MXPA00003490A - Aqueous borate-containing compositions and their preparation - Google Patents

Abstract

The invention relates to aqueous boron-containing compositions and their preparation. In particular the invention provides self-structured aqueous sodium pentaborate gels. The gels according to the invention may be prepared by reacting boric acid or boric oxide and sodium tetraborate or metaborate in suspension in water and under mixing such that a self-structured sodium pentaborate gel is formed. The gels according to the invention are physically stable and easily handled.

Description

"AQUEOUS COMPOSITIONS CONTAINING BORATO AND ITS PREPARATION" This invention relates to aqueous compositions containing boron and its preparation. - The compositions containing borate have different applications in the industry, e.g., in the fields preservatives or vitreous preservation, agriculture and wood as well as flame retardant applications. Conventionally, the borate has been provided in granular form and, particularly, for application by spraying, it has been necessary to dissolve the granules, requiring heating before application. Aqueous borate suspension formulations have been proposed for the treatment of wood. Therefore, AU-A-574389 proposes the use of a preservative composition comprising a colloidal microthrystalline suspension of boron salts and a thickener, which serves to maintain the stability of the suspension. The particles of the colloidal microcrystalline suspension are observed to be in the order of 15 to 30 microns. Similarly, Patent Number EP-A-0289317 describes wood preservative compositions comprising a preservative containing boron, which may be a micro-crystalline suspension, e.g., from 10 to 30 microns, and - a thickening agent, such as xanthan gum polysaccharide. The aforementioned preservative compositions were prepared by heating, dissolving and rapidly cooling the ingredients, followed by the addition of a thickening agent such as xanthan gum.

The resulting compositions are not self-structured as evidenced, of course, by their need for always employed thickeners. In accordance with one aspect of the present invention, a self-structured aqueous sodium pentaborate gel is provided. It has surprisingly been found that it is possible to provide sodium pentaborate in the form of a self-structured gel, ie, a gel which does not require thickeners as suspension aids for the particles. The gels according to the present invention can be easily prepared, are physically stable and can be easily handled. The gels can be pumpable and easily diluted for application as required. The gels according to the invention comprise particles of sodium pentaborate in a saturated aqueous solution.

- - The gels according to the invention can have high solids contents, e.g., up to about 80 weight percent, preferably in the order of 60 percent to 70 weight percent. If the solids content becomes too high, the gel can become too rigid for practical use. The gels in accordance with the present invention may have a high borate content, eg, from 8 percent to 13 percent by weight of boron as sodium pentaborate but may still be able to be easily handled, since the gel is pumpable and can be easily diluted by the addition of water. Preferably, the gels contain up to 9 percent to 12 percent by weight, more preferably about 10 percent by weight, of boron such as sodium pentaborate. The gel according to the invention comprises fine particles of sodium pentaborate ~~ within the saturated aqueous solution. To produce a self-structured gel, at least a considerable number of the particles must be less than 10 microns in size, preferably within the range of 0.1 to 10 microns, and more preferably less than 5 microns (eg, 0.1 to 5 microns) in size.

- Under some circumstances, however, a voidable product having a Jooro concentration of at least about 12 percent can be appreciated. In these cases, the products of the invention may contain particles, most of which will still generally be less than 10 microns, but the rest may be larger in size, e.g., up to 50, e.g., 40 microns in size. The compositions according to the present invention are easy to disperse in aqueous media and have a rapid dissolution rate at ambient temperatures and also under field conditions, where the water temperature can be as low as 5 ° C, such as that which can be found in agriculture or wood treatment conditions. In addition, even with high boron contents, the compositions are physically stable and capable of being pumped. When left to rest for prolonged periods, there may be certain syneresis, that is, a certain amount of liquid can be separated from the gel. This is unlikely to present a problem, since homogeneity can be easily restored by simple mixing. The syneresis can be reduced by adding an anti-sedimentation agent by techniques well known to those skilled in the art. The anti-sedimentation agents can be selected from polymers, high molecular weight, hydroxyethyl cellulose, crosslinked polyacrylates, bentonite gels, silica and combinations thereof. The mechanism of the gel system according to the invention is not completely understood. However, it is believed to be caused by the weak attraction of the particles by Van der Waals forces. This is demonstrated by the thixotropic nature of the compositions. During the shear stress of the sample and the removal of the shear force, the sol / gel transformation occurs. The gels according to the invention can be generally described as flocculated. Using a rotational viscometer, the shear flow versus stress regime flow curve, carried out in one cycle (whereby the shear rate was increased to 200 seconds and then reduced to 0) showed hysteresis with the reduction in the shear stress curve (descending) that is less than the increase in the shear stress curve (ascending). The gels according to the invention can be stable at temperatures between -10 ° C and 60 ° C, depending on their composition. The gels can be recovered from the frozen state, that is, they have freeze / thaw stability.

