The catalytic degradation of high-density polyethylene to hydrocarbons was studied over different zeolites. The product range was typically between C3 and C15 hydrocarbons. Distinctive patterns of product distribution were found with different zeolitic structures. Over large-pore ultrastable Y, Y, and β zeolites, alkanes were the main products with less alkenes and aromatics and only very small amounts of cycloalkanes and cycloalkenes. Medium-pore mordenite and ZSM-5 gave significantly more olefins. In the medium-pore zeolites secondary bimolecular reactions were sterically hindered, resulting in higher amounts of alkenes as primary products. The hydrocarbons formed with medium-pore zeolites were lighter than those formed with large-pore zeolites. The following order was found regarding the carbon number distribution:  (lighter products) ZSM-5 < mordenite < β < Y < US-Y (heavier products). A similar order was found regarding the bond saturation:  (more alkenes) ZSM-5 < mordenite < β < Y < US-Y (more alkanes). Dependent upon the chosen zeolite, a variety of products was obtained with high values as fuel, confirming catalytic degradation of polymers as a promising method of waste plastic recycling.

High-density polyethylene (HDPE) was pyrolyzed over HZSM-5 catalyst using a specially developed laboratory fluidized-bed reactor operating isothermally at ambient pressure. The influence of reaction conditions including temperature, ratios of HDPE to catalyst feed, and flow rates of fluidizing gas was examined. The sodium form of siliceous ZSM-5, silicalite, containing very few or no catalytically active sites, gave very low conversions of polymer to volatile hydrocarbons compared with HZSM-5 (Si/Al ) 17.5) under the same reaction conditions. Experiments carried out with HZSM-5 gave good yields of volatile hydrocarbons with differing selectivities in the final products dependent on reaction conditions. Catalytic pyrolysis of HDPE performed in the fluidized-bed reactor was shown to produce valuable hydrocarbons in the range of C 3 -C 5 carbon number with a high olefinic content. The production of olefins with potential value as a chemical feedstock is potentially attractive and may offer greater profitability than production of saturated hydrocarbons and aromatics.

The catalytic degradation of high-density polyethylene (hdPE) over ultrastable Y zeolite in a semibatch reactor was studied at different heating rates and reaction temperatures. Catalytic degradation of the polymer occurred at much lower temperatures than pure thermal degradation. When gel permeation chromatography was used to determine the molar mass distribution, it was found that solid state reactions occur only in the presence of a catalyst. These reactions change the polymer structure well before the formation of significant amounts of volatile products. The pattern of formation of gaseous and liquid products was studied and found to follow the temperature increase. After the system reached its final temperature, the reaction rate of formation of volatile products decreased rapidly. The product range was typically between C 3 and C 15 . Isobutane and isopentane were the main gaseous products. The liquid product fraction was alkane-rich, as alkenes rapidly undergo bimolecular hydrogen transfer reactions to give alkanes as secondary products.