CA2065879A1

CA2065879A1 - Liquid membrane modules with minimal effective membrane thickness and methods of making the same

Info

Publication number: CA2065879A1
Application number: CA002065879A
Authority: CA
Inventors: Ravi Prasad
Original assignee: Ravi Prasad; Hoechst Celanese Corporation
Current assignee: CNA Holdings LLC
Priority date: 1991-04-22
Filing date: 1992-04-13
Publication date: 1992-10-23
Also published as: GR3022209T3; KR950008629B1; DE69216290D1; EP0515033B1; NO921535D0; KR920019404A; JPH0751217B2; EP0515033A1; ES2096031T3; ATE146987T1; DE69216290T2; TW223665B; JPH05123541A; US5449457A; DK0515033T3; NO921535L

Abstract

ABSTRACT
Modules for use in fluid separations, especially contained liquid membrane separations, exhibit minimal effective membrane thickness. The modules have a module case and at least one pair of superposed fabric sheets disposed within the case, the fabric sheets being pleated and nested in the lengthwise direction of the case. Each fabric sheet contains warp-wise extending hollow fiber membrane.
The hollow fiber membranes within the folds of one fabric sheet will therefore form alternating rows with the hollow fiber membranes within the folds of the other fabric sheet by virtue of the length-wise nested pleating. As a result, the effective membrane thickness value of the module is minimized thereby enhancing the efficacy of fluid separations.

Description

LIOUID MEMBRANE MODULES WIT~ MINIMAL EFFECTIVE
M~M~AN~T~ICKNESS AND MET%ODS OF MARING THE SAME

RELATEV APPI.ICATIONS

Thi~ application i8 related to commonly owned and copending U.S. Application Serial No. ~
Atty. Docket No. 426-33 ~2007) and U.S. Application Serial No. ---,---, Atty. Docket Nos. 426-35 (2009), filed on even date herewith and entitled the same as thi~ application, the entire contents of each application being expressly incorporated hereinto by reference.

BACKGROUND AND SUMMARY OF TEE INVENTION

It ha~ recently been suggested that microporou~
hollow fibers (MHF) may be employed in a liquid membrane separation technique whereby feed and sweep ga~e~ flow through the lumens of two different sets of hydrophobic MHF (de~ignated feed-fibers and sweep-flbers, respectively), while a liquid on the shell ~ide of the MHF 3erves a~ the membrane. See generally, Majumdar et al, "A New Liquid Membrane Technigue for Ga~ Separation", AICHE Journal, vol.
34, No. 7, pages 1135-1145 (1988), and Sengupta et al, "Separation o solute~ from Aqueous solution~ by Contalned Liquid Membrane~", AIChE Journal, vol. 34, no. 10, page~ 1698-1708 ~1988), the entir~ content of each being expre~sly incorporated hereinto by reference, This ~o-called "contained liquid 2~5879 membrane" (CLM) technique is reported to have several advantages over conventional immobilized liguid membrane (ILM) separation technology.

For example, conventional ILM technology typlcally require~ periodic replacement of the immobilized membrane liquid due to solute saturation, depletion and/or contamination (depending upon the type of separation being conducted). As a result, conventional ILM
technology is typically only limited to batch separation proce~sing. However, since the membrane liquid according to the recently proposed CLM
technique is physically present in the shell-side of a separation module, it may be repleni~hed and/or replaced more or less continually thereby allowing separation proce~sing to be accomplished on an essentially continuous basis.

Modules for performing CLM separation processes typically include a bundle of hollow fiber membrane~
divided approximately equally into a ~et of feed-fibers (through which the feed fluid flows), and a set of ~trip-fibers (through which the ~trip fluid flows). The MHF bundle i-~ phy~ically housed within a module ca~e of de~ired size and configuration such that the lumens of the feed- and strip-fiber~ are in fluld-communication with supply and discharge ports of the module ca~e a~sociated with the flow of feed and ~trip fluids, respectively. In thi~ manner, a cocurrent or countercurrent gas 10w through the respective s2to 20~5879 of feed- and strip-fibers within the module case may be established.

