WO2005094975A1

WO2005094975A1 - Membrane adsorption module

Info

Publication number: WO2005094975A1
Application number: PCT/CA2005/000468
Authority: WO
Inventors: Raja Ghosh
Original assignee: Mcmaster University
Priority date: 2004-04-02
Filing date: 2005-03-30
Publication date: 2005-10-13
Also published as: CA2463386A1

Abstract

A fluid distributor for use in a membrane adsorption module has a plurality of fluid distribution channels extending radially from a central passage for fluid flow and formed on an interior surface of a housing or housing adaptor that receives a membrane stack. The channels are cut so that they are deeper adjacent to the central passage in the housing or housing adaptor and shallower remote from the central passage. Fluid is distributed through the channels before impinging on the membranes or on a porous disc lying adjacent to the membranes. The fluid distributor may also be used as a fluid collector to collect fluid after the fluid leaves the membrane stack and before entering a fluid outlet passage formed in the housing.

Description

MEMBRANE ADSORPTION MODULE

FIELD OF INVENTION

The invention relates to a membrane adsoφtion module, and in particular relates to the configuration of the housing whereby membrane discs are held in a stacked configuration and a fluid is directed to flow through the membranes.

BACKGROUND OF THE INVENTION

In the field of membrane adsoφtion (or membrane chromatography), conventional membrane modules for such adsorptive processes suffer from poor flow distribution and collection particularly near the fluid inlet and outlet, respectively. This in turn leads to reduced efficiency of adsorbent utilisation in such processes.

Poor flow distribution is aggravated by the large radial to axial dimension ratio between the membranes and the fluid inlet or outlet. In currently available membrane modules, the liquid feed enters the zone where the membrane is housed through a circular channel and then comes in contact with the much larger circular cross-section of the first membrane surface. Ideally, the feed should be uniformly distributed over the entire leading surface of the membrane so that in a step adsoφtion process, the solute front hits all points of the leading membrane simultaneously. With current designs, this is not the case, and efficiency of the membrane is reduced.

In a conventional membrane adsorber module identified in Fig. 2 by reference numeral 10, the inlet 12 and outlet 14 are tapered for flow distribution and collection, respectively and porous discs 16 have been placed on either side of the membrane stack for support and to further aid fluid flow distribution and collection. Overall, the effect of these designs has been modest. In the step adsoφtion mode, the initial solute entering the module is likely to flow through the central region of the membrane, leading to rapid saturation of this region. Transport of the solute to the peripheral regions of the membrane is much slower. Hence, there is still uneven flow distribution of the solute within the membrane, such that the capacity of the membrane adsorber is lower, as seen by the broadened shape of the breakthrough curve.

Another approach to address this problem is described in US4,895,806 where anti-jetting discs are provided at the fluid inlet and outlet. The anti-jetting disc which faces the fluid inlet operates to prevent fluid from impinging at a high velocity onto the membranes while the disc at the outlet ensures an orderly fluid exit from the module. In one embodiment, the disc comprises a series of channels forming a dendritic arrangement which radiates outwardly from the centre.

An object of this invention is to provide an improved means for fluid distribution across the membrane surface to improve efficiency in a membrane adsoφtion module.

SUMMARY OF THE INVENTION

In accordance with this invention, there is provided a fluid distributor for use in a membrane adsoφtion module, the fluid distributor having a plurality of fluid distribution channels extending radially from a central passage for fluid flow, the channels having a depth which is deeper adjacent to said central passage and shallower remote from said central passage.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an exploded, perspective view of a membrane adsoφtion module assembly made in accordance with the invention;

FIG. 2 is a schematic cross-sectional view of a prior art membrane adsoφtion module;

FIG. 3 is a cross-sectional view of the assembly of Fig. 1;

FIG. 4 is a plan view taken on line 4-4 of Fig. 3;

FIG. 5 is a cross-sectional view of a membrane adsoφtion module assembly for single use and made in accordance with the invention;

FIG. 6 is a cross-sectional view of an alternative embodiment of the invention featuring a discrete fluid distributor made in accordance with the invention and incoφorated into a membrane adsoφtion module;

FIGS. 7 to 9 are graphical representations showing breakthrough curves comparing adsoφtion adsoφtion module efficiencies obtained using a prior art membrane adsoφtion module and a membrane made in accordance with the invention.

DETAILED DESCRIPTION WITH REFERENCE TO DRAWINGS

An assembly for a membrane absoφtion module is generally indicated in the accompanying drawings by reference numeral 20. The assembly 20 has a housing 22 which consists of an upper portion 24 which is cooperable with a lower portion 26 to define an interior cavity 28. A pair of porous discs 30, 32 are disposed in the interior cavity 28 and sandwich a plurality of membranes 34 therebetween.

