Co-hydrothermal Liquefaction of Lignin and Macroalgae: Effect of Process Parameters on Product Distribution

Hydrothermal liquefaction (HTL) is an effective process for bio-oil production. To date, various co-liquefaction studies have been performed using biomasses with significantly different compositions in the presence of various solvents. The present study investigates the co-hydrothermal liquefaction of Prot lignin (PL) and Sargassum tenerrimum macroalgae (ST) in water, ethanol, and water–ethanol solvent mixture in different ratios of feedstocks (1:1, 7:3, and 3:7) at 280 °C for 15-min reaction residence time. The bio-oil and bio-char yields are measured at different operating temperatures, solvent mixture, and biomass blending ratios to understand the compound distribution. Lower bio-oil and higher solid yields were obtained in co-liquefaction experiments as compared to the liquefaction of individual lignin feedstock, whereas the opposite was found with macroalgae feedstock. Individual solvent such as water and ethanol produced bio-oil yield as 5.0 wt% and 13.5 wt% (with 1:1 feedstock), respectively. Maximum bio-oil yield (51.66 wt%) was obtained with 7:3 (lignin: macroalgae feed) under water–ethanol solvent mixture. With an increase in macroalgae feed, the bio-oil yield was reduced by a significant amount (16.1 wt%). Gas chromatography with mass spectrometry (GC–MS) results showed that organic compounds were detected in all bio-oils in the order of phenol derivatives > acids/esters > ketones/aldehydes > nitrogen-containing > aromatics compounds. Furthermore, bio-chars from co-liquefaction have been analyzed using Fourier transform infrared spectroscopy (FTIR) and elemental methods for understanding the carbon and functionality distribution in bio-chars. The present study demonstrated an efficient co-HTL process for the production of functional compounds.