NL8005307A - METHOD FOR CUTTING HOLLOW FIBER MEMBRANES; PERMEATOR. - Google Patents

Abstract

For severing a plurality of hollow fiber membranes comprised of thermoplastic material which membranes are arranged in the form of a bundle and also sealing the bores of the membranes in an essentially fluid-tight manner without any significant decrease in membrane performance or strength, a heated member is passed through the bundle in a path transverse to the orientation of the hollow fiber membranes wherein the temperature of the heated member is above the melt temperature of the hollow fiber membranes. Advantageously, the hollow fiber membranes which are severed have a significant void volume and may be anisotropic with a thin, dense skin. The heated member can be a hot wire or ribbon.

Description

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Method for cutting hollow fiber membranes permeator.

The invention relates to methods useful for the manufacture of permeators containing hollow fiber membranes for the separation of at least one fluid from a fluid mixture containing at least one other fluid. More particularly, the invention relates to cutting methods by which multiple hollow fiber membranes arranged in the form of a bundle are cut and the ends of the bores of the hollow fiber membranes are also sealed in a fluid-tight manner.

Hollow fiber membranes are often advantageous for use in permeators because of the relatively large membrane area that can be realized per unit volume of the permeator. In addition, hollow fibers can be self-supporting and withstand high pressure differences across their walls. The use of large pressure differences is very attractive in many separating operations, e.g. ultrafiltration, reverse osmosis, separation of gas mixtures and the like, in order to realize greater permeation driving forces and thereby provide a greater flow through the membranes.

Hollow fiber membranes containing permeators are usually characterized by means that prevent fluid communication between the supply side and the discharge side for permeate from the membranes except through the walls of the hollow fiber membranes. Generally, at least one end of each of the hollow fiber membranes in the permeator is contained or embedded in a substantially fluid-tight manner in a tube sheet, so that the bore of the hollow fiber membrane through the tube sheet is in fluid communication. The tube sheet is often in a substantially fluid tight relationship with a vessel containing the hollow fiber membranes so that fluid on the outside of the hollow fiber membranes does not pass to the side of the 8005307-2 bores than through the walls of the hollow fiber membranes. The other end of each of the hollow fiber membranes also has a substantially fluid-tight relationship between the exterior and the bores of the membrane. The desired relationship can be achieved by embedding the end of the hollow fiber membrane into a tube sheet, which may be a separate tube sheet or may also be the same tube sheet in which the other end of the hollow fiber membrane is embedded. On the other hand, the other end of the hollow fiber membrane may be sealed in a substantially fluid-tight manner. This sealed end is hereinafter further referred to as the plug end. In this description, further permeators, in which each end of the hollow fiber membranes is embedded in a separate tube sheet, will be referred to as double-ended permeators and permeators in which only one end of each of the hollow fiber membranes is embedded in a tube sheet, or in which both ends of the hollow fiber membranes embedded in the same tube sheet will be referred to as single-ended permeators.

It is desirable that the manufacture of tube plates and in single-ended permeators the plug end not adversely affect the strength or separation behavior of the hollow fiber membranes. Hollow fiber membranes, especially anisotropic membranes with a thin dense skin or barrier layer, supported by a more open wall structure, can be fragile. Therefore, pipe sheet and plug end manufacturing procedures should minimize the risk of damaging the hollow fiber membranes. The damage that may occur to the hollow fiber membranes can be observed as a decrease in the selectivity of the membrane or a weakening of the structure of the hollow fiber membrane so that the ability to use the preferably large differential pressures may decrease . Moreover, these manufacturing procedures should preferably be carried out quickly, easily and without too much expertise on the part of the manufacturer.

An operation usually required in the manufacture of permeators is e.g. cutting a bundle of hollow fiber membranes. 80 0 5 30 7 * * - 3 - s. This cutting can be done with a sharp knife, eg a razor. However, the pressure applied during cutting of hollow fiber membranes can damage the areas of the membrane near the cutting zone. In addition, with bundles containing multiple hollow fiber membranes, the likelihood that multiple cutting motions are required to cut through all hollow fiber membranes in the bundle increases and more pressure during cutting is required to accelerate the cutting movement. Therefore, the risk of damaging the hollow fiber membranes can also increase. Other drawbacks may also result from the use of sharp blades for performing the cutting operation. The use of a knife can e.g. present a risk of injury to the manufacturer. Furthermore, hollow fiber membranes cut with a sharp knife blade generally have open bores. Therefore, when the tube sheet is to be formed after the hollow fiber membranes have been cut, means must be used to prevent the material forming the tube sheet from being drawn into the bores of the hollow fiber membranes by capillary action. Typically, applying a cement, wax or other removable material 20 to the ends of the hollow fiber membranes prior to the formation of the tube sheet is to prevent filling of the bores of the hollow fiber membranes with the material of the tube sheet. The end of the tube sheet can be removed so that the bores of the hollow fiber membranes are exposed. This technique requires 25 additional operations (e.g. applying cement or liquefied material to the end of the bundle), which requires manpower and handling, which could increase the risk of damaging the hollow fiber membranes.

