(383l) Development of an Adsorptive Separation Process of Turquoise Hydrogen Using Layered Adsorption Bed

As environmental problems caused by anthropogenic greenhouse gas emissions have increased, interest in hydrogen as an alternative energy carrier has soared. Among the various hydrogen production methods, direct methane cracking reaction, commonly referred to as turquoise hydrogen, has recently gained attention because it produces only gaseous hydrogen and solid carbon. The latter, a byproduct of the reaction, could be utilized as a raw material in several industrial fields. The typical reaction temperature for producing turquoise hydrogen exceeds 800 ℃, with thermodynamic calculations indicating that methane conversion reaches approximately 80% at 10-bar. This suggests that turquoise hydrogen contains massive amounts of unreacted methane, and side reactions also generate light hydrocarbon, such as ethane and ethylene. Therefore, developing a separation process to remove byproduct and unreacted methane to obtain high-purity hydrogen is essential.

In this study, a layered adsorption column to capture unreacted methane and light hydrocarbons is suggested as a means to achieve an efficient separation process for turquoise hydrogen. The adsorption column would be packed with activated carbon and zeolite, with their packing ratio controlled within a range of 50:50 to 90:10 by height. Furthermore, the adsorbent was thermally treated to modify its textural properties. The impact of layering ratios on methane recovery and the influence of textural properties on diffusion were monitored through breakthrough curve tests. Based on the breakthrough time of each adsorbent, time-dependent column operation steps for designing a pressure swing adsorption (PSA) unit were established. The performance of the PSA unit with these steps was then evaluated using a single adsorption column. The experimental results demonstrated an increase in hydrogen purity when utilizing a layered bed compared to using only activated carbon. By optimizing breakthrough time, the optimal length ratio was determined, facilitating the design of a compact process. Simulating the proposed PSA steps in a single column, we successfully demonstrated the production process of high-purity hydrogen from the tail gas of a direct methane cracking reaction. Our study on a layered adsorption column could have a significantly impact on its integration with the direct methane cracking reaction, potentially enabling the development of a viable turquoise hydrogen production system as a sustainable method for large-scale hydrogen production.