LAUSR

Abstract The depolymerization reaction of Protobind lignin (PL) was conducted over metal supported on ZSM-5 catalysts in supercritical ethanol without supplying additional hydrogen in order to obtain the high yield of monoaromatic compounds. The reaction was performed by changing the various variables of catalyst such as the types of transition metals (Co, Ni and Cu), the amount of metal loading (5 wt.%, 10 wt.% and 30 wt.% of Cu) and the Si/Al2 ratio of ZSM-5 (30, 50, 80 and 200). Cu/ZSM-5 displayed the highest yield of monoaromatic compounds among the transition metals. When it comes to the Si/Al2 ratio of Cu/ZSM-5, 10 wt.% Cu/ZSM-5 with Si/Al2 of 30 demonstrated the highest yield (98.2 wt.%) of monoaromatic compounds. Moreover, the linear correlation between yield of monoaromatic compound and acid density of Cu/ZSM-5 was identified. Meanwhile, HSQC NMR analysis provided the evidence about the promotion of the depolymerization of Protobind lignin via hydrogenolysis. In addition, some products such as ethylated compounds were confirmed by HSQC NMR spectra resulting from the alkylation between monoaromatic compounds and ethanol. It was also found that Cu metal plays a promotional role in enhancing the lignin depolymerization.