DK148735B - MEMBRANE OF THE MULTI COMPONENT TYPE FOR GAS SEPARATION - Google Patents

Description

143735

This invention relates to a multi-component gas separation membrane of the kind set forth in the preamble of claim 1.

Separation, including increasing the concentration of at least one selected gas from a gaseous mixture, is a particularly important method in view of the requirements imposed on the supplies of chemical starting materials. Frequently these requirements are met by separating one or more desired gases from gaseous mixtures and by using the gaseous products for treatment. Proposals have been made to use separation membranes for selective separation of one or more gases from gaseous mixtures. To achieve selective separation, the membrane presents less resistance to transport of one or more gases than to at least one other gas of the mixture. Thus, selective separation may provide selective removal or concentration of one or more desired gases in the mixture with respect to at least one other gas, and therefore provide a product exhibiting a deviating relationship between one or more desired gases and at least a gas other than the corresponding ratio in the mixture. However, for selective separation of one or more of the desired gases using separation membranes to be commercially attractive, the membranes must not only be able to withstand the conditions they are exposed to during the separation process, but must also provide an appropriate selective separation. of the desired gas (s) under a sufficiently high flow rate, i.e. migration rate of permeate per surface area, so that the separation method can be used on an economically attractive basis. Separation membranes exhibiting a suitably high selective separation but undesirably low flow rates may thus require such a large surface area of the separating membrane that the use of these membranes is not economically attractive. Similarly, separation membranes exhibiting a high flow but low selective separation are also not commercially attractive. As a result, work has continued on developing separation membranes which can provide both an appropriate selective separation of one or more of the desired gases and a satisfactorily high flow, so that the use of these separation membranes is economically attractive on a commercial basis.

In general, the passage of a gas through a membrane can take place through pores, i.e. continuous fluid flow channels in communication with both supply and output surfaces of the membrane (which pores may be suitable for separation by Knudsen flow or diffusion); by another mechanism, in accordance with currently prevailing views with regard to membrane theory, the passage of gas through the membrane may occur by interaction between the gas and the material of which the membrane consists. By this last postulated mechanism, the permeability of a gas through a membrane is thought to involve the solubility of the gas in the membrane material and the diffusion of the gas through the membrane. The permeability constant of a single gas is presently assumed to be the product of the solubility and diffusivity of this gas in the membrane. A given membrane material has a particular permeability constant for passing a given gas upon interaction of the gas with the material in the membrane. The rate of migration of the gas, namely the flow, through the membrane is related to the permeability constant, but it is also influenced by such variables as the thickness of the membrane, the physical nature of the membrane, the partial pressure differential of the moving gas across the membrane, the temperature and the like.

To date, various modifications of membranes to be used for fluid separation have been proposed in an attempt to solve particular problems associated with the separation operation. The following illustration is illustrative of specific modifications made to membranes used for fluid separation to solve particular problems and to provide a basis on which the invention can be fully understood. Eg. For example, cellulose membranes first utilized for salting water were first developed and these membranes could generally be described as "dense" or "compact" membranes. "Dense" or "compact" membranes are membranes that are substantially pore-free, namely fluid channels that communicate between the surfaces of the membrane and are substantially free of voids, namely regions within the thickness of the membrane that do not contain membrane material. In the case of compact membranes, any surface is suitable for the contact surface of the starting material because the properties of the compact membrane are the same from each surface direction, i.e. the membrane is symmetrical. Since the membrane is essentially the same throughout its structure, it falls within the definition of isotropic membranes. Although some of these compact membranes are quite selective, one of their main drawbacks is a low permeate flow due to the relatively large thickness associated with the membranes. It has therefore been uneconomical to build plants that are necessary for desalination of significant quantities of water using compact membranes. Attempts to increase flow through membranes for Vskese paration have e.g. included adding fillers to the membrane to change the porosity and make the membrane as thin as possible to increase the rates of permeate flow. Although, to a limited extent, improved rates of migration through the membrane have been obtained, these improved rates have generally been obtained at the expense of the selectivity of the particular membranes.

In another attempt to improve membrane properties, Loeb and his staff in e.g. United States Patent No. 3 133 132 discloses a method for preparing a modified membrane of cellulose acetate for desalination of water by first casting a solution of cellulose acetate as a thin layer and then forming a dense membrane skin on the thin layer by various means. techniques such as solvent evaporation followed by cooling in cold water. The formation of these thick-skin membranes generally involved a final cure in hot water. The membranes made by the Loeb method consist of two separate regions made of the same cellulose acetate material, a thin, dense, semi-permeable skin and a less dense, void-containing, non-selective support region. As the membranes do not exhibit substantially the same density throughout their structure, they fall within the definition comprising anisotropic membranes. Because of these separate regions and the differences in membrane properties which can be observed depending on which surface of the membrane surfaces contact with an added saline solution, Loeb-type membranes can be described as being asymmetric.

It has e.g. in practical salting experiments, asymmetric thick-skin membranes have been found to exhibit superior permeate flow compared to the older type compact membranes. The improvement of the permeability velocity of the Loeb-type membranes has been attributed to the reduction of the thickness of the dense, selective region.

The less dense region of such a membrane provides sufficient structural support to prevent rupture of the membrane under operating pressure, but it offers little resistance to permeate flow. Thus, the separation is essentially accomplished by the dense skin, and the primary function of the less dense support area is physical support of the dense skin. However, in such Loeb-type membranes, the less dense support area is frequently compressed by pressures such as pressures useful for desalination of water, and under such conditions the less dense support area loses some of its void volume.

As a result, the free flow of permeate is prevented from the exit side of the dense skin, resulting in a reduced permeate rate. In addition, the cellulose acetate membranes described by Loeb and co-workers are also subject to soiling and various chemical degradations. Therefore, efforts have been directed towards developing Loeb-type membranes of materials other than cellulose acetate, which can provide better structural properties and increased chemical resistance. The "running" of polymeric materials to obtain a single-component membrane exhibiting good selectivity and good migration speed has proved to be extremely difficult. Most experiments result in the preparation of membranes that are either porous, ie. have fluid flow channels through the dense skin and which will not separate or where the dense skin is too thick to produce useful rates of migration. Therefore, in many cases, these asymmetric membranes cannot be used in fluid separation, such as reverse osmosis. As will be described in more detail below, it is even more difficult to provide Loeb type membranes which exhibit good selectivity and good migration rates in connection with gas separation.

Further developments to provide advantageous separation membranes suitable for desalination of water and other liquid-liquid separations, such as separations of organic materials from liquids, have led to composite membranes comprising a porous support which, due to the presence of flow channels, can easily pass fluid, but is sufficiently strong to withstand operating conditions and a thin, semi-permeable membrane supported thereon. Composite membranes that have been proposed include the so-called "dynamically formed" membranes formed by continuously precipitating a polymeric film material from a starting material solution onto a porous support. This continuous precipitation is required because the polymeric film material tends to be introduced into the pores and through the porous substrate, and therefore additional amounts must be added. In addition, the polymeric film material is frequently sufficiently soluble in the liquid mixture subjected to separation that it is also usually subjected to lateral erosion, ie. it leaches from the substrate.

It has also been proposed to prepare composite desalination membranes by providing a substantially solid diffusion or separation membrane on a porous substrate. For example, Reference is made to Sachs et al., U.S. Patent No. 3,676,203, which discloses a polyacrylic acid separation membrane on a porous substrate such as cellulose acetate, polysulfone, etc. The thickness of the separating membrane is relatively large, e.g. up to 60 µu, so that the separation membrane is sufficiently strong that it does not tend to flow into the porerae or disintegrate at the porerae of the porous support. Other suggestions have included the use of an anisotropic support with a closer surface area, i.e. skin, as the immediate support surface of the separation membrane. Reference is made e.g. to Cabasso, et al., Research and Development of NS-1 and Related Poly-sulfone Hollow Fibers for Reverse Osmosis Desalination of Seawater,

Gulf South Research Institute, July, 1975, distributed by the National Technical Information Service, U.S. Department of Commerce, Publication PB 248 666. Cabasso et al. discloses composite membranes for desalination of water consisting of anisotropic hollow polysulfone fibers coated with e.g. in situ cross-linked polyethyleneimine or furfuryl alcohol polymerized in situ to provide a superimposed separation membrane. Another possibility of providing reverse osmosis membranes has been described by Shorr in U.S. Patent No. 3,556,305. Shorr discloses three-part reverse osmosis separation membranes comprising an anisotropic porous substrate, an ultra-thin adhesive layer over the porous substrate, and a thin, semi-permeable membrane bonded to the substrate with the adhesive layer. Often, these ultra-thin, semi-permeable membranes are made in laminate form with porous support materials by separately fabricating the ultra-thin membrane and a porous support, followed by arranging the two members so that their surfaces have mutual contact.

Other types of membranes that have been used to treat liquids are the so-called "ultrafiltration" membranes in which pores of a desired diameter are provided. Sufficiently small molecules can pass through the pores, whereas larger, more bulky molecules are retained on the supply surface of the membrane. An example of ultrafiltration membrane types is disclosed in Massucco's U.S. Patent No. 3,556,992. These membranes exhibit anisotropic support and a gel that is irreversibly compressed in the support to provide membranes exhibiting appropriate pore size for separation of caustic hydroxides from hemicellulose , and the ultrafiltration takes place through the gel.

The above discussion of the background of the invention has been directed to membranes for separating a liquid from a liquid mixture, such as by desalination of water. Recently, more emphasis has been placed on developing separation membranes suitable for separating a gas from a gaseous mixture. The migration of gases through separation membranes has been the subject of various studies; however, gas separation membranes that exhibit both high flow and useful selective separation do not appear to be at least non-commercial. The following discussion is illustrative of specific modifications that have been made to membranes used for gas separation and provides a basis on which the invention can be fully understood.

Attempts have been made to draw on knowledge developed in connection with liquid-liquid-type separation membranes. However, there are many different ways of considering the development of a suitable gas separation membrane for gas systems in comparison with the development of a suitable liquid systems membrane. The presence of small pores in the membrane can e.g. do not exert any detrimental effect on the properties of the membrane for liquid separation, such as desalination resulting from adsorption on and swelling of the membrane and from the high viscosity and high cohesive effects resulting from the liquids. Since the gases have extremely poor absorption, viscosity and cohesion, no barrier is provided to prevent the gases from easily passing through the pores of such a membrane, resulting in little - if any - separation of gases. An extremely important difference between liquids and gases that could affect the selective separation upon migration through membranes compared to the solubility of liquids in such membranes is the generally lower solubility of gases in membranes compared to the solubility of liquids in such membranes. which results in lower permeability constants for gases compared to the permeability constants for liquids. Other differences between liquids and gases that could influence selective separation through membrane migration include density and internal pressure, the effect of temperature on viscosity, surface tension and degree of order.

It has been recognized that materials exhibiting good separation of gases often exhibit lower permeability constants than the permeability constants of the materials exhibiting poor gas separation. In general, efforts have been made to provide the material of a gas separation membrane in as thin a form as possible, given the low permeabilities, to provide appropriate flow, but also to provide a membrane which is as pore-free as possible. gases are passed through the membrane by interaction with the material in the membrane. One possibility of developing separation membranes suitable for gaseous systems has been to provide composite membranes which exhibit a superimposed membrane supported on an anisotropic porous support where the superimposed membrane provides the desired separation, ie. the superimposed membrane is semi-per- mable. Conveniently, the superimposed membranes are sufficiently thin, namely ultra-thin, to provide reasonable flow. The essential function of the porous substrate is to support and protect the superimposed membrane without damaging the sensitive, thin, superimposed membrane. Suitable supports provide low resistance to permeate gases after the superimposed membrane has performed its function of selectively separating the permeate from the starting material mixture. Thus, these supports are suitably porous to provide low resistance to permeate passage and yet sufficiently supportive, i.e. with pore sizes sufficiently small to prevent the breakage of the superimposed membrane under separation conditions. Klass et al., U.S. Patent No. 3,616,607, Stancell et al., U.S. Patent No. 3,657,113, and Yasuda, U.S. Patent No. 3,775,303 exemplify gas separation membranes with superimposed membranes on a porous support.

Such composite membranes for gas separation have not been problem-free. P.eks. US Patent No. 3,980,456 discloses the manufacture of composite membrane films for separating oxygen from air comprising a support of a microporous polycarbonate layer and a separately formed, i.e. preformed, super-thin, ultra-thin separation membrane of 80 percent poly (phenylene oxide) and 20 percent organopolysiloxane-polycarbonate copolymer. Browall states in connection with the preparation of membrane sera that the exclusion of extremely small particulate impurities, i.e. particles with a size less than approx. 3000 Å, from the manufacturing area of the membranes, is practically impracticable or impossible. These fine particles can precipitate beneath or between pre-formed ultrathin membrane layers and, due to their large size in comparison to the ultrathin membranes - puncture the ultrathin membranes. Such breakage reduces the efficiency of the membrane. The Browall patent discloses applying a pre-formed layer of organopolysiloxane polycarbonate copolymer serving as a sealing material between the ultrathin membrane and the porous polycarbonate support as an adhesive. Browall * s composite membranes are thus complex in terms of the materials and construction technique.

ίο 148736

In summary, suitable anisotropic gas separation membranes do not appear to exist, namely membranes which, in the absence of an superimposed membrane, provide selective separation and exhibit sufficient flow and selectivity for separation for general commercial operation. In addition, gas separation composite membranes having an overlying membrane to provide the selective separation have only been subject to slight or moderate improvement in membrane properties, and no successful, large-scale, commercial application of these gas separation membranes appears to be available. . Although the superimposed membrane is possibly ultra-thin to provide the desired selectivity in the separation, it can significantly reduce the flow of the permeate gas through the composite membrane as compared to the flow associated with the porous support on which there is no superimposed membrane.

It is an object of the invention to provide a multi-component gas separation gas membrane comprising a coating material in contact with a porous support, which membrane must not only be able to withstand the conditions to which it is subjected during the separation process but also provide an appropriate selective separation of the desired gas (s) under a sufficiently high flow rate, i.e. migration rate of permeate per surface area of unit, which membrane does not necessarily involve the use of an adhesive, which membrane has high structural strength, toughness, resistance to abrasion and chemical resistance, low sensitivity to static electricity and low adhesion to adjacent multi-component type membranes, and which membrane can are prepared from many different gas separation membrane materials and thus produce a greater leeway than what has hitherto been found in selecting such membrane material which is advantageous in a given gas separation.

. The membrane according to the invention is characterized by the characterizing part of claim 1. The definition of the specified separation factors is given below. Surprisingly, it has been found that the membrane according to the invention fulfills the object of the invention.

11

14873S

A particularly preferred embodiment of the membrane is characterized by the characterizing part of claim 2.

The membrane of the invention may exhibit a greater permeability than a membrane which is substantially the same as the porous separation membrane, except that at least one surface of this membrane has been treated such that the membrane has been sufficiently densified to relative to at least one pair of gases to provide a separation factor equal to or greater than the separation factor exhibited by the membrane of the invention.

