Hydrogen generation by oxidation of coarse aluminum in low content alkali aqueous solution under intensive mixing

Simple, safe, scalable and low-cost method of hydrogen production via aluminum-water reaction was proposed. Hydrogen generation method is based on oxidation of coarse aluminum of centimetric scale in alkali aqueous solution with alkali concentration of no more than 0.1 M under intensive mixing of reaction medium. In presented work aluminum conversion (hydrogen yield) was studied depending on the aluminum to solution mass ratio (α changed from 30.1 to 2.7), the concentration of alkali in aqueous solution, the mixing rate, the form of aluminum particles (granules or chips) and chemical purity of aluminum. It was shown that under implemented experimental conditions alkali is continuously regenerated during oxidation reaction and synergistic effect of low content alkali aqueous solution and intensive mixing works. Aluminum conversion degree after 5 h oxidation of aluminum chips at 90 °C in 0.1 M KOH aqueous solution with α = 4 and mixing rate of 400 rpm was 75.4%. With alkali concentration increasing from 0.01 M to 0.3 M the conversion of aluminum increases from 20.7 to 95.7% (after 5 h at 90 °C, α = 4). Proposed method was strongly affected by mixing of reaction medium inside the reactor while it didn't feel the difference between aluminum chips and granules having specific surface area of 22 and 5.5 cm2/g respectively. Chemical purity of aluminum had little effect on aluminum conversion as well. Generally, proposed method can be used for hydrogen generation, aluminum waste utilization and special-grade alumina production.