WO2016126691A1

WO2016126691A1 - An ammonium magnesium borate useful for delayed release of borate and methods of making

Info

Publication number: WO2016126691A1
Application number: PCT/US2016/016145
Authority: WO
Inventors: David M. Schubert; Michelle K. MCCRAY; Regis THYOT
Original assignee: U.S. Borax Inc.
Priority date: 2015-02-02
Filing date: 2016-02-02
Publication date: 2016-08-11

Abstract

This invention relates to an ammonium magnesium borate and its use in applications. Some applications involve the release of borate into solution. The release of the borate may be rapid or slow. This invention also relates to a method for making the ammonium magnesium borate.

Description

AN AMMONIUM MAGNESIUM BORATE USEFUL FOR DELAYED RELEASE OF BORATE AND METHODS OF MAKING

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application No. 62/110,753 filed on February 2, 2015, and U.S. Provisional Application No. 62/134,994 filed on March 18, 2015. All references are incorporated by reference in their entirety.

FIELD OF THE INVENTION

This invention relates to an ammonium magnesium borate compound of the formula

lOFtiO, and its use in several applications. Some applications involve the release of borate into solution. The release of borate can be rapid or slow. Slow release of borate is useful to delay the crosslinking of polyhydroxylated polymers. This invention also relates to a method for making the compound and methods to prepare the compound in forms having different dissolution rates in order to fine tune its performance for practical purposes. The invention also includes other uses of the compound.

BACKGROUND

Ammonium and magnesium borate chemistries are extensively described in the literature. However, there is a dearth of information regarding mixed ammonium- magnesium borates. Review of the literature revealed few references to well defined substances described as ammonium magnesium borates or ammonium magnesium borates and no references could be found to any substances having the same composition as the ammonium magnesium borate disclosed herein. The Supplement to Mellor 's Treatise on Inorganic and Theoretical Chemistry, Volume V, Part A: Boron-Oxygen Compounds, Longman Group Limited, London, 1980 references "magnesium ammonium borate." The Mellor reference states that "only one magnesium ammonium double salt has been reported." It further provides the composition of a single salt as (NH₄)₂0-MgO-3B₂0₃* H₂0 and references a publication, A. Keshan and E. Svarcs, Latvinjas PSR Zinatu Akad. Vestis, 1954, No. 8, 137. The Mellor reference further states that "if the product is washed with alcohol and then ether, or dried at or above 20 °C, the product is a heptahydrate" and references A. Keshan, Synthesis of Borates in Aqueous Solution and Their Investigation, [in Russian] Riga, 1955 (portions translated to English by A.A. Ostrowski). It can be noted that the ammonium magnesium borate disclosed herein was routinely dried above 20 °C (typically at 60 °C) and the composition is ( Η₄)₂θ MgO 6B₂O₃ IOH₂O. Arthur Messinger Comey, ed., A Dictionary of Chemical Solubilities states that "Ammonium magnesium borate, Sol. in H₂0, decomp. by boiling. Rammelsberg, Pogg. Annakn. 49, 451." The ammonium magnesium borate compound disclosed herein is not decomposed by boiling.

Two patents, U.S. Patent 2,331,232 to Ross ("Ross") and U.S. Patent 2,347,968 to Ross ("Ross II") list "magnesium-ammonium borate" as one of several reagents that can be used in the making of refractory materials, but the Ross and Ross II patents do not provide a compound or any other information on the specific nature of this substance.

The present invention overcomes these and other issues.

SUMMARY

Borate compounds are useful as crosslinking agents for polyhydroxylated polymers to produce rheological fluids and gels used in hydraulic fracturing operations for oil and gas recovery. Borate crosslinking is also used to tackify polymers in the manufacturing of adhesives, films and laminates. Refined borates, such as boric acid and sodium, potassium and ammonium borates, dissolve relatively quickly in water and provide no substantial delay before polymer crosslinking occurs. In many cases it is advantageous to delay the onset of crosslinking and concomitant development of high viscosity. For example, hydraulic fracturing operations for oil and gas recovery utilize viscous fluids to suspend proppant materials. However, it is advantageous in oilfield operations involving deep subterranean formations to delay the onset of crosslinking until the fluid can be pumped a considerable distance into the well. Ulexite, a mineral borate, is often used in such applications because it dissolves somewhat more slowly and provides delayed crosslinking. However, as a processed mineral, ulexite can be inconsistent in composition and can also contain unwanted impurities. In addition, relatively long delay times are difficult to achieve reliably using ulexite.

Starch and starch-dextrin adhesives are often used in the manufacture of paper goods, such as wound tubes, corrugated boxes, and related products. As described in this application, starch and/or dextrin can be crosslinked using a borate, often borax pentahydrate or borax decahydrate. Such borates provide immediate crosslinking resulting in rapid tackification of adhesives formulations. This immediate crosslinking can be disadvantageous in manufacturing operations involving high speed application of the adhesives and methods to delay the onset of crosslinking would provide a benefit by allowing higher application speeds.

Borates can also be used in engineered wood, wood-plastic and agrifiber composites to provide protection against decay fungi and wood-boring insects. Ammonium magnesium borate will provide similar protection.

Borates can also be used to provide fire retardancy to wood, paper and other cellulosic materials. In addition, ammonium and other borates are currently used in the manufacture of fire retardant including intumescent coatings. Ammonium magnesium borate disclosed herein will provide such fire retardant benefits when incorporated into cellulosic materials and coatings.

