Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – Composite article making
Reexamination Certificate
2002-09-20
2003-12-16
Spitzer, Robert H. (Department: 1724)
Plastic and nonmetallic article shaping or treating: processes
Pore forming in situ
Composite article making
C096S010000, C096S013000, C055SDIG005, C264S172110, C264S209500
Reexamination Certificate
active
06663805
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a spinning process for making hollow fiber membranes that are used in gas separation processes. More specifically, it relates to a process for spinning hollow fibers having mixed matrix membrane compositions.
BACKGROUND OF THE INVENTION
The use of selectively gas permeable membranes to separate the components of gas mixtures is a well developed and commercially very important art. Such membranes are traditionally composed of a homogeneous, usually polymeric composition through which the components to be separated from the mixture are able to travel at different rates under a given set of driving force conditions, e.g. transmembrane pressure and concentration gradients.
Gas separation membranes are provided in various forms such as flat, spiral wound and pleated sheets and tubes. The hollow fiber membrane module is a commercially preferred form of gas separation membrane equipment because it presents an extremely large gas transfer area per unit volume and especially per unit of module cross section area. The basic element of such a module is a very small diameter hollow fiber comprising a selectively gas permeable material. Typically hundreds or thousands of the hollow fibers are aligned substantially parallel to each other in bundles and positioned within a cylindrical housing to form a module. The ends of the bundles are “potted” usually in a polymeric resin and the fiber ends are kept open. The module is thus structured much like a conventional tube and sheet style fluid heat exchanger. U.S. Pat. No. 3,339,341 to J. M. Maxwell et al. the entire disclosure of which is hereby incorporated herein by reference provides a thorough description of the structure of certain hollow filament membrane modules.
Many embodiments of gas separation membrane modules use fibers of asymmetric structure in which the selectively gas permeable material forms an ultra-thin fiber skin that ideally fully covers the gas transfer area, i.e., the external generally cylindrical surface of the fiber. The skin is the active gas separation portion of the fiber.
In other embodiments, the hollow fibers can be a composite structure in which the selectively gas permeable material is in a layer on one surface of a microporous substrate material layer. The separating material can be in the form of an ultra thin dense layer or an asymmetric layer. The separating material can be deposited either on the outside surface of the fiber or the inside surface of the fiber.
A relatively recent advance in this field utilizes mixed matrix membranes. Such membranes are characterized by a heterogeneous, active gas separation layer comprising a dispersed phase of discrete particles in a continuous phase of a selectively permeable polymeric material. The dispersed phase particles are microporous materials, such as zeolites, carbon molecular sieves and other molecular sieve materials, that have discriminating adsorbent properties for certain size molecules. Chemical compounds of suitable size can selectively migrate through the pores of the dispersed phase particles. In a separation of gases involving a mixed matrix membrane, the dispersed phase material is desirably selected to provide separation characteristics which provide improved permeability and/or selectivity performance of the mixed matrix membrane relative to that of a homogeneous polymeric membrane of the continuous phase material.
The fabrication of hollow fibers for gas separation modules typically involves extruding the nascent fiber through narrow channel extrusion dies, occasionally called “spinnerettes”, at very high shear rates. The manufacture of mixed matrix hollow fibers also normally calls for axially drawing the nascent fibers to provide them with precise and uniform cross section dimensions. For these and other reasons, the production of hollow fiber mixed matrix is highly problematic and conventional hollow fiber membranes do not utilize mixed matrix compositions. It is very desirable to provide hollow fiber which utilize mixed matrix compositions for the active gas separation membrane portion of the fiber so as to obtain better permeance and selectivity than polymer-only membrane compositions.
SUMMARY OF THE INVENTION
Accordingly there is now provided a process for making mixed matrix hollow fiber membrane for gas separation comprising,
(A) providing a spinnerette adapted to extrude at least one nascent hollow fiber,
(B) feeding a bore fluid through the spinnerette to form a cylindrical fluid stream for each hollow fiber,
(C) feeding through the spinnerette to an annular channel surrounding the fluid stream for each hollow fiber a suspension comprising molecular sieve particles uniformly dispersed in a polymer solution comprising a selectively gas permeable polymer and a solvent for the selectively gas permeable polymer, and
(D) immersing the nascent hollow fiber in a coagulant for a duration effective to solidify the selectively gas permeable polymer, thereby forming a monolithic mixed matrix membrane hollow fiber.
This invention also provides a process as just described which further comprises feeding through the spinnerette to a second annular channel surrounding the fluid stream for each hollow fiber a core polymer solution comprising a core polymer dissolved in a core solvent, thereby depositing a nascent annular core layer of core polymer solution around the bore fluid stream and a nascent annular sheath layer of the suspension around the nascent annular core layer, to form a nascent composite mixed matrix membrane hollow fiber, in which the nascent composite mixed matrix membrane hollow fiber is immersed in a coagulant for a duration effective to solidify the core polymer and the selectively gas permeable polymer, thereby forming a composite hollow fiber having an inner polymer core and an outer mixed matrix membrane sheath.
There is further provided a mixed matrix hollow fiber membrane for gas separations comprising a monolithic annular wall comprising a continuous phase of a selectively gas permeable polymer and a discrete phase of selectively gas permeable molecular sieve particles uniformly dispersed throughout the continuous phase in which the weight ratio of selectively gas permeable molecular sieve particles of the discrete phase to selectively gas permeable polymer of the continuous phase is within the range of about 0.05-0.4.
Yet additionally the invention provides a mixed matrix composite hollow fiber membrane for gas separations having an annular core comprising a core polymer and an annular, mixed matrix sheath externally adjacent to the core, in which the sheath comprises a continuous phase of a selectively gas permeable polymer and a discrete phase of selectively gas permeable molecular sieve particles uniformly dispersed throughout the continuous phase in which the weight ratio of selectively gas permeable molecular sieve particles of the discrete phase to selectively gas permeable polymer of the continuous phase is within the range of about 0.05-0.4.
The invention still further provides a method of separating components of a gas mixture utilizing a hollow fiber gas separation module having a tube side and a shell side, the method comprising feeding the gas mixture through the tube side or the shell side of the hollow fiber gas separation module and withdrawing a permeate gas mixture from the shell side or tube side, in which the module comprises a plurality of mixed matrix hollow fiber membranes each of which comprises a monolithic annular wall comprising a continuous phase of a selectively gas permeable polymer and a discrete phase of selectively gas permeable molecular sieve particles uniformly dispersed throughout the continuous phase and in which the weight ratio of selectively gas permeable molecular sieve particles of the discrete phase to selectively gas permeable polymer of the continuous phase is within the range of about 0.05-0.4.
In a particular aspect of the invention the nascent fiber is drawn from the spinnerette through an air gap and a liquid coagulation bath at a
Ekiner Okan Max
Kulkarni Sudhir S.
L'Air Liquide Societe Anonyme a Directoire et Conseil de Su
Lew Jeffrey C.
Russell Linda
Spitzer Robert H.
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