Production of Waxes and Tars from the Continuous Pyrolysis of High Density Polyethylene. Influence of Operation Variables

Abstract

This work studies the influence of temperature on the distribution of liquid and solid products obtained in the pyrolysis of high density polyethylene in a bubbling fluidized bed. The compositions of the products obtained vary widely depending on the operating conditions. The solid fraction (waxes) is markedly olefinic, with high molecular weight alkenes of up to sixty carbon atoms. The liquid fraction is a mixture of olefins and aromatic compounds. The gaseous fraction shows a high heating value of up to 35900 kJ/Nm3 at around 750−780 °C, and can be used for electricity generation. A limiting factor for this use is the presence of tars. The gas yield was analyzed by GC, while waxes and oils were analyzed using MS/GC. The results show that when the temperature increases, cracking of heavier olefinic fractions occurs to yield lighter fractions and higher concentrations of aromatics are obtained in the liquid fraction. The formation of polyaromatic hydrocarbons is also analyzed.