Crystallization process of zeolite ZSM-5 and zeolite ZSM-35 in a special autoclave

By use of a special autoclave, the crystallization process of the dehydrated amorphous gels was studied in the Na₂OAl₂O₃SiO₂⁻ ethylenediamine (EDA) — triethylamine (Et₃N) — H₂O system. In one run, zeolites ZSM-5 and ZSM-35 can be simultaneously synthesized at different areas of the autoclave. The data demonstrate that Gabelica's hypothesis (Gabelica, Z., Blom, N. and Derouane, E.G.Appl. Catal. 1983,5, 227) could be correct at some conditions.     

Steaming of ZSM-5 zeolite film

The change in morphology of the ZSM-5 zeolite films during steaming at 443 K was studied. The crystal growth of zeolite, 5–10 μm in size, from the layer of microcyrstalline ZSM-5 zeolites was first visualized by scanning electron microscopy.     

Crystallization kinetics of zeolite ZSM-5

Zeolite ZSM-5 was synthesized from aluminosilicate gels in the presence of organic templates — tetrapropylammonium bromide (TPABr) and pyrrolidine (Py) — at temperatures of 423, 438 and 453 K. Nucleation and crystallization processes were subjected to a detailed kinetic analysis. The nucleation region is subdivided into two periods: induction and transition ones. Values of nucleation energy and crystallization energy, preexponential factor, rate of crystallization, and geometric factor have been calculated. Correlations between the estimated kinetic characteristics were found. The activation energy and the preexponential factor for the transitional and crystal-growth periods have the character of a kinetic compensation effect. The mechanism of the crystallization process is discussed on the basis of the kinetic features and correlations.     

ZSM-5 zeolite films on cordierite modules. Effect of dilution on the synthesis medium

Continuous, multilayered ZSM-5 zeolite films have been grown by direct synthesis on cordierite modules. The influence of the H₂O/SiO₂ ratio used in the synthesis mixture on the film properties was studied by inspecting the film formed in the external module surface at several water contents. It is shown that dilution prevents the film to become dense, modifies zeolite crystal morphology and reduces markedly the crystallization of zeolite into a non-adhered powder form.     

ZSM—5沸石膜的合成与表征

叙述了沸石膜的发展与应用,综述了 Ｚ Ｓ Ｍ － ５ 沸石膜的合成、修饰与表征方法．制备膜最常用的方法为水热法在载体上直接就地合成．气相化学沉积法（ Ｃ Ｖ Ｄ） 、溶胶－ 凝胶法（ｓｏｌ － ｇｅｌ） 以及合成后积炭等方法被用来对膜的缺陷进行修饰．膜的表征手段为 Ｘ Ｒ Ｄ、 Ｓ Ｅ Ｍ、气体渗透等     

Crystallization of ZSM-5 zeolite under microgravity

Crystal growth of ZSM-5 zeolite under microgravity was carried out using a Soviet reentry system. The space-grown zeolite was composed of grains of uniform shape and size (ca. 10 μm). Most of zeolite grains were linked with each other by the edge of the grain. The electron diffraction of each grain showed a single-crystal diffraction pattern, indicating the presence of well-crystallized zeolite crystal. The relatively large difference in the surface Al concentration existed between different crystals of the space-grown zeolite, as compared with the zeolite crystals synthesized in the ground with stirring. Based on these results, the crystals growth of zeolite in the microgravity environment was discussed.     

Nonaqueous synthesis of ZSM-35 and ZSM-5

ZSM-35 and ZSM-5 were prepared from nonaqueous systems for the first time. The kinetics of crystallization was studied. The apparent activation energy of nucleation (En) and the growth of crystal (Ec) were measured. En = 7.2 Kcal/mol; Ec = 6.2 Kcal/mol. The trinary phase diagram of ZSM-35 and ZSM-5 is illustrated. During the synthesis, the molar ratio of SiO₂/Al₂O₃ does not change in the solid phase and the aluminosilicate polyanions do not exist in the liquid phase. This is evidence of a solid-phase transformation mechanism in the synthesis of the zeolites. It can be seen from i.r. spectra that the band at about 550 cm⁻¹ increases with the increase of crystallization time, which further confirms that the procedure of crystallization of zeolite in the nonaqueous system takes place in the solid phase.     

