GB1583333A

GB1583333A - Membrane apparatus for fluid separation

Info

Publication number: GB1583333A
Application number: GB1075778A
Authority: GB
Original assignee: Rhone Poulenc Industries SA
Current assignee: Rhone Poulenc Industries SA
Priority date: 1977-03-18
Filing date: 1978-03-17
Publication date: 1981-01-28
Also published as: FR2383694A1; JPS53116284A; DE2811826A1

Description

(54) MEMBRANE APPARATUS FOR FLUID SEPARATION (71) We, RHONE-POULENC INDUSTRIES, a French Body Corporate of 22 Avenue Montaigne, Paris 8eme, France, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement-: The present invention relates to membrane apparatus for the separation of a fluid into two fractions, and may particularly be used in gas permeation, and to a process for making such apparatus.

In such membrane apparatus, a fluid to be treated, which comprises at least two constituents is separated into two fractions, one of which is enriched in the constituent which has passed through the membranes, whilst the other fraction which has circulated in contact with them is depleted in this constituent. This apparatus can be used especially in gas permeation and, in this case, the fraction of the treated fluid which has passed through the membrane is called "permeate" or "diffusate".

According to the present invention there is provided membrane apparatus for the separation of a fraction of a fluid to be treated, said apparatus comprising: a pressure-resistant housing having at least one fluid inlet orifice for the admission of fluid to be treated and at least one outlet orifice for the recovery of treated fluid; a hollow mandrel within the housing and connecting with the exterior of the housing to permit the separated fluid fraction to pass out of the housing; a stack of membrane cells spaced from one another, each cell comprising a porous support with a fluid permeable membrane on each of its faces, said porous support communicating with openings on the mandrel and each cell being fixed to the mandrel in a fluidtight manner to permit fluid to pass along the cell and into the mandrel; and a fluidtight wall on an inner surface of the housing, at least part of the periphery of each cell being embedded in a fluidtight manner in said wall, the arrangement being such that, in use, having entered via said inlet orifice, fluid to be treated will pass along at least one passage defined by said membrane cells through the housing and will contact surfaces of the cells.

Thus, the apparatus embodying the present invention may be particularly suitable for recovery of the fraction of the fluid to be treated which has not passed through the membranes, this fraction being called "treated fluid" throughout the present description and claims, and moreover may be suitable when it is desired that this fraction should be significantly depleted in at least one constituent of the fluid to be treated. The fluid which is introduced into the apparatus may come into rigorous contact with the membranes of the cells before leaving the apparatus.

Preferably the apparatus has at least one first cell providing a passage, adjacent said wall, through which fluid to be treated may pass along the length of the housing, two successive first cells being arranged in the housing so that the passages are located at positions substantially diametrically opposite one another. Also the apparatus may have at least one second cell providing at least two passages, through which fluid to be treated may pass, the passages being diametrically opposite one another, and being located between two first cells, one of the two passages of the or each second cell being substantially in alignment with the passage of a first cell.

The apparatus of the present invention is of simple construction and docs not require, between two successive menibrane cells, baffles or discs to set up a separate circuit for the fluid to be treated. Moreover the membrane cells may have flexible and thin porous supports, and the complate apparatus may have a very low weight, which makes it possible to use the apparatus in aeronautical applicalions, especially for purifying aeroplane tanks.

According to a second aspect of the present invention, there is provided a process for the manufacture of a membrane apparatus according to the first aspect of the invention and comprising arranging within the housing the membrane cells affixed in a leaktight manner about the mandrel, rotating the assembly thus obtained about the longitudinal axis of the mandrel and introducing a resin into the housing to form by centrifugal action the inner wall member in which at least part of the circumference of each membrane cell is embedded, and then curing said centrifugally cast resin in situ.

