Principal component analysis for kinetic scheme proposal in the thermal pyrolysis of waste HDPE plastics

• Formation rates of polyolefins thermal pyrolysis products are analyzed by PCA.
• PCA allows discriminating grouping by molecular size or bond nature.
• Grouping by molecular sizes is helpful for the proposal of kinetic schemes.
• A scheme based on the formation of waxes as intermediates is proposed.
• These intermediates crack to form gas (C1–C4), liquid (C5–C11), and aromatics.

Principal Component Analysis (PCA) has been used to process the data obtained from the batch pyrolysis of high density polyethylene (HDPE) in order to recognize trends in the formation rates of the large number of components in the product stream. Two different criteria for component grouping have been compared, i.e., according to molecular size, and the nature of CC bond. The choice of the suitable criterion is crucial in order to establish the kinetic scheme, and PCA has proven to be a very helpful tool. The multivariate analysis applied to the lumps obtained according to the molecular size of the components provides very useful information, which allows proposing similar kinetic schemes to those in the literature, but with significant details involved in the definition of the lumps and their distribution between primary and secondary reactions. Furthermore, although there are substantial differences in the formation rate of single-ring aromatics (which are particularly affected by temperature), PCA carried out by grouping the products according to the nature of their CC bond does not provide relevant information concerning differences in the performance of the main products (aliphatic hydrocarbons).