FR2585965A1 - Monolithic ultrafiltration or microfiltration module made of porous carbon or graphite and process for its manufacture - Google Patents

Abstract

The ultrafiltration module comprises a porous support 3 made of amorphous carbon or of graphite pierced with parallel channels 5 at a distance from each other and provided internally with a coating 7 generally of metal oxide, for example zirconium oxide. The use of a support made of porous carbon or graphite makes it possible to produce the module under good conditions, by piercing channels in a block of porous carbon or graphite. In this way, it is possible to easily produce blocks in which the distribution and the diameter of the channels are different and are chosen according to the intended application.

Description

Ultrafiltration or microfiltration module
monolithic carbon or porous graphite and its
manufacturing process
The present invention relates to a monolithic ultrafiltration or microfiltration module that can be used in ultrafiltration or microfiltration devices making it possible to separate the constituents of a fluid taking into account their size, their shape and their physical characteristics. by applying pressure.

According to this technique, the fluid is circulated on one of the faces of a porous membrane having appropriate characteristics and under the influence of a pressure difference between the two faces of the membrane, one of the constituents of the fluid. passes selectively through the membrane and is thus separated from the other constituents; the membranes used which are selected according to the nature of the constituents to be separated, are generally supported by a porous substrate and they may be in the form of hollow tubes or in the form of plates. Generally, these membranes are assembled together to form modules which are provided at their ends with appropriate connection tips for circulating the fluid to be treated. The geometry of the membranes used thus defines the exchange surface per unit volume. of the module and the latter can vary in significant proportions as can be seen in Table 1 below where the dimensional characteristics of various cylindrical ultrafiltration modules of length L and diameter O or of parallelepipedic shape of length
L, of thickness I and height h.

TABLE 1

<tb><SEP> Constitution <SEP> of <SEP> 1 <SEP> S / V <SEP> Dimensions <SEP> S <SEP> V
<tb><SEP> module <SEP> (m / m) <SEP> of the <SEP> module <SEP> (m) <SEP> (10-3m) <SEP>
<tb><SEP> Fibers <SEP> Hollow <SEP> 740 <SEP> L = 63 <SEP> cm <SEP> 2 <SEP> 2.86
<tb><SEP># = <SEP><SEP> 7.6cm <SEP>
<tb><SEP> Membranes <SEP> planes <SEP> L = 107.3 <SEP> cm <SEP>
<tb><SEP> rolled up <SEP> into <SEP> 300 <SEP># = <SEP><SEP> 10.9 <SEP> cm <SEP><SEP> 2.8 <SEP> 10
<tb><SEP> spirals
<tb><SEP> Membranes <SEP><SEP> planes <SEP> 26 <SEP> L = 130 <SEP> cm <SEP><SEP> 21 <SEP> 820
<tb><SEP> L = <SEP> 40 <SEP><SEP> cm <SEP>
<tb> h = <SEP> 158 <SEP> cm <SEP>
<tb><SEP> Membranes <SEP><SEP> planes <SEP> 89 <SEP> L = 244 <SEP> cm <SEP><SEP> 1.7 <SEP> 19
<tb><SEP>#<SEP><SEP> = <SEP> 10 <SEP> cm <SEP>
<tb><SEP> Membranes <SEP><SEP> 122 <SEP> MembranesL = 120 <SEP> cm <SEP><SEP> 5.69 <SEQ> 46.4
<tb><SEP> Tubular <SEP># = <SEP><SEP> 22.2 <SEP> cm <SEP>
<Tb>
According to this table, it is found that flat zebranes when spirally wound have a greater capacity than tubular membranes.

However, when the diameter of the tubular membranes decreases to lead to what are called hollow fibers, the compactness obtained is then significantly greater than that of the flat membranes and the exchange surface / volume ratio of the apparatus is very high.

