Ex-situ catalytic upgrading of vapors from microwave-assisted pyrolysis of bamboo with chemical liquid deposition modified HZSM-5 to enhance aromatics production

Abstract

The ex-situ catalytic upgrading of vapors from the microwave-assisted pyrolysis of bamboo sawdust for aromatics-rich bio-oil production was investigated. It was found that the sequential two-stage reactor, with microwave-assisted fixed bed and independent vertical reforming furnace, could separately optimize both the pyrolysis and catalytic upgrading processes. Besides, for purpose of decreasing coke generation and enhancing aromatics yield during the catalytic fast pyrolysis (CFP) of bamboo, chemical liquid deposition (CLD) was used to modify HZSM-5, which played a significant role in reducing external acid sites and narrowing the pore-opening size of catalyst. Experimental results illustrated that the yield of pyrolyzed oil initially increased, and then decreased, with increasing pyrolysis temperature, achieving its maximum at 550 ℃. In addition, the effect of different CLD modifying conditions (modifier type, deposited amount, and deposition time) on aromatics proportion of the obtained bio-oil was further explored. The consequences presented the TiO2-modified HZSM-5 (deposited amount, 4%; deposition time, 4 h) provided the maximal yield of BTX (benzene, toluene and xylene, 23.58%) compared to the original HZSM-5 (BTX: 16.96%), and the coke generation clearly declined. Simultaneously, the catalytic temperature and catalyst to biomass mass ratio (C/B) in ex-situ upgrading process were also investigated, and it was found that the concentration of BTX was maximized at catalytic temperature of 500 ℃, and C/B = 1.