Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~ 093/10889 PCr/US91/08825
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Spirally ~o~nd ~mbraneD2vice Having lhr~e Ch~
Back~round of The Invention
The present invention relates generally tospirally wound membrane devices useful for membrane
separations on fluid ~eed streams. The present
invention is broadly useful in the processing o~ liquids
and gases. ~-
Related Art
Simple, single leaf spirally wound membrane
10 devices have been known for some time. For example,
British Patent 489,6~4 (September 1, 1938) describes a
countercurrent spiral membrane device containing a
cellulosic membrane material used for dialyzing caustic
soda lye. As discussed therein, with such a design it
is possible to fit considerable effective surface area
of dialyzing membrane into an extraordinarily small
volume, for example, a cylindrical container. Similar
single leaf spiral membrane devices are broadly used
20 today in a variety of plications. The advent of
reverse osmosis desaiination of saline waters in the ~-
early 1960's led to a number of improvements in spiral s
membrane devices, especially in terms of size. U.S.
Patent 3,417,870 describes a means of spirally winding a
WO93/10889 PCT/US91/0882~ ~
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2 1 ~. ~ 2 ~ 3 -2- ! :
plurality of reverse osmosis membrane sheets and spacer
materials around a perforated hollow core in a manner so
as to provide large diameter spiral devices. The design
illustrated and described in U.S. Patent 3,417,870 has
since been commonly applied to reverse osmosis~
ultrafiltration, gas separations, and other types of
membrane applications. U.S. patent 4,235,723 describes
an alternate method of assembling spiral membrane -
devices, in which a flow guide member is attached to a
lO perforated hollow core, and a parallel array of membrane -
envelopes are attached together in a manner such that
the permeate from each membrane envelope empties into
the flow guide member. Such an arrangement has been
termed a "tributary design," since a series of
tributaries feed into a main stream, that is, the flow
guide member, which empties into the hollow core.
More recently, a number of patents have
appeared which incorporate improved materials and
modified flow paths in single and multiple leaf spiral
elements. U.S. Patent 4,834,881 discloses a variety of
improved corrugated spacers for use in feed fluid ~`
channels. U.S. Patents 4,8612,487 and 4,902,417 ;
describe improved channel spacers consisting of ribbed
plastic nettings. Flow channel spacers in the context
of spiral wound membrane elements are occasionally
described as two dimensional articles, when the context
permits. However, it is essential that the flow channel
s~pacer have a thickness and open volume for the movement
of fluid between membrane layers. A similarly ribbed
plastic screen useful as a permeate channel flow spacer
is described in U.S. Patent 4,476,022. U.S. Patent ~`~
3,872,014 describes a design employing a perforated
hollow mandrel having a plug located internally so as to ` ;~
wos3/to8xs PCT/US91/08825
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cause a feed stream entering one end to flow out into an
attached flow channel leaf. A flow diversion barrier
extends out from the hollow mandrel along a fractional
length of the attached leaf so as to force the feed
stream flow path to encompass the full radial length of
the leaf before returning to the hollow mandrel
downstream from khe plug. Similar approaches are
described in U.S. Patents 4,033,878 and 4,765~893. U.S.
Patent 4,765,893 also describes the use of a flow
diversion barrier extending radially inward from the
outer circumference of a spirally wound membrane device
on the opposite side of the spirally wrapped membrane~
that is, in the flow channel separated from the hollow
mandrel compartment by the membrane. Use of a multiple
array of flow diversion barriers to achieve a convoluted
flow path is described in U.S. Patent 4,814,079 as well
as in U.S. Patent 4,033,878.
A commonly shared characteristic of all of -~
these spiral designs is that only two compartments exist
therein, each of which is in fluid communication with at
least one port~ In the case of reverse osmosis, one
compartment would consist essentially of a flow channel
for the saline feed stream, and the other compartment
would consist of a flow channel for the membrane
permeate. In the case of pervaporation, one compartment
would similarly consist essentially of a flow channel
for a liquid feed stream, and the other compartment
would consist of a flow channel for permeated vapor
removed through the pervaporation membrane. In the case
of gas separation, a gas mixture would be fed through
one compartment, and a selectively permeated fraction
removed through the other compartment. All such spiral
designs are capable, therefore, of effecting only a
W093/10889 PCT/US91/OX825
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single separation. If two distinct membrane operations
were needed, two separate membrane devices would be
required.
In some cases, even a single membrane
separation cannot be accomplished satisfactorily in a
conventional two-compartment membrane device. ;
Facilitated transport membrane separation is an example
of such a case. In facilitated transport, separations
between two fluid streams are effected by means of a
liquid extractant medium held within the interstices of
a porous membrane, the medium being immiscible with the
fluid streams on either side. The life expectancy of a
facilitated transport membrane is relatively short
because of problems associated with loss of the
extractant medium and with emulsification and
breakthrough. One approach used to solve this problem -~
has been to incorporate two sets of hollow fibers into a
hollow fiber membrane module, one for a feed stream and
20 one for a permeate stream, both sets of fibers being -`
immersed in a liquid facilitated transport medium. Such
a devicé is described in U.S. Patent 4~7501918. With ` ;~`
such a hollow fiber design, the facilitated transport ~`
medium can be separately replenished or renovated by
25 means of ports connected thereto. This application is `~;`
one of potentially many examples wherein current
spirally wound membrane modules are inadequate due to ~`
their dual compartment design limitations. The present , --;
invention described herein below overcomes the above
limitations inherent in dual compartment spiral element -;
designs. i
, . ~.
