Aluminosilicates

Description

FIELD OF THE INVENTION:

[0001] This invention relates to aqueous suspensions of sodium aluminosilicates which are pumpable and stable, that is redispersable after standing. The aluminosilicates may be of the crystalline, that is zeolite e.g. of the A or X types, or amorphous varieties having cation exchange properties. The term amorphous is used herein to define materials which provide amorphous spectra when subjected to x-ray examination. The stabilised aluminosilicates are usable as detergency builders and the aqueous suspensions can be used as a feedstock in the preparation of detergent compositions, especially particulate compositions. Aluminosilicates are also of value in catalytic materials for treating petroleum feedstocks.

BACKGROUND OF THE INVENTION:

[0002] Aluminosilicate suspensions having a concentration of about 10% to about 60% by weight are manufactured in bulk for use as detergency builders. However these suspensions, being slurries of extremely fine particles, usually from about 0.5 to about 10 microns, are not always stable during storage. Frequently, without treatment, the suspended particles sediment to form a hard cake on standing and considerable effort is required to redisperse it as a feedstock. Indeed the properties of the sedimented cake in commercial quantities will sometimes not be amenable to any treatment to recover the original suspension.

[0003] Therefore stabilisation by aggregation of the suspended particles is necessary to ensure the slurry can be transported in commercial quantities and remain standing for a considerable period while still being pumpable or redispersible.

GENERAL DESCRIPTION OF THE INVENTION:

[0004] The invention proposes the use of an effective amount of a water soluble cationic surfactant containing one long chain (C12 to C18) substantially saturated hydrocarbon group to provide stabilisation for an aqueous suspension of sodium aluminosilicate having cation exchange capacity of at least 150 mg/g as calcium oxide containing from about 10% to about 60% by weight in hydrated form, preferably from about 30% to about 50%, of the aluminosilicate.

[0005] The presence of the cationic surfactant is believed to induce an aggregation of the suspended particles which hinders the formation of a hard cake on storage. The surface charge of the suspended aluminosilicate is negative under normal conditions and the small amount of cationic surfactant added adsorbs on the particle surfaces and reduces the negative charge. Ideally the nett surface charge should be reduced to zero for maximum aggregation but an approximation to this point is usually sufficient for stabilisation at a practical level.

[0006] The cationic surfactant is present at low levels but the amount utilised should be related to the amount of accessible surface area of the suspended aluminosilicate particles. This ensures the optimum level for stabilisation is approximated. A preferred level of cationic surfactant is from about 0.001% to about 0.5% by weight of the total suspension.

[0007] The cationic surfactant is required to contain one substantially saturated C12 to C18 hydrocarbon group and usually this will be an alkyl group which may be branched or straight chain with the latter being preferred. The hydrocarbon group may include an aromatic ring which, because of its stabilisation, is regarded as saturated for the purposes of this definition.

[0008] Examples of cationic surfactants usable in the invention are dodecyl trimethyl ammonium bromide and the tetradecyl, hexadecyl and octadecyl homologues. The compatible anion may be bromide or chloride with the latter being preferred because of its higher water solubility. Other examples are para dodecylbenzene triethyl ammonium chloride, in which the hydrocarbon group has 18 carbon atoms and tetradecyl pyridinium chloride which has a hydrocarbon group containing 14 carbon atoms with the pyridinium carbon atoms being associated with the quaternary nitrogen atom.

[0009] The aluminosilicate may be of the zeolite type, for example prepared as described in US 2882243 (Union Carbide), or the amorphous type, for example prepared as described in EP 0097512 (Unilever) or mixtures thereof. There is no criticality in the type of aluminosilicate or method of preparation in the application of the present invention. Preferably the amorphous aluminosilicate has the general formula:
0.8 to 1.5 Na₂O;Al₂O₃; 2.0 to 3.0SiO₂.3 to 6 H₂O

[0010] The amorphous aluminosilicates and zeolites may contain from 5% to 30% of structurally bound water in their hydrated form.

[0011] The aluminosilicate suspension will usually have a pH in the range from about 10 to about 12 to ensure the optimum cation exchange capacity required to provide detergency building properties is obtained.

[0012] Preferably the cationic surfactant has the formula:

R₁R₂R₃R₄ NX

wherein R₁ is the one long chain (C12 to C18) substantially saturated hydrocarbon group, N is a quaternary nitrogen atom, R₂ R₃ and R₄ are each C1 to C4 alkyl groups, or form together with the nitrogen atom a pyridinium ring and X is a compatible anion.