This invention involves a compound of matter, an ammonium magnesium borate compound of the formula ( I₄)₂MgBi₂O₂₀ 10H₂O [oxide formula ( I₄)₂0 MgO 6Β₂0₃ 10H₂O], methods for synthesis of the compound and practical applications for the compound. An advantage of the synthetic methods disclosed herein is the preparation of ammonium magnesium borate under mild conditions from economical and readily available starting materials without the generation of wasteful byproducts. The compound can be used to delay crosslinking of polyhydroxylated polymers, which has value for rheological fluids used in oil and gas extraction operations and other applications. Delayed crosslinking results from a controlled rate of solubility and thus a delayed release of borate into aqueous solutions. This controlled rate can be advantageous in many applications, including in the manufacture of adhesives, the protection of wood composites and related building materials against insect and microbial attack, and in agriculture for delivery of boron as a crop micronutrient in a controlled fashion. This invention also entails methods to produce ammonium magnesium borate having tunable dissolution rates, and therefore controllable crosslinking delay times. Another use of the compound can be as a fire retardant, an advantage of the compound exhibiting fire retardant properties.

Unlike the Comey reference, the crystals used for the single crystal X-ray structure of the compound of the invention were obtained from boiling water. In wood preservation, it can be advantageous to dissociate the compound to a more soluble borate and a less soluble borate, so that the borate active ingredient is rapidly soluble for immediate protection, but borates also remain present in the wood substrate for long term protection. In contrast, when the compound is hydrolyzed, the borate is less soluble. Thus, it is possible to alter the compound so that borates can be released quickly or over a period of time. By way of example, low solubility of borate offers longer protection in wood applications or delayed crosslinking time in other operations. An advantage of high solubility borates is an increased initial response in wood preservation or low crosslinking time in other operations.

An aspect of the invention is a method of preparing a compound of a formula of ( H₄)₂MgBi₂O₂₀* 10H₂O. The method includes reacting an ammonium source, a boron containing compound, and at least one magnesium compound to prepare the compound of the formula (NF^MgB^o' lOFtO.

An aspect of the invention is a method to treat a fluid useful in an oil field application. The method includes adding a crosslinking agent to the fluid, wherein the crosslinking agent comprises an ammonium magnesium borate compound.

An aspect of the invention is a method to reduce flammability. The method includes providing a fire retardant comprising an ammonium magnesium borate compound to reduce the flammability of an object.

An aspect of the invention is a method of crosslinking polymers of a polymer- containing composition by contacting the composition with an ammonium magnesium borate compound.

An aspect of the invention is a method to provide a nutrient to an agricultural field by providing the agricultural field with the nutrient. The nutrient comprises an ammonium magnesium borate compound of a formula (N¾)₂MgBi₂O₂₀* 10H₂O.

An aspect of the invention is an ammonium magnesium borate compound of formula (NF^MgB^o' lOF^O.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 illustrates the structure of

2H₂0;

Figure 2 illustrates an x-ray diffraction of (NH₄)₂MgBi₂O₂₀* 10H₂O formed using the method described in Example 1;

Figure 3 illustrates an x-ray diffraction of (NH₄)₂MgBi₂O₂₀* 10H₂O formed using the method described in Example 2;

Figure 4 illustrates an x-ray diffraction of (NH₄)₂MgBi₂O₂₀* 10H₂O formed using the method described in Example 3;

Figure 5 illustrates an x-ray diffraction of (ΝΗ₄)₂]ν¾Βΐ2θ2ο· 10H₂O formed using the method described in Example 4;

Figure 6 illustrates an x-ray diffraction of (NH₄)₂MgBi₂O₂₀* 10H₂O formed using the method described in Example 6; Figure 7 illustrates an x-ray diffraction of (NH₄)₂MgBi₂0₂o* 10H₂0 formed using the method described in Example 7;

Figure 8 illustrates crosslinking delay curves for ammonium magnesium borate samples prepared under different conditions;

Figure 9 illustrates linear crosslinking delay plots for ammonium magnesium borate samples prepared under different conditions;

Figure 10 illustrates a graph of the crosslinking delay times for the two samples discussed in Example 9;

Figure 11 illustrates a thermogravimetric analysis (TGA) graph illustrating dehydration/deammoniation processes for a sample of the ammonium magnesium borate over the temperature range of room temperature to about 1000°C; and

Figure 12 illustrates the differential scanning calorimetry (DSC) graph of a sample of the ammonium magnesium borate over the temperature range of room temperature to about 1000°C illustrating graph illustrating dehydration/deammoniation processes.

DETAILED DESCRIPTION

The invention relates to an ammonium magnesium borate of the formula (NH )₂MgBi₂0₂o 10H₂O, its use in applications and a method for making the compound.

This ammonium magnesium borate provides advantageous delay times in crosslinking studies. The invention also includes methods to prepare the compound not only by the reaction of magnesium oxide with ammonium pentaborate in aqueous solution, but also by reactions of mixed ammonium and alkali metal borate salts with magnesium salts and by reactions of ammonia, boric acid and magnesium oxide, magnesium hydroxide or magnesium hydroxy carbonate. The latter processes are especially practical because they eliminate the formation of wasteful byproducts. It was also learned in these studies that the practical synthesis of ammonium magnesium borate from ammonia, boric acid, and magnesium oxide, magnesium hydroxide or magnesium hydroxyl carbonate is facilitated by a stoichiometric excess of ammonia, a non-obvious finding.

