Catalytic pyrolysis of corncob residues and pubescens over pristine and alkalis-treated HZSM-5

Abstract

The catalytic pyrolysis of corncob residues and pubescens was carried out using HZSM-5 and alkalis-treated HZSM-5 as catalysts. HZSM-5 treated with different alkalis (TPAOH and a mixture of NaOH and Na2CO3) to get TPHZSM-5 and DHZSM-5. It was shown that the acid sites of the DHZSM-5 and TPHZSM-5 catalyst decreased compared to pristine HZSM-5. The hierarchical structures combining micro- and meso- porosity was formed in DHZSM-5, which was more conducive to promoting the formation of mono-phenols. However, the pore size of the catalyst decreased and the strength strong acid site increased with TPAOH treatment, which was beneficial for promoting C-O bond cleavage and generating more monocyclic aromatic hydrocarbons (MAHs). Under the same conditions, HZSM-5 was most beneficial for improving the yield of bio-oil (45.9 wt% of corncob residues and 52.0 wt% of pubescens). Analysis of the bio-oil showed that the catalytic pyrolysis of biomass over HZSM-5 achieved the highest PAHs yield (31.45 % from corncob residues and 18.38 % from pubescens), while TPHZSM-5 obtained the highest MAHs yield (5.92 % from corncob residues and 2.03 % from pubescens). However, DHZSM-5 catalyst appeared to have no significant effect on the increase of MAHs and PAHs yield, which may be attributed to its promotion of secondary polymerization of pyrolysis products. Additionally, the catalyst promoted the secondary cracking of pyrolysis vapor and reduced the average molecular weight (Mn) of the bio-oil. DHZSM-5 and TPHZSM-5 catalysts offered significant potential for the valorization of lignin, facilitating the production of value-added mono-phenolic compounds, MAHs, and high-quality fuels.