Alumino-silicate derivatives

Details Alumino-silicate derivatives Alumino-silicate derivatives

1997-04-14

2001-03-13

Dunn, Tom (Department: 1754)

Catalyst, solid sorbent, or support therefor: product or process

Zeolite or clay, including gallium analogs

Clay

C502S060000, C502S086000, C502S064000, C502S080000, C502S085000, C501S141000, C423S328100

Reexamination Certificate

active

06200919

ABSTRACT:

FIELD OF THE INVENTION
THIS INVENTION relates to the formation of new materials in the form of alumino-silicate derivatives from 2:1 clay minerals as hereinafter described and processes to form these new materials which are obtained by the chemical modification of 2:1 clay minerals.
The derivatives of these layer minerals are characterised by a predominance of tetrahedrally-coordinated Al
+3
which has resulted from the chemical modification of octahedrally-coordinated Al
+3
in the parent mineral. This atomic-scale transformation makes available a higher number of exchangeable sites than would be normally available in the original clay structure.
BACKGROUND OF THE INVENTION
Two features of the new materials which may result from the chemical modification of these 2:1 clay minerals are an enhanced capacity to exchange cations from solution (i.e. a cation exchange capacity) and/or an increase in the available surface area when compared with the properties of the initial starting mineral. These two features are of considerable significance to the cost-effective use of these derivative materials in a wide range of applications for cation-exchange (e.g. for removal of toxic metal ions from aqueous and non-aqueous solutions; removal of NH
4
+
from aqueous and non-aqueous solutions, as detergent builders and as water softeners), absorption (e.g. for the removal of gases from the environment, for absorption of cations from solutions), as agents for the controlled release of desired cations into an environment and as substrates for catalysis reactions in the modification of hydrocarbons and other chemicals.
Clay minerals are part of the larger family of minerals called phyllosilicates—or “layer” silicates. These clay minerals are typically characterised by two-dimensional arrangements of tetrahedral and octahedral sheets, each with specific elemental compositions and crystallographic relationships which define the mineral group. Thus, the tetrahedral sheet may have the composition T
2
O
5
(where T, the tetrahedral cation, is Si, Al and/or Fe) and the octahedral sheet may commonly contain cations such as Mg, Al and Fe, but may also contain other elements such as Li, Ti, V, Cr, Mn, Co, Ni, Cu and Zn (Brindley and Brown, Crystal Structures of Clay Minerals and their x-ray identification, Editors G. W. Brindley and G. Brown, Mineralogical Society, London, 1980). Each of these clay mineral groups can be further classified into trioctahedral and dioctahedral varieties, depending on the occupancy of the octahedra in the respective sheet arrangement(s). Some specific mineral species may show cation occupancies which are intermediate between the two varieties. Nevertheless, the relative arrangement of these tetrahedral and octahedral sheets also defines the basic mineral groups in that an assemblage which links one tetrahedral sheet with an octahedral sheet is known as a 1:1 type mineral. An assemblage which links two tetrahedral sheets with one octahedral sheet is known as a 2:1 mineral. This basic classification of mineral species, based upon the crystallographic relationships of specific sub-units, is well-known to those skilled in the art of clay mineralogy and forms a basis for description of this invention.
The production of an amorphous derivative, termed “kaolin amorphous derivative” (KAD), from kaolin clays which are 1:1 alumino-silicates, has been described in an earlier disclosure (WO95/00441). We have now surprisingly found that an amorphous derivative can also be manufactured from 2:1 clays which include montmorillonites and other members of the smectite group. The production of an amorphous derivative from these 2:1 clays is surprising insofar as the structure and chemistry of these minerals is markedly different to that of the 1:1 kaolin group minerals. A unit layer of the clays in the kaolin group consists of one octahedral sheet and one tetrahedral sheet so that both sheets are exposed to the interlayer space, a region which is accessible to reacting species. However, a 2:1 clay mineral comprises one octahedral sheet and two tetrahedral sheets. The octahedral sheet, which contains octahedrally coordinated aluminium, is sandwiched between the tetrahedral sheets. The transformation of this octahedral sheet is not readily predictable using metal halides since the interlayer space is surrounded by tetrahedral sheets. It is also relevant to point out that the octahedral sheet in 2:1 clay minerals would not be readily accessible to metal halides. It would be assumed by those skilled in the art that reacting species with 2:1 clay minerals would provide different products to reaction products described in WO95/00441 for these reasons.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide the abovementioned modified 2:1 clay minerals possessing the two features discussed above.
In one aspect, the invention provides modified 2:1 clay minerals by a process using a metal halide which may react with a 2:1 clay mineral or combination of 2:1 clay minerals to provide a modified 2:1 clay mineral which includes the two features described above.
Examples of 2:1 clay minerals which may be modified by the process(es) of the invention include montmorillonite, illite, palygorskite and saponite. The 2:1 layer clay mineral derivatives of the invention are characterised by predominant tetrahedral Al
+3
and for the sake of convenience, are hereinafter termed “alumino-silicate derivatives” or “ASDs”. In the case of, e.g. montmorillonite clays, the octahedral Al within the parent (i.e. clay) has been transformed to tetrahedral co-ordination. Further elucidation of this ASD, henceforth designated M-ASD, where M is the exchanged cation obtained by the specific formation process, can be obtained by conventional mineral characterisation techniques which demonstrate the following properties:
(1) an “amorphous” nature (to X-ray diffraction), i.e. without any apparent long range order of the repeat units;
(2) an enhanced capacity to exchange cations (compared with the original starting mineral) from solution;
(3) an increase in the available surface area of the material (compared with the original starting mineral) as measured by the conventional BET isotherm;
(4) an enhanced capacity compared to the original starting material to adsorb anionic species or complex polyanions from solution; and/or
(5) an enhanced capacity compared with the original starting material to absorb oil and/or organic molecules.
In relation to property (2), this may be exemplified by the ASDs of the invention having a cation exchange capacity of 20-900 milli-equivalents per 100 g as measured by exchange of ammonium or metal cations from an aqueous solution. Most preferably the cation exchange capacity as measured by exchange of ammonium is between about 300-450 milli-equivalents per 100 g.
In relation to property (3), this may be exemplified by the ASDs of the invention having a surface area less than 400 m
2
/g as measured by the BET isotherm which is higher than the 2:1 clay mineral starting material. Most preferably the BET surface area is between 25 m
2
/g and 200 m
2
/g.
Properties (4) and (5) are demonstrated in International Application No PCT/AU95/00699 having the same international filing date as the present application.


REFERENCES:
patent: 3140251 (1964-07-01), Plank et al.
patent: 3976598 (1976-08-01), Daviditz
patent: 4271043 (1981-06-01), Vaughan et al.
patent: 917630 (1972-12-01), None
patent: 499887 (1976-03-01), None
patent: WO 95/00441 (1995-01-01), None
“Data Handbook for Clay Materials and Other Non-Metallic Minerals,” H. van Olphen, Ed., Pergamon Press, pp. 19 & 22 (1979).
M. H. Battey, “Mineralogy for Students,” Department of Geology, Univ. of Newcastle upon Tyne, Longman, Publ. P. 237 (Year Unknown).

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