Synthesis Of ZSM-23 And High Silica ZSM-5 Molecular Sieves And Study On The Isomerization Reaction Of O-cresol

As fine chemicals and one of the most important chemical intermediates,m-cresol has an attractive application prospects in the manufacture of pesticides,medicines,and dyes.In the existing industrial production,high-quality o-cresol and p-cresol monomers can be produced in batches,but the meta-cresol monomers are still prepared by the separation of cresol mixtures or the production of meta-toluidine by hydrolysis,which is not conducive to large-scale industrial production.Therefore,it is imperative to find a catalyst from abundant raw materials and with low synthesis cost,to be used to directly prepare m-cresol in one step through simple reaction.Zeolite molecular sieves have been widely used in the chemical industry because of their unique pore structure and adjustable acidity.All these merits have encouraged people to try to use zeolite molecular sieves to prepare high-quality m-cresol.In this paper we have studied the ZSM-23 zeolite with MTT structure and the ZSM-5 zeolite with high silica-to-aluminum ratio and MFI structure.The effects of various factors such as alkalinity and template agent on the morphology and the performance of the synthesized molecular sieve are systematically investigated.Using crystals with uniform morphology and high crystallinity,we have prepared H-type catalyst and carried out the catalytic reaction of o-cresol isomerization to m-cresol to explore the factors affecting the catalytic performance of o-cresol isomerization.The main research conclusions of this paper are as follows:1、Using isopropylamine as the structure-directing agent,a ZSM-23zeolite molecular sieve with a silicon-to-aluminum ratio of 100 was prepared by a dynamic hydrothermal method,and the effects of alkalinity,amount of template,water content and crystallization time on the synthesis of ZSM-23were investigated.The results show that:the best Na₂O/Si O₂for the synthesis of MTT crystal phase is 0.08,too low alkalinity leads to incomplete crystallization,and too high alkalinity results in the synthesis of MFI crystal phase;the best IPA/Si O₂is 0.67,followed by The template is gradually increased,and crystals grow along a specific crystal phase;the best H₂O/Si O₂is 30,and the water content has little effect on the entire synthesis system;pure phase MTT crystals can be synthesized within 40-48 h,but with As the crystallization time is prolonged,the degree of crystallinity is reduced,and MFI miscellaneous crystals are formed.2、Using relatively cheap n-butylamine（ZDA）as a structure-directing agent,under static conditions,a two-stage hydrothermal method was used to synthesize ZSM-5 zeolite with a silica-to-aluminum ratio of 500,and explore the alkalinity and water content,amount of template,crystallization time,silicon source and other influencing factors affect the product.The results show that the optimal ratio of alkali to silicon for the synthesis of high silica molecular sieve is 0.025,the crystal morphology is all hexagonal flakes,and the particle size gradually decreases with the increase of alkalinity;the water content has little effect on the synthesis of high silica molecular sieve,but Too high water content will cause the relative crystallinity to decrease;the best ZDA/Si O₂is 0.16,too low template content is not enough to induce the synthesis of molecular sieves,appropriately increase the template content,crystal morphology,particle size and relative crystallinity.After crystallization for 24 hours,the extension of the crystallization time will not have much impact on the crystals,too long crystallization time may dissolve part of the crystals;molecular sieve shape synthesized with Meigao silica gel as the silicon source The appearance is relatively uniform,but the molecular sieve synthesized with Baishahe silica gel as the silicon source has a small particle size and shows irregular accumulation,and the relative crystallinity has a certain decrease.3、By selecting the original ZSM-5 molecular sieve powder with high crystallinity and uniform morphology,and through ammonium exchange,a series of H-type catalysts with different acid properties,morphologies,and silicon-to-aluminum ratio were prepared.Then under the best process conditions,the performance the catalysts on o-cresol isomerization reaction was evaluated.The results show that:for acid properties,the 80 Na catalyst with more L acid has a higher selectivity to m-cresol,up to 73.33%,while the conversion and yield of the 80 H catalyst with less L acid is much higher,indicating that L acid is the active center of o-cresol isomerization to prepare m-cresol;for the morphology,the small particle size of the Z-1 catalyst sample has a shorter diffusion channel,which is conducive to the timely diffusion of reaction products.The conversion rate of o-cresol is higher,but the timely diffusion of the side reaction product to cresol causes the selectivity of m-cresol to be slightly lower.Conversely,the conversion rate of o-cresol is slightly lower for the Z-2 catalyst sample with a larger particle size.Low,the selectivity of m-cresol is higher;For the silicon-to-aluminum ratio,the catalyst with high silicon-to-aluminum ratio has more L acid centers and higher m-cresol selectivity,but the decrease in the amount of L acid makes the conversion rate of cresol is low.