Theoretically, when performin~ CLM separations, each of the feed-fibers should be in an immediately adjacent non-contacting relationRhip to a respective one of the strip-fibers so that the distance therebetween i~ filled with the membrane liquid.
According to this ideal configuration, therefore, a theoretical minimum effective membrane thicknes (EMT) is established whereby the closest packing of the feed and strip fibars is achieved so that the dlstance therebetween i~ mlnimized. However, conventional module manufacturing techniques fall far short of the theoretical minimum EMT since individual feed-fiber~ cannot exactly and reliably be interposed with individual strip-fibers. As a result, groupings o feed-fibers will reside in the module ad~acent to groupings of strip-fibers thereby significantly increasing the module EMT over the theoretical minimum value.

It i8 towards providing ~olutions to the above problem~ that the present invention is directed.
Broadly, therefore, the present invention is directed to modules containing hollow fiber membrane~ adapted to be~ng used for contained liq~id membrane separation~ whlch exhibit effective membrane thicknes~es which are closer to the theoretical minimum value than can be obtained using conventional membrane manufacturing techniques.
.

More specifically, the present invention i8 directed to modules having superposed fabric sheats in which hollow fiber membranes are disposed in the fabric' 8 warp-wise direction. The warp-wise hollow fiber membranes in one of the fabric sheets can therefore be dedicated a3 feed-fiber~ through which a feed fluld flowa, whereas the hollow flber membrane~ in the other of the fabric sheets can be dedicated as strip-fibers through which a strip fluid flows.

The ~uperpo~ed fabric sheetq are also co-pleated with one anot~er in the warp-wise direction so that the respective folds of the fabric sheet~ will be nested with one another. In thi~
manner, the feed- and strip-fibers of the respective fabric sheets are alternately disposed within the module and are ad~acent to strip- and feed-fibers, respectively. A~ a result, reduced EMT values a8 compared to conventional CLM module~ may be obtained.

Preferably, the fabrics employed in the pre~ent invention ar~ woven fabrics in which the warp-wise hollow fiber membranes are interwoven with weft-wlse monofilamentary fibers. However, other fabric form~
may also be utilized according to the present invent~on -- for example, a knitted structure in whlch the hollow fiber membranes are inserted as a filling.

The weft-wise fibers ~erve to provide structural ~upport for the warp-wiRe hollow f~ber 206a879 me~ rane8 60 as to maintain fiber-to-fiber parallelism between the hollow fiber mem~ranes in the lengthwiQe direction of the module. In addition, the weft-wi~e fibers serve as "spacers"
which minimize (if not essentially eliminate) contact between the microporous hollow feed- and strip-fibers as well as imparting self-centering functlon~ to the hollow fiber membranes in the superposed fabric layer3. These functional characteri~tic~ of the weft-wiQe fibers further minimize the EMT value of the module (i.e., the module EMT approaches the theoretical value).

Further a~pects and advantages of thi 8 invention will become more clear after careful consideration i~ glven to the detaiIed de~cription of he preferred exemplary em~odiment~ thereof which follow~.

BRIEF DESC~IPTION OF TffE ACCOMPANYI~G DRAWINGS

Reference will hereinafter be made to the accompanying drawings wherein like reference numeral~ throughout the variou~ FIGURES denote like structural elements, and wherein;

FIGURE 1 i~ a side per~pective view of a module according to the present invention which i8 partly ~ectioned to expo~e the superposed pleated ~abric layer~ contained within the module case;

20~5879 FIGURE 2 is a partial cross-sectional view of the module shown in FIGURE l a~ taken along line 2~2 therein, but ~n a greatly snlarged manner for clarity of presentation;

FI~URE 3 is a block diagram illustrating the basic manufacturing steps employed in making the module~ of the present invention; and FIGURES 4a-4c are diagrammatic perspective view~ showing the manner in which fabric layers containing microporous hollow feed- and strip-fibers are superposed on one another, pleated and as~embled wlthin the module ca e.

