1. Shaanxi Key Laboratory of Low Metamorphic Coal Clean Utilization, School of Chemistry and Chemical Engineering, Yulin University, Yulin 719000, P. R. China
2. National Coal and Salt Chemical Product Quality Supervision and Inspection Center (Yulin), Yulin 719000, P. R. China
3. Department of Chemical Engineering, School of Chemical Engineering and Technology, Xi’an Jiaotong University, Xi’an 710049, P. R. China