Fly Ash Derived FAU Zeolite for Desulfurization of Petroleum Feedstocks and Water Purification

Abstract

Januario Da Costa Hossi, Diakanua Nkazi, Josias van der Merwe, Atuman Samaila Joel and Kevin Graham Harding

Zeolites are expensive materials which find broad applicability as adsorbents and catalyst for a variety of industrial processes attributed to their structure with specific surface, well defined pore dimension, and chemical properties. The synthesis of zeolites from coal fly ash (CFA) is widely reported and offers an opportunity to valorize waste in such a way that creates great environmental and economic impacts. In this study the alkaline hydrothermal synthesis method was used to identify the key synthesis parameters for fly ash-to-zeolites conversion and what their effects are on physiochemical properties of the resulting zeolite. The raw CFA was obtained from Sasol Coal mining, Mpumalanga, South Africa, and used as source of alumina and silica that gave the zeolite formation. Prior to hydrothermal synthesis, the CFA was calcined at high temperature, fused with sodium hydroxide, dissolved with appropriate volume of deionized water, and exposed to an aging step with stirring for a few hours. The synthesis was optimized by varying the reaction conditions, such as composition of starting materials, synthesis temperature, and time which achieved a faujasite (FAU) zeolite with good crystallinity yield. Treated CFA revealed good properties of Si/Al ratio, surface area, thermal stability, improved morphology, N2 -adsorption, and good cationic exchange capacity characteristic of FAU zeolites. The as-prepared FAU zeolite showed very satisfactory desulfurization capacity, reducing sulfur to less than half of its initial concentration in diesel and gasoline. Thus, the CFA-to-zeolite conversion can gain notice amongst investors due to its potential market value while assisting with solid waste management as practical way to relieve environmental pressures of coal ash dumps to support sustainable development.

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