Oxidative cracking of octadecane, as a model compound of HDPE, into useful chemicals and fuel

Abstract

Plastics are polymers that have dominated the chemical industry for over seven decades, which has led to environmental problems due to their short lifetimes and slow decomposition rates. This study explores an alternative method for utilizing plastics whereby they are transformed into smaller useful molecules, either to form fuel (gasoline, diesel) or chemical building blocks (olefins) through cracking.

This study explores the oxidative cracking of HDPE as an alternative process to thermal cracking. At first, we investigated the role of oxygen in oxidative cracking of octadecane, as a model compound to HDPE, and compared results to that of the thermal cracking process. It was found that oxygen boosts the radical chemistry by increasing the concentration of radical propagation steps (OH.). At temperatures as low as 600°C, oxygen concentration as low as 10% showed high octadecane conversion (68 wt. %) and good area % of light olefins (43.57%). Moreover, presence of oxygen enhanced oil production. Finally, to prove concept, we performed preliminary experiments on domestic HDPE shredded bottles. Results showed that the introduction of low concentration of oxygen significantly enhanced the light olefins production.

In an attempt to develop an active and selective catalyst for the oxidative cracking of HDPE, we explored the performance of Li/MgO catalyst for the oxidative cracking of octadecane and compared results to that obtained with the H-Beta zeolite. Li/MgO showed very low activity compared to H-Beta mainly due to its low surface area and low concentration of active sites. Basic-acidic mesoporeous catalyst systems could be potential catalyst systems for future investigation.