NL8301322A - PROCESS FOR PREPARING ALKALINE METAL SILICATE SOLUTIONS IN A STATIC REACTOR. - Google Patents

Description

4-1 VO 4661

Process for preparing alkali metal silicate solutions in a static reactor.

The invention relates to a process for preparing solutions of alkali metal silicate by reacting silica with an alkaline solution.

The process for preparing alkali metal silicate by alkaline melting of silica is known in particular from "Soluble. Silicates", J.G. Vail, Reinhold Pub. Corp. Full. 1, p. 6 (1952).

It is currently still the only practiced process.

Another well-known process is autoclaving silica with an alkaline solution. For example, in "Gmelins Handbuch 10 der inorganischen Chemie" vol. 21 (1928), p. 861 cited the experiments by Liebig (1857) and other authors, but the results have only resulted in silicates containing too much sodium hydroxide for industrial exploitation.

Patents, such as British Patent 788,933, show the importance of a process operating at a temperature between 175 ° C and 320 ° C while the alkaline melting requires temperatures in the vicinity of or above 1300 ° C.

US patent 3,971,727 describes obtaining alkali metal silicates in aqueous solution under pressure at a temperature between 138 ° C and 210 ° C, but it is necessary to stir mechanically and filter and the reaction involves rather long residence times as well as the presence of a third product to achieve interesting results.

European Pat. Nos. 33,108 and 33,109 claim the preparation of sodium silicate, but the processes described require stirring the suspension and filtering.

The importance of a process in which silica is attacked by an alkaline solution increases with the need to be energy efficient. The following conditions must be combined: - possibility of obtaining silicate solutions sufficiently rich in SiO ^ For example, for the detergent industry and the preparation of sodium silicate aluminates (type A zeolites), the use of sodium silicate necessary, the weight ratio of SiO 2 / Na 2 O being equal to or greater than 2 and at most equal to 2.5.

8301322 '--------------------------------- 9 »-2- - Obtaining these solutions continuously to reduce investment costs to decrease.

The applicant has now developed a method which not only responds to the above circumstances, but also permits:. the use of quartz sand of high granulometry and no silica flour, which makes it possible to economize on grind energy,. the absence of agitation of the mixture of sand and solution ensuring good mass transfer of reactant / sand / reaction product,. non-filtering of the solutions obtained with devices specially designed for this purpose,. obtaining alkali metal silicates with a high SiO 2 / Me 2 O ratio.

The result of this is an important simplification of the design, as well as a great flexibility of application and therefore an important reduction of investment costs.

The process consists of feeding crystallized silica with an average granulometry between 0.1 mm and 2 mm and an aqueous solution of alkali metal hydroxide, for example consisting of an aqueous solution of sodium hydroxide, to a vertical tube serving as a reactor. Controlling the temperature and the feed rate of the reactants as well as that of the concentration of the alkali solution ensure the concentration and the weight ratio of SiO 2 / Me 2 O of the product obtained.

The silica used is a quartz sand whose granulometry cannot be less than 0.1 mm due to batch loss of the system. It should not have a granulometry greater than 2 mm in order that the reaction is not slowed down.

Although the same reaction can take place in the presence of alkali solutions other than aqueous solutions of sodium hydroxide, the latter are most industrially used. They must have a Na 2 O concentration of between 8.9 and 28.6% by weight at the time of attack of the silica. Too strong a dilution results in solutions of sodium silicate which are not directly usable for industrial purposes and an excessive concentration causes blockages in the sand bed due to the formation of sodium disilicate crystals 830 1 32 2 .......... ...— .......'............................

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The reactor is fed from the top, the reaction taking place on the sand bed which serves both as a silica source and as a filter, which promotes good material transfer and the formation of a clear solution of alkali metal silicate.

The interior of the reactor in contact with the hot a-alisilicate solutions is made of a metal or a soot alloy which is corrosion resistant. Nickel is well suited for this purpose, but the common steels such as those used for boiling pans can also be used, especially if carbonate is added to the alkaline solution as prescribed by French Patent 2,462,390. This reactor is equipped with a metallic grating in its lower part to retain the sand or any other means that is suitable for this and means a minimal charge loss. The cross section of the reactor determines the rate of passage of the solution through the silica. This speed should be between 2 and 15 m / hour. A slower speed does not allow sufficient productivity or proper transfer and too large a speed leads to a batch loss so that reaction control is not possible. This reactor also fulfills the role of sand filter, which results in a minimum sand height of 20 and leads to completely clear solutions.

The weight ratio SiO / Me.0 and the reaction rate which is a function of the temperature in the reactor bed, the latter must be between 150 and 240 ° C in order to allow both sufficient attack of the silica and control of the reaction. Since the reaction is slightly exothermic, the reactor does not need to be heated. In contrast, the alkaline solution should be introduced at a temperature such that the temperature in the reactor is maintained. The temperature of the products received is sufficient to ensure a concentration of the solution, and / or preheating of the reactants.

A preferred embodiment of the process of the invention consists in forming the aqueous alkali metal hydroxide solution entering the reactor in such a way that no external caloric energy supply is required.

