Effect of volatile reactions on the yield and quality of tar from pyrolysis of Shenhua bituminous coal

Pyrolysis was an important route for coal conversion and also the fundamental for clean and efficient utilization of coal. As an important product of pyrolysis, coal tar can be used as the raw material for producing premium liquid fuels and high value-added chemicals (benzene-toluene-xylene, naphthalene, phenols, etc.). The products' distribution and quality were significantly affected by the secondary reaction of volatiles. In this work, Shenhua bituminous coal was pyrolyzed with a two-stage reactor at a relatively low temperature, and the released volatiles underwent secondary reactions at various temperatures and residence time. The yields and quality of coal tar were characterized by gas chromatography-mass spectroscopy (GC-MS) and Fourier transformed infrared spectroscopy (FTIR). The results showed that secondary volatile reactions decrease tar yield but increase gas and coke yield. The volatile reaction results in a decrease in the content of aliphatics and phenols, and an increase in the content of arenes and polar compounds. The volatile reaction includes the following reactions: dehydroxylation, deoxygenation, cleavage of long chain aliphatic structures into short ones, and condensation of aromatic clusters, etc. The higher heating rate of pyrolysis reduces the content of aliphatic and polar compounds while increases that of arenes and phenols in the light tar (HS).