HOLLOW FILAMENT SEPARATORY MODULE AND METHOD OF FABRICATION

MODULE SEPARATEUR A FIBRES CREUSES, ET METHODE DE FABRICATION CONNEXE

English Abstract

Abstract of the Disclosure
A hollow filament separatory module is described as
well as a method of producing the filament, including in
combination an annulus of filaments consisting of a plurality
of layers of semi-permeable hollow filaments with each of the
layers being disposed in a helix with adjacent layers wound
in opposite hand and the length of filament in each layer
being within ten percent of a single preselected desired
length. Means are provided for isolating open ends from main
portions of the filaments. First flow means are provided for
flowing fluid in contact with the outer surfaces of the fila-
ments at the main portions thereof, and second flow means are
provided for flowing fluid within the hollow filaments and
through the open ends thereof.

Claims

The embodiments of the invention in which an exclu-
sive property or privilege is claimed are defined as follows:
1. A hollow filament separatory module including in
combination an annulus of filaments consisting of a plurality
of layers of semi-permeable hollow filaments with each of
said layers being disposed in a helix with adjacent layers
wound in opposite hand and the length of filament in each
layer being within ten percent of a single preselected desired
length, open ends of said filaments, main portions of said
filaments, means for isolating said open ends from said main
portions, first flow means for flowing fluid in contact with
the outer surfaces of said filaments at the main portions
thereof and second flow means for flowing fluid within said
hollow filaments and through the open ends thereof.
2. A hollow filament separatory module in accordance
with claim 1, in which said annulus includes a bore and a
sleeve within said bore which projects from the bore and is
rolled around one end of said annulus to provide protection
therefor.
3. A hollow filament separatory module in accordance
with claim 1, in which the outside diameter of hollow filament
is above 100 microns.
4. A hollow filament separatory module in accordance
with claim 3, in which the inside diameter of the hollow
filament is between 0.2 and 0.9 times the outside diameter.
5. A hollow filament separatory module in accordance
with claim 1, in which the outside diameter lies between
100µ and 1000µ and whose inside diameter lies between 0.3 and
0.8 times the outside diameter.
34

6. A hollow filament separatory module in accordance
with claim 1, in which the filament is a composite hollow
fiber comprising a porous substrate overcoated with a
rejection barrier.
7. A hollow filament separatory module in accordance
with claim 5, in which the filament is a composite hollow
fiber comprising a porous substrate overcoated with a high
filtration rejection barrier for use in reverse osmosis
applications.
8. A hollow filament separatory module in accordance
with claim 1, in which the flow direction of fluid over the
outside surface of such filaments is generally parallel to
the axis of the filament bundle.
9. A hollow filament separatory module in accordance
with claim 4, in which the flow direction of fluid over the
outside surface of said filaments is generally parallel to
the axis of the filament bundle.
10. A hollow filament separatory module in accordance
with claim 5, in which the flow direction of fluid over the
outside surface of said filaments is generally parallel to
the axis of the filament bundle.
11. A hollow filament separatory module in accordance
with claim 6, in which the flow direction of fluid over the
outside surface of said filaments is generally parallel to
the axis of the filament bundle.
12. A hollow filament separatory module in accordance
with claim 7, in which the flow direction of fluid over the
outside surface of said filaments is generally parallel to the
axis of the filament bundle.

13. A hollow filament separatory module in accordance
with claim 1, in which each length of fiber is open at both
ends and the path length therebetween is no greater than
"Lcrit" centimeters, where
<IMG>
wherein .
P = Module inlet feed pressure in Kg/cm2;
= Osmotic pressure difference between feed
solution and permeate in Kg/cm
ID = Filament internal diameter in microns (µ),
R = Ratio of filament inside diameter to outside
diameter,
F = Flux of filament based on its outside diameter
at the effective operating pressure, expressed
as a velocity of microns per second (µ/sec.).
14. The method of producing a hollow filament separatory
module including the steps of preparing an annulus by winding
a plurality of layers of hollow fiber, one on top of the
other, at pre-calculated limits for the specific ratio of
rotational velocity and traverse speed so that the helices
are laid at selected radial positions in the annulus varying
in length within preselected amounts.
15. The method of producing a hollow filament separatory
module in accordance with claim 14, in which the helix length
in each of the layers is within 10% of the preselected
length.
16. The method of producing a hollow filament separatory
module in accordance with claim 15, in which a series of
discrete ratios of the winding and traverse rates is selected
36

and changed from one ratio to the next during the winding at
predetermined annular positions whereby build-up of hills and
valleys is avoided.
17. The method of producing a hollow filament separatory
module including the steps of winding the hollow fibers con-
tinuously in alternating helices starting on a small diameter
and building an annulus, the winding being accomplished at pre-
calculated limits for the specific ratio of rotational velocity
and end-to-end traverse speed so that the helices are laid at
selected radial positions in the annulus varying in length
within preselected amounts.
18. The method of producing a hollow filament separatory
module in accordance with claim 17, in which the helix length
from the innermost to the outermost regions of the annulus
varies within 10% of the preselected length.
19. The method of producing a hollow filament separatory
module in accordance with claim 18, in which a series of
discrete ratios of the winding and traverse rates is selected
and changed from one ratio to the next during the winding at
predetermined annular positions whereby the build-up of hills
and valleys is avoided.
20. The method of producing a hollow filament separatory
module in accordance with claim 17, in which fibers having an
outside diameter above 100 microns are utilized.
21. The method of producing a hollow filament separatory
module in accordance with claim 17, in which prior to winding
the annulus an expansible sleeve is secured over a winding
mandrel at a distance greater than the axial length of the
annulus to support the inner surface of the annulus which is
37

