Geopolymer-zeolite and geopolymer- iron (III) ion exchanged zeolite pellets as highly regenerable CO2 adsorbents

Powdered zeolites have been reported as effective CO2 capture materials. However, pellet form is needed for industrial application. In this study, shaped zeolite X (ZX) and Fe3+ ion-exchanged zeolite X (ZXFe) with geopolymer as binder were produced in forms of cylinder pellets (o = 5 mm, h = 5 mm) at low temperature. The geopolymer was obtained through the geopolymerization of metakaolin using NaOH as an alkaline activating agent. The material formed by this way remained the zeolite X structure that was confirmed by X-ray diffraction (XRD) analysis. Additionally, scanning electron microscopy (SEM) results of the two different kind geopolymer - zeolite pellets were considered for observation and comparison. BET analysis was also conducted to determine the specific surface area of the GZX3 samples and GZXFeL3 samples. This kind of analysis also provided the information about the adsorption - desorption curves and pore size distributions of the two pellet samples. The difference of the temperature in the pretreatment process affected the degas ability of the pellet and the series of experiments were carried out to make clear comparison. The highest CO2 adsorption capacities of pellets were found in the GZX3 (containing the zeolite X) and GZXFeL3 (containing the ZXFe). Despite the rapid decrease in the surface areas from 409 to 261 m2/g for GZX3 and GZXFeL3 respectively, GZXFeL3 showed higher CO2 capacities than the other (1.03 compared to 0.96 mmol/g). In the regeneration study, after several cycles of adsorption - desorption of GZXFeL3 pellets, the adsorption capacity of CO2 decreased about 10%. These adsorption and desorption experiments implied that the pellets formed by ZXFe could be a promising adsorbent for the CO2 capture.

Automated summary

This study produced shaped zeolite X and Fe3+ ion-exchanged zeolite X in the form of cylinder pellets, with geopolymer as binder. The geopolymerization process maintained the structure of zeolite X. BET analysis showed that GZXFeL3 pellets had higher CO2 adsorption capacities compared to GZX3 pellets. After multiple cycles of adsorption - desorption, the CO2 adsorption capacity of GZXFeL3 pellets decreased by about 10%.