Investigation And Development Of Catalytic Cracking Catalysts For Polyolefin Waste Plastics

Among the various recycling methods for waste plastics,the selective catalytic degradation of waste plastics to clean oil or valuable hydrocarbons is the most promising approach.In the present study,a series of hierarchical ZSM-5 and micro-mesoporous composite MCM-41 were prepared,characterized and applied in catalytic degradation of waste plastics.Due to its special pore structure and acidity,ZSM-5 exhibits the best selectivity for aromatics and high yield of C₃⁺?>95%?in PE,PP degradation.It was found that the reactivity of PP was higher than that of PE due to its highly branched nature favoring the formation and transformation of carbonium ion intermediates.An optimal modification method including alkaline and successive steam treatment was provided for catalyst preparation.The corresponding catalyst showed good aromatization activity in polyolefin transformation reaction due to its enhanced mass transfer property.For example,the C₃⁺hydrocarbons yield on ZSM-5-AT-ST under 380°C was higher than 98%in PP degradation reaction.And the C₅⁺gasoline components took up 62%.The LPG products can be used as clean automobile LPG.The content of high RON components?aromatics,iso-paraffin and olefins?was higher than 85%in C₅⁺product.A serial of mesoporous MCM-41 with the pore walls containing the secondary building units of ZSM-5 are synthesized using the nano-crystalline in the alkaline treated ZSM-5solutions as?partial?silica-alumina source.XRD,N₂ adsorption,NH₃-TPD and SEM techniques were applied to characterize the porous and acidity information.The results showed that the synthesized samples exhibited good micro-mesoporous composite pores,high surface area and pore volume?as high as 937.6 m²/g and 0.91cm³/g,respectively?.To realize the continuous production of high RON clean gasoline from waste plastics,a novel technology of waste plastic catalytic-degradation reforming with part of the LPG product recycling back to the inlet of the reactor was proposed.Under the optimal reaction conditions,the content of C₃⁺hydrocarbons was higher than 98%,among which 60%was in gasoline range.The C₅⁺hydrocarbons was rich in high RON aromatics and i-paraffins,which may provide guide to the selective transformation of waste plastic to value-added hydrocarbon products.