1. Key Laboratory of Coal Processing and Efficient Utilization of Ministry of Education, China University of Mining & Technology, Xuzhou 221116, P. R. China
2. State Key Laboratory of Mesoscience and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, P.O. Box 353, Beijing 100190, P. R. China
3. School of Chemical Engineering, University of Chinese Academy of Sciences, Beijing 100049, P. R. China