Fabrication of structurally improved KNaTiO₃ pellets derived from cheap rutile sand for high-temperature CO₂ capture

For the practical applications of CO₂ sorbents, more studies on pellet rather than powder-type sorbents is a more mainstream research trend. In addition, high sorption kinetics, excellent cycling stability, and cheap raw precursors are far more important than its initial CO₂ uptake value to a certain extent. Recently, alkali titanates have attracted growing attention as emerging and attractive high-temperature CO₂ sorbent materials. Among the existing Na-doped alkali titanates, potassium sodium titanate (KNaTiO₃) is one of the most promising high-temperature CO₂ sorbent due to its high CO₂ sorption rate and excellent cyclic stability. In order to promote its practical application in industry, a low-priced titanium ore was selected for the synthesis of KNaTiO₃, and the optimized resulting sorbent maintained a rapid and reversible sorption capacity of 15.5 wt% after 100 cycles. Spherical pellets were fabricated by extrusion-spheronization method with cellulose and alumisol additives. The optimal pellets exhibited a relative compression strength of 4.15 MPa and an attrition rate of 1.2 wt% as well as maintaining a sorption capacity of 14.3 wt% after 50 cycles. It also showed superior CO₂ capture kinetics, reaching a high CO₂ removal rate of 92.5% within only 4 min (under 20% CO₂). The role and mechanism of cellulose as pore-former were explored by SEM analysis and diffusion model fitting. In all, the optimized resulting sorbent pellets not only retained rapid CO₂ sorption kinetics, high CO₂ removal rate, excellent cyclic performance, but also ensure robust mechanical properties. These properties, as well as the low cost aspect, makes this newly developed KNaTiO₃-based pellets to be highly promising for high temperature CO₂ capture such as for biomass fired power plants or hydrogen production.