IE910486A1

IE910486A1 - Spherical granules of hydrated alkali metal silicates,¹process for preparing them and their application in¹detergent compositions

Info

Publication number: IE910486A1
Application number: IE048691A
Authority: IE
Original assignee: Rhone Poulenc Chimie
Priority date: 1990-02-16
Filing date: 1991-02-13
Publication date: 1991-09-11
Also published as: EP0450989A1; NO910590L; NO910590D0; FR2658497B1; FI910742A; FR2658497A1; FI92577B; PT96794B; FI910742A0; PT96794A

Abstract

Process for the preparation of granules of alkali metal hydrated silicates by spraying water or an aqueous solution of alkali metal silicates onto a moving bed of particles of alkali metal hydrated silicates travelling as a thin layer in a rotating plate-type device left at room temperature, optionally densification of the granules obtained and then drying. Use of the granules obtained in detergent compositions or in water treatment.

Description

SPHERICAL GRANULES OF HYDRATED ALKALI METAL SILICATES, PROCESS FOR PREPARING THEM AND THEIR APPLICATION IN DETERGENT COMPOSITIONS The present invention relates to spherical 5 granules of hydrated alkali metal silicates, their process of preparation and their application in detergent compositions, in particular for dishwashing or laundry, as well as for water treatment.

The Applicant has found spherical granules of hydrated alkali metal silicates which have a particle size and density which may be controlled as desired, show low abrasion and have a good flowability and a rapid rate of dissolution in water.

A first object of the present invention comprises a process for preparing spherical granules of hydrated alkali metal silicates by granulation of particles of hydrated alkali metal silicates by spraying water or an aqueous solution of alkali metal silicates on a rolling bed of the said particles, and then drying, the said process being characterised in that: - the spraying operation is conducted on particles moving in a thin layer at ambient temperature in a rotary device of the turning plate type, the axis of rotation of which is inclined relative to the horizontal by an angle of more than 20°, preferably of more than 40, the speed of movement of the particles, the thickness of the thin layer of moving particles and the flow rate of the sprayed water or solution being such that each particle is converted to a malleable granule on coming into contact with the other particles, and - the operation of granulation by spraying is followed, if appropriate, by a densification operation at ambient temperature, which latter operation is carried out before drying.

Amongst the alkali metal silicates, those which may be mentioned are those of the metals of group Ia of the periodic classification and very particularly those of sodium and potassium.

The sprayed aqueous silicate solution may have a concentration of the order of 0 to 55 % by weight, preferably of 30 to 45 % by weight, of an alkali metal silicate having an SiO2/M2O molar ratio which can range from 1.6/1 to 5/1, generally of the order of 1.8/1 to 3.5/1 and very particularly close to 2/1.

The spraying of water or the silicate solution is carried out at a temperature of the order of 20 to 95’C, preferably of the order of 70 to 95eC; the latter may be promoted by the conjoint introduction (for example using a two-fluid nozzle) of air under pressure at a temperature of the same order.

The amount of water or of solution to be sprayed corresponds to the ratio of the flow rate of liquid/flow rate of particles entering into the device of the turning plate type, which can range from 0.1 to 0.6 1/kg and preferably from 0.15 to 0.25 1/kg (per hour).

The particles of hydrated alkali metal silicate used to prepare the granules have: - an SiOj/l^O molar ratio of the order of 1.6/1 to 5/1, generally of the order of 1.8/1 to 3.5/1 and very particularly of the order of 2/1, - a water content of 15 to 30 % by weight, preferably of the order of 18 to 25 % by weight, and - a non-bulk density of the order of 0.3 to 1 g/cm3, preferably of the order of 0.4 to 0.8 g/cm3; % by weight of the said particles having a diameter smaller than 100 pm, preferably smaller than 55 pm.

These particles may be obtained by any known method, in particular by drying by atomisation of an aqueous solution of silicate having the same SiO2/M2O ratio, followed by grinding if necessary.

The device used to carry out the operation of granulation by spraying may be any rotary device of the turning plate type, in particular a dish, the geometry of which may be very diverse: truncated cone, flat, stepped, a combination of these three forms, etc. The particles of hydrated silicate move at ambient temperature (generally 15-30°C) in the said device, which is left at ambient temperature.

The flow rate of the sprayed water or solution, the speed of movement of the particles and the thickness of the layer of moving particles are such that each particle absorbs liquid and agglomerates to the other particles with which it comes into contact and it does so in a thin layer in order to obtain malleable granules and not a paste. The speed of movement of the particles and the thickness of the layer are controlled by the rate of introduction of the particles into the device and by the characteristics of the latter.

The residence time of the particles in the plate is generally of the order of 15 to 40 minutes.

It is within the scope of those skilled in the art to adapt the following characteristics of a dish: . geometry (truncated cone, flat, stepped or a combination of the three forms), . dimensions (depth, diameter), . angle of inclination, . speed of rotation, relative positions of the solid and liquid feeds, as a function of a given starting material, to the desired product.

The granules obtained before drying have characteristics which depend on the conditions employed for carrying out the granulation. They generally have: - an SiOa/MgO ratio of the order of 1.6/1 to 5/1, generally of the order of 1.8/1 to 3.5/1 and very particularly close to 2/1, and - a water content of the order of 20 to 35 % by weight, preferably of the order of 25 to 30 % by weight.

The granules are then dried by any known means. One method which performs particularly well is drying in a fluidised bed with the aid of a stream of air at a temperature (depending on the humidity of the latter) of the order of 50 to 150°C, preferably of 60 to 90°C. This operation is conducted for a period which depends on the humidity of the air, the water content of the granules at the outlet of the granulation device and the desired water content of the dried silicate granules, as well as the fluidisation conditions; those skilled in the art know how to adapt these various conditions to the desired product.

The dry granules generally have: - a water content of the order of 17 to 25 % by weight, preferably of the order of 18 to 23 % by weight, - a non-bulk density of the order of 0.3 to 1 g/cm3, preferably of the order of 0.4 to 0.8 g/cm3, and - a median diameter (in the sense of cumulative percentages passing) of the order of 0.2 to 3 mm, preferably of the order of 0.4 to 2.5 mm and very particularly of the order of 0.5 to 1 mm, with a log10 standard deviation of 0.02 to 0.2, preferably of 0.05 to 0.1.

According to a development of the said process, the granulation operation is followed by a densification operation, which is carried out before drying.

The said densification operation may be carried out at ambient temperature by rolling the granules obtained in the granulation step in a rotary device.

This device is preferably independent of the granulation device. This densification step may, for example, be effected by introduction of the granules into a rotary drum and residence of said granules in said drum. The dimensions of said drum, its speed of rotation and the residence time of the granules depend on the desired density of the granules; the residence time is generally of the order of 20 minutes to 3 hours, preferably of the order of 20 to 90 minutes. The granulation and densification operations may also be carried out in the same device, for example in a stepped dish, the densification of the granules being obtained by rolling the said granules on the final steps of the equipment.

The dense granules obtained are then dried, preferably in a fluidised bed as indicated above.

The dried dense granules have: - an SiOa/i^O ratio of the order of 1.6/1 to 5/1, generally of the order of 1.8/1 to 3.5/1 and very Ί particularly close to 2/1, - a water content of the order of 17 to 25 % by weight, preferably of the order of 18 to 23 % by weight, - a non-bulk density of the order of 0.6 to 1.2 g/cm3, preferably of the order of 0.8 to 1 g/cm3, and - a median diameter (in the sense of cumulative percentages passing) of the order of 0.2 to 3 mm, preferably of the order of 0.5 to 1 mm, with a log10 standard deviation of 0.02 to 0.2, preferably of 0.05 to 0.1.

The granulation/drying or granulation/ densification/drying steps according to the process of the invention enable dense hydrated alkali metal silicate granules to be obtained which dissolve rapidly in water. They are particularly suitable for use in making up detergent compositions (for dishwashing, washing linen etc.) and for water treatment.

A second object of the invention comprises hydrated sodium silicate granules which are particularly suitable for the preparation of a detergent composition for dishwashing.

The granules concerned are hydrated sodium silicate granules having the following characteristics: - an SiO2/Na2O molar ratio of the order of 1.8 to 2.4 and very particularly of the order of 2/1, - a water content of 18 to 23 % by weight, - a non-bulk density of the order of 0.8 to 1 g/cm3, - a median diameter of the order of 0.4 to 1.4 mm, preferably of the order of 0.5 to 1 mm, with a log10 standard deviation of 0.05 to 0.1, - a speed of dissolution in water of the order of minutes for 90 % dissolution and of the order of 4 minutes for 99 % dissolution, and - an abrasion resistance of the order of 1 to 6 %, generally of the order of 1 to 3 %.

The rate of dissolution in water for 90 % or 99 % dissolution is understood to be the time required to dissolve 90 % or 99 % of product to give a concentration of 35 g/1 in water at 20’C.

The abrasion resistance is measured by elutriation. The product to be tested is placed in a chamber through which a stream of air passes which fluidises the product. The grains are subjected to impacts, between themselves and on the walls. The fine particles created fly off and are recovered for weighing at the top of the equipment. (The details of the method are given in Example 1).

The hydrated sodium silicate granules of the invention are used in the detergent compositions for dishwashing in an amount of 20 to 60 % by weight, preferably of 30 to 50 % by weight of the said compositions.

The following examples are given by way of illustration and may not be regarded as restricting the scope and the spirit of the invention.

EXAMPLE 1 The granulation system consists of a flat 5 plate 800 mm in diameter and 100 mm deep. During granulation, the speed of rotation is of the order of 30 rpm and the inclination of the axis of rotation relative to the horizontal is of the order of 53°. The granulating plate is fed continuously at a rate of kg/h with a powder consisting of fine particles of sodium silicate (sprayed and ground), the main characteristics of which are as follows: - SiO2/Na2O ratio (by weight) = 2 - water content (by weight) = 18.2 % - non-bulk density = 0.45 g/cm3 - median diameter = 54 pm - 99 % (by weight) of the product dissolves in 180 s (35 g/1 aqueous solution at 20°C) - ambient temperature A sodium silicate solution is sprayed, with the aid of air at 80°C, at a rate of 5 1/h at a temperature of 80 °C through a two-fluid nozzle located 20 cm away from the bottom of the dish onto the said powder which is set in rotation in the granulating plate. The proportion of active substance and the SiO2/Na2O ratio of the sprayed solution are, respectively, 45 % (by weight) and 2 (by weight).

The mean residence time of a particle in the plate is about 15 min. The temperature of the particles leaving the plate is ambient temperature.

The granules thus obtained are dried in a 5 fluidised bed at a temperature of the order of 65 °C (temperature of the fluidisation air is 70°C) for 10 min.

The granulated product dried in this way has the following characteristics: - SiO2/Na2O ratio (by weight) = 2 - water content (by weight) = 22.2 % - non-bulk density = 0.58 g/cm3 - % by weight larger than 1 mm = 60 % - median diameter = 1.1 mm - % by weight passing 0.2 mm = 0 % - 99 % (by weight) of the product dissolves in 200 s (35 g/1 aqueous solution at 20eC) - abrasion resistance : 5.5 % The granules have excellent stability on storage.

Measurement of the abrasion resistance Equipment: The flourometer, a standardised apparatus used to qualify hydraulic binders and described in French standard P 15-443, is used.

Method: Sieve 50 g of product between 1200- and 180-micron sieves using a ROTO-LAB* laboratory screener (marketed by PROLABO).

Recover the fraction between 180 and 1200 microns.

Weigh precisely approximately 25 g of the product to be tested; this is M, the precise weight.

Place the weighed products in the flourometer.

Weigh an empty and dry Soxhlet*-type filter 10 (marketed by PROLABO) and place it in the upper part of the fluidisation tube; its weight is Ml.

Fluidise for 5 min. (flow rate of dry air : 1/min.).

Recover the product which has flown into the 15 filter and any fines deposited on the vertical walls of the fluidisation tube, using a brush of suitable diameter. Weigh; this is M2, the weight of these fines and the filter.

Sieve the residue in the bottom of the 20 fluidisation tube again on the ROTO LAB* and recover, for weighing, the fines smaller than 180 microns; this is M3, the weight of these fines.

Calculation. Expression of the results: The degree of abrasion is equal to the 25 percentage of fines < 180 microns formed during the fluidisation time of the product.

Abrasion % = (M3 + M2-Ml) x 100 M EXAMPLE 2 The granulation is carried out under the conditions described in Example 1. The granules leaving the plate are introduced, before drying, into a smooth5 walled turning tube 500 mm in diameter and 1300 mm in length. The outlet diaphragm is adjusted such that the average residence time of a particle is about 1.5 h.

The speed of rotation of the drum (15 rpm) is chosen so as to have a rolling bed of particles, which promotes the densification of the latter.

The densified granulated product resulting from this operation is dried under the conditions described in Example 1.

The final granules thus obtained have the 15 same characteristics as those in Example 1 except for the density, which in this case reaches a value of 0.83 g/cm3, and the abrasion resistance of 1.5 %.

EXAMPLE 3 Using a fine sodium silicate powder having 20 the same characteristics as that of Example 1 but having a higher density (0.55 g/cm3), the granules obtained by the preparation method described in Example 2 have a higher density of the order of 0.93 g/cm3, the other characteristics of the granules again remaining unchanged.

EXAMPLE 4 The influence of the quality of the spraying on the quality of the granules was studied using the starting material of Example 3. The fineness and the homogenisation of the spraying are improved by modifying the pressure of the air, used for spraying, in the nozzle.

The increase in the pressure of the air, used for spraying, makes it possible, for example, to reduce the particle size of the granules prepared under the conditions of Example 2 without modifying the other characteristics of the latter.

The results obtained using a Schlick type 932 nozzle are as follows: Air pressure (bar) % oversize at 1 mm Median diameter (mm) % passing at 0.2 mm EXAMPLE 5 0.4 1.1 0.8 .5 0.88 The aim of this experiment is to show that the process of the invention makes it possible, starting from particles which have a mediocre rate of dissolution in water, to obtain granules which have dissolution characteristics in water which are significantly improved compared with those of the said particles.

The preparation conditions used in Example 2 applied to a fine sodium silicate powder having the following characteristics: - SiO2/Na2O ratio (by weight) = 1.95 - water content (by weight) = 20.2 % - non-bulk density = 0.55 g/cra3 - median diameter = 54 pm - fairly mediocre rate of dissolution (99 % by weight of the product dissolves in 560 s 5 35 g/1 aqueous solution at 20°C) enabled dense granules to be obtained having a better rate of dissolution than the starting powder. The characteristics of the granules obtained are as follows: - water content (by weight) = 22.4 % - density = 0.83 g/cm3 - median diameter = 1 mm - 99 % by weight of the product dissolve in 370 s (35 g/1 aqueous solution at 20°C) - abrasion resistance = 2 % Granulation in a plate enables the average particle size of the particles to be increased and promotes the homogeneous diffusion of water within the grains.

This partly explains the improvement recorded in the rate of dissolution between the fine feed powder and the finished product of large particle size.

EXAMPLE 6 Under the preparation conditions described in Example 1, a reduction in the concentration of the sprayed solution enables the particle size of the granules to be controlled. The following results have been obtained: Solids content of the solution (% by weight) 35 % oversize at 1 mm 5 Median diameter (mm) 0.55 % passing at 0.2 mm 4 Water content (% by weight) 20 1.1 22.2 the other characteristics of the granules again remaining the same.

Claims

1. Process for preparing spherical granules of hydrated alkali metal silicates by granulation of particles of hydrated alkali metal silicates by 5 spraying water or an aqueous solution of alkali metal silicates on a rolling bed of the said particles, and then drying, the said process being characterised in that: - the spraying operation is conducted on particles 10 moving in a thin layer at ambient temperature in a rotary device of the turning plate type, the axis of rotation of which is inclined relative to the horizontal by an angle of more than 20°, the speed of movement of the particles, the thickness of the thin 15 layer of moving particles and the flow rate of the sprayed water or solution being such that each particle is converted to a malleable granule on coming into contact with the other particles, and - the operation of granulation by spraying is 20 followed, if appropriate, by a densification operation at ambient temperature, which latter operation is carried out before drying.

2. Process according to claim 1, characterised in that the sprayed aqueous silicate 25 solution has a concentration of the order of 0 to 55 % by weight of an alkali metal silicate having an SiC^/M^ molar ratio ranging from 1.6/1 to 5/1.

3. Process according to claim 2, .1, characterised in that the sprayed aqueous silicate solution has a concentration of the order of 30 to 45 % by weight of an alkali metal silicate having an SiOa/MaO molar ratio ranging from 1.8/1 to 3.5/1.

4. 5 4. Process according to claim 3, characterised in that the SiOj/^O molar ratio is close to 2/1. 5. Process according to any one of claims 1 to 4, characterised in that the spraying of water or 10 the silicate solution is carried out at a temperature of the order of 20 to 95 e C.

5. 6. Process according to claim 5, characterised in that the spraying of water or the silicate solution is carried out at a temperature of 15 the order of 70 to 95°C.

6. 7. Process according to any one of the preceding claims, characterised in that the amount of water or of solution to be sprayed corresponds to the ratio of the flow rate of liquid/flow rate of particles 20 entering into the device of the turning plate type, which can range from 0.1 to 0.6 1/kg.

7. 8. Process according to claim 7, characterised in that the amount of water or of solution to be sprayed corresponds to the ratio of the 25 flow rate of liquid/flow rate of particles entering into the device of the turning plate type, which can range from 0.15 to 0.25 1/kg.

8. 9. Process according to any one of the Λ. preceding claims, characterised in that the particles of hydrated alkali metal silicate used to prepare the granules have: - an SiO 2 /M 2 O molar ratio of the order of 1.6/1 to 5 5/1, - a water content of 15 to 30 % by weight, and - a non-bulk density of the order of 0.3 to 1 g/cm 3 , 50 % by weight of the said particles having a diameter smaller than 100 pm.

9. 10 10. Process according to claim 9, characterised in that the particles of hydrated alkali metal silicate used to prepare the granules have: - an Si0 2 /M 2 0 molar ratio of the order of 1.8/1 to 3.5/1, 15 - a water content of the order of 18 to 25 % by weight, and - a non-bulk density of the order of 0.4 to 0.8 g/cm 3 ; 50 % by weight of the said particles having a diameter smaller than 55 pm. 20

10. 11. Process according to claim 10, characterised in that the SiC^/MaO molar ratio is close to 2/1.

11. 12. Process according to any one of the preceding claims, characterised in that the residence 25 time of the particles in the granulation device is of the order of 15 to 40 minutes.

12. 13. Process according to any one of the preceding claims, characterised in that the granulation device of the turning plate type is a dish.

13. 14. Process according to any one of the preceding claims, characterised in that a densification operation is carried out at ambient temperature by 5 rolling the granules obtained in the granulation step in a rotary device.

14. 15. Process according to claim 14, characterised in that the densification operation is carried out in a rotary drum. 10

15. 16. Process according to claims 13 and 14, characterised in that the granulation operation is carried out in a stepped dish, the densification of the granules being obtained by rolling the said granules on the final steps of the equipment. 15

16. 17. Process according to any one of the preceding claims, characterised in that the granules obtained in the granulation or densification step are dried in a fluidised bed.

17. 18. Granules of hydrated alkali metal 20 silicates, characterised in that they have: - an SiOa/MjO ratio of the order of 1.6/1 to 5/1, - a water content of the order of 17 to 25 % by weight, 25 - a non-bulk density of the order of 0.6 to 1.2 g/cm 3 , and - a median diameter of the order of 0.2 to 3 mm, with a log 10 standard deviation of 0.02 to 0.2.

18. 19. Granules according to claim 18, characterised in that they have: - an SiO 2 /M 2 O ratio of the order of 1.8/1 to 3.5/1 and very particularly close to 2/1, - a water content of the order of 18 to 23 % by weight, - a non-bulk density of the order of 0.8 to 1 g/cm 3 , and - a median diameter of the order of 0.5 to 1 mm, with a log 10 standard deviation of 0.05 to 0.1.

19. 20. Granules of hydrated sodium silicate, characterised in that they have: - an SiO 2 /Na 2 O molar ratio of the order of 1.8 to 2.4 and very particularly of the order of 2/1, - a water content of 18 to 23 % by weight, - a non-bulk density of the order of 0.8 to 1 g/cm 3 , - a median diameter of the order of 0.4 to 1.4 mm, preferably of the order of 0.5 to 1 mm, with a log 10 standard deviation of 0.05 to 0.1, - a speed of dissolution in water of the order of 3 minutes for 90 % dissolution and of the order of 4 minutes for 99 % dissolution, and - an abrasion resistance of the order of 1 to 6 %, preferably of the order of 1 to 3 %.

20. 21. Use of the granules obtained by the process which is the subject of any one of claims 1 to 17 or of the granules which are the subject of any one of claims 18 to 20 for making up detergent compositions .

21. 22. Use of the granules which are the subject of claim 20 for making up detergent compositions for dishwashing.

22. 23. A process according to claim 1 for preparing spherical granules of hydrated alkali metal silicates, substantially as hereinbefore described and exemplified.

23. 24. Spherical granules of hydrated alkali metal silicates, whenever prepared by a process claimed in a preceding claim.

24. 25. Granules according to claim 18 or 20, substantially as hereinbefore described and exemplified.

25.

26. Use according to claim 21, substantially as hereinbefore described.