U.S. patent application number 14/848674 was filed with the patent office on 2015-12-31 for hollow fiber membrane mats with fluid impermeable segments and related methods.
The applicant listed for this patent is Membrana GmbH. Invention is credited to Kwantai Cho, James Clifton Delozier, Christian MUEHLINGHAUS, Eric J. Penegar, Gareth Peter Taylor.
Application Number | 20150375172 14/848674 |
Document ID | / |
Family ID | 43297007 |
Filed Date | 2015-12-31 |
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United States Patent
Application |
20150375172 |
Kind Code |
A1 |
MUEHLINGHAUS; Christian ; et
al. |
December 31, 2015 |
HOLLOW FIBER MEMBRANE MATS WITH FLUID IMPERMEABLE SEGMENTS AND
RELATED METHODS
Abstract
In at least one embodiment, the invention preferably relates to
a hollow fiber membrane mat having hollow fiber membranes arranged
parallel to one another and adjacent to one another, the membranes
having a wall and a continuous lumen, wherein the hollow fiber
membranes are connected to one another by means of a plurality of
linear connecting elements which are arranged spaced apart from one
another and parallel to one another and the membranes are kept
apart from one another by the linear connecting elements and
wherein the hollow fiber membranes are composed of a thermoplastic
polymer and wherein the walls of the hollow fiber membranes
arranged adjacent to one another are fluid-tight in at least one
stripe extending parallel to the linear connecting elements, inside
of which stripe the hollow fiber membranes are fluid-tight,
preferably have a superheated steam shrinkage of at most 5%. Other
embodiments of the invention preferably relate to a method for
producing and/or using such hollow fiber membrane mats.
Inventors: |
MUEHLINGHAUS; Christian;
(Schwelm, DE) ; Taylor; Gareth Peter; (Indian
Trail, NC) ; Delozier; James Clifton; (Fort Mill,
SC) ; Penegar; Eric J.; (Fort Mill, SC) ; Cho;
Kwantai; (Charlotte, NC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Membrana GmbH |
Wuppertal |
|
DE |
|
|
Family ID: |
43297007 |
Appl. No.: |
14/848674 |
Filed: |
September 9, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13498594 |
May 10, 2012 |
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PCT/EP2010/064131 |
Sep 24, 2010 |
|
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14848674 |
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61247205 |
Sep 30, 2009 |
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Current U.S.
Class: |
210/500.23 |
Current CPC
Class: |
B01D 69/02 20130101;
B01D 2323/286 20130101; B01D 61/38 20130101; B01D 63/026 20130101;
B01D 69/08 20130101; B01D 2313/02 20130101; B01D 63/04 20130101;
B01D 2319/06 20130101; Y10T 29/49826 20150115; B01D 2325/08
20130101; B01D 63/021 20130101; B01D 67/0088 20130101 |
International
Class: |
B01D 63/04 20060101
B01D063/04; B01D 63/02 20060101 B01D063/02 |
Claims
1. A hollow fiber membrane mat having hollow fiber membranes
arranged parallel to one another and adjacent to one another, said
membranes having a wall and a continuous lumen, wherein the hollow
fiber membranes are connected to one another by means of a
plurality of linear connecting elements which are arranged spaced
apart from one another and parallel to one another and said hollow
fiber membranes are kept apart from one another by the linear
connecting elements and wherein the hollow fiber membranes are
composed of at least one thermoplastic polymer, characterized in
that the walls of the hollow fiber membranes arranged adjacent to
one another are fluid-tight in at least one stripe extending
parallel to the linear connecting elements within the hollow fiber
membrane mat, that the linear connecting elements have a melting
temperature that is at least as high as the melting temperature of
the thermoplastic polymer composing the hollow fiber membranes, and
that the linear connecting elements outside of the at least one
stripe extending parallel to the linear connecting elements, inside
of which stripe the hollow fiber membranes are fluid-tight, have a
superheated steam shrinkage of at most 5% at a temperature of
121.degree. C. and an atmospheric humidity of 100%.
2. The hollow fiber membrane mat according to claim 1,
characterized in that the linear connecting elements have a
superheated steam shrinkage of at most 2% at a temperature of
121.degree. C. and an atmospheric humidity of 100%.
3. The hollow fiber membrane mat according to claim 1,
characterized in that the at least one polymer composing the hollow
fiber membranes is a polyolefin.
4. The hollow fiber membrane mat according to claim 1,
characterized in that the linear connecting elements are connecting
threads.
5. The hollow fiber membrane mat according to claim 4,
characterized in that the connecting threads are multifilament
polyester yarns.
6. The hollow fiber membrane mat according to claim 1,
characterized in that the membrane mat contains at least two
different types or sizes of hollow fiber membranes.
7. The hollow fiber membrane mat according to claim 1,
characterized in that the walls of the hollow fiber membranes in
the at least one stripe are pore-free on the surface facing the
lumen as well as on the surface facing outward.
8. A hollow fiber membrane mat with at least one stripe-shaped area
in which the walls of the hollow fiber membranes are fluid
impermeable and formed by the method of providing a hollow fiber
membrane mat having hollow fiber membranes arranged parallel to one
another and adjacent to one another, said membranes having at least
one of a porous, microporous, and semi-permeable wall and a
continuous lumen, wherein the hollow fiber membranes are connected
to one another by means of a plurality of linear connecting
elements which are arranged spaced apart from one another and
parallel to one another and said membranes are kept at a distance
by the linear connecting elements and wherein the hollow fiber
membranes are composed of a thermoplastic polymer, and the linear
connecting elements have a melting temperature that is at least as
high as the melting temperature of the thermoplastic polymer
composing the hollow fiber membranes, and the linear connecting
elements have a superheated steam shrinkage of at most 5% at a
temperature of 121.degree. C. and an atmospheric humidity of 100%,
b. transporting the hollow fiber membrane mat by means of a
transport equipment and at a transport speed in the direction of
the extension of the linear connecting elements and under a tension
acting in the transport direction through at least one heating
device extending in the transport direction having heating elements
arranged above and below the hollow fiber membrane mat and at a
distance from the surface of the hollow fiber membrane mat as well
as from one another via which heat is supplied to the hollow fiber
membranes in a treatment zone over a width B transverse to the
transport direction, whereby the hollow fiber mat is treated in a
treatment area, and simultaneously c. gripping of the hollow fiber
membrane mat in zones, which are located to the right and left of
the at least one heating device when viewed in the transport
direction, by clamping devices, which are adjustable regarding
their contact pressure perpendicular to the flat extension of the
hollow fiber membrane mat, by means of which clamping devices the
hollow fiber membranes are held under tension transverse to the
transport direction, wherein in the treatment zone the temperature
is adjusted to a temperature 5 to 15% below the melting temperature
of the polymer composing the hollow fiber membranes by means of the
heating elements so that a shrinkage of the hollow fiber membranes
is initiated in the treatment area, and wherein by adjusting the
contact pressure of the clamping devices, the hollow fiber
membranes are held under tension in their longitudinal extension so
that the hollow fiber membranes retain a straight-line course in
their longitudinal extension.
