# The Fundamentals of the NP-Gram Method for the Characterisation of Pyrolysis Oils Based on the Estimated Boiling Points of Pyrolysis Products from Polypropylene

## TL;DR

This paper explains the NP-gram method for analyzing pyrolysis oils from polypropylene using boiling points and carbon numbers.

## Contribution

The paper clarifies the fundamentals of the NP-gram method and its application for characterizing pyrolysis oils.

## Key findings

- Estimated boiling points of polypropylene pyrolysis products align well with gas chromatogram positions.
- The NP-gram method distinguishes between actual carbon atoms and the carbon number used in characterization.
- The method shows potential for application to different polymers beyond polypropylene.

## Abstract

The pyrolysis of polymers is a thermal processing method largely used to convert polymeric waste into valuable products such as oils and carbonaceous residues. The NP-gram method (NP standing for normal paraffins) is useful for the global characterisation of pyrolysis oils with complex composition. Here, we present the fundamental of this method, which is based on the concept of “carbon number”, in conjunction with the boiling point and the chromatographic retention time of chemical compounds. Polypropylene was selected as the model polymer due to its simple mechanism of thermal degradation. The boiling points of the main compounds in polypropylene pyrolysis oil were estimated based on the equations of Egloff and Wiener. A good correspondence was obtained for the estimated boiling points and the position of the compounds in the gas chromatogram. A distinction was made between the number of carbon atoms in the molecule and the corresponding carbon number used in characterisation of pyrolysis oils by NP-gram. Correlation with the chromatographic retention index was also discussed. The application of the NP-gram method for different polymers was also presented.