Ammonium magnesium borate

An aspect of the invention is an ammonium magnesium borate compound of the formula (NH₄)₂MgBi₂O₂₀ 10H₂O [oxide formula: (NH₄)₂0 MgO 6B₂0₃ 10H₂O]. This compound can also be described as an ammonium magnesium bis(hexaborate) compound or an ammonium magnesium dodecaborate.

This ammonium magnesium borate is a crystalline compound having a well- defined chemical composition. It was structurally characterized by single crystal X-ray diffraction analysis and its formula is ( H₄)₂MgBi₂0₂o 10H₂O [oxide formula: ( l₄)₂O MgO 6B₂0₃ 10H₂O]. The structural formula for the compound was determined to be ( H₄)2{Mg(H₂0)2[B607(OH)6]2} -2H₂0. The structure of this compound is illustrated in Figure 1. Only one of two symmetrically equivalent ammonium cations and free water molecules are illustrated in Figure 1.

The X-ray powder diffraction data for ( H₄)₂MgBi₂0₂o 10H₂O, including diffraction peaks and their relative intensities are listed in Table 1. All values listed throughout the Specification are approximate.

Table 1

In some embodiments, compositions of the invention comprise an ammonium magnesium borate, and can further include at least one polyhydroxylated polymer, such as, but not limited to, for example guar gum, modified guar gum, xanthan gum or polyvinyl alcohols.

Method for forming ammonium magnesium borate

An aspect of the invention is a method of preparing a compound of the formula ( H₄)₂MgBi₂0₂o 10H₂O. The method includes reacting at least one ammonium source, at least one boron containing compound and at least one magnesium compound. Ammonium magnesium borate can be prepared by reactions of an ammonium source, such as ammonium borate, a boron containing compound, such as borate salts, and at least one magnesium compound, such as magnesium salts. In some embodiments, the ammonium sources include but are not limited to aqueous ammonia, anhydrous ammonia, ammonium salts, including ammonium carbonate, ammonium bicarbonate, ammonium chloride, ammonium sulfate and ammonium borate compounds such as ammonium pentaborate, ammonium tetraborate and the like, and combinations thereof. Suitable ammonium salts include, but are not limited to, ammonium pentaborate ammonium sulfate, ammonium chloride, or combinations thereof. The boron containing compound can include but is not limited to boric acid, boric oxide, alkali metal borates (for example sodium tetraborate, or sodium pentaborate), ammonium borates, magnesium borates and the like, and combinations thereof. In some embodiments, the boron containing compound can be a tetraborate compound, a metaborate compound, a pentaborate compound, and an octaborate compound. The magnesium compound can include but is not limited to magnesium oxide, magnesium salt, magnesium borates, magnesium sulfate or magnesium hydroxy carbonate, and combinations thereof. Magnesium salts can include, but are not limited to, magnesium carbonate, magnesium hydroxide, and combinations thereof. In some embodiments, the ammonium source can be aqueous ammonia, the boron containing compound can be boric acid and the magnesium compound can be magnesium oxide. In an embodiment, the ammonium source can be aqueous ammonia, the boron containing compound can be boric acid and the magnesium compound can be magnesium hydroxy carbonate. In an embodiment, the ammonium source can be an ammonium salt, the boron containing compound can be sodium tetraborate and the magnesium compound can be magnesium sulfate.

A sufficient amount of ammonia (i.e., ammonium hydroxide) is required for formation of ( ^^MgB^Cho' lOH^O to occur. If an insufficient amount of ammonia is used a mixture of products was obtained including synthetic admontite as a major component. A stoichiometric excess of ammonia can be used to avoid the presence of admontite in the product. In practice, an about 10-20% molar excess of ammonia (i.e, ammonium hydroxide) can be usefully employed.

The ammonium magnesium borate compound can also be prepared by reactions of aqueous ammonia, boric acid and magnesium hydroxide, magnesium carbonate, or magnesium hydroxy carbonate in the presence of a stoichiometric amount of ammonia or an excess of ammonia. The molar ratio of B/Mg can be between about 12 and about 16. In some embodiments, the molar ratio of B/Mg can be about 12, about 12.1, about 14, or about 16.

The reaction can be carried out using several methods. In some embodiments, the reaction can be carried out by combining water, such as deionized water, and an ammonium source. The boron containing compound can be added and the mixture can be heated to between about 20°C and about 100°C (boiling point), while mixing the mixture using any suitable method, such as stirring, agitating or any other suitable method. Throughout the description, stirring is used as the method for mixing, but one skilled in the art would understand any suitable method can be used. In some embodiments, the temperature can be about 20°C, about 30°C, about 40°C, about 50°C, about 60°C, about 70°C, about 80°C, about 90°C or about 95°C. The magnesium compound can be added to the mixture and the mixture can be stirred at a temperature between about 20°C and about 95°C for between about 2 hours and about 100 hours to form a slurry. In some embodiments, the temperature can be about 20°C, about 30°C, about 40°C, about 50°C, about 60°C, about 70°C, about 80°C, about 90°C or about 95°C. The slurry can be filtered to remove the solids, which can then be washed with water, for example, deionized water. The solids can be dried in an oven at a temperature between about 55°C and about 75°C, in some embodiments about 60°C.

