Compositions and processes for synthesizing borohydride...

Details Compositions and processes for synthesizing borohydride... Compositions and processes for synthesizing borohydride...

2000-11-08

2002-08-13

Truong, Duc (Department: 1711)

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

Synthetic resins

From carboxylic acid or derivative thereof

C528S394000, C528S396000

Reexamination Certificate

active

06433129

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to compositions and processes for producing borohydride compounds. In particular, the present invention provides efficient processes and compositions 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 trimethoxyborate, 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
). These reactions, however, provide poor molar economy by requiring four moles of sodium to produce one mole of sodium borohydride.
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 excess 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 17,566 BTU (18,528 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 dispose of these materials.
Typical improvements of the prior art describe simple modifications of the two processes given in equations 1 and 2. Accordingly, such improvements also suffer from the disadvantages stated above, and do not provide any improved energy efficiency. Furthermore, with the widespread adoption of borohydride as a source of hydrogen, a recycle process that allows regeneration of borohydride from borate is attractive. Thus, borohydride can be used as a fuel, and the resulting borate can then be recycled back to generate borohydride. 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.
SUMMARY OF THE INVENTION
The present invention provides processes for producing large quantities of borohydride compounds, which overcome these deficiencies. In addition, the efficiencies of the processes of the present invention can be greatly enhanced over the typical processes for producing borohydride compounds.
In one embodiment of the present invention, a process is provided for producing borohydride compounds, which includes: (A) reacting methane with a Y-containing species of formula Y
2
O to obtain Y, carbon monoxide and H
2
; (B) reacting the Y with H
2
to obtain YH; (C) reacting a boron-containing species of the formula BX
3
with the YH to obtain YHBX
3
; (D) separately reacting BX
3
with H
2
to obtain B
2
H
6
and HX; and (E) reacting the YHBX
3
with B
2
H
6
to obtain YBH
4
and BX
3
. Y is selected from the group consisting of the alkali metals, pseudo-alkali metals, an ammonium ion, and quaternary amines of formula NR
4
−
, wherein R is independently selected from H and straight or branched C1 to C4 alkyl groups; and X is selected from the group consisting of halides, alcohols, alkoxides, chalcogens, and chalcogenides.
In another embodiment of the present invention, a process is provided for producing borohydride compounds, which includes: (A) reacting a boron-containing species of the formula BX
3
with H
2
to obtain B
2
H
6
and HX; and (B) reacting the B
2
M
6
with a Y-containing species of the formula Y
2
O to obtain a YBH
4
and a YBO
2
. Y and X are the same as defined above.
In either of these embodiments, the Y-containing species of the formula Y
2
O and the boron-containing species of the formula BX
3
can be obtained by the following two processes. The first process includes: (I) reacting a borate of the formula YBO
2
with HX to obtain YX, BX
3
, and water; (2) reacting the YX with water to obtain YOH and HX; and converting the YOH to Y
2
O and H
2
O. The second process includes: (i) reacting a borate of the formula YBO
2
with CO
2
and H
2
O to obtain YHCO
3
and B
2
O
3
; (ii) converting the YHCO
3
to Y
2
O, CO
2
, and H
2
O; and (iii) reacting the B
2
O
3
with HX to obtain BX
3
and H
2
O.
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 B
2
O
3
; (B) converting the YHCO
3
to Y
2
O, CO
2
, and H
2
O; (C) reacting the B
2
O
3
with C and X
2
to obtain BX
3
and CO
2
; (D) reacting methane with 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
. Y and X are the same as defined above.
In still another embodiment of the present invention, the process described in the previous embodiment is altered by replacing steps (D) to (H) with the following steps (D
2
) and (E
2
): (D
2
) reacting the BX
3
with H
2
to obtain B
2
H
6
and HX; and (E
2
) reacting B
2
H
6
with the Y
2
O to obtain a YBH
4
and a YBO
2
.


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