In order that the invention may more readily be understood, a description is given, by way of example only, reference being made to the accompanying drawings, in which: Figure 1 is a cross-section along the longitudinal axis of an embodiment of the apparatus according to the present invention, with accessories used in the manufacture of the apparatus being shown on the righthand side of the Figure; Figure 2 shows a plan view of a membrane cell used in the apparatus of Figure 1; Figure 3 is a view along the line III--III of Figure 2; Figure 4 is a plan view of another form of membrane cell used in the apparatus of Figure 1; Figure 5 is a cross-section of the mandrel in Figure 1 surrounded by a sealing ring; Figure 6 shows a different embodiment of a membrane cell; and Figure 7 is a different embodiment of an apparatus according to the present invention.

The apparatus shown in Figure 1 comprises an outer housing having two side plates 1 and 2 and a preferably cylindrical envelope 3, for example made of metal or epoxy resin, in which glass fibres are embedded. Each side plate 1, 2 comprises an orifice 4 or 5 for the introduction of the fluid to be treated or for the discharge of the treated fluid. Along the longitudinal axis of the apparatus, between the two side plates 1, 2 there is a mandrel 6 which is held by the side plates 1, 2 and on which a stack of membrane cells 8 is fixed in a fluidtight manner. The stack of membrane cells may comprise cells 8a alone as shown to the left of the broken line in Figure 1, or cells 8a having a number of cells 8b between the cells 8a, as shown to the right of the broken line in Figure 1, the two types of cell 8a and 8b being described in further detail below. Two consecutive membrane cells are spaced apart by a ring 7, each membrane cell comprising at least one support 9 having a membrane 10 on each face, the support 9 being permeable to the fluid which passes through the membranes (see Figure 3). The mandrel 6 is in the shape of a tube which is open at least at one of its ends and is provided with holes 11 in the part surrounded by the membrane cells 8 so that the fluid which has passed through the membranes 10 can be recovered outside the apparatus.

Figure 5 shows a cross-section of the mandrel 6 surrounded by a ring 7, which has on each of its faces, a section of extra thickness forming a rib 19 which facilitates the production of a seal between two successive membrane cells. The mandrel 6 may have one or more longitudinal grooves or one or more surface planes to aid the positioning of the membrane cells having corresponding cut-away sections. Alternatively, the permeate or diffusate can be recovered at the surface of the mandrel, for example by means of longitudinal grooves provided on the latter, or the permeate can be recovered at the end of the mandrel by means of notches adjacent the mandrel made in the rings 7 themselves, the outer face of which can then be smooth.

Inside the housing of Figure 1 is a wall 12, in which each membrane cell 8 is embedded in a fluidtight manner along at least part of its periphery. This wall 12 adheres to the side plates 1 and 2 so as to be fluidtight, and it can likewise adhere to the cylindrical envelope 3. This wall 12 is, for example, made of silicone, polyurethane, epoxy or polyester resins and, in general, of any resin which polymerises in situ.

A plan view of an embodiment of a membrane cell 8a is shown in Figure 2, whilst Figure 3 is a partial cross-section of the same cell 8a, on a larger scale, along 111-111 of Figure 2. This membrane cell 8a comprises a porous support 9, on each face of which rests a membrane 10. The support 9 and the membranes 10 of a cell have a central opening 13 through which the mandrel 6 may pass. The cell 8a is of generally circular cross-section with a section 14 cut out, this section 14 forming a chord of the generally circular periphery 16; the cell 8a has a mass of resin 15 which provides a seal over the whole periphery so that the performance of each cell may be tested before fitting them into the apparatus. When arranged inside the apparatus of the present invention, the seal 8a has at least 70o of its periphery 16 embedded in the wall 12 inside the housing, the part 14 of this cell 8a forming a passage through which fluid to be treated may pass. The broken line indicated by the number 17 on the membrane cell of Figure 2 shows the positioning of the inner face 17 of the wall 12 when a cell 8a is embedded therein.