The upper portion 24 of the housing 22 is in the form of a cylinder 36 and an overlying flange 38. The cylinder 36 has a peripheral groove 40 for receiving a sealing o-ring 42. The flange 38 is adapted to lie over a peripheral wall 44 of the lower portion 26 of the housing 24. In the embodiment shown, four diametrically opposed holes 46 have been drilled in the flange 38 and four corresponding holes 48 have been drilled in the wall 44 to receive respective fasteners 50 for securing the upper portion 24 of the housing to the lower portion 26. Each fastener 50 is associated with a respective washer 52. It will be understood that the wall 44 of the lower portion of the housing 26 has an internal diameter and shape which correspond to the external diameter of the cylinder 36 of the upper portion 24 of the housing 22 so that there is a snug fit between the upper and lower portions 24, 26.

A central passage for fluid flow is defined in the housing 22 with a fluid inlet passage 54 formed in the upper portion 24 and a fluid outlet passage 56 formed in the lower portion 26 (see Fig. 3). Both the fluid inlet passage 54 and fluid outlet passage 56 communicate between an exterior surface for the housing 22 and the interior cavity 28 for receiving the porous discs 30, 32 and membranes 34. In each case, the fluid inlet passage and the fluid outlet passage 54, 56 are threaded along a portion of their lengths to receive a spigot and spigot adaptor 58, 60.

To further seal the interior cavity 28, opposing surfaces of the upper portion and the lower portion 26 of the housing 22 are provided with respective grooves 62, 64 in which are received an upper and a lower o-ring 66, 68.

It will thus be understood that fluid flow through the membrane absoφtion module assembly 20 progresses through upper spigot and spigot adaptor 58, 60 into the fluid inlet passage 54 and into the interior cavity 28 where it is directed through the porous disc 30, the membranes 34, the porous disc 32 and out of the outlet passage 56 and through the spigot adaptor 60 and spigot 58. It will also be understood that the interior cavity 28 is substantially filled with porous discs 30, 32 and the membranes 34 so that the porous discs 30, 32 are contiguous to the associated interior surfaces of the upper portion 24 and lower portion 26 of the housing 22 respectively.

In accordance with the invention, there is provided a plurality of fluid distribution channels 70 on the interior surface of the upper portion 24 of the housing 22 and similarly, there is provided a plurality of fluid collection channels 71 on the interior surface of the lower portion 26 of the housing 22. It will be understood that the relative location of the channels 70, 71 in the assembly 20 to the fluid inlet passage 54 and the fluid outlet passage 56 will determine whether the channels operate as fluid distribution channels or fluid collection channels. Otherwise, the channels are identical. For simplicity, only the fluid collection channels 71 are described in the remaining description. However, it will be understood that the features of the fluid collection channels 71 and fluid distribution channels 70 are similar and that a fluid distributor in accordance with the invention may be used for a fluid collection and fluid distribution so that they are interchangeable.

The lower portion 26 of the housing 22 is shown in a plan view in Fig. 4 drawn on line 4-4 of Fig. 3. In the drawing of Fig. 4, it will be appreciated that the porous disc 32 has been removed to expose the interior cavity 28. The fluid collection channels 71 may be formed by cutting the interior surface of the housing 22 adjacent to the interior cavity 28 by means of a radial saw blade cutting across the fluid outlet passage 56 so as to extend radially from the passage and by repositioning the saw to make additional cuts according to the number of passages required. One of the cuts in the housing is seen in cross-section in Fig. 3 and has the shape of a segment of a circle and therefore the fluid collection channel 71 has a depth deeper adjacent to the central fluid outlet passage 56 and shallower remote from the passage 56. The interior surface of the upper portion 24 of the housing 22 has a similar pattern of fluid distribution channels 70.

In this way, when fluid passes through the fluid inlet passage 54, it is distributed through the fluid distribution channels 70 in radial paths in order to cover a substantial area of the porous disc 30 so that it is well distributed before reaching the membranes 34 from which it is collected through the porous disc 32 into the fluid collection channels 71 formed in the lower portion 26 to exit the fluid outlet passage 56.

Alternative embodiments of the invention are shown in Figs. 5 and 6. In Fig. 5, there is illustrated a membrane adsoφtion module assembly 80 which is similar in most respects to the assembly 20 of Figs. 1, 3 and 4 with the exception that its housing 82 is an integral housing in which the upper and lower portions are fused after assembly to form a single use type disposable unit. It will be appreciated that the housing 82 likewise defines an interior cavity for receiving a pair of porous discs 30, 32 sandwiching a membrane stack 34 therebetween. Like numerals are used in Fig. 5 to denote components which are similar to those shown in Figs. 1, 3 and 4. Likewise, interior surfaces of the housing 82 adjacent to the cavity are formed with fluid distribution channels 70 for distributing fluid from a fluid inlet passage 54 and fluid collection channels 71 for collecting fluid prior to exiting the assembly 80 through the fluid outlet passage 56.

