CA1047412A

CA1047412A - Tubular membrane separation device with crossed tubes

Info

Publication number: CA1047412A
Application number: CA208,105A
Authority: CA
Inventors: Michikage Matsui; Isao Hamana; Ryozo Hasegawa; Shoji Mizutani
Original assignee: Teijin Ltd
Current assignee: Teijin Ltd
Priority date: 1973-08-30
Filing date: 1974-08-29
Publication date: 1979-01-30
Also published as: FR2242129A1; NL7411572A; GB1481064A; DE2441333C3; BE819424A; DE2441333B2; DE2441333A1; FR2242129B1

Abstract

ABSTRACT OF THE DISCLOSURE
A fluid treatment apparatus comprising a receptacle and accomodated therein a multi-layered structure assembly composed of hollow filaments. The assembly consists of at least one multi-layered structure, and in the multi-layered structure, the filament orienting direction in a given layer intersects with that in a layer adjacent thereto at an angle of 10 to 90 degrees. The hollow filament used in the assembly can be produced, for example, by deacetylating hollow cellulose acetate filaments with a 0.25-10% by weight aqueous solution of sodium hydroxide or potassium hydroxide at a temperature of 65 to 100°C.
The fluid treatment apparatus can be used for various separating operations for fluid mixtures, and its especially useful applica-tion is found in artificial kidneys.

Description

This invention relates to an apparatus for treating fluids comprising a receptacle and accomodated therein an assembly for treating fluids composed of hollow filaments having selective permeability, a process for producing the assembly suitable for use in the apparatus, and a process for producing hollow filaments of regenerated cellulose suitable for use in the assembly.
The term "treating fluids" or "fluid treatment", as used in the present specification and claims, means the separation of certain components from a fluid mixture or solution by utilizing the selective permeability of hollow filaments, that is, the property of the hollow filaments to permit certain components contained in the fluid mixture or solution to pass more easily than the other components. The fluid treatment in accordance with this invention includes various types of separation, such as the reverse osmosis whereby a solution is placed under a pressure higher than its osmotic pressure to leach out only a pure solvent, the pres-surized separation whereby a pressure is applied to a gaseous mixture to concentrate certain components therein, the ul-trafiltration whereby a liquid mixture is placed under an elevated or reduced pressure to separate certain components, the normal osmosis whereby certain components are separated by utilizing the difference in chemical potential between fluid mixtures through a membrane, and the dialysis whereby certain components are removed by the diffusion of the concen-trations of the solutes between solutions.
It has previously been known to use a selectively permeable membrane in performing the various types of ~`

-2- ~ ~

separation exemplified above. It has also been known that a capillary tube or hollow filament having selective permeability is used to separate or exchange substances between fluid A in the capillary tube and fluid B outside the capillary tube.
The use of capillary tubes is an effective technique because it has two great advantages: that the area of a permeable membrane which can be filled in a unit volume is large and that the capillary structure supports not only an equal hydrostatic pressure from outside but also the own weight of the membrane.
Since, however, the area of a permeable membrane for one thin capillary tube is very small in an apparatus using a ~-capillary tube or hollow filament, it is necessary to use a number of capillary tubes. FurthermoreJ the quality of such a fluid treating apparatus is affected by the method for bundling such a number of capillary tubes. If the fluid B
flowing outside the capillary tube forms a certain specific flow path without uniformly flowing around the capillary tube, the components of the fluid are scarcely separated through the -membranous wall of the capillary tube where the specific flow path does not exist. ThusJ there is no significance in bundl-ing a plurality of capillary tubes.
Japanese Patent Publication No. 28625/64 discloses a fluid treatment apparatus comprising a cylindrical receptacle forming a treating chamber and a number of selectively per-meable hollow filaments accomodated therein which are bundled parallel to the longitudinal direction of the receptacle.
The parallel arrangement of capillary tubes in this manner may result in an increase in the number of capillary tubes that can be filled in a unit volumeJ but has the defect that adjoining capillary tubes are apt to make contact with each other along their longitudinal direction and consequently fluid components cannot substantially be separated at the contacting portions. Hollow filaments composed of an organic polymer are especially prone to ma~e such contact because of their suppleness and flexibility. Furthermore, with a parallel arrangement, capillary tubes cannot substantially be filled uniformly when seen in the cross section of the bundle of the tubes, but the filling density of the tubes in the bundle tends to become non-uniform. This results in the selective passage of the fluid B through that portion of the capillary tube bundle which has a coarse filling density, and fluid components can scarcely be separated at that portion of the bundle which has a high filling density.
United States Patent 3,422,008 discloses a fluid separatory apparatus comprising a porous core tube and hollow filaments spirally wound on the core tube. Such an apparatus, however, has the defect that the size of the separatory re-ceptacle increases because of using a porous core. In addition, fluid B flowing outside the hollow filaments cannot form a laminar flow with respect to the hollow filament layers wound spirally on the core tube, and also tends to form a turbulently cross flow. As a result, the efficiency of separating fluid components is poor. Further disadvantages of the separatory apparatus of this U.S. Patent are that a path of the fluid B
flowing outside a hollow filament is technically difficult to separate completely from that of fluid A flowing inside the hollow filament by means of a partition wall at the terminal portion of the filament and the opening for feeding fluid A