Alternatively, the bundle could be formed with looped hollow fiber membranes, so that a single continuous hollow fiber forms many lengths in the bundle, i.e., the hollow fiber membranes are in the form of strands. Although the ends of the bundle are closed by this technique, the loop configuration of the hollow fibers to form the strands may cause stresses that can damage the hollow fiber membranes, and damage the hollow fiber membranes. Can be difficult to obtain a desired population distribution of the hollow fiber membranes in the tube sheet. An uneven population distribution of the hollow fiber membranes can lead to poor distributions of fluid in the permeator outside the hollow fiber membranes during the separation operations.

In that case, local areas within the permeator may have little fluid flow while other areas have such a great fluid flow that e.g. when the feed to the permeator is fed to the exterior of the hollow fiber membranes, a significant portion of the feed can pass through the permeator without separation.

In single-ended permeators, the plug end of the bundle can be formed by looping the hollow fiber membranes or by plugging the open ends of the hollow fiber membranes. Bundles in which the plug end is formed by looping the hollow fiber membranes can lead to uneven population distribution and / or cause stress on the hollow fiber membranes that can damage the membranes. The problem of stresses on the looped 2Q portion of the hollow fiber membranes can be further exacerbated when the bundle is designed to accurately fit into the permeator shell to allow fluid to pass between the bundle and the vessel in which the bundle is located , to prevent.

The plug end is thus typically formed by embedding the ends 25 of the hollow fiber membranes in a material to be fixed. Although this procedure leads to good closure of the hollow fiber membranes at the plug end with greater reliability, the actions associated with embedding the hollow fiber membranes in a material to be affixed may increase the risk of damaging the membranes. Furthermore, the casting and solidification operations to form the plug end may require a long time, i.e., one or several days, before they are completed.

Since the hollow fiber membranes in a bundle often vary in length 35, it may be desirable to trim the bundle such that the hollow fibers are of substantially the same length, allowing further treatment of the bundle when manufacturing of the permeator is facilitated. In these cutting operations and possibly other cutting operations, small pieces of hollow fiber membrane waste can be obtained. It can be difficult to keep the workspace free of these waste particles, and any waste particles trapped in the bundle can give rise to stresses on the hollow fiber membranes during permeator manufacturing operations, which stresses have a detrimental effect on the membrane. can exercise.

Therefore, alternatives to cutting knives with sharp knives to manufacture the permeators have been sought, with a minimum number of treatment steps and minimal application of pressure or stresses that can adversely affect the hollow fiber membranes.

The use of heat to cut textile fibers has been proposed. For example, according to Central Patents Index, published by Derwent Publications, Ltd., September 8, 1973, accession No. 42798u from Japanese Patent Publication 7325005, a method of manufacturing hollow staple fibers by a sheathing hollow fiber with a hot cut is known. instrument, the temperature of the hot cutting instrument being higher than the melting point of the inner hollow fiber material, but lower than the melting temperature of the casing material. It has further been noted that the resulting hollow staple fiber has sealed ends and therefore the penetration of soil into the hollow fiber is eliminated without losing the benefits [apparently excellent insulating properties and light weight] of hollow fibers.

However, the requirements for cutting and sealing hollow fiber membranes are much more demanding than for the case of manufacturing hollow staple fibers for textile applications.

For example, a hollow fiber membrane serves after being cut to maintain its strength so that it is able to withstand advantageous pressure differentials for separation operations. Breaking even a Λ λ A C Ύ Λ 7 - 6 - pair of hollow fiber membranes during the separating movements Can significantly affect the selectivity achievable with the permeator. In addition, the seal formed by sealing the end of the hollow fiber membrane must be substantially fluid-tight, especially when the seal provides the plug end. The plug end preferably exhibits at least as much strength as the hollow fiber membrane. Also, the plug end of each of the hollow fiber membranes in a permeator preferably serves in a substantially fluid-tight manner. 10 because the existence of even a pair of open hollow fiber membranes can significantly affect the selectivity achievable by the permeator. While techniques are available to circumvent the impact of these punctured hollow fiber membranes, repair can be difficult, time consuming, and often lead to a loss of available membrane area.

On the other hand, hollow staple fibers do not have to tolerate pressure differences as are often used in separation operations. In addition, the presence of broken hollow staple fibers or punctured hollow staple fibers will have no consequences with respect to their intended use.

The use of heat and pressure to repair permeators with punctured hollow fiber membranes has been proposed in U.S. Patent 3,968,192. In the proposed method, the punctured hollow fiber membrane is traced in a set of many hollow fiber membranes embedded in and extending through a tube sheet of fusible resin. The face of the tube sheet is heated in the immediate vicinity of the location of the punctured hollow fiber and pressure is applied to the heated area with the aid of a rod-shaped member. This repair operation can be performed using a small-tip electric soldering gun. The pressure exerted by the rod-shaped member is apparently at least to some extent axial to the orientation of the hollow fiber membrane. Therefore, one would expect the rod-shaped member to flow the molten material of the hollow fiber and possibly the tube sheet into the bores of the hollow fiber membrane causing clogging.

