GB2048841A

GB2048841A - Suspensions of zeolites

Info

Publication number: GB2048841A
Application number: GB8013923A
Authority: GB
Original assignee: Montedison SpA
Current assignee: Montedison SpA
Priority date: 1979-05-02
Filing date: 1980-04-28
Publication date: 1980-12-17
Also published as: IT7922294A0; FR2455479A1; IT1112790B; DE3016433A1; GB2048841B

Abstract

Stable suspension of zeolites in water having good rheological properties are characterized by the presence of a stabilizer selected from the polyacrylamides and the copolymers of the formula: <IMAGE> wherein Z is H or Na, X is at least 4.7, and n is high enough for the molecular weight to be from 7.5 x 10<6> to 12 x 10<6>.

Description

SPECIFICATION Stable aqueous suspensions of zeolites The invention relates to stable suspensions of zeolites in water, and to spray-dried products obtained therefrom.

It is known from German patent 2,615,698 that by dissolving an acrylic acid polymer in water and adding a zeolite, it is possible to obtain stable suspensions, storable without risk of sedimentation and having a viscosity low enough for easy pumping, even after long storage. The patent also discloses that it is possible to use copolymers of acrylic acid with acrylamide, and that it is necessary to employ a coadjuvant agent (not being a surfactant) such as a phosphatic builder if stable suspensions are required with a high zeolite content and with good rheological properties, suitable for preparing detergentformulated compositions by spray-drying.

An object of the invention is to prepare stable, mobile aqueous suspensions of zeolites, without the need for any coadjuvant agent. Other objects will appear from the description hereinbelow.

The invention consists, in one aspect, in an aqueous suspension of a zeolite containing from 0.05% to 0.20% by weight of a polymeric acrylamide stabilizer of the (average) formula:

wherein Z is H or Na, X is at least 4.7, and n, with X, is high enough to afford a molecular weight of 7,500,000 to 12,000,000.

Although the foregoing formula exhibits an acrylic acid or sodium acrylate unit it will be understood that X may be e.g. 100,000 or more, within the permitted ranges of X and n, the stabilizer then being for practical purposes an acrylamide homopolymer.

It will also be understood that X is in general an average figure with respect to each molecule, as well as for the total material. That is to say, in the copolymer the acid or acid salt units are not required to be exactly regularly spaced along the chain. In the case of a copolymer sodium salt it is not required that every acrylic acid unit be in salt form, i.e. some Z may be Na and some H, although in the suspensions according to the invention, the pH will generally be well above 7.

It has surprisingly been found that by using these high mwt polyacrylamides, or copolymers in which acrylamide preponderates over acrylic acid, the resulting suspensions are more stable and less viscous, even if the amount of stabilizer is lower than hitherto adopted for a polyacrylic stabilizer; furthermore there is no need of phosphatic or of other kind of coadjuvant agent.

The suspension according to the invention may also contain up to 70% by weight of zeolite 4A, of the general formula: Na2O.Ai203.2SiO2.4-5H2O corresponding to 56% by weight of the an hydros zeolite.

The presence of the stabilizer, according to the invention allows easy adjustment of the viscosity of the suspensions and, by consequence, of their rheological characteristics during storage, pumping and spraying; generally the viscosity of the suspensions according to the invention ranges from 200 to 3,500 and preferably from 500 to 2,000 centipoise. Due to their high stability, the suspensions can be stored and transported by conventional tank cars, without formation of deposits which are difficult to redisperse.

The suspensions can advantageously be used to obtain, suitably by spraying-drying, products of general application in water softening and in particular for detergent-formulated compositions. The invention accordingly also consists in a zeolitic powder containing a surfactant and a minor proportion of suspension stabilizer of the foregoing formula, obtained from an aqueous suspension thereof by drying, suitably by spray-drying. Further, the invention consists in detergent compositions containing such zeolitic powder.

The suspensions according to the invention can be prepared in several ways. For example, it is possible first to add the stabilizer to the water and then to add the zeolite; or it is possible to synthesize the zeolite as an aqueous suspension, starting from aqueous solutions of sodium aluminate and sodium silicate, as described, for example, in French patent 80/01283, and then to add the stabilizer directly to the zeolite in the wet state as it comes from the centrifuge (from which, otherwise, it would be sent to drying). If the amount of water is not sufficient, make-up water can be added at this stage. By operating in this way, the disadvantages associated with the handling of dry powders are avoided.

The alkalinity of the suspensions -- generally varying from pH 11 to pH 13 - does not significantly affect their susceptibility to stabilization in aqueous suspension.

The following Examples are given to illustrate the present invention, without however limiting the wider scope thereof; in particular it niay be noted that, although the Examples illustrate only the use of zeolites of type 4A, the invention is successfully applicable also to other types of zeolites and in particular to mixtures of zeolites of types 4A and X, which are well known to those skilled in the art. The particular size of the zeolites should desirably be lower than 100 pm, preferably lower than 30 and, still more preferably, lower than 15 m.

EXAMPLES 1-23 The stabilizer was dissolved, at room temperature, in deionized water, and a sample of zeolite was added, whilst stirring and at room temperature; the suspension so obtained, having a pH value of from 11 to 12, was kept stirred until thorough homogenization was attained. Then it was allowed to sediment at a temperature from 20 to 250C in a cylindrical vessel, having a diameter of about 3 cm and filled up to a height of 120 mm. Finally the stability of the suspension was determined by the formula: S = (H-h)/ H x 100, wherein S is the empirical % degree of stability, H is the total height of the suspension in the vessel (120 mm), and h is the height of the decanted layer of sediment at the conclusion of the test; when h = 0, the maximum of stability is achieved (S = 100%).In the various tests, different types of zeolite 4A, obtained according to the method described in French patent 80/01283, were employed. The characteristics of the zeolites employed were as follows: Zeolite A/I Formula: Na2O.Al2O3.2SiO2.4.5H2O; crystallinity: 100% (determined in a X-ray apparatus).

Exchange power: 1 72 mg of CaO per gram of anhydrous zeolite (i.e. without crystallization H2O; determination carried out according to the method described in French Patent 80/01283, which comprises intense stirring of a zeolite suspension in a CaCI2 solution for 15 minutes at 22 + 20C).

Granulometry (Coulter Counter Analysis): Size of the Amount of the Particles Particles (%) Size Amount % > 15 ym 1.0 > 6Atm 6.5 > 10 ,stm 2.0 > 4 m 35.0 > 8 ,ttm 3.0 > 2 m 97.0 Zeolite A/II Formula and crystallinity: as for Zeolite A/I; exchange power: 173.5 mg of CaO/g of anhydrous zeolite.

Granulometry: Size Amount (%) Size Amount (%) > 15,um 1 > 6 m 5 > 10Atm 2 > 4Atm 32 > 8 ,um 3 > 2,um 85 The stabilizers used were the following Montedison products, commercially known as "ECOCLAR", all of the foregoing formula: E2: molecular weight from 7.5 x 106 to 8 x 105; X ranging from 4.7 to 9; E4: molecular weight from 8 xl 06 to 8.5 x 106; X ranging from 7 to 1 9; E: molecular weight from 10.5 x 106 to 11 x 106; X ranging from 9 to a very high level, practically corresponding to the homopoiymer.

Data and results are set out in Table I together with the corresponding figures for a control, run in the same way but without stabilizer. The viscosities of the suspensions were determined by means of a rotary BROOKFIELD viscosimeter, at 250C, with a rota meter speed of 50 rpm.

TABLE 1

Final stability Initial Stabi lizer Zeolite Deionized viscosity Of (H-h) water suspension - x 100 Examples Type 9 Type 9 (grams) (centipoise) Test time H absent - A/I 60 40 50 5 days 75 %(*) 1 E7 0.20 " 60 " 480 11 days 100 % 2 E 2 0.25 A/II 55 45 1480 10- days 100 % 3 E 2 0.25 ,, 55 45 1480 12 days 99.5% 4 E 2 0.15 ,, 60 40 640 1 day 100 % 5 E 2 0.15 ,, 60 40 640 12 days 97.5% 6 E 2 0.20 ,, 60 40 1200 7 days 100 % 7 E 2 0.20 ,, 60 40 1200 12 days 98.5% 8 E 2 0.25 ,, 60 40 2400 12 days 100 % 9 E 4 0.20 ,, 60 40 560 1 day 100 % 10 E 4 0.20 ,, 60 40 560 6 days 98.5% 11 E 4 0.25 ,, 60 40 880 4 ,, 100 % 12 E 4 0.25 ,, 60 40 880 12 ,, 98.5% 13 E 2 0.20 A/II 65 35 1500 7 days 100 % 14 E 2 0.20 ,, 65 35 1500 12 ,, 98.5% 15 E 2 0.20 ,, 65 35 1500 21 ,, 96 % 16 E 2 0.20 ,, 67 33 3080 12 ,, 100 % 17 E 2 0.05 ,, 69 31 320 3 ,, 98.5% 18 E 2 0.10 ,, 69 31 640 3 ,, 99.5% 19 E 2 0.10 ,, 69 31 640 7 ,, 98.5% 20 E 2 0.15 ,, 69 31 1200 2 ,, 100 % 21 E 2 0.15 ,, 69 31 1200 5 ,, 99.5% 22 E 2 0.15 ,, 69 31 1200 8 ,, 98.5% 23 E 2 0.20 ,, 69 31 3200 12 ,, 100 % (*) The sedimentation layer appears as a consistent mass, absolutely not transferable by normal pumping methods.

EXAMPLE 24 to 27 Tests were carried out with a critical variant in respect of the preceding Examples: instead of adding the zeolite to the water plus stabilizer, the zeolite was first dispersed in deionized water, whilst stirring, and successively, with continued stirring, the predetermined amount of stabilizer was added.

The favourable results so obtained, which are set out in Table 2, suggest the possibility of using the wet mass of zeolite coming from the production plants, so avoiding a drying operation. The appropriateness of such procedure is confirmed by the subsequent Examples (28 to 34). In the present Examples (24 to 27) two types of zeolite were used, namely zeolite A/II of the preceding Examples and a new zeolite A/III, having the same formula and crystallinity of zeolite A/II, an exchange power of 176 mg of CaO/g of anhydrous zeolite and the following granulometry:: Size Size Amount (%) Size Amount (%) > 15ym 0 > 6um 10.0 > 10,um 1.5 > 4ym 65.0 > 8,um 2.5 > 2 ym 98.5 TABLE II

Final stability Initial Stabllizer Zeolite Deionized viscosity of (H-h) water suspension - x 100 Examples Type g Type g (grams) (centipolse) Test time H 24 E 2 0.20 A/II 65 35 1700 12 days 100 % 25 E2 0.20 A/lI 65 35 1700 34 " 97 % 26 E 2 2(*) A/III 620 380 1200 12 ,, 100 % 27 E Z 2 (*) A/Ill 620 380 1200 30 .. 97.5 (*) equivalent to 0.20 % by weight.

EXAMPLES 28 to 34.

As source material use was made of 20 kg of an aqueous dispersion of zeolite Allll (as in Examples 26 and 27) having a pH of 11.5 and procured directly from the zeolite synthesis plants, without having been subjected to any drying operation; this dispersion contained about 46% by weight of water (including the crystallization water of the zeolite) and 54% by weight of anhydrous zeolite (residue after calcination at 8000 C). 40 grams of stabilizer in powder form (0.20% by weight referred to the suspension) were added whilst stirring, the suspension was homogenized and the stability was evaluated after a long dwell; the results are as follows: Final Stability initial Viscosity (H-h) of Suspension - x 100 Ex. No. Stabilizer (Centipoose) Test Time H 28 E 2 1200 1 day 100 % 29 E 2 1200 5 days 99.5 % 30 E 2 1200 8 days 98.5 % 31 E 2 1200 12 days 98.5 % 32 E 7 240 3 days 99.5 % 33 E 7 240 6 days 98.5 % 34 E7 240 12 days 94 % EXAMPLES 35 to 41 Examples 28 to 34 were repeated, whilst causing the suspension containing the stabilizer (E2) to sediment at different temperatures for different times, thus obtaining the following results: (H-h) - x 100 Examples Temperature Test Time H 35 39 C 3 days 100 % 36 39 C 3 days 99.5 % 37 39 C 12 days 98.5 % 38 39 C 30 days 97.5 % 39 8 C 3 days 100 % 40 89C 5 days 99 5 % 41 8 C 12 days 98.5 %

Claims

CLAIMS 1. An aqueous suspension of a zeolite characterized by the presence of a suspension stabilizer of the average formula:

wherein Z is H or Na, X is at least 4.7 and wherein n and X correspond to a molecular weight of 7.5 x 106 to 12 x 106.
2. A suspension according to claim 1, in which the amount of stabilizer is from 0.05% to 0.20% by weight, referred to the weight of the suspension.
3. A suspension according to claim 1 or 2, in which the amount of zeolite, calculated as the anhydrous form, is from 30 to 56% by weight referred to the weight of the suspension.
4. A suspension according to claim 3, wherein the amount of zeolite as aforesaid is 48 to 54%.
5. A suspension according to any of the foregoing claims having a viscosity of from 200 to 3500 centipoises.
6. A suspension according to claim 5 in which the viscosity is 500 to 2000 centipoises.
7. A suspension according to any of the foregoing claims having an alkalinity of from pH 11 to pH 13.
8. A suspension according to any of the foregoing claims in which the zeolite is of type 4A.
9. A suspension according to any of the foregoing claims 1 to 7, in which the zeolite is a mixture of type 4A and of type X.
10. An aqueous suspension according to claim 1, substantially as described in any of the foregoing Examples.
11. A zeolitic powder obtained by drying a suspension according to any of the foregoing claims.

1 2. A detergent composition comprising a surfactant and a minor proportion of a zeolitic powder according to claim 11.