The especially advantageous advantage provided by such. mode of operation is achieved thanks to a judicious application of the available calories in the alkali metal silicate solution leaving the reactor for heating a concentrated aqueous solution of an alkali metal hydroxide and water on the one hand, and on the other hand of the calories provided by the exothermic dilution of this concentrated alkali solution by that water to form the alkaline solution entering the reactor.

Thus, for example, when an aqueous sodium hydroxide solution is used, it is possible to obtain clear solutions of sodium silicate containing 35 to 46% by weight of sodium silicate without supply of caloric energy from the outside.

The particularly advantageous result of the method according to the invention according to its preferred embodiment lies not only in the savings on caloric energy realized with regard to a mode of operation that differs within the scope of the invention, but also in the possibility offered economically a clear solution of alkali metal silicate which is directly usable in industry.

The drawing depicts a schematic of the method according to the preferred embodiment: The silica, for example, a quartz sand, originating from, for example, storage vessels, thanks to a known system with which it is possible to continuously switch from higher pressure to atmospheric pressure from solid Products initially under atmospheric pressure are introduced via line 1 into the top of reactor 2. The sand-25. bed that forms in the lower part of this reactor is supported by any member, not shown in the drawing, which is suitable for this purpose and which offers a minimal batch loss, for example a grid or metal mesh.

A concentrated aqueous solution of an alkali metal hydroxide supplied through line 3 is preheated at 4 by indirect heat exchange with the alkali silicate solution circulating in the tubing.

It is then supplied in a homogeneous manner, diluted at 6 by water through the tube 7 and it itself preheated at 8 by indirect heat exchange with the alkali metal silicate solution circulating in the line 9.

8301322 ----------------- “-5-

The alkaline solution thus obtained enters the upper part of the reactor 2 above the silica bed via the line 10.

The alkali metal silicate solution which leaves the reactor 2 at the bottom continuously through the tube 1-1 and whose flow is distributed 5 in the lines 5 and 9 becomes one again in the line 12 after preheating the concentrated alkaline solution and water is finally discharged to be collected through this tube 12.

The invention is further illustrated by the following non-limiting examples. Examples IX and X more particularly illustrate the invention in its preferred embodiment.

Front I.

In a thermally insulated vertical nickel tube with an internal diameter of 90 mm and a length of 6 m, a batch of 53 kg of quartz sand with an average granulometry of 300 µm is introduced. An aqueous 19.6 wt.% Na2O sodium hydroxide solution is passed through for 1 hour for 20 minutes at a flow rate of 50 l / h. The temperature in the tube is maintained at 225 ° C.

A sodium silicate solution containing 194 g / l Na 2 O and 485 g / l SiO 2 is recovered at the foot of the reactor.

The unreacted sand remains in the reactor which is reloaded with fresh sand for the next reaction.

Example II.

A vertical nickel tube thermally insulated with an inner diameter of 90 mm and a length of 2 m is continuously fed with quartz sand of average granulometry 300 µl in an amount of 22 kg / h and a warm aqueous sodium hydroxide solution. solution with 11.2 wt.% Na 2 O with a flow rate of 69 l / h solution. The temperature in the tube is maintained at 220 ° C.

The silicate solution recovered at the base of the reactor contains 125 g / 1 Na 2 O and 306 g g / 1 SiO 2.

Example III.

Into the tube used in Example 2, silica is continuously introduced at a flow rate of 27 kg / h and an aqueous sodium hydroxide solution containing 17.6 wt.% Na 2 O at a flow rate of 50 l / h solution. The silica is a quartz sand with an average granulometry of 850 µm. The temperature in the reactor is maintained at 218 ° C. The at the foot of the 830 1 32 2 ---------------------------------------- Silicate solution formed in a reactor contains 175 g / l Na 2 O and 429 g / l SiO 2 Example IV.

Silica at a rate of 8/4 kg / h and the mixture is continuously introduced into the tube of Example II. aqueous sodium hydroxide solution 5 containing 19.6 wt.% Na 2 O with a flow rate of 33 l / h solution. The silica is a quartz sand with an average granulometry of 300 µm. The temperature in the reactor is maintained at 160 ° C. The silicate solution formed at the base of the reactor contains 197 g / 1 Na 2 O and 200 g / 1 SiO 2 · 10 Example V.

Into the tube of Example II, silica is continuously introduced at a rate of 25 kg / h and aqueous sodium hydroxide solution containing 23.4 wt% Na 2 O at a flow rate of 40 l / h solution. The silica is a quartz sand with an average granulometry of 300 µm. The temperature in the reactor is 190 ° C. The silicate solution formed at the base of the reactor contains 226 g / 1 Na 2 O and 454 g / 1 SiO 2 · Example VI.

Into a mild steel vertical tube equipped with a double jacket with an inner diameter of 90 mm and a length of 2 mm, 20 silica is continuously fed at a rate of 23 kg / h and a solution containing 14.9 wt% Na20 and 20 g / 1 Na ^ O ^ with a flow rate of 50 1 / hour solution. The silica is a quartz sand with an average granulometry of 300 µm. The temperature in the tube is maintained at 218 ° C. The pressure in the reactor is maintained by control. The silicate solution formed at the base of the reactor contains 160 g / l Na2 <0 and 384 g / l SiO2.

