High-quality bio-oil production via catalytic pyrolysis of biocrude oil from hydrothermal liquefaction of microalgae Spirulina

Abstract

Hydrothermal liquefaction (HTL) is an effective method for the conversion of wet microalgae to fuels. However, the biocrude oil from direct HTL is inferior to fossil fuels in quality. Catalytic hydrogenation is normally used to upgrade the biocrude, but the cost-intensive hydrogen with high pressure is needed. In this study, the raw biocrude from HTL of Spirulina was upgraded through catalytic pyrolysis using Fe-HZSM-5 as the catalyst without hydrogen. The effects of temperature and reaction time on the yield and quality of the upgraded bio-oil were explored. The yield of upgraded bio-oil ranged from 75% to 86%. With the addition of the catalyst, the carbon content and higher heating value (HHV) of the upgraded bio-oil were improved obviously. The carbon, hydrogen contents and HHV of the upgraded bio-oil were 78.89%, 10.51% and 40.8MJ/kg at 320 °C for 3 h, respectively. The composition of the upgraded bio-oil changed evidently compared with the raw biocrude, the peak area of the nitrogen-containing compounds was reduced by 50%, while the peak area of the hydrocarbons in the upgraded bio-oil with catalyst was twice of that in the raw biocrude. The catalyst still retained certain activity after 5 cycles. The HHV and nitrogen content of the upgraded bio-oil were 41.52MJ/kg and 0.39%, respectively, when the feedstock was switched to high-lipid salad waste. Results of this study demonstrate that high-quality bio-oil could be produced through coupling catalytic pyrolysis and HTL.