The invention relates to a method for making a membrane module, in particular for exchangers for use in micro-, ultra-or nanofiltration or the separation of gasses, comprising a bundle of hollow fibres with a flange at each end, which method comprises the following steps: positioning the hollow ceramic or metal fibres with one end on a mould plate, making a ceramic or metal flange in the mould plate between and round the ends of the fibres, removing the mould plate, removing the binder in the flange and/or the fibres using thermal diffusion, and sintering the flange and/or the fibres.

Prior art.

Such a method is known from European patent application EP-A-0 941 759.

With this known method the flange is made by filling the mould plate with a ceramic slurry prepared beforehand and then sintering the fibres and the slurry into a solid ceramic object.

In this method, the slurry is selected in such a way that the difference between the thermal coefficient of expansion of the flange and that of the fibres is less than 5, 10-6 K-'.

Summary of the invention.

An objective of the invention is to provide a method of the type described in the preamble which is simpler and less expensive than the known method. For this purpose, the method according to the invention is characterized in that the positioning of the ends of the fibres on the mould plate is done by placing at least one rod in each fibre, which protrudes from that fibre at least at one end, and then inserting the free ends of the rods into openings in the mould plate, and making the flange is done by heating the ends of the fibres until they flow and fill the mould plate. With the method according to the invention it is not

necessary to make a slurry beforehand nor is it necessary to put any slurry in the mould plate. The flange is made from parts of the non-sintered fibres by heating them until they become fluid. In this way, the method according to the invention is simpler and less expensive than the known method.

The fibres can be made in accordance with the method described in European patent application EP-A-0 693 961 in which a paste, consisting of a polymer binding system filled with a ceramic powder, is made plastic by heating, and formed into hollow fibres by means of melt-extrusion with a spinning head.

Another way the fibres can be made is described in European patent application EP-A-0 949 960 in which a paste is made by mixing a ceramic powder with a binder, and extruding this paste without heating it to make hollow fibres. In this process, a binder dissolved in water or any other simple solvent, a thermo-setting binder, or an organic binder is used.

An embodiment of the method according to the invention is characterized in that apart from the fibre mentioned above an additional fibre is placed on each rod, which after being positioned is situated between the fibre mentioned above and the mould plate, and when heated these additional fibres become fluid and form the flange. In this method, this additional fibre is a so-called'green'fibre which means that it is a non-sintered fibre. The fibre mentioned above is preferably sintered so that only the additional fibre becomes fluid when heated. In this way, by selecting the length of the additional fibres, it is easy to arrive at the amount of material required for the flange, and while being heated it is not necessary to pay attention to the length required of the fibres which must become fluid in order to make the flange.

A further embodiment of the method according to the invention is characterized in that the rods protrude from the fibre at both ends and each end is placed in a mould plate. Because of this, a flange can be made at each end of the fibres simultaneously. If additional non-sintered fibres are used according to the embodiment described above, then an additional fibre should be placed on the rod at each end of the fibre.

Still a further embodiment of the method according to the invention is characterized in that apart from the rod mentioned above, an additional rod is placed in each fibre, in which one end of the rod protrudes from one end of the fibre and the end of the

additional rod protrudes from the other end of the fibre, and in which the ends of the rod and the additional rod protruding from the fibre are placed on a mould plate and on an additional mould plate respectively. The advantage of this is that length of the fibres is not limited to the rods'length. A further important advantage of this is that the fibres do not have to be straight, as a result of which any fibres which are crooked due to the manufacturing process are not a hindrance in making the membrane module.

Preferably the mould plate and the fibres are pressed towards each other while being heated.

A further favourable embodiment of the method according to the invention is characterized in that the method also comprises the following steps: the preparation of a ceramic suspension or an inorganic sol, the placing of the suspension or sol in a tank that is connected at its bottom by a hose to the bottom of a vertically positioned membrane module, the moving upwards of the tank from a position lower than the membrane module, as a result of which the suspension or sol flows to the membrane module through the hose and fills the inside of the fibres, the moving downwards of the tank, as a result of which the fibres are emptied, the uncoupling of the hose from the membrane module, the drying of the membrane module, and finally the heating of the membrane module, through which the coating is calcined. In this way, a coating can be applied in a simple manner to the inside of the hollow fibres. In this process, the coating is made from the ceramic suspension or inorganic sol.

