Enhancement of reactivity in Li4SiO4-based sorbents from the nano-sized rice husk ash for high-temperature CO2 capture

Using the cost-effective, renewable and nano-sized of citric acid pretreatment rice husk ash (CRHA) as silicon source, high efficient Li4SiO4 (lithium orthosilicate)-based sorbents (CRHA-Li4SiO4) for high-temperature CO2 capture were prepared through the solid-state reaction at lower temperature (700 °C). Two typical raw materials (nano-structured Aerosil and crystalline Quartz powders) were used to synthesize Li4SiO4 sorbents (Aerosil-Li4SiO4 and Quartz-Li4SiO4) for comparison purposes. The phase composition behavior, surface area, and morphology of the silicon sources, heat treated raw materials and as-received Li4SiO4 sorbents were studied by analytical techniques. The CO2 adsorption capacity and adsorption–desorption performance were tested by the thermo-gravimetric analyses (CO2 atmosphere) and a fixed bed reactor, respectively. Compared with the case of its original samples, the morphology of heat treated raw materials had a greater effect on the phase composition, microstructure, special surface area and CO2 adsorption properties of their resulting sorbents. Although the calcined Quartz sample maintained the structure of micron particles, its reactivity was not enough to react completely with Li2CO3. Due to the greater reactivity of nanoparticles, Aerosil-Li4SiO4 presented pure of Li4SiO4 whereas it obtained large particles with dense morphology, which was coming from the pronounced fusing of silica nanoparticles during the calcined process. Conversely, CRHA-Li4SiO4 achieved porous agglomerates of submicron particles resulting from a high anti-sintering character of its calcined CRHA. This more favorable structure of CRHA-Li4SiO4 could lead to the higher CO2 adsorption capacity of 30.5 wt% (6.92 mmol/g Li4SiO4, corresponding to 83.1% efficiency), faster kinetic behavior and better regenerability (its adsorption capacity only decreased 2.1 wt% from the first cycle to the 15th cycle), which was illustrated by the thermogravimetric analyses and fix bed results.