IE46054B1 - 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

The invention relates to crystalline silico-aluminates, their production and their use as detergents. The usual way of preparing synthetic zeolites has been know for a long time (Kurnakow, Journal of the USSR Academy of Science, 1381 (1937). The method of preparation comprises putting a g 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 silico-aluminates 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 Mo. 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 wore discontinuous. Ibis has been explained in terms of the complex structure of tho crystals, which normally require a relatively long time to form from amorphous compounds distributed at random tlirough the liquid and solid phases of the reaction mixture. For this reason U.S, Patent Specification Mo. 3,071,434 proposed improving the kinetics of tho formation of type 4A zeolites hy seeding the mix with a paste recycled from a point down stream of the reaction zone. However, U.S, Patent Specification No. 5,425,800 criticises this method on the ground that it is difficult to carry it out, and proposes the use of a three2 layer crystallising vessel, the suspension of the fcold-preeipitated gel being heated to 100°C and then placed in a crystallising vessel, where the crystalline silico-aluminate is formed. In this method the crystalline silico-aluminate is collected hy decantation. French Patent Specification No. 2,096,360 proposes avoiding passing through a multi-stage process hy 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 jirecipitation 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 sieves. 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 silico-aluminate can be incorporated in cleaning products. But there has been a great revival of interest in this possibility since the supremacy of sodium tripolyphosphate (STP?) as a detergency aid has been challenged on uccount of its polluting action, and since an advance has been made in the art of manufacturing silico-uluminates in u reliable and reproducible wanner. Detergency aids such as Sl'PP 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.

Thus 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, Bn fortunately these silico-ahiriirr t.:· have two disadvantages. Firstly, they cannot totally replace STEP, 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 incrustation effect is still little understood at present. It has merely been found that the particles have to he well individualised. More specifically, as far as the replacement metal of sodium tripolyphosphate by an alkali / 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 silicoaluminates. In accordance with the present invention, an alkali metal silico-aluminate is obtained hy 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 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.

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 SiOg. Λ12°5* — M2°‘ — Π2° in is 311 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 SiOg. AlgO^. Na20. (4 to 5) UgO 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 μ and 2 with a large BET surface area ranging from 0.5 to 10 s/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 silicoaluminate according to the invention of a small particle size, particularly from 0.2 to 3 μ , with a surface area from 1 to 10 m /g and with high cationexeliange capacity and speed of exchange. Silico-aluminates of this type are particularly well adapted for use in detergency; their properties hear comparison with those of the best known silico-aluminates, hut they show far less incrustation.

The silico-aluminnte may he 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 +10°C and a solution of sodium silicate at ambient temperature, over· 10°C for convenience.

The two solutions are stirred together, using any appropriate ® 0 S 4 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 iB 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 Na,,0 and 10 g/l of AlgO^ in equilibrium with at least 200 g/l of crystalline silico-aluminate.

In cases where a small particle size of 0.2 to 3 μ 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 NagO and 30 g/l of AlgOy 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 Νβ^Ο, and less than 30 g, preferably 10 to 30 g/l, of AlgOy The method of the invention can he carried out discontinuously hut it has the advantage continuous operation is also possible.

It is -convenient to operate as follows s 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 ungolled mix into a first zone that comprises a water-immiscible heat-carrying medium, such as a hath 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 hath in a second downstream zone until conversion to the crystalline pha.se is complete, while providing a plug flow reaction in the downstream zone; collect the reaction medium containing the crystallites of silico-aluminates as a suspension; separate the crystallites from the suspension try any known means such ns filtering or centrifuging; and wash and collect the crystallites. 43054 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 5 particularly suitable for use in detergency, although the invention is not so restricted.

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

Comparative tests with known products have been carried out to show 10 the properties of the product according to the invention. The tests were as follows: I j 'hange of particle size - ' This is carried out with a Coulter counter, using the following j solution as electrolyte (percentages are by weight): water...................................78/ glycerine....... 20/ NaCl.................... 1/ sodium hoxawetaphosphate................0.5/ forma 1 d chyd e............. 0,5/ Dispersion 2 minutes (ultra sonic) - 40,000 TIerz - 100 watts.