 The hollow fibers thus make it possible to increase the exchange surface for the same volume of the module, but when it is necessary to use hollow mineral fibers, their manufacture and their assembly in a module suffers certain problems because of the great fragility of the mineral materials used which are generally ceramic materials.

To overcome this drawback, monolithic ultrafiltration modules constituted by a porous ceramic support block having a large number of parallel channels having diameters equal to those of the hollow fibers, as described in US Pat. In this case, the inner wall of the channels is coated with an ultrafiltration membrane and the liquid to be treated is circulated in the channels. The fraction which has diffused through the ultrafiltration membrane flows through the porosity of the ceramic support and can thus be collected outside the ultrafiltration module. Such modules are particularly interesting because it is possible to obtain in these membrane surface conditions / module volume very high; thus, in the case of a cylindrical block having a height of 150 mm and a diameter of 95 mm pierced with 46 to 62 ca 2 naux per cm, a membrane surface area / module volume of approximately 2600 is obtained 3
Such modules are made by conventional techniques of powder metallurgy, for example by extrusion or spinning followed by sintering. This method of manufacture therefore requires extrusion or spinning tools adapted to the diameters and the spacing of the channels to be formed in the block of porous ceramic material. However, the ultrafiltration and / or microfiltration techniques are applicable to many liquids which have very varied characteristics. Among these characteristics, the viscosity is a quantity which has a considerable influence on the configuration of the ultrafiltration or microfiltration. Indeed, this viscosity can vary from 1 mPa.s to 1000 mPa.s and with such variations in viscosity, the pressure drops at the outlet of the installation vary dramatically. To avoid this, it is preferable to use ultrafiltration modules whose channel diameter is adapted to the viscosity of the liquid to be treated because the pressure losses can be reduced by using channels of larger section when the viscosity of the liquid. to be treated is higher.

 However, with the technologies used for the production of porous ceramic ultrafiltration modules, it is difficult to adapt the section of the channels to the viscosity of the liquid to be treated since they are made by extrusion or spinning during manufacture of the module. As a result, a change in the section and distribution of the channels implies the need to have a large number of dies and nozzles with different geometries.

 The present invention specifically relates to a monolithic ultrafiltration module which can be manufactured under better conditions and thereby have channels whose section and distribution are adapted to the fuLuide to be treated.

 The ultrafiltration or microfiltration module according to the invention comprises a porous support pierced with parallel channels, spaced from each other and internally provided with a coating, and characterized in that the support is made of porous amorphous carbon or porous graphite.

 The use of such a porous support provides many advantages.

 Firstly, the carrier has better chemical resistance in various media, particularly in acidic and alkaline media, than alumina substrates which only withstand the pH range of 2 to 13.

 The carbon supports can be machined by drilling to form the channels, which makes it easy to produce channels of different diameters without the need for complicated and expensive tools. Similarly, this machining possibility makes it easy to produce media having different channel distributions. Moreover, these supports are easy to make and assemble and therefore a lower cost than the ceramic supports.

 Carbon supports can also be sterilized with steam, which makes them interesting for certain applications.

 Finally, since the support is in the form of a monolithic block, its mechanical properties are better than those of unitary tubes, especially when they must have a high porosity.

 Generally, the diameter of the channels is 1.5 to 15 mm, preferably 2 to 10 mm.

In the module of the invention, the spacing between the channels is chosen according to the speed of circulation that one wants to obtain. Generally, ultrafiltration processes require very high circulation speeds, of the order of 4 to 5 ms to limit the deposition of material on the surface of the membrane. However, in the case of very low concentration fluids, for example for the production of pyrogen-free water where the concentration of the pyrogenic elements is of the order of ng, the speed of circulation can be significantly reduced. This speed can be achieved by appropriately choosing the pumps for circulating the fluid in the channels. However, pumps represent a very important fraction of the cost price of the installation. Also, it is difficult to have suitable pumps to diffe
traffic flows. With the modules of the invention, it is possible to easily obtain the desired speed of circulation by playing on the number of channels drilled in each module, because it is sufficient to vary the distance between the channels, which does not pose of particular problem of manufacture of the modules.

