(205g) Effects of Solvents and Upgrade on the Hydrothermal Liquefaction Products of Saccharina Latissima

We converted the brown macroalga, Saccharina latissima using hydrothermal liquefaction in three solvent schemes (water-only, water-methanol co-solvent, and methanol-only), and the heterogenous catalyst, HZSM-5. We investigate the effects of these on the yields of product, as well as biocrude composition. We conducted the experiments in a batch reactor at 330^oC (sub-critical water, supercritical methanol) and 1hour residence time. We found the highest biocrude yield (27.8 wt.%) in the catalytic run with methanol-only solvent, but the absence of water in this run led to the removal of the aqueous product phase (WSP). The impact of the zeolite catalyst, HZSM-5 in hydrothermal liquefaction appears to be solvent-dependent. The most significant impact of the zeolite catalyst was seen in the runs with water only, while methanol-containing runs only show marginal improvements in biocrude yield. We identified fatty acids and esters as the prevalent compounds in the analysis of the biocrude (43.9% - 69.1%), and their selectivities increased with methanol volume used as solvent (from co-solvent to only solvent). We also observed the occurrence of aliphatic chain alcohols in runs involving methanol, and these were not significantly present in water-only runs, with alcohol selectivity ranging from 1.0% (20% methanol) to 6.1% (100% methanol). The highest yield of hydrocarbons (0.8 wt.%) was obtained from the catalytic run with HZSM-5 and 20% methanol as co-solvent. We further subjected the obtained biocrude to upgrading in a pyrolyzer, and HZSM-5 catalyst proved most effective at the biocrude-to-catalyst ratio 1:5, producing 4.1 wt.% hydrocarbons yield, primarily composed of aromatics. We compared biocrude pyrolysis to that of raw macroalgae in the presence of HZSM-5 catalyst and found the quantitative yield and combined selectivities for alkenes, aromatics, and cycloalkanes from the direct pyrolysis of the macroalgae to be slightly lower than that of the biocrude, suggesting that pyrolysis of biocrude obtained from hydrothermal liquefaction of macroalgae could be a more efficient process for producing desired hydrocarbons than direct catalytic pyrolysis. These findings are promising to support the utilization of S. latissima as a potential substitute to produce transportation drop-in fuels.