Role of Hydrogen Transfer during Catalytic Copyrolysis of Lignin and Tetralin over HZSM-5 and HY Zeolite Catalysts

In the present study, catalytic pyrolysis of lignin and tetralin was explored in a tandem micropyrolyzer using HY and HZSM-5 as the catalysts. Tetralin is an effective hydrogen donor at atmospheric pressure and its molecular size is bigger than the static pore size of HZSM-5 but smaller than that of HY zeolite. Therefore, copyrolysis of lignin and tetralin is also useful in understanding the role of hydrogen transfer in the zeolites related to shape selectivity. A strong synergistic effect between lignin and tetralin was found with HY zeolite as catalytic coke decreased from an additive yield of 12.72 C% to an experimental yield of 3.8 C%, whereas the aromatic hydrocarbon yield increased from 48.79 C% to 66.23 C% at catalyst temperature of 600 degrees C. Carbon balance of the measurable pyrolysis products was high because lignin-derived phenols were effectively deoxygenated by HY zeolite in the presence of tetralin. Hydrogen transfer from tetralin to phenols within HY zeolite pores changed the mode of oxygen removal by zeolite to promote hydrodeoxygenation and suppressed decarboxylation or decarbonylation. Bimolecular reactions between tetralin and lignin also produced alkylated aromatics. It was also found that the extent of coke reduction and aromatic increase by copyrolysis linearly correlate with the amount of hydrogen transferred from tetralin to lignin at HY zeolite pores. In comparison, hydrogen transfer at the catalyst surface of HZSM-5 was less effective as nearly no synergistic effect between lignin and tetralin was observed at low catalyst temperatures. Pore enlargement and stable acid sites better promote the synergistic effects between lignin and tetralin.