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` tends to become complicated in structure. Accordingly, apparatuses of this . . .
type have not yet come into practical use as artificial kidneys because dialysis on these apparatuses is apt to pose side-effect problems such as thrombus or hemolysis.
According to one aspect of this invention, there is provided a fluid treatment assembly composed of hollow filaments having an outside diameter of 30 to 3,000 microns and an inside diameter of 20 to 2,400 microns, ; having selective permeability and containing two open ends; said assembly being obtained by rolling at least one sheet-like multi-layered shape-retaining coreless structure composed of a plurality of filament layers superimposed on each other, each of said filament layers being composed of at least one said hollow filament oriented in a substantially fixed direction, the filament orienting direction of each of said filament layers forming a substantially predetermined angle of intersection of 10 to 40 degrees with that of an adjoining filament layer.
This aspect of the invention also provides a fluid treatment appara-tus for treating a fluid comprising a receptacle, a fluid treatment chamber located within said receptacle for treating the fluid, two compartments with-in said receptacle, each partitioned from said fluid treatment chamber by a partition wall, an inlet opening to one of said compartments, an outlet open-ing from the other of said compartments, an inlet opening and an outlet opening for the fluid treatment chamber, and a fluid treatment assembly of the above type accommodated in said chamber, the two open ends of each hollow filament being positioned in respective ones of said partitioned com-partments.
According to another aspect of this invention, there is provided a process for producing a fluid treatment assembly mentioned apparatus, which comprises winding up selectively permeable hollow filaments on a bobbin of a winding device having a traverse mechansim and forming a multi-layered structure composed of a plurality of superimposed filament layers with the orienting direction of the filament in each filament layer intersecting with that of the filament in an adjoining filament ~, .

~ ~c . ~047~Z
layer at an angle of 10 to 40 degrees, cutting the multi-layered structure .. wound up on said bobbin at at least one point in a direction substantially -parallel to the axis of rotation of said bobbin, removing the cut multi-layered structure from said bobbin to form a substantially rectangular sheet-like multi-layered structure, and then rolling the sheet-like multi-layered structure so as to form a round rod having an opening at its end.
~: In the accompanying drawings which illustrate examplary embodi-:
::. ments of the present invention:
~: Figure 1 is a side elevation of a fluid treatment apparatus in :. ~
accordance with this invention in which a fluid treatment assembly is placed;
. Figures 2, 3 and 4 each are a side elevation of another embodi-ment of the fluid treatment apparatus in accordance with this invention;
Figure 5 is a perspective view of a multi-layered structure in accordance with this invention wound up on a bobbin, with the direction of the rotating axis of the bobbin being shown by a short arrow;
Figure 6 is a perspective view of a rectangular sheet-like multi-layered structure having an opening at its side, which has been removed from the bobbin after cutting;
Figure 7 is a perspective view of the multi-layered structure used in this invention, showing an intersecting angle ' , .

. -- 6 --.

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formed between a given layer of hollow filaments and a filament layered ., adjacent thereto;
` Figure 8 is a perspective view of another embodiment of a multi-layered structure used in this invention; and .-Figure 9 is a view showing the production of a fluid treatment assem-bly by rolling the multi-layered structure in accordance with one embodiment of the process of this invention.
, The fluid treatment apparatus of this invention consists of a fluid ,:.
~-~ treatment assembly composed of hollow filaments and a receptacle including the assembly and being suitable for fluid treatment.
' Referring to Figure 1, a receptacle 1 has an inlet opening 2 and an outlet opening 3 for fluid B flowing outside a hollow filament. The recep-tacle also includes an inlet opening 7 and an outlet opening 8 for fluid A
flowing inside the hollow filament. Furthermore, in the embodiment shown in Figure 1, the receptacle 1 is partitioned into a treating chamber 11 and com-partments 9 and 10 by partition walls 4 and 5. These partition walls can have a width that can substantially withstand pressure. An assembly 6 for fluid treatment is trimmed at both ends and embedded in *he partition walls 4 and 5 ~ made, for example, of an epoxy resin, and the opening of each of the hollow ; 20 filaments constituting the assembly 6 is positioned in the compartments 9 and 10. Fluid A flows from the inlet opening 7 into the hollow filaments posi*ion in the treating chamber 11 via the compartment 9. On the other hand, fluid B
enters the treating chamber 11 from the inlet opening 2. In the treatment chamber 11, the components of fluids A and B are separated through the mem-` brane wall of hollow filaments. The fluid A treated flows through the hollow filaments, passes the compartment 10, and is withdrawn from the outlet opening 8. On the other hand, the treated n uid B is withdrawn from the outlet open-ing 3.
The cross-sectional shape of the receptacle is optional, but prefer-ably, is changed according to the desired cross-sectional shape of the assembly.Por example, when the desired cross-section of the assembly is rectangular, the cross-section of the receptacle is preferably rendered rectangular, and :; 1047~Z
when it is circular, the cross-section of the receptacle is preferably rendered circular.
The fluid treatment apparatus shown in Figure 2 is the same as the apparatus shown in Figure 1 except that one open end of the assembly 6 is com-pletely embedded in the partition wall 4, and the apparatus does not include the feed opening 7 for fluid A and the compartment 9. This type of apparatus is especially useful for gas separation.

. ., The apparatus shown in Figure 3 is the same as the apparatus shown in Figure 1 except that the inlet opening 7 for fluid A is bifurcated (Al and A2). The inlet opening 7 may also be divided into more than two branches, and by this division, two or more kinds of fluid A can be separately fed at the same time.
;.
In the other embodiment shown in Figure 4, the partition walls and the inlet opening 7 and the outlet opening 8 for fluid A are provided on one side of the receptacle, and the assembly is filled in it in a U-shape. In : this embodiment, the use of at least a single partition wall is sufficient for performing the function of partitioning. The fluid component separating action of this apparatus is equivalent to that of the apparatus shown in Figures 1 to 3.
The fluid treatment assembly used in the apparatus of this invention is composed of at least one multi-layered structure composed of a plurality of hollow filaments intersecting each other, and is produced in the following manner.
The production of the assembly starts with the production of the multi-layeret structure. The multi-layered structure is prepared by winding : at least one hollow filament on a bobbin by, for example, a traverse mechanism, to superimpose layers of the hollow filaments. Preferably, the number of hol-low filaments used is 2 to 50 when the diameter of each filament is at least lOO microns, and 2 to 200 when it is less than 100 microns. The wind-up of the hollow filaments on the bobbin is performed in such a manner that the ori-enting direction of the filament in a given hollow filament layer intersects with that of the filament in an adjacent hollow filament layer at an angle of ,. . , ' .