9. A hollow fiber membrane mat having hollow fiber membranes
arranged adjacent to one another, said membranes having a wall and
a continuous lumen, wherein the hollow fiber membranes are composed
of a thermoplastic polymer, characterized in that the walls of the
hollow fiber membranes arranged adjacent to one another are at
least one of reduced porosity and fluid-tight in at least one heat
formed band, stripe or section extending along the length of the
mat.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to and the benefit of U.S.
Patent Application Ser. No. 61/247,205, filed on Sep. 30, 2009, PCT
Patent Application No. PCT/EP2010/064131 filed Sep. 24, 2010, and
is a divisional application of co-pending U.S. patent application
Ser. No. 13/498,594 filed May 10, 2012.
FIELD OF THE INVENTION
[0002] The invention relates to membrane contactors or modules,
hollow fiber membrane contactors, membrane contactors with selected
areas of impermeability, hollow fiber membrane mats with selected
areas of impermeability, and/or hollow fiber membranes with
selected areas of impermeability. In accordance with at least one
embodiment, the hollow fiber membrane mat has hollow fiber
membranes arranged parallel to one another and adjacent to one
another, the membranes having a wall and a continuous lumen,
wherein the hollow fiber membranes are connected to one another by
means of a plurality of connecting threads which are arranged
spaced apart from one another and parallel to one another and the
membranes are kept apart from one another by the connecting
threads, and wherein the hollow fiber membranes are composed of a
thermoplastic polymer. The invention further relates to methods for
producing and/or using such contactors, modules, or mats.
BACKGROUND
[0003] Membrane modules based on hollow fiber membranes or
capillary membranes are used for the most varied purposes to filter
or separate individual components out of a liquid or to add such
components to liquids. Hollow fiber membranes as a rule have a
semi-permeable wall with a porous structure via which the
respective components permeate into the liquid or out of the
liquid. In many cases, hollow fiber membranes are integrated in
mats, such as e.g. woven or knitted mats for better processability
as well as for the production of membrane modules with improved
fluid dynamics. Mats of this type and multilayer wound bodies
produced therefrom are described for example in U.S. Pat. No.
4,940,617 hereby incorporated by reference herein.
[0004] In the meantime, hollow fiber membrane modules have found
broad use in the area of adding gases to liquids, degassing of
liquids or in gas separation. Hollow fiber membrane modules,
contactors, fabrics, or cartridges are described for example in US
Patent documents U.S. Pat. No. 4,220,535, U.S. Pat. No. 5,186,832,
U.S. Pat. No. 5,264,171, U.S. Pat. No. 5,284,584, and U.S. Pat. No.
5,352,361, each incorporated by reference herein.
[0005] In various processes in the pharmaceutical and chemical
industries, it is necessary to run multi-step extraction processes,
during which a dissolved component in an e.g. aqueous phase is
initially extracted by means of an organic phase and this component
is subsequently separated from the organic phase by means of a
second aqueous phase. Multi-step processes of this type can be
combined in a one-step process in membrane modules, which contain
two groups of hollow fiber membranes, wherein the feed stream flows
through the hollow fiber membranes of the one group and the stream
finally containing the separated component (strip stream) flows
through the hollow fiber membranes of the second group. The outer
space around the hollow fiber membranes is filled with an
extraction liquid, which transports the component to be extracted
from the hollow fiber membranes of the first group to the hollow
fiber membranes of the second group. Here, the liquid surrounding
the hollow fiber membranes functions as a liquid membrane.
Processes of this type are also described in the literature as CLM
(contained liquid membrane) separation processes (see e.g. Majumdar
et al., AIChE Journal, vol. 34 (1988), No. 7, pp. 1135-1145;
Sengupta et al., AIChE Journal, vol. 34 (1988), No. 10, pp.
1698-1708; Basu et al., J. of Membrane Science, vol. 75 (1992), pp.
131-149). By means of these separation processes, components can be
separated from liquid as well as from gaseous media. The membrane
modules delineated in the literature cited have two groups of
hollow fiber membranes which are arranged parallel to each other in
the middle section of the housing.
[0006] In various applications in the area of CLM separation
processes, the stability of the liquid phase, i.e. of the liquid
membrane, is insufficient, and there exists a need for alternative
module designs that enable a long-lasting stability of the liquid
membrane.
[0007] An example for a membrane module design of this type or for
a membrane contactor of this type with increased stability of the
liquid phase is disclosed in U.S. patent application Ser. No.
12/112,071, filed on Apr. 30, 2008, published as US 2009/0272684
A1, published Nov. 5, 2009, hereby incorporated by reference
herein. The CLM contactor described therein has a first and a
second mat, composed of semi-permeable hollow fiber membranes which
are arranged offset with respect to one another in the longitudinal
direction of the hollow fiber membranes, said mats are wound around
a perforated central tube. The ends of the hollow fiber membranes
offset with respect to one another of the mats wound in this way
into a hollow fiber membrane wound body are embedded at one end of
the CLM contactor in a first and a third sealing compound and at
the other end of the contactor in a second and a fourth sealing
compound, wherein a first chamber is formed between the first and
third sealing compounds as well as a second chamber between the
second and fourth sealing compounds. Thereby, the walls of the
hollow fiber membranes of the first hollow fiber membrane mat are
fluid impermeable in the area of the first chamber and the walls of
the hollow fiber membranes of the second hollow fiber membrane mat
are fluid impermeable in the area of the second chamber, whereas
the walls of the hollow fiber membranes are porous and
semi-permeable outside of the respective chambers.
SUMMARY OF THE INVENTION
[0008] In accordance with at least one aspect or embodiment
thereof, the present invention addresses the need for an
alternative module design that enables a long-lasting stability of
the liquid membrane.
[0009] In accordance with at least certain aspects or embodiments
of the present invention, there are provided improved or
alternative membrane contactors or modules, hollow fiber membrane
contactors, membrane contactors with selected areas of
impermeability, hollow fiber membrane mats with selected areas of
impermeability, and/or hollow fiber membranes with selected areas
of impermeability. In accordance with at least one particular
embodiment, the hollow fiber membrane mat has hollow fiber
membranes arranged parallel to one another and adjacent to one
another, the membranes having a wall and a continuous lumen,
wherein the hollow fiber membranes are connected to one another by
means of a plurality of connecting threads which are arranged
spaced apart from one another and parallel to one another and the
membranes are kept apart from one another by the connecting
threads, and wherein the hollow fiber membranes are composed of a
thermoplastic polymer.
[0010] In accordance with at least selected aspects or embodiments
of the present invention, there are provided improved or
alternative methods for producing and/or using membrane contactors,
modules, and/or mats.
[0011] It is one object of the present invention to provide hollow
fiber membrane arrangements for CLM contactors of this type with
increased stability of the liquid phase, i.e. with increased
stability of the liquid membrane. It is a further object of the
present invention to provide a method for producing hollow fiber
membrane arrangements of this type.
