Process and Device for Generating High Purity Hydrogen Based on Hydrolysis Reaction of Aluminum Dross

Progress of energy systems depends on the development of new efficient and environmentally sustainable sources of clean energy. There are several ways to develop such sources. One way of perspective is based on the generation of hydrogen [1- 3]. Hydrogen is known as one of the best clean energy carrier because of its minimal impact on the environment regarding to greenhouse gas emissions such as carbon dioxide and other gases [1, 4-6]. Hydrogen can be used directly in molecular form , (i.e. as a fuel for vehicles) or indirectly to generate electricity for other industrial applications [4-7] .A major advantage which it has over other fuels is that not cause pollution because of its burning reaction results only water. Hydrogen is also an almost ideal fuel gas and in terms of reducing smog when it is burned. However, safe storage and generation at low cost are technical challenges that need to be considered. For these reasons there are sought new ways to produce hydrogen at low cost from other sources than are known [8-10].The alkali metals (such as sodium, potassium, lithium) and alkaline earth (calcium, strontium, aluminum, magnesium, etc.) are very active when they come in contact with water, react spontaneously, generating hydrogen and heat. Based on this chemical property, the hydrolysis reaction of pure aluminum powder is commonly used for high purity hydrogen generation [6, 11,12,13, 14].Although the use of pure aluminum in reaction with water to produce hydrogen is a viable method, it is expensive, if it takes into account the cost of producing pure aluminum and the use of an alkali metal hydroxide, also an expensive product. The alkali metal hydroxide is used to remove the protective layer of aluminum oxide on the surface of the aluminum particles, which prevent the contact between the metal and water, and thus slow down or substantially avoid reaction between the aluminum and water [15, 16, 17, 18] .As a result, other methods should be studied and utilized to activate the surface of the aluminum particles, to initiate and accelerate the reaction of hydrolysis. Different methods to enhance the rate of aluminum reaction and other metals with water have been developed [19,20, 21, 22].One such method is mechanical activation (crushing, cutting, grinding). This is a method not so expensive and leads to removal of aluminum oxide layer and obtaining a surface clean and active. Also, the replacement of an alkali metal hydroxide with less expensive other chemical compound [19] can be effective. Another way to reduce the costs is to replace pure aluminum with another source of aluminum. As is known from the literature, large amounts of aluminum are present in the solid metal wastes resulting from the production of aluminum, or from recycling processes, this being known as dross or slag [10, 12.13]. The use of this source of aluminum to generate hydrogen has both benefits to environment by waste recycling, and to the cost of hydrogen producing, that decreases substantially. In this work, we have investigated the hydrolysis properties of Al powder and Al dross mechanically treated by ball milling to form a fresh chemically active metal surface, with the use of tap water, in which was added a small amount of ammonia solution 25 wt %, to increase the pH (i.e. from 6.95 to 10.45) and to create a strong alkali environment that determines the metal surface activation. The aim is to accelerate the hydrolysis rate and to improve the hydrogen yields of the mixture in water. Removal of the aluminum oxide layer on aluminum particle surface by mechanical means, sustains aluminum assisted water split reaction.