IE903364A1

IE903364A1 - Process for the preparation of bridged clays and bridged¹clays obtained by this process

Info

Publication number: IE903364A1
Application number: IE336490A
Authority: IE
Original assignee: Rhone Poulenc Chimie
Priority date: 1989-09-18
Filing date: 1990-09-17
Publication date: 1991-04-10
Also published as: FR2652079B1; FR2652079A1; PT95330A; EP0424187A1; JPH03174316A

Abstract

Process for the preparation of bridged clays and the bridged clays prepared by said process. The characteristic of the process of the invention is to treat thermally a reaction mixture comprising the clay in aqueous suspension, at least one salt of a cation M and a compound which supplies OH<-> ions by hydrothermal decomposition under the reaction conditions, and then to separate the product obtained. The process of the invention applies particularly well in the case of alumina bridging.

Description

PROCESS FOR THE PREPARATION OF BRIDGED CLAYS AND BRIDGED CLAYS OBTAINED BY THIS PROCESS The subject of the present invention is a process for the preparation of bridged clays and the bridged clays prepared by this process.

Certain clays have an expansible lattice structure. They have, indeed, the property of being able to absorb water, especially between the different layers of which they are composed. This property is exhibited by clays from the group of smectites and vermiculites. The structure of these clays can be described in a simplified manner as a sheet structure of three layers having a thickness of about 1 nm and comprising two layers of SiOA tetrahedra separated by a layer of MX6 octahedra, where M can be a trivalent ion, for example Al3+, in the case of dioctahedral clays, or a divalent ion, for example Mg2+, in the case of trioctahedral clays; X is an oxygen atom, a hydroxyl group OH or a fluorine atom F.

The silicon atoms of the tetrahedra can be replaced in part by aluminium atoms and the aluminium and magnesium atoms of the octahedra can be substituted in particular by magnesium or iron and lithium atoms respectively.

Due to the expansible nature of the clays, they have been used in the area of catalysis, where the largest surface area accessible to reactants has to be found. - 2 However, the importance of unbridged clays as catalysts or catalyst supports is restricted to liquid phase catalysis, since the expanded clays undergo desiccation as soon as the boiling temperature of the solvent has been reached. As a result, they lose this characteristic expansion and thus their accessible interlayer surface area.

The attempt has therefore been made to expand the clays by a different technique, to enable them to be used as catalysts or catalyst supports also in the gas phase.

It has thus been possible to expand the clays by introducing between the clay sheets a mineral substance which thereby creates pillars or bridges. The clays thus obtained have been named bridged clays.

A well-known technique consists in effecting the bridging by oligomers of a metal hydroxide, especially of aluminium.

In general, the bridging of the clays is usually carried out using a process in three steps: - manufacturing the aluminium pillar Al13 of the formula [Al13O4 (OH)24+X (H20)n] (7-x) + (where x is between 0 and 4 and n varies most often between 8 and 12), starting from an aluminium salt and a base, - mixing the solution containing the Al13 source with the aqueous clay suspension, - washing or dialysing the final product.

FR-A 2,512,043, which describes a process of this - 3 type, may be mentioned in particular.

The present invention aims at proposing a new process for the preparation of bridged clays which has the advantage, described in detail below, of having one step less compared with the abovementioned process.

Specifically, the object of the invention is a process for the preparation of a bridged clay which consists in heat-treating a reaction medium comprising the clay in aqueous suspension, at least one salt of a cation M and a compound which supplies OH ions by hydrothermal decomposition under the reaction conditions, followed by separation of the product obtained.

The characteristic feature of the process of the invention consists in using, when the bridging of the clay is carried out, a compound which decomposes under the temperature conditions of the reaction according to a reaction of type (1): AB + H20 -> AH + B+ + OH (1) The compound which is preferably used is urea, which decomposes in the heat according to the reactions: O=C-(NH2)2 + HZO -> CO2 + 2NH3 (2) 2NH3 + 2H2O -> 2NH/ + 20H (3) - 4 possible to do without its preparation beforehand, such as described in the prior art.

In the following description of the present invention, compound AB designates the compound supplying OH ions by hydrothermal decomposition.

