Liquid-phase degradation of polyethylene (PE) over MFI zeolites with mesopores: Effects of the structure of PE and the characteristics of mesopores

Four kinds of MFI-meso zeolites with both micro- and mesopores were prepared, characterized, and their catalytic activities were evaluated in the liquid-phase degradation of high-density, low-density, and linear low-density polyethylene (HDPE, LDPE, and LLDPE) in order to discuss their catalytic performance in relation to their porous characteristics and acidity. MFI-syn that was synthesized from partially dissolved MFI zeolite and MFI-sda that was prepared by using a special structure directing agent exhibited highly ordered mesopores with strong acidity and achieved high conversions, about 95%, even with small catalyst loadings (HDPE/catalyst = 20 g/0.05 g) at 380 °C. However, MFI-oxy prepared from an oxyacid-added mixture exhibited a poor catalytic activity because of its low acidity and small pore volume. MFI-alk prepared by an alkali treatment exhibited irregular mesopores and medium conversions. MFI-meso zeolites were especially suitable for the degradation of HDPE and LLDPE, which required a high external surface for the initial degradation of polyethylene and a rapid mass transfer, resulting in a higher catalytic activity. The enhancement of catalytic activity in the degradation of LDPE by the introduction of mesopores was relatively small because of its rapid initial degradation.