.

r ~()474~2 . 10 to 90 degrees. The intersecting angle is preferably 10 to 40 degrees, es-pecially preferably 10 to 25 degrees. If the intersecting angle is less than 10 degrees, a twill pattern does not appear, and the effect of the present in-vention is difficult to expect. On the other hand, if the intersecting angle exceeds 90 degrees, it is difficult to produce the intended multi-layered structure, and disadvantages arise. For example, when winding up hollow fila-ments on a bobbin, the wind-up operation becomes difficult, and the length of that portion of the assembly which is to be embedded in the partition wall be-` comes relatively large. Furthermore, the flows of fluids A and B cross each other to reduce the efficiency of separating the components of the fluids.
; When a plurality of hollow filament layers wound up on a bobbin in the above-mentioned manner are cut at at least one point in the direction of the long arrow shown in Figure 5, and removed from the bobbin, there can be ~- obtained a sheet-like multi-layered structure having the openings of the indi-vidual filaments in its cut cross-section. The multi-layered structure of hollow filaments so obtained is not a bundle of hollow filaments arranged para-llel to each other, but is of the structure in which a plurality of constitu--:; ent hollow filaments are superimposed in layers while intersecting with each ... .
other.
Figure 7 shows the state of intersection of the hollow filament .- layers each containing a relatively few number of filaments. As is shown, in the direction of the arrow, the hollow filaments in a given layer intersect with those in an adjacent layer at an intersecting angle of about 10 degrees.
If the number of filaments in each layer is increased, and the filaments are uniformly arranged in each layer, the adjoining two layers form a dense twill ' pattern over the entire surfaces of the layers. This twill pattern is formed continuously in the superimposing direction, and for example, hollow fila-ments in a given layer i intersect those of a layer ~i ~ 1) and a layer 1) at the intersecting angle mentioned above ~ being a positive integer showing an ordinal number).

Figure 8 shows another embodiment of the multi-layered structure in ' accordance with this invention. In this embodiment, the hollow filaments ex-_9_ ~ ~ \
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tend so that they bend upon arrival at both ends and turn to form a new layer.
As illustrated in Figure 8, when the hollow filaments in the layer 1) reaches its edge (the upper edge in Figure 8), they turn in a differ-ent direction to extend so as to belong to layer i. The hollow filaments in - the layer i similarly turn in a different direction upon arrival at the edge portion (the lower edge in Figure 8~ to extend as to belong to the layer (i l 1). The hollow filaments which do not pass the edge portions extend substan-tially straight. In this way, the hollow filaments in one layer intersect with those in an adjacent layer. In the embodiment shown in Figure 8, the intersecting angle of the hollow filaments in this case is about 35. When the intersecting angle is large, the embodiment shown in Figure 8 is advanta-geous. Since the hollow filaments turn at the edge portions, greater quanti-ties of hollow filaments can be filled in a certain predetermined volume.
Then, the multi-filament structures so obtained are assembled to form the fluid treatment assembly for use in the fluid treatment apparatus of this invention.
The assembly may consist of only asingle sheet-like multi-layered - structure as shown in Figure 6. The assembly can also be formed by stacking - a plurality of such sheet-like multi-layered structures. The round rod-like fluid treatment assembly as another embodiment of the assembly can be prepared by rolling one sheet-like multi-layered structure or two or more of such multi-layered structures arranged side by side in the same direction, as shown in Figure 9. This round rod-like assembly has an open surface at both ends.
According to still another embodiment of the fluid treatment assem-- bly, a plurality of layers of hollow filaments wound up on a bobbin are cut at at least one point in a direction parallel to the rotating axis of the bobbin (the direction shown by a long arrow in Figure 5), removed from the bobbin, and bended in a U-shaped to form a U-shaped assembly. This U-shaped assembly is especially suitable for use in a fluid treatment device of the type shown in Figure 4.
As described above, the fluid treatment assembly to be incor-porated in the fluid treatment device of this invention assumes a twill pattern `
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as a result of a plurality of the constituent hollow filaments being super-imposed in layers and intersecting with each other. Usually, one such assem-bly contains 1,000 to 10,000,000 hollow filaments. Accordingly, in the fluid treatment device of this invention, uniform open spaces are formed in the treatment chamber, especially in the assembly. Thus, fluid B can flow uniform-ly in the open spaces, and there can be obtained a superior efficiency of separating the components of fluid without the occurrence of deviated flows or dead spaces. Furthermore, since the hollow filaments are not substantially arranged in parallel, but form a multi-layered structure of a twill pattern, the arrangement of the filaments opened in the compartment at the inlet open-ing differs from that of the filaments opened in the compartment at the outlet opening in the same layer. This, therefore, offers the advantage that even when the mixing of the components of a feed fluid is not uniform, the fluid flowing out from the outlet opening becomes uniform.
Furthermore, unlike the bundle of hollow filaments arranged parallel to each other as shown in Japanese Patent Publication No. 28625/64 cited above, the multi-layered structure of the hollow filaments in accordance with this invention have an excellent ability with shape retention. This is because the hollow filaments in the multi-layered structure in accordance with this invention intersect with each other, and thus support each other at the points of intersection. Accordingly, the multi-layered structure of this in-vention does not separate into the constituent filaments as in the bundle of parallel-arranged hollow filaments of the prior art. This makes it easy to accomodate the structure in a receptacle, and obviates any likelihood of the breakage or damage of the hollow filaments when accomodating in the receptacle.
The multi-layered structure of hollow filaments in accordance with this in-vention withstands higher pressures of fluids flowing exteriorly thereof than the bundle of parallel-arranged hollow filaments does. Since the hollow fila-ments su~ort each other at the points of intersection, even when fluid B is flowed in a great amount to exert a high fluid pressure on the hollow fila-ments, any such troubles can be prevented as the local deviation or breakage of a specific filament which may be caused as a result of the fluid pressure being .
concentrated on it.
In addition to the above-described advantages, the fluid treatment assembly used in this invention is easy to manufacture unlike the apparatus disclosed in United States Patent 3,422,008 cited above, and because there is no need to use a core tube, is compact and extremely easy to handle. Moreover, since a flow of fluid B outside the hollow filaments is approximate to a para-llel flow (preferably, a counter-current flow) owing to the specific intersec-; ting angle defined in this invention, the fluid treatment apparatus of this invention permits good efficiency of separating the components of a fluid.
- 10 Each of the hollow filaments that constitute the fluid treatment as-; ..
sembly in accordance with this invention usually has an outside diameter of 30 to 3,000 microns and an inside diameter of 20 to 2,400 microns. The hollow filaments can be any hollow filaments which are flexible and selectively per-meable. For example, these hollow filaments can be made from polyesters, poly-amides, polycarbonate, cellulose,or cellulose esters.
Of these hollow filaments, those prepared from regenerated cellulose are known, and a process for manufacture of such hollow regenerated cellulose filaments is also known.
For example, there is known a method for preparing hollow regener-ated cellulose filaments which comprises treating hollow cellulose acetate filaments with an aqueous solution of an alkali hydroxide at a temperature of less than 65C., usually at room temperature, to deacetylate the filaments sub-stantially. According to this method, however, the hollow filaments shrink considerably turing the treatment with the alkali hydroxide solution to cause an increase in the thickness of their wall, an extreme reduction in the pro-portion of their hollow portions and also a considerable distortion in the shape of the hollow portion. Consequently, hollow cellulose filaments of good quality cannot be obtained commercially. In addition, such hollow cellulose filaments allow a poor flowing of fluids therethroughJ and also exhibit a poor efficiency of separating the components of fluids.

