Solid-phase Synthesis,Modification,and Crystallization Tendency Prediction Of ZSM-5 Zeolite

The traditional preparation method of ZSM-5 zeolite is hydrothermal synthesis.Because it needs a lot of water or organic solvents,which not only pollutes water resources,but also has potential safety hazards in the high temperature hydrothermal process.Based on the concept of"green chemistry",the one-step method without solvent and solid-state synthesis of ZSM-5 zeolite and heteroatom ZSM-5 zeolite is explored,in order to obtain a green and environmental protection synthesis method of zeolite,which has important practical significance.In this paper,the effects of mineralizer,silicon source,crystallization temperature,crystallization time,grinding time,ratio of water to silicon,dosage of template,ratio of ammonium to silicon and ratio of silicon to aluminum on the crystallinity and morphology of ZSM-5 zeolite synthesized by solvent-free solid-state reaction were investigated;On this basis,the feasibility of one-step solvent-free solid-state synthesis of heteroatom ZSM-5 zeolite was explored,and the morphology and acidity of the samples were characterized;Finally,the crystallization tendency of ZSM-5 zeolites was predicted by machine learning method.The main conclusions are as follows:（1）Under solvent-free condition,it is feasible to synthesize ZSM-5 zeolite by one-step grinding method.When NH₄Cl is used as mineralizer,the morphology of synthesized samples is mainly"cross shaped";When NH₄HF₂is used as mineralizer,the morphology of the synthesized sample is mainly flat hexagonal prism.Based on the crystallinity and morphology,the optimum conditions of solvent-free solid-state synthesis of ZSM-5 were determined.The results were as follows:n（TPABr）:n（NH₄⁺）:n（Si O₂）:n（crystalline water）:n（Al₂O₃）=0.10:0.80:1.0:4.3:0.025,the grinding time is 15 min、the crystallization temperature is 160℃and the crystallization time is 24 h.（2）It is feasible to synthesize heteroatom ZSM-5 zeolite by one-step grinding method in solvent-free condition.XRD and SEM results show that the crystallinity,morphology and size of ZSM-5 zeolites are different after the introduction of Zn,Ti and Cu;The results of EDS characterization show that when Si/R=50（R=Zn,Ti,Cu）,Zn atoms are easy to be doped into ZSM-5 zeolite,while Ti and Cu are difficult to be doped.However,the presence of Cu compounds in the system can significantly change the specific surface area of ZSM-5 zeolite.Compared with that before adding Cu compounds,the specific surface area of ZSM-5 zeolite increases from 302.8m²·g^-1to 374.4 m²·g^-1;When Si/R（Zn）=50,L-acid increased,B-Acid decreased and B/L decreased significantly.（3）Random forest regression（RFR）,support vector machine regression（SVMR）,neural network（NN）and XGBoost model were used to predict the crystallization tendency of ZSM-5 zeolite synthesized in solvent-free solid phase.It was found that Sodium metasilicate nonahydrate and crystallization temperature were the most important parameters affecting the crystallization tendency.