Figure 4 shows an embodiment of a membrane cell 8b having all the structural elements of the cell 8a, but whose periphery 16 comprises two sections 14 which are cut out, these sections 14 being substantially diametrically opposite one another on the periphery.

The membrane cells 8a and 8b may be sealed only over that part of the periphery forming section 14 by sticking a thin adhesive tape on the edge of the porous support 9, which is preferably rectilinear at this point, this tape adhering to the membranes on both sides of the porous support 9, so as to be fluidtight over its entire width. The circular portion of the periphery of each membrane cell is closed by the wall 12 in which it is embedded.

A grid (not shown) can be arranged around each ring 7 between the membranes 10 of two successive membrane cells. This grid can comprise two superposed webs each of mutually parallel threads, the said webs being welded at their point of intersection and the threads of the webs making an angle of, for example, 60 with each other. A grid can optionally be made of a wide mesh fabric. Each grid is advantageously embedded, at least along part of its circumference, in the wall 12 inside the enclosure, and it can optionally be produced in a single unit with the ring 7 arranged between two successive membrane cells.

As is shown in Figure 1, a deflector 18 is provided at the end of the stack near which the fluid to be treated is introduced into the apparatus. This deflector 18, which has essentially the same shape as a cell 8b described above, is made of a rigid and impermeable material. The essential function of this deflector 18 is to prevent the fluid to be treated, which is introduced into the apparatus under pressure, from coming into contact perpendicularly with the first membrane cell.

When using the apparatus of Figure 1, for example in gas permeation, the fluid to be treated is caused to enter under pressure through the inlet orifice 4 of the side plate 1, and it circulates inside the apparatus following the path represented schematically by the single-headed solid arrows.

The fraction of the injected fluid which has come into contact with the membranes 10 without passing through them leaves the apparatus through outlet orifice 5 of the side plate 2, whilst the fraction of the injected fluid which has passed through the membranes, this fraction being called "permeate" or "diffusate", leaves the apparatus through the mandrel 6, as shown by the arrows.

The stack of membrane cells in the apparatus can comprise only membrane cells 8a, as described above, in which case the fluid to be treated circulates sequentially along the surface of each membrane cell as shown in lie lefthand part of the apparatus of Figure 1. Alternatively, the stack can comprise membrane cells 8a, between pairs of which a plurality of cells 8b are arranged, as shown in the righthand part of the apparatus of Figure 1; in this embodiment of the stack, the fluid to be treated circulates in parallel between the membrane cells 8b situated between two cells 8a, whilst it circulates in series from one cell 8a to the other. The stack can comprise membrane cells 8b of which the number between two cells 8a decreases with their distance from the inlet orifice of the apparatus. Alternatively, the stack can comprise, at one end, cells 8b between cells 8a whilst at the other end of the stack, it comprises only cells 8a. The membranes are not necessarily the same throughout the entire stack of membrane cells, especially in the case where the fluid treated (which does not pass through the membranes) must be separated from two of the constituents of the fluid to be treated. The apparatus according to the present invention can optionally comprise only cells 8b.

In an alternative embodiment of the cells, the membrane cells 8a and 8b can be circular around their entire periphery 16, which is totally embedded in the wall 12 inside the housing, The cells 8a then comprise at least one aperture 14a near the periphery 16, which forms a passage through which fluid to be treated may pass; the passage 14a may be circular, or elongate as shown in Figure 6, whilst the cells 8b comprise two or more apertures to form two passages 14 substantially diametrically opposite one another and through which fluid to be treated may pass. The cell 8a is shown in Figure 6 with a peripheral seal around its entire circumference, this seal being produced, for example, by a layer of resin 15 arranged around the membranes and the support, as shown in Figure 3 for the case of the cell according to Figure 2.

