AU593730B2

AU593730B2 - Filter membrane and method of manufacture

Info

Publication number: AU593730B2
Application number: AU13865/88A
Authority: AU
Inventors: Marie-Paule Besland; Stanislas Galaj; Jacques Gillot; Raymond Soria; Alain Wicker
Original assignee: Societe des Ceramiques Techniques SA
Current assignee: Societe des Ceramiques Techniques SA
Priority date: 1988-03-17
Filing date: 1988-03-30
Publication date: 1990-02-15
Anticipated expiration: 2008-03-30
Also published as: DE3887979T2; AU1386588A; EP0332789A1; DE3887979D1; EP0332789B1; CA1332215C; ES2050716T3; JPH01262902A; JP2537657B2

Description

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AUSTRALIA

Patents Act b9373 0 COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Prior ity C 4

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Related Art: APPLICANT'S REFERENCE: F 16649/DL Name(s) of Applicant(s): Societe Des Ceramiques Techniques Address(es) of Applicant(s): 65460, Bazet,

FRANCE.

Address for Service is: PHILLIPS ORMONDE FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street Melbourne 3000 AUSTRALIA Complete Specification for the invention entitled: FILTER MEMBRANE AND METHOD OF MANUFACTURE Our Ref :89191 POF Code: 1501/83107 The following statement is a full description of this invention, including the best method of performing it known to applicant(s): 6003q/1 1- 4

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tt ~t 4: 4: FILTER MEMBRANE AND METHOD OF MANUFACTURE Cheap anid effective filter membranes are known comprising a porous structure made of a material selected from: sintered ceramics, sintered metals, microporous carbon, and microporous glass. The term "microporous glass" designates either a body obtained by heating a stack of calibrated glass particles, or else a body obtained by melting a mixture of oxides, then segregating said mixture into two phases, and preferentially dissolving one of the two phases by chemical attack, as, for example, when manufacturing VYCOR glass as described in the book CHEMISTRY OF GLASS published by The American Ceramic Society 1985, pages 108 to 114.

When using a sintered ceramic, filter membranes are frequently constituted mainly or exclusively by grains of 15 sintered alumina.

The term "filter membrane" designates a porous structure having a surface layer with pores of well-defined diameter determining the separation power of the membrane. Such a membrane is frequently formed on a macroporous support using 20 one or more superposed microporous layers.

For a membrane comprising several superposed layers, it is generally the surface layer which has the smallest diameter pores and which thus performs the filter function.

It has been observed that the performance in operation of such membrari3s depends not only on the pore diameter of the surface layer, but also on chemical and physico-chemical interactions between the surfaces of the pores and the fluids to be filtered. It is therefore essential to match the nature of the surface with the fluid under consid~eration.

In the past it has been the practice either to make an assembly constituted by a macroporous support and one or more microporous layers in which the entire assembly is made of a material which is well-matched to the fluid, or else to make an assembly comprising a maqroporous support made of any convenient material together with one or more layers made of a material which is well-adapted to the fluid.

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i-I i a~ \i.C This solution suffers from the major drawback of requiring a method of manufacturing a microporous layer constituted by a material which is well-adapted to each particular fluid. When ceramics, metals, and porous glasses obtained by particle agglomeration are used, this means that: powders need to be prepared having a grain size which is carefully controlled as a function of the desired pore diameter; a homogeneous suspension, i.e. in general a suspension which is well deflocculated, and having rheological characteristics which are well-adapted to deposition needs to be developed, as does a method of deposition; and an appropriate sintering temperature must be sought, which temperature will depend on the size of the particles to be bonded by sintering, i.e. on the pore diameter.

When using microporous glasses obtained by segregating a 15 liquid and dissolving one of its phases, this requires the development of a composition which can be segregated to give a first phase whose composition matches the fluid and a second phase which is soluble, together with accurate control of the segregation process so as to obtain a porous structure having the desired pore diameter after the second phase has been dissolved.

The object of the present invention is to provide filter membranes which are well matched to each specific utilization in a manner which is simpler and cheaper.

