Public defence in Mechanical Engineering, M.Sc. Shouzhuang Li

A novel and sustainable process to convert PET plastic waste into hydrogen and high-value-added chemicals.

Polyethylene terephthalate (PET) is a common plastic widely used as packaging and textile materials. In European Union countries, only 10% of PET plastic is recycled in a closed loop, and the remaining is discarded in nature. Therefore, a novel solar-assisted sorption-enhanced gasification was proposed to convert PET plastic waste into hydrogen and other valuable chemicals toward a circular economy. This research aims to design and investigate the process's performance. 

The study started with an experiment of PET steam gasification, followed by PET steam gasification with CaO as a catalyst and solar-assisted calcium looping experiments. Response surface methodology was implemented to investigate the combined interaction effects of various operating conditions. Based on the experimental results, the process simulation was performed in Aspen Plus to evaluate the techno-economic assessment of the whole process. 

The results showed that, in PET steam gasification, H2, CO2 and benzene were the leading products in gas and tars, respectively, and the temperature had a remarkable effect on the compositions of the products than other operating conditions. At 700 °C–800 °C, the presence of CaO would significantly enhance H2 yield and reduce tar yield, however, CO2 capture was difficult due to its low partial pressure. Thus, a lower temperature syngas upgrading was included to capture CO2 and further improve the hydrogen yield by water gas shift reaction. Calcination reaction was considered to regenerate the CaO, and concentrated solar heat provides the required heat for calcination and gasification. The temperatures of carbonation and calcination were 650 °C and 800 °C for optimizing the CaO deactivation, solar energy carrying capacity, and heat transfer from calcination to gasification. Based on these results, the process model was built in Aspen Plus, and the techno-economic analysis indicates that the energy and exergy efficiencies were 60%–70% for both day and night modes. The project is economically feasible when the benzene price is more than 1092 €/t, and the CO2 price is higher than 80–120 €/t. 

This research provides a novel method for PET plastic waste upcycling, sustainably with zero CO2 emission, and a renewable heat source without burning additional fuels to achieve the zero plastic waste goal in the future.

Doctoral Student: Shouzhuang Li

Opponent: Prof. Cristoph Pfeifer, University of Natural Resrouces and Life Sciences, Vienna

Custos: Prof. Mika Järvinen, Aalto University School of Engineering, Department of Mechanical Engineering

The public defense will be organized in Lecture Hall D, Otakaari 1 and online on Zoom.

The thesis is publicly displayed 10 days prior to the defense in the publication archive Aaltodoc of Aalto University. 

Contact information of doctoral student:

Doctoral theses in the School of Engineering: https://aaltodoc.aalto.fi/handle/123456789/49