Pyrolysis of rubber wastes from the mining industry for the production of fuels: pilot scale studies

Abstract

In this work, the pyrolysis of three different rubber wastes used in the mining industry, i.e. milling (based on styrene butadiene rubber, SBR), sieves and conveyor belts (based on natural and butadiene rubber, NR/BR) and offroad waste tires (based on complex mixture of nitrile, butadiene, styrene and natural rubber) was investigated in a pilot plant at 450, 600 and 800°C. Reactions at 450°C showed incomplete pyrolysis whereas at 600 and 800°C the rubber wastes were completely converted into three products:15-25% gas, 34-45% liquid and 42-44% solids. The gas products analyzed by gas chromatography (GC) showed mainly the presence of C₁-C₄ hydrocarbons with LHV (Low Heating Value) values between 8496 and 7325 Kcal kg^-1, similar to liquefied petroleum gas (LPG). The solid products analyzed by elemental analysis of carbon, hydrogen and nitrogen (CHN), atomic emission spectrometry with inductively coupled plasma (ICP-AES) Spectro Ciros CCD for the determination of sulfur, thermogravimetry and differential thermal analysis (TG/DTA), fixed carbon, ash and volatile compounds showed the presence of 72-89% carbon and 2% sulfur. The liquid products analyzed by gas chromatography applied mass spectrometry (GC-MS) indicated the presence of complex mixtures of hydrocarbons containing mainly compounds up to C₂₀. The NR/BR and waste offroad tire samples produced ca. 50% aromatics whereas SBR rubber resulted in the formation of near 87% aromatics. The mixtures of these liquids products (without any purification) with a commercial diesel fuel at 0.5, 1 and 3 vol% did not significantly change the fuel quality parameters defined by the ANP (Agency National Petroleum, Natural Gas and Biofuels).

Keywords:
rubber waste; mining; pyrolysis