According to this invention, there can be provided hollow filaments of regenerated cellulose suitable for use in the apparatus of this invention ~ o4741Z
:
which have hollow portions having a complete circular cross-section and are free from flaws.
These hollow filaments of regenerated cellulose can be com-mercially produced in accordance with this invention by melt-spinning a mixture of cellulose acetate and a plasticizer to form hollow filaments, and deacetyla-ting the hollow filaments with a 0.25 - 10% by weight aqueous solution of sodi-um hydroxide or potassium hydroxide at a temperature of 65 to 100C.
The term "deacetylation", as used in the present application, denotes the deacetylation of cellulose acetate to a degree of acetylation of . .
not more than 10%. The hollow filaments obtained by the deacetylation have a .~:
~, substantially cellulose II-type crystalline structure.
Cellulose acetate having a degree of acetylation of 46 to 58%
is especially suitable for use in the manufacture of hollow filaments. If the degree of acetylation is outside this range, it is difficult to perform the melt spinning in good condition using a plasticizer.
';~ Water-soluble plasticizers are especially desirable as the ,~
plasticizer used in this invention, and examples of suitable plasticizers are polyhydric alcohols such as glycol, and glycerih, polyalkylene glycols(especial-ly polyethylene glycol having a molecular weight of 200 to 600) and esters of :~, these formed with carboxylic acids, especially triacetin, and sulfolane. The " .
i permeability of the hollow filaments can be changed according to the purpose !, of use by selecting the plasticizer.
The melt spinning can be performed using known spinnerets and spinning conditions for preparation of hollow filaments by melt spinning.
Preferably, prior to deacetylation, the melt-spun hollow fila-ments of cellulose acetate are pre-treated with a liquid medium inert to the cellulose acetate and heated at a temperature of 65 to 98C., preferably 70 to 85C. Liquid media having the ability to dissolve the cellulose acetate are .
unsuitable because they cause damage to the hollow filaments.

The liquid medium inert to cellulose acetate may, for example, be water, ethylene glycol, liquid paraffin, or light oil. The use of water is especially preferred. If desired, the liquid medium can contain known addi-~ 104~4~Z

. .
tives, for example, a bleaching agent such as oxalic acid or sodium hypochlor-ite, a surface modifier such as sodium carbonate, sodium chloride or sodium sulfate, and a delusterant such as titanium oxide. This pre-treatment changes the outer surface of the hollow filament into a rigid texture due to heat.
Therefore, even when the hollow filaments are subsequently deacetylated with an aqueous solution of an alkali hydroxide, the shrinkage or distortion of the hollow filaments scarcely occurs, and there can be obtained hollow filaments of regenerated cellulose having a more circular cross-section and a high ratio of the hollow portion.

The pre-treated hollow cellulose acetate filaments can be sub-jected to the deacetylation treatment as they are in the wet state or after having been dried.
.~:
The critical feature of this invention is that the cellulose acetate hollow filaments obtained by melt-spinning are treated with an aqueous solution containing sodium hydroxide and/or potassium hydroxide in a concentra-tion of 0.25 to 10% by weight, preferably 0.5 to 5% by weight, and being heated -~ at a temperature of 65 to 100C., preferably 70 to 80C., to deacetylate the filaments substantially.
When the concentration of sodium hydroxide and/or potassium hydroxide in the aqueous solution is lower than 0.25% by weight, the ability of the aqueous solution to saponify, i.e., deacetylate, cellulose acetate, is low, and it is substantially difficult to produce deacetylated hollow regener-ated cellulose filaments commercially. On the other hand, if it is higher than 10% by weight, the ability of the aqueous solution to saponify cellulose ace-tate is so high that non-uniformity in saponification occurs in the longitudi-nal and transverse directions of the filaments when they are treated with the above aqueous solution, thus leading to the difficulty of obtaining hollow re-generated cellulose filaments having uniform quality. Furthermore, in such a case, flaws are apt to be caused on the surfaces of the hollow filaments.
When the temperature of the aqueous solution is lower than 65 C., the hollow filaments considerably shrink during treatment to cause an increase in the thickness of their walls, and the resulting hollow filaments ~ .