Toward the rational design of zeolite synthesis: The synthesis of zeolite ZSM-18

ZSM-18 has, until now, only been made using one trisquaternary ammonium ion, 2,3,4,5,6,7,8,9-octahydro-2,2,5,5,8,8-hexamethyl-1H-benzo[1,2-c:3,4-c′:5,6-c″]tripyrrolium, 1. This trisquaternary is difficult to make and destabilizes the zeolite during calcination. We used modeling to aid the design and selection of new templates for ZSM-18. The geometry and charge distribution of these templates were chosen to best fit our estimate of “templating.” Template 2, tris-(2-trimethylamonioethyl)amine, is easy to synthesize in high yield and can be routinely calcined to produce highly sorptive ZSM-18. Template 3, tris-(2-trimethylamonioethyl)methane, produces ZSM-18 only when seeded. Si n.m.r. and Al n.m.r, indicate that aluminum is not located exclusively in the three rings as has been predicted theoretically. [H]-ZSM-18 can be steam-dealuminated. The Si n.m.r, of the dealuminated material agrees with the number of sites and relative occupancies expected.     

ZSM—5型沸石膜的合成及应用于乙苯脱氢反应研究进展

重点介绍了国内外关于ZSM－5沸石膜的合成及应用于乙苯脱氢反应应用现状,分析和阐述了当今ZSM－5沸石膜合成的方法和特点及今后面临的挑战。     

The investigations on the synthesis of zeolite ZSM-5 with the use of ethylenediamine as a templating agent

The effect of the chemical composition of the reacting mixture (RM),aswell as of time and temperature of crystallization, on the synthesis of zeolite ZSM-5 was investigated. Ethylenediamine (ED) served as a templating agent. The crystallization was conducted at 180-120°C for 1–20 d. The quantitative estimation of the phase composition was made on the ground of X-ray diffraction measurements. Zeolite ZSM-5 (max. purity 96%), contaminated with quartz, mordenite, and an amorphous phase, was obtained.     

Oxidative dehydrogenation of lower paraffins with ZSM-5 zeolite catalysts

It was found that the oxidative dehydro-aromatization of lower paraffins was effectively catalysed by either a protonic or metal ion-exchanged ZSM-5 zeolite at temperatures from 450 to 550°C. Oxygen reacted selectively with surface hydrogen to promote its removal as water, to decrease its surface concentration, and, thus, to enhance the formation of aromatic hydrocarbons.     

A novel route to synthesis Aluminum silicate hollow spheres having ZSM-5 structure in absence of template

A novel route to synthesize Aluminum silicate hollow spheres with thick walls having ZSM-5 structure without using any template at 150 °C was presented. X-ray diffraction (XRD), Scanning electron microscopy (SEM), TG/DTA, FT-IR and nitrogen adsorption were employed to characterize the morphology and microstructures of the as-prepared silica hollow spheres. Experimental results indicated that the hollow spheres had an average diameter of nearly 200 nm with a surface area of 342 m²/g.     

ZSM-5/Y复合结构分子筛的制备及其复合结构形成机制的探索

以工业ZSM 5分子筛作为硅源,采用水热法制备ZSM-5/Y复合结构分子筛,并对其进行了X射线衍射(XRD)、N2吸附(BET)、核磁共振(NMR)和扫描电镜(SEM)表征.结果表明,产物同时具有ZSM-5分子筛和Y型分子筛的晶相结构特征.晶种的加入能有效地提高晶化反应进程.NaOH溶液的碱性越高,对ZSM-5的溶解性越高.随着晶化时间的延长,属于ZSM-5分子筛的特征峰强度降低、Y分子筛的特征峰强度升高.在晶化时间为10、20和30h时,对体系中加入铝源和晶种进行了研究.结果发现,复合结构分子筛的合成过程伴随着分子筛上骨架硅解离、部分骨架铝解离、硅源和铝源在分子筛骨架外及骨架上晶化形成新的晶体的过程.推断ZSM-5/Y复合结构分子筛形成机制有两种:(1)铝源和溶液中溶解的硅结合;(2)铝源直接和ZSM-5分子筛骨架上的硅结合.