Abstract:
A membrane bag, a winding module and a method of making the membrane bag and winding module. The membrane bag and winding module comprise two separation membranes interconnected at their rims and having supply and drain conduits. The membrane bag and winding module are pressure tight and operationally safe at high pressures and temperatures. The rims of the separation membranes are flanged-in at least twice and glue layers are provided between superposed flange rims.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a membrane bag. The bag comprises two separation membranes interconnected at their rims and having supply and drain conduits. The invention also relates to a winding module made of the membrane bag as well as a method of producing the membrane bag and winding module. 2. Description of the Related Prior Art 
     In the prior art, separation membranes consist of a thin, comparatively permeable carrier foil. On one side of the carrier foil an active coating is applied. This is the so-called asymmetrical separation membrane. There also exist separation membranes consisting exclusively of the active layer itself. Also, so-called symmetrical separation membranes are known. These membranes have an active coating on both sides of a carrier foil. 
     A great number of polymers, such as cellulose derivatives, e.g., cellulose acetate, various polyamides, polysulfones and also inorganic materials, such as graphite oxide and zirconium hydroxide, are known as active coatings. The active coatings usually have a thickness of between 10 -3  to 10 -1  mm. 
     Membrane bags and winding modules are used in apparatuses for carrying out membrane separation methods, such as inverted osmosis, ultra or microfiltration, gas separation and pervaporations. In these methods, the media to be treated, i.e. liquids, solutions or vapors, are guided past a separation membrane under pressure. As a result of the pressure, certain components of the media which are permeable to the membrane pass through the membrane as permeate. 
     In the prior art membrane bags and winding modules, the separation membranes have simply been glued together at their rims and subsequently sewn, stapled or clamped together at the glued rim regions. However, the media in the interior of the membrane bags and winding modules is under substantial pressure of up to approximately 80 bars. Only in separation membranes consisting sometimes sufficiently durable to withstand the pressure. At higher temperatures, or a multi-layer separation membrane system, the prior art membrane bags are not satisfactory. The connections leak, or with multi-layer membranes, the inner active coating becomes detached. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the present invention is to overcome the deficiencies of known membrane bags and winding modules indicated and to provide tight and operationally safe products for high pressures and temperatures. 
     These and other objects of the present invention are achieved by providing separation membranes with rims which are at least twice flanged-in. Glue layers are provided between the superposed flanged-in rims. 
     Another object of the invention is the production of a membrane bag. This object is achieved by gluing two superposed separation membranes (optional with insertion of a layer of porous material between the separation membranes) at their rim regions. The glued together rims are flanged-in relative to one of the two separation membranes while interposing a layer of glue. The flange ledge thus formed is flanged-in a second time relative to the separation membrane while interposing a second layer of glue. Thus, the forces resulting from pressure do not act only on the rim gluing located at the separation membrane sides facing each other; rather, they are distributed over both sides of the separation membranes. A detachment of the inner active coating is completely avoided in this manner. 
     According to a preferred embodiment, the glue layers having the double flanging are formed of a strip bent to a U-shape and coated at both sides with glue. The stability of the resulting membrane bags is increased, and their production is simplified. Also, a layer of porous material is arranged as an inner spacer between the separation membranes within the flangedin rims. Adhesion of the inner active coatings is prevented by the porous layer, and the dimensional stability of the membrane bags is increased. A woven fabric, a knitted fabric or a nonwoven fabric or organic or inorganic fibres may be used for the porous material. Natural as well as synthetic fibres may be used as the organic fibres. The inorganic fibres are preferably glass fibres. Also a layer of open-porous foam material is suitable for certain applications. 
     Another object of the invention is to provide a winding module comprising the membrane bag and tubes arranged at the inner side of two opposite flanged-in rims of a rectangular membrane bag. The membrane bag is rolled in around one of the tubes, and the rolled membrane bag is arranged in an enveloping tube. Winding modules are utilized for pervaporations, e.g. for the pervaporation of ethanol. 
     A further object of the invention is the production of a winding module. This object is achieved by introducing tubes into the interior of the membrane bag inside of two opposite flange rims of a rectangular membrane bag and parallel to these flange rims. The membrane bag (optionally after positioning a layer of porous material onto the outer side of the membrane bag) is rolled around one of the tubes. The rolled-up membrane bag, having substantially the shape of a cylinder, is put into an enveloping tube, and the enveloping tube is closed with a layer of pourable sealing mass at one of its ends. The tubes lead away from the rolled-up membrane bag. 
     Two superposed webs of separation membranes may be simultaneously interconnected at both longitudinal sides in the manner described. A membrane bag in the form of a flat, tight hose is formed. This may (optionally with insertion of a layer of porous material) be directly rolled up into a winding module. The mutual longitudinal displacement of the two separation membranes resulting during the rolling-up procedure may be compensated as long as the glue has not set. 
