Synthesis and Application of South African Fly Ash-Based Zeolite Membrane for Gas Separation

Abstract

Out of 190 different frameworks of zeolite structures that are known, less than 20 zeolite membranes have been fabricated. These fabricated membranes are synthesized from aluminosilicate gels prepared from pure sources of Al and Si. Although research is still on-going in growing of zeolite membranes on a support, using coal fly ash as a feedstock has not been extensively investigated. In this study, zeolite-NaA membrane was synthesized from an extract of fused South African fly ash on a porous titanium support by a secondary growth method. The influence of the synthesis molar regime on the formation of zeolite NaA membrane layer was investigated. Two synthesis mixtures were generated by adding either aluminium hydroxide or sodium aluminate to the fused fly ash extract. The feedstock material and the synthesized membranes were characterized by X-diffraction (XRD), scanning electron microscopy (SEM), X-ray fluorescence spectroscopy (XRF) and fourier transform infrared spectroscopy (FT-IR). It was found by XRD and SEM that the cubic crystals of a typical zeolite NaA with a dense intergrown layer was formed on the porous Ti support. The study shows that the source of Al used had an effect on the membrane integrity as sodium aluminate provided the appropriate amount of Na+ to form a coherent membrane of zeolite NaA whereas aluminium hydroxide did not. The single hydrothermal stage seeded support formed an interlocked array of zeolite NaA particles with neighbouring crystals. Also, a robust, continuous and well-intergrown zeolite NaA membrane was formed with neighbouring crystals of zeolite fused to each other after the multiple stage synthesis. The synthesized membrane was permeable to He (6.0 x 106 L/m2h atm) and CO2 (5.6 x 106 L/m2h atm) which indicate that the layer of the membrane was firmly attached to the porous Ti support and can be used for gas separation. The zeolite membrane selectivity was maintained with permselectivity of 1.1, which shows that fly ash could be utilized to prepare robust zeolite NaA membranes on Ti support for gas separation.

Department(s)

Mining Engineering

Keywords and Phrases

Crystal; Fly ash; Fused fly ash; Fused fly ash extract; Hydrothermal; Multiple stage; Permeance; Porous support; Single stage; Zeolite; Zeolite NaA membrane

International Standard Book Number (ISBN)

978-153610533-9;978-153610516-2

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2024 Elsevier, All rights reserved.

Publication Date

01 Jan 2017

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