Study and kinetic analysis of calcined carbide slag doped with silicon nitride for cyclic CO2 capture

Using solid waste carbide slag (CS) as a calcium precursor and silicon nitride (Si3N4) as a new inert dopant, a series of calcium oxide (CaO)-based adsorbents were prepared by a simple dry mixing method and high temperature CO2 cyclic adsorption property was tested in a thermogravimetric analyzer (TGA). A lot of matters were studied in this work like the effects of Si3N4 type, dopant content, pre-calcination conditions, CO2 concentration and long-term cycles on CO2 adsorption property. The phase composition, surface morphology and surface area of the adsorbents were characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Nitrogen Physisorption analyses. The cyclic conversion experiments of three kinds of Si3N4 such as alpha-Si3N4 , beta-Si3N4 and the self-prepared Si3N4 by sol-gel method showed that the adsorbents doped with the self-prepared Si3N4 had a superior cyclic adsorption property (68.34% after 10 cycles). The calcined CS (CCS) doped with 5 wt% selfprepared Si3N4 , pre-calcined at 850 degrees C for 4 h (CCS-Si3N(4)-5-4-850) exhibited a higher conversion (>70% after 10 cycles, 57.09% after 20 cycles). The incorporation of Si3N4 inhibited the sintering between the adsorbent particles, which is in favor of enhancing the cyclic adsorption durability. The adsorption kinetics showed that the activation energies of CCS-Si3N4-5-4-850 chemisorption and diffusion were estimated to be 68.17 kJ/mol and 102.34 kJ/mol, respectively, which are consistent with the actual adsorption process.