| In this study, several mesoporous molecular sieves, modified by Ti or Sn, weresynthesized under hydrothermal conditions. And some strong acidic groups likeBO33-, SO42- and ZrO2, or alkaline groups like K2O, were incorporated into the frameof the mesoporous molecular sieves to obtain the strong acidic or alkalinemesoporous molecular sieves catalysts. The obtained materials were used ascatalysts in the pyrolysis of polyolefins. The synthesized mesoporous molecularsieves were characterized with XRD, nitrogen adsorption-desorption, FT-IR,UV-VIS and NH3-TPD. The results showed that the obtained materials weremesoporous molecular sieves with better long-range order and crystallinity. Strongacidic or alkaline groups had been combined with the frame of the mesoporousmolecular sieves so that the acidity or alkalinity of MCM-41 was improved. Thecatalytic cracking performances of different modified mesoporous molecular sieveswere investigated by the catalytic pyrolysis reaction models of HDPE, LDPE, PP andPS. In the catalytic pyrolysises of HDPE, LDPE and PP, Liquid fuel was the targetproduct, while in the catalytic pyrolysis of PS, the target product was styrenemonomer. According to the characterization of these catalysts, the relationshipsamong acidity or alkalinity, pore structure, and catalytic activity of differentmodified mesoporous molecular sieves were studied. The results indicated that theacid strength of catalyst had more significant effect on the catalytic pyrolysis ofHDPE and LDPE, and the catalytic activity of mesoporous molecular sieves can becontrolled by their pore structure in the catalytic pyrolysis of PP. However, to obtainstyrene monomer by the catalytic pyrolysis of PS, the alkali strength of catalyst hadmore deciding effect on reaction activity. The catalysts that were of best catalytic activities were used in the catalyticpyrolysis of polyolefins. The influences of reaction conditions such as n(Si): n(M)(M=Ti, Sn), content of supported active substance, reaction temperature, reactiontime and dosage of catalyst on the pyrolysis were examined and the optimumconditions were obtained. SO42-/Sn-MCM-41(n(Si):n(Sn)=50) was of better catalyticperformance in the catalytic pyrolysis of LDPE, under the optimum conditions ofreaction temperature 440℃, m(SO42-/Sn-MCM-41)/m(LDPE)=2％and reaction time50min, the conversion of LDPE was 83.0％and the yield of liquid products was73.7％. ZrO2/Ti-MCM-41 (n(Si): n(Ti)=40) was of better catalytic performance in thecatalytic pyrolysis of HDPE, under the optimum conditions of reaction temperature440℃, m(ZrO2/Ti-MCM-41)/m(HDPE)=3％and reaction time 50min, theconversion of HDPE was 73.6％and the yield of liquid products was 63.7％.18％ZrO2/Ti-MCM-41(n(Si): n(Ti)=40) had better catalytic performance in thecatalytic pyrolysis of PP, under the optimum conditions of reaction temperature400℃, m(18％ZrO2/Ti-MCM-41)/m(PP)=2％and reaction time 30min, theconversion of PP was 91.2％and the yield of liquid products was 83.6％.9％K2O/MCM-41 had better catalytic performance in the catalytic pyrolysis of PS,under the optimum conditions of reaction temperature 400℃,m(9％K2O/MCM-41)/m(PS)=2％and reaction time 30min, the conversion of PS was90.5％, the yield of liquid products was 85.7％and the yield of styrene monomerreached 69.0％.To our knowledge, there is no reported literature about above studies andresults.
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