In the membrane of the invention, the porous separation membrane may be an anisotropic hollow fiber capable of maintaining the configuration of the hollow fiber under gas separation conditions, and the membrane may exhibit greater permeability than an hollow fiber anisotropic membrane consisting of the material of the porous separating membrane and being able to maintain the configuration of the hollow fiber under gas separation conditions, whereby this membrane exhibits a separation factor equal to or greater than the separation factor of the membrane according to the invention for the stated one pair of gases.

In the membrane of the invention, both the separation factor and the permeability of the membrane may be influenced by the ratio of the total surface area to the total cross-sectional area of the pores and / or the average diameter of the pore cross-section of the porous separation membrane.

In the membrane of the invention, both the separation factor and the permeability of the membrane may be influenced by the relative resistances of gas flow through the pores of the porous separation membrane and through the solid portions of the porous separation membrane.

In the membrane of the invention, the coating material may have a molecular size sufficient to prevent the coating material from passing through the pores of the porous separation membrane during gas separation.

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The use of the membrane according to the invention is carried out in the form of a method for separating at least one gas into the gaseous mixture by selective migration and to provide a permeated product containing at least one permeating gas, thereby contacting the gaseous mixture with at least one gas. one surface of the membrane, thereby maintaining the opposite surface of the membrane at a lower chemical potential for the specified one traveling gas than the chemical potential of the surface, allowing the indicated one gas to flow into and through the membrane and thereby from the vicinity of the the opposite surface removes permeated product having a different ratio of the indicated one gas to the other gas in the gaseous mixture than in the original gas mixture.

The following diagram shows examples of the separations that can be made with the membrane of the invention.

One of the other of the separated gas-separated gas or the other group of gases_separated gases_Gasbi the other oxygen air hydrogen at least one of the gases carbon monoxide, carbon dioxide, helium, nitrogen, oxygen, argon, hydrogen sulfide, ammonia or a hydrocarbon having 1 to approx. 5 carbon atoms ammonia ammonia and at least one of the gases hydrogen, nitrogen, methane or argon dioxide carbon dioxide and at least one of the gases carbon monoxide, a hydrocarbon having 1 to 5 carbon atoms or nitrogen 13

One of the The other of the separated gas-separated looks or the other group of gases_separated gases_Gasbi the other helium helium and at least one hydrocarbon having 1 to about 5 carbon atoms hydrogen sulfide sulfide fid and at least one hydrocarbon having 1 to about 5 carbon atoms carbon carbon monoxide and monoxide at least one of the gases is hydrogen, helium or a hydrocarbon having between 1 and approx.

5 carbon atoms

The invention thus relates to a multi-component type membrane or a gas separation composite membrane comprising a coating in contact with a porous separation membrane, wherein the separation properties of the multi-component type membranes are in principle determined by the porous separation membrane and not by the coating material. These multi-component type membranes for separating at least one gas from a gaseous mixture exhibit a desirable selectivity and, moreover, a useful flow. The invention provides multicomponent gas separation membranes which can be prepared from a variety of gas separation membrane materials and thus can provide a greater leeway than has been found so far in selecting such membrane material which is advantageous in a given gas separation. The invention provides multi-component type membranes which can provide the desired combinations of flow and selectivity for the separation resulting from the configuration and manufacturing methods and the combination of the components. Thus, a material exhibiting high selectivity for the separation but a relatively low permeability constant can be utilized to provide multicomponent type membranes with desirable migration rates and desirable selectivity for the separation. In addition, the membranes of the invention are relatively insensitive to the effects of contamination, namely fine particles in their preparation, which have previously produced difficulties in the preparation of composite membranes with a preformed, ultra-thin separation membrane superposed on a support. The use of adhesives in the preparation of the multi-component type membranes of the invention need not be necessary, which is an advantage. As a result, the multi-component type membranes of the invention need not be complex in construction engineering. The multicomponent type membranes of the invention can be manufactured to provide high structural strength, toughness and abrasion and chemical resistance, yet exhibit a commercially advantageous flow and selective separation. These multicomponent type membranes may also exhibit desirable processing properties, such as low sensitivity to static electricity, low adhesion to adjacent multicomponent type membranes, and the like.

According to the invention, the multi-component gas separation membranes comprise a porous separation membrane which exhibits supply and discharge surfaces and a coating material which contacts the porous separation membrane. The porous separation membrane has substantially the same composition throughout its structure, viz. the porous separation membrane is substantially homogeneous in chemistry. The material of the porous separation membrane exhibits selective migration for at least one gas in a gaseous mixture compared to at least one residual gas in the mixture, and as a result, the porous separation membrane is defined as a "separation" membrane. When describing the separation membrane as "porous", it is intended that the membrane carry continuous channels for gas flow, i.e. pores that communicate between the supply surface and the output surface. If these continuous channels are sufficiently bulky in terms of number and cross-section, they allow substantially the entire amount of a gaseous mixture to flow through the porous separation membrane, thereby providing the - if any - separation resulting from interaction with the material of the porous separation membrane. The present invention advantageously provides multicomponent type membranes in which the separation of at least one gas from a gaseous mixture by interaction with the material of the porous separation membrane is enhanced, as compared to what can be obtained with the porous separation membrane alone.

The multicomponent type membranes of the invention comprise porous separation membranes and coatings exhibiting particular conditions. Some of these ratios may conveniently be expressed as relative separation factors relative to a pair of the gases for the porous separation membranes, coating and the multi-component type membranes.

A separation factor (© <^). for a membrane for a given gas pair a and b is defined as the ratio of the permeability constant (P_) of the membrane for gas a and the permeability constant (P ^) of the membrane for gas b. A separation factor is also equal to the ratio of permeability (PJ1). of a membrane of thickness l for gas a in a gas mixture and the permeability of the same membrane for gas b, (For which the permeability of a given gas is the volume of gas, under standard temperature and pressure (STP), which passes through one membrane per qu -rate centinets surface area per second, with a partial pressure drop of 1 centimeter Hg across the membrane per unit of thickness, and it is expressed as P = cm 2 / cm 2 sec-cm Hg / J.

In practice, the separation factor of a given pair of gases for a given membrane can be determined using numerous techniques that provide sufficient information for the calculation of permeability constants or permeabilities for each of the gas pairs. Several of the many techniques available for determining permeability constants, permeabilities, and separation factors are described by Hwang et al., Techniques of chemistry, Volume · VII, Membranes in Separations, John Wiley & Sons, 1975 »Chapter 12, page 296 to 322.

An internal separation factor referred to in this specification is the separation factor of a material having no gas flow channels across the material and it is the highest separation factor obtainable for the material. Such a material may be termed continuous or non-porous. The internal separation factor of a material can be approximated by measuring the separation factor of a compact membrane of the material. However, there may be several difficulties in determining an internal separation factor, including inaccuracies introduced in the preparation of the compact membrane, such as the presence of pores, the presence of fine particles in the compact membrane, and a molecular scheme resulting from variations in the production of the membrane and the like. As a result, the particular internal separation factor may be lower than the internal separation factor. Accordingly, a "determined internal separation factor" in this specification refers to claims for the separation factor of a dry, compact membrane of the material.

A multicomponent type gas separation membrane according to the invention has at least one gas pair a separation factor significantly greater than the determined internal separation factor of the coating material in occluding contact with a porous separation membrane. By the term "significantly greater" used in relation to the ratios of the multi-component membrane separation factor and the particular inner separation factor of the coating material, it is believed that the difference between the separation factors is important, e.g. generally at least approx. 10% larger. By the term "occlusive contact" is meant that the coating contacts the porous separation membrane, so that for the multi-component type membrane, the ratio of gases passing through the porous separation membrane material to gases passing through the pore is larger in comparison to the corresponding ratio in the porous separation membrane alone. The contact is such that the multicomponent-type membrane provides an increased contribution of the porous separation membrane material to the separation factor exhibited by the multicomponent-type membrane for at least a couple of gases. , compared to the corresponding contribution in the porous separation membrane alone. Thus, with respect to at least this one pair of gases, the separation factor exhibited by the multicomponent-type membrane will be greater than the separation factor exhibited by the porous separation membrane. With respect to at least a few gases, the material of the porous separation membrane further exhibits a particular internal separation factor greater than the particular internal separation factor of the material in the coating. With respect to at least this one pair of gases, the separation factor exhibited by the multi-component type membrane is also often equal to or less than the particular internal separation factor of the material in the porous separation membrane. Regardless of the intended multi-component membrane gas separation application, the ratios of the separation factors can often be detected for at least a couple of gases, one consisting of one of the gases hydrogen, helium, ammonia and carbon dioxide and the other of which is one of the gases carbon monoxide. nitrogen, argon, sulfur-hexafluoride, methane and ethane. In certain multicomponent type membranes of the invention, the ratio of the separation factors can also be shown for gas pairs which are carbon dioxide and one of the gases hydrogen, helium and ammonia, or ammonia and eh of the gases carbon dioxide, hydrogen and helium.

Conveniently, a multi-component type membrane according to the invention exhibits a separation factor with respect to at least one gas pair which is at least approx. 35% greater, preferably at least approx. 50% larger, and sometimes at least approx. 100% greater than the determined internal separation factor of the material in the coating. As to at least one of the pairs of gases specified, the separation factor of the multi-component type membrane is frequently at least approx. 5> often at least approx. 10% larger, and sometimes at least approx. 50 or approx. 100% larger than that of the porous separation membrane.

The membrane comprises a coating in occlusive contact with a porous separation membrane of a material which exhibits selective migration of at least one gas into a gaseous mixture as compared to one or more of the other gases in the gaseous mixture, whereby the porous separation membrane exhibits a substantial void volume, whereby the membrane exhibits at least a pair of gases a separation factor significantly greater than the determined internal separation factor of the material in the coating. Cavities are areas within the porous separation membrane in which no material of the porous separation membrane is present. Thus, when voids are present, the density of the porous separation membrane is less than the density of most of the material of the porous separation membrane. Describing the void volume as "substantial" means that sufficient voids exist, e.g. at least approx. 5% by volume, within the thickness of the porous separation membrane, to provide a reasonable increase in the rate of migration through the membrane as compared to the rate of migration observable through a compact membrane of the same material and thickness. Preferably, the void volume is up to approx. 90, e.g. ca. 10 to 80, and sometimes approx. 20 or 30 to 70%, based on the superficial volume, namely the volume contained within the gross dimensions of the porous separation membrane. One method of determining the void volume of a porous separation membrane comprises a density comparison with a volume of the majority of the porous separation membrane, which volume would correspond to a membrane of the same physical gross dimensions and configurations as the porous separation membrane. As a result, the bore of a hollow fiber porous separation membrane would not affect the density of the porous separation membrane.

The density of the porous separation membrane may be substantially the same throughout its thickness, namely isotropic, or the porous separation membrane may be characterized in that it has at least a relatively dense region within its thickness in a gas flow barrier over the porous separation membrane, i.e. . the porous separation membrane is anisotropic. Preferably, the coating is in occlusive contact with the relatively dense region of the anisotropic porous separation membrane. Since the relatively dense region can be porous, it can be made quite thin in comparison with the fact that a compact membrane of the same thickness can be made. The use of porous separation membranes with relatively dense, thin regions provides improved flow through the multi-component type membrane.

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The membranes may also comprise an coating in occlusive contact with a porous separation membrane of a material which exhibits selective migration of at least one gas in a gaseous mixture relative to one or more of the remaining gases in the gaseous mixture, thereby applying the coating during use. of a substantially liquid substance suitable for forming the coating and wherein the membrane, with respect to at least one pair of gases, exhibits a separation factor significantly greater than the determined internal separation factor of the material of the coating. The substance to be applied to the porous separation membrane is substantially liquid in the sense that it is unable to retain a shape in the absence of outer support. The material of the support may be liquid, or it may be dissolved in or suspended as finely divided solids (e.g., of colloidal size) in a liquid solvent, to provide the substantially liquid substance for application to the porous separation membrane. Conveniently, wetting the material in the coating, or the material of the coating in the liquid solvent, i.e. it tends to adhere to the material of the porous separation membrane. Thus, the contact between the coating and the porous separation membrane is facilitated frequently. The use of substantially liquid material to provide the coating on the porous separation membrane allows simpler techniques than the one used to provide composite membranes of separately formed solid materials. In addition, a wide range of the coating material can be used, and the application technique can be easily adapted to the use of porous separation membranes with different configurations.

The membrane may also comprise an coating in occlusive contact with a porous separation membrane comprising polysulfone, wherein the multi-component membrane for at least one pair of gases exhibits a separation factor substantially greater than the particular internal separation factor of the material of the coating. In another embodiment, the multicomponent-type membrane comprises a coating in occlusive contact with a hollow fiber porous separation membrane and of a material exhibiting selective permeability for at least one gas in a gaseous mixture in comparison with one or more of the remaining gases in the gaseous mixture, whereby the multi-component type membrane, with respect to at least a few gases, exhibits a separation factor significantly greater than the particular internal separation factor of the coating material. In hollow filaments (i.e. hollow fibers), the outer surface may be the supply or exit surface of the porous separation membrane and the inner surface will be the exit or supply surface, respectively. Hollow filaments advantageously facilitate the provision of a gas separating apparatus having high available surface areas for separation within the given volumes of the apparatus. It is known that hollow filaments can withstand greater pressure differentials than unsupported films of substantially the same overall thickness and morphology.

In a process for separating gases using a membrane of the invention, at least one gas in a gaseous mixture is separated from at least one other gas by selective migration to provide a permeate containing at least one migrating gas. The method comprises contacting the gaseous mixture with a multi-component membrane (supply surface) surface which exhibits a selective permeability for a gas of the pair of gases with respect to at least one pair of gases in the gaseous mixture. with the permeability of the second gas in the pair of gases keeping the opposite surface (the starting surface) of the multi-component type membrane at a lower chemical potential for at least one migratory gas than the chemical potential at the specified one surface, that at least this one gas is allowed to flow into and through the multicomponent-type membrane, and a permeable product having a different ratio of at least one gas of the gaseous mixture to at least one gas is removed from the environment of the stated opposite surface. at least the other of the gases in the gaseous mixture than the ratio of the gaseous mixture between at least one of the gases and in at least the other of the gases. The separation processes include concentrating at least one of the gases on the supply side of the multicomponent-type membrane to provide a concentrated product, and allowing at least one of the gases to pass through the multicomponent-type membrane to provide of a permeated product in which the deviating ratio indicated exhibits a higher value.

In using the membrane of the invention, hydrogen is selectively separated from a gaseous mixture which also comprises at least one of the gases carbon monoxide, carbon dioxide, helium, nitrogen, oxygen, argon, hydrogen sulfide, nitric oxide, ammonia and a hydrocarbon having 1 to 5 carbon atoms. In another application of the membrane of the invention, at least one gas in a gaseous mixture is separated from at least one other gas, which involves contacting the gaseous mixture with a multi-component type membrane comprising an coating in occlusive contact with a porous separation membrane comprising polysulfone.

