Ortho-para hydrogen conversion (OPC) is a catalytic process in which ortho-hydrogen is converted to para-hydrogen at cryogenic conditions. It is a critical requirement of hydrogen liquefaction in terms of both energy and boil-off management. Literature studies have shown that the kinetic reaction rate of this conversion can be adequately represented by both first-order and Elovich (logarithmic) expressions. Such cryogenic OPC reaction kinetic data is generated here for two catalysts – IONEX (commercial hydrous iron oxide) and a metal-organic framework (MOF) and subsequently compared using the framework of both reaction rate expressions.
The Objectives
The specific objectives are to:
- Evaluate the applicability of both a first-order kinetic model and the Elovich (logarithmic) kinetic model to describe the OPC reaction for both IONEX and the MOF catalyst.
- Determine the first-order reaction rate constant for each catalyst as a function of temperature (30-70K).
- Determine the Elovich kinetic parameters, particularly K, for each catalyst as a function of temperature (30-70K).
- Compare the kinetic parameters obtained from the two models to assess the relative reaction performance of the catalysts.
Project Findings
The Baker Hughes MOF catalyst consistently exhibits higher kinetic coefficients than the IONEX catalyst for both reaction rate expressions, indicating faster intrinsic ortho-para hydrogen conversion. This improvement is most pronounced at low temperatures, with the MOF-to-IONEX first-order kinetic coefficient ratio exceeding 2.5 at 30 K for example. Overall, the results demonstrate that the BH MOF catalyst provides a significant OPC kinetic advantage, particularly under cryogenic conditions relevant to hydrogen liquefaction.
A preliminary catalyst fouling study showed that trace (ppm) impurities in the hydrogen feed caused catalyst deactivation. Both the MOF And IONEX catalysts experienced a decline in activity, with the MOF stabilising after approximately 300 operational minutes, whilst IONEX continued to deactivate. Further testing is required to quantify the extent and mechanism of impurity-induced fouling.
Recommendations
Overall, these findings highlight the strong potential of the MOF catalyst for low-temperature OPC applications, offering opportunities to improve reactor performance, reduce reactor size, and enhance the efficiency of hydrogen liquefaction and storage systems. Future work will focus on further characterisation of the effect of fouling on catalyst performance including formulation of the catalysts to be more hydrophobic so as to minimise fouling by moisture.
Project researchers
- Prof. Michael Johns
- Dr Fuyu Jiao
- Dr Kwanghee Jeong
Project Status
Complete
Partners
