Captured Ocean Plastics Recycled by Hydrothermal Liquefaction

Researchers successfully trialed real samples of ocean cleanup plastic in their study of hydrothermal liquefaction. The technique uses supercritical water to break down plastic into oils.

The North Pacific garbage patch is a region of ocean with high concentrations of plastic debris, which accumulates there because of the currents of the North Pacific gyre. The Ocean Cleanup is a nonprofit foundation that has set a goal of cleaning up half of this plastic by 2027.

Debris was sourced from waste collected by The Ocean Cleanup during its operations in the North Pacific in 2019. The debris included hard plastics, nets and ropes. The hard plastics, composed mostly of polyolefins, were selected for analysis. The materials were characterized by FTIR, and placed into a study designed to characterize the oil outputs’ dependency on feed characteristics and the process parameters temperature (420-480°C), dwell time (60-120 minutes), pressure (225-275 bar) and plastic load (30-60%).

After the reactor treatment, samples were analyzed to determine the composition of the solid residue and liquid phase oils. The liquid phase oils were composed of paraffins, aromatics and olefins. Researchers noted that the resulting oil is not an ideal naphtha, and would require further processing to be used as a feedstock for olefin production.

The research team concluded that hydrothermal liquefaction has potential for converting ocean waste plastics into a synthetic crude oil, and that the reaction parameters’ dwell time, temperature and dry feed matter can be modified to maximize oil production and tuned to produce aromatic or aliphatic (olefin and paraffin) rich oils.

These findings have been published in the scientific journal Resources, Conservation and Recycling by Juliano Souza dos Passos and Patrick Biller of Aarhus University; Chantal Lorentz and Dorothée Laurenti of Claude Bernard University Lyon 1; and Sarah-Jeanne Royer and Ioannis Chontzoglou of the Ocean Cleanup.