Thermal decomposition of individual and mixed plastics in the presence of CaO or Ca(OH)2

Abstract

Individual and mixed plastics consisting of polyethylene (PE), polypropylene (PP), polystyrene (PS), and poly(ethylene terephthalate) (PET) were decomposed at 600°C in the presence and absence of either calcium oxide (CaO) or calcium hydroxide (Ca(OH)2) under a steam atmosphere. In the presence of CaO, steam cracking was enhanced, increasing gas and liquid yields and decreasing the wax content derived from PE and PP. The production of sublimating substances from PET was also reduced. However, the presence of CaO and steam had a negative influence on PS degradation, reducing the oil yield. In addition, synergistic effects were observed in plastic mixtures. PET enhanced gasification, PS and PET reduced wax production from PE and PP, and mixing all four plastics enhanced oil production in the presence of CaO and steam. Both CaO and Ca(OH)2 enhanced the total gas and oil yield of mixed plastics, achieving a maximum oil yield of 52.2wt% in the presence of steam. Furthermore, solids were almost completely decomposed at 700°C, with only 0.2wt% of residue remaining.