البحث — المستودع الرقمي العراقي

المستخلص: Silica nano particles were prepared from Iraqi rice husk (al - Najaf province) by precipitation method. Rice husk (RH) was treated with two different concentrations of inorganic acid (i.e. 1 & 3 N HCl) then burning at 700 °C under two heating rates. Chemical composition of rice husk ash (RHA) determined by X - Ray fluorescence (XRF) was contained about 89.5 wt% and 95.2 wt% SiO2 by treatment with 1N HCl at 10 and 5 °C/min heating rates for 3 hrs, respectively. While, XRF analysis was given 97.5 wt% SiO2content in RHA by treatment with 3 N HCl at 5 °C/min heating rates for 2 hrs. 3N HCl and heating rate at 5°C/min seems to be the best method to reduce the metallic ingredients and to obtain highly purified nanosilica powder at a purity of 98.9 wt%.The prepared nanosilica was also characterized by X - ray diffraction (XRD), BET surface, Fourier transform infrared spectroscopy (FTIR) and Atomic Force Microscope (AFM), in order to investigate its properties.X - ray results revealed a strong single beak of 2? at about 22° with an amorphous phase. Surface area was measured for nano silica to be 298 m2/g. The average diameter of prepared nanosilica is 89.58 nm as obtained by AFM analysis. Rice husk is seen to be a frugal waste material, high silica content, and it will be able to apply as a natural source of silica for preparation the zeolite - Y catalysts rather than burnt or dumped it as waste, causing environmental and health problems. On the other hand, the commercial source of silica (i.e. Ludox As - 40) is industrially used with other materials for synthesizing the zeolite type - Y catalyst and economically it has an expensive cost. Hence, it is essential to find out another pathway for silica source.This work deals with the replacing of costly commercial precursors of silica by a cheap natural nano - source silica from Iraqi RH. As such this study focuses on the optimization of percentages of natural and/or commercial silica applied within either seed gel or feed stock gel in the zeolite - Y synthesis process in order to investigate the effect of the nature of the silica used on both the structural properties of produced of Y - catalyst as well as on the catalytic performance of these catalysts in hydrocarbon cracking reactions forimproving the production catalytic activity and selectivity. Commercial zeolite - Y catalyst was laboratory prepared by means of commercial silica source and named as “A” sample, whereas other four samples of zeolite catalysts were successfully synthesized with a desired zeolite - Y phase and so - called “B, C, D and E” using different percentages of natural silica source. All the achieved samples are investigated by characterization techniques (i.e. XRD, BET - surface area, Pore volume, FTIR SEM, AAS, and EDX). The synthesized HY - catalyst samples were catalytically tested in the cracking of Hexane (C6H14) through an experimental cracking rig, and the reaction products were analyzed by GC. The performance of Iraqi RH zeolite type - Y catalysts was compared with the commercial lab HY - catalyst. Catalyst B prepares from only natural nanosilicasource and in comparison with other synthesized Y - catalysts; it gives the best catalytic behavior with 98 - 95 mol% conversion together with the selectivity domination of isomer and normal paraffin within the reaction products during more than 2 hrs at 450 °C. This result confirms that the use of natural silica source can be enhanced the catalytic properties of zeolite type - Y catalyst.