Effects of Plasma Modification and Atmosphere on the Catalytic Hydrothermal Liquefaction of Chlorella

The development of third-generation biofuels from microalgae has been extensively researched over the last few years. Hydrothermal liquefaction (HTL) is a promising route for producing bio-oils from wet algae. The major drawback in HTL is the high temperature and high pressure that result in the high capital cost of the process. To make HTL an economical process for bio-oil production, the temperature and pressure should be reduced, which can be achieved by adding alcohol to water for HTL. The efficiency of the HTL process can also be improved by using a suitable heterogeneous catalyst with additional modifications. In this work, we investigated the effect of dielectric barrier discharge (DBD) plasma (argon and hydrogen plasma) modified zeolite Y as catalysts on the yield and quality of bio-oils produced in a hydrogen atmosphere versus air at different reaction times (0 and 15 min) and temperatures (240 and 250 degrees C). The mixture of solvents (50 vol % water and 50 vol % ethanol) was used in HTL to increase the yield and quality of bio-oils. Two sequential extractions were used to extract bio-oils from HTL products using dichloromethane. Different analytical techniques, such as thermal gravimetric analysis, elemental analysis, and gas chromatography-mass spectrometry, were used to understand the physicochemical properties of the bio-oils and for the determination of the higher heating value (HHV). The introduction of DBD plasma to modify zeolite Y improved the bio-oil quality and yield from HTL processes. The H2 plasma modified catalyst enhanced the bio-oil yield at 240 degrees C from 46.83 +/- 1.48% (240-0H2-ZY) to 50.04 +/- 0.88% (240-0-H2-ZY-HP) and from 50.24 +/- 1.96% (250-0-H2-ZY) to 53.01 +/- 0.73% (250-0-H2-ZY-HP) at 250 degrees C. The argon plasma modified catalyst reduced N-containing compounds from 29.42% (240-0-H2-ZY) to 2.94% (240-0-H2-ZYAP) and decreased O-containing compounds from 4.02% (240-0-H2-ZY) to 1.38% (240-0-H2-ZY-AP) at 240 degrees C.