Abstract:
The present invention is directed to a method of making a hollow fiber membrane contractor comprising the steps of: winding a hollow fiber fabric around a center tube, potting the fabric and the tube together, forming thereby a unitized structure, placing the structure into a shell, potting the structure and the shell together, and forming thereby a cartridge. The invention, also, includes a hollow fiber membrane contactor comprising a unitized structure. The structure includes a center tube, a hollow fiber fabric wound around the tube and a first potting material joining together the fabric and the tube. A second potting material joins together the structure and the shell.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention is directed to a hollow fiber membrane contactor and the method for making the same.  
         BACKGROUND OF THE INVENTION  
         [0002]    Hollow fiber membrane contactors are known. For example, see U.S. Pat. Nos. 3,288,877; 3,755,034; 4,220,535; 4,664,681; 4,940,617; 5,186,832; 5,264,171; 5,284,584; and 5,449,457. Hollow fiber membrane contactors are commercially available under the name of LIQUI-CEL® from Celgard Inc. of Charlotte, N.C. and under the name of SEPAREL® from Dianippon Ink and Chemicals of Tokyo, Japan. Such contactors have numerous uses, one being the degassing of liquids.  
           [0003]    To facilitate manufacture of these contactors, the hollow fiber membranes are typically formed into a fabric (e.g., woven or knitted). The fabric is wound around a mandrel (e.g., a perforated center tube) and fixed into place by potting the fabric edges, with either thermosetting or thermoplastic materials. See, for example, U.S. Pat. Nos. 4,940,617 and 5,284,584. This unit can then be inserted within a shell and sealed, i.e., with or without O-rings. See, for example, U.S. Pat. No. 6,207,053. Because of potting shrinkage, the uniformity of the unit is poor and causes unit-to-shell sealing problems that are costly to rectify. As the size (e.g., the diameter) of the contactor increases, the shrinkage problem becomes more severe, particularly with centrifugal potting. Accordingly, by this method, the size of the unit has been limited, to about six inch diameters, because of shrinkage arising from the solidification of the potting materials.  
           [0004]    Celgard Inc. offers a 10-inch diameter contactor. This contactor is difficult to seal because of potting shrinkage. This shrinkage, which is not uniform from one contactor to the next, makes potting-to-shell sealing difficult. To meet this difficulty, a system of four O-rings is used to form the seal between the potting and the shell. While this has been adequate, these seals are labor-intensive and complex, thereby driving up the cost of the contactor.  
           [0005]    Accordingly, there is a need for an improved hollow fiber membrane contactor, which minimizes or eliminates the problems arising from potting shrinkage, and a method of making it.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention is directed to a method of making a hollow fiber membrane contactor comprising the steps of: winding a hollow fiber fabric around a center tube, potting the fabric and the tube together, forming thereby a unitized structure, placing the structure into a shell, potting the structure and the shell together, and forming thereby a cartridge.  
           [0007]    Additionally, the invention includes a hollow fiber membrane contactor comprising a unitized structure. The structure includes a center tube, a hollow fiber fabric wound around the tube, and a first potting material joining together the fabric and the tube. A second potting material joins together the structure and the shell. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0008]    For the purpose of illustrating the invention, there is shown in the drawings a form which is presently preferred; it being understood, however, that this invention is not limited to the precise arrangement and instrumentalities shown.  
         [0009]    [0009]FIG. 1 is a schematic illustration of a hollow fiber membrane contactor.  
         [0010]    [0010]FIG. 2 is an illustration of the first potting step.  
         [0011]    [0011]FIG. 3 is an illustration of the second potting step, before potting.  
         [0012]    [0012]FIG. 4 is an illustration of the second potting step, after potting.  
