath. The spinning speed is about 20 m / minute. The coagulation bath has a temperature of 5 C, the first Godet bath of 5 ° C and the second and third Godet bath each temperatures of about room temperature. The residence time in each of the three Godet baths is about 86 seconds. The outside diameter of the hollow fiber is about 685 microns and the inside diameter is about 380 microns. The permeabilities were determined using the method described in Example 9. The coated water

table

Artmoniac treatment (days) Storage time - in Bütte (days) Uncoated Isopentane rinse coated - Coated after Iscpentan rinse - Coated after Iscpentane Flush Permeability (GPU) at 68 at  > 0 7 Permeability (GPU) at 7.8. at* Permeability, (GPU) at 7.8 at Permeability, (GPU) at 7.8 at 68 at - Permeability, (GPU) at 7.8 at 68 at 1 day 3 days Arrrnoniak- Arrrocsiiak- Bhdlg. Shdlg. 0 7 626 270 - 143 178 ^H 2 0 ' 22 213 23 - 2.4 3.5 _ _ ^CH 4 0 22 380 193 193 161 140 _ _ ^H 2. 0 23 94 19 4.0 -. 2,2 2,3 - CH ₄ 0 23 518 246 - 29 131 127 68 62 ^H 2 *. 3 23 143 40 - 0.2 2.6 1.9 l »0 1,3 CH ₄ 3 23 39 34 30   - _. - ^H 2 0.18 1.9 0.26 - - CH ₄

All prints are absolute pressures on the outer surface

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The hydrogen permeability is about 80 GPU and the coated carbon monoxide permeability is about 2.9 GPU. The hollow fiber has a fine, spherical structure as seen in scanning electron microscope photographs.

is, and has an inner surface according to BET analysis

of about 75 m / g.

Example 13

The procedure of Example 2 was essentially repeated. brings, but with the following exceptions. The degassed polymer solution contained 32% by weight of poly (phenylene ether) sulfone marketed by ICI, Ltd., United Kingdom, and 68% by weight of a liquid carrier consisting of 90% by weight of 1-formylpiperidine and 10% by weight of formamide consists. The spinneret had an outside diameter of 533 microns, an inside diameter of 203 microns and an injection capillary diameter of 134 microns. The rate of polymer solution through the spinneret was about 7.1 cm / minute and the take up speed about 42.4 m / minute. The temperature of the coagulation bath and the first wash bath was about 1 ° to 2 ° C, and the temperatures of the second and third wash baths each about 19 ° C. The approximate temperature of the polymer solution varied from about 40 ° to 55 ° C and the hollow fiber had an outer diameter of about 435 μm before drying.

crown and an inner diameter of about 150 microns; however, a sample had a hollow fiber core of oval shape. The observed behavior of the hollow fiber membranes is shown in Table VI below.

Table VI

Approximate Permeabilities (GPU *) 120 140 50 Coated (68). CH ₄ opxnnjLO ^ sungsternp. uncoated (7,8) "2 1.3 1.0 0.3 Verse no. (° C) * · ^H 2 41 47 35 55 50 40 325 400 • 170 1 2 3

* All permeabilities were performed at a pressure in the hollow fiber core of about 1 atmosphere absolute. The shell-side prints are given absolutely in brackets in atmospheres. ·

Example 14

The procedure of Example 2 was substantially repeated, but with the following exceptions. The degassed polymer solution contains 32 weight percent polysulfone (P-35OO) and 68 weight percent of a liquid carrier consisting of about 1 weight percent acetylpiperidine and 10 weight percent formamide. The spinneret has an outer diameter

- ί »- 2 1997

of 584 microns, an inner diameter of 178 microns and an injection capillary diameter of 101 microns. The spinneret is located about 5 cm above the level of the liquid coagulant and maintained at a temperature of about 57 ° C. The coagulation bath and the first wash bath each have temperatures of about 2 ° C, and the second and third wash baths both have temperatures of about 16 C. Further details are given in Table VII below ,

Example 15

A hollow fiber is prepared according to the method substantially similar to Experiment No. 533-1 of Example 2, except that the hollow fiber was stored in water for 7 days. Samples of the hollow fiber were dried in a temperature- and humidity-controlled atmosphere (air) under various conditions and then processed into experimental loops. The hydrogen and methane permeabilities of coated and uncoated hollow fibers were determined. The results are given in Table VIII below.