wound thereon and after winding with the inner end of the
sleeve remaining within the bore of the annulus the outer end
of the sleeve is wrapped over the annulus to provide a
protective surface for the external surface of the annulus,
the mandrel being removed.
22. The method of producing a hollow filament separatory
module in accordance with claim 17, in which each filament
has two open ends and the distance therebetween is no greater
than "Lcrit" centimeters, where "Lcrit" is defined according
to:
<IMG>
wherein.
P = Module inlet feed pressure in Kg/cm2;
.DELTA..pi. = Osmotic pressure difference between feed solution
and permeate in Kg/cm2;
ID = Filament internal diameter in microns (µ),
R = Ratio of filament inside diameter to outside
diameter;
F = Flux of filament based on its outside diameter
at the effective operating pressure, expressed
as a velocity of microns per second (µ/sec.).
38

Description

~7~
Background of the Invention
. _ _
The use of membranes to effect separation of gas/gas,
liquid/liquid, and liquid/solid mixtures and solutions has
achieved general industrial applicability. In general, membrane
elements are contained in vessels called modules, comprising a
container having various inlet and outlet ports and an assembly
of membranes within said container. The internal configurations
are so arranged as to permit the introduction of a feed stream
with or without pressure on the upstream face of the membranes
and to include means for collecting permeate which passes through
the membranes and emerges on their downstream faces, and means
for keeping feed and permeate materials from commingling.
Membranes have been fabricated in the form of open-
ended hollow fibers so organized and sealed into header plates
as to provide a separation of the flows over the external surfaces
of the hollow fibers from any flow within the bores of the hollow
fibers.

i~7~ 4
This invention presents a new hollow filament
separatory module and method of fabricating the same which
includes unique features enabling the maximization of use of
the attributes of hollow fibers for the purpose.
The invention contemplates fibers of selected
diameters consistent with the flow requirements of high flux
membranes. For example, by our methods we are capable of
utilizing fibers with diameters as little as lOOu to as much
as 500u or more. The specific dimensions of length and
diameter of fibers can be very important, depending upon the
application. The present invention allows for easy selection
of these dimensions. In reverse osmosis applications, we
prefer fibers at least in the order of 250u in diameter.
Additionally, by winding the fibers in a helical fashion with
adjacent layers wo~-nd in opposite hand there is provided more
uniform distribution of the channel spaces and surfaces of
the fibers usable for separation.
Thus, while conventional teachings have considered
50-100 microns as the typical range of outside diameter for
the hollow fine fiber membrane, we prefer the hollow fiber
having diameters of 250 microns or larger. Indeed, in some
cases we have made very successful use of fibers over S00
microns in outside diameter.

94
In this approach to the utilization of large and
controlled ranges of diameter, we have used as a preferred
embodiment a composite hollow fiber comprising a porous
substrate, overcoated with a selected high filtration reject-
ion barrier.
The module of this invention overcomes serious
deficiencies in the prior art hollow fine fiber module design.
One of these deficiencies which has been overcome largely
relates to the methods of pottiny fibers into sealing tube
sheets or end plates, and subsequently openiny the fibers
to provide exits from the individual fiber bores into the
permeate collection chamber.
,

1~7~ 4
In the subject invention there is provided, first,
that the module internal pressure acting against the fiber
potting medium is taken to grourld by a surface of the fiber
potting medium in which no cut fiber ends appear. Second,
the surface of the potting medium which supports the thrust
developed by the internal hydraulic pressure is generally at
right angles to the principal axis of the module (i.e.,
generally parallel to the surface of the potting medium which
faces inward to the pressurized region of the module). Third,
cut ends of fibers which provide exit for the permeate flow
appear in access surfaces within the potting medium at either
a different elevation or a different angle than the surface
of the potting medium required to take the pressurizing thrust
force, or both.
A fourth feature of the technique of providing
access surfaces disclosed herein is that the sum of areas of
the projections of the access surfaces on a plane at right
angles to the direction of thrust of the pressurization
forces acting on the potting medium is substantially less
than half of the cross-sectional area of any plane parallel
-- 4 --

~7~94
thereto within the potting medium. This provision results
in very little degradation in the compressive strength of the
potting medium.
Another feature of the subject invention concerns
the sealing of the pressurized concentrate regions of the
module separate from the permeate collection regions of the
module.
Another feature of this invention solves problems
present in conventional modules regarding the pressure losses
associated with bore ~low within a hollow fiber. It has been
_ 5 _
, ~. ; ' ': .
. . ~ . .
- ~ :

1~7`~D~94
demonstrated that with inherently high flux membrane capabil-
ities unless due account is taken of fiber length and bore
diameter, adverse results will occur. The results are an
increase in per cent salt passage and a decrease in the eff~
ective use of surface of the fiber in respect to the normal
"zero" -length flux. In effect, both flux and rejection are
diminished when fibers are "too long" relative to their bore
size and inherent permeation rate.
It should be noted that it is possible to use
hollow fibers in reverse osmosis either with the bore open
at one end and sealed at the other, or with the bore open at
both ends. In the former case, the open fiber end is sealed
in a mass of potting medium and its bore discharged into a
low pressure permeate collec-tion zone or chamber. The closed
end may be potted into a resin mass or the like to help
support one end of the bundle of which the fiber is a member.
In the case of both bore ends open in each fiber
length, both ends of the fiber must be sealed in a potting
medium in such a way tha~ the bore discharge exits into low
pressure permeate collection zones or chambers. The two ends
of any one fiber may appear in the same mass of potting
medium and each bore exit may discharge to the same collection
zone, or the fiber may be potted in such a way that each bore
exit discharges into a separate collection zone.