The invention now provides methods of cutting many hollow fiber membranes, which are arranged in the form of a bundle, and also sealing the bores of these hollow fiber membranes in a substantially fluid-tight manner. The methods of the invention can be easily performed and process cutting and sealing the hollow fiber membranes in just one operation. In addition, the hollow fiber membranes are subjected to a minimum amount of treatments in these processes and the membranes need not be subjected to pressures during cutting and sealing, which treatments and pressures may give rise to a risk of damage to the hollow fiber membranes . The methods of the invention can be relatively non-complex and do not require great skill in obtaining cut and sealed membranes in which substantially all of the hollow fiber membranes in the bundle are sealed in the desired, substantially fluid-tight manner. The cutting and sealing of hollow fiber membranes according to the invention can therefore often be easily performed without any significant deterioration of the membrane properties or strength. Furthermore, the methods of the invention can be performed relatively safely.

In the methods of the invention, many thermoplastic material comprising hollow fiber membranes are arranged in the form of a bundle; a heated member is passed through the zone along a path transverse to the orientation of the hollow fiber membranes, the heated member having a temperature above the melting temperature of the hollow fiber membranes and passed through the zone at a sufficiently high speed to cutting and sealing the bores of the hollow fiber membranes to be processed in a substantially fluid-tight manner; and the beam next to the path of the heated member is held in substantially desired cross-sectional configuration as the heated member passes through the beam. Preferably, at least a portion of the hollow fiber membranes in the zone adhere to adjacent hollow fiber membranes after cutting due to melting and softening of the thermoplastic material of the hollow fiber membranes during cutting and sealing. When a significant portion of the hollow fiber membranes adhere together

Cd i.e. the ends of the hollow fiber membranes are glued together), the cut end of the bundle may practically maintain its cross-sectional configuration without external support. Because often adjacent hollow fiber membranes are glued together as a result of cutting, waste from e.g. trimming operations are in the form of agglomerated high fiber particles, thereby facilitating removal of residues from the work areas.

According to a preferred aspect of the present method 15, the hollow fiber membranes which are cut and sealed have walls with a significant void volume. Voids are areas in the walls of the hollow fiber membranes that do not contain material of the hollow fiber membranes. Therefore, when voids are present, the density of the walls of the hollow fiber membranes is less than the density of the mass of hollow fiber membrane material.

According to the invention it has been found that hollow fiber membranes with walls with a considerable void volume are often easier to cut and seal than hollow fiber membranes of the same material and dimensions of the bores but with denser walls. In addition, even when the hollow fiber membranes are anisotropic with thin and very fragile dense skins (especially external skins), cutting and sealing can be performed without affecting the membrane properties or strength. Often the void volume according to this aspect of the invention is about 20-80, usually about 30-70%, based on the surface volume, i.e. the volume within the gross dimensions of the hollow fiber membrane walls.

Since the cutting and sealing operations are performed almost simultaneously by passing the heated member 35 through the beam, there is little chance that expertise will affect the cutting and sealing operations. In addition, it may be that only a minimal amount of time is required in a manufacturing procedure for cutting and sealing the hollow fiber membranes, thereby increasing the efficiency of the permeator manufacturing operation. Furthermore, the cut and sealed bundle of hollow fiber membranes is available almost immediately for further processing to produce a permeator. It is an advantage that these advantages can be realized with the aid of relatively non-complex, and therefore inexpensive, cutting equipment.

Any suitable heated member can be used in the methods of the invention. The heated member need not be sharp because the heat emitted from the heated member essentially effects cutting. Therefore, preferably suitable heated members may even be blunt and have a radius of curvature of up to 0.5 mm or more. Suitable heated members include wires, tapes (including non-braided as well as braided or helically wound tapes), blades, bars, rods and the like.

20 '* The heated member may be preheated only or may be heated during cutting, e.g. by electrical resistance. Preferably, if the heated member is only preheated, sufficient heat must be retained in the heated member to effect the cutting and sealing of substantially all of the hollow fiber membranes in the cutting region in a single pass. Otherwise, multiple passes of the heated member in the bundle may be required to accomplish the desired cutting and sealing. The use of such multiple passes may increase the risk that bumps of the hollow fiber membranes may not be sealed as desired, while further increasing the time and effort required to cut and seal the hollow fiber membranes. When the heated member is heated only before cutting, it is desirable that it be sufficiently large in terms of its heat capacity so that sufficient heat is available to cut and seal nearly 80 0 5 30 7 - 10 all hollow fiber membranes in the cutting area. Although less suitable, the zone of the hollow fiber membranes can also be cut a little each time.

Preferably, the heated member is heated during cutting. Any suitable means can be used to provide heat to the heated member during cutting. In such heated members, usually enough heat is produced during cutting to effect cutting and sealing. The cutting and sealing can therefore be realized in a single pass. The dimensions of the cross-section and heat capacity of the heated member need not then be as important a consideration as in the case where the heated member is heated only before cutting.