The gel according to the invention can be easily handled and does not suffer from the disadvantages of fines, fine powders, agglomeration and segregation encountered with solid products. In addition, the gel capable of being pumped according to the invention can be delivered in an exactly regulated manner. The gel is self-structured. If desired, the gel may contain additives, for example micronutrient fertilizers, herbicides, fungicides and insecticides. The compositions containing borate according to the present invention may be high density. For example, a gel of sodium pentaborate crystals having an equivalent of 10 percent boron by weight can have a density in the order of 1.3 grams per cubic centimeter. The gels according to the present invention can be prepared by reacting boric acid or boric oxide and sodium tetraborate or sodium metaborate suspended in water and under mixing. According to a second aspect of the present invention, there is provided a method for preparing a self-structured sodium pentaborate gel, which method comprises reacting boric acid or boric oxide and sodium tetraborate or sodium metaborate in suspension in water and mixed bass, in such a way - that a self-structured sodium pentaborate gel forms. Borax and / or sodium metaborate will usually be used in hydrated form, e.g., Na2B4? 7.5 or 10H2O and NaB02-8H20. The starting materials react with the formation of a precipitated material of sodium pantaborate, the particles from which under the influence of mixing are small enough (usually less than 10 microns) so that a self-structured gel is formed. The starting materials for example may be in dry or wet crystalline form, such as a wet filter cake or a wet product obtained after centrifugation in the production of borate, eg, boric acid or borax, by well known processes in the art. technique. In addition, plant liquids from borate production processes can be used. These liquids therefore provide the water for the preparation method as well as a certain amount of the starting materials. Generally speaking, the particle size of the starting materials is not critical. Three variables that contribute particularly to the production of a self-structured gel are the agitation regime, the concentration of the solid ingredients and the temperature used. However, there is a stipulation that solid ingredients should not be allowed to dissolve completely. This allows nucleation to be carried out easily. Agitation may be at low speed or high speed depending on the concentration of the solids. In general, the higher the concentration, the less intense the mixing will be. Slow agitation tends to provide particles that have a coarser nature that can contribute to a product capable of being emptied. The temperature will generally be at room temperature to near the boiling temperature, e.g., 90 ° C, preferably up to 60 ° C. The use of an elevated temperature tends to reduce the mixing times. It is often preferred to use mixing at high speed, high concentration and high temperature (normally up to approximately 60 ° C but possibly up to 90 ° C). Mixing at low speed usually provides a product with thicker particles and requires more time to form but the product is capable of being emptied. The starting materials are preferably used in stoichiometric amounts for sodium pentaborate. However, "the molar ratio of B2? 3: Na2? Can be from 3: 1 to 8: 1. The materials used to achieve these ratios would be selected from boric acid, boric oxide, sodium tetraborate or sodium metaborate, being Preferred are boric acid and borax pentahydrate If one of the reagents is in excessive amount, the excess of the unreacted material will usually be present in the resulting gel, and some coarse granules may be retained in the product. It may be advantageous to carry out the gel-forming reaction, in the presence of a previously prepared gel, to act as seminal or initial crystals in the production of the gel. In this way, there is a significant reduction in the preparation time. Typically, seminal or initial crystals represent 10 percent to 50 percent by weight of the final product. In accordance with a further aspect of the present invention, there is provided a method for preparing a self-structured sodium pentaborate gel, which method comprises adding agglomerated water-soluble sodium pentaborate particles comprising boric acid, borax pentahydrate and pentaborate. of sodium to water and mixed in such a way as to form a self-structured sodium pentaborate gel. In this method, boric acid and borax pentahydrate react with sodium pentaborate which acts as seminal crystals or initiation in the production of the gel. The starting agglomerated particles can be obtained by the process described in Patent Number O-A-93/17963. These particles can be obtained commercially, e.g., under the trademark SOLUBOR DF. Again, the intensity of the mixing and the temperature employed will depend on each other and on the concentration. However, the material should not be allowed to dissolve completely. As mentioned above, it may be advantageous to have some larger crystals present in the gel according to the invention. These gels can be obtained by the methods described above whereby the reactants are heated to dissolve a part (but not all) of sodium pentaborate. During cooling, some larger crystals (but less than 50, e.g., less than 40 microns in size) are formed. The gels according to the present invention can be applied, e.g., in agricultural fields, in the treatment of wood and flame retardant agents, as they are or after dilution. The invention is further illustrated with reference to the following Examples.

- Example 1 Technical grade boron acid (H3BO3) (224 grams) was mixed with borax pentahydrate (Na2B4? 7.5H2O - 176"grams) and water previously heated to a temperature of about 50 ° C (260 grams) in a Silverson mixer. having a disintegrator head and operating at approximately 3,000 revolutions per minute.The mixing was continued for a period of 10 minutes.The resulting product is a self-structured gel comprising 10 percent boron as sodium pentaborate crystals and which have particle sizes generally of less than 10 microns and density of 1.3 grams per cubic centimeter.

EXAMPLE 2 50 grams of the product of Example 1 were placed in a Silverson mixer as described above and seeds and water (65 grams) were added together with boric acid (56 grams) and borax pentahydrate (44 grams). grams). The mixture was stirred at 3,000 revolutions per minute for 5 minutes. The resulting product was a gel having the same properties as the product of Example 1.

