Fast microwave-assisted catalytic co-pyrolysis of microalgae and scum for bio-oil production

•We used a microwave-based system for catalytic co-pyrolysis of microalgae and scum.•Scum proved to be a good hydrogen supplier to increase the overall EHI of feedstock.•Temperature, catalyst to feed ratio, and microalgae to scum ratio were optimized.•The EHI value of feedstock needed to be above 0.7 to achieve the synergistic effect.

In this study, fast microwave-assisted catalytic co-pyrolysis of microalgae and scum on HZSM-5 catalyst for bio-oil production was investigated. The effects of co-pyrolysis temperature, catalyst to feed ratio, and microalgae to scum ratio on bio-oil yield and composition were examined. Experimental results show that temperature had great influence on the co-pyrolysis process. The optimal temperature was 550 °C since the maximum bio-oil yield and highest proportion of aromatic hydrocarbons in the bio-oil were obtained at this temperature. The bio-oil yield decreased when catalyst was used, but the production of aromatic hydrocarbons was significantly promoted when the catalyst to feed ratio increased from 1:1 to 2:1. Co-feeding of scum could improve the bio-oil and aromatics production, while the optimal microalgae to scum ratio was 1:2 from the perspective of bio-oil quality. The synergistic effect between microalgae and scum during the co-pyrolysis process became significant only when the effective hydrogen index (EHI) of feedstock was larger than about 0.7.