Abstract
Characteristics of ZSM-5 synthesized from H2SO4-treated coal fly ash and fused coal fly ash extracts are compared in this study. In the synthesis process, fused coal fly ash extract (without an additional silica source) was used in the synthesis of ZSM-5. The effect of the structure-directing agent (tetrapropylammonium bromide, 1,6-hexanediamine or 1-propylamine) on the properties and methanol-to-olefins (MTO) effectiveness of the fly ash-based ZSM-5 was also investigated. A pure ZSM-5 synthesized from the fused coal fly ash extract led to a methanol conversion higher than 90% after 5 h on stream. The template 1,6-hexanediamine led to the synthesis of the most stable fly ash-based catalyst keeping a 44% methanol conversion after 24 h on stream.
Highlights
The fly ash has been used as a starting material for the synthesis of zeolites because of its high content of amorphous aluminosilicate glass [1]
The use of different aluminum extraction conditions than that reported by Missengue and coworkers did not increase the Si/Al ratio of the solid residue [13], there was still a need to add a source of silica; the substitution of tetrapropylammonium bromide (TPABr) by other structure-directing agents such as 1,6-hexanediamine (HDA) and 1-propylamine (PA) may lead to a cheaper way of synthesizing ZSM-5 from fly ash solid residue
TPABr were used during the synthesis of ZSM-5 (FFAE–TPABr) even if the precursor silica extract (FFAE) had a Si/Al ratio of 10.4 (Table 1), which was within the range for the synthesis of ZSM-5 zeolite
Summary
The fly ash has been used as a starting material for the synthesis of zeolites because of its high content of amorphous aluminosilicate glass [1]. Several routes to prepare various zeolite types have been suggested based on the pre-treatment of the fly ash, alkalinity of the hydrothermal solution, molarity of alkaline agents, solution/solid ratio, templating agent, time, temperature and time of incubation [2–9]. ZSM-5 is synthesized from a hydrothermal solution containing Al and Si sources, a mineralizing agent (OH− or F− ) and an organic structure-directing agent (OSDA) [10–13], with tetrapropylammonium cation (TPA+ ) being the most-used OSDA [9,14–16]. The OSDAs that give pure ZSM-5 increase as follows: alcohols < amines < tetrapropylammonium halide. Some studies have reported the synthesis of ZSM-5 zeolite without any OSDA [14]. In addition to OSDAs, other parameters that influence the crystallization as well as the morphology of ZSM-5 zeolite include
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