WO93/10889 PCT/US91/08825 ~
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Summary of The Invention
The present invention comprises a spirally
wound membrane module having three separate, distinct
flow chanr~ls ~or fluid streams. This invention differs
from all earlier spirally wound membrane devices by
virtue of its triple channel design. The triple channel
design be tows a high level of versatility not possessed
by earlier spiral designs. Thus, more than one membrane
type may be assembled into the triple channel spiral
module, and up to three separate fluids may be flowed
through the respective channels simultaneously. Each
channel may be individually designed to have a
combination of inlet and outlet ports; alternatively,
one or two of the three channels may be designed to have
only outlet ports. Specific combinations of choice on
channel flow and porting will depend appropriately upon
the desired application or end use.
The triple channel spiral module, in its~
20 simplest embodiment, is assembled by winding a serially ;
arrayed pair of membranes upon a perforated hollow
mandrel. Such assembly contrasks with other
conventional spiral modules where the membranes are
Z5 always positioned in a parallel array one to another.
In the fabrication of a spirally wound membrane module,
a membrane sheet is typically folded once upon itself,
and the edge delineated by the folding is inserted into ~-
a winding nip adjacent to the core, that is, adjacent to
the hollow perforated mandrel. In the triple channel
spiral module, a second membrane sheet, also typically
folded upon itself, is nested within the first folded
membrane sheet, to provide a serially positioned
membrane et. Appropriate fluid flow channel spacers
are located between the membrane layers so as to
W093/10889 PCT/US91/08825 ~ ~
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delineate flow channels. This serial membrane set is
wound upon the core. The three channels are isolated
from one another by bonding methods, such as glue
application, at the sides and ends of channels where
appropriate. A plurality of nested membrane envelopes
may be stacked upon one another and wound upon the core~
following in a generally analogous manner the approaches
used in two-compartment spirally wound membrane modules.
Certain separations~ for example those in the
10 pharmaceutical industry require separation of compounds ~-
in a molecular weight range from a liquid fermentation
broth. The prior art would permit a feed stream to be
divided into two streams, a permeate (the portion
passing through the semi-permeable membrane) and a -`
retainate (the portion not passing through the semi-
permeable membrane). The present method using a triple
channel spiral wound membrane permits separations of the
feed stream into three streams: the retainate, as with
the prior art, a first permeate stream which has passed
through one membrane envelope, but not a through a ~-
second membrane, and a second permeate stream which has
passed through both membrane envelopes~
Still other separations make use of chemical
reactions and chemical changes to facilitate a
separation. For example, in separating ethylene from
ethane in a mixture to the two gases, it is known that
ethylene may be selectively absorbed in an aqueous
3 solution of a silver salt. A gas/liquid contactor is ~ ~~
necessary for the absorbtion step. Next, a stripper or
other means of desorbing the ethylene from the aqueous ~ ;
silver salt ~olution is required. The present apparatus
and method permits a single apparatus to absorb a fluid
;,
i`~. :
WO93/10g89 PCT/US91/0~825 ~.~
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in an appropriate facilitating liquid and desorb the
fluid from the absorbing liquid. ~ :
The inve~tive triple channel spiral wound `~
membrane element may be comprised of a hollow mandrel
having at least one aperture in the wall thereof, a
first fluid channel spacer, a portion of which is in
contact with said mandrel along an outer surface portion `
of the mandrel's wall wherein the aperture is located, a
first sheet-like membrane having a first and second
surface, the first surface being substantially in co-
extensive contact with both surfaces of said first fluid
channel s~acer, the first sheet-like membrane being
sealed such that fluid communication with the first
fluid channel space is substantially limited to the
mandrel bore or through the first sheet-like membrane, a
second fluid channel spacer, the second surface of the
first sheet-like membrane juxtaposed with a first
surface of the second fluid channel spacer, a second
sheet-like membrane having a first and a second surface,
the first surface being juxtaposed with the second
surface of the second fluid channel spacer, a
substantially fluid tight seal joining the the second
surface of the first sheet-like membrane with the first
surface of the second sheet-like membrane at a location
radially remote from the mandrel, e~fectively parallel
with the mandrel, such that fluid communication with the
second fluid channel space is substantially limited to
flow su~stantially parallel to the mandrel or through
the f ~ sheet-like membrane with the first channel
space c. through the second sheet-like membrane, a third ~ ~-
fluid channel space.-, the second surface of the second ~'
sheet-like membrane being juxtaposed with both surfaces , :.
