Development of two different catalytic cracking processes to convert waste plastics into liquid and gaseous hydrocarbons ´jjjjj ºº

MARÍA S. RENZINI; LAURA C. LERICI; LILIANA B. PIERELLA

Rosario, Argentina

Workshop; 1st Argentinean Workshop in Environmental Science at Rosario; 2009

Thermo-catalytic degradation of low density polyethylene (LDPE) over microporous zeolite H-ZSM-11 was studied. The catalyst was characterized by XRD (> 98.5% of crystallinity), FTIR in the fingerprint zone (> 97% of crystallinity) and surface area by BET (> 378 m2/g). Pure LDPE and polymer/H-ZSM-11 mixtures were analyzed by thermal analysis TG-DSC. With the aim to evaluate the stability of the catalyst and to determine the coke content over the zeolite and its possible location, two different procedures (A and B) were used. The catalytic tests were carried out employing a fixed-bed quartz tubular reactor, operating at atmospheric pressure, from room temperature to 500°C, with a nitrogen flow of 25 ml/min and polymer to catalyst ratio of 2 in both cases. Procedure A: The reaction temperature (500°C) was maintained for 280 min and the polymer was feed to the reactor each 20 min to keep constant LDPE/H-ZSM-11 ratio. Polymer conversion was 100 wt.%. The final products distribution was: 18.36 wt.% of liquid hydrocarbons, 79.40 wt.% of gaseous hydrocarbons and 2.23 wt.% of solid residues (unconverted LDPE + Coke). The results showed a slight increase in liquid products to the detriment of the gaseous products with the reaction time. A high selectivity towards aromatic hydrocarbons (benzene, toluene, xylenes and trimetylbenzenes) was observed in the liquid products, while C5 in the gaseous one. Procedure B: Eleven cycles of 20 min each one were performed at 500°C.  After each run, the reactor was cooled down at room temperature and plastic was loaded and mixed with used catalyst, so the overall plastic/catalyst mass ratio was kept constant in regards to that the precedent run. Then, a new cycle was performed following the previous procedure. After the 11 tests, the zeolite held a high activity and stability with a ~ 27 wt.% of liquid hydrocarbons, ~72 wt.% of gaseous hydrocarbons and accumulated coke of 8.71.wt %.