Development of effective heterogeneous catalytic process for chemical deconstruction technology of polyethylene

Abstract

Chemical recycling which enables transformation of various types of plastic into valuable chemical products has attracted great attention as a key technology to increasing circularity of polyethylene (PE) waste—largest proportions of global annual plastics waste stream—due to their economic and environmental benefits. The aim of the research performed in this thesis is to develop chemical processes that can effectively activate polymer’s highly stable C-C bonds and convert them into valuable products. ☐ In the first half of this work (Chapter 3-4), non-catalytic thermal cracking and catalytic cracking of low-density PE (LDPE) were investigated using an in-house-built semi-batch reactor. The thermal cracking conducted at different reaction conditions (reaction temperature and nitrogen flow rate) reproduced the results reported in the literature, thereby validating the operation of the semi-batch reactor. For the catalytic cracking, three zeolite samples having different acid strength, acid site density, topology, and morphology were used to investigate the effects of these differences on the catalytic results. ☐ In the next half of this work (Chapter 5-6), a batch reaction system was developed to effectively proceed alkane metathesis reaction in which supported tungsten oxide played an important role as an effective olefin metathesis catalyst. The developed alkane metathesis reaction conducted at 300 °C showed high efficiency gain with respect to reaction time, reduction in molecular weight of solid wax product, and required short-alkane mass per unit mass of PE compared to other reports which employed rhenium oxide metathesis catalyst at ~200°C. A following parametric study conducted with the model reactions designed in studies above revealed that types of zeolite-A and nitrogen pressure could have an impact on the catalytic results; however, further investigation is required to draw clear conclusions.