of the ~hird fluid channel spacer and sealed at the - -
WO93/10889 PCT/US91/Og8~5 ~ ;
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2 .l . . ~ rJ !~ 8--
spiral wound edges such that fluid communication with ;
the third fluid channel space is substantially limited
to the unsealed portion at the radially outward
extremity of the second sheet-like membrane or through
the second sheet-like membrane from the second fluid
channel space. :~
The inventive triple channel spiral wound :~.
membrane element may also be described as a first
membrane envelope having a fluid flow channel within the ::~
membrane envelope in fluid communication with at least
one first-fluid port throùgh the containment vessel, a
second membrane envelope having a fluid flow channel ~-
within the second membrane envelope in fluid
communication with at least one second-fluid port, and a .
third membrane envelope having a fluid flow channel
within the third membrane envelope in fluid
communication with at least one third-fluid port. :
The process of the present inventlon for
separation of fluid components comprises contacting the
fluid in a first fluid flow channel enclo3ed in a first -~ `
semi-permeable membrane of a spiral wound membrane
module, wherein the first membrane has an upper
molecular weight cut-off, contacting in a second fluid
flow channel the leachate from the first membrane with a ;
second semi-permeable membrane having a lower molecular `~
weight cut-off enclosing a third fluid flow channel, ~ ;
collecting She selected molecular weight fluid fractions
3 from one or more ports in fluid communication with the .
first fluid flow channel, the second fluid flow channel,
and the third fluid flow channel. ~ ~:~
The process of the invention as particularly .
adapted for facilitated transport of a gas component of
~! ' :
WO93/10889 PCT/US91/08825
-- _9_ 2 ~ a '
a gas mixture comprises contacting a gas mixture in a
first fluid flow channel enclosed in a first semi-
permeable membrane of a spiral wound membrane module,
contacting th~ first semi-permeable membrane with a
chemical fluid which selectively absorbs at least one
component of the gas mixture, the chemical fluid is
within a second fluid flow channel 7 contacting the
chemical fluid with a second semi-permeable membrane
under conditions which cause the at least one component
of the gas absorbed in the fluid to desorb and p~ss
through the second semi-permeable membrane into a thircl
fluid flow channel, collecting the desorbed gas from one
or more ports in fluid communication with the third
fluid flow channel.
The triple channel spiral module design,
methods of assembling of such a design, and separations
of fluid components advantageously such a cesign will
become evident in the following description of
invention.
Brief Description of The Drawin~s
Figure 1 shows an arrangement of materials
useful for winding a triple ehannel s~iral module.
Figure 2 shows a partially fabricated triple
channel spiral module.
Figure 3 shows a spirally wound triple channel
module complete with containment vessel.
Figure 4 shows a cross-section through the
module of Figure 3 at A-A.
Figure 5 shows a cross-section through the
module of Figure 3 at B-B.
WO93/l0889 PCT/U591/08825 '~
Figure 6 shows a hollow mandrel having a plug
located intermediate in its length, and an a~tached
fluid flow channel spacer having a flow diversion
barrier therein. ~;
Figure 7 shows a triple channel spiral module
complete with containment vessel wherein each channel
has an inlet port and an outlet port. ;
Figure 8 shows the area identified as 37 in ~
10 Fig. 2 in an expanded view of a typical seal between the -
second surfaces of a second membrane sealing a third
fluid flow channel along the spiral wound edges while
leaving the radially remote edge of the third flow ~ -
channel open to fluid flow.
Description of a Preferred Embodiment ~;
Figure 1 shows an arrangement of materials
which, when spirally wound, give rise to a triple
channel membrane device. A layer of a first channel
spacer material 1 is attached or otherwise in contact
with the outer periphery of a hollow mandrel 2 having at
least one aperture 3 therein for fluid communication
between She mandrel's interior and external zones.
Channel spacer material preferably at least one layer of
this first channel spacer material l is juxtaposed ~ -
between any sub~equent membrane layers and the outer
surface of the mandrel 2, so that all of the outer
periphery of the mandrel 2 is in contact with a first
3 flow channel thereby formed. A layer of a first ~;~
membrane 4 is placed in contact with the first layer of '~
channel spacer l. The membrane 4 is preferably a sheet- I ~
like material. This layer of membrane 4 is conveniently ~;`
folded upon itself, forming a fold edge 5 that is
positioned parallel to the axis of the mandrel 2. First
WO9311088~ PCT/US91/08~2~ ~
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membrane 4 has a first s~rface 4a and a second surface
4b. The first surface 4a is in contact with the firs~
spacer material 1. The second surface 4b is in contact
with a second channel spacer material 6. This second '~
channel spacer material 6 is interposed between the
first membrane 4 and a second membrane 7. The second
membrane 7 is preferably folded upon itself just as with
the first membrane 4, and is typically nested within the
first membrane fold during a spiral winding assembly
operation. The second membrane 7 has a first surface 7a
and a second surface 7b. The first surface 7a is in
contact the second channel spacer material 6. The
second surface 7b is in contact with a third channel
spacer 8. Thus, three flow channels are formed, the
first (or inner) flow channel being effectively
separated from the second (or middle) flow channel by
the first membrane 4, and the second (middle) flow
channel being separated from the third (or outer) flow
channel by the second membrane 7, when these layers are
2~ spirally wound upon a core along with appropriate glues
or bonding agents at the channel edges as will be more
fully described hereafter. By the expression glues or
bonding agents at the channel edges, the practitioner
will understand a benefit results from locating the glue
lines near the edge of the spiral wound membrane element
and near the radial edge of a membrane/flow channel. A
resulting benefit is to make maximum use of the membrane
area included in the spiral wound element. Of course ~, "
less advantageous placement of the glue lines is
possible and contemplated.