A membrane according to the invention may be part of a gas separation apparatus. The apparatus comprises an enclosure having at least one membrane according to the invention, wherein the membrane has a supply surface and an opposite exit surface, and wherein the enclosure comprises means which allow a gaseous mixture to be applied to the surrounding surface of the supply surface, and means which allow gases are removed from the vicinity of the feed surface of the membrane, and means which allow a permeated product to be removed from the vicinity of the exit surface of the membrane.

Surprisingly, it has been found that a coating material which may have a low determined internal separation factor can be provided on a porous separation membrane which may have a low separation factor to provide a multi-component type membrane having a separation factor which is larger than both the coating and the porous separation membrane. This result is quite surprising, in contrast to previous proposals for composite gas separation membranes with a superimposed membrane supported on a porous substrate, which essentially necessitated that the superimposed membrane exhibit a high separation factor to provide the selective separation of the membrane.

The recognition that coatings exhibit low separation factors can be used in conjunction with porous separation membranes to provide multicomponent-type membranes with a greater separation factor than both the coating and the porous separation membrane, leading to highly advantageous multicomponent-type membranes for separation. of gases. Materials which have advantageous internal separation factors but which were difficult to utilize as superimposed membranes may e.g. is used as the material for the porous separation membrane in the membrane of the invention, whereby the selectivity for the separation of the material in the porous separation membrane contributes significantly to the separation factor. the multi-component membrane tower.

It is clear that the multi-component membrane porous separation membrane may be anisotropic with a thin but relatively dense separating region. Thus, the porous separation membrane can benefit from the low resistance to permeation provided by anisotropic membranes, thus providing multicomponent type membranes which exhibit desirable separation factors. Furthermore, the presence of flow channels that may render anisotropic single-component (non-composite) membranes unacceptable for gas separation may be acceptable, and even desirable, in porous separation membranes used in the multi-component type membranes of the invention. The coating may preferably provide a low resistance to permeation and the material of the coating may exhibit a low determined internal separation factor. In certain multicomponent-type membranes, the coating may tend to selectively reject the desired permeate gas, yet the resulting multicomponent membrane utilizing this coating may exhibit a separation factor greater than that of the coating. porous separation membrane.

The invention relates to the multicomponent-type membranes formed by combining a pre-formed porous separation membrane, i.e. a porous separation membrane made prior to application of the coating, and a coating. In particular, the invention relates to multi-component gas separation membranes, wherein the selectivity for the separation of the material of the porous separation membrane contributes significantly to the selectivity and relative rates of migration of the permeate gases through the multi-component type membrane. The multicomponent-type membranes of the invention can generally exhibit higher rates of migration than composite membranes described prior to this invention utilizing superimposed membranes exhibiting high separation factors. In addition, the multi-component type membranes of the invention provide a separation factor superior to the separation factors of the coating and the porous separation membrane. The multicomponent-type membranes of the invention may, in some but superficial, transmitters, be analogous to the gas separation membranes described prior to this invention which exhibited superimposed membranes exhibiting a high separation factor on a porous substrate. These composite membranes described prior to the invention do not make use of a support or substrate which provides a substantial portion of the separation.

The multi-component type membranes of the invention allow a great deal of flexibility in generating specific separations because both the coating and the porous separation membrane contribute to the overall separation properties. The result is an increased ability to "tailor" these membranes for specific separation purposes, e.g. for separating a desired gas or gases from various gas mixtures into commercially desirable combinations in terms of speed and selectivity of the separation. The multicomponent type membranes can be made from many different gas separation materials and thus provide a greater leeway than what has hitherto existed in the selection of an advantageous membrane for a given gas separation. In addition, these multi-component type membranes are capable of providing good physical properties such as toughness, abrasion resistance, strength and durability, and good chemical resistance.

The invention relates to special multi-component type membranes for gas separations which comprise a coating in contact with a porous separation membrane, wherein separation properties of the multi-component type membrane are in principle determined by the porous separation membrane and not by the coating.

The multicomponent type membranes are highly applicable to gas separation. Gaseous mixtures suitable as starting materials include gaseous materials, or substances which are normally liquid or solid, but which are vapor-shaped at the temperature below which the separation is carried out. The invention is then described in detail with reference to the separation of e.g. oxygen from nitrogen? hydrogen from at least one of the gases carbon monoxide, carbon dioxide, helium, nitrogen, oxygen, argon, hydrogen sulfide, nitric oxide, ammonia and a hydrocarbon having from 1 to approx. 5 carbon atoms, especially methane, ethane and ethylene; ammonia from at least one of the gases hydrogen, nitrogen, argon, and a hydrocarbon having from 1 to about 5 carbon atoms, e.g. methane; carbon dioxide from at least one of the gases carbon monoxide and a hydrocarbon having from 1 to approx. 5 carbon atoms, e.g. methane; helium from a hydrocarbon having from 1 to about 5 carbon atoms, e.g. methane; hydrogen sulfide from a hydrocarbon having from 1 to about 5 carbon atoms, for example methane, ethane or ethylene; and carbon monoxide from at least one of the gases hydrogen, helium, nitrogen and a hydrocarbon having from 1 to about 5 carbon atoms. It is emphasized that the invention is not limited to these particular separation applications or gases or to the specific multi-component type membranes set forth in the Examples.

The membranes of the invention may be films or hollow filaments or fibers exhibiting a porous separation membrane or substrate, and a coating in occlusive contact with the porous separation membrane. Some factors affecting the properties of the multicomponent-type membranes are the permeability constants of the coating materials and the porous separation membranes, the total cross-sectional area of the holes (i.e., the pores or flow channels) relative to the total surface area of the porous separation membrane, the relative thickness. of both the coating and the porous separation membrane of the multicomponent type membrane, the morphology of the porous separation membrane and - what is most important - the relative resistance to the permeate flow resulting from both the coating and the porous separation membrane of a multicomponent type membrane. In general, the degree of separation of the multi-component type membrane is influenced by the relative gas flow resistance of each gas in the gas mixture of the coating and the porous separation membrane which can be selected specifically for their values of the gas flow resistance.

The material used for the porous separation membrane may be a solid, natural or synthetic substance having useful gas separation properties. In the case of polymers, both additive and condensation polymers that can be cast, extruded or otherwise prepared to provide porous separation membranes are included. The porous separation membranes can be prepared in porous form, e.g. by casting from a solution comprising a solvent for the polymeric material, into a poor solvent for the material or an agent which is not a solvent for the material. The spinning and / or molding conditions and / or treatments after the initial formation and the like may affect the porosity and resistance to gas flow of the porous membrane.

Generally, organic polymers or organic polymers mixed with inorganic filters are used to prepare the porous separation membrane. Typical polymers suitable for the porous separation membrane of the membrane of the invention may be substituted or unsubstituted polymers and may be selected from polysulfones; poly (styrenes), including styrene-containing copolymers such as acrylonitrile-styrene copolymers, styrene-butadiene copolymers, and styrene-vinylbenzyl halide copolymers; polycarbonate sulfonates; cellulose polymers such as cellulose acetate butyrate, cellulose propionate, ethyl cellulose, methyl cellulose, nitrocellulose, etc .; polyamides and polyimides, including aryl-polyamides and aryl-polyimides; polyethers; poly (arylene oxides) such as poly (phenylene oxide) and poly (xylene oxide); poly (esteramide-diisocyanate); polyurethanes; polyesters such as poly (ethylene terephthalate), poly (alkyl methacrylates), poly (alkyl acrylates), poly (phenylene terephthalate), etc .; polysulphides; polymers from monomers having other cu-olefinic unsaturation than the above, such as poly (ethylene), poly (propylene), poly (butene-1), poly (4-methyl-penten-1), 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 (vinyl pyrrolidones), poly (vinyl ethers), poly (vinyl ketones), poly (vinyl aldehydes) such as poly (vinyl formalde) and poly (vinyl butyral), poly (vinylamides), poly (vinylamines), poly (vinyl urethanes), poly - (vinyl ureas), poly (vinyl phosphates) and poly (vinyl sulfates); polyallyler; poly (benzobenzimidazol); polyhydrazides; polyoxadia-zoler; polytriazoler; poly (benzimidazole); polycarbodiimides; poly-phosphazines; etc., and interpolymers, including block interpolymers containing repeating units, among the above, such as terpolymers of acrylonitrile-vinyl bromide sodium salt of para-sulfo-phenylmethallyl ethers; and inoculations and mixtures containing any of the foregoing materials. Typical substituents which provide substituted polymers include halogens such as fluorine, chlorine and bromine; hydroxyl groups; lower alkyl groups; lower alkoxy groups; monocyclic aryl; lower acyl groups and the like.

Selection of the porous separation membrane for the present multicomponent-type membrane for gas separations can be performed on the basis of the heat resistance, solvent resistance and mechanical strength of the porous separation membrane, and on the basis of other factors dictated by the operating conditions of selective migration, when coated alone. and the porous separation membrane exhibits the prescribed relative separation factors in accordance with the invention for at least a pair of gases. The porous separation membrane is preferably at least partially self-supporting, and in some cases it can be substantially self-supporting. The porous separation membrane may provide substantially all of the structural support for the membrane, or the multi-component type membrane may comprise a structural support member capable of providing little - if any - resistance to the passage of gases.

27 148735

One of the preferred porous separation membranes used in the formation of multi-component type membranes comprises polysulfone. Among the polysulfones that can be used are those exhibiting a polymeric skeleton comprising the repeating structural unit:

II

R S R 0 wherein R and R ', which may be the same or different, are aliphatic or aromatic hydrocarbyl-containing molecular moieties having e.g. 1 to approx. 40 carbon atoms where the sulfur in the sulfonyl group is bonded to aliphatic or aromatic carbon atoms and the polysulfone has an average molecular weight suitable for film or fiber formation, often at least about 40 10,000. When the polysulfone is not cross-linked, the molecular weight of the polysulfone is generally less than ca. 500,000, and it is frequently below approx. The repeating units may be bound, i.e. R and R * may be bonded with carbon-to-carbon bonds or with various bonding groups such as 0 0 0 0

II II II II

-0-, -S-, -C-, -C-N-, -N-C-N-, -0-C-, etc.

I I I

Η Η H

Particularly advantageous polysulfones are those wherein at least one of the radicals R and R 'comprises an aromatic hydrocarbyl-containing moiety and the sulfonyl moiety is bonded to at least one aromatic carbon atom. Common aromatic hydrocarbyl-containing moieties include phenylene and substituted phenylene moieties; bisphenyl and substituted bisphenyl moieties, bisphenyl methane and substituted bisphenyl methane moieties having the core tf i

y / 1 "YT

R4 R8 R2 R10 R6 28 148735 substituted and unsubstituted bisphenyl ethers of the formula r3 r7 r9 r5 - get -'- ®- r4 r8 r10 r6 where X is oxygen or sulfur; and the like. In the depicted bisphenyl-

1 IC

methane and bisphenyl ether moieties represent R to R substituents which may be the same or different and may have the structure X1 - (- cz I p X2 1 p where X and X which are the same or different are hydrogen or halogen (e.g. fluorine, chlorine and bromine); p is 0 or an integer, e.g.

1 to approx. 6; and Z is hydrogen, halogen (e.g., fluorine, chlorine and bromine), fY4 · R ·, ·, (where q is 0 or 1, Y is -O-, -S-, -SS-, and o II 11 is -OC-, or -C-, and R 2 is hydrogen, substituted or unsubstituted alkyl of, for example, 1 to about 8 carbon atoms, or substituted or unsubstituted aryl, e.g., monocyclic or bicyclic of about 6 to about 15 carbon atoms), heterocyclic, wherein the hetero atom is at least one of the atoms nitrogen, oxygen and sulfur, and monocyclic or bicyclic with about 5 to 15 ring carriers, sulfato and sulfono, especially lower alkyl containing or monocyclic or bicyclic aryl containing sulfato or sulfono, phosphorus containing moieties such as phosphino and phosphato and phosphono, especially lower alkyl containing or monocyclic or bicyclic aryl containing phosphato or phosphono, amine, including primary, secondary, tertiary and quaternary amines, wherein the secondary, tertiary and quaternary amines often contain lower alkyl or monocyclic or bicyclic aryl moieties, isothioureyl, thioureyl, guanidyl, trialkylsilyl, trialkylstannyl, trialkyl dialkylstibinyl, etc. Frequently, the substituents on the phenylene groups of the bisphenyl-methane and bisphenyl-ether moieties are found in ortho-position, ie. R to R are hydrogen. The polysulfones with aromatic hydrocarbyl-containing moieties generally exhibit good thermal stability, are resistant to chemical attack, and exhibit an excellent combination of toughness and flexibility. Applicable polysulfones are sold under such trademarks as "P-1700" and P-3500 ”by Union Carbide, both commercial products with a linear chain of the general formula CEU 0 - * - © -? - (Eh0— & -1— 0 - ° - CH3 0 Jn where n representing the degree of polymerization is about 50 to 80.

Poly (arylene-ether) sulfones are also useful. Polyether sulfones of structure 0 - s - (o} - o which can be purchased from ICI, Ltd., England, are also useful. Various other useful polysulfones can be prepared by polymer modifications, for example, by crosslinking, grafting, quaternization and the like.

In the preparation of porous separation membranes with hollow filaments, many different spinning conditions can be used. One method of making hollow filaments of polysulfone is described by Cabasso et al., In Research and Development of NS-1 Spirit Related Polysulfone Hollow Fibers for Reverse Osmosis Desalination of Seawater, cited above. Particularly advantageous hollow fibers of polysulfones, e.g.

P-3500 polysulfone manufactured by Union Carbide and polyether sulfones from ICI, Ltd. can be prepared by spinning the polysulfone in a solution of a solvent for the polysulfone. Typical solvents are dimethylformamide, dimethylacetamide and N-methylpyrrolidone. The weight percent of the polymer in the solution may vary within wide limits, but it is sufficient to provide a hollow fiber under the spinning conditions. Often, the weight percent of polymer in the solution is approx. 15 to 50, e.g. ca. 20 to 35. If the polysulfone and / or solvent contains contaminants such as water, particulate material, etc., the amount of contaminants should be so low that spinning can be carried out. If necessary, contaminants can be removed from the polysulfone and / or solvent. The size of the spinning nozzle will vary with the desired inner and outer diameter of the hollow filament present as a product. A category of spinning nozzles can exhibit aperture diameters of approx. 0.38 to 0.88 mm and needle diameters of approx. 0.2 to 0.38 mm with an injection capillary inside the needle. The diameter of the injection capillary may vary within the limits established by the needle. The spinning solution is generally kept under a substantially inert atmosphere to prevent contamination and / or coagulation of the polysulfone prior to spinning and to avoid undue fire risk with volatile and combustible solvents. A suitable atmosphere is dry nitrogen. The presence of excessive amounts of gas in the spinning solution can result in the formation of large voids.