In some embodiments, the ammonium source and the boron containing compound are mixed to form a first mixture. The mixture can be maintained at about room temperature (about 20°C), but can be heated to affect the rate of the reaction. The first mixture can be heated to a temperature above about 40°C. In some embodiments, the temperature can be between about 40°C and about 100°C. In some embodiments the first temperature can be about 40°C, about 50°C, about 60°C, about 70°C or about 80°C. The magnesium source can be added to the first mixture to form a second mixture. The second mixture can be maintained at a second temperature while the magnesium source is added to the first mixture. The mixture can be maintained at about room temperature (about 20°C), but can be heated to affect the rate of the reaction. The second temperature can be greater than about 40°C. In some embodiments, the second temperature can be between about 40°C and about 100°C. In some embodiments the second temperature can be about 40°C, about 50°C, about 60°C, about 70°C or about 80°C. A second mixture can form a slurry. The ammonium magnesium borate compound can be recovered as the solid by filtering the slurry. Suitable methods to filter the slurry include, but are not limited to, centrifuging, filtering, decanting, evaporating, other similar methods, and combinations thereof.

Although not required, in some embodiments a seed of ammonium magnesium borate can be included to facilitate the reaction. The amount of seed can range from as little as a single seed crystal up to a large amount. The seed can be added before or after the magnesium source is added to the reaction and the reaction is at the reaction temperature. In some embodiments, the weight of the seed can be greater than about 0.01 weight percent. In some embodiments, the amount of seed added can be about 0.2 weight percent.

Equations 1-3 illustrate example equations for producing the ammonium magnesium borate. For example, mixing ammonium pentaborate, borax pentahydrate and magnesium sulfate in water resulted in precipitation of

as given by Equation 1 and described in Example 7.

2NH₄B₅0₈ ^■ 4H₂0 + Na₂B₄0₇ ^■ 5H₂0 + MgS0₄→ (NH₄)₂ MgB₁₂O₂₀ ^■ 10H₂O (s) +

Na₂S0₄(aq. ) +

2B(OH)₃ (aq. ) (1)

Alternatively, the ammonium magnesium borate compound can be prepared by reaction of aqueous ammonia, boric acid and magnesium oxide in water, as given by Equation 2 and described in Examples 1-4.

H₂o

2NH₄OH + 12B(OH)₃ + MgO^→ (NH₄)₂MgB₁₂O₂₀ ^■ 10H₂O + 9H₂0 (2)

The ammonium magnesium borate compound can also be prepared by reactions of aqueous ammonia, boric acid and magnesium hydroxide, magnesium carbonate, or magnesium hydroxy carbonate in the presence of a stoichiometric excess of ammonia. The reaction of aqueous ammonia, boric acid and hydromagnesite to produce this ammonium magnesium borate compound is given by Equation 3 and described in Examples 5 and 6.

10NH₄OH + 60B(OH)₃ + Mg₅(C0₃)₄(OH)₂ ^■ 4H₂0→

5(NH₄)₂MgB₁₂O₂₀ ^■ 10H₂O + 4C0₂ + 50H₂O (3) Metal hexaborates can also be produced as illustrated in Equation 4. Aqueous ammonia, boric acid and magnesium oxide are reacted in water to produce ammonium magnesium bis(hexaborate).

2NH₄OH + 12B(OH)₃ + MgO→ (NH₄)₂{Mg(H₂0)₂ [B₆0₇(OH)₆]₂)^■ 2H₂0 + 9H₂0 (4)

The ammonium magnesium bis(hexaborate) exhibits relatively slow dissolution kinetics that provides utility in applications requiring controlled rates of release of borate in solution.

Use of the ammonium magnesium borate

An aspect of the invention is the use of the ammonium magnesium borate of the invention to control or delay the release of borate into a fluid. The ammonium magnesium borate of the invention can be used as a delayed crosslinking agent in oilfield applications, such as in a fracturing fluid. Other fluids can include industrial fluids, such as lubricants. The ammonium magnesium borate of the invention can be used to control the dissolution rate and crosslinking delay time. One skilled in the art would understand that the dissolution rate and the crosslinking delay time can depend upon the amount of the ammonium magnesium borate of the invention that is added to the fluid and the properties of the fluid. Other factors to consider when determining the amount of ammonium magnesium borate required to provide cross linking or control the dissolution rate can include, but are not limited to, the fluid, additives included in the fluid, additives included in the ammonium magnesium borate, the polyhydroxylated polymer, the pH, the temperature, other additives, and other factors that would be understood by one skilled in the art. By way of non-limiting example only, the minimum amount of ammonium magnesium borate that can be used can be greater than about 0.001 wt. % in the solution. Furthermore, one skilled in the art would understand that the amount of the ammonium magnesium borate used in the solution would also be a factor to consider. For example, if a small amount of crosslinking and delay time is required, a smaller amount of the ammonium magnesium borate should be used. Conversely, if a high amount of crosslinking is desired, then a higher amount of the ammonium magnesium borate should be used. Figures 10 and 11 illustrate exemplary delay curves for embodiments of the invention. One skilled in the art would understand how to create these curves for a particular combination of factors when determining the amount of ammonium magnesium borate to be used for an application.

Another aspect of the invention is the use of the ammonium magnesium borate as a fire retardant. In other aspect of the invention, the ammonium magnesium borate can be used as a fungicide, an insecticide, a microbicide, a fertilizer, and/or in the manufacture of adhesives. Another application of the ammonium magnesium borate is as a crosslinking agent.

