Thermal and catalytic cracking of a LDPE–EVA copolymer mixture

Abstract

Catalytic cracking of a plastic mixture consisting of LDPE and ethylene–vinyl acetate (EVA) copolymer (86/14 w/w) over mesoporous Al-SBA-15 and Al-MCM-41 materials as well as nanocrystalline HZSM-5 zeolite (crystal size ∼35 nm) has been carried out in a batch reactor at 400–420 °C. The release of acetic acid formed from the EVA decomposition was observed within the temperature range 350–400 °C. The most active catalyst was nanometer size HZSM-5 that led to complete conversion of the plastic mixture at 420 °C whereas both Al-MCM-41 and Al-SBA-15 were meaningfully less active. In addition, the polymer mixture was more difficult to be cracked both thermally and catalytically than pure LDPE. This result has been ascribed to the occurrence of cross-linking reactions leading to a fast deactivation by coke fouling especially over mesoporous catalysts (Al-MCM-41 and Al-SBA-15) because of their open structure. A high selectivity towards C 1–C 5 hydrocarbons (∼75%) was attained over nanometer size HZSM-5, most of them being valuable C 3–C 4 olefins. PIONA analyses of the C 6–C 12 hydrocarbon fraction obtained at 420 °C indicates that olefins were the main components whereas a significant amount of aromatics was also obtained both thermally and catalytically (>15%).