Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B6/00—Hydrides of metals including fully or partially hydrided metals, alloys or intermetallic compounds ; Compounds containing at least one metal-hydrogen bond, e.g. (GeH3)2S, SiH GeH; Monoborane or diborane; Addition complexes thereof

Definitions

• borates and mixtures of metallic oxide and boric oxide of any desired composition can be used, as, for example, those obtainable by contacting and optionally heating metallic oxides or compounds yielding metallic oxides with boric acid or boric oxide, such as sodium orthoborate Na BO sodium metaborate NaBO or higher borates such as Na B O Na B O etc., preferably mixtures with an Na O:B O ratio of between about 3:1 and 1:4 are employed; however mixtures with other ratios can be used, since alkali metal oxides and B 0 are miscible in every proportion forming clear glasses (Gmelin No. 13, Vol. of Addition, p. 134); to some extent also the alkaline earth metal oxide boron trioxide mixtures are concerned (loc. cit. p.
• the process of the invention is carried out in a hydrogen atmosphere to which an inert gas such as nitrogen or gases of the argon group may be added, the reduction can be effected with an alkali metal as well as with the corresponding alkali metal hydrides.
• an inert gas such as nitrogen or gases of the argon group
• the new process can be carried out in the range where sodium hydride exists as well as at temperatures and pressures at which sodium hydride is completely dissociated, as may be seen from the following table:
• the aluminum is used in a state of fine subdivision and preferably in a particle size below 1 mm. diameter (aluminum bronze, aluminum grains, aluminum flakes, aluminum powder or aluminum turnings).
• aluminum-containing alloys preferably those having a content of more than 50% Al.
• Suitable for use in the process of this invention are aluminum or alloys of aluminum with Si, Mg, Ca, Cu, Zn, Mn, Fe, Ni, etc., such as Magnalium, Duralumin, Lantal, Hydronalium as well as other readily available, technically used alloys.
• the purity requirements of the aluminum are not very high so that the process of the invention can be carried out with the waste material of the aluminum industry.
• the ratio between the sodium and aluminum is preferably chosen so that, in addition to alkali metal borohydride, the reaction product essentially consists of sodium aluminate.
• the process can also be accomplished with an excess of aluminum in such a manner that A1 0 is obtained as a by-product according to the equation 3Na2B407 6N3.
• the reaction can be accelerated by the addition of activating substances, such as, for example, alkali metal hydroxide, mercury, copper compounds as well as organic boron or aluminum compounds.
• activating substances such as, for example, alkali metal hydroxide, mercury, copper compounds as well as organic boron or aluminum compounds.
• the process is carried out at reaction temperatures above C., preferably at temperatures between about 300 and 620 C. Especially good yields are achieved at temperatures of 300 to 550 C.
• the hydrogen pressure to be used (about l-15 atm.) depends substantially upon the temperature conditions. At very low temperatures (below 200 C.) it is necessary to apply high pressures, but above about 300 C. the reaction proceeds with almost quantitative yields at hydrogen pressures of 1-10 atmospheres, preferably 2 to 6 atmospheres. The use of pressures higher than about 15 atm. is possible but does not appear to be expedient for the reasons mentioned above.
• the process can further be carried out in such a manner that a mixture of sodium, hydrogen and borax is used and the required amount of aluminum is subsequently added either totally or in portions or continuously.
• a mixture of sodium hydride and borax can be prepared in a first step at temperatures below 350 C. and the aluminum added thereto at temperatures of 300 to 620 C.
• the continuous performance of the new process is preferably accomplished in mixing screws or similar devices. It is possible to use multistage screws wherein in the first step the starting products borax, sodium, aluminum and hydrogen are heated to temperatures of 350 C. with intimate mixing. In the second step the reaction mixture which contains sodium hydride which has been formed in the first step is heated to temperatures up to 620 C. while in the third step there may occur a secondary reaction and cooling of the reaction products.
• the continuous performance of the new process can further be accomplished by continuously adding either the dehydrated borax and/or aluminum to the other reaction components.
• the finishing of the product obtained according to the process of the invention can be performed by an extraction with ammonium or alkyl amines such as isopropyl amine. If borax, aluminum, sodium and hydrogen have been used as starting materials, the crude product containing besides sodium borohydride sodium aluminate as by-product and non-reacted aluminum, borax and sodium hydride can be worked up on the other hand by pouring it into water, whereby temperatures of about -40 0., preferably 1030 C. are used.
• the resulting suspension is then separated from the solids, e.g., by filtering through a finely meshed sive and to the solution there is afterwards added an alkaline earth metal chloride such as calcium chloride, strontium chloride or barium chloride in an amount to precipitate the by-products or impurities as e.g., calcium aluminate and calcium borate.
• an alkaline earth metal chloride such as calcium chloride, strontium chloride or barium chloride in an amount to precipitate the by-products or impurities as e.g., calcium aluminate and calcium borate.
• the aqueous solution of sodium borohydride can now be used as such as reducing agent. Furthermore, the solution can be worked up to yield a solid borohydride-sodium chloride mixture.
• the pH of the solution is adjusted to a value above 8, preferably to a pH between 10 and 11, by saturating the solution with calcium hydroxide; however, other alkaline earth metal hydroxides and alkali metal hydroxides can be used. Higher pH- values are not harmful, the higher the pH the more stable is the borohydride.