However, this peripheral seal is not essential and only serves to facilitate the testing of the performance of the cell before it is fitted into the apparatus. It is only necessary to provide a good seal of the cell around the periphery of each aperture forming a passage 14a so that the fluid to be treated does not run the risk of passing into the support 9 of the cell. In general, in order to produce a membrane cell as shown in Figure 6, the edges of the apertures forming the passage 14a of the porous support 9 are first sealed, for example by heat-welding this support under pressure, so that the pores of the support are closed and thus it is fluidtight. Another method for sealing the porous support 9 along the periphery of the aperture(s) forming passage 14a is to make this zone thinner under pressure, and then in producing a thin peripheral mould in the cut-away section of the passage 14a and on its edges. Then the previously cut membrane is stuck onto the periphery of the passage 14a so as to be fluidtight. If the membrane used can be heat-welded, the thin mould is preferably produced from a material which makes it possible for the membrane to adhere to the mould so as to be fluidtight.

The apparatus shown in Figure 1 is produced by the following procedure: The deflector 18 and the desired number of membrane cells (8a and/or 8b) which are to form the stack are first arranged on the mandrel 6 which has a stop 20, two successive cells being held apart on the mandrel 6 by a ring 7, so as to be fluidtight, and a grid (not shown) being optionally arranged between two membrane cells; the side plate 2 is fixed onto the mandrel 6 by means of a screwing device comprising, for example, a nut 21 screwed onto the mandrel, the side plate 2 comprising a sealing ring 23, preferably an O-ring seal; the envelope 3 is positioned on the side plate 2 and the side plate 1 is arranged on the mandrel 6, screwing it onto the latter by means of the nut 22, the side plate 1 comprising a sealing ring 24, preferably an O-ring seal; a device 25 of circular cross-section, shown by fine lines in Figure 1, is arranged on the apparatus, this device being fixed onto the mandrel, for example, by a nut, which is not shown, and comprising a nozzle 26 which, as shown in Figure 1, passes through the orifice 4 of the side plate 1; the apparatus, with its device 25 and preferably being in a horizontal position, is set in rotation about the longitudinal axis of the mandrel 6, by placing the apparatus, for example, on a lathe and holding it at one end by the tailstock of the latter; a liquid resin is poured into the device 25 through means which are represented schematically by a funnel 27 and a tap 28, this resin passing through the nozzle 26 under the effect of the centrifugal force acting against the walls of the device 25, and thus enters the apparatus and spreads itself along the inner face of the envelope 3 to form the wall 12 in which at least part of the periphery of each membrane cell is embedded; after a sufficient amount of resin has been injected and has spread over the entire inner face of the envelope 3, the apparatus is allowed to rotate for the time required for the resin to solidify and the rotation of the apparatus is then stopped; and finally the device 25 is removed and the apparatus is then ready to be used.

The apparatus thus obtained comprises membrane cells, each of which has at least the greater part of its periphery embedded in the wall 12 of hardened resin, the said wall 12 adhering both to the side plates 1 and 2 and to the inner face of the envelope 3.

The magnitude of the centrifugal force required to produce the apparatus depends, in particular, on the viscosity of the resin which is to form the wall 12, as well as on the surface tension forces between the resin and the circumference of each membrane cell.

Centrifugal forces of between a few times and one hundred times the force of gravity are generally used. Centrifugal forces of between 8 and 80 times, and more advantageously between 30 and 60 times, the force of gravity are more generally used.

In order to accelerate the solidification of the resin during the production of the wall 12, the envelope 3 may be heated once the resin is well spread over the entire inner face of the envelope 3 and has the desired thickness, by any known means, for example with an electric heating strip placed near the envelope 3.

The illustrated apparatus has numerous advantages. Firstly, the fluid to be treated may be caused to follow a rigorously imposed path, which ensures that the fluid is very effectively separated. In this apparatus production, for each membrane cell, of the peripheral seal of that part of the periphery which is embedded in the wall 12 is not necessary. By virtue of its shape, the apparatus of the present invention can be operated under pressures of 1 to 100 bars, and advantageously of 4 to 30 bars. This apparatus also uses porous supports which are very thin and of low rigidity, because they are held at their centre against the mandrel and are also held around a large part of their periphery, which moreover improves the resistance of the membrane stack to vibrations. Furthermore, rotating the apparatus about the mandrel 6 in order to produce the wall 12 assists the positioning of the membrane cells relative to each other and makes it possible, in certain cases, to dispense with the spacer grid between two successive membrane cells.