. '`;' have a low ratio of the hollow portionsJ and are of low quality. Moreover, :
~ the hollow filaments become flat to give rise to bad shapes of the hollow . ,.
"~ portions. The rate of deacetylationJ tooJ decreases relatively. If it is , higher than 100C.J the aqueous solution boilsO This is not practicalJ and flows of boiling fluid exert localized forces on the hollow filaments and . ~ ., cause poor shapes of the hollow portions.
., .
According to this inventionJ the gasJ usually airJ in the . ., hollow filaments is expanded by the heat of the hot aqueous solutionJ and consequentlyJ the hollow portions of the flattened hollow filaments expand to ,: -,- 10 an extent that their cross-sectional shape is approximate to a complete circle.
;~ If the concentration of sodium hydroxide and/or potassium hydroxide is in-i.;
; creased and the temperature of the aqueous solution is elevated beyond the ., .
ranges specified in the present inventionJ the walls of the hollow filaments are apt to be swollen during the treatment with the aqueous solutionJ and the ,~
expanding force of the gas within the hollow filaments becomes high. Conse-~, quentlyJ the ratio of the hollow portions of the hollow filaments obtained 'i~
as a result of the treatment with the aqueous solution tends to increase over ~' that of the hollow filaments before the treatment.
~i~ In order to perform the present invention commerciallyJ the ~' 20 hollow filaments are continuously treated with the above-described aqueous solution of alkali hydroxideu The treating time is preferably set as short as possible so long as the treatment can be carried out effectively. Suit-able treating periods are 0.25 to 10 minutes, above all 0.5 to 5 minutes.
' Since the hollow cellulose filaments obtained by this inven-tion have a cross-sectional hollow portion approximate to a complete circleJ
f they permit a smooth passage of fluids therethrough when used to move the . . .
components of fluids through their walls by flowing a fluid within the hollow filaments and another fluid outside the hollow filamentsO AccordinglyJ they allow the movement of components between fluids to be performed with good efficiency.
One particularly useful application of the hollow regenerated cellulose filaments in accordance with this invention is an artificial kidney , capable of removing waste products present in the blood.
` The following Examples illustrate the present invention in ~
greater detail.
Example 1 A mixture of cellulose acetate having a degree of acetylation of 55% and 30% of polyethylene glycol having a molecular weight of about 300 ;; as a plasticizer was melt-spun to form hollow filaments each having an outside -; diameter of 300 microns and an inside diameter of 220 microns and a cross- ,., ` section being approximately of a complete circle (the ratio of hollow portion ~ 10 being about 54%). The hollow filaments were treated in a 3% by weight aqueous .- solution of sodium hydroxide for 3 minutes while allowing the filaments to ,:
shrin~ 5% in their longitudinal direction. During the treatment, the tempera-ture of the aqueous sodium hydroxide solution was varied to examine the effect of the temperature upon the resulting hollow filaments. The results are shown ,~ in Table 1.
~ Table 1 , .
Temperature of ShapeRatio of Degree NaOH aqueous of thehollow of solutOon hollowportion acetyla-Runs Nos. ( C.) _ portion (%) tion (%) 201 (comparison) 60 Ellipse 33 0 2- 2 (invention) 70 Nearly 41 0 complete circle

3 (invention) 80 Ditto 55 0

4 (invention) go Ditto 70 0

5 (comparison) 101 Ellipse 90 0 It can be seen from Table 1 that according to this invention, ` hollow regenerated cellulose fila~ents having a cross-section of nearly com-pletely circular shape could be obtained.
Example 2 A mixture of cellulose acetate, 37% by weight of polyethylene glycol having a molecular weight of about 300 as a plasticizer and 4% by weight of sodium sulfate as an additive was melt-spun to form hollow filaments : -16-~`-1047~1Z

