| Summary: | The catalytic cracking of linear low density polyethylene (lldPE), polypropylene (PP) and plastic waste were investigated using commercial zeolites (ZSM-5, zeolite β, Mordenite, and USY), USY modified by ion-exchange, mixed catalyst (ZSM-5/ zeolite β, ZSM-5/USY), and nanocrystaline-ZSM-5. USY was modified by ion-exchange with ammonium salt at two different temperatures (298K and 353K) and for various reaction times. The cracking of PP and lldPE was performed using mixed catalysts and in addition a detailed study was carried out employing statistical design of response surface methodology to obtain the optimum reaction condition to produce maximum products. Nano crystalline ZSM-5 catalysts were prepared with/without the presence of alcohol (ethanol and isopropanol) and sodium and statistical analysis of completely random design was used to determine the effect of these constituents in the reaction mixture on the characteristics of ZSM-5 material and on their catalytic performance. The catalytic studies using commercial zeolites revealed that the zeolite β and mordenite produced higher liquid yield from lldPE and plastic waste, respectively. However, by using a modified USY, by ion-exchange at temperature 298K for 48hours, a further improvement to the liquid yield was achieved. Using a mixer of ZSM-5/ zeolite β it was possible to achieve very good conversions for both lldPE and PP with least amount of coke formation. Further studies on catalytic cracking of lldPE using nanocrystalline ZSM-5 indicate that the highest liquid yield that could be achieved was by using the material synthesised in the presence of alcohol and sodium in the starting solution. The effect of constituents in the starting gel mixture for ZSM-5 synthesis appears to influence surface area, acidity and particle size; however it appears that this does not affect the catalytic performance for cracking of lldPE. However the study suggest that control of external surface area and particle size is highly significant.
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