Example 3 A suspension consisting of 57 parts by weight of Solubor DF in water was mixed gently at about 150 revolutions per minute for 15 minutes using a Heidolph agitator. The resulting product was a gel having the same properties as the product of Example 1.

Example 4 _ Technical grade boric acid (56 grams) was mixed with borax pentahydrate (44 grams) in water (65 grams) previously heated to 40 ° C using a Silverson mixer operating at approximately 3,000 revolutions per minute and placed on a hot plate at 150 ° C. The heat was disconnected as soon as the mixing started. A gel was formed having the same properties as the product of Example 1 after 5 minutes when the temperature had reached 53 ° C.

EXAMPLE 5 Boric acid, technical grade (560 grams), borax pentahydrate (440 grams) and water (650 grams) previously heated to 40 ° C were dispersed well by hand and then mixed using a Silverson mixer operating at approximately 3,000 revolutions per minute.

- - A gel having the same properties as the product of Example 1 was formed after 12 minutes.

Example 6 A mixture of 50 grams of the product of Example 1, water (65 grams), boric acid (56 grams) and borax pentahydrate (44 grams) were placed on a hot plate and gently stirred at 100 revolutions per hour. minute. A gel was formed having the same properties as the product of Example 1 after 15 minutes, when the temperature had reached 60 ° C.

Example 7 __ Technical grade boric acid (64 grams) (in stoichiometric excess), the borax pentahydrate (44 grams) and water (65 grams) previously heated at 40 ° C were mixed using a Silverson mixer at approximately 3,000 revolutions per minute on a hot plate were heated to 70 ° C for 4.5 minutes. The mixture was observed to become creamy in its consistency and then thinned. The mixture was cooled with stirring in a Heidolph agitator at 100 revolutions per minute for 0.5 hour and then in a Silverson at 3,000 revolutions per minute for 1 minute. A self-structuring gel product capable of emptying containing 12 weight percent boron was obtained.

Example 8 _ .. -_ _ .. - - - - • - ---- - The boric acid, technical grade (112 grams), the borax pentahydrate (88 grams) and water (52 grams) were stirred at revolutions per minute on a hot plate brought to a temperature of 90 ° C. The mixture was creamy at 60 ° C and then thinner at 80 ° C. The mixture was thickened by cooling with gentle agitation with a Heidolph stirrer. The resulting self-structured gel containing 13 weight percent boron contained a majority of particles less than 10 microns and some less than 40 microns.

Example 9 _. . "- - - - - Boric acid (280 grams) was added followed by borax pentahydrate (220 grams) to water stirred at a temperature close to boiling (248 grams). The mixture was stirred with high agitation to mix the 1 ingredients and then the agitation was slowed down to 100 revolutions per minute and was continued for a period of 15 minutes. The mixture was then stirred at 3,000 revolutions per minute for 2 minutes. A self-structuring gel product capable of emptying containing 11 weight percent boron was obtained.

Example 10 Boric acid (224 grams) and borax pentahydrate (176 grams) were added consecutively to boiling water almost boiling (260 grams) in a Silverson mixer operating at 3,000 revolutions per minute. Stirring was continued for a period of four minutes. A gel was formed which has the same properties as the product of Example 1.

Claims (15)

- CLAIMS:

1. A self-structured aqueous sodium pentaborate gel.

2. A gel in accordance with the claim 1, which contains 8 percent to 13 percent by weight of boron as sodium pentaborate.

3. A gel according to claim 1, containing from 9 percent to 12 weight percent of boron as sodium pentaborate.

4. A gel according to claim 1, which contains about 10 weight percent boron as sodium pentaborate.

5. A gel according to any of the preceding claims, wherein the sodium pentaborate particles are of a size smaller than 10 microns.

6. A gel according to claim 5, wherein the sodium pentaborate particles are of a size of less than 5 microns.

7. A gel in accordance with the claim 1, where most of the particles are less than 10 microns in size and the rest are up to 50 microns in size.

8. A gel according to claim 7, which contains from 12 percent to 13 percent by weight of boron as sodium pentaborate.

9. A gel according to any of the preceding claims which also contains a micronutrient fertilizer, a herbicide, a fungicide or an insecticide.

10. A gel according to any of the preceding claims that also contain an anti-sedimentation agent.

11. A method for preparing a self-structured sodium pentaborate gel, which method comprises reacting boric acid or boric oxide and sodium tetraborate or metaborate in a suspension in water and under mixing in such a way as to form a Sodium pentaborate gel self-structured.

12. A method according to claim 11, wherein the molar ratio of B2? 3: Na2? in the starting materials it is from 3: 1 to 8: 1.

13. A method according to claim 11 or 12, wherein the gel prepared above is added as seed or seed crystals in an amount of 10 percent to 50 percent by weight of the final product. -

14. A method for preparing a self-structured sodium pentaborate gel, which method comprises adding agglomerated water-soluble particles comprising boric acid, borax pentahydrate and sodium pentaborate to water and mixing in such a way that a pentaborate gel is formed. self-structured sodium.

15. A method according to any of claims 11 to 13, wherein the reaction mixture is heated to dissolve a part (but not all) of sodium pentaborate and allowed to cool with the formation of larger sized crystals. .