While Figure 1 and the above description
utilize folded sheets of the membranes, two pieces of a
m~mbrane may also be bonded or spliced together at an
WO93/1088~ PCT/U591/08825
~ ?~ ~ -12- ~;
edge, the spliced or bonded edge-serving as an insertion ``
point into the assembly arrangement~ just as with the
folded edge. Also, the second channel spa~er 6 need not ;~
be a single folded sheet. It may optionally be a ;~-`
spliced pair of sheets as well, or may even consist of
two sheets, one placed above and the other placed below
the nested membrane 7.
,, ::
Turning now to Figure 2, these layers of -~
membrane and ehannel spacer material are wound upon the
mandrel 2, with appropriate application of a bonding
material such as a glue so as to isolate the three ~ -
resulting flow chambers one from another. Figure 2
shows the hollow mandrel 2 having already wrapped about ~-
it a layer of the first channel spacer 1 and a layer of
the first membrane 4. Both layers together are bonded
to the mandrel 2 in zones 9a and 9b by means of a glue,
sealant, or other agent. The first membrane 4 extends
radially outward from the mandrel 2, enveloping in a
20 typically co-extensive manner on both sides the layer of :;
first channel spacer material 1 that also extends `
radially outward from the mandrel 2. The two side
regions 10a, 10b and the end region 10c of this membrane ;~
envelope leaf are sealed by means of a glue, sealant, or
other bonding method, thereby creating the first flow
channel in the open volumes provided by the first ~
channel spacer material. This first channel is open -
only to the mandrel, and is in fluid communication with
the hollow core of the mandrel by means of at least one
perforation or aperture 3 through the wall of the
mandrel. The bonding method for sealing the three sides 'i
of this flow channel and for sealing the envelope around ;~-
the mandrel is conveniently accomplished by means of a
two-part urethane or epoxy glue which, upon being mixed,
W093/10889 PCT/US91/08825
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.
has an appropriate pot life for working and for movement
and assembly of the layers of materials spirally arou~nd `
the mandrel before the glue gels and hardens. Other
types of bonding may be employed, such as for example,
by ultrasonic welding9 gluing with hot melt adhesives,
or sealing with moisture-activated silicone sealants,
although some of these may increase the complexity of
the spiral winding assembly operation.
The second channel spacer material 6 is shown
in Figùre 2 as a sheet folded upon itself~ the fold edge
being inserted into the nip made by the first membrane 4
at the mandrel 2. This second channel spacer can
consist of material identical to the first channel
spacer~ or may be entirely different. Spacer materials
may consist of porous fabrics, plastic nets, corrugated
plastic sheeting, metallic screens, or any of a wide
variety of materials. In Figure 2, the spacer is
depicted as an open netting, but subsequent figures
depict it as a corrugated spacer for sake of clarity.
Similarly to the folded channel spacer 6, a fold edge of
the second membrane 7 is inserted (nested) into the nip
thus formed by this second channel spacer material. The
folded ~heet o~ this second membrane 7 is shown as being
coextensive with a sheet or layer of the third channel
spacer ~terial 8, though this is not a strict
requirement for membrane 7 (or for membrane 4). The
membrane sheet ma~ allowably extend beyond the length of
the channel spacer sheet, for example.
The two sldes of the membr2ne envelope formed
by side 7b of the second membrane 7 and the third
channel spacer material 8 are sealed from fluid flow by
a glue 12d or other bonding means in zones 12a, and 12b
similar to the first membrane envelope. At the distal
WO93/10889 PCT/U591/08825
, ,t ~ 14~
end 12c of this second membrane envelope the third
channel spacer and the side 7b of the second membrane 7
is left at least partially unsealed. As a consequence
of not sealing the distal edge 12c the channel formed by
means of the channel spacer material 8 sandwiched
between the folded layers of membrane 7 may be in fluid
communication with external ports in a resulting module.
