Performance Comparison of Spray-dried Mn-based Oxygen Carriers Prepared with γ-Al 2 O 3 , α-Al 2 O 3 , and MgAl 2 O 4 as Raw Support Materials

Abstract

In chemical-looping combustion, pure oxygen is transferred to fuel by solid particles called as oxygen carrier. Chemical-looping combustion process usually utilizes a circulating fluidized-bed process for fuel combustion and regeneration of the reduced oxygen carrier. The performance of an oxygen carrier varies with the active metal oxide and the raw support materials used. In this work, spray-dried Mn-based oxygen carriers were prepared with different raw support materials and their physical properties and oxygen transfer performance were investigated to determine that the raw support materials used are suitable for spray-dried manganese oxide oxygen carrier. Oxygen carriers composed of 70 wt% Mn 3 O 4 and 30 wt% support were produced using spray dryer. Two different types of Al 2 O 3 ,  -Al 2 O 3 and  -Al 2 O 3 , and MgAl 2 O 4 were applied as starting raw support materials. The oxygen carrier prepared from  -Al 2 O 3 showed high mechanical strength stronger than commercial fluidization catalytic cracking catalyst at calcination temperatures below 1100  C, while the ones prepared from  -Al 2 O 3 and MgAl 2 O 4 required higher calcination temperatures. Oxygen transfer capacity of the oxygen carrier prepared from  -Al 2 O 3 was less than 3 wt%. In comparison, oxygen carriers prepared from  -Al 2 O 3 and MgAl 2 O 4 showed higher oxygen transfer capacity, around 3.4 and 4.4 wt%, respectively. Among the prepared Mn-based oxygen carriers, the one made from MgAl 2 O 4 showed superior oxygen transfer performance in the chemical-looping combustion of CH 4 , H 2 , and CO. However, it required a high calcination temperature of 1400 °C to obtain strong mechnical strength. Therefore, further study to develop new support compositions is required to lower the calcination temperature without decline in the oxygen transfer performance.