[0012] It is yet another object of the present invention to provide
improved or novel membrane contactors (including without
limitation, single or multi-stage, shelled or shell-less, cartridge
type, end port, side port, 3 port, 4 port, 6 port, cylindrical,
rectangular, and/or the like), filters, cartridges, or modules,
hollow fiber membrane contactors, filters, cartridges, or modules,
membrane contactors with selected areas of impermeability,
impermeable sections or portions thereof, hollow fiber membrane
arrangements, membrane mats or fabrics, and/or the like. It is a
further object of the present invention to provide a method for
producing and/or using such membrane contactors, filters,
cartridges, or modules, hollow fiber membrane contactors, filters,
cartridges, or modules, membrane contactors with selected areas of
impermeability, impermeable sections or portions thereof, hollow
fiber membrane arrangements, or membrane mats or fabrics.
[0013] At least the object according to the invention to provide
hollow fiber membrane arrangements for CLM contactors with
increased stability of the liquid phase is addressed or solved by a
hollow fiber membrane mat having hollow fiber membranes arranged
parallel to one another and adjacent to one another, said membranes
having a wall and a continuous lumen, wherein the hollow fiber
membranes are connected to one another by means of a plurality of
linear connecting elements which are arranged spaced apart from one
another and parallel to one another and said membranes are kept
apart from one another by the linear connecting elements, and
wherein the hollow fiber membranes are composed of a thermoplastic
polymer, characterized in that the wall of the hollow fiber
membranes arranged adjacent to one another is fluid-tight in at
least one stripe extending parallel to the linear connecting
elements within the hollow fiber membrane mat, that the linear
connecting elements have a melting temperature that is at least as
high as the melting temperature of the thermoplastic polymer
composing the hollow fiber membranes, and that the linear
connecting elements outside of the at least one stripe extending
parallel to the linear connecting elements, inside of which stripe
the hollow fiber membranes are fluid-tight, preferably have a
superheated steam shrinkage of at most 5% at a temperature of
121.degree. C. and an atmospheric humidity of 100% (saturated
steam).
[0014] This object is further solved or addressed by a method for
producing a hollow fiber membrane mat with at least one
stripe-shaped area in which the wall of the hollow fiber membranes
is fluid impermeable, wherein the method comprises the steps:
[0015] a) providing a hollow fiber membrane mat having hollow fiber
membranes arranged parallel to one another and adjacent to one
another, said membranes having a porous, semi-permeable wall and a
continuous lumen, wherein the hollow fiber membranes are connected
to one another by means of a plurality of linear connecting
elements which are arranged spaced apart from one another and
parallel to one another and said membranes are kept at a distance
by the linear connecting elements and wherein the hollow fiber
membranes are composed of a thermoplastic polymer, and the linear
connecting elements have a melting temperature that is at least as
high as the melting temperature of the thermoplastic polymer
composing the hollow fiber membranes, and the connecting threads
preferably have a superheated steam shrinkage of at most 5% at a
temperature of 121.degree. C. and an atmospheric humidity of 100%,
[0016] b) transporting the hollow fiber membrane mat by means of a
transport equipment and at a transport speed in the direction of
the extension of the linear connecting elements and under a tension
acting in the transport direction through at least one heating
device extending in the transport direction having heating elements
arranged above and below the hollow fiber membrane mat and at a
distance from the surface of the hollow fiber membrane mat as well
as from one another via which heat is supplied to the hollow fiber
membranes in a treatment zone over a width B transverse to the
transport direction, whereby the hollow fiber mat is treated in a
treatment area, and simultaneously [0017] c) gripping of the hollow
fiber membrane mat in zones, which are located to the right and
left of the at least one heating device when viewed in the
transport direction, by clamping devices, which are adjustable
regarding their contact pressure perpendicular to the flat
extension of the hollow fiber membrane mat, by means of which
clamping devices the hollow fiber membranes are held under tension
transverse to the transport direction, wherein in the treatment
zone the temperature is preferably adjusted to a temperature 5 to
15% below the melting temperature of the polymer composing the
hollow fiber membranes by means of the heating elements so that a
shrinkage of the hollow fiber membranes is initiated in the
treatment area, and wherein by adjusting the contact pressure of
the clamping devices, the hollow fiber membranes are held under
tension in their longitudinal extension so that the hollow fiber
membranes retain a straight-line course in their longitudinal
extension.
[0018] In accordance with at least selected embodiments or aspects
of the invention, the treated zone, band or stripe may be fluid
impermeable or fluid-tight, such as the wall of the hollow fiber
membranes in the treatment areas becomes impermeable to fluid
passage due to the temperature treatment during passage through a
treatment zone between radiant heat elements. The temperature
treatment of the hollow fiber membranes may initiate a shrinkage or
contraction of the hollow fiber membranes in the areas treated,
whereby the pores there apparently collapse and the porous
structure disappears.
[0019] Alternatively, one can control or change the desired overall
permeability from full permeability (no heated sections) to little
or no permeability (all heated sections) based on the desired
permeability of the membrane contactor, filter, cartridge, or
module. For example, one may change a very porous membrane
contactor to a less porous membrane contactor by heat treating
several stripes along its length.
[0020] Further, one may desire to close the pores in an initial
section of a membrane contactor, filter, cartridge, or module,
hollow fiber membrane contactor, hollow fiber membrane arrangement,
mat, fabric, or the like to provide a heat transfer section
upstream of a porous or permeable fluid transfer section. Such a
dual function module having a heat transfer section and a fluid
transfer (or separation or filtration) section may replace a
multi-module system having a heat transfer module and a fluid
transfer module.
[0021] At least selected embodiments of the invention preferably
relate to a hollow fiber membrane mat having hollow fiber membranes
arranged parallel to one another and adjacent to one another, said
membranes having a wall and a continuous lumen, wherein the hollow
fiber membranes are connected to one another by means of a
plurality of linear connecting elements which are arranged spaced
apart from one another and parallel to one another and said
membranes are kept apart from one another by the linear connecting
elements and wherein the hollow fiber membranes are composed of a
thermoplastic polymer and wherein the walls of the hollow fiber
membranes arranged adjacent to one another are fluid-tight in at
least one stripe extending parallel to the linear connecting
elements inside of the hollow fiber membrane mat. The linear
connecting elements have a preferred melting temperature that is at
least as high as the melting temperature of the thermoplastic
polymer composing the hollow fiber membranes, and the linear
connecting elements outside of the at least one stripe extending
parallel to the linear connecting elements, inside of which stripe
the hollow fiber membranes are fluid-tight, preferably have a
superheated steam shrinkage of at most 5%. At least selected
embodiments of the invention preferably further relate to a method
for producing and/or using such hollow fiber membrane mats.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIGS. 1 to 6 are respective images of hollow fiber membrane
wall structures or surfaces at 5000.times. magnification made using
a scanning electron microscope.
[0023] FIGS. 1 and 2 are respective before and after (or untreated
and treated) images related to Example 1 below.
[0024] FIGS. 3 and 4 are respective before and after (or untreated
and treated) images related to Example 2 below.
