Effects of plastic wastes on coal pyrolysis behaviour and the structure of semicokes

Recently, plastic wastes of different structures and origins (agriculture, municipal, electronic, automobile) have been proposed as minor components of coal blends for metallurgical coke manufacture in order to contribute to the protection of the environment and natural resources. Since an adequate development of coal fluidity in high-temperature carbonization is a prerequisite for producing a graphitizable carbon material of high quality, this paper investigates the role of HDPE, PP, PET and a mixture containing these three thermoplastics in the formation of semicokes, an intermediate carbon material in the transformation of coal to coke. These plastic wastes blended with a bituminous coal in amounts of 1, 2 and 5 wt.% cause a decrease in coal fluidity as measured by the Gieseler plastometer, the extent of the reduction being dependent on the amount, the structure and the thermal behaviour of the plastic waste added. Model hydrocarbons have been used to explain the differences in the fluidity of the blends with HDPE and PP. Evidence of the incorporation of HDPE into the carbon matrix of semicokes comes from diffuse reflectance infrared spectroscopy and scanning electron microscopy as well as from the study of the evolution of volatile products in the post-plastic stage of coal by thermogravimetry coupled to mass spectrometry. The non-agglomeration of blends with PET is clearly observed by SEM and optical microscopy, the latter revealing the isotropic nature of the resultant semicoke.