Abstract:
MCM-22 was able to be hydrothermally synthesized by rotating crystallization and using hexamethyleneimine (HMI) as a structure directing agent with the gel composition 1.00 SiO₂: 0.15 Na₂O: 0.033 Al₂O₃: 0.9 HMI: 40 H₂O. The gel was crystallized at 140 ℃ for 7 days. The MCM-22 catalysts with various SiO₂/Al₂O₃ molar ratios were synthesized and the organic template was removed from as-synthesized samples by calcination in a muffle furnace at 540 ℃. The del-MCM-22 was prepared by swelling and exfoliating the MCM-22 precursor. The del-MCM-22 consists of thin sheet with an extremely high external surface area. The proton form of MCM-22 and del-MCM-22 catalysts could be obtained by treatment with 1.0 M NH4Cl solution under reflux at 80 ℃ for 2 h, 5 times. The synthesized catalysts were characterized using X-ray diffraction, inductive coupled plasma atomic emission, solid stage 27Al-NMR, nitrogen adsorption and scanning electron microscopy. Catalytic cracking of PP waste over Na-MCM-22 and H-MCM-22 catalysts are studied under different conditions. The optimum polypropylene cracking condition was set to reaction temperature of 380 ℃, 10 wt% of catalyst and under N₂ flow of 20 cm3/min. Using H-MCM-22 as catalyst, the conversions of PP waste greatly increase compared to that in the absence of catalyst. The conversions, gas and liquid fractions depend on the SiO₂/Al₂O₃ ratio in catalyst and the reaction temperature. The product selectivity is affected slightly. The gas fraction obtained by PP waste cracking mainly consists of n-butane, C₅⁺ and propene and in the range from C₇ to C₈ for the liquid fraction with the same boiling point range compared to that of standard gasoline. The catalysts with various SiO₂/Al₂O₃ ratios after the treatment with ammonium chloride provide higher yield of liquid fraction and lower yield of coke than that before the treatment except H-MCM-22(30) catalyst. The used H-MCM-22 catalysts can be regenerated by calcination, the obtained product composition close to the fresh catalyst but the activity is lower. In case of del-H-MCM-22 catalyst, it shows the polypropylene conversion slightly higher than non-delaminated one in the range of 82 % - 92 %. The obtained gas product is mainly n-butane and C₅⁺ and the liquid fraction is mainly in the range from C₆ to C₈.