~7~
Generally, when both open ends appear in the same
mass of potting medium and the bore exits discharge into the
same collection zone, the length of fiber between the cut
ends comprises some form of loop. The loop may be of simple
fairly straight-legged hairpin shape, or it may follow a
more intricate spatial path in two or three dimensions.
However, if each ~iber end is potted in separate sealing
masses, the fiber shape between the cut ends conceivably
could be quite straight or could follow an infinite variety
of either random or geometrically organized paths.
We generally prefer to arrange our fibers in helical
paths, the axes thereof being congruent and parallel to the
principal direction of flow of the pressurized feed. The cut
fiber ends may be sealed into the same mass of potting medium
and discharge into a common chamber, or they may be sealed
into two separate masses of potting medium, and discharge
into two separate zones, generally at opposite ends of the
axis of the fiber helix.
In the present invention, a hollow filament
separatory module is provided, including in combination an
annulus of filaments consisting of a plurality of layers of
semi-permeable hollow filaments with each of the layers
being disposed in a helix with adjacent layers wound in oppo-
site hand. The length of filament in each layer is within
ten percent of a single preselected desired length, open ends
of the filaments, main portions of the filaments, means for
isolating the open ends from the main portions, first flow
means for flowing fluid in contact with the outer surfaces
of the filaments at the main portions thereof and second flow
means for flowing fluid within the hollow filaments and through
the open ends thereof.

~7~D~9~
There is also provided a method of producing a
hollow filament separatory module including the steps of
preparing an annulus by winding a plurality of layers of
hollow fiber, one on top of the other, at pre-calculated
limits for the specific ratio of rotational velocity and
traverse speed so that the helices are laid at selected
radial positions in the annulus varying in length within
preselected amounts.
For purposes of considering the examples illus-
trating the adverse effect of fiber length on bore flow
effects, the actual path shape of each fiber need not be
considered. It is important, however, to take numerical
account of the consequence of operating with one sealed
end versus both ends open. In the sealed-end case, it i5
obvious that flow within the fiber bore can only be from the
sealed end toward the open end. In the two-ands-open case,
flow within the fiber bore is bi-directional with respect
to some point
.

94
or zone alon~ the fiber path. That is to say, there must be a
stagnatio~ point or re~ion in the bore correspondiny to the sealed
end of the one-end-open case; bore flow on one side of said point or
; zone will be toward the bore exit at the one cut end, ~thile bore
flow on the other side of said zone will be toward the bore exit
at the other cut end. Thus,' a position approximately half-way
along the path between the ends of a two-end open fiber corresponds
to the sealed end of a one-end open fiber.
Reference is made herein to a length, L, as the path
length between the cut ends of double-open-ended fiber. It should
be borne in mind that for single-open-end cases the fiber length
from cut to open end ordinarily corresponds to one-half of a length
associated with a two-end-open case. The corresponding set of fiber
properties and module operating conditions will result in limits on
length from cut end to sealed end essentially one-half that allow-
able for the path length between the ends of a two-open-end con-
figuration.
We prefer to employ in our system fibers with both ends
open. We have found that there is a unique relationship between
various geometric and hydraulic features of the module and its
operation that must be met to achieve superior results in module
productivity and the rejection qualities of the permeate. Thus,
we provide in our method that the path length between the open ends
of each fiber must not exceed a certain value, ''LCrit'~r ~in cm.)
~5 which depends upon the variables: fiber O.D., fiber I.D. f; effec-tive
dri~ing ressure~ and fiber inherent flux at said pressUre ~ccord-
- 8 -
: I
.
,

~71~
¦ing to our design, we limit the length of the path between the cut
¦open ends according to the following equation:
crit ~ ~P-~n) X (ID) X (R)
where: P - Module inlet feed pressure in Kg/cm
Q~ = Osmotic pressure difference between
` feed solution and permeate in Kg/cm
ID ~ Filament internal diameter in microns
(~)
R = Ratio of filament inside diameter to
outside diameter
F = Flux of filament based on its outside
- diameter at the effective operaking
pressure, expressed as a velocity of
microns per second t~sec.).
The operation of this relationship will be illustrated
in several following examples. In each instance a group of fibers
was formed into a loop, and the legs of the loop of fibers sealed
in a potting medium and open ends of fiber eY.posed all on one side
~15 of said medium. The lengths of fiber loop on the opposite side of
the medium were mounted inside pressure tubing and subject to
flowing feed of salt solution under pressure. The length of loop,
L, was taken as the overall distance from one cut end to the other
cut end of the fiber, substantially all of said length being within
the pressurized feed zone, and a relatively inconsequential amount
comprising the length of fiber in the potting medium. A slight
correction might be made for the so-called "inactive length" of
fiber sealed in the potting medium. It will be recognized by one
.,
:

7~D~9~
familiar with the art,'however, that this''len~-th represents a
small fraction of ~he "active lenc~th" of fiber. Correction for
the ~ortion of "inactive length" is ~uantitatively unimportant
when the ratio inactive len~th/active length is about O.l or less;
for all practical cases this requ;rement is easily met.
All the fi~ers emploved in the examples helo~ ere
a composite of polvsulfone substrate with a rejection barrier of
sul~onated polyfuran resin. The outside diameters were all 250
and inside diameters 80~ (within tolerances of ~ + 5~). The
several samples were selected to cover a fairly wide range of flux
and rejection properties.
Each sample ~as prepared with different end-to-end
lengths. Each sample was tested for'permeate flux and reject;on
of 2000 ppm ~aCl solution at 58 Kg/cm applied pressure down to
as low as 14.5 Kg/cm2 applied pressure (200 psi). The osmotic
pressure (~n) of the feed is taken as l.4 Xg/cm .
The flux and rejection of each fiber sa~ple were mea-
surea at each of three fiber lengths and comprise the experimental
data appearing in Tables IA and IB. Plux was plotted vs. lenyth
~20 as shown in Plates l and 2. Fairly reliable extrapolations to
"zero" length flux were made on these plots and are included in
parentheses in the tabulated property values shown in Tables IA
and IB. Included also in the Table are the values of Lc it cal-
culated by use of Equation (l) for each fiber sample and operating
pressure. Using these several calculated values of LCritt the
~; ratio of L/LC for each sample length ~as calculated and are also
':~
~;
- 10 -

ZL71~94
presented in the Table. Rejection is calculated in the conven-
tional fashion, R=100 (l-salt conc. permeate/salt conc. feed).
Flux is presented both as gallons per sq. ft. per day (gfd) and
the velocity parameter, microns per second (y/sec.). These are
related by 1 gfd= 0.466 y/sec. The ratio of flux at any given
length to "zero"-length flux, F/For is also tabulated.
- 11 -

7~ 4
~;
~A~6E I.
Flu~ and Rejection U8. Fiher Len~th
A; Several Dlfforent Fiber S~rlples at B. One Fiber Sarç~le Z367-S-4 at
One Pressure P - ~7r n 56.7 l~e/em2 Several Pressures
._ .___
L L7Lc F1ux _ F/Fo Rej. L L/Lc Flu~ F/Fo Rej.
tem)- (~fd7_ t~l/sec) - ~S) _ - tcm) ~ t~fd) tll~SCC) - (S) _
SArlPLE 2292-14-2 LCrit D 173 em. P-1~77 - 13.1 1~g/em~ Le7 it ~ 108 cn.
: - ~ __
0 0tl3-6) t6-3) ~ ~ 0 tB.2) (3.8) - _.
43 .2413.3 6.2 .98 99.0 41 .38 8.0 3.7 .98 97.1
182 1.0512.1 5_6 .8~ 98.3 82 .76 7.6 3.5 .93 96.6
365 1.99 9.2 4.3 .68 92.8 123 1.14 ~.2 2.9 .76 96.5
SA.'1PLE2292-14-3 L 1121 en P-l~7r 20-3 I~/en LCrit 113 en.
0 O t28.2) ~13.1) _ 0 0 tll.3) (5.3~ - -
44 .3627.1 IZ.6 .96 99.1 - 41- .36 11.1 5.2 .9Y 97.7
178 1.4721.5 10.0 .7698.9 82 .73 10.1 4.7 .89 97.
362 2.9912.5 5.8 .4489.7123 1.09 8.7 4.1 .77 97.2
5AUPLE 2292-6-3. LCrit D 170 em. P-~7r ~ 34.9 K~tem2 LCrit ~ 118 em-
O Otl4.4) t6.7) _ O n tl8.1~ ~8.4) -
41 .2414.0 6.5 .97 99.4 41 .35 17.7 8.2 .99 911.5
122 .6811.5 . 5.4 .8099.1 82 .6g 17.n 7.9 .94 98.S
183 1.0810.3 4.8 .~2 9~.8 123 1.04 14.2 6.6 .~9 97.a
SAr5 LE2292-2-1 LCrit s 230 em. P-l~ D 42.1 1;g~em2 Lcrit - 120 en.
0 0 t~.7) (3. 6) - 0 0 (20.7) t9.7)
.1~ 7.6 3.5 .99 41 .34 211.5 9.6 .99 98.6
127 .55 6.8 3.2 .88 98.6 82 .68 20.0 9.3 .97 98.7
181 .~9 6.9 3.2 .90 98.9 ~23 1.03 16.6 7.7 .~0 98.2
SA~rE2367-5-4 LCTit ~122 cn. --P-~77 49;4 1~1/cr~ LCrit - 120 em.
0 0 ~27.4) tl2.8) - O n (24.5) tll.4) _
41 .33 . - Z6.8 12.S .98 98.7 41 .34 24.1 11.2 .98 9~.6
82 .67 `25.6 11.9 .9398.9 82 .68 22.1 10.5 . ~2 98.7
123 1.01 22.0 10.2 .8097.8 123 1.03 19.6 9.1 .80 9B.O
.
-- 12
@~ ,
.
, ' ~ ,
,~ , .

~:~7`1~
Flux
~n o ~n o
-- 13

~L~7~4
~/Fo
1~ 1~ N t~ W
o ~
~ 1~ ~ ~
1 3 Oq .' ,'~ ~ t~ ~t . ~ ;. ;:': i.'. : ji: ' :: ~
tn ~ r ~ ~. W O ~ N ~ O~ ! ~ ~ ~ _; ~ --i ; ., .. _
ul ~, L. .. t-- ~t ~ cq . ~ . ~ ~ . ! ' ' . . . j. . .
1,l, . 3n j,Ir,, ,i.. l! l. .-.',
. .-- - t -~ I ' J ~ . ~ . . i ~
_ 14 _
: .

~L7~
F/Fo
c:~ O o c~ ~
~ ~ ~ o~ . o .
o i ~ ~ ~ ;!;;i ~ ' '~ ! . .
~ "1 1 . .. ~ .,.., ,
o
~ . ~ iZli T ~~
. . . .~----' Z . ~ ¦ - ~ I I ' ' ¦ i ~ ~ " . , , , . , ., .
r ~ ~a I~
: ~ ~ C
Iw
I t Z Z I ~ ¦~, ZZ~ !Z, tt~ZI i ~ ZiZ I iZ Z¦ l l.Z ¦
Zl Z i~ iL
.~.
_ 15 _
,~
:~ .
.`, ' ~ .

