Cracking of high density polyethylene and polypropylene over zeolite beta/ai-hms mixed catalysts

Abstract

PP and HDPE cracking were investigated over zeolite beta/Al-HMS mixed catalysts. Zeolite beta with gel the mole composition of 1SiO2: 0.0083 Al2O3: 0.73 TEAOH : 19 H2O (Si/Al = 60) were synthesized by hydrothermal crystallization at 135°C whereas Al-HMS with the gel mole composition of 1SiO2: 0.0125 Al2O3: 0.25 HDA: 8.3 EtOH: 100 H2O were synthesized by sol-gel method and crystallization at room temperature. Octahedral aluminium from Al-HMS was removed by treating with 1M NH4Cl at boiling temperature for 3 h. The catalysts were characterized by X-ray power diffraction, scanning electron microscope, ICP-AES, 27Al-MAS-NMR, nitrogen adsorption and ammonia-temperature programmed desorption techniques. Catalytic cracking of PP over mixed catalysts between zeolite beta and Al-HMS were studied with various conditions. The optimal condition for PP cracking was 95%Al-HMS in the presence of mixed catalysts, 10%wt catalyst and at the reaction temperature of 380˚C whereas for HDPE was 5%Al-HMS in the presence of mixed catalyst, 10%wt catalyst and at the reaction temperature of 410˚C. With increasing reaction temperature, degradation rate were faster but the products distribution of gas and liquid fraction were not different. The liquid products had the same boiling point range compared to that of standard gasoline. The regeneration of catalysts was acceptable for 1-2 cycles due to a high conversion of PP and HDPE cracking over 80%. However, the structure of mesoporous Al-HMS should be aware after reusing of catalyst.