DETAILED DESCRIPTION OF 'D~
PREFERRED EXEMPLARY EMBODIMENTS
Accompanying FIGURE 1 depicts a preferred embodiment of a contained liquid membrane module 10 according to the present invention. In this connection, the module l0 includes a case C and a microporous hollow fiber bundle B disposed within the interior space S (see ~IGURE 2) of the case.

A8 i~ more clearly ~een in the expanded scale of FIGURE 2, the bundle B within the case C 1~
comprised of ~uperposed fabrl~ sheet~ ~de~lgnated in FIGURE 2 by the single-da~h chain line l2 and t~e double-dash chain line l4, respectively) which are co-pleated ~o a~ to be nested r21ationship wlth one another. The fabric sheets 12 and 14 include 2~6~879 lengthwi~e coextensive microporous hollow feed-fiber~ and strip-fibers (a few of each are identified in FIGURE 2 as Ff and F5, re~pectively~.
The lumens of the feed-fibers Ff thus provide a path through which a fee~ fluid may flow, wherea~ the lumen~ of the strip-fibers Fs provide a path through which the ~trip fluid may flow when the module 10 is placed into service during contained liquid membrane s~parations.

The module case C i~ most preferably comprised of a elongate central tube Cc and a pair of Y-configured end tubes Yl and Y2 are coupled to a re~pective end of the central tube Cc. Th~ terminal ends of fabric sheet 12 will thus be separated from the terminal end~ of fabric ~heet l~ (preferably in a manner to be described below) and are d~spo~ed within a respective branch of each of the Y-conflgured tube~ ~o as to allow the lumens of each of the microporous hollow feed- and strip-fibers Ff and F8, respectively, to be connected to a fluid ~ource. That i~, the terminal ends of the microporou~ hollow feed-fibor~ Ff in fabrlc sheet 12 may be disposed within branch Ylf of Y-conigured tube Yl while the opposite terminal end~ of the feed-fibers Ff in fabric ~heet 12 may b~ disposed within branch Y2f of Y-conflgured tube Y2.
Similarly, the terminal ends of the strip-fibers F~
ln fabric ~heet 14 may b~ disposed within branch~s Yl8 and Y28, respectively, of Y-configured tube~ Y
and Y2. In this manner, th~refore, the branches, Ylf, Y2, Y1~ and Y28 ~erve as supply and di~charg~
port~ for the fluid during separation proces~es in dependen~e upon the de~irad relative flow through the module 10. For example, countercurrent 1uid flow iq depicted in FIGURE l, but cocurrent fluid flow i8 slmilarly posslble.

Each of the fabric sheet~ 12, 14 is nlost preferably a woven fabric in which the feed- and strip-fibers Ff and F~, respectively, are dispo ed in tha warp-wise direction of the fabric. The weft-wi~e fibers W which are interwoven with the hollow fiber membrane~ constituting the feed-fibers Ff and strip-fibers Fq, respectively, are preferably ~ynthetic monofilamentary fibers, for example, monofilamentary fibers of nylon, polye~ter and the like. In thi~ regard, it i~ e~pecially preferred that the weft-wise fibers be ormed essentially of th~ same nynthetic resin a~ the feed- and ~trip-flbers F~ and F8.

The dia~eter of the monofilamentary weft-wiae ib~rs W i~ preferably cho~en 80 as to be significantly le88 th~n the dla~eter of the hollow fiber me~braues which constitute the feed- and ~trip-fibers Ff and Fs, r~spectively. In this regard, the ~trength ~haracteri~tics o the weft fibors W provide a practical lower limit on their diam~ter given the synthetic re~in from which they are formed. The w~ft fiber~ W should likewise ~ot have too great a diameter as otherwise the separation performanco of the module lO may detrimentally be affectad. A~ an exemplary guidaline, t~e diameter~ of the weft fiber~ 10 are mo~t preferably chosen 80 as to be greater than about lO denier.