Example VII.

Into the tube of Example II, the silica is charged continuously at a rate of 21 kg / h and the aqueous sodium hydroxide solution containing 16.7 wt.% Na 2 O at a flow rate of 50 l / h solution. The silica is a quartz sand with an average granulometry of 130 µm. The temperature in the reactor is maintained at 190 ° C. The silicate solution formed contains 165 g / 1 Na 2 O and 338 g / 1 SiO 2

Example VIII.

Into the tube of Example II, silica is continuously introduced at a rate of 31 kg / h and aqueous potassium hydroxide solution. . Contains 26.7 wt% K20 at a flow rate of 50 l / h solution. The silica ..... 8301322 -7- is a kwaxts-zanö with: average granulometry 300 μΐπ. The temperature in the reactor is maintained at 195 ° C. The silicate solution formed at the base of the reactor contains 264 g / 1 K 2 O and 462 g / 1 SiO 2.

Example IX.

5 In the top part of a reactor consisting of a vertical cylindrical tube of normal steel which has been carefully thermally insulated, such as the entire device with an inner diameter of 90 mm and a height of 6 m, 13.3 kg / hour of quartz sand with a average granulometry of 300 µ and whose temperature is that of the environment.

Into the top of the same reactor and above the sand bed, 33.6 kg / h of a concentrated aqueous sodium hydroxide solution containing 19.8 wt.% Na 2 Obat, the temperature of which is 192 ° C, is introduced.

This alkaline solution of 192 ° C is obtained thanks to a homogeneous and exothermic mixing of 17.9 kg of a concentrated aqueous solution of sodium hydroxide with 37.2% by weight Na 2 O and brought to 171 ° C by indirect heat exchange with the sodium silicate solution leaving the reactor at 188 ° C with 15.7 kg / h water brought to 171 ° C by heat exchange as described above.

The clear sodium silicate solution prepared in an amount of 46.9 kg / h contains 42.6 wt% sodium silicate in which the weight ratio is S102 / ^ 2.

Example X.

In the same device according to the same processing principle and with the same quality of sand as in example IX, the method according to the invention is carried out by introducing into the reactor 25.5 kg / hour of sand, the temperature of which is the ambient temperature, as well as 59, 5 kg / hour of an alkaline solution containing 21.4 wt.% Na2 <3 and of which the temperature is 213 ° C.

This alkaline solution at the temperature of 213 ° C is obtained thanks to a homogeneous and exothermic mixing of 34.27 kg / h of a concentrated aqueous sodium hydroxide solution containing 37.2 wt% Na 2 O and brought to 192 ° C by indirect heat exchange with the sodium silicate solution leaving the reactor at the temperature of 207 ° C with 25.23 kg / hour of water brought to 192 ° C by a heat exchange as described above.

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The clear sodium silicate solution prepared in an amount of 85 kg / h contains 45% by weight of sodium silicate, in which the weight ratio is SiO 2 / Na 2 O 2.

ψ ~ ..... 33 0 1 322 --------------------------------------- -----------------------------------

Claims (9)

1. A process for preparing a clear solution of alkali metal silicate, the weight ratio of which is SiCl 2 / alkali metal oxide of at most 2.5 by attacking crystallized silica with an average granulometry between 0.1 mm and 2 mm, using an aqueous solution of an alkali metal hydroxide passes through a silica bed formed in a vertical tubular reactor without mechanical stirring and is fed from the top down with silica and an aqueous solution of an alkali metal hydroxide. 2. Process according to claim 1, characterized in that the aqueous alkali metal hydroxide solution passes through the silica bed at a speed between 2 m / h and 15 m / h. Process according to claims 1 to 2, characterized in that the temperature at which the silica is attacked by the aqueous alkali metal hydroxide solution is between 150 and 240 ° C. 4. Process according to claims 1-3, characterized in that the aqueous alkali metal hydroxide solution entering the reactor is an aqueous sodium hydroxide solution containing 8.9 to 28.6% by weight Na 2 O. 5. Process according to claims 1-4, characterized in that the aqueous alkali metal hydroxide solution introduced into the reactor is formed by homogeneous and exothermic mixing of a concentrated aqueous solution of alkali metal hydroxide and water which are preheated by indirect heat exchange with the alkali metal silicate solution leaving the reactor in such a way as to avoid all external heat energy input. Process according to claim 5, characterized in that the prepared clear sodium silicate solution contains the silicon and the sodium in the weight ratio SiC 2 Afe 2 O = 2 and is directly usable in industry. Method according to claims 1-6, characterized in that the silica used is a quartz sand. 8. A method according to claims 1-7 *, characterized in that the silica bed plays the role of filter for the product obtained. 8301322: -10- Process according to claims 1-8, characterized in that the alkali metal hydroxide solution contains an alkali metal carbonate. 830 1 32 2 ...........