CHEMICAL LOOPING STRATEGIES FOR SUSTAINABLE HYDROGEN AND SYNGAS PRODUCTION: A STUDY ON WATER-GAS SHIFT, METHANE REFORMING, AND BIOMASS GASIFICATION

Abstract

Hydrogen fuel is attractive as an energy carrier because of its mass-specific energy density, abundance, and availability from a variety of feedstocks, and environmentally safe byproducts. Gasification and methane reforming are valuable pathways toward hydrogen production, and currently, they represent nearly 79% of the worldwide hydrogen production market share. This work presents a comprehensive investigation into some of the chemical looping (CL) strategies for sustainable hydrogen and syngas production. The research starts by identifying the chemical looping water-gas shift (CL-WGS) cycle as a promising pathway that inherently separates CO₂ while maximizing hydrogen yield. A detailed thermodynamic screening of candidate oxygen carriers (OCs), including 13 nonstoichiometric materials such as ceria (CeO2-δ), CZO20 (Ce0.8Zr0.2O2-δ), and LSMA4060 (La0.6Sr0.4Mn0.4Al0.6O3-δ), was conducted. Using equilibrium calculations, Gibbs free energy analysis, and redox swing assessments, the research concluded that CZO20 and LSMA4060 have especially excellent reduction and oxidation extents at relatively low operating temperatures. It also showed that only CZO20 is viable for isothermal operation, but higher temperatures are required. This work also compares thermodynamic modeling approaches for fixed-bed gas-solid equilibrium in chemical looping processes using nonstoichiometric oxygen carriers. The objective is to evaluate and compare different modeling approaches—closed-system (sequential and simultaneous) and extended open-system (oxygen activity and spatial) approaches—to accurately capture the equilibrium behavior. This work extends the analysis by comparing three reactor configurations (closed system, thin packed bed, finite length packed bed), highlighting the impact of reactor configuration on predicting products. Closed-system models often neglect realistic reactor configurations, so they can be used only for preliminary screening to provide baseline predictions. The study also models chemical looping gasification (CLG) of sugarcane bagasse integrated with steam splitting using the stoichiometric iron oxide and the nonstoichiometric ceria. These two OCs were evaluated across varying pyrolysis, reduction, and oxidation temperatures and biomass-to-OC ratios. Results show that while both OCs achieve a theoretical maximum upgrade factor of 42.4%, ceria achieves a higher thermal efficiency (38%) and superior syngas quality at 900 °C under isothermal operation, compared to iron oxide’s 36.3% at lower temperatures.