Maximum recovery of aromatic compounds from medium temperature pyrolysis of polyethylene-polystyrene mixture waste

Abstract

To enhance the energy recovery level of pyrolysis process, the design and operating parameters should be scientifically determined through the cause and effect relationships of quantity \& chemical composition of the pyrolysis products (oil, gas, and char) to the operating factors. And the purpose of this study is to quantify the effect of various operating factors on the pyrolysis products of polymer wastes for the maximum resource recovery. The experiment is performed using a batch reactor type of conventional retort tube, and the operating factors considered are temperature and heating time at constant heating rate. The polyethylene(PE) and polystyrene(PS) which are the most popular plastic waste in Korea are selected for the experiment. And the mixing effects of PE and PS in input stream are seriously investigated. Results show that the pyrolysis time of PE-PS mixture for the maximum oil production is occurred more rapidly than the case of the single PE waste, which shows the enhancement effect of PS on the longer pyrolysis process of PE. And from the chemical composition analysis of the product, the small aromatic compounds which can be a valuable chemical are produced at maximum in the condition of 50-50\% mixture of PE and PS at $600\,^\circ\!C$, which shows the possibility of process control for the maximum recovery of desirable pyrolysis product. The maximum recoveries of the toluene, xylene, styrene, and1-properly benzene are 8.6, 8.9, 51.0, and 7.4\%$_w$ of feed in the pure PS pyrolysis, and the level of the naphthalene is 1.3\%$_w$ of feed at the 50-50\% PE-PE input ratio. During the analysis of results, it is found that the application of Diels-Alder theory of the coal pyrolysis reaction to the formation mechanism of oily aromatics in the polymer waste pyrolysis is possible, and turns out to be useful.