The spinning can be carried out using the technique using a wet jet or a dry jet, i.e. the jet may be in or removed from the coagulation bath. The wet beam technique is often used for simplicity. The spinning condition is preferably not such that the filament is unduly stretched. Frequently, spinning speeds are within the range of approx. 5 and approx. 100 m / minute, although higher spin speeds can be used, provided that the filament is not unduly stretched and that the residence time in the coagulation bath is sufficiently long. Any substantially non-solvent for the polysulfone can be used for the coagulation bath. Appropriate water is used as the primary material in the coagulation bath. A fluid is usually injected into the interior of the fiber. The fluid chamber may e.g. include air, isopropanol, water or the like. The residence time of the spun fiber in the coagulation bath is at least sufficient to ensure solidification of the filament. The temperature of the coagulation bath can also vary widely, e.g. from -s-15 to 90 ° C or higher, and most often it is approx. 1 to 35 ° C, e.g. ca. 2 to 8 or 10 °. The coagulated hollow fiber is conveniently washed with water to remove solvent and can be stored in a water bath for a period of at least approx. 2 hours. The fibers are usually dried prior to application of the coating and assembly in a gas separation apparatus. The drying can be carried out at approx. 0 to 90 ° C, conveniently about room temperature, e.g. ca. 15 to 35 ° C, and at approx. 5 to 95 percent relative humidity, preferably approx. 40 to 60 percent relative humidity.

The foregoing description of methods for preparing hollow filament polysulfone porous separation membranes is provided merely to illustrate the technique available for the preparation of porous separation membranes.

The coating may be in the form of a substantially unbroken membrane, i.e. a substantially non-porous membrane, in contact with the porous separation membrane, or the coating may be discontinuous or discontinuous. When the coating is disconnected, it is sometimes described as an occluding material because it can occlude channels for gas flow, namely pores. Preferably, the coating is not so thick as to adversely affect the properties of the multi-component type membrane, e.g. by producing an excessive decrease of flow or by producing such resistance to gas flow that the separation factor of the multi-component type membrane has substantially the same value as that of the coating. The coating has an average thickness of up to approx. 50 ^ u. Of course, when the coating is disconnected, there may be areas where there is no coating material. The coating can often have an average thickness that is between approx. 0.0001 and 50 µl. In some cases, the average thickness of the coating is less than approx. lyU, and it may even be under approx. 0,5yU. The coating may comprise a layer or at least two separate layers which may optionally be of the same materials. When the porous separation membrane is anisotropic, i.e. exhibiting a relatively dense region within its thickness in a gas flow barrier relationship, the coating is suitably applied such that it is in occlusive contact with the relatively dense region. A relatively dense region may exist either at. one or both of the surfaces of the porous separation membrane 32 or it may be at a center position of the thickness of the porous separation membrane. Conveniently, the coating is applied to at least one of the two surfaces, namely the feed and exit surface, of the porous separation membrane, and when the multi-component type membrane is a hollow fiber, the coating can be applied to the outer surface so that protection is also provided. for and / or facilitating the handling of the multi-component type membrane.

While any suitable method may be used, it should be noted that the method by which the coating is applied may have some bearing on the overall properties of the multi-component type membranes. The multi-component type membranes of the invention can e.g. is prepared by coating a porous separation membrane with a substance containing the coating material such that the coating in the multicomponent type membrane has a resistance to gas flow which is low compared to the total resistance of the multicomponent type membrane. The coating may be applied in any suitable manner, e.g. in a coating operation such as spraying, brushing, immersion in a substantially liquid material comprising the material of the coating or the like. As previously stated, the coating material is preferably contained in a substantially liquid substance when coated, and may be present in a solution which uses a solvent for the coating material, which solvent is essentially a non-solvent. agent for the material of the porous separation membrane. Advantageously, the fabric containing the material from the coating is applied to a surface of the porous separation membrane and the other side of the porous separation membrane is subjected to a lower absolute pressure.

If the substantially liquid substance comprises polymerizable material and the polymerizable material is polymerized after application to the porous separation membrane to provide the coating, the second surface of the porous separation membrane is advantageously subjected to a lower absolute pressure during or before polymerization. However, the invention itself is not limited to the particular method by which the coating material is applied.

* 7 33 148735 Particularly advantageous materials for the coating have relatively high gas permeability constants, so that the presence of a coating does not unduly reduce the rate of migration in the multi-component type membrane. Preferably, the resistance to gas flow of the coating is relatively small compared to the resistance of the multi-component type membrane. As previously stated, the selection of materials for the coating of the particular internal separation factor depends on the material of the coating relative to the particular internal separation factor of the porous separation membrane material to provide a multicomponent type membrane exhibiting a desired separation factor. The coating material must be capable of providing occlusive contact with the porous separation membrane. When applied, it should e.g. exhibit sufficient wetting and adhesion to the porous separation membrane to enable occlusive contact to occur. The wetting properties of the material of the coating can be readily determined by contacting the coating material, either alone or in a solvent, with the material of the porous separation membrane. In addition, based on assessments of the average pore diameter of the porous separation membrane, materials can be selected for the coating with a suitable molecular size. If the molecular size of the coating material is too large to be absorbed by the pores of the porous separation membrane, the material may not be capable of providing occlusive contact. On the other hand, if the molecular size of the coating material is too small, it can be drawn through the pores of the porous separation membrane during coating and / or separation processes. Thus, with porous separation membranes with larger pores, it may be desirable to use coating materials having larger molecular sizes than with smaller pores. When the pores exhibit many different sizes, it may be desirable to use a polymerizable material for the coating material, which is polymerized after application to the porous separation membrane, or to use two or more different molecular size coating materials, e.g. by applying the materials for coating in a sequence similar to their growing molecular size.

34 148735

The coating materials can be natural or synthetic and are often polymeric and advantageously exhibit the appropriate properties for providing occlusive contact with the porous separation membrane. Synthetic substances include both addition and condensation polymers. Typical examples of usable materials for the coating are polymers which may be substituted or unsubstituted and which are solid or liquid under gas separation conditions; these may be synthetic rubbers, natural rubbers, liquids of relatively high molecular weight and / or high boiling point, organic prepolymers; poly (siloxanes) (silicone polymers); polysilazanes; poly-urethanes; poly (epichlorohydrin); polyamines; polyimines; polyamides; acrylonitrile-containing copolymers such as poly (α-chloroacrylonitrile or opolymers; polyesters (including polylactams), for example poly (alkyl acrylates) and poly (alkyl methacrylates) wherein the alkyl groups have, for example, 1 to about 8 carbon atoms, polysebacates, polysuccinates and alkyd resins; terpinoid resins such as flaxseed oil; cellulosic polymers; polysulfones, especially aliphate-containing poly sulfons; poly (alkylene glycols) such as poly (ethylene glycol), poly (propylene glycol), etc. ; poly (alkyl) -poly sulfate; polypyrrolidones; polymers from monomers with α-olefinic unsaturation, such as poly (olefins), for example poly (ethylene), poly (propylene), poly (butadiene), poly (2,3-dichlorobutadiene), poly (isoprene), poly (chloroprene), poly (styrene), including poly (styrene) copolymers, for example styrene-butadiene copolymers, polyvinyls such as poly (vinyl alcohols), poly (vinyl aldehydes), (e.g. poly (vinyl formal) and poly (vinyl butyral)), poly (vinyl ketones) (e.g. poly (methyl vinyl ketone)), poly (vinyl esters) (e.g. poly (viny (benzoate), poly (vinyl halides) (e.g. poly (vinyl bromide)), poly (vinylidene halides), poly (vinylidene carbonate), poly (methylisopropenyl ketone), fluorinated ethylene copolymer; poly (arylene oxides), e.g. poly (xylylene oxide); polycarbonates; polyphosphates, e.g. poly (ethylene-methyl phosphate); and the like, and any interpolymer, including block interpolymers containing repeating units selected from the foregoing, and grafting and blends containing any of the foregoing materials. The polymers may optionally be polymerized after application to the porous separation membrane.

Particularly useful materials for the coatings include poly (siloxanes). Typical poly (siloxanes) may comprise aliphatic or aromatic moieties and often exhibit repeating units containing 1 to ca. The molecular weight of the poly (siloxanes) can vary widely, but is usually at least approx. Often, poly (siloxanes) have a molecular weight of approx. 1000 to 300,000 when applied to the porous separation membrane. Conventional aliphatic and aromatic poly (siloxanes) include those poly (monosubstituted and disubstituted siloxanes), e.g., where the substituents are lower aliphatic, e.g. lower alkyl, including cycloalkyl, especially methyl, ethyl and propyl, lower alkoxy; aryl, including mono- or bicyclic aryl, including biphenylene, naphthalene, etc., lower mono- and bicyclic aryloxy; acyl, including lower aliphatic and lower aromatic acyl; and the like. The aliphatic and aromatic substituents may be substituted, e.g. with halogens, e.g. fluorine, chlorine and bromine, hydroxyl groups, lower alkyl groups, lower alkoxy groups, lower acyl 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 support the crosslinking. Typical catalysts to promote crosslinking include organic and inorganic peroxides. The cross-linking can be made before the application of poly (siloxane) to the porous separation membrane, but preferably cross-linked poly (siloxane) after application to the porous separation membrane. Frequently, the poly (siloxane) has a molecular weight of approx. 1000 to 100,000 before crosslinking. Particularly advantageous poly (siloxanes) include poly (dimethylsiloxane), poly (phenylmethylsiloxane), poly (trifluoropropylmethylsiloxane), copolymers of α-methylstyrene and dimethylsiloxane, and post-cured poly (dimethylsiloxane) -containing silicone rubber of about one molecular weight rubber.

1000 to 50,000 before crosslinking. Some poly (siloxanes) do not humidify a polysulfone porous separation membrane sufficiently to provide as much occlusive contact as desired. However, dissolution or dispersion of the poly (siloxane) in a solvent which does not significantly affect the polysulfone can facilitate the generation of occlusive contact. Suitable solvents include, under normal conditions, liquid alkanes, e.g. pentane, cyclohexane, etc.; aliphatic alcohols, e.g. methanol; certain halogenated alkanes; and dialkyl ethers; and the like, and mixtures thereof.

36 148735

The following materials for porous separation membranes and coatings are representative as useful materials for providing the membranes of the invention. However, these materials are only representative of the wide range of materials applicable to the invention, and they do not constitute a limitation of the invention but merely serve to illustrate the invention. Typical materials for porous separation membranes for separating oxygen from nitrogen include cellulose acetate, e.g. cellulose acetate with a degree of substitution of approx. 2.5; polysulfone; styrene-acrylonitrile copolymer, e.g. with approx. 20 to 70% by weight styrene and approx. 30 to 80% by weight acrylonitrile, mixtures of styrene-acrylonitrile copolymers and the like. Suitable coating materials include poly (siloxanes) (polysilicones), e.g. poly (dimethylsiloxane), poly (phenylmethylsiloxane), poly (trifluoropropylmethylsiloxane), pre-vulcanized and post-vulcanized silicone rubber species, etc .; poly (styrene), e.g. poly (styrene) with a degree of polymerization of approx. 2 to 20; poly (isoprene), e.g. isoprene prepolymer and poly (cis-1,4-isoprene); aliphatic hydrocarbyl-containing compounds having approx. 14 to 30 carbon atoms, e.g. hexadecane, flaxseed oil, especially crude flaxseed oil, etc., and the like.

Typical materials for porous separation membranes for separating hydrogen from gaseous mixtures containing hydrogen include cellulose acetate, e.g. cellulose acetate with a degree of substitution of approx. 2.5; polysulfone; styrene acrylonitrile copolymer, e.g. with approx. 20 to 70 wt% styrene and approx. 30 to 80% by weight acrylonitrile, mixtures of styrene-acrylonitrile copolymers, etc .; polycarbonates; poly (arylene oxides) such as poly (phenylene oxide), poly (xylylene oxide), brominated poly (xylylene oxide), brominated poly (xylylene oxide) post-treated with trimethylamine, thiourea, etc. and the like. Suitable coating materials include poly (siloxane) (polysilicones); eg. poly (dimethylsiloxane), pre-vulcanized and post-vulcanized silicone rubber, etc .; poly (isoprene); alpha-methylstyrene-dimethylsiloxane block copolymers; aliphatic hydrocarbyl-containing compounds having approx. 14 to 30 carbon atoms; and the like.

37 148735

The porous separation membranes used according to the invention are advantageously not extremely porous and thus provide a sufficient area of the porous separation membrane material to produce separation on a commercially attractive basis. The porous separation membranes significantly affect the separation of the multi-component type membranes of the invention, and as a result, it is desirable to provide a large ratio of total surface area to the total pore cross-sectional area of the porous separation membrane. This result clearly contrasts with the prior art objectives of the manufacture of composite membranes, wherein the superimposed membrane substantially produces the separation, and the supports are suitably designed as porous as possible in accordance with their primary function, namely supporting the superimposed advantageously, the support does not interfere with the permeate gas, either in terms of delay or inhibition of the gas flow from the superimposed membrane.

It will be appreciated that the amount of gas passing through the material of the porous separation membrane and its influence on the properties of the multi-component type membranes of the invention are affected by the ratio of total surface area to total pore cross-sectional area and / or the average pore diameter of the porous separation membrane. Frequently, the porous separation membranes exhibit total surface area to total pore cross-sectional area of at least about 10: 1, preferably at least about And certain porous separation membranes may have ratios of approx. 10 ^: 1 to 108: 1 or Ί 2 10: 1. The average cross-sectional diameter of the pores can vary widely and can often be in the range of approx. 5 and 20,000 Å, and in certain porous separation membranes, particularly in certain polysulfone porous separation membranes, the average cross-sectional diameter of the pores may be about 5 to 1000 or 5000 Å, even approx. 5 to 200 Å.

The coating is in occlusive contact with the porous separation membrane, so that with respect to the models developed on the basis of observations of the properties of the multi-component type membranes of the invention, increased resistance to the passage of gases through the pores of the separation membrane is provided. and that the proportion of gases passing through the material of the porous separation membrane relative to the gases passing through the pores is improved compared to the corresponding proportions using the non-provided porous separation membrane. with the coating.

A useful property of gas separation membranes is the effective separation thickness. In this context, the effective separation thickness means the thickness of a continuous (non-porous) and compact membrane of the material of the porous separation membrane which would exhibit the same rate of migration of a given gas as the multi-component type membrane, i.e. that the effective separation thickness is the quotient of the permeability constant of the material of the porous separation membrane for a gas and the permeability of the multi-component type membrane for the gas. By providing lower effective separation thicknesses, the migration speed of a particular gas is increased. Often, the effective separation thickness of the multicomponent-type membranes is substantially smaller than the total membrane thickness, especially when the multicomponent-type membranes are anisotropic. Frequently, the effective separation thickness of the multicomponent type membranes with respect to a gas, which can be demonstrated by at least one of the gases carbon monoxide, carbon dioxide, nitrogen, argon, sulfur hexafluoride, methane and ethane, is less than ca. 100 000 Å, preferably less than approx. 15,000 Å, in a typical case approx. 100 to 15,000 Å. In multi-component type membranes, e.g. polysulfone porous separation membranes, the effective separation thickness of the multicomponent membrane for at least one of these gases is suitably less than ca. 5,000 Å. In certain multicomponent type membranes, the effective separation thickness, especially with respect to at least one of these gases, is less than ca. 50, preferably less than ca. 20% of the thickness of the multi-component type membrane.

