Fast co-pyrolysis of lignin with spent bleaching clay into monocyclic aromatic hydrocarbons over a novel low-cost composite catalyst

Abstract

Improving the anti-coking performance of catalyst during lignin-catalyzed pyrolysis without affecting the selectivity of the monocyclic aromatic hydrocarbons (MAHs) is a challenge. In this paper, a low-cost composite catalyst (CSHZ) was prepared using calcined spent bleaching clay (CSBC) as a binder for HZSM-5 to resolve the issue. In order to evaluate the performance of the composite catalyst, an ex-situ fast catalytic co-pyrolysis experiment was performed in a fixed-bed reaction system with lignin and spent bleaching clay (SBC) as raw materials. The impacts of the temperature, CSBC-to-HZSM-5 ratios, raw material-to-catalyst ratios, and cycle-regeneration times on MAHs distribution, are then studied. The selectivity of CSHZ11 (CSBS-to-HZSM-5 ratio of 1:1) for MAHs in bio-oil reached 78.02 % at 550 ℃ and the raw material-to-catalyst ratio of 1:1, which exceeded those of HZSM-5 alone by 19.12 %. After 3 reaction-regeneration cycles, the catalytic activity of CSHZ11 for MAHs was 71.11 % of fresh catalyst. The characterization (TEM, Py-IR, TGA, etc.) of the catalysts (fresh and discarded) revealed that the addition of CSBC regulated the acidity and pore channels of HZSM-5 and inhibited the formation of catalyst graphite-like coke. This study demonstrates the feasibility of using binder modification to improve the anti-coking performance of HZSM-5. It also serves as a reference for the integrated utilization of SBC and lignin.