Comparison between leached metakaolin and leached diatomaceous earth as raw materials for the synthesis of ZSM-5
Inexpensive raw materials have been used to prepare ZSM-5 zeolites with SiO2/Al2O3 molar ratios in the range 20 – 40. Kaolin or Bolivian diatomaceous earth was used as aluminosilicate raw materials and sodium hydroxide and n- butylamine were used as mineralizing agents and template. Dealumination of the raw materials by acid leaching made it possible to reach appropriate SiO2/Al2O3 ratios and to reduce the amount of iron and other impurities. After mixing the components and aging, hydrothermal treatment was carried out and the products were recovered The results clearly show for the first time that well-crystallized ZSM-5 can be directly prepared from leached metakaolin or leached diatomaceous earth using sodium hydroxide and n-butylamine as mineralizing agents and template under appropriate synthesis conditions. A longer induction time prior to crystallization was observed for reaction mixtures prepared from leached diatomaceous earth, probably due to slower digestion of the fossilized diatom skeletons as compared with that for microporous leached metakaolin. The use of leached diatomaceous earth allowed higher yield of ZSM-5 crystals within comparable synthesis times. However, low amounts of Mordenite formed, which was related to the high calcium content of diatomaceous earth. Another considerable advantage of diatomaceous earth over kaolin is that diatomaceous earth does not require heat treatment at high temperature for metakaolinization.
Kaolin as a Source of Silica and Alumina For Synthesis of Zeolite Y and Amorphous Silica Alumina
Kaolin is the clay mineral which containing silica (SiO 2 ) and alumina (Al 2 O 3 ) in a high percentage, that can be used as a nutrient in the synthesis of zeolites and amorphous silica alumina (ASA). The objective of this research is to convert the Belitung kaolin into silica and alumina as nutrients for the synthesis of zeolites and amorphous silica alumina, which are required in the preparation of the catalysts. Silica and alumina contained in the kaolin were separated by leaching the active kaolin called as metakaolin, using HCL solution, giving a solid phase rich silica and a liquid phase rich alumina. The solid phase rich silica was synthesized to zeolite Y by adding seed of the Y Lynde type, through the hydrothermal process with an alkaline condition. While, the liquid phase rich alumina was converted into an amorphous silica alumina through a co precipitation method. Characterization of zeolite and ASA were done using XRD, surface area and pore analyzer and SEM. The higher of alumina in liquid phase as a result of the rising molar of HCL in the leaching process was observed, but it didn’t work for its rising time. Products of ASA and zeolite Y were obtained by using liquid phase rich alumina and solid phase rich silica, respectively, which resulted through leaching metakaolin in 2.5 M HCl at temperature of 100° C for 2 hours.
Template-free synthesis and catalytic behaviour of aluminium-rich MFI-type zeolites
Abstract A systematic study of MFI-like zeolites synthesis starting from template-free reaction gels was carried out. It was possible to prepare either MFI- or MOR-like zeolites from the same synthesis gel by only changing either temperature or crystallisation time. An upper limit for the incorporation of silica in the MFI framework was observed regardless of the silica-to-alumina ratio of the starting gel, the resulting solids having Si/Al ratios ranging from 12 to 29. A good linear correlation between the corrected rate for n -hexane cracking and the Al loading confirmed the composition and purity of the zeolitic MFI-phase obtained. Hydrothermal treatments applied to two MFI zeolites with different Si/Al ratio caused a higher percentage of dealumination for the one containing the highest Al loading, but the number of Al atoms per unit cell remaining after severe (1023 K) steaming was the same (1.4±0.35) in both cases. Enhancement of the catalytic activity for n -hexane cracking was observed for the samples steamed under mild (873 K) conditions with this effect being more pronounced for the aluminium-rich zeolite. Treatments of the sample showing the highest activity enhancement with HCl solutions of increasing concentration caused a progressive removal of extraframework Al species (EFAL) with a concomitant decrease in the catalytic activity. However, only a partial extraction of EFAL was observed, even with the more concentrated acid solution, suggesting a strong interaction of these species with the zeolite framework.