Spray-Dried Sodium Zirconate: A Rapid Absorption Powder for CO2 Capture with Enhanced Cyclic Stability

Improved powders for capturing CO2 at high temperatures are required for H-2 production using sorption-enhanced steam reforming. Here, we examine the relationship between particle structure and carbonation rate for two types of Na2ZrO3 powders. Hollow spray-dried microgranules with a wall thickness of 100-300nm corresponding to the dimensions of the primary acetate-derived particles gave about 75wt% theoretical CO2 conversion after a process-relevant 5min exposure to 15vol% CO2. A conventional powder prepared by solid-state reaction carbonated more slowly, achieving only 50% conversion owing to a greater proportion of the reaction requiring bulk diffusion through the densely agglomerated particles. The hollow granular structure of the spray-dried powder was retained postcarbonation but chemical segregation resulted in islands of an amorphous Na-rich phase (Na2CO3) within a crystalline ZrO2 particle matrix. Despite this phase separation, the reverse reaction to re-form Na2ZrO3 could be achieved by heating each powder to 900 degrees C in N-2 (no dwell time). This resulted in a very stable multicycle performance in 40cycle tests using thermogravimetric analysis for both powders. Kinetic analysis of thermogravimetric data showed the carbonation process fits an Avrami-Erofeyev 2D nucleation and nuclei growth model, consistent with microstructural evidence of a surface-driven transformation. Thus, we demonstrate that spray drying is a viable processing route to enhance the carbon capture performance of Na2ZrO3 powder.