FI57091B - FRAME STATION FOR AMMONIUM-ZIRCONIUM CARBONATE - Google Patents

Description

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United Kingdom-UK (GB) U91M / 71 (71) Magnesium Electron Limited, Lunin's Lane, Clifton Junction, Swinton, Manchester, England-England (GB) (72) Raymond Francis Phillips, Ceadle Holme, Cheshire, England-England ( This invention relates to aqueous solutions of ammonium zirconium carbonate and to their preparation. The present invention relates to aqueous solutions of ammonium zirconium carbonate and their preparation.

Ammonium zirconium carbonate solutions containing 10% by weight of zirconia are commercially available and can be used whenever soluble zirconium is required in an alkaline environment. These solutions are usually prepared by dissolving basic zirconium carbonate at room temperature in a solution containing 3 moles of either commercial ammonium carbonate or a mixture of ammonium bicarbonate and ammonium hydroxide. Based on the preparation method and analysis of the crystalline materials obtained from these solutions, it is likely that the main compound present in the solution is (NH 4) 2 ZrOH (CO 2) 3, which crystallizes as the dihydrate.

Such ammonium zirconium carbonate solutions are widely used to insolubilize starch binders used in paper coating compositions. However, their use for rendering starch insoluble and other purposes is

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2,57091 limited because these solutions are irreversibly hydrolyzed at temperatures above 40 ° C to form zirconia gels. In addition, because these solutions are dilute, most of their transportation costs are water transportation costs.

Some zirconium compounds are known to impart thixotropy to certain polymer or copolymer dispersions, for example emulsion paints, but commercially available ammonium zirconium carbonate solutions have not been found to be effective for this purpose.

It has been found that concentrated ammonium zirconium carbonate solutions capable of imparting thixotropic properties to polymer and copolymer dispersions are more resistant to hydrolysis at elevated temperatures than the more dilute solutions currently available or can be readily prepared. Only small additions of carbonates may be used in these preparations, generally on the order of 1 mole instead of 3 moles, which has been found to be advantageous both economically and in terms of providing solutions that act as gelling agents for emulsion paint polymers. According to the present invention, there is provided an aqueous solution of ammonium zirconium carbonate which imparts thixotropic properties to aqueous dispersions of polymers and copolymers when mixed therewith.

It has been found that according to the present invention ammonium zirconium carbonate solutions can be obtained which are stable for at least 10 hours at 60 ° C.

In this specification and the appended claims, the term "stable" means the property that the solution has no tendency to gel and does not form a solid precipitate from the components dissolved in the solution during storage.

According to another aspect of the invention, there is provided a process for preparing such an ammonium zirconium carbonate solution, which process comprises reacting basic zirconium carbonate with an aqueous ammonium carbonate solution or slurry containing 1-1.5 moles of ammonium carbonate per mole of basic zirconium carbonate.

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Alkaline zirconium carbonate usually contains 0.45 to 0.55 moles of carbonate per mole of zirconium, so the use of ammonium carbonate in the above amount makes it possible to obtain a solution containing up to 2 moles of carbonate per mole of zirconium.

In the preparation of the ammonium zirconium carbonate solution, it has been found that as the amount of ammonium carbonate increases by more than 1.5 moles, the ability of the solution to impart thixotropic properties to the aqueous dispersions of the polymer progressively decreases. It is also generally desirable to use as little ammonium carbonate as possible for reasons of economy. However, the stability of the resulting solution progressively deteriorates and the viscosity of the solution increases as the amount of carbonate therein decreases, and it has been found that 1.0 mole of ammonium carbonate per mole of basic zirconium carbonate is a practical lower limit.

In the preparation of ammonium zirconium carbonate solutions, the addition of relatively large amounts of ammonium carbonate, e.g., 2.0 moles per mole of basic zirconium carbonate, requires further dilution of the final solution to prevent gradual separation of water-hydrated ammonium ironyl carbonate crystals at room temperature. These crystals also separate from the concentrated solution when cooled to near 0 ° C, but this can be avoided by limiting the amount of ammonium carbonate present to a maximum of 1.5 moles per mole of basic zirconium carbonate.

