Relating Structural and Microstructural Evolution to the Reactivity of Cellulose and Lignin during Alkaline Thermal Treatment with Ca(OH)2 for Sustainable Energy Production Integrated with CO2 Capture

The transition toward a low carbon economy necessitates the implementation of a wide range of negative emissions technologies, including bioenergy integrated with CO2 capture and storage. Advancing large-scale or modular technologies for bioenergy with carbon capture and storage requires a fundamental understanding of chemo-morphological coupling in these material systems. In this context, integrated chemical pathways such as alkaline thermal treatment (ATT) of biomass which involves the production of bio-H-2 while converting and storing CO2 as solid carbonates provides promising potential for integrating bioenergy with carbon capture and storage. In this study, we elucidate the structural and morphological changes when biomass feedstocks such as cellulose and lignin are reacted with calcium hydroxide to capture, convert, and store CO2 as calcium carbonate while producing energy carrier such as H-2. These structural and morphological changes were monitored using synchrotron based in operando multiscale X-ray scattering measurements. Enhanced CO2 capture at temperatures above 375 degrees C was evident from the significant growth of the calcium carbonate phase at these conditions. Increase in the surface area and porosity of cellulose was noted compared to lignin due to the relatively fast decomposition of cellulose. Pore-solid interfaces in Ca(OH)(2) + cellulose system became smoother in the temperature range of 500-700 degrees C compared to Ca(OH)(2) + lignin system, where the interfaces became rougher. Enhanced roughness of the pore-solid interfaces in the presence of lignin is attributed to the simultaneous slow decomposition of lignin and formation of calcium carbonate.