Co-processing of single plastic waste streams in low temperature carbonisation

To investigate the yields of specific compounds and compound classes that c an be achieved by co-processing single-stream plastic waste in carbonisatio n, a series of Gray-King tests have been conducted on blends of Gascoigne W ood (UK high volatile bituminous coal) and both low density polyethene (500 and 600 degrees C) and polystyrene (600 degrees C). For both polymers the tar yields were found to increase linearly as a function of the amount of p olymer used in the coal blend, with the actual and predicted tar yields bei ng identical within experimental error, indicating that no synergism exists between the coal and the polymers under the conditions used. The higher ta r yields obtained with increasing polyethene content are accounted for by t he increase in the concentration of aliphatics in the tars. Although little variation was evident in the distribution of n-alkanes obtained with incre asing polyethene content, average n-alkane/n-alkene ratios for low levels o f polymer addition were considerably higher than predicted, indicating that dehydrogenation of the alkanes may be taking place, with hydrogen transfer to the coal. Furthermore, the presence of coal was found to have a signifi cant effect on the major products derived from polystyrene. Ethylbenzene, a s opposed to styrene monomer, was the major product from all coal/polystyre ne blends studied, indicating that in the case of coal/polystyrene blends, hydrogen is transferred from the coal to the polymer. A clear advantage of using polyethene and other alkane polymers in low temperature carbonisation processes would be the considerable reductions achieved in the viscosities of the resultant tars which eases handling problems. Further, it was obser ved in tests that there was no reduction in the quality of the coke (in ter ms of Gray-King type) until 10 wt% polyethene and 2-3 wt% polystyrene had b een added to the coal blend. (C) 1999 Elsevier Science Ltd. All rights rese rved.