Preparations Of Alumina Matrixes And Y Zeolites For FCC Catalyst

As one of the most important oil-refining processes, fluid catalytic cracking (FCC) process has drawn much attention. And as the essential part, the design and manufacture of FCC catalyst play key roles because the properties of the catalyst, i.e., compositions and structures of matrixes and molecular sieves, directly affect the catalytic performance in the oil cracking process.Towards the modification of the catalysts, two aspects can be concerned, matrix aluminas and zeolites. Lots of attempts have been devoted to the synthesis and modifications of alumina matrixes and zeolites until now.On the basis of the previous investigations, the thesis is mainly about the catalyst related alumina matrixes and zeolites and includes firstly, preparation of large-sized mesoporous aluminas, and secondly post-treatment of Y zeolite, namely, sodium removal, dealumination and introduction mesopores into zeolite, thirdly combination of the aluminas with zeolites to form meso-microporous hierarchical composites. The details of the dissertation include:Part1, The preparation of large-sized mesoporous alumina matrixes. In this part, organic and inorganic aluminum sources are used and mesoporous aluminas with different textural and structural properties can be synthesized in different processes, such as:1. aluminum isopropoxide is used as aluminum source, organic acids, including formic acid, acetic acid, propionic acid and their mixtures, as condensation agent and structural controlling agent, alumina precursors, aluminum carboxylate salts with different structures and morphologies can be prepared by adjusting the acid nature and mixture compositions. After calcination at high temperatures, alumimun carboxylate salts can transform to mesoporous aluminas with morphologies inherited. The resultant aluminas display high surface areas (>100m2/g) and large-sized mesopores (>10nm). Large-sized mesopores in the aluminas can improve the diffusion of large molecules in the cracking oil.2. Organized mesoporous aluminas can be obtained with cationic/anionic aluminum salts as aluminum sources in the presence of catanionic surfactants. The textural properties of the resultant aluminas can be tuned by adjusting the ratios of cationic surfactant to anionic surfactant. In the synthesis process, the addition amount of surfactant is low (S/Al=0.1) and the aluminas own high specific surface areas (261m2/g), large pore volume (0.79cm3/g) and large mesopore sizes (12.1nm).3. Crystalline bayerite (Al(OH)3) can be prepared by stirring the mixture of NaAlO2with diethyl adipate and the morphologies of the bayerite can be controlled by varying the pH adjustor. After calcination at high temperatures, bayerite samples can transform to η-Al2O3, and the aluminas display large specific surface areas (322m2/g) and organized pore size distribution. Furthermore, the pore size gets larger when the calcination temperature increases which can inhibit pore plugging by pore shrinkage.4. Bayerite particles prepared by mixing NaAlO2and diethyl adipate solutions at room temperature can morphologically transform to boehmite in the dry-gel conversion process in the presence of steam. During the conversion process, the morphologies of the particles remain unchanged while the morphologies of boehmite nanoparticles changed from plates to rods and fibers with increasing the amount of acetic acid in the steam source. The selective adsorption of acetic acid on the boehmite facet makes boehmite crystalline preferentially grow along one directions, resulting in the formation of boehmite1D rods and fibers.5. Boehmite samples with different morphologies, such as rods, fibers and nano-particulates, can be prepared with NaAlO2as aluminum source and inorganic acids as pH adjustors in the absence of surfactant in the sol-gel method. By self-assembling of the particles, mesoporous structures can be obtained.Part2, Post-treatment of NaY:sodium removal and dealumination.1) Na+ions can be removed using acetic acid as proton donor. As acetic acid is a weak acid with part dissolution, the acidity can be strong enough for the sodium removal but not strong enough for zeolite structure collapse.2) The steam of organic acids with low boiling point, such as formic acid and acetic acid, can be used to coordinate with framework aluminum species, resulting in the dealumination of zeolite Y and an increase in the framework silica to alumina molar ratio without obvious structure collapse. After increasing the SiO2/Al2O3molar ratio, the extra-framework sodium ions can be removed more easily.3) Sodium can also be removed in SiCl4ethanol solution and the sodium content can be decreased to less than2.0%with one single exchange operation.Part3, Post-treatment of Y zeolites:the introduction of mesopore. Mesopores can be successfully introduced into Y zeolite samples with low silica to alumina molar ratios. During the treatment, NaY zeolite is used as precursor, and mesopores can form in the presence or absence of surfactant.Part4, Preparation of hierarchical alumina-Y zeolite composites.1) hierarchical composites can be obtained by combining boehmite and Y zeolites and the composites display improved acidic properties and textural with both mesoporosity and microporosity. The composites show much better catalytic performance in the cracking of large organic molecules.2) Hierarchical Meso-Micro-Mesoporous composites can be prepared by combining boehmite with micro-mesoporous Y zeolite and the composites clearly display tri-modal pore structures.From the work described above, we now know much more about the preparation and pore formation mechanisms of alumina matrixes and the post-treatment of zeolites related to FCC catalyst.