Liquid-phase degradation of HDPE over alkali-treated MFI zeolites with mesopores

The catalytic activities of MFI zeolites treated with NaOH solutions of various concentrations were investigated in the liquid-phase degradation of HDPE. The changes in the crystallinity, pore structure and acidity of MFI zeolites according to the alkali treatment were also examined. The parent MFI zeolite composed of large particles showed very poor activity, but the treatment with moderate NaOH solutions of 0.4-0.7 N enhanced considerably the catalytic activity of MFI zeolite by enlarging its external surface area due to the formation of mesopores. The activity of MFI zeolite was improved by about 20 times treated with 0.5 N NaOH solution. The formation of mesopores also contributed to the enhancement of the yield of liquid products by suppressing further cracking due to the rapid diffusion of products. The treatment with strong NaOH solution, however, lowered the catalytic activity because the treatment caused the loss of both crystalline structure and strong acid sites.