COMPARATIVE STUDIES OF THE EFFECT OF CALCIUM OXIDE (CaO) AND ZEOLITE ZSM-5 CATALYST ON WASTE PLASTIC PYROLYSIS

Abstract

ABSTRACT Increase in waste plastic disposal continues to pollute the environment and fuel oil production from waste plastic using pyrolysis have been suggested as a better option for mitigating these wastes. It was in view of this that the study compares the effect of CaO and ZSM-5 zeolite catalyst on waste plastic pyrolysis through the realization of objectives such as; characterization of CaO and ZSM-5 zeolite catalyst using XRF and XRD, catalytic pyrolysis of waste plastic using CaO and ZSM-5 zeolite catalyst, optimization of the parameters of pyrolysis using CaO and ZSM-5 zeolite catalyst, characterization of the pyrolysis oil product using GCMS and FTIR analysis as well as analysis of the properties of the catalyzed plastic pyrolysis oil. The XRD characterization was carried out and it shows that the crystalline structure of the CaO catalyst contains mainly CaO and small quantity of Ca(OH)2at 2θ angle of 32.340°, 37.487°, 54.005°, 64.483° and 67.503° diffraction peak forportlandite (CaO) and 2θ angle of 28.881°, 34.417°and 64.203° for Ca(OH)2 phase in the CaO catalyst while 98.848 wt.% CaO and <1% of other oxide were identified from XRF analysis, while ZSM-5 zeolite catalyst contains mainly silicate crystals with presence of a highly crystalline ZSM-5zeolitic structure and welldefined diffraction peaks at 2θ angle of 8.101°, 8.968°, 23.254°, 24.094°, 29.477°, 30.108°, 45.260° and 45.654°, of a high structural orderthat are indication of those of ZSM-5 zeolite, and a silica to alumina ratio of 50.03 from the XRF analysis were observed. The pyrolysis oil produced shows that zeolite catalyst gives much higher yield with better quality at lower temperature compared to CaO catalyst. The optimum temperature, heating rate and catalyst type observed for maximum plastic pyrolysis oil yield (58.385%) were 597 oC temperature, 29.909 oC/min and ZSM-5 zeolite catalyst type respectively while the optimum temperature and heating rate for CaO catalyst are 600 oC and 30 oC/min respectively for a maximum oil yield of 54.868% with temperature, heating rate and catalyst type as well as interaction between this parameters having predominant effect on the amount of liquid product yield. Furthermore, both the FTIR and GCMS analysis affirms that the zeolite catalyzed plastic pyrolysis oil comprises of better hydrocarbon mixture range of alkane, alkenes, cycloalkanes, aromatics and very minute organic acid compounds compared to CaO catalysed plastic pyrolysis oil. Additionally, the fuel properties of the zeolite catalyzed plastic pyrolysis oil compared favorably with diesel fuel oil, while CaO required upgrade to meet recommended diesel fuel standard, hence ZSM-5 zeolite catalyzed plastic pyrolysis oil show better fuel performance than CaO catalyzed plastic pyrolysis oil. Therefore, ZSM-5 zeolite catalyzed pyrolysis oil may be considered as a valuable component for use with automotive diesel fuels and may be directly used as fuels for industrial boilers, furnaces and power plants, as it shows better fuel quality than CaO catalyzed plastic pyrolysis oil.