1. Centre of Excellence in Carbon-based Fuels, School of Chemical and Minerals Engineering, North-West University, Potchefstroom 2520, South Africa
2. Centre of Excellence in Carbon-based Fuels, School of Physical and Chemical Sciences, North-West University, Potchefstroom 2520, South Africa
3. Sustainability Division, Research, Testing and Development, Eskom, Brackenfell 7560, South Africa