CO2 capture and MWCNTs synthesis using mesoporous silica and zeolite 13X collectively prepared from bottom ash

Ground power plant bottom ashes were alkali-fused at 600 °C for 1 h and silicate extraction was conducted in water at room temperature. The supernatant solution was then used to make mesoporous silicas after adding a triblock copolymer, Pluronic P123, as a template, whereas the solid precipitate was used to make zeolite 13X. This combined synthesis scheme enabled high levels of silicate recycling close to 100%. The mesoporous silica prepared using butanol as a swelling agent (MS-b) resulted in higher surface areas and higher pore volumes than those prepared using mesitylene (MS-m). MS-b, used as a support material for impregnating PEI (polyethyleneimine) for capturing CO2, achieved excellent CO2 capture capacity (218 mg/g-adsorbent with 70 wt% PEI) at 75 °C. Removal of a portion of silicate species by aqueous extraction rendered the composition of the remaining precipitate more favorable for 13X synthesis, and the lower Si/Al ratio in the prepared zeolite 13X led to increased carbon dioxide adsorption. Finally, high content of Fe impurity (ca. 12.6 wt%) remained in the porous structure of the zeolite 13X, enabling uniform growth of multi-wall carbon nanotubes (MWCNTs) by chemical vapor deposition in a quartz reactor using acetylene as a carbon source at 700 °C.