The wot-wl~e flbere W ~erve a~ ~pacer8 to e~sentlally maintain a separation distance between the feed-fibers Ff in fabric sheet 12 and the ad~acent strip-fibers F8 in fabric sheet 14. That is, ad~acent ones of the feed- and strip-fiber~ Ff and F8, respectlvely, will be separated one from another at leaqt by a dimension corresponding essentially to the denler of the weft-wise flber~
W.

rt will also be observed that the weft-wise fibers W serve self-centerlng function~. In other words, the weft-wise fibers W aC3ist in orienting the ad~acent individual fe~d-fibers Ff and F8 in the fabric sheets 12 and 14, re~pectively, in ~taggered relationship to one another (i.e., ~ince the "peakq"
of the wet-wlse ibers bounding one of the warp-wi~e hollow fiber membranes of one fabric ~heet will seat within respective weft-wise "valleys"
between ad~acent hollow flber membranes withln the ad~acent nested fabric sheet.) Virtually a~y hollow fiber having wall~ whlch exhibit permeability with re3pect to the s~lected chemical species desired to be separated may b~
employed in the module~ lO according to the present invent$on. Thus, a~ used herein and in tho accompanying claims, the term "hollow fiber membranq" and like terms are intended to refer to hollow fibers whose wallo are permeable to a 206a879 selected chemical species. Thus, hollow fibers which are physically permeable (e.g., due to the pre~ence of pore~ ln the hollow fiber wall3) and/or hollow fibers that are chemically perme~ble (e.g., due to the mas~ tran~port of a chemical specie3 through the hollow fiber walls) are included within the meaning of this definition.

Preferably, however, the hollow fiber membranes employed in the module~ of this invention are microporous hollow fibers made by the "up-spinning"
techniques disclosed in U.S. Patent Nos. 4,405,68~
and 4,451,981, each in the name of James J. Lowery et al, and each being expre~sly incorporated hereinto by reference. Briefly, non-porou~
precur~or hollow fibers are produced according to the techniques dicclo~ed in these prior patents by melt spinning the precursor fibers in a ~ubstantially vertically upward direction (i.e., up-spinning). The thu~ melt spun hollow precursor fiber~ are then spin-oriented while subjecting them to a ~ymmekrical quenching ~tep using a hollow annular structure ~urrounding the precursor 1ber which has one or more openings on it~ inner ~urface that distribute the quenching medium against the precursor fiber in a substahtlally uniform manner.
The thu~ formed hollow precur~or fiber may then be heat annealed by, for example, ~ub~ecting the non-porou~ precursor hollow fiber to a temperature of between about 5C to 100C for a time p~rlod of at lea~t a few seconds (e.g., from a few ~econds up to about 24 hour~, preferably b~tween about 30 minutes to about 2 houro).

20~5879 The fln1 shed m~ croporou~ hollow fi~er~ wlll posse~s an average inner diameter in the range of from about S to about lS00 micron~, and preferably in the range of from about 70 to about 1500 microns. The fibers are moreover characterized by a ~ubstantially uniform internal diameter (I.D.), for example, a coefficient of variation in inner diameter through a croR3-section taken perpendicular to the axi~ of the fiber of leq~ than about 8X, preerably les~ than about 5%, and more preferably le~s than about 3%.