,. ..
, each having an outside diameter of 300 microns and an inside diameter of 220 .
microns and a cross-section of a nearly complete circular shape (the ratio of - hollow portion being 54%). The hollow filaments were immersed for 5 minutes in an aqueous solution containing 2% by weight of oxalic acid and heated at ~-~ each of the temperatures indicated in Table 2, and immediately then, deacety-. .
lated with an aqueous solution containing 5% by weight of potassium hydroxide ., ` to form hollow regenerated cellulose filaments.
~ For comparison, another run was conducted in the same way as ,~ above except that the pre-treatment with the aqueous oxalic acid solution was omitted.
;;- The conditions used in the above runs, and the shape of hollow portion and the ratio of hollow portion of the resulting regenerated cellulose hollow filaments are shown in Table 2.
It can be seen from Table 2 that according to this invention, ' hollow regenerated cellulose filaments having a cross-section of a nearly com-- plete circular shape and being of good quality could be obtained.
Table 2 , ~ Hollow regenerated ,,, `: Temperature of cellulose filaments i; the oxalic acid Ratio of ~- 20 aqueous solution Shape of hollow ~- Runs Nos. ~C.) hollow portion portion (%) 7 ~comparison)The aqueous oxalic Marked 23 , acid solution not deformation used 8 (comparison) 60 Hollow portion 30 '~ eccentric 9 (invention) 70 Nearly complete 51 circle 10 (invention) 85 Ditto 59 11 (invention) 95 Ditto 67 12 (comparison) 100 Markedly 91 rendered elliptical and the wall having flaws example 3 Eight hollow cellulose filaments each having an outside diameter of 300 ~0474~2 microns and an inside diameter of 240 microns prepared in the same way as in Example 1 were plied and wound up on a bobbin having a diameter of 20 cm while ; adjusting the traverse stroke to 10 cm ancl the traYerse angle of about 10 de-grees. ~The traverse angle corresponds to one half of the angle (intersecting angle) formed between a filament in a given layer of filaments wound up on the bobbin and a filament in a layer adjacent thereto~7 The hollow filaments were cut at two places at equal intervals as shown in Figure 5, and removed from the bobbin. Then, they were formed into a sheet-like multi-layered structure having an intersecting angle of about 20 degrees - 10 as shown in Figure 6. Two such multi-layered structures were superimposed to ~ form an assembly of the hollow filaments. The assembly was accomodated in a f receptacle of the type shown in Figure 1, and both ends of the hollow fila-"
~ ments were embedded in partition walls 4 and 5 made of an epoxy resin so as to -~ extend through them and open in the compartments 9 and 10 respectively. A
~ .
~' total of 5,000 hollow filaments were thus accomodated, and the effective , . .
length of the hollow filaments for fluid treatment was about 25 cm.
Deionized water was passed as fluid B from an inlet passage 2 to an out-let passage 3 at a flow rate of 100 ml./min. As fluid A, 2% by weight saline solution was passed into the inside of the hollow filaments at a flow rate of 20 40 ml./min. from a feed inlet 7, and a dialysis test was conducted. The con-centration of sodium chloride in the fluid A withdrawn from a withdrawal open-ing 8 was found to be decreased to 0.25%.
On the other hand, for comparison, 5000 hollow cellulose filaments, same as those used above, were bundled in a parallel arrangement, and the bundle was accomodated in the same receptacle 1. The same dialysis test as above was conducted using the resulting fluid-treatment device. It was found that the concentration of sodium chloride in the fluid A withdrawn from with-drawal opening 8 was 0.4%, showing an inferior rate of removal of sodium chlor-ide to that attained with the device of this invention manufactured above.
30 Example 4 ~ight hollow cellulose filaments each having an outside diameter of 300 ; microns and an inside diameter of 240 microns prepared in the same way as in .

., .

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. Example 1 were plied and wound up on a bobbin having a diameter of 20 cm while adjusting the traverse stroke to 10 cm and the traverse angle of about 10 de-grees. The hollow filaments so wound up were cut at two places at equal in-,.
tervals in the direction shown in Figure 5, and removed. Then, they were formed into a sheet-like multi-layered structure shown in Figure 6. Two of such sheet-like multi-layered structures were arranged side by side and rolled in the manner shown in Figure 9 to form a round rod-like assembly of the hol-low filaments, and accomodated in a cylindrical receptacle of the type shown in Figure 1. Both ends of the filaments were embedded in partition walls made of an epoxy resin so as to extend therethrough and open on the surfaces of the partition walls. The number of the hollow filaments so accomodated was 5,000, and the effective length of the hollow filaments for fluid treatment was about 25 cm. Deionized water was passed as fluid B from an inlet passage 2 to an ~, outlet passage 3 at a flow rate of 100 ml./min. As fluid A, 2% by weight saline solution was passed from a feed opening 7 through the insides of the hollow filaments at a flow rate of 40 ml./min., and a dialysis test was con-ducted. The concentration of sodium chloride in fluid A withdrawn from a withdrawal opening 8 was found to be decreased to 0.25%.
For comparison, 5000 hollow cellulose filaments prepared same as above : 20 were bundled in a parallel arrangement, and accomodated in the same receptacle.
As a result of the same dialysis test, the concentration of sodium chloride in - fluid A withdrawn from withdrawal opening 8 was found to be 0.4%, and the rate of removal of sodium chloride was inferior to that attained with the device produced above in accordance with this invention.
Twenty such devices were manufactured, and a fluid pressure resistance ; test was conducted. 3% saline solution was passed as fluid A at a flow rate of 50 ml./min., and deionized water was passed as fluid B at a flow rate of 1,000 ml./min. The de~ices were continuously operated for 30 hoursJ and then - the breakage of the hollow filaments was examined. It was found that the hol-low filaments in one device out of twenty were broken.
The detection of breakage was performed as follows: Water was filled in the receptacle, and air was filled in the insides of the hollow filaments.

` --The inlet passage 2 was closed, and a negative pressure (about -300 mmHg) was applied from the outlet passage 3. When the filaments were broken, air bub-: bles were generated from the broken parts. Thus, the breakage of the filaments could be detected by observing the evolution of bubbles.
For comparison, the same fluid pressure test was conducted on twenty ; fluid treatment devices manufactured by accomodating a bundle of5000 hollow filaments arranged parallel to each other in the same receptacles. It was `~ found that the hollow filaments in six devices out of twenty were broken. The ., ~ broken portions all existed in the vicinity of the inlet passage 2 for fluid B.
', 10 Example 5 A mixture of cellulose diacetate and 30% of glycerin as a plasticizer ~,, ! was melt-spun through a spinneret having 16 holes. The resulting hollow fila-ments were treated with hot water at 80C. to extract the glycerin and compact the hollow filament membrane, and thus, hollow cellulose acetate filaments each having an outside diameter of 80 microns and an inside diameter of 60 microns were produced. The hollow filaments were wound up on a bobbin in the same way as in Example 4. The hollow filaments were formed into a round rod-like assembly by the method shown in Figures 5 to 9 in the same way as in Example 4. The assembly was accomodated in a receptacle of the type shown in 20 Figure 2. The number of the accomodated filaments was about 130,000. The left end portions of the filaments were completely embedded in the partition wall 4 of an epoxy resin and had no opening. The right end portions of the filaments however, extended through the partition wall 5 and opened in the compartment 10.
0.5% by weight saline solution as fluid B was pressuri~ed at a pressure of 45 Kg/cm2, and passed from inlet passage 2 at a flow rate of 600 ml./min., and discharged from outlet passage 3. In this manner, the saline solution was circulated. Thus, from the withdrawal opening 8, water from which 95% of sodium chloride had been rejected flowed out at a rate of 55 ml./min.

