Evaluation of temperature role in the HDPE steam cracking product distribution with a focus on light olefins production

Abstract

The selective conversion of waste plastics into valuable chemicals, such as light olefins and single ring aromatics, was approached in an original fountain confined conical spouted bed reactor. The aim was the evaluation of the role played by temperature on product distribution and reaction mechanism in the steam cracking of High Density Polyethylene (HDPE). Therefore, continuous runs were conducted between 675 and 800 ºC using a bed made up of inert sand. The reactor operated under vigorous spouting conditions to promote gas-solid contact and, at the same time, reduce the gas residence time. The proposed reactor design performs very well and is highly versatile to operate in a wide temperature range without operational problems. The steam cracking at 675 ºC led to partial conversion with a high oil fraction (44.9 wt%). The maximum yield of light olefins of 54.5 wt% was obtained at 700 ºC, with this yield steadily decreasing as temperature was increased. Cracking temperature had also an influence on the light olefin composition, with a marked decrease in the content of propylene and butenes and an increase in that of ethylene when temperature was raised. In addition, high temperatures also promoted the production of valuable single ring aromatics, i.e., a Benzene, Toluene and Xylenes (BTX) fraction yield of approximately 16 wt% was obtained between 750 and 800 ºC. Therefore, steam cracking in a fountain confined spouted bed reactor is an encouraging strategy to selectively convert plastics into valuable chemicals, such as light olefins and BTX aromatic compounds.