In the alternative embodiment of the invention shown in Fig. 6, the membrane adsoφtion module assembly 90 includes a housing having an upper portion 92 and a lower portion 94 secured to each other by means of threaded fasteners 50 and washers 52 associated with the fasteners 50. The housing portion 92 defines a fluid inlet passage 96 which is threaded to receive a spigot adaptor (not shown). Similarly, the housing lower portion 94 has a central aperture which is threaded and which defines a fluid outlet passage 98. The housing upper and lower portions 92, 94 when assembled define an interior cavity of rectangular cross- section which receives a housing adaptor 100. While the housing adaptor 100 is shown as one piece, it will be understood that it will be constructed from upper and lower portions which are fused together in the manner exemplified by the membrane adsoφtion module shown in Fig. 5. The housing adaptor 100 defines a fluid inlet passage 54 and a corresponding fluid outlet passage 56 each disposed in fluid communication with the respective passage 96, 98 of the housing upper portion 92 and housing lower portion 94. In order to better seal the housing adaptor 100 inside the housing upper and lower portions 92, 94 a circumferential groove is cut around the fluid inlet passage 54 and also the fluid outlet passage 56 to receive respective o-rings 102 which will mate and seal with the surrounding housing portion. The housing adaptor 100 likewise defines an interior cavity for receiving porous discs 30, 32 which sandwich a membrane stack 34 therebetween. An interior surface of the housing adaptor cavity is cut to form fluid distribution channels 70 which receive fluid from the fluid inlet passage 54 and fluid collection channels 71 for collecting fluid prior to exiting the assembly 90 through the fluid outlet passage 56. In this way, the housing adaptor 100 may be fabricated with a disposable unit for use with a more durable housing.

The flow distributor embodied in each of the above-described embodiments is expected to improve the flow distribution of fluid or collection of fluid, as the case may be, by providing greater and more direct access of the solute to the peripheral regions of the membrane stack, by creating turbulence due to flow instability in the curved portion of the fluid distribution or collection channels 70, 71 and by defining a more constant solute flow path length.

Experimental work conducted using a membrane adsoφtion module assembly of the kind shown in Figs. 1, 3 and 4 and a prior art module of the kind shown in Fig. 2 is described further below with reference to Figs. 7 to 9.

Fig. 7. This figure shows breakthrough curves for the adsoφtion of lysozyme on a stack of PVDF membranes. This membrane is known to bind to lysozyme by cation-exchange mechanism. These breakthrough curves were obtained with the prior art and the invention respectively using stacks to 6 membrane discs in each case. The membranes used in the stacks had effective diameters of 42 mm. The lysozyme concentration in the feed used to obtain the breakthrough curves was 10 g/1 and this was allowed to flow through the prior art and invention at identical flow rates of 10 ml/min. The figure shows that the breakthrough took place later with the invention and the shape of the breakthrough curve was shaφer with the invention. Both of these indicate better membrane binding capacity utilization with the invention.

Fig. 8. This figure shows breakthrough curves for the adsoφtion of lysozyme on a single PVDF membrane disc obtained with the prior art and the invention respectively. This membrane is known to bind to lysozyme by cation-exchange mechanism. The membrane discs used had effective diameters of 42 mm. The lysozyme concentration in the feed used to obtain the breakthrough curves was 5 g/1 and this was allowed to flow through the prior art and invention at identical flow rates of 5 ml/min. This figure also shows that the breakthrough took place later with the invention and the shape of the breakthrough curve was shaφer with the invention. Both of these indicate better membrane binding capacity utilization with the invention.

Fig. 9. This figure shows breakthrough curves for the adsoφtion of lysozyme on a single PVDF membrane disc obtained with the prior art and the invention respectively. This membrane is known to bind to lysozyme by cation-exchange mechanism. The membrane discs used had effective diameters of 42 mm. The lysozyme concentration in the feed used to obtain the breakthrough curves was 5 g/1 and this was allowed to flow through the prior art and invention at identical flow rates of 2.5 ml/min. This figure also shows that the breakthrough took place later with the invention and the shape of the breakthrough curve was shaφer with the invention. Both of these indicate better membrane binding capacity utilization with the invention.

Observations made after experimental work was conducted using a membrane adsoφtion module assembly made in accordance with the invention show reduced fouling of the membranes possibly resulting from a more uniform distribution of any foulant on the membrane surface.

