A solid composition containing at least one borohydride compound and at least one base.
Filed;
Aug. 16,2007
US 2007/0187636 A1
BOROHYDRIDE FUEL FORMULATION
[0001] This application claims the bene?t of priority under
35 U.S.C. §119(e) of US. Provisional Patent Application
No. 60/774,253 ?led on Feb. 16, 2006.
[0002] This invention relates to a solid borohydride-con
taining formulation useful for hydrogen generation in fuel
than 35% solids, alternatively no more than 30%. The Water
may contain small amounts of additives, e.g., anti-foaming agents, surfactants, etc.
[0009] The present invention is further directed to a
method for improving How of poWdered metal borohydride salts, and to a solid composition having improved ?oW.
Addition of at least 2.5% of at least one base to at least one
metal borohydride prevents clumping and caking of the
cells.
solid. In one embodiment of the invention, at least 3% of a
[0003] Borohydride-containing compositions are knoWn as hydrogen sources for hydrogen fuel cells, usually in the
base is added, alternatively at least 5%. In one embodiment of the invention, no more than 40% of a base is added,
form of aqueous solutions. Solid borohydride-containing compositions also have been used. For example, US. Pub.
alternatively no more than 20%, alternatively no more than
17%, alternatively no more than 15%, alternatively no more
No. 2005/0238573 discloses the use of solid sodium boro
than 14%, alternatively no more than 13.5%. Preferably, the
hydride, Which is combined With aqueous acid to produce
metal borohydride compound is an alkali metal borohydride;
hydrogen. However, the problem of rapid dissolution of
alternatively it comprises sodium borohydride or potassium
borohydride is not addressed by this reference.
[0004] The problem addressed by this invention is to ?nd
a solid formulation of borohydride that dissolves at least as
methoxide, or mixture thereof, alternatively lithium, sodium
quickly as pure borohydride salts.
or potassium hydroxide or sodium or potassium methoxide, or a mixture thereof, alternatively sodium hydroxide or
STATEMENT OF INVENTION
the base is an alkali metal hydroxide or sodium or potassium
potassium hydroxide; alternatively sodium hydroxide. More than one alkali metal borohydride and more than one base
[0005]
The present invention provides a solid composition
comprising: (a) from 50% to 98% of at least one borohydride compound; and (b) from 2% to 50% of at least one base.
may be present.
[0010] The solid composition of this invention may be in any convenient form. Examples of suitable solid forms
include poWder, granules, and compressed solid material.
DETAILED DESCRIPTION
[0006]
Percentages are Weight percentages and tempera
tures are in ° C., unless speci?ed otherWise. A “base” is a compound With a pKa>8 Which is solid at 400 C. A “boro
hydride compound” is a compound containing the borohy dride anion, BH4_.
[0007] In one embodiment, the amount of borohydride compound(s) is at least 75%, alternatively at least 83%, alternatively at least 85%, alternatively at least 86%, alter natively at least 87%; the amount of base(s) is no more than
25%, alternatively no more than 17%, alternatively no more than 15%, alternatively no more than 14%, alternatively no more than 13%. In one embodiment of the invention, the amount of base is at least 2.5%, alternatively at least 3%, alternatively at least 5%; the amount of borohydride com pound is no more than 97.5%, alternatively no more than
97%, alternatively no more than 95%. Preferably, the boro hydride compound is a metal salt Which has a metal cation
from groups 1, 2, 4, 5, 7, 11, 12 or 13 ofthe periodic table, or a mixture thereof. In one embodiment, the borohydride
compound is an alkali metal borohydride or combination
thereof, alternatively it comprises sodium borohydride
(SBH) or potassium borohydride or a mixture thereof,
alternatively sodium borohydride. Preferably, the base is an alkali metal hydroxide or combination thereof, alkali metal
Preferably, poWders have an average particle siZe less than
80 mesh (177 um). Preferably, granules have an average particle siZe from 10 mesh (2000 pm) to 40 mesh (425 um).
Compressed solid material may have a siZe and shape
determined by the equipment comprising the hydrogen generation system. In one embodiment of the invention, compressed solid material is in the form of a typical caplet used in other ?elds. The compaction pressure used to form compressed solid material is not critical.
[0011] In one embodiment of the invention, the solid
composition is substantially free of substances that catalyZe hydrolysis of borohydride, e.g., salts of transition metals such as Co, Ru, Ni, Fe, Rh, Pd, Os, Ir, Pt, or mixtures thereof, and borides of Co and/or Ni.
[0012] Preferably, the Water content of the solid compo sition is no more than 0.5%, alternatively no more than
0.2%, alternatively no more than 0.1%. Preferably, the solid
composition contains less than 20% of anything other than
the borohydride compound and the base, alternatively less than 15%, alternatively less than 10%, alternatively less than
5%. Other possible constituents of the solid composition include, e.g., catalysts, acids, anti-foam agents and surfac tants. [0013] The solid composition of this invention also may be used in the ?elds of synthesis and metal recovery.
alkoxide or alkaline earth alkoxide or combination thereof, alternatively it is an alkali metal hydroxide or sodium or
EXAMPLES
potassium methoxide, or mixture thereof, alternatively
Example 1
sodium, lithium or potassium hydroxide or sodium or potas sium methoxide, or a mixture thereof, alternatively sodium
Effect of NaOH on SBH Dissolution Rate
hydroxide or potassium hydroxide; alternatively sodium hydroxide. More than one alkali metal borohydride and
[0014]
more than one base may be present.
NaOH contents. The preWeighed solid mixtures Were
[0008]
blended by mixing in a coffee grinder for about tWo minutes, and the resulting poWder sieved through an 80 mesh (177 um) sieve. The sieved poWders Were placed in Water to make
The present invention is also directed to a method
for rapid production of an aqueous borohydride solution.