[0025] FIGS. 5 and 6 are respective before and after (or untreated
and treated) images related to Example 3 below.
[0026] FIG. 7 is a schematic illustration of an embodiment of the
invention.
DETAILED DESCRIPTION
[0027] In accordance with at least one aspect or embodiment
thereof, the present invention addresses the need for an
alternative module design that enables a long-lasting stability of
the liquid membrane.
[0028] In accordance with at least certain aspects or embodiments
of the present invention, there are provided improved or
alternative membrane contactors or modules, hollow fiber membrane
contactors, membrane contactors with selected areas of
impermeability, hollow fiber membrane mats with selected areas of
impermeability, and/or hollow fiber membranes with selected areas
of impermeability. In accordance with at least one particular
embodiment, the hollow fiber membrane mat 1 has hollow fiber
membranes 2 arranged parallel to one another and adjacent to one
another, the membranes having a wall and a continuous lumen,
wherein the hollow fiber membranes are connected to one another by
means of a plurality of connecting threads 3 which are arranged
spaced apart from one another and parallel to one another and the
membranes are kept apart from one another by the connecting
threads, and wherein the hollow fiber membranes are composed of a
thermoplastic polymer.
[0029] In accordance with at least selected aspects or embodiments
of the present invention, there are provided improved or
alternative methods for producing and/or using membrane contactors,
modules, and/or mats.
[0030] Within the context of the present invention, fluid
impermeable and fluid-tight are understood to mean that the wall of
the hollow fiber membranes in the treatment area or treated area is
impermeable, i.e. sealed against a convective transport or passage
of gases or liquids. When examining the fluid impermeable or
fluid-tight hollow fiber membranes under scanning electron
microscopic at a 5000.times. magnification, no pores are visible at
least in one of the surfaces of the walls of the hollow fiber
membranes in the at least one treated area or in the at least one
stripe 4a and/or 4b extending parallel to the linear connecting
elements, whereas this surface has pores outside of the at least
one treated area or the at least one stripe extending parallel to
the linear connecting elements.
[0031] By the heating elements, heat may be supplied in the
treatment zone to the hollow fiber mat by convection, e.g. by using
hot-air blowers. The heat may also be supplied by conduction, e.g.
in cases when the hollow fiber mat is covered with temperature
stable carrier belts as will be described below.
[0032] For the preferred method according to at least one
embodiment of the invention it is important that during the
temperature treatment of the hollow fiber membranes in the
treatment zone movements of the hollow fiber membranes towards each
other during the application of heat is avoided or at least are
kept low. More particularly, the hollow fiber membranes should not
move toward one another to an extent, that could lead to a contact
of the hollow fiber membranes with one another and to a fusing or
adhering of the hollow fiber membranes with one another in the
treatment areas. Therefore, in a preferred embodiment of the
process of the invention, the at least one heating device extending
in the transport direction has radiant heating elements arranged
above and below the hollow fiber membrane mat and at a distance
from the surface of the hollow fiber membrane mat as well as to one
another. The use of radiant heating elements instead of e.g. hot
air blowers has the additional advantage that a sharp transition
from the treated to the untreated area of the hollow fiber
membranes can be obtained instead of a transition extending over
several millimeters or even centimeters, which, in regard to the
applications in e.g. CLM contactors, would be a disadvantage.
[0033] With regard to the radiant heating elements, in a preferred
embodiment they can be hotplates, which are heated to a
sufficiently high temperature so that the temperature at the hollow
fiber membrane mat lies 5 to 15% below the melting temperature of
the polymer composing the hollow fiber membranes. The hotplates can
have a rectangular contour with a width B transverse to the
transport direction corresponding to the intended width of the
stripe or segment in the hollow fiber membrane mat in which stripe
the wall of the hollow fiber membranes is fluid-tight. The length L
of the hotplates in the transport direction is determined
considering the transport speed according to the required residence
time of the hollow fiber membranes in the area of the radiant heat
elements and can lie within the preferred range of approximately 5
cm to approximately 20 cm. The distance of the hotplates to one
another is as a rule a few millimeters and lies preferably in the
range of 4 to 8 mm.
[0034] The radiant heating elements can also comprise infrared (IR)
radiators that are located at a suitable distance to the hollow
fiber membrane mat so that a temperature is present at the hollow
fiber membrane mat which preferably lies 5 to 15% below the melting
temperature of the polymer composing the hollow fiber membranes. In
this case it may be advantageous to limit the infrared radiation,
e.g. by appropriately dimensioned apertures, to the required
treatment area of the hollow fiber membrane mat.
[0035] With respect to fluid impermeable or fluid-tight hollow
fiber membranes, the wall of the hollow fiber membranes in the
treatment areas becomes impermeable to fluid passage due to the
temperature treatment during passage through the treatment zone
between the radiant heat elements. The temperature treatment of the
hollow fiber membranes at a preferred temperature 5 to 15% below
the melting temperature of the polymer composing the hollow fiber
membranes initiates a shrinkage or contraction of the hollow fiber
membranes in the areas treated, whereby the pores there apparently
collapse and the porous structure disappears.
[0036] Alternatively, one can control or change the desired overall
permeability from full permeability (no heated sections) to little
or no permeability (all heated sections) based on the desired
permeability of the membrane contactor, filter, cartridge, or
module. For example, one may change a very porous membrane
contactor to a less porous membrane contactor by heat treating
several stripes along its length.
[0037] Further, one may desire to close the pores in an initial
section of a membrane contactor, filter, cartridge, or module,
hollow fiber membrane contactor, hollow fiber membrane arrangement,
mat, fabric, or the like to provide a heat transfer section
upstream of a porous or permeable fluid transfer section. Such a
dual function module having a heat transfer section and a fluid
transfer (or separation or filtration) section may replace a
multi-module system having a heat transfer module and a fluid
transfer module.
[0038] The length of the treatment zone and thereby also the length
of the heating elements is to be determined in the transport
direction, so that considering the transport speed of the hollow
fiber membrane mat the residence time of the hollow fiber membranes
in the treatment zone is sufficient to allow the shrinkage process
to proceed to the desired extent, for example, that the porous
structure disappears and the wall of the hollow fiber membranes in
the treated area becomes fluid impermeable. The residence time of
the hollow fiber membrane mat in the treatment zone lies preferably
in the range of 0.5 to 5 minutes, more preferably between 1 and 3
minutes.
[0039] It was found that the porous structure in the treated areas
of the hollow fiber membranes disappears due to the temperature
application not only on the outer side of the hollow fiber membrane
but, at a sufficient residence time, also on the inner side facing
the lumen. In hollow fiber membranes that prior to the treatment
had a distinct porous structure on the surfaces in the treatment
areas, as proven by an examination using a scanning electron
microscope, sealed surfaces free from pores on the outer as well as
on the inner side were obtained as a result of the treatment
according to the invention. Basis for the judgment was the
examination of the surfaces at 5000.times. magnification using a
scanning electron microscope. In a preferred embodiment of the
hollow fiber membrane mat according to the invention or of the
hollow fiber membrane mat produced according to the method of the
invention, the wall of the hollow fiber membranes is free of pores
in the at least one stripe on the surface facing the lumen as well
as on the surface facing outward.