The process of the invention is suitable for all clays of natural or synthetic origin, as long as they have a swelling structure.

The preferred clays belong to groups named smectites. The following may be mentioned by way of example: montmorillonite [Alx 67 Mg0 33 (Na0 33)]Si4 O10 (0H)2 beidellite Al2 [Al0 33 (Na0 33)Si3 67 ]O10 (0H)2 hectorite [Mg2 67 Li0 33 (Na0 33)]Si4 O10 (0H)2 The formulae are given for guidance and without any limiting character.

It is likewise possible to use a clay of the vermiculite type.

A preferred variation of the process of the invention is to use a clay which has undergone a treatment which consists in exchanging the calcium cations present in the clay for sodium cations. This treatment is known and has the effect that the swelling of the clay is improved. Specifically, the clay is in general brought into contact with an aqueous solution of a sodium salt, preferably sodium chloride.

The amount of sodium salt is most frequently in excess with respect to the exchange capacity of the clay. - 5 The excess sodium salt can be removed by washing the clay thus modified with water.

As mentioned before, the process of the invention is distinguished by the use of the compound (AB).

Examples of compounds (AB) which are entirely suitable for carrying out the process of the invention are urea, but also any other compound which behaves like urea. Examples which may be mentioned are substituted ureas, thiourea and substituted thioureas, cyanamide, substituted cyanamides, hexamethylenetetramine and melamine, which can be used by themselves or in a mixture.

The substituted ureas and the substituted thioureas are in each case ureas and thioureas substituted at the nitrogen by one, two, three or four saturated or unsaturated aliphatic and/or aromatic radicals.

Examples of suitable radicals are in particular alkyl radicals having 1 to 4 carbon atoms, the allyl radical and/or the phenyl radical.

Below, examples of substituted ureas and thioureas which are suitable for the invention are given: methylurea; symmetrical dimethylurea; unsymmetrical dimethylurea; trimethylurea; tetramethylurea; ethylurea; N-methyl-N'-ethylurea; symmetrical diethylurea; unsymmetrical diethylurea; triethylurea; tetraethylurea; npropylurea; symmetrical di-n-propylurea; tetra-n-propylurea; n-butylurea; symmetrical di-n-amylurea; allylurea; symmetrical diallylurea; unsymmetrical diallylurea; phenylurea; N-methyl-N'-phenylurea; N-methyl-N-phenylIE 903364 - 6 urea; N-ethyl-N'-phenylurea; N-ethyl-N-phenylurea; N,Ndimethyl-N'-phenylurea; symmetrical diphenylurea; methylthiourea; symmetrical dimethylthiourea; unsymmetrical dimethyl thiourea; trimethyl thiourea; tetramethylthiourea; ethylthiourea; N-methyl-N'-ethylthiourea; Ν,Ν-dimethylN'-ethylthiourea; symmetrical diethylthiourea; unsymmetrical diethylthiourea; triethylthiourea; tetraethyl thiourea; n-propylthiourea; N-methyl-N'-n-propylthiourea; N-ethyl-N'-n-propylthiourea; symmetrical di-npropylthiourea; unsymmetrical di-n-propylthiourea; Nethyl-N-N'-di-n-propylthiourea; n-butylthiourea; ibutylthiourea; di-sec .-butylthiourea; tert.-butylthiourea; allylthiourea; N-methyl-N'-allylthiourea; N,Ndimethyl-N'-allylthiourea; N-ethyl-N'-allylthiourea; N,Ndiethyl-N'-allylthiourea; symmetrical diallylthiourea; phenylthiourea; symmetrical diphenylthiourea.

The substituted cyanamides are cyanamides substituted at the nitrogen by one or two aliphatic and/or aromatic radicals, such as defined above.

Examples of suitable substituted cyanamides are especially the following compounds: methylcyanamide; dimethylcyanamide; ethylcyanamide; diethylcyanamide; din-propylcyanamide; di-n-butylcyanamide; allylcyanamide; diallylcyanamide; phenylcyanamide; diphenylcyanamide.

