Enhanced hydrogen production of mid-temperature chemical looping steam methane reforming using lithium-based sorbent particles

Coupling chemical looping steam methane reforming (CL-SMR) with sorbents comprises a promising approach for enhancing high-purity H-2 production. However, the lack of energy-efficient pathway with high CO2 capture performance sorbents hinders its development. Herein, we prepare lithium-based absorbent particles with porous micromorphologies and large surface areas using various Li-precursors, alkali metal dopants, and particle sizes, achieving fast CO2 sorption-desorption kinetics, high absorption capacity of 0.30 g CO2 g(-1) Li4SiO4, and excellent cyclic stability at a low CO2 concentration (10 vol%). Absorbent paritcles measuring 1 mm, using lithium carbonate as Li-precursor and doped with 20 mol% potassium, demonstrated a high CO2 conversion of 63.7% and a crushing mechanical strength of 25 N over 200 isothermal sorption-desorption cycles. In addition, the enhancement of absorbent particles for CL-SMR was evaluated in a fixed-bed reactor. Mechanical mixed with nickel-based oxygen carriers, lithium-based absorbent carbonation enables the in-situ CO2 removal in CL-SMR process, along with elevated methane conversion (93.3%), hydrogen purity (92.8%), and hydrogen production rate (9.45 mL min(-1) g(-1)) in a single step, while the energy demand of calcination is reduced at mild temperatures (500-600 degrees C). The incorporation of lithium-based absorbents facilitated an alternative reforming mechanism, yielding a notable 15.2% reduction in the apparent activation energy. In-situ DRIFTs experiments, combined with XRD and XPS characterization, further revealed that lithium ions in the absorbent interact with CO2 to form lithium carbonate. This process facilitates in-situ decarbonization, promotes the water-gas shift reaction, and enhances the production of high-purity hydrogen.