Physicochemical properties and pyrolysis characteristics of mild liquefaction solid product of Hami coal

In order to make rational use of mild liquefaction solid product of Hami coal (MLS), the physicochemical properties of MLS were investigated, and the characteristics and interactive effects of MLS and its extraction fractions during pyrolysis were studied by thermogravimetric analyzer (TGA) in this work. The results show that MLS contains higher content of hexane soluble fraction (HS, 36%) than Shenhua direct liquefaction residue, but has the lower asphaltene (A, 13%) and preasphaltene (PA, 9%). The results of GC-MS show that HS consists of higher content of alkane (41.8%) and the results of infrared spectra indicate that the contents of alkane side chains and substituted functional groups decrease in the order of HS, A, and PA. Whereas, alkane side chains and substituted functional groups do not exist in THFIS, indicating its high aromaticity. The minerals in MLS are mainly CaCO₃ produced by liquefaction process, and inert components of SiO₂, NaCl, Al₂O₃·2SiO₂·2H₂O in raw coal and Fe_1-xS, which is the product of catalyst. The results of TGA show that, compared with Shenhua direct liquefaction residue, the temperatures of initial decomposition and the maximum rate of mass loss of MLS are lower, however, the final mass loss (54%) up to 950 ℃ is higher, which suggest that the pyrolysis activity of MLS is higher. In addition, there are two kinds of interactive effects among the extraction fractions of MLS during pyrolysis, which are related to the amount of HS. When the content of HS is high, it can supply small free radicals and play a driving role for the evolution of volatile during the pyrolysis process. However, when the content of HS is low, large free radicals in MLS extraction fractions will combine with each other, which inhibits the release of volatile.