A sealing means 11 such as a bead of a glue is
disposed on each of the distal ends of the second
channel spacer material 6 effects a leak-free bond
between the surface 7a and surface 4b of the first
membrane 4, when these layers are spirally wound into a
membrane scroll upon the hollow mandrel 2. "~
Fig. 8 is an enlarged view of a corner of a
flow channel formed about channel spacer material 8 by ~''7
membrane sheet 7 and glue or bonding agent 12d. The -
unsealed end 12c of the membrane envelope is readily --
seen to be open to fluid communication with external
fluid ports of a resulting membrane module. A membrane
module identifies a spiral wound membrane element
adapted for fluid connections within a containment
vessel. -
-
Further clarification of the design of this
triple channel spiral element may be gained by reference
to Figures 3, 4, and 5~ Figure 3 depicts a triple
channel spirally wound membrane module complete with a
oontainment vessel 13 for fluid treatment. Two sets of
nested membrane envelopes are pre-~ent in the membrane
scroll of this module, which will become evident later ~~
by reference to the A-A cross-section depicted in Figure
4. The spirally wound membrane element is contained in
a vessel 13 having one or more ports 14 for flow
W093/10889 PCT/US91tO8825
associated with the channel formed by the first channel
spacer material l, one or more ports 15 for flow ~ '
associated with the channel formed by the second channel ~ :
spacer ma;~erial 6, and one or more ports 16 for flow .
associated with the channel formed by th~ third channel
spacer material 8. The membrane and spacer layers have
been spirally wound upon a hollow mandrel 2, which is
then brought into connection with its ports 14.
Extensions 22 of the mandrel 2 beyond the ends 23 of the
membrane scroll can themselves serve as ports through
the ends of the containment vesse1 as depicted in
Figure 3. A seal tc the mandrel extension 22 can be
made by means of an O-ring 19 mounted in an orifice
within an end plate 20 held in position by a snap ring
1~ 21. This example is an illustration of just one of -
several means known in the art for ponting the fluid
stream flowing fr^m the internal space of the hollow
mandrel 2. The e~ternal periphery of the spirally wound
element is fitted circumferentially with sealing cuf~s
17 at each end, which are in a sealing contact with the
inner wall of the vessel 13. These cuffs 17 in
combination with the sealant means 11 (see Figure 2)
effectively isolate the second channel ports 15 from the
25 third channel ports 16. One leaf ending 18 is shown in ~ `.
: Fig. 3. The corresponding leaf ending for the other
third channel is not shown in this figure, since it ` :
would cuqtomarily have its terminus at 120 to 180 from
the first ending 18. The open endPd channel 12c of
30 Figure 2 comprises the open gap betweèn the leaf ending - .
18 and the underlying membrane surface, with the third
channel spacer 8 shown in Figure 2 herein extending `
outward from the open end and wrapping once around the
outer circumference. . ;:
WO93/108X9 PCT/US91/08825
Figure 4 shows a cross-section at A-A for this
spirally wound device, illustrating the cross-section of
the double set of nested membrane envelopes. Herein,
the terminus 24 of the secondary membrane envelope
5 (i.e., the envelope formed by the second membrane 7 and -
the third channel spacer material 8) would correspond to
the leaf ending 18 in Figure 3, and the terminus 25 of -
the companion secondary membrane envelope is shown as
being on the opposite side of the device. The cross- ~ ;
section in Figure 4 also shows: a first flow channel 26
associated with the first channel spacer material 1,
which is in fluid communication with the perforated
mandrel 2; a second flow channel 27 formed by the second
channel spacer material 6, which is in fluid ;
communication with the enclosed volume 34 formed by the
vessel 13 and the end of the membrane scroll 23; and a
third flow channel 28, which is associated with the
third channel spacer material 8. The third flow channel
28 opens into, and is in fluid communication with, an
annular space 29 between the membrane scroll and the
internal surface 30a o~ the vessel wall 30, and is in ;
fluid communication with a port 16. The folded edges of
the first membranes (corresponding to 4 in Figs 1 and 2
are shown at their insertion points 31a, and 31b).
Channel endings of the flow channels 26 enclosed by
these first membranes 4 are shown a`t terminus points
32a, 32b. The folded edges of the ~econd membranes , :~
(corresponding to 7 in Figs 1, 2, and 3) are shown at
3~ -their insertion points 33a, 33b, and the corresponding
terminus points at 24 and 25. The third channel spacer
8 is preferably and conveniently extended beyond the ` I -
terminus points 24 and 25, being wrapped once ? or more, `~
around the outer circumference of the membrane scroll so
, ,, ., , ,, . . . ... . " ., .. ,,, ., ... " , , .. , . ~ ., , , .. . - ~.. . - -. , , , , . . -.. ..
W093/l0889 21 2~ 0 PCT/US91/088~S
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17
as to enhance fluid flow between channel 28 and the
fluid port 16. ~ ~
It will be evident to practitioners skilled in i
the art that the various layers of membranes and channel
spacers need not end exactly at the leaf terminus
points; individual layers may very well extend beyond
the terminus points without altering the functional
features shown in Figs. 3 and 4.