[0013] Surfactants within this definition are quoted in "Cationic Surfactants", ED Jungermann published by Marcel Dekker 1970.

[0014] Normally the average particle size of the aluminosilicate is in the range from about 0.5 to about 10 microns, preferably 0.5 to 6.0 microns, measured by a Micromeritics Sedigraph No 5000D

[0015] The invention extends to a process for preparing a suspension according to the invention wherein a sodium aluminosilicate formed by reaction of sources for alumina, silica and soda is washed to remove electrolyte and then formed into a suspension in the presence of the cationic surfactant using a high speed disperser of the type supplied by Baker Perkins or Greaves and a process for the preparation of a particulate detergent wherein a suspension according to the invention is mixed with the other components and subjected to a procedure for removing water from the mixture, preferably spray drying.

LITERATURE

[0016] Japanese Kokai 58172225 (Lion Corporation) describes the use of a slightly water soluble cationic surfactant to stabilise zeolite suspensions containing 40 to 50% by weight of fine zeolite. The surfactants described by Lion are required to have two alkyl groups having carbon numbers in the range C8 to C22, in distinction the present invention is directed to more soluble cationic surfactants. The use of more soluble surfactants allows a more rapid dispersion of the surfactant in the preparation of the aluminosilicate slurry. The specific examples quoted by Lion are known as fabric softening agents and thus in general these materials are not desirable in fabric washing compositions.

[0017] EP 0194116 (Unilever) describes a redispersable silica dispersion containing cationic surfactants having one or two long chain alkyl groups to provide a stable suspension. However, in this silica dispersion the particle size range and pH are selected to ensure only the minimal amounts of surfactant to stabilise the dispersion are present.

[0018] GB 1483610 (Henkel) describes the formation of aluminosilicates in the presence of surfactants to obtain products in which the surfactant is included within the aluminosilicate structure.

[0019] There are a number of disclosures which relate to stabilisation of aluminosilicate suspensions using nonionic surfactants, for example EP 0088866 (Degussa) describes the use of alkyl phenol ethoxylate derivatives having high and low cloud points whereas GB 2 015 488 (Unilever) discloses the use of high cloud point nonionics. GB 2048841 (Montedison) describes the use of an acrylamide polymer to stabilise zeolite suspensions.

SPECIFIC DESCRIPTION OF INVENTION:

[0020] Examples to illustrate but not limit the invention will now be given.

Example 1

[0021] The stabilisation of aluminosilicates, crystalline and amorphous, was demonstrated using cetyl trimethyl ammonium bromide (CTAB) as the cationic surfactant. The crystalline material, a 4A zeolite, was supplied by Degussa AG under the Trade Name Wessalith P and the average particle size was 4 micron. The amorphous material in the filter cake form had a solids concentration of 46% by weight and a pH of 11 as a 5% slurry and an average particle size of 12 micron. This particle size is reduced to below 10 micron by further processing for example by passing through a vibrating ball mill.

[0022] The aluminosilicate samples had been washed with deionised water to reduce the level of electrolyte to the required level.

[0023] 0.01 to 4cc of a 0.5% by weight CTAB solution (obtainable from BDH Chemicals of Poole England) were added to l0cc aliquots of the zeolite suspension in l0cc measuring cylinders. The dispersions were mixed and allowed to stand for 65 hours. The sediment volumes, as a percentage of tne total aqueous volume, and ease of redispersion, by rotation of the cylinders, were measured. The sediment volumes by percentage and volume are given in Table I with the CTAB concentrations together with the ease of redispersion

TABLE I

CTAB concentration % w/v	Sediment volume percentage	cm³	Ease of redispersion
none	64	6.4	very difficult
5.10⁻⁴	66	6.6	"
1.5.10⁻³	68	6.8	"
2.5.10⁻³	72	7.2	"
3.5.10⁻³	77	7.8	"
5.10⁻³	98	9.9	readily dispersible
9.8.10⁻³	100	10.2	"
**
1.1.10⁻¹	100	12.8	"
1.3.10⁻¹	79	10.7	difficult
1.4.10⁻¹	49	6.9	very difficult

** concentrations of CTAB in this range gave satisfactory redispersion.

[0024] These results demonstrate the suspension is completely stabilised over a range of CTAB conditions; at the highest concentrations stability reduces as CTAB is absorbed to a level which gives a nett positive charge. Similar results were achieved with the amorphous material.