The apparatus of the present invention also has a low weight relative to the exchange surface available, because it makes it possible, in particular, to use very thin porous supports and because it does not require complementary baffles in order to guide the fluid to be treated between two consecutive cells.

A different embodiment is shown in Figure 7, this apparatus comprising most of the elements of the apparatus according to Figure 1, which elements are indicated by the same reference numbers. The stack of membrane cells (8a and/or 8b) on the mandrel has not been shown in order to simplify the drawing. In the same way as the apparatus of Figure 1, the apparatus of this Figure 7 comprises a wall 12 made of hardened resin, inside which at least part of the circumference of each membrane cell (8a or 8b) is embedded. The particular characteristic of the apparatus of Figure 7 is that the outer enclosure comprises threads 29, for example made of glass fibre, carbon or plastics such as polyester, polyamides and the like, which are wound around at least part of the side plates 1 and 2 and on the wall 12, these threads 29 advantageously being held together by a resin. This method of producing the apparatus by filament winding makes it possible to make the apparatus as light as possible, whilst allowing it to retain its high pressure resistance.

The apparatus of Figure 7, and more especially the wall 12, are produced by following the same procedure as for the apparatus which is described above and shown in Figure 1. However, the envelope (not shown in Figure 7) which is arranged between and around the two side plates 1 and 2 is only temporary and is withdrawn when the wall 12 which is formed has hardened. This temporary envelope can be in two parts, for example two half-shells which are removed after the wall 12 of resin has solidified. The inner face of this temporary envelope is made of a material to which the resin which is to form the wall 12 does not adhere (or which material is treated so that the resin does not adhere to it). After removal of the temporary envelope used to produce the inner wall 12, the unit obtained comprises in particular, between two side plates 1 and 2, a wall 12 in which at least part of the circumference of each membrane cell is embedded. At least one thread 29 is wound onto this unit, the thread being wound around the two side plates 1 and 2 essentially in accordance with the winding plane represented schematically by the dotted line 30 shown in Figure 7. Whilst the fibre 29 is being wound around the two side plates 1 and 2, the unit defined above is being rotated about the longitudinal axis of the mandrel 6 by any known means, the mandrel being held at least at one of its ends. Whilst rotating about itself and remaining in a plane which is perpendicular to the winding plane 30 of the thread 29, the mandrel 6 can optionally be displaced in a controlled manner so that the winding plane of the thread essentially covers the zone of each side plate indicated by 31. In order to wind the thread or threads around the side plates 1 and 2 and the wall 12, this unit can be arranged inside a wheel, comprising spools and thread guides, such as that shown in Figure 13 of French Patent 2,236,537 the plane of rotation of this wheel essentially corresponding to the line indicated by 30 in Figure 7. By means of a spraying system, resin can be deposited on the threads 29 as they are arranged around the side plates and around the wall 12. Alternatively, the thread 29 can be wound using conventional filament-spooling machines, by alternately .and successively laying down a circular turn around the wall 12 and a polar turn around the side plates 1 and 2.