[0040] During the preferred temperature treatment of the hollow
fiber membrane mats in accordance with at least selected
embodiments, it is of importance on the one hand that the hollow
fiber membranes are held under tension in their longitudinal
direction, i.e. in the direction of their extension, in order to
prevent a crimping together as well as a complete collapse of the
hollow fiber membranes and with this a choking of the lumen of the
hollow fiber membranes in the at least one treatment area. On the
other hand, it is important that the linear connecting elements
have a melting temperature that is at least as high as the melting
temperature of the thermoplastic polymer composing the hollow fiber
membranes, and that the linear connecting elements are
low-shrinkage, i.e. they have a superheated steam shrinkage of
preferably at most 5% at a temperature of 121.degree. C. and at an
atmospheric humidity of 100% (saturated steam). Otherwise, the
linear connecting elements may have a shrinkage that is too high
under the temperature application, which could result in the
constriction of the hollow fiber membranes by the linear connecting
elements and--depending on the connecting elements used--even in a
choking of the hollow fiber lumen. Moreover, in case of a too high
shrinkage, the adjacent hollow fiber membranes may come into
contact and may fuse together, thereby leading to undesirable stiff
segments in the hollow fiber mat. More preferably, the linear
connecting elements of the hollow fiber membrane mat according to
at least certain embodiments of the invention or produced by the
method according to at least selected embodiments of the invention
have a superheated steam shrinkage of at most 2% at a temperature
of 121.degree. C. and at an atmospheric humidity of 100%. To
determine the superheated steam shrinkage, the linear connecting
element material is treated for 30 minutes at a temperature of
121.degree. C. and at an atmospheric humidity of 100% (saturated
steam).
[0041] Finally, it is preferred in at least certain embodiments
that the hollow fiber membrane mat is held under a tension acting
in the transport direction, i.e. in the direction of the extension
of the linear connecting elements, during passage through the
heating device. By this means, the hollow fiber membranes also
remain spaced apart from one another during the heat application
and an adhesion of adjacent hollow fiber membranes is prevented.
The tension in transport direction thereby can only be applied via
the linear connecting elements of the hollow fiber membrane mat,
since the hollow fiber membranes themselves are not in contact with
each other. Therefore the tension acting in the transport direction
is preferably in the range of 5 to 15 cN per linear connecting
element which is present over the width of the hollow fiber
membrane mat (1 cN=1.02 g). To achieve a uniform tension over the
mat width, it can be advantageous that the hollow fiber membrane
mat is fed over a support, e.g. in the form of a plate, or is laid
on a carrier belt driven at the transport speed.
[0042] As described, the temperature treatment of the hollow fiber
membranes at a temperature somewhat below the melting temperature
of the polymer composing the hollow fiber membranes initiates
shrinkage or contraction of the hollow fiber membranes in the
treatment areas, whereby the pores in these areas apparently
collapse and the porous structure disappears (or is reduced).
Moreover, a crimping together as well as a complete collapse of the
hollow fiber membranes and with this a choking of the lumen of the
hollow fiber membranes can occur. To counteract this, in the
preferred method according to at least selected embodiments of the
invention, the hollow fiber membrane mat is gripped in zones to the
right and left of the at least one heating device by clamping
devices, which are adjustable regarding their contact pressure
perpendicular to the flat extension of the hollow fiber membrane
mat. Here, the contact pressure should be adjusted so that the
hollow fiber membranes can indeed shrink in their longitudinal
extension, however they are held under tension so that they retain
a straight-line course. It should be noted here that at a contact
pressure that is too high, the necessary movement in the direction
of extension of the hollow fiber membranes resulting from the
shrinkage initiated by the temperature treatment in the treatment
area of the hollow fiber membrane mat is suppressed. As a result,
capillaries in the treatment area shrink in their outer diameter,
i.e. become thinner or even tear if the elongation at break is
exceeded. On the other hand, a contact pressure that is too low
leads to a mat that contracts uncontrolled in the treatment area
and warping and/or kinking of the capillaries occurs, or the lumen
of the hollow fiber membranes collapses also. The contact pressure
suitable in each case can be visually determined by simple
tests.
[0043] The clamping devices can be e.g. metal belts fed via driven
rollers, which belts press against the hollow fiber membrane mat
and which belts move along at the speed with which the hollow fiber
membrane mat is fed through the at least one heating device, i.e.
at the transport speed. The clamping devices can however also be
static elements, e.g. in the form of skid-shaped and adjustable
clamping shoes by means of which the hollow fiber membrane mat is
preferably gripped on the side edges and by which a contact
pressure is exerted on the mat. The clamping devices must of course
be located along the transport direction of the hollow fiber
membrane mat at the height of the treatment zone.
[0044] According to the invention, the hollow fiber membranes
arranged in the hollow fiber membrane mat are composed of a
thermoplastic polymer. In particular synthetic polymers selected
from the group of polyolefins, such as e.g. polyethylene,
polypropylene, polybutylene, polyisobutylene or fluorinated
polyolefins, sulfone polymers, such as e.g. polysulfone,
polyethersulfone, polyarylethersulfone, polyamides,
polyetherimides, polyacrylonitriles, polyesters, polyetherimides,
polyetheretherketones (PEEK), polymethylmethacrylates (PMMA),
polymethyl pentene (PMP), ethyl vinyl alcohols (EVA), copolymers of
these polymers or blends or mixtures of these polymers come into
consideration here. Particularly preferred, the polymer composing
the hollow fiber membranes is a polyolefin, more particularly
preferred polypropylene. The hollow fiber membrane mat may be made
up of more than one type and/or size of hollow fiber membranes.
[0045] The hollow fiber membranes are preferably connected in the
hollow fiber membrane mat according to the invention by means of a
plurality of linear connecting elements spaced apart from one
another and running parallel to one another. The linear connecting
elements by which the hollow fiber membranes are incorporated into
the mat and by which the hollow fiber membranes are kept at a
distance with respect to each other may be strip-shaped elements
which may be laminated onto the hollow fiber membranes or which may
be adhered to the hollow fiber membranes by an adhesive. The linear
connecting elements may also be made of a ribbon-like material. In
a preferred embodiment of the hollow fiber membrane mat and of the
process according to the invention, the linear connecting elements
are connecting threads, i.e. are yarns or fibers which connect the
hollow fiber membranes with each other. The connecting threads may
be entwined around the single hollow fiber membranes. The hollow
fiber membranes in the mat are preferably connected by means of
connecting threads using a knitting method, i.e. the hollow fiber
membrane mat is preferably a knitted mat. In an especially
preferred embodiment, the connecting threads are multifilament
yarns. Multifilament polyester yarns are most preferred for the
connecting threads. Within the context of the present invention,
preferred yarns have a melting temperature that is as high as the
melting temperature of the thermoplastic polymer composing the
hollow fiber membranes and that have a superheated steam shrinkage
of preferably at most 5% and more preferably have a superheated
steam shrinkage of at most 2% at a temperature of 121.degree. C.
and at an atmospheric humidity of 100%. The hollow fiber membranes
may be connected in the hollow fiber membrane mat by means of a
plurality of different types and/or sizes of linear connecting
elements. Further, the hollow fiber membranes or mats may be spaced
apart by spacers, may be connected or fixed in the hollow fiber
membrane mat, contactor, filter, cartridge, or module by means of
potting, such as epoxy resin at each end, and/or tube sheets,
and/or may be formed about a perforated center tube.
