1. Department of Chemistry and Chemical Engineering Taiyuan Institute of Technology Taiyuan 030008 P. R. China
2. State Key Laboratory of Coal Conversion Institute of Coal Chemistry Chinese Academy of Sciences Taiyuan 030001 P. R. China
3. School of Chemical Engineering and Technology North University of China Taiyuan 030051 P. R. China
4. Taiyuan Institute of Mine Design and Research Taiyuan 030012 P. R. China