Hydrothermal liquefaction of Undaria pinnatifida residues to organic acids with recyclable trimethylamine

•Trimethylamine had positive effect on hydrothermal liquefaction.•The temperature of hydrothermal liquefaction does not exceed 260 °C.•Cellulose cleaved into organic acids by peeling reaction in low temperature.•The hydrothermal route of glycolic acid was presented.•The highest recovery rate of TMA was 98.89%.

This study investigated the effect of trimethylamine (TMA) on the hydrothermal liquefaction (HTL) process and the recycle of TMA. The results suggest that the peeling reaction occurred on the surface and the cleavage of cellulose leading to water-soluble substances and bio-oil. The highest content of organic acids was found in the water-soluble phase. Model compounds, different glucides with TMA were used to investigate the mechanism of the HTL. Results suggest that the OH− appeared to selectively interact with C-O-C bonds, and thus causing the key linkages of cellulose to become much easier to be cleaved under mild conditions. In addition, the conditions for TMA recovery were optimized and the highest TMA recovery rate reached 98.89%. The recovered TMA had the same properties as the original compound, and it was perfectly re-usable in the conversion process of HTL.

Graphical abstractThe ends of cellulose conduct peeling reaction cleavage into water-soluble substances in the process of hydrothermal liquefaction (HTL) with trimethylamine (TMA).Download high-res image (193KB)Download full-size image