Figure 5 shows a cross-section at B-B. The
sealing relationship of the cuff 17 between the outer
circumference of the spirally wound element and the
inner surface 30a of the containment vessel wall 30 is
illustrated in this figure. Essentially, the cuff is
formed by filling the annular space 29 wlth a sealing
means to block annular flow or mixing between channels
27 and 28 at the spiral wound element periphery. Also
at section B-8 is a glue or sealant in flow channels 26
and 28 at their exposed ends at the edge 23 of the
membrane scroll, corresponding to zones 10a, 10b and
12a, 12b in Figure 1. Flow channel 27 is open, however,
and flow in a vector orthogonal to the plane of cross- ~`
section B-B is permitted. The hollow mandrel 2 need not
have provision for wall apertures in this region, of
course. The cuff 17 may consist of a bead of sealant,
such as derived from a silicone, urethane, or epoxy
resin composition. It may also consist of an annular
rubber ring or shaped rubber seal. Alternatively, the
3 cuff may consist of a molded or machined annular sleeve
of plastic or metallic compoqition which fits over the
outer circumference of the wound membrane scroll, and ~ ~`
contains a channel for a rubber O-ring or ga~ket on its
outer periphery, so that a seal can be made to the inner
wall of the containment vessel. Open spaces between
WO93/10889 PCT/US91/08825 ~ ~
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such plastic or metallic sleeve and the membrane scroll
can be filled with a sealant. A variety of such ~ -
techniques are known in the art of spirally wound
membrane elements. A potential advantage associated ' ;-
with annular sleeves of plastic or metallic composition
is that their use would fix the outer dimension of
spirally wound membrane scrolls, preventing them from
unwindingO Wrapping the outer periphery of membrane
scrolls such as with a pressure sensitive adhesive tape
may also be employed to maintain the scroll in its wound
condition, as long as some openings are provided in the
tape wrap for interchange of fluid between the third -
channel 28 and the annular space 29.
Each of the three flow channels can be designed
to accommodate both an inlet flow into and through the -~
channel to an exit port. Figure 6 shows a modified
hollow mandrel 40, coupled with a modified flow channel
spacer sheet 41 which, upon substitution into the
~0 arrangement shown in Figure 2, will lead to a triple
channel spiral module having a flow-through capability
in the first channel 26 (Figure 4). In Figure 6, the
hollow mandrel 40 has a plug 42 in its hollow core at
some point generally midway in its length. Apertures 3
are located in the walls of the mandrel 40 on both sides
of the plug. A first permeate channel spacer material 1
is attached to the mandrel 40, and extends radially
outward therefrom. A flow diverting means 43 is
positioned generally near or on the midline of the sheet
of permeate channel spacer material 1, extending
radially outward from the mandrel 40. The flow
diverting means 43 does not extend to the distal end of
the spacer material sheet; however, provision is made
for fluid flow to pass from the first side of the sheet
W093/10889 PCT~US91/08825
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around the tip of the flow diverting means 43 to the
second side of the sheet. Thus, a fluid can be -
~introduced through one of the modified mandrel 40, exit
through apertures ~ nto the flow channel defined by the
channel spacer mater al 1, percolate down to the distal
end of the flow cha lel on one side of the sheet, return
to the core on ~he other side of the sheet, re-enter the
hollow mandrel 40 by apertures 3 and exit ne mandrel 40
through an appropriate port. The outer boundaries of
10 the flow channel can be fixed by means of glue lines or -
other sealing methods in zones 10a~ b, and c as
described earlier. Means for diverting the flow may
include, for example, a band of a glue or sealant, a
foam strip, or a strip of a plastic or metal. It need
not be a perfectly impervious barrier to achieve the
intended effect. The flow diverting means 43, shown in
Fig. 6, can be eliminated while still maintaining an
inlet-to-outlet fluid flow in the flow channel. -
However, this would generally not be preferable because
it would allow inlet flow to selectively channel to the
outlet by the path of least flow resistance. Other
shapes and designs for flow diversion through a channel `
spacer sheet are possible and include those describe~ in
U.S Pate:~ 5~034,126, and U.S. Patent Application
385,230 ailowed allowed July 19, 1991.
In a manner analogous to the approach in Figure
6, it is possible to apply a flow diverting means to the .~
- 30 third channel spacer sheet 8, and, by means of an inlet ~;~
and an outlet port, establish capability for inlet-to- ~;
outlet flow in the ird channel 28. In such a case, ~
the flow diverting ~ns would extend from the outer ~ `
terminus 8 radiall inward towards, but not all the way
to, the insertion polnt of the third channel spacer `
WO93/10889 PC~/US91/OB825 ~ ~
f`' -' ' J '- ~ ;f ~ - 20-
material 8 within the folded second membrane 7. The
flow diverting means would preferably be mated at the~
membrane scroll's outer periphery with an additional
sealing cuff so as to separate inlet and outlet zones of
the annular space 29 corresponding to inlet and outlet
ports.