Prior to the present invention, a method of preparing gas separation membranes from membranes containing pores has included treating at least one surface of the membrane with pores to densify the surface, thereby reducing the presence of pores, which pores reduce the selectivity of the membrane separation. This assumption is e.g. by chemical treatment with solvents or swelling agents for the material of the membrane or by curing which can be carried out with or without contact with a liquid with the membrane. Such densification methods usually result in a significant reduction of flow through the membrane. Some particularly advantageous multicomponent-type membranes of the invention exhibit a greater permeability than the permeability of a membrane which is substantially the same as the porous separation membrane used in the multicomponent-type membrane, except that at least one surface of the membrane has been treated to be sufficiently densified, or has been sufficiently cured, with or without the presence of a liquid which, with respect to at least a couple of gases, provides a separation factor equal to or greater than the separation factor exhibited by the multi-component type membrane. Another method of increasing the selectivity of a membrane separation is to modify the conditions of its preparation so that it is less porous than a membrane made under the unmodified conditions. In general, the increase in selectivity in separation resulting from the manufacturing conditions is accompanied by a substantially lower flow through the membrane. Some particularly advantageous multi-component type membranes of the invention, e.g. such that the porous separation membrane is an anisotropic hollow fiber exhibits a greater permeability than an anisotropic hollow fiber membrane consisting of the material of the porous separation membrane which is capable of retaining the configuration of the hollow fiber under gas separation conditions, e.g. absolute pressure differentials of at least approx. And which hollow fiber anisotropic membrane with respect to at least one pair of gases exhibits a separation factor equal to or greater than the separation factor of the multi-component type membrane.

Advantageously, the porous separation membrane is sufficiently thick that no special apparatus for handling it is required. Frequently, the porous separation membrane has a thickness of approx. 20 to 500, e.g. ca. 50 to 200 or 300 ^, u. When the multi-component type membrane has configuration as a hollow fiber, the fiber can often have an outer diameter of approx. 200 to 1000 / h, e.g. ca. 200 to 800 / h, and wall thickness of approx. 50 to 200 or 300 / h.

In carrying out gaseous separations, including concentrations, using the multi-component type membranes of the invention, the exit side of the multi-component type membrane is kept at a lower chemical potential for at least one moving gas than the chemical potential at the input side. The driving force associated with the desired migration through the multi-component type membrane is a differential of chemical potential across the multi-component type membrane as described by Olaf A. Hougen and K.M. Watson in Chemical Process Principles, Part II, John Wiley, New York, (1947) may be due to a differential of the partial pressure. Migrant gas passes into and through the multicomponent-type membrane and can be removed from the exit side of the multicomponent-type membrane to maintain the desired driving force for the migrating gas. The functionality of the multi-component type membrane does not depend on the direction of the gas flow or the surface of the membrane which first contacts a gaseous starting mixture.

In addition to providing a method for separating at least one gas from gaseous mixtures which do not require expensive amounts of energy used for cooling and / or other costly energy consuming measures, the invention provides numerous advantages with a high degree of flexibility in selective migration operations. The multi-component gas separation membranes - whether in the form of a plate or hollow fiber - are useful for separating industrial gases, oxygen enrichment for medical applications, pollution control devices and for any need where it is desired to separate at least one gas. from gaseous mixtures. It is relatively rare for a single-component membrane to exhibit both a reasonably high degree of selectivity in terms of separation and good migration rates, and even in such cases, these single-component membranes are well suited for separating a few specific gases. The multi-component gas separation membranes of the invention can make use of many different materials for the porous separation membranes, which have not been desirable as single component membranes for gas separation due to undesirable combinations of migration rates and separation factors. Since the selection of the porous separation membrane material can be based on its selectivity and permeability constants for given gases and not its ability to form thin and substantially pore-free membranes, the multi-component type membranes of the invention can advantageously "tailor" for separation. of many different gases from gaseous mixtures.

The cross-sectional diameter of pores in a porous separation membrane can be of the order of some Å, and as a result, the pores of the porous separation membrane and the interface between the coating and the porous separation membrane cannot be directly observed using currently available optical microscopes. which can produce larger magnifications of a sample, such as scanning electron microscope and transmission electron microscope, involve special preparations of the samples, which limit their viability in terms of accurate depictions of the details of the sample, especially in an organic sample. For example, when In the case of scanning electron microscopy, an organic sample is coated, for example, with at least a bO or 50 Å thick layer of gold, to produce the reflectivity that provides the perceived image. Even the way the coating is applied can affect the perceived image. Furthermore, the mere presence of the coating required by scanning electron microscopy may obscure or seemingly alter details of the sample. In addition, both by scanning electron microscopy and by transmission electron microscopy, the methods used to produce sufficiently small portions of the sample can significantly alter the features of the sample. As a result, the complete structure of a multi-component type membrane cannot be visually perceived, even with the best available microscopic technique.

The membranes of the invention of the multi-component type behave in a unique way and one can develop mathematical models which - as demonstrated using various techniques - generally correlate with the observed operating conditions of a multi-component type membrane according to the invention. However, the mathematical models are not a limitation of the invention, but rather serve to further illustrate the technical advantages that the invention brings.

In order to gain a better understanding of the following mathematical models of multicomponent-type membranes according to the invention, reference is made to the depicted models in FIG. 1, 2, 3, 4, 6 and 7. The models depicted are intended to facilitate the understanding of the concepts developed in the mathematical model only and do not depict nor attempt to depict actual structures of the multi-component type membranes of the invention. Consistent with the purpose, which includes facilitating the understanding of the concepts underlying the mathematical model, the illustrated models illustrate the presence of traits associated with the mathematical model; however, the models depicted are greatly exaggerated in terms of the relative proportions of these features to facilitate the observation of these features. FIG. 5 is provided to support the detection of the analogy between the concepts of resistance to flow of permeate in the mathematical model and resistance to electric flow.

FIG. 1, 2 and 4 are depicted models which serve to understand the mathematical model and which illustrate an intermediate surface of the coating and a porous separation membrane, i.e. an enlarged region, shown in FIG. 6 as this region between lines A-A and B-B, but not necessarily on the same scale. FIG. 3 is an enlarged model of the region shown in FIG. 7 exists as the region between lines C-C and D-D. In the models depicted, the same conditions correspond to the same features.

FIG. 1 is an enlarged cross-sectional view for illustrative purposes, showing a model having a substantially continuous and uninterrupted overlying layer 1 of the material X of the coating in contact with the material Y of a porous separation membrane with solid portions 2 having pores 3; which is filled or partially filled with the material X.

43 148735

FIG. 2 is an enlarged view of another depicted model in which the material Y of the porous separation membrane is in the form of curved surface intermediate areas which are either empty or partially filled with the material X of the coating by a uniform contact, namely in uninterrupted fashion.

FIG. 3 is an enlarged illustration of a model depicted having the material X within the pores 3, but no continuous overlying layer 1 exists.

FIG. 4 is yet another model illustrated to assist in describing concepts in accordance with the mathematical model of the invention. FIG. 4 in the context of FIG. 5 shows an analogy to the well-known electrical current resistance circuit illustrated in FIG. 5 ·

FIG. 6 is yet another cross-sectional view of a model in which the material X of the coating is provided with a pore blocking film cast on a denser surface of the porous separation membrane which is characterized by a reciprocally graded density and porosity structure through the thickness of the membrane. .

Finally, FIG. 7 is a cross-sectional view of a model of an occluded anisotropic separation model that does not necessarily require any continuous or uninterrupted overlying layer 1.

The following formulas illustrate a mathematical model that has been developed to explain the observed properties of the multi-component type membranes of the invention. By appropriate application of this mathematical model, porous separation membranes and coating materials can be selected which will provide advantageous multi-component type membranes of the invention.

As will be seen from the following, the flow, 0 ^, a, of gas a through a multi-component type membrane can be represented as a function of the resistance to flow of gas a through each part (see, for example, the model depicted on Figure 4) of the multi-component type diaphragm by an analogy with the mathematically equivalent equivalent electrical circuit of Figure 1; 5th

44 148735 Γ η -i Γ 1

Ri a (R? Q + R ^ a) Ro a + R * a 1) -¾ - «*,» 1 + -U * y R3'a 2 »a 3, a * 2a K3a where ^ Pm is the pressure differential for gas across the multicomponent 1 / a membrane, the ponent type, and wherein R 2a, R 2a ° S 3a, respectively, represent the resistance to flow of the gas a originating from the overlying layer 1, the solid portions 2 of the porous separation membrane. , and the pores 3 of the porous separation membrane. The flow, Qj of a second gas b through the same multi-component type membrane can be expressed in the same way, but with the corresponding expression of the pressure differential of gas b and the resistance to flow of gas b through the overlying layer 1, the solid parts 2 of the porous separation membrane and the pores 3. Each of these resistors of gas b may differ from the resistances of the gases. Thus, selective migration may occur in connection with a multi-component type membrane. Advantageous multicomponent type membranes can be modeled by varying R 1, R 2 and R 2 relative to each other for each of the gases a and b to produce desirable calculated currents for each of the gases a and b, and varying the resistances of gas a in relation to the resistances of gas b to provide a calculated selective migration of gas a in relation to gas b.

Other formulas useful for understanding the mathematical model are listed below.

For any given separation material, the separation factor of two gases a and b, cx ^, is defined by formula 2 for a membrane of material n of a given thickness -l and surface area A: ^ ", a Pnta Qa ^ pd 2)"> where Pn ^ a and are the permeability constants of the material n for gases a and b, and Qa and are the respective flows of gases a and b through the membrane when Δρ ^ © g Apb are the driving forces, namely partial pressure drop, for gases a and b across the membrane. The flow Qa through a membrane of material n for gas a can be expressed as 45

3) a = in => CT

where A ^ is the surface area of the membrane of material η, / · η is the thickness of the membrane of material n, and a is for the purpose of the model defined as the resistance of a membrane of the material n to the flow of gas a.

From formula 3, it is seen that the resistance a is represented mathematically by formula 4.

4) 'pnfa \

This resistance is mathematically analogous to the electrical resistance of a material to an electric current.

To illustrate this mathematical model, reference may be made to the depicted model of e.g. FIG. 4. The porous separation membrane is represented as comprising solid portions 2 of the material Y and pores or holes 3. Material X is present in the model depicted in FIG.

4 as the overlying layer 1 and as the material entering the pores 3 of the porous separation membrane. Each of these regions, the overlying layer 1, the solid portions 2 of the porous separation membrane and the pores 3 containing the material X, have a resistance to gas flow so that the total multi-component type membrane can be compared with the analog electrical circuit which is represented in FIG. 5, wherein a resistor, R 1, is connected in series with two resistors, R 2 and R 2, which are connected in parallel.

If the material X is in the form of a continuous, compact, overlying layer 1, the resistance R R thereof to flow for a given gas can be expressed by formula 4 and will be a function of the thickness, overlying layer, surface area, A the overlying layer and the permeability constant, P 1, of the material X.

The porous separation membrane of a multi-component type membrane according to the invention is represented by the model as two resistors in parallel. In accordance with formula 4, the resistance R2 of the solid portions 2 of the porous separation membrane comprising material Y is a function of the thickness i2 of these solid portions, the total surface area Ag of the solid portions 2, and the permeability constant Py of the material Y The resistance of the pores 3 of the porous separation membrane is parallel to Rg. The resistance of the pores is represented, as in formula 4, by a thickness divided by a permeability constant and a total pore cross-sectional area A.. For the sake of the mathematical model, the assumption is represented by the average depth of penetration of the material X in the pores 3, as shown in the depicted model in FIG. 4, and the permeability constant P1 is represented by the permeability constant PX of the material X present in the pores.

The permeability constants, Ρχ and Py, are measurable properties — of materials. The surface area A ^ can be established by the configuration and size of the multicomponent-type membrane, and the surface areas Ag and A ^ can be determined, or boundaries can be established using conventional scanning microscopy in combination with methods based on measurements. of gas flow through the porous separation membrane. The thicknesses of p in g and can be determined in the same way. a for a multicomponent type membrane can thus be calculated from formulas 1 and 4 using the values of pT a, f I 2, Px, Py, A-j_, Ag and A ^ which can be established. The separation factor (oc ^) can also be similarly determined on the basis of formulas 1 and 2.

The mathematical model can be beneficial in developing advantageous multi-component type membranes of the invention. Since the separation of at least one gas in a gaseous mixture from at least one residual gas is substantially influenced by the porous separation membrane in particularly advantageous multicomponent type membranes, e.g. selecting a material for the porous separation membrane on the basis of its particular internal separation factor for these gases as well as its physical and chemical properties such as strength, toughness, durability, chemical resistance and the like. The material can then be transformed into a porous membrane using any suitable technique. The porous separation membrane, as indicated above, can be characterized by scanning electron microscopy, preferably in combination with measurements of. gas flow, as described by H. Yasuda et al., Journal of Applied Science, Vol. 18, pp. 805-819 (1974).

47 148735

For the sake of the model, the porous separation membrane can be represented as two resistors of gas flow in parallel, the solid parts 2 and the pores 3. The resistance of the pores, R 2, depends on the average size of the pores which determines whether the gas flow through the pores will be a laminar flow or a Knudsen diffuse flow (as discussed, for example, in Hwang et al., cited above, and by the number of pores. Since the diffusion rates of gases through open pores are much greater than through solid materials, the calculated resistance is against gas flow of the pores, R 2 is usually considerably less than the calculated resistance of the solid parts, R 2, of the porous separation membrane, even when the total pore cross-sectional area is much smaller than the total surface area of the solid parts.

In order to increase the proportion of permeate gas flow through the solid parts 2 in terms of flow through the pores 3, the resistance of the pores, R 1, must be increased relative to the resistance of the solid parts, R 2. This can be accomplished in accordance with this model by providing a material X in the pores to reduce the rate of diffusion of gases through the pores.

By obtaining an assessment of the resistance to gas flow through the pores and knowing the resistance to gas flow of the material of the porous separation membrane, one can judge the desired increase of the resistance to gas flow through the pores which is necessary to provide a multi-component type membrane with a desired separation factor. Conveniently, although not necessary, it can be assumed that the depth of the material of the coating in the pores (afstand) and the distance (JJ 2) for the minimum passage of the gas through the material of the porous separation membrane are the same. Based on a knowledge of the permeability constants of the coating material, a coating material can then be selected to provide the desired resistance. The coating material may also be selected for other properties besides the increase of R 2, as will be described below. If the coating material also forms an overlying layer on the porous separation membrane as illustrated in FIG. 4, it can reduce the flow. Such a situation is described according to the mathematical model using formula 1. In such a case, the properties of the material of the coating should also be such that the flow is not unduly reduced.

