Process Characteristics and Mechanisms for Catalyzed Pyrolysis of Low-Temperature Coal Tar

The influences of two kinds of natural mineral zeolite catalysts and the mass ratios of low-temperature coal tar (CT) to natural mineral zeolite on the yield and distribution of volatile products, such as alkanes, light aromatic hydrocarbons, phenolic compounds, and other products, during catalytic fast pyrolysis of CT were investigated using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). The results indicate that the two catalysts have a high catalytic activity for the formation of long straight-chain alkanes and light aromatics; moreover, the deoxygenation of oxygenated compounds is remarkable. In comparison to the fast pyrolysis (FP) of CT, when the mass ratio of CT to natural mineral zeolites A (NMZ-A) is 1:2, the total yields of long straight-chain alkanes and light aromatics increase by about 32.3 and 143.4%, respectively, while the total yield of phenolic compounds decreases by about 70.4%. In comparison to the FP of CT, when the mass ratio of coal tar to catalyst (MRCTC) decreases from 2:1 to 1:1 to 1:2, the total yields of volatile products (GC/MS-analyzable part) obtained under the catalysis of NMZ-A increase by about 17.7, 25.1, and 34.9%, respectively. These total yields obtained under natural mineral zeolites B (NMZ-B) increase about 10.8, 20.7, and 24.6%, respectively. The number of acid sites increases when MRCTC decreases from 2:1 to 1:1 to 1:2, resulting in that the content of total coke (C-TC) also becoming more and more in each used NMZ-A or NMZ-B, which indicates that the intensity of the reaction increased gradually. When MRCTC is 1:2, the maximum C-TC in used NMZ-A and NMZ-B is 9.45 and 9.03 wt %, respectively.