 In Table 2 below, the influence of the distance between the channels on the exchange surface and the circulation velocity in the case of a module constituted by a carbon cylindrical block having a diameter of 200 is indicated. mm, a height of 300 mm and channels of 6 mm diameter, when the circulation pump of the module provides a flow of 100 m3th.

TABLE 2

<tb> Distance <SEP> between <SEP> Number <SEP> of <SEP> Surface <SEP> Speed <SEP> of
<tb> the <SEP> channels <SEP> exchange <SEP> channels <SEP> circuLation
<tb><SEP> (mm) <SEP><SEP> (.2) <SEP><SEP> in <SEP><SEP> Channels
<tb><SEP> (Zs ~ 1) <SEP>
<tb><SEP> 5 <SEP> 240 <SEP> 1.35 <SEP> 4.09
<tb><SEP> 4 <SEP> 296 <SEP> 1.67 <SEP> 3.32
<tb><SEP> 3 <SEP> 369 <SEP> 2.08 <SEP> 2.66
<tb><SEP> 2 <SEP> 470 <SEP> 2.65 <SE> 2.09
<tb><SEP> I <SEP> 624 <SEP><SEP> 3.52 <SEP> 1.57
<Tb>
Thus, by increasing the number of channels, the flow velocity of the fluid can be reduced.
According to the invention, the internal lining of the channels is generally made of metal oxide, for example Group III-A metal oxides,
IV-A, IV-B, VA, VB, VI-B, VII-B and VIII of the Periodic Classification of Elements or of oxides of lanthanides or actinides. Preferably, the coating is made of zirconium oxide because this oxide is known to be chemically inert with respect to strong and weak acids, bases and many solvents, even at high temperature.

 The ultrafiltration or microfiltration modules of the invention can be used in a wide variety of fields. Thus, they can be used to concentrate and separate from an aqueous phase suspensions, colloids and high molecular weight materials, for example for concentration and separation of oil emulsions in water. These modules can also be used for concentrating and separating solutions used in textile operations, for example for concentrating and separating the polyvinyl alcohol present in textile finishing solutions. They can also be used for recovery and recycling. detergents of various wash waters, as well as in electrophoretic coating operations for concentrating and returning to the coating bath the entrained solids. They can also be used in the food industry, for example for the concentration and separation of used seed treatment liquors used in the preparation of brown or blond beer, for the concentration of whey proteins in the preparation of the cheese, for clarification of vinegar and clarification of water. They can also be used in the fruit juice industry, the fermentations industry, the wine industry, the dairy industry and in the field of biotechnology.

 Finally, they can also be used for concentration and separation of blood serum, egg albumin, enzymes and the like.

 The invention also relates to a method for manufacturing an ultrafiltration or microfiltration module meeting the above characteristics.

 The method includes drilling a plurality of parallel channels into a porous amorphous carbon block or porous graphite, and then depositing a coating material on the inner surface of the channels.

 The drilling of the channels can be achieved by conventional machining techniques using conventional tools for example using pins with a plurality of drills. This machining mode allows to choose the spacing and the diameter of the channels according to the use. It is also possible to use a numerically controlled machine to perform drilling with the desired spacing and diameters, which leads to a relatively low cost of machining.

However, in order to meet the requirements
of drilling, it is necessary that the height of the support block carbon or porous graphite is adapted to the diameter of the channels perces in said block. Indeed, diameters of the order of 10 Mm can not be drilled over long lengths. In Table 3, below, the drilling heights adapted to different channel diameters ranging from 2 to 10 m have been reported.

