IL84830A - Alkali and alkaline earth metal bromide and bromate solid mixtures and process for preparation thereof - Google Patents

Description

REF : 850/87 84830/2 ALKALI AND ALKALINE EARTH METAL BROMIDE AND BROMATE SOLID MIXTURES AND PROCESS THEREOF 850/87 - 1 - The present invention relates to a process for the preparation of mixtures of bromides and bromates of alkali or alkaline earth metals, to mixtures obtained thereby and to their use as bromine sources.

Bromine, which is an important reagent in a variety of reactions in organic and inorganic chemistry, is difficult to store, ship and handle in its pure form. Furthermore, safety and environmental regulations are becoming increasingly strict in many countries, with respect to bromine handling and storage. Therefore, the problem of diminishing health and safety hazards connected with the handling of bromine is ever increasing.

It is known that bromine can be stored in non-free form, as a relatively harmless derivative which can be reacted to give free bromine and harmless by-products, thereby storing it in an easily handled form until shortly before use. Particularly, the reaction: 5NaBr (aq) + NaBr03 (aq) + 6HX > 3Br2 + 6NaX (aq) + 3H20 wherein HX represents a strong acid, and NaX its sodium salt, is known to be a possible way to obtain free bromine from relatively harmless compounds. Throughout this specification, whenever reference is made to sodium, it is intended that the same applies to other alkali or alkaline earth metals, e.g. potassium or magnesium, with the appropriate changes, as will be apparent to a person skilled in 850/87 - 2 - the art.

However, the above described reaction, while simple and applicable, has never found a practical industrial application because no suitable bromine carrier has been made available by an industrially practical process and at acceptable prices. As will be apparent to a person skilled in the art, in order to obtain the maximal bromine yield a 5:1 bromide:bromate molar ratio must be present in the bromine carrier. Whenever mixtures of alkali metal bromides and bromates have been employed for this purpose, these have been obtained by mixing the bromide and the bromate, which were prepared separately, to give the desired proportion in the mixture. This, while affording a 5:1 mixture, is extremely expensive because of the high cost of the pure components, and therefore this procedure has seldom been employed.

A similar situation is that which exists with respect to the production of chlorine dioxide, which is useful, e.g., in the paper industry, and of chlorine, as described, e.g., in U.S. Patents Nos. 3,667,912 and 3,823,225. Chlorine dioxide is normally generated from solutions containing an alkali metal chloride and an alkali metal chlorate, by the addition of a strong mineral acid, in a manner analogous to that outlined above with respect to bromine production. The art, however, does not consider solid mixtures of chlorides and chlorates and, instead, teaches to prepare and employ slurries (U.S. Patent No. 4,283,287) or concentrated solutions (U.S. Patent No. 4,434,033) for such purposes.

It is therefore clear that it is highly desirable and advantageous able directly to prepare such a bromide:bromate mixture.

The reaction: 3Br2 + 6NaOH (aq) » 5NaBr (aq) + NaBrO3 (aq) + 3H2O is known in the art. However, this reaction yields also NaBr02 and NaBrO which, together with the bromide and the bromate, are present in various amounts which change with time to yield different mixtures. Also, the product of the reaction is in aqueous form which is both unpractical and uneconomic for shipping and storage purposes, besides being unstable.

It is an object of the present invention to provide a process by which the above problems and disadvantages can be overcome, and a solid mixture can be provided, which can be conveniently stored and used as a safe bromine source.

It is a further object of the invention to provide highly homogeneous solid mixtures of alkali or alkaline earth metal bromides and bromates.

The process for the preparation of a solid homogeneous mixture of bromides and bromates of alkali or alkaline earth metals according to the invention, having a Homogeneity Factor, as hereinafter defined, lower than 3.5, is characterized by the steps of: a) providing an aqueous mixture of the alkali or alkaline earth metal bromide and of the alkali or alkaline earth metal bromate in the desired predetermined ratio; b) feeding the said aqueous mixture to a dryer adapted to obtain particulate solids; and c) recovering the dry particulate solid mixture of the alkali or alkaline earth metal bromide and alkali or alkaline earth metal bromate.