Detergent action liffectiveness as a detergent is shorn! in washing tests at 90°C on samples of cotton soiled with a standardised stain and prepared by W&schereiforschungsinstitut Krefeld.

The tests are carried out with u Linitest apparatus (manufactured by Original Ilonau). Two soiled samples (4.2 gj and two samples of non~soilcd cotton (4.2 g) are placed in each vessel with 100 ml of a detergent solution, the composition of which is given below, iiashing is followed by four successive rinses each lasting 50 seconds.

Water of 28.5° TH hardness is used. The detergent composition, used in quantities of 9 g/1, is as follows: Alkylbenzene sulphonate Non ionic (C 16/14 OE) .

Sodium Stearate........

Sodium tripolyphosphate Sodium silico-aluminate Perborate ..............

Sodium silicate ........

Carboxy methyl cellulose Magnesium silicate ..... Sodium sulphate ........ .3% 2.8% 4.2% % 22.1% 2.5% 1.2% 1.7% . 2.1% 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 g/1 Sodium tripolyphosphate ............... 1.6 g/1 Alkyl benzene sulphonate .............. 0.8 g/1 Ethoxylated alcohol (demulsol DB 25/17)...0.4 g/1 Sodium stearate ........................0.4 g/1 Sodium Sulphate ....................... 0.8 g/1 - 8 46054 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 cm of the solution 5 described above. The hardness of the water is 30° TH.(NFT ¢0 003) Washing proper is carried out at 60°C for 35 minutes (25 minutes to reach the correct temperature + 10 minutes at 60°C).

There are then two rinses, a rapid one lasting about 1 3 minute in 350 cm of water, and a slow one lasting 5 minutes in 450 cm^ of town water (30°TH).

The samples are allowed to drip and dried.

Finally, the cotton samples are calcined at 900° C 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/1 expressed as Na^O and 200 g/1 expressed as Al2°3 is chilled in a flask at 4°C. 0.4 litre of a sodium silicate solution at 20°C, containing 25.4% of SiO^ and 7.42% of Na^O 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. - 9 46054 Agitation is stopped and the temperature is allowed to η rise to near room temperature, which causes the medium to gel. h The flask is then kept in a water thermostat set to 83°C, 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 silico-aluminate in the suspension of micro-crystals is approximately 320 g/1.

The washed cake is then dried to constant weight in an oven at 100°C before being analysed.

The zeolite when dried and analysed is substantially of the formula; 1.85 SiO2 . 1 A12O3 . 1 Na20 . 3 HjO .

Under X-rays it has the structure of the 4 A 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 m /g.

Test 2, in which the initial cooling step is omitted, is carried out by way of comparison as follows; litre of a sodium aluminate solution containing 74 g/1 expressed as A12O3 and 127 g/1 expressed as Na20 is brought to 83°C 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/1 expressed as SiO2 and 239 g/1 expressed as Na20, 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 tten 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 A12O3 . 1 il^O . 3.8 1^0.

Under X-rays it has the structure of the 4 A 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 m /g.

A test for the speed of Na^—»Ca exchange is carried out as follcws with the powders from tests 1 and 2: g of powder dried at 100°C with a weight loss of approximately 19% when heated to 1000°C is deposited in one litre of solution containing 594 mg of CaClj 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 far 1 minute, 4 minutes and 14 minutes before being removed rapidly (20 seconds) by draining under vacuum over a millipare filter RAM? 047. A volute of 2+ clear liquid sufficient to analyse the Ca icns is left in solution.

The following results are obtained. These show a clear advantage in the kinetics of exchange far the very fine silico-aluminate according to the invention! MEQ/G QUANTITY OF Ca2+ EXCHANGED IN MEQ/G of DRY MOLECULAR SIEVE After 2 minutes After 5 minutes After 15 minutes TEST 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 sane.

