Abstract
Zeolites are aluminosilicate crystalline materials known for their unique characteristics, and have been prominent for nearly half a century due to their wide and important industrial applications. The production of zeolites, however, remains a challenge due to the high cost of commercial reagents conventionally used as feedstocks. In the current study, hydroxy sodalite (HS) zeolite samples were synthesised from coal fly ash feedstock by a direct hydrothermal synthesis method. The effects of hydrothermal crystallisation synthesis time on phase crystallinity, crystal size, and morphology of the formed HS were investigated. The prepared samples were characterised using XRD, SEM, EDS and FT-IR techniques. The XRD results of the samples prepared with varying synthesis times confirmed the formation of HS from low to high phase purity and crystallinity from 11 to over 98%. The SEM results reflected gradual variation in crystal morphology, of which highly crystalline HS samples were associated with hexagonal-cubic and cubic-platelet crystals. The FTIR, depicting zeolite characteristics of T–O and T–O–T stretching vibrations in the molecular framework, further confirmed the formation of HS zeolites for samples obtained above the 24-h synthesis time. These zeolite samples were then evaluated for their catalytic activities in the conversion of maggot oil to biodiesel. The application of the various hydroxy sodalite samples for the transesterification of maggot oil yielded up to 84.10% biodiesel (FAME) with physicochemical properties that were in compliance with the biodiesel specification standards. This study investigated the novel use of a coal fly ash-derived, heterogeneous HS catalyst in biodiesel production from maggot oil, and indicates its potential to enhance biodiesel yield and quality upon process optimisation tests.
Highlights
Zeolites are aluminosilicate materials that have been known for over 250 years; they occur naturally, but have been synthetically produced on a large-scale due to their wide use in various applications [1]
This study showed that a pure phase hydroxy sodalite (HS) zeolite could be successfully synthesised from coal fly ash
The mineral phase of good crystallinity and high purity was represented by samples produced over longer hydrothermal synthesis time (≥48 h)
Summary
Zeolites are aluminosilicate materials that have been known for over 250 years; they occur naturally, but have been synthetically produced on a large-scale due to their wide use in various applications [1]. By the nature of their synthetic pathways, the conventional production of zeolites in large quantities is a challenge associated with the use of commercial compounds as feedstocks, which results in the high cost of zeolite products [5,6]. Zeolites can be prepared synthetically from various aluminosilicate sources, the above concern motivated this research to explore the use of coal fly ash as an alternative, potentially cheaper and highly-abundant feedstock source, for the preparation of hydroxy sodalite zeolite as a candidate catalyst in biodiesel production. Coal fly ash (CFA) is a solid waste residue resulting from coal burning at power stations, of which over 30 Mt is generated yearly in South Africa (and 800 Mt globally)
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