7~
Salt P.LSSage, %
o ~ ~ ~ o ~
~ ~ ~ ~ 1 1 i ~ ~ ' ~ ' I j; j j j j l ~ ! ., . _ ,
¦ ! .¦ . . 1:, ' 7' ~! L ~ ~ -~- - r . - iJII. . .. --
~ ~ ~ ~ ¦~ , ¦¦i i i r I I i i ~ , ! ' ;. . _
i ! ~ ¦~ ~ - ~ 1, i . 'i . ¦ ~ . . . . . , _ ~ , ~ . .
~ ~ - ~ ~ ~ ~; ~ ~:; ~ ~1!
o ~ ~ i~l ~
i ' ,;~; '~ ~ ~", ~ ~ ~ , ~ i i~ j,j- T! I 7l i ~ ~ ~! ,i .j
r ; t~ ~ ~
. ~b ~ ~g j~ lj ~L~ ~ IL,~
D i~
~ . ~ --L ~1r ~. ~ ¦ " ~
W ~ I~ T
~ 16 --

`. , .., The data in Table I clearly indica-te that both flux
¦l and rejection decline with increasing length of ~iber, L.
¦ consistent analysis of the effect of L on flux appears in Plate 3,
¦ where the ratio of flux at any length to "zero"-length flux (F/Fo)
¦ is plotted against the ratio of the fi~er lenqth under test, L,
to the critical fiber length, Lc, calculated according to
Equation 1, (L/Lg). The points are clearly distributed in such a
wa~ that the graph can be partitioned into four quadrants by a
~ertical line corresponding to L/LC = 1 and a horizontal line
corresponding to F/Fo = .88. At values of L less than Lc, the
flux is 87.5~ of the "zero"-length flux or greater for all but 1
of 15 points; at values of L greater than Lc, the observed flux
is 83% of the "zero"-length flux or less for 7 of 8 point6. When
L is as great as 2 to 3 times Lc, the experienced flux can fall
to as little as 40% - 50% of the "~ero"-length flux.
The effect of length on rejection shown in Table I is
also represented in Plate 4 for several of the samples. For
this plot, the value ~ Salt Passage is used and found from:
Salt Passage = (100% - % Rejection). The % Salt Passage is ~lotted
against the ratio L/LC in Plate 4~ It-will be seen that as L
increases toward Lc, % Salt Passage rises only a few tenths of a
per c`ent, but at L/L = 1, % Salt Passage starts to rise fairly
rapidly.
¦ It will be seen, therefore, that the critical end-to-
~25 I end le gth, Lc, calculated through the Equation set forth above
- 17 -
,. ~

Lt7~4
can be used as a practical criterLon for preserving both a high
percentage of "zero"-length flux and the su~erior salt rejection
properties attendant therewith. In 2 corollarv sense, contructing
modules with fibers of end-~o-end length sreater than Lc should
be avoided, since there is both a fairly significant loss of
permeate production efficiency as well as a degradation in per-
meate quality that can become intolerable. The exact value of Lc
does not, however, always determine an absolute boundary of
acceptable performance. It might well be that "zero"-length
flux and rejection values are so favorable that a flux efficiency
of somewhat less than .85 could be tolerated along with a ~ew per
cent increase of salt passage. In recognition of this, we use
limits of ~ 10% around L for practical module fabrication.
In the preferred method of preparing fiber bundles
according to the present invention, the hollow fihers are wound
continuouslY in alternating helices starting on a small diameter
shaft, building an annular bundle. The path length of fiber
forming a helix from one end of the hundle to the other is a
function of the radial position of the fiber in the annulus and
its helix an~le. Therefore, unless appropriate adjustments are
made in the relative speed of rotation of the windin~ shaft and
the end-to-end traverse speed of the bundle of filaments during
the winding, there will be a continuously increasing length of
fiber in any pass between the t~o ends of the bundle as the radial
position increases. The changes can result in as much as a
:-
.
- 18 -
. ~

7~4
several-old increase in the length of the helix or ~ore. ~er-
haps in some conditions as much as 6- to l0-- fold. Thus, if the
length of helical loop from one end to the other has been deter-
mined for optimun flux and rejection, and the initial winding
; on the mandrel were to accomplish that optimun length, the
external wraps in the annulus would be far in excess of the de-
sired length. ~y selecting precalculated limits for the specific
ratio of the rotational velocity of the winding mandrel and the
reciprocating traverse mechanism, helices can be laid at selected
radial positions in the annulus varying very slightly in respect to
their length. For example, a helix length from the innermosk to
, the oute most regions of the annulus never varying more than l0
around the optimun length can be achieved.
One might assu~e that this condition could be achieved
by having a continuously decaying ratio of the rotational velocity
; of the mandrel to the traverse speed, But this leads to other
problems obviated by our invention. It can be shown that at
selected ratios of the rotational and traverse speeds the helix
~, winds will build explicity on top of one another thereby forming
ridges. These ratios are unavoidable in any monotomically de-
cli,ning scheme. The result of the xidges is to build an annular
package OI helices having hills and valleys which are never
properly filled as winding proceeds. In our method, we avoid
this problem by selecting a series of discrete ratios of the
winding and traverse rates and changing from one ratio to the
neXt during the winding at predetermined annular positions.
It is another feature of our invention that the
. _ 19 _
.

