(429d) Thermodynamic Evaluation of Mixed Metal Redox Carriers for Biomass Utilization Using Chemical Looping

Anthropogenic climate change poses a severe threat to the environment and human well-being, necessitating a transition to a sustainable, carbon-neutral future. Biomass, a renewable resource with abundant availability, offers a promising alternative to fossil fuels for producing electricity, hydrogen, and liquid fuels. Due to its carbon-neutral nature, biomass has become an attractive source for producing hydrogen and liquid fuels with a minimal carbon footprint. However, the relatively low energy density and wide geographical distribution of biomass necessitate effective strategies to ensure the techno-economic viability of biomass conversion technologies.

Chemical looping technologies have emerged as a promising approach for biomass conversion into high-purity syngas and hydrogen utilizing iron-based redox carriers in a multi-reactor system. This technology generates high-purity products, negating post-reactor separation processing before utilization in various chemical industries, such as liquid fuel or ammonia synthesis. The scheme involves reducing the redox carrier in the first reactor (reducer) with biomass, operating in either co-current or counter-current mode to generate syngas or carbon dioxide, respectively. In counter-current mode, the reduced carrier undergoes steam-mediated partial oxidation in the second reactor (oxidizer) to produce hydrogen. While the exothermic oxidizer compensates for the endothermic reducer, the latter's heat demand depends heavily on the thermodynamics of the redox carrier. Consequently, optimizing process efficiency requires developing redox carriers with favorable thermodynamic properties that can significantly reduce the endothermic heat demand of the process. Such a reduction in heat requirement can significantly reduce the oxygen carrier requirement of the entire process.

This study conducts comprehensive process simulations using biomass as the feedstock to investigate the design of chemical looping carriers for syngas and hydrogen production, aiming to minimize the endothermic heat requirement of the reduction process. Thermodynamic evaluations are performed for various metal oxides, and based on their endothermic heat requirements in the reducers, two metal oxides are selected and used to create bimetallic metal oxides with varying compositions. Thermodynamic evaluations for hydrogen and syngas generation are performed for the mixed metal oxide composites, and exergy efficiencies are compared across different compositions. Product yields are also compared across all compositions to assess the efficiency gains achieved using bimetallic oxygen carriers. The findings from this study contribute to the development of more efficient and cost-effective biomass conversion technologies, paving the way for a more sustainable energy future.