A preferred process according to the invention comprises the steps of: a) preparing an aqueous mixture of the alkali metal bromide and of the alkali metal bromate in the desired predetermined ratio, by reacting bromine with the appropriate alkali metal hydroxide; b) feeding the said aqueous mixture to a dryer adapted to obtain particulate solids, the temperature of the feed to the said dryer being not lower than the temperature at which the aqueous solution of step (a) has been prepared; and c) recovering the dry particulate solid mixture of the alkali metal bromide and alkali metal bromate.

Preferably, the reaction temperature is comprised between 50°C and 90°C. The reaction temperature is of importance in obtaining high yields of the process. In fact, the higher the final reaction temperature, the higher the concentration of the reagents in the reaction mixture. This, as will be apparent to a person skilled in the art, is also important in the drying of the bromide bromate mixture, since it is desirable to feed the smallest possible amounts of water in order to reduce the power consumption of drying.

Preferably, the dryer employed in the process of the invention is a spray-dryer. However, any other dryer which is adapted to obtain particulate solids from liquid solutions can be employed, as will be understood by the skilled engineer.

According to a preferred embodiment of the invention, the alkali or alkaline earth metal is selected from among, Na, Mg and K.

The invention is also directed to novel particulate solid mixtures of alkali or alkaline earth metal bromides and bromates, having high homogeneity, as hereinafter defined.

The Homogeneity Factor (HF) is a measure of the homogeneity of a given mixture, and provides a characterizing parameter thereof. The lower the value of the HF, the more homogeneous is the mixture. A typical HF value for a 5:1 NaBr:NaBr03 mixture prepared by the process of the invention is 1.29, while for the same mixture prepared by thoroughly mixing NaBr and NaBr03, by mechanical means, a typical value is HF=3.5. The HF is defined as the Relative Standard Deviation (RSD) of 12 samples taken as hereinafter described under "Homogeneity Testing". The RSD is defined as follows: ∑ Xi N wherein Xj is a measured value, and N is the number of samples.

Solid mixtures of an alkali or alkaline earth metal bromide and an alkali or alkaline earth metal bromate, whenever prepared by the process of the invention, therefore, also form part of the present invention. According to a preferred embodiment of the invention the alkali metal is sodium and the solid mixture obtained is a mixture of sodium bromide and sodium bromate.

As hereinbefore stated, the highest bromine yield is obtained when the molar ratio between the bromide and the bromate in the carrier is 5:1, and mixtures having a bromide :bro mate ratio of about 5:1 are therefore preferred.

The above and other characteristics and advantages of the invention will be better understood from the following illustrative and non-limitative description of preferred embodiments.

Example 1 Preparation of a 5:1 Drv Mixture of Sodium Bromide and Sodium Bromate (on a molar basis).

A) Preparation of a sodium bromide sodium bromate liquid mixture. * 42.6 kg of sodium hydroxide 43.5% aqueous solution was fed into a 500 lit. reactor containing 160 lit. of water. The reactor was heated to 70°C and liquid bromine was fed to the reactor at a rate of 18 kg hr. The total amount of bromine fed to the reactor was 37.5 kg. The pH of the final mixture was adjusted to a value of about 9.5 and the reaction mixture was kept at 70°C for an additional 2 hours, until the reaction was completed, as determined by the method described in Analyt. Chem., Vol. 35, No.7, June 1963 (p.908).

The solution so obtained contained: NaBrO: 0.97 g/1; NaBrOa: 66.47 g/1; NaBr: 207,22 g/1; NaBr02: 0 g/1.