An aspect of the invention is a method to reduce flammability of an object. The method includes providing a fire retardant comprising an ammonium magnesium borate compound to the object. The object can be a structure, such as a home or building, or the like. The ammonium magnesium borate compound of the invention can be provided to the object using any suitable method of incorporation into articles to be protected from flammability. The fire retardant can also be incorporated into products (such as cellulosic or lignocellulosic products, paper products, wood products, or agro products), caulks, sealants, coatings, or other systems. The fire retardant can also be used in biostatic applications. The ammonium magnesium borate provides borate, a known fire retardant component, and can also be dehydrated and/or deammoniated when used as a fire retardant additive.

An aspect of the invention is a crop nutrient mixture provided to an agricultural field. The method includes providing a material comprising the ammonium magnesium borate of the invention to the field. By way of example only, the ammonium magnesium borate of the invention can be provided to a crop field, or garden to provide a nutrient, such as nitrogen, boron, or magnesium or combinations thereof to the crop field or garden. The ammonium magnesium borate can be mixed with the soil, incorporated into a fertilizer or mixed with another polymer before it is provided to the field.

An aspect of the invention is a method of crosslinking polymers of a polymer containing composition. The method includes contacting the composition with an ammonium magnesium borate compound of the invention. Suitable polymers to be crosslinked include, but are not limited to, polyhydroxylated polymer, such as, but not limited to, for example guar gum, modified guar gum, xanthan gum or polyvinyl alcohols, and combinations thereof.

Dispersability in non-aqueous solvents.

Ammonium magnesium borate was found to readily disperse in non-aqueous solvents, such as hydrocarbons. This dispersion property is important in that it provides utility in applications including oil field use since it is common practice to disperse crosslinking agents in oils, such as those that are low in benzene, toluene, ethylbenzene and xylenes, or other non-aqueous carrier fluids so they can be handled and added as liquids.

EXAMPLES

Preparation of ammonium magnesium borate from ammonia, boric acid and magnesium oxide.

Example 1

A flask was charged with about 100 g of deionized water and about 34 g of ca. 28 wt.% aqueous ammonia (about 0.28 moles Η₄ΟΗ). Boric acid (about 92.75 g, about 1.5 moles) was added to this solution and the mixture was heated to about 50°C with stirring.

Magnesium oxide (about 5.04 g, about 0.125 mole) was then added to the mixture. The mixture was maintained at about 50°C with stirring for about 16 hours after which time the slurry was filtered and the filtered solids were washed with about 100 mL deionized water and dried in an oven at about 60°C to give about 78.70 g ( L^MgB^Cho' lOFFiO as a white fine granular material identified by chemical analysis and by X-ray powder diffraction, (about 91.2% recovered yield) as illustrated in Figure 2.

Example 2

A flask was charged with about 100 g deionized water and about 34 g of ca. 28 wt% aqueous ammonia (about 0.28 moles H₄OH). Boric acid (about 93.52 g, about 1.51 moles) was added to the solution and the mixture was heated to about 50°C with stirring.

Magnesium oxide (about 5.04 g, about 0.125 mole) was then added to the mixture. The mixture was maintained at about 50°C with stirring for about 2.5 hours after which time the slurry was filtered and the filtered solids were washed with about 100 mL deionized water and dried in an oven at about 60°C to give about 51.7 g (N¾)₂MgB₁₂O₂₀* l()H₂O as a white fine granular material identified by chemical analysis and by X-ray powder diffraction, (59.9% recovered yield) as illustrated in Figure 3.

Example 3

A flask was charged with about 100 g deionized water and about 34 g of ca. 28 wt% aqueous ammonia (about 0.28 moles H₄OH). Boric acid (about 93.52 g, 1.51 moles) was added to this solution and the mixture was heated to about 70 °C with stirring. Magnesium oxide (about 5.04 g, 0.125 mole) was then added to the mixture. The mixture was maintained at about 70°C with stirring for about 2.5 hours after which time the slurry was filtered and the filtered solids were washed with 100 mL deionized water and dried in an oven at 60°C to give about 30.8 g ( H₄)₂MgBi₂O₂₀* 10H₂O as a white fine granular material identified by chemical analysis and by X-ray powder diffraction, (about 35.7% recovered yield) as illustrated in Figure 4.

Example 4

A flask fitted with a temperature controller and mechanical stirrer was charged with about 5.00 L deionized water. About 6235 g boric acid (about 100.8 moles) and about 2265 g ca. 28 wt% aqueous ammonium hydroxide (about 18.6 moles H₄OH) was added to the water with stirring. The resulting slurry was heated to about 50°C and about 335.9 g magnesium oxide (about 8.33 mole) was added with stirring. The temperature was raised to about 60°C and maintained with stirring for about 5 hours after which time the slurry was filtered and the filtered solids were washed with about 600 mL deionized water and dried in an oven at about 60°C. The resulting product was a white powder that was identified as (NH₄)₂MgBi₂O₂₀* 10H₂O by chemical analysis and by X-ray powder diffraction as illustrated in Figure 5. The weight of the dried product was about 4933 g (about 85.8% recovered yield based on Mg).

Preparation of ammonium magnesium borate from ammonium hydroxide, boric acid and hydromagnesite.

Example 5

Hydromagnesite, Mg₅(C0₃)₄(OH)₂ 4H₂0, (about 11.72 g, about 0.025 mole) was then added to the mixture. The mixture was maintained between about 50-55°C with stirring for about 2.5 hours after which time the slurry was filtered and the filtered solids were washed with about 100 mL deionized water and dried in an oven at about 60°C to give about 64.9 g ammonium magnesium borate as a white powder (about 75.2% recovered yield) identified by chemical analysis.