         [0013]    [0013]FIG. 5 is a schematic illustration of the inventive contactor, in use. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]    Referring to the drawings wherein like numerals indicate like elements, there is shown in FIG. 1 a hollow fiber membrane contactor  10 . Contactor  10  includes a center tube  12 . Tube  12  has a plurality of perforations  14 . Hollow fiber fabric  16  is wound around tube  12 . A tube sheet  18  is located at each of the lateral ends of fabric  16 . The tube  12 , fabric  16 , and tube sheets  18  define a unit or a unitized structure. Shell  20  surrounds that unit. Tube sheets  18 , tube  12 , fabric  16 , and shell  20  are joined together, thereby fixing these components in place and forming a gas and/or liquid tight seal therebetween. The unit and the shell define a cartridge. End caps  22  and  24  are placed at the lateral ends of the cartridge. The cartridge and the end caps define a contactor.  
         [0015]    Within the contactor  10 , there is a shell side passageway and a lumen side passageway. The shell side refers to the flow over the exterior surface of the membranes. In FIG. 1, the shell side passageway is defined by port  26 , center tube  12 , perforations  14 , the exterior surfaces of the membranes of the fabric  16 , tube sheet  18 , shell  20 , and port  28 . The lumen side refers to flow through the lumens of the hollow fibers. In FIG. 1, the lumen side passageway is defined by port  30 , headspace  25 , tube sheet  18 , the lumens of the hollow fibers of fabric  16 , headspace  23 , and port  32 . As will be readily apparent to those of ordinary skill, placement of ports may vary, so long as the integrity of the shell side and the lumen side passages is maintained.  
         [0016]    With regard to the location of port  28 , it is preferably located between end caps  22  and  24 , specifically on the center line between the end caps. With regard to the orientation of ports  30 , 32 , and port  28 , they are preferably offset from each other, e.g., 180° or preferably 90°. One consideration for port orientation is the subsequent ease of piping the contactor into a system.  
         [0017]    In preferred operation, a liquid, for example laden with an entrained gas, is introduced to contactor  10  via port  26 . Liquid enters center tube  12  and exits the tube via perforations  14 . The liquid travels over the exterior surface of the hollow fibers of fabric  16  and exits contactor  10  via port  28 . Ports  30  and  32  are coupled with a vacuum source and are in communication with the lumen side of the hollow fibers. Thus, as the gas-laden liquid travels over the exterior surface of the hollow fibers, vacuum drawn on the lumen side of the fibers provides the driving force for the diffusion of the gas from the liquid to the lumen side of the fibers where it is exhausted via ports  30  and  32 . Alternatively, liquid may be introduced via port  28  and discharged via port  26 . Also, a sweep gas may be introduced via either port  30  or  32  which, in some cases, can facilitate diffusion of the gas from the liquid.  
         [0018]    Spacer  34  is used to maintain the space between the layers of the wound fabric so that fluid may be evenly distributed over the entire surface of all the hollow fibers. This distribution is important to maximize removal efficiency of the contactor. See U.S. Pat. No. 4,940,617. The spacer, also, functions as a baffle. See U.S. Pat. Nos. 4,220,535 and 5,264,171.  
         [0019]    With regard to the contactor&#39;s materials of construction, lightweight, inert, solvent or corrosion resistant, and capable of withstanding various pressures are considerations. The hollow fibers of fabric  16  are any membranes suitable for use in diffusion operations. See Kesting, R. E.,  Synthetic Polymeric Membranes,  2 nd  ed., John Wiley &amp; Sons, New York, N.Y., (1985), incorporated herein by reference. Examples include, but are not limited to, microporous polyolefin membranes, commercially available under the name of CELGARD® hollow fibers from Celgard Inc. of Charlotte, N.C. or asymmetric membranes from Dainippon Ink and Chemicals of Tokyo, Japan, see U.S. Pat. No. 4,664,681 incorporated herein by reference. The center tube  12  is preferably a 1.5-inch Schedule 40 ABS pipe. The shell is preferably a 6-inch Schedule 40 ABS pipe. Alternatively, shell  20  may be a fluoropolymer lined fiber reinforced body, see U.S. Pat. No. 6,063,277 incorporated herein by reference. The end caps  22  and  24  are preferably made of thermoplastic materials. Tube sheets  18  will be discussed in greater detail below.  
         [0020]    Referring to FIGS.  2 - 4 , the manufacture of the contactor  10  will be illustrated.  