Example II

[0025] A 36% w/w slurry of amorphous aluminosilicate with an average particle size of 5 micron was prepared by dispersing a 48% solids filter cake together with 0.02% w/w cetyl trimethyl ammonium chloride in water using a Baker Perkins high speed disperser and then passing the resultant dispersion to a vibrating ball mill. The aluminosilicate had been prepared by the method of EP 0097512. The suspension remained stable over three weeks whereas a control suspension with no cationic surfactant had settled within two days to a shear thickening sediment which was extremely difficult to redisperse.

Example III

[0026] A series of cationic surfactants were screened for their ability to stabilise a suspension of the zeolite used in Example I. A 10cm³ aliquot of a 40% w/w aluminosilicate suspension was placed in a standard 10cm³ measuring cylinder and tritrated against cationic solutions at a known concentration (ca 0.5%). After addition of each drop (ca 0.01 cm³) the contents of the tube were mixed by rotating the tube end over end for 15 rotations over a period of 30 seconds. The end point was the volume which provided gelling of tne suspension so the contents would not flow on inversion. The volumes are give in Table 2.

Table 2

Surfactant	wt of cationic to gell (mg)
Dodecyl trimethyl ammonium bromide	3.6
Tetradecyl trimethyl ammonium bromide	0.9
Cetyl trimethyl ammonium bromide	0.5
Hexadecyl trimethyl ammonium chloride (obtainable under the trade name Arquad 16 from Armour Hess	0.6
Octadecyl trimethyl ammonium chloride	0.4
Stearyl trimethyl ammonium chloride (obtainable under the trade name Arquad 18-55 from Armour Hess)	0.5
P-dodecyl benzene triethyl ammonium chloride (obtainable under the trade name Loraquat B41)	1.4
Tetradecyl pyridinium bromide	0.9

[0027] These results demonstrate these cationics are capable of stabilising the suspensions although in practise the levels of surfactant used would be considerably lower than the values quoted in Table 2.

Claims

1. A pumpable stable aqueous suspension of sodium aluminosilicate having cation exchange capacity of at least 150 mg/g as calcium oxide containing from about 10% to about 60% by weight of the aluminosilicate in hydrated form and a stabilising effective amount of a water soluble cationic surfactant containing one long chain (C12 to C18) substantially saturated hydrocarbon group.

2. An aqueous suspension according to claim 1 wherein the amount of cationic surfactant is from about 0.001% to about 0.5% by weight of the total suspension.

3. An aqueous suspension as claimed in Claim 1 or 2 wherein the aluminosilicate is a zeolite A or X, or an amorphous aluminosilicate with the general formula:

0.8 to 1.5 Na₂O;Al₂O₃; 2.0 to 3.0SiO₂ 3 to 6 H₂O; or mixtures thereof.

4. An aqueous suspension according to any preceding claim wherein the pH of the suspension is in the range from about 10 to about 12.

5. An aqueous suspension according to any preceding claim containing aluminosilicate in the range from about 30% to about 50%.

6. An aqueous suspension according to any preceding claim wherein the cationic surfactant has the formula:

R₁R₂R₃R₄ NX

wherein R₁ is the one long chain (C12 to C18) substantially saturated hydrocarbon group, N is a quaternary nitrogen atom, R₂ R₃ and R₄ are each C1 to C4 alkyl groups, or form together with the nitrogen atom a pyridinium ring and X is a compatible anion.

7. An aqueous suspension as claimed in any preceding claim wherein the average particle size of the aluminosilicate is in the range from about 0.5 to about 10 microns, preferably 0.5 to 6.0 microns.

8. A process for preparing a suspension according to claim 1 wherein a sodium aluminosilicate formed by reaction of sources for alumina, silica and soda is washed to remove electrolyte and then formed into a suspension preferably using a high speed dispenser in the presence of the cationic surfactant.

9. A process for the preparation of a particulate detergent wherein a suspension according to any of claims 1 to 7 is mixed with the other components and subjected to a procedure for removing water from the mixture, preferably spray drying.

10. The use of a water soluble cationic surfactant containing one long chain (C12 to C18) substantially saturated hydrocarbon group to stabilise a pumpable aqueous suspension of sodium aluminosilicate having cation exchange capacity.