~3L7[D~
annular bundle of helics is self-supporting. Where~s the prior
" art describes in some instances helical bundles, these are
generall~ firml~ and permanently associated with the winding
shaft or tube originally comprising the mandrel surface. Con-
trary to that, we have found superior results in both thewinding and subsequent handling of the fiber bundle preparatory
to potting and the like, by the use of a collapsible e~pansible
sleeve as the surface immediately upon which the irst wraps
of the bundle are wound. This sleeve may be a braided tube
of yarn, for example. Said sleeve is secured over the windiny
shaft for a distance greater than the axial length of the
annulus for support of the inner surface of the annulus. An
additional length of the expansible sleeve sufficient to
provide a continuous protective surface for the external fibers
of the annulus, rolled around one end o the annulus, is also
carried on the winding shaft.
Another feature of our invention relates to the
method of encapsulating one end of the annulus in what has
been referred to as the potting medium.
,;
- 20 -

ll
ll 117~94
. i
¦ Brief Descriotion of the Drawings
In the accompanying drawings:
~ig. 1 is a perspective view of a hollow filament
separatory module constructed in accordance with the teachings
o~ this invention;
:: Fig. 2 is a partially sectional longitudinal view of
t'ne module shown in Fig. 1 taken along the line 2-2 in the
. direction o~ the arrows therein;
.~ Figs~ 3, 4 and 5 are transverse sectional ,views ta~en
respectively along the lines 3-3~ 4-4 and 5~.5 in the direction of
the arrows in Fig, 2;
. Fig, 6 is an exploded perspective yiew of cylindrical
: ~7inding support shaft and collapsi.ble ex~ansible sleeve about
which hollow filaments are wound during the fabrication of the
fiber bundle of the mod~le shbwn in Fig, l;
. Fig. 7 i5 a perspective ~iew o the support shaft with the sleeve in position thereon prior to winding;
~ig. 8 is a perspective view of support shaft and
sleeve with the fiber helix being ~70und thereon to provide the
120 fiber bundle;
: Fig. 9 is a perspective view illustrating re~oval o~
: the support shaft and stretching and folding of the sleeve after
completion of the winding of the bundle;
- ¦ Figs. 10, 11 and 12 are partially diagrammatic
~25 ¦ longitudinal segmentary views illustrating the ~7inding respective
~'
.
~ I - 21 ~
.
~,

7~
. .. .. ... ... . .. . . .....
of the first, an intermediate and the final or outer wrap in
bundle annulus;
Fig. 13 is a diagrammatic vie~r of inner, oute~, and
intermediate annulus wrap illustratlng the location in each of
these wraps where the fiber of the respective wrap crosses the
fiber of the previous wra~ of layer in the com~leted bundle;
Fig. 14 is a perspective vie~ illustrat.ing the
relative positions of bundle annulus and collapsible, eY~pansible
sleeve in the completed bundle;
L0 . Fig~ lS is a partially sectional longitudinal view of
: the completed bundle positioned in a mold during the potting
: operation wherein an end of the annular bundle o fibers is
. encapsulated;
Fi~. 16 is a partially sectional vie~7 of an alternate
embodiment of the invention wherein the fiber access surface
. planes in the potting medium are obtained in a different manner;
: and
Fig. 17 is a partially sectional view wherein still
another method of obtaining fiber access surface pl~nes is
shown.
Description of the Preferred Embodiment
,,
A module constructed in accordance ~Jith the teachings
of this invention is designated in the Figs. generally by the
numeral 20. The module in completed form is seen in ~igs. l-S
and includes an annulus 22 formed of wound permeable hollo~
-22

~j ~
filaments and braid sleeve 26 folded over to sand~ich the fila-
ments for the most part between inner and outer sleeve sections
26a and 26b with solid rod 28 projecting within and occupying the
annulus core 30.
The specific manner in which the annulus is wound is
described in detail below. The fibers which are of relatively
large diameter are wound in helical fashion with adjacent layers
wound in opposite hand. There is relatively uniform distribution
of the large diameter fi~ers and the channel spaces and surfaces
of the fibers usable for separation. In the preferred embodiment
the hollow fibers are 250 microns or greater in outside diameter.
In certain applications 500 microns outside diameter is preferred.
Although any suitable hollow fiber can be used, the preferred
embodiment contemplates a composite hollow fiber comprising a
porous substrate, overcoated with a selected high filtration
rejection barrier.
The annulus 22 is encased within pressure resistant
shell 32 and pressure sleeve 34 between end pla~es 36 and 38
held in position by stringers 40 passing through holes 42 Eormed
in the end plates. Axial feed-in port 44 is provided in end
plate 36 to allow the fluid which is being operated upon to wash
the`outside of the fibers 22 after passing through prefilter 46
and perforated disk 48. In certain applications either or both
prefilter 46 and disk 48 can be omitted. In the preferred
embodiment prefilter 46 is a felt structure through t~hich the
i~