The heated member can be heated by any suitable means. The heat can e.g. are supplied to the heated member in an area remote from the area passing through the bundle of hollow fiber membranes, the heat being transferred through the heated member. A particularly attractive and suitable means for heating the room

heated member during cutting is the application of an electric current through the heated member, the heated member consisting of an electrical resistance material such as a TM

Nichrome alloy phene nickel, chromium and iron containing empty ring). When using an electric current which flows through the heated member as a means of generating heat, it is usually preferred for safety reasons that relatively low voltages be used. The cross-sectional area of the heated member should therefore be adequate to allow generation of sufficient heat and temperature to cut and seal the hollow fiber membranes at these lower voltages.

The heated member must have a temperature above the melting temperature of the hollow fiber membranes. If the temperature BraTure is too low, the bores of the hollow fiber membranes 8005307 will not be sealed in the desired fluid tight manner. The maximum temperature that can be used if desired depends, of course, on the materials of which the hollow fiber membranes are composed. The temperature of the heated member should not be so high that the material of the hollow fiber membranes deteriorates, thereby significantly decreasing the strength of the hollow fiber membrane. Sometimes, however, the material of the hollow fiber membrane, which contacts or is very close to the heated member during cutting, can deteriorate.

While such deterioration may not adversely affect the hollow fiber membranes, adequate ventilation may be required to remove harmful vapors that could be generated during cutting. Cutting can be done in an inert atmosphere to minimize deterioration; in many cases, however, the cutting can be performed in the air without adverse effects.

Also, with certain thermoplastic materials, when the temperature of the heated member is too high, the hollow fiber membranes can become tacky or tacky, and cutting the hollow fiber membranes becomes more difficult.

The temperature of the heated member will be determined in part by the melting temperature and the flow properties of the material of the hollow fiber membranes. Because the hollow fiber membranes often comprise amorphous polymer, it can be difficult to accurately determine the polymer melt temperature. In addition, depending on the properties of the polymer melt, the minimum temperature above the polymer melt temperature required to process cutting and sealing may vary. Generally, however, the temperature of the heated member is preferably at least about 10 ° C, more preferably at least about 50 ° C, and usually at least about 100 ° C above the melting temperature of the hollow fiber membrane.

The melting temperature used here is the temperature at which the hollow fiber membrane leaves a liquid trace when it is advanced over a temperature gradient bar. Often, the temperature of the heated member, at least before the cutting and sealing operation is started, is at least about 650 ° C or 700 ° C, and sometimes about 700-950 ° C or 1000 ° C. In general, for any given hollow fiber membrane, the heated member can be used within a wide range of temperatures, with appropriate cutting and sealing being achieved.

Since measuring the temperature of the heated member often requires devices such as pyrometers, which are not readily available and can be extremely difficult to accurately determine the temperature of the heated member during cutting, a suitable method for determining whether the heated member has reached a suitable temperature to cut a narrow bundle of hollow fiber membranes. When the heated member readily passes through the beam and melting is observed, the heated member is likely to be a suitable temperature for cutting and sealing, otherwise the temperature should be increased. When an unacceptable deterioration of material in the hollow fiber membrane or adhesive phenomena is observed, the temperature of the heated member should preferably be reduced or if the deterioration is due to combustion, an inert atmosphere may be desirable.

The cutting of the hollow fiber membranes of the invention is believed to be caused by the melting of the thermoplastic material of the hollow fiber membrane in the zone through which the heated member is passed. The thermoplastic material of the hollow fiber membranes located immediately adjacent to the heated member is often sufficiently liquid that the thermoplastic material can flow into the bores of the hollow fiber membranes by capillary action and / or under the influence of gravity, as a result of which the desired seal is obtained. Therefore, exertion of an axially applied pressure to promote such flow and sealing (i.e., a pressure applied to a surface adjacent to the ends of the hollow fiber membranes) is advantageously not required. It is believed that at least in some cases, the heated member 80 need not be in contact with the hollow fiber membranes to effect cutting and sealing. In other instances, the heated member can promote movement of the molten thermoplastic material thereby closing the bores. Often it has been found that the choice of material of the heated member need not be limited to only those materials which are not easily wetted by the material of the hollow fiber membranes,

The speed at which the heated member is passed through the bundle 10 is such that the bores of the hollow fiber membranes are sealed in a substantially fluid-tight manner. When the heated member is passed through the beam too quickly, there will be a tendency for at least some bores to remain open. Often when the heated member is at a higher temperature, it will be possible for the heated member to pass through the beam more quickly than at lower temperatures. Also, in many cases, the heated member can be passed through the bundle more quickly when the hollow fiber membranes have a significant void volume than when the hollow fiber membranes are denser and have substantially the same bore size and polymer mass per unit length.