[0046] Regarding the transport equipment used in step b) of the
preferred method according to at least certain embodiments of the
invention, it can be conventional equipment such as that used for
continuous transport of sheet-like products. For example, the
transport equipment can have driven rollers from which the hollow
fiber mat is unwound or on which the hollow fiber mat is wound in a
controlled manner. The transport equipment can additionally have
pairs of rollers by means of which the hollow fiber mat, together
with, for example, a transport belt is fed to and withdrawn from
the at least one heating device. It is advantageous for a gentle
and uniform transport of the hollow fiber membrane mat through the
at least one heating device, if the hollow fiber membrane mat is
transported through the heating device between carrier belts
located above and below the hollow fiber membrane mat and covering
the hollow fiber membrane mat. Covering the hollow fiber membrane
mat in the treatment zone between the heating elements at the same
time has the advantage that the hollow fiber membranes are fed in a
gentle manner through the treatment zone and in particular vertical
or horizontal movements of the hollow fiber membranes in this area
resulting from the temperature treatment are also prevented.
Movements of this type can for example lead to contact between
adjacent hollow fiber membranes and result in an adhesion of the
hollow fiber membranes.
[0047] The carrier belts can preferably be stretched polymer films
with a sufficient strength and a low elongation, such as e.g. those
made of polytetrafluoroethylene. In a further preferred embodiment,
the carrier belts can be fine fabrics made of temperature-stable
yarns, such as e.g. fabrics made of polytetrafluoroethylene and/or
aramid yarns. The hollow fiber membrane mat is preferably covered
by the carrier belts over its entire width and therefore also in
the areas that pass through the treatment zones, wherein the
carrier belts therefore are composed of a temperature-stable
material and sticking between the mat and carrier belts does not
occur, so that the carrier belts can be withdrawn,
unproblematically and without leaving a residue, from the hollow
fiber membrane mat after passage through the at least one heating
device. The carrier belts are therefore preferably non-stick. The
carrier belts may also act as spacers between the heating elements
and the hollow fiber mat during passage through the treatment zone.
The carrier belts located on the upper and lower sides are
preferably driven and transport the hollow fiber membrane mat at
the required speed in the transport direction, and therefore
simultaneously constitute the transport device.
[0048] The use of carrier belts which cover the hollow fiber
membrane mat on its entire upper and lower side has the further
advantage that the hollow fiber membrane mat can be fed uniformly
and warp-free through the treatment equipment containing at least
one heating device. In addition, a gentle gripping and feeding
through the clamping devices, which effect a stabilization of the
hollow fiber membrane mat in the direction of the extension of the
hollow fiber membranes, is also possible. Therefore, in a preferred
embodiment of the method according to the invention, the hollow
fiber membrane mat is covered in the area of its side edges with
carrier belts and together with the covering carrier belts is fed
through skid-shaped clamping devices.
[0049] Depending on the use of the hollow fiber mat according to
the invention or produced by the method according to the invention,
it can be necessary that this mat has more than one area or more
than one stripe in which the walls of the hollow fiber membranes
arranged in the mat are fluid impermeable. To produce this type of
hollow fiber membrane mats, the hollow fiber membrane mat is fed
through at least one second heating device which is arranged
transverse to the transport direction at a distance from the first
heating device, by means of which at least one further stripe
shaped area is created in the extension direction of the linear
connecting elements, in which area the walls of the hollow fiber
membranes are fluid impermeable. The at least one second heating
device thereby preferably can have the same design as the first
heating device.
[0050] Due to the fluid impermeable areas, the preferred hollow
fiber membrane mats according to the invention or the preferred
hollow fiber membrane mats produced according to the method
according to the invention can be best used in e.g. CLM contactors,
which require a high stability of the liquid membrane formed in
these contactors.
[0051] FIGS. 1 to 6 are respective images of hollow fiber membrane
wall structures or surfaces at 5000.times. magnification made using
a scanning electron microscope.
[0052] At least selected embodiments of the invention will now be
described in more detail by way of the following examples:
Example 1
[0053] A hollow fiber membrane knitted mat with a width of 750 mm
was provided. The hollow fiber membranes arranged in the hollow
fiber membrane mat were stretched polypropylene hollow fiber
membranes (type X40, Celgard, LLC of Charlotte, N.C.) with a
throughout porous wall, a diameter of 400 .mu.m and a wall
thickness of 40 .mu.m. The hollow fiber membranes were bound into
the hollow fiber membrane mat by means of multifilament polyester
threads, wherein 150 warp threads, i.e. connecting threads were
distributed uniformly over the width of the mat in the transport
direction. The polyester threads had a superheated steam shrinkage
of less than 1%.
[0054] The hollow fiber membrane mat was withdrawn from a roll at a
transport speed of 7.6 cm/min, fed together with driven carrier
belts made of a fabric made of polytetrafluoroethylene yarns and
aramid yarns on the upper and lower sides of the mat through a
heating device and after the temperature treatment wound onto a
roll with a tension of approximately 10 cN per warp thread.
[0055] The heating device comprised a radiant heat element located
over and under the mat respectively. Each radiant heat element
comprised a hotplate made of aluminum having a width of 125 mm and
a length of 100 mm which were heated by two heating cartridges per
hotplate to a temperature of 155.degree. C. The hotplates were
spaced 5 mm from one another; the hollow fiber membrane mat,
together with the carrier belts, was fed through in the center
between the hotplates. By this means, also in the area of the
hollow fiber membrane mat the temperature was approximately
155.degree. C., which temperature was approximately 7% below the
melting temperature of the polypropylene.
[0056] In the area of the side edges, skid-shaped clamping devices
were pressed against the hollow fiber membrane mat, under which
clamping devices the hollow fiber membrane mat was drawn through
together with the carrier belts. The contact pressure of the
clamping devices was adjusted so that a straight-line course of the
hollow fiber membranes was guaranteed in the area of the heating
device, however simultaneously shrinkage of the hollow fiber
membranes was possible in the longitudinal direction in the area of
the heating device as a result of the temperature application.
[0057] During the passage through the heating device, the hollow
fiber membranes shrank in the treatment area by approximately
35-40%. After passage through the heating zone, the structure of
the hollow fiber membrane wall was altered, which was recognized by
a change in the optical appearance from white to transparent. In
the transparent areas of the hollow fiber membranes, the originally
porous wall structure (FIG. 1) had transformed into a dense film
structure (FIG. 2). The hollow fiber membrane mat thus treated had
a stripe extending parallel to the connecting threads, in which
stripe the wall of the polypropylene hollow fiber membranes was
fluid impermeable.
