Gas chromatographic study of the volatile products from co-pyrolysis of coal and polyethylene wastes

The aim of this study was to determine the volatile products distribution o f co-processing of coal with two plastic wastes, low-density polyethylene f rom agriculture greenhouses and high-density polyethylene from domestic use s, in order to explain the observed decrease in coal fluidity caused by pol yethylene waste addition. Polymeric materials, although they are not volati le themselves, may be analysed by gas chromatography through the use of pyr olysis experiments. In this way, a series of pyrolysis tests were performed at 400 and 500 degreesC in a Gray-King oven with each of the two plastic w astes, one high-volatile bituminous coal and blends made up of coal and pla stic waste (9:1, w/w, ratio). The pyrolysis temperatures, 400 and 500 degre esC, were selected on the basis of the beginning and the end of the coal pl astic stage. The organic products evolved from the oven were collected, dis solved in pyridine and analysed by capillary gas chromatography using a fla me ionization detector. The analysis of the primary tars indicated that the amount of n-alkanes is always higher than that of n-alkenes and the format ion of the alkenes is favoured by increasing the pyrolysis temperature. How ever, this effect may be influenced by the size of the hydrocarbon. Thus, t he fraction C-17-C-31 showed a higher increase of n-alkenes/n-alkanes ratio than other fractions. On the other hand, the difference between the experi mental and estimated values from tars produced from single components was p ositive for n-alkanes and n-alkenes, indicating that co-pyrolysis of the tw o materials enhanced the chemical reactivity during pyrolysis and produced a higher conversion than that from individual components. (C) 2001 Elsevier Science BN. All rights reserved.