Synthesis,Characterization And Post Treatment Of ZSM-34 Zeolite With Short Synthesis Period

Aluminosilicate zeolite ZSM-34 is intergrowth of offretite and erionite zeolite,also zeolite with small pores maily containing 8-menbered ring,which is known to be promising catalyst for the conversion of methanol to lower olefins,adsorption of hydrocarbon and so on.However,both difficult to study for complicated structure and long synthesis period with template severely hinder the practical applications of ZSM-34 zeolite.It's a ongoing concern that how to shorten the synthesis period and simple the process.In this work,thanks to adding seeds and adjusting crystallization condition,pure ZSM-34 zeolite has been synthesized with shorter crystallization time and half amount template.At the same time,ZSM-34 has been modified with different kinds of post treatment methods.What's more,comparison between post treated products and synthesized ZSM-34 in structure and catalytic test of the MTO reaction have been done.Synthesizing ZSM-34 with traditional template methods needs rather a long time and the crystal size is larger.It's hard to solve the problems above by adjusting silicon or aluminum source of feed,amount or species of alkali metals for the narrow synthesis range and slashing synthesis condition.Then,we change the crystallization mode from one step at 160? to two steps(first step at 90?,second at 160?).Consequently,zeolite synthesis with two steps could shorten synthesis period and reduce crystal size based on the characterization of XRD,SEM.When adding seeds to the two steps synthesis system,crystallization time and crystal size could be even knocked down to 1/5 and 1/3 of the one step method respectively.The crystallization conditons,such as crystallization time,crystallization temperature,ways and amount of adding the seeds,have deeper influence on the crystal size over the relative crystallization in two step system.And the three crystallization(one step,two steps,two steps with seeds)diagrams belonging to the three modes stated were compared.The result shows that seeds can help shorten the induction greatly by produce more crystal nucleus and quickly grow to the critical volume during the induction period.Then the crystal nucleus went on growing to intact crystal and the raw materials were used up during the crystallization period so system with more crystal nucleus would get small crystal.We can conclude that the method called two steps with seeds tends to produce small in size and well-distributed products in rather short time,which is quite valuable.Hydrothermal,acidic treatments and combining the two methods are effective ways to adjust the acidity,textual structure and other characteristic of zeolite.The treated products show lower relative crystallization,acidity(especially for strong acidity),re-distribution the aluminum and outstanding stability without destroy zeolite's structure.When it comes to the MTO reaction,treated zeolites put up high conversion and selectivity of olefins,what's more,various post treated methods tend to different product distribution.On our reaction conditions,zeolite with hydrothermal treatment at 700? or acidity treatment show both good methanol conversion and the propylene selectivity has increased from 8.13% to 30% above successfully.