Journal of Chemical Engineering of Japan, Vol.51, No.7, 596-604, 2018
Effect of Mg-Al Layered Double Hydroxide Use on the Performance of a Spray-Dried NiO Oxygen Carrier
In chemical looping combustion (CLC), CO2 is captured inherently during fuel combustion because the oxygen for fuel combustion is supplied from oxygen carrier (OC) in a pure oxygen form. NiO/Al2O3 OC particles tend to agglomerate when NiO is reduced to Ni. Even though MgO addition alleviates the agglomeration phenomenon, excess MgO addition over some quantity reduces the oxygen transport reactivity before satisfactory prevention of the agglomeration. In this work, Mg-Al layered double hydroxide (LDH) was tested as a new starting raw support material to develop a spray-dried NiO OC containing sufficient amount of Mg, with achieving less performance loss. This new NiO OC with Mg content of 0.054g/g, or 0.09 g/g as MgO, showed much faster oxygen transport rate compared with previous spray-dried NiO OCs made from MgO (0.084g/g) and alpha-Al2O3 or gamma-Al2O3 . Furthermore, high mechanical strength could be obtained at a lower calcination temperature. The reason of performance improvement was explained with the mixed effect of the improved physicochemical properties. This work indicates that the use of Mg-Al LDH as a support for NiO OC can overcome several shortcomings found in the Mg added NiO/Al2O3 OC prepared from MgO and alpha-Al2O3 or gamma-Al2O3 such as bigger grain growth caused by high calcination temperature, agglomeration easily occurring in OC with high mechanical strength, and low limit of the amount of MgO addition due to the reactivity decrease with increasing MgO content.