Example 16 The procedure of Example 1 is essentially repeated,

Table VII

Experiment Dust Dissolution Rate No. (ml / min)

water injection

Rate (ml / min)

Pressure (itimHg)

Fiber dimensions *

Permeabilities (GPU) ** Coated (68)

CH

8.4 9.9 8.4

0.75

0.75

0.6

455/150 500/150 465/130

70 0.9 73 0.7 53 1.4

*. Before drying.

** 'All permeabilities were determined with an inside pressure of about 1 at absolute. The prints on the outside surface are shown in parentheses.

table

VIII

Permeabilities, (GPU) *

Drying temperature <° C) Relative humidity (%) Absolute humidity (g / ni ³ ) 10 50 4.7 15 77   ; 9.8 22 50 9.8 25 50 11.5 35 25 9.8 40 50 26 60 50 65 80 50 147

Uncoated

Coated ϊο CH,

739 (7,8) 205 (34) 4/7 (68)

730 (7.8) 126 (68) 2.8 (68)

795 (7.8) 163 (34) 4.1 (68)

1128 (7.8) 413 (7.8) 160 (34) 4.0 (68)

• - 771 (7.8) 158 (34) 3.6 (68)

1343 (7.8) 496 (7.8) 138 (68) 2.7 (68)

603 (7.8) 193 (7.8) 94 (68) 1.1 (68)

252 (7.8) 62 (7.8) 68 (68) 0.6 (68)

All permeabilities were determined absolutely with an inside pressure of about 1 at. The prints on the outside surface are shown in parentheses.

but with the following exceptions. The polysulfone is dried for about 2 days at atmospheric pressure in a dry air atmosphere with forced circulation. The degassing of the polymer solution is carried out at atmospheric pressure under an atmosphere of dry air.

The polymer solution is extruded through the spinneret at about 8.1 cm / minute and a wind-up speed of about 42.4 m / minute. The outside diameter of the wet hollow fiber is about 450 microns and the inside diameter is about 155 microns. When the hollow fiber hanks are hung to dry, the hollow fibers remain connected to the loop, i. they are not open on the ground. The dried hollow fiber membranes have an outer diameter of about 400 microns and an inner diameter of about 140 microns.

Example 17

The procedure of Example 12 is essentially repeated, but with the following exceptions. The polymer solution contains 34% by weight of a suspension polymerized copolymer of 33% by weight of acrylonitrile and 67% by weight of styrene in 66% by weight of a liquid carrier containing 75% by weight of 1-formylpiperidine and 25% by weight of formamide. The spinneret is mounted about 0.6 cm above the level of the liquid coagulant and the take-up speed

2 1997Λ

is about {L3 to 14 m / minute. The coagulation bath and the first washing bath have a temperature of about 2 ° to 3 ° C, and the second and third washing bath each have a temperature of about 17 ° C. The hollow fibers are dried and dipped in methanol or pentane and then exposed to low partial pressure steam. The hollow fiber membranes are then coated with a solution of about 3 weight percent Sylgard in pentane. The coated hydrogen permeability is about 20 to 40 GPU and the separation factor for hydrogen over carbon monoxide is about 20 TdIs 40.

Example 18

The procedure of Example 12 is essentially repeated, but with the following exceptions. The polymer solution contains 30 weight percent of a methyl brominated poly (phenylene oxide) (about 45 mole percent brominated) in 70 weight percent 1-formylpiperidine. The spinnerette is located about 2.6 cm above the level of the liquid coagulant and the take up speed is about 13 to 14 m / minute. The coagulation bath and the first wash bath have a temperature of about 46 ° to 48 ° C, and the second and third wash baths each have temperatures of about 14 ° C. When coated, the hollow fiber membranes have a hydrogen permeability of about 90 to 100 GPU and a hydrogen separation factor over carbon monoxide of about 13.

Claims (34)

