Synthesis of Magnesium Hydroxide and Oxide Nanoparticles Using a High-gravity System
Date Issued
2005
Date
2005
Author(s)
Chang, Ming-Hui
DOI
zh-TW
Abstract
The high-gravity system has been developed for many years. It consists of a high-gravity rotating packed-bed reactor and a spinning disk reactor. In recent years, it has been successfully applied in distillation and adsorption process. In the field of crystal engineering, it can be used to produce nanoparticles.
Magnesium hydroxide is usually used in flame retardant materials, and it can be also used in medicines and cosmetics. It can be calcined to produce magnesium oxide, which is one of the most useful ceramic materials and is usually used in fire-resisting bricks or crucibles. Many methods for synthesis magnesium hydroxide nanoparticles, including hydrothermal method and sol-gel method, have been developed, but they were always high-cost and hard to scale up. Size of magnesium oxide cannot be developed to nano-order because of no suitable nano-sized precursors.
The purpose of this research was to synthesize nanoparticles in a high-gravity system. Nanoparticles of magnesium hydroxide were synthesized in a high-gravity system, and used as precursors for magnesium oxide. First, magnesium hydroxide was prepared in the high-gravity system by a continuous, MgCl2-NaOH liquid-liquid phase reaction. Then the product was calcined to produce magnesium oxide. In this research, the effects of operating variables, including rotating speed, reactant concentration, liquid flow rate, and packing material on particle size and shape of magnesium hydroxide nanoparticles was studied. Besides, the effect of calcination temperature on particle size of magnesium oxide was also investigated. The aim of this project was to explore operation conditions for producing Mg(OH)2 and MgO particles as small as possible.
In this study, lamellar-like magnesium hydroxide nanoparticles, which is 50-100nm in length, less than 10nm in thickness, can be obtained either in a spinning disk reactor or in a rotating packed-bed reactor, with rotating speed being 2000rpm, MgCl2 concentration being 0.83M, and NaOH concentration being 1.66M. Using a spinning disk reactor, the number mean size of Mg(OH)2 particles measured by a dynamic light scattering analyzer decreases from 143.6nm to 47.5nm when liquid flow rates of MgCl2 and NaOH solutions both decrease from 0.75L/min to 0.28L/min. The BET surface area of 47.5nm Mg(OH)2 particles is 77m2/g. On the other hand, using a rotating packed-bed reactor filled with stainless-steel meshes, Mg(OH)2 particle size decreases from 61.9nm to 51.8nm when liquid flow rates of reactants solutions both increase from 0.32L/min to 0.75L/min. When a rotating packed-bed reactor is filled with ceramic Intalox saddles, liquid flow rate shows no significant effect on the particle size of Mg(OH)2.
Polyhedral nanoparticles of magnesium oxide, which is about 50nm observed by a scanning electron microscope, can be obtained by calcination of 47.5nm Mg(OH)2 powder in lamellar shape, using a programmed heating up to 600oC. The number mean size of these MgO particles is about 150nm and the BET surface area of that is 32m2/g.
The Mg(OH)2 nanoparticles of lamellar-like and 50nm in equivalent diameter obtained in this research would present great advantages when applied to flame-retardant materials. MgO particles produced in this research are about 150nm for number mean size, which can be used as fine catalyst. This research shows that the high-gravity system is a powerful tool to synthesize nanoparticles. This technology has a great potential in commercialization because of its low energy consumption and its simplicity in scale-up.
Subjects
超重力
氧化鎂
氫氧化鎂
旋轉填充床
旋轉盤反應器
high-gravity
magnesium oxide
magnesium hydroxide
rotating packed-bed
spinning disk reactor
SDGs
Type
thesis