# Review of Studies on Joint Recovery of Macroalgae and Marine Debris by Hydrothermal Liquefaction
## 2 Experience of Hydrothermal Liquefaction of Macroalgae
### Using Macroalgae for Biorfied Production in a One-Step Process
[28], [PERSON] [62], and other authors (see Table 2), but maximum oil yield was a bit higher: for _Amphiroa fragilissima_ oil yield was 28.9% at 320 \({}^{\circ}\)C (HHV of the fuel--23.25 MJ/kg) and for _Saccharina_ spp. oil yield was 27.7% at 364 \({}^{\circ}\)C. \begin{table}
\begin{tabular}{l l l l} \hline \hline
**Algae Type** & **Conditions** & **Fuel Yield Efficiency** & **Reference** \\ \hline \multicolumn{4}{c}{HTL water as solvent, without catalyst} \\ \hline _Sargassum tenerrinum_ & Temperature 260–300 \({}^{\circ}\)C, 15 min & Maximum 16.3\% & [61] \\ _Amphiroa fragilissima_ & Temperature 280 \({}^{\circ}\)C, pressure 16–24 MPa & Maximum fuel yield 28.9\% & [28] \\ _Saccharina_ spp. & 364 \({}^{\circ}\)C, 40 min & Maximum fuel yield was 27.7\% & [62] \\ \hline \multicolumn{4}{c}{HTL different solvents, with or without catalyst} \\ \hline \multirow{4}{*}{_Gracilaria corticata_} & Temperature 260, 280, 300 \({}^{\circ}\)C, solvent: water, ethanol, methanol, acetone, a mixture of ethanol and water & Maximum yield 16.6\% (with acetone), 5.25 wt\% (water) & [63] \\ \hline \multirow{4}{*}{_Entenormorpha clathrata; mixture_} & Optimal conditions: temperature 300 \({}^{\circ}\)C, 50\% ethanol as a co-solvent, 45 min & Maximum oil yield 71.7\% for the mixture 1:1 algae:husk. For _Entenormpha cl._ maximum & [64] \\  & & yield 26.0\% & Maximum fuel yield was 24.0\% with water, 20\% with N-heptane, 21\% with toluene and 28\% with anisole & [65] \\ \hline \multirow{4}{*}{_Entenormpha clathrata_} & Temperature 250–350 \({}^{\circ}\)C, pressure & Maximum oil yield 46.75\% with a conversion rate of 95.5\% with 300 \({}^{\circ}\)C, 45 min, 75\% ethanol; with HZSM-5 oil yield decreased to 44.5\% & [66] \\  & & & \\ \hline \multirow{4}{*}{_Gracilaria corticata_} & Temperature 260–300 \({}^{\circ}\)C with iron-nickel catalysts at a temperature of 260–300 \({}^{\circ}\)C using water, methyl, and ethyl alcohol as solvents & Maximum fuel yield was 56.2\% when using Ga/NiFe-LDO/AC catalyst at 280 \({}^{\circ}\)C & [67] \\ \cline{1-1} \cline{2-3}  & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Results of hydrothermal liquefaction of macroalgae. The experience of using co-solvents that provide on average a three-fold increase in biofuel yield is of interest. [PERSON] et al. processed red algae _Gracilaria corticata_ at 260 \({}^{\circ}\)C, 280 \({}^{\circ}\)C, and 300 \({}^{\circ}\)C using water, ethanol, methanol, acetone, and a mixture of ethanol and water as solvents and obtained maximum yield (16.16 wt%) of bio-oil in the experiment with acetone at 300 \({}^{\circ}\)C; when using water at the same temperatures, the yield was 5.25 wt% [63]. Assessing influence of alcohol co-solvent and catalysis with HZSM-5 on HTL of _Enteromorpha clathrata_, [PERSON] et al. [64] showed that presence of HZSM-5 slightly reduced the oil yield, however it enhanced the quality of oil by forming ester compounds. This effect of ethanol is associated with its lower dielectric constant and, as a consequence, a higher ability to degrade macromolecules. In addition, the likelihood of its repolymerization increases. The addition of ethanol significantly affected the fuel yield, providing an increase in yield from 17% to 46.75% (+175%) with the addition of ethanol 75% by weight. However, the authors recommend using an ethanol concentration of 50%, since this gives an almost identical effect to increase the fuel yield, while the load on the reactor is significantly reduced (the pressure is 70% lower) and the operating costs are reduced. The average increase in the yield of biofuel when using alcohols as co-solvents is 175-700%, while the effective dose of alcohol is 50-75% [63; 64; 65]. Poor results were achieved by the group of scientists using 10% N-heptane, 10% toluene, and 10% anisole as co-solvents; fuel yield decreased in comparison with water use from 24.0% to 20-21%. One of the promising options for hydrothermal liquefaction process modernization is the use of catalysis.