Synthesis of Coal Fly Ash-Based Zeolites for Carbon Capture

Abstract

In the growing interest of creating novel technologies to combat the rise of CO 2 in the atmosphere, zeolites have emerged as a sustainable solution for carbon sequestration. Zeolites are aluminosilicate-based material that are highly porous, low cost, and highly stable. This research focuses on the production and utilization of hydrothermally-synthesized coal fly ash (CFA)-based zeolites. The CFA type utilised in this study is categorised as Class F, it had a total percentage of 𝑆𝑖𝑂 2, 𝐴𝑙 2 𝑂 3, and 𝐹𝑒 2 𝑂 3 as 86.23%. The CFA used in this study was 90-125µm. Loss on Ignition (LOI) for the CFA was also conducted and the median LOI for the samples was 3.95%. During pre-treatment using a permanent magnet, an average of 48.232% of magnetics were removed from the CFA. After synthesis of the zeolites, the samples were analysed and the results showed that the addition of NaOH gradually increased the concentration of sodium oxide (𝑁𝑎 2 𝑂) in CFA from an average of 6.34% to an average of 7.23%. The results also revealed a significant reduction in 𝑆𝑖𝑂 2 and 𝐴𝑙 2 𝑂 3 percentage by an average of 43.26% and 40.10% respectively, and the concentration of 𝑆𝑖𝑂 2 was always higher than that of 𝐴𝑙 2 𝑂 3 in all the samples. The compositions of 𝑆𝑖𝑂2and 𝐴𝑙2𝑂3 gradually increased with an increase in the four controlled variables but started to decrease at higher values of each variable. The zeolites were subjected to a carbon capture test and the highest carbon capture was at 4M NaOH, hydrothermal treatment time of 30 hours, hydrothermal treatment temperature of 120℃ and CFA: NaOH ratio of 1:12.5. It was also observed that there was a rapid increase of the adsorption capacity of 𝐶𝑂2 from 10 minutes to 30 minutes followed by a progressively slow increase with the increase in contact time. The adsorption of 𝐶𝑂2 approached equilibrium within 30 min. The carbon capture test for CFA-based zeolites was then compared with that for the commercial zeolites and the carbon capture capacity of the commercial zeolites was approximately twice that of the CFA-based zeolites.