Figure 7 illustrates a membrane module
comprising a triple channel membrane element and a
containment vessel havin~ provision for inlet-to-outlet
fluid flow for all three channels of a triple channel
device. The spirally wound membrane device is enclosed
in a containment vessel 13 having an endplate 20 at each
end, held in place by a restraining means such as a snap
ring 21. An inlet port 45 is connected to a modified
hollow mandrel 40 (indicated by a dashed line) by means
of a coupling 46. The mandrel modification may be a
plug 42 as illustrated by Fig 6, or other means to
accommodate a fluid inlet and a fluid outlet through the
mandrel for a first flow channel. The outflow end of
this mandrel 40 may be similarly connected to an outlet
port 47. Inlet 48 and outlet 49 ports for fluid flow
through a second fluid flow channel formed by a second
channel spacer are positioned in the wall 30 of the `
vessel. These two ports may alternatively be located in
the opposing endplates 20 of the vessel. Cuffs 17 at
each end of the spirally wound element seal off the flow
chamber for the second fluid flow channel from the
annular space 29. A cuff 50 ls positioned at a location
intermediate to the end cuffs on the spiral element
periphery. The intermediate cuff 50 di~ides the annular
space 29 into a first annular compartment 29a and a
second annular compartment 29b. The first annular
compartment 29a is in fluid co~munication with an inlet
W093~10~89 PCT/US91/08825
-21- t~
port 51, the second annular compartment 29b is in fluid
communication with an outlet port 52. Fluid entering~
the inlet port 51 into the annular compartment ~9a would
thereupon enter into the flow channel defined by the
third channel spacer material at the exposed leaf
terminus 18a. The fluid would typically be guided by a
flow diverting means within the fluid flow channel.
After circulating through the fluid flow channel, the `
fluid exits from the third fluid flow channel at the
terminus zone 18b into annular space 29b, and therefrom
passing through exit port 52.
The device illustrated in Figure 7 is ~`~
representative of only one means by which the concept of
the invention may be employed. Other variations within - ~
the context of this invention may be readily apparent to ~;
the practitioner skilled in the art. Inlet-to-outlet ~
flow may be employed in one, two, or all three channels. -
If inlet-to-outlet flow were employed in only one of the `~`
channels, each of the other two channels would naturally
function essentially as outflow channels, producing for
example a filtrate or permeate stream by filtration or
permeation of fluid through the membrane layers. In
this particular example, inlet-to-outlet flow would
25 preferably take placc through the middle channel. ~
Utility may even be f und where no inlet-to-outlet flow ^ ~-
occurs in any of the ~hree channels. Rather, a dead end
filtration design may be employed, such as where a fluid
to be filtered through a microfiltration membrane enters
into the middle channel, and filtrate exits from the
first and third channels. ~-~
Inlet-to-outlet flows are arranged in Figure 7
to provide generally counter-current or cross-current
flow of fluid streams along the surfaces of the
WO93/10889 PCT/US91/08825 ~ ~
`- :.
-22- -
~ a
membranes contained in the device, but the invention is
not limited by this flow arrangement. Co-current,
cross-current and counter-current flow paths are all
considered within the overall context of the invention,
as well as reversal of flow directions during operation
of the device.
The two membranes which define, in conjunction
with the three channel spacer layers, the three channels
of the triple channel spiral device need not be
identical one membrane to the other. The two membranes
may differ from one another in composition and
performance function. Thus, one membrane could be a
polyamide-ba3ed composition performing as reverse
osmosis membrane, for example, the other being a
silicone-based composition performing as a pervaporation
membrane. Thus, potential exists for simultaneously
performing two different types of membrane-based
separations on a fluid feed stream. Membranes can be ~--
chosen to provide separations in the areas of reverse
osmosis, nanofiltration, ultrafiltration,
microfiltration, dialysis, pervaporation, coupled
transport separations, gas separations, piezodialysis,
membrane distillation, solvent vapor recovery, and so
forth. Any number of nested membrane sets may be wound
into spiral modules o~ this triple channel design to
achieve a variety of module sizes and membrane areas.
Individual single sheets of the two membranes may also
be accordion-folded (i.e., multiply pleated), with
appropriate interleaving of channel spacer materials, to
delineate a plurality of membrane envelopes wound upon i~
the mandrel, wherein the first membrane layer may
consist of a continuous single sheet of membrane, as may
the second membrane layer also. The overall area of the
W093/tO~89 PCT/US91/0~825
~` 23 '~
first membrane in a triple channel device may also be
varied considerably relative to the overall area of the
second membrane, depending u~on the intended application
of the device. Other aspects and modifications of this ' ;~;~
novel triple channel design will become apparent to the
practitioner skilled in the art.
Semi-permeable membrane suitable for use in the
inventive process and apparatus may be selected from
materials exhibiting appropriate chemical and physical ;~
0 properties. Microporous polyethylene, polypropylene,
and polytetraflouroethylene membranes may be selected ~;
for hydrophobic properties. Such hydrophobic membranes
would find advantage in a chemically facilitated gas `~
separation where the facilitating fluid is aqueous based `~;
as the mem~rane sheet would not be wetted by the aqueous
based fluid.
.~
Pslyamide, and composite polyamide membranes ~-
29 may be selected for hydrophilic properties. Such
hydrophilic membranes would find advantage in a
separation of molecular weight fractions from an aqueous
based solution such as a fermentation solution where --~
wetting of the membrane sheet would be advantageous.