The present invention provides a filter membrane compris- S cc ing a porous structure made of a material selected from: sintered ceramics, sintered metals, microporous carbon, and microporous glass, wherein the entire external surface of the membrane including the surface inside the pores in said structure, is covered with a thin and continuous film of carbon or of an oxide selected from: ZrO 2 MgO, Al20 3 SiO 2 TiO 2 Cr 2 03, MnO, Fe20 3 CoO, NiO, CuO, ZnO, Ga203, GeO 2 T02, Nb20 5 MoO 3 RuQ 2 PdO, CdO, SnO 2 La 2 0 3 HfO 2 Ta 2 0 5

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3 PbO 2 Ce20 3 and Bi 2 0 3 alone or in combination, and B203, BaO and CaO mixed together with at least one of the above-specified oxides.

1 i< r 3 When said structure is constituted in conventional manner by grains which are fixed to one another by "bonded" portions of their surfaces leaving pores tivarebetween delimited by the remaining "exposed" portions of their surfaces, only said exposed portions of the grain surfaces are covered with said thin film which runs continuously from one grain to the next.

The mechanical strength of the porous structure is therefore not in danger of being degraded by the presence of the film.

Further, if the corrosion resistance of the film with respect to the fluids to be filtered or the fluids used for washing the membrane is better than the corrosion resistance of said structure, then the film acts as a protective film therefor.

The thickness of said film preferably lies between 2 nanometers (nm) and 1000 nm. This allows the protective film to be *~15 both thick enough to provide its isolation function while simultaneously being thin enough for temperature variations to 0 *give rise to stress at relatively low levels which do not lead to cracking and deterioration.

The invention is advantageously applied when the average 20 pore diameter of the layer of the structure having the smallest diameter pores, i the pores in the surface layer if there 0 4**are several layers, lies between about 0.02 microns and r microns.

The thickness of said film preferably lies between 0. 01l and 10% of the. average pore diameter in the layer of the membrane having the smallest diameter-pores. The porosity of the membrane is then substantially that of its initial porous The present invention also provides a method of manufacturing such a filter membrane, said method comprising a step of manufacturing a porous structure as defined above, said method including a step of forming on said structure a thin and continuous film of carbon or of an oxide selected from: ZrO 2 MgO, A1 2 0 3 SiO 2 TiO 2 Cr20 3 MnO, Fe 2

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3 COO, NiO, CuO, ZnO, Ga03 Ge2, T10 2 Nb 2 0 5 Mo0 3 Ru0 2 PdO, CdO, SnO 2 La 2 0 3 HfO 2 Ta 2

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5 W0 3 PbO 2 Ce 2 0 3 and B1 2 0 3 alone or in combination, and B203, BaO and CaO mixed together with at least one of the above-specified oxides.

4 Naturally the film may be made by any method which is suitable for depositing a thin layer in the mass of a porous body. Known methods includes coating, vapor phase deposition, soaking, etc However, it is preferable for said step of forming said film to comprise stages specified below.

SWhen the film is a carbon film made by carbonizing an organic material, the stages are as follows: preparing a solution containing: an organic material selected for leaving a carboncontaining residue when heated in a non-oxidizing atmosphere, specific mention may be made, for example, of coal pitch, phenolic polymers, and furfurylic polymers; and a solvent for said organic material; impregnating said porous structure with said solution in such S* a manner as to cause all of the pores of said structure to be filled with said solution; and heating said impregnated structure progressively up to about 20 800*C to 1500*C in a non-oxidizing atmosphere in order to S* evaporate the solvent and then decompose said organic material into a fraction which is removed in the form of gas and a carbo-containing residue which remains in the form of a continuous film.

When the film is a carbon film made by vapor phase deposi- Stion, said structure is maintained in a non-oxidizing atmosphere including a hydrocarbon gas at low pressure (<10 bar) and at I high temperature (1000'C to 1500*C), Fo that said hydrocarbon decomposes on coming into contact with the surface of said structure and deposits a thin film of pyrolytic carbon thereon.

