Thermal and catalytic pyrolysis of automotive plastic wastes to diesel range fuel

Abstract

This study investigated the pyrolysis of automotive plastic wastes (APW) for the production of diesel-grade oil products using a modified calcium bentonite clay catalyst. The research aimed to optimize the process for maximum oil yield and diesel range organics yield. The APW was characterized by its chemical composition and physical properties and the optimal temperature and catalyst amount were determined for maximum oil yield and diesel range hydrocarbons. The results showed that the APW contained mixed Acrylonitrile Butadiene Styrene (ABS), High/Low Density Polyethylene (H/LDPE), Polypropylene (PP), Polystrene (PS) and fiberglass, with a large quantity of volatiles and ash. The average oil yield was higher in the catalytic process compared to that in the thermal process. Generally, higher temperature above 450 $°C$ produced waxy oil, thus lower temperature favoured more Diesel Range Organics (DRO). Both processes yield similar yields of C₈-C₂₄ DRO, and in both cases, lower temperature favoured high yield of C₈-C₂₄ hydrocarbons. The catalyst significantly increased the yield of oil, but did not significantly increase C₈-C₂₄ DRO yield. The optimal conditions for a maximum oil yield of 78.6 % and DRO yield of 79.5 % was a temperature of 416 $°C$ and 24.3 wt% clay. Thus, the modified calcium bentonite clay can be used to improve oil yield from pyrolysis of APW. The oil produced had properties such as calorific value (49.85 MJ/kg), flash point (113 $°C$ ) and total aromatics 3.55 area%, similar to those of commercial diesel, and comprised mostly of 2,4-Dimethyl-1-heptene (25.37 ± 2.01 %) of thermal and 2, 4 - Dimethyl - 1 - heptane (23.44 ± 2.42) in the catalytic process. The study suggests further research to explore different catalysts, maximization of both DRO and gasoline range organics, recover energy from residues, and conduct techno-economic assessments for plant-scale operations. Additionally, policies on the management of end-of-life vehicles should include provisions for stripping and segregation of plastic components by accredited providers for the purpose of plastics recycling.

Keywords: Automotive plastic waste; Calcium bentonite; Pyrolysis.

Fig. 1

Automotive plastic waste pyrolysis study methodology.

Fig. 2

Thermogravimetric analysis (TGA) mass loss curves at 5 (a), 10 (b), 15 (c), and 20K/min (d).

Fig. 3

FTIR spectra of APW sample (a), and comparison of FTIR spectra of APW sample with other polymer samples.

Fig. 4

DSC curves for the APW samples at 10, 15, and 20 K/min heating rate.

Fig. 5

Yield of condensable liquid/wax, residue, and non-condensable gas from thermal pyrolysis of APW.

Fig. 6

Effect plot of temperature (A), catalyst (B), and the temperature - catalyst interaction (AB).

Fig. 7

Surface plot of oil yield from catalytic pyrolysis.

Fig. 8

Effect of temperature (a) and clay amount (b), and interaction effects (c).

Fig. 9

Box Plot of the oil yield from thermal, and catalytic pyrolysis processes.

Fig. 10

Chromatograph of commercial diesel fuel sample.

Fig. 11

FTIR spectra of oil produced by at 428 °C, 20 % and 372 °C and 20 %.

Fig. 12

Yield of C₆ – C₁₀, C₉ – C₂₀, C₈ – C₂₄, and C₂₅+ and unsaturated, cyclic, aromatic, alcohol, and organic acid compounds from thermal pyrolysis of APW.

Fig. 13

Box Plot of the C8 - C24 DRO yield from thermal, and catalytic pyrolysis processes.