Enhancement of the production of light aromatics from poplar wood by combined approach of wet torrefaction pretreatment and catalytic fast pyrolysis using metal modified hierarchical zeolite

Light aromatics are extremely important building blocks in the chemical industry which can be produced from the catalytic fast pyrolysis (CFP) of biomass. In this work, wet torrefaction pretreatment (WTP) was employed to improve the quality of poplar wood (PW) in terms of the synergetic deoxygenation and demineralization. Then, metal-modified hierarchical HZSM-5 was prepared by the combined approach of NaOH desilication pretreatment and metal (Zn, Ga, and Fe) modification. At last, the CFP of torrefied PW was carried out by using the metal-modified hierarchical HZSM-5 as catalyst to produce light aromatics. Results showed that the deoxygenation and demineralization rates gradually increased with the increase of WTP temperature from 180 to 260 ℃, the maximum removal rates of oxygen, K, Mg, Ca, and Na were 47.96%, 90.99%, 86.65%, 66.09%, and 36.29%, respectively. NaOH desilication pretreatment and metal modification on HZSM-5 promoted the formation of light aromatics. The Zn-modified hierarchical HZSM-5 presented the highest yield of light aromatics. The yield of aromatics increased first with the raise of catalyst-to-torrefied PW ratio from 1:1 to 1∶3, then decreased slightly at the highest catalyst-to-torrefied PW ratio of 1∶5. At last, the operation parameter of WTP and CFP was optimized which the maximum yield of light aromatics was 7.83 × 10⁷ p.a./mg at WTP temperature of 220 ℃, catalyst-to-biomass ratio of 3∶1, and CFP temperature of 850 ℃.