EXAMPLE An apparatus has been produced which corresponds to that acording to Figure 1 and the structural elements of which have the following dimensions and compositions: a) envelope 3 made of glass fibre and epoxy resin internal diameter 150 mm wall thickness 1.5 mm length 640 mm resistance to a pressure of more than 100 bars in a hydrostatic test b) mandrel 6 made of aluminium alloy length 750 mm external diameter 25 mm internal diameter 10 mm, grooved with holes in grooves connected to the inside of the mandrel c) side plates 1 and 2 made of aluminium alloy d) rings 7 made of rubber internal diameter 25 mm external diameter 40 mm thickness 3 mm e) membrane stack comprising 16 groups of nine cells 8b (as shown in Figure 4) separated by cells 8a (as shown in Figure 2) f) each membrane cell 8a or 8b comprises: a porous support 9 made of bakelized paper thickness 0.4 mm diameter of the peripheral circular part 148 mm diameter of the central opening 13 25 mm a membrane 10 on both sides of the porous support 9 and having the same cut-away section as the support made of polyvinyltrimethylsilane resin according to French Patent 70,07570 of Messrs Rhone-Pouleoc equivalent thick ness 0.2 micron selectivity 0 2/N2 3 flow rate 02=0.54 m3 (S.T.P.)/ hour-bar m2 the peripheral seal in the rectilinear part is produced by means of SCOTCH MINNESOTA reference 810 adhesive tape the peripheral seal in the circular part 15 is produced by means of MINNESOTA reference EC22-26 neoprene emulsion each cell 8a (according to Figure 2) has a rectilinear part corresponding to a cut-away section which is 62 mm from the centre of the cell each cell 8b (according to Figure 4) has two rectilinear parts which are parallel to each other and correspond to two cut-away sections which are each 62 mm from the centre of the cell g) centrifugation resin for the production of the inner wall 12: TRV (room temperature vulcanisable) silicone, marketed by Rhone-Poulene Company reference 20587 A+B centrifugation speed 600 revolutions/ minute thickness of the wall 12 obtained = 4 mm 1. Use of the apparatus for the production of air depleted in oxygen (O J (In this application, it is desired to pro duce a depletion in O, 2 of the treated air which circulates in contact with the membranes without passing through them.) Air under an absolute pressure of 10 bars is caused to enter the apparatus through the orifice 4.

The flow rate through the mandrel 6 of the permeate or diffusate collected is 7 m3/hour.

The proportion of oxygen in the treated fluid which has cirdulated in contact with the membranes without passing through them, and which is collected through the orifice 5, is 5(vo for a flow rate of 2.5 m3/hour.

2. Use of the same apparatus for the production of oxygen-enriched air (In this case, it is desired to produce an enrichment in O2 of the permeate or diffusate.) Air under an absolute pressure of 10 bars is caused to enter the apparatus through the orifice 4.

The flow rate of the permeate is 8 m 3/hour and its proportion of O, 2 is 35(to.

The flow rate of the stream escaping through the orifice 5 is 17.3m3/hour.

WHAT WE CLAIM IS: 1. Membrane apparatus for the separation of a fraction of a fluid to be treated, said apparatus comprising: a pressure-resistant housing having at least one fluid inlet orifice for the admission of fluid to be treated and at least one outlet orifice for the recovery of treated fluid; a hollow mandrel within the housing and connecting with the exterior of the housing to permit the separated fluid fraction to pass out of the housing; a stack of membrane cells spaced from one another, each cell comprising a porous support with a fluid permeable membrane on each of its faces, said porous support communicating with openings on the mandrel and each cell being fixed to the mandrel in a fluidtight manner to permit fluid to pass along the cell and into the mandrel; and a fluidtight wall on an inner surface of the housing, at least part of the periphery of each cell being embedded in a fluidtight manner in said wall, the arrangement being such that, in use, having entered via said inlet orifice, fluid to be treated will pass along at least one passage defined by said membrane cells through the housing and will contact surfaces of the cells.

2. Apparatus as claimed in claim 1, wherein at least one cell of a first type provides a passage, adjacent said wall, through which fluid to be treated may pass along the length of the housing.

3. Apparatus as claimed in claim 2, wherein two successive cells of the first type are arranged in the housing so that the passages are located at positions substantially diametrically opposite one another.

4. Apparatus as claimed in any one of the preceding claims and having at least one cell of a second type providing at least two passages, through which fluid to be treated may pass, the passages being diametrically opposite one another.

