Thesis (M.Sc.)--Chulalongkorn University, 2007

Composites of microporous and mesoporous materials have been studied as catalyst in the cracking of high density polyethylene (HDPE) and polypropylene (PP). Microporous ZSM-5 with the Si/Al molar ratio in gel of 40 and mesoporus Al-HMS with the Si/Al molar ratios in gel of 20, 60 and 200 were physically mixed. All synthesized catalysts were characterized using XRD, ICP-AES, 27Al-MAS-NMR, N2 adsorption-desorption, NH3-TPD and SEM techniques. Catalytic cracking of HDPE and PP over various ZSM-5/Al-HMS catalysts were studied under different conditions. When ZSM-5/Al-HMS was used as catalyst, the conversions of both plastics greatly increased comparing with those in the absence of catalyst. The conversions and yields of gas fraction, liquid fraction and solid coke depended on reaction temperature, catalytic to plastic ratios, weight of ZSM-5 per Al-HMS ratios, and Si/Al ratios in Al-HMS. The product selectivity was not significantly changed. The gas fraction obtained by HDPE and PP cracking composed mainly propylene, iso-butylene and C5+. The liquid fraction obtained by cracking of both types of plastic mainly composed of hydrocarbons in the range of C7 to C8. The optimal condition for catalytic cracking of composite ZSM-5/Al-HMS catalyst in this work was at the temperature of 400?C, ratio of ZSM-5 per Al-HMS as 1:1, and the Si/Al ratio of Al-HMS as 60. The catalyst to plastic ratios for HDPE and PP were 10 and 5 wt%, respectively. The reuse of ZSM-5/Al-HMS-60 (1:1) catalyst was performed by calcination. The activity of the reused catalyst for one cycle was not much different from the fresh catalyst.