Another favourable embodiment of the method according to the invention is characterized in that the method also comprises these steps: the preparation of a ceramic suspension or an inorganic sol, the putting of the suspension or sol in a tank that is connected by means of a feed line to one end of the membrane module and by means of a return line is connected to the other end of the membrane module, the regulated pumping of the suspension or sol through the inside of the fibres for a specific period of time, as a result of which the suspension or sol forms a deposit on the inside of the fibres, the uncoupling of the feed and return lines from the membrane module, the drying of the membrane module, and finally the heating of the membrane module, through which the coating is calcined.

The invention also relates to a membrane module made in accordance with the method according to the invention. By membrane module is meant here a bundle of

hollow fibres which are connected to flanges at their ends. Such a membrane module is a half-finished product for, among other things, exchangers, for example, for use in microfiltration, ultrafiltration or the separation of gasses.

Brief description of the drawings.

The invention will be elucidated more fully below on the basis of drawings in which an embodiment of the method and the membrane module according to the invention is shown. In these drawings : Figure 1 shows a set-up during employment of the method according to the invention for making a membrane module ; Figure 2 shows a membrane module made in accordance with the method in Figure 1 ; and Figure 3 shows an exchanger fitted with the membrane module shown in Figure 2.

Detailed description of the drawings.

For the purpose of separation processes, which take place at high temperatures, it is desirable to have available an inexpensive ceramic membrane module.

This membrane module 1, see Figure 2, consists of a number (tens, hundreds or more) of bundled ceramic or metal hollow fibres 3, which are connected to each other at their ends by means of two flanges 5,7 made of the same material, the fibres 3 being coated on the inside or outside with one or more high-selectivity coatings. The membrane module 1 is employed for the purpose of mass transfer (such as a membrane, soot filter, fuel cell, etc.) and/or for the purpose of heat transfer (heat exchanger, membrane reactor, etc.).

Such a membrane module 1 is made in the following preferred manner, see Figure 1, in which a set-up during employment of the method is shown. Several tens or hundreds of porous, sintered, hollow aluminium oxide fibres 3 are made in the manner described in European patent application EP-A-0 693 961 or in European patent application EP-A-0 949 960. Each fibre 3 is slid over a metal (stainless steel) rod 9. A short, non- sintered additional fibre 11, 13 is placed at both ends of each fibre 3, also on the metal rod

9. The method of making these green fibres is also described in the previously mentioned patent applications, in which with respect to the entire process the sintering step is not performed.

Each end of every metal rod is positioned in a hole in a perforated metal mould plate 15,17. There are two perforated metal (aluminium) mould plates 15, 17 parallel to each other, in which the number of holes in each plate is equal to the number of metal rods. The perforation pattern is the same on both plates and determines the packing density of the bundle of fibres. Two metal rings 19,21 are placed round or on top of the mould plates 15,17.

The entire combination of fibres 3, rods 9, perforated mould plates 15, 17 and rings 19,21 is placed vertically on a heating plate 23. By doing this, the lower perforated mould plate 15 and the metal ring 19 are in direct or indirect contact with the heating plate.

The heating plate 23 is heated up, and when the lower perforated mould plate 15 reaches the desired temperature, pressure is applied downwards on the upper perforated mould plate 17. Because of this, the set of lower green fibres 11 comes in contact with the heated perforated mould plate 15, becomes viscous and flows into the space between the perforated mould plate 15 and the lower ring 19, as a result of which a flange 5 (see Figure 2) is formed between the hollow fibres 3, the perforated mould plate 15 and the ring 19.

Then the entire combination of fibres 3, rods 9, perforated mould plates 15, 17, rings 19,21 and the first flange is turned upside down and a second flange is made.

An alternative for the above mentioned 2x one-sided pressure-application process is a two-sided process in which both perforated mould plates are heated up simultaneously, and in which two flanges are made at the same time by applying pressure once. In this process, the entire combination of fibres, rods, perforated moulding plates and rings can be positioned vertically or horizontally.