He f. I ndungsanspruch A process for producing an anisotropic membrane in which a polymer solution of a membrane-forming polymer is provided in a liquid carrier containing a solvent for the membrane-forming polymer in the form of a precursor and then coagulated in a liquid coagulant containing water, characterized in that the liquid carrier is an N-acylated, heterocyclic solvent of the following general formula X N-C-R wherein X is -CH ₂ -, -N (R ¹ ) - or -O-, R is hydrogen, methyl or ethyl, and R ^{1 is} hydrogen or methyl. , 2. The method of item 1 for the preparation of an anisotropic hollow fiber membrane, characterized in that (a) the polymer solution through an annular spinneret extruding to form a hollow fiber precursor and maintaining the polymer solution at a temperature sufficient to substantially expose the polymer during extrusion To keep the solution (b) injecting a liquid into the hollow fiber precursor hollow fiber core as extruded from the spinneret, wherein the injection liquid is miscible with the liquid carrier and injected at a rate sufficient to keep the hollow fiber precursor core open . (c) contacting the outside of the hollow fiber precursor with the liquid coagulant consisting essentially of water and containing less than about 5% by weight of the liquid carrier, the liquid coagulant being miscible with the liquid carrier and the injection liquid, and the contact is sufficient to coagulate the polymer in the hollow fiber precursor under the conditions of the liquid coagulant to form a hollow fiber, and (d) washing the hollow fiber with non-solvent for the polymer to reduce the level of liquid carrier in the hollow fiber to less than about 5 weight percent, based on the weight of the polymer in the hollow fiber. ' 3. The method according to item 1, characterized in that the N-acylated, heterocyclic solvent at least one of the listed below, namely ΛΧΧ 1-formylpiperidine, X-acetylpiperidine, 1-formylrnorpholine and 1-acetylmorpholine. 4. The method according to any one of the functons 1 to 3, characterized in that with respect to the polymer, the liquid carrier and the polymeric system, a second Virialkoef factors of up to about 15x10 mol. Cm * '/ g at 25 ° C. 5. A method according to any one of items 1 to 4, characterized in that the liquid carrier has a heat of dilution at 25 ° C in the liquid coagulant of more than about -3.5 kilocalories per mole. 6. The method according to any one of items 1 to 5, characterized in that the polymer includes polysulfone. 7. The method according to item 6, characterized in that the polymer polysulfone with the fol lowing specified, recurring structural units > 1 S-R Il 1 2 wherein R and R are the same or different and are all-phatic or aromatic, hydrocarbyl-containing radicals having from 1 to about 40 carbon atoms, and the sulfonyl groups are attached to an aliphatic or aromatic carbon atom. 8. Method according to item 7, characterized 12 since you r h h, that at least one of the radicals R and R an aromatic / hydrocarbyl-containing part. 9. The method according to item 7, characterized in that the polysulfone has a structure of the following formula CH- in which the index η has a value of about 50 to 80. 10. The method according to any one of items 1 to 9, characterized in that the liquid carrier contains a non-solvent. 11. Method according to one of the items 1 to 10, g e k e η η characterized in that the washed hollow fibers "^ ⁵⁰ '' 2 19 9 7 This is dried at a temperature which the
Selectivity or the flow of the hollow fiber membrane is not adversely affected adversely. 12. The method according to any one of items 1 to 11, characterized marked characterized in that the liquid coagulant contains at least about 75 weight percent water. 13. Procedure according to one of the items 1 to 12, marked, t. in that the temperature of the
liquid coagulant at least about -15 C to below about 2O ° C. 14. Method according to item 13, characterized in that the temperature of the liquid coagulant is about 0 ° to 10 ° C. 15. The method according to one of the items 1 to 14, characterized marked characterized in that the annular
Spinneret is disposed above the surface of the liquid Koaguliermittels. 16. The method according to any one of items 1 to 15, characterized marked characterized in that the polymer solution
contains at least about 25 weight percent polymer. - «21- 219976 17. Method nac.h any of the items 1 to 16, characterized in that the polymer solution contains about 28 to 40 weight percent of polymer. 18. The method according to any one of items 1 to 17, characterized in that the polymer solution at the extrusion temperature has a viscosity of about 10,000 to 500 000 centipoise. 19. The method according to any one of items 1 to 18, characterized 'characterized in that the liquid carrier non-solvent, and the non-solvent at least one of the group formamide, ethylene glycol and water. 20. Anisotropic membrane, characterized in that it is after one of the points. 