GB2137528A

GB2137528A - Membrane pack

Info

Publication number: GB2137528A
Application number: GB08412693A
Authority: GB
Inventors: John Mark Michaels; Gerald Allan Croopnick; Richard Alfred Morris
Original assignee: Dresser Industries Inc
Current assignee: Dresser Industries Inc
Priority date: 1981-02-13
Filing date: 1984-05-18
Publication date: 1984-10-10
Also published as: GB2137528B; GB8412693D0

Abstract

A membrane pack (18) for a fluid purification apparatus comprises a porous carrier (74) on the faces of which are located membranes (70,72). The carrier is sealed at the edge of holes (22) formed in the pack by inserting a non-porous polymer ring (76) in a hole (78) in the carrier (74) and ultrasonically welding the membranes (70,72) to the ring (76). <IMAGE>

Description

SPECIFICATION Membrane pack This invention relates to a membrane pack and to a method of joining or sealing a membrane to a porous carrier.

The purification of waste water or other fluids can be accomplished by the use of membrane packs which include membranes lying on the outside of a highly porous carrier. Feed fluid such as waste water can be applied under pressure to the outside of the membrane pack, so that permeate such as pure water can pass through the membrane into the porous carrier and travel along the carrier to a permeate outlet. U.S. Patent 4, 025,425 by Croopnick et al, describes an apparatus of this type wherein the feed fluid (e.g. waste water) passes between membrane packs, permeate (e.g. pure water) passes through the membranes into the carrier and is expelled from the extreme periphery of the carrier, and the concentrate (left after much of the permeate has been removed) passes through several large exit holes in the pack to reach a collecting location.At any location where an edge of the membrane pack comes in contact with impure fluids such as the feed fluid or concentrate, as occurs in the exit holes of the device in the above-mentioned patent, there is danger of contamination of the permeate. It is necessary to construct such edges to securely seal the pores of the carrier against the influx of impure fluid, and to seal the carrier to the membranes to prevent leakage of impure fluid between them. A very secure seal is required in many applications, such as where the feed fluid and concentrate contain bacteria that could contaminate a pure water filtrate.

The sealing of a membrane structure to a carrier is complicated by the fact that many of the most useful membrane structures must be kept continuously wet, and are irreparably damaged if allowed to dry for even a short period of time. One technique for sealing a carrierto such membrane structures isto utilize a hydrophobic adhesive such as a silicone adhesive to join them, since water will not wet the silicone and it therefore can join to the surface of a membrane structure. However, silicone adhesives cannot be utilized in the presence of certain chemicals with a high pH such as 10 to 12 or more, as are encountered in the pulp processing industry. Other adhesives such as neoprene can provide a strong joint that is useful in the presence of such chemicals, but neoprene is wetted by water and will not stick to a wet membrane structure.

According to the present invention there is provided a membrane pack with a sealed edge comprising: a sheet-like carrier which is permeable to the lateral flow of fluid therein, said carrier having an edge; an insert of substantially nonporous thermoplastic polymer lying in the same plane as the carrier and having a first edge lying against said edge of said carrier but free of interlocking connection therewith, and an opposite second edge forming an edge of the membrane pack; and a membrane structure lying over a face of said carrier and extending beyond said carrier edge to lie over said insert, said insert being heat welded to the portion of said membrane structure which lies beyond said carrier edge, whereby to seal the carrier against the inflow of fluid therein which passes across said second edge of the insert.

Also according to the present invention there is provided a method for forming a membrane pack having a fluidsealed edge, comprising: laying a nonporous insert that has a hole, in a hole of a carrier to fit closely within the carrier hole, but with the insert and carrier being free of interlocking connection; laying a membrane structure having a hole that is smaller than said carrier hole, over said carrier and insert and with the membrane structure hole substantially aligned with the insert hole; and ultrasonically welding said membrane facewise to said insert.

The invention will be best understood from the following description of a preferred embodiment thereof, given by way of example only, reference being had to the accompanying drawing, wherein: Figure 1 is a partial perspective and sectional view of a purification apparatus; Figure 2 is a partial sectional view of the purification apparatus shown in Figure 1; Figure 3 is an enlarged sectional view of a portion of a membrane pack of the apparatus of Figure 2, with the vertical dimensions exaggerated; and Figure 4 is a plan view, partly broken away of the membrane pack of Figure 3.

