1. Department of Chemical Engineering, Hankyong National University, Anseong 456-749, Korea
2. Samsung Total, Dokgod-ri 411-1, Daesan-up, Seosan-si, Chungnam 356-711, Korea
3. Division of Chemical Engineering, University of Queensland, Brisbane, Queensland 4072, Australia
4. School of Chemical and Biological Engineering, Seoul National University, Seoul 151-744, Korea