Compared to ammonium magnesium borate made using MgO as the magnesium source, the product of Example 5 was easier to screen to less than about 325 U.S. mesh (about 44 microns). The vortex closure delay also appeared to be longer for the product of

Example 5 compared to products with MgO as the magnesium source, though not quantified. Example 6

A flask fitted with a temperature controller and mechanical stirrer was charged with 3.00 L deionized water. About 3741 g boric acid (about 60.50 moles) and about 1349 g ca. 28 wt% aqueous ammonium hydroxide (about 11 moles H₄OH) was added to the water with stirring. The resulting slurry was heated to about 50°C and about 471.5 g hydromagnesite, Mg₅(C03)4(OH)₂-4H₂0, (about 1.01 mole) was added with stirring. An additional approximately 50 mL DI water was added to rinse down adhering reagents from the addition funnel. Mild effervescence with very little foaming occurred after addition of the hydromagnesite. The mixture was maintained at about 50°C with stirring for about 2 hours after which time the slurry was filtered and the filtered solids were washed with about 500 mL deionized water and dried in an oven at about 60°C. The resulting product was a white powder that was identified as ( H₄)₂MgBi₂0₂o* 10H₂0 by chemical analysis and by X-ray powder diffraction as illustrated in Figure 6. The weight of the dried product was about 2798 g (about 80.3% recovered yield based on Mg).

Preparation of ammonium magnesium borate from magnesium sulfate, ammonium pentaborate and sodium tetraborate

Example 7

A flask was charged with about 1500 g deionized water and heated to about 65- 70°C. About 272 g (about 1.00 mole) Η₄Β₅0₈·4Η₂0, about 205 g (about 0.48 moles) Na₂B₄0₇-5H₂0, and about 174 g (about 1.42 moles) MgS0₄-7H₂0 were added to the heated water. The resulting clear solution was maintained between about 65-70°C with stirring. A precipitation of ammonium magnesium borate began to occur after about 2 days. After about 4 days the slurry was filtered providing ammonium magnesium borate as a free flowing fine granular material. The filtrate was maintained at about 65-70°C for another day resulting in further precipitation of ammonium magnesium borate, which was also recovered by filtration. The product was identified by X-ray powder diffraction as ( H₄)₂MgBi₂O₂₀- 10H₂O as illustrated in Figure 7.

Delayed crosslinking using ammonium magnesium borate prepared under different conditions

Example 8

Control of dissolution rates and crosslinking delay times using ammonium magnesium borate

In the context of oil and gas recovery operations, borates are used to crosslink polyhydroxylated polymers in order to form gels that are employed to suspend proppant materials. Guar gum and modified guar gums are polymers commonly used for this application. Crosslinking delay times are often measured using a vortex closure test carried out with a laboratory blender. The procedure is described in G. J. Rummo, Oil & Gas Journal, 1982, 80 (September 13), 84-89 ("Rummo"). This test involves adding guar gum, modified guar gum or other suitable polymer to a salt solution in a blender and mixing at high speed in order to produce a vortex. The crosslinking agent is then added to the blender and the elapsed time until the viscosity of the mixture becomes high enough to close the vortex is recorded. Crosslinking delay times are a function of the amount of crosslinking agent used. By measuring the vortex closure times for different amounts of added crosslinking agent a delay curve can be produced that one can use to calculate the amount of crosslinking agent required to achieve a desired delay time. Processed ulexite mineral is often used in oilfield applications to provide crosslinking delay and a commercial grade of ulexite used in the oilfield industry was used for comparative purposes. Since solid crosslinking agents are often suspended in oil or other liquid medium to allow for liquid handling, they are generally supplied as fine powders that can readily form suspensions.

Ammonium magnesium borate of the invention provides advantageous delay times in the onset of polymer crosslinking and these delay times can be controlled by changing the conditions used to prepare this compound. Samples of ammonium magnesium borate were prepared under different reaction conditions in which the reaction temperatures, times, and concentrations were varied. The resulting products, after screening to -325 U.S. mesh (<0.45 μπι), were tested for delayed crosslinking using a vortex closure test described in Rummo. These tests revealed that samples of ammonium magnesium borate prepared under different conditions provided substantially different delay times. It was found that ammonium magnesium borate samples prepared under specific conditions provide crosslinking delay times that are highly reproducible. It was also determined that reaction temperature is a factor determining the dissolution rate of the ammonium magnesium borate product, with reaction concentration, time and magnesium reagent being secondary factors. In general, it was found that preparing ammonium magnesium borate at higher temperatures leads to slower dissolution rates and thus greater crosslinking delay times.

Example 8 illustrates samples of ammonium magnesium borate prepared at about 70°C (Example 3) provide substantially longer delay times at a given addition rate compared to samples of the compound prepared at about 50°C (Example 2). In both cases the delay times were substantially longer than found for ulexite mineral. Crosslinking delay times longer than about three minutes are difficult to achieve reliably using ulexite, whereas delay times in the approximate 3-10 minute timeframe are easily achieved using ammonium magnesium borate.