TABLE 3

<tb><SEP> e <SEP><SEP> 2 <SEP> 3 <SEP> 4 <SEP> 5 <SEP> 6 <SEP> 7 <SEP> | <SEP><SEP> 10
<tb> Height
<tb> of <SEP> perceived <SEP> 75 <SEP> 150 <SEP> 200 <SEP> 250 <SEP> 300 <SEP> 300 <SEP> 400
<tb> ge <SEP> (mm)
<Tb>
From the conditions given above, one can determine the different possibilities offered by the invention. These possibilities are given in Table 4, below, for different cylindrical modules all having a diameter of 200 mi and heights adapted to the diameters of the channels drilled in the block.

In this table, it is also indicated the spacing between the channels, the number of channels, the surface of the membranes, the number of blocks that must be assembled in series to obtain a membrane surface of about 5 m2 and the total height of the blocks assembled in series.

TABLE 4

<tb><SEP> Height <SEP> Space <SEP> Number <SEP> Surface <SEP> Number <SEP> Height
<tb> (mm) <SEP> of <SEP> between <SEP> I <SEP><SEP> of <SEP> deve <SEP> I <SEP><SEP> of <SEP> of
<tb><SEP> Channels <SEP> 2 <SEP><SEP> Channels <SEP> Missing <SEP> Block <SEP> The <SEP>
<tb><SEP> (mm) <SEP> naux <SEP> (m2) <SEP> for <SEP> seems
<tb><SEP> (mi) <SEP><SEP> have
<tb><SEP> 5 <SEP> a <SEP>
<tb><SEP> 7 <SEP> m2 <SEP>
<tb><SEP> 2 <SEP> 75 <SEP> 2 <SEP> 1910 <SEP> 0.9 <SEP> 6 <SEP> 450
<tb><SEP> 3 <SEP> 150 <SEP> 2 <SEP> 1220 <SEW> 1.72 <SEP> 3 <SEP> 450
<tb><SEP> 4 <SEP> 200 <SEP> 2 <SEP> 846 <SEP> 2,12 <SEP> 3 <SEP> 600
<tb><SEP> 5 <SEP> 250 <SEP> 3 <SEP> 465 <SEP> 1.82 <SEP> 3 <SEP> 750
<tb><SEP> 6 <SEP> 300 <SEP> 3 <SEP> 369 <SEP> 2.08 <SEP> 3 <SEP> 900
<tb><SEP> 7 <SEP> 300 <SEP> 3 <SEP> 298 <SEP> 1.96 <SEP> 3 <SEP> 900
<tb><SEP> 10 <SEP> 400 <SEP> 3 <SEP> 176 <SEP> 2.21 <SEP> 3 <SEP> 1200
<Tb>
The porous amorphous carbon or porous graphite blocks used as the starting material can be prepared by conventional methods. Thus, a porous amorphous carbon block having a very low density of 0.1 to 0.2 can be prepared by calcining an open cell polyurethane foam.

Generally the porosity of the support is between
10 and 95% and the majority of the pore radius is in the range of 0.2 to 10 μm.

 In order to deposit the coating on the inner surface of the channels, conventional methods are used, this can be achieved by contacting the inner surface of the channels drilled in said block with a suspension in a liquid of the coating material.

 Preferably, the coating is carried out using the technique described in European Patent EP-A 0 040 282 which consists in putting the internal surface of the channels pierced in the block made of carbon or porous graphite into contact with a suspension in a first Liquid site of a coating material after having previously saturated the substrate with a second volatile liquid medium, miscible with this first liquid medium, unsatisfactory for the coating material and capable of sucking this coating material in this support and desolvate this coating material, and then heat the coated support to a temperature such that the second liquid medium is volatilized to remove it from the support and coating material, so that The removal of the coating material before the end of the removal of this second liquid medium leads to a withdrawal of the coating material and the subsequent filling of the coating material. This coating material voids produced under the effect of this withdrawal.

When the coating material is zirconium oxide, water is preferably used as the first liquid medium and methanol or
Acetone as a second liquid medium.

