1. Egyptian Petroleum Research Institute (EPRI) , PO Box 11727 , Nasr City, Cairo , Egypt , Tel.: +201006137150; Fax: +202 22747433
2. Department of Chemistry, Faculty of Science , El-Mansoura University , El-Mansoura , Egypt
3. Egyptian Petroleum Research Institute (EPRI) , PO Box 11727 , Nasr City, Cairo , Egypt