When the film material is an oxide or a mixture of oxides, the stages are as follows: preparing a solution containing: one or more organic precursors of the alcoholate or the acetylacetonate type corresponding to the selected oxide or oxides;

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1 1 ^i 1 1 1 1 1 11 1 1 1 1 1 a plasticizer, cross-linking agent of the triethyleneglycol or triethanolamine type; and a solvent constituted by an alcohol; impregnating said porous structure with said solution so that the pores in said structure are filled with said solution; and progressively baking said impregnated structure so as to eliminate all of the components of said solution other than the oxide( s) formed from said precursor( s).

Such solution preferably contains 1% to 10% by mass oxide equivalent, 5% to 20% by mass plasticizer, and the remainder being alcohol. The alcohol solvent is preferably the alcohol too of the alcoholate, or isopropanol. if acetylacetonate is used.

Also preferably, said progressive baking stage itself a *4 15 comprises the following steps: 0 of drying in ambient air at substantially ambient temperature; *oaf*:slowly raising the temperature to about 350 0 C, with the rate of temperature rise being less than Soc per minute, at a 0 20 least over those temperature ranges in which gas is given of f a because of evaporation or decomposition of the organic materials in the solution; rising to a baking temperature lying between 350 0 C and 1200 0

C;

maintaining the baking temperature for at least about minutes; and cooling.

The major advantages of tht, method compared with making a microporous layer which is entirely constituted by the material which is matched to the fluid to be filtered, are as follows: A wide variety of membrane surface types may be obtained using a single composition for the porous structure with only the pore diameter of said structure being modified, and by changing the composition of the film. It is much easier to change the nature of the surface by changing the starting substances usedij~r forming the film than it is to modify said nature by developing on each occasion a micropprous layer with

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6 the appropriate pore diameter and constituted by the appropriate mixture of oxides.

When using the above-mentioned preferred method, the composition of the film can be modified simply by changing the nature of the organic precursor or by mixing organic precursors of different metals.

The method of the invention enables said film to be obtained while using baking temperatures which are generally considerably less than the temperatures which would be required for sintering prior art microporous layers.

This is particularly advantageous for obtaining membranes in which the pore diameter of the filter layer is relatively large, e.g. 2 microns to 15 microns, for which sintering temperatures may be as high as 1800°C.

15 Other characteristics and advantages of the present invention appears from the following description of embodiments of membranes in accordance with the invention together with the methods of manufacturing them, said embodiments being given purely by way of non-limiting example.

20 The starting material is a porous alumina structure constituted by a macroporous support whose pore diameter is about 15 microns having a microporous layer of sintered alumina fixed thereon by sintering, with the -pore-diameter in the microporous layer being about 0.2 microns and with the thickness of the layer being about 40 microns.

A thin film of titanium oxide is to be made on said structure. To do this, a coating solution is prepared comprising 36 grams of titanium tetraisopropoxide (Ti(OiPr) 4 20 g of triethanolamine (N(CH 2

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OH]

3 and 70 g of isopropylic alcohol.

The tube of alumina is slowly immersed in said solution.

After a few seconds, the tube is removed and is subject to drying for several hours in ambient air. The tube is then baked using the following heating cycle: slow temperature rise (0.5°C/min) up to 100°C; a pause of 20 min; followed by a rise to 700°C at 1C/min to 3°C/min. The temperature is then maintained for 40 min, and cooling is performed by switching off the power stipply to the oven.

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I o 0*~ *i 0 00003 0 00 00 r 0: 0 0e 0,ie 0 0+ 00 c. r 'C bs ~r fS- (S (S 7 For the other above-mentioned oxides, the procedure is the same as for titanium oxide, and the various components of the coating solution are indicated together with the proportions thereof in Table I. The following abbreviations are used.

TEA triethanolamine TEG triethylene glycol Acac acetylacetonate or pentanedionate EtOH ethanol iPrOH isopropanol n PrOH n propanol tPeOH tertiopentanol OtPe tertiopentanolate EtO ethanolate OEt ethanolate OiPr isopropoxide OnPr n propoxide 15 There follows an example when the film material is constituted by two oxides: CuO and TiO 2 The solution used then contains: 8 g Cu(OEt) 2 11 g Ti(OEt) 4 20 78 g EtOH 14 g TEG The method then continues using the steps described above.