B) 120 liters of the solution obtained from step A were fed to a spray dryer. The spray dryer had a drying cell with a diameter of 2,900 mm, an atomizer wheel having a diameter of 160 mm and having four outlets of 10 mm diameter each and operated at 16,000 rpm. The solution was fed at a flow rate of 65-70 1/hr and at a temperature of 70°C. Air was fed with a flow rate of 3,100 m3/hr and at a mean temperature of 300°C. The outlet temperature of the air was in the range 105-110°C. The solid obtained during 45 minutes consisted of 42 kg of 5.13:1 bromide:bromate mixture, as a particulate solid having a bulk density of 1.01 g/cm3, and a residual moisture (as determined by I.R. lamp) of 0%.

Example 2 A sodium bromide/sodium bromate solution was prepared, containing: NaBrO: 0 gr/1; NaBr02: 0.9 gr/1; NaBr03: 68 gr/1; NaBr: 233 gr 1.

The solution was fed to a NIRO atomizer with a 1000 mm diameter of drying cell, a 120 mm atomizer diameter, having four ceramics 10 mm outlet and an atomizer operating at 20,000 rpm. The mean inlet air temperature was 240°C, and the mean outlet temperature 105°-110°C. Particulate solids were obtained (about 0.3 kg solid for each liter of solution). The properties of the solids obtained were comparable to those of Example 1.

Example 3 This example illustrates the preparation of a KBr:KBrO3 solution ready for drying. 338 g of a 85.7% solution of KOH was added to a 2 liters flask containing 870 ml water at ambient temperature. The contents of the flask were heated to 90°C after which 404 g of bromine were added dropwise at a rate of 50-60 ml/min. The total volume of the mixture reached 1080 ml. 850/87 - 9 - The results at the end of the reaction were: KBrO: 0 gr/1; KBr02: 2.9 gr/1; KBr03: 126 gr/1; KBr: 465 gr/1. Molar ratio bromide:bromate = 5.18:1.

The results after 30 mins after the end of the reaction were: KBrO: 0 gr/1; KBrO2 = 1 gr/1; KBrO3: 127 gr/1; KBr: 459 gr/1. Molar ratio bromide:bromate = 5.08:1.

The reaction mixture was allowed to cool and to remain at room temperature overnight. The resulting molar ratio of bromide to bromate was 41:1, after solids precipitated. The mixture was reheated to 90°C and the resulting molar ratio was 5.05:1.

Example 4 This example illustrates the preparation of a MgBr2:Mg(BrO3)2 solution ready for drying.

A slurry of 51 g Mg(OH)2 in 1000 ml water was prepared. The slurry was fed to a reaction vessel and heated to 55°C. 13 g of liquid bromine were fed from a bromine funnel into the slurry, through a deep pipe. The bromine was fed at such a rate as to avoid its evaporation from the slurry. The reaction mixture was heated for additional 30 minutes. The reaction was completed when turbidity of the mixture was not observed any more. The solution was cooled to room temperature and 850/87 - 10 analyzed, giving the following results: Mg(BrO)2 = 0 Mg(Br02)2 = 0 Mg(Br03)2 = 39.0 g/lit MgBr2 = 128 g/lit Molar ratio MgBr2:Mg(Br03)2 = 4.9:1 Homogeneity Testing The value of the Homogeneity Factor (HF), referred to in the specification, is measured as follows. A sampling device is provided, consisting of a straight flat elongated slab into which 12 identical bores have been drilled. The diameter of the bores is 5 mm, their depth is 9 mm, and their volume ca. 177 mm3. The center-to-center distance between two adjacent bores is 28 mm.

Sampling is effected by pouring the solid particles onto the sampling device, completely covering its surface. Surplus material is then shaved-off the sampling device by means of a blade, thus leaving particulate material to fill the 12 bores. The contents of each of the 12 bores is separately emptied into a separate test tube and dissolved in water. The 12 water solutions so obtained are then analyzed to determine the concentration of the alkali metal bromide and bromate, which is expressed in terms of moles of alkali metal bromide per 1 mole of alkali metal bromate.

