Hydrogen Production And High Purity Hydrotalcite From Al-Mg Alloys Hydrolysis

Hydrogen is a green and clean energy with great potential,but the safety and efficiency in hydrogen transportation and storage is the main obstacle to its large-scale application.Hydrolysis of metal aluminum for hydrogen production is a fast and simple method,but the hydrolyzed product Al(OH)3 will prevent the water decomposed hydrogen.Magnesium aluminum hydrotalcite is a new type of water treatment and catalytic material with rapid development in recent years.It has been found that the use of Al(OH)3 can be used to prepare water treatment material-hydrotalcite(LDH).However,the purity of the traditional coprecipitation method for preparing hydrotalcite is not high enough,which seriously affects the water treatment efficiency and catalytic performanceIn order to solve the above problems,this paper proposed the simultaneous preparation of high purity hydrogen and hydrotalcite by hydrolysis of magnesium aluminum alloy.By studying the effects of the composition of the alloy(Mg/Al ratio),initial pH value(1-9),reaction temperature and pressure(25-70℃),particle size(42-237 μm)and preparation of alloy(ball milling and melting)on the kinetics of hydrogen production and hydrotalcite formation,using XRD,TEM,SEM and model fitting characterization and analysis methods,exploring the structure and purity of hydrotalcite by alloy hydrolysis,compared differences of hydrotalcite structure and purity with the alloy hydrolysis method,mechanization method and coprecipitation.The mechanisms of hydrogen and high purity hydrotalcite was discussed by alloy hydrolysis,the main results were as follows:The activation energy of Al-Mg alloy hydrolysis reaction is 1/3 of Al and the hydrogen production rate is 6%,which is higher than that of Al.The hydrogen production rate increases with decreasing of initial pH of solution,increasing of reaction temperature,increasing of Mg/Al ratio and decreasing of alloy particle size.In the process of hydrolyzing,the increase of pressure in the reaction system caused by the generation of hydrogen can improve the specific surface area of hydrotalcite,and it was 45%at high pressure(1.5 MPa)higher than that at normal pressure.In the crystal growth process of hydrotalcite,the crystal nucleation growth model was followed.The reaction rate constant was 0.155 h-1 and the reaction order was 0.789.The purity of LDH increased with increasing of Mg/Al in the alloy,reaction temperature and hydrolysis time.The highest purity of hydrotalcite was 99.99%.The purity,crystallinity,specific surface area and morphology of LDH obtained by hydrolyzing of Al-Mg alloy were better than coprecipitation and were similar to mechanochemical method.Hydrolysis of Al-Mg alloy is a ready-to-use method for hydrogen production.It is also a method for the preparation of high purity hydrotalcite,which can avoid the safety problems in the process of hydrogen storage and catalytic degradation in the process of using hydrotalcite.This study provides a new method for the preparation of hydrogen and hydrotalcite,and opens up potential applications of Al-Mg alloy.