Study On Pyrolysis Of Polyolefins Catalyzed By Modified Mesoporous Molecular Sieves

Currently, the most efficient route for the reuse of waste plastics is catalyticpyrolysis by which waste plastics are transformed into fuels or chemicals. Thismethod not only gets urgent needed fuels or chemicals but also resolve theenvironmental pollution resulting from waste plastics. So, the method has very goodeconomic and environmental benefits.In this study, a series of metal-doped mesoporous molecular sieves M-SBA-15(M=Al, Ti, Zr or Sn) and MAS-7, MAS-9, MTS-9, MZS-7with crystalline structurehave been synthesized by hydrothermal system and ionthermal system. The obtainedmesoporous molecular sieves are characterized by XRD, SEM, TEM, NH3-TPD andN2adsorption/desorption. The results show that the obtained mesoporous molecularsieves have ordered structures. MAS-7, MAS-9, MTS-9and MZS-7have goodcrystallinity and high hydrothermal stability.The obtained mesoporous molecular sieves have been used for catalyticcracking of low density polyethylene (L-LDPE), high density polyethylene (HDPE)and polypropylene (PP). The relationships of the catalytic performances and thestructures of mesoporous molecular sieves are investigated. The results are asfollows:The mesoporous molecular sieves synthesized by ionthermal system exhibit thebetter catalytic performances than the mesoporous molecular sieves synthesized byhydrothermal system. MAS-7exhibits the better catalytic activity and the yield ofliquids for catalytic cracking of L-LDPE and HDPE. Under the optimal conditions,the conversion and the yield of liquid products for L-LDPE are97.1%and76%. Theconversion and the yield of liquid products for HDPE are89.5%and71.2%.Zr-SBA-15and MZS-7show the better catalytic activity and the yield of liquids forPP. The conversion and the yield of liquid products for PP catalyzed by Zr-SBA-15are92.4%and77.5%. The conversion and the yield of liquid products for PPcatalyzed by MZS-7are94.5%and78%. The results of carbon distribution of liquidproducts show that the catalytic cracking has more centralized carbon distribution, which has relation with pore size distribution of the mesoporous molecular sieves.The test of hydrothermal stability shows that MAS-7has high hydrothermal stability.MAS-7also shows more excellent recycling.