The pore~ of the preferred microporou~ hollow fibers are essentially interconnected through tortuou~ paths which may extend from one exterior ~urface or ~urface region to another, i.e., open-celled. Further, the pore~ of the preferred microporous hollow fi~ers of the present invention are micro~copic, i.e., the details of the pore configuration or arrangement are described only in term3 of micro~copic dimen~ions. Thus, the open cell~ or pores in the fibers are ~maller than those which can be mea~ured using an ordinary light microscope, because the wavelength of visible light, which i~ about 5,000 Angstroms, i~ lonqer th~n the longest planar or surface dimen~ion of the open cell or pore. The pore size of the microporous hollow fiber~ may be defined by u~ing electron micro~copy technlque~ which are capable of re~olvlng detaila of pore structure below 5,000 An~troma or by mercury porosimitry technique~.

2~6a879 The average effective pore size of the microporous hollow fiber~ u~eable in the practice of this invention i~ preferably between S0 to 2000 Angstroms, and more typically between 100 to 1000 Ang~trom~. By "average effective pore siza" is meant the ~mallest dimension of a pore which would allow a qenerally ~pherical particle of that ~ame dimension to pas~ therethrough. The pore~ generally have an elongated -~hape with a width of from 50 to 2000 Angstroms, and a length of from 500 to 10,000 Angstroms. Hence, the "average effective pore size"
of the preferred microporou~ hollow fibers will u~ually be determined by the width dimension of the pore~. These pores will, moreover, be fairly uniform around the circumference of the fiber. For example, the preferred microporouQ hollow fiber~
will exhibit an average ratio of the maximum pore density to the minimum pore density around the circumference of the fiber of less than about 3:1, and usually les~ than about 2:1.

Microporous hollow fibers of the type described above are commercially available from Hoechst Celanese Corporation, Separations Products Division, Charlotte, North Carolina under the reqistered trademark CELGARD~.

Accompanying EIGURE 3 ~howc in block fashion the principal fabrication step~ employed to make tho module 10 de~cribed above. In thi~ connection, the fabric sheets 12, 14 are superpo~ed with one another in ~tep 20 a~ i~ schematlcally ~hown ln accompanying FIGURE 4a. Durlng thl~ step, care 19 taken to ensure that end portion~ of the fabric sheet are separated from one another (i.e., 90 as to segregate the set of hollow microporou3 feed-fiber3 from the set of microporous hollow strip-fiber~ in the ~uperpo~ed fabric layers). Preferably, segregation of the fabric sheet end portions is accomplished by interposing separator ~trip~ S between superposed end reglons of the fabrlc sheets 12, 14 as shown in FIGURE 4a.

The thus superposed fabric sheets 12, 14 having the separator strips S interpo~ed between ad~acent end regions thereof, are then co-pleated in step 22 along the lengthwi~ dimension of the fabric sheets 22 (i.e., in an accordion fashion). The re~ulting accordion-pleated ~tructure is schemati,cally shown in FIGURE 4b whereby the fabric ~heets 12 and 14 are ne~ted with one another.

Once the accordion pleated structure has been obtained, the respective end region3 of the fabric sheets 12 and 14 are segregated from one another in step 24 by gatharing each end region and bandlng it wlth a ~ultable wrapping material (e.g., tape and/or th~ separator strip~ s). During ~tep 24, the accordion-pleated fabric sheets are al~o gathered and banded with one anothe~ 90 as to facilitat~
their in~ertlon with th~ module case C. The bundled and accordlon pleated fabric ~heets lZ, 14 are then first introduced into the central tube Cc durlng step 26, with the ~eparated terminal end reglonc of fabric ~heets 12, 14 then being in~erted into their respective branch of the Y-configured end~ Yl and Y2 2Q~5879 as schematically shown in accompanying FIGURE 4c.
The Y-configured tubes Yl and Y2y are then assembled to the central tube by means of the tube couplings TC.

The module 10 is then fini~hed in step 28, for example, by potting the termlnal end~ of the hollow fiber membrane~ within their respective branch of the Y-configured connectors Yl and Y2~ and conducting any needed quality control incpection~.
The finished module 10 i~ then packaged and shipped to the customer.

