Investigation of some scale-up conditions on the synthesis of faujasite zeolites from South African coal fly ash

Abstract

Coal fly ash waste produced from the coal combustion process is becoming an ever increasing concern. It is produced in such abundance due to not only South Africa, but the whole of the world relying mainly on coal combustion for the main source of energy production. With the growing rate of the human population this energy production is ever increasing. The current methods of disposal of this fly ash is not sustainable, it is being dumped in ash dumps, and poses a risk to the surrounding environment and human population. Therefore, processes need to be developed to take this waste and turn it into useful materials. This would not only solve the problem of its disposal but also create useful products that can be applied to further protect the environment. It was discovered that one of the useful materials that can be synthesised from fly ash are zeolites. These nano-porous structures have a wide variety of uses. Therefore, many studies have been conducted around optimising the synthesis of various zeolites from coal fly ash. More recently these studies have focused on the scale-up conditions needed to synthesise these zeolites on the large industrial scale, regarding the sheer volume of fly ash produced annually. The most robust and widely used technique for zeolite synthesis involves a pre-synthesis fusion of the fly ash with sodium hydroxide at a temperature of 550 0C. This would not be feasible to scale-up to industrial scale because of the energy intensity. Therefore, alternative pre-synthesis techniques have been proposed. One of those techniques involves using a sonochemical treatment as a pre-synthesis. It can be argued that this technique may not be able to be easily scaled. To solve this problem, another alternative technique was investigated within this study. It involves the use of a jet loop pilot plant mixing system, which can be scaled-up very readily to industrial scale.