Development of Large Pore Zeolite from Kaolinite Clays
This thesis is focused on the synthesis of faujasite type NaY zeolite from both Kankara and Elefun kaolinite clays. The raw kaolins were subjected to various treatments, for the purpose of upgrading them and making them useable as an active monomer for zeolite synthesis. The kaolins were beneficiated using wet method, calcined at various temperatures namely; 600,700,750, 800, 850, 900 and 950 degree Celsius. The silica and alumina in kaolin sourced from Elefun was observed to attain it optimal activated state at 8500C, while that of Kankara was at 9000C. Sulfuric acid was used to alter the silica-alumina ratio of the optimally calcined metakaolin. A novel approach to dealumination, independent of external source of heating was developed and employed in this work. Furthermore, the synthesis process took place without using any structure directing agent, while parameters such as ageing, seeding, alkalinity (NaOH and pH), dyeing (blanking) were investigated and a reproducibility corrective investigation was done. The transformation stages involved in this work were monitored using X-Ray Flourescence (XRF), X-Ray Diffractograph (XRD), Braunner-Emmett-Teller for surface area analysis (BET), Scanning Electron Microscopy (SEM) and partially Fourier Trace Infrared (FTIR). Faujasite type Y zeolite was synthesized from shelf soluble salts for control reason. Zeolite Y was synthesis from red Kankara kaolin sample aged for 9 days having about 40% NaX and 15% NaY aside other phases and an unnamed zeolite. Post-synthesis aging of this product, for 95 days, established an insitu seeding and formation of more stable phase ZSM3, in company of prominent persistent peak attributed to quartz. Irrespective of the type of kaolin (Kankara or Elefun) 9 days of gel aging was observed to be sufficient for appearance of peak attributable to zeolite Y. The SEM for the resulting products from aging process indicated increase in crystallinity with aging period, with presence of other highly siliceous phase. Introduction of dye into the gel was observed to suppress nucleation of inherent impurities as well as enhance rate of amorphosity, but with attendant indications that the same dye enveloped the soluble ingredients from reacting, by increasing their degree of segregation. Both Elefun and Kankara were observed to give zeolite NaY, though at different dye/metakaolin ratio. The gel from Kankara and Elefun with Na2O/SiO2 ratio of 7 and 9, were observed to give NaY zeolite peak. Increase in the alkalinity (NaOH and/or pH) gave increased crystallinity though not favourably disposed to the synthesis of zeolite Y. Elefun gel seeded with 1, 1.5, 2.0 and 2.5wt% commercial zeolite Y, were noticed to give zeolite Y with increased crystallinity. NaY zeolite peak were noticed for samples from Kankara seeded with 1.5 and 2.5wt%, respectively. The appearances of highly siliceous zeolite phases along with NaY were blamed either on the inability of NaOH to depolymerize the silica, high level of sulfate salts in the gel and/or low level of reconstitution reaction between the already dissociated silica and alumina. The improvement studies conducted proved successful as highly crystalline NaY zeolite were characterized using XRD analysis. Zeolites belonging to the SSZ, ITQ, ZSM families, were synthesized without the use of templating agent, which gives an insight also of the usability of Nigerian kaolin in an environmental friendly synthetic route.
Keywords: Kankara, Elefun, XRD, XRF, SEM, crystal violet, dealumination, nucleation
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