Usually, the heated member is passed slowly through the beam, i.e. at a rate of less than about 50 cm per minute, usually at a rate of less than about 10 cm per minute. The heated member often passes relatively easily through the beam, which means that the cutting of the hollow fiber membranes is primarily caused by the heat from the heated member. In most cases, the passing of the heated member through the bundle is slow enough to create an apparently distinguishable zone indicative of melting of the thermoplastic material comprising the hollow fiber membranes. Typically, similar zones are visible on both sides of the heated organ path. The heated member is preferably passed through the beam at such a rate that the zone preceding the heated 8005307-14 member is approximately the same thickness as the zones on either side of the pad. Usually the diameter of the zone is at least about 0.1, e.g. at least about 0.25 times the diameter of the hollow fiber membrane, and sometimes this thickness is about 0.2 to 10 ', preferably about 0.5-5mm, Once 8 and suitable speed for passing the heated member determined by the bundle, a mechanized one can, of course, e.g. motorized drive means are used to move the heated member through the bundle 10 at the predetermined speed. The cutting and sealing can therefore be carried out on a very reliable basis.

The hollow fiber membranes are cut transverse to the longitudinal orientation of the hollow fiber membranes. Because some methods of the invention do not require pressure perpendicular to the cross section of the hollow fiber membranes. applied to process the sealing of the bores of the hollow fiber membranes, great flexibility is provided in the shape of the cut end. The end of the bundle may e.g. be substantially flat and perpendicular to the longitudinal orientation of the hollow fiber membranes, or angled with the orientation of the hollow fiber membranes. Alternatively, the end of the beam may be curved, i.e., convex, concave, or both, or hemispherical, conical, or any other suitable shape. Typically, it is preferred that the end of the bundle be substantially flat and perpendicular to the longitudinal orientation of the hollow fiber membranes for ease of manufacture.

Preferably, the hollow fiber membranes are nearly dry (eg, the membranes contain less than about 5, preferably less than about 1-2 wt% liquid) during cutting so that the heat from the heated member is used for cutting and sealing and not for evaporation of liquid such as water.

Sometimes it may be desirable to ensure that substantially all of the hollow fiber membranes are sealed and bonded together at the cut 8005307-15 end of the bundle. Although virtually all bores of the hollow fiber membranes are sealed during cutting, it may be desirable to apply heat and apply axial pressure to the ends of the 5 hollow fiber membranes if necessary so that the hollow fiber membranes at the end of the bundle are bonded together and closure of almost all bores is ensured, preferably the ends of the hollow fiber membranes are heated to a temperature above the melting temperature of the hollow fiber membrane, and the pressure (if used) applied while the thermoplastic material is melted to join the ends of the hollow fiber membranes. Care should be taken to ensure that no unacceptable damage is done to the hollow fiber membranes. When an axially applied pressure is required, usually a relatively low pressure will be sufficient to allow sufficient flow of the thermoplastic material to join the ends of the hollow fiber membranes together in the bundle. Preferably, the pressure is applied through a surface that is continuously heated, e.g. by electrical resistance that generates heat at the surface or by conduction of heat to the surface. Very suitable surfaces for joining the ends of the hollow fiber membranes are flat top soldering irons, flat bands of electric resistance

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material such as Nichrome, and the like.

Typically, the ends of the hollow fiber membranes will be easily joined during the cutting of the bundle. This joining together can significantly reduce the ability of liquids to pass between the hollow fiber membranes at the end of the bundle. When embedding the end of the bundle in a resin mass for e.g. for example, forming a pipe sheet is e.g. required that the liquid resin mass pass through the end of the bundle of hollow fiber membranes into the area to be embedded in the resin mass. When the cut end of the bundle is strongly glued together, virtually all of the resin mass fed into the bundle must enter from the sides of the bundle. Therefore, there is a high risk that the resin mass will not be sufficiently uniformly distributed across the cross section of the hollow fiber membrane bundle, especially in the interior or middle regions of the hollow fiber membrane bundle.

There is a technique for improving the openness between the hollow fiber membranes at the end of the bundle. According to this technique, an insertion member is placed in the bundle of hollow fiber membranes at the cut zone to act as a barrier to joining the hollow fiber membranes during cutting. The cutting element also cuts the icing member, e.g. by scorching, melting, or pressure.

After cutting, the insert can be removed and left in the hollow fiber bundle if desired. The insertion member thus provides fluid passageways at the end of the beam, e.g. facilitate permeation of a liquid resin material at the end of the bundle to form a tube sheet or plug end, while the passages also improve fluid distribution within the bundle during a fluid separation operation.

The hollow fiber membranes at the zone through which the heated cutting member is to be passed are preferably arranged and held during cutting in substantially the desired cross-sectional configuration for the bundle when it is incorporated into a permeator. It is understood that any manipulation of the cut end configuration of the bundle containing joined membranes may increase the risk of damage to the hollow fiber membranes and should therefore be avoided. The zone through which the heated member passes during cutting can be maintained in the desired cross-sectional configuration by any known means. For example, if the cross-sectional configuration of the beam is to be circular, e.g. sufficient support to maintain the desired configuration of the bundle at the zone is provided by encasing or tying the bundle at 80 0 5 30 7 - 17 site from near the zone. On the other hand, rigid supports for holding the bundle in a desired configuration may be provided on one or both sides of the zone. With bundles that have small cross sections or where significant tolerances in the cross-section configuration are acceptable, the cross-section configuration of the bundle at the zone to be cut can be sufficiently maintained by hand.

