Effect of coal ranks on light aromatics production during reforming of pyrolysis volatiles over HZSM-5 under Ar and H2-assisted atmospheres

Abstract

Light aromatics (LAs) can be produced from catalytic fast pyrolysis or catalytic hydropyrolysis of coals, which represents one of the most promising alternatives to liquid fossil fuels. In this work, catalytic upgrading of volatiles was performed in a drop bed reactor under an inert atmosphere (Ar) and a reducing atmosphere (H2) over HZSM-5. H2 is consumed during hydropyrolysis process. Coal samples were hydropyrolyzed to produce higher gas yield and lower content of residual char. The presence of H2 can yield more reactive H radicals which acts on C–O bond and C–C bond during pyrolysis conversion of coal. The released behavior of LAs is closely related to coal structure to a large extent. Catalytic pyrolysis of low rank coals produces more BTEXN than that of high rank coals. The H2 accelerated the formation of LAs, especially for low rank coals. A correlation was established between the aromatic-C structure of coals and LAs through the characterization and semi-quantitative analysis of coal structure and tar. The co-effect of HZSM-5 and H2 showed the highest yield of LAs during the low rank coals pyrolysis. The organic-oxygen species and C–H groups in the upgraded tar decreased gradually with the increase of coalification degree. Meanwhile, high aromaticity in coal can cause a poor pyrolysis reactivity, which may have influenced the secondary cracking reaction over HZSM-5.