~L~7~
liquid can pass and disk 48 is a ri~id plastic mernber.
The pressure sleeve 34 is provided with radial ports
50 and 52 which respectively provide outlets for permeate and
concentrate. Port 54 functions as a weep hole. Suitable 0-rings
56, 58, 60, 62 and 64 are provided. Tne end of annulus 22 within
pressure sleeve 3~ is encased in potting compound 66 as ~7ill be
described below.
The manner of winding annulus 22 is seen in Figs. 6
through 14. Collapsible expansible braided sleeve 26 is secured
.;10 over suitable winding shaft 68 for a distance greater than the
axial length of the annulus to support the inner surface of the
annulus. This is the surface immediately upon which the first
raps of the bundle 22 are wound. An additional length of
expansible sleeve sufficient to provide a continuous ~rotective
surface for the external surface of the annulus, rolled around
one end of the annulus, is provided.
In the preferred method of preparing fiber bundles
according to the present invention, the hollo~l fibers are wound
continuously in alternating helices s~arting on a small aiameter
shaft, building an annular bundle. As stated above, the path
; length of fiber forminy a helix from one end of the bundle to the
other is a function of the radial position of the Eiber in the
: annulus and its helix angle. Therefore, unless appropriate
adjustments are made in the relative speed of rotation of the
winding shaft and the end~to-end traverse speed of the bundle
::
:~

~7~ 4
of filaments during the windiny, there will be a continuously
increasing length of fiber in any pass between the two ends
of the bundle as the radial position increases. We select
i pre-calculated limits for the specific ratio of the rotat-
ional velocity of the winding mandrel and the reciprocating
traverse mechanism, and lay down helics at selected radial
positions in the annulus varying very slightly in respect to
their length. For example, a helix length from the innermost
to the outermost regions of the annulus never varying more
than 10% around the optimun length is preferred and readily
achieved.
A series of discrete ratios of the winding and
traverse rates is selected and changed from one ratio to the
next during the winding at predetermined annular positions
thus avoiding the building up of hills and valleys.
In the Figs. the first layer of helical winding by
way of example is indicated by the numeral 23, a second by
the numeral 24 and a third by the numeral 25, there being
~` adjacent intermediate unindicated windings wound in opposite
hand.
This solves problems present in conventional modules
':

regarding the pressure losses associated with bore flow
within a hollow fiber and takes into account fiber length and
bore diameter. This avoids an increase in per cent salt
passage and a decrease in the effective use of surface of the
fiber in respect to the nominal "zero"-length flux and flux
and rejection are not diminished because fibers are "too long"
relative to their bore size and inherent permeation rate.
- Upon completion of the winding operation the outer
end 26b of the braid is wrapped over the annulus 22 with the
10 inner end 26a of the braid left within and the mandrel 68
removed exposing bore 30.
; After winding, one end of annulus 22 is encapsulated
in potting medium 66. The art of casting fibrous and other
materials into a common matrix is well known and referred to
as "potting". It is also well known to select potting
compounds of which epoxies are but one example, so that their
compatibility with fibers or other materials to be encapsulated
makes for intimate bonding in the interfaces between the fibers
~ or particles, and the encapsulating medium. Thus, in the case
20 of hollow fibers to be sealed in the potting medium 66 it
would be most desirable that the fiber surfaces be wet well
by the potting medium in its prepoly~erized fluid form. As
a natural consequence of good wettability of the fibers by the
potting compound before it is cured, there will be a tendency
for the potting compound in its precured state to migrate by
capillarity among the fibers, perhaps to considerable
- 26 -

lP~7~ 4
distance beyond the position where it would be useful for
the cured potti~g compound to be. In the potting this would
lead to occlusion and loss of membrane surface of some of the
~iber, possible pockets of unsealed regions, and unnecessary
utilization of epoxy compound.
In the subject invention a ring of rubbery cement
as indicated in Fig. lS by the numeral 70 is applied to -the
extensible sleeve member on the winding shaft 68 during the
winding operation at a position that will correspond ultimately
to the upper regions 72 of the potting medium 66 when it is
later placed in mold 74 as shown in Fig. 5. Then during the
~ .
winding of the fibers on first the extensible sleeve and sub-
sequently on top of the preceeding fiber wraps as shown in
Figs.10-13, a continuous deposit of the same rubbery cement
is made at generally the same axial position in the annulus.
At the completion of the winding of the entire annulus, there
exits with it a substantially doughnut or 0-ring barrier
- membrane of the rubbery cement in the plane generally desig-
nated by numeral 70 in Fig. 15 separating the portion of the
fibers which will ultimately become imbedded in the potting
medium from the remainder of their lengths. In the same
sense, the end of inner extensible sleeve member 26a also has
- the barrier membrane, applied thereto, so that if it too has
a capability for inducing capillary migration of the precured
potting medium, said capillarity would be obstructed at the
`~ same axial point of position.
';
- 27 -
' . ' ' ' -

The completion of the pottin~ operation af~er
winding is illustrated in Fig. 15 with the mold and potting
medium designated respectively by the numerals 74 and 66.
The uncured potting compound 66 in mold 74 is subject to
vibration Erom subsonis to ultrasonic frequencies by a
. suitable impulsing device, such as a vibrating hammer or
ultrasonic transducer, not shown. The fiber bundle 22 is
immersed into the mold 74 containing the precured potting
compound 66 which, under the urging of the vibratory energy
supplied to the mold, tends to migrate within and fill the
interstices of the bundle with much greater ease than would
have been secured by gravity alone.
After potting the fibers of the annulus must be
opened so that permeate within the individual bores thereof
cah be received and collected in the collection chamber or
annular gallery 71 provided in the mold potting compound,
for removal through port 50. A feature of the subject
- invention is to provide that the internal pressure force
developed in the module during use and acting against the
fiber potting medium 66 is resisted by a surface of the
potting 66 in which no fiber ends
':
'
~ - 28 -