The methods of the invention can be used to cut and seal bundles of a wide variety of cross-section configurations and sizes. The cross-sectional configuration Can be circular, oval, polygonal (e.g. rectangular, square, trapezoidal, etc.), or free-form. The maximum size of the cross section of a bundle Can be up to 1 m or more. The methods according to the invention can also be used for cutting test beams, e.g. bundles containing only 5 or 10 hollow fiber membranes. Bundles with circle-shaped cross-section configurations are usually preferred for use in permeators and often have cross-section diameters of e.g. about 0.02 or 0.05 to 0.5 or 1 m.

The methods of the invention may be useful for cutting and sealing bundles with a wide variety of packing factors of the hollow fiber membranes. A packing factor as used herein is the percentage of a given cross-sectional area occupied by hollow fiber membranes (including the area occupied by the bores of the hollow fiber membranes). The packing factor, based on the internal cross-sectional dimensions of the permeator shell and the cross-sectional area of the hollow fiber membranes, is preferably at least about 35, most preferably about 40 or 45 to 50 or 60%. The packing factor, based on the internal dimensions of the permeator jacket, may differ from the actual packing factor of the beam at the area to be cut. In many cases it may be desirable to compress the area to be cut laterally. This lateral compression can promote the joining of adjacent hollow fiber membranes at the end of the cut bundle.

q λ η ς vn 7 - especially when the hollow fiber membranes are sufficiently joined together at the cut end and the end retains its cross-sectional configuration without outside support, the lateral compression permits insertion of the bundle of hollow fiber membranes into a permeator jacket or in a mold for casting eg a pipe sheet, easy. Usually the actual gasket. factor of the bundle at the zone to be cut based on the external dimensions of the bundle at the zone through which the heated member is to be passed, sufficiently high that almost all hollow fiber membranes contact other hollow fiber membranes in the zone stand. Often the actual packing factor of this zone is at least about 45% and it can range up to 70 or more%, e.g. from about 50 - 65%.

The hollow fiber membranes can have any suitable cross-sectional configuration, although usually the hollow fiber membranes are circular with a concentric bore. The methods of the invention are suitable for cutting hollow fiber membranes with a wide range of diameters. However, the hollow fiber membranes preferably have a sufficient wall thickness to provide sufficient strength during the intended separation movement. Often the outside diameter of the hollow fiber membranes is at least about 20, preferably at least about 50 µm, and hollow fiber membranes of equal or different outside diameter may be present in a bundle. Often D <= the external diameters carry up to about 800 or 1000 µm. Preferably, the outer diameter of the hollow fiber membranes is about 50-800 µm, most preferably about 150-800 µm. Generally, the wall thickness of the hollow fiber membranes is at least about 5 µm, and in some hollow fiber membranes, the wall thickness can be up to about 200 or 300 µm, say about 50-200 µm. The internal diameter (bore diameter) of the hollow fiber membranes is preferably less than about 500 µm, e.g. about 50-500 ym, most preferably about 50-300 ym.

The methods of the invention are useful for cutting and sealing hollow fiber membranes that have solid walls, as well as hollow fiber membranes with walls that have a significant volume of 80. The hollow fiber membranes can be isotropic or anisotropic.

The bores of the hollow fiber membranes are preferably barely obstructed. Cutting the hollow fiber membranes 5 according to the invention serves to bar the bores of the hollow fiber membranes only at the cut end of the bundle. Often the thickness of the material that closes the bores of the hollow fiber membranes is at least about 25 or 50, say at least about 75 or 100 to about 1000 or 5000 µm.

The hollow fiber membranes can be made of any synthetic or natural material suitable for separating fluids or for supporting materials that process the separations between fluids. The hollow fiber membrane comprises thermoplastic material, and preferably the thermoplastic material makes up at least about 70 or 80 or more% by weight of the hollow fiber membrane. The choice of material for the hollow fiber membrane may be based on the heat resistance, chemical resistance, and / or chemical strength of the hollow fiber membrane as well as on other factors imposed by the intended separation of flu-ida for which it is used and the operating conditions where it will be subjected to.

