Microalgae cultivated in wastewater catalytic hydrothermal liquefaction: Effects of process parameter on products and energy balance

Abstract

Different harvested process can be decreased the costs of microalgae growth, to remove nutrients and improve the carbon cycle. Promising process for the conversion of biomass to fuel or bio-crude oil has been used for the better quality bio-oil. Hydrothermal liquefaction is promising process for the aquatic biomass conversion, as it has been operated in the presence of high moisture in the biomass. Catalytic hydrothermal liquefaction of ozone-air flotation for harvesting microalgae grown in wastewater was investigated for bio-crude production. The effect different reaction parameters in the catalytic HTL on the distribution of bio-crude and hydrocarbons was experimentally evaluated using microalgae grown in wastewater, and harvested by ozone-air flotation and gravity-sedimentation, respectively. Hydrothermal liquefaction was carried out under water solvent at temperature range of 300–350 °C, reaction times (30–120 min) and ZSM-5 and MCM-41 catalyst with different catalysts amount. The bio-crude yields obtained from non catalytic and catalytic bio-oil yield range of 17.3–39.7 wt%. Maximum bio-oil yield (39.7 wt%) was found with ZSM-5 catalytic hydrothermal liquefaction process. Using ZSM-5 catalysts the production of hydrocarbon yield was doubled compared to the non-catalytic and MCM-41 catalytic HTL reaction. After HTL reaction the obtained bio-oil has been utilization was analyzed to understand Net Energy Ratio value and the carbon footprint. It has been found that harvested microalgae catalytic HTL bio-oil significantly decreased greenhouse gas emissions compared to the conventional grow microalgae HTL bio-oil. The deamination and deoxygenation reactions were observed in the tests without catalyst as the temperature increased and improved with ZSM-5 catalyst, resulted decreasing the content of N and O in the bio-oil.