• the stabilized solution is then evaporated under moderate conditions, i.e., with low temperatures and short drying time, e.g., in a spray drier with a starting temperature of between about 150-200 C. and an exit temperature of the gases of about 50-110 C.
• EXAMPLE 2 A mixture of 202.5 grams of dehydrated borax, 130 grams of sodium and 110 grams of aluminum bronze was heated to about 300 C. under a hydrogen pressure of 3 atmospheres with stirring in an autoclave of 2 liter capacity and maintained at this temperature and this pressure until the NaH-formation was terminated, if necessary with cooling. The mixture was then heated to about 485 C. with further stirring and maintenance of the hydrogen pressure at 3 atmospheres and kept at this temperature, if necessary by cooling, until the hydrogen absorption had terminated (4 hours). After cooling there was obtained a grey powder from which the sodium borohydride formed in very good yield was extracted, e.g., With liquid ammonia.
• EXAMPLE 3 A mixture of 130 grams of aluminum grains and 130 grams of sodium was heated to about 450 C. in a 2 liter autoclave with stirring at a hydrogen pressure of 4 atmospheres. 202.5 grams of dehydrated, coarse-grained borax were added within 2 /2 hours to the resulting mixture of sodium hydride and aluminum while slowly in creasing the temperature up to 510 C. and maintaining the hydrogen pressure of 4 atmospheres. Sodium hydride was thereby obtained in very good yield.
• EXAMPLE 7 Following the procedure set out in Example 6, a mixture of 120 grams of aluminum grains, 130 grams of sodium and 14.5 grams of sodium hydroxide were heated with stirring to 450 C. under a hydrogen pressure of 4 atmospheres. 230 grams of borax were then added within 1 hour while the temperature was increased to 620 C. Sodium borohydride was thereby obtained in good yield.
• EXAMPLE 9 Following the procedure of Example 3, a mixture of 285 grams of aluminum grains and 130 grams of sodium were heated with stirring to about 400 C. under a hydrogen pressure of 4 atmospheres. While the tempera- 7 ture was increased up to 550 C. 200 grams of dehydrated borax were added within 45 minutes. Sodium borohydride was obtained in this manner in very good yield.
• EXAMPLE 11 Following the disclosure of Example 8, 78 grams of sodium were hydrogenated in a mixture of 138 grams of dehydrated borax, 100 grams of aluminum bronze and 100 grams of aluminum grains with stirring at 300 to 350 C. under a hydrogen pressure of 4 atmospheres, yielding sodium hydride. The resulting mixture was then added with stirring within 1% hours at 455 to 480 C. and under a hydrogen pressure of 4 atmospheres to a mixture as set out in Example 8 after reaction of the latter. Sodium borohydride was obtained in very good yield.
• EXAMPLE 12 78 .grams of sodium and 138 grams of dehydrated coarse-grained borax were hydrogenated at 300 to 350 C. under a hydrogen pressure of 4 atmospheres. 100 grams of aluminum bronze and 100 grams of aluminum grains were then added at about 350 C. and the temperature was increased up to 560 C. under a hydrogen pressure of 4 atmospheres within 30 minutes. Sodium borohydride was obtained in this manner in good yield.
• EXAMPLE 13 400 grams of a crude product, containing 22.5% sodium borohydride, sodium aluminate, unreacted aluminum, borax and sodium hydride and which had been prepared according to the equation 2Na B O 14Al 11Na+16H 2 4 7+ 8NaBH +7NaAlO +7Al were dissolved in a mixture of 500 grams ice and 700 ml. water, then shifted through a sieve of fine mesh size (6400 meshes per cm?) to remove aluminum and was then filtered. The residue was washed on the filter with water. There were obtained 1880 ml. of a solution containing 88 grams of sodium borohydride NaBH (97.8% of the theoretical).
• the borohydride solution was then mixed while stirring at room temperature with an aqueous solution of 362 grams calcium chloride hexahydrate. Following filtration, the precipitate was washed with 300 ml. water There were obtained 3220 ml. of a filtrate containing 80.5 grams sodium borohydride. Thus, the total yield was 89.4% of the theoretical.
• the solution can be used directly for reducing purposes.
• EXAMPLE 14 A mixture of 2.025 grams dehydrated finely divided borax and 130 grams of sodium is heated in a 2 liter autoclave under a hydrogen pressure of 1 atmosphere to a temperature of 320 C. while stirring. To this mixture there are added with stirring 109 grams of aluminum bronze, whereby the hydrogen pressure of 1 atmosphere is kept constant, while heating the mixture to a temperature of 515 C. in 1% hours. Sodium borohydride is ob- 8 tained with a good yield and extracted with anhydrous liquid ammonia.
• EXAMPLE l5 NaBH +NaAlO A mixture of 200 grams of dehydrated sodium metaborate, 70 grams of sodium and grams of aluminum bronze is heated in a 2 liter autoclave to a temperature of 300 C. and under a hydrogen pressure of 3 atmospheres. The mixture is kept under this pressure and temperature with stirring until sodium hydride has been formed. Afterwards the mixture is heated to a temperature of 510 C., whereby stirring is continued and the hydrogen pressure is kept contant at 3 atmospheres. After 3 hours the mixture does not take up a further amount of hydrogen. The sodium borohydride formed with high yields is extracted with anhydrous liquid ammonia.
• EXAMPLE 16 A mixture of grams of aluminum bronze and grams of sodium is heated in a 2 liter autoclave with stirring to a temperature of 460 C. under a hydrogen pressure of 3 atmospheres. To this mixture there are added 250 grams finely pulverized NaB O whereby the temperature is increased slowly to 540 C. under a constant pressure of 3 atmospheres. The pentaborate is added in the course of 2 /2 hours. Sodium borohydride is obtained in good yields.
• said group member is an alloy of aluminum with a member selected from the group consisting of silicon, magnesium, calcium, copper, zinc, manganese, iron, nickel, and mixtures thereof having an aluminum content of more than 50%.
• alkaline earth metal chloride is a member selected from the group consisting of calcium chloride, strontium chloride, and barium chloride.

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