Mechano-chemical synthesis is a promising method for producing sodium borohydride (NaBH4) that has advantages over traditional methods. It involves ball milling mixtures of magnesium hydride (MgH2) and sodium metaborate (NaBO2) which results in a chemical reaction producing NaBH4 along with magnesium oxide (MgO) as a byproduct. This method is safer, more economical, environmentally friendly, efficient, and simpler than the commonly used Brown-Schlesinger process. While further optimization is still needed, mechano-chemical synthesis shows potential as a green alternative for generating the hydrogen storage compound NaBH4.

1. Review of Chemical Processes for the synthesis of
Sodium Borohydride
Digvijay Singh

2. Contents
•Introduction
•Glimpse of all the methods
•Mechano-Chemical synthesis
•Why Mechano-Chemical method is suitable?
•Conclusion
•References

3. Why all this ?

4. Hydrogen as a source of energy
•Hydrogen fuel cells- Chemical energy to electrical energy directly using Hydrogen
•H2 can be stored in different forms like gas, liquid or solid
•Storing H2 in solid form has its own advantages
•Solid form- metal borohydrides (NaBH4, LiBH4, Mg(BH4)2, Ca(BH4)2)
Why NaBH4?- more stable
NaBH4 +2H2O 4H2 +NaBO2 (aq)+300kJ

5. FCV

6. What was the problem and what we did-
1. We can use H2 for producing Electrical energy using Fuel cells but the
storage of fuel H2 is a costly affair so decreasing the cost will be an incentive.
1. Present commercial method is expensive and inefficient so our task was-
a. To find the ways to increase the efficiency of present available method.
b. To review the available methods.
c. To suggest a method which can replace the present commercial method.

7. Methods we studied and analyzed-
1. B.S. process
2.Bayer process
3.Through BSG
4. Through Ulexite mineral
5. Using dynamic behaviors of protide at the extreme surface of magnesium
particles.
6.Mechano-Chemical synthesis

8. Various Preparatory
Methods
A Glimpse

9. Brown-Schlesinger Process
4 NaH + B(OCH3)3 → NaBH4+ 3NaOCH3
Hydrogen cost in
the range of
$188-259/kg H2
CH4

10. Possible cost Saving
▪Electrolysis of NaCl to get Na metal: more energy is required to electrolyze
NaCl (efficiency:50%) than other sodium salts (saving upto $50/kg H2)
▪Purchasing of Na metal from other producers: Integration of NaBH4 & Na
metal production will provide benefits such as significant shipping cost savings,
efficient process integration, and safety (Sodium is difficult to handle).
▪Combine Steps 3 and 4: Millennium Cell has developed a solution, wherein
borax is treated with CO2 & CH3OH to directly obtain trimethylborate. This
replaces Na2SO4 with Na2CO3, which is a more industrially valuable chemical.

11. Bayer Process
▪The Bayer Process combines borax, Na metal & H2 in the presence of silica to
produce NaBH4.
Na2B4O7 + 16 Na + 8 H2 + 7 SiO2 → 4 NaBH4 + 7 Na2SiO3
T= 700 °C P:3 atm
▪Energy cost of the process = US$ 2/kg NaBH4 (assuming ideal conditions & the
energy cost of by-product removal is excluded).
Cost of raw materials = US$ 10/kg NaBH4
Cost of 1 kg Hydrogen produced from 4.73 kg NaBH4 (with catalyst)= US$ 80
Otherwise Reaction cost= US$ 260

12. Elemental Processes
Synthesis of sodium borohydride from elemental sodium, boron and hydrogen
Temperature: High (600-800°C) pressure:150 atm
Na + B + 2 H2 → NaBH4
A slight excess of sodium metal, or alternatively sodium hydride, and the use of
amorphous boron is claimed to improve yields.
Efficient utilization of sodium, although at the expense of more demanding
reaction conditions.

13. Carbothermal Processes
A variation of the elemental synthesis route
NaBO2 + 2 CH4 → Na + B + 2 H2 + 2 CO
Na + B + 2 H2 → NaBH4
raw material: aqueous Sodium Metaborate & Methanol
Specialized equipment are used to achieve the elevated temperatures

14. Pathway Reaction
Brown-Schlesinger Process 4 NaH + B(OCH3)3 → NaBH4 + 3 NaOCH3
Bayer Process Na2B4O7 + 16 Na + 8 H2 + 7 SiO2 → 4 NaBH4 + 7 Na2SiO3
Metal reduction NaBO2 + 2x/y M + 2H2 →NaBH4 + 2/y MxOy
Elemental Na + B + 2 H2 → NaBH4
Carbothermal NaBO2 + 2H2 + CH4 +O2 →NaBH4+ CO2+2H2O

