Effects of low molecular compounds in coal on the catalytic upgrading of gaseous tar

The main purpose of this study was to investigate the effects of low molecular compounds in coal on the formation of benzene, toluene, xylene and naphthalene (BTXN) in the catalytic upgrading of tar from coal pyrolysis by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Low molecular compounds were extracted from mineral-free lignite (Coal DA) and bituminous coal (Coal DB), and then the gaseous tars from the pyrolysis of residual coal (Coal DAR and Coal DBR), extraction solution (AE and BE) and mineral-free coal were subjected to catalytic cracking using USY zeolite as catalyst. The results show that the total amount of BTXN in the extraction solution and residual coal is 27% and 4.8% lower than that in Coal DA and Coal DB during catalytic upgrading of gaseous tars, respectively. The presence of low molecular compounds can result in a significant increase in the BTXN amount after catalytic reforming. The extraction solution in Coal DA are predominantly aliphatic compounds (72.7%) and Oxygen-containing aromatics (21.9%), whereas that in Coal DB is naphthalene series (33.1%), condensed aromatics (29.4%), and aliphatic compounds (23.5%). Phenols and condensed aromatics in low molecular compounds can be cracked into BTXN under the catalysis of USY zeolite. More heavy aromatics are cracked to light arene instead of polycondensation in the presence of aliphatic compounds.