Conversion of the greenhouse gas CO2 to the fuel gas CO via the Boudouard reaction: A review

The remediation of carbon dioxide emitted into the atmosphere has become the topic of the day due to the enormous contribution of CO2 to the devastating global warming. The Boudouard reaction, in which solid carbon (char) reacts with CO2 to produce carbon monoxide (CO2 (g)+C(s)↔CO (g)), is a straightforward route for the CO2 emission mitigation. Through this reaction, the CO2 coming from variety of combustion plants, including exhaust/flue gas and synthesis gas, can be upgraded to the fuel gas, CO. This work presents a review on the CO2 gasification of char, from coal, biomass, municipal solid wastes, sewage sludge or any co-utilized blend of them, to produce CO through the Boudouard reaction. An outline of the most effective parameters on the char gasification rate is presented. The parameters which affect the char reactivity are reviewed as those related to the char and its structural features (surface area and porosity, active sites, mineral content, structural evolution of char during gasification, pyrolysis condition and carbon source) and operation parameters (use of catalyst, gasification temperature, gasification pressure and CO2 partial pressure, char particle size and gasification heat source). The kinetics of the char gasification reaction is studied and several theoretical or semi-empirical kinetic models used to interpret the reaction rate data and calculation of kinetic parameters, specifically activation energy, are reviewed and discussed.