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, hy a continuous process which enables the invention to be applied industrially (see fig. 4).

A solution of sodium aluminate containing 200 g/1 expressed hy Na20 and 200 g/1 expressed as AljO^ to ” 4°C Li a tubular ex20 changer 1 at a flow rate of 10 l/hour. The cooled stream is mixed continuously with a stream 3, comprising 4 l/hour of a sodium silicate solution at 2O°C and containing 25.4% of SiO2 and 7.42% of Na20 by weight, in an agitated reactor 2. 4605 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 85°C 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/1. 6 0 5 4 The average particle size of the silica-aluminate is found to be larger, as shown in Figure 3 where the magnification is 4500.

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

A sodium-aluminate solution containing 110 g/1 expressed as Na^O and 150 g/1 expressed as Al.,03 is cooled to 0°C in a tubular exchanger 1 at a flow rate of 10 l/hour. The cooled stream is mixed continuously with a stream 3 comprising 4 l/hour of a sodium silicate solution taken at 20°C and containing 25% of SiO2 and 11.6% of Na20 ty weight, in an agitated reactor 2.

The temperature of the homogeneous mixture settles in the vicinity of 12°C, and the mixture is fed hy 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 85°C hy a heated brine circuit 7.

The density of the bath is adjusted so that the average tine taken for the drops formed hy the capillary tubes to fall is three seconds. After this tine 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 l/hour, following 2 hours during which the reagents are fed in continuously, in order to define an average residence tine of the reagents in the reactor of 2 hours. 46034 In this example the concentration of crystalline sodium silico-aluminate in the suspension of micro crystals is approximately 340 g/1. The liquid phase, which is virtually free from SiO^, contains 76 g/1 of Na^O and 12 g/1 of AljOj. The suspension of micro crystals obtained is drained and washed on a filtering wall with an average aperture of 1 μ . The washed cake is then dried to constant weight in an over at 100°C before being analysed.

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

The product has a BET surface area of lm /g EXCHANGE POWER QUANTITY OF Ca2+ EXCHANGED IN MEQ/G OP DRY MOLECULAR SIEVE After 2 minutes After 5 minutes After 15 minutes 4.2 4.7 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 Example 2 Example 4 % particles smaller than 1 μ 0 20 2 2 μ 12 68 i 20 i 5 μ 87 95 92 J 1 10 μ 95 98 98 j 1 Average diameter of 1 i i particles in μ 3 1.5 3 I 1 -i It will be noted that (a) finer particles 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

Claims (13)

1. CLAIMS:1. A method of preparing a synthetic crystalline silieo-aluminate that comprises forming an alkali metal aluminate solution; chilling the solution to a temperature below ambient temperature; adding an alkali metal 5 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 100°C and maintaining the medium at that temperature for 0.2 to 5 hours, pending complete redispersion of the silieo-aluminate in a suspended state; ond separating and recovering the crystals of silico10 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 15 -10 to +10°C, and a solution of sodium silicate at ambient temperature.

4. A method according to Claim 2 or 3 in which (lie 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 arc such that, nt the end 2q of development, the liquid phase contains at least 70 g/l of Ka„0 and 10 g/l of Al,0„ in equilibrium with at least 200 g/l of silieo-aluminate.

6. Λ coiilinuuas method according to any one of Claims 2 to 5 that comprises forming a solution of sodium aluminate wiuii 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, waterimmiscible medium, of a density lower than that of the aqueous mixture and heated to a temperature such that, after contact, heat transfer brings the 5 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 10 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 25 in any one of the Examples.

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

10. Crystalline silino-aluminate according to Claim 9 having the formula x SiOg. AlgO_. z MgO. w HgO in which M is an alkali metal, ϊ is 1.5 to 6, z is 20 1 and w is 0 to 5s and having a particle size substantially from 0.2 to 8 μ and a BET surface area of from 0.5 to 10 m /g.

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

12. Silico-aiuminate according to Claim 11 in which z is 1, x is l.Sp and w is from h 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.