Synthesis Of IM-5Zeolites And Their Catalytic Application In Toluene Alkylation With Methanol

Zeolites are crystalline, hydrated aluminosilicates having microporous, regularstructures. The zeolite micropores are of molecular size which give them adsorption,catalytic and ion exchange properties of paramount importance the chemical industrialfield. Zeolite which has novel structure and acid properties draws much attention forits expansion of the application. In recent years, diquaternary ammonium compoundsas the SDA for the synthesis of new multidimensional porous zeolites have becomemore and more attractive. The diquaternary ammonium compounds with theproperties of flexibility and the higher charge density have many advantages thatsmall rigidity molecules don’t have. Toluene alkylation reaction is a novel way toobtain PX which is catalyzed by Br nsted acid and relies on zeolite selectivity.ZSM-5is a good catalyst for this reaction but there still exist some problems such aslow toluene conversion and catalyst stability.IM-5is a novel microporous zeolite with2-dimensional intersections synthesizedusing MPPB diquaternary ammonium compounds as SDA under kinetic hydrothermalconditions. IM-5has a limited3D pore system which is different from other zeolites.IM-5is rather comparable as for the acidic properties with TNU-9, and possessessimilar strength of Br nsted sites and Br nsted to Lewis acid site ratio like ZSM-5.there are five most favorable sites for Al substitution and about40favorable H protonlocations with relatively high acidity. For a long time, IM-5has been synthesizedaccording to original patent which has some problems such as long synthetic cycleand low efficiency because the synthesis of the zeolites and SDA was separated. Inour work, we use a mixture of DBP and NMP with given ratio as the in-situ templateso that makes two synthesis steps(SDAs and zeolites) together. By this means,thesynthetic efficiency was improved.According to this in-situ method, We investigated the relationships between thesynthetic factors and the results of the synthesis. It was found that the suitable Si/Alratio was between10~30. The lower Si/Al ratio prefer quartz phase while higher Si/Alratio tend to ZSM-12phase. The proper NaOH/Si ratio may be0.65-0.7. The proper template ratio may be DBP:NMP:Si=0.16:0.35:1, and any excessive in-situ templatewill lead to unexpected phase. Seeing that no IM-5phase obtained when use TEOS assilica source, we successfully synthesized IM-5zeolite when use SiO2hydrolyzedfrom TEOS as silica source. We also synthesized Cs-IM-5used as catalyst for toluenealkylation with methanol. It was found from the synthesis result that Cs-IM-5processa similar synthetic condition with IM-5zeolite and has the same NaOH/Si ratio andSi/Al ratio. When use CsNO3as Cs source can get a wider range of Si/Cs ratio thanother Cs sources.We use IM-5and modified IM-5zeolite for toluene alkylation with methanol andinvestigate the influence of Si/Al ratio on the reaction result and make comparisonwith other zeolites. We found from the reaction result that IM-5with different Si/Alratio exhibit the same PX selectivity and toluene conversion,because their similar acidproperties. Oxide Modification can successfully remove the acid sites located on theexternal zeolite surface and modify channel system. Modified IM-5used for thisreaction can rise the selectivity of PX but lower the toluene conversion.