Example 2
[0058] The procedure was the same as in Example 1. Instead of the
hollow fiber membrane mat made of stretched polypropylene hollow
fiber membranes used in Example 1, a hollow fiber membrane mat made
of unstretched polypropylene hollow fiber membranes (type PP 50280,
Membrana GmbH of Wuppertal, Germany) was provided.
[0059] After passage through the treatment zone, the structure of
the hollow fiber membrane wall was altered, which was recognized by
a change in the optical appearance from white to transparent. As
proven by examination in the scanning electron microscope, in the
treated, transparent areas of the hollow fiber membranes, the
original porous wall structure (FIG. 3) had changed into a
fluid-tight film structure (FIG. 4).
Example 3
[0060] The procedure was the same as in Example 1. Contrary to
Example 1, hollow fiber membranes made from
poly-(4-methyl-1-pentene) were used (type 90200, Membrana GmbH).
The hotplates were heated to 210.degree. C. and thereby to a
temperature approximately 15% below the melting temperature of
poly-(4-methyl-1-pentene).
[0061] Due to the temperature treatment, the hollow fiber membranes
made of poly-(4-methyl-1-pentene) likewise changed in appearance
from white to transparent. The original porous inner surface of the
hollow fiber membranes facing the lumen (FIG. 5) was dense after
the temperature treatment (FIG. 6). For these
poly-(4-methyl-1-pentene) hollow fiber membranes, too, a mat was
obtained for which the hollow fiber membrane walls were fluid-tight
in a stripe parallel to the connecting threads.
Comparative Example 1
[0062] The procedure was the same as in Example 1. Contrary to
Example 1, the hot plates were heated to a temperature of
170.degree. C. and thereby to a temperature just above the melting
temperature of the polypropylene.
[0063] As a result of the high temperature stress in the treatment
zone, a fusing of adjacent hollow fiber membranes and a collapse of
the lumina of the hollow fiber membranes was found for a large part
of the hollow fiber membranes.
Comparative Example 2
[0064] The procedure was the same as in Example 3. Contrary to
Example 3, the hotplates were heated to 195.degree. C. and thereby
to a temperature approximately 20% below the melting temperature of
poly-(4-methyl-1-pentene).
[0065] In the treatment area, there was no change in the appearance
of the hollow fiber membranes. The hollow fiber membranes were
still white after the treatment, i.e. the walls of the hollow fiber
membranes continued to have a porous structure in this area.
[0066] At least selected embodiments of the invention preferably
relate to a hollow fiber membrane mat having hollow fiber membranes
arranged parallel to one another and adjacent to one another, said
membranes having a wall and a continuous lumen, wherein the hollow
fiber membranes are connected to one another by means of a
plurality of linear connecting elements which are arranged spaced
apart from one another and parallel to one another and said
membranes are kept apart from one another by the linear connecting
elements and wherein the hollow fiber membranes are composed of a
thermoplastic polymer and wherein the walls of the hollow fiber
membranes arranged adjacent to one another are fluid-tight in at
least one stripe extending parallel to the linear connecting
elements inside of the hollow fiber membrane mat. The linear
connecting elements preferably have a melting temperature that is
at least as high as the melting temperature of the thermoplastic
polymer composing the hollow fiber membranes, and the linear
connecting elements outside of the at least one stripe extending
parallel to the linear connecting elements, inside of which stripe
the hollow fiber membranes are fluid-tight, have a superheated
steam shrinkage of at most 5%. At least selected embodiments of the
invention preferably further relate to a method for producing
and/or using such hollow fiber membrane mats.
[0067] In accordance with at least selected embodiments of the
invention, a hollow fiber membrane mat has hollow fiber membranes
arranged parallel to one another and adjacent to one another, the
membranes having a wall and a continuous lumen, wherein the hollow
fiber membranes are connected to one another by means of a
plurality of linear connecting elements which are arranged spaced
apart from one another and parallel to one another and the hollow
fiber membranes are kept apart from one another by the linear
connecting elements and wherein the hollow fiber membranes are
composed of at least one thermoplastic polymer, characterized in
that the walls of the hollow fiber membranes arranged adjacent to
one another are fluid-tight in at least one stripe extending
parallel to the linear connecting elements within the hollow fiber
membrane mat, that the linear connecting elements have a melting
temperature that is at least as high as the melting temperature of
the thermoplastic polymer composing the hollow fiber membranes, and
that the linear connecting elements outside of the at least one
stripe extending parallel to the linear connecting elements, inside
of which stripe the hollow fiber membranes are fluid-tight, have a
superheated steam shrinkage of at most 5% at a temperature of
121.degree. C. and an atmospheric humidity of 100%.
[0068] The above hollow fiber membrane mat, characterized in that
the linear connecting elements have a superheated steam shrinkage
of at most 2% at a temperature of 121.degree. C. and an atmospheric
humidity of 100%.
[0069] The above hollow fiber membrane mat, characterized in that
the polymer composing the hollow fiber membranes is a
polyolefin.
[0070] The above hollow fiber membrane mat, characterized in that
the linear connecting elements are connecting threads.
[0071] The above hollow fiber membrane mat, characterized in that
the connecting threads are multifilament polyester yarns.
[0072] The above hollow fiber membrane mat, characterized in that
the connecting threads holding the hollow fiber membranes at a
distance are introduced via a knitting method.
[0073] The above hollow fiber membrane mat, characterized in that
the walls of the hollow fiber membranes in the at least one stripe
are pore-free on the surface facing the lumen as well as on the
surface facing outward.
[0074] In accordance with at least certain embodiments of the
invention, a method for producing a hollow fiber membrane mat with
at least one stripe-shaped area in which the walls of the hollow
fiber membranes are fluid impermeable, includes the following
steps: [0075] a) providing a hollow fiber membrane mat having
hollow fiber membranes arranged parallel to one another and
adjacent to one another, the membranes having at least one of
porous, microporous, and semi-permeable wall and a continuous
lumen, wherein the hollow fiber membranes are connected to one
another by means of a plurality of linear connecting elements which
are arranged spaced apart from one another and parallel to one
another and the membranes are kept at a distance by the linear
connecting elements and wherein the hollow fiber membranes are
composed of a thermoplastic polymer, and the linear connecting
elements have a melting temperature that is at least as high as the
melting temperature of the thermoplastic polymer composing the
hollow fiber membranes, and the linear connecting elements have a
superheated steam shrinkage of at most 5% at a temperature of
121.degree. C. and an atmospheric humidity of 100%, [0076] b)
transporting the hollow fiber membrane mat by means of a transport
equipment and at a transport speed in the direction of the
extension of the linear connecting elements and under a tension
acting in the transport direction through at least one heating
device extending in the transport direction having heating elements
arranged above and below the hollow fiber membrane mat and at a
distance from the surface of the hollow fiber membrane mat as well
as from one another via which heat is supplied to the hollow fiber
membranes in a treatment zone over a width B transverse to the
transport direction, whereby the hollow fiber mat is treated in a
treatment area, and simultaneously [0077] c) gripping of the hollow
fiber membrane mat in zones, which are located to the right and
left of the at least one heating device when viewed in the
transport direction, by clamping devices, which are adjustable
regarding their contact pressure perpendicular to the flat
extension of the hollow fiber membrane mat, by means of which
clamping devices the hollow fiber membranes are held under tension
transverse to the transport direction, wherein in the treatment
zone the temperature is adjusted to a temperature 5 to 15% below
the melting temperature of the polymer composing the hollow fiber
membranes by means of the heating elements so that a shrinkage of
the hollow fiber membranes is initiated in the treatment area, and
wherein by adjusting the contact pressure of the clamping devices,
the hollow fiber membranes are held under tension in their
longitudinal extension so that the hollow fiber membranes retain a
straight-line course in their longitudinal extension.