, . , For comparison, 130,000 hollow cellulose diacetate filaments same as prepared above were bundled in a parallel arrangement, and the same test as above was conducted. The flow rate of the water from the withdrawal opening ':

was decreased to 50 ml./min., and sodium chloride was rejected only to an , extent of 89%.
~:, ~^ Example 6 Polyethylene terephthalate having an intrinsic viscosity of 0.65 was spun by a customary method using a spinneret having 36 holes to afford hollow filaments each having an outside diameter of 55 microns and an inside dia-: meter of 30 microns. The hollow filaments were superimposed as shown in Fig-ure 8 to form a multi-layered structure having a length of 170 cm, a width of 100 cm, and an intersecting angle of about 25C. The multi-layered structure ` 10 was accomodated in a cylindrical receptacle of the type shown in Figure 2.
The filaments at each end of the structure were bonded using an epoxy resin, and the filament ends were opened only on the partition wall 5 shown on the right side in Figure 2. The number of hollow filaments accomodated was about ; 2,000,000. A gaseous mixture consisting of 63% of helium and 37% of oxygen ,~
was passed as fluid B from inlet passage 2 at a flow rate of 18.5 Nm3/hr by means of a compression pump, and discharged from outlet passage 3. The pres-sure exerted to the inside of the receptacle 1 was maintained at 50 Kg/cm2.
As a result of this pressurized separation, a gaseous mixture consisting of 93%
of helium and 7% of oxygen was obtained at a rate of 10.7 Nm3/hr from the withdrawal opening.
ThusJ by using the apparatus of this invention, a helium gas of high purity could be obtained in a high yield from a helium gas of low purity.
For comparison, the same test as above was conducted except that the assembly consisted of a bundle of the same number of hollow filaments arranged parallel to each other9 A gaseous mixture consisting of 87% of helium and 13%
; of oxygen was obtained from the withdrawal opening 8 at a flow rate of 10.1 , Nm3/hr. Both the purity and yield of helium were inferior to those attained above in accordance with the present invention.
Example 7 Polyethylene terephthalate having an intrinsic viscosity of 0.65 was ;~ ~pun by a customary method using a spinneret having 36 holes to form hollow filaments each having an outside diameter of 55 microns and an inside diameter :
~:: 104741Z
of 30 microns. The hollow filaments were superimposed as shown in Figure 8 to ' form a sheet-like multi-layered structure having a length of 170 cm and a width of 100 cm. The intersecting angle of the filaments was about 25 degrees.
` ~ Two such sheet-like multi-layered structures were arranged side by side and ,~ rolled in the manner shown in Figure 9 to form a round rod-like assembly having a length of 170 cm. The assembly was accomodated in a cylindrical receptacle of the type shown in Figure 2. Both ends of the assembly were each - bonded with an epoxy resin, and the hollow filaments were opened only in the : compartment 10 shown on the right side of Figure 2. The number of the hollow 10 filaments so accomodated was about 2,000,000.
A gaseous mixture consisting of 63% of helium and 37% of oxygen was fed from inlet passage 2 at a flow rate of 18.5 Nm3/hr by means of a compression .
pump, and discharged from outlet passage 3. The pressure exerted on the in-side of the receptacle 1 was maintained at 50 Kg/cm2. As a result of this pressurized separation, a gaseous mixture consisting of 94% of helium and 6%
of oxygen was obtained from the withdrawal opening at a flow rate of 11.5 Nm3/hr.
Thus, helium gas of high purity could be obtained in high yield from helium gas of low purity using the apparatus of this invention manufactured in the above-mentioned manner.
For comparison, the same test as above was conducted except that the hollow filaments were bundled parallel to each other. A gaseous mixture con-sisting of 89% of helium and 11% of oxygen was obtained from the withdrawal opening at a flow rate of 10.6 Nm3/hr. Both the purity and yield of helium , were inferior to those attained with the apparatus of this invention used above.
Example 8 A fluid treatment apparatus of this invention was manufactured in the -same way as in Example 4 except that a bifurcated adapter was attached to the end of the feed opening 7. A 20% aqueous solution of edible starch syrup was passed as fluid Al at a rate of 10 ml./min., and as fluid A2 a 20% aqueous ; solution of edible food red was passed at a rate of 0.5 ml./min. from the feed .
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opening 7. As fluid B, deionized water was passed at a flow rate of 10 ml./min. The pressure inside the receptacle 1 was a negative pressure (about -500 mmHg). From the withdrawal opening 8, a beautiful starch syrup ~, concentrated to 31% and having uniformly dispersed therein the food red was obtained. Although the starch syrup and the food red were non-uniformly mixed ; in the vicinity of the feed opening 7, uniform mixing was attained when the . . .
~ mixture reached the withdrawal opening 8. This is because the hollow fila-,,j .
~ ments intersected with each other, and the arrangement of the hollow filaments ~; ~
~- at the cross section of the partition wall 4 almost randomly differed from that of the hollow filaments at the cross section of the partition wall 5.
For comparison, the same test as above was conducted except that the - hollow filaments were bundled parallel to each other. The mixing of the -- starch syrup with the food red was non-uniform, and the mixture withdrawn from the withdrawal opening exhibited a striped pattern.
Example 9 - A U-shaped multi-layered structure was manufactured from hollow regener-ated cellulose filaments each having an outside diameter of 300 microns and an inside diameter of 220 microns which were produced in the same way as in Example 1.
The resulting multi-layered structure was accomodated in a fluid treat-ment receptacle of the type shown in Figure 4, and the same dialysis test as in Example 3 was performed. Good results weré obtained.
Example 10 Twenty-four hollow cellulose filaments each having an outside diameter of 320 microns and an inside diameter of 250 microns were plied, and wound up on a bobbin having a diameter of 13 cm while adjusting the traverse stroke to 15 cm and the traverse angle to about 5 degrees. After winding up 12,000 filaments, the filaments on the bobbin were cut at one point to form a sheet-~; like multi-layered structure having an intersecting angle of 10 degrees as shown in Figure 6. Then, the structure was rolled in the manner shown in Figure 9 to form a round rod-like assembly. The round rod-like assembly was ~xx~modated in a cylindrical receptacle of the type shown in Figure 1. Both `` 104741Z

