Abstract
The membrane reactor is proposed in this work as a system with high potential to efficiently recover the hydrogen (H2) stored in ammonia (NH3), which has been recently proposed as an alternative for H2 storage. With this technology, NH3 decomposition and high-purity H2 separation are simultaneously performed within the same unit, and high H2 separation efficiency is achieved at lower temperature compared to conventional systems, leading to energetic and economic benefits. NH3 decomposition was experimentally performed in a Pd-based membrane reactor over a Ru-based catalyst and the performance of the conventional packed bed reactor were used as benchmark for a comparison. The results demonstrate that the introduction of a membrane in a conventional reactor enhances its performance and allows to achieve conversion higher than the thermodynamic equilibrium conversion for sufficiently high temperatures. For temperatures from and above 425 °C, full NH3 conversion was achieved and more than 86% of H2 fed to the system as ammonia was recovered with a purity of 99.998%. The application of vacuum at the membrane permeate side leads to higher H2 recovery and NH3 conversions beyond thermodynamic restrictions. On the other hand, the reactor feed flow rate and operating pressure have not shown major impacts on NH3 conversion.
Highlights
World power generation is nowadays largely dependent on the use of fossil fuels
The catalytic decomposition of ammonia to recover pure H2 has been experimentally investigated in a tubular membrane reactor over a Ru-based catalyst and for the selective H2 separation double-skin Pd-based membranes with either dead-end or double sealing configu ration were used
For temperatures from and above 425 ◦C, virtual full ammonia conversion is achieved and more than 86% of the H2 fed to the system in the form of ammonia is recovered from the membrane reactor with a minimum purity of 99.998%
Summary
World power generation is nowadays largely dependent on the use of fossil fuels. With a continuously increasing world population, fossil fuels consumption has achieved an unprecedent scale [1] and their availability is significantly decreasing over time. The depletion of fossil fuels, combined with rising concerns about climate change, is moti vating the substitution of conventional technologies and energy sources for power generation with innovative strategies to maintain the continuously increasing worldwide energy demand. Renewable sources are by nature intermittent and highly fluctuating, renewable energy is not always capable to closely follow the power demand of the grid. Since chemicals offer high energy density and are stored, transported and distributed, one option for large scale energy storage could be storing energy in the form of chemical bonds
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