In the following example, the film material is a glass ccmprising five oxides: SiO 2 Dl 2 0 3 A1 2 0 3 Cad, BaO; three of these oxides: B 2 0 3 CaO, and BaO, do not appear in Table I since they are incapable of producing a worthwhile film on their own.

The steps of the method are the same as before, and the initial solution comprises: precursor: 19.3 g Si(OEt)A 1.1 g 7.3 g g 0.7 g alcoho 70 g plasticizer: 20 g Two examples of making a In the first example, an B(OEt)4 A1Acac 3 CaAcac 2 BaAcac 2 EtOH

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i' ar desecr41nr tu~~: organic material is carbonized.

8 To do this, a 5% solution of coal. pitch is prepared in toluene, the porous structure is soaked in said solution so as to be completely impregnated, it is drained and heated slowly in a non- oxi4dizingj atmosphere, initially up to about 100*C in order to evaporate the toluene, and then up to 10006 C in order to carbonize the film of coal pitch which remains on the surface of the porous structure. This provides a carbon film having a thickness of about 1% of the pore diameter.

The secondx example uses vapor phase deposition. The porous structure is placeci in an enclosure which is evaporated and heated up to 1200*C. A mixture containing 10% methene and argon is then inserted into the enclosure up to a total *o pressure of 100 millibars. The methane then decomposes on coming into contact with the surface of the porous structure and foirms a thin and continuous film thereon of pyrolytic carbon whose thickness increases progressively. The treatment is stopped when said thickness reaches the desired value, for example 0.1 pm; the duration of the treatment is about one hour and depends on the shape and structure of the sample and on the type of the enclosure.

Naturally, the invention is not limited to the various methods of preparation mentioned.

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OXIDE

Zr02 Mgo A1203 Si02 Cr203 Mn0 Fe203 Coo NiO H D CuO ZnO Ga203 Ge02 T102 Nb205 MoQ3 Ruo2 PdO CdO Sno2 La203 Hf02 Ta205 W03 Pb02 Ce203 Bi203 PRECURSOR ALHOL PLASTICIZER -IF7 1 F-=Pl 13 g Zr(OnPr)4 27 g nPrOH 8 g TEA 12 p, Mg(OEt)4 88 g EtOH 8 g TEA 44.5 g AlAcac3 86 g iPr0H 7 g TEG 4 g Si(OEt)4 94 g EtOH 5 g TEA 27.6 g CrAcac3 86 g iPrOH 8 g TEG 14.3 g MnAcac2 90 g iPrOH 6 g TEG 35.3 g FeAcac3 80 g iPrOH 12 g TEA 32.8 g CoAcac3 83 g iPrOH 10 g TEA 31 g NiAcac 2H20,, 82 g iPrOH 10 g TEG 19.8 g CuAcac2 85 g iPrOH 9 g TEA 13 g ZnAcac2 84 g iPrOH' 12 g TEA 19.6 g GaAcac3 80 g iPrOH 15 g TEG 10 g Ge(EtO)4 89 g EtOR 7 g TEA 7.4 g T1(OEt) 75 g EtOH 18 g TEG 14 g Nb(OEt)5 79 g EtOH 15 g TEG 14.3 g MoO2Acac2 79 g iPrQH 13 g TEA 30 g RuAcac3 75 g iPrOH 15 g TEA 12.5 g PdAcac2 87 g iPrOH 8 g TEA 12 g CdAcac2 87 g iPrOH 10 g TEA 13.8 g SnAcac3 88 g iPrOH 7 TEG 24 g LaAcac3 79 g iPrOH, 12 g TEG 17.5 g Hf(OtPe) 4 78 g tPeOH 15 g TEA 14.8 g Ta(OEt)5 79 g EtOH 13 g TEA 10 g WAcac3 83 g iProH 12 g TEA 5 g PbAcac2 91 g iPrOH 6 g TEG 13 a CeAcac3 83 g iPrOH 12 g TEA 15 g BiAcac3 79 g iPrOH 14 g TEA, *s ee 0 C* S *tS~

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