15. Option Criteria
Energy Consumption 25 2 7 4
Raw material consumption 25 3 7 5
Few chemical reactions 5 5 8 9
Few separation / processing steps 5 5 8 9
Low technical risk 5 10 7 5
emissions, wastes, CO2 10 10 8 7
toxicity, safety, flammability, H2O-reactive 5 8 7 7
abundant raw materials 5 10 8 10
Total 415 620 495
Weight
Schlesinger
MetalReduction
CarboThermal

16. Mechanochemical
Synthesis

17. 1.Using MgH₂ and NaBO₂
Sample Preparation
● Mg powder : dp < 74 µm, Purity = 99.5 wt %
Mg +H₂ MgH₂ (300ºC, 6Mpa)

18. ● Anhydrous NaBO₂
NaBO2.4H2 O

20. Fig. 1. XRD patterns of the powders produced after ball milling the MgH₂-NaBO₂
mixture (in 2:1 mol ratio) for different durations (a) 30 min (b) 1 h (c) 2 h (d)3 h (e) 4 h.
L.Z. Ouyang et al. / Journal of Power Sources 269 (2014) 768e772

21. 2. Using Mg₃La
Sample Preparation
• Preparation of Mg₃La by melting of Mg(99.9%) and La(99.9%) under argon
atmosphere.
• NaBO₂ powder dried at 280ºC to obtain anhydrous NaBO₂ .

22. Chemical Reactions :
1.Mg₃La + 9/2H₂ →3MgH₂ + LaH₃ (T=25⁰C, ΔfG⁰= -74.778 kJ/mol)
2. 9NaBO₂ + 12MgH₂ + 4LaH₃ →9NaBH₄ + 2La₂O₃ + 12MgO

23. Purification
a. Extracting NaBH4 with anhydrous ethylene diamine(0.99%)
b. Separation of remaining solution from by products and remaining reactants
through polytetrafluoroethylene filter.
c. Filtrate is then dried in a vacuum oven at 50⁰C to obtain NaBH₄

24. Fig. 3. XRD patterns of the white solid product obtained after purifying.

25. Advantages of using Mg₃La over MgH₂
Hydrogenation of Mg₃La is relatively easier than that of Mg.
Using H-Mg₃La reduces the energy consumption.

26. Process Performance
Process performance can be judge against the five key performance objective:
Flexibility(Simplicity)
Cost
Safety
Environmental friendly
Efficiency

27. Safety
“Safety comes first”
No hazardous and toxic substance
4NaH+B(OCH3)3→ NaBH4 +NaOCH3 (brown schlesinger process)
NaBO2 + 2MgH2 → NaBH4 +2MgO (mechano-chemical syntthesis)
No severity
Ambient Temp and pressure

28. Simplicity
Solubility of NaBH4 in IPA
NaBH4 is soluble in IPA(isopropylamine)
IPA is simply available
No extra by product in process except MgO
MgO can be removed by electrolysis process, can be used further in commercial process

29. Economic
Price of reactant
Na-25$/100gm
Mg-1.93$/kg
Recycling of MgO
By the recycling of MgO, Mg can be produced which can be utilized further in commercial process
No waste product
(source-US department of energy)

30. Environment friendly
Reduce-reducing of raw material and cost(Na)
Reuse-reusing of byproduct(Mg)
Recycle-remaining unreacted product(NaBO2)
Sustainable

31. yield
Yield obtained during process 71%
Yield =obtained mass NaBH4/Theoretical mass NaBH4*100%

32. Mechano-chemical vs Schlesinger process
Parameter Brown-schlesinger Ball-mill
Reaction 4NaH+B(OCH3)3→ NaBH4 +NaOCH3 NaBO2 + 2MgH2 → NaBH4 +2MgO
Hazardous,Toxic Yes,NaOCH3 No
Safe No, High T,P Yes 25o C,200KPa
Economic No, NaOCH3 Yes, No waste
Byproduct Usable No Yes,

33. Disadvantages
Ball milling time-
at industrial level rotation rate of ball mill is low compared to laboratory
experiment, may required high energy and high operating cost.
Reaction of Na with Air-
Explosion may occur if Na react with air, inert atmosphere(Ar,He2) is necessary.
Process has not been established yet

34. Conclusion
● What is the importance of H2 as Fuel cell?
● What are the various methods for the production of NaBH4?
● What are the various forms of process performance?
● What is Mechano-chemical synthesis and how it is used for for production
of NaBH4?
● What are the advantages and disadvantages of Mechano-chemical
synthesis?
● Comparison of Mechano-chemical synthesis with various methods?

36. Thank
you…!