Abstract
To obtain basic knowledge on supercritical water chemical recycling of polyethylene, engineering parameters such as reaction temperature, reaction time and reaction pressure were studied to determine how they affect the conversion of polyethylene into oil in a supercritical state. Targeting on this, the study also focussed on discriminating the recovered oil (non-volatile) from the cracked oil (volatile and non-volatile) and the reaction mechanisms. The base conditions were a reaction temperature of 425 °C, reaction time of 120 min, water fill rate of 30 % and a water/PE ratio of 5 : 1. At reaction temperatures of 415 °C and 425 °C, the non-volatile oil rate was about 90.2 wt %. Above 425 °C the rate lowered and the rate of volatile components increased. At up to 425 °C, the major components were l-alkenes and n-alkanes, and, at higher temperatures, the l-alkenes decreased. Above 435 °C, aromatic hydrocarbons were produced. With a longer reaction time of 180 min, the recovered oil rate decreased, resulting in a non-volatile oil rate of 77.7 wt % and volatile oil rate of 8.1 wt %. With an increase in the water fill rate, the non-volatile oil rate rose and was 90.2 wt % at a rate of 30 %. As the water fill rate was increased, the products in the aqueous phase after the reaction increased, with 2-propanol, 2-butanol and 2-propanone as the major components. Also, as the rate increased, the compositions of the recovered oil and gas resulted in a decrease in l-alkenes with n-alkanes as the major component following the increase in hydrogen production. This implies that the increase in the water fill rate, as a reaction mechanism, strengthens the ionic character of water. There is a consequent increase in water-soluble substances such as 2-propanol, which when further oxidized to 2-propanone, liberates hydrogen, and this hydrogen participates in the cracking of hydrocarbons.
