Role of temperatures and solvents on hydrothermal liquefaction of Azolla filiculoides

Abstract

The effects of temperatures (260–300 °C), reaction times (15–60 min), and various solvents including water (H2O), methanol (CH3OH), and ethanol (C2H5OH) were studied on hydrothermal liquefaction (HTL) of Azolla filiculoides. The products distribution in terms of bio-oil and bio-residue and its characterization were investigated. It was observed that the bio-oil yield significantly increased to 21.5–28.8 wt% under CH3OH and C2H5OH solvents as compared to H2O solvent (11–21.3 wt%). Maximum bio-oil was obtained with C2H5OH solvent (28.8 wt%), CH3OH solvent (28.7 wt%) and H2O solvent (21.5 wt%) at a temperature of 280, 260 and 280 °C for 60, 15 and 15 min reaction times, respectively. Gas Chromatography-Mass Spectrometry (GC-MS), Fourier Transform-Infrared Spectroscopy (FT-IR) and Nuclear Magnetic Resonance (1H NMR) analysis of bio-oils indicated that Azolla filiculoides was converted to various valuable compounds including aromatics, nitrogenated and oxygenated compounds. Total organic carbon (TOC) of aqueous phase was observed to be highest at 31,000 mg/L liquefaction with water solvent, but when alcoholic solvent was used it decreased to 23,000–21,000 mg/L. However, opposite trend was observed in the case of total nitrogen (TN) concentration. The bio-residues characterization showed that the different solvents had different effects on biomass macromolecule decomposition into products.