;
ends of the assembly were embedded in the partition walls of a silicone resinJ
and in the same manner as in Example 3, the ends of the filaments were opened in the compartments to produce a dialyzing deviceO -The device was sterilized with a 2% aqueous solution of formal-dehyde, and washed and defoamed with an isotonic sodium chloride solution.
Using the device, a clinical evaluation was madeO The blood was first heparinized, and fed as fluid A at a flow rate of 200 mlO/min. using a blood .; ,j pump. On the other hand, a Kindaly Solution (registered trademark), a dialyzate, was fed countercurrently as fluid B at a flow rate of 500 mlO/min.
by means of a negative-pressure pump. The different in pressure between the blood and the dialyzate was adjusted to 200 mmHgO
Dialysis was performed for 6 hours on 10 male adults with an aver-; age body weight of 55 Kg. It was found that the concentration of the blood ~ urea nitrogen was decreased from 60-70 mg/dQ to 20-30 mg/dQ, the concentration .~
of creatinine was decreased from 12-20 mg/dQ to 5-8 mg/dQ, and 0O5 to 105 Kg of water could be removed from the bodyO
An in vitro evaluation of this dialyzing device was madeO The ~.,, _ urea dialysance was 155 ml/minO and that of creatinine dialysance, 125 ml./
min. with respect to thé model blood. These results showed about 10% superior ,~ 20 performance over that attained with a comparison device manufactured using ... .
a bundle of 12,000 hollow filaments arranged parallel to each otherO The ., ' .
amount of water ultrafiltered was 280 ml/hrO 100 mmHg, showing good results.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A fluid treatment apparatus for treating a fluid comprising a receptacle, a fluid treatment chamber located within said receptacle for treating the fluid, two compartments within said receptacle, each partitioned from said fluid treatment chamber by a partition wall, an inlet opening to one of said compartments, an outlet opening from the other of said compartments, an inlet opening and an outlet opening for the fluid treat-ment chamber, and a fluid treatment assembly accommodated in said chamber and composed of hollow filaments having an outside diameter of 30 to 3,000 microns and an inside diameter of 20 to 2,400 microns having selective permeability and containing two open ends; said assembly being obtained by rolling at least one sheet-like multi-layered shape-retaining coreless structure composed of a plurality of filament layers superimposed on each other, each of said filament layers being composed of at least one said hollow filament oriented in a substantially fixed direction, the filament orienting direction of each of said filament layers forming a substantially predetermined angle of intersection of 10 to 40 degrees with that of an adjoining filament layer, the two open ends of each said hollow filament being positioned in respective ones of said partitioned compartments.

2. The apparatus of claim 1 wherein said intersecting angle is 10 to 25 degrees.

3. The apparatus of claim 1 wherein said hollow filaments are made of a material selected from the group consisting of polyesters, polyamides, polycarbonates, cellulose esters and regenerated cellulose.

4. The apparatus of claim 3 wherein said hollow filaments are made of regenerated cellulose.

5. A fluid treatment assembly composed of hollow filaments having an outside diameter of 30 to 3,000 microns and an inside diameter of 20 to 2,400 microns, having selective permeability and containing two open ends;
said assembly being obtained by rolling at least one sheet-like multi-layered shape-retaining coreless structure composed of a plurality of fila-ment layers superimposed on each other, each of said filament layers being composed of at least one said hollow filament oriented in a substantially fixed direction, the filament orienting direction of each of said filament layers forming a substantially predetermined angle of intersection of 10 to 40 degrees with that of an adjoining filament layer.

6. The assembly of claim 5 wherein said intersecting angle is 10 to 25 degrees.

7. The assembly of claim 5 wherein said hollow filaments are made of a material selected from the group consisting of polyesters, polyamides, polycarbonates, cellulose esters and regenerated cellulose.

8. The assembly of claim 7 wherein said hollow filaments are made of regenerated cellulose.

9. A process for producing a fluid treatment assembly which comprises winding up selectively permeable hollow filaments on a bobbin of a winding device having a traverse mechanism and forming a multi-layered structure composed of a plurality of superimposed filament layers with the orienting direction of the filament in each filament layer intersecting with that of the filament in an adjoining filament layer at an angle of 10 to 40 degrees, cutting the multi-layered structure wound up on said bobbin at at least one point in a direction substantially parallel to the axis of rotation of said bobbin, removing the cut multi-layered structure from said bobbin to form a substantially rectangular sheet-like multi-layered structure, and then rolling the sheet-like multi-layered structure so as to form a round rod having an opening at its end.