It will be appreciated that the particular geo~etry of the module 10 described above i8 only illu~trative in that it represents a particularly preferred embodiment of thi~ invention. Those in thi~ art will recognize that the reduce EMT that en~ue~ by virtue of the fabrication technique~ of the present invention may have applicability in other end-u~e application~ in which hollow flber membranes are employed.

Therefore, whlle the pre~ent invention ha~ been de~cribed in connection with what i~ presently con~idered to be the most practical and preferred embodlment, it i~ to be understood that the invention i8 not to be limited to the di~clo~ed embodiment, but on the contrary, i~ intended to cover variou~ modifications and equivalent arrangement~ included within the ~pirit and scope of the appended claim~.

Claims

1. In a module having a module case and sets of microporous hollow feed-fiber and strip-fiber membranes within an interior space of said module case, the improvement wherein said sets of microporous hollow feed-fiber and strip-fiber membranes constitute re pective superposed fabric sheets which are co-pleated and nested with one another along the length-wise direction of the module case.

2. An improved module as in claim 1, wherein said hollow feed-fiber membranes and said strip-fiber memranes are disposed in the warp-wise direction of their respective fabric sheet.

3. An improved module as in claim 1 or 2, wherein said feed-fiber membranes and said strip-fiber membranes in their respective fabric layers are interwoven with weft-wise fibers.

4. An improved module as in claim 3, wherein said weft-wise fiber membranes are synthstlc monofilamentary flbers.

5. An improved module as in claim 1, wherein said module case has respective supply and discharge ports for each of said feed-fiber membranes and strip-fiber membranes, and wherein terminal end portions of said fabric sheets are separated from one another and disposed within said respective supply and discharge ports associated with said feed-fiber and said strip-fiber membranes.

6. An improved contained liquid membrane module comprising:
an elongate module case having an interior space for containing a membrane liquid; and superposed length-wise pleated and nested sheets of feed-fluid and strip-fluid fabrics disposed within said interior space of said module case, wherein each of said feed-fluid and strip-fluid fabrics includes hollow fiber membranes coextensive with the length-wise direction of said module case constituting feed-fibers through which a feed fluid may flow and strip-fibers through which a strip fluid may flow, respectively.

7. A hollow fiber membrane module including a module case and a bundle of hollow fiber membranes within an interior space of the module case, wherein said bundle of hollow fiber membranes is comprised of at least one pair of superposed length-wise pleated and nested woven fabric sheets in which said hollow fiber membranes constitute warp-wise fibers of each said fabric sheet.

8. A hollow fiber membrane module as in claim 7, wherein said hollow fiber membranes of each said superposed fabric sheet are maintained in parallel to one another and to hollow fiber membranes of an adjacent fabric sheet by means of weft-wise fibers interwoven therewith.

9. A microporus hollow fiber membrane module as in claim 8, wherein said weft-wise fibers are synthetic monofilament fibers having a denier less than the diameter of said warp-wise hollow fiber membrane 8.

10. A method of making a module containing hollow fiber membranes comprising the steps of:
superposing at least one pair of fabric sheets each coextensively containing a number of parallel warp-wise hollow fiber membranes;
pleating the superposed fabric layers in a lengthwise direction so that the pleated fabric sheets are nested with one another in the lengthwise direction; and then positioning said superposed lengthwise pleated and nested fabric sheets within a module case such that the warp-wise hollow fiber membranes extend in the lengthwise direction of the case.

11. A method as in claim 10 wherein said step of superposing said fabric sheets includes the step of separating end regions of the superposed fabric sheets.

12. A method as in claim 11, wherein said end portions are positionally restrained so as to maintain said separation thereof.

13. A method as in claim 11, wherein said step of separating the end regions of superposed fabric sheets includes interposing separator strips between said end regions.

14. A method as in claim 13, wherein said step of separating the end regions of superposed fabric sheets includes bundling the separated end regions and removing said interposed separator strips.