Client Background
The client is a materials technology company developing metal–organic framework (MOF) products for hydrogen storage. They required quantification of the energetics and capacity of a MOF to adsorb hydrogen.
A full thermal stability and chemical reaction hazards assessment of the material was conducted to provide the necessary data and support safe handling and future process development.
Client Objectives
Quantification of the total volume of hydrogen adsorbed and the associated energy was required to understand the efficiency of this material in storing hydrogen. It was also noted that MOF materials can exhibit exothermic behaviour and multi-stage decomposition when heated. If not understood, this can present a risk during processing, storage, or loss-of-control scenarios.
The client required clarity on:
- Quantification of the enthalpy and temperature onset associated with hydrogen adsorption or other secondary reactions.
- Quantification of the pressure changes associated with the adsorption process or any other reactions/decompositions.
- The temperature at which secondary reactions may occur.
- Whether the desired reaction could escalate under adiabatic conditions and trigger decompositions.
- How the results should inform safe operating limits.
Strategy
Accelerating Rate Calorimetry (ARC) was selected to assess the desired adsorption process and the overall thermal stability of a MOF under near-adiabatic conditions, in accordance with ASTM E1981-22.
The sample was tested as received using a heat–wait–search methodology under a hydrogen backpressure of 10 bar to identify the onset of the desired reaction in addition to any subsequent thermal behaviour. Phi-factor correction was applied to account for thermal inertia and better represent larger-scale behaviour.
Insights
Sigma-HSE found that:
- Hydrogen adsorption was initiated with an onset at approximately 110 °C
- Applying a conservative safety margin, the exothermic activity could reasonably occur from ~80 °C
- The initial exothermic event resulted in a modest adiabatic temperature rise.
- A coincident pressure decrease was observed during this event.
- A second region of exothermic activity was identified at higher temperatures (from ~180 °C)
- This secondary reaction was associated with pressure increase, consistent with material decomposition
- Visual inspection post-test showed discolouration of the material, supporting thermal degradation
The data indicates that heat generated by the initial reaction could, under adiabatic conditions, trigger further decomposition.
Outcomes
Sigma-HSE was able to:
- Quantify the energy associated with hydrogen adsorption measured from an onset of 110 °C.
- Quantify the volume of hydrogen adsorbed during the process.
- Advise on conservative maximum operating temperatures set well below the onset of potentially hazardous secondary exothermic activity.
- Demonstrate that there is a potential for multi-stage reactions, with increased hazard severity at higher temperatures
The testing provided the client with a clear understanding of the hydrogen adsorption process and any thermal hazards thereafter. This enabled informed decisions to be made regarding safe handling, processing, and future development activities.