The process of the invention is particularly -~
attractive for separation of feed-gas mixtures utilizing
a chemical facilitation means. A feed comprising a
mixture of gases is circulated to a first envelope - `-
30 consisting of a semi-permeable membrane. The membrane ~`
is permeable to at least one gas component o~ the ~ ~
mixture. In contact with the first semi-permeable ~ ~`
membrane envelope is a fluid which selectively
facilitates, as by absorption, the removal of at least ~ -
one gas component from the mixture. The facilitating ~ -
WO93/10889 PCT/US91/08~25
,
-24-
~ ,J
fluid is itself contained within a second membrane
envelope. A third envelope formed of a membrane semi~
permeable to at least one component absorbed by the
facilitating liquid is also in contact with the
facilitating liquid. At least one component absorbed in
the facilitating liquid is stripped from the
facilitating liquid.
The facilitating liquid used in the process
will in general be selected for the particular gas
mixture separation attempted. For instance,
facilitating liquid for carbon dioxide as a permeate gas
is preferably an aqueous solution of a alkali-metal
carbonate. Alternative facilitating liquids include
monoethanolamine, diethanolamine and hindered amines, as
aqueous solutions or undiluted. Carbon monoxide may be
absorbed from a mixture with carbon dioxide by an
aqueous solution of cuprous chloride and an alkali-metal
chloride such as potassium chloride. Ethylene and
propylene may be selectively absorbed from a gas mixture
including ethane and propane in an aqueous solution of
silver nitrate or other water-soluble silver salt.
Hydrogen sulfide may be selectively absorbed from
natural gas by an aqueous solution of an alkali-metal
carbonate such as potassium carbonateO Sulfur dioxide
may be selectively absorbed from stack gas by an aqueous
solution of an alkali metalbisul~ite or sulfite or polar
organic compounds such a sulfolane or polyethylene
glycol-
Variations and modifications of the apparatusand methods described will be apparent to the
practitioner skilled in the art of fluid separations by
semi-permeable membranes. All such variations and
WOg3/10X89 PC~/US91/0~825 ~ ~
-25- 2 L / L~ r :~
modifications are considered within the scope of the
claims below. ~ ~ ~
Examples i ;;;
Example 1
A 50 liter sample of a biological fermentation
liquor containing a range of molecular weight compounds
up to 20,000 including growth nutrients, growth ~ -
products, cell fractions and inorganic salts is
10 circulated through inlet and outlet ports of a triple -~
channel spiral wound membrane module at (400 psig). The
membrane enclosing the inlet fluid flow channel has a
molecular weight cut off of 10,000. The second membrane
of the triple channel membrane element has a molecular
15 weight cut off of 8,000. Fluid from the second membrane --~
envelope in contact with both the first and second ``~
membranes is recirculated through inlet and outlet ports
of the second membrane envelope with a pressure
maintained at t350 psig). Makeup water of 50 liters is ;~
added to the initial sample sufficient to maintain a -
recirculating sample fluid level of 20 liters.
When 80 liters of fluid has passed through the
membrane having a molecular weight cut off of 10,000,
5 liters of a fraction of biological fermentation fluid
having a molecular weight range from 8000 to 10,000 has
been collected as the recirculating fluid from the
second fluid flow envelope. `-~
Example 2
A triple channel spiral wound membrane module
substantially configured according to Fig. 7, except as
noted, is used to separate a gas stream containing
ethylene a~d ethane in a volume ratio of 1:2 by means of
W093/lOX89 PCIIUS91/088~5 ~ ~
. `
-26-
a a
a chemically facilitated transport. The mixed gas
stream is circulated to a first annular compartment
corresponding to 29a in fluid communication with a ~,
microporous semi-permeable hydrophobic third membrane ~--
envelope such as a polyethylene having a porosity of 0.3
and a pore size range from 0.05 to 2.0 ~m. An exhaust
of the mixed gas stream is removed ~rom the second
annular compartment corresponding to 29b. A third
channel spacer material is provided with a flow
diverting means comprising a line of polyurethane ~lue.
An aqueous solution of silver nitrate is
circulated through a second membrane envelope at a rate
of 7.6 l/min (2 gpm) through an inlet port corresponding
to 48 and an outlet port corresponding to 49.
A first membrane envelope also comprises of
microporous polyethylene. The first channel spacer
material has no flow diverting means. The mandrel does
not contain a plug. A valve connected the mandrel inlet
port is closed. A vacuum is connected to the mandrel ~
outlet port. `
The feed gas to the third membrane envelope
beginning at a pressure of 103 kPa (15 psig) the
pressure of the circulating feed gas becomes 69 kPa (10
psig) after circulation of 10 minutes. Thereafter gas ,`
circulation continued. There no significant reduction
! of pressure in the feed gas after the feed gas stream is , -
circulated for 20 minutes. The ethylene is quickly and
efficiently separated leaving the feed gas comprising ~j"
essentially ethane. c`
'~ '''' ''