5. Apparatus as claimed in claims 2 or 3 and claim 4, wherein at least one cell of the second type is located between two cells of the first type, one of the two passges of the or each cell of the second type being substantially in alignment with the passage of a cell of the first type.

6. Apparatus as claimed in any one of claims 1 to 5, wherein at least some of the cells are embedded along at least 70 70 of their periphery in the wall, that part of the periphery not embedded in the wall bounding the passage or passages.

7. Apparatus as claimed in any one of the preceding claims, wherein the cells have a generally circular cross-section.

8. Apparatus as claimed in claim 7, wherein that part of each cell which is not embedded forms a chord of the circular cross-seciton.

9. Apparatus as claimed in any one of claims 6 to 8, wherein the part of the periphery of each cell not embedded in the walls is made fluidtight to the interior of the cell by an adhesive tape covering the edge of the porous support and each membrane.

10. Apparatus as claimed in any one of

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

part is produced by means of SCOTCH MINNESOTA reference 810 adhesive tape the peripheral seal in the circular part

15 is produced by means of MINNESOTA reference EC22-26 neoprene emulsion each cell 8a (according to Figure 2) has a rectilinear part corresponding to a cut-away section which is 62 mm from the centre of the cell each cell 8b (according to Figure 4) has two rectilinear parts which are parallel to each other and correspond to two cut-away sections which are each 62 mm from the centre of the cell g) centrifugation resin for the production of the inner wall 12: TRV (room temperature vulcanisable) silicone, marketed by Rhone-Poulene Company reference 20587 A+B centrifugation speed 600 revolutions/ minute thickness of the wall 12 obtained =

4 mm 1. Use of the apparatus for the production of air depleted in oxygen (O J (In this application, it is desired to pro duce a depletion in O, 2 of the treated air which circulates in contact with the membranes without passing through them.) Air under an absolute pressure of 10 bars is caused to enter the apparatus through the orifice 4.

The flow rate through the mandrel 6 of the permeate or diffusate collected is 7 m3/hour.

The proportion of oxygen in the treated fluid which has cirdulated in contact with the membranes without passing through them, and which is collected through the orifice 5, is 5(vo for a flow rate of 2.5 m3/hour.

2. Use of the same apparatus for the production of oxygen-enriched air (In this case, it is desired to produce an enrichment in O2 of the permeate or diffusate.) Air under an absolute pressure of 10 bars is caused to enter the apparatus through the orifice 4.

The flow rate of the permeate is 8 m 3/hour and its proportion of O, 2 is 35(to.

The flow rate of the stream escaping through the orifice 5 is 17.3m3/hour.

WHAT WE CLAIM IS: 1. Membrane apparatus for the separation of a fraction of a fluid to be treated, said apparatus comprising: a pressure-resistant housing having at least one fluid inlet orifice for the admission of fluid to be treated and at least one outlet orifice for the recovery of treated fluid; a hollow mandrel within the housing and connecting with the exterior of the housing to permit the separated fluid fraction to pass out of the housing; a stack of membrane cells spaced from one another, each cell comprising a porous support with a fluid permeable membrane on each of its faces, said porous support communicating with openings on the mandrel and each cell being fixed to the mandrel in a fluidtight manner to permit fluid to pass along the cell and into the mandrel; and a fluidtight wall on an inner surface of the housing, at least part of the periphery of each cell being embedded in a fluidtight manner in said wall, the arrangement being such that, in use, having entered via said inlet orifice, fluid to be treated will pass along at least one passage defined by said membrane cells through the housing and will contact surfaces of the cells.
2. Apparatus as claimed in claim 1, wherein at least one cell of a first type provides a passage, adjacent said wall, through which fluid to be treated may pass along the length of the housing.
3. Apparatus as claimed in claim 2, wherein two successive cells of the first type are arranged in the housing so that the passages are located at positions substantially diametrically opposite one another.
4. Apparatus as claimed in any one of the preceding claims and having at least one cell of a second type providing at least two passages, through which fluid to be treated may pass, the passages being diametrically opposite one another.
5. Apparatus as claimed in claims 2 or 3 and claim 4, wherein at least one cell of the second type is located between two cells of the first type, one of the two passges of the or each cell of the second type being substantially in alignment with the passage of a cell of the first type.
6. Apparatus as claimed in any one of claims 1 to 5, wherein at least some of the cells are embedded along at least 70 70 of their periphery in the wall, that part of the periphery not embedded in the wall bounding the passage or passages.
7. Apparatus as claimed in any one of the preceding claims, wherein the cells have a generally circular cross-section.
8. Apparatus as claimed in claim 7, wherein that part of each cell which is not embedded forms a chord of the circular cross-seciton.
9. Apparatus as claimed in any one of claims 6 to 8, wherein the part of the periphery of each cell not embedded in the walls is made fluidtight to the interior of the cell by an adhesive tape covering the edge of the porous support and each membrane.
10. Apparatus as claimed in any one of

