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หน้าแรก > งานวิจัย > Production of ZSM-5 Zeolite from Lignite Fly Ash

Production of ZSM-5 Zeolite from Lignite Fly Ash

Metta Chareonpanich, Marisa Samran, Teerapong. Namto and Paisan Kongkachuichay Department of Chemical Engineering, Kasetsart University, Chatuchak, Bangkok 10900, Thailand.

Summary

In Thailand, low quality lignite is found predominantly. It contains high amount of moisture and heteroatoms such as sulfur, nitrogen and inorganic minerals. Approximately 74% of coal produced are supplied to power station as energy source. The major problem in coal-fired power generation is that the plenty of solid waste so-called fly ash (of about 37 % of raw coal). Almost all fly ash is disposed of by landfill, which becomes increasingly expensive and causes an environmental pollution. Therefore, fly ash utilization such as the productions of building materials based on their pozzolanic properties was studied by many investigators 1-4. However, due to abundance of coal fly ash and strictly environmental regulations in the near future, the efficient and cleaner utilization of fly ash is necessary. Since fly ash generated by Mae-Moh lignite combustion is mainly composed of amorphous forms of silica and alumina, therefore the use of this fly ash as a raw material for zeolite synthesis is feasible technically 5-13. Various zeolites produced from fly ash should be used as the catalyst in the petroleum and petrochemical processes, adsorption agent, water softener, ion-exchange agent and detergent builder. In this study, lignite fly ash from the power generation plant at Mae-Moh basin, Thailand, was used as the raw material for ZSM-5 zeolite synthesis. Factors affecting the yield of ZSM-5 zeolite produced from fly ash were investigated as follows: SiO2/Al2O3 mole ratio, 3 - 200; the presence of tetrapropyl ammonium bromide (TPABr, the structure-directing material for ZSM-5 zeolite synthesis); initial pressure, 1-5 bar; holding temperature, 150 - 210oC and holding time, 0 - 4 h. It was found that at the SiO2/Al2O3 mole ratios of 3 - 200 without TPABr, only zeolite P could be synthesized. Similarly, without the addition of the sodium silicate solution, the SiO2/Al2O3 mole ratio in raw ash obtained in this case is 3, the ZSM-5 zeolite also could not be synthesized. The highest yield of ZSM-5 zeolite (43 wt%) was found at the following conditions: SiO2/Al2O3 mole ratio, 40; the initial pressure, 4 bar; the temperature, 210oC and the holding time, 4 h. XRD patterns of lignite fly ash from Mae-Moh basin and ZSM-5 zeolite are shown in Figure 1. SEM photographs of fly ash and products obtained from synthesis experiments with TPABr at SiO2/Al2O3 mole ratios of 20, 40, 60, 80, 100 and 200 are shown in Figures 2 and 3, respectively. Keywords: Fly ash; ZSM-5 zeolite; Synthesis; Hydrothermal treatment Acknowledgements
This research has been financially supported by the Kasetsart University Research and Development Institute (KURDI) and the Faculty of Engineering, Kasetsart University. The lignite fly ash sample was supplied by the Electricity Generating Authority of Thailand (EGAT).

References

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