Solvothermal Liquefaction of Sargassum: Optimization via Response Surface Methodology

Abstract

Invasive Sargassum fluitans and Sargassum natans accumulate along the coasts of Martinique, causing ecological, health, and economic challenges. Efficient valorization of this biomass is therefore required. This study investigates the potential of solvothermal liquefaction for energy recovery from these Sargassum species through bio-oil production. Experiments were conducted in a batch autoclave reactor using a 50:50 (v/v) water-ethanol co-solvent system under autogenous pressure (43–160 bar at reaction temperature). A Central Composite Design was applied to evaluate the effects of reaction time (15–45 min), reaction temperature (260–300 °C), and solvent-to-biomass ratio (4:1–9:1) on product yields and to determine the optimal operating conditions for maximizing bio-oil yield. The results showed that the solvent-to-biomass ratio was the most influential parameter, followed by reaction temperature, while reaction time had a negligible effect. The experimental data were in good agreement with model predictions (R² = 0.8738), confirming the reliability of the model. A maximum bio-oil yield of 44.62 wt% was achieved at 295 °C, 19 min, and a solvent-to-biomass ratio of 9:1. The higher heating value of the resulting bio-oil (6.55 MJ/kg) was lower than that of the raw biomass (9.33 MJ/kg), likely due to the high ash and oxygen contents. GC-MS and FTIR analyses revealed that the bio-oil mainly consisted of esters, alcohols, hydrocarbons, and ketones. In addition, the distribution of inorganic elements and the physicochemical properties of both bio-oil and solid residues were characterized, providing insights into their potential applications. These findings provide a basis for further development of integrated valorization strategies for Sargassum and its solvothermal liquefaction-derived products.

Graphical Abstract