claims 1 to 5, wherein at least some of the cells are embedded in the wall along their entire periphery, each cell having at least one aperture therein to form said passage or passages
11. Apparatus as claimed in any one of the preceding claims, wherein two successive cells are held apart on the mandrel by a ring arranged between them and located around the mandrel.
12. Apparatus as claimed in any one of the preceding claims, wherein at least part of a grid is arranged between two successive membrane cells, at least part of the periphery of the grid being embedded in said wall.
13. Apparatus as claimed in claims 11 and 12, wherein the ring and the grid are formed as a single unit.
14. Apparatus as claimed in any one of the preceding claims, wherein said wall is adhered to the housing.
15. Apparatus as claimed in any one of the preceding claims, wherein two end plates are fixed on the mandrel and adhere at their peripheries to said wall.
16. Apparatus as claimed in claim 15, wherein the housing is at least partly formed by a plurality of threads arranged about the said side-plates and the wall.
17. Apparatus as claimed in claim 16, wherein the threads are made of glass fibre, carbon or plastics material.
18. Apparatus as claimed in claims 16 or 17, wherein the threads are bonded together by a resin.
19. A process for the manufacture of apparatus as defined in any one of claims 1 to 15 comprising arranging within the housing the membrane cells affixed in a leaktight manner about the mandrel, rotating the assembly thus obtained about the longitudinal axis of the mandrel and introducing a resin into the housing to form by centrifugal action the inner wall member in which at least part of the circumference of each membrane cell is embedded, and then curing said centrifugally cast resin in situ.
20. A process as claimed in claim 19, wherein a side plate having an orifice is fixed at each end of the mandrel.
21. A process for the manufacture of apparatus as defined in claims 16 or 17, comprising arranging and fixing the membrane cells on the mandrel in a leaktight manner at each end of which there is provided a side plate having an orifice for the admission of the fluid to be treated or for the recovery of the treated fluid which has not passed through the membranes, arranging a cylindrical envelope in a fluid tight manner between and around the side plates, rotating the obtained assembly about the longitudinal axis of the mandrel and injecting a resin through one of the side plates, in situ curing the centrifugally cast resin in contact with the inner face of the cylindrical envelope to form the inner wall member in which at least part of the circumference of each membrane cell is embedded, the said wall member being adhered to the side plates, removing the cylindrical envelope used to fabricate the inner wall member, and spooling at least one thread around said wall and around the side plates.
22. Process according to claim 21, in which the threads are bonded by a resin.
23. Membrane apparatus substantially as hereinbefore described with reference to and as illustrated in Figures 1 to 5, Figure 6 or Figure 7 of the accompanying drawings.
24. A process for the manufacture of a membrane apparatus as claimed in claim 23, substantially as hereinbefore described with reference to the accompanying drawings.