Production optimization of refined bio-oil through plasma coupling catalysis and composite zeolite effect of Al-SBA-15/HZSM-5

Waste biomass was initially subjected to catalytic pyrolysis for aromatic bio-oil using HZSM-5 coupled with plasma discharge, and response surface methodology based on Box-Behnken design was employed to study the effects of process factors on bio-oil yield. Then, the mesoporous Al-SBA-15 was integrated at optimal conditions to investigate the effect of composite zeolites on bio-oil composition and catalyst stability. Results indicated that process factors on bio-oil yield and their interactions were significant. The maximum bio-oil yield of 41.80 % was obtained at the discharge current of 186 mA, catalytic height of 18 mm, and catalyst diameter of 2.5 mm. The selectivity of MAHs when using HZSM-5 alone reached 71.56 %, where the plasma discharge activation and the plasma sheath mass-transfer played an important role in synergy. When the ratio of Al-SBA-15 to HZSM-5 layers was 1:3, the highest MAHs selectivity of 79.45 % was acquired with a lower bio-oil yield of 35.33 %; herein, Al-SBA-15 provided suitable macromolecular cracking performance. 1H NMR clearly revealed the rich aliphatic sidechains characteristic of aromatic hydrocarbons from the perspective of hydrogen bonding structure. Used HZSM-5 contained thermal and catalytic cokes with higher decomposition temperatures (541-649℃ and 676-702℃) due to plasma discharge. Increased Al-SBA-15 ratio reduced the coke content from 1.19 % to 0.11 % on used HZSM-5, and thermal coke decreased more obviously from 0.78 % to 0.05 %; besides, the coke on used Al-SBA-15 also decreased from 6.66 % to 2.80 % and tended to be surface thermal coke (from 3.65 % to 2.80 %). In sum, the refined bio-oil produced at Al-SBA-15/HZSM-5 ratio of 1:3 was more suitable to be used as the fuel additive, and the composite zeolite had elevated stability.