Processes for synthesizing borohydride compounds

Details Processes for synthesizing borohydride compounds Processes for synthesizing borohydride compounds

2002-12-27

2003-12-30

Truong, Duc (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From boron-containing reactant

C528S240000, C528S241000, C528S482000, C528S486000, C528S488000, C528S493000, C528S495000, C528S503000

Reexamination Certificate

active

06670444

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to processes for producing borohydride compounds. In particular, the present invention provides efficient processes for the large-scale production of borohydride compounds.
BACKGROUND OF INVENTION
Environmentally friendly fuels, e.g., alternative fuels to hydrocarbon based energy sources, are currently of great interest. One such fuel is borohydride, which can be used directly as an anodic fuel in a fuel cell or as a hydrogen storage medium, e.g., hydrogen can be liberated by the reaction of sodium borohydride with water, which produces sodium borate as a byproduct. As with all fuels, borohydride must be manufactured from readily available materials. Thus, there is a need for improved and energy efficient industrial scale manufacturing processes for producing borohydride compounds.
Typical industrial processes for the production of sodium borohydride are based on the Schlesinger process (Equation 1) or the Bayer process (Equation 2), which are both described below. Equation 1 illustrates the reaction of alkali metal hydrides with boric oxide, B
2
O
3
, or trimethyl borate, B(OCH
3
)
3
, at high temperatures, e.g., ca. 330° to 350° C. for B
2
O
3
and 275° C. for B(OCH
3
)
3
.
4NaH+B(OCH
3
)
3
→3NaOCH
3
+NaBH
4
  (1)
 Na
2
B
4
O
7
+16Na+8H
2
+7SiO
2
→4NaBH
4
+7Na
2
SiO
3
  (2)
The primary energy cost of these processes stems from the requirement for a large amount of sodium metal, e.g., 4 moles of sodium per mole of sodium borohydride produced. Sodium metal is commercially produced by electrolysis of sodium chloride with an energy input equivalent to about 37,500 BTU (39,564 KJ) per pound of sodium borohydride produced. In contrast, the hydrogen energy stored in borohydride is about 10,752 BTU (11,341 KJ) of hydrogen per pound of sodium borohydride. The Schlesinger process and the Bayer process, therefore, do not provide a favorable energy balance, because the energy cost of using such large amounts of sodium in these reactions is high compared to the energy available from sodium borohydride as a fuel.
Furthermore, in view of the large quantities of borohydride needed for use, e.g., in the transportation industry, these processes would also produce large quantities of NaOCH
3
or Na
2
SiO
3
waste products. Since these byproducts are not reclaimed or reused, further energy and/or expense would need to be expended to separate and properly dispose of these materials.
Typical improvements of the prior art describe simple modifications of the two processes given in equations (1) and (2). As such, however, these improvements also suffer from the disadvantages stated above and do not provide any improved energy efficiency. It can be seen, therefore, that the widespread adoption of borohydride as a source of hydrogen would almost necessitate a recycle process that would allow the regeneration of borohydride from the borate byproduct. Thus, borohydride can be used as a fuel, and the resulting borate can then be recycled back to generate borohydride. However, such a process cannot rely on the same sodium stoichiometry shown in the current borohydride manufacture processes, e.g., the Schlesinger process of Equation (1) or the Bayer process of Equation (2).
The present invention provides processes for producing large quantities of borohydride compounds, which overcome the above-described deficiencies. In addition, the efficiencies of the processes of the present invention can be greatly enhanced over the typical processes for producing borohydride compounds.
SUMMARY OF THE INVENTION
In one embodiment of the present invention, a process is provided for producing borohydride compounds, which includes reacting the boron-containing compound BX
3
with hydrogen to obtain diborane (B
2
H
6
) which, is turn, reacted with a Y-containing base selected from those represented by the formulae Y
2
O, Y
2
CO
3
and YOH to obtain YBH
4
and a YBO
2
, wherein Y is selected from the group consisting of the alkali metals, pseudo-alkali metals, alkaline earth metals, an ammonium ion, and quaternary amines of formula NR
4
+
, wherein each R is independently selected from hydrogen and straight- or branched-chain C
1-4
alkyl groups; and X is selected from the group consisting of halide ions, hydroxyl, alkyl or alkoxy groups, chalcogens, and chalcogenides.
In another embodiment of the present invention, a process is provided for producing borohydride compounds, which includes reacting a boron-containing compound of the formula BX
3
with a Y-containing base of the formula YH to obtain YHBX
3
; and separately reacting BX
3
with hydrogen to obtain diborane which is, in turn, reacted with YHBX
3
to obtain YBH
4
and BX
3
, wherein X and Y are as defined above.
In either of these embodiments, the Y-containing base of the formula Y
2
O and the boron-containing compound of the formula BX
3
can be obtained by the following processes. The first process includes: (A) reacting a borate of the formula YBO
2
with CO
2
and H
2
O to obtain YHCO
3
, and borax; (B) heating YHCO
3
to obtain Y
2
O, CO
2
and H
2
O; (C) separately reacting borax with an acid to obtain boric acid B(OH)
3
which is isolated and dehydrated to B
2
O
3
; (D) reacting the B
2
O
3
with carbon and X
2
to obtain BX
3
and CO
2
. The second process includes: (I) reacting a borate of the formula YBO
2
with CO
2
and an alcohol to obtain YHCO
3
and B(OR)
3
wherein R is a lower alkyl group; (II) heating YHCO
3
to obtain Y
2
O, CO
2
and H
2
O; (III) reacting the B(OR)
3
with H
2
O to obtain B(OH)
3
, which is dehydrated to form B
2
O
3
; and (IV) reacting the B
2
O
3
with carbon and X
2
to obtain BX
3
and CO
2
. The Y-containing base compounds of the formula Y
2
CO
3
can be obtained by replacing steps (B) and (II) with the following step (B2): converting the YHCO
3
to Y
2
CO
3
, CO
2
and H
2
O. Alternatively, the boron-containing compounds BX
3
can be obtained by replacing steps (C) and (D) with one of the following steps: (Cl) where X is a halide, reacting borax with carbon and X
2
to obtain BX
3
and CO
2
; or (C2), where X is an alkoxy group, reacting borax with an alcohol to obtain BX
3
.
In still another embodiment of the present invention, a process is provided for producing borohydride compounds, which includes: (A) reacting a borate of the formula YBO
2
with CO
2
and H
2
O to obtain YHCO
3
and a B
2
O
3
compound; (B) heating the YHCO
3
to obtain Y
2
O, CO
2
, and H
2
O; (C) reacting the B
2
O
3
compound with an alcohol to obtain BX
3
; (D) reacting methane with the Y
2
O to obtain Y, carbon monoxide and H
2
; (E) reacting the Y with H
2
to obtain YH; (F) reacting the BX
3
with the YH to obtain YHBX
3
; (G) separately reacting BX
3
with H
2
to obtain B
2
H
6
and HX; and (H) reacting the YHBX
3
with B
2
H
6
to obtain YBH
4
and BX
3
wherein Y and X are as defined above.


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