Typical hollow fiber membrane materials include thermoplastic organic polymers or thermoplastic organic polymers mixed with inorganics, e.g. fillers, reinforcements and the like. Thermoplastic polymers suitable for hollow fiber membranes can be substituted or unsubstituted polymers, especially carbon-based polymers with carbon-carbon or carbon-oxygen backbones, and can be selected from polysulfones; polystyrenes, including styrene-containing copolymers such as acrylonitrile-styrene copolymers, styrene-butadiene copolymers, and styrene-vinylbenzyl halide copolymers; polycarbonates; cellulose polymers [thermoplastic]; polyamides and polyimides, including aryl polyamides and aryl polyimides; polyethers, polyCarylene oxides] such as polyCphenylene oxide], and polyClylene oxide); poly (ester amide diisocyanates); polyurethanes; art ft R 3 (1 7 - 20 - polyesters (including polyarylates), eg poly (ethylene terephthalate), poly (alkyl methacrylates), poly (alkyl acrylates), polyphenylene terephthalate), etc. polysulfide polymers of «C-ethylenically unsaturated monomers, other than those mentioned above such as poly (ethylene), poly (propylene), poly (butene-1), poly (4-methylpentene-1), polyvinyl compounds, eg 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-10 pyrrolidones), poly (vinyl ethers), poly (vinyl ketones), poly (vinyl aldehydes) such as poly (vinyl formal] and poly (vinyl butyral), polyivinyl amines), poly (vinyl phosphates), and poly (vinyl sulfates) j and poly (vinyl acetal) s polyallyl compounds? poly (benzafcsnztatdazoiDt polylhy-drazidenj polyoxadiazoles? polytriazolenj poly (benzimldazool)? poly-15 carbodiimides? polyfosfazinenj etc., and interpolymers, including blakinterpolymeren containing repeating units of the above types such as terpolymers of acrylonitrile-vinyl bromide-sodium salt of parasulfofenylmethallylethers? and grafted, and mixed materials containing one or more of the foregoing series Typical substituents for substituted polymers include halogens such as fluoro, chloro and bromo hydroxyl groups, lower alkyl groups, lower alkoxy groups, monocyclic aryl groups, low acyl groups and the like.

The invention is further elucidated by means of the examples.

Example I

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A size 24 Nichrome wire (3.5 ohms per 30.5 cm) was stretched between and attached to two bolts mounted on an electrically insulated arrangement. The bolts were about 6-8 cm apart. Each of the tap wires of a variable

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transformer (110 V) was connected to the Nichrome wire at a distance of about 4 cm. The room temperature resistance between the drain wires was about 0.5 ohms. About 1.5-2V was delivered to the wire through the transformer and the wire took on a red hot appearance.

8005307 - 21 - OAK from a group of 10 test bundles containing 10 anisotropic hollow fiber membranes with an outer skin, was held by hand and passed perpendicularly to the orientation of the hollow fiber membranes through the hot wire around the end portion of the 5 bundle to cut. The hollow fibers consisted of polysulfone

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(P-3500, available from Union Carbide Corporation), which had the recurring structure of the formula from the formula sheet. The hollow fibers had an outside diameter of about 450 µm, an inside diameter of about 150 µm, and a void volume of about 60%. The outer skin had a thickness of less than 0.5 µm and an open wall structure. In view of the cut end of the test bundle, no open bores could be observed by eye. The cut ends of the hollow fibers were found to be joined (or glued together).

Similar test bundles (three) were made for comparison purposes, except that the end of the bundle was cut with a razor blade and sealed with epoxy in a fluid-tight manner. The epoxy was in a glass tip.

The hot wire cut test bundles and the epoxy-coated test bundles were coated using a

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solution of 1% Sylgard 184 (a silicone available from Dow Corning Corporation) in isopentane for 10 minutes and then examined for hydrogen and methane permeability and rupture pressures under external load. These procedures were virtually repeated, except that the polysulfone hollow fibers had an outer diameter of about 560 µm and an inner diameter of about 250 µm. The results are shown in the following table.

30 8005307 - 22 -

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Example II

The procedure of Example I was substantially repeated, except that the hollow fiber membrane of a styrene / acrylonitrile copolymer containing 53% by weight of styrene had an outer diameter of about 540 µm / as well as an inner diameter of approximately

spring 340 µm and void volume of about 60%. Sufficient hollow fiber membranes were used to obtain a bundle with a packing factor of about 50% and a diameter of about 2 cm. A similar equipment as described in Example I was used before cutting the beam. About 1.6 V.

was fed to the hot wire. The hot wire was also passed through the bundle at a rate of about 10 cm per minute. The hollow fiber bores were found to be closed with a microscope on visual inspection, and nearly all hollow fiber membranes 15 were joined at the cut end with adjacent hollow fiber membranes. When the voltage of the hot wire was lowered, the bores of the hollow fiber membranes were found not to be closed. Also, when the hot wire propagation speed was increased through the beam, e.g. with a factor of about 2 more, the bores were found not to be closed.

Example III

The procedure of Example I was essentially repeated except that the polysulfone hollow fiber membranes were melt spun, with virtually void-free walls, and an outside diameter of about 310-320 µm and a wall thickness of about 50 µm. About 2800 hollow fiber membranes were used to fabricate a bundle about one inch in diameter. A similar equipment as in Example I has been described with this

TM

difference that a Nichrome tape about 0.025 cm thick and about 0.16 cm wide was used instead of a wire was used. The tape was positioned so that the end face of the bundle was parallel to the width of the tape.