It will be understood that the material of construction of a housing or a housing adaptor containing a fluid distributor in accordance with the invention may vary widely according to the intended use of the module. In particular, more durable materials such as Teflon®, Delrin® or stainless steel may be used for multiple use permanent modules whereas single use types may be made from more lightweight material such as polycarbonate or PVDF. While the embodiment shown in Fig. 4 provides eight fluid distribution channels, it will be appreciated that the number of the channels may well vary and decrease or increase. Prototype models containing eight and sixteen such channels have been made and tested. The results of the tests are described with Figs. 7 to 9.

It will further be appreciated that the manner of forming the channels may vary and will in part be determined by the nature of the material from which the housing or housing adaptor is fabricated. The channels could, for example, be cut by high pressure water jets or lasers, and may also be formed in situ by molding or casting.

Other variations will be apparent to those skilled in the art. It will be appreciated that the fluid distribution and collection channels may have profiles of different curvature than the circular segments illustrated in the accompanying drawings. Other variations within the scope of the invention would include adding additional channels for fluid distribution to the radially extending ones shown in the drawings.

Finally, it will be appreciated that a fluid distributor made in accordance with the invention could be incoφorated into other assemblies in which fluid flow distribution problems exist, including: other types of membrane separation modules which are non-adsoφtive; packed bed chromatography, particularly for large diameter columns; packed bed reactors and dead- end microfiltration devices.

Claims

CLAIMS: ^' 1. A fluid distributor having a central passage for fluid flow and a plurality of fluid distribution channels extending radially from the passage, the fluid distribution channels having a depth which is deeper adjacent to said central passage and shallower remote from said central passage.

2. A fluid distributor according to Claim 1 in which the fluid distribution channels are congruent and symmetrically disposed about said central passage.

3. A fluid distributor according to Claim 1 in which the fluid distribution channels have an arcuate radial cross-section.

4. A fluid distributor according to Claim 3 in which the cross-section corresponds to a segment of a circle.

5. A fluid distributor according to Claim 1 in which the width of the channels is substantially constant.

6. A fluid distributor according to Claim 1 in which the channels are formed by cutting segments of a circle using a radial saw blade.

7. A housing for a membrane adsoφtion module, the housing defining a fluid inlet passage and a fluid outlet passage each communicating between an exterior surface for the housing and an interior cavity for receiving a plurality of membranes, at least one interior surface of the housing having a plurality of fluid distribution channels extending radially from at least one said fluid inlet passage and fluid outlet passage, the fluid distribution channels having a depth which is deeper adjacent to said at least one of said fluid inlet passage and fluid outlet passage and shallower remote from said at least one fluid inlet passage and fluid outlet passage.

8. A housing according to Claim 7 in which the fluid distribution channels are congruent and symmetrically disposed about said central passage.

9. A housing according to Claim 7 in which the fluid distribution channels have an arcuate radial cross-section.

10. A housing according to Claim 7 in which the cross-section corresponds to a segment of a circle.

11. A housing according to Claim 7 in which the width of the channels is substantially constant.

12. A housing according to Claim 7 in which the channels are formed by cutting segments of a circle using a radial saw blade.

13. A housing adaptor for a membrane adsoφtion module, the housing adaptor defining a fluid inlet passage and a fluid outlet passage each communicating between an exterior surface for the housing adapter and an interior cavity for receiving a plurality of membranes, the housing adaptor being adapted to be received between upper and lower portions of a surrounding housing defining respective passages for fluid flow and fluid communication with said fluid inlet passage and fluid outlet passage, at least one interior surface of the housing adaptor having a plurality of fluid distribution channels extending radially from at least one said fluid inlet passage and fluid outlet passage.

14. A housing adaptor according to Claim 13 in which the fluid distribution channels have a depth which is deeper adjacent to said at least one of said fluid inlet passage and fluid outlet passage and shallower remote from said at least one of said fluid inlet passage and fluid outlet passage.

15. A housing adaptor according to Claim 14 in which the fluid distribution channels are congruent and symmetrically disposed about said central passage.

16. A housing adaptor according to Claim 14 in which the fluid distribution channels have an arcuate radial cross-section.

17. A housing adaptor according to Claim 14 in which the cross-section corresponds to a segment of a circle.

18. A housing adaptor according to Claim 14 in which the width of the channels is substantially constant.

19. A housing adaptor according to Claim 14 in which the channels are formed by cutting segments of a circle using a radial saw blade.

20. An assembly for a membrane adsoφtion module having a housing according to any one of Claims 7 to 12, a pair of porous discs disposed in said interior cavity adjacent to a respective one of said fluid inlet passage and fluid outlet passage, and a plurality of membranes disposed between said porous discs.

21. An assembly for a membrane adsoφtion module having a housing in which upper and lower portions define respective passages for fluid flow, a housing adaptor according to any one of Claims 13 to 19 received in said housing, a pair of porous discs disposed in said interior cavity adjacent to a respective one of said fluid inlet passage and fluid outlet passage, and a plurality of membranes disposed between said porous discs.