According to the invention, a salt of a cation M is used. The cation M is the cation which is involved in the bridging pillar between the sheets.

According to the invention, the cation M is - 7 understood to mean any cation which has the property of being hydrolysed in a pH range between 3.0 and 10.0 and preferably between 4.0 and 8.0.

The cations M which are preferably used are trivalent cations and in particular, aluminium, chromium, iron or a mixture thereof. It is also possible to add to these trivalent cations a minor amount of a divalent cation which has the property of precipitating in the same pH range as the one defined above.

A minor amount is understood to mean an amount of less than about 20 % of the total weight of the mixture of cations. Examples of suitable divalent cations are cobalt, nickel, copper, zinc, etc.

As for the type of salt, any soluble salt of the cation M can be used. It is in general used in the form of nitrate or chloride.

Aluminium chloride and/or chromium chloride, aluminium nitrate and/or chromium nitrate are chosen as the preferred salts of metal cations. Even more preferably, aluminium chloride or aluminium nitrate is chosen.

In the process of the invention the salt can be introduced, either in solid form or in the form of an aqueous solution.

In the process of the invention, another reactant is involved, i.e. the compound (AB). The compound (AB) can be introduced into the reaction medium in solid or aqueous form.

In the first step of the process of the - 8 invention, the mixing of the different reactants is carried out. The order in which the reactants are added is not critical.

According to a first variation, the clay can be suspended in water, and the aqueous solution of at least one salt of the cation M and then the aqueous solution of the compound (AB) or the other way round are added.

According to a second variation, the three reactants can be mixed simultaneously.

According to a third variation, the powdered clay can also be introduced into an aqueous solution of at least one salt of the cation M and of the compound (AB).

The mixture is preferably prepared with stirring.

The concentration of the clay in the reaction medium is chosen as high as possible while maintaining conditions of easy handling.

This concentration can be, for example, between 0.1 g/1 and 20 g/1.

The concentration of the compound (AB) in the reaction medium is advantageously chosen between 103 and 2 mol/litre.

As for the proportion of the different reactants, the weight ratio between the weight of the salt of the cation M, expressed in weight of the oxide used, and the weight of the suspended clay is preferably chosen to be between 0.1 and 6.0 and preferably between 1.0 and 5.0.

As for the amount of the compound (AB) employed, it is determined in such a manner that the molar ratio of - 9 the number of moles of the compound (AB) to the number of moles of the cation M is preferably between 0.5 and 3.0.

The process of the invention consists in mixing the different reactants mentioned above, generally at ambient temperature (most frequently between 15°C and 25eC), then heating the reaction medium at a temperature between 80 °C and 180 °C, preferably between 80 °C and 120°C. This heating results in the decomposition of the compound (AB) and thus leads to the formation of the interlayer pillars.

It is easier to carry out the reaction at the reflux temperature, which is easy to control and to reproduce.

The duration of the operation is very variable, lasting, for example, from 1 hour to about 10 hours and preferably from 3 to 8 hours. It is preferred to stir the reaction medium throughout the process of the invention.

At the end of the treatment, the clay is recovered by conventional techniques of solid/liquid separation, such as, for example, filtration or centrifugation.

The bridged clay can then be subjected to an operation to remove the anions. This may prove necessary, since an improvement in the thermal stability of the bridging is sometimes observed.

To find out whether this operation is desirable, a person skilled in the art can easily determine this by carrying out two comparative experiments, one using the - 10 operation to remove the anions, the other without using it. This operation is not carried out if a reduction in the basal spacing is observed. The basal spacing is defined as the sum of the thickness of a sheet and the interlayer spacing, i.e. the spacing between two sheets.

A practical method of removing the anions is washing, preferably with water, or dialysis according to a well known technique described in particular in FR-A 2,512,043.

In the next step, the clay is subjected to a heat treatment. It can be directly subjected to a calcination operation or undergo drying beforehand.

The drying conditions can vary within wide limits. Thus, the temperature chosen can be between 80°C and 120eC, preferably about 100 °C. The drying time chosen is preferably between 2 and 48 hours. The drying operation can be carried out in air or under reduced pressure, for example, between 1 and 100 mm of mercury (133.322 Pa and 13332.2 Pa).