         [0021]    In FIG. 2, center tube  12  is used as a mandrel. Fabric  16  is wound around tube  12 . Simultaneously with winding, potting resin beads  36  are laid at the lateral edges of fabric  16  and form tube sheets  18 , i.e., the first or bead-potting step. Optionally, a bead  38  may also be laid between beads  36 , thereby forming spacer  34 . At the conclusion of this step, the potting is, preferably, a gelatinous solid  37  and the unitized structure is formed.  
         [0022]    After the first potting step, the unitized structure is inserted into the shell  20 . Shell  20  and the structure are inserted into a mold  42 .  
         [0023]    Referring to FIG. 3, mold  42 , preferably, consists of a part that engages shell  20 , a center mold piece  44  that engages tube  12 , and potting injection ports  46 . The mold thereby centers the unit within the shell.  
         [0024]    Referring to FIG. 4, a second potting material  48  is injected through the mold, into the space between shell  20  and solid  37 , and thereby joins the shell to the unitized structure, i.e., the second or mold-potting step. Preferably, serrations  40  are formed on the internal end portion of shell  12  to improve joining and creation of a seal.  
         [0025]    The potting resins are allowed to solidify. The cartridge is removed from the mold. The ends are, preferably, subjected to a rotary cut to open the end of the hollow fibers and to generate a planar cut surface that is perpendicular to the centerline of the cartridge.  
         [0026]    After the second potting step, the cartridge is heat-treated. Heat-treatment increases the thermal/mechanical integrity of the cartridge by reducing residual stress. Additionally, when an epoxy potting is used, this heat-treatment further cross-links and hardens the potting. Reduced stress lessens the occurrence of cracking at interfaces and joints. Heat-treating is, preferably, for a period of time sufficient for the cartridge to come to thermal equilibrium. For example, a six-inch diameter contactor with an epoxy potting may be adequately heat-treated in about 16 hours at 60° C. in a hot air oven (i.e., the cartridge at room temperature is placed in the 60° C. oven for about 16 hours).  
         [0027]    The end caps are then joined to the cartridge. Joining is preferably by solvent weld techniques, but may include the hot-plate welding techniques, see U.S. Pat. No. 6,207,053 incorporated herein by reference.  
         [0028]    Preferably, a second heat-treatment is performed after the end caps are joined. As before, this heat-treatment improves the thermal/mechanical integrity of the module. Additionally, this heat-treatment causes radial shrinkage of the end caps. The radial shrinkage of the end caps on the shell creates a compression fit of the cap to the shell and gives added mechanical robustness to the module. Heat-treatment is, preferably, for a period of time sufficient for the module&#39;s ends (i.e., where the end caps are joined to the shell) to come to thermal equilibrium. For example, a six-inch module with an epoxy potting may be adequately heat-treated in about 6 hours at 60° C. in a hot air oven (i.e., the vertically oriented module at room temperature is placed in the 60° C. oven for about 6 hours).  
         [0029]    The potting materials  36 ,  38 , and  48  may be thermosetting materials or thermoplastic materials. Thermosetting materials include, but are not limited to, epoxy and polyurethane. Thermoplastic materials include, but are not limited to, polyolefins and polyurethanes. Epoxies are preferred. The first potting material  36  and second potting material  46  may be the same or different, depending upon the requirements of the contactor. For example, the first potting material may be an epoxy, for strength and chemical inertness, and the second potting material may be a polyurethane, for flexibility in the joint between the unit and the shell.  
         [0030]    Referring to FIG. 5, there is shown a system  60  for degassing a liquid. System  60  comprises two contactors  62  and  64 . Contactors  62  and  64  are coupled in series via center ports  66 ,  68 . Port  70  is an inlet and port  72  is an outlet. Ports  74  are coupled to a source of vacuum or vacuum/sweep gas. Contactors  62  and  64  are preferably the contactors described above, e.g., contactor  10 . Preferably, these contactors have diameters of 6 inches or greater. The illustrated configuration enables a unique flow pattern. Liquid enters contactor  62  via port  70 , flows “inside to out,” and exits via port  66 . Liquid, then, enters contactor  64  via port  68 , flows “outside to in,” and exits via port  72 .  
         [0031]    The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention.