Synthesis Of Small Crystal-size Zeolite NaY

Zeolites are famous for their characteristic three-dimensional pore/channel structure and have been found various important industrial application as catalysts or the basic component of catalysts in oil refining process, e.g., fluid catalytic cracking, hydrocracking, dewaxing, isomerization and alkylation, etc., and in gas conversion process, e.g., methanol to olefins, methanol to gasoline, olefin oligomerization and light petroleum gas to aromatics, etc. They are also commercially very useful in adsorption/separation process and ion exchange process.In the above heterogeneously catalyzed process, the catalytic performance of zeolite-based catalyst is known to be a function of the surface of zeolite accessible to reaction molecules. In the conversions that reactant molecules are bigger than the pore of zeolite, much external surface area and in turn more amounts of active site in this region must be provided. While in the case that the converted molecules have the comparable size with the pore of zeolite and that necessitate the desired products leave fast from zeolite channel, the easy accessibility of these molecules inside/outside zeolite crystal should be often sufficed. The similarity is also found in the adsorption/separation application of zeolite. On the other hand, when preparing zeolite-based composite catalyst or bifunctional catalyst, it is important that zeolite crystals are well-dispersed in inert matrix or active metal compositions are highly dispersed inside the channel of zeolite. All these properties of zeolite can be mostly decided by the crystallite size, which is responsible for the diffusion-controlled process.The commercial zeolite usually has the crystal size of about one to several microns in size. However, it has been now realized that zeolite with small crystal size, especially the nanometer crystal-sized ones, are more superior for its larger external surface area, higher diffusion coefficient of reactant and/or product molecules as well as its excellent dispersion in matrix. These decide that the nanometer crystal-sized zeolite may be well used in nearly all the hydrocarbon process, e.g., FCC, HC, and isomerization of chain hydrocarbon, etc., behaving larger ability to process bigger hydrocarbon molecules and higher capacity to beU1)~ 98~VIIAbstractmodified post synthesis, as well as better selectivity to oil product and longer catalytic lifetime.It was therefore thought worthwhile to study the control over crystal size of zeolites during crystallization. The objective of present work is to find an effective method to synthesis the small crystal sized zeolites, especially that in nanometers level. Zeolite NaY is selected to investigate the influence of synthesis parameters on the crystal size, such as, the aging time of nucleation gel, the crystallization temperature, the reagents mixing orders, addition of aluminum complexing compounds and the addition of light rare earth ions. The principle results are summarized as follow:i. Investigation on synthesizing conditions of zeolite NaYSynthesis of zeolite NaY consists of several processes, such as the preparation of nucleation gels and reaction gels, crystallization of NaY, etc. Self-nucleation synthesis of NaY is selected to investigate the primary influence parameters of preparation of nucleation gels, including the temperature of preparation and the aging time of nucleation. Nucleation gel was firstly prepared by dissolving NaOH into silica sol to gain a clear solution, in which Al2(SO4)3~ 1 8H20 and H20 were added and homogenized with a turbine mixer rotating at -2000 rpm, at 275K icy-water temperature and room temperature 298K, respectively. The resultant gel had the molar composition of l6Na2O:Al203:l6SiO2:300H20 and was aged for different period of time (4, 8, 16, 24, 64 and 168 hours, respectively) at 275K and 298K, respectively. Then, reaction gel with the final molar composition of7.8Na2O:Al203:l6SiO2:410H20 was prepared by adding sulfuric acid to adapt the alkalinity of...