Another variation of the invention consists in subjecting the separated clay to a lyophilization treatment. This is effected by rapid freezing of the product to a temperature preferably between -10 °C and -50eC, followed by sublimation under reduced pressure: this pressure is not critical and is preferably chosen to be between 10'5 and 0.5 atmospheres.

In accordance with the final step of the process, the optionally dried product is subjected to calcination - 11 at a temperature chosen between 300eC and 800°C, but preferably between 350°C and 600°C. It lasts about 1 to 6 hours and preferably about 2 hours.

The clays prepared according to the process of the invention show a basal spacing which varies, for example, between 1.4 and 2.0 nm in the case of an aluminic bridging.

They have good heat stability and are therefore perfectly suitable for applications in the area of catalysis, such as catalytic cracking of paraffinic hydrocarbons or isomerization of paraffinic hydrocarbons and olefins.

Below, examples of carrying out the process of the invention are given, without any limiting character.

EXAMPLE 1 - In this example, a clay of the montmorillonite type originating from WYOMING and called VOLCLAY bentonite is used.

A 20 g/1 aqueous suspension of this clay is prepared, which is stirred vigorously and allowed to settle over a period of 24 hours.

Sampling of the 2 pm size fraction is then carried out to give an aqueous suspension of the clay, called A.

- The next step, a treatment with a sodium salt is carried out. To this end, excess sodium chloride, relative to the exchange capacity of the clay, is added to the suspension A, i.e. 200 milliequivalents of sodium - 12 IE 903364 per 100 g of clay.

The suspension is stirred for 1 hour at ambient temperature (2 2 ° C).

Filtration through a glass frit no. 4 is then carried out. The treatment with sodium chloride is then repeated This is followed by a second filtration and washing of the clay with distilled water until the chloride ions have completely disappeared from the washings .

The clay is suspended in water at a concentration of 20 g/1. This is suspension B.

- An aqueous aluminium nitrate solution at a concentration of 0.4 mole/litre of Al(NO3)3x9H2O is prepared. 1.2 litres of this solution are added to 0.85 litre of suspension B.

It is stirred at ambient temperatures for a few minutes to give suspension C.

- An aqueous urea solution 14.4 g/litre is prepared, 1.2 litres of which are gradually added to suspension C.

The molar ratio of urea/Al3+ is equal to 1.16.

At the end of the urea addition, the reaction mixture D is obtained.

- It is then heated to reflux with stirring for hours. - 13 The suspension is then dialysed by a conventional method by means of a cellulose hydroxyacetate membrane for molecular weights equal to 10,000 and above.

The clay is separated by filtration through a glass frit no. 4.

- The separated product is dried in a furnace at 100°C for 24 hours and then calcined in a muffle furnace at 350°C for 2 hours.

X-ray diffraction analysis of the clay shows the existence of a d001 line at 1.8 nm, which is characteristic of the aluminic bridging: the symbol d001 defines the basal spacing, which is the sum of the thickness of a sheet and the interlayer spacing.

EXAMPLE 2 Example 1 is repeated, except that the dialysis operation is omitted.

The diffraction spectrum RX of the clay obtained shows the existence of a d001 line at 1.4 nm.

It is concluded that the dialysis operation is desirable since, if it is omitted, the basal spacing diminishes.

EXAMPLE 3 Example 1 is repeated, except that the amount of urea in suspension C is changed and the dialysis operation is not carried out.

The urea solution has a concentration of 28.8 g/1; hence the molar ratio of urea/Al3+ is equal to 2.32. - 14 The diffraction spectrum RX of the clay obtained shows the existence of a d001 line at 1.8 nm, which is characteristic of the aluminic bridging.

EXAMPLE 4 Example 3 is repeated, except that the dialysis operation is additionally carried out.

Consequently the dialysis operation involves in this case a diminishing of the basal spacing; hence this operation proves undesirable. - 15 IE 903364

Claims

1. Process for the preparation of a bridged clay, characterized in that it consists in heat-treating of a reaction medium comprising the clay in aqueous suspension, at least one salt of a cation M and a compound which supplies OH' ions by hydrothermal decomposition under the reaction conditions, followed by separating the product obtained.

