Selective production of valuable hydrocarbons from waste motorbike engine oils via catalytic fast pyrolysis using zeolites

• Highly oxidized, unusable automobile engine oil was fast pyrolyzed in Py-GC/MS.
• Non-catalytic fast pyrolysis resulted in C31-60 alkanes and C3-15 alkenes.
• Catalytic fast pyrolysis was performed using zeolites belonging to ZSM5, Zβ, and ZY.
• Catalytic fast pyrolysis of 1:1 oil:ZYH at 400 °C resulted in 50% of C6-15 alkanes.
• Observed yields of different hydrocarbon groups correlated well with catalyst pore volume.

Aged automobile engine oils contain highly oxidized and hazardous organic compounds, and their disposal adversely affects the environment, underground, and surface waters. Therefore, it is imperative to develop innovative strategies to solve the problem of disposal of waste engine oils. One way is to recover value added chemicals and intermediates from it. This study focuses on recovery of useful hydrocarbons from highly oxidized, waste motorbike engine oils via catalytic fast pyrolysis using zeolites belonging to ZSM-5, Zeolite-β and Zeolite-Y (ZY) families. Pyrolysis experiments were conducted in a micropyrolyzer connected to a gas chromatograph–mass spectrometer. Initially, non-catalytic fast pyrolysis was performed at temperatures from 300 to 800 °C, and it was found that high temperatures led to the formation of C3-10 alkenes, while low temperatures resulted in high yields of heavy fractions like C31-60 alkanes and oxidized aromatics. In order to selectively improve the production of C6-15 alkanes that are valuable as fuel molecules, catalytic fast pyrolysis was performed at 400 °C using 1:1 wt./wt. of oil:zeolites. Hydrogen form of ZY resulted in c.a. 65% of C6-15 linear, branched, and cyclic alkanes, while other catalysts promoted the formation of alkenes. The yields of C6-15 linear and cyclic alkanes increased with micropore area, pore volume, and surface acidity of the zeolites. An increase in catalyst quantity significantly increased the yield of C6-10 alkanes, while reducing the C11-15 alkane yield and promoting the formation of C3-5 alkanes. High temperatures led to a significant drop in the production of linear and branched alkanes, but promoted the formation of alkenes and cyclic hydrocarbons. This work has demonstrated that catalytic fast pyrolysis using zeolites is a potential technique to selectively recover value added hydrocarbons from highly oxidized engine oils.