Membrane separation module

#The present invention relates to a countercurrent flow membrane separation module wherein a shellside feed is introduced to a bundle of hollow fiber membranes. The module achieves countercurrent flow between the feed mixture fed to the exteriors (i.e. shellside) of the fibers and the feed components which permeate into the fiber bores.

#Semipermeable membranes in the form of hollow fibers have been used to separate components in fluid mixtures for many years. Hollow fibers, which can be spun from a wide variety of materials which have suitable membrane separation properties, provide high surface area for contact with the fluid feed mixture. Each component of the feed mixture coming in contact with the membrane material has a characteristic permeation rate that is a function of its ability to dissolve in and diffuse through the membrane material. This enables the separation of the faster permeating components from the slower permeating components. The driving force for the separation is the difference between each component's partial pressure across the inner and outer walls of the hollow fiber.

#Large numbers of hollow fibers of similar length are generally grouped together in a bundle in a pressurizable shell or housing in which opposite ends of the fibers are potted and sealed in a material which serves to form a tubesheet at each end, similar in fashion to a shell and tube heat exchanger. One of the tubesheet's potting material is then cut to open the bores of the fibers and thus allow the faster permeating components to pass through this tubesheet into a permeate compartment. The volume within the shell which has access to the exteriors of the fibers (shell side) is effectively sealed by the tubesheets and other peripheral sealing devices from the volumes within the shell which permeate into the fiber bores and subsequently collect in the permeate compartment.

#FIG. 1 is a drawing illustrating a typical shellside feed, countercurrent flow, hollow fiber membrane separation module as found in the prior art.

#FIG. 2 is a drawing illustrating a first embodiment of the present invention.

#FIG. 3 is a drawing illustrating a second embodiment of the present invention.

#To better understand the present invention, it is important to understand the prior art. As an example, a typical shellside feed, countercurrent flow, hollow fiber membrane separation module is illustrated in FIG. 1. Referring to FIG. 1, a pressurizable shell or housing 30 contains a bundle 20 of individual semi-permeable hollow fiber membranes such as hollow fiber membrane 22. The hollow fiber membrane may be any material which is capable of separating one or more components of the feed stream such as cellulose acetate, polysulfone, polyolefins, silicone rubber and the like. The fiber bundle typically contains thousands of the hollow fiber membranes, each having a closed end and an open end. The closed ends terminate into a first tubesheet 24 while the open ends penetrate through a second tubesheet 26 into an adjacent permeate compartment 28. A feed inlet port 40 is in flow communication with the exterior of fiber bundle 20 at or near second tubesheet 26. This feed inlet port allows for the introduction of a feed stream 10 to housing 30 such that feed stream 10 can be separated into a permeate stream 11 and a non-permeate stream 12 which represent those portions of feed stream 10 which, respectively, have or have not permeated into the interiors of the individual hollow fiber membranes. A permeate outlet port 42 is in flow communication with permeate compartment 28 for withdrawing permeate stream 11 from housing 30. Similarly, a non-permeate outlet port 44 is in flow communication with the exterior of fiber bundle 20 at or near first tubesheet 24 for withdrawing the non-permeate stream from housing 30.

#The design of the above described conventional module has a deficiency in that it promotes undesirable flow patterns in the interior of fiber bundle 20 at or near both tubesheets.

#The undesirable flow pattern in the interior of fiber bundle 20 at or near first tubesheet 24 is an energy robbing channeling of the non-permeate flow as such flow is forced to abruptly change directions and go around the first tubesheet before exiting the module in non-permeate stream 12. This particular undesirable flow pattern is particularly significant because of the smaller partial pressure driving force for the permeating component at this end of the module.