2. Process according to Claim 1, characterized in that the clay is a clay from the group of smectites or vermiculites .

3. Process according to one of Claims 1 or 2, characterized in that the clay is montmorillonite, beidellite or hectorite.

4. Process according to any of Claims 1 to 3, characterized in that the clay used has undergone a prior treatment of exchanging calcium cations for sodium cations.

5. Process according to any of Claims 1 to 4, characterized in that the cation M is any cation which has the property of being hydrolysed in a pH range between 3.0 and 10.0, preferably between 4.0 and 8.0 .

6. Process according to any of Claims 1 to 5, characterized in that the cation M is a trivalent cation.

7. Process according to Claim 6, characterized in that the cation M is aluminium, chromium and/or iron or a mixture thereof.

8. Process according to one of Claims 6 or 7, characIE 903364 - 16 terized in that the cation M is admixed with a minor amount of a divalent cation.

9. Process according to Claim 8, characterized in that the divalent cation is cobalt, nickel, copper or zinc.

10. Process according to any of Claims 1 to 9, characterized in that the cation M is in the form of nitrate or chloride.

11. Process according to any of Claims 1 to 10, characterized in that the salt of a cation M is aluminium chloride and/or chromium chloride, aluminium nitrate and/or chromium nitrate.

12. Process according to any of Claims 1 to 11, characterized in that the salt of a cation M is aluminium chloride or aluminium nitrate.

13. Process according to any of Claims 1 to 12, characterized in that the compound (AB) is urea, a substituted urea, thiourea, a substituted thiourea, cyanamide, a substituted cyanamide, hexamethylenediamine or melamine.

14. Process according to Claim 13, characterized in that the compound (AB) is urea.

15. Process according to any of Claims 1 to 14, characterized in that the clay can be suspended in water, and the aqueous solution of at least one salt of the cation M and then the solution of the compound (AB) or the other way round are added; or in that the powdered clay is introduced into an aqueous solution of at least one salt of the cation M and of the compound (AB); or in that the three reactants are mixed simultaneously. - 17

16. Process according to any of Claims 1 to 15, characterized in that the concentration of the clay in the reaction medium is between O.JL g/1 and 20 g/1.

17. Process according to one of Claims 1 or 16, characterized in that the concentration of the compound (AB) in the reaction medium is between 10 3 and 2 mol/litres.

18. Process according to any of Claims 1 to 17, characterized in that the weight ratio between the weight of the salt of the cation M, expressed in weight of the oxide used, and the weight of the suspended clay is between 0.1 and 6.0 and preferably between 1.0 and 5.0.

19. Process according to any of Claims 1 to 18, characterized in that the molar ratio of the number of moles of the compound (AB) to the number of moles of the cation M is between 0.5 and 3.0.

20. Process according to any of Claims 1 to 19, characterized in that the reactants are mixed and the reaction medium is heated at 80°C to 120 e C.

21. Process according to any of Claims 1 to 20, characterized in that the anions are removed from the clay obtained after separation.

22. Process according to Claim 21, characterized in that the removal of the anions is effected by washing with water or by dialysis.

23. Process according to any of Claims 1 to 22, characterized in that the clay is subsequently dried between 80°C and 120’C.

24. Process according to any of Claims 1 to 22, - 18 characterized in that the clay is subjected to a lyophilization treatment.

25. Process according to any of Claims 1 to 24, characterized in that the clay is subsequently calcined at a temperature between 300 e C and 800’C, preferably between 350*C and 600”C.

26. Bridged clays obtained by the process described in any of Claims 1 to 25.

27. Bridged clays according to Claim 26, characterized in that they have a basal spacing between 1.4 and 2.0 nm in the case of an aluminic bridging.

28. A process according to claim 1 for the preparation of a bridged clay, substantially as hereinbefore described and exemplified.

29. A bridged clay whenever prepared by a process claimed in a preceding claim. Dated this the 17th day of September, 1990 F. R. KELLY & CO.