1 to 19 has been made. 21. Dry, integral, anisotropic hollow fiber membrane for the separation of at least one gas from a gas mixture, characterized in that it contains a homogeneously formed, thin, outer release layer on an open-pore carrier and polysulfone, wherein a larger volume fraction of the wall the hollow fiber membrane Cells having a mean major dimension of less than about 2 microns and having substantially no macropores in the open cell support having a major dimension greater than about 3 microns and a maximum length to maximum width ratio greater than about 10, the hollow fiber membrane a ratio of the permeability of at least one of the group consisting of hydrogen, helium and ammonia to the permeability constant of the material of the hollow fiber membrane for the gas of at least about 5x10 reciprocal centimeters, a permeability ratio of (I) the permeability of a gas to lower molecular weight divided by the permeability of a higher molecular weight gas to (II) the square root of the molecular weight of the lower molecular weight gas divided by the square root of the molecular weight of the higher molecular weight gas of at least about 6; LOW molecular weight is hydrogen or helium and the higher molecular weight gas is a gas of the group consisting of nitrogen, carbon monoxide and carbon dioxide and has a permeability constant in the polysulfone which is at least about 10 times smaller than the permeability constant of the lower molecular weight gas in the material, and a collapse pressure of at least about 4 (T _c ) (t / D), where T _{g is} the tensile strength of the polysulfone, t - 2 19976 Wall thickness and D is the outer diameter of the hollow fiber membrane. 22. Polysulfone hollow fiber membrane according to item 21, characterized in that it is substantially free of macropores. 23. Hollow fiber membrane according to any one of items 21 and 22, characterized in that at least about 90 vol% of the wall of the hollow fiber membrane consist of cells having a major dimension of less than about 2 microns. " 24. hollow fiber membrane according to any one of items 21 to 23, characterized in that at least about 90 vol% of the wall of the hollow fiber membrane of cells having a major dimension of less than about 1 micron. 25. Hollow-fiber membrane according to any one of items 21 to 24, characterized in that the mean configuration ratio of the segments of the wall of the hollow-fiber membrane containing the cells with the largest average Hauptdimensioh, which are free of macropores, at least about 0, 03 is. β. Hollow fiber membrane according to any one of items 21 to 25, eken η is characterized in that the wall sr hollow fiber membrane has cells with a major dimension of 2hr than 0.2 microns and the ratio of average wall thickness to central cell cross-sectional area of the large cells at least about 1 reciprocal centimeter. K hollow-fiber membrane according to one of the items 21 to 26, ekennzeichnet in that the pore lumen of the wall of the hollow fiber membrane is at least about id up to about 70 vol%. Hollow-fiber membrane according to one of the items 21 to 27, characterized in that the pore lumen of the wall of the hollow-fiber membrane is larger than etv / a 45 | t and up to about 65 vol% is .. · j Hollow fiber membrane according to one of the points 21 to 28,. i characterized by the fact that the pressure | in collapse of the hollow fiber membrane greater than about j (Φ) (Tg) (t / D) ³ , where φ is the volume fraction of material c hollow fiber membrane in the wall of the hollow fiber membrane. - "Γ-. 2 1997 A hollow fiber membrane according to any one of items 21 to 29, characterized in that it has a relationship of (I) the quotient of the difference between the permeabilities of a gas permeated more easily and a gas less easily permeated divided by the permeability of the less easily penetrated gas Gas, times (II) the ratio of the permeability constant of the less permeated gas to the permeability constant of the more easily permeated gas of at least about 0.01, the more easily permeated gas having a permeability constant of at least about 5 times the permeability constant of the less permeated gas; the lighter gas permeated and the less easily penetrated gas have approximately the same molecular weight. 31. Hollow fiber membrane according to any one of items 21 to 30, characterized in that the outer skin is smaller than about 1000 angstroms. 32. Hollow fiber membrane according to any one of items 21 to 31, characterized in that the outer skin is smaller than about 500 angstroms. 33. Hollow fiber membrane according to any one of items 21 to 32, characterized in that the per-Meability ratio is at least about 7.5. 34. Hollow fiber membrane according to any one of items 21 to 33, characterized in that it has a maximum pore size of less than about 150 angstroms. 35. Hollow fiber membrane according to one of the items 21 to 34, characterized in that the polysulfone is a polysulfone having the recurring structural units of the following general formula 1 2 -R ¹ -S-R - Il i 2 in which R and R are the same or different and denote aliphatic or aromatic, hydrocarbyl-containing radicals having 1 to about 40 carbon atoms and the sulfonyl group is bonded to an aliphatic or aromatic carbon atom. 3.6. Hollow fiber membrane according to one of the points 21 to 35, characterized in that at least 12 one of R and R is an aromatic, hydrocarbyl including part. . · 37. hollow fiber membrane according to one of the items 21 to 36, characterized in that the Polysulfon a polysulfone of a structure of the following general formula CH. in which the index η has a value of about to 80. 38. Hollow-fiber membrane according to any one of items 21 to 37, characterized in that the material of the hollow-fiber membrane has a tensile strength of at least at least about 350 kg / cm. Hlerzü. "^ L: .. Draw drawings