Three batches of ammonium magnesium borate were prepared using the procedure given in Example 2 with a set reaction temperature of about 50°C (Rl, R2 and R3). Another three batches of ammonium magnesium borate were prepared using the procedure given in Example 3 with a set reaction temperature of about 70°C (R5, R6, R7). Crosslinking delay data were measured for samples from each batch after screening to - 325 U.S. mesh (<0.44 μπι) using a standard vortex closure method described in Rummo. These data gave good linear regression fits to power functions of the form t = ax ', where t is the crosslinking delay time (vortex closure time), x is the amount of ammonium magnesium borate added, and a and p are constants. The crosslinking delay data and their respective power function curves are illustrated in Figure 8. It can be seen that the samples prepared at about 50°C (Rl, R2, R3) give almost identical crosslinking delay curves, indicating that the dissolution rates of samples prepared under the same conditions are highly reproducible. It can also be seen that the samples prepared at about 70°C (R4, R5, R6) give nearly identical and highly reproducible crosslinking delay curves that are substantially different from those of the samples prepared at about 50°C. Notably, the delay times measured for samples of ammonium magnesium borate prepared at about 70°C are considerably longer than those of samples prepared at about 50°C. Thus, products prepared at 70°C resulted in a longer crosslinking delay than products made at 50°C.

The crosslinking delay data obtained as described above can be converted into linear form by plotting t versus 1/x. The linear plots of these data are illustrated in Figure 9 and serve to further illustrate both the reproducibility of dissolution rates for ammonium magnesium borate prepared under the same conditions as well as the difference in dissolution rates for samples of this compound prepared under different conditions.

Example 9

Crosslinking delay measurements were made for a sample of ammonium magnesium borate prepared according to Example 5, using hydromagnesite as the magnesium source and 50°C as the reaction temperature. Crosslinking delay times were also measured for a sample of commercial ulexite mineral that is sold as a crosslinking agent for oilfield applications. Both samples were screened to -325 U.S. mesh prior to making the crosslinking delay measurement using the method of Rummo. Figure 10 illustrates a graph of the crosslinking delay times for the two samples, illustrating the substantially longer delay times that can be achieved with ammonium magnesium borate compared to ulexite mineral.

Effect of temperature, time and ammonium magnesium borate seed

Example 10

Example 10 illustrates the effect of reaction temperature, reaction time and the addition of ammonium magnesium borate seed on the reaction yield, as listed in Table 2. Experiments were conducted using ca. 28 wt% H₄OH, B(OH)₃ and MgO. All of the values in Table 2 are approximate.

Table 2

It can be seen by comparing the product yields in Table 2, for example experiments D, E and F with those of experiments K and L, that yield decreases with increasing temperature. It can also be seen from the data in Table 2 that yields increase as a general trend with increasing reaction time. Also, it can be seen that yields of experiments G and H and experiments N and O that the addition of 0.2 wt. % ammonium magnesium borate seed increases the yield after 4 hours reaction time at both 50°C and 70°C.

Effect of B/Mg mole ratio Example 11

Experiments were conducted to prepare ammonium magnesium borate with varying B/Mg molar ratios at temperature between about 60°C and about 90°C with reaction times between about 14 hours and about 18 hours. It was found that reaction yields generally decrease with increasing B/Mg mole ratio.

Example 12

Example 12 illustrates the dispersability of ammonium magnesium borate in oils, a property that provides utility in applications such as oil field use where handling of crosslinking agents as liquid dispersions is commonly practiced. An about 1.0 g sample of ammonium magnesium borate that had been screened to -325 U.S. mesh (about 44 microns) was dispersed in about 25 g mineral oil and placed in a glass test tube. An about 1.0 g sample of commercial ulexite, which was specified by the supplier to also be -325 U.S. mesh, was dispersed in about 25 g mineral oil and placed in a glass test tube. The two tests were placed side by side to observe the settling behavior of each material. It was observed that the ammonium magnesium borate dispersed more readily than the ulexite and after being dispersed exhibited a settling rate that was no greater than that of the ulexite, remaining suspended for an extended period of time.

Thermal Properties

Example 13

Thermogravimetric analysis (TGA) was carried out on a sample of

( H₄)₂MgBi₂0₂o- 10H₂0 from room temperature (about 25°C) to 1000 °C under a flow of nitrogen gas with a temperature ramp rate of about 5 °C/min. Figure 12 illustrates weight loss associated with dehydration and deammoniation processes. The onset of weight loss occurs at about 90 °C and proceeds with two main events. Weight loss is complete by about 450 °C with a total weight loss of about 35 wt%. The weight loss is close to the theoretical loss expected for full dehydration and deammoniation to MgBi₂0i9, an amorphous compound, according to Equation 5.

( H₄)₂Bi₂O₂₀ 10H₂O → MgBi₂0i9 + 2NH₃ + 11H₂0 (5)

Differential scanning calorimetry (DSC) was carried out on a sample of ( H₄)₂MgBi₂O₂₀- 10H₂O from room temperature (about 25°C) to 1000 °C under a flow of nitrogen gas with a temperature ramp rate of 5 °C/min. Figure 12 illustrates this scan showing the thermal events that occur upon heating. The two main weight loss events observed in the TGA scan are seen as corresponding endothermic events in the DSC scan, consistent with dehydration and deammoniation processes. A third exothermic event is also seen in the DSC scan occurring in approximately the 715-750 °C temperature range which is associated with a crystallization process. To confirm this, a sample of ( H₄)₂MgBi₂O₂₀* 10H₂O was heated in a furnace to 1050 °C and resulting product was submitted to powder X-ray diffraction analysis. This analysis revealed the presence in the sample of crystalline synthetic suanite, Mg₂B₂0₅, indicating that thermal the exothermic observed in the DSC experiment is associated with the crystallization of this compound as given by Equation 6.