Adding to Water a su?icient amount of the borohydride/base composition described above to form a 1% to 40% solids solution produces a maximum dissolution rate. In one
embodiment of the invention, the solution has at least 5% solids, alternatively at least 10%; the solution has no more
SBH poWders Were formulated With different
10 mL of a 30% solution (% based on SBH+NaOH) and alloWed to dissolve With sloW stirring With a magnetic stir bar. Average complete dissolution times for 2 runs are displayed in Table 1 beloW.
Aug. 16,2007
US 2007/0187636 A1
Example 3
TABLE 1
Dissolution Rate of Caplets vs. Solution Size
Dissolution time (sec)
% NaOH
26
26
18
16
14
12
10
10
10
10
10
0
1
2
3
5
10
13
15
20
25
50
[0017]
Caplets of SBH, and of a formulation of 87%
SBH/13% NaOH were dissolved as described in Example 1 to form solutions weighing 10 g and 100 g. The results are
presented below in Table 5.
TABLE 5
Dissolution Times sec
Wt. of Solution (g)
87% SBH/13% NaOH
SBH
10
100
177
303
249
576
When the data are normalized to 100% SBH content, the
following pro?le of corrected times (Corr. diss. time) is obtained, shown below in Table 2.
[0015]
The data demonstrate that when a larger amount of solution is prepared, the difference between SBH and the NaOH
formulation increases. Therefore, the advantage of including
TABLE 2
NaOH in the formulation increases with solution size.
Corr. diss. time (sec)
% NaOH
26
26.3
18
16
14
13
11
11.7
12.5
13
20
0
1
2
3
5
10
13
15
20
25
50
Example 4
Dissolution Time vs. Weight % of Solids
[0018]
Caplets, granule and powdered forms of SBH and
of a formulation of 87% SBH/13% NaOH were dissolved as
described in Example 1 to form solutions having different percentages of dissolved solids (Wt. %). The results are presented below in Table 6. Times are reported in seconds.
TABLE 6
These results show that the dissolution time per gram of
SBH begins to decrease at 2% NaOH and then begins to increase again at about 15-20% NaOH, with a marked
increase beyond 25% NaOH.
Example 2
Dissolution Time for Caplets
[0016] Caplets were formed under a pressure of 10,000 psi
(68.9 kPa), and dissolved as described in Example 1. Results
0%
2%
5%
10%
13%
15%
25%
Dissolution time (sec)
(data for two runs)
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
699,
579,
450,
405,
339,
299,
290,
Wt. %
caplets
granules
powder
caplets
granules
powder
10
20
30
124
158
170
27.5
39.5
20.5
24
40
140
208
249
40
59.5
29.5
50
135
659
545
510
408
354
324
269
with the weight percent solids of the solution being pre pared. Therefore, the advantage of adding NaOH to the formulation increases with the concentration of the solution
being prepared.
Example 5
Test of Flowability of Borohydride/Hydroxide
Composition
[0019]
polypropylene bottles. The samples were then left on a lab
Data Normalized to 100% SBH
Corr. dissol. time (sec)
0%
2%
5%
10%
13%
15%
25%
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
Mixtures of SBH and NaOH were pulverized in a
coffee grinder for 2 minutes and then placed into 100 mL
TABLE 4
Composition
SBH
The dissolution times show that the difference in dissolution times between SBH and the NaOH formulation increases
are presented below in Tables 3 and 4.
TABLE 3
Composition
87% SBH/13% NaOH
(data for two runs)
699,
590,
473,
458,
389,
351,
386,
659
556
536
453
406
381
358
bench for 2 months, at which time each sample was lightly tapped and checked for its ability to ?ow. Results are
reported below.
TABLE 7
% NaOH
% SBH
1
2
3
5
99
98
97
95
Flow
Hard clumps
Hard clumps
Free flowing
Free flowing
Aug. 16,2007
US 2007/0187636 A1
4. The composition of claim 3 in which the borohydride compound is sodium borohydride and the base is sodium
TABLE 7-continued
hydroxide.
% NaOH
% SBH
Flow
10
13
15
20
25
50
90
87
85
80
75
50
Free
Free
Free
Free
Free
Free
?owing
?owing
?owing
?owing
?owing
?owing
5. The composition of claim 4 having from 3% to 17% sodium hydroxide and from 83% to 97% sodium borohy dride. 6. The composition of claim 5 having 15% sodium hydroxide and at least 85% sodium borohydride.
7. A method for rapid production of an aqueous borohy dride solution comprising a step of adding the composition of claim 1 to water in an amount suf?cient to produce a
1. A solid composition comprising:
solution having from 1% to 40% solids.
8. The method of claim 7 in which the solution has from
(a) from 50% to 98% of at least one borohydride com
5% to 35% solids.
pound; and
(b) from 2% to 50% of at least one base.
2. The composition of claim 1 in which said at least one
borohydride compound is sodium borohydride, potassium borohydride or a combination thereof, and said at least one
base is sodium, lithium or potassium hydroxide, sodium or potassium methoxide, or a combination thereof.
3. The composition of claim 2 having at least 2.5% of said
9. A method for improving ?ow of powdered metal
borohydride salts; said method comprising adding at least
2.5% of at least one base selected from alkali metal hydrox ides, alkali metal alkoxides and alkaline earth alkoxides to at least one metal borohydride.
10. The method of claim 9 in which said at least one base is sodium hydroxide and said at least one metal borohydride
is sodium borohydride.
at least one base and no more than 97.5% sodium or
