Gasification of polyethylene over solid catalysts. 3. Gasification over calcium X zeolite in a fixed bed tubular flow reactor.

Abstract

Direct gasification-degradation of polyethylene (PE) over CaX zeolite was studied in a fixed bed flow reactor at 452-526°C and under 14-150g-cat•min/g-PE in order to obtain fundamental data for direct catalytic gasification reaction.At initial stages of the reaction. the degrees of gasification of PE (RgF) at W/F=25.0g-cat. min/g-PE was 0.30 at 452°C and 0.72 at 526°C. The value at 452°C corresponds to that at about 570°C for thermal degradation. The RgF increased remarkably with contact time, but the degree of increase was very small in the range of W/F>50g-cat•min/g-PE. On the other hand, the RgF decreased with process time, and the lowering in the activity level of CaX was the result of coke deposition on the catalyst.The main products were C3, C4 and iso-C4 fractions. The ratio of olefin to paraffin for the C2-C4 fractions decreased with increasing reaction temperature and contact time. The decline in the ratio could be attributable to the frequent occurence of hydrogen transfer reactions.When the catalyst was treated with pyridine, its activity dropped, and the formation of iso-C4 was depressed, whereas the formation of C2-C4 olefins was accelerated remarkably. These results suggest that the gasification-degradation reaction proceeds through the carbonium ion mechanism. The apparent activation energy, 14.0kcal/mol, was determined from the initial rates of gasification. The value is about two-fifths of that of thermal degradation.