Pyrolysis of high-density polyethylene in a fluidised bed reactor. Influence of the temperature and residence time

Abstract

The pyrolysis of HDPE in a fluidised bed reactor was performed and the influence of the temperature and the residence time on the product distribution and gas composition investigated. Experiments at five different temperatures, 650; 685; 730; 780 and 850°C were carried out and the residence time was varied from 0.64 to 2.6 s. A total number of 20 runs were performed. Polyethylene was fed continuously into the bed and nitrogen was used as carrier gas and as fluidising agent. The results obtained showed the effect of these operating parameters on the production and composition of gases, oil and waxes. The temperature and residence time had a great influence on the pyrolysis product distribution within the range evaluated in this paper. At 640°C the main product obtained was a waxy cream coloured material (wax). The yield of this product varied from 79.7 wt.% at 0.8 s to 68.5wt.% at 1.5 s. At these conditions the gas yield varied between 11.4 wt.% at 1 s and 31.5 wt.% at 1.5 s. The waxes obtained are rich in aliphatic hydrocarbons up to C 30. At high temperatures the product distribution changed drastically. The higher gas yields was obtained at 780°C, 86.4 wt.% of gas and 9.6 wt.% of oil, both at 1.34 s. The main hydrocarbons in this gas were ethylene, methane and propylene, the remaining products being oils with a high aromatic hydrocarbon (benzene and naphthalene) content. The H 2, CH 4, N 2 and C 2H x to C 5H x compounds on the gas produced were analysed by gas chromatography, using a packed column and a molecular sieve.