Preparation Of Two Dimensional MWW Zeolite And Study On The Performance Alkylation Of Aromatics

Two-dimensional(2D)zeolite have attracted widespread attention due to its excellent performance from catalysis to selective separation,including the advantages of higher external surface area,enhanced mass transfer process,dense and strong acid center,and good hydrothermal stability.Based on the existing work and research,this thesis uses a hydrothermal method to synthesize a series of two-dimensional multi-porous MWW zeolite catalysts,and alkylation of 1,3,5-trimethylbenzene and benzyl alcohol and benzene and1-dodecene in liquid phase is used as an activity test.Firstly,MWW precursors were synthesized by hydrothermal method and then MWW zeolite with different interlayer spacing were synthesized by using TEOS as pillars.The crystal form,morphology,acid properties and diffusion properties of MWW zeolite were characterized by different characterization methods.The activity of liquid-phase Friedel-crafts alkylation of 1,3,5-trimethylbenzene with benzyl alcohol was evaluated in explore the effect of hierarchical structure and surface topology of MWW zeolite on the catalytic performance of Friedel-crafts alkylation.The crystal form of pillared MWW zeolite is basically consistent with the standard card.Small angle XRD shows that MWW zeolite keeps ordered lamellae and introduces mesoporous structure between lamellae.The activity test of liquid phase alkylation of 1,3,5-trimethylbenzene with benzyl alcohol shows that the conversion of MCM-22 zeolite is ～43.4%,while that of pillared MWW zeolites is as high as ～100%.The BTMB selectivity of MCM-22 is ～58.8% and that of PMWW zeolites is ～100%.Therefore,the introduction of mesoporous of pillared MWW zeolites can greatly improve the activity of liquid-phase alkylation of 1,3,5-trimethylbenzene with benzyl alcohol.Moreover,Thiele modulus(φ)and efficiency factor(η)show that the pillared MWW zeolites have high utilization and its internal diffusion limitation is negligible.Secondly,d MWW zeolites,a series of disordered two-dimensional lamellar MWW zeolites,was synthesized by hydrothermal method which commercial surfactants were used as templates and swelling agents in the synthesis of delamination MWW zeolite.The catalyst was characterized by the crystal form,characterization of morphology,pore parameters and acidity,and its activity was tested by alkylation of benzene with 1-dodecene.The addition of surfactant hindered the MWW lamellar growth to the c-axis direction.Combined with XRD,MWW zeolite showed long-range disorder,and the crystal structure in the layer was preserved.With the increase of carbon chain of surfactant,the delamination degree of layered structure of MWW zeolite increases,resulting in the formation of d MWW zeolite with different thickness.And the BET area and surface area also increase accordingly,thus exposing more accessible active sites,which is conducive to the alkylation reaction.The results showed that the catalytic activity of d MWW-16 zeolite was ～70%,and that of d MWW-14 and d MWW-12 was ～64% and ～46%,respectively,which were higher than that of MCM-22(～ 38%).Finally,the length of the carbon chain of the surfactant determines the degree of delamination of the d MWW zeolites,which affects its catalytic activity in the reaction.Thirdly,a series of MWW zeolite with different Si/Al ratios were synthesized by hydrothermal method,and their catalytic activities were tested in the liquid phase Friedel crafts alkylation of benzene with 1-dodecene.PMWW zeolites has more ordered lamellar structure,larger surface area and more accessible active sites,which can improve its service life and promote the reaction.Moreover,the acidity of PMWW zeolites was adjusted to explore its effect on the Friedel crafts alkylation process,and compared with d MWW zeolites.The pillared MWW zeolites were successfully verified by small angle and wide angle XRD,SEM,TEM and nitrogen adsorption desorption isotherms.2,6-di-tert-butylpyridine infrared spectroscopy was used to determine the total acid content and external Br(?)nsted of PMWW zeolites.The activity test results show that the catalytic activity of PMWW zeolites is higher than MCM-22 zeolite,and PMWW zeolites has larger BET area and surface area,which improves the catalytic performance in alkylation reaction.With the increase of aluminum content,the Si/Al ratio of PMWW zeolites decreased,and the framework silicon was replaced by aluminum source,which made the total acid concentration increase,but the external Br(?)nsted acidity concentration decreased.Combined with small angle XRD and nitrogen adsorption desorption isotherm,the small angle characteristic peak of PMWW-15 zeolite decreased,and the mesoporous volume and surface area of PMWW-15 zeolite were lower than those of PMWW-45 zeolite,indicating that the increase of aluminum content was not conducive to pillaring.The high selectivity of2-LAB is explained by Vd W and Coul effect.Catalytic durability test results show that PMWW-45 zeolite has better service life and coke resistance.