     Other features and advantages of the invention are described below, with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 to 5 show in section the rim zone of two superposed separation membranes in various stages of the production method according to the invention. 
     FIG. 6 shows a schematical longitudinal section through an embodiment of a membrane bag having an inner and an outer layer of porous material. 
     FIG. 7 shows schematically a partly cut-away top view of a membrane bag according to FIG. 6. 
     FIG. 8 shows a cross-section through an embodiment of a winding module. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, the two separation membranes of the present invention are shown as 1a and 1b. In the first step of the invention, a first glue layer 2 is introduced into the rim region of the separation membranes. Gluing is completed by the application of pressure and possibly heat. One method of gluing is by rolling the rims of membranes 1a and 1b between two rollers indicated with 3a and 3b (FIG. 2). 
     The first gluing need not, as in the case illustrated, take place immediately at the rim of the separation membranes, but may also be made slightly spaced inwardly from the rim. Also, a strip with glue or foil coated at both sides thereof with glue may be used for making this first gluing. 
     Referring to FIG. 3, the glued together rims are flanged-in or bent-over relative to one of the two separation membranes (1b in the case illustrated), while interposing a strip 4 coated at both sides thereof with glue. 
     As can be seen from FIG. 4, the flange rim thus formed is flanged-in once more in the same direction. The portion of the strip 4 located in the flange rim is also bent over. Thus, strip 4 becomes U-shaped in cross-section. The two legs of the U thus function as glue layers. 
     Finally, referring to FIG. 5, the rim connection of the separation membranes 1a and 1b is finished. The rim regions of membranes 1a and 1b are simply pressed together or rolled together by means of the rollers 3a and 3b. 
     Of course, instead of using the gluing strip or foil coated at both of its sides, gluing together is also possible with each of the other glues, so long as the glued sites are sufficiently resistant to the media and temperature utilized. 
     The gluings can be made with a cold-setting glue, such as a silicone glue. According to another embodiment, the gluings are made with a glue that is to be processed in the hot state, such as a melting glue or a heat sealing glue. 
     At room temperature, melting glues are present in solid form and without solvents. These glues belong to the group called thermoplastics. The most important glues of this group are: polyamides, copolyamides and polyaminoamides; saturated polyesters and ethylen-vinyl acetate-copolymers. Heat sealing glues are glues that are applied as dispersion glues or glue lacquers. These glues are dried before the gluing, and subsequently are pressed together simultaneously with heat being applied to the opposite side. 
     The membrane bag according to FIGS. 6 and 7 and generally illustrated as 5 has a rectangle shape. Two perforated tubes 6a and 6b are provided for supplying and draining the media to be separated. Tubes 6a and 6b are inserted into the interior of the membrane bag 5 and are located inside and parallel to two opposite flange rims 7a and 7b. Perforations are provided in the sections of tubes 6a and 6b that are located in the interior of membrane bag 5. 
     Between the separation membranes 1a and 1b, which are indicated in broken lines in FIG. 6, a layer 8 of porous material is arranged as an inner spacer within the flange rims 7a, 7b, 9a and 9b. 
     If a winding module is to be produced, a further layer 10 of porous material is placed upon membrane bag 5. The membrane bag is rolled about one of the tubes with the layer 10 as an outer spacer. In the embodiment illustrated, membrane bag 5 is rolled about perforated tube 6a, as indicated in FIG. 6 by arrow 11 in broken lines. 
     A flexible web material 12 may be attached to the flange rim 7b located on the outer side of membrane bag 5. The material 12 is positioned around the rolled membrane bag thus forming an outer shield. A substantially cylindrical body is formed which is inserted into an enveloping tube 13 of suitable diameter (FIG. 8). At one end of the enveloping tube 13, tubes 6a and 6b lead away from the rolled-up membrane bag, and a layer of pourable sealing mass 14 is introduced. This end is closed by pourable sealing mass 14. Pourable sealing mass 14 provides sealing around tubes 6a and 6b of flange rims 7a, 7b and 9b, and thus a closed inner space between the separation membranes 1a and 1b is formed. Also, the rolled-up membrane bag is kept in place. The other end of the enveloping tube 13 remains open. 
     In operation, the medium to be separated is supplied under pressure through one of the tubes 6a or 6b. Additionally, a vacuum may be applied to the open end of enveloping tube 13. The medium is drained through the other tube. The permeate passing through the separation membranes 1a and 1b is drawn off from the open end of the enveloping tube 13. 
     Although the present invention has been described in connection with a plurality of preferred embodiments thereof, many other variations and modifications will now become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims.