GB1563467A - Production of alkali metal silicoaluminates - Google Patents

Abstract

An alkali metal silicate solution is added to an alkali metal aluminate solution with stirring, the homogeneous mixture is made to gel by being maintained at a high temperature, and the crystalline silicoaluminate obtained, which corresponds to the formula xSiO2.yAl2O3.Na2O.wH2O in which, y = 1, x = 1.5 to 6, z = 1, w = 0 to 5 and which has a particle size substantially between 0.2 and 8 mu and a BET surface of between 0.5 and 10 m<2>/g, is then separated off. This product is useful as an ingredient of detergent compositions.

Description

(54) PRODUCTION OF ALKALI METAL SILICOALUMINATES (71) We, RHONE-POULENC INDUSTRIES, a French body corporate, of 22, avenue Montaigne, 75 Paris (8), France, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to crystalline silico-aluminates, their production and their use as detergents. The usual way of preparing synthetic zeolites has been known for a long time (Kurnakow, Journal of the USSR Academy of Science, 1381 (1937). The method of preparation comprises putting a solution of silicate and aluminate into contact to obtain a gel, which undergoes crystallisation.The formation of the silico-aluminates depends on a large number of factors such as the concentration of the reagents, the temperature at which they are brought into contact, the temperature in the maturing stage, the duration of the maturing stage and the homogeneity of the medium. Methods such as seeding, to obtain silicoaluminates with specific properties, e.g. faujasite, in a medium already containing a zeolite of the 4A type, have also been applied in French Patent Specification No.

2,281,315.

The influence of certain factors, particularly the presence of sodium hydroxide and the alkalinity of the medium, has already been shown by Kurnakow. In French Patent 1,404,467 it is pointed out that the concentration of sodium hydroxide in the liquid medium in which the silico-aluminate precipitate appears has a decisive effect on the regularity and crystalline purity of the 4A zeolite obtained, and that the more constant the concentration is kept, the greater the purity and homogeneity of the zeolite.

Until quite recently the methods proposed were discontinuous. This has been explained in terms of the complex structure of the crystals, which normally require a relatively long time to form from amorphous compounds distributed at random through the liquid and solid phases of the reaction mixture. For this reason U.S.

Patent Specification No. 3,071,434 proposed improving the kinetics of the formation of type 4A zeolites by seeding the mix with a paste recycled from a point downstream of the reaction zone. However, U.S. Patent Specification No.

3,425,800 criticises this method on the ground that it is difficult to carry it out, and proposes the use of a three-layer crystallising vessel, the suspension of the coldprecipitated gel being treated to 1000C and then placed in a crystallising vessel, where the crystalline silico-aluminate is formed. In this method the crystalline silico-aluminate is collected by decantation. French Patent Specification No.

2,096,360 proposes avoiding passing through a multi-stage process by pre-heating the aqueous sodium silicate solution to approximately precipitation temperature and adding it hot to the aluminate solution, which is also kept at the precipitation temperature.

Products thus obtained have usually been valued for their very good absorbent properties. These have a selective action on molecules, on account of their size and shape, which explains the fact that they are currently described as "molecular seives". However, the use of this type of product in other ways, particularly as cation-exchangers, has also been considered. One of the commonest applications in this field is the use of such compounds in detergent compositions.

It has been known since biblical times that derivatives based on silicoaluminate can be incorporated in cleaning products. But there has been a great revival of interest in this possibility since the supremacy of sodium tripolyphosphate (STPP) as a detergency aid has been challenged on account of its polluting action, and since an advance has been made in the art of manufacturing silico-aluminates in a reliable and reproducible manner. Detergency aids such as STPP act in several ways and particularly as cation exchangers. Since silico-aluminates have this property, it was natural to think of using them, especially as there was nothing to fear from the ecological point of view.

The various types of generally crystalline silico-aluminates, distinctive in having a high cation-exchange capacity and/or a high speed of exchange, have been proposed recently. Unfortunately these silico-aluminates have two disadvantages.

Firstly, they cannot totally replace STPP, since they appear to act in the detergent medium only as a cation exchanger, whereas STPP has a more diverse action and particularly a dispersing and complexing action. In addition, the silico-aluminates are insoluble; this results in an effect known as incrustation or mineralisation and leads to the deposit of particles of the silico-aluminate on the fabric and particularly on cotton.

It was thought that the incrustation effect could be reduced by using a fine particle size, but the influence of the particle size on detergency and particularly on the incrustration effect is still little understood at present. It has merely been found that the particles have to be well individualised. More specifically, as far as the replacement of sodium tripolyphosphate by an alkali metal silico-aluminate is concerned, operating conditions are found to be more critical as the quantity of tripolyphosphate is decreased relative to the quantity of silico-aluminate.

The present invention is based on the discovery of a new method of obtaining alkali metal silico-aluminates, preferably sodium silico-aluminates. In accordance with the present invention, an alkali metal silico-aluminate is obtained by forming an alkali metal aluminate solution; chilling the solution to a temperature below ambient temperature; adding an alkali metal silicate solution with agitation so as to keep the medium homogeneous; gelling the initially homogeneous medium while bringing it to a temperature in the range 60 to 1000C and maintaining the medium at that temperature for 0.2 to 5 hours, pending complete redispersion of the silicoaluminate in a suspended state; and separating and recovering the crystals of silicoaluminate obtained.

The silico-aluminates obtained are of the crystalline type, with a fine particle size and a high degree of dispersion, and are usually of the general formula x SiO2 . A12O3 . z M2O. w H2O in which M is an alkali metal, preferably sodium, x is in the range from 1.5 to 6, z is 1 and w is in the range from 0 to 5.

The silico-aluminate advantageously corresponds to the formula 1.85 SiO2 . Al2O3 . Na2O . (4 to 5) H2O and is of the 4A type.

Observation under a microscope reveals the existence of small individualised cubes of a particle size substantially from 0.2 to 8 N and with a large BET surface area ranging from 0.5 to 10 m2/g.

The silico-aluminates obtained in accordance with the invention have very specific particle sizes within a vast field of average particle size values. This makes them suitable for use in diverse fields, e.g. detergency, drying by association with a binder, and separation.

In the case of detergency it is found helpful to take a silico-aluminate according to the invention of a small particle size, particularly from 0.2 to 3 No with a surface area from 1 to 10 m2/g and with high cation-exchange capacity and speed of exchange. Silico-aluminates of this type are particularly well adapted for use in detergency; their properties bear comparison with those of the best known silicoaluminates, but they show far less incrustation.

The silico-aluminate may be obtained by a discontinuous process, but for practical purposes it is advantageous to use a continuous process.

When carrying out the process of the present invention, it is preferable for the initial mixture to comprise a solution of sodium-aluminate cooled to a temperature in the range -10 to +100C and a solution of sodium silicate at ambient temperature, over 10 C for convenience.

The two solutions are stirred together, using any appropriate apparatus to homogenise the medium, within a time shorter than the gelling time of the medium at the equilibrium temperature of the mix. This time is advantageously shorter than 15 minutes.

The concentrations of the two reagents are preferably selected so that, at the end of the development, there is a liquid phase containing at least 70 g/l of Na2O and 10 gel of Al203 in equilibrium with at least 200 g/l of crystalline silico-aluminate.

In cases where a small particle size of 0.2 to 3 N is required, the concentrations of the reagents should be chosen so that, at the end of the development, the liquid phase will contain at least 100 g/l of Na2O and 30 g/l of Awl203, in equilibrium with at least 200 g/l of silico-aluminate, whereas for a larger particle size it is preferable to choose a liquid phase containing less than 100 g/l, preferably 70 to 100 g/l, of Na2O, and less than 30 g, preferably 10 to 30 g/l, of Awl203.

The method of the invention can be carried out discontinuously but it has the advantage continuous operation is also possible.

It is convenient to operate as follows: blending a sodium aluminate solution, cooled within the range indicated above, with a sodium silicate solution at a temperature close to room temperature; spray the ungelled mix into a first zone that comprises a water-immiscible heatcarrying medium, such as a bath of oil or petroleum, that has a density lower than that of the aqueous mix and that is heated to a temperature such that after contact the aqueous mix is brought to the chosen reaction temperature; maintain that temperature in the bath in a second downstream zone until conversion to the crystalline phase is complete, while providing a plug flow reaction in the downstream zone; collect the reaction medium containing the crystallites of silicoaluminates as a suspension; separate the crystallites from the suspension by any known means such as filtering or centrifuging; and wash and collect the crystallites.

The first zone is advantageously a transfer zone where the medium is agitated during a very short residence time of 1 to 2 seconds, whereas the second zone has a plug flow and corresponds to a far longer residence time.

As mentioned above, the products according to the invention are particularly suitable for use in detergency, although the invention is not so restricted.

The invention will be more easily understood from the exemplifying figures and illustrative examples, which follow.

Comparative tests with known products have been carried out to show the properties of the product according to the invention. The tests were as follows: Range of particle size This is carried out with a Coulter counter, using the following solution as electrolyte (percentages are by weight): water 78% glycerine 20% NaCI 1% sodium hexametaphosphate O.50/o formaldehyde 0.5% Dispersion 2 minutes (ultra sonic) - 40,000 Herz - 100 watts.

Detergent action Effectiveness as a detergent is shown in washing tests at 900C on samples of cotton soiled with a standardised stain and prepared by Wäschereiforschungs- institut Krefeld.

The tests are carried out with a Linitest apparatus (manufactured by Original Honau). Two soiled samples (4.2 g) and two samples of non-soiled cotton (4.2 g) are placed in each vessel with 100 ml of a detergent solution, the composition of which is given below. Washing is followed by four successive rinses each lasting 30 seconds.

Water of 28.5 TH hardness is used. The detergent composition, used in quantities of 9 g/l, is as follows: Alkylbenzene sulphonate 5.3% Non ionic (C 16/14 OE) 2% Sodium Stearate 2.8% Sodium tripolyphosphate 4.2% Sodium silico-aluminate 45% Perborate 22.1% Sodium silicate 2.5% Carboxy methyl cellulose 1.2% Magnesium silicate 1.7% Sodium sulphate 2.1% H20 100% The reflectance of the samples is measured before and after washing, using an Elrepho photoelectric photometer, manufactured by Zeiss, with filter 6.

Incrustation effect A formulation of the following composition is used: Silico aluminate 2.4 gel Sodium tripolyphosphate 1.6 g/l alkyl benzene sulphonate 0.8 g/l Ethoxylated alcohol (cemulsol DB 25/17) 0.4 g/l Sodium stearate 0.4gel Sodium Sulphate 0.8gel Washing is carried out in a Lini Test apparatus. Samples of cotton (the cotton used is prepared by Test Fabrics Inc., reference Bleached Cotton Sheeting, Style 405) measuring 10 x 12 cm each receive 450 cm3 of the solution described above.

The hardness of the water is 30 TH. (NFT 90003).

Washing proper is carried out at 600C for 35 minutes (25 minutes to reach the correct temperature +10 minutes at 600C).

There are then two rinses, a rapid one lasting about 1 minute in 350 cm3 of water, and a slow one lasting 5 minutes in 450 cm3 of town water (30 TH).

The samples are allowed to drip and dried.

Finally, the cotton samples are calcined at 9000C for 2 hours. The acids collected are weighed.

In addition to these tests it is appropriate to carry out others bearing on the product itself: - a test of BET surface area.

- a test of the speed of exchange.

Example 1.

1 litre of a sodium aluminate solution containing 200 g/l expressed as Na2O and 200 g/l expresses as Al203 is chilled in a flask at 40C.

0.4 litre of a sodium silicate solution at 200C, containing 25.4% of SiO2 and 7.42% of Na2O on a weight basis, is then stirred in vigorously so that the medium is always kept homogeneous. When it has all been added the temperature is raised to about 15"C, the medium still being very fluid. Agitation is stopped and the temperature is allowed to rise to near room temperature, which causes the medium to gel. The flask is then kept in a water thermostat set to 830C, for two hours; the rigid mass of initial gel has by then been converted into a suspension of micro-crystals, which is drained and washed continuously on a filtering wall with an average aperture of 1 micron.The concentration of crystalline silicone aluminate in the suspension of micro-crystals is approximately 320 go. The washed cake is then dried to constant weight in an oven at 1000C before being analysed.

The zeolite when dried and analysed is substantially of the formula: 1.85 SiO2 . 1 Al203 . 1 Na2O . 3 H2O Under X-rays it has the structure of the 4A molecular sieve.

An electron microscope reveals very small individualised cubes of a homogeneous particle size of approximately 1 micron or less, well distributed as illustrated in Fig. 1 with a magnification of 4500.

The BET specific surface area equals 7 m2/g.

Test 2, in which the initial cooling step is omitted, is carried out by way of comparison as follows: 1 litre of a sodium aluminate solution containing 74 g/l expressed as Al203 and 127 g/l expressed as Na2O is brought to 830C with vigorous agitation in a flask.

0.271 litre of a silicate solution, obtained by diluting 50 ml of a commercial sodium silicate solution containing 477 g/l expressed as SiO2 and 239 g/l expressed as Na2O, is then added rapidly. When the temperature has risen to 83"C it is kept constant for two hours, still with agitation. The suspension of crystals is then drained and washed on a filter without any special precautions. The washed cake is then dried and analysed as in the previous example.

The dried zeolite is of the formula: 1.85 SiO2 . 1 Al203 . 1 Na2O . 3.8 H2O Under X-rays it has the structure of the 4A sieve and the appearance shown in Fig. 2 (magnification of 4500).

An electron microscope reveals micronic cubes which are fairly well individualised, with a range of particle sizes (1 to 5 microns). The BET specific surface area equals 1.2 m2/g.

A test for the speed of Na 5 Ca exchange is carried out as follows with the powders from tests 1 and 2: 1 g of powder dried at 1000C, with a weight loss of approximately 19% when heated to 10000C is deposited in one litre of solution containing 594 mg of Cacti2 for 1 minute, using an ultraturax turbine (revolving at 9000 reVs/minute and fitted with a T 45 K head. After dispersion the suspension is kept on a magnetic agitator for 1 minute, 4 minutes and 14 minutes before being removed rapidly (20 seconds) by draining under vacuum over a millipore filter RAWP 047. A volume of clear liquid sufficient to analyse the Ca2+ ions is left in solution.

The following results are obtained. These show a clear advantage in the kinetics of exchange for the very fine silicon-aluminate according to the invention:

QUANTITY OF (spa2+ EXCHANGED MEQ/G IN MEQ/G of DRY MOLECULAR SIEVE After 2 minutes After 5 minutes After 15 minutes T.EST 1 4.9 5.12 5.3 TEST 2 2.1 3.2 4 Theoretical power 5.8.

Detergent action Reflectance before Reflectance after washing washing Silico-aluminate according to the invention 39.4 59.1 Control sample 39.3 60.7 It will be seen that the detergent action is substantially the same.

Incrustation Effect Results as a % of the weight of the fabric according to the invention 0.35% control 0.9% In this case a very marked difference appears.

Example 2.

A type 4A silico-aluminate is prepared, with properties identical to those described in Example 1, by a continuous process which enables the invention to be applied industrially (see Fig. 4).

A solution of sodium aluminate containing 200 g/l expressed as Na2O and 200 g/l expressed as Alp03 is cooled to C in a tubular exchanger 1 at a flow rate of 10 Vhour. The cooled stream is mixed continuously with a stream 3, comprising 4 Vhour of a sodium silicate solution at 209C and containing 25.4% of SiO2 and 7.42% of Na2O by weight, in an agitated reactor 2.

The temperature of the homogeneous mixture settles in the vicinity of 15"C, and the mixture is fed by a vermicular pump 4 to an injector 5 with capillary tubes 0.5 mm in diameter, which continuously forms drops. The drops fall into the top of a reactor 6 filled with petroleum, which is kept at 850C by a heated brine circuit 7.

The density of the bath is adjusted so that the average time taken by the drops formed by the capillary tubes to fall is three seconds. After this time the spherical particles are gelled and accumulate above a grid 8 arranged at the bottom of the reactor. They are gradually converted into a fluid suspension of silico-aluminate, which collects in the conical part 9 of the reactor 6. This suspension is drawn off continuously through a suction tube 10, at the rate of 14 metres per hour, following 1 hour of continuous feeding of the reagents, and thus defining an average residence time of the reagents in the reactor of 1 hour.

The suspension sucked out is then drained and washed by any known means.

Example 3.

The procedure is the same as in Example 1, except that 0.6 litre of the silicate solution is added instead of 0.4 litre.

As a result the concentration of silico-aluminate in the suspension is approximately 450 g/l.

The average particle size of the silico-aluminate is found to be larger, as shown in Figure 3 where the magnification is 4500.

Example 4.

A type 4A silico-aluminate according to the invention is prepared by the continuous process, which enables the invention to be applied industrially as illustrated in Figure 4.

A sodium-aluminate solution containing 110 g/l expressed as Na2O and 150 gfl expressed as Awl203 is cooled to OOC in a tubular exchanger 1 at a flow rate of 10 Vhour. The cooled stream is mixed continuously with a stream 3 comprising 4 Uhour of a sodium silicate solution taken at 20"C and containing 25% of SiO2 and 11.6% of Na2O by weight, in an agitated reactor 2.

The temperature of the homogeneous mixture settles in the vicinity of 12"C, and the mixture is fed by a vermicular pump 4 to an injector 5 with capillary tubes 0.5 mm in diameter, which continuously forms drops. The drops fall into the top of a reactor 6 filled with petroleum, which is kept at 850C by a heated brine circuit 7.

The density of the bath is adjusted so that the average time taken for the drops formed by the capillary tubes to fall is three seconds. After this time the spherical particles are gelled and accumulate above a grid 8 at the bottom of the reactor.

They are gradually transformed into a fluid suspension of silico-aluminate which collects in the conical part 9 of the reactor 6. This suspension is drawn off continuously through a suction tube 10 at the rate of 14 Vhour, following 2 hours during which the reagents are fed in continuously, in order to define an average residence time of the reagents in the reactor of 2 hours.

In this example the concentration of crystalline sodium silico-aluminate in the suspension of micro crystals is approximately 340 g/l. The liquid phase, which is virtually free from SiO2, contains 76 g/l of Na2O and 12 g/l of A1203. The suspension of micro crystals obtained is drained and washed on a filtering wall with an average aperture of 1 N The washed cake is then dried to constant weight in an oven at 100 C before being analysed.

The product obtained, which is of the 4A type, has an average homogeneous particle size of 3 to 4 N with a wide spread as illustrated in figure 5 (magnification of 4500).

The product has a BET surface area of lm2/g.

-EXCHANGE POWER QUANTITY OF Ca2+ EXCHANGED IN MEQ/G OF DRY MOLECULAR SIEVE

After 2 minutes T After 5 minutes After 15 minutes .4.2 4.7 1 5.3 The table below gives the Coulter particle sizes after drying, for the control sample and the products of Example 2 and Example 4.

Control small than Control Example 2 Example 4 % particles smaller than 1 IL O 20 2 12 12 68 20 5 87 95 92 10 IL 95 98 98 Average diameter of particles in IL 3 1.5 3 It will be noted that (a) finer particle sizes can be obtained and (b) the particle size spectrum is different for an identical average particle size.

The degree of mineralisation is given in the following table:

Control Example 2 Example 4 1 wash 0.3 0.15 0.25 10 washes 1.0 0.45 0.9 WHAT WE CLAIM IS: 1. A method of preparing a synthetic crystalline silico-aluminate that comprises forming an alkali metal aluminate solution; chilling the solution to a temperature below ambient temperature; adding an alkali metal silicate solution with agitation so as to keep the medium homogeneous; gelling the initially homogeneous medium while bringing it to a temperature in the range of 60 to 100 C and maintaining the medium at that temperature for 0.2 to 5 hours, pending

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (13)