Other features and benefits of
The invention will become more apparent on reading the following examples given of course by way of illustration and not by way of limitation with reference to the appended drawing on:
FIG. 1 represents in vertical section an ultrafiltration module according to the invention, and
FIG. 2 diagrammatically shows the mounting of such a module in an ultrafiltration device.

 In FIG. 1, it can be seen that the module 1 comprises a support made of amorphous carbon or porous graphite 3 pierced with parallel channels 5 which are lined internally with a layer 7 of coating material. The diameter of the channels d is chosen according to the nature of the fluid treated, and the spacing e between two neighboring channels is chosen according to the intended use.

 Figure 2 illustrates the mounting of the module of Figure 1 in an ultrafiltration device. For this assembly, the module 1 is provided at one of its ends with a sealed connection flange 13 connected to a pipe 15 through which the fluid to be treated is introduced to circulate it in the channels 5 of the module. At its other end, the module is provided with a sealed connection flange 17 to collect the fluid leaving the channels 5 and discharge it into the pipe 19. The fluid is circulated in the module 1 by a circulation pump 21 A pump 22 makes it possible to introduce fluid to be treated in the pipe 15 upstream of the pump 21. The pump 21 also serves to recycle in the ultrafiltration module via the pipes 23 and 15 a part of the fluid coming out of that -this. The other part is drawn off by the pipe 19 provided with a valve 25.The fluid which has diffused through the wall 3 of the channels 5 is evacuated by the porosity of the support 3 and collected in the enclosure 27.

 The following examples illustrate the embodiment of two modules according to the invention.

EXAMPLE 1
The porous support of the carbon foam obtained by very slow calcination of an open-cell polyurethane foam results in a porous carbon support having an open porosity and a very low density of the order of 0.1 to 0.2. The porosity is 90% and the pore volume, of the order of 4.5 cm3 # g, is obtained using pores whose diameters are between 0.2 and 10 pm. In this cylindrical block of porous carbon having a diameter of 100 μm and a length of 300 mm, 71 channels parallel to the axis of the block having a diameter of 6 mm are then machined. Under these conditions, a ratio of the filtration area to the volume of the module equal to 170 m 2 / m 3 is obtained. This module is then fixed at each of its ends to the connecting flanges 13 and 17 illustrated in FIG. Epoxy resin marketed under the Poxycomet brand and strengthening the assembly by tie rods.

 This channel-pierced block is then mounted on the ultrafiltration circulation loop shown in FIG. 2 to measure its flow rate to water. Then introduced into the water module under an inlet pressure of 0.2 MPa with a scanning speed of 7.10-2 m.s-1, the outside of the module being at atmospheric pressure. Under these conditions, the water flow that diffuses through the support is 1234 l.h n at 25 C. It is thus verified that the porous support is very permeable.

 The coating 7 of the channels 5 of the support is then made with zirconium oxide. For this purpose, after having closed the channels of the support at one of the ends of the module and arranged the latter vertically, the acetone channels are first filled and then acetone is added as soon as the level drops. because of the absorption of acetone by the support in order to keep the filling level of the channels constant. After 30 seconds, the support is saturated with acetone and the excess acetone is removed. A suspension of zirconium oxide particles in water is then introduced into the channels to fill the channels and suspension is added to keep the filling level of the channels constant for 1 minute. and subjecting the module to air drying in an upright position for 1 h and then to heat treatment in an oven starting at 250C increasing the temperature to 6500C in about 15 min and holding the assembly together. at this time for another 15 min.

 It is specified that the aqueous suspension of zirconium oxide contains 6% (w / v) of zirconium oxide stabilized with yttrium (88% zirconium oxide, 12% yttrium). The particles of the suspension have a surface area of 45 m 2 # 1 and particle sizes of 0.1 to 1 μm. This gives a coating of 1.7 mg zirconia per cm 2 of channel area.