Next the perforated mould plates 15,17, metal rods 9 and metal rings 19,21 are removed from the entire combination of flanges 5,7 and fibres 3 (see Figure 2). This takes place preferably at room temperature, but generally at a temperature lower than that of the pressure-application process. When removing the metal rods 9 it is desirable, but not necessary, to heat up the formed flanges 5,7 so that the rods 9 can easily be extracted from the entire combination of flanges and fibres. The metal rings 19,21 preferably should be built up of several parts so that their removal from the flanges can be done easily.

If the flanges 5,7 (see Figure 2) are not entirely round, they are then polished into a round shape while in the green phase. The side of each flange, in which the ends of the fibres are situated is polished smooth. A circumferential groove (not shown in Figure 2) can be made in the side of each flange which is still green, for attaching the flanges to an outer tube at a later moment.

The entire combination of fibres 3 and flanges 5,7 is then placed in an oven for burning out the organic binder and for sintering. The preferred orientation is that the entire combination of fibres 3 and flanges 5,7 lies on an oven plate (positioned horizontally) whether supported by special devices or not. In an alternative, the entire combination of fibres 3 and flanges 5,7 is positioned vertically, hanging and/or standing, whether supported internally or externally or not at all.

As an alternative to the method described above with a combination of long sintered fibres and short green fibres, one might also consider an entire combination of fibres and flanges which is completely made from material in the green phase. For this purpose, the above description is followed, provided that the three fibres 3,11, 13 (one long sintered fibre and two short green ones) are replaced by one long green fibre. The pressure- application procedure is similar. During removal of the binder and during sintering the entire combination of fibres and flanges, whether positioned horizontally or vertically, is supported both internally as well as externally by ceramic material to prevent sagging.

The sintered entire combination of fibres 3 and flanges 5,7 make up the membrane module 1 shown in Figure 2. It can be used in this form as it is for cross-flow microfiltration. For this purpose, two fluoropolymer 0-rings 25 are placed in the circumferential grooves 27 in the flanges, see Figure 3. The membrane module 1 is then put into a metal or polymer outer tube 29 and secured in it. A maximum of four connections 31 can be coupled to the outer tube 29. The maximum application temperature is dictated by the non-ceramic materials which for a cross-flow microfiltration module is approx. 200 °C.

Furthermore, the membrane module can serve as a basis for a high-selectivity separation module. A low-temperature ultrafiltration, nanofiltration, gas separation or pervaporation membrane module is made by applying one or more coatings to the membrane module. It is also possible to make the flanges gas tight beforehand by infiltrating and/or coating them with a glazing substance and then heating the entire combination in an oven.

Next a ceramic suspension or an inorganic (particulate or polymer) sol is prepared. The

suspension or sol is poured into a tank that is connected by a hose at its bottom to the bottom of a vertically positioned membrane module. At the start, the position of the tank is lower than that of the membrane module. The tank is moved upwards vertically at a constant speed. Through the principle of communicating vessels the suspension or sol passes through the hose to the membrane module and fills the inside of the ceramic fibres. The tank is moved upwards as long as needed until the suspension or sol appears at the top of the membrane module. At that moment, the tank remains in position for awhile, and/or moves vertically downwards at a constant speed as a result of which the inside of the fibres is emptied. The hose is uncoupled from the membrane module and the membrane module is dried in the air for awhile. The membrane module is then placed in an oven after which the coating is calcined. If necessary, the process of coating, drying and calcining is repeated several times with the same or other coatings. The result is a membrane module with pores between the subnanometer and (sub) micron scales.

A high-temperature ultrafiltration, nanofiltration, gas separation or pervaporation membrane module is made by, if necessary, making the flanges of the membrane module gas tight (see above) and connecting the membrane module to a ceramic or metal outer tube employing existing high-temperature joining techniques (using carbon and/or copper and/or iron-nickel-cobalt alloys and/or ceramic adhesives and/or other materials). The coating procedure described above is then followed. The result is a membrane module with pores between the subnanometer and (sub) micron scales, with application possibilities to 1000 °C.

Although in the above the invention is explained on the basis of the drawings, it should be noted that the invention is in no way limited to the embodiment shown in the drawings. The invention also extends to all embodiments deviating from the embodiment shown in the drawings within the context defined by the claims.