Synthesis And Characterization Of ZSM-22 Zeolite With Different Morphologies

With the development of modern science and technology,people’s requirements of high-quality life and living environment are increasing.How to get high-quality and affordable energy is on the agenda.The isomerization process of normal paraffin hydrogenation in the presence of hydrogen condition is a very effective method for making a new type environment-friendly fuel. ZSM-22 is an important catalyst in this process,which has one-dimensional duct system,proper pore size（0.46×0.57nm）and the acid strength,and is easy to diffuse product and suppress carbon deposits.So how to make ZSM-22 at a cheaper cost is becoming very important.Studies have shown that in processes of molecular sieve adsorption,separation and catalytic,morphology of zeolite greatly affects the accessibility of molecular sieve.So in the catclytic process,to prepare ZSM-22 zeolite with good accessibility is of great theoretical and practical significance.In this paper,we prepared ZSM-22 with the static hydrothermal method.We investigated the influence of crystallization time,crystallization temperature,alkalinity,the amount of templating agent,water and other conditions by using different silicon source or templating agent.On this basis,we prepared five different morphology ZSM-22 and studied their physical and chemical properties,and we also tried to use NaOH to replace KOH in synthesis of ZSM-22.We found out:if we use silicon dioxide as the silicon source,DAH as template,the synthesis of pure zeolite ZSM-22 was successfully achieved under this condition:crystallization temperature was 160℃,K₂O/Al₂O₃ was 4.5⁷.5,DAH/Al₂O₃ was 11²7,H₂O/Al₂O₃ was 3200⁴400,Si/Al was 30⁶0.If we use white carbon black as the silicon source,DAH as template,the synthesis of pure zeolite ZSM-22 was successfully achieved under this condition:crystallization time was 3d,K₂O/Al₂O₃ was 5.5⁷.5,DAH/Al₂O₃ was27,H₂O/Al₂O₃ was 2800³600,Si/Al was 45⁵0.If we use silicon dioxide as the silicon source,A as template,the synthesis of pure zeolite ZSM-22 was successfully achieved under this condition:K₂O/Al₂O₃ was 5.5⁷.5,A/Al₂O₃was11²7,H₂O/Al₂O₃ was 3200⁴400,Si/Al was 35⁶0.We also prepared ZSM-22 with five different morphologies under different synthesis conditions and studied their physical and chemical properties.We found that:The specific surface area of ZSM-22 using DAH as template is greater than that using A or N-ethyl Bromide as template.The microporous specific surface area of ZSM-22 using A as template is roughly the same to that using DAH as template,The specific surface area of ZSM-22 using N-ethyl Bromide as template is minimum.All of these five different morphology of ZSM-22 have strong acid and weak acid,in which weak acid is more.The ZSM-22 synthesized by using DAH as template contains more acid sites and stronger acid strength.Study about the synthesis of ZSM-22 by replacing KOH with NaOH shows that:AS long as we control maintain concentration of K⁺in gel system,using the high active silicon sources,and replace KOH with NaOH up to n（KOH）:n（NaOH）=0.5:7.We can get the ellipsoidal crystal of ZSM-22,when we use A as template and n（KOH）:n（NaOH）=0.5:7.