2 MgBi₂0i₉ (amorphous)→ Mg₂B₂0₅ (crystalline) + 11 B₂0₃ (6)

Ranges have been discussed and used within the forgoing description. One skilled in the art would understand that any sub-range within the stated range would be suitable, as would any number within the broad range, without deviating from the invention. Furthermore, values set forth in the description are approximate.

The foregoing description of the present invention has been presented for purposes of illustration and description. Furthermore, the description is not intended to limit the invention to the form disclosed herein. Consequently, variations and modifications commensurate with the above teachings, and the skill or knowledge of the relevant art, are within the scope of the present invention. The embodiment described hereinabove is further intended to explain the best mode known for practicing the invention and to enable others skilled in the art to utilize the invention in such, or other, embodiments and with various modifications required by the particular applications or uses of the present invention. It is intended that the appended claims be construed to include alternative embodiments to the extent permitted by the prior art.

Claims

1. A method of preparing a compound of a formula of ( ^^MgB^Cho' lOH^O, comprising:

reacting an ammonium source, a boron containing compound, and at least one magnesium compound to prepare the compound of the formula ( H^MgB^O^* 10H₂O.

2. The method of Claim 1, wherein the ammonium source is selected from the group consisting of anhydrous ammonia, aqueous ammonia, an ammonium salt and combinations thereof.

3. The method of Claim 1, wherein the boron containing compound is selected from the group consisting of boric acid, boric oxide, alkali metal borate, ammonium borate, and combinations thereof.

4. The method of Claim 1, wherein the boron containing compound is selected from the group consisting of a tetraborate compound, a metaborate compound, a pentaborate compound, an octaborate compound, and combinations thereof.

5. The method of Claim 1, wherein the at least one magnesium source is selected from the group consisting of magnesium oxide, magnesium hydroxide, magnesium salt, magnesium sulfate, magnesium carbonate, magnesium hydroxy carbonate, magnesium borate, and combinations thereof.

6. The method of Claim 1, wherein the ammonium source is aqueous ammonia, the boron containing compound is boric acid and the magnesium compound is magnesium oxide.

7. The method of Claim 1, wherein the ammonium source is aqueous ammonia, the boron containing compound is boric acid and the magnesium compound is magnesium hydroxyl carbonate.

8. The method of Claim 1, wherein the ammonium source is an ammonium salt, the boron containing compound is sodium tetraborate and the magnesium compound is magnesium sulfate.

9. The method of Claim 8, wherein the ammonium salt is ammonium pentaborate.

10. The method of Claim 1, wherein there is a stoichiometric excess of the ammonia source.

11. The method of claim 10, wherein the stoichiometric excess of the ammonia source is between about 10-20%.

12. The method of Claim 1, wherein the ammonium source is aqueous ammonia.

13. The method of Claim 1, wherein the step of reacting comprises:

mixing the ammonium source and the boron containing compound to form a first mixture; and

heating the first mixture to a first temperature of at least about 40 °C.

14. The method of Claim 13, wherein the first temperature is between about 40°C and about 100°C.

15. The method of Claim 13, wherein the first temperature is at least 40°C, 50°C, 60°C, 70°C or 80°C.

16. The method of Claim 1, further comprising seeding the reaction of the ammonium source, the boron containing compound, and the at least one magnesium compound, with an ammonium magnesium borate seed of the formula ( i₄)₂MgBi₂0₂o* 10H₂0.

17. The method of Claim 16, wherein the ammonium magnesium borate seed is in an amount greater than 0.01 wt. %.

18. A method to treat a fluid useful in an oil field application, comprising:

adding a crosslinking agent to the fluid, wherein the crosslinking agent comprises an ammonium magnesium borate compound.

19. The method of Claim 18, wherein the fluid is a fracturing fluid.

20. The method of claim 18, wherein the ammonium magnesium borate compound is of a formula ( H₄)₂MgBi₂O₂₀- 10H₂O.

21. A method to reduce flammability, comprising:

providing a fire retardant comprising an ammonium magnesium borate compound.

22. The method of claim 21, wherein the ammonium magnesium borate compound is of a formula ( H₄)₂MgBi₂O₂₀- 10H₂O.

23. A method of crosslinking polymers of a polymer-containing composition comprising contacting the composition with an ammonium magnesium borate compound.

24. The method of Claim 23, wherein a formula of the ammonium magnesium borate compound is ( H₄)₂MgBi₂O₂₀- 10H₂O.

25. The method of claim 23, wherein the ammonium magnesium borate compound is of a formula ( H₄)₂MgBi₂O₂₀- 10H₂O.

26. A method to provide a nutrient to an agricultural field, comprising providing the agricultural field with the nutrient, wherein the nutrient comprises an ammonium magnesium borate compound of a formula (NH₄)₂MgBi₂0₂o* 10H₂0.

27. The method of claim 26, wherein the nutrient is mixed with the soil of the agricultural field.

28. The method of claim 26, wherein the nutrient further comprises a polymer or a fertilizer.

29. An ammonium magnesium borate compound of formula ( ^MgB^Cho' lOH^O.

30. The ammonium magnesium borate compound of claim 29, wherein the compound is at least partially dehydrated.

31. The ammonium magnesium borate compound of claim 29, where the compound is fully dehydrated.

32. The composition of claim 29, further comprising an additive.