The reaction between basic zirconium carbonate and ammonium carbonate is promoted by heating. According to a suitable procedure, a mixture of 30% ammonium hydroxide and an equivalent amount of ammonium bicarbonate, rather than more expensive ammonium carbonate, is used in the preparation to form a slurry. The coupling reaction of ammonium bicarbonate with 30% ammonium hydroxide takes place endothermically, so that the slurry has to be heated to return it to room temperature. The basic zirconium carbonate is gradually added to the slurry to such an extent that the viscosity of the slurry allows sufficient agitation to be maintained, and the temperature of the slurry is raised using direct steam or indirect heating. As the reaction progresses, the viscosity of the slurry decreases and the slurry becomes brighter so that more basic zirconium carbonate can be added. The temperature of the solution is finally raised to a maximum of 65 ° C, and the solution is kept at this temperature until the reaction has time to complete.

It should be noted that according to the procedure described, the temperature is gradually raised to a maximum of 65 ° C during the addition of basic zirconium carbonate. Raising the temperature of the slurry before the addition of basic zirconium carbonate would result in losses of ammonia from the reaction medium when the reaction is carried out in an open vessel.

The concentration of ammonium zirconium carbonate solution obtained is up to 25% by weight of zirconium, expressed as ZrO 2; the use of a concentration close to this upper limit is preferred because the stability of the solutions tends to deteriorate with increasing dilution.

The use of high concentration also provides significant savings, especially in transportation costs. Concentrations of 18-22% by weight, expressed as zirconia, are preferred.

The stability of the ammonium zirconium carbonate solution of the invention can be further improved by the addition of tartaric acid or Gluonic acid, preferably from about 1-2% by weight of the final solution. Tartaric acid or gluconic acid can be added after the reaction of ammonium carbonate and basic zirconium carbonate.

The following example is provided to illustrate the invention.

Example 1 This example relates to the preparation of an ammonium zirconium carbonate solution containing at least 20% ZrCl 2 and 1.3 moles of ammonium carbonate.

10.3 kg (130 moles) of solid ammonium carbonate, NH 4 HCO 3, was slowly added, with stirring, to a mixture of 7.4 liters of 30% ammonium hydroxide (130 moles) and 8 liters of water, whereby

Claims (2)

5707091 A thick ammonium carbonate slurry formed. Since this reaction is endothermic, heat was introduced to return the slurry to room temperature. With further stirring and heating of the slurry, 15 kg (50 moles) of basic zirconium carbonate containing 42% by weight of ZrO 2 was added. remained such that it could be easily confused. The temperature of the slurry was allowed to rise to 60 ° C, at which time the heat input was stopped, and stirring was continued for another hour to complete the reaction. A small amount of filtration aid was added to the reaction medium, which was then filtered under pressure. The clear solution thus obtained was found to contain 22% by weight of ZrO 2 and was diluted with water to reduce the ZrO 2 content to 20% by weight. When this 20% solution was heated at 60 ° C for at least 4 hours, no hydrated gels formed and storage in the refrigerator at 0 ° C for four weeks did not cause crystalline material to separate. Attempts to isolate a stable solid from solution by spray drying at low temperature were unsuccessful. The solution was found to be able to impart thixotropy to aqueous dispersions of polymers and copolymers, i.e., the solution was found to be a gel for emulsion paints. 1. an aqueous solution of itoinone zirconium surfactant which imparts thixotropic properties to aqueous dispersions of polymers and copolymers when mixed with them, characterized in that the molar ratio of carbonate to zirconium is at most 2 and the aqueous solution contains at least 18% by weight of zirconium for at least 10 hours, At 60 ° C. Solution according to Claim 1, characterized in that it contains at most 25% by weight of zirconium, expressed as zirconium dioxide.