Synthesis And Post-Treatment Of ZSM-5 And The Application In The Reaction Of Methanol To Gasoline

ZSM-5 is an aluminosilicate zeolite having 5.5?×5.1?elliptical channels running along the a axis in a sinusoidal manner and 5.6?×5.3?elliptical channels running straight along the b axis.ZSM-5 has many excellent properties,such as high hydrothermal stability,high chemical stability,special shape selectivity and catalytic activity.As catalysts,ZSM-5 zeolite is widely applied in the areas of petrochemical technology,fine chemical engineering,environmental protection industry,etc.Among the applications,ZSM-5 zeolites show excellent performance in catalyzing methanol to gasoline,aromatics,alkane,olefin etc.,and catalyzing olefin aromatization.With the global industrialization,the demand for energy is increasing;but the oil reserves are decreasing.Therefore,the ZSM-5 catalyzed energy related reactions are attracting more attention.In this work,firstly,ZSM-5 zeolite was hydrothermally synthesized in a seed-induced method.The effects of the amount of Na₂O,the ratios of SiO₂/Al₂O₃,the amount of seeds,different aluminum sources and different seeds in the synthesis mixture on the synthesis of ZSM-5 were studied.It was found that ZSM-5 zeolites with wide SiO₂/Al₂O₃ ratios,even pure silica zeolite Silicalite-1,could be synthesized by adjusting the amounts of the starting materials;large amount of Na₂O facilitated the decrease of the crystal sizes;large amount of seeds facilitated the decrease of the crystal sizes and the increase of the crystallinities;ZSM-5 could also be used as seeds to synthesize ZSM-5 with large sizes;spherical ZSM-5 and cross-sheet-like ZSM-5were obtained by using NaAlO₂ and pseudoboehmite,respectively.Secondly,the optimal synthesis conditions for ZSM-5 and the application in the reaction of methanol to gasoline?MTG?was studied.The amount of Na₂O,the ratio of SiO₂/Al₂O₃,the amount of H₂O and seed in the synthesis mixture was studied.Mesoporous ZSM-5 aggregates with the large BET and external surface areas and large micropore and mesopore volumes were obtained under the following synthesis conditions:the molar compositions were 12Na₂O-100SiO₂-2Al₂O₃-2500H₂O-1Seed,and the hydrothermal treatment was first at 120°C for 20 h and then at 170°C for 10h.Applied in the reaction of MTG,the catalyst lifetime was much longer than a commercial ZSM-5.Thirdly,mesoporous ZSM-5 zeolites were prepared with the treatment of hydrofluoric acid solution,and were applied in the reaction of MTG.At room temperature,ZSM-5 was treated with different molar concentrations.It was found that with increasing the concentrations of HF solutions,the SiO₂/Al₂O₃ ratios,mesopore surfaces areas and pore volumes all increased,but the relative crystallinities did not change appreciably,the amounts and strenth of the acid sites decreased.In the reaction of MTG,the catalyst lifetime was prolonged significantly compared with the parent ZSM-5.Compared with the alkali treatment method,the HF treatment is time-saving,energy-efficient and simple.Finally,ZSM-5 was desilicated and dealumicated indiscriminately by the treatment of mixtures of HF and NH₄F at room temperature.It was found that after the treatment,the crystallinities decreased slightly,but external surface areas and mesopores volumes increased,however,the micropore surface areas and volumes were retained.In some range of the treatment mixture concentrations,the SiO₂/Al₂O₃ratio was retained.In the reaction of MTG,the liquid hydrocarbon yields were high and the catalyst lifetime of the treated ZSM-5 was significantly prolonged.