7LD~4
IL
~ppear. The numeral 67 in Fig. 2 designates this surface~
Additionally the surface 67 of the potting supports the thrust
developed by the internal hydraulic pressure acting agains-t the
inwardly facing surface of the potting.
~ In the subject in~ention ends of fibers which are cut
., or exposed to provide exit for the permeate flow are in access
surfaces within the potting medium at either a difEerent elevation
or a different angle than the surface of the potting medium re-
guired to take the pressurizing thrust force, or both.
'~10 ~le have found that if a number of angular slices are
made into the end of the cylinder of fiber-containing potting,
connecting points near the center of surface 69, upwardly, and
out~ardly with points in the surface 71 of the annular gallery
of the potting providing continuous channels connecting surfaces
69 and 71 and providing an apex in the slice along 78 as seen
in the Figs., all fibers will have open ends exposed to gallery
76.
As seen in Fig. 3, the three v-shaped slices comprise
; six access surfaces, 79, lying at an oblique angle to the base of
`20 the potting medium. These access surface planes resulting from
; the cutting communicate with the annular gallery within the low
pressure region of the assembled module, providing thereby ready
access to the permeate collection system. The creation of the
planes by cutting of the potting medium is accomplished in the
~ preferr e~bodiment ~t a time in the curing cycle of the potting
I
; - 29 -

:~7~D~g~L
medium prior to its final cure-. By the selection o a potting
compound and control of the time and temperature after imrnersion
of the fiber bundle in the mold, the potting compound achieves a
- state in which it is readily cut without creation of unwanted
detritus to block the fiber openings yet of suficient resilient
integrity to slice cleanly by means of a sharp-edged blade. After
cutting, cure of the potting compound is completed by heat and/or
the passage of time.
An alternate embodiment of the invention directed tot~ard
~10 the creation of cut fiber ends in an access surface plane of the
potting medium is sho~m in Figure 16. In this example, the fiber
helix bundle is wound in such a way that at one end the helix
wra~ping takes a continuously increasingly steeper angle, forming
a conical taper inner surface over a distance indicated by the
bracketed length marked "80" in Fig. 16. ~en this conically
tapered end of the annular array of fibers is potted in a mold,
it is mounted along with a stepped plug, 81, in such a way that
the potting compound encapsulates concurrently the end of the
fiber bundle and the plug. After curing, a narrow annular access
surface, 79, is machined into the potting compound at an elevation
above the support surface ~rovided by the plug.
Still another embodiment of our invention is illustrated
by Fig. 17. ~lere a wound bundle of filaments is prepared having
loops at one end extending at right angles to the main axis o the
bundle. This can be accomplished, for example, by mounting on th~
~ 30 -

Il ~3'7~
winding mandrel a thin, disklike member several inches larger in
diameter than the mandrel. During the winding operation, the
traverse of the yarn is carried axially beyond said disk so that
there is a section of yarn from each loop of the wind that passes
over the exLreme edge of the disk before the yarn direction is
reversed. The result of such a winding process is to provide at
one end of the helically wound bundle a flange-like circular array
of fibers ~hose axes at that point lie generally at right angles to
the annulus axis. Later, the entire flange-like circular array o.f
lC ¦ fibers plus an additional region axially inward of said array
. ¦ become the site for the infusion of potting compound. The mold
¦ for such an assemblage provides means for creating se~ents in the
¦ potting compound with fibers of the flange-like blmdle extension
¦ lying in said segments of potting compoun~. After the full cure
¦ of said potting compound, it is possible to create open fiber ends
¦ in the fiber lengths lying at right angles to the main axis of the
¦ annulus by shearing off the segmented zones of po~ting compound in
¦ which the flange-like array of fibers has been embedded. Thus an
, access plane~ 79, will be created where each such segmented zone
20 of po~tting compound has been fractured from the body of the pot.
Open ends of fibers will again be found in planes lying at some
angle, generally at a right angle, to the surface against whlch the
thrust on the potting compound is applied during module operation.
: Another feature of the subject invention concer~s the
sea~ling of the pressurized concentrate regions of the module

~'7~
separate from the permeate collection reglons of the module.
In the subject invention the permeate collection
chamber 76 is sealed apart from the pressurized concentrate
region of the potting medium by "0"-rings 56 and 58 with
weephole 54 additionally pxotected by 0-ring seal 60 to allow
any leak of concentrate to exit the module assembly without
inadvertently commingling with the permeate. The pressuri~ed
concentrate is removed at port 52 which is sealed by 0-rings
60 and 62. Although the "0"-rings are hidden during operation
o~ the module, any leakage past them can readily be ~tected
and corrective action taken.
The 0-rings 5g and 60 define an intermediate zone
between the collection zone containing the collection chamber
71 and the pressurized zone which is surrounded by the
pressure resistant shell 32.
In the prior art modules the pressure shell has been
a cylindrical chamber in view of the accepted manner of
resisting the high hydrostatic pressures. The requirement
has been imposed on the shell to accept both the hoop stress
loadings and axial loading developed by connections to the
end plates. In addition, the end plates were frequently mounted
to the shell and connected by snap rings or the like, which
carried the thrust on the end plates to shell surface through
grooves or some other connective ridges or the like. This
required that the shell be of substantial thickness and
mechanical integrity in all directions. In the subject in-
vention the stringer bolts 40 secure the two end plates 36
- 32 -

~IL 3L'7(~
; - and 38 of the pressure cylinder to one another, thereby
eliminatlng axial stress on the shell. By use of these
stress-bearing stringer members, prohlems associated with
connecting end plates to the shell by snap rings and the
like are also eliminated. These features allow for simpler
fabrication of the shell itself and the assembly and dis-
assembly of the entire system, as well as access to i-ts
internal parts.
Thus, among others the aforementioned objects are
achieved.
This application is a divisional of application
Serial No. 335,910, filed September 19, 1979.
- 33 -
,