**WARNING** start of CLMS field may overlap end of DESC **. formed by the capillary tubes to fall is three seconds. After this time the spherical particles are gelled and accumulate above a grid 8 at the bottom of the reactor. They are gradually transformed into a fluid suspension of silico-aluminate which collects in the conical part 9 of the reactor 6. This suspension is drawn off continuously through a suction tube 10 at the rate of 14 Vhour, following 2 hours during which the reagents are fed in continuously, in order to define an average residence time of the reagents in the reactor of 2 hours. In this example the concentration of crystalline sodium silico-aluminate in the suspension of micro crystals is approximately 340 g/l. The liquid phase, which is virtually free from SiO2, contains 76 g/l of Na2O and 12 g/l of A1203. The suspension of micro crystals obtained is drained and washed on a filtering wall with an average aperture of 1 N The washed cake is then dried to constant weight in an oven at 100 C before being analysed. The product obtained, which is of the 4A type, has an average homogeneous particle size of 3 to 4 N with a wide spread as illustrated in figure 5 (magnification of 4500). The product has a BET surface area of lm2/g. -EXCHANGE POWER QUANTITY OF Ca2+ EXCHANGED IN MEQ/G OF DRY MOLECULAR SIEVE After 2 minutes T After 5 minutes After 15 minutes .4.2 4.7 1 5.3 The table below gives the Coulter particle sizes after drying, for the control sample and the products of Example 2 and Example 4. Control small than Control Example 2 Example 4 % particles smaller than 1 IL O 20 2 12 12 68 20 5 87 95 92 10 IL 95 98 98 Average diameter of particles in IL 3 1.5 3 It will be noted that (a) finer particle sizes can be obtained and (b) the particle size spectrum is different for an identical average particle size. The degree of mineralisation is given in the following table: Control Example 2 Example 4 1 wash 0.3 0.15 0.25 10 washes 1.0 0.45 0.9 WHAT WE CLAIM IS:

1. A method of preparing a synthetic crystalline silico-aluminate that comprises forming an alkali metal aluminate solution; chilling the solution to a temperature below ambient temperature; adding an alkali metal silicate solution with agitation so as to keep the medium homogeneous; gelling the initially homogeneous medium while bringing it to a temperature in the range of 60 to 100 C and maintaining the medium at that temperature for 0.2 to 5 hours, pending

complete redispersion of the silico-aluminate in a suspended state; and separating and recovering the crystals of silico-aluminate obtained.

2. A method according to Claim 1 in which sodium is the alkali metal in both aluminate and silicate.

3. A method according to Claim 2 in which the initial mixture comprises a solution of sodium aluminate chilled to a temperature in the range -10 to +100C, and a solution of sodium silicate at ambient temperature.

4. A method according to Claim 2 or 3 in which the medium is homogenised by agitating it for less than 15 minutes.

5. A method according to any one of Claims 2 to 4 in which the concentrations of the two reagents in the solutions are such that, at the end of development, the liquid phase contains at least 70 g/l of NO and 10 g/l of Al203 in equilibrium with at least 200 g/l of silico-aluminate.

6. A continuous method according to any one of Claims 2 to 5 that comprises forming a solution of sodium aluminate with a solution of sodium silicate that is at a temperature close to ambient temperature; spraying the ungelled mixture into a first zone comprising a heat-carrying, water-immiscible medium, of a density lower than that of the aqueous mixture and heated to a temperature such that, after contact, heat transfer brings the aqueous mixture to a temperature at which the reaction develops; maintaining this temperature in the bath in a second downstream zone until conversion to the crystalline phase is complete, while a plug flow is provided in the downstream zone; collecting the reaction medium containing the crystallites of silico-aluminates as a suspension; separating the crystallites from the suspension and washing and collecting them.

7. A method according to Claim 6 in which the medium is agitated for a period of 1 to 2 seconds in the first zone and to a plug flow in the second zone.

8. A method according to Claim 1 substantially as hereinbefore described in any one of the Examples.

9. Crystalline silico aluminate obtained by a method according to any one of Claims 1 to 8.

10. Crystalline silico-aluminate according to Claim 9 having the formula x Six,. Al203 . Z M20 w w H20 in which M is an alkali metal, x is 1.5 to 6, z is 1 and w is 0 to 5, and having a particle size substantially from 0.2 to 8 N and a BET surface area of from 0.5 to 10 m2/g.

11. Silico-aluminate according to Claim 10 in which M is sodium.

12. Silico-aluminate according to Claim 11 in which z is 1, x is 1.85 and w is from 4 to 5.

13. A detergent composition with a high capacity for cation exchange, a high speed of cation exchange and substantially no incrustation effect and comprising a sodium silico-aluminate according to any one of Claims 9 to 12 as an aid to detergency.