From waste to high value utilization of spent bleaching clay in synthesizing high-performance calcium-based sorbent for CO_2 capture

摘要

A novel calcium looping (CaL) process integrated with a spent bleaching clay (SBC) treatment is proposed whereby fuels and/or heat from regeneration of SBC provide extra energy for the calcination process, in addition, the regenerated SBC can be used to synthesize enhanced CaO-based sorbents. Different kinds of composite samples were prepared with the regenerated SBC and/or aluminate cement at various doping ratios via a pelletization process. All pellets were subjected to thermogravimetic analyzer tests employing severe reaction conditions to determine the optimal doping ratios and regeneration method for the SBC based sorbents. These results demonstrate that pellets containing combustible components showed higher CO2 uptakes, due to the improved pore structure, which was verified by N-2 adsorption measurements. The as-prepared sorbent "L-10PC" (90 wt.% CaO/10 wt.% pyrolytic SBC) achieved a final CO2 uptake of 0.164 g(CO2) g(calcined sorbent)(-1) after 20 cycles, which was 67.3% higher than that of natural limestone particle. A new lamite (Ca2SiO4) phase was detected by X-ray diffraction analysis, however the weak diffraction peak associated with it indicated a low content of lamite in the pellets, which produced a smaller effect on performance compared to cement. A synergistic effect was achieved for a sample designated as "L-5PC-10CA" (85 wt.% CaO/5 wt.% pyrolytic SBC /10 wt,% cement), which resulted in the highest final uptake of 0.208 g(CO2) g(calcined sorbent)(-1) after 20 cycles. Considering the simplicity of pyrolysis regeneration process and the excellent capture capability of pellets doped by pyrolytic SBC, the proposed system integrating CaL with SBC pyrolysis treatment appears to offer particular promise for further development.