 This porous carbon support, pierced with parallel channels coated internally with zirconia, is then used to treat, by ultrafiltration, an aqueous solution at 1 g / l of the product marketed under the trademark FICOLL 400M, that is to say a solution containing a hydrolyzed starch having a molecular weight of 400,000 Dalton. From a transmembrane pressure of 0.4 MPa and a circulation rate of 5 m / s of the aqueous solution at 1 g / l, a release rate of greater than 99 is obtained.

EXAMPLE 2
In this example, a cylindrical support of 300 mm in height and 100 mm in diameter made of porous graphite with a density of 1.5, a porosity of 16.8 × and a mean pore radius of 2.1 μm is used. 71 channels with a diameter of 6 mm are drilled in this block of porous graphite, then the assembly is connected to the flanges 13 and 17 of FIG. 2, as in example 1.

 The permeability of the support is then tested with water as in Example 1 using a scanning speed of 7 × 10 -2 m.sup.-1 and various introduction pressures. The results obtained are given in Table 5 which gives the value of the water flow rates as a function of the pressure difference between the outside and the inside of the module.

TABLE 5

<tb><SEP> Flow rate <SEP> to <SEP> water <SEP> (25 C)
<tb> Difference <SEP> of <SEP> pressure <SEP> L / hm <SEP> L / hm / MPa
<tb><SEP> 0.1 <SEP> 320 <SEP> 3200
<tb><SEP> 0.2 <SEP> 755 <SEP> 3770
<tb><SEP> 0.3 <SEP> 1055 <SEP> 3510
<tb><SEP> 0.4 <SEP> 1211 <SEP> 3050
<Tb>
We note that the water flow rate is roughly proportional to the pressure. So,
The increase in the permeate flow rate through the porosity of the support for the pressure range considered does not cause the appearance of a pressure drop capable of limiting its flow. All channels must therefore be debited in the same way.

 The porous graphite block is then treated to deposit a layer of zirconium oxide inside the channels and this deposit is made under the same conditions as those of Example 1. The porous graphite support is then used. whose channels have been coated with zirconium oxide to perform the ultrafiltration of a solution of 400 M FICOLL and one obtains under the same experimental conditions that the exemption 1 a rejection rate greater than 99X.

Claims (9)

 An ultrafiltration or microfiltration module comprising a porous support (3) pierced with parallel channels (5) spaced from each other and internally provided with a coating (7), characterized in that the support (3) is porous amorphous carbon or porous graphite.  2. Module according to claim 1 for the treatment of liquids, characterized in that the diameter of the channels is adapted to the viscosity of the liquid to be treated.  3. Module according to any one of claims 1 and 2, characterized in that the channel diameter is 1.5 to 15 mm.  4. Module according to any one of claims 1 and 2, characterized in that the diameter of the channels is 2 to 10 mm.  5. Module according to any one of claims 1 to 4, characterized in that the coating is metal oxide.  6. Module according to any one of claims 1 and 2, characterized in that the coating is zirconium oxide.  7. A method of manufacturing an ultrafiltration or microfiltration module according to any one of claims 1 to 6, characterized in that it consists in drilling a plurality of parallel channels in a porous amorphous carbon block or graphite porous and then depositing on the inner surface of the channels a coating material.  8. Method according to claim 7, characterized in that the coating material is deposited by contacting the inner surface of the drilled channels in the carbon block or porous graphite with a suspension of the coating material in a first medium liquid.  9. Process according to claim 8, characterized in that the support block is first saturated porous carbon or porous graphite with a second volatile liquid medium miscible to the first medium l; - quid, nonsolvating for the coating material and capable of sucking the coating material therein and desolvating the coating material, and in that the coated support is heated to a temperature such that the second liquid medium is volatilized to remove this material. second liquid medium of the support and the coating material, such that the desolvation of the coating material before the end of the removal of the second liquid medium leads to removal of this coating material and subsequent filling by this coating material voids produced under the effect of this withdrawal.