Catalytic Performance of Waste-Based Metal Oxides Towards Waste-Based Combustion Process

The catalytic performance of mixed metal oxides in the combustion of paper industrial waste (bark, paper sludge, and waste paper reject) was investigated. The mixed metal oxide catalyst with, SiO2, Al2O3, Fe2O3, and CaO percentages of 78.57, 9.28, 4.28, and 7.85, respectively, was prepared by mixing iron mill scale, clinker, used cement, and bentonite clay, which were employed as metal oxide precursors. An analysis of the combustion behavior of bark, paper sludge, and waste paper reject with and without a mixed metal oxide catalyst, using the thermogravimetric analysis technique, showed that the ignition temperature remained unchanged after the addition of the catalyst. In contrast, the burnout temperature was reduced from 616.9 to 482.6 °C, 682.0 to 672.5 °C, and 678.1 to 669.9 °C for bark, paper sludge, and waste paper reject, respectively. These results indicated that adding a mixed metal oxide catalyst enhanced the combustion reactivity via the accelerated char combustion of biomass. Furthermore, the products formed during the combustion process with and without a catalyst were investigated in a packed-bed reactor. The gaseous products (H2, CO, CH4, C2H4, C2H6, and CO2) were observed during the combustion process of bark, paper sludge, and waste paper reject at 700 °C, both with and without a mixed metal oxide catalyst. However, higher H2 and CO2 compositions, which are attributed to the catalyst addition, were found in the presence of a catalyst, which improved the tar decomposition and the water–gas shift reaction.