48 148735

The selection of a material for the coating depends on its particular internal separation factor relative to the particular internal separation factor of the material of the porous separation membrane and its ability to provide the desired resistance in the multicomponent type membrane. The material of the coating must be capable of making occlusive contact with the porous separation membrane. Based on the average pore size of the porous separation membrane, materials can be selected for the appropriate molecular size coating. If the molecular size of the coating is too large, or if the coating material bridges the pores at the surface, it is evident from the model that the resistance of the pores, R 2, would not increase relative to the resistance, R 2, of the solid portions of the porous. separation membrane, and in such a case, the proportion of gases passing through the solid portions 2 relative to gases diffusing through the pores would not be increased in comparison with the proportion of the porous separation membrane alone. On the other hand, if the molecular size of the material of the coating is too small, it can be drawn through the pores during coating and / or separation operation.

The coating is frequently in the form of an overlying layer 1 (see the model depicted in Figure 4) in addition to the material of the coating which enters the pores. In these cases, the overlying layer 1 represents a resistance to gas flow, R 1, connected in series with the combined resistances of the porous separation membrane. When this situation exists, the material of the coating should advantageously be selected such that the overlying layer of the multi-component membrane will not present too much resistance to gas flow (while the coating still provides sufficient resistance in the pores) so that the porous separation membrane substantially affects the separation of at least a few gases in the gaseous mixture. This can be done, for example. is accomplished by providing a coating material which exhibits high permeability constants for gases and low selectivity.

The thickness of the overlay represented by the model may also have some influence on the flow and selectivity of the multi-component membrane type s, because the resistance (RT) of the overlay 1 is a function of its thickness

K

148735 49

If a suitable material X and material Y are selected, various configurations of multi-component type membranes comprising these materials can be modeled using formulas 1, 2 and 4. Information which e.g. comprising more desirable ratios of total pore cross-sectional area (λ) for the porous separation membrane and more desirable thicknesses for the separating layer of the porous separation membrane may result from this mathematical modeling. This information can, e.g. may be useful in determining methods for preparing the porous separation membranes having desirable area ratios, A 2 / (A 2 + A 2), and desirable separation thicknesses of desirable thicknesses J L 2 of the overlying layer. In the case of porous separation membranes of anisotropic hollow fibers, this can be accomplished by appropriate selection of spinning conditions and / or finishing conditions.

The above discussion is illustrative of the way in which various multi-component membrane configurations can be mathematically modeled. Several methods have been discussed in respect of at least one pair of gases to vary the relative resistances of the overlying layer 1, the solid portions 2 and the pores 3 of the porous separation membrane to provide high multicomponent advantageous membranes exhibiting high flow and high selectivity for at least a couple of gases.

The following is the mathematical derivation which, in combination with formulas 3 and 4, will lead to formula 1.

Based on the known Ohm's law of electrical resistances, a mathematical expression of the total resistance, Rp, of the electrical circuit illustrated in FIG. 5th

5) Hr = R]. + r23 = R1 + ϊφίζ where R2 ^ is the combined resistance of R2 and R ^ in parallel and equal to the last expression of formula 5.

By analogy, it is seen that the mathematical model described above uses the same mathematical formula to express the total resistance to flow of a given gas for a multicomponent-type membrane, as shown in excessive fashion by the image shown in FIG. This model of FIG. 4. The resistance, R 2, represents the combined resistance of both parts of the porous separation model, the solid parts 2 and the pores 3 filled with material X. If the coating is not provided as a substantially continuous overlying layer 1, but only as a material. X entering the pores 3, a situation illustrated by the model depicted in FIG. 3, the resistance of the overlying layer is zero and the term is based on formula 5 and all subsequent formulas derived from formula 5 ·

The total flow of a given gas a through the multicomponent type membrane is equivalent to the flow by electric flow and is in the stationary state indicated by formula 6.

6) QT, a = Q1, a = Q23, a - Where Q-, _ is the flow of gas a through the overlying layer 1, and xja ®23 a is ^ a combined flow of gas a through both the solid parts 2 and pores 3 (filled with material X) of the porous separation membrane.

Q23, a = ° 2, a + Q3, a

The total partial pressure of gas a over the multi-component type membrane is the sum of the partial pressure drops over the overlying layer 1, 4p a> and the partial pressure drop over the solid parts 2 and the filled pores 3 of the porous separation membrane is' 2, ό f 9.

8) ώρτ, 5. = * Pl, a: ^ 23.3

The flow of gas a through each part of the multi-component type membrane can be expressed by formula 3 using the resistances and partial pressure drops specific to each part.

9) Q-, = Åpl, a 1, a R, l, a 10) Q ', _ = 4p23, a _ 4p23, a (E2, a * R3, a' E23, a = E2.a E3, a 148735 51

From formulas 6, 8, 9 and 10, one can deduce an expression of δ p23f a depending on the resistances and the total partial pressure drop.

r -i -1% a (R2 a + ^ a ^ «23,. ** .. 1 + Ί Ί h

L 2, and R 3, and J

By combining Formula 11 with Formulas 6 and 10, Formula 1 is obtained.

In accordance with this invention, a coating is in occlusive contact with the porous separation membrane to provide a multi-component type membrane. This mathematical model, developed to explain the phenomena exhibited by the multi-component type membranes of the invention, involves the pores 3 of the porous separation membrane containing material X. The resistance to gas flow, R 1, of the pores containing material X, is much greater than the resistance to gas flow of pores not filled with material X because the permeability of gases of any material is much less than the permeability of an open flow channel. As a result, R 1 is increased in the multicomponent-type membrane, and as far as formula 10 is concerned, it should be stated that it becomes more significant in terms of the influence of R 23. As R 2 is increased relative to R 2 in the multi-component type membrane, an increased proportion of gas passes through the solid portions of the porous separation membrane as compared to passage through the pores 3 filled with material X relative to the proportion passing through the porous separation membrane alone. As a result, the separation factor of at least a couple of gases in the multi-component type membrane is enhanced by interaction with the material Y, as compared to the separation factor in the porous separation membrane alone.

The following examples are illustrative of the invention. All parts and percentages of gases are by volume, and all parts and percentages of liquids and solids are by weight unless otherwise indicated.

52 148735 EXAMPLES 1-5

Examples 1 to 3 of Table I represent multicomponent type membranes comprising cellulose acetate consisting of porous separation membranes and a coating. Examples 2 and 3 show the same composite hollow fiber membranes separating two different gas mixtures. It is seen in these two examples that the porous substrate membrane to some extent separates both gas mixtures, even in the absence of a coating, but in both cases the separation factor is much smaller than the particular internal separation factor of the cellulose acetate. In such porous separation membranes, most of the gases pass through the pores and relatively little permeate flows through the cellulose acetate.

After coating, the separation factor of the gases exhibited by the multicomponent-type membranes of Examples 2 and 3 is greater than both the determined internal separation factor of the coating material and the separation factor of the porous separation membrane.

Thus, in the multicomponent-type membrane, a greater proportion of the gas flows through the cellulose acetate as compared to the gas flow through the pores; as a result, the multi-component membrane separation factor is much closer to the particular cellulose acetate internal separation factor.

Example 1 shows another sample of hollow fibers of cellulose acetate, wherein the properties in the coated state differ from those in the non-coated state and can be compared with Example 2. Although the porous separation membrane has a greater permeability for C> 2 and a lower separation factor, For example, the multi-component type membrane exhibits a higher separation factor than each of the materials constituted by the coating and the porous separation membrane separately.

53 148735 · »

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(A) the permeability of the membrane for a given gas is the amount of gas (expressed as cnr 5 under normal temperature and pressure) passing through the membrane per cm surface area per second for a partial pressure drop of 1 cm Hg between the inlet and outlet side of the membrane per unit thickness (permeability unit = cm 2 / cm 2 sec-cm Hg).

(b) cellulose acetate (degree of substitution about 2.5) obtained from Eastman Kodak and spun according to OSW Final Report No. 14-30-3066, "Development of High Flux Hollow Reverse Osmosis for Brackish Water Softening (1973)". The fiber of Example 2 is post-treated in hot water.

(c) all coatings are liquid when applied and are not further cured, polymerized or crosslinked after coating.

(d) the key of the coating methods is listed (Table XVI) following the examples.

(e) the separation factor of a membrane for a pair of gases is defined as the permeability of the membrane for a first gas divided by the permeability of a second gas in the gas pair.

EXAMPLES 4-10

Examples 4 to 10 illustrate various liquid coatings on porous separation membranes of hollow polysulfone fibers for the selective separation of oxygen from air, and they are presented in Table II.

The porous separation membranes do not separate oxygen from nitrogen.

The coating materials used are representative of high molecular weight organic materials and silicone liquids having vapor pressures sufficiently low to not readily evaporate from the coated surface, and having oxygen separating factors over nitrogen which are generally below ca. 2.5. The molecular sizes of the coatings are sufficiently small to provide occlusive contact with the porous separation membrane, but they are not extremely small so that the coating material can pass through the pores under coating and / or separation conditions. The observed separation factors for the multicomponent type membranes are greater than each of the separation factors for the porous separation membrane (1.0 in all examples) and the coating material (2.5 or less for the coating materials in the examples).

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Examples 11 to 15 illustrate various coatings which are either applied to the porous separation membranes as liquids and reacted in situ to form solid polymeric coatings (post-vulcanized) or applied as normally solid polymers dissolved in a solvent. The results are listed in Table III. In the examples, oxygen is enriched from supplied air by a multi-component type membrane and many different treated porous separation membranes of hollow polysulfone fibers are used.

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Examples 16, 17, and 18 show that the multicomponent-type membranes which use porous separation membranes with hollow polysulfone fibers can also effectively separate H2 from CO / H2 mixtures according to the invention. The separation factor of the porous separation membrane was not measured prior to coating for example 16 and 18, but numerous experiments with similar porous separation membranes show that it can be expected that the separation factors are between ca. 1.3 and approx. 2.5. This expectation is verified in Example 17 where the separation factor of the porous separation membrane for H2 over CO was measured to 1.3.

Thus, these separation membranes exhibit some separation of H2 and CO due to Knudsen diffusion. These examples illustrate the use of various coatings, coating methods, permeabilities and separation factors of the multicomponent and porous type separation membranes in providing the multicomponent type membranes of the invention. Examples 14 and 17 and Examples 15 and 18 are carried out with the same multi-component type membrane, and comparison between these examples shows that the use of a multi-component type membrane for a separation or with a mixture of gases will not prevent it from later can work with a different set of gases. The examples are given in Table IV.

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Eh ft O OWPPfttocOdPftd ^^^ - EXAMPLE 19-21 60 U8735

Examples 19, 20 and 21 (Table V) show migration properties of multicomponent-type membranes consisting of various coating materials on porous, bulbous copoly (styrene-acrylonitrile) separation membranes for air and CO / H 2 separation. In each example, the multi-component type membrane has a higher separation factor than each of the materials coated and the porous separation membrane alone. Example 21 shows a porous separation membrane which exhibits a separation factor of H₂ over CO of 15 »before applying the coating, i.e. there are relatively few pores in the porous separation membrane and the average pore diameter may be small. A comparison of Examples 20 and 21 shows that the multicomponent type membrane of Example 20 has a higher migration rate and a higher separation factor than the porous separation membrane of Example 21, although the membrane has a greater separation factor than the porous separation membrane of Example 20. Multi-component membranes Thus, the type of the invention may exhibit a greater rate of migration than a membrane having equal or greater separation factor, consisting essentially of the material of the porous separation membrane.

61

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A five-component gas stream is used as the input material for a multi-component type membrane of Examples 15 and 18. The input stream comprises hydrogen, carbon dioxide, carbon monoxide, nitrogen and methane with amounts of water and methanol up to saturation value. The input stream present at a pressure of 4.5 kg / cm and at a temperature of 40 ° C is introduced on the shell side of the multi-component type membrane. The pressure in the bore is 1 atm. The following gas permeabilities and separation factors with respect to hydrogen are considered;

Permeability *: for; Separation Factor H2 over H2 (8.5x10 ~ 5) --- CO2 (3.7x10 ~ 5) CO2 2.3 CO for 27x10 5) CO 31.0 N2 (0.68x1O-5) N2 12.4 CH4. ( 0.23x10-5) CH4 36.9 * in cm 2 (STP) / cm2- sec.-crn Hg.

It is apparent from this example that the separation of hydrogen from gaseous mixtures containing at least one of the gases CO, N2 and CH4 can be readily accomplished. The presence of one or more additional gases in the gaseous mixture, such as saturated water and methanol vapor, does not appear to prevent the multi-component type membrane from carrying out the separation. It is also clear that various of the other gases in the mixture can be separated from each other, e.g. For example, the separation factor of CO 2 over CO can be the ratio of permeability sites, namely 14. Example 22 also illustrates the effect of the porous separation membrane in providing the relative migration conditions through the multi-component type membrane. The coating material (Syl-gard 184) exhibits a definite internal separation factor of approx. 0.3 to 0.4 for H2 over CO2 (i.e., CO2 is faster than H2), yet the multicomponent membrane exhibits a separation factor of 2.3 for H2 over CO2. This value is substantially - within the experimental uncertainty - equal to the particular internal separation factor of the poly sulfone for H2 over CO2.

Example 25 63 148735

Example 23 (Table VI) shows the permeabilities (P / 00 for a number of gases through a multi-component type membrane using a porous hollow polysulfone fiber separation membrane. Example 23 shows the same value for the same gases through a continuous, compact film of The ratio of two arbitrary values of P or T? / J / defines an approximate separation factor for these gases through the compact film or the multicomponent-type membrane, respectively. The example illustrates clearly a tendency in the sense that the permeabilities of the membrane The multicomponent type generally varies from gas to gas in the same order as for the compact polysulfone film, which shows that the material in the porous separation membrane provides a significant portion of the separation exhibited by the multicomponent type membrane. the multi-component type membrane can be used to separate any of a number of gases from any of the others. For example, it appears. of the table that NH 1 can be easily separated from H2 or N 2, He from CH 2, N 2 O from N 2, O 2 from N 2, or H 2 S from CH 2, using this multi-component type membrane. The advantage of the high migration rates of the multicomponent-type membranes is evident from the data shown in Table VI.

Table VI. Permeability of fixed gases through a multi-component type membrane gains the use of porous separator.

t) C

polysulfone membrane and compact polysulfone film.

Qas. Membrane0 of multicomponent- Continuously compact film _ type P / l (x10 ^) a_- of polysulfoneC P (xlO ^) 5 m3 210 530 • H2 55 130 *

He 55 50 N20 45 82 C02 38 69 H2S 31 31 02 8.3 11

Ar 3.3 4.5 CH4 2.3 2.5 CO 2.4 3.2 N2 1.4 1.8 C2H4 lf7 2.2 64 148735 (a) Permeabilities of the multi-component type membrane are P / t values and have units as described in footnote a in Table I. Permeabilities for polysulfone films are P values because in or thickness of the compact film can be easily measured. Units for P are cm 2 (normal temperature and pressure) -cm / cm-sec-cm Hg.

