Calcium Borohydride Synthesis via Solid-State Hydrogenation
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Solution Overview
Problem
Current methods for producing calcium borohydride are inefficient and hazardous due to the use of diborane gas and require high temperatures for hydrogen storage, which is not suitable for automotive applications.
Innovation Solution
A three-step process involving mechanical milling and compacting of metal boride and alkaline earth metal hydride powders followed by high-pressure hydrogenation at elevated temperatures, using a metal chloride catalyst in a dry inert atmosphere, to synthesize alkaline earth metal borohydrides like calcium borohydride.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If diborane gas is used as a precursor material, then calcium borohydride can be synthesized, but the process becomes hazardous due to spontaneous ignition in moist air and respiratory distress
Solution Approach 1:
The patent replaces diborane gas with sodium borohydride and calcium chloride as precursor materials. These solid precursors are safer, non-hazardous alternatives that can be handled without special precautions, eliminating the ignition and respiratory distress issues associated with diborane while still enabling calcium borohydride synthesis through a controlled reaction process
Solution Approach 2:
The patent employs an inert atmosphere (nitrogen or argon) throughout the synthesis process to prevent moisture exposure and unwanted reactions. This inert environment protects the reaction materials from humid air, preventing the hazardous spontaneous ignition that would occur with diborane gas while maintaining safe and controlled synthesis conditions
2Productivity
If high temperature hydrogenation is used to produce calcium borohydride, then the synthesis can proceed, but the operating temperature exceeds the upper limit for automotive applications
Solution Approach 1:
The patent changes the synthesis approach by using a two-step process with intermediate formation. First, calcium boride is formed from calcium chloride and boron powder at elevated temperature. Then, hydrogenation of the boride occurs at lower temperature (below 120°C) to produce calcium borohydride. This parameter change in the reaction pathway enables synthesis while maintaining operating temperatures suitable for automotive applications
Solution Approach 2:
The patent divides the synthesis into two distinct steps: (1) formation of calcium boride precursor, and (2) hydrogenation to form calcium borohydride. This segmentation allows each step to occur under optimized conditions, with the second step proceeding at low temperature to avoid exceeding the 120°C operating limit while still achieving complete conversion to the desired product
3Reliability
If simple binary hydride compounds like magnesium hydride are used, then good hydrogen reversibility and fast reaction kinetics are achieved, but the hydrogen equilibrium pressure reaches 1 bar at 300°C, which is too high for automotive applications
Solution Approach 1:
The patent uses calcium borohydride as a composite hydrogen storage material that combines the benefits of reversibility with lower operating temperatures. The material exhibits good hydrogen reversibility similar to simple hydrides, but the equilibrium pressure remains below 1 bar at temperatures below 120°C, making it suitable for automotive applications where simple binary hydrides fail due to excessively high equilibrium pressures
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method achieves a high yield of calcium borohydride with improved reversibility and hydrogen storage capabilities, suitable for on-board hydrogen storage systems, with a safer and more efficient process compared to existing methods.
Implementation Method 1
high pressure hydrogenation of the compacted powders at an elevated temperature
Implementation Method 2
mechanically milling and compacting powders of a metal boride powder with an alkaline earth metal hydride
Implementation Method 3
using a metal chloride catalyst in a dry inert atmosphere
Data Source
AI summary
A method is disclosed for directly preparing an alkaline earth metal borohydride, i.e. Ca(BH4)2, from the alkaline earth metal hydride and the alkaline earth metal boride. The borohydride thus prepared is doped with a small portion of a metal chloride catalyst compound, such as RuCl3, TiCl3, or a mixture of TiCl3 and palladium metal. The process provides for mechanically mixing the dry reagents under an inert atmosphere followed by charging the mixed materials with high pressure hydrogen at about 70 MPa while heating the mixture to about 400° C. The method is relatively simple and inexpensive and provides reversible hydride compounds which are free of the usual contamination introduced by prior art wet chemical methods.