Catalytic upgrading of gaseous tar from coal pyrolysis over Mo and Ni-modified HZSM-5

The distributions of light aromatic hydrocarbons in the gaseous tar were investigated upon upgrading over Mo and Ni-modified HZSM-5 catalysts during coal pyrolysis. The results show that the yield of light aromatic hydrocarbon from lignite (XM) pyrolysis is increased by 220% after the cracking of gaseous tar over HZSM-5 zeolite, due to the aromatization of olefins or alkanes and the dehydroxylation of phenols. The loading of Mo and Ni on HZSM-5 is able to enhance the formation of light aromatic hydrocarbons; Ni can obviously promote the side chain cracking, whereas Mo is more effective for the formation of aromatic compounds with side chains such as toluene and xylene. Without catalysts, the yield of light aromatic hydrocarbons from coking coal (FX) pyrolysis is about 2.2 and 2.4 times higher than that from XM and bituminous coal (PS) pyrolysis, respectively. By using catalysts, however, the yield of light aromatic hydrocarbons from XM pyrolysis is obviously higher than that from PS pyrolysis and close to that from FX pyrolysis, as XM is provided with abundant oxygen containing functional group and aliphatic structure that can be transformed to light aromatic hydrocarbons over the HZSM-5 catalysts.