Direct reduction of calcium carbonate by coupling with methane dry reforming using NiO/S-1 as catalyst

Abstract

Thermal decomposition of carbonate is an important process in the production of cement, refractory materials, and steel. Nevertheless, this process requires high temperature and is always accompanied with large amounts of CO2 emission. To reduce the decomposition temperature and simultaneously mitigate CO2 emissions, direct reduction of carbonate under a reducing atmosphere has been proposed as a novel strategy. This work mainly investigated the feasibility of direct reduction of CaCO3 by CH4 in the presence of a highly dispersed NiO/S-1 catalyst. It was found that the introduction of a CH4 atmosphere without a catalyst had little promotion effect on CaCO3 decomposition (as compared to air atmosphere), and no notable conversion of CO2 was observed. However, the presence of a highly dispersed NiO/S-1 catalyst significantly decreased the decomposition temperature of CaCO3 in a CH4 atmosphere, and most of the carbon species in CaCO3 can be converted to CO. To gain a comprehensive understanding of CaCO3 reduction in CH4, the effects of reaction temperature, CH4 concentration, and NiO loading in the NiO/S-1 catalyst were systematically explored. With the best-performing catalyst, i.e., 7NiO/S-1, complete CaCO3 decomposition and approximate 90 % CH4/CO2 conversion can be achieved under the condition of 750 °C and 25 vol% CH4. Characterization results indicated that the CaO particles obtained in the CH4 reducing atmosphere exhibited a more porous structure compared to that attained in air, due to the more intensive CaCO3 decomposition in CH4. Further data analysis revealed that reverse water-gas shift reaction also contributed to CO2 conversion during the reduction of CaCO3 in CH4. The findings obtained in this research can provide new perspectives for CO2 emission control and energy saving in traditional heavy-emission and high energy consumption industries.