A Quasi-solid-phase Approach To Activate Natural Aluminosilicate Minerals For Zeolite Synthesis

In the past half century,zeolites have been widely used in petrochemical and fine chemical industries as catalysis,adsorption,and ion exchange materials.At present,the main raw materials for commercially synthesizing aluminosilicate zeolites are silicon-and aluminum-containing chemicals such as aluminum sulfate and water glass.While various synthesis methods based on these chemicals have matured in terms of both process technology and product quality,they are facing great challenges for their sustainable development:on the one hand,the conventional chemicals such as water glass and aluminum sulfate for synthesizing zeolites are usually obtained from nature quartz and bauxite minerals via complicated reaction and separation processes which are associated with huge energy and material consumptions and waste emissions;on the other hand,the increasing demands for various zeolites due to their increasingly wide applications require significantly reduction in synthesis cost.This situation calls for alternative feedstocks whose manufacture is green yet cost-effective.Many researchers have attempted to synthesize zeolites directly from natural aluminosilicate minerals and have achieved promising results.It has been recognized that the key to succeeding in synthesizing high-quality zeolites or zeolite/clay composites from natural aluminosilicate clay minerals is their effective activation,i.e.,the transformation of an aluminosilicate clay mineral to an activation product that provides part or all of active SiO₂ and Al₂O₃ species which can be leached by acidic or basic solutions and contribute Si and Al species for zeolite synthesis.However,the conventional thermal activation usually conducted at a temperature of as high as600¹000 ^oC is energy-intensive,even so it can only destruct part of aluminum-oxygen bonds in natural aluminosilicate minerals such as kaolin,with silicon-oxygen bonds being intact.In the first part of this thesis,we propose a novel and green quasi-solid-phase?QSP?approach to activate natural aluminosilicate minerals.By investigating the QSP activation process of a natural kaolin mineral and characterizing the physicochemical properties of the activated products,the optimal QSP activation conditions were obtained.The results showed that,at a temperature as lower as 100 ^oC,much lower than that employed in the conventional thermal activation,the QSP activation can effectively destroy the structure of the natural kaolin mineral and lead to the complete depolymerization of Si and Al species into highly reactive Q⁰ and Al^IV species,respectively.The mechanistic analyses of the QSP activation process lead to the conclusion that kneading and extruding exert fracturing and cleaving forces on the natural kaolin mineral in the QSP activation and play a significant role similar to that reported in the mechanochemical activation of the raw kaolin mineral.The combined use of the mechanochemical actions leads to the successful development of the QSP activation method for preparing a highly-reactive feedstock from a natural kaolin mineral for zeolite synthesis.In the second part,based on above QSP activation method,pure-phase NaY zeolite was hydrothermally synthesized using QSP activation product as the main provider of alumina source and part provider of silica source,and thermally treated diatomite as a makeup silica source of the synthesis system.When used as a FCC catalyst,the resultant zeolite Y derived catalyst showed outstanding catalytic performance in terms of the yields of lighter fractions,dry gas,and coke compare with a commercial zeolite Y derived catalyst.By using QSP activation product as the sole starting materials,we have also successively synthesized zeolite A which is now widely used as adsorption and ion exchange materials in the petrochemical industry.Currently considering that the synthesis of hetero-atom zeolite is a non-green process and natural minerals all have a certain amount of iron impurity,FeY zeolites were hydrothermally synthesized using low-grade natural aluminosilicate minerals with high Fe content as raw materials in the third part of this thesis.Through the analysis of the conversion behavior of Fe atoms in the activation process and in the synthesis of Y zeolite,the controllable synthesis of FeY zeolites with different content and distribution of iron were achieved.The fourth part of this thesis illustrates a new route to synthesizing hierarchical micro-meso-porous TiY zeolite neither using any mesoscale template,titanium-containing inorganic chemical nor involving any post-treatment.The formation of the hierarchical structure is attributed to the unique reactivity of the SMS activated rectorite and the thermally activated diatomite.The titanium in the resultant zeolite is derived from the natural rectorite miniral.The resultant zeolite Y has a significantly larger external surface area and mesopore volume than the commercial one.When used as a FCC catalyst,the hierarchical micro-meso-porous TiY zeolite derived catalyst showed outstanding catalytic performance.