Investigation of simultaneous production of H2 and separable carbon from CH4 in a fluidised bed of NiO/Ca2Fe2O5/CaO particles

Alkhatib, Karine; Santihayu Sukma, Made; Scott, Stuart A.; Zheng, Yaoyao

Abstract

This work investigated the possibility of simultaneous production of hydrogen/syngas and separable solid carbon in a fluidised bed by using CH4-CO2 cycles and exploring the carbon growth over solid catalytic particles of NiO/Ca2Fe2O5/CaO. This two-stage process included i) stage I: H2-rich gas and carbon were simultaneously generated from the interaction between CH4 and NiO/Ca2Fe2O5/CaO particles; and ii) stage II: the reduced/carbon-deposited particles were regenerated in CO2. Following our previous successful demonstration of the process for stable hydrogen production over cycles, this study focused on the formation of solid carbon and aimed at understanding its growth mechanism as well as demonstrating the potential of using fluidisation as a means of automatic carbon separation. By tracking the carbon growth history and the change in phases of the reacted NiO/Ca2Fe2O5/CaO particles at temperatures from 700 to 900 °C, we discovered the formation of various forms of nano-structured carbon from CH4 conversion (e.g. partial oxidation, pyrolysis). These include carbon nanotubes (CNTs), carbon graphite sheets, carbon onions (CNOs), and carbon fibres. Amorphous carbon was also observed, particularly in the initial stage of CH4 conversion. Higher temperatures like 800 °C and 900 °C gave faster kinetics of CH4 conversion and more formation of solid carbon. Fe3C phase was observed on the reduced catalytic particles and could act as an intermediate phase or carbon sink for carbon growth. The results suggested that other mechanisms for carbon deposition, such as directly over Fe sites, may also exist. Fluidisation with a higher U/Umf ratio separated more carbon-rich fines from the bulk catalytic particles in the fluidised bed. Fluidising with air at 700 °C effectively removed amorphous carbon on the reacted catalytic particles, whilst structured carbon remained. Full separation and purification to obtain pure carbon require furthers optimisation of e.g. fluidisation parameters and material design.

Citation

Alkhatib, K., Santihayu Sukma, M., Scott, S. A., & Zheng, Y. (2024). Investigation of simultaneous production of H2 and separable carbon from CH4 in a fluidised bed of NiO/Ca2Fe2O5/CaO particles. Fuel, 377, Article 132816. https://doi.org/10.1016/j.fuel.2024.132816

• Journal Article Type: Article
• Acceptance Date: Aug 15, 2024
• Online Publication Date: Aug 19, 2024
• Publication Date: Dec 1, 2024
• Deposit Date: Aug 24, 2024
• Publicly Available Date: Aug 27, 2024
• Journal: Fuel
• Electronic ISSN: 1873-7153
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 377
• Article Number: 132816
• DOI: https://doi.org/10.1016/j.fuel.2024.132816
• Keywords: Nanostructured carbon; Hydrogen production; Chemical looping; Fluidised bed; Carbon growth and separation
• Public URL: https://nottingham-repository.worktribe.com/output/38649176
• Publisher URL: https://www.sciencedirect.com/science/article/pii/S0016236124019653?via%3Dihub