Figures 1 and 2 illustrate portions of a purification apparatus 10 which can receive a feed fluid such as waste water, and separate out a selected portion such as pure water, from the rest of the feed fluid which may contain solid waste particles including bacteria. In the particular apparatus 10, feed fluid is pumped along a central passageway 12, while the apparatus is rapidly rotated about its axis 14. The feed fluid passes through spaces 16 between membrane packs 18 of the apparatus to flow rapidly outwardly. During such flow, a component (e.g. pure water) of the feed fluid which can pass through membranes of the membrane packs 18, passes into the inside of the membrane packs. Such fluid, which may be referred to as permeate, moves radially within the membrane packs until it reaches the extreme peripheries of the packs and flies out against a wall 20 where it is collected.The portion of the feed fluid left after permeate has passed out of it, and which may be referred to as a concentrate, passes upwardly through aligned holes 22 in the membrane packs, for removal from the apparatus.

The membrane packs must be securely sealed in the regions immediately around the holes 22, to assure that concentrate moving through the holes does not enter any of the membrane packs 18 to mix with the permeate moving therethrough.

Figures 3 and 4 show a portion of a membrane pack 18, in the region which includes a hole 22 through which concentrate passes. The pack includes a highly porous carrier 74, and membrane structures 70, 72 lying over either face of the carrier.

A ring-shaped insert 76 of thermoplastic polymer lies closely within an enlarged hole 78 formed in the carrier. Although the carrier 74 is porous, the insert 76 is nonporous. The holes 22 in the membrane structures and the hole 82 in the insert are of substantially the same diameter. The faces of the insert 76 are sealed to the membrane structures by ultrasonic welding. Where the membrane structures are unbacked, they can be directly sealed to the insert without the use of any impregnating.

As described in our patent application 8204128 (G.B. 2092914), from which this application is divided out, the use of ultrasonic welding enables a wet membrane to be welded to an underlying polymer layer without first drying the membrane.

The insert 76 is initially thicker than the carrier 74, and is reduced in thickness in the course of ultrasonic welding. A membrane pack of the type shown in Figures 3 and 4 has been constructed using an insert 76 of Veristrate, a double sided sealant tape manufactured by the 3M Company. An adhesive was utilized, not because of its adhesive characteristics, but because it has a low melting temperature, to avoid damage to the membrane. The adhesive will not stick to a wet membrane. The ultrasonic welding displaces the water on the membrane structures, and heats the adhesive so it is more flowable and active. The carrier 74 was about 50 mil (1.27 mm) thick, while the insert 76 was initially about 10 (0.254 mm) to 30 mil (0.162 mm) thicker. A stop was utilized on the welding horn to limit compression of the insert. The insert had an inside hole diameter of about 2 inches (50.8 mm) and an outside diameter of about 2-1/4 inches (57.15 mm).

The preferred embodiment of the invention provides a pack and method for constructing it, which enables the secure sealing of an edge of the carrier and secure sealing of the membrane structures lying against one or both surfaces of the carrier, and which is useful in joining a wet membrane structure.

Claims

1. A membrane pack with a sealed edge comprising: a sheet-like carrier which is permeable to the lateral flow of fluid therein, said carrier having an edge; an insert of substantially nonporous thermoplastic polymer lying in the same plane as the carrier and having a first edge lying against said edge of said carrier but free of interlocking connection therewith, and an opposite second edge forming an edge of the membrane pack: and a membrane structure lying over a face of said carrier and extending beyond said carrier edge to lie over said insert, said insert being heat welded to the portion of said membrane structure which lies beyond said carrier edge, whereby to seal the carrier against the inflow of fluid therein which passes across said second edge of the insert.

2. The membrane pack described in claim 1, wherein: said carrier has a hole with walls forming said carrier edge, said insert is of annular shape and lies closely within said hole, and said membrane has a hole of about the same diameter as the inside diameter of said annular insert and is aligned therewith.

3. A membrane pack comprising: a porous sheet-like carrier having a hole; a substantially ring-shaped nonporous insert lying closely within said carrier hole, but with said insert being free of undercut surfaces interlocking with said carrier, to permit simple placement of the insert in the hole; and a membrane structure lying over said carrier and having a hole of about the same diameter as the hole in said ring-shaped insert; the holes in said membrane structure and insert being aligned, and said membrane structure and insert being aligned, and said membrane structure being joined facewise to said insert.

4. A method for forming a membrane pack having a fluid sealed edge, comprising: laying a nonporous insert that has a hole, in a hole of a carrier to fit closely within the carrier hole, but with the insert and carrier being free of interlocking connection.

laying a membrane structure having a hole that is smaller than said carrier hole, over said carrier and insert and with the membrane structure hole substantially aligned with the insert hole; and ultrasonically welding said membrane facewise to said insert.