# Review of Studies on Joint Recovery of Macroalgae and Marine Debris by Hydrothermal Liquefaction
## 3 Prospects for Joint Processing of Macroalgae Biomass and Marine Debris
### Hydrothermal Liquefaction of Polymers and Their Mixtures  
[PERSON] and [PERSON] [42] assessed the prospects of using the HTL process for processing nine types of solid polymers, including polybutylene terephthalate, polycarbonate, polyethylene terephthalate, polyaticate, polymethyl methacrylate, polyoxymethylene, styrene butadiene, polyvinyl acetate, and polyphenylene oxide. The process was carried at the temperature of 400 \({}^{\circ}\)C and pressure of 25 MPa for 15 min and the mass dose of raw materials was 10%. The polymers have shown that they are readily degraded in the HTL process, with the formation of water-soluble organic compounds, biofuels, gaseous products, and a solid residue. Figure 2 shows the average oil and solid matter yield for each polymer [42]. Analysis of the data establishes that the processing of a typical representative of marine debris, polyethylene terephthalate, even under supercritical conditions (400 \({}^{\circ}\)C, 25 MPa) did not lead to the formation of a liquid fraction, almost the entire volume of carbon passed into a solid phase (biochar). Good fuel yield was obtained during processing of polycarbonate, styrene butadiene, and polyphenylene oxide, but the proportion of these polymers in marine debris is negligible. \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Polymers** & **Conditions** & **Fuel Yield Efficiency** & **HHV of the Oil** & **References** \\ \hline Cellulose, starch, soybean protein isolate, lignin, stearic acid, glucose and various polymers: polypropylene, polystyrene, polycarbonate, and polyethylene terephthalate & & 27.9-32.1 MJ /kg for oil from biomolecules blend; (45\%), with joint processing with polystyrene, decrease in the decomposition temperature of polyolefins (up to 300 \({}^{\circ}\)C). & 27.9-32.1 MJ /kg for oil from biomolecules blend; (45\%), with joint processing with polystyrene, decrease in the decomposition temperature of polyolefins (up to 300 \({}^{\circ}\)C). & 27.9-32.1 MJ /kg for oil from biomolecules blend; (45\%), with joint processing with polystyrene blend; (45\%), with joint processing with polystyrene blend; (45\%), with joint processing with polystyrene blend & 27.9-32.1 MJ /kg for oil from biomolecules blend; (45\%), with joint processing with polystyrene blend & 27.9-32.1 MJ /kg for oil from biomolecules blend; (45\%), with joint processing with polystyrene blend; & 28.6-38.5 MJ /kg for oil from biomolecules blend; & 28.6-38.5 MJ /kg for  
[PERSON] et al. [43] studied in detail the effect of temperature and reaction time on the degradation of polyethylene. As a result of the study, it was found that during the process (up to 4 h) at temperatures below 400 \({}^{\circ}\)C, the formation of liquid biofuel did not occur. At a temperature of 425 \({}^{\circ}\)C, the total yield of fuel and paraffins varied from 69% to 87%, reaching a maximum at a process time of 2.5 h. With time increase the yield of the gas phase increased from 1% to 21% at process times of 1 and 4 h, respectively. At 450 \({}^{\circ}\)C, a similar maximum fuel yield was achieved with a process time of 45 min. Another research group obtained the maximum yield (97 wt%) of paraffine and \(\alpha\)-olefin waves mixture during the HTL processing of polyethylene at 425 \({}^{\circ}\)C and a reaction time of 30-40 min, while the solid fraction all experiments was not found [42]. [PERSON] et al. processed polypropylene at a temperature of 425 \({}^{\circ}\)C and achieved a fuel yield of 91 wt% after 2 h, which indicates a faster conversion of PP than from PE. The polypropylene fuel contained more olefins and cycloparaffins (about 90 wt%) and less paraffins (about 10 wt%) [44]. A research group from Xi'an University of Technology processed Tetrapak at different temperatures and found that the bio-oil yield increased from 4.56% to 24.34% when the temperature was raised from 300 \({}^{\circ}\)C to 360 \({}^{\circ}\)C. However, temperatures above 360 \({}^{\circ}\)C had some negative impacts on bio-oil yield.