Study on the mechanism of acid modified H-Beta zeolite acidic sites on the catalytic pyrolysis of Kraft lignin

In this study, Sn modified molecular sieves with Lewis (L) acid center and Al modified molecular sieves with Brönsted (B) acid center were prepared by post-synthesis method. They were applied to the catalytic pyrolysis of Kraft lignin for the preparation of bio-oil. The acid properties of acid modified zeolites were systematically investigated by XRD, SEM, EDS and Py-FT-IR, and the bio-oil is analyzed by heteronuclear single quantum coherent nuclear magnetic resonance (HSQC-NMR). By separating L acid and B acid from zeolite molecular sieves, the conformational relationships between these two acids on the oxygen-containing functional groups in Kraft lignin bio-oil are investigated separately. The results show that acid modified molecular sieves’ L acid and B acid can effectively improve the cleavage of aromatic C-O bonds including methoxy and ether bonds. The L acid of Sn modified molecular sieve tends to break the O-C4 bond and the natural methoxy bond, while the B acid of Al modified molecular sieve generates aliphatic hydrocarbon intermediates and phenolic compounds by breaking the Cβ-O bond and rearranging the methoxy bond. By chemical characterization of the acid modified molecular sieves and the bio-oil, the conformational relationship between the L acid and B acid of zeolite molecular sieves on the deoxygenation efficiency of Kraft lignin pyrolysis bio-oil is established.