Value-addition of water hyacinth and para grass through pyrolysis and hydrothermal liquefaction

Hydrothermal liquefaction (HTL) and pyrolysis (Py) of Loktak lake biomass mixture of water hyacinth (WH) and para grass (PG) were carried out at 260–300 °C and 300–500 °C to compare the products yield and chemical characteristics of the products. In case of HTL, the maximum bio-oil yield was obtained 13.34 wt.% at 280 °C while for Py, the maximum bio-oil yield was observed 38.8 wt.% at 350 °C. The obtained bio-oils and bio-chars were analyzed using GC–MS, FT-IR, NMR, TGA, TOC, and SEM. GC–MS analysis of the bio-oils were showed that the HTL bio-oil majorly contains of nitrogen containing compounds whereas the Py bio-oil contains majority of phenolic compounds. Other compounds like ketones, alcohols, acids were also observed in bio-oil. Higher intensity broad band at 3300–3500 cm−1 was observed in the Py bio-oil compared to HTL bio-oil. TGA and proximate analysis of bio-char revealed the higher devolatilization occured during the HTL compared to Py process. The surface morphology of the HTL bio-char was found to be rough and fragmented as compared to the pyrolysis bio-char, clearly showing the biomass macromolecules breakdown differently in HTL and Py process. Keywords: Hydrothermal liquefaction, Pyrolysis, Aquatic biomass, Bio-oil, Functional compounds, Bio-char