1. Department of Basic Science and Engineering, Faculty of Engineering, University of Khartoum, P.O. Box 321, Khartoum, Sudan
2. Department of Chemistry, Faculty of Science, University of Khartoum, P.O. Box 321, Khartoum, Sudan
3. Department of Chemical Engineering, Faculty of Engineering, University of Khartoum, P.O. Box 321, Khartoum, Sudan