Solar Thermal Depolymerization Process

Plastic pollution has become one of the most pressing environmental issues, as rapidly increasing the production of disposable plastic products overwhelms the world’s ability to deal with them. Conventional thermal depolymerization process still depends on the non-renewable fossil fuels. Therefore, a depolymerization process driven by a renewable energy source (such as solar thermal energy) will become the best solution.

The proposed work will focus on the development of solar thermal depolymerization reaction set-up. The novel concept is proposed to enhance or maintain the overall efficiency of the depolymerization process without using any of fossil energy resources. The primary objective of the work proposed here is to demonstrate the feasibility of solar thermal depolymerization process with a conversion of 60~70%. The set-up includes heliostat, two-stage depolymerization reactors, heat recuperator, and distillation column. The feedstock polymers are firstly ground into small chunks and mixed with a homogeneous catalyst (Y-zeolite or MgCO₃) and water. It is then fed into the first stage depolymerization reactor, and the temperature and pressure are controlled at 375°C and 225bar respectively to create supercritical water. The products of this process include slurry with polymer and catalyst, which is sent to a second-stage reactor which is located inside the heliostat. The solar energy generates heat and the reaction temperature keeps at 460~500°C, breaking down the longer hydrocarbon chains. The product then flows through a heat recuperator and recycle the heat for the first stage reactor. Finally, the shorter hydrocarbons are sorted through distillation, generating oil and ethylene.