1. Department of Chemical Engineering, Korea Advanced Institute of Science and Technology, 373-1, Kusung-dong, Yusung-Ku, Taejeon 305-701, Korea, Department of Chemical Engineering and RIIT, Gyeongsang National University, 900, Kajwa-dong, Chinju 660-701, Korea, and Korea Gas Safety Corporation, 332-1, Daeya-dong, Shihung-shi, Kyonggi-do 429-010, Korea