[0078] The above method, characterized in that the hollow fiber
membrane mat is transported between a carrier belt arranged above
and below the hollow fiber membrane mat and covering the hollow
fiber membrane mat at least in the area of the at least one heating
device through the at least one first heating device.
[0079] The above method, characterized in that the hollow fiber
membrane mat is covered in the area of its side edges by the
carrier belts and together with the covering carrier belts is fed
by skid-shaped clamping devices.
[0080] The above method, characterized in that the length of the
heating elements in the transport direction as well as the
transport speed are adjusted so that the residence time of the
hollow fiber membrane mat in the treatment zone lies in the range
of 0.5 to 5 min.
[0081] The above method, characterized in that the heating elements
are radiant heating elements.
[0082] The above method, characterized in that the radiant heating
elements are flat hotplates.
[0083] The above method, characterized in that the distance between
the hotplates is 4 to 8 mm.
[0084] The above method, characterized in that the hollow fiber
membrane mat is fed through at least one second heating device
which is arranged transverse to the transport direction at a
distance from the first heating device, by means of which at least
one further stripe-shaped area is created in the extension
direction of the linear connecting elements, in which area the
walls of the hollow fiber membranes are fluid impermeable.
[0085] The above method, characterized in that the tension acting
in the transport direction lies in the range of 5 to 15 cN per
linear connecting element.
[0086] The above method, characterized in that the polymer
composing the hollow fiber membranes is a polyolefin.
[0087] The above method, characterized in that the linear
connecting elements are connecting threads, members or fibers.
[0088] The above method, characterized in that the connecting
threads are multifilament polyester yarns.
[0089] A hollow fiber membrane mat with at least one stripe-shaped
area in which the walls of the hollow fiber membranes are fluid
impermeable and formed by the above method.
[0090] In at least one embodiment, there is provided a hollow fiber
membrane mat having hollow fiber membranes arranged adjacent to one
another, the membranes having a wall and a continuous lumen,
wherein the hollow fiber membranes are composed of a thermoplastic
polymer, characterized in that the walls of the hollow fiber
membranes arranged adjacent to one another are at least one of
reduced porosity and fluid-tight in at least one heat formed band,
stripe or section extending along the length of the mat.
[0091] It is believed that the heat setting and/or shrinkage
control steps in typical hollow fiber production processes may play
a role in the heat shrinkage (pore collapse) mechanism utilized to
close or reduce the porosity of the pores in accordance with the
present invention. If the hollow fibers are heated to a higher
temperature than was used to do the heat setting during hollow
fiber production, then the process that created the pore structure
starts to reverse and the existing pores will close up. This may
happen because the surface area within the pore structure is
extremely large (>500 m.sup.2/gram). When sufficient energy is
added through heat, the surface tension of the polymer, as it
approaches the crystalline melting point may cause rapid fiber
contraction and pore closure. It may be critical to control the
temperature so that this process just begins but does not reach
full and complete melting of the polymer crystallinity. If that
happens, the tubular nature of the fibers may disappear. Since the
hollow fibers are preferably contained within the woven mat
structure, some shrinkage may occur but it may be held in check by
the warp threads. What is desired is a resultant hollow fiber
having a tubular structure but with the pores in the walls in at
least certain segments having reduced size, or being collapsed and
effectively removed.
[0092] In accordance with at least certain embodiments, there is
provided a method of selectively heat treating a stripe or band of
the hollow fiber array while leaving the untreated array
unaffected. This method may be most effective when used on dry
stretch formed hollow fiber membranes. By applying specifically
controlled temperature and mechanical load conditions the porosity
within the heat treated zone may be reduced or eliminated
completely. Also, within a width of array, one can create one or
more heat treated zones of varying widths.
[0093] This technique may be very useful for contactors or modules
that have multiple tube sheets. The tube sheets create different
volumes within a single module. It may be beneficial to apply this
special heat treatment within the volume created by one or more of
these zones. For example, if one of the fluid streams entering one
of these volumes is gaseous it will inadvertently enter the pore
structure of the membrane. By heat treating this zone selectively
one can make the membrane impermeable and direct the gaseous flow
to the membrane it is intended for.
[0094] In one possibly preferred embodiment, the present heat treat
method may be used is in a Contained Liquid Membrane (CLM) Module
having two different gas streams flow from zones B1 to B2 and from
zones C1 to C2. Selective heat treatment is applied in the volumes
created between the tube sheets in the B1 and C2 zones. This
prevents the two gas streams from mixing together before they enter
the CLM portion of the module in the middle.
[0095] In at least one embodiment, the invention preferably relates
to a hollow fiber membrane mat having hollow fiber membranes
arranged parallel to one another and adjacent to one another, the
membranes having a wall and a continuous lumen, wherein the hollow
fiber membranes are connected to one another by means of a
plurality of linear connecting elements which are arranged spaced
apart from one another and parallel to one another and the
membranes are kept apart from one another by the linear connecting
elements and wherein the hollow fiber membranes are composed of a
thermoplastic polymer and wherein the walls of the hollow fiber
membranes arranged adjacent to one another are fluid-tight in at
least one band, section or stripe extending parallel to the linear
connecting elements, and inside of which stripe the hollow fiber
membranes are fluid-tight. Other embodiments of the invention
preferably relate to a method for producing and/or using such
hollow fiber membrane mats.
[0096] In at least certain embodiments, the invention preferably
relates to a hollow fiber membrane mat or arrangement (or contactor
including one or more such mats) having hollow fiber membranes
arranged overlapping and adjacent to one another, the membranes
having a wall and a continuous lumen, wherein the hollow fiber
membranes are composed of a thermoplastic polymer and wherein the
walls of at least the hollow fiber membranes arranged adjacent to
one another are fluid-tight in at least one stripe extending along
the length of the mat (or contactor), and inside of which stripe
the hollow fiber membranes are fluid-tight. Other embodiments of
the invention preferably relate to a method for producing and/or
using such hollow fiber membrane mats.
[0097] The above examples and embodiments are not limiting and the
present invention may be embodied in other forms or modifications
without departing from spirit and scope of the invention, and,
accordingly reference may be made to the appended claims as
indicating the scope of the invention.
* * * * *