(b) The multi-component type membrane in this example is constituted by Dow Sylgard 184 post-vulcanized silicone rubber coated on a polysulfone porous separation membrane, as in Example 15, using coating method F of Table XVI

(c) As footnote b in Table II.

* Another compact film used to determine the permeability is that used to determine the permeabilities of the other gases.

Comparative Examples 24 to 26 (not according to the invention)

Examples 24 to 26 are reported in Table VII and illustrate that not all composite membranes will fall within the scope of the invention, i.e., provide a multicomponent type membrane which exhibits a separation factor significantly greater than the determined internal separation factor of the coating material. although they consist of porous separation membranes and coating materials which can be used separately with other coating materials or porous separation membranes to provide multi-component type membranes according to the invention.

Example 24 provides a multicomponent type membrane which exhibits a pre-vulcanized silicone rubber coating on a polysulfone porous separation membrane. Since the pre-vulcanized silicone rubber may have too large molecular dimensions to be expected to occlude the pores in accordance with the model, e.g. the molecules can only bridge the pores, the coating will not change the resistance of the pores to the flow of gas. In Example 24, the coating compound is a pre-vulcanized polymer having the same essential polymeric backbone as the illustrated Sylgard 184, e.g. in Examples 11, 14 and 15 of Table III. However, the pre-vulcanized silicone rubber has a much higher molecular weight and size due to pressurized vulcanization than Sylgard 184, and thus does not appear to fill the pores, and as a result, the composite membrane exhibits a separation factor which (within the test accuracy) is equal to the separation factor of the coating material.

Example 25 illustrates a multicomponent type membrane in which Sylgard 184 is used as a coating material and using a porous polyacrylonitrile porous separation membrane. Polyacrylonitrile exhibits a very low permeability to gases when in continuous, non-porous form. In relation to the model, such a porous separation membrane will have a very high resistance to flow through the solid parts thereof, so that in the event that a high permeability coating material such as Sylgard 184 is in occluding contact, the gas flow preferably takes place through the coating. and the clogged pores, and the multi-component type membrane thus exhibits a separation factor equal to or less than the separation factor of the coating membrane.

A multicomponent-type membrane illustrated in Example 26 exhibits a separation factor lower than the determined internal separation factor of the coating material. This situation is similar to the situation of Example 24 in the sense that the poly (vinyl butyral) used as a coating material has a high molecular weight. In addition, it does not humidify the polysulfone as well as many silicones and other preferred coatings. In addition, poly (vinyl butyral) has relatively low permeability. The observation that the separation factor exhibited by the multicomponent-type membrane is less than that expected by the coating material indicates errors in the coating itself.

TABLE VII (not according to the invention) Example 24

Coating General Electric 4164 pre-vulcanized silicone gum

Porous hollow fiber membrane Polysulfon P-3500 Union Carbide

Gas supplied Air

Enriched gas (permeate) 02

Coating methods E

Determined internal separation factor of coating material 02 over N2 lf7

Permeability0 of porous air separation membrane 1.8 x ΙΟ ”4- * u *

Separation factor0 of porous separation membrane 02 over N2 1.0

Multi-component membrane separation factor 02 over N2 1.61

C multicomponent membrane permeability0 For 02 4.1 x 10 ~ 5 EXAMPLE 25

Coatings Dow Corning Sylgard 184 post & Lcanized silicone rubber

Porous, hollow fiber-roembrane Polyacryloni tril

Gas supplied Air

Enriched gas (permeate) 02

Coating methods F

Determined internal separation factor0 of coating material 02 over N2 2.3

Permeability0 of porous separation membrane For air 2 x 10 "-5 i.

Separation factor0 of porous separation membrane 02 over N2 1.0

Multicomponent-type membrane separation factor13 over N2 1.9

Multi-component Membrane Type Permeability0 For 02 1.7 x 10 "-3 EXAMPLE 26 148736 Ό 7

Poly (vinyl butyl) coating

Porous, hollow fiber membrane Polysulfone P-3500 Union Carbide

Gas supplied Air

Enriched gas (permeate) 02

Coating method3 C

* L

Determined internal separation factor of coating material 02 over N2 4.7

Permeability0 of porous separation membrane For air 1.8 x 10

Separation factor0 of porous separation membrane 02 over N2 1; 0

Separation factor * 3 of multicomponent type 02 membrane over N2 4.0

Multi-component membrane permeability0 For 02 1.4 x 10 ”° (a) As footnote d in Table I. (b) As footnote e in Table I. (c) As footnote a in Table I.

EXAMPLES 27-54

Examples 27 to 34 are reported in Table VIII and illustrate a series of post-spinning treatments of porous separation membranes and the way in which these treatments affect the separation properties of multicomponent type membranes made from such post-treated porous separation membranes. In Table VIII, the coating material and application method are essentially the same to emphasize that changes in the migration rate and separation factor of the multicomponent type membranes (for both air oak as starting material serving C0 / H2 gas mixture) are apparently due to changes in the relatively dense regions. of the porous separation membrane.

It is believed that the treatments affect the available cross-sectional area of the pores (A ^) relative to the total surface area (A2 + A ^) of the porous separation membrane. A reduction of A 2 relative to the total surface area will increase the relative resistance to flow through the pores of the porous separation membranes and the multi-component type membranes. This, in turn, will force more of the migrating gas to flow through the material of the porous separation membrane, and the separation factor exhibited by the multi-component type membrane will move closer to the internal separation factor of the material of the porous separation membrane. .

In all the examples in Table VIII, the separation membrane used is a polysulfone hollow fiber membrane (Union Carbide, P-3500) from the same coil wet-spun from a liquid of 25% solids in dimethylformamide solvent in a coagulant of water at approx. 3 ° C through a jet from a tube into an opening through which water was injected into the bore and the fiber was absorbed at a rate of 21.4 mpm. The porous separation membrane used in each example is stored in deionized water at room temperature after spinning until the post-treatment process is used.

TABLE VIII

Examples 27 to 34

Post-treatment of hollow fiber membrane.

The multicomponent type membranes of Examples 27 to 34 utilize a Dow Corning Sylgard 184 post-vulcanized silicone rubber coating followed by the coating F as in Table XIV. The post-treatment was carried out on the membrane of the hollow fibers after spinning, but before the coating was applied.

EXAMPLE 27

Finishing Air evaporation of the water

Gas supplied Air

Enriched gas (permeate) And

Membrane Permeability _ Multicomponent Type For 00 1.5 x ΙΟ ”* 3

Multi-component membrane separation factor0 And over Ng 4.7

Permeability3 of finishing.

slightly porous separation membrane For air 3.7 x 10 "4

Separation Factor of Finished Porous Separation Membrane And Above Ng 1.0 69 148735 EXAMPLE 28

Finishing Air evaporation of the water

Supply gas CO

Enriched gas (permeate) Hg

Multi-component membrane c permeability3 For HP 7.6 x 10 ”p

Separation factor0 of multi-component Hg membrane over CO 23/1

Permeability3 of Finishing λ Slightly Porous Separation Membrane For HP -V2.0 x 10

Separation Factor of Finished Porous Separation Membrane Hg over CO Th 2.6 2.6 TcMPEL 29

Post-treatment Air evaporation of the water, followed by exposure to acetone vapor at 25 ° C with borehole vacuum, followed by alternate immersion in water and methanol with borehole vacuum (3 cycles), followed by alternate immersion in water and isopropyl alcohol (2 cycles).

Gas supplied Air

Enriched gas (permeate) And

Multi-component membrane permeability3 for 0P 7.7 x 10 “°

Multicomponent-type membrane separation factor And above Ng 5.3

Permeability3 of Finished Porous Separation Membrane And Above Ng 1.0 Example 50

Post-treatment Air evaporation of the water, followed by exposure to acetone vapor at 25 ° C with borehole vacuum, followed by alternate immersion in water and methanol with borehole s vacuum (3 cycles), followed by alternate immersion in water and isopropyl alcohol (2 cycles).

Supply gas CO

Enriched gas (permeate) Hg

Multi-component Membrane Type Permeability3 For HP 4.5 x 10 "^ V%"

Separation factor0 of multi-component type Hg membrane over CO 30.4 EXAMPLE 30 (continued) 70 148735

Permeability3 of finishing.

light, porous separation membrane For H? 1.5 x 10 “^

Separation Factor of Finished Porous Separation Membrane H2 over CO 5; EXAMPLE 31

Finishing Air evaporation of the water followed by heating in hot air oven to 80-95 ° for approx. 3 hours.

Gas supplied Air

Enriched gas (permeate) 02

Membrane Permeability3 · Multicomponent Type For 02 1.6 x 10 "-3

Multicomponent-type membrane separation factor13 over N2 5.0

Permeability3 of finishing, light, porous separation membrane For air 3.7 x 10 "4 u"

Separation Factor0 of Finished Porous Separation Membrane 02 over N2 1.0 EXAMPLE 32

Finishing Air evaporation of the water followed by heating in hot air oven to 80-95 ° for approx. 3 hours.

Gas CO, H2 supplied

Enriched gas (permeate) H2

Multi-component membrane permeability3 For H «9.8 x 10- * 3

Multi-component membrane H2 separation factor over CO 23

Permeability3 of finishing, lightweight, porous separation membrane For H2 For2; 5 x 10;

Separation Factor13 of Finished Porous Separation Membrane H2 over CO / Vl, EXAMPLE 33

Finishing Dry by exchanging water with isopropyl alcohol, followed by exchanging the isopropyl alcohol with pentane, followed by air evaporation of the pentane.

Gas supplied Air

Enriched gas (permeate) 02

Multi-component Membrane Type Permeability3 For 02 2.0 x 10 5 EXAMPLE 55 (continued) i.

71 148735

Multi-component membrane 02 separation factor O over N2 4.2

Permeability3 · of finishing, light, porous separation membrane For air 1.5 x 10 "-5 • u '

Separation Factor0 of Finished Porous Separation Membrane 02 over N2 1.0 EXAMPLE 54

Finishing Dry by exchanging water with isopropyl alcohol, followed by exchanging the isopropyl alcohol with pentane, followed by air evaporation of the pentane.

Supply gas CO, h2

Enriched gas (permeate) H2

Membrane Permeability, Multicomponent Type For H5 1.2 x 10 "^ • u ^

Separation factor0 of multi-component type H2 membrane over CO. 15.9

Permeability31 of finishing,.

light, porous separation membrane For H2 n 2.5 x 10 6

Separation factor * 5 of post-treated porous separation membrane H2 over CO ^ 1.3 (a) As footnote a in Table I. (b) As footnote e in Table I.

EXAMPLES 55-59

Examples 35 to 39 reported in Table IX illustrate the effect that additives in the coating material have on the separation factor of a multi-component type membrane for two gas mixture feed streams (air and CO / H2). These additives are incorporated into the coating material in small quantities before the coating is applied to the porous separation membrane. Such additives may alter the separation properties of the multi-component type membranes, e.g. by altering the wetting properties of the coating material, and may thereby affect its ability to be in occlusive contact with the porous separation membrane. If the additive improves the occlusive contact, the separation factor of a multicomponent-type membrane with such additive is expected to be closer to the internal separation factor of the porous material of the separation membrane than the separation factor of a similar multicomponent-type membrane without such an additive.

148735 72

The hollow fibers of the porous separation membrane utilized in Examples 35 to 39 were all from the same coil and were made of polysulfone (P-3500) in a highly porous form (see footnote a), by spinning according to the same method as the hollow fibers of Examples 27-34. The determined internal separation factor of the polysulfone for O 2 over N 2 from a starting material of air is approx. 6.0 and for H2 over CO from a CO / H2 mixture approx. 40th

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Examples 40 to 43 of Table X illustrate multicomponent type membranes in which the porous separation membranes are prepared under various spinning conditions. The multicomponent type membranes of Examples 40 to 42 use a post-vulcanized silicone rubber type Dow Corning Sylgard 184 (coating method F, Table XVI) on polysulfone porous separation membranes. The hollow fiber substrate membranes of porous polysulfone are wet spun on the basis of the indicated fluids in a water coagulant at the indicated temperature and spinning speed by a hollow fiber spinning nozzle with an aperture to provide coagulant injection into the fiber bore when formed. The range of permeability (θ £ and H2) and the separation factors of the multi-component type membranes (0 £ over Np and H2 over CO) exhibited in Examples 40 to 43 for both air supply and CO / H2 mixture can be . is related to the variability of the relative resistances of the pores and the material of the porous separation membranes to gas flow. The conditions under which the porous substrate material is spun determine to a large extent the porosity properties and the effective separating thickness that this substrate will exhibit. In addition, these properties can be altered with post-spinning treatments of the porous substrate (see Examples 27 to 34).

TABLE X Spinning conditions for porous separation membranes of hollow fibers of P-3500 polysulfone

Example 40

Solvent 'Dimethylformamide

Coagulation temperature, ° C 3 °

Spinning speed, mpm 21.4 mpm Liquid concentration ·, wt% polymer 25%

Separation factor, 0 «over N« * 5, of multi-component membrane type 4.5

Permeability for 0 "a 7.7 x 10" ^

Separation factor, Hp over CO, of multi-component membrane type 16.7

Permeability for H2a 5.0 x 10

Permeability for Porous Separation Membrane Air 6 x 10-it 75 EXAMPLE 41

Solvent Dimethylformamide

Coagulation temperature, ° C 5 °

Spinning speed, mpm 21.4 mpm Liquid concentration, weight% polymer 25%

Separation factor, Op over No **, of multi-component membrane 5.09

Permeability for 02a 6.2 x 10

Separation factor, Hp over CO * 3, of multi-component type 25 membrane

Permeability for H2a 4.9 x 10

Permeability3 for porous air.

Separation Membrane 9 x 10 10 EXAMPLE 42

Solvent Dimethylformamide

Coagulation temperature, ° C 4 °

Spinning speed, mpm 33 mpm Liquid concentration, wt% polymer 28%

Separation factor, Op over Np * 3, of multi-component membrane type 5f9

Permeability for Op 8.0 x 10 ”^

Separation factor, H2 over CO, of multi-component type membrane 30

H2A 5.9 x 10 ”permeability **

Permeability3, for porous air separation membrane 2 x 10 ”4 EXAMPLE 45

Solvent Dimethylformamide

Coagulation temperature, ° C 5 °

Spinning speed, mpm 33 mpm Liquid concentration, weight% polymer 27%

Separation factor, Op over Np, of multi-component membrane type 5.6

Permeability of Op b 6.0 x 10

Separation factor, H2 over CO, of multi-component meriibran type 27

Permeability3 for H2 3.8 x 10

Permeability3 for air of porous separation membrane 4.5 x 10 4

(a) As Table I

b) As footnote e in Table I

EXAMPLE 44-51 76 148735

Examples 44 to 47 of Table XI illustrate multicomponent type membranes wherein the porous separation membrane is in the form of an anisotropic film comprising an acrylonitrile / styrene copolymer with a specific Hg internal separation factor of CO of 76. The films had been cast from solvents comprising dimethylformamide and non-solvents as indicated in the table on a plate, freed from solvent in air for 5-45 seconds, coagulated as indicated below and then immersed in water at 25 ° C for washing, removed and dried. Examples 48 to 51 illustrate multicomponent type membranes in the form of films that are dense. These examples illustrate multicomponent-type membranes of the invention in the form of films and may comprise porous separation membranes exhibiting coatings on both surfaces.