The distance between the tap wires of the transformer was about 3.2 cm and the resistance between the wires at room temperature was about 1 Ohm. About 2.4 V was used to supply the hot belt 8005307-24 with energy and heat. The tape was passed through the bundle at a speed of about 7 cm per minute and a slight Force was applied such that the surface of the tape was in contact with and stroked the molten polysulfone. The bores of the hollow fiber membranes were sealed and the hollow fiber membranes were joined at the cut end.

When a hot wire was used instead of a hot strip, some of the hollow fiber membranes on the outside of the bundle tended not to be sealed.

By coating the molten polysulfone via contact with the tape, closure of the bores of all hollow fiber membranes in the bundle was found to be ensured. With smaller beam diameters, e.g. containing only about 100 melt-spun polysulfone hollow fibers, the use of a similar equipment as described in Example 1 resulted in sealing all hollow fiber membranes in the bundle.

Example IV

A bundle of about 100,000 anisotropic polysulfone hollow fiber membranes, as described in Example I, was prepared and had a generally circular cross-sectional configuration.

The end of the bundle was tied together toe diameter of approximately 18 cm3 with adhesive tape to aid in maintaining the desired configuration. The bundle was suspended vertically with the tied end down.

TM

A size 24 Nichrome wire was placed between two wound springs attached to insulators located on the ends of a U-shaped arm. One end of the arm was rotatably mounted on an arrangement so that the wire extended radially from the pivot and the wire and arm turned in a horizontal plane. The depth of the U-shaped arm was about 30 cm and the width of the arm about 30 cm. Variable transformer was connected to the wire with the supply wires spaced about 30 cm apart. The resistance at room temperature between the terminals was about 3.5 ohms. The arrangement was arranged so that the arm, when rotated, could move horizontally where the hot wire passed through the bundle almost perpendicular to the orientation of the hollow fiber membranes at the hot wire. . The height of the arm was adjusted so that the beam was cut at the desired location. The bundle was held above and below the desired cutting site using thick elastic bands attached to a support arrangement.

About 12-14 V was passed through the wire and the wire became red hot. The arm was rotated to allow the hot wire to pass through the bundle. The hot wire was slowly passed through the bundle at a speed of about 5-10 cm per minute. A band of discolored material due to scorching and melting of about 1mm thickness was observed on both sides of the hot wire pad after cutting. The hot wire was passed through the bundle slowly enough for a similar band to appear in front of the hot wire. The end of the bundle was cut and the bores of the hollow fiber membranes were sealed using the hot wire. The hollow fiber membranes were joined at the cut end.

8005307

Claims (14)

1. A method for cutting many hollow fiber membranes comprising thermoplastic material and arranged in the form of a bundle, and also for sealing the bores of the hollow fiber membranes, characterized in that a heated member is passed through the bundle is guided in a path transverse to the orientation of the hollow fiber membranes, the heated member being at a temperature above the melting temperature of the hollow fiber membranes and passed through the bundle at a speed sufficient to cut and seal the bores of to process the hollow fiber membranes in a substantially fluid-tight manner, and wherein the bundle is held in substantially a desired cross-sectional configuration near the path of the heated member during passage of the heated member through the bundle. A method according to claim 1, characterized in that neighboring hollow fiber membranes are adhered together sufficiently after cutting so that the bundle end formed by cutting can substantially maintain its cross-sectional configuration in the absence of external support. A method according to claim 1 or 2, characterized in that a melting zone precedes the heated member guided through the beam and has approximately the same thickness as the melting zones on both sides of the path of the heated member. 4. Method according to one or more of claims 1-3, characterized in that the heated member is a thread. Method according to one or more of claims 1 to 4, characterized in that the temperature of the heated member is at least 50 ° C above the polymer melting temperature of the hollow fiber membranes. Method according to one or more of claims 1 to 5, characterized in that the temperature of the heated member is 700 -1000 ° C. 80 05 30 7 - 27 - 23SEPJ980 Method according to one or more of claims 1 to 6, characterized in that heat is supplied to the heated member during cutting. 8. Method according to one or more of claims 1-7, characterized in that the heated member comprises an electrical resistance material and heat is generated by passing an electric current through the heated member. 9. Method according to one or more of claims 1-8, characterized in that the packing factor of the bundle at the zones through which the heated member passes is, 5, -70%. Method according to one or more of claims 1-9, characterized in that the internal diameter of the hollow fiber membranes is 50-500 µm. 11. Method according to one or more of claims 1-10, characterized in that the hollow fiber membranes have walls with a considerable void volume. Method according to claim 11, characterized in that the hollow fiber membranes are anisotropic with a thin, dense external skin and a void volume of 20-80%. Method according to one or more of claims 1-12, characterized in that the hollow fiber membrane comprises polysulfone. ____ 14, _. Process according to any one of claims 1 - k, characterized in that the temperature of the heated member at least 10 ° C above the melting point of the polymer of the hollow fiber membranes. Permeator manufactured using the method according to one or more of claims 1 - I. 80 0 5 30 7