The HF is defined as the RSD of the 12 measured concentrations of the 850/87 - 1 1 samples taken as described above. The HFs obtained with different mixtures are illustrated by the following examples.

Example 5 The mixture prepared according to Examples 1(B) and 2 were analyzed in the homogeneity test described above. The values found were: Example 1: HF=1.29; Example 2: HF=1.15.

Example 6 (comparative) A mixture was prepared by mixing pure 60-100 mesh crystalline sodium bromide and sodium bromate (ex Bromine Compounds Ltd.), in a 5.38:1 ratio. The mixture was thoroughly mixed in a mechanical shaker and ground in a mortar to a fine powder.

The homogeneity test gave: HF=3.53.

Example 7 (comparative) Example 6 was repeated, but without grinding. The result was: HF=18.7.

Example 8 (comparative) 50.0 g of a 5:1 sodium bromide:sodium bromate mixture were dissolved in 2000 ml water. Water was evaporated in a Rotavapor under a pressure of 25 mmHg and temperature of 80±5°C, to give a solid product. 850/87 - 12 - Two homogeneity tests were carried out on this material. Test No. 1 was carried out on the upper layer of the precipitate, and Test No. 2 on the lower layer. The results obtained were: Test No. 1; Br:Br03- = 12.97:1; HF=6.3 Test No. 2; Br:Br03- = 3.65:1; HF=12.

The above description and examples have been provided for the purpose of illustration and are not intended to be limitative. Many modifications can be effected in the process of the invention. For example different bromide/bromate ratios can be obtained, if desired, or different dryers can be employed, all without exceeding the scope of the invention.

Claims (13)

850/87 - 13 - CLAIMS:

1. A process for the preparation of a solid homogeneous mixture of bromides and bromates of alkali or alkaline earth metals, characterized by the steps of: a) providing an aqueous mixture of the alkali or alkaline earth metal bromide and of the alkali or alkaline earth metal bromate in the desired predetermined ratio; b) feeding the said aqueous mixture to a dryer adapted to obtain particulate solids; and c) recovering the dry particulate solid mixture of the alkali or alkaline earth metal bromide and alkali or alkaline earth metal bromate.

2. A process according to claim 1 , characterized by the steps of: a) preparing an aqueous mixture of the alkali or alkaline earth metal bromide and of the alkali or alkaline earth metal bromate in the desired predetermined ratio, by reacting bromine with the appropriate alkali or alkaline earth metal hydroxide; b) feeding the said aqueous mixture to a dryer adapted to obtain particulate solids, the temperature of the feed to the said dryer being not lower than the temperature at which the aqueous solution of step (a) has been prepared; and c) recovering the dry particulate solid mixture of the alkali or alkaline earth metal bromide and alkali or alkaline earth metal bromate.

3. A process according to claim 2, wherein the reaction temperature is comprised between 50°C and 90°C. 850/87 - 14

4. A process according to claims 1 to 3, wherein the dryer is a spray-dryer.

5. A process according to claims 1 to 4, wherein the alkali or alkaline earth metal is selected from among, Na, Mg and K.

6. A solid mixture of an alkali or alkaline earth metal bromide and an alkali or alkaline earth metal bromate, whenever prepared by the process of any one of claims 1 to 5.

7. A mixture according to claim 6, wherein the alkali metal is sodium.

8. A mixture according to claim 6 or 7, wherein the ratio between the bromide and the bromate is about 5:1.

9. A mixture according to claim 6, characterized in that it has a Homogeneity Factor, as defined in the specification, lower than 3.5.

10. A mixture as claimed in claim 8, wherein the alkali metal is sodium.

11. A mixture according to claim 10, wherein the ratio between the bromide and the bromate is about 5:1.

12. A process according to any one of claims 1 to 5, essentially as 850/87 - 15 - described and illustrated, with particular reference to the examples.

13. A solid mixture according to any one of claims 6 to 8, essentially as described with particular reference to the examples. LUZZATTO & LUZZATTO