7 steps in the traditional Brown-Schlesinger process for industrial production of NaBH4. (Borax = Na2B4O5(OH)4 · 8 H2O)
Taiwanese research from 2015 regarding the recycling of spent NaBH4, i.e. after this reaction has occurred and the hydrogen has been released:
NaBH4 + 2H2O → [catalyst] NaBO2 + 4H2 + 217kJ
The question is: how do we get NaBH4 back in the most energy-efficient manner and close the fuel cycle?. The traditional answer is: via the Brown-Schlesinger process. The electrolysis of molten NaCl in order to obtain metallic Na (Sodium) is an important step in that process. An alternative approach is presented here, namely producing metallic sodium through electrolysis of seawater.
Candidate metal borohydrides for hydrogen storage: LiBH4, NaBH4, KBH4, LiH, NaH, and MgH2. Of these NaBH4 is the prime candidate because of its higher hydrogen content (i.e., 10.8 wt%).
Traditional industrial method of producing NaBH4 according to the Brown-Schlesinger process (see picture above):
Step 1. Hydrogen produced from steam reforming of methane.
Step 2. Metallic sodium obtained through the electrolysis of sodium chloride.
Step 3. Boric acid converted from borax.
Step 4. Trimethyl borate synthesized from esterification of boric acid in methanol.
Step 5. Sodium hydride produced from metallic sodium reacting with hydrogen.
Step 6. Synthesis of NaBH4 via the reaction of trimethyl borate with sodium hydride.
Step 7. Methanol recycled from the hydrolysis of sodium methoxide.
The original fuel cycle, based on sodium borohydride (NaBH4) and ammonia borane (NH3BH3).
The revision in the concept combining the regeneration of the spent borohydrides and the used catalysts with the green electricity is reflected in(1) that metallic sodium could be produced from NaCl of high purity obtained from the conversion of the byproduct in the synthesis of NH3BH3 to devoid the complicated purification procedures if produced from seawater; and (2) that the recycling and the regeneration processes of the spent NaBH4 and NH3BH3 as well as the used catalysts could be simultaneously carried out and combined with the proposed life cycle of borohydrides.
[mdpi.com] – The Concept about the Regeneration of Spent Borohydrides and Used Catalysts from Green Electricity
Note that this research was published before H2-Fuel came out in the open about their method of extracting as much hydrogen as possible from NaBH4, namely via ultra-pure water and limited amounts of HCL.
[deepresource] – Production of NaBH4
[deepresource] – NaBH4 – The Vice-Admiral Has a Message for Dutch Parliament
[deepresource] – H2Fuel – Hydrogen Powder NaBH4