Synthesis And Commercial Scale-up Of ZSM-35 Molecular Sieve

ZSM-35 molecular sieve belongs to FER type zeolites.It has unique cross-channel structure of 8-membered rings and 10-membered rings with mild acid intensity.It is widely used in olefin isomerization,aromatic hydrocarbon alkylation,and catalytic cracking.The research reports existed on ZSM-35 zeolites have focused mainly on the synthesis in laboratory scale,and the industrial scale experimental research is relatively scarce.Based on this consideration,the experimental studies in both small-scale and pilot-scale have been carried out,with repeatedly optimizing the synthesis conditions and the preparation processes in order to realize the replacement of reagent-grade materials with industrial-grade raw materials.In this paper,we have first compared the differences in the quality of synthesized ZSM-35 under two different methods,namely,dynamic and static crystallization in 100 m L high-pressure reactors,and then,under conditions of dynamic hydrothermal crystallization,we have systematically examined the effects of the crystallization conditions,aluminum source,silicon aluminum ratio,template-silicon ratio,water-silicon ratio,and alkalinity on the synthesis of ZSM-35.Furthermore,by performing the scale-up synthesis with 1 L reactor,the reaction conditions and the compositions of the synthesis raw materials are investigated.In the end of this work,under the optimized conditions,the amplified synthesis of ZSM-35 molecular sieves with different acid intensity is performed in a 5 m3 industrial kettle.The experimental results are summarized as:(1)Research on the synthesis of ZSM-35 by dynamic and static crystallization methods reveals that the crystallinity and dispersion of ZSM-35 are relatively high under dynamic crystallization conditions.Therefore,the dynamic crystallization procedure are employed through out our investigations on the effects of crystallization temperature and crystallization time,which give the optimal crystallization conditions as: 150 ? ~ 170 ?/ 24 h ~ 48 h.(2)The synthesis of ZSM-35 molecular sieves using Na Al O2 and Al2(SO4)3·18H2O as aluminum sources is investigated.The results show that by adjusting the synthesis parameters,using both aluminum sources,we obtain ZSM-35 with high crystallinity andregular morphology.The use of Al2(SO4)3·18H2O as an aluminum source,however,will introduce a large amount of SO42-ions,which result in the difficulty of subsequent wastewater treatment.Due to this reason,this work uses Na Al O2 as an aluminum source in follow-up ZSM-35 synthesis.(3)The influence of synthetic parameters on the ZSM-35 molecular sieve is investigated.The results showed that the alkalinity,template content,water content and aluminum content all seriously affect the properties of ZSM-35.When Na2O/Si O2 ? 0.115,it is easy to generate impurity crystals(although the impurity crystal peaks are not observed in the diffraction pattern,but they can be clearly observed in the electron microscope image);when Na2O/Si O2 ? 0.065,the obtained products are amorphous;when Na2O/Si O2 = 0.075 ~ 0.105,the crystal size of the synthesized molecular sieve is small and the morphology is regular.When the template-silicon ratio is lower than 0.016,the product appears amorphous and the crystals are severely clustered;when the template-silicon ratio is too high(? 0.366),the crystal grain size enlarges and impurity crystal appears.Excessive water content(H2O/Si O2 ?29)will reduce the concentration of various substances in the system,making it impossible to reach the supersaturated state,and resulting amorphous product;when H2O/Si O2 ? 23,it will cause serious gelation during the feeding process.The ZSM-35 molecular sieve with pure phase and regular morphology can be obtained in the range of H2O/Si O2 = 25~27.The investigation results of different silicon-aluminum ratios show that,when Si O2/Al2O3 ?24 or ? 34,the crystallinity of the obtained products is relatively low,and when the silicon-aluminum ratio is too high,impurity phase may be formed.(4)The intrinsic properties of ZSM-35 product may be affected by amplifying synthesis process and a 1 L stainless steel autoclave is used for the scale-up synthesis.Firstly,the effects of outside factors such as the type of stirring paddle and the feeding order on the synthesis were investigated.It was found that the use of the propulsion method and the first dissolving alkali method can effectively suppress the formation of heterogeneous crystals and solve the problem of gel wall-hanging.The altering the feeding order decrease the crystallinity of the product.From the investigation of the alkali-silicon ratio,it was also found that when the alkali-silicon ratio was 0.05~0.07,the productobtained shows a relatively high crystallinity and a high degree of dispersion.From the water-silicon ratio studies,the results show that,when the water-silicon ratio is 23,a higher crystallinity product is obtained,but the solution seriously gelates,which is unfavorable in industrial production.When H2O/Si O2 is between 26 and 29,the gelating phenomenon disappears and the crystallinity is relatively high;The results are basically consistent with that of the pilot scale test.(5)Under the above optimized reaction conditions,ZSM-35 molecular sieves with different acid intensity are synthesized in a 5 m3 amplificatory kettle and products of ZSM-35 with high crystallinity and regular morphology are obtained.To obtain ZSM-35 molecular sieves with regular morphology.Various characterizations indicate that the synthesis conditions in small-scale are not much different as that performed in 1 L kettle,so the knowledge gained from the laboratory small-scale test is worthy of being referring.