TABLE XI

Multicomponent membranes in film form EXAMPLE 44

Coating Dow Corning Sylgard 184 post-vulcanized silicone rubber

Porous separation membrane Copoly (acrylonitrile / styrene) 32% / 68 $ by weight

Supply gas Hg, CO

Coating methods B

Coating material, determined internal separation factor, 1.9 E0 over CO 2 Ή

Separation factor0 of porous separation membrane, H0 over CO 13 L ^

Separation Factor O, Hg of Multicomponent Type Membrane 34.8 EXAMPLE 45 77 148735

Dow Coming 200 poly (dimethyl siloxane) coating

Porous separation membrane Copoly (acrylonitrile / styrene) 32% / 68% by weight

Supply gas H2, CO

Coating methods B

Coating material, determined internal separation factor * 3, h_ above CO 1.9

Separation factor O, H2 over CO, of porous separation membrane 12.2

Separation factor, h2 over CO, of multicomponent membrane type 23 8 EXAMPLE 46

Coating Dow Coming Sylgard 184 vulcanized silicone rubber

Porous separation membrane Copoly (acrylonitrile / styrene) 32% / 68% by weight

Supply gas El · ,, CO

Coating methods B

Coating material, determined internal separation factor0, H "over CO. Separation factor, H2 over CO, of porous separation membrane

Separation factor * 3, H_ over CO, of multi-component type 23 membrane 5 EXAMPLE 47

Coating Dow Corning 200 poly (di methyl siloxane)

Porous separation membrane Copoly (acrylonitrile / styrene 32% / 68% by weight

Supply gas H2, CO

Coating methods B

Coating material, determined internal separation factor * 3, Hn above CO 1.9 b ^

Separation factor ", H2 over CO, of porous separation membrane 3j4

L

Separation factor0, H2 over CO, of the multi-component membrane, 7j6 coating on a page 78 Example 47 (continued) »fa

Separation factor0, H2 over CO, of multicomponent membrane, coating on both sides 34

(a) As explained in Table XVI

b) As footnote e in Table I

c) Coagulated in 50/50 by volume ethylene glycol / water for 30 min. at 25 ° C.

d) Coagulated in 90/10 by volume isopropyl alcohol / water for 30 min. at 25 ° C

e) Coagulated in 10/90 on volume isopropyl alcohol / water for 30 min. at 25 ° C

f) Coagulated in water at 25 ° C.

EXAMPLE 48

Coating Dow Corning Sylgard 184 post-vulcanized silicone rubber

Porous separation membrane Copoly (acrylonitrile / styrene) 25% / 75% by weight

Gas supplied Air

Enriched gas (permeate) 02

Coating methods E

Oversized material, determined internal separation factor; . 2.3

* U

Separation factor0 of porous separation membrane 02 over N2 3.6

Separation factor * 3 of multi-component type 02 membrane over N2 5.4 EXAMPLE 49

Coating Dow Corning 200 poly (dimethylsiloxane)

Porous separation membrane Poly mixture of two acrylonitrile / styrene copolymers

Gas supplied Air

Enriched gas (permeate) 02

Coating methods A

Coating material, determined internal separation factor0 2.3

Separation factor * 1 of porous separation membrane 02 over N2 4.9 • i «.

Multicomponent-type membrane separation factor O over N2 6.1 79 EXAMPLE 50 148735

Coating Dow Corning 200 poly (dimethylsiloxane)

Porous separation membrane Copoly (acrylonitrile / styrene) 32 µ / 68% by weight, suspension polymerized

Gas supplied Air

Enriched gas (permeate) And

Coating methods A

Coating material, determined internal separation factor 2.3

Separation factor0 of porous separation membrane O2 over Ng 1 »0

Multicomponent-type membrane separation factor13 over Ng 6.3 EXAMPLE 51

Coating Dow Corning 200 poly (dimethylsiloxane)

Porous separation membrane Copoly (acrylonitrile / styrene) 32% / 68% by weight, mass polymerized

Gas supplied Air

Enriched gas (permeate) And

Coating methods A

Coating material, determined internal separation factor0 2.3

• U

Separation factor0 of porous separation membrane And above Ng 3.6

Multi-component membrane separation factor13 And over Ng 4.9

(a) As explained in Table XVI

b) As footnote e in Table I

Examples 52-57

Examples 52 to 57 illustrate several multicomponent type membranes in hollow fiber form. The porous hollow fibers can be made by wet spinning, as generally described below. The fiber of polycarbonate from Examples 52 and 53 was spun into a wet jet from a liquid of 27.5 weight polycarbonate in N-methyl-pyrrolidone in a water coagulant at 25 ° C at a rate of 21.4 mpm. The hollow fiber of polysulfone of Example 54 was spun from a 27.5 wt. Polysulfone (P-3500) liquid in a mixed 80/20 dimethylacetamide / acetone solvent in a water coagulant at 2 ° C at a rate of 21 ° C. , 4 p.m. The acrylonitrile styrene copolymer fiber of Example 55 was spun from a liquid of 27.5 wt. Copolymer in a mixed solvent of 80/20 dimethylformamide / formamide in a water coagulant at 3 ° C at a rate of 21.4 mpm. The copolymeric fiber of acrylonitrile styrene of Examples 56 and 57 was spun from a liquid of 25 wt. Copolymer in the same mixed solvent as in Example 55 in a water coagulant at ca. 20 ° C at a rate of 21.4 mpm. The results of the multicomponent hollow fiber experiments in separating a hydrogen / carbon monoxide gas mixture are given in the following Table XII.

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This example illustrates a multi-component multi-coating membrane to obtain a desired separation factor. A porous hollow fiber separation membrane consisting of a copolymer of 63% acrylonitrile and 37% styrene was wet spun from a solution of 27.5% by weight copolymer in a mixed solvent of 93/7 dimethylformamide / formamide in 2 ° C water with a speed of 21.4 mpm. This fiber was first treated by dipping into methanol while drawing a vacuum on the bore after which it was dried and the methanol treatment and drying repeated. The dried substrate fiber was then coated using Method D with poly (cis -isoprene) in pentane solvent, cured for 30 minutes at 85 ° C and then coated with 10% solution of Sylgard 184 in pentane using Method F. coated substrate was then again coated with the poly (cis-isoprene) solution, dried and again coated with the Sylgard 184 solution, and then cured for 30 minutes at 90 ° C, 30 minutes at 100 ° C and finally 30 minutes at 105 ° C. The results of the experiments with the uncoated, porous and the multi-layer coated membrane of the multicomponent type are given in Table XIII.

TABLE XIII

Coating material, determined Cis-isoprene 3.5 internal separation factor, Sylgard 184 1.9

H2 over CO

Separation factor, Hv, above CO, of ^ porous separation membrane, 1

Separation factor, Hp over CO, of multi-component membrane type 82

Permeability for Hp of membrane _7 of the multi-component type 6; 5 x 10

Permeability for Hp of porous - (- separation membrane 2.65 x 10

Determined internal separation factor,

Hp over CO, of material of 320 porous separation membrane EXAMPLES 59 and 60 83 148735

Examples 59 and 60 illustrate multicomponent-type membranes which use a porous brominated poly (xylylene oxide) separation membrane in hollow fiber form with a coating. The hollow fibers were spun wet from a liquid of 30 wt% polymer in N-methylpyrrolidone in a water coagulant at 85 ° C at a rate of 14.8 mpm. In Example 59, the brominated poly (xylylene oxide) is coated, wherein the bromination is essentially carried out on methyl groups without any post-spinning treatment. In Example 60, the brominated poly (xylene oxide) is post-treated by allowing it to be soaked for 20 hours in a solution of 10% trimethylamine in water. The coating in each case was Dow Corning Sylgard 184 silicone rubber applied by Method B (see Table XVI). The results are shown in Table XIV below.

TABLE · XIV

59 60

Dow Coining Syl- Dow Corning Sylgard 184 post yard 184 post-vulcanized vulcanized silicone rubber silicone rubber

Brominated poly (xybrominated poly (xylylene oxide) lylene oxide) after treatment with (ch3) 3n

Coating material, determined internal separation factor, 1.9 1.9

H2 over CO

Separation factor, H2 over CO, of porous separation membrane 1.48 2.85

Separation factor Hp over CO, of multi-component membrane type 11.1 9.59

Multi-component membrane permeability Hp 9.58 x 10 "^ 1.27 x 10" -3

Permeability for Hp of porous separation membrane 1.25 x 10 ”· 3.83 x 10” -5

Determined internal separation factor, Hp over CO, for material 34 axial porous separation membrane EXAMPLE 61 148735 84

This example illustrates a multicomponent type membrane utilizing another porous separation membrane of modified brominated poly (xylylene oxide) in the form of hollow fibers. The hollow fiber of brominated poly (xylylene oxide) of Example 59 was post-treated by soaking it for approx. 70 hours at 50 ° C in a solution of 5 weight -? *! thiourea dissolved in a 95/5 volume water / methanol mixture. After drying, the hollow fiber membrane was coated with a 5% solution of Dow Corning Sylgard 184 in pentane by Method F (see Table XVI). Examination of the post-treated hollow fiber porous separation membrane and of the multicomponent type coated membrane showed the following results:

Coating material, determined internal separation factor, H2 over CO 1.9

Separation factor, Ho over CO, of porous separation memorandum 5; 6

Separation factor, H2 over CO, of multicomponent membrane type 46.1

Permeability for H2 of multi-component membrane 7.2 x 10-0

Permeability for Hp of Porous Separation Membrane 3.9 x 10 5

Determined internal separation factor, H2 over CO, for material of porous ^ 150 'separation membrane Examples 62 and 65

These examples serve to illustrate the flexibility of the invention where the coating may be present on the inner surface and both on the inner and outer surfaces of a hollow fiber separation membrane.

They also illustrate the invention in connection with a process in which the gaseous stream of feed material is contacted with the multi-component membrane type surface which is opposite to the coating. In Example 62, a porous hollow fiber polysulfone separation membrane was coated on the inside with a 3% solution of Sylgard 184 post-vulcanized silicone rubber in pentane by slowly pumping such a solution through the bore of the hollow fiber substrate and allowing the fiber to dry in the air. The permeability was determined by migrating an H2-CO mixture from the exterior to the bore of the resulting composite membrane. In Example 63, the fiber of Example 85 was coated with a further bore with the same solution of Sylgard 184 by Method F. The results of examining multicomponent type membranes are given in the following Table XV.

TABLE XV

62 65

Dow Corning Syl- Dow Corning Syl- gard 184 post-farm 184-post-vulcanized silicon vulcanized silicone pump. liconegummi_

Polysulfone3 (only Polysulfona (borehole overbore and outer coated) they coated)

Coating material, determined internal separation factor, H2 over CO 2.5 2.5

Separation factor, H «over CO, of porous separation membrane 3.23 3.23

Separation factor, Hp over CO, of membrane of 22.0 21.2 multicomponent type

Permeability for Hp of ς ς multi-component membrane 5.6 x 10 "5 2.31 x 10" -7 type

Permeability for Hp of po-,.

(a) Polysulfone, Union Carbide, P-3500, wet spun from a 30 wt. liquid into a 50/50 dimethylformamide / N-methylpyrrolidone solvent mixture in water at 2 ° C at a rate of 21.4 mpm and after washing and stretching recorded at 33 mpm.

EXAMPLE 64

This example illustrates a method for producing a hollow fiber multicomponent type membrane using a porous separation membrane of polysulfone and a coating of Sylgard 184. Polysulfone polymer (P-3500 from Union Carbide) is dried at 100 ° C. lands a pressure of 125 mm Hg for approx. 25 hours. The dried polysulfone is mixed at a temperature of approx. 65 to 70 ° C with dimethyl acetate amide (moisture content below about 0.1% by weight) to provide a solution containing 27.5% by weight polysulfone. The solution is transported to a holding tank having a nitrogen atmosphere of approx. 1.4 kg / cm.

86 148735

The solution is not heated while in the holding tank and can thus be cooled to ambient temperature.

The polymeric solution is pumped from the holding tank to a hollow fiber spinning nozzle immersed in an aqueous bath at a temperature of approx. The spinning nozzle has an outer diameter of the opening of 0.0559 cm, an inner needle of 0.0229 cm and an injection opening in the needle of 0.0127 cm. The polymeric solution is pumped and dosed to the spinning nozzle at a rate of approx. 7.2 ml per minute and withdrawn from the spinning nozzle at a rate of approx. 33 m per minute. The polymeric solution coagulates in the form of a hollow fiber upon contact with the aqueous bath. Through the injection orifice of the spinning nozzle, distilled water is provided to coagulate the inside of the hollow fiber. The fiber passes through the aqueous bath at a distance of approx. An amount of the aqueous bath is continuously purified to maintain a concentration of dimethylacetamide of less than ca. 4% by weight in the bath.

The fiber is then immersed in a secondary aqueous bath maintained at a temperature of approx. 4 ° C at a distance of approx. After leaving the secondary aqueous bath, the fiber contains some dimethylacetamide.

The fiber from the secondary aqueous bath is immersed in two additional aqueous baths at room temperature, each at a distance of approx. 5 m, and the fiber is wound on a coil, just under enough tension to produce the coil. The fiber is kept wet with water during rewinding, and after rewinding, the coil is immersed in a water container and stored at room temperature. Then, the fiber is dried to the ambient temperature, preferably at ca. 20 ° C and 50% relative humidity. The dried fiber is then coated with a solution of approx. 5% dimethylsiloxane-containing prepolymer of silicone rubber (Sylgard 184 from Dow Corning) and a curing agent in n-pentane. Application of the coating is accomplished by immersing the fiber in the prepolymer solution while holding the solution to a positive pressure. The fiber is air dried and crosslinked to provide the coating with silicone rubber.

Table XVI Coating Methods A. The hollow fiber porous membrane was immersed ± undiluted, liquid coating material. The excess liquid was allowed to drip.

B. The hollow fiber porous membrane was dipped in undiluted liquid coating material while exposing the bore of the porous hollow fiber to a vacuum. After the fiber was removed, the vacuum was cut off and excess liquid was allowed to drip.

C. The hollow fiber porous membrane was dipped in liquid coating material diluted with hydrocarbon solvent. The solvent was evaporated.

D. The hollow fiber porous membrane was dipped in liquid coating material with a hydrocarbon solvent while exposing the hollow fiber to a vacuum. After the fiber was removed, the vacuum was quenched and the solvent was evaporated.

E. The hollow fiber porous membrane was dipped in a solution containing coating material in the form of a polymerizable prepolymer, the appropriate curing agent and hydrocarbon solvent.

The solvent was evaporated and the membrane prepolymer cured in situ.

F. The coating method was carried out as described under E, except that the hollow fiber bore was exposed to a vacuum while dipping it into the coating solution.