1. Centre of Excellence in Carbon-Based Fuels, School of Chemical and Minerals Engineering, North-West University (NWU), Potchefstroom 2520, South Africa
2. Chemical Engineering Department, Vaal University of Technology, Vanderbjilpark 1911, South Africa
3. School of Physical and Chemical Sciences, North-West University, Potchefstroom Campus, Private Bag X6001, Potchefstroom 2520, South Africa