Use of polypropylene pyrolysis oil in alternative fuel production

Abstract

In this study, polypropylene (PP) was recycled in a non-stirred batch reactor by slow pyrolysis at low temperature. Virgin PP and waste PP as well as mixed material of equal amounts of virgin PP plus virgin PP pyrolysis oil (ratio 1:1 w/w) were used as raw material. The highest yields of liquid product were obtained at 350°C and 400°C (82.0 and 82.3 w/w%, respectively). The density, viscosity and calorific value of the gasoline and diesel fractions of the obtained pyrolysis oils comply with EN228 and EN590 standards, respectively. The flash point corresponded to the standard only for some of the oils, but the cold filter clogging point, the pour point and especially the oxidation stability were far above the stated reference values of the standards. The pyrolysis oils as products of thermal decomposition were determined by the methods of ¹H and ¹³C and two-dimensional-heteronuclear single quantum coherence nuclear magnetic resonance (2D-HSQC NMR) spectra. Spectral analysis showed that only very little aromatic compounds were present in the oils, but they contained many unsaturated compounds, which is presumably consistent with the measured oxidation stability and limits their use in the production of alternative fuels. The research octane number (RON) calculated from the NMR analyses corresponds to the lower limit of gasoline.

Keywords: Polypropylene; fuel; low temperature; slow pyrolysis.

Figure 1.

PP yields of pyrolysis products at different temperatures (mean ± standard deviation).

Figure 2.

Yields of pyrolysis products at 350°C with different PP feedstocks (mean ± standard deviation).

Figure 3.

¹H NMR spectra of virgin PP (a) and mixture PP (b) pyrolysis oil.

Figure 4.

¹³C NMR spectra of virgin PP (a) and mixed PP (b) pyrolysis oil.

Figure 5.

HSQC